JP2008139692A - Prism sheet and diffusion sheet manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of producing a prism sheet and a diffusion sheet with high light utilization efficiency by effectively using a birefringent translucent substrate.
[MEANS FOR SOLVING PROBLEMS] The present invention relates to a cut raw fabric A in which a birefringent translucent base material manufactured by biaxial stretching is cut in a winding direction and an optical axis angle is within a predetermined range; The prism sheet and the diffusion sheet are manufactured by separating into a cut original fabric B, producing a diffusion sheet using the cut original fabric A as a base material, and manufacturing a prism sheet using the cut raw fabric B as a base material. Is the method.

[Selection] Figure 12

Description

  The present invention relates to a prism sheet and a diffusion sheet manufacturing method used in an edge light type surface light source device.

  In recent years, color liquid crystal display devices have been widely used in various fields as display units for notebook personal computers, liquid crystal televisions, mobile phones, small game machines, and the like. In addition, with the increase in the amount of information processing, diversification of needs, compatibility with multimedia, and the like, liquid crystal display devices have been increased in screen size and definition.

  The liquid crystal display device basically includes a surface light source device portion and a liquid crystal display element portion. As the surface light source device section, there are a direct-type system in which a light source is disposed directly below a liquid crystal display element section and an edge light system in which a light source is disposed so as to face a side end surface of a light guide. The edge light method is often used from the viewpoint of compactness.

  In the edge light type surface light source device, light emitted from the primary light source enters the light incident end face of the light guide. The light introduced into the light guide travels in the light guide along the main surface while repeating total reflection on the two main surfaces of the light guide. A part of the light traveling in the light guide body is changed in the traveling direction by the concavo-convex structure formed on the light emitting surface which is one of the main surfaces, and the light emitting surface normal line from the light emitting surface to the outside of the light guiding body. The light is emitted in a direction oblique to the direction. Note that another part of the light traveling in the light guide is emitted from the back surface, which is the other of the main surfaces, reflected by the reflection sheet disposed opposite to the back surface, and returned to the light guide again. . Light emitted from the light exit surface in a direction oblique to the normal direction is incident on a prism sheet as a light deflecting element disposed opposite the light exit surface, and the traveling direction is guided by the prism sheet. The light is deflected in a substantially normal direction of the light emitting surface. In order to exhibit such a deflection function, a large number of prism rows formed in parallel with each other on the light incident surface of the prism sheet extend along the direction of the light incident end surface of the light guide. A light diffusion sheet may be disposed on the light exit surface of the prism sheet.

  In the liquid crystal display element, the first polarizing plate is disposed on the light incident side of a liquid crystal cell having a liquid crystal layer and an electrode for applying a voltage to each pixel unit, and the light is emitted from the light emitting surface of the surface light source device. Polarized light is created by transmitting light through the first polarizing plate, and the plane of polarization is rotated according to the pixel signal for each pixel portion by the liquid crystal layer, and is disposed on the light emitting side of the liquid crystal cell. By passing the second polarizing plate, an image is displayed by the amount of light emitted from the second polarizing plate. Thus, in the liquid crystal display element, most of the light emitted from the light emitting surface of the surface light source device is absorbed by the first polarizing plate, and the light use efficiency is low. For this reason, improvement of the utilization efficiency of light is desired.

In order to improve the light utilization efficiency, for example, in Japanese Patent Application Laid-Open No. 2001-166116 (Patent Document 1), the polarization axis of the first polarizing plate of the liquid crystal display element and the polarization axis of the polarized light that has passed through the translucent substrate are A prism sheet is disclosed in which the polarization axis of a translucent substrate is rotated by a predetermined angle with respect to the ridgeline of the prism sheet so as to be substantially the same.
JP 2001-166116 A

  If this invention is used, for example, a resin composition is injected between a sheet piece of a birefringent translucent substrate of about A4 size and a transfer mold, and the resin composition is cured with active energy rays, heat, or the like. In the so-called batch type manufacturing method in which prism sheets are manufactured one by one, it is possible to manufacture a prism sheet for a liquid crystal display device with improved light utilization efficiency. This is because in the case of the batch type, the optical axis of the single-piece piece of the birefringent translucent substrate can be freely rotated with respect to the ridge line of the prism.

  However, when mass-producing prism sheets at low cost, a birefringent translucent substrate is drawn around a cylindrical transfer mold from a roll, and the transfer mold and the birefringent translucent substrate are wound. It is preferable to use a so-called continuous production method, in which the resin composition is injected between and cured by active energy rays, heat, or the like.

