JP2010282184A - Optical sheet, surface light source device, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress luminance unevenness in the vicinity of an LED light source from being caused by leakage light of a level difference part of a light guide body without reducing luminance, in a surface light source device which is made thin. <P>SOLUTION: A thickness of a light guide body 10 in a light incident surface 11 is thicker than the thickness of the light guide body in a light emission surface 12 and the light guide body includes the level difference part 13 gradually reducing the thickness of the light guide body between the light incident surface and the light emission surface. An optical sheet 30 includes a first surface on which a lens layer is formed, a second surface on which a light diffusion layer is formed and a side end surface nearly orthogonal to the first and second surfaces. The optical sheet is disposed so that the side end surface comes close to the level difference part. An attenuation structure preventing light incidence in the inner part of the optical sheet from the side end surface is provided on the side end surface of the optical sheet or in the vicinity thereof. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical sheet used in a surface light source device, a surface light source device using the optical sheet, and a liquid crystal display device using the surface light source device.

  The liquid crystal display device includes a backlight unit (surface light source device) and a liquid crystal display surface (liquid crystal panel). As the surface light source device, there are a direct type device in which a light source is arranged directly below a liquid crystal display surface and an edge light type device in which a light source is arranged on a side surface of a light guide. Edge light type devices are often used for applications such as notebook personal computers and mobile phones where importance is placed on the lightweight and thin liquid crystal display devices.

  In a liquid crystal display device using an edge light type surface light source device, light is incident on the side surface of the light guide from the light source, the surface of the light guide is emitted, emitted to the liquid crystal display surface, and surface emission is performed. In such a liquid crystal display device, an optical sheet for concentrating and emitting light from a surface light source in a specific direction is used in order to more efficiently use light obtained from the light source.

  In such an optical sheet, a lens array such as a prism array is formed on one surface, and the light is aligned in a certain direction by the lens array. Then, light is diffused within a viewing angle range according to the use of the liquid crystal display device by a light diffusion layer provided on the surface opposite to the lens array.

  On the other hand, in recent years, a point light source such as a light emitting diode (LED) is increasingly used as a light source in a notebook personal computer in which portability is important. This is because the use of an LED has advantages such as a reduction in power consumption, an improvement in luminance, and a reduction in the thickness of the light guide as compared with a cold cathode tube. However, there is a lower limit to the thickness of a point light source such as an LED, and in addition, since a thin light source is expensive, a step portion is provided near the light incident surface, compared to the thickness of the light guide on the light incident surface. By using a light guide that has a light guide with a reduced thickness on the light exit surface, the backlight portion is further reduced in weight and thickness (for example, Patent Document 1).

JP 2007-27002 A

  However, by using a point light source such as an LED and a light guide having a stepped portion as described above, bright lines are generated unevenly only in the vicinity of the light source as disclosed in Patent Document 1, There is a problem that the quality of the liquid crystal display device is degraded due to uneven brightness.

  FIG. 3 shows the brightness unevenness in the vicinity of the light source. FIG. 3 is a perspective view of a surface light source device using LEDs arranged as a primary light source and a light guide having a stepped portion. A plurality of point light sources 20 are arranged close to the light incident surface of the light guide 10 and spaced from each other. The light guide 10 has a step portion 13, and an optical sheet 30 is installed in the vicinity of the step portion 13. In such a surface light source device, a bright portion occurs in a direction perpendicular to the light source array, and a light streak extends from the light source to a portion corresponding to the light source, resulting in luminance unevenness.

  In order to prevent such luminance unevenness, a light diffusion layer provided on the light exit surface side of the optical sheet is provided with a difference in refractive index between the light transmissive resin and the light diffusion material constituting the light diffusion layer, thereby diffusing the light. By forming an interface having a different refractive index inside the layer, when a light beam guided through the optical sheet 30 passes through the light diffusion layer, it reaches the surface of the light diffusion layer (that is, the interface with air) and reflects it. Previously, the occurrence of uneven brightness is prevented by scattering light rays.

