JP2009053686A - Curved surface-forming prism sheet having concave curve-forming valley part cross section, its manufacturing method, surface light source and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a curved surface-forming prism sheet which is constituted by arranging a lot of linear prisms and making a valley part of a prism surface into a concave-curved surface that is effective in reducing side lobe and which can be easily manufactured and has practical structure, and further to provide its manufacturing method, a surface light source and a liquid crystal display apparatus using the curved surface-forming prism sheet. <P>SOLUTION: A coating solution 3A containing a resin and a solvent is applied on a prism surface of an original form prism sheet 2 where a lot of linear prisms 1 are arranged, is subjected to solvent drying to cause volume contraction. Thus, a transparent layer 3 with a concave curve where a contour shape of a main cutting section becomes concave toward an original form prism projection direction is formed at least at the valley part. The transparent layer is made to be a pattern shape to prevent light source unevenness and particles such as resin beads are contained in the transparent layer to prevent luminance exterior view unevenness owing to light diffusion, optical adhesion, damaging or the like. The curved surface-forming prism sheet is arranged at a light emission surface side of a light transmission body to form the surface light source. The surface light source is used as the light source of a liquid crystal panel to form the liquid crystal display apparatus. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a curved prism sheet in which a large number of linear prisms are arranged and a trough portion of the prism surface is a concave curved surface, a manufacturing method thereof, a surface light source using the prism sheet, and a liquid crystal display device.

  The liquid crystal display device usually has a liquid crystal panel and a surface light source that illuminates the liquid crystal panel, and the surface light source usually illuminates the liquid crystal panel from the back (opposite to the image observer side) as a backlight. As the surface light source, a prism sheet in which a large number of linear prisms typified by triangular prisms are arranged in parallel is used in order to collect light rays in a specific direction such as a normal direction to improve light utilization efficiency. The prism sheet is used in an edge light type or direct type surface light source. For example, in an example of an edge light type surface light source, the surface light source 20 illustrated in FIG. 12 (a conceptual diagram, the scale and the aspect ratio are exaggerated so that they can be easily seen. The same applies to other drawings). As described above, the diffusion sheet 23 is disposed on the light exit surface of the light guide plate 22 in which the light source 21 such as fluorescence is disposed on the side surface, and the prism sheet 24 is disposed on the diffusion sheet 23.

  However, in the simple case where the main cut surface of the prism (the cut surface perpendicular to the ridge line direction of the linear prism of which the unit prism is a columnar body, hereinafter also referred to as “cross section”) is simply a triangle, a specific direction The brightness of the light increases and the light use efficiency improves, but unnecessary light called sidelobe light deviates in a direction other than the specific direction. Therefore, in order to reduce sidelobe light, Patent Document 1 introduces a curved surface on the prism surface by changing the shape of the main cut surface of the prism to a concave curve at the valley, or a convex curve at the top, and a curve. Discloses a prism sheet that reduces the sidelobe light while maintaining the luminance in the normal direction.

  Further, in Patent Document 2, in terms of a prism sheet, a lenticular lens sheet in which a large number of columnar concave lenses having a concave curved surface on the entire slope including the valley including the main cut surface of the linear prism are arranged in parallel. In addition, it is disclosed that the side lobe light is reduced together with the luminance improvement in a specific direction such as a normal direction.

Japanese Patent No. 3410766 Japanese Patent Laid-Open No. 6-201904

However, the prism sheet with the curved surface of the main cut surface, especially the valley surface where the valley shape is a concave curve, has a problem to be solved when it is actually manufactured as an industrial product. there were.
That is, a mold is used for manufacturing the prism sheet, but in order to finish the trough cross-sectional shape of the prism sheet with a concave curve, the top of the mold surface needs to be a convex curve in the mold. However, in the manufacture of the mold, the reverse uneven shape of the linear prism is formed by cutting with a cutting tool or the like on the surface to be the mold surface, but in the cutting process, the trough of the mold corresponding to the top of the prism is recessed. Machining into a curve can be easily done by selecting a bite shape, but when the top of the mold (corresponding to a trough in the prism) is a convex curve, machining is difficult. A first mold is formed in a shape that can be cut with a cutting tool, and a molded product obtained by taking a mold from the first mold and inverting the concaves and convexes is formed as a second mold, and a prism is formed using the second mold. Although it is conceivable to finish the cross-sectional shape of the valley portion of the sheet into a concave curve, the number of processes increases and productivity is poor. There is also a problem that the fidelity reproducibility of the shape is lowered by repeating the mold taking.
Furthermore, in order to cope with required performances that differ depending on the type of surface light source, it is necessary to prepare a large number of prism sheets having different shapes little by little. In the case of such a prism sheet having a shape that is difficult to manufacture, it is difficult to prepare a large number of types of molds.

In other words, the problem of the present invention is that the curved prism sheet in which the concave curved surface is introduced into the prism surface so that the main cut surface shape of the valley portion of the linear prism becomes a concave curve can be easily obtained in various shapes. It is to provide a manufacturing method that can be manufactured and a layer configuration that can be easily manufactured, and also to provide a light source unevenness prevention function, a light diffusion function, an optical adhesion prevention function, and the like.
Another object of the present invention is to provide a surface light source and a liquid crystal display device using such a curved prism sheet.

  Therefore, in the present invention, a curved prism sheet having the following configuration, a manufacturing method thereof, a surface light source, and a liquid crystal display device are provided.

(1) With respect to the original prism sheet in which a large number of linear prisms are arranged, at least the valley of the prism surface is filled, and the contour shape at the prism main cutting surface is concave at the valley so as to protrude toward the original prism. Curved prism sheet with a transparent layer that has a concave curve.
In this configuration, since the main cut surface shape of the valley is a concave curve as described above due to the transparent layer filling the prism valley, the valley of the prism surface is not a concave curve even if the prism valley before filling is not a concave curve. By forming the concave curved surface, the curved prism sheet having a configuration that can reduce sidelobe light and can be easily manufactured. In addition, the original prism sheet before the provision of the transparent layer remains in the same shape that can be manufactured with the same mold, and the concave curve shape of the cross section can be freely adjusted by the transparent layer that fills the valleys.

