JP4680635B2 - Surface light source device, light guide used therefor, and manufacturing method thereof - Google Patents

Description

  The present invention relates to an edge light type surface light source device and a light guide used therefor, and in particular, a streaky emission line along the light incident end surface in the vicinity of the light incident end surface facing the primary light source. The present invention also relates to a surface light source device intended to reduce unevenness in luminance distribution observed as dark lines, and in particular, to a light guide used therefor and a method for manufacturing the same.

  The surface light source device of the present invention is preferably applied to, for example, a backlight of a liquid crystal display device.

  In recent years, liquid crystal display devices have been widely used as monitors for portable notebook computers or the like, as display units for liquid crystal televisions and video-integrated liquid crystal televisions, and in various other fields. The liquid crystal display device basically includes a backlight unit and a liquid crystal display element unit. As the backlight unit, an edge light type is often used from the viewpoint of making the liquid crystal display device compact. Conventionally, as an edge light type backlight, at least one end face of a rectangular plate-shaped light guide is used as a light incident end face, and a linear or rod-like shape such as a straight tube fluorescent lamp is provided along the light incident end face. A primary light source is disposed, light emitted from the primary light source is introduced from the light incident end surface of the light guide into the light guide, and the light exit surface is one of the two main surfaces of the light guide. What is emitted from the projector is widely used.

  In such a backlight, the luminance distribution on the light emitting surface may be non-uniform (decrease in luminance uniformity) due to the propagation form of light emitted from the primary light source and emitted through the light guide. One form of this reduction in brightness uniformity is that the brightness in the area close to the primary light source is higher than in other areas.

  As methods for preventing such a decrease in luminance uniformity, for example, Japanese Utility Model Publication No. 40-26083 (Patent Document 1), Japanese Utility Model Application Publication No. 60-60788 (Patent Document 2) and Japanese Utility Model Application Publication No. 62-154422. The gazette (Patent Document 3) discloses disposing a light-absorbing film or a light-adjusting film for suppressing light transmission at a position near the primary light source of the light exit surface of the light guide. This method is merely a small distance from the primary light source as a countermeasure against the fact that the intensity of light emitted from the light guide light exit surface in the region near the primary light source is larger than the intensity of light emitted in the region far from the primary light source. This is intended to limit the light emission from the light emission surface area.

  By the way, in recent years, as the light guide has been made thinner (for example, about 2 to 3 mm), the light intensity has become close to the light incident end face of the light guide (for example, about 2 to 4 mm) as a special form for reducing the luminance uniformity. Corresponding to the position of the light exit surface, streaky bright parts (bright lines) that are brighter than the surroundings may be observed in parallel with the light incident end face. When a technique such as the above-mentioned Patent Documents 1 to 3 is employed to prevent a local rapid brightness change due to the bright line (that is, there is a large brightness change corresponding to a small position change in the brightness distribution), it is formed. Since the width of the light absorbing film or the like is wide, there arises a problem that not only the bright line but also the entire brightness thereof is lowered, or a dark line is easily generated.

  On the other hand, as a technique for preventing a local rapid luminance change due to such a bright line, Japanese Patent Laid-Open No. 9-197404 (Patent Document 4) discloses a light emitting surface of a light incident end surface of a light guide and its light emitting surface. It has been proposed to attach a light shielding member such as ink to an edge that forms a boundary with the opposite surface.

Further, along with the local rapid brightness change due to the generation of the bright line as described above, a streaky dark part (dark line) darker than the surroundings may be observed between the adjacent bright lines in parallel with the light incident end face. In JP-A-8-227074 (Patent Document 5), as a technique for preventing the generation of such dark lines, light having a light absorption pattern in which the light absorption rate gradually decreases as the distance from the light incident end face is increased. It is disclosed to form an absorbent layer.
Japanese Utility Model Publication No. 40-26083 Japanese Utility Model Publication No. 60-60788 Japanese Utility Model Publication No. 62-154422 JP-A-9-197404 JP-A-8-227074

  In the method of Patent Document 4, a light shielding member is attached to the edge of the light guide light incident end face, and a part of the light shielding member is also applied to the light incident end face. Part of the light will be blocked, and the amount of light incident on the light guide from the primary light source will be reduced by that amount, and the overall brightness will be easily reduced. In this case, since the light to be guided is also shielded, there is a problem that dark lines are easily generated in the display area.

  In addition, since this method forms a light-shielding member having a very narrow width, it cannot be said that the effect of suppressing the generation of bright lines is sufficient. In addition, this method is actually very difficult to realize that a light-shielding member is applied to the edge, and it is difficult to form the light-shielding member at a desired position and the light shielding property attached to the edge. There is a problem that the member is easily dropped.

  Furthermore, in the method of Patent Document 5, a pattern such as a dot-like pattern is adopted as the light absorption pattern. In this case, there is a region that does not partially absorb light, and light shielding in this region is insufficient. Therefore, there is a problem that bright lines are observed.

  In the edge light type backlight, a light source reflector is used in order to efficiently introduce light emitted from the primary light source into the light guide. The light source reflector is a reflecting member disposed adjacent to a portion excluding the portion facing the light guide light incident end face of the primary light source, and specifically, a sheet-like or film-like one is used.

  There are two types of light source reflectors that have a strong diffuse reflection tendency and a strong regular reflection tendency in their reflection characteristics. A light source reflector having a strong diffuse reflection tendency has a low reflectance and a large number of multiple reflections inside the light source reflector, so that the light incident efficiency to the light guide tends to be slightly reduced. On the other hand, regular reflection is a reflection mode in which there are few reflection components of light having diffusibility and many reflection components having high directivity due to specular reflection. Accordingly, a light source reflector having a strong regular reflection tendency has a higher reflectance and a higher light incident efficiency to the light guide than a light diffuser having a strong tendency to diffuse reflection, thereby increasing the luminance of the backlight (several% to 15%). There is an advantage that it can be). Examples of the light source reflector having a strong regular reflection tendency include a stainless steel reflector, a silver coating reflector, an aluminum reflector, and a highly reflective aluminum (multilayer film) reflector.

  By the way, when the light source reflector having a strong regular reflection tendency is used, it has been found that the bright line near the light guide light incident end face appears particularly strongly when the light source reflector having a strong diffuse reflection tendency is used. Therefore, in this case, it is particularly desirable to prevent a local rapid luminance change that generates a bright line so as not to impair the quality of the backlight.

  An object of the present invention is to solve the technical problems as described above, and the light that comes from the primary light source and enters the light incident end face and is introduced into the light guide body is not blocked. Prevents the generation of bright lines near the light incident end face over a long period of time without causing a decrease in brightness or causing dark lines by blocking the light that should be guided. Is to prevent. In particular, the present invention focuses on achieving the above object even when a light source reflector having a strong regular reflection tendency is used in combination with a primary light source in an edge light type surface light source device.

  Another object of the present invention is to provide a method advantageous in manufacturing a light guide for a surface light source device that can solve the technical problems as described above.

According to the present invention, as a solution to the above technical problem,
A light guide that guides light emitted from the primary light source and has a light incident end surface on which light emitted from the primary light source is incident, a light exit surface from which the guided light is emitted, and a back surface opposite to the light exit surface. A light body,
A light absorption band having a width of 50 μm to 1000 μm extending along the light incident end face is formed on the back surface, and a side edge of the light absorption band close to the light incident end face has a distance from the light incident end face of 300 μm or less. A light guide for a surface light source device,
Is provided.

  In one aspect of the present invention, an edge portion that forms a boundary between the back surface and the light incident end surface is formed along the light incident end surface as a protruding portion raised with respect to another region of the back surface, The full width at half maximum of the protrusion is 1 to 50 μm. In one aspect of the present invention, a prism row forming surface region including a plurality of prism rows extending in a direction substantially orthogonal to the light incident end surface and arranged in parallel to each other is formed on the back surface. Is formed with a substantially flat surface region extending along the light incident end surface, and at least a part of the light absorption band is located in at least a part of the substantially flat surface region. In one aspect of the present invention, the light absorption band is formed such that the visible light transmittance is higher at the side edge farther from the side edge near the light incident end face. In one aspect of the present invention, the width of the light absorption band is 50 μm to 800 μm, and the second light extends along the light incident end face on the back surface at a position farther from the light incident end face than the light absorption band. An absorption band is formed, and a side edge of the second light absorption band close to the light incident end face is located 500 μm to 3000 μm away from the light incident end face. In one aspect of the present invention, the visible light transmittance of the second light absorption band is higher than the visible light transmittance of the light absorption band.

Further, according to the present invention, as a solution to the above technical problem,
A light guide that guides light emitted from the primary light source and has a light incident end surface on which light emitted from the primary light source is incident, a light exit surface from which the guided light is emitted, and a back surface opposite to the light exit surface. A light body,
A prism row forming surface region having a plurality of prism rows extending in a direction substantially orthogonal to the light incident end surface and arranged in parallel to each other is formed on the light emitting surface or the back surface. A substantially flat surface region extending along the light incident end surface is formed on the light emitting surface or the back surface where the light emitting surface is formed, and at least a part of the substantially flat surface region extends along the light incident end surface. A light guide for a surface light source device, wherein a light absorption band having a width of 50 μm to 1000 μm is formed;
Is provided.

  Further, according to the present invention, as a solution to the above technical problem, a method of manufacturing the above-described light guide for a surface light source device, wherein a cutting process is performed on the light incident end face corresponding portion of the light guide material. There is provided a method of manufacturing a light guide for a surface light source device, wherein the light incident end face is formed and then the light absorption band is formed.

  In one embodiment of the present invention, ink dots are ejected from a large number of nozzles by an ink jet method to form independent or partially continuous ink dots in at least a region near the light incident end surface on the back surface of the light guide. Then, the ink dots are leveled and adjacent ones are joined together to form a continuous ink layer over the entire region, and then the ink layer is cured to form the light absorption band.

Further, according to the present invention, as a solution to the above technical problem,
The light guide for the surface light source device, the primary light source disposed adjacent to the light incident end surface of the light guide, and a light deflection element disposed adjacent to the light exit surface of the light guide. The light deflection element has a light incident surface located opposite to the light exit surface of the light guide and a light exit surface opposite to the light incident surface. A surface light source device comprising a plurality of prism rows extending on a surface in a direction substantially parallel to a light incident end surface of the light guide and parallel to each other;
Is provided.

  In one aspect of the present invention, a light diffusing element is disposed adjacent to the light exit surface of the light deflecting element, and the light diffusing element is located at a position at least 2 mm from a light incident end face of the light guide. A dot pattern portion in which a light absorbing dot pattern is formed is provided in a region having a width including the above, and the dot pattern portion is formed by dispersing and arranging dot-shaped light absorbing coating materials having a diameter of 30 μm to 70 μm.

  According to the present invention as described above, a primary light source is formed by forming a thin light absorption band having a specific width extending along the light incident end surface at a position close to the light incident end surface on the back surface of the light guide. The light coming from the light incident end face is not blocked, and there is no decrease in the amount of light incident on the light guide from the primary light source, that is, by reducing the overall luminance or shielding the light that should be originally guided. Generation of bright lines in the vicinity of the light incident end face can be prevented without causing generation of dark lines.

  In addition, according to the present invention, since the light absorption band is formed on the back surface of the light guide, the production thereof is easy. Further, the formed light absorption band does not easily fall off, and the above bright line is satisfactorily good for a long time. It is possible to exert the effect of preventing the occurrence and preventing the occurrence of a local rapid brightness change.

  Further, according to the present invention, the edge portion forming the boundary between the back surface and the light incident end surface is formed by cutting the light incident material corresponding to the light incident end surface corresponding portion to form the light incident end surface. Can be formed along the light incident end face as a protruding part protruding from the region of the light source, and when forming the light absorption band after that, the distance from the light incident end face of the side edge close to the light incident end face of the light absorption band Can be easily set to 0 μm.

  Furthermore, according to the present invention, ink dots are formed on the light exit surface of the light guide by the ink jet method, and then the ink dots are leveled to increase the size of the ink dots in a pseudo manner, so that the uninked portion is inked. Thus, a light absorption band is formed by curing the ink layer, and then setting the required leveling time according to the degree of the viscosity of the ink. By controlling the coupling state, the surface state of the light absorption band can be easily controlled, and the distance from the light incident end face of the side near the light incident end face of the light absorption band can be easily set to 0 μm. .

  Furthermore, according to the present invention, the second light absorption band is formed on the back surface of the light guide at a predetermined distance from the light absorption band, so that a light source reflector having a strong regular reflection tendency can be used in combination with the primary light source. Even in such a case, it is possible to satisfactorily prevent the generation of bright lines in the vicinity of the light incident end face, and to effectively prevent the occurrence of a sharp local brightness change.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view showing one embodiment of a surface light source device according to the present invention, and FIGS. 19 and 20 are a partial perspective view and a partial bottom view of the light guide.

  As shown in FIG. 1, in the surface light source device of this embodiment, the light guide 3 has at least one side end surface as a light incident end surface 31 and one surface substantially orthogonal thereto as a light emitting surface 33. A linear primary light source 1 disposed opposite to the light incident end surface 31 of the light guide 3 and covered with the light source reflector 2, and a light deflection element 4 disposed on the light exit surface of the light guide 3. And the light diffusing element 6 disposed on the light exit surface 42 of the light deflecting element 4 so as to oppose it, and the light disposed on the back surface 34 opposite to the light emitting surface 33 of the light guide 3. The reflection element 5 is comprised.

  The light guide 3 is arranged in parallel with the XY plane and has a rectangular plate shape as a whole. The light guide 3 has four side end surfaces, and at least one of the pair of side end surfaces parallel to the YZ plane is a light incident end surface 31. The light incident end face 31 is arranged to face the primary light source 1, and light emitted from the primary light source 1 enters the light guide 3 from the light incident end face 31. In the present invention, for example, the light source may be disposed opposite to another side end face such as the side end face 32 opposite to the light incident end face 31.

  Two main surfaces that are substantially orthogonal to the light incident end surface 31 of the light guide 3 are respectively positioned substantially parallel to the XY plane, and one of the surfaces (the upper surface in the drawing) serves as the light emitting surface 33. At least one of the light emitting surface 33 and the back surface 34 thereof is a directional light emitting mechanism having a rough surface, and a large number of lens rows such as a prism row, a lenticular lens row, a V-shaped groove, etc. By providing a directional light emitting mechanism composed of lens surfaces formed in parallel with each other substantially in parallel, the light incident end surface 31 is guided from the light emitting surface 33 while the light incident from the light incident end surface 31 is guided through the light guide 3. 31 and light having a directivity are emitted in a plane (XZ plane) orthogonal to the light exit surface 33. The angle between the peak direction (peak light) of the emitted light luminous intensity distribution in the XZ in-plane distribution and the light emitting surface 33 is defined as α. The angle α is, for example, 10 to 40 degrees, and the full width at half maximum of the emitted light luminous intensity distribution is, for example, 10 to 40 degrees.