In addition, the optical axis direction of the birefringent translucent substrate is determined by its manufacturing conditions, and normally the manufacturing conditions are not flexible enough to arbitrarily set the optical axis direction. The angular relationship between the ridgeline and the optical axis of the birefringent translucent substrate cannot be arbitrarily set, that is, the implementation of the invention described in Patent Document 1 is virtually impossible. In addition, when the birefringent translucent base material having an optical axis angle that conforms to the conditions described in Patent Document 1 is taken out from a part of the raw material, the birefringent translucent base material is not suitable. The rest of the web will not be used effectively.

  As a result of intensive studies, the inventors have made a diffusion sheet in which a diffusing agent is applied to a base material taken out from the central part of the birefringent translucent base material when the prism sheet is manufactured by a continuous manufacturing method. If the prism sheet is manufactured by forming a prism on the base material taken out from the end of the birefringent translucent base material, the position to be taken out from the birefringent translucent base material It has been found that the light use efficiency is higher than when the diffusion sheet and the prism sheet are produced without selection, and that the birefringent translucent substrate can be used effectively.

  In the present invention, a birefringent translucent base material manufactured by biaxial stretching is cut in the winding direction, and an optical axis angle is within a predetermined range, and other cut originals The prism sheet and the diffusion sheet manufacturing method are characterized in that the sheet is divided into B, a diffusion sheet is manufactured using the cut original fabric A as a base material, and a prism sheet is manufactured using the cut original fabric B as a base material.

  By carrying out the present invention, it is possible to produce a prism sheet and a diffusion sheet with high light utilization efficiency by effectively using a birefringent translucent substrate.

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

  FIG. 1 is a schematic partially cutaway view showing an embodiment of a prism sheet according to the present invention, an edge light type surface light source device according to the present invention using the prism sheet, and a liquid crystal display device according to the present invention using the surface light source device. FIG. 2 is a perspective view, and FIG. 2 is a schematic partial sectional view thereof. In the present embodiment, the surface light source device includes a light guide 3 having at least one side end surface as a light incident end surface 31 and one main surface substantially orthogonal thereto as a light emitting surface 33, and the light guide 3. A linear primary light source 1 disposed opposite to the light incident end surface 31 and covered with the light source reflector 2, a prism sheet 4 as a light deflection element disposed on the light emitting surface of the light guide 3, A light diffusing element 6 disposed on the light exit surface 4 of the prism sheet; and a light reflecting element 5 disposed to face the back surface 34 which is the main surface opposite to the light exit surface 33 of the light guide 3. It consists of In the present embodiment, the liquid crystal display device includes a surface light source device and the liquid crystal display element 8 disposed on the light exit surface 62 of the light diffusing element 6.

  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 disposed to face the primary light source 1, and the light emitted from the primary light source 1 enters the light incident end face 31 and is introduced into the light guide 3. 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. By providing the light emitting surface 33 with a directional light emitting mechanism including a rough surface or a lens array, the light incident from the light emitting surface 33 is guided while the light incident from the light incident end surface 31 is guided through the light guide 3. Light having directivity is emitted in a plane (XZ plane) orthogonal to the end face 31 and the light emission face 33. The angle formed by the peak direction (peak light) of the emitted light luminous intensity distribution in the XZ in-plane distribution with the light emitting surface 33 is denoted by φ. The angle φ 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.

  Further, the light guide 3 preferably has a light emission rate in the range of 0.5 to 5%, and more preferably in the range of 1 to 3%. By setting the light emission rate to 0.5% or more, the amount of light emitted from the light guide 3 is increased, and sufficient luminance tends to be obtained. Further, by setting the light emission rate to 5% or less, emission of a large amount of light in the vicinity of the primary light source 1 is prevented, attenuation of the emitted light in the X direction within the light emission surface 33 is reduced, and light emission is reduced. The brightness uniformity on the surface 33 tends to be improved. 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. Light with high directivity and emission characteristics can be emitted from the light guide 3, the emission direction can be efficiently deflected by the prism sheet 4, and a surface light source device having high luminance can be provided. .

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 d, the following formula I = I ₀ (A / 100) [1− (A / 100)] ^{L / d}
Satisfying such a relationship. Here, the constant A is the light output rate, and the light guide 3 per unit length (a length corresponding to the light guide thickness d) 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.

  In the present invention, instead of forming the light emitting mechanism on the light emitting surface 33 as described above, or in combination with this, the light diffusing fine particles are mixed and dispersed in the light guide so as to emit directional light. A mechanism may be added.

  Moreover, in order to control the directivity in the surface (YZ surface) parallel to the primary light source 1 of the emitted light from the back surface 34 which is the main surface to which the directional light emitting mechanism is not provided, It is a prism row forming surface in which a large number of prism rows are arranged in a direction crossing the light incident end surface 31, more specifically in a direction substantially perpendicular to the light incident end surface 31 (X direction). The prism row on the back surface 34 of the light guide 3 can have an arrangement pitch in the range of, for example, 10 to 100 μm, and preferably in the range of 30 to 60 μm. Moreover, the prism row | line | column of the back surface 34 of this light guide 3 can make the apex angle into the range of 85-110 degree | times, for example. 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. More preferably, it is the range of 90-100 degree | times.

