JP4435199B2 - Prism sheet, surface light source device, and transmissive display - Google Patents

Description

This invention is a transmissive liquid crystal display device using the backlight surface light source to be used for illuminating the translucent display of billboards and the like from the back preferred back diffusion type prism sheet, with the sheet The present invention relates to a surface light source device and a transmissive display body.

  In recent liquid crystal display devices, a surface light source device for illuminating the liquid crystal display device from the back side is naturally required to be thin and light as required for low power consumption, thinness and weight reduction. In order to reduce power consumption, light from the light source is effectively used to reduce power consumption in the light source.

  Based on such a request, as disclosed in, for example, JP-A-60-70601, JP-A-2-84618, JP-A-3-69184, JP-A-7-191319, etc. There has been proposed one that condenses light from a light source in a specific direction (in many cases, the normal direction of the light exit surface).

  As a surface light source device used for a transmissive liquid crystal display device or the like, there are an edge light type and a direct type.

  An edge-light type surface light source device usually enters light from one side end face of a plate-shaped light guide made of transparent acrylic resin, etc., and guides light from a light exit surface that is one surface of the light guide. From here, light is emitted to the back surface of a liquid crystal panel or the like.

  In this case, in order to improve the light utilization efficiency, a light reflecting plate or a light reflecting film is provided on the surface opposite to the light emitting surface of the light guide, and in order to make the emitted light uniform, In many cases, a diffusion sheet having a light diffusing action is provided on the light exit surface side.

  Also, a direct-type surface light source device usually reflects light source light on the back surface of a liquid crystal panel or the like by a reflector, and a diffusion sheet is disposed on the light exit surface side so that the shape of the light source cannot be identified by human eyes. Idemitsu is diffused.

  Further, in the edge light type or direct type surface light source device as described above, the light from the surface light source is concentrated on a specific direction and emitted on the surface side of the translucent substrate as described above. Some have prism sheets (lens films) on which a plurality of unit prisms or unit lenses are arranged.

  Various types of use of the prism sheet have been proposed, such as the set direction of the unit prism or unit lens side (prism surface) with respect to the light source, the combination of a plurality of prism sheets, and the like.

  In any case, the prism sheet as described above has a smooth surface on the surface (back surface) opposite to the prism surface.

  When the above prism sheet is combined with a light guide, a diffusion sheet, another prism sheet, etc., a repeated pattern of light and dark due to light from a surface light source is observed, and this is used, for example, in a liquid crystal display device In addition, there is a problem that an image formed from each pixel is disturbed.

  On the other hand, as disclosed in, for example, Japanese Patent Application Laid-Open No. 7-151909, the light-dark repeating pattern is obtained when, for example, two prism sheets are used, the prism surface of one prism sheet and the other prism sheet are used. A method for eliminating the interference fringes generated by an external light source has been proposed.

  However, as a result of confirmation by the present inventor, a bright and dark repetitive pattern was observed in the surface light source device even in a dark room where light from an external light source did not enter.

  That is, the present inventor has generated interference fringes by surface light source light, not by external light source light, and the interference fringes are formed on the smooth surface of the prism sheet and the smooth surface of the light guide plate, the smooth surface of the diffusion plate, or other prisms. It was confirmed that it occurred between the smooth surface of the sheet.

  On the other hand, as disclosed in the above-mentioned JP-A-7-151909, a method of forming minute irregularities satisfying a specific condition on the smooth surface of the prism sheet is also conceivable. In this case, however, the light from the surface light source is used. There is a problem in that the original function of the prism sheet, which improves the brightness by condensing light in a specific direction, for example, the normal direction of the light exit surface, is deteriorated.

The present invention, the was made in view of the conventional problems, without luminance reduction Idemitsu surface side, the rear diffusion type which is adapted the formation of interference fringes can be suppressed prism sheet, the prism It is an object of the present invention to provide a surface light source device and a transmissive display body using a sheet.