  The rough surface and the lens array formed on the surface of the light guide 3 have a luminance within the light emitting surface 33 that the average inclination angle θa according to ISO 4287 / 1-1984 is in the range of 0.5 to 15 degrees. It is preferable from the point of aiming at the degree of uniformity. The average inclination angle θa is more preferably in the range of 1 to 12 degrees, and more preferably in the range of 1.5 to 11 degrees. The average inclination angle θa is preferably set in an optimum range by a ratio (L / t) between the thickness (t) of the light guide 3 and the length (L) in the direction in which the incident light propagates. That is, when the light guide 3 having a L / t of about 20 to 200 is used, the average inclination angle θa is preferably 0.5 to 7.5 degrees, more preferably 1 to 5 degrees. It is a range, More preferably, it is the range of 1.5-4 degree | times. When the light guide 3 having L / t of about 20 or less is used, the average inclination angle θa is preferably 7 to 12 degrees, and more preferably 8 to 11 degrees.

The average inclination angle θa of the rough surface formed on the light guide 3 is obtained in accordance with ISO 4287 / 1-1984 by measuring the rough surface shape using a stylus type surface roughness meter and setting the coordinate in the measurement direction as x. From the obtained slope function f (x), the following equations (1) and (2)
Δa = (1 / L) ∫ ₀ ^L | (d / dx) f (x) | dx (1)
θa = tan ⁻¹ (Δa) (2)
Can be obtained using Here, L is the measurement length, and Δa is the tangent of the average inclination angle θa.

  Further, the light guide 3 preferably has a light emission rate in the range of 0.5 to 5%, more preferably in the range of 1 to 3%. This is because when the light emission rate is smaller than 0.5%, the amount of light emitted from the light guide 3 tends to be small and sufficient luminance cannot be obtained. When the light emission rate is larger than 5%, the vicinity of the primary light source 1 is present. This is because a large amount of light is emitted, the attenuation of the emitted light in the X direction within the light emitting surface 33 becomes significant, and the luminance uniformity on the light emitting surface 33 tends to decrease. Thus, by setting the light emission rate of the light guide 3 to 0.5 to 5%, the angle of the peak light in the emission light intensity distribution (in the XZ plane) of the light emitted from the light emission surface is the same as that of the light emission surface. The full width at half maximum of the emitted light luminous intensity distribution (in the XZ plane) in the XZ plane that is in the range of 50 to 80 degrees with respect to the normal and is perpendicular to both the light incident end face and the light emitting face is 10 to 40 degrees. Provided is a surface light source device that can emit light having a high directivity from the light guide 3 and can efficiently deflect the emission direction by the light deflection element 4 and has high luminance. it can.

In the present invention, the light emission rate from the light guide 3 is defined as follows. The relationship between the light intensity (I ₀ ) of the emitted light at the edge on the light incident end face 31 side of the light emitting face 33 and the emitted light intensity (I) at a distance L from the edge on the light incident end face 31 side is When the thickness (dimension in the Z direction) of the light guide 3 is t, the following equation (3)
I = I ₀ (α / 100) [1- (α / 100))] ^{L / t} (3)
Satisfying such a relationship. Here, the constant α is the light output rate, and the light guide 3 per unit length (a length corresponding to the light guide thickness t) in the X direction orthogonal to the light incident end surface 31 on the light output surface 33. It is the ratio (percentage:%) at which the light is emitted from. The light emission rate α is obtained from the gradient by plotting the relationship between the logarithm of the light intensity of the light emitted from the light exit surface 23 on the vertical axis and (L / t) on the horizontal axis. be able to.

  In addition, the other main surface to which the directional light emitting mechanism is not provided is light in order to control the directivity on a surface (YZ surface) parallel to the primary light source 1 of the light emitted from the light guide 3. It is preferable to form a lens surface in which a large number of lens rows extending in a direction substantially perpendicular to the incident end surface 31 (X direction) are arranged. In the embodiment shown in FIG. 1, a lens surface formed by arranging a rough surface on the light emitting surface 33 and an array of a large number of lens rows extending on the back surface 34 in a direction substantially perpendicular to the light incident end surface 31 (X direction). Is forming. In the present invention, conversely to the embodiment shown in FIG. 1, a lens surface may be formed on the light emitting surface 33 and the back surface 34 may be a rough surface.

  As shown in FIG. 1, when a lens array is formed on the back surface 34 or the light emitting surface 33 of the light guide 3, the lens array includes a prism array, a lenticular lens array, and a V-shaped groove extending substantially in the X direction. However, it is preferable that the YZ section has a substantially triangular prism array.

  In the present invention, when a prism row is formed as a lens row on the back surface 34 of the light guide 3, the apex angle is preferably in the range of 85 to 110 degrees. This is because the light emitted from the light guide 3 can be appropriately condensed by setting the apex angle within this range, and the luminance as the surface light source device can be improved, and more preferably It is in the range of 90 to 100 degrees.

  In the light guide of the present invention, the desired prism array shape is accurately manufactured to obtain stable optical performance, and the purpose is to suppress wear and deformation of the prism top during assembly work or use as a light source device. A flat portion or a curved surface portion may be formed at the top of the prism row.

  In the present invention, light diffusing fine particles are mixed and dispersed in the light guide instead of or in combination with the light emitting surface 33 or the back surface 34 as described above. A neutral light emitting mechanism may be provided.

  The light incident end face 31 is preferably roughened in order to adjust the spread of light in the XY plane and / or the XZ plane. Examples of the rough surface forming method include a method of cutting with a milling tool or the like, a method of polishing with a grindstone, sandpaper, buff or the like, a method of blasting, electric discharge machining, electrolytic polishing, chemical polishing or the like. Blasting particles used for blasting include spherical particles such as glass beads and polygonal particles such as alumina beads, but the use of polygonal particles has a greater effect of spreading light. It is preferable because the surface can be formed. An anisotropic rough surface can also be formed by adjusting the processing direction of cutting or polishing. In order to adjust the spread of light in the XY plane, a Z-direction machining direction can be adopted to form a streak-like uneven shape in the Z direction, and to adjust the spread of light in the XZ plane. Can adopt a processing direction in the Y direction to form a streak-like uneven shape in the Y direction. This rough surface processing can be performed directly on the light incident end face of the light guide, but a portion corresponding to the light incident end face of the mold can be processed and transferred at the time of molding.

  The degree of roughening of the light incident end face 31 is, in the light guide thickness direction, an average inclination angle θa of 1 to 5 degrees, a centerline average roughness Ra of 0.05 to 0.5 μm, and a ten-point average roughness. Rz is preferably 0.5 to 3 μm. This is because, by setting the degree of roughening of the light incident end face 31 within this range, it is possible to suppress the occurrence of bright bands or dark bands and to make it difficult to see bright lines and dark lines. The average inclination angle θa is more preferably in the range of 2 to 4.5 degrees, particularly preferably 2.5 to 3 degrees. The center line average roughness Ra is more preferably in the range of 0.07 to 0.3 μm, particularly preferably in the range of 0.1 to 0.25 μm. The ten-point average roughness Rz is more preferably in the range of 0.7 to 2.5 μm, particularly preferably 1 to 2 μm. The degree of roughening of the light incident end face 31 is, in the longitudinal direction, for the same reason as described above, the average inclination angle θa is 1 to 3 degrees, the centerline average roughness Ra is 0.02 to 0.1 μm, The ten-point average roughness Rz is preferably 0.3 to 2 μm. The average inclination angle θa is more preferably in the range of 1.3 to 2.7 degrees, particularly preferably 1.5 to 2.5 degrees. The centerline average roughness Ra is more preferably in the range of 0.03 to 0.08 μm, particularly preferably 0.05 to 0.07 μm. The ten-point average roughness Rz is more preferably in the range of 0.4 to 1.7 μm, particularly preferably 0.5 to 1.5 μm.

  On the back surface 34 of the light guide 3, a substantially flat surface region 137 having a width WP extending along the light incident end surface 31 is formed in the vicinity of the light incident end surface 31. The substantially flat surface region 137 may be a smooth surface or may be roughened (that is, a mat surface). In the substantially flat surface region 137, a prism array (in FIG. 20, the ridge line and the valley line are respectively indicated by reference numerals 34a and 34b) that is formed over the most area of the back surface 34 is not formed. . The substantially flat surface region 137 is at substantially the same height position (Z-direction position) as the valley line 34b of the prism row. The width WP of the substantially flat surface region 137 is, for example, 50 μm to 1000 μm, and is preferably about the same as or slightly larger than the width W of the light absorption band 36. A light absorption band 36 extending along the light incident end face 31 is formed in the substantially flat surface region 137. The light absorption band 36 can be formed, for example, by applying a black coating material. In order to improve the adhesion or fixability of the coating material in this coating material application, it is preferable that the substantially flat surface region 137 is roughened.

  The application of the light absorption band 36 is not particularly limited, but it is particularly preferable to use ink jet printing, screen printing, tampo printing, or thermal transfer printing. Moreover, as a material of the light absorption band 36, it is preferable to use a quick-drying material from the viewpoint of productivity, and a material having a drying time of 60 seconds or less is preferable, more preferably 40 seconds or less, and still more preferably 20 seconds or less. belongs to. Examples of such a light absorption band material include organic solvent-based paints using organic solvents such as ethyl methyl ketone, evaporative drying inks, thermosetting inks, ultraviolet curable paints, and ultraviolet curable inks. It is done. This light absorption band absorbs a part of the light introduced into the light guide 3 from the light incident end face 31, thereby preventing the generation of bright lines in the vicinity of the light incident end face 31. The visible light transmittance (JIS-K7105B) is, for example, 0 to 90%, preferably 0 to 60%, more preferably 2 to 45%, and particularly preferably 4 to 30%. Moreover, it is preferable that the reflectance (JIS-K7105B) of the light absorption band 36 is 0 to 20%, More preferably, it is 0 to 15%. In addition, although it is thought that the light which penetrates into the inside of a light guide from the back surface 34 by reflection by the light source reflector 2 without passing through a light incident end face contributes to this bright line generation, Absorption of bright lines is prevented by partially absorbing light.

  In the present embodiment, a width WT has a width WT between a region (namely, a prism row forming surface region) 139 in which the prism row is formed in a substantially complete shape on the back surface 34 of the light guide and a substantially flat surface region 137. A transition region 138 is formed. In the transition region 138, the transition from the prism row forming surface to the substantially flat surface is gradually made from the side close to the prism row forming surface region 139 to the side close to the substantially flat surface region 137. The width WT of the transition region 138 is, for example, 50 μm to 2000 μm.

  In the present embodiment, since the light absorption band 36 is formed in the substantially flat surface region 137 in which no prism row is formed, when applying the light absorption band 36 by printing or coating, the coating material is between adjacent prism rows. A surface light source device that has almost no oozing (leaching) into the prism row forming surface region 139 through the groove, can reliably form the light absorption band 36 having a predetermined width, and has good optical performance. Can be obtained stably.

  FIG. 2 is a schematic bottom view showing the light guide 3 together with the primary light source 1. As shown in FIG. 2, the light absorption band 36 does not block the light incident from the light incident end face 31, but decreases darkness due to a decrease in the amount of incident light and dark lines by blocking light to be guided. In order to suppress the occurrence of this, it is necessary to form only on the back surface 34 of the light guide 3 and not on the light incident end surface 31. The light absorption band 36 has a width (dimension in the X direction) of W, and the distance between the side edge closer to the light incident end face 31 of the two side edges defining the width and the light incident end face 31. Is D. The width W is 50 to 1000 μm, preferably 50 to 800 μm, more preferably 100 to 700 μm, and particularly preferably 200 to 400 μm. When the width W is less than 50 μm, the required bright line generation preventing effect tends to be reduced, and when the width W exceeds 1000 μm, dark lines are likely to be generated or the overall luminance tends to be reduced. The width W is preferably 0.4 times or less, more preferably 0.3 times or less, and particularly preferably 0.2 times or less of the thickness of the light guide 3 at the light incident end face position. . Further, if the distance D is 300 μm or less, the above-described bright line generation preventing effect can be obtained, preferably 200 μm or less, and particularly preferably 100 μm or less.

  In forming the light absorption band 36 on the back surface 34 of the light guide 3, a recess is formed in at least a part of the light absorption band forming portion of the back surface 34, and a coating or the like is applied to the recess to form a light absorption band. May be. That is, as shown in FIG. 8 and FIG. 9, a concave portion 70 having a triangular cross section or a lenticular shape, for example, is formed on the back surface 34 to a depth of, for example, 150 μm or less, preferably 100 μm or less, more preferably 50 μm or less. Then, the light absorption band 36 is formed so as to include the inside of the recess. If the depth of the recess 70 is too large, the waveguide mode in the light guide is lost and dark lines are likely to appear.

  The light guide 3 is not limited to the shape shown in FIG. 1, and various shapes such as a rust shape with a thicker light incident end face can be used.

  An example of the manufacturing method of the above light guide will be described with reference to FIGS. 3 and 4.

  FIG. 3 is a schematic bottom view showing a light guide material 3 ′ obtained by applying a coating material that is molded by resin molding and becomes a light absorption band. This light guide material 3 ′ is a light incident end face corresponding portion 31 ′, a back surface corresponding portion 34 ′, and a light absorption band corresponding portion when the portions corresponding to the respective portions of the light guide 3 finally obtained are shown as corresponding portions. 36 '. A required prism row is formed on the back surface corresponding portion 34 ′. A matte surface as a rough surface constituting a required light emitting mechanism is formed on the light emitting surface corresponding portion on the opposite side. A light absorption band corresponding portion 36 ′ is formed in a substantially flat region adjacent to the light incident end surface corresponding portion 31 ′ of the back surface corresponding portion 34 ′.

  As shown in FIG. 4, the light incident end face 31 is formed as a cut surface by cutting the light incident end face corresponding portion 31 ′ to remove unnecessary portions, and the light absorption band 36 is formed at the same time. . Thereby, the light emitted from the primary light source 1 can be easily incident until the light incident end surface 31 reaches the boundary with the light emitting surface 33. Further, as shown in FIGS. 3 and 4, the light absorption band corresponding portion 31 ′ is formed up to an unnecessary portion cut away by cutting, and the light incident end face correspondence of the light absorption band corresponding portion 31 ′ is obtained in the cutting process. The light emitted from the primary light source 1 is easily cut by removing the side edge portion close to the portion 31 ′ at the same time until the distance D is set to 0 μm and the light incident end surface 31 reaches the boundary with the light emitting surface 33. Can be configured to be incident.

  The light deflection element 4 is disposed on the light emitting surface 33 of the light guide 3. The two main surfaces 41 and 42 of the light deflection element 4 are arranged in parallel with each other as a whole, and are located in parallel with the XY plane as a whole. One of the main surfaces 41 and 42 (the main surface located on the light emitting surface 33 side of the light guide 3) is a light incident surface 41, and the other is a light emitting surface 42. The light exit surface 42 is a flat surface parallel to the light exit surface 33 of the light guide 3. The light incident surface 41 is a prism row forming surface in which a large number of prism rows extending in the Y direction are arranged in parallel to each other. The prism row forming surface may be provided with a relatively narrow flat portion (for example, a flat portion having a width equal to or smaller than the X direction dimension of the prism row) between adjacent prism rows. From the viewpoint of improving the utilization efficiency, it is preferable to arrange the prism rows continuously in the X direction without providing a flat portion.