(2) A curved prism sheet in which the transparent layer is formed in a pattern in (1) above.
In this configuration, by forming the transparent layer in a pattern, light source unevenness can be improved by a pattern corresponding to the light source, and the required optical performance can be designed. In addition, it is possible to reduce the thickness by improving the light source unevenness.

(3) The curved prism sheet according to (1), wherein the transparent layer contains particles.
In this configuration, the particles can further prevent appearance unevenness due to the light diffusing function, optical adhesion at the time of sheet stacking, and damage.
(4) A curved prism sheet in which the transparent layer containing the particles is formed in a pattern in (3).
In this configuration, by forming the transparent layer in a pattern, light source unevenness can be improved by a pattern corresponding to the light source, and the required optical performance can be designed. In addition, it is possible to reduce the thickness by improving the light source unevenness.
(5) A curved prism sheet formed in a pattern by combining the transparent layer not containing particles and the transparent layer containing particles in (1) above.
In this configuration, by combining the particle-free transparent layer and the particle-containing transparent layer into a pattern shape, the light source unevenness can be improved by the pattern corresponding to the light source, and the required optical performance can be designed. In addition, it is possible to reduce the thickness by improving the light source unevenness.
(6) The curved prism sheet according to any one of the above (3) to (5), wherein the particles include particles in which at least a part of the particles protrudes from a prism top as the particles.
In this configuration, optical sticking and damage can be prevented by the protruding particles.

(7) After applying a coating liquid containing at least a resin and a solvent on the prism surface of the original prism sheet in which a large number of linear prisms are arranged, the prism contracts by utilizing volume shrinkage due to solvent removal. A curved prism sheet manufacturing method for forming a transparent layer having a concave curve that fills at least a trough portion and has a trough portion with a contour shape at a prism main cutting surface that is concave toward the protruding direction of the original prism. .
In the manufacturing method with this configuration, the transparent layer that fills the prism valley and changes the valley shape to the concave curve as described above can be easily obtained by utilizing the volume shrinkage at the time of removing the solvent by drying the concave curve shape. Therefore, it is possible to easily manufacture a curved prism sheet that has a concave concave valley shape and can reduce sidelobe light. Moreover, the original prism sheet remains in the same shape that can be manufactured with the same mold, and the concave curve shape of the cross section can be freely adjusted by the transparent layer filled in the valleys.

(8) The method for producing a curved prism sheet according to (7), wherein the coating liquid contains particles and forms a transparent layer containing particles. In the manufacturing method according to this configuration, the particles can further prevent appearance unevenness due to the light diffusion function, optical adhesion at the time of sheet stacking, and damage.

(9) A surface light source in which the curved prism sheet according to any one of (1) to (6) is disposed on the light exit surface side of the light guide. In the present invention, the above-mentioned effect of the curved prism sheet can be obtained with a surface light source, and side lobe light can be reduced, or optical adhesion, scratches, uneven appearance, etc. can be prevented.

(10) A liquid crystal display device using the surface light source of (9) above. In the present invention, the above-mentioned effect of the surface light source can be obtained in the liquid crystal display device, and the sidelobe light can be reduced, or the appearance nonuniformity can be prevented by the light diffusing function, and the optical adhesion at the time of sheet stacking can be prevented.

(1) In the curved prism sheet according to the present invention, the shape of the main cut surface of the valley is changed from a concave straight original prism sheet that is easy to manufacture into a concave curve that is concave toward the original prism protruding direction by a transparent layer. Therefore, a curved prism sheet having a configuration that can reduce sidelobe light and can be easily manufactured can be provided. In addition, since the original prism sheet remains in the same shape by the same mold and the shape of the concave curve can be freely adjusted by the transparent layer, it can easily cope with the production of various types.
(2) Furthermore, by making the transparent layer into a pattern, it is possible to improve light source unevenness and to design required optical performance. Moreover, it can respond to thickness reduction.
(3) Furthermore, if particles are contained in the transparent layer, it is possible to prevent appearance unevenness due to the light diffusing function, optical adhesion at the time of sheet stacking arrangement, and scratches.
(4) Moreover, light source nonuniformity can be improved and the required optical performance can be designed also by making it the pattern shape which combined the transparent layer and the transparent layer containing particle | grains. Moreover, it can respond to thickness reduction.
(5) Further, if the particle head protrudes from the top of the prism, optical adhesion and damage can be prevented.

(6) Further, in the method of manufacturing the curved prism sheet according to the present invention, the transparent layer that fills the prism valley and makes the valley shape concave toward the protruding direction of the original prism, Since the concave curve shape can be easily realized by utilizing the volume shrinkage at the time of solvent removal, a curved prism sheet that can reduce sidelobe light can be easily manufactured even if the prism valley before filling is not a concave curve. In addition, the original prism sheet remains in the same shape with the same mold, and the shape of the concave curve can be freely adjusted by adjusting the amount of solvent added to the volume shrinkage when the transparent layer is dried.
(7) Further, if particles are contained in the transparent layer, the light emitted from the prism surface can be diffused, and appearance unevenness due to the light diffusing function can be prevented, or optical adhesion and scratching at the time of sheet stacking can be prevented. . Further, the diffusion sheet on the prism light exit surface side can be omitted when used as a surface light source.

(8) According to the surface light source of the present invention, the effect of the curved prism sheet can be obtained. For example, it is possible to prevent side lobe light, or prevent unevenness in appearance due to the light diffusion function, optical adhesion, and scratches. Further, the arrangement of the diffusion sheet on the prism light exit surface side can be omitted.
(9) According to the liquid crystal display device of the present invention, the effects described in the above surface light source can be obtained.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

[Outline by representative composition]
As illustrated in FIG. 1, the curved prism sheet according to the present invention is shaped like the curved prism sheet 10 of FIG. 1 (c) schematically illustrating one form in a partially enlarged sectional view. The trough of the prism surface is filled with the transparent layer 3, and the contour of the main cut surface of the prism trough is changed by the surface of the transparent layer to the protruding direction of the original prism (upward in FIG. 1C). It can be expressed as a concave curve (convex curve toward the original prism, a concave curve upward with reference to FIG. 1C), or a convex curve downward. In other words, a curve in which the center of curvature of the contour curve in the vicinity of the valley is located in the original prism protruding direction (above the curve in FIG. 4 (c)). In the following, such a specific recess is simply referred to as “concave” or “concave curve”. , And abbreviated as such "concave surface", as appropriate abbreviation is also used.), It is of the configuration in which the.