According to the present invention, the interference fringes generated when the surface of the prism sheet opposite to the prism surface is disposed adjacent to the smooth surface of the light guide plate, etc. are due to light from the internal light source (surface light source). The prism sheet according to claim 1, wherein at least one of unit prisms and unit lenses is arranged on the surface of the translucent substrate, and the back surface is covered with a coating layer made of a translucent material. The coating layer is composed of a translucent resin and a translucent bead dispersed in the translucent resin and having a smaller specific gravity than the translucent resin, and the translucent bead has a specific gravity with the translucent resin. differences, allowed to localize more the surface opposite the transparent substrate in the coating layer, by providing a large number of minute hills shaped projection projecting from the surface, the fine hillocks shaped protrusions, other When arranged in contact with the smooth surface of the translucent material, the gap generated between the smooth surface and the surface is set to 1 μm or more, and at least a part of the micro hill-shaped projections has a particle size. The ratio of the refractive index of the material constituting the micro hill-shaped protrusion and the refractive index of the material of the coating layer in contact with the micro hill-shaped protrusion is 0.9 to 10 μm. The above-mentioned problem is solved by the prism sheet set to 1.1.

The invention relating to the surface light source device is a plate-like body made of a light-transmitting material as in claim 2, and emits light introduced from at least one side end face from a light emission face which is one face. A light guide that is configured to be arranged, a light source that allows light to enter inside from at least one side end face of the light guide, and a coating layer, provided on the light emission surface side of the light guide, A prism sheet on which light emitted from the light emitting surface is incident from the coating layer side, and the prism sheet includes a plurality of unit prisms and unit lenses on the surface of the translucent substrate. The back surface is covered with a coating layer made of a translucent material, and the coating layer is dispersed in the translucent resin and the translucent resin, and is composed of translucent beads having a smaller specific gravity. , The KiToruhikarisei beads, the specific gravity difference between the translucent resin, allowed to localize more the surface opposite the transparent substrate in the coating layer, providing a large number of minute hills shaped projection projecting from the surface Thus, when the micro hill-shaped projection is arranged in contact with the smooth surface of the light guide, the gap generated between the smooth surface and the surface is configured to be 1 μm or more, A surface light source device characterized in that a ratio of a refractive index of a material constituting the micro hill-shaped protrusion and a refractive index of a material of a coating layer in contact with the micro hill-shaped protrusion is set to 0.9 to 1.1. Thus, the above object is achieved.

The invention related to the transmissive display body is as described in claim 3 and is disposed on the back surface of the flat transmissive display body and the transmissive display body, and the transmissive display body is separated from the back surface by the emitted light. The said objective is achieved by the transmissive display body provided with the surface light source device of Claim 2 which irradiates.

  Since the present invention is configured as described above, it is possible to eliminate the interference fringes that do not depend on the external light generated in the prism sheet, and in the surface light source device and the transmissive display using the prism sheet, the interference fringes can be obtained. Has an excellent effect of obtaining a high-quality image in which no image is observed.

  Further, according to the present invention, the translucent beads are unevenly distributed in the vicinity of the surface of the coating layer, so that the ratio of the translucent beads to be used is small, efficient without waste, and the entire coating layer. It has the effect that the fall of the light transmittance of can be suppressed.

  Further, the translucent beads are raised on the surface due to the difference in specific gravity, and the translucent beads can be unevenly distributed near the surface of the coating layer easily and reliably.

  According to the present invention, the transparent beads are dispersed in the coating layer covering the back surface on the opposite side of the prism surface of the prism sheet to provide a large number of micro hill-like projections having a projection height of 1 to 10 μm. Since the optical beads are unevenly distributed near the surface of the coating layer, the ratio of the light transmitting beads to be used is small, it is efficient without waste, and the decrease in the light transmittance of the entire coating layer is suppressed. In addition, when the light diffusion layer is formed on the back surface opposite to the prism surface of the prism sheet, the original function of the prism sheet, which is focused in the normal direction of the light exit surface and improves the luminance, is deteriorated. This phenomenon can be suppressed.