  FIG. 5 shows a state of light deflection by the light deflection element 4. This figure shows the traveling direction of peak light (light corresponding to the peak of the outgoing light distribution) from the light guide 3 in the XZ plane. The peak light emitted obliquely at an angle α from the light emitting surface 33 of the light guide 3 is incident on the first surface of the prism row, is totally reflected by the second surface, and is emitted in the direction of the normal line of the light emitting surface 42. To do. Further, in the YZ plane, the luminance in the direction of the normal line of the light exit surface 42 can be sufficiently improved in a wide area by the action of the prism row on the light guide back surface 34 as described above.

  The shape of the prism surface of the prism row of the light deflection element 4 is not limited to a single plane, and can be, for example, a convex polygonal shape or a convex curved surface shape, thereby achieving high brightness and narrow field of view. it can.

  In the light deflecting element of the present invention, a desired prism shape is accurately produced, and stable optical performance is obtained, and the purpose of suppressing wear and deformation of the prism top during assembly work or use as a light source device is as follows: A flat portion or a curved surface portion may be formed at the top of the prism row. In this case, the width of the flat portion or curved surface portion formed on the top of the prism row is preferably 3 μm or less from the viewpoint of suppressing the occurrence of a nonuniform luminance pattern due to a decrease in luminance or a sticking phenomenon as a light source device. More preferably, it is 2 μm or less, and further preferably 1 μm or less.

  In the present invention, the light diffusing element 6 can be adjacently disposed on the light exit surface of the light deflecting element 4 in order to appropriately control the visual field range according to the purpose without causing a decrease in luminance as much as possible. Further, in the present invention, by disposing the light diffusing element 6 in this manner, it is possible to suppress glare, brightness spots and the like that cause deterioration in quality and to improve quality.

  The incident surface 61 of the light diffusing element 6 facing the light deflecting element 4 is preferably provided with an uneven structure in order to prevent sticking with the light deflecting element 4. Similarly, also on the exit surface 62 of the light diffusing element 6, an uneven structure is formed on the exit side surface of the light diffusing element 6 in consideration of prevention of sticking with the liquid crystal display element disposed thereon. It is preferable to give. In the case of providing this concavo-convex structure only for the purpose of preventing sticking, the concavo-convex structure is preferably a structure having an average inclination angle of 0.7 ° or more, more preferably 1 ° or more, more preferably 1 .5 degrees or more.

  The light diffusing property of the light diffusing element 6 is that the light diffusing element 6 is mixed with a light diffusing agent such as a homopolymer or copolymer such as silicone beads, polystyrene, polymethyl methacrylate, and fluorinated methacrylate. Or by providing a concavo-convex structure on at least one surface of the light diffusing element 6. The degree of the concavo-convex structure formed on the surface differs depending on whether it is formed on one surface of the light diffusing element 6 or on both surfaces. In the case of forming a concavo-convex structure on one surface of the light diffusing element 6, the average inclination angle is preferably in the range of 0.8 to 12 degrees, more preferably 3.5 to 7 degrees, and more Preferably it is 4 to 6.5 degrees. When the concavo-convex structure is formed on both surfaces of the light diffusing element 6, the average inclination angle of the concavo-convex structure formed on one surface is preferably in the range of 0.8 to 6 degrees, more preferably 2 to 2. It is 4 degrees, more preferably 2.5 to 4 degrees. In this case, in order to suppress a decrease in the total light transmittance of the light diffusing element 6, it is preferable to make the average inclination angle on the incident surface side of the light diffusing element 6 larger than the average inclination angle on the exit surface side.

  Further, the haze value of the light diffusing element 6 is preferably in the range of 8 to 82% from the viewpoint of improving luminance characteristics and improving visibility, more preferably in the range of 30 to 70%, more preferably 40. It is in the range of ~ 65%.

  FIG. 6 is a schematic plan view showing the light diffusing element 6 together with the primary light source 1. As shown in FIGS. 1 and 6, a dot pattern portion 64 is formed in the light diffusing element 6. The dot pattern portion is formed by dispersing dot-shaped light-absorbing coating materials having a diameter of 30 μm to 70 μm on the emission surface 62, and is located at a distance d 2 from a position d 1 from the light incident end face of the light guide. It exists in the area | region of the width | variety (d2-d1) including. It is preferable that the distance d1 is 2 mm or less and the distance d2 is 4 mm or more. As a result, it is possible to moderately suppress the overall brightness in the vicinity of the primary light source position and obtain a luminance distribution with less discomfort on the light emitting surface. In order to obtain such an effect efficiently, the dot pattern portion 64 preferably has a visible light transmittance of 60% to 95%. Further, in order to obtain a luminance distribution with less discomfort, the density of the dispersed arrangement of the dot-like light-absorbing coating material is increased as it moves away from the primary light source in at least a partial width region near the position of the distance d2 from the light incident end face. It is preferable to make it gradually smaller.

  The primary light source 1 is a linear light source extending in the Y direction. As the primary light source 1, for example, a fluorescent lamp or a cold cathode tube can be used. In this case, as shown in FIG. 1, the primary light source 1 is not only installed to face one side end face of the light guide 3, but is further placed on the opposite side end face as necessary. You can also. In the present invention, the primary light source 1 is not limited to a linear light source, and a point light source such as an LED light source, a halogen lamp, a metahalo lamp, or the like can also be used. In particular, when used in a display device having a relatively small screen size such as a mobile phone or a portable information terminal, it is preferable to use a small point light source such as an LED. As described above, when a point light source is used as the primary light source 1, the primary light source 1 can be arranged at a corner portion or the like of the light guide 3. In this case, the light incident on the light guide 3 propagates radially in the light guide around the primary light source 1 in the same plane as the light exit surface. Forming a light emitting mechanism in which a large number of lens rows are formed in parallel in a substantially arc shape so as to surround the point light source is preferable in terms of luminance uniformity. Further, since the emitted light emitted from the light emitting surface of the light guide 3 is also emitted radially with the primary light source 1 as the center, the emitted light emitted in such a radial manner can be efficiently used regardless of the emission direction. In order to deflect in a desired direction, it is preferable from the viewpoint of luminance uniformity that the prism rows formed in the light deflection element 4 are arranged in parallel in a substantially arc shape so as to surround the primary light source 1.

  The light source reflector 2 guides the light from the primary light source 1 to the light guide 3 with little loss. As the material, for example, a plastic film having a metal-deposited reflective layer on the surface can be used. As shown in the drawing, the light source reflector 2 avoids the light diffusing element 6 and the light deflecting element 4, and passes through the outer surface of the primary light source 1 from the outer surface of the edge of the light reflecting element 5 to the light emitting surface of the light guide 3. It is wound around the edge. On the other hand, the light source reflector 2 can be wound from the outer surface of the edge of the light reflecting element 5 to the edge of the light emitting surface of the light deflecting element 4 through the outer surface of the primary light source 1, avoiding only the light diffusing element 6. Alternatively, it is possible to wrap the light reflecting element 5 from the outer surface of the edge of the light reflecting element 5 through the outer surface of the primary light source 1 to the edge of the light emitting element 6 or avoid the light reflecting element 5. It is also possible to wind from the back surface 34 of the light guide.

  A reflection member similar to the light source reflector 2 can be attached to a side end surface other than the side end surface 31 of the light guide 3.

  As the light reflecting element 5, for example, a plastic sheet having a metal vapor deposition reflecting layer on the surface can be used. In the present invention, it is also possible to use a light reflecting layer or the like formed on the back surface 34 of the light guide 3 by metal vapor deposition or the like, instead of the reflecting sheet, as the light reflecting element 5.

  The light guide 3, the light deflecting element 4, and the light diffusing element 6 of the present invention can be made of a synthetic resin having a high light transmittance. Examples of such synthetic resins include methacrylic resins, acrylic resins, polycarbonate resins, polyester resins, and vinyl chloride resins. In particular, methacrylic resins are optimal because of their high light transmittance, heat resistance, mechanical properties, and molding processability. Such a methacrylic resin is a resin mainly composed of methyl methacrylate, and preferably has a methyl methacrylate content of 80% by weight or more. When forming a surface structure such as a rough surface or hairline of the light guide 3, the light deflecting element 4 and the light diffusing element 6 or a surface structure such as a prism array or a lenticular lens array, a transparent synthetic resin plate is formed with a desired surface structure. It may be formed by hot pressing using a mold member, or may be formed simultaneously with molding by screen printing, extrusion molding, injection molding or the like. The structural surface can also be formed using heat or a photocurable resin. Furthermore, the surface of a transparent substrate such as a polyester resin, acrylic resin, polycarbonate resin, vinyl chloride resin, polymethacrylamide resin, or the like, or a rough surface made of an active energy ray curable resin is used. A structure or a lens array arrangement structure may be formed, or such a sheet may be bonded and integrated on a separate transparent substrate by a method such as adhesion or fusion. As the active energy ray-curable resin, polyfunctional (meth) acrylic compounds, vinyl compounds, (meth) acrylic acid esters, allyl compounds, (meth) acrylic acid metal salts, and the like can be used.

  On the light emitting surface (the light exit surface 62 of the light diffusing element 6) of the surface light source device comprising the primary light source 1, the light source reflector 2, the light guide 3, the light deflecting element 4, the light diffusing element 6 and the light reflecting element 5 as described above. In addition, by arranging the liquid crystal display element LC as shown in FIG. 7, a liquid crystal display device using the surface light source device of the present invention as a backlight is configured. In FIG. 7, the dot-shaped light-absorbing coating material in a dispersed arrangement constituting the dot pattern portion of the light diffusing element 6 is indicated by reference numeral 64 '. The liquid crystal display device is observed by an observer through the liquid crystal display element LC from above in FIG. The display area of the liquid crystal display device is determined by the display area of the liquid crystal display element LC or the opening area of the frame that holds the liquid crystal display element. The effective light emission area of the surface light source device is larger than the display area of the liquid crystal display device, and exists so as to cover the entire display area. The light absorption band 36 is disposed outside the display area and outside the effective light emitting area.

  FIG. 7 shows a case where the distance D is 0 μm in the light guide 3. As shown in the figure, the light absorption band 36 extends to the boundary with the light incident end face 31, but does not extend to the light incident end face 31. That is, the light incident end face 31 is configured such that light emitted from the primary light source 1 is incident on the boundary with the rear face 34.

  Further, the light source reflector 2 is arranged so that the edge portion covers the light absorption band 36. A region having a width of about 2 to 4 mm at the outer peripheral portion of the light emitting surface of the surface light source device is covered with a frame, and no light is emitted to the outside from this region (frame-shaped region). The edge of the light source reflector 2 is located in the frame-like region, and therefore the light absorption band 36 is located in the frame-like region, that is, outside the effective light emitting region of the surface light source device.

  Of the light introduced into the light guide 3 from the light incident end face 31, most of the light L1 that reaches the light absorption band 36 is absorbed by the light absorption band. The rest is reflected by the back surface 34 and becomes light L2 traveling in the light guide. The light L2 exits from the light exit surface 33. In the present invention, the light L2 is sufficiently weaker than the light L1 due to light absorption in the light absorption band 36, and therefore hardly causes the generation of bright lines. If the light absorption band 36 does not exist, the intensity of the light L2 is considerably strong. The light L2, that is, the reflected light at the portion with the light absorption band 36 according to the present invention is the largest cause of the generation of the bright line. When the light absorption band 36 is not present, a conspicuous bright line is generated.

  A part of the light emitted from the primary light source 1 is reflected by the light source reflector 2 and reaches the light absorption band 36 without reaching the light incident end face 31, where most of it is absorbed. If the light absorption band 36 does not exist, light enters the light guide from the back surface 34 of the portion to which the light absorption band 36 is attached in the present invention. This light is also a cause of the generation of the bright line, and if the light absorption band 36 does not exist at this point, the bright line is generated.

  In the present invention, a sufficiently collimated light with a narrow luminance distribution (in the XZ plane) can be made incident on the liquid crystal display element LC from the light source device, so that there is no gradation inversion in the liquid crystal display element, brightness, Image display with good hue uniformity can be obtained, and light irradiation concentrated in a desired direction can be obtained, and the use efficiency of the emitted light amount of the primary light source 1 for illumination in this direction can be enhanced.

  In the above description of the embodiment, the light absorption band 36 has been described as having a substantially uniform light absorption characteristic in the width direction. However, in the present invention, the light absorption band may have its light absorption characteristic changed in the width direction. . As a preferable form of such light absorption characteristics, one formed so that the visible light transmittance is higher at the side edge farther from the side edge near the light incident end face of the light absorption band 36 may be mentioned. By doing so, a sudden change in light absorption at the boundary between the light absorption band 36 and the region of the light guide back surface 34 where it is not formed can be prevented, and the occurrence of uneven brightness can be further reduced. be able to.

  For example, as shown in FIG. 10, the light absorption band 36 is composed of two regions, a first region 36-1 close to the light incident end surface in the width direction (X direction) and a distant second region 36-2. By setting the thickness of the first region 36-1 to about twice the thickness of the second region 36-2, the visible light transmittance T2 of the second region 36-2 is made visible light of the first region 36-1. It can be made higher than the transmittance T1. In such a light absorption band 36 in which the visible light transmittance changes in two steps, first, a coating material is applied to both the first region 36-1 and the second region 36-2 with a uniform thickness. Later, it can be obtained by applying an additional coating material only in the first region 36-1. Similarly, it is possible to form a light absorption band in which the visible light transmittance changes in three or more stages.

  Further, as shown in FIG. 11, the thickness of the light absorption band 36 is gradually decreased from the side edge close to the light incident end face 31 to the side edge far from the light incident end face 31 in the width direction (X direction) of the light absorption band 36. The visible light transmittance of the absorption band 36 may be continuously changed in the width direction of the light absorption band 36. The light absorption band 36 having such a form can be obtained by applying the coating material while moving the mask member in the X direction from the side closer to the light incident end face 31 to the side farther from it. The continuous change in the visible light transmittance in the light absorption band 36 does not have to be over the entire width direction and may be a part in the width direction.

  The change in the visible light transmittance in the light absorption band 36 may be a combination of the step change described with reference to FIG. 10 and the continuous change described with reference to FIG.

  The visible light transmittance of the light absorption band 36 is preferably such that the lowest value is in the range of 0% to 60% and the highest value is in the range of 40% to 90%. By being in this range, the generation of dark lines can be sufficiently prevented while maintaining the effect of preventing the generation of bright lines, and the occurrence of uneven brightness can be further reduced.

  Still another example of the light guide manufacturing method as described above will be described with reference to FIGS. FIGS. 12A and 13A are partial bottom views, and FIGS. 12B and 13B are XZ partial cross-sectional views thereof.