  However, in the prior art, the difference in refractive index between the light diffusing material and the translucent resin is large, and part of the light that should be used for light emission of the liquid crystal display device is scattered in an unintended and unnecessary direction. There was a problem that caused a decrease in. Accordingly, an object of the present invention is to provide a surface light source device and a liquid crystal display device that can prevent the luminance unevenness without causing a decrease in luminance.

  FIG. 4 is a partial cross-sectional view of the surface light source device as shown in FIG. A step portion 13 is provided between the light incident surface 11 and the light exit surface 12 of the light guide 10, and the optical sheet 30 is optical so that the lens layer 32 faces the light guide light exit surface 12. The sheet end portion 31 is disposed close to the light guide step portion 13. Further, the reflection sheet 40 is disposed in contact with the surface on the back side of the light emitting surface 12 of the light guide 10, and the light source reflection sheet 21 is disposed so as to cover other than the irradiation surface of the light source 20. Although the cause of the brightness unevenness has not been elucidated in detail, the present inventors have found that the leaked light emitted from the step portion 13 of the light guide is the end of the optical sheet as shown in FIG. Incoming from 31, guided inside the optical sheet 30, exited after guiding a certain distance from the end of the optical sheet, and the amount of emitted light increases only at that part, so that it is visually recognized as luminance unevenness I found.

In the present invention, a first surface on which a plurality of lens rows are formed in parallel, a second surface on which a light diffusion layer is formed, and a side end surface substantially orthogonal to the first surface and the second surface are provided. The optical sheet is provided with an attenuation structure for attenuating light incident on the optical sheet from the outside of the optical sheet through the side end surface, at or near the at least one side end surface. An optical sheet is provided.
By using such an optical sheet, it is possible to suppress light from entering from the side end face of the optical sheet, and to prevent occurrence of luminance unevenness.

  Further, in the present invention, a primary light source composed of a plurality of point light sources, at least one light incident surface facing the primary light source, and light incident from the light incident surface substantially orthogonal to the light incident surface. A light guide having a light emitting surface to be emitted, a first surface having a lens layer in which a plurality of lens rows are arranged substantially in parallel, a second surface on which a light diffusion layer is formed, the first surface, and the first surface An optical sheet having a side end surface substantially orthogonal to the second surface, wherein the light guide has a thickness of the light guide on the light incident surface that is the light guide on the light output surface. And a step portion in which the thickness of the light guide gradually decreases between the light incident surface and the light emitting surface, and the optical sheet has the side end surface close to the step portion. Arranged to the side end surface of the optical sheet. In the vicinity thereof, the side surface light source device from the end face, characterized in that the damping structure for attenuating the light incident on the optical sheet is formed is provided. According to another aspect of the present invention, the diffusion layer of the optical sheet has a total haze of 60% or less, and a ratio of internal haze in the total haze is 50% or less.

  In this way, by using a light guide having a stepped portion, the surface light source device can be thinned, and leakage light from the stepped portion can be prevented from entering from the side end surface of the optical sheet. Generation of unevenness can be prevented. Furthermore, it can prevent that the brightness | luminance of a surface light source device falls by setting all the hazes of an optical sheet to 60% or less.

  According to the present invention, it is possible to suppress the occurrence of luminance unevenness in the vicinity of the light source due to the leakage light of the step portion of the light guide without reducing the luminance.