  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.

  The light guide 3 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 of the light guide 3 or a surface structure such as a prism array or a lenticular lens array, the transparent synthetic resin plate is formed by hot pressing using a mold member having a desired surface structure. Alternatively, the shape may be imparted 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.

  The prism sheet 4 is disposed on the light emitting surface 33 of the light guide 3. The prism sheet 4 is made of a sheet-like translucent member, and the two main surfaces, the first surface 41 and the second surface 42, are arranged in parallel to each other as a whole, and are respectively located in parallel with the XY plane. . The first surface 41 that is one main surface (the main surface that faces the light emitting surface 33 of the light guide 3) is a light incident surface, and the other main surface 42 is a light output surface. . The light incident surface 41 is a prism row forming surface in which a plurality of prism rows are arranged in parallel to each other. The light exit surface 42 is a smooth surface or an uneven surface.

  In FIG. 3, the typical partial expanded sectional view of the prism sheet 4 is shown. The prism sheet 4 includes a translucent base material 43 and a translucent prism array forming portion 44 attached to one surface of the base material. These translucent base material 43 and prism row forming portion 44 constitute a sheet-like translucent member. Plural prism rows 411 are formed on the lower surface of the prism row forming portion 44, and the lower surface forms the light incident surface 41. Further, the upper surface of the translucent substrate 43 forms the light exit surface 42. A light diffusion layer may be formed on the upper surface of the translucent substrate 43.

  The material of the translucent base material 43 is preferably a material that transmits active energy rays such as ultraviolet rays and electron beams. Examples of such materials include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, and acrylic resins such as polymethyl methacrylate. Resins, cellulose resins such as diacetyl cellulose and triacetyl cellulose, styrene resins such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, and olefins such as ethylene / propylene copolymers Transparent resin sheets and films such as polyamide resins, polyamide resins such as nylon and aromatic polyamide, polycarbonate resins, vinyl chloride resins and polymethacrylimide resins are preferred. The thickness of the translucent substrate 43 is preferably, for example, 10 to 500 μm, more preferably 20 to 400 μm, and particularly preferably 30 to 300 μm from the viewpoint of workability such as strength and handleability. In addition, in order to improve the adhesiveness between the prism array forming portion 44 made of the active energy ray curable resin and the translucent base material 43, the surface of the translucent base material 43 is adhesive such as anchor coating treatment. What performed the improvement process is preferable.

  The raw material of a translucent base material can be produced by stretching the above synthetic resin into a film. In that case, in general, the molecules are oriented by the stretching process, and the resultant light-transmitting base material has birefringence. FIG. 12 shows such a birefringent translucent base material 38. Since the birefringent translucent base material 38 is mass-produced at low cost, for example, the width is about 3 m to 4 m. The birefringent translucent base material 38 is stretched in the biaxial direction 38A and then wound in the winding direction 38B to form a roll. The birefringent translucent base material 38 has different longitudinal and lateral stretch degrees in the stretching direction 38A depending on the position. Therefore, the winding direction 38B and the molecular orientation direction 38C are parallel to each other at the center, but at the end. As it approaches, the molecular orientation direction 38C deviates from the winding direction 38B. When the winding direction 38B of the birefringent translucent base material 38 is 0 ° and the directions perpendicular thereto are + 90 ° and −90 °, respectively, the range of the molecular orientation direction 38C varies depending on the degree of stretching. In the same birefringent translucent base material 38, for example, it continuously changes from −45 ° to + 45 °.

  In addition, a cut original fabric 38D obtained by dividing the birefringent translucent base material 38 in the winding direction 38B is created, and a prism sheet and a diffusion sheet are manufactured using the cut original fabric 38D. Therefore, the molecular orientation angle 38C of the cut raw fabric 38D is manufactured at a constant ratio between those substantially parallel to the winding direction 38B and those inclined to the + 90 ° side or the −90 ° side.

  The upper surface of the prism row forming portion 44 is a flat surface and is joined to the lower surface of the translucent substrate 43. The lower surface, that is, the light incident surface 41 of the prism array forming portion 44 is a prism array forming surface, and a plurality of prism arrays 411 extending in the Y direction are arranged in parallel to each other. The thickness of the prism row forming portion 44 is, for example, 10 to 500 μm. The arrangement pitch P of the prism rows 411 is, for example, 10 μm to 500 μm.

  Each prism row 411 includes two prism surfaces 411a and 411b. These prism surfaces are preferably optically sufficiently smooth surfaces (mirror surfaces) from the viewpoint of maintaining desired optical characteristics of the prism sheet. The apex angle θ of the prism row 411 is in the range of about 40 to 75 °, and preferably in the range of 45 to 70 °.