  First, as shown in FIG. 12, it is a region in the substantially flat surface region 137 of the back surface 34 of the light guide 3 and is close to the light incident end surface 31 and separated from the light incident end surface by a distance D ′. Ink dots 36 </ b> A that are independent or partially continuous with each other are formed in the region of the width W ′ by the ink jet method. Examples of the apparatus used for carrying out the ink jet method include a continuous (continuous ejection) type printer and a DOD (drop on demand) type printer using a piezo nozzle. With these devices, ink is ejected from a large number of nozzles, and if necessary, the light guide 3 is scanned in a required direction parallel to the light emitting surface 33 with respect to the nozzles. A large number of independent ink dots 36A as shown in the region are formed. The adjacent ones of these ink dots may be completely independent as illustrated, but some of them may be partially overlapped and continuous.

  Next, adjacent ink dots are combined to form a continuous ink layer (hereinafter referred to as “leveling”). This leveling is performed for a time required to obtain a required leveling amount (degree). As a result, as shown in FIG. 13, adjacent ink dots are combined to form an ink layer 36 </ b> B that is continuous over the entire region having a width W that is a distance D from the light incident end face 31. The region of width W includes all of the region of width W ′, and the width W is slightly larger than W ′ by leveling.

  Next, the light absorption band 36 is formed by curing the ink layer 36B.

  As the ink, for example, ultraviolet curable ink is used. The ultraviolet curable ink is preferably used because a required leveling amount (degree) can be easily realized by controlling the timing of ultraviolet irradiation. Further, in order to easily control the time for obtaining a required leveling amount, it is preferable to keep the temperature of the ink discharge nozzle, that is, the temperature of the ink constant. In addition, heating the light guide 3 can also reduce the viscosity of the ink dots 36A after ink ejection such as ink drops, thereby shortening the time for obtaining the required leveling amount. The time required for printing can be shortened.

  As described above, the surface state of the light absorption band 36, that is, the degree of unevenness, can be controlled by controlling the combined state of the ink dots in the ink layer 36 </ b> B according to the leveling time. By forming appropriate irregularities on the surface of the light absorption band 36, unnecessary light can be made less noticeable. That is, as described above, when a part of the light emitted from the primary light source 1 is reflected by the light source reflector 22 and reaches the light absorption band 36 without reaching the light incident end face 31, most of the light is absorbed here. Is done. At this time, the remaining light is reflected toward the rear surface 34 of the light guide, but the reflected light is diffusely reflected by the irregularities on the surface of the light absorption band 36 so that it can be made inconspicuous.

  Higher printer resolution is desirable because ink dots can be formed closer together and the time required for leveling for combining ink dots can be reduced.

  In order to satisfactorily form the light absorption band 36 as described above, the presence of the substantially flat surface region 137 is important. That is, since the substantially flat surface region 137 having a width WP of 50 μm or more exists, a coating material is applied to the region, leveled and cured, and a light absorption band 36 having a required width extending along the light incident end surface 31 is formed. Easy to do. Here, even if the coating material oozes out into the prism row valley during application and leveling, the oozing can be prevented from becoming excessive. The width of the light absorption band 36 can be controlled by adjusting the viscosity, coating amount, etc. of the coating material to be used, thereby stably obtaining a light guide for a surface light source device with good optical performance. be able to. When the width WP of the substantially flat surface region 137 is smaller than 50 μm or the substantially flat surface region 137 does not exist, the coating material directly adheres unevenly to the slope of the prism row, and a portion where the coating material is not applied appears. Therefore, uniform leveling tends to be difficult. As a result, it becomes difficult to form a light absorption band having a required width, light absorption becomes insufficient, and the effect of preventing bright line generation in the vicinity of the light incident end face 31 tends to be difficult to obtain.

  With reference to FIG. 14, still another example of the above-described light guide manufacturing method will be described.

  In this example, first, a light guide material 3 ′ as shown in FIG. 14A is prepared. Next, as shown in FIG. 14B, the light incident end face 31 is formed by cutting the light incident end face corresponding portion 31 '. By this cutting process, a protruding portion 39 protrudes toward the back surface 34 at the boundary between the light incident end surface 31 and the back surface 34 (that is, protrudes to protrude from another region of the substantially flat surface region of the back surface 34). Is formed. The protrusion 39 extends along the boundary line between the light incident end surface 31 and the back surface 34, that is, along the light incident end surface 31. The protrusion 39 can be formed by cutting as described above, but may be formed by molding at the time of injection molding.

  Next, as shown in FIG. 14C, ink dots 36 </ b> A are formed in a required region of the back surface 34 (region in the substantially flat surface region 137). The ink dots are formed as described with reference to FIG. Next, ink dots are leveled to form an ink layer 36B in a required region of the back surface 34, as shown in FIG. The ink layer is formed as described above with reference to FIG. 13, but here, the side edge of the ink layer 36 </ b> B formed by leveling near the light incident end surface 31 reaches the protrusion 39. The position of the ink dot formation area is set. That is, the region where the ink dots 36 </ b> A shown in FIG. 14C are formed is slightly separated from the light incident end face 31. As a result, the ink flowing when the ink dots are leveled is prevented from moving to the light incident end face 31 by the protrusion 39.

  Finally, the light absorption band 36 is formed by curing the ink layer 36B.

  According to the above method, the light absorption band 36 can be easily formed without being applied to the light incident end face 31 and very close to the light incident end face 31. According to this light absorption band 36, it is possible to suppress a decrease in the amount of light incident on the light guide 3 from the light incident end face 31.

  In order to improve the action of blocking the movement of the ink to the light incident end face 31 by such a protrusion 39 at an appropriate position and facilitate the formation of the protrusion 39, the dimension of the protrusion 39 is set. It is preferable to be within the following appropriate range. That is, as shown in FIG. 18, the height of the protrusion 39 (height from another area of the substantially flat surface area of the back surface 34) is H, and the height of the protrusion 39 in the XZ cross-sectional shape is The full width at half maximum is W, preferably H is 1 to 50 μm, more preferably 2 to 30 μm, still more preferably 5 to 20 μm, and W is 1 to 50 μm, more preferably 2 to 30 μm, still more preferably 5 to 20 μm. It is. If the protrusion height H is too small, the ink movement blocking action tends to be insufficient. If the protrusion height H is too large, it becomes difficult to assemble the surface light source device, or the protrusion is chipped. Or the ink tends to be difficult to move to near the top of the protrusion. In addition, when the full width at half maximum W is too small, it is difficult to form protrusions, and the mechanical strength is low and the action of preventing ink movement tends to be uncertain, and the full width at half maximum W is too large. Assembling of the surface light source device becomes difficult, and it tends to be difficult to move the ink to the vicinity of the top of the protrusion.

  In any of the methods described above, an ultraviolet curable ink containing a (meth) acrylate monomer and / or an organic solvent is used as the ultraviolet curable ink that is a coating material for forming the light absorption band 36. preferable. This is because it is advantageous for improving the bonding force of the light absorption band 36 formed by curing the ink layer to the surface of the light guide 3. Due to the presence of the organic solvent in the ink, the anchor effect can be improved by melting and roughening the surface of the light guide 3. In particular, when a (meth) acrylic resin is used as the light guide 3, the presence of the (meth) acrylate monomer in the ink causes the ink and the light guide to be separated during polymerization in the ink. A crosslinking reaction is likely to occur in the meantime, and the anchor effect can be improved.

  The (meth) acrylate monomer and the organic solvent preferably have a number average molecular weight of 100 or more, preferably 150 or more, more preferably 200 or more so that the ink concentration does not change greatly. The (meth) acrylate monomer is, for example, methyl methacrylate, and is preferably contained, for example, by 0.5 to 10% by weight in the ink. The organic solvent preferably has a boiling point of 60 ° C. or higher, preferably 80 ° C. or higher, more preferably 100 ° C. or higher, for example, methyl ethyl ketone, ethyl acetate, chloroform, cellosolve acetate and methacrylic acid so that the ink concentration does not change greatly. Examples comprising at least one of the above are exemplified.

  Examples of such ultraviolet curable inks include those having the compositions shown below.

Ink 1:
Acrylic acid oligomer: 30-50% by weight
Isobornyl acrylate: 10 to 20% by weight
1,6-hexanediol acrylate: 1 to 20% by weight
Tetrahydrofurfuryl acrylate: 10 to 20% by weight
Benzophenone: 1 to 5% by weight
Carbon black: 1-5% by weight
Ink 2:
Isobornyl acrylate: 10 to 20% by weight
1,6-hexanediol acrylate: 1 to 20% by weight
Acrylate amine / acrylate ester mixture: 30-50% by weight
Benzophenone: 1 to 5% by weight
Carbon black: 1-5% by weight
In the present invention, when the light absorption band is formed by an inkjet method or the like, as such an ultraviolet curable ink, the ink viscosity is 1 to 100 cp and the surface tension is 20 to 55 mN / m at the head temperature at the time of ink ejection. Are preferably used, more preferably have an ink viscosity of 1 to 50 cp and a surface tension of 20 to 45 mN / m, more preferably an ink viscosity of 1 to 20 cp and a surface tension of 25 to 35 mN / m. Is. The head temperature is preferably 10 to 100 ° C., more preferably 35 to 85, from the viewpoint of leveling property of ink dots, adhesion to the light guide, and accurate application position stability of the ejected ink. ° C, more preferably in the range of 40-60 ° C.

  Further, when the light absorption band is formed by an inkjet method or the like, the head speed is set to 10 to 1000 mm / h from the viewpoint of shortening the tact time, leveling of the ink dots, adhesion to the light guide, and the like. The second is preferable, more preferably 200 to 800 mm / second, and more preferably 250 to 500 mm / second.

  In the present invention, the light absorption band 36 containing light diffusing or light absorbing fine particles can be used. The particle diameter of the fine particles is preferably 20 μm or less, more preferably 14 μm or less, and particularly preferably 8 μm or less. Such fine particles can be contained in an amount of 10 to 125% by weight based on 100 parts by weight of the coating material solid content excluding the fine particles. Examples of the light absorbing fine particles include those made of black polymer fine particles such as an acrylic resin containing carbon black, a styrene resin, a (meth) acryl / styrene copolymer resin, a benzoguanamine resin, and the like. The light diffusing fine particles include polymer fine particles such as acrylic resin, styrene resin, (meth) acryl / styrene copolymer resin and silicone resin, and inorganic fine particles such as silica, alumina and calcium carbonate. It can be illustrated. The light diffusing fine particles may use light diffusion due to surface reflection, or may be light transmissive and use light diffusion due to refraction of internally transmitted light. The light-absorbing fine particles contribute to the improvement of the light-absorbing property of the light-absorbing band 36, and the light-diffusing fine particles indirectly improve the light-absorbing property by performing light diffusion in the light-absorbing band 36, and further absorb the light. This contributes to the averaging by diffusion of the emitted light.

  FIG. 15 shows an embodiment of a light absorption band 36 containing light diffusing or light absorbing fine particles. In this embodiment, fine irregularities are formed on the surface of the light absorption band 36. The uneven projection 37 is formed by light diffusing or light absorbing fine particles 38 contained in the light absorption band 36. The unevenness can be formed along with the formation of the coating film by allowing the coating material constituting the light absorption band 36 to contain light diffusing or light absorbing fine particles 38. By forming fine irregularities on the surface of the light absorption band 36 in this way, unnecessary light can be made less noticeable. That is, as described above, when a part of the light emitted from the primary light source 1 is reflected by the light source reflector 22 and reaches the light absorption band 36 without reaching the light incident end face 31, most of the light is absorbed here. Is done. At this time, the remaining light is reflected toward the rear surface 34 of the light guide, but the reflected light is diffusely reflected by the irregularities on the surface of the light absorption band 36 so that it can be made inconspicuous.

  In FIG. 16, the enlarged view of the boundary part of the back surface 34 of the light guide 3 and the light-incidence end surface 31 is shown. The edge portion that forms the boundary between the back surface 34 and the light incident end surface 31 (the same applies to the edge portion that forms the boundary between the light emitting surface 33 and the light incident end surface 31) ideally forms a substantially right angle. Actually, in many cases, a curved surface with a small curvature radius is often accompanied with processing. In particular, when the light incident end surface 31 is formed by cutting as described above, the synthetic resin of the light guide material is partially melted by the processing, and the edge portion at the boundary between the back surface 34 and the light incident end surface 31 is formed. It may become a curved surface based on the surface tension. From the viewpoint of prevention of luminance uniformity deterioration such as prevention of bright line generation, the curvature radius R of this edge portion is preferably 50 μm or less. This is because if the radius of curvature R of the edge portion is too large, light incidence from the edge portion becomes remarkable, and this portion acts like a convex lens, and abnormal light is emitted from the light guide 3 or light. This is because the effect of preventing the bright line from being generated by the absorption band 36 may be reduced. The radius of curvature R of the edge portion is more preferably 10 μm or less, and particularly preferably 5 μm or less.

  FIG. 17 shows an enlarged view of the boundary portion between the back surface 34 and the light incident end surface 31 when the light incident end surface 31 and the side edge near the light incident end surface of the light absorption band 36 are simultaneously formed by cutting. A curved surface having a radius of curvature R (corresponding to the protrusion 39 described above) is formed at the edge portion of the boundary between the back surface 34 and the light incident end surface 31 by the surface tension, and the edge of the light absorption band 36 is one of the light guide edge portions. It is located to expose the part. The exposed portion of the light guide edge portion constitutes the light incident end face 31.

  FIG. 31 is a schematic partial bottom view showing one embodiment of a light guide for a surface light source device according to the present invention. In this figure, members or portions having the same functions as in FIGS. 1 to 20 are given the same reference numerals. FIG. 31 corresponds to FIG.

  In the present embodiment, the light absorption band 36 is formed so as to cover the entire substantially flat surface region 137 of the width WP on the back surface of the light guide and further cover a part of the transition region 138. Since the coating material applied when forming the light absorption band 36 flows through the valleys of the prism row and advances farther than the part other than the valleys, the light incident end face 31 of the light absorption band 36 is formed. The edge farther away is a zigzag shape. Thereby, the gradation effect in the light absorptivity of the light absorption zone 36 is exhibited, and the occurrence of uneven brightness can be further reduced. However, if the zigzag width of the edge far from the light incident end face 31 of the light absorption band 36 is too large, a dark band may be reflected. preferable.

  Next, even when a light source reflector with a strong regular reflection tendency is used in combination with a primary light source, it is easy to prevent the occurrence of bright lines in the vicinity of the light incident end face and to prevent the occurrence of sudden local brightness changes. 1 illustrates an embodiment of a surface light source device. As a material of the light source reflector having a strong regular reflection tendency, for example, a plastic film having a metal vapor deposition reflection layer on the surface can be used.

  FIG. 21 is a schematic perspective view showing one embodiment of a surface light source device according to the present invention. In this figure, members or portions having the same functions as in FIGS. 1 to 20 are given the same reference numerals.