It is a perspective view of the surface light source device based on this invention. It is a fragmentary sectional view of the surface light source device based on this invention. It is the perspective view which showed the surface light source device of the state which the brightness nonuniformity generate | occur | produced. It is sectional drawing of the surface light source device shown in detail about generation | occurrence | production of the brightness nonuniformity in a surface light source device. It is a figure which shows an example of the surface light source device based on this invention. It is a figure which shows an example of the surface light source device based on this invention. It is a fragmentary sectional view which shows an example of the surface light source device based on this invention. It is a fragmentary sectional view which shows an example of the surface light source device based on this invention. It is a figure which shows an example of the surface light source device based on this invention.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the attached drawings and the following description, and various modifications may be added as necessary.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view of a surface light source device of the present invention. As shown in FIG. 1, the surface light source device of the present invention includes a primary light source in which a plurality of point light sources 20 such as LEDs are arranged, a reflection sheet 40, a light guide 10, and an optical sheet 30. The light source 20 is disposed so as to face the light incident surface 11 of the light guide 10. A reflective sheet 40 is disposed below the light guide 10. The optical sheet 30 is disposed so that the surface on which the lens layer is formed faces the light emitting surface 12 of the light guide 10. Further, the side end face 31 of the optical sheet is disposed in the vicinity of the step portion 13 of the light guide 10.

<Light guide>
Although the thickness of the light incident surface 11 of the light guide 10 is about the same as that of the light source 20, the light exit surface 12 is provided by providing a step portion 13 between the light incident surface 11 and the light exit surface 12 of the light guide 10. The thickness of the light guide 10 is smaller than the thickness of the light guide 10 on the light incident surface 11. The thickness of the light guide 10 on the light incident surface 11 is usually about 0.5 mm to 2 mm, and the thickness of the light guide 10 on the light exit surface is usually about 0.1 to 1.5 mm. Further, the shape of the step portion 13 is various such as a slope shape or a step shape. The height of the step portion (that is, the difference between the thickness of the light guide 10 on the light incident surface 11 and the thickness of the light guide 10 on the light exit surface 12) is usually about 0.05 to 1 mm. In addition, the width (that is, the depth) of the step when having the sloped or stepped shape is usually about 0.3 to 5.0 mm.

  The light guide 10 is made of a highly transparent synthetic resin. Examples of such synthetic resins include methacrylic resins, acrylic resins, polycarbonate resins, polyolefin resins having a cyclic or norbornene structure, polyester resins, and vinyl chloride resins. In particular, a methacrylic resin is preferably used from the viewpoints of high light transmittance, heat resistance, mechanical properties, and moldability. As the methacrylic resin, a resin containing methyl methacrylate as a main component is preferable, and one having 80% by mass or more of methyl methacrylate is more preferable.

<Optical sheet>
An example of an optical sheet used in the surface light source device of the present invention will be described with reference to the drawings.
FIG. 2 is a cross-sectional view of the optical sheet 30. The optical sheet 30 is provided with a light diffusion layer 34 composed of a translucent resin 35 and a light diffusing material 36 on one surface of a sheet-like translucent base material 33 to form a second surface of the optical sheet. is doing. Further, the other surface of the sheet-like translucent substrate 33 is provided with a lens layer 32 in which a prism row having apex angle θ and pitch P is formed, and the first surface of the optical sheet is formed. Yes. A light beam emitted from the light guide 10 at an angle α is totally reflected by the prism row and is emitted in the normal direction of the surface light source device. In addition, the optical sheet 30 is disposed substantially orthogonal to the second surface provided with the light diffusion layer 34 and the first surface provided with the lens layer 32 and in proximity to the step portion 13 of the light guide 10. Side end face 31 is provided. The optical sheet side end surface 31 is provided with an attenuation structure that attenuates light incident on the optical sheet 30.

(Attenuation structure)
The optical sheet 30 of the present invention is provided with an attenuation structure that attenuates light incident on the inside of the optical sheet 30 on at least one side end face 31. As shown in FIG. 4, the cause of the uneven brightness is that light incident from the sheet side end face 31 is guided inside the sheet and is emitted away from the side end face. Since the side end face 31 is provided with an attenuation structure, it is possible to reduce the light that enters the optical sheet from the side end face 31 and guides the light guide, thereby making the luminance unevenness inconspicuous. It becomes possible.

  The attenuation structure is not particularly limited as long as it attenuates light, but is preferably a light shielding layer that shields incident light rays, a light diffusion layer that diffuses incident light rays, or the like.