  The prism array forming portion 44 is preferably made of, for example, an active energy ray curable resin and has a high refractive index from the viewpoint of improving the luminance of the surface light source device. Specifically, the refractive index is 1.55. More preferably, it is 1.6 or more. The active energy ray curable resin for forming the prism array forming portion 44 is not particularly limited as long as it is cured with active energy rays such as ultraviolet rays and electron beams. For example, polyesters and epoxy resins , (Meth) acrylate resins such as polyester (meth) acrylate, epoxy (meth) acrylate, and urethane (meth) acrylate. Among these, (meth) acrylate resins are particularly preferable from the viewpoint of optical characteristics and the like. As the active energy ray-curable composition used for such a cured resin, a polyvalent acrylate and / or a polyvalent methacrylate (hereinafter referred to as a polyvalent (meth) acrylate) in terms of handleability and curability. , Monoacrylate and / or monomethacrylate (hereinafter referred to as mono (meth) acrylate), and a photopolymerization initiator by active energy rays are preferred. Typical polyvalent (meth) acrylates include polyol poly (meth) acrylate, polyester poly (meth) acrylate, epoxy poly (meth) acrylate, urethane poly (meth) acrylate, and the like. These are used alone or as a mixture of two or more. Examples of mono (meth) acrylates include mono (meth) acrylates of monoalcohols and mono (meth) acrylates of polyols.

  FIG. 4 schematically shows the state of light deflection in the XZ plane by the prism sheet 4. This figure shows an example of 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. Most of the peak light obliquely emitted from the light emitting surface 33 of the light guide 3 at an angle φ is incident on the first prism surface 411a of the prism row 411 and is almost totally internally reflected by the second prism surface 411b. The light travels in the direction of the normal of the light exit surface 42 and exits from the light exit surface. Further, in the YZ plane, there is also the action of the prism rows on the light guide back surface 34 as described above, so that the luminance in the normal direction of the light exit surface 42 can be sufficiently improved in a wide range.

  Note that the shape of the prism surfaces 411a and 411b of the prism row 411 of the prism sheet 4 is not limited to a single plane, and can be, for example, a convex polygonal shape or a convex curved surface shape. A narrow field of view can be achieved.

  In the prism sheet 4, the prism array is formed for the purpose of accurately producing a desired prism array shape, obtaining stable optical performance, and suppressing wear and deformation of the top of the prism array during assembly work or use of the light source device. A top flat portion or a top curved surface portion may be formed on the top of the top. In this case, the width of the top flat part or the top curved surface part is preferably 3 μm or less from the viewpoint of suppressing the occurrence of a non-uniform luminance pattern due to a decrease in luminance or a sticking phenomenon as the surface light source device. The width of the top flat part or the top curved part is 2 μm or less, more preferably 1 μm or less.

  The formation of the prism rows as described above is performed on the surface of the synthetic resin sheet by using a mold member having a shape transfer surface for transferring and forming the light incident surface 41 including the prism row forming surface having the prism rows 411. This can be realized.

  FIG. 5 is a schematic diagram for explaining the production of the original prism sheet for obtaining a prism sheet having a desired size and shape by cutting. In the following description, the names and symbols of the constituent parts of the original prism sheet will be described with reference to the names and symbols of the constituent parts of the prism sheet 4.

  In FIG. 5, reference numeral 7 denotes a mold member (roll mold) formed by forming a shape transfer surface for transferring and forming the light incident surface 41 on a cylindrical outer peripheral surface. This roll type | mold 7 shall consist of metals, such as aluminum, brass, and steel. FIG. 6 is a schematic perspective view of the roll mold 7. A shape transfer surface 18 is formed on the outer peripheral surface of the cylindrical roll 16. FIG. 7 is a schematic exploded perspective view showing a modified example of the roll mold 7. In this modification, a thin plate-shaped mold member 15 is wound around and fixed to the outer peripheral surface of the cylindrical roll 16. The thin plate-shaped member 15 has a shape transfer surface formed on the outer surface.

  As shown in FIG. 5, the roll mold 7 is supplied with a translucent base material 9 along the outer peripheral surface, that is, the shape transfer surface, and the roll mold 7 and the translucent base material are supplied. The active energy ray-curable composition 10 is continuously supplied from the resin tank 12 through the nozzle 13 between the opposite side.

  A nip roll 28 for making the thickness of the supplied active energy ray-curable composition 10 uniform is provided outside the translucent base material 9. As the nip roll 28, a metal roll, a rubber roll, or the like is used. Moreover, in order to make the thickness of the active energy ray-curable composition 10 uniform, the nip roll 28 is preferably processed with high accuracy with respect to roundness, surface roughness, etc. In the case of a rubber roll A rubber having a high hardness of 60 degrees or more is preferable. The nip roll 28 is required to accurately adjust the thickness of the active energy ray-curable composition 10 and is operated by the pressure mechanism 11. As the pressure mechanism 11, a hydraulic cylinder, a pneumatic cylinder, various screw mechanisms, and the like can be used, but a pneumatic cylinder is preferable from the viewpoint of simplicity of the mechanism. The air pressure is controlled by a pressure regulating valve or the like.