  In addition, the coating layer is solidified in such a way that an ink in which the specific gravity of the translucent beads is smaller than the specific gravity of the translucent resin is applied to the translucent substrate and the translucent beads are raised on the surface due to the difference in specific gravity. Therefore, the translucent beads can be unevenly distributed in the vicinity of the surface of the coating layer.

  The back surface of the prism sheet is covered with a coating layer having micro hill-shaped projections, and between the back surface and the smooth surface of the light guide plate adjacent thereto, the smooth surface of the diffusion plate, the smooth surface of other prism sheets, etc. Since the gap is 1 μm or more, the distance between the back surface and the smooth surface of the light guide plate, etc., prevents interference between the straight light and the reflected light, and prevents the occurrence of interference fringes or Newton rings. To do.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  As shown in FIGS. 1 and 2, the prism sheet 10 according to the present invention includes a triangular prism unit prism 14 on one surface (upper surface in FIGS. 1 and 2) of a transparent base sheet 12, and a ridge line 14A. Are arranged in parallel in a one-dimensional direction so as to be parallel to each other to form a prism surface 16, and a coating layer 18 is provided on the back side opposite to the prism surface 16. The surface is provided with a number of micro hill-like projections 20 protruding from the surface.

  The micro hill-shaped protrusion 20 includes a light-transmitting bead having a particle diameter of 1 to 10 μm.

  The micro hill-shaped protrusions 20 are provided on the surface of the coating layer 18 in a random two-dimensional distribution state.

  The prism sheet 10 is arranged with its coating layer 18 side in contact with a smooth surface 22A of another light transmissive material 22, such as a smooth surface of a light guide plate, a smooth surface of a diffusion sheet, or a smooth surface of another prism sheet. Then, conventionally, as described above, interference fringes are generated by the surface light source light from the direction of the light guide plate or the like. However, in the prism sheet 10 of the present invention, as shown in FIG. Since the smiling hill-shaped protrusion 20 protruding from the surface of the light-emitting element contacts the smooth surface 22A of the light-transmitting material 22 such as a light guide, there is always a gap 24 between the smooth surface 22A and the surface of the coating layer 18. Occurs.

  For this reason, even if light enters from the opposite side (lower side in FIG. 2) of the smooth surface 22A of the translucent material 22, no interference fringes are generated.

  Here, the particle size of the translucent beads partially contained in the micro hill-shaped protrusion 20 is set to 1 μm or more. When the height is less than 1 μm, the distance of the gap 24 is the surface light source light (visible light). There is a problem that the color becomes close to the wavelength of light), and if it is less than 1 μm, it is difficult to mass-produce translucent beads as the material of the micro hill-like projections 20, and this translucency This is to avoid the problem that it is difficult to disperse the beads in a binder (described later) constituting the coating layer 18. Furthermore, this is also to avoid the problem that light from the translucent material directly enters the coating layer 18 as an evanescent wave and cannot maintain a uniform luminance in the plane.

  Also, the particle size of the translucent beads is set to 10 μm or less because when the gap 24 is larger than 10 μm, the light from the surface light source is collected in a specific direction, for example, the normal direction of the light exit surface on the prism surface 16 side. This is to avoid a significant decrease in the effect of light.

  As described above, the micro hill-like projections 20 are randomly distributed two-dimensionally on the surface of the coating layer 18 and are not periodically arranged.

  If the micro hill-like projections 20 are periodically arranged in the coating layer 18 and the period overlaps with the arrangement period of the unit prisms 14, moire fringes are generated.

  For example, when the prism sheet as described above is provided on the light exit surface side of the backlight of the color liquid crystal display device, if the micro hill-shaped projections 20 are periodically arranged, similarly, the pixels of the liquid crystal display device There is a possibility that moire fringes are generated due to overlapping with the arrangement period.

  In the prism sheet 10 according to the present invention, since the micro hill-like projections 20 are randomly arranged two-dimensionally, the occurrence of moire fringes as described above is prevented.