  In the present embodiment, two light absorption bands are provided. That is, on the back surface 34 of the light guide, in addition to the light absorption band 36 (also referred to as “first light absorption band”) similar to that of the embodiment of FIGS. A second light absorption band 136 extending along the light incident end surface 31 is formed at a position far from the light incident end surface 31. That is, the first light absorption band 36 and the second light absorption band 136 extending along the light incident end face 31 are arranged in this order from the side closer to the light incident end face 31 on the back surface 34 of the light guide. These first and second light absorption bands 36 and 136 can be formed by applying, for example, a black coating material in the same manner as the light absorption band 36 of the embodiment of FIGS.

  The second light absorption band 136 absorbs a part of light introduced into the light guide 3 from the light exit surface 33 due to light introduced from the light incident end surface 31 into the light guide 3 or reflection by the light source reflector 2. Thus, the luminance in the region near the region where the bright line is prevented from being generated by the first light absorption band 36 and the luminance is lowered is lowered. As a result, bright lines are prevented from being generated by the first light absorption band 36, and a local sudden brightness change is prevented in the area where the brightness is lowered and in the vicinity thereof. In order to satisfactorily realize the brightness adjusting action of the second light absorption band 136, it is preferable that the visible light transmittance of the second light absorption band 136 is higher than the visible light transmittance of the first light absorption band 36. . The reason is as follows. The generation factor of the bright line related to the second light absorption band 136 is generally light introduced into the light guide 3 from the light incident end face 31 or reflection from the light source reflector 2 into the light guide 3 from the light exit surface 33. Part of the light taken into the light is totally reflected by the back surface 34 and reflected on the light guide light emitting surface 33 within the effective light emitting area of the surface light source device and further within the display area of the liquid crystal display device. It is. These emission lines are generally weak light bands having a broader spread than the emission line involving the first light absorption band 36, and in order to improve the sudden change in luminance and make a smooth emission light distribution, It is suitable to use a light absorption band having a transmittance higher than that of the first light absorption band 36 (that is, having a low absorption rate). Further, since the second light absorption band 136 is located farther from the light guide light incident end face 31 than the first light absorption band 36, the mode of the light guided through the light guide is remarkably lost and effective. There is a high risk of inducing dark lines and dark spots in the light emitting area and in the display area. Also from this viewpoint, it is preferable to use a material having a high visible light transmittance (a material having a low visible light absorption rate) as the second light absorption band 136. The visible light transmittance (JIS-K7105B) of the second light absorption band 136 is, for example, 40 to 95%, preferably 60 to 90%, and more preferably 70 to 90%. In the state where the light source reflector is disposed, the reflectance (JIS-K7105B) of the second light absorption band 36 is preferably 40 to 95%, preferably 60 to 90%, and more preferably 70. ~ 90%.

  The thickness of the light guide 3 is, for example, about 1.5 to 4 mm, preferably 2 to 3 mm in the vicinity of the light incident end face 31.

  FIG. 22 is a schematic bottom view showing the light guide 3 together with the primary light source 1. As shown in FIG. 22, the first light absorption band 36 does not block the light incident from the light incident end face 31, but blocks the decrease in luminance due to the decrease in the amount of incident light and the light to be guided. In order to suppress the generation of dark lines due to the light, it is necessary to form only on the back surface 34 of the light guide 3 and not on the light incident end surface 31. The first light absorption band 36 has a width (X-direction dimension) of W1, and of the two side edges defining the width, the side edge closer to the light incident end face 31 and the light incident end face 31 The distance is D1. The width W1 is 50 to 800 μm, preferably 100 to 500 μm, and particularly preferably 150 to 400 μm. When the width W1 is less than 50 μm, the required bright line generation preventing effect tends to be reduced, and when the width W1 exceeds 800 μm, dark lines are generated or the overall luminance tends to be reduced. The width W1 is preferably not more than 0.4 times the thickness of the light guide 3 at the light incident end face position, more preferably not more than 0.3 times, and particularly preferably not more than 0.2 times. . Further, if the distance D1 is 300 μm or less, the above-described bright line generation preventing effect is obtained, preferably 200 μm or less, and particularly preferably 100 μm or less.

  On the other hand, the second light absorption band 136 has a width (X-direction dimension) of W2, and of the two side edges defining the width, the side edge closer to the light incident end face 31 and the light incident end face 31 The distance is D2. The width W2 is preferably 50 to 800 μm, more preferably 100 to 700 μm, and particularly preferably 150 to 600 μm. If the width W2 is less than 50 μm, the required brightness adjustment effect tends to be reduced, and if the width W2 exceeds 800 μm, the overall brightness tends to decrease and the dark band appears. Moreover, if the distance D2 is in the range of 500 to 3000 μm, the above luminance adjustment effect is obtained, preferably in the range of 700 to 2000 μm, and particularly preferably in the range of 900 to 1500 μm.

  1 to 20, the first light absorption band 36 is described with reference to FIGS. 8 and 9, and the second light absorption band 136 also has the second light absorption on the back surface 34. The second light absorption band may be formed by forming a recess in at least a part of the band forming portion and applying a paint or the like to the recess.

  An example of a method of manufacturing the light guide as described above will be described with reference to FIGS. These drawings correspond to FIGS. 3 and 4 described above, and members or portions having the same functions as those in FIGS. 3 and 4 are denoted by the same reference numerals. In FIG. 23, a required prism row is formed on the back surface corresponding portion 34 '. A matte surface as a rough surface constituting a required light emitting mechanism is formed on the light emitting surface corresponding portion on the opposite side. In the substantially flat region near the light incident end face corresponding portion 31 ′ of the back surface corresponding portion 34 ′, the first light absorption band corresponding portion 36 ′ and the second light absorption band separated from the first light absorption band corresponding portion 36 ′. A corresponding portion 136 ′ is formed. As shown in FIG. 24, the light incident end face 31 is formed by cutting the light incident end face corresponding portion 31 ′ to remove unnecessary portions, and the first light absorption band 36 is formed at the same time. Is done. The second light absorption band corresponding portion 136 ′ can be used as it is as the second light absorption band 136.

  On the light emitting surface (the light exit surface 62 of the light diffusing element 6) of the surface light source device comprising the primary light source 1, the light source reflector 2, the light guide 3, the light deflecting element 4, the light diffusing element 6 and the light reflecting element 5 as described above. In addition, by disposing the liquid crystal display element LC as shown in FIG. 25, a liquid crystal display device using the surface light source device of the present invention as a backlight is configured. This figure corresponds to FIG. 7 described above, and members or parts having the same functions as those in FIG. 7 are denoted by the same reference numerals.

  FIG. 25 shows a case where the distance D1 in the light guide 3 is 0 μm. As shown in the drawing, the first light absorption band 36 extends to the boundary with the light incident end face 31, but does not extend to the light incident end face 31. That is, the light incident end face 31 is configured such that light emitted from the primary light source 1 is incident on the boundary with the rear face 34.

  Further, the light source reflector 2 is arranged so that the edge portion thereof covers the first and second light absorption bands 36 and 136 via the light reflecting element 5. However, the edge portion of the light source reflector 2 may be disposed inside the light reflecting element 5 so as to directly cover the first and second light absorption bands 36 and 136. Further, the light source reflector 2 may not cover the second light absorption band 136. A region having a width of about 2 to 4 mm at the outer peripheral portion of the light emitting surface of the surface light source device is covered with a frame, and no light is emitted to the outside from this region (frame-shaped region). The edge of the light source reflector 2 is located within the frame-like region, and therefore the first and second light absorption bands 36, 136 are located within the frame-like region, that is, outside the effective light emitting region of the surface light source device. is doing. However, the second light absorption band 136 may be located outside the frame-shaped region, that is, within the effective light emitting region of the surface light source device.

  Of the light introduced into the light guide 3 from the light incident end face 31, most of the light L1 that reaches the first light absorption band 36 is absorbed by the first light absorption band. The rest is reflected by the back surface 34 and becomes light L2 traveling in the light guide. The light L2 exits from the light exit surface 33. In the present invention, the light L2 is sufficiently weakened than the light L1 by the light absorption in the first light absorption band 36, and therefore hardly causes the generation of bright lines. If the first light absorption band 36 does not exist, the intensity of the light L2 is considerably strong. The light L2, that is, the reflected light at the portion with the first light absorption band 36 in the present invention is the largest cause of the generation of the bright line, and when the first light absorption band 36 is not present, a conspicuous bright line is generated.

  In particular, when the light source reflector 2 or the light reflecting element 5 having a strong regular reflection tendency is used and the first light absorption band 36 does not exist, a part of the light in the light guide 3 is the back surface 34. And is specularly reflected by the light reflecting element 5 (in FIG. 25, the light reflecting element 5 is arranged on the inner side of the edge of the light source reflector 2 so that it is specularly reflected by the light reflecting element 5). When the edge portion of the light source reflector 2 is disposed inside the light reflecting element 5, it is regularly reflected by the light source reflector 2), and is again transmitted through the back surface 34 and introduced into the light guide 3. Based on this, a very noticeable bright line is generated. In order to prevent the generation of such very conspicuous bright lines, it is desirable to use a first light absorption band 36 having a sufficiently low visible light transmittance. However, in the case where the occurrence of the noticeable bright line is prevented by the first light absorption band 36 as described above, the brightness of the area where the bright line is reduced is too low compared with the brightness of the area in the vicinity thereof. The brightness contrast of the image becomes large (that is, a sudden local brightness change occurs), and the bright line removal area is visually recognized as a dark line, or the area near the bright line reduction area is weak but visually recognized as a bright line. Sometimes. That is, even if the conspicuous bright line is removed, a sudden and rapid change in luminance may occur, and the quality of the display image when used as a backlight of a display device may be reduced.

  However, in the present invention, by arranging the second light absorption band 136, the luminance of the region in the vicinity of the bright line reduction region is adjusted so that the difference from the luminance of the bright line reduction region is small, and in these regions, In other words, the luminance contrast in these regions is not increased. Therefore, the bright line reduced area is not visually recognized as a dark line, or the area in the vicinity thereof is not visually recognized as a bright line.

  That is, most of the light L3 reaching the second light absorption band 136 among the light introduced into the light guide 3 from the light incident end face 31 is absorbed by the second light absorption band. The remainder is reflected by the back surface 34 and becomes light L4 traveling in the light guide. The light L4 is emitted from the light emitting surface 33. In the present invention, the light L4 is sufficiently weakened than the light L3 by the light absorption in the second light absorption band 136. Therefore, the intensity difference from the light L2 is reduced, and thus the light L2 There is no significant difference in luminance between the region where light is first emitted from the emission surface and the region where light L4 in the vicinity of the region is first emitted from the light emission surface (that is, the luminance contrast is not large).

  In particular, the light L5 introduced into the light guide 3 from the edge portion that forms the boundary between the light guide light emitting surface 33 and the light incident end surface 31 and reaching the second light absorption band 136 is the second light absorption band. Part of it is absorbed. The remaining light is reflected by the back surface 34 and becomes light L6 traveling in the light guide. The light L6 is emitted from the light emitting surface 33. In the present invention, the light L6 is weaker than the light L5 due to light absorption in the second light absorption band 136. Therefore, the intensity difference from the light L2 is reduced, and thus the light L2 is emitted from the light emitting surface. There is no significant difference in luminance between the region where light is emitted first from and the region where the light L6 in the vicinity thereof is first emitted from the light emitting surface (that is, the luminance contrast is not large).

  A part of the light emitted from the primary light source 1 is reflected by the light source reflector 2 and reaches the first and second light absorption bands 36 and 136 without reaching the light incident end face 31, where Most of it is absorbed. If the light absorption bands 36 and 136 do not exist, light enters the light guide body from the back surface 33 of the portion to which the light absorption bands 36 and 136 are attached according to the present invention. This light is also the cause of the generation of the bright line. In this respect, if the light absorption bands 36 and 136 do not exist, the bright line is generated.

  In the above description of the embodiment, the first and second light absorption bands 36 and 136 have been described as having substantially uniform light absorption characteristics in the width direction. However, in the present invention, the first and second light absorption bands are used. The band may have its light absorption characteristic changed in the width direction. As a preferable form of such light absorption characteristics, one formed so that the visible light transmittance is higher at the side edge farther from the side edge near the light incident end face of the first light absorption band 36 can be cited. . By doing so, a sudden change in light absorption at the boundary between the first light absorption band 36 and the region of the light guide back surface 34 where it is not formed can be prevented, and a sudden brightness change locally. Can be further reduced. Similarly, the second light absorption band 136 may be formed so that the visible light transmittance is higher at both side edges than at the center. By doing so, a sudden change in light absorption at the boundary between the second light absorption band 136 and the region of the light guide back surface 34 where it is not formed can be prevented, and a local abrupt brightness change can be achieved. Can be further reduced.

  For example, as shown in FIG. 26, the first light absorption band 36 is composed of a first region 36-1 close to the light incident end face in the width direction (X direction) and a second region 36-2 far away. By setting the thickness of the first region 36-1 to approximately twice the thickness of the second region 36-2, the visible light transmittance T2 of the second region 36-2 is set to be the same as that of the first region 36-1. It can be made higher than the visible light transmittance T1. In the first light absorption band 36 in which the visible light transmittance changes in two steps, first, the coating material is applied to both the first region 36-1 and the second region 36-2 with a uniform thickness. Thereafter, it can be obtained by applying additional coating material only in the first region 36-1. Similarly, it is possible to form a first light absorption band in which the visible light transmittance changes in three or more stages.

  Similarly, the second light absorption band 136 is composed of the first region 136-1, the second region 136-2, and the third region 136-3 in the order closer to the light incident end face in the width direction (X direction). And the thickness of the second region 136-2 is about three times the thickness of the first and third regions 136-1, 136-3, so that the first and third regions 136-1, 136 are -3 visible light transmittance T2 can be higher than the visible light transmittance T3 of the second region 136-2. In the second light absorption band 136 in which the visible light transmittance changes in two steps, first, the coating material is applied to the first to third regions 136-1 to 136-3 with a uniform thickness. After that, it can be obtained by applying an additional coating material only in the second region 136-2. Similarly, it is possible to form a second light absorption band in which the visible light transmittance changes in three or more stages.

  Further, as shown in FIG. 27, the thickness of the first light absorption band 36 is gradually reduced from the side edge close to the light incident end face 31 to the side edge far from the light incident end face 31 in the width direction (X direction) of the first light absorption band 36. Thus, the visible light transmittance of the first light absorption band 36 may be continuously changed in the width direction of the first light absorption band 36. Similarly, the visible light transmittance of the second light absorption band 136 is reduced by gradually decreasing the thickness of the second light absorption band 136 from the center to both side edges in the width direction (X direction) of the second light absorption band 136. The second light absorption band 36 may be continuously changed in the width direction. The first and second light absorption bands 36 and 136 having such a form can be obtained by applying the coating material while moving the mask member in the X direction from the side closer to the light incident end face 31 to the side farther from the side. it can. The continuous change in the visible light transmittance in the first and second light absorption bands 36, 136 does not need to extend over the entire width direction and may be a part of the width direction.