  The transparent layer 3 that realizes such a concave curve in the valley shape (more specifically, the valley contour shape in the main cutting plane, the same applies hereinafter) is a triangular column or the like as shown in FIG. A large number of unit linear prisms 1 (hereinafter simply referred to as linear prisms) made of similar columnar bodies are arranged in a direction perpendicular to the ridge line direction, with the ridge line directions of the unit linear prisms aligned in parallel (hereinafter referred to as the linear line prisms). A coating liquid containing a resin and a solvent is applied to the prism surface of the original prism sheet 2 (also referred to as a linear arrangement) as shown in FIG. 1B (in FIG. By using the volume shrinkage phenomenon at the time of solvent removal due to flow and drying due to gravity and surface tension before coating, after application, the coating liquid is illustrated by applying a uniform thickness over the entire prism surface) As shown in FIG. 1C, the original prism is formed on the surface of the transparent layer 3. Toward the projecting direction side of the unit linear prism sheet (upper In terms of the figure), shaping the concave curve recessed. Therefore, the original prism sheet does not need to have a convex curve at the top of the mold surface in the mold and can be easily manufactured because the main cutting surface may be a simple right triangle or the like.

Further, like the curved prism sheet 10 illustrated in FIG. 8, the transparent layer 3 may contain particles 4, the unevenness of the emitted light reflecting the optical appearance unevenness and the luminance distribution of the light source, and the prism surface. In-plane unevenness of brightness, interference fringes, and the like due to optical contact with other members that come into contact with the substrate can be prevented.
The surface light source of the present invention may be configured using such a curved prism sheet, and the liquid crystal display device of the present invention may be configured using such a surface light source for illumination of the liquid crystal panel.

[Original prism sheet]
The original prism sheet 2 is a prism sheet before the transparent layer is filled in the valleys, and as illustrated in the perspective view of FIG. 2, a sheet shape made of a transparent substrate in which a large number of linear prisms 1 are linearly arranged. This is an optical member. The figure is an example in which a large number of linear prisms are densely arranged in a linear manner.
In the original prism sheet 2, the contour shape of the valley portion of the main cut surface of the linear prism 1 is not a “concave curve” but is preferably a “concave straight line” like a trough portion of a triangular prism from the viewpoint of easy manufacture. The main cut surface is a cross section perpendicular to the ridge line 1a where the both side slopes of the linear prism are in contact with each other or the extended surfaces of the both side slopes are in contact. The main feature of the present invention is that the transparent layer can be changed to a concave curve even if the contour shape of the valley at the main cut surface is a concave linear shape. However, in the present invention, even if the contour shape is a concave curve, there is an advantage that the concave curve can be adjusted and changed by the transparent layer, so the concave curve is excluded as the contour shape of the valley before the transparent layer is formed. Not what you want. However, as described above, as the valley shape of the original prism sheet before forming the transparent layer, a concave straight line is preferable in terms of easy manufacture.

The main cut surface shape of the linear prism itself in the original prism sheet before forming the transparent layer is an isosceles triangle in FIG. 3A and an unequal side in FIG. Triangle, one or both of the slopes on both sides of FIG. 3 (c) are curved (when the drawing is a convex curve), the top of FIG. 3 (d) is a convex curve [both slopes on both sides of FIG. 3 (c) are curved. Or other polygons other than triangles, for example, a quadrangle (corresponding to a triangular bevel on a polygonal line), a pentagon (both triangular bevels on a polygonal line) It is possible to use various types of conventionally known shapes. A suitable shape is a shape in which the troughs are concave straight lines.
In addition, as long as the transparent layer can be curved, a large number of linear prisms may be linearly arranged at intervals, so that a bottom surface may be parallel to the sheet surface.

  The specific shape of the prism is a case where the linear prism is a triangular prism with a triangular cross section, and the prism period P is 10 to 500 μm, preferably 25 to 75 μm, and the prism height H is The prism apex angle θ is 45 to 125 °, preferably 80 to 110 °, preferably 5 to 500 μm, preferably 12 to 75 μm. These dimensions are selected based on light utilization efficiency such as light collection characteristics, light diffusion characteristics, and sidelobe light loss.

  Further, as illustrated in FIG. 4, the original prism sheet 2 has a configuration in which the prism array portion 2 </ b> A and the base material portion 2 </ b> B in FIG. 4A are laminated and integrated, and the prism array portion 2 </ b> A in FIG. 4B. A multilayer structure in which the base material portion 2 </ b> B is a separate layer may be used.

  The original prism sheet may be manufactured by a conventionally known material and manufacturing method. For example, the material is thermoplastic resin, thermosetting resin, ionizing radiation curable resin, glass, quartz, meteorite, diamond (golden stone), transparent ceramics such as PLZT, and the like. Thermoplastic resins include acrylic resins, polycarbonate resins, polyester resins, styrene resins, olefin resins, etc. Thermosetting resins include epoxy resins, thermosetting polyester resins, etc. As the curable resin, acrylate type is representative, oligomers (or prepolymers) such as polyester acrylate, urethane acrylate, epoxy acrylate, monomers such as trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, other monomers, An oligomer or the like is used. The acrylate referred to here includes methacrylate. Examples of the glass include soda glass, potash glass, borosilicate glass, and lead glass. In the case of a multilayer structure, the base material portion can be made of a thermoplastic resin or glass, and the prism array portion can be made of an ionizing radiation curable resin.

  As the manufacturing method, when the resin material of the prism array portion is a thermoplastic resin, a hot pressing method using an embossed plate, a melt extrusion molding method or the like is used. When an ionizing radiation curable resin is used, ionizing radiation is applied on a shaping mold. A photocuring method for curing by irradiation is used.