  Transparent materials for forming the transparent base sheet 12, the unit prism 14, and the micro hill-shaped protrusions 20 constituting the prism sheet 10 include polyester resins such as polyethylene terephthalate and polybutylene terephthalate, acrylic resins such as polymethyl methacrylate, Ionizing radiation curable resins composed of thermoplastic resins such as polycarbonate resin, polystyrene resin, polymethylpentene resin, oligomers such as polyester acrylate, urethane acrylate, epoxy acrylate and / or acrylate monomers, etc. A resin having good transparency such as a resin cured by electromagnetic radiation is used. In the case of such a resin, those having a refractive index of about 1.4 to 1.6 are usually used. In addition, other than resin, glass, ceramics, etc. may be used as long as it is transparent.

  The coating layer 18 including the micro hill-shaped protrusions 20 as described above is spray-coated with a paint (ink) in which translucent beads serving as the material of the micro hill-shaped protrusions 20 are dispersed in a translucent resin (binder). The coating layer 18 is formed by coating with a roll coat or the like, and part or all of the translucent fine particles are projected on the surface of the coating layer 18 to form the micro hill-shaped projection 20.

  The translucent beads constituting a part of the paint (ink) are selected so that the specific gravity thereof is smaller than the specific gravity of the translucent resin as a binder.

  Further, when the coating material is applied, the coating film is pressed against the back surface of the transparent base sheet 12 by gravity. For example, as shown in FIG. 3, the coating material is applied to the transparent base sheet 12 in a state opposite to that in FIGS.

  When applied in this way, immediately after application, as shown in FIG. 3 (A), the translucent beads are dispersed in the thickness direction in the coating film in a fluid state, but the passage of time (3-60) After that, the translucent beads emerge due to the difference in specific gravity, gather on the surface of the coating layer 18 (is unevenly distributed), as shown in FIG. 20 is formed.

  In this state, the coating layer 18 may be cured by a curing means corresponding to the type of translucent resin such as ultraviolet light, electron beam, or radiation.

  In addition, even when the ink composition is a thermosetting ink containing a large amount of solvent having a specific gravity smaller than the specific gravity of translucent beads such as toluene and MEK (methyl ethyl ketone), the specific gravity of the translucent beads volatilizes when dried. Is smaller than the specific gravity of the translucent resin (binder) is an essential condition of the present invention.

  In the case of thermosetting ink, the specific gravity of the liquid substance mixture (translucent resin + solvent) other than the translucent beads in the ink is often smaller than the specific gravity of the translucent beads. The state immediately after coating of the coating layer 18 formed by applying the ink to the surface opposite to the direction of gravity of the translucent substrate is as shown in FIG. Although it is in a state of being dispersed in the light-sensitive resin (binder), the mixture volatilizes over time (usually 3 seconds to 300 seconds) by volatilization of the solvent by the drying process after coating. Since the specific gravity of the translucent beads is smaller than the specific gravity of the translucent resin due to the volatilization of the solvent component of the translucent resin + solvent), the surface of the coating layer 18 is formed as shown in FIG. A part of the translucent bead protrudes, So that the micro mound-like protrusion 20 is formed by Les.

  Here, the translucent fine particles as the material of the micro hill-shaped protrusion 20 are polymethyl methacrylate (acrylic) beads having a diameter of 1 to 10 μm, polybutyl methacrylate beads, polycarbonate beads, polyurethane beads, carbonic acid Calcium beads, silica beads and the like are used. Further, the diameter of the light-transmitting fine particles as the material of the micro hill-shaped protrusion 20 means an average value of the diameters of the particles of 1 μm or more.

  As the binder resin for forming the coating layer 18, a transparent material such as acrylic, polystyrene, polyester, or vinyl polymer is used. The refractive index of the light-transmitting fine particles that form the micro hill-shaped protrusions 20, and the binder resin are used. The ratio of the refractive index to the refractive index is preferably in the range of 0.9 to 1.1, and the concentration of the translucent fine particles is preferably 2 to 15% of the binder resin.

  In the range of the refractive index ratio of 0.9 to 1.1, when the refractive index ratio is out of the above range, the surface light source light incident from the surface of the coating layer 18 is directed in a specific direction, for example, the normal of the light exit surface It is determined from the fact that the original action of the prism sheet, in which the light is condensed in the direction and the luminance is improved, is significantly reduced.