  The change in the visible light transmittance in the first and second light absorption bands 36, 136 may be a combination of the step change described with reference to FIG. 26 and the continuous change described with reference to FIG. .

  The visible light transmittance of the first light absorption band 36 is preferably such that the lowest value is in the range of 0% to 60% and the highest value is in the range of 40% to 90%. Further, it is preferable that the visible light transmittance of the second light absorption band 136 has a lowest value in the range of 40% to 90% and a highest value in the range of 60% to 95%. By being within these ranges, the generation of dark lines can be prevented while maintaining the effect of preventing the generation of bright lines, and the occurrence of sudden local brightness changes can be further reduced.

  28 and 29, still another example of the light guide manufacturing method as described above will be described. These drawings correspond to FIGS. 12 and 13 described above, and members or parts having the same functions as those in FIGS. 12 and 13 are denoted by the same reference numerals.

  First, as shown in FIG. 28, the light guide 3 is located in the substantially flat surface region 137 on the back surface 34, close to the light incident end surface 31 and separated from the light incident end surface by a distance D1 ′. In the same manner as described above with reference to FIGS. 12 and 13, the ink dots 36 </ b> A that are independent of each other or partially continuous are formed in the region of the width W <b> 1 ′ by the inkjet method.

  Next, ink dots are leveled in the same manner as described above with reference to FIGS. As a result, as shown in FIG. 29, adjacent ones of the ink dots are combined to form an ink layer 36B that is continuous over the entire area of the width W1 separated from the light incident end face 31 by the distance D1. The region having the width W1 includes the entire region having the width W1 'and is slightly larger than the width W1' due to leveling.

  Next, the first light absorption band 36 is formed by curing the ink layer 36B.

  The above description of the first light absorption band 36 also applies to the second light absorption band 136. That is, as shown in FIG. 28, in the same manner, an area within the substantially flat surface area 137 of the back surface 34 of the light guide 3 and distant from the area of the width W1 ′ is mutually connected by the inkjet method. Independent or partially continuous ink dots 136A are formed. The adjacent ones of these ink dots may be completely independent as illustrated, but some of them may be partially overlapped and continuous. Next, ink dots are leveled in the same manner. As a result, as shown in FIG. 29, adjacent ones of the ink dots are combined to form an ink layer 136B that is continuous over the entire area away from the area of the width W1. Next, the second light absorption band 136 is formed by curing the ink layer 136B. As described above, the surface state of the second light absorption band 136, that is, the degree of unevenness, can be controlled by controlling the ink dot coupling state in the ink layer 136B to a desired one by the leveling time. By forming appropriate irregularities on the surface of the second light absorption band 136, unnecessary light can be made less noticeable. That is, as described above, when a part of the light emitted from the primary light source 1 is reflected by the light source reflector 22 and reaches the second light absorption band 136 without reaching the light incident end face 31, most of the light is here. Is absorbed. At this time, the remaining light is reflected toward the rear surface 34 of the light guide, but this reflected light can be made inconspicuous by diffusing and reflecting the unevenness of the surface of the second light absorption band 136.

  In addition, the time for formation is shortened by forming the 1st and 2nd light absorption bands 36 and 136 as mentioned above in parallel.

  Still another example of the above-described light guide manufacturing method will be described with reference to FIG. This figure corresponds to FIG. 14 described above, and members or parts having the same functions as those in FIG. 14 are denoted by the same reference numerals.

  In this example, first, a light guide material 3 ′ as shown in FIG. 30A is prepared. Next, as shown in FIG. 30B, the light incident end face 31 is formed by cutting the light incident end face corresponding portion 31 ′. By this cutting process, a protruding portion 39 protruding toward the back surface 34 is formed at the boundary between the light incident end surface 31 and the back surface 34. The protrusion 39 extends along the boundary line between the light incident end surface 31 and the back surface 34, that is, along the light incident end surface 31. The protrusion 39 can be formed by cutting as described above, but may be formed by molding at the time of injection molding.

  Next, as shown in FIG. 30C, ink dots 36 </ b> A and 136 </ b> A are formed in a required region of the back surface 34. The ink dots are formed as described with reference to FIG. Next, ink dots are leveled, and ink layers 36B and 136B are formed in a required region of the light emitting surface 33, as shown in FIG. These ink layers are formed as described above with reference to FIG. 29, but here, the side edge of the ink layer 36B formed by leveling near the light incident end face 31 reaches the protrusion 39. The position of the ink dot formation area is set. That is, the region where the ink dots 36 </ b> A shown in FIG. 30C are formed is slightly separated from the light incident end face 31. As a result, the ink flowing when the ink dots are leveled is prevented from moving to the light incident end face 31 by the protrusion 39.

  Finally, the ink layers 36B and 136B are cured to form the first and second light absorption bands 36 and 136.

  According to the above method, as described above with reference to FIG. 14, the first light absorption band 36 can be easily formed without being applied to the light incident end face 31 and very close to the light incident end face 31. . According to the first light absorption band 36, it is possible to suppress a decrease in the amount of light incident on the light guide 3 from the light incident end face 31. This method also applies to what has been described with reference to FIG.

  In the present invention, as described with reference to FIG. 15, the first and second light absorption bands 36, 136 containing light diffusing or light absorbing fine particles can be used. .

  FIG. 32 is a schematic partial perspective view showing one embodiment of a light guide for a surface light source device according to the present invention. In this figure, members or portions having the same functions as those in FIGS.

  In the present embodiment, a substantially flat surface region 137 a having a predetermined width extending along the light incident end surface 31 is formed in the vicinity of the light incident end surface 31 on the back surface 34 of the light guide 3. A region of the back surface 34 other than the substantially flat surface region 137a is a prism row forming surface region 139. The substantially flat surface region 137a may be a smooth surface or roughened, similar to the substantially flat surface region 137. However, unlike the substantially flat surface region 137, the substantially flat surface region 137a is substantially at the same height position (Z-direction position) as the ridge line of the prism row. The width of the substantially flat surface region 137a is approximately the same as that of the substantially flat surface region 137. A light absorption band 36 extending along the light incident end face 31 is formed in the substantially flat surface region 137a. A transition region having the same function as described in the above embodiment may be provided between the substantially flat surface region 137a and the prism row forming surface region 139.

  In the present embodiment, since the substantially flat surface region 137a is at substantially the same Z-direction position as the ridge line of the prism row, there is an advantage that it is easy to manufacture a mold for manufacturing a light guide. Such a substantially flat surface region 137a can be used in place of the substantially flat surface region 137 in all the above embodiments.

  Furthermore, in the present embodiment, a light absorption band 236 extending along the light incident end surface 31 is also formed on the light emitting surface 33 which is a mat surface constituting the directional light emitting mechanism. The light absorption band 236 is configured such that the width (dimension in the X direction) and the positional relationship with respect to the light incident end face 31 are the same as those described with respect to the light absorption band 36, and the same as the light absorption band 36. It has a function.

  According to the present embodiment, since the light absorption band 236 is further provided in addition to the light absorption band 36, generation of bright lines in the vicinity of the light incident end face can be more effectively prevented. However, in this case, it is preferable that the visible light transmittance of the light absorption band 236 is lower than the visible light transmittance of the light absorption band 36.

  Similarly, in the embodiment shown in FIGS. 21 to 30, a light absorption band 236 extending along the light incident end surface 31 can be formed on the light emitting surface 33. Further, as shown in FIG. 33, in the embodiment of FIGS. 21 to 30 described above, the light emission surface 33 has a width (dimension in the X direction) and a positional relationship with respect to the light incident end surface 31 in addition to the light absorption band 236. The second light absorption band 336 configured to be equivalent to that described for the second light absorption band 136 may be formed. Here, the operation of the light absorption band 236 and the second light absorption band 336 will be described (the operation of the light absorption band 36 and the second light absorption band 136 is as described above).

  Of the light introduced into the light guide 3 from the light incident end face 31, most of the light L1 'reaching the light absorption band 236 is absorbed by the light absorption band. The remainder is reflected by the light emitting surface 33 to become light L2 'that travels in the light guide. The light L <b> 2 ′ is emitted from the back surface 34, reflected by the light reflecting element 5, reentered into the light guide, and emitted from the light emitting surface 33. In the present invention, the light L2 'is sufficiently weaker than the light L1' due to light absorption in the first light absorption band 36, and therefore the generation of bright lines is further suppressed.

  Of the light introduced from the light incident end face 31 into the light guide 3, a part of the light L <b> 3 ′ reaching the second light absorption band 336 is absorbed by the second light absorption band. The remaining light is reflected by the light emitting surface 33 and becomes light L4 'traveling in the light guide. The light L 4 ′ is emitted from the back surface 34, reflected by the light reflecting element 5, reenters the light guide, and is emitted from the light emitting surface 33. In the present invention, the light L4 ′ is weaker than the light L3 ′ due to light absorption in the second light absorption band 336, and thus the intensity difference from the light L2 ′ is reduced, and thus the light L2 ′. However, there is no significant difference in luminance between the region where light is first emitted from the light emitting surface and the region where light L4 ′ in the vicinity thereof is first emitted from the light emitting surface (that is, it contributes to reduction of luminance contrast).

  In particular, the light L5 ′ introduced into the light guide 3 from the edge part forming the boundary between the light guide back surface 34 and the light incident end surface 31 and reaching the second light absorption band 336 is caused by the second light absorption band. Part of it is absorbed. The remaining light is reflected by the light emitting surface 33 and becomes light L6 'traveling in the light guide. The light L 6 ′ is emitted from the back surface 34, reflected by the light reflecting element 5, reentered into the light guide, and emitted from the light emitting surface 33. In the present invention, the light L6 ′ is weaker than the light L5 ′ due to light absorption in the second light absorption band 336, and thus the intensity difference from the light L2 ′ is reduced, and thus the light L2 ′. However, there is no significant difference in luminance between the region where light is first emitted from the light emitting surface and the region where light L6 ′ in the vicinity thereof is first emitted from the light emitting surface (that is, it contributes to reduction of luminance contrast).

  A part of the light emitted from the primary light source 1 is reflected by the light source reflector 2 and reaches the light absorption band 236 and the second light absorption band 336 without reaching the light incident end face 31, where Most are absorbed. For this reason, generation of bright lines is further suppressed.

  Such formation of the light absorption band 236 and the second light absorption band 336 on the light emitting surface 33 may be additionally employed in the embodiment of FIGS.

  In the above embodiment, the prism array forming surface is provided on the back surface 34 of the light guide 3 and the light emitting mechanism is provided on the light emitting surface 33. A rough surface may be provided, and a prism row forming surface may be provided on the light emitting surface 33. That is, in the embodiment shown in FIGS. 1 to 20, the embodiment shown in FIGS. 21 to 30, the embodiment shown in FIG. 32, and the other embodiments, the light absorption bands 36 and 236 and the second light absorption bands 136 and 336 are used. The arrangement of the light guide 3 is reversed upside down, or the arrangement of the light guide 3 is reversed upside down while maintaining the arrangement of the light absorption bands 36 and 236 and the second light absorption bands 136 and 336 to form a prism array. The surface may be a light emitting surface and the rough surface may be disposed on the back surface side. Even with such an arrangement, the same effects as described in the above embodiment can be obtained based on the action of the light absorption band and further the second light absorption band.

  In this case, the substantially flat surface regions 137 and 137a are formed even in the case where the light absorption band 36 and the second light absorption band 136 are not formed on the light emission surface or the back surface where the prism row is formed. By doing so, generation of bright lines is further suppressed. This is because, when the substantially flat surface regions 137 and 137a are not formed, a gap is easily formed between the edge of the light source reflector 2 and the prism row forming surface of the light guide, and the primary light source is formed through the gap. There is a case where light is incident on the prism array forming surface from 1 and this may cause a bright line. However, when the substantially flat surface regions 137 and 137a are formed, the edge of the light source reflector 2 and the light guide are formed. This is probably because a gap is not easily formed between the body and the prism array forming surface, and therefore, light incidence from the primary light source 1 to the prism array forming surface is unlikely to occur.

  Hereinafter, the present invention will be described by way of examples.

[Examples 1-9, Comparative Examples 1-3]
By injection molding using an acrylic resin (Acrypet [trade name] manufactured by Mitsubishi Rayon Co., Ltd.), one surface is a mat surface, the other surface is a prism apex angle of 100 degrees, the apex tip curvature radius is 15 μm, and the pitch is 50 μm. A rectangular and wedge-shaped light guide material, which is a prism array forming surface provided with prism patterns arranged in a row so that the prism arrays are parallel to the short sides, was produced. However, this light guide material is not a prism row formed on the entire other surface on which the prism row is formed, and has various widths (Examples 1 to 9 and Comparative examples 1 to 3) have a region consisting of a substantially flat surface at substantially the same height as the valley line of the prism row, and a transition region having a width of 500 μm that gradually transitions from the flat surface to the prism row formation surface. It was supposed to have.

  The following black ink is formed by screen printing on the substantially flat surface region of the prism array forming surface of the light guide material from the longer side having the larger thickness to various widths (Examples 1 to 11 and Comparative Examples 1 to 5). Was applied to form a light absorption band corresponding part. There was substantially no occurrence of ink bleeding transfer to the transition region and the prism row forming surface region. In the same manner, the visible light transmittance of the ultraviolet curable black ink was 30% when black ink was printed on a transparent acrylic plate having a thickness of 2 mm to a size allowing visible light transmittance to be measured.

Black ink:
Acrylic acid oligomer: 45% by weight
Isobornyl acrylate: 17% by weight
1,6-hexanediol acrylate: 15% by weight
Tetrahydrofurfuryl acrylate: 15% by weight
Benzophenone: 3% by weight
Carbon black: 5% by weight
Next, by cutting the light incident end face corresponding portion of the light guide material and cutting off unnecessary portions including a part of the light absorption band corresponding portion, the light incident end surface and the light absorption formed as the cut surface. A light guide with a band was obtained. The light guide has a wedge plate shape of 230 mm × 290 mm and a thickness of 2.6 mm-0.7 mm, the radius of curvature R of the edge portion is 40 μm, and the light absorption band has a distance of 0 μm from the light incident surface. The width of was as follows. The light guide material was prepared so that the width of the substantially flat surface region of the obtained light guide was about 50 μm larger than the width of the light absorption band:
Example 1—800 μm
Example 2—700 μm
Example 3—600 μm
Example 4—500 μm
Example 5—400 μm
Example 6—300 μm
Example 7—200 μm
Example 8—150 μm
Example 9—75 μm
Comparative Example 1 --- 20μm
Comparative Example 2—1500 μm
Comparative Example 3—20 μm (a light absorption band having a width of 20 μm is continuously formed on the light incident end face side).