For example, when the attenuation structure is a light shielding layer, most of the light incident from the side end face 31 is shielded, the amount of light incident on the inside causing the brightness unevenness is reduced, and the occurrence of brightness unevenness is suppressed. can do.
The light shielding layer is not particularly limited as long as it can block the light entering the optical sheet 30, and may be appropriately selected from those using black ink, those deposited by metal vapor deposition, those adhered with metal foil, and the like. In consideration of ease of manufacture, light shielding ability, etc., it is preferable to form a light shielding layer on the side end face 31 using black ink.

In addition, when the attenuation structure is a light diffusion layer, the light rays incident from the side end face 31 are diffused, so that the light rays incident at an angle that causes luminance unevenness are diffused, and the amount of light that causes luminance unevenness is reduced. This can reduce the occurrence of luminance unevenness.
The structure of the light diffusion layer is not particularly limited as long as it can attenuate the light entering the optical sheet 30. For example, a rough surface, a microlens, or a slope is formed on the side end surface 31. And those having through holes formed in the vicinity of the side end face 31. The microlens is not particularly limited, and may be a microlens having a semicircular or semielliptical cross section, or a prism array having a triangular cross section.

When the light diffusion layer is formed of a rough surface, when light rays enter the rough surface, the light diffuses at various angles due to refraction, and the amount of light incident at an angle that causes uneven brightness decreases. The occurrence of uneven brightness can be suppressed.
In addition, when the light diffusion layer is formed of a microlens or a slope, the amount of light that is refracted when the light enters the microlens or the slope and is incident at an angle that causes luminance unevenness is reduced. Generation of unevenness can be suppressed.
In addition, when the light diffusion layer is formed by a through hole, a part of the light beam that causes uneven brightness is diffused or reflected when passing through the interface between the light guide and the air in the through hole. By reducing, the occurrence of uneven brightness can be suppressed.

  As the attenuating structure, a light shielding layer is preferable in terms of efficiently attenuating light rays that cause luminance unevenness, and a light diffusion layer is preferable in terms of ease of formation of the structure. Further, in the light diffusion layer, a microlens is preferable because it is possible to form a light diffusion layer on the side end face simultaneously with the punching process of the optical sheet. Furthermore, as the microlens, a prism array having a triangular cross section is particularly preferable because it can be processed with a finer pitch during the punching process.

A case where the attenuation structure is a light diffusion layer will be described with reference to FIGS.
An example when the light diffusion layer is a microlens is shown in FIG. In this figure, the side end face 31 of the optical sheet 30 assembled on the surface light source device is viewed from the side of the light diffusion layer formed on the second face of the optical sheet 30, and the side end face 31 has a half-section. A plurality of circular or semi-elliptical microlenses are formed. In addition, the cross section of the side end surface 31 here is a cross section when the side end surface is cut by a plane parallel to the surface of the optical sheet 30, and is formed on the second surface of the optical sheet 30 as shown in FIG. This is the shape of the side end face 31 when viewed from the light diffusion layer side.

  By forming such a micro lens, the incident light from the light source 20 is diffused in the arrangement direction of the light sources 20, and the emitted light from the adjacent light sources 20 is mixed to reduce luminance unevenness. If the cross section of the microlens is semi-elliptical, either one of the two axes of the semi-ellipse is arranged in the direction of extension of the side end face (lateral direction in FIG. 5) and in the vertical direction (longitudinal direction in FIG. 5); It is preferable to dispose the other axis of the semi-ellipse in a direction parallel to the extending direction of the side end face in order to uniformly diffuse the light beam that causes uneven brightness.

  In the case of the above arrangement, the ratio of the length of the axis in the direction perpendicular to the extending direction of the side end face and the length of the axis parallel to the extending direction of the side end face is in the range of 1: 1 to 2: 1. preferable. Note that the lengths of the two axes indicate the length when the semi-ellipse is a complete ellipse. When this ratio is 1: 1 or more, that is, when the length of the axis in the direction perpendicular to the extending direction of the side end face is larger than the length of the axis parallel to the extending direction of the side end face, There is a tendency that the diffusion is sufficient and the effect of improving luminance unevenness is improved. Further, when this ratio is 2 to 1 or less, the processing of the side end face 31 is facilitated, the strength of the side end face is sufficient, and there is a tendency that the lens is not chipped.