[Transparent layer]
The transparent layer 3 is a transparent layer that is applied to the prism surface of the original prism sheet and realizes the concave curve as described above by the surface of the transparent layer itself with respect to the cross-sectional shape at least at the main cutting surface of the prism valley. Thereby, the trough part of a prism surface can be made into a concave curved surface as mentioned above. In order to make the surface of the transparent layer have a concave curve (or concave curved surface) at least at the valleys, a coating liquid containing a resin and a solvent for forming the transparent layer is applied to the prism surface, and the transparent layer is dried and the like. This can be easily realized by utilizing the volume shrinkage of the coating film when the solvent is removed from the inside to the outside.

At this time, if the coating liquid applied to the prism surface exhibits complete fluidity before solidification, the surface tension between the prism surface and the coating liquid can be ignored, and the valley is directed in the direction of gravity with respect to the top of the prism. Then, the coating liquid applied to the prism surface with a uniform thickness and without filling up to the top completely flows into the valley, and the surface of the coating liquid finally filled in the valley is the prism sheet surface. It becomes a flat plane with a horizontal cross section. After that, if the volume shrinkage due to solvent drying is completely ideal and uniform in the whole part, the surface of the obtained transparent layer becomes a concave straight line.
However, adjustment of the degree of flow of the coating liquid into the valley by limiting the surface shape change due to the skinning phenomenon of the coating liquid during drying and adjusting the solvent ratio, coating liquid viscosity, solvent removal speed, temperature, etc. (suppression) ), The degree of dent can be adjusted by utilizing volume shrinkage at the time of solvent removal, and the shape of the concave curve of the valley shape can be adjusted.

  In addition to the solvent removal, the volume shrinkage of the coating film can be cured shrinkage when a curable resin is used as the resin. Therefore, it is not impossible to make a concave curve only by curing shrinkage of the solvent-free coating liquid, but the solvent removal shrinkage has a larger volume shrinkage than that due to cure shrinkage, and the degree of adjustment of the shrinkage change amount by the solvent blending ratio. It has many advantages such as being easy. Moreover, in the coating liquid of curable resin and a solvent, both hardening shrinkage and solvent removal shrinkage act.

The part which becomes a concave curve by the transparent layer is only the valley part (see FIG. 5 (a)), and all the parts from the valley part to the top part (see FIG. 5 (b)), from the valley part to the top part of the prism. Any of a valley and a middle part except for the top may be used, but at least the valley is essential. In any of these cases, the transparent layer may be covered up to the top of the prism or may not be covered. It is not necessary for the entire transparent layer covering the prism to be a concave curve, and the transparent layer may have a uniform thickness, or at least the surface of the transparent layer may be a portion other than a portion that realizes a concave curve such as a valley. The thickness may change so as to draw a linear outline. Moreover, when a transparent layer also coat | covers a top part, it is good also considering a top part as a convex curve [refer FIG.5 (c)]. Whether to cover the top part or the middle part is adjusted by the viscosity of the coating liquid for forming the transparent layer, the condition of flowing into the valleys, and the like.
The radius of curvature R of the concave curve is approximately in the range of 1 μm to the prism period P. When the thickness is 1 μm or less, the effect of curved surface cannot be obtained sufficiently.

  Further, the cross-section of the coating end portion of the transparent layer covering the prism surface may be a convex curve instead of a concave curve depending on the surface tension between the prism surface of the original prism and the transparent layer forming coating liquid. (Of course, even in this case, the valley has a concave curve).

The resin material used for the transparent layer is not particularly limited as long as it is transparent. For example, a thermoplastic resin, a thermosetting resin, an ionizing radiation curable resin, or the like can be used.
The thermoplastic resin is, for example, an acrylic resin, a polycarbonate resin, a polyester resin, a styrene resin, an olefin resin, or the like.
Examples of the thermosetting resin include a thermosetting acrylic resin, a thermosetting urethane resin, an epoxy resin, a thermosetting polyester resin, and a silicone resin.
The ionizing radiation curable resin is typically one using a radical polymerizable compound such as an acrylate type or a cationic polymerizable compound such as an epoxy type. Examples of the acrylate radical polymerizable compound include oligomers (or prepolymers) such as polyester acrylate, urethane acrylate, and epoxy acrylate, monomers such as trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, and other monomers and oligomers. Etc. are used. In addition, as the epoxy-based cationic polymerizable compound, a novolak-type or bisphenol-type epoxy prepolymer or the like is used. In addition, what is necessary is just to select an ultraviolet-ray, an electron beam, etc. suitably as ionizing radiation.
In addition, the ionizing radiation curable resin is advantageous in terms of mutual adhesiveness, etc., when the resin forming the prism surface of the prism original sheet is the same type of resin as the ionizing radiation curable resin.

  The solvent of the coating solution is not particularly limited as long as it can dissolve or disperse the resin and can be removed in the process of forming the transparent layer, such as aromatic hydrocarbons such as toluene and xylene, acetone, mercyl ethyl ketone, cyclohexanone. Various known solvents used for coating liquids such as ketones such as hexane, aliphatic hydrocarbons such as hexane and heptane, and alcohols such as ethyl alcohol and propyl alcohol are appropriately selected, and one kind alone or two or more kinds are mixed. And use it. The use of the solvent has effects of adjusting the coating suitability by reducing the volume shrinkage and the viscosity of the coating solution and promoting the flow into the trough in the coating film forming process. Further, the use of a solvent also has an effect of improving the adhesion between the transparent layer and the prism surface when a resin is used for the original prism sheet and a material that appropriately dissolves and swells the prism surface in the solvent is selected.

  In addition, what is necessary is just to adjust suitably the mixture ratio of resin and a solvent with the shape of the concave curve implement | achieved. For example, the solid content ratio [total solid content / (total solid content + solvent amount)] of the total solid content of the resin or the like is 5 to 70% (mass basis).

  The coating liquid may contain other known additives in addition to the resin and the solvent. For example, fluidity adjusting agents, leveling adjusting agents, surfactants, fillers, light stabilizers (ultraviolet absorbers, radical scavengers), heat stabilizers, colorants, antistatic agents and the like. Moreover, when the particle | grains mentioned later are included in a coating liquid, the transparent layer containing particle | grains is obtained.