  The cold cathode fluorescent lamp is connected to the light source reflector (long side) so as to face one side end surface (end surface on the side of 2.6 mm thickness) corresponding to the side (long side) of the light guide having a length of 290 mm. A silver reflective film manufactured by Reiko Co., Ltd.) was placed. Furthermore, a light diffusive reflection film (E60 [trade name] manufactured by Toray Industries, Inc.) was attached to the other side end surface, and a reflection sheet was disposed so as to face the surface (back surface) of the prism array. The above configuration was incorporated into the frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  Here, the light source reflector is wound from the outer surface of the edge of the back surface of the light guide to the edge of the light output surface of the light guide through the outer surface of the primary light source, and the light absorption band is covered by the edge of the light source reflector. (However, in Comparative Example 2, the edge of the light source reflector is moved 1.3 mm above the back surface of the light guide body light incident end surface so that a part of the light absorption band is covered by the edge portion of the light source reflector). Protruded. Further, the frame body was configured to shield a region having a width of 2.5 mm on the outer peripheral portion of the light guide light emitting surface (that is, the width of the frame-shaped region was 2.5 mm). That is, the edge part of the light source reflector is located in the frame-like region, and the light absorption band is located in the frame-like region, that is, outside the effective light emitting region of the surface light source device.

  On the other hand, using an acrylic ultraviolet curable resin having a refractive index of 1.5064, a large number of prism rows having a convex curved surface shape with a radius of curvature of one prism surface of 400 μm, the other prism surface having a planar shape, and a pitch of 50 μm. A prism sheet was produced in which a prism array in parallel was formed on one surface of a 125 μm thick polyester film.

  In the obtained prism sheet, the prism array forming surface faces the light exit surface (matte surface) side of the light guide, and the ridge line of the prism array is parallel to the light incident end surface of the light guide, so that the light incident on the light guide The prisms were placed so that the planar prism surfaces of each prism row faced toward the end surface.

  For the surface light source devices of Examples 1 to 9 and Comparative Examples 1 to 3 obtained as described above, the primary light source was turned on under the same conditions and the light emitting surface was visually observed. In the case, the bright line and dark line in the vicinity of the light guide light incident end face are inconspicuous to the extent that they do not interfere with actual use, and the decrease in the overall luminance is such that they do not interfere with actual use. In the comparative example 1, a clear bright line is recognized in the vicinity of the light guide light incident end face, and in the comparative example 2, the light guide light incident end face is nearer than those in Examples 1-9. A decrease in brightness was observed, and in Comparative Example 3, a decrease in luminance and dark lines in the display area were observed compared to those in Examples 1-9.

[Example 10]
A light guide material was prepared in the same manner as in Example 1. Thereafter, the light-receiving material was cut into the light incident end face corresponding portion to obtain a light guide having a light incident end face formed as a cut surface. The light guide had a wedge plate shape of 230 mm × 290 mm and a thickness of 2.6 mm-0.7 mm. A large number of the following ultraviolet curable black inks are dropped by an ink-jet method onto a substantially flat surface region having a width of about 400 μm on the prism row forming surface (back surface) of the light guide material on which this prism pattern is formed, as shown in FIG. A large number of independent ink dots having a diameter of about 70 μm were formed in a region where the width W ′ was about 210 μm and the distance D ′ was about 60 μm. In this state, the ink dots were leveled for 5 seconds to form a continuous ink layer over the entire region having a width W of about 300 μm and a distance D of about 10 μm as shown in FIG. At that time, the ink layer was cured by irradiating ultraviolet rays to form a substantially linear light absorption band.

Inkjet method:
Head speed: 400 mm / second Head temperature: 55 ° C.
Piezoelectric feeding method UV curable black ink (ink 95% by weight + methyl methacrylate 5% by weight):
Ink composition:
Acrylic acid oligomer: 42% by weight
Isobornyl acrylate: 15% by weight
1,6-hexanediol acrylate: 20% by weight
Acrylate amine / acrylate ester mixture: 15% by weight
Benzophenone: 3% by weight
Carbon black: 5% by weight
Ink viscosity (55 ° C.): 10 cp
Ink surface tension (55 ° C.): 30 mN / m
In the same way, when the ultraviolet curable black ink was printed on a transparent acrylic plate having a thickness of 2 mm so that the visible light transmittance could be measured, the visible light transmittance of the ultraviolet curable black ink was 20%. It was.

  The obtained light guide was combined with a cold cathode tube, a light source reflector, a light diffusing reflection film, and a reflection sheet in the same manner as in Example 1, and the resulting structure was incorporated into a frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  With respect to the surface light source device obtained as described above, when the primary light source was turned on and the light emitting surface was visually observed, bright lines and dark lines in the vicinity of the light guide light incident end face were hardly noticeable.

[Comparative Example 4]
A light guide material similar to that in Example 1 is manufactured, and then the light incident end surface corresponding portion of the light guide material is cut to obtain a light guide having a light incident end surface formed as a cut surface. It was. In this comparative example, no light absorption band was formed.

  The obtained light guide was combined with a cold cathode tube, a light source reflector, a light diffusing reflection film, and a reflection sheet in the same manner as in Example 1, and the resulting structure was incorporated into a frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  With respect to the surface light source device obtained as described above, the primary light source was turned on under the same conditions as in Example 10 and the light emitting surface was visually observed. As a result, a clear bright line in the vicinity of the light guide light incident end surface was observed. Admitted.

[Example 11]
A light guide material was prepared in the same manner as in Example 1. Thereafter, the light-receiving material was cut into the light incident end face corresponding portion to obtain a light guide having a light incident end face formed as a cut surface. The light guide had a wedge plate shape of 230 mm × 290 mm and a thickness of 2.6 mm-0.7 mm. In the same manner as in Example 10, a large number of ultraviolet curable black inks were dropped on the substantially flat surface region having a width of about 400 μm on the prism row forming surface (back surface) of the light guide material on which this prism pattern was formed, by the inkjet method, A large number of ink dots having a diameter of about 70 μm were formed in a region having a width W ′ of about 210 μm and a distance D ′ of about 60 μm as shown in FIG. Immediately thereafter, the ink dots were cured by irradiating with ultraviolet rays so as not to level the ink dots, and a substantially linear light absorption band was formed. In this light absorption band, each ink dot was positioned independently of each other, the width was about 210 μm, and the distance from the light incident end face was about 60 μm.

  In the same way, when the ultraviolet curable black ink was printed on a transparent acrylic plate having a thickness of 2 mm so that the visible light transmittance could be measured, the visible light transmittance of the ultraviolet curable black ink was 20%. It was.

  The obtained light guide was combined with a cold cathode tube, a light source reflector, a light diffusing reflection film, and a reflection sheet in the same manner as in Example 1, and the resulting structure was incorporated into a frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  For the surface light source device obtained as described above, the primary light source was turned on under the same conditions as in Example 10 and the light emitting surface was visually observed. Furthermore, some bright lines were observed in the vicinity of the light guide light incident end face.

[Examples 12 to 20, Comparative Examples 5 to 7]
In the same manner as in Example 1, one surface is a mat surface, and the other surface is arranged in a row so that prism rows with a prism apex angle of 100 degrees, a apex tip radius of curvature of 15 μm, and a pitch of 50 μm are parallel to the short side. A rectangular and wedge-shaped light guide material, which is a prism row forming surface provided with a prism pattern, was prepared. However, this light guide material is not a prism row formed on the entire other surface on which the prism rows are formed, but has various widths (Examples 12 to 20 and In Comparative Examples 5 to 7), a transition region having a substantially flat surface at substantially the same height as the ridgeline of the prism row and having a width of 50 μm gradually transitioning from the flat surface to the prism row formation surface is provided. It was supposed to have. In the substantially flat surface region of the prism array forming surface of the light guide material, the same as in Example 1, except that various widths from the longer side with the larger thickness (Examples 12 to 20 and Comparative Examples 5 to 7). ), Black ink was applied by screen printing to form a light absorption band corresponding part. There was no occurrence of ink bleeding transfer to the transition region and the prism row forming surface region. In the same manner, the visible light transmittance of the ultraviolet curable black ink was 40% when black ink was printed on a transparent acrylic plate having a thickness of 2 mm to a size allowing visible light transmittance to be measured. Further, a black ink was applied to the mat surface of the light guide material by screen printing as in Example 6 to form a light absorption band corresponding portion.

Next, cutting is performed on the light incident end face corresponding portion of the light guide material, and unnecessary portions including part of the light absorption band corresponding portions on both sides of the light guide material are cut off, thereby forming a cutting surface. A light guide having a light incident end face and light absorption bands on both sides was obtained. The light guide has a wedge plate shape of 230 mm × 290 mm and a thickness of 2.6 mm-0.7 mm, the radius of curvature R of the edge portion is 40 μm, and the distance from the light incident surface is 0 μm. The width of the light absorption band was as follows. The light guide material was prepared so that the width of the substantially flat surface region of the obtained light guide was about 100 μm larger than the width of the light absorption band:
Example 12—800 μm
Example 13—700 μm
Example 14 --- 600 μm
Example 15--500 μm
Example 16--400 μm
Example 17—300 μm
Example 18--200 μm
Example 19--150 μm
Example 20—75 μm
Comparative Example 5——20 μm
Comparative Example 6—1500 μm
Comparative Example 7—20 μm (a light absorption band having a width of 20 μm is continuously formed on the light incident end face side).

  The obtained light guide was combined with a cold cathode tube, a light source reflector, a light diffusing reflection film, and a reflection sheet in the same manner as in Example 1, and the resulting structure was incorporated into a frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  Here, the light source reflector is wound from the outer surface of the edge of the back surface of the light guide to the edge of the light output surface of the light guide through the outer surface of the primary light source, and the light absorption band is covered by the edge of the light source reflector. (However, in Comparative Example 6, a part of the light absorption band is covered by the edge part of the light source reflector). It was made to protrude above the emission surface. Further, the frame body was configured to shield a region having a width of 2.5 mm on the outer peripheral portion of the light guide light emitting surface (that is, the width of the frame-shaped region was 2.5 mm). That is, the edge part of the light source reflector is located in the frame-like region, and the light absorption band is located in the frame-like region, that is, outside the effective light emitting region of the surface light source device.

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  About the surface light source devices of Examples 12 to 20 and Comparative Examples 5 to 7 obtained as described above, the primary light source was turned on under the same conditions and the light emitting surface was visually observed. Although the bright lines and dark lines in the vicinity of the light guide light incident end face were hardly noticeable in the case of Comparative Example 5, a clear bright line in the vicinity of the light guide light incident end face was observed in Comparative Example 5, and In comparison with Examples 12-20, a decrease in brightness in the vicinity of the light guide light incident end face was observed, and in Comparative Example 7, the luminance decreased and compared with Examples 12-20. Dark lines were observed in the display area.

[Example 21]
A light guide material was produced in the same manner as in Example 12. Thereafter, the light-receiving material was cut into the light incident end face corresponding portion to obtain a light guide having a light incident end face formed as a cut surface. The light guide had a wedge plate shape of 230 mm × 290 mm and a thickness of 2.6 mm-0.7 mm. A plurality of independent ink dots are formed by an ink jet method in the substantially flat surface area of the light guide body on which the prism row is formed (back surface) having a width of about 250 μm, and the ink dots are leveled. As a result, a continuous ink layer was formed over the entire region having a width W of about 150 μm and a distance D of about 10 μm as shown in FIG. At that time, the ink layer was cured by irradiating ultraviolet rays to form a substantially linear light absorption band. In the same way, the ultraviolet ray curable black ink had a visible light transmittance of 40% when the ultraviolet curable black ink was printed on a transparent acrylic plate having a thickness of 2 mm in a size that allows the visible light transmittance to be measured. It was.

  Furthermore, by forming a large number of independent ink dots on the light exit surface of the light guide by the same ink jet method as in Example 10, and leveling the ink dots, the width is about 250 μm from the light incident end surface. A continuous ink layer was formed over a region having a distance of about 10 μm. At that time, the ink layer was cured by irradiating ultraviolet rays to form a substantially linear light absorption band. In the same way, when the ultraviolet curable black ink was printed on a transparent acrylic plate having a thickness of 2 mm so that the visible light transmittance could be measured, the visible light transmittance of the ultraviolet curable black ink was 20%. It was.

  The obtained light guide was combined with a cold cathode tube, a light source reflector, a light diffusing reflection film, and a reflection sheet in the same manner as in Example 1, and the resulting structure was incorporated into a frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  With respect to the surface light source device obtained as described above, when the primary light source was turned on and the light emitting surface was visually observed, bright lines and dark lines in the vicinity of the light guide light incident end face were hardly noticeable.

[Examples 22 to 32, Comparative Examples 8 to 12]
In the same manner as in Example 1, one surface is a mat surface, and the other surface is arranged in a row so that prism rows with a prism apex angle of 100 degrees, a apex tip radius of curvature of 15 μm, and a pitch of 50 μm are parallel to the short side. A rectangular and wedge-shaped light guide material, which is a prism row forming surface provided with a prism pattern, was prepared. However, this light guide body material does not form a prism row on the entire other surface where the prism row is formed, but has various widths (Examples 22 to 32 and Examples 22 to 32 and Comparative Examples 8 to 12) have a region composed of a substantially flat surface at substantially the same height as the ridge line of the prism row, and further have a transition region with a width of 50 μm that gradually transitions from the flat surface to the prism row forming surface. It was supposed to have. In the substantially flat surface area of the prism row forming surface of the light guide material, the same screen as that of the first embodiment with various widths (Examples 22 to 32 and Comparative Examples 8 to 12) from the longer side having the larger thickness. A black ink was applied by printing to form a first light absorption band corresponding part. In the same manner, the visible light transmittance of the ultraviolet curable black ink was 30% when the black ink was printed on a transparent acrylic plate having a thickness of 2 mm so that the visible light transmittance could be measured. At the same time, black ink was applied by screen printing to form a second light absorption band in a region away from the first light absorption band corresponding part. In the same manner, the visible light transmittance of the ultraviolet curable black ink was 80% when the black ink was printed on a transparent acrylic plate having a thickness of 2 mm so that the visible light transmittance could be measured.