  FIG. 6 shows another example when the light diffusion layer has a microlens shape. This figure is an example when the microlens is a prism array, and is a view seen from the light diffusion layer side of the optical sheet 30. Each side of the prism array is straight and has apex angle β, the prism array extending direction is arranged in parallel with the optical sheet thickness direction, and the apex is directed to the outside of the optical sheet side end face. Has been placed. Similarly to the semi-elliptical microlens shown in FIG. 5, this prism array can also mainly diffuse incident light from the light source 20 in the arrangement direction to reduce luminance unevenness. The apex angle β is not particularly limited, but is preferably 50 ° to 90 °. When the apex angle β is 90 ° or less, light diffusion by the prism array is sufficient, and the effect of improving luminance unevenness tends to be improved. Further, when the apex angle β is 50 ° or more, the processing of the side end face 31 is facilitated, and the strength of the side end face is sufficient, so that there is a tendency that the lens is not easily chipped. The lower limit value of the apex angle β is more preferably 60 ° or more, and the upper limit value of the apex angle β is more preferably 80 ° or less.

  FIG. 7 shows another example in which the light diffusion layer is a prism array. This figure is a view of a cross section perpendicular to the side end face 31 of the optical sheet as viewed from the extending direction of the side end face 31, and the extending direction of the prism rows is arranged in parallel to the direction perpendicular to the optical sheet thickness direction. And the apex angle is arranged toward the outside of the end face on the optical sheet side.

  When the light diffusing layer is a prism array, there is no particular limitation on the arrangement of the prism array in the extending direction, and the direction shown in FIG. 6 or the direction shown in FIG. 7 may be used. From the viewpoint, the direction shown in FIG. 6, that is, the direction in which the extending direction of the prism row is arranged in parallel with the optical sheet thickness direction is preferable.

  The microlens repetition period P, that is, the pitch is preferably 30 μm to 1000 μm. When the pitch is 30 μm or more, processing tends to be easy and defects such as chipping of the optical sheet tend not to occur. On the other hand, when the pitch is 1000 μm or less, the luminance unevenness does not break up and the strength becomes uniform and tends to be inconspicuous. The lower limit value of the pitch is more preferably 200 μm or more, and the upper limit value of the pitch is more preferably 800 μm or less.

  In addition, the microlens shape of this invention can use a two-dimensional structure other than the one-dimensional structure extended | stretched to one direction like FIGS. As such a shape, for example, a hemispherical shape, a conical shape, a triangular pyramid shape, a quadrangular pyramid shape, a hexagonal pyramid shape and the like can be formed side by side.

Next, the case where the light diffusion layer is a slope will be described with reference to FIG.
FIG. 8 is a cross-sectional view in a direction perpendicular to the extending direction of the side end face 31 of the optical sheet 30. The slope is the side end face 31 when the angle γ formed by the light diffusion layer 34 and the side end face 31 is an angle other than 90 degrees. At this time, the angle γ formed by the diffusion layer 34 and the inclined surface is preferably in the range of 30 ° to 75 °, or 105 ° to 150 °. If γ is less than 30 ° or exceeds 150 °, it becomes difficult to form a slope and the optical sheet tends to be easily damaged. On the other hand, when γ is more than 75 ° and less than 105 °, the light diffusibility is lowered and the effect of improving luminance unevenness tends to be reduced.