  In order to apply the coating liquid to the prism surface, a known coating method and printing method such as gravure coating, comma coating, die coating, roll coating, spray coating, dipping, pouring, and other printing methods may be appropriately selected. Immediately after applying the coating liquid, the top of the prism may be completely filled or may not be filled. It selects suitably by the concave curve shape implement | achieved.

The refractive index of the transparent layer approximates the refractive index of the original prism sheet with which the transparent layer is in contact (in the case of a multilayer structure, the refractive index of the prism surface portion of the prism array portion). From the viewpoint of suppressing the light interference fringes. Specifically, the refractive index n _t of the transparent layer, the refractive index n _p of the original prism sheet, a refractive index difference | n _t -n _p | amount may be ≦ 0.14. In particular, it is more preferable if | n _t −n _p | = 0.
For this purpose, for example, it is easy to use the same material system as the resin of the transparent layer and the resin of the prism array portion, but it can be realized by using different material systems.

  Further, the transparent layer may be a double layer such as two layers. In this case, the desired concave curve is realized by the transparent layer exposed on the surface.

In addition, the transparent layer has an entire surface (at least a predetermined valley) in the plane of the original prism sheet (in the plane perpendicular to the protruding direction of the original prism (in the plane parallel to the horizontal direction in FIG. 1C)). In addition to the form (FIG. 1 (c)) that covers the partial area), the form (FIG. 6, 7, 10, or 11) that partially covers only a partial area within the surface of the original prism sheet. In other words, the transparent layer may be formed in a pattern, which is impossible when the prism shape is formed as a molded product. This is an advantage unique to the present invention that makes the prism valleys curved.By forming the transparent layer in a pattern, it is possible to take a pattern corresponding to the shape (line, point) and arrangement of the light source in the pattern of the transparent layer. Therefore, the image of the light source can be seen The light source unevenness that looks brighter can be made inconspicuous, and the required optical performance can be designed, such as the brightness unevenness caused by the light source unevenness, etc. Also, the light source unevenness can be improved, so that it can cope with the thinning. Light sources that cause light source unevenness include linear light sources (for example, cold cathode tubes), point light sources (for example, light emitting diodes), and the like.
For example, in FIG. 6 in which a direct type surface light source is assumed, the transparent layer 3 is disposed in a valley portion in a region between the light sources other than a region in the vicinity of the light source including a portion arranged immediately above the light source 6 in the valley portion 5. Is a cross-sectional view illustrating a curved prism sheet 10 formed in a pattern, and the curved prism sheet 10 has a prism surface on the light exit surface side.

Examples of the pattern are preferably congruent or similar to the planar view shape of the light source 6, for example, depending on the luminance distribution of the light source, the shape of the original prism sheet, etc. (Vertical stripes, horizontal stripes, diagonal stripes, etc.), block patterns (such as patterns in which squares are arranged at square lattice points), checkered patterns, other patterns, and combinations thereof. For example, the line light source is a stripe pattern, and the point light sources arranged in a lattice pattern is a block pattern. Further, when the pattern is congruent or similar to the planar view shape of the light source 6, the negative pattern of the light source 6 contour shape (in accordance with the positional relationship between the prism protruding direction of the curved prism sheet 10 and the light source 6 ( 6 or 7) or a positive pattern (see FIG. 10).
Further, when the transparent layer is formed in a pattern, the degree of filling of the valley-shaped transparent layer may be changed instead of making the entire surface of the curved prism sheet uniform. For example, the degree of filling may be reduced as it approaches the light source. The change is gradation or stepwise. In this way, for example, the contour portion of the pattern of the transparent layer can be made inconspicuous. FIG. 7 is a cross-sectional view illustrating the case where the above change is applied to FIG.

(Contains particles)
The transparent layer may contain particles. The particles can impart a light diffusing function to prevent appearance unevenness (brightness surface unevenness), and prevent optical adhesion, scratching, interference fringe generation, and the like when the sheets are stacked. The curved prism sheet 10 shown in FIG. 8 conceptually illustrates a form in which the transparent layer 3 contains particles 4.
The particles are typically transparent resin beads, but particles having various shapes and materials can be used. For example, the particle shape may be arbitrary, such as a spheroid, a spheroid, a polyhedron, a mounted polyhedron (a solid with the corners of the polyhedron cut), a needle shape, a rod shape, and the like. Of these, spherical shapes such as resin beads are typical. The particle diameter of the particles is about 1 to 501 μm. The particle material is organic particles such as resin beads made of acrylic resin, polycarbonate resin, urethane resin, melamine resin, glass beads made of glass such as soda glass, potassium glass, borosilicate glass, silica beads, alumina Inorganic particles such as beads may also be used.

  The content of the particles may be appropriately adjusted according to the expected effect amount, and is, for example, in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the resin component that is the coating liquid solid content. If the content is too small, sufficient effects cannot be obtained. If the content is too large, an adverse effect on the original light-collecting effect as a prism sheet and dropout of particles tend to occur.

The particles contained in the transparent layer are typically in the form of a part of one particle protruding from the surface of the transparent layer as illustrated in FIG. 8, but the entire part of one particle is embedded inside the transparent layer and buried. May be present (not shown). However, the former is effective in terms of preventing appearance irregularities, optical adhesion, scratches, and the like.
Further, in the drawing, which is also a conceptual diagram, a part of the particles 4 protrudes from the transparent layer 3 and the surface of the protruding part of the particle is not covered with the transparent layer. It may be coated with, and is usually coated.