  The active energy ray-curable composition 10 supplied between the roll mold 7 and the light-transmitting base material 9 can be kept at a constant viscosity in order to keep the thickness of the obtained prism portion constant. preferable. In general, the viscosity range is preferably in the range of 20 to 3000 mPa · S, and more preferably in the range of 100 to 1000 mPa · S. By setting the viscosity of the active energy ray-curable composition 10 to 20 mPa · S or more, it is necessary to set the nip pressure extremely low or extremely increase the molding speed in order to make the prism portion constant in thickness. Disappear. If the nip pressure is extremely low, the pressure mechanism 11 tends to be unable to operate stably, and the thickness of the prism portion is not constant. On the other hand, when the molding speed is extremely increased, the irradiation amount of the active energy ray is insufficient, and the curing of the active energy ray curable composition tends to be insufficient. On the other hand, by setting the viscosity of the active energy ray-curable composition 10 to 3000 mPa · S or less, the curable composition 10 can be sufficiently distributed to the details of the roll-shaped shape transfer surface structure, and the accuracy of the lens shape is improved. Transfer is difficult, defects due to mixing of bubbles are not easily generated, and productivity is not deteriorated due to an extremely low molding speed. For this reason, in order to keep the viscosity of the active energy ray-curable composition 10 constant, a sheathed heater, a hot water jacket, or the like is provided outside or inside the resin tank 12 so that the temperature of the curable composition 10 can be controlled. It is preferable to install a heat source facility.

  After supplying the active energy ray-curable composition 10 between the roll mold 7 and the translucent base material 9, the active energy ray curable composition 10 becomes the roll mold 7 and the translucent base material 9. The active energy ray irradiating device 14 irradiates the active energy ray through the transparent base material 9 to polymerize and cure the active energy ray curable composition 10, and roll type 7 The shape transfer surface formed on is transferred. As the active energy ray irradiation device 14, a chemical reaction chemical lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, a visible light halogen lamp, or the like is used. The irradiation amount of the active energy ray is preferably such that the integrated energy at a wavelength of 200 to 600 nm is 0.1 to 50 J / cm <2>. The irradiation atmosphere of active energy rays may be air or an inert gas atmosphere such as nitrogen or argon. Next, the prism sheet original fabric composed of the translucent base material 9 and the prism row forming portion (44) formed of the active energy ray curable resin is released from the roll mold 7.

  Returning to FIG. 1, 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

  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 prism sheet 4 and winds from the outer surface of the light reflecting element 5 to the edge of the light emitting surface of the light guide 3 through the outer surface of the primary light source 1. It is attached. On the other hand, the light source reflector 2 may be wound from the outer edge of the light reflecting element 5 to the light emitting surface edge of the prism sheet 4 or the light emitting element 6 of the light diffusing element 6 through the outer surface of the primary light source 1. Is possible. A reflection member similar to the light source reflector 2 can be attached to the side end face other than the light incident end face 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 by metal vapor deposition or the like on the back surface 34 of the light guide 3 instead of the reflecting sheet as the light reflecting element 5.

  The light diffusing element 6 is disposed in order to minimize the decrease in luminance and appropriately control the visual field range according to the purpose. Further, by disposing the light diffusing element 6, it is possible to suppress glare, brightness spots and the like that cause deterioration of the quality and to improve the quality.

  In order to prevent sticking with the prism sheet 4, it is preferable to provide a concavo-convex structure on the incident surface 61 of the light diffusing element 6 facing the prism sheet 4. Similarly, in consideration of prevention of sticking between the emission surface 62 of the light diffusing element 6 and the liquid crystal display element 8 disposed thereon, a concavo-convex structure is also provided on the emission surface 62 of the light diffusing element 6. It is preferable. 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%.

  On the other hand, in the transmissive liquid crystal display element 8, the liquid crystal 83 is interposed between two light transmissive substrates 81 and 82 made of a glass sheet, a synthetic resin sheet, or the like arranged in parallel with each other. A voltage is applied according to the image signal between the transparent electrode 85 formed in the above and a required one of the pixel electrodes 84 formed on the upper surface of the substrate 81. This constitutes a liquid crystal cell.

  FIG. 8 is a schematic partially cutaway partial plan view for explaining the positional relationship between the liquid crystal display element 8 and the surface light source device. As shown in FIG. 8, a pixel portion 88 is formed corresponding to each pixel electrode 84, the pixel portion 88 is arranged in an XY matrix, and an X-direction pixel portion row 88B and A Y-direction pixel portion row 88A is formed.