  Furthermore, the thickness of the coating layer 18 is preferably in the range of 1 to 20 μm, excluding the protruding height of the micro hill-shaped protrusion 20.

  This is because if the thickness of the coating layer 18 is less than 1 μm, it becomes impossible to fix the light-transmitting fine particles, which are the material of the micro hill-shaped projections 20, to the back surface of the transparent substrate sheet 12. This is because the transmittance is lowered, and the above-described original luminance improving action of the prism sheet is significantly reduced.

  As a manufacturing method of the prism sheet 10, a single-layer prism sheet (an intermediate sheet before coating) is a thermoplastic resin hot pressing method disclosed in, for example, Japanese Patent Laid-Open No. 56-157310, or injection. It can be produced by a molding method, cast molding of a curable resin by ultraviolet rays or heat, and the like.

  Further, as another method for manufacturing the intermediate sheet as described above, for example, as disclosed in Japanese Patent Laid-Open No. 5-1699015, a concave portion having a shape opposite to the shape of a desired lens arrangement (exactly uneven Filling the roll intaglio with a shape) with an ionizing radiation curable resin liquid, overlaying the translucent substrate sheet 12 on this, and irradiating ionizing radiation such as ultraviolet rays and electron beams from the transparent substrate sheet side as it is, By curing the ionizing radiation curable resin liquid and then peeling the transparent base sheet together with the cured resin from the roll intaglio, the cured ionizing radiation curable resin liquid becomes a lens array of a desired shape and becomes a transparent base. Some form on the material sheet. The total thickness of the prism sheet 10 is usually about 20 to 1000 μm.

  In the prism sheet 10, the prism surface 16 is configured by arranging a plurality of triangular prism unit prisms 14 in parallel. However, the present invention is not limited to this, and the half is shown in FIG. A prism sheet 10A provided with a cylindrical unit prism 15A, a prism sheet 10B provided with a unit prism 15B having a sine curve cross section shown in FIG. 5, and a unit prism 15C having a trapezoidal cross section shown in FIG. The prismatic sheet 10C is provided with a columnar unit prism as in the prism sheet 10D provided with the unit prism 15D having a shape in which the cross section shown in FIG. , And may be arranged adjacent to each other so that the axis thereof is parallel to the one-dimensional direction.

  Further, the cross section of the unit prism is not limited to a semicircular shape or a sine curve shape, and may be a polygon other than a caroid, a Rankine egg, a cycloid, a limboline, or a triangle.

  Furthermore, as shown in FIG. 7, for example, a prism sheet 10 </ b> E having a so-called fly-eye lens or the like in which unit lenses 15 </ b> E each having a hemispherical shape independently protruded are arranged in a two-dimensional direction may be used.

  Next, a surface light source device 30 according to an example of an embodiment of the present invention will be described with reference to FIG.

  This surface light source device 30 is provided with the prism sheet 10 shown in FIG. 1 on the light emission surface side, and is a plate-like body made of a translucent material, and from the left side end surface 32A in FIG. The introduced light is disposed along and parallel to the light guide 32 configured to emit light from the upper light emitting surface 32B, and the side end surface 32A of the light guide 32, and the side end surface 32A. A linear light source 34 for allowing light to enter the light guide 32, a surface of the light guide 32 opposite to the light emission surface 32B, and a side end surface other than the left side end surface 32A. And a light reflecting plate 36 for reflecting the light emitted from these surfaces and returning it into the light guide 32.

  The coating layer 18 of the prism sheet 10 is disposed in contact with the light emitting surface 32 </ b> B of the light guide 32. In general, the light guide 32 is housed in a housing (not shown) having the light emitting surface 32B as a window.

  The light guide 32 is selected from the same translucent material as the material of the prism sheet 10 as its material, but usually acrylic or polycarbonate resin is used. Further, the thickness of the light guide 32 is usually about 1 to 10 mm, and is the thickest at the position of the side end surface 32A on the linear light source 34 side, and has a tapered shape that gradually decreases in the opposite direction. .