Moreover, although the particle | grain presence location becomes a part filled with the transparent layer among prism surface slopes, any may be sufficient only from a trough part, from a trough part and a trough part to a top part. Further, the particles may protrude from the top of the original prism. Further, it is possible to make one particle protrude from the trough to the top and from the top by selecting the particle size with respect to the prism size, but a plurality of particles may be in the same state. Moreover, when forming only a trough part in a transparent layer, it can also make it exist with more probability in a trough bottom especially in a trough part (refer FIG. 14). In this case, the particles may fill the entire length of the valley bottom line formed by the valley bottom (the line corresponding to the ridge line at the top), or may be partially present or scattered without being filled. When the particles are present at the bottom of the valley where the particles are present and at least a part protrudes from the transparent layer, the contour of the valley of the prism formed by the transparent layer containing the particles is limited to the particles existing portion (the particles and Depending on the relative size of the prism, the particles may be convex instead of concave. That is, the concave curve and the convex curve are often mixed. However, when viewed from the entire length of the valley bottom line, it is considered that the effect of making the prism sheet into a curved surface as a whole is obtained by the portion where the main cut surface is a concave curve. In addition, there is a concave curve in the contour shape at the main cut surface that reaches the transparent layer on both sides of the protruding particles.
In the present invention, in the case of a valley curved surface where such uneven portions are mixed, the contour-shaped unevenness refers to the contour-shaped envelope surface (envelope in the main cutting surface), This refers to unevenness of a curved surface (or curved line) smoothed by filtering a short period component sufficiently shorter than the entire length of the valley bottom line.

The fact that at least a part of the particle protrudes from the prism top means that when attention is paid to one particle, at least a part of the particle itself, in other words, the head of the particle protrudes from the prism top. If such particles are contained at least in the particles contained in the transparent layer, the effect of preventing optical adhesion and damage can be obtained. All particles contained in the transparent layer may not protrude. As described above, the transparent layer may be covered up to the top of the original prism, and in such a case, the particles are projected to be the top of the original prism covered with the transparent layer, that is, transparent. It means that it protrudes from the prism top part in the curved prism sheet after layer formation.
FIG. 9 is a conceptual cross-sectional view showing a state in which particles protrude from the top of the prism (the curved surface depiction of the trough is omitted here). In the figure, the particle 4 is a true sphere, and the prism is conceptually shown as a right-angled isosceles triangle. In this case, when the particle size of the particle 4 is D and the height of the prism is h, from the top of the prism. The condition that the head of the particle protrudes (the condition that the protruding amount g> 0) is such that the particle size and particle diameter D are (1 + 2 ^1/2 ) × (D / 2) ≧ h. For the purpose of preventing the optical adhesion of the curved prism sheet 10 of the present invention, the protrusion height g of the particle 4 from the apex of the original prism needs to be equal to or greater than the wavelength of visible light, and is visible to the light source light. In the case where the entire wavelength range of light rays includes 380 to 780 nm, g> 780 nm is set. Usually, it is about 1 to 2 μm.
As described above, by projecting at least part of the particles with respect to the prism top, the curved prism sheet 10 is adjacent to another member (another prism sheet, light diffusion sheet, polarization separation sheet, polarizing plate, light guide plate). Etc.) and interference fringes, Newton rings, wet out (a phenomenon in which the close contact portion appears to be wet) can be prevented.
Moreover, it is preferable from the point of optical adhesion prevention that the particle | grains which have the size which protrudes are the surface density of 2 or less per mm < ² >. When the surface density exceeds two, particles having a protruding size are recognized as defects.

  When the particles as described above are present in the transparent layer, it is possible to prevent the prism sheet from being scratched, optical adhesion when arranged as a surface light source component, and uneven appearance. And, due to the appearance non-uniformity prevention effect, when a prism sheet is used as the surface light source, the same light diffusion effect as when a light diffusing film is further arranged on the main light surface side of the prism sheet is obtained. Can be reduced.

  As an example of a preferable form in which particles are contained in the transparent layer, a light diffusing material is selected as the particles, and the light diffusing transparent layer containing such particles is selected from the valleys of the original prism sheet. A form in which the line (or point) light source part of the direct type surface light source is selectively filled in the vicinity immediately above the light source unit is exemplified. If this form is adopted, the light emitted from the area directly above the linear light source in the direct-type surface light source itself is diffused and attenuated, while the relative light other than the area directly above the linear light source is attenuated. In particular, in the prism valley where the luminance is low, the diffusion attenuation of the emitted light is low. For this reason, the brightness distribution of the direct type surface light source itself is made uniform. In this case, in order to prevent the luminance from becoming discontinuous at the boundary between the transparent layer forming part and the non-forming part containing the particles, the concentration of the particles is gradually (continuously) as the distance from the line light source part increases. (Or step by step). Further, in order to sufficiently exhibit the effect of improving the optical properties of the prism sheet by the transparent layer, the particle-free transparent layer is formed in the prism valley where the particle-containing transparent layer is not formed. In this case, the prism protrusion is preferably on the light source side. Referring to FIG. 10, the curved prism sheet 10 has a prism surface as a light incident surface side (light source side) and forms a particle-containing transparent layer 3a in a pattern in a region immediately above the light source including directly above the light source 6. It is sectional drawing of an example. This improves light source unevenness.

  In addition, when the particle-containing transparent layer is formed in a pattern, it is preferable to use the transparent layer containing particles as shown in FIG. Referring to FIG. 11, the curved prism sheet 10 has the prism surface as the light exit surface side, and the particle-containing transparent layer 3 a is formed in a pattern in a region between the light sources other than the region immediately above the light source including immediately above the light source 6. It is sectional drawing of an example. The transparent layer 3a is light diffusive. This improves light source unevenness. In the region immediately above the light source, retroreflection due to total internal reflection of the prism is used to prevent the region directly above the light source from becoming brighter than the region between the light sources, and in the region between the light sources, the transparent layer 3a containing particles and having light diffusibility is used. The light of the light source that passes through obliquely is diffused to prevent the brightness in the front direction from becoming dark.

  In addition, when forming a particle-containing transparent layer in a pattern, for example, a transparent layer that does not contain particles (particle-free transparent layer) is formed in the valley of the non-formed portion of the particle-containing transparent layer. The transparent layer and the transparent layer containing particles may be combined to form a pattern (two-color transparent layer). This improves light source unevenness.

Additional layers
In addition to the original prism sheet and the transparent layer described above, other layers may be further added as necessary. For example, a light diffusion layer, an adhesion prevention layer, and the like. Any conventionally known prism sheet can be appropriately used as the curved prism sheet. These are appropriately provided on the prism surface, the opposite surface, or both surfaces. For example, on the back side of the non-prism surface, the light diffusing layer is applied by diffusing film (or film), diffusing plate lamination, coating or the like. Further, the light guide plate may be laminated and integrated on the non-prism surface side.