Next, the case where a light-diffusion layer is a through-hole is demonstrated using FIG.
The attenuation structure of the present invention is limited to the outermost surface of the side end face 31 as long as it is in the vicinity of the side end face 31 of the optical sheet and does not affect the quality of the liquid crystal display device, that is, outside the effective display area of the liquid crystal display face. Alternatively, it can be provided inside the side end face 31. For example, a through hole is provided in the thickness direction in the vicinity of the side end surface of the optical sheet 30, and luminance unevenness can be reduced by the light diffusion effect at the interface between the formed through hole and the translucent substrate 33. Although there is no restriction | limiting in particular as a shape and space | interval of such a through-hole, A perforated shape can be used conveniently for the simplicity of a punching process. An example of the perforation shape is shown in FIG. In the figure, the perforations are arranged in two rows, but the present invention is not limited to this example, and the optimum number of rows and arrangement shape can be selected as appropriate.

(Sheet-like translucent substrate)
The material of the sheet-like translucent base material 33 is not particularly limited, but is preferably one that transmits active energy rays, for example, an acrylic resin such as polymethyl methacrylate, a polycarbonate resin, a polyester resin such as polyethylene terephthalate and polyethylene naphthalate, Cellulose resins such as diacetyl cellulose and triacetyl cellulose, styrene resins such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, and olefin resins such as ethylene / propylene copolymers, It is possible to use films, sheets, plates, etc. made of polyamide resins such as nylon and aromatic polyamide, vinyl chloride resins, polymethacrylimide resins, etc. That. In addition, other treatments such as antistatic, antireflection, and adhesion prevention between substrates can be performed.

  Further, the sheet-like translucent substrate 33 may have a surface treatment portion (an easy adhesion layer) for improving the adhesion with the lens layer 32. Examples of the surface treatment include those having easy adhesion made of polyester resin, acrylic resin, urethane resin, and the like. Moreover, what roughened the surface of the sheet-like translucent base material 33 may be used. Furthermore, an antistatic agent may be contained in the easy-adhesion layer as necessary, and the antistatic performance can be imparted to the optical sheet 30. Thereby, the workability at the time of assembling the liquid crystal display device can be improved, and the adsorption of foreign matters due to static electricity can be prevented.

(Light diffusion layer formed on the second surface)
The light diffusion layer 34 preferably has a surface haze of H1 and an internal haze of H2, and the total haze (H1 + H2) is 60% or less. If the total haze exceeds 60%, the occurrence of luminance unevenness can be suppressed, but the luminance of a liquid crystal display device using such a surface light source device tends to be low. Further, a more preferable value of the total haze is 55% or less, and particularly preferably 50% or less.

  The ratio of the internal haze H2 to the total haze (H1 + H2) of the light diffusion layer 34 is preferably 50% or less. When the ratio of the internal haze H2 exceeds 50%, unnecessary scattering in an unintended direction is likely to occur, and the brightness of the surface light source device and the half-value angle of the brightness tend to be reduced.

  The haze was measured using a haze meter (for example, product name: HM-150, manufactured by Murakami Color Research Laboratory) so that the light diffusion layer 34 faces the light receiving side. It is a value specified in conformity.

  The structure of the light diffusing layer 34 is not particularly limited as long as the ratio of the internal haze H2 is 50% or less, but a paint containing the light transmissive resin 35 and the light diffusing material 36 is applied onto the light transmissive substrate 33. Can be formed. Moreover, the coating material which contains 2 or more types of resin components and forms uneven | corrugated shape by the effect | action of phase separation can also be used.

  Further, as another method of forming the light diffusion layer 34, a method of forming a cured resin layer by transferring and curing a mold having an uneven shape on the surface onto a transparent substrate 33 using an ultraviolet curable composition. Alternatively, a method of forming a light diffusion layer by thermally transferring a concavo-convex shape by pressing a mold having a concavo-convex shape on the surface to the transparent substrate 33 under heating can be used.

  As a method of forming the light diffusing layer, a case where a method of forming a light diffusing layer 35 by applying a paint including the light transmissive resin 35 and the light diffusing material 36 on the light transmissive substrate 32 will be described below.