  In order to emit light from a wide surface (light emission surface 32B), the light guide 32 has a light scattering function added to the inside or the surface thereof. The linear light source 34 is preferably a fluorescent lamp in order to obtain uniform brightness on the light emission surface 32B.

  Further, in the surface light source device 30, the light source for entering the light into the light guide 32 is not limited to a linear light source, but a point light source such as an incandescent light bulb or LED (light emitting diode) is formed in a line shape. You may arrange. A plurality of small flat fluorescent lamps may be arranged along the side end face 32A.

  In the surface light source device 30 shown in FIG. 8, the prism sheet 10 contacts the light emitting surface 32 </ b> B of the light guide 32 via the micro hill-like protrusions 20 protruding from the coating layer 18, as described above. Interference fringes are prevented from occurring at a position between the surface of the coating layer 18 and the light emitting surface 32B. Therefore, a good light emitting surface can be formed as a surface light source for a transmissive liquid crystal display device or the like.

  For example, the light guide 32 may be formed in a plate shape having a uniform thickness, and a linear light source may be provided on the side end surface opposite to the side end surface 32A to guide light from here. In this way, the prism surface 16 can have higher luminance, and the uniformity of the luminance distribution on the prism surface 16 can be improved.

  Next, a direct type surface light source device 40 will be described with reference to FIG.

  In the surface light source device 40, a light diffusion sheet 42 is disposed along the coating layer 18 on the back surface side of the prism sheet 10 shown in FIG. 1, and light from the light source 34 is transmitted to the light reflecting plate 44 on the concave surface. And the light is directly emitted from the light diffusion sheet 42 to the prism sheet 10.

  Also in this surface light source device 40, the distance between the surface of the coating layer 18 of the prism sheet 10 and the light diffusion sheet 42 is regulated by the micro hill-like projections 20 in the same manner as the surface light source device 30 described above. No interference fringes occur.

  As the light reflecting plates 36 and 44, a thin metal plate deposited with aluminum or the like, or white foamed PET (polyethylene terephthalate) is used.

  In addition, the shape of the light reflection plate 44 in the direct type surface light source device 40 may be any shape as long as the light from the linear light source 34 can be uniformly reflected as a parallel light beam, such as a concave arc shape, a parabolic column shape, a hyperbola. A shape such as a columnar shape or an elliptical columnar shape is selected.

  In the surface light source device 30, the coating layer 18 of the prism sheet 10 is directly disposed on the light emitting surface 32B of the light guide 32. However, the present invention is not limited to this, and for example, shown in FIG. As in the case of the surface light source device 30A, the light diffusion sheet 46 may be disposed between the prism sheet 10 and the light emission surface 32B.

  Further, in each of the prism sheets 10, the coating layer 18 is arranged toward the light incident side. This is because, for example, the surface light source devices 30B and 40A shown in FIGS. The 14 side may be arranged toward the light emitting surface 32B of the light guide 32 or the light reflecting plate 44 side.

  Further, each of the surface light source devices 30, 30A, 30B, 40, and 40A uses a single prism sheet 10, but the present invention is not limited to this, and FIGS. As shown, two or three or more prism sheets may be used in an overlapping manner.

  A surface light source device 50A shown in FIG. 13 has the second prism sheet 52 disposed between the light emitting surface 32B of the light guide 32 and the prism sheet 10 in the surface light source device 30 shown in FIG. It is.

  The second prism sheet 52 basically has the same configuration as the prism sheet 10, but has no hill-like projections on the coating layer side, and has a smooth surface similar to the conventional one. .

  Further, the ridge line 54A of the unit prism 54 in the second prism sheet 52 is arranged in a direction orthogonal to the ridge line 14A of the unit prism 14 in the prism sheet 10.

  In the case of this surface light source device 50A, an interference fringe is generated between the light emitting surface 32B of the light guide 32 at a smooth surface position opposite to the prism surface of the second prism sheet 52. By covering the upper side with the prism sheet 10, interference fringes could not be observed from the outside.