Next, by performing cutting on the light incident end face corresponding portion of the light guide body material and cutting off unnecessary portions including a part of the first light absorption band corresponding portion, the light incident end face formed as the cutting processed surface and A light guide having a first light absorption band and further a second light absorption band was obtained. The light guide has a wedge plate shape with a size of 230 mm × 290 mm and a thickness of 2.6 mm-0.7 mm, the curvature radius R of the edge portion is 40 μm, and the distance D1 from the light incident end face is 0 μm. The width W1 of the light absorption band, the distance D2 between the light incident end face and the second light absorption band, and the width W2 of the second light absorption band were as follows. The light guide material is such that a substantially flat surface region of the obtained light guide exists from the side edge far from the light incident end face of the second light absorption band to a position far from the light incident end face by about 100 μm. Made to:
Example 22 --- W1 = 500 μm, D2 = 1000 μm, W2 = 200 μm
Example 23 --- W1 = 400 μm, D2 = 1000 μm, W2 = 200 μm
Example 24 --- W1 = 300 μm, D2 = 1000 μm, W2 = 200 μm
Example 25 --- W1 = 200 μm, D2 = 1000 μm, W2 = 200 μm
Example 26 --- W1 = 150 μm, D2 = 1000 μm, W2 = 200 μm
Example 27 --- W1 = 75 μm, D2 = 1000 μm, W2 = 200 μm
Example 28 --- W1 = 300 μm, D2 = 1100 μm, W2 = 700 μm
Example 29 --- W1 = 300 μm, D2 = 900 μm, W2 = 300 μm
Example 30 --- W1 = 300 μm, D2 = 900 μm, W2 = 150 μm
Example 31--W1 = 300 μm, D2 = 900 μm, W2 = 75 μm
Example 32 --- W1 = 300 μm, D2 = 1100 μm, W2 = 200 μm
Comparative Example 8--W1 = 20 μm, D2 = 900 μm, W2 = 200 μm
Comparative Example 9 --- W1 = 800 μm, D2 = 900 μm, W2 = 200 μm
Comparative Example 10 --- W1 = 300 μm, D2 = 2700 μm, W2 = 200 μm
Comparative Example 11 --- W1 = 300 μm, D2 = 400 μm, W2 = 1000 μm
Comparative Example 12 --- W1 = 20 μm, D2 = 900 μm, W2 = 200 μm (a light absorption band having a width of 20 μm is continuously formed on the light incident end face side).

  The cold cathode fluorescent lamp tends to be regularly reflected along the long side so as to face one side end surface (end surface on the side of 2.6 mm thickness) corresponding to the side (long side) of the light guide body having a length of 290 mm. A strong light source reflector (silver reflection film manufactured by Reiko Co., Ltd.) was used. Furthermore, a light diffusive reflection film (E60 [trade name] manufactured by Toray Industries, Inc.) was attached to the other side end surface, and a reflection sheet was disposed so as to face the surface (back surface) of the prism array. The above configuration was incorporated into the frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  Here, the light source reflector is wound from the outer surface of the edge of the back surface of the light guide to the edge of the light output surface of the light guide through the outer surface of the primary light source, and the first light absorption band and the second light absorption band are The edge of the light source reflector is guided so that it is covered by the edge of the light source reflector (however, in Example 28 and Comparative Example 10, a part of the second light absorption band is covered by the edge of the light source reflector). From the body light incident end face, it was projected upward by 1.3 mm above the back face. Further, the frame body was configured to shield a region having a width of 2.5 mm on the outer peripheral portion of the light guide light emitting surface (that is, the width of the frame-shaped region was 2.5 mm). That is, the edge part of the light source reflector is located in the frame-like region, and the first and second light absorption bands are located in the frame-like region, that is, outside the effective light emitting region of the surface light source device ( However, in Comparative Example 10, the second light absorption band was located outside the frame-shaped region, that is, within the effective light emitting region of the surface light source device).

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  For the surface light source devices of Examples 22 to 32 and Comparative Examples 8 to 12 obtained as described above, the primary light source was turned on under the same conditions and the light emitting surface was visually observed. However, the bright lines and dark lines in the vicinity of the light guide light incident end face are inconspicuous to the extent that they do not interfere with actual use, and the overall reduction in luminance is such that they do not interfere with actual use. Among them, those of Examples 4 and 7 were the best. In Examples 22 to 26, 28 to 30, and 32, bright lines and dark lines in the vicinity of the light guide light incident end face were hardly recognized. In Examples 23 to 27 and 29 to 32, almost no reduction in the overall luminance was observed. On the other hand, in the comparative example 8, a clear bright line is recognized in the vicinity of the light guide light incident end face, and in the comparative example 9, the light guide light incident end face as compared with the examples 22 to 32. In comparison examples 10 and 11, bright lines and dark lines in the vicinity of the light guide light incident end face were recognized in comparison examples 10 and 11, compared with those in examples 22 to 32. In comparison with Examples 22 to 32, a decrease in overall luminance and dark lines in the effective light emitting region were observed in the samples.

[Example 33]
A light guide material was produced in the same manner as in Example 22. Thereafter, the light-receiving material was cut into the light incident end face corresponding portion to obtain a light guide having a light incident end face formed as a cut surface. The light guide had a wedge plate shape of 230 mm × 290 mm and a thickness of 2.6 mm-0.7 mm. A large number of ultraviolet curable black inks are dropped on the substantially flat surface region having a width of about 1100 μm on the prism array forming surface (back surface) of this light guide by the ink jet method in the same manner as in Example 10, and as shown in FIG. A large number of independent ink dots for the first light absorption band having a diameter of about 70 μm were formed in a region having a width W1 ′ of about 300 μm and a distance D1 ′ of about 60 μm. At the same time, a large number of independent ink dots for the second light absorption band having a diameter of about 70 μm were formed by the inkjet method. In this state, the ink dots were leveled for 5 seconds to form an ink layer for the first light absorption band that was continuous over the entire region having a width W1 of about 400 μm and a distance D1 of about 10 μm as shown in FIG. . At the same time, an ink layer for the second light absorption band was formed by the same leveling. At that time, the ink layer was cured by irradiating ultraviolet rays to form first and second light absorption bands that were substantially linear.

  In the same way, the visible light transmittance of the ultraviolet curable black ink when the ultraviolet curable black ink is printed on a transparent acrylic plate having a thickness of 2 mm to a size capable of measuring the visible light transmittance is the first light. The absorption band was 20%, and the second light absorption band was 80%.

  The obtained light guide was combined with a cold cathode tube, a light source reflector, a light diffusing reflection film, and a reflection sheet in the same manner as in Example 1, and the resulting structure was incorporated into a frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  With respect to the surface light source device obtained as described above, when the primary light source was turned on and the light emitting surface was visually observed, bright lines and dark lines in the vicinity of the light guide light incident end face were hardly noticeable.

[Example 34]
In the same manner as in Example 33, a large number of ultraviolet curable black inks were dropped on the substantially flat surface region of the prism array forming surface (back surface) of the light guide obtained in the same manner as in Example 33, and the FIG. A plurality of independent ink dots for the first light absorption band having a diameter of about 70 μm were formed in a region having a width W1 ′ of about 300 μm and a distance D1 ′ of about 60 μm as shown in FIG. At the same time, a large number of independent ink dots for the second light absorption band having a diameter of about 70 μm were formed by the inkjet method. Immediately thereafter, the ink dots were cured by irradiating with ultraviolet rays so as not to level the ink dots, thereby forming substantially linear first and second light absorption bands.

  In the same way, the visible light transmittance of the ultraviolet curable black ink when the ultraviolet curable black ink is printed on a transparent acrylic plate having a thickness of 2 mm to a size capable of measuring the visible light transmittance is the first light. The absorption band was 20%, and the second light absorption band was 80%.

  The obtained light guide was combined with a cold cathode tube, a light source reflector, a light diffusing reflection film, and a reflection sheet in the same manner as in Example 1, and the resulting structure was incorporated into a frame. In this light guide, the maximum peak of the outgoing light luminous intensity distribution (in the XZ plane) was 70 degrees with respect to the normal direction of the light outgoing face, and the full width at half maximum was 22.5 degrees.

  The prism sheet produced in the same manner as in Example 1, the prism row forming surface faces the light exit surface (mat surface) side of the light guide, and the ridge line of the prism row is parallel to the light incident end surface of the light guide, The light guide was placed so that the planar prism surface of each prism row faces the light incident end surface of the light guide.

  With respect to the surface light source device obtained as described above, the primary light source was turned on under the same conditions as in Example 33, and the light emitting surface was observed visually. Furthermore, some bright lines were observed in the vicinity of the light guide light incident end face.

[Example 35]
A light guide was obtained in the same manner as in Example 33. As a result of the cutting process, a protruding portion protruding from the other region of the substantially flat surface region was formed at the boundary between the light incident end surface and the substantially flat surface region of the back surface. This protrusion had a height of 10 μm and a full width at half maximum of 10 μm. In the same manner as in Example 33, ink dots were formed and leveled to form an ink layer. However, the position of the ink dot formation region with respect to the first light absorption band was set so that the ink layer reached the protruding portion by leveling.

  For the surface light source device obtained in the same manner as in Example 33 using the obtained light guide, the primary light source was turned on and the light emitting surface was visually observed. As a result, the bright line in the vicinity of the light guide light incident end face and The dark line was hardly noticeable.

It is a typical perspective view which shows one embodiment of the surface light source device by this invention. It is a typical top view which shows a light guide with a primary light source. It is a figure for demonstrating an example of the manufacturing method of the light guide by this invention. It is a figure for demonstrating an example of the manufacturing method of the light guide by this invention. It is a figure which shows the mode of the optical deflection by an optical deflection element. It is a typical top view which shows a light-diffusion element with a primary light source. It is a typical fragmentary sectional view of the liquid crystal display device which used the surface light source device by this invention as the backlight. It is a typical fragmentary sectional view of a light guide. It is a typical fragmentary sectional view of a light guide. It is a figure which shows the visible light transmittance of a light guide and a light absorption zone. It is a figure which shows the visible light transmittance of a light guide and a light absorption zone. It is explanatory drawing which shows the example of the manufacturing method of a light guide. It is explanatory drawing which shows the example of the manufacturing method of a light guide. It is explanatory drawing which shows the example of the manufacturing method of a light guide. It is a fragmentary sectional view of a light guide. It is an enlarged view of the edge part of a light guide. It is an enlarged view of the edge part of a light guide. It is a typical perspective view which shows one embodiment of the surface light source device by this invention. It is a typical fragmentary perspective view which shows a light guide with a primary light source. It is a typical partial bottom view which shows a light guide. It is a typical perspective view which shows one embodiment of the surface light source device by this invention. It is a typical top view which shows a light guide with a primary light source. It is a figure for demonstrating an example of the manufacturing method of the light guide by this invention. It is a figure for demonstrating an example of the manufacturing method of the light guide by this invention. It is a typical fragmentary sectional view of the liquid crystal display device which used the surface light source device by this invention as the backlight. It is a figure which shows the visible light transmittance of a light guide and a light absorption zone. It is a figure which shows the visible light transmittance of a light guide and a light absorption zone. It is explanatory drawing which shows the example of the manufacturing method of a light guide. It is explanatory drawing which shows the example of the manufacturing method of a light guide. It is explanatory drawing which shows the example of the manufacturing method of a light guide. It is a typical partial bottom view which shows a light guide. It is a typical fragmentary perspective view which shows a light guide. It is a typical fragmentary sectional view of the liquid crystal display device which used the surface light source device by this invention as the backlight.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary light source 2 Light source reflector 3 Light guide 3 'Light guide material 31 Light incident end surface 31' Light incident end surface corresponding portion 32 Side end surface 33 Light emitting surface 34 Back surface 34 'Back surface corresponding portion 36, 236 Light absorption band (first Light absorption band)
36-1 Light Absorption Band First Area 36-2 Light Absorption Band Second Area 36A Ink Dot 36B Ink Layer 36 ′ Light Absorption Band Corresponding Part 136, 336 Second Light Absorption Band 136-1 Second Light Absorption Band First Area 136-2 Second light absorption band second area 136-3 Second light absorption band third area 136A Ink dots for second light absorption band 136B Ink layer for second light absorption band 136 ′ Second light absorption band corresponding Portion 137 Substantially flat surface region 138 Transition region 139 Prism row forming surface region 37 Convex / convex convex portion 38 Light diffusing fine particles 39 Protruding portion 4 Light deflecting element 41 Light incident surface 42 Light emitting surface 5 Light reflecting element 6 Light diffusing element 61 Entrance surface 62 Outgoing surface 64 Dot pattern part 64 'Dot-shaped light-absorbing coating material 70 Concave part

Claims (9)

A light guide that guides light emitted from the primary light source and has a light incident end surface on which light emitted from the primary light source is incident, a light exit surface from which the guided light is emitted, and a back surface opposite to the light exit surface. A light body,
A light absorption band having a width of 50 μm to 1000 μm extending along the light incident end face is formed on the back surface, and a side edge of the light absorption band close to the light incident end face has a distance from the light incident end face of 300 μm or less. It is in,
An edge portion that forms a boundary between the back surface and the light incident end surface is formed along the light incident end surface as a protruding portion protruding from the other region of the back surface, and the height half width of the protruding portion is full width Is 1-50 micrometers, The light guide for surface light source devices characterized by the above-mentioned. A prism row forming surface region including a plurality of prism rows extending in a direction substantially perpendicular to the light incident end surface and arranged in parallel to each other is formed on the back surface, and the back surface is formed along the light incident end surface. 2. The surface light source according to claim 1 , wherein a substantially flat surface region that extends is formed, and at least a part of the light absorption band is located in at least a part of the substantially flat surface region. Light guide for device. The light absorption band is characterized in that towards the far side edge from the side edge closer to the light incident end face is formed so as visible light transmittance is high, according to any one of claims 1-2 A light guide for a surface light source device. The light absorption band has a width of 50 μm to 800 μm, and a second light absorption band extending along the light incident end face is formed on the back surface at a position farther from the light incident end face than the light absorption band, 4. The surface light source device according to claim 1 , wherein a side edge of the second light absorption band close to the light incident end face is located 500 μm to 3000 μm away from the light incident end face. Light guide. The light guide for a surface light source device according to claim 4 , wherein the visible light transmittance of the second light absorption band is higher than the visible light transmittance of the light absorption band. A method for producing a light guide for a surface light source device according to any one of claims 1 to 5 , wherein the light incident end face is formed by cutting the light incident end face corresponding portion of the light guide body material, Thereafter, the light absorption band is formed, and a method for manufacturing a light guide for a surface light source device. By ejecting ink from a large number of nozzles by the inkjet method, ink dots that are independent or partially continuous with each other are formed in at least a region near the light incident end surface of the back surface of the light guide, and then the ink dots are leveled. by coupling the adjacent ones by a continuous ink layer and without throughout the region, and forming the light absorption band by curing the ink layer thereafter, to claim 6 The manufacturing method of the light guide for surface light source devices of description. A light guide for a surface light source device according to any one of claims 1 to 5, the primary light source disposed adjacent to the light incident end face of the light guide, and a light exit surface of the light guide. A light deflection element disposed adjacent to the light deflection element, the light deflection element having a light incident surface located opposite to the light emission surface of the light guide and a light emission surface on the opposite side thereof. A surface light source device comprising: a plurality of prism rows extending in a direction substantially parallel to a light incident end surface of the light guide and parallel to each other on a light incident surface of the light deflection element. A light diffusing element is disposed adjacent to the light exit surface of the light deflection element, and the light diffusing element emits light in a region having a width that includes at least 2 mm to 4 mm from the light incident end surface of the light guide. includes a dot pattern portion formed absorption dot pattern, the dot pattern portion is characterized by being distributed to dot-like light-absorbing coating material of diameter ranges from 30 m to 70 m, according to claim 8 Surface light source device.

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