  The translucent resin 35 can be used without particular limitation as long as it can disperse the light diffusing material 36, has high translucency, and has desired heat resistance, scratch resistance, elasticity, and the like. Such translucent resins include polyamide resins, polyurethane resins, polyester resins, acrylic resins and other thermoplastic resins, thermosetting resins, active energy ray curable resins (ionizing radiation curable resins), etc. Among these, it is preferable to select appropriately in consideration of adhesion to the light-transmitting substrate 33 and the light diffusing material 36, and the use of an acrylic resin having a high transmittance is particularly preferable. Examples of acrylic resins include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) acrylic acid. Polymers are preferred. In particular, an acrylic polyol containing hydroxyalkyl (meth) acrylate as a monomer unit is dissolved in a solvent such as toluene or methyl ethyl ketone, and an isocyanate bifunctional monomer or an oligomerized isocyanate compound such as isocyanurate or melamine An acrylic resin obtained by mixing with a cross-linking agent, coating, and curing is preferable in terms of strength and adhesion to a translucent substrate. Moreover, from a heat resistant viewpoint, the thing whose glass transition point is 60 degreeC or more is preferable.

  In addition, a leveling agent, a thixotropic agent, a slip agent, an antifoaming agent, an antistatic agent, an ultraviolet absorber, and the like can be added and contained in the translucent resin 35. Among these, by incorporating a leveling agent, aggregation of the light diffusing material 36 can be suppressed and irregularities due to the light diffusing material 36 can be easily formed. Moreover, the damage at the time of friction with the liquid crystal panel surface can be prevented by adding a slip agent. As the slip agent, commercially available products such as silicon-based, fluorine-based, paraffin-based, and mixtures thereof can be used without particular limitation, and examples thereof include BYK series manufactured by BYK Japan.

  Examples of the light diffusing material 36 include inorganic particles such as glass, silica, talc, and barium sulfate. Examples of organic particles include cross-linked organic fine particles such as polymethyl methacrylate, polystyrene, polyurethane, acrylic-styrene copolymer, benzoguanamine, and melamine, fine particles of silicone resin, acrylic rubber, butadiene, styrene-butadiene, acrylonitrile-butadiene-styrene (ABS). ) And the like, and silicone rubber particles. The light diffusing material 36 may be a commercially available one or one obtained by suspension polymerization or emulsion polymerization. For example, methacrylates such as methyl methacrylate and octyl methacrylate, acrylates such as methyl acrylate and butyl acrylate, vinyl aromatic compounds such as styrene, α-methyl styrene, chlorostyrene and vinyl toluene, vinyl nitriles such as acrylonitrile and methacrylonitrile, ethylene Acrylic crosslinked particles obtained by suspension polymerization or emulsion polymerization of propylene, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl propionate, alkyl fumarate, and other ethylenically unsaturated compounds be able to.

  As an example of the said acrylic type crosslinked particle, the polymethyl methacrylate crosslinked particle containing 20-50 mass% of crosslinking agents is mentioned. As a commercial item, Sekisui Plastics Co., Ltd. techpolymer SSX series etc. are mentioned.

  The flexible rubber particles are effective for preventing damage to the liquid crystal panel surface, particularly when the liquid crystal panel surface is a smooth surface. For example, silicone composite powder KMP-600 series manufactured by Shin-Etsu Chemical Co., Ltd., Techpolymer BMX series, ARX series manufactured by Sekisui Plastics Co., Ltd. may be mentioned.

  The shape of the light diffusing material 36 can be appropriately selected and used regardless of the shape such as a spherical shape, an indeterminate shape, a bowl shape, a spheroid shape, or a needle shape.

  As a structure of the light diffusing material 36, a refractive index difference (absolute value) Δn represented by the following formula (1) between the refractive index N1 of the translucent resin 35 is 0.00 to 0.06, preferably Preferably has a refractive index N2 of 0.00 or more and 0.04 or less. If Δn exceeds 0.06, scattering at the interface between the light diffusing material 36 and the translucent resin 35 tends to be strong, and the ratio of the internal haze H2 may exceed 50%. .

Δn = | N1-N2 | (1)
The thickness of the light diffusion layer 34 is not particularly limited, and is preferably determined in the range of 1 to 20 μm, for example. If the thickness is less than 1 μm, the production tends to be difficult, and if it exceeds 20 μm, the luminance unevenness tends to deteriorate.