  A surface light source device 50B shown in FIG. 14 has a configuration of FIG. 13 in a direct type, and the same portions as those in FIGS. 13 and 9 are denoted by the same reference numerals, and description thereof is omitted.

  Further, in the surface light source devices 50A and 50B in which two prism sheets as described above are stacked, the second prism sheet 52 is disposed with the unit prism 54 facing the light exit surface side. However, the present invention is not limited to this. For example, as in the surface light source devices 50C and 50D shown in FIGS. 15 and 16, the unit prism 54 of the second prism sheet 52 is arranged on the light guide 32 or light diffusion sheet 46 side. You may make it arrange | position toward.

  In FIG. 15 and FIG. 16, the same parts as those in FIG. 13 and FIG.

  Next, a liquid crystal display device 60 according to an example of the embodiment of the liquid crystal display according to the present invention shown in FIG. 17 will be described.

  In the liquid crystal display device 60, a liquid crystal panel 62 is disposed on the light exit surface side of the surface light source device 50 as shown in FIG. 8, FIG. 10, FIG. 11, FIG.

  This liquid crystal display device is a transmissive type, and each pixel forming a liquid crystal screen is illuminated from the back side by light emitted from the surface light source device 50.

  In the liquid crystal display device 60, as described above, since there is no interference fringe in the illumination light from the surface light source device 50, a good image can be formed. In addition, since the distance between the surface of the coating layer 18 of the prism sheet 10 and the smooth surfaces of the light guide 32, the light diffusion sheet, and the other prism sheet opposed thereto is 10 μm or less as described above, The light collecting performance in the normal direction is not deteriorated and good luminance can be obtained.

  Next, examples of the present invention will be described.

  The prism sheet 10 is formed by coating a transparent adhesive layer on a transparent biaxially stretched PET film (film thickness 125 μm) so as to have a thickness of about 1 μm, and an epoxy acrylate prepolymer that forms a unit prism pattern thereon. By applying an ultraviolet curable resin as a main component and releasing the mold after curing (solidifying) the resin coating film, the unit prism shape cross section is an isosceles triangle having an apex angle of 85 ° and a ridge line 14A. Are arranged adjacent to each other so that they are parallel to each other. On the side surface (back surface) opposite to the prism surface 16 of the transparent base sheet 12 on which the unit prisms 14 were formed, the micro hill-shaped projections 20 were formed in the following manner.

  The translucent beads as the material of the micro hill-shaped protrusion 20 are a cross-linked acrylic resin (n = 1.49) having an average particle diameter of 5 μm and a specific gravity of 1.19, and a specific gravity of 1.26 polyester resin (n = 1.55) is applied.

  Specifically, an ink containing 8% of the binder resin in the translucent beads was diluted with a solvent of MEK: toluene = 1: 1, and the viscosity was set to 27 seconds with a Zaan cup viscometer # 3. .

  This ink was applied to the back surface of the transparent substrate sheet 12 on which the unit prisms 14 were formed by the slit reverse coating method, and then the solvent was dried to solidify the coating film.

  In this dried coating film, hill-like projections 20 having an average roughness of 10 points Rz = 3 μm according to JISB0601 were formed in a two-dimensional random arrangement with an average interval d = 30 μm.

  When the prism sheet 10 formed in this way was observed in a dark room, for example, in contact with the light emitting surface of the light guide 32, no interference fringes were observed.

  The average particle diameter of the light transmitting beads is variously changed to form a prism sheet 10 similar to the above, and this is incorporated into a surface light source device as shown in FIGS. 8 to 16 and observed in a dark room. The result is as shown in Table 1 below.

  As a result, interference fringes were observed only in Comparative Examples 1 and 2 in Table 1.

  Further, when one prism sheet of Example 1 of Table 1 and a prism sheet having a smooth back surface with an isosceles triangular prism unit having a top angle of 90 ° on the front side are assembled as shown in FIG. The result was as follows.