  Further, as shown in FIGS. 1 and 2, a polarizing plate 86 functioning as a polarizer is disposed on the lower side of the liquid crystal cell, that is, the side on which light from the light emitting surface of the surface light source device is incident. A polarizing plate 87 that functions as an analyzer is disposed on the upper side of the liquid crystal cell. These polarizing plates 86 and 87 are arranged so that the polarization transmission axis directions (directions in which the transmittance of the polarization component in the XY plane is maximum) are orthogonal to each other. In FIG. 8, the polarization transmission axis direction of the polarizing plate 86 is indicated by an arrow 86A. Here, as an example, the polarization transmission axis direction 86A forms an angle of 45 ° with respect to both the X direction and the Y direction. Thereby, light from the light emitting surface of the surface light source device is converted into linearly polarized light by the polarizing plate 86, and the image signal is output by each pixel unit 88 of the liquid crystal cell in which the state of the liquid crystal 83 is appropriately changed by applying a voltage according to the image signal. Is subjected to modulation (rotation of the polarization plane) in accordance with. Accordingly, the amount of light that passes through the polarizing plate 87 corresponds to the image signal, thereby displaying an image. In general, the polarization transmission axis direction 86A is either + 45 ° or −45 ° with respect to both the X direction and the Y direction.

  In addition, the liquid crystal display element 8 may include a color filter for color display and other known appropriate functional members.

  As described above, the light emitting surface of the surface light source device including the primary light source 1, the light source reflector 2, the light guide 3, the prism sheet 4, the light reflecting element 5, and the light diffusing element 6 (the emitting surface of the light diffusing element 6). 62) By disposing the transmissive liquid crystal display element 8 on the liquid crystal display device, the surface light source device of the present invention is used as a backlight. The liquid crystal display device is observed by an observer from above.

  From the viewpoint of stabilizing the amount of light emitted from the surface light source device, in this embodiment, the birefringent translucent substrate used for manufacturing the diffusion sheet is a part having a specific optical axis angle as described below, The birefringent translucent base material used for manufacturing the prism sheet is the remaining part.

  That is, as shown in FIG. 8 and FIG. 9, in the XY plane, the negative direction of the Y axis is 0 °, the positive direction of the X axis is 90 °, and the positive direction of the Y axis is the angle. When the rotation direction around the Z-axis is set to 180 °, the optical axis angle of the diffusion sheet is changed from −δ to + δ (positive and negative indicate the direction of rotation around the Z-axis, and counterclockwise or counterclockwise in FIGS. 8 and 9) Of the birefringent translucent base material in such a manner that the direction of the film is within the range of “+” and the clockwise or clockwise direction in FIGS. The cut original fabric is used for manufacturing the diffusion sheet, and the other cut original fabric is used for manufacturing the prism sheet. The reason is as follows.

  As described above, light emitted from the light guide light emitting surface 33 in an oblique direction with respect to the normal direction of the light emitting surface has polarization characteristics. When the emitted light having this polarization characteristic enters the prism sheet 4, it passes through the transmission surface 411a of each prism row 411, is totally reflected by the reflection surface 411b, and is deflected in the direction of the light guide light emission surface normal line. Is done. At that time, the polarization characteristic of light is basically maintained. The polarization characteristic of the deflected light has a component in a direction orthogonal to the light guide light incident end face 31 larger than a component in a direction parallel to the light guide light incident end face 31.

  FIG. 10 shows an example of the polarization characteristics of the deflected light when the light emitted from the light guide 3 is deflected by the prism array 411 and exits the prism array forming unit 44. This figure shows the relative light intensity of each polarization component with respect to the angle defined in FIGS. 8 and 9 for the deflected light. A polarized light component having a polarization angle of 90 ° has the highest luminance, and this is the maximum polarized light component. The polarization component with a polarization angle of 0 ° (180 °) has the lowest luminance, and this is the minimum polarization component. The difference in light quantity between the maximum polarization component and the minimum polarization component is, for example, 5% to 40%.

  When the deflected light exiting the prism array forming portion 44 passes through the birefringent translucent base material 43, retardation occurs and the polarization characteristics change. The molecular orientation direction of the translucent substrate 43 coincides with either the fast axis or the slow axis. For example, when the translucent substrate 43 is made of PET, the molecular orientation direction of the translucent substrate 43 coincides with the fast axis. The fast axis and the slow axis are orthogonal. The fast axis and slow axis may be referred to as the optical axis or simply the optical axis. Retardation occurs between the direction of the optical axis of the translucent substrate 43 (the molecular orientation direction or a direction orthogonal thereto) 43A and the maximum polarization component direction of incident light having polarization characteristics to the prism array forming unit 44. It depends on the angle that you make. Further, when the diffusion sheet is made of the birefringent translucent substrate 43, retardation is further generated and the polarization characteristics are changed.