[Surface light source]
The surface light source according to the present invention is a surface light source using the curved prism sheet described above. The surface light source may be an edge light type, a direct type, or a surface light source made of an electroluminescent material (EL). Other components and the like of the surface light source combined with the curved prism sheet may be the same as those of conventionally known various surface light sources. For example, a solid light guide plate made of a transparent resin such as an acrylic resin or a hollow light guide is used as the light guide. In addition, a resin layer or a coating film containing a light diffusing agent such as resin beads is used for the diffusion sheet.
Such a surface light source is, in the case of the surface light source 20 illustrated in FIG. 12, a light guide 22, a light source 21 such as a fluorescent lamp arranged near the light incident surface of the light guide, and a light emission surface. And the curved prism sheet 10 disposed on the diffusion sheet 23. In FIG. 12, the curved prism sheet 10 is also an example of an edge light type surface light source arranged with the prism surface facing the light exit surface.
Further, although not shown, another diffusion sheet may be arranged on the curved prism sheet 10, and a plurality of curved prism sheets such as two may be arranged. In the edge light type surface light source, the curved prism sheet 10 may be arranged so that the prism (protruding) surface faces the light guide 22 side, contrary to FIG.

[Liquid Crystal Display]
A liquid crystal display device according to the present invention is a device that uses a surface light source using the curved prism sheet described above for illumination light of a liquid crystal panel, and includes the surface light source and the liquid crystal panel as described above. A liquid crystal display device used as illumination light for the liquid crystal panel. In a liquid crystal display device, a surface light source is usually arranged behind a liquid crystal panel as a backlight, and a transmissive display panel is used as the liquid crystal panel. A known liquid crystal panel is appropriately selected.

  Further, the present invention will be described in detail by examples and comparative examples. In addition, this invention is not limited to a following example. Further, hereinafter, “part” means “part by mass”, and “%” means “% by mass”.

[Example 1]
A curved prism sheet was prepared as follows, a surface light source was prepared using the prism sheet, and the characteristics were measured and evaluated.

(Original prism sheet)
The original prism sheet has a linear isosceles triangle with an apex angle θ of 90 ° as the main cut surface shape and a prism period P of 50 μm, and is densely attached to one side of a transparent biaxially stretched polyester resin film having a thickness of 188 μm. A multi-layer (two-layer) structure arranged in the above was prepared. As illustrated in FIG. 4B, a prism array portion 2A made of a cured product of an ultraviolet curable resin made of an acrylate-based prepolymer that is an ionizing radiation curable resin is laminated on the base portion 2B of the resin film. This is an integrated original prism sheet 2.

(Formation of transparent layer)
As a coating liquid for forming a transparent layer, a coating liquid in which a mixed solvent of methyl ethyl ketone and toluene in a mass ratio of 1: 1 is added so that a curable polyester resin (composition) containing isocyanate as a curing agent has a solid content of 10%. Applying, drying, and curing to the prism surface of the original prism sheet, a transparent layer having a concave curve so that the contour shape at the main cutting surface is a trough and concave toward the protruding direction of the original prism. It formed and the target curved-surface prism sheet was produced.
FIG. 13 is a micrograph of a cross section of the obtained curved prism sheet. In the figure, the cross section of the transparent layer covering up to the middle part of the prism surface has a straight section, but the section of the transparent layer that fills and covers the valleys of the prism surface has a concave curve.
Moreover, the transparent layer has a convex curve at the end portion where the coating ends at the middle part.

(Production of surface light source)
The edge light type surface light source 20 schematically shown in the exploded plan view of FIG. 15 was assembled. The surface light source 20 shown in FIG. 1 is a light source 21 using a cold cathode tube, which is a solid light guide plate 22 made of a transparent resin having a rectangular front shape, a horizontal direction in the long side direction, and a vertical direction in the short side direction. Arranged in the vicinity of the long sides on both sides, the (lower) diffusion sheet 23 is disposed on the light exit surface of the light guide plate, and the curved prism sheet 10 obtained above is disposed on the diffusion sheet 23 on the ridge line of the prism. One sheet is arranged with the direction facing the horizontal direction and the prism surface as the light-emitting surface side of the surface light source.
The characteristic measurement results are summarized at the end.

[Example 2]
(Original prism sheet)
The original prism sheet is the same as that in Example 1, and a linear prism having a main cutting plane shape of a right isosceles triangle having an apex angle θ of 90 ° and a prism period P of 50 μm is formed into a transparent biaxial film having a thickness of 188 μm. The thing of the multilayer (2 layer) structure which arranged closely on the single side | surface of the extending | stretching polyester resin film was prepared.

(Formation of transparent layer)
As a coating liquid for forming the transparent layer, 40 parts of transparent acrylic resin beads having a spherical shape and an average particle diameter of 10 μm are used as particles with respect to 100 parts of curable polyester resin (composition) containing isocyanate as a curing agent. The coating liquid, which is blended in proportions and adjusted to a solid content (resin + particles) of 10% by adding a solvent, is applied to the prism surface of the original prism sheet, dried and cured to contain particles and main cutting The target curved curved prism sheet was produced by forming a transparent layer with a concave curve on the trough where the contour shape on the surface is a trough and concave toward the protruding direction of the original prism. FIG. 14 is a photomicrograph showing a plan view of the obtained curved prism sheet from the front side on the prism surface side. In the figure, most of the particles are concentrated in the valleys of the prism surface and are discretely distributed in the vicinity of the valley line.

[Example 3]
(Original prism sheet)
The same original prism sheet as in Example 1 was prepared.