The perspective view which expands and shows a part of prism sheet which concerns on the example of embodiment of this invention. Sectional drawing in which a part of the prism sheet is further enlarged Sectional drawing which shows the coating layer formation process by the prism sheet manufacturing method concerning this invention The perspective view which shows the 2nd example of embodiment of a prism sheet The perspective view which shows the 3rd example of the embodiment The perspective view which shows the 4th example of the same embodiment The perspective view which shows the 5th example of the embodiment The perspective view which shows the principal part of the surface light source device which concerns on the example of embodiment of this invention. The perspective view which shows the 2nd example of embodiment of a surface light source device. Schematic sectional view showing a third example of the embodiment of the same surface light source device Schematic sectional view showing a fourth example of the embodiment Schematic sectional view showing a fifth example of the embodiment The perspective view which shows the principal part of the 6th example of the same embodiment The perspective view which shows the principal part of the 7th example of the same embodiment The perspective view which shows the principal part of the 8th example of the embodiment The perspective view which shows the principal part of the 9th example of the same embodiment Schematic side view showing a liquid crystal display according to an example of an embodiment of the present invention

Explanation of symbols

10, 10A, 10B, 10C, 10D, 10E ... Prism sheet 12 ... Transparent substrate sheet 14, 15A, 15B, 15C, 15D ... Unit prism 14A, 54A ... Aya line 15E ... Unit lens 16 ... Prism surface 18 ... Coating layer 20 ... Minute hill-shaped projection 22 ... Translucent material 22A ... Smooth surface 24 ... Gap 30, 30A, 30B, 40, 40A,
50, 50A, 50B, 50C, 50D ... Surface light source device 32 ... Light guide 32A ... Side end face 32B ... Light emission surface 34 ... Linear light source 36, 44 ... Light reflection plate 42,46 ... Light diffusion sheet 52 ... Second Prism sheet 54 ... unit prism 60 ... liquid crystal display device

Claims (3)

In the prism sheet in which at least one of unit prisms and unit lenses is arranged on the surface of the translucent substrate and the back surface is covered with a coating layer made of a translucent material,
The coating layer is composed of a translucent resin and a translucent bead dispersed in the translucent resin and having a smaller specific gravity than the translucent resin, and the translucent bead is formed by a difference in specific gravity from the translucent resin. , allowed to localize more the surface opposite the transparent substrate in the coating layer, by providing a large number of minute hills shaped projection projecting from the surface, the fine hillocks shaped projections, the other translucent material The gap generated between the smooth surface and the surface when placed in contact with the smooth surface is 1 μm or more,
At least a part of the micro hill-like projections are made of translucent beads having a particle diameter of 1 to 10 μm, the refractive index of the material constituting the micro hill-like projections, and the coating layer in contact with the micro hill-like projections A prism sheet characterized in that the ratio of the material to the refractive index is 0.9 to 1.1. A light guide that is a plate-like body made of a light-transmitting material and emits light introduced from at least one side end face from a light emission surface that is one surface;
A light source that causes light to enter from at least one side end face of the light guide;
A prism sheet provided with a coating layer, provided on the light emitting surface side of the light guide, and light emitted from the light emitting surface is incident from the coating layer side;
Having
The prism sheet has a plurality of unit prisms and unit lenses arranged on the surface of the translucent substrate, and the back surface is covered with a coating layer made of a translucent material.
The coating layer is composed of a translucent resin and a translucent bead dispersed in the translucent resin and having a smaller specific gravity than the translucent resin, and the translucent bead is formed by a difference in specific gravity from the translucent resin. , allowed to localize more the surface opposite the transparent substrate in the coating layer, by providing a large number of minute hills shaped projection projecting from the surface, the fine hillocks shaped projections, the smooth surface of the light guide The gap formed between the smooth surface and the surface when arranged in contact with the surface is 1 μm or more, the refractive index of the material constituting the micro hill-shaped projections, and the micro hill A surface light source device characterized in that the ratio of the refractive index of the material of the coating layer in contact with the projections is set to 0.9 to 1.1. 3. A planar light-transmitting display body, and a surface light source device according to claim 2 , which is disposed on the back surface of the light-transmitting display body, and is adapted to irradiate the light-transmitting display body from the back surface with emitted light. A transmissive display body comprising:

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