  In FIG. 11, a diffusion sheet having the optical axis direction 63A is placed on the prism sheet translucent substrate 43 having the optical axis direction 43A for the polarized light having the polarization characteristics as shown in FIG. An example of a change in luminance and the optical axis direction 63A of the diffusion sheet when a liquid crystal panel having an angle of −45 ° is mounted is shown.

  When the optical axis direction 63A of the diffusion sheet changes with respect to the optical axis direction 43A of the prism sheet, the luminance changes. In the example shown in FIG. 11, the optical axis angle with high brightness, that is, the efficiency of using light, is negative in the optical axis angle 43A of the prism sheet and the optical axis angle 63A of the diffusion sheet, for example, −30 °. This is realized. When a liquid crystal panel having a transmission axis angle of + 45 ° is mounted, the sign of FIG. 11 is reversed, and the optical axis angle 43A of the prism sheet and the optical axis angle 63A of the diffusion sheet are both set to positive values. Get better. However, when the optical axis angle 43A of the prism sheet and the optical axis angle 63A of the diffusion sheet are close to 0 °, the light use efficiency remains low even if a liquid crystal panel having any transmission axis angle is mounted. .

  Therefore, all the cut original fabric A taken out from the central portion of the birefringent translucent base material is used as a diffusion sheet. Unlike the prism sheet, the diffusion sheet can be used with any optical anisotropy of the base material, and can be manufactured by cutting out so as to have an arbitrary optical axis angle. Therefore, it is possible to produce a diffusion sheet that increases the light use efficiency by cutting out so as to have the same optical axis angle as the cut original fabric B cut out from the end of the birefringent translucent base material. Thus, all of the birefringent translucent base material can be used efficiently. The optical axis angle of the birefringent translucent substrate of the cut raw fabric A used for the production of such a diffusion sheet having good light utilization efficiency is preferably −15 ° to + 15 °, more preferably −10 ° to It is + 10 °, more preferably −5 ° to + 5 °.

  For this reason, the birefringent translucent light is selected and used by selecting the cut raw material taken from the birefringent translucent base material in order to manufacture the diffusion sheet and the prism sheet according to the optical axis direction of the present embodiment. A liquid crystal display device with good light utilization efficiency can be manufactured while effectively using the substrate.

  Examples of the present invention will be described below.

  In the present example and the comparative example, the measurement in the optical axis direction of the birefringent translucent substrate of the prism sheet was performed as follows. Two polarizing plates are stacked in parallel so that the polarization transmission axis directions are orthogonal to each other. Next, the translucent base material to be measured is inserted between two stacked polarizing plates, white light is incident from one polarizing plate side, and the other polarizing plate side is rotated while the translucent base material is rotated. Find the point (quenching point) where the transmitted light emitted from the darkest point becomes the darkest. When the translucent substrate is at the extinction point, the polarization transmission axis direction of the two polarizing plates is the optical axis direction of the translucent substrate (there are two optical axes and are orthogonal to each other).

Now, B1, B2, B3, B4, B5, and B6, which are cut originals obtained by dividing the PET film into six in the winding direction, were prepared as the birefringent translucent base material A. When the optical axis angle of this cut original fabric was measured, B1 was 20.5 °, B2 was 10.5 °, B3 was 1.5 °, B4 was −8.2 °, B5 was −15 °, and B6 was −25.0 °. A prism row forming portion was formed on one surface with an active energy ray curable resin to shape the prism row, and prism sheets C1, C2, C3, C4, C5, and C6 were produced. Diffusion sheets D1, D2, D3, D4, D5, and D6 were manufactured by applying a diffusing agent to the same cut raw materials B1, B2, B3, B4, B5, and B6. The haze values of the diffusion sheets D1, D2, D3, D4, D5, and D6 were all 62%. A surface light source device was manufactured using these prism sheet and diffusion sheet. Table 1 shows the names of the manufactured surface light source devices and combinations of prism sheets and diffusion sheets. Table 1 shows a combination of the prism sheet and the diffusion sheet used for manufacturing the surface light source device.

  The brightness of the surface light source devices we made was measured and all measured 3100 nt.

In addition, a liquid crystal panel F1 having a transmission axis angle of + 45 ° and a liquid crystal panel F2 having a transmission axis angle of −45 ° were prepared and mounted on these surface light source devices to prepare a liquid crystal display device. Table 2 shows a combination of a name of the liquid crystal display device and a prism sheet, a diffusion sheet, and a liquid crystal panel. Table 2 shows a combination of a prism sheet, a diffusion sheet and a liquid crystal panel used for manufacturing the liquid crystal display device.