(Formation of transparent layer)
As a coating liquid for forming a transparent layer, in Example 1, an ultraviolet curable resin coating liquid composed of the same acrylate-based prepolymer as that in which the prism array portion was formed was mixed with methyl ethyl ketone and toluene so as to have a solid content of 10%. A coating solution formed by adding a mixed solvent of 1: 1 mass ratio is applied to the prism surface of the original prism sheet, dried after solvent drying, and cured by ultraviolet irradiation, so that the contour shape on the main cut surface is a trough. The objective curved curved prism sheet was prepared by forming a concave curved transparent layer so as to be concave toward the original prism protruding direction.
The cross section of the obtained curved prism sheet had the same shape as FIG.

(Production of surface light source)
A surface light source was produced in the same manner as in Example 1.

[Comparative Example 1]
In Example 1, it is an original prism sheet before forming a transparent layer.
Then, similarly to Example 1, a surface light source was produced using this original prism sheet.

[Characteristic evaluation]
For the surface light sources of the examples and comparative examples, the angle distribution from the normal direction of the front luminance is measured, the sidelobe luminance and the half width are obtained, and the brightness unevenness (luminance unevenness) occurring at the edge portion is also determined. evaluated.
The front luminance and the side lobe luminance were comparatively evaluated using the original prism sheet of Comparative Example 1 as a reference (100%). The half width is an angle [°] from the normal direction when the luminance is half of the front luminance.
Edge brightness unevenness is brightness unevenness caused by the boundary between the back surface of the light guide plate and the side surface of the light guide plate, and this is a comparative evaluation by visual inspection, which is the most evaluated based on the original prism sheet without a transparent layer. Low level 0 (unmeasured), when another (upper) diffusion sheet is arranged on the light exit surface of the original prism sheet, the level unevenness of the brightness is the highest level 5 (best) The degree of reduction was subjected to sensory evaluation in 6 stages.

The main items of the specifications of each prism sheet are shown in Table 1, and Table 2 shows the measurement results of characteristics. In addition, the graph of FIG. 16 shows the luminance viewing angle distribution in the vertical direction, and the graph of FIG. 17 shows the luminance viewing angle distribution in the horizontal direction. In each graph, the angle of the horizontal axis is the angle from the normal direction, Ps0 is Comparative Example 1 of the original prism sheet, Ps1 is Example 1 of applying a transparent layer, and Ps2 is Example 2 of applying a particle-containing transparent layer. . In addition, the brightness | luminance of Table 2 is an evaluation result in the perpendicular | vertical direction which is a direction where sidelobe light is conspicuous.

  As shown in Table 1, Table 2, FIG. 16 and FIG. 17, in each example in which a transparent layer is provided and the valley is curved, the front luminance remains roughly maintained (only a decrease of 5% or less). The sidelobe light that was large in the vertical direction was remarkably reduced. The reduction is about 30% in both Example 1 and Example 2, and Example 2 containing particles is slightly less reduced than Example 1. However, the brightness unevenness of Example 2 was further improved than that of Example 1.

Sectional drawing which illustrates notionally the curved-surface prism sheet by this invention, and its manufacturing method by an example. The perspective view which illustrates the original prism sheet of the transparent layer formation object used as the origin. Sectional drawing which illustrates the various forms of a prism main cut surface shape. Sectional drawing which illustrates the example of a layer structure of an original prism sheet. Sectional drawing which illustrates the various of the part made into a concave curve in a transparent layer. Sectional drawing which shows an example which formed the transparent layer in pattern shape. Sectional drawing which shows another example (filling degree change) which formed the transparent layer in pattern shape. Sectional drawing which illustrates one form which made the transparent layer contain particle | grains. The conceptual sectional view showing the state where particles protrude from the top of the prism. Sectional drawing which shows an example which formed the particle-containing transparent layer in the pattern form. Sectional drawing which shows another example which formed the particle-containing transparent layer in the pattern form. Sectional drawing explaining a surface light source by an example of an edge light type. The drawing substitute photograph (microscope photograph) which shows sectional drawing of the curved prism sheet which provided the particle-free transparent layer in Example 1. FIG. The drawing substitute photograph (micrograph) which shows the top view of the curved prism sheet which provided the particle-containing transparent layer in Example 2. FIG. The top view explaining the surface light source (edge light type back light source) used for physical property measurement evaluation. The graph which shows the viewing angle distribution of the brightness | luminance in the perpendicular direction in the surface light source of each example. The graph which shows the viewing angle distribution of the brightness | luminance in the horizontal direction in the surface light source of each example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 (Unit) Linear prism 1a Edge line 2 Original prism sheet 2A Prism arrangement | sequence part 2B Base material part 3 Transparent layer 3a Particle-containing transparent layer 3A Coating liquid before solidification (for transparent layer formation) 4 Particles 5 Valley part 6 Light source 10 Curved prism sheet 20 Surface light source 21 Light source 22 Light guide plate (light guide)
23 Diffusion sheet 24 Prism sheet

Claims (10)

  For the original prism sheet in which a large number of linear prisms are arranged, at least the valleys of the prism surface are filled and the contour shape at the prism main cutting surface is a valley, which is concave toward the original prism protruding direction. A curved prism sheet on which a transparent layer having a concave curve is formed.   The curved prism sheet according to claim 1, wherein the transparent layer is formed in a pattern.   The curved prism sheet according to claim 1, wherein the transparent layer contains particles.   The curved prism sheet according to claim 3, wherein the transparent layer containing the particles is formed in a pattern.   The curved prism sheet according to claim 1, wherein the curved prism sheet is formed into a pattern by combining a transparent layer containing no particles and a transparent layer containing particles.   The curved prism sheet according to any one of claims 3 to 5, wherein at least a part of the particles protrudes from the top of the prism as the particles.   After applying a coating liquid containing at least a resin and a solvent on the prism surface of the original prism sheet in which a large number of linear prisms are arranged, at least valley portions of the prism are formed by utilizing volume contraction due to solvent removal. A method for producing a curved prism sheet, comprising forming a transparent layer that fills and forms a concave curve with a trough at the main cut surface of the prism, and is concave toward the protruding direction of the original prism.   The method for producing a curved prism sheet according to claim 7, wherein the coating liquid contains particles and forms a transparent layer containing particles.   The surface light source which has arrange | positioned the curved prism sheet in any one of Claims 1-6 in the light emission surface side of the light guide. A liquid crystal display device using the surface light source according to claim 9.