When the liquid crystal display devices were turned on and the luminance was measured, the results shown in Tables 3 and 4 were obtained. Table 3 shows the luminance when the liquid crystal display devices G1, G2, G3, G4, G5, and G6 are turned on, and Table 4 shows the luminance when the liquid crystal display devices H1, H2, H3, H4, H5, and H6 are turned on. .

  That is, the liquid crystal display devices G1 and G2 using the cut original fabrics B1 and B2, respectively, increase the light utilization efficiency by using the liquid crystal panel F1 having a transmission axis angle of + 45 °. The liquid crystal display devices G5 and G6 used each had a high light utilization efficiency by using the liquid crystal panel F2 having a transmission axis angle of −45 °. However, in the liquid crystal display devices G3, G4, H3, and H4 using the prism sheets C3 and C4 using the cut original fabrics B3 and B4, respectively, the light use efficiency is low.

Accordingly, a diffusion sheet J1 obtained by cutting out the diffusion sheet D3 whose base material is the cut original fabric B3 so that the optical axis angle is + 22.5 °, and an optical axis angle of the diffusion sheet D4 whose base material is the cut raw fabric B4 is −22.5. A diffusion sheet J2 cut out so as to be at ° is manufactured, and a liquid crystal display device K1, a prism sheet C6, a diffusion sheet J2, and a liquid crystal panel F2 mounted with a prism sheet C1, a diffusion sheet J1, and a liquid crystal panel F1 are mounted. When the device K2 was manufactured and the luminance was measured, K1 was 215 nt and K2 was 213 nt. Therefore, the raw fabrics B3 and B4, which were unsuitable as the prism sheet substrate, could be effectively used as the diffusion sheet substrate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic partially cutaway perspective view showing an embodiment of a prism sheet according to the present invention, an edge light type surface light source device according to the present invention using the prism sheet, and a liquid crystal display device according to the present invention using the surface light source device. is there. It is a typical fragmentary sectional view of FIG. It is a typical partial expanded sectional view of a prism sheet. It is a schematic diagram which shows the mode of the light deflection | deviation in XZ plane by a prism sheet. It is a schematic diagram for demonstrating preparation of the prism sheet original fabric for obtaining the prism sheet of a desired dimension and shape by cutting out. It is a typical perspective view which shows the roll type | mold used for preparation of a prism sheet original fabric. It is a typical exploded perspective view which shows the roll type | mold used for preparation of a prism sheet original fabric. It is a typical partial notch partial top view for demonstrating the positional relationship of a liquid crystal display element and a surface light source device. It is a schematic diagram for demonstrating the positional relationship of a liquid crystal display element and a surface light source device. It is a figure which shows an example of the polarization characteristic of the said deflection | deviation light when the emitted light from a light guide receives the deflection | deviation by a prism row | line | column and exits a prism row | line | column formation part. The figure which shows an example of the change of the brightness | luminance of a liquid crystal display device when putting the prism sheet from which an optical axis angle differs with respect to the optical axis direction of a diffusion sheet translucent base material about the polarized light with the polarization characteristic of FIG. It is. It is a schematic diagram for demonstrating the mode of the molecular orientation direction by biaxial stretching of a birefringent translucent base material, and the direction which cuts out a cut original fabric.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary light source 2 Light source reflector 3 Light guide 31 Light incident end surface 32 Side end surface 33 Light output surface 34 Back surface 4 Prism sheet 41 Light incident surface 411 Prism rows 411a and 411b Prism surface 42 Light output surface 43 Translucent base material 43A Optical axis Direction 44 Prism array forming part 5 Light reflecting element 6 Light diffusing element 61 Incident surface 62 Output surface 63A Optical axis direction 7 Mold member (roll type)
DESCRIPTION OF SYMBOLS 8 Liquid crystal display element 81, 82 Translucent board | substrate 83 Liquid crystal 84 Pixel electrode 85 Transparent electrode 86, 87 Polarizing plate 86A Polarization transmission axis direction 88 Pixel part 88A Y direction pixel part row | line | column 88B X direction pixel part row | line | column 9 Translucent base material Original fabric 10 Active energy ray curable composition 11 Pressure mechanism 12 Resin tank 13 Nozzle 14 Active energy ray irradiation device 15 Thin plate member 16 Cylindrical roll 18 Shape transfer surface 28 Nip roll 38 Birefringent translucent base material 38A Biaxial stretching direction 38B Winding direction 38C Molecular orientation angle 38D Original cut

Claims (1)

The birefringent translucent base material produced by biaxial stretching is cut in the winding direction and separated into a cut stock A whose optical axis angle is within a predetermined range and other cut stock B. A prism sheet and a diffusion sheet manufacturing method, wherein a diffusion sheet is manufactured using the cut original fabric A as a base material, and a prism sheet is manufactured using the cut original fabric B as a base material.

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