(Lens layer formed on the first surface)
The material of the lens layer 32 is not particularly limited, and is made of, for example, an active energy ray curable resin, and the refractive index is about 1.50 to 1.6. The active energy ray curable resin is not particularly limited as long as it is cured with active energy rays such as ultraviolet rays and electron beams. For example, polyesters, epoxy resins, polyester (meth) acrylates, epoxy Examples include (meth) acrylate resins such as (meth) acrylate and urethane (meth) acrylate. Among these, urethane (meth) acrylate resins are particularly preferable from the viewpoint of optical characteristics and the like. These may be used alone or as a mixture of two or more, and usually contain a photopolymerization initiator by active energy rays.

  The lens array formed in the lens layer 32 is not limited to the substantially triangular prism array as shown in FIG. 2, and can be determined according to the application. For example, a lenticular lens, a polygonal pyramid, a conical lens, and the like can be mentioned, but a prism array having a substantially triangular cross section is particularly preferable. When the lens array is a prism array, the apex angle of the prism array is not particularly limited, but is preferably in the range of 40 to 75 °, more preferably in the range of 45 to 70 °. The pitch of the lens array is not particularly limited, but the pitch is preferably 50 μm or less, more preferably 20 μm or less.

<Light source and reflection sheet for light source>
The light source 20 is not particularly limited as long as it is an LED, and can be determined according to a desired surface light source device and liquid crystal display device. For example, a pseudo-white light emitting diode or a light emitting diode that emits white light using a red / green / blue light emitting diode chip as one light source can be used.

  The light source reflection sheet 21 that covers the light source 20 is not particularly limited as long as it can reduce the loss of light from the light source 20 and can be guided to the light guide 10, and is a plastic film having a metal-deposited reflective layer on its surface, a refractive index. A multilayer film composed of a plurality of different resin layers, a light diffusing material-containing plastic film, and the like can be used.

<Reflection sheet>
The reflection sheet 40 is not particularly limited as long as it reflects light emitted from the back surface of the light emitting surface 12 of the light guide 10 and makes it incident on the light guide 10 again. Examples thereof include polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyolefin. Of these, polyethylene terephthalate is preferable. Moreover, it is preferable that the reflection sheet 40 is a white sheet containing a pigment or a fine void. Examples of the pigment include titanium oxide, barium sulfate, calcium carbonate, and magnesium carbonate. Instead of the reflective sheet 40, a reflective layer may be formed on the light guide 10 side surface on the reflective sheet 40 side by metal vapor deposition or the like.
The thickness of the reflection sheet 40 is not specifically limited, For example, it is preferable to determine in the range of 30-300 micrometers.

<LCD panel>
The liquid crystal panel is not particularly limited, and any of an active matrix driving TFT liquid crystal display element and a simple matrix driving STN liquid crystal display element can be used. In the TFT type liquid crystal display element, various active elements such as polysilicon, amorphous silicon, metal insulator, and metal can be used as the element.

[Production method]
Below, an example of the manufacturing method of the optical sheet 30 is demonstrated.
First, the light diffusing material 36, the translucent resin 35, and other additives are added to and mixed with the dispersion medium to form a coating liquid, and the coating liquid is applied to one surface of the translucent substrate 33. As the dispersion medium, it is preferable to select a dispersion medium in which the light diffusing material 36 is dispersed and the translucent resin 35 is dissolved well, and is determined according to the type of the light diffusing material 36 and the translucent resin 35. Can do. Examples thereof include methyl ethyl ketone, methyl isobutyl ketone, toluene, ethyl acetate, butyl acetate, isopropyl alcohol, ethanol and the like.

  Although content of the light-diffusion material 36 in the said coating liquid is not specifically limited, It is preferable that it is 2-40 mass%. If it is within the above range, the application of the coating solution and the volatilization of the solvent are good, and the operation becomes easy.

  The coating method of the coating liquid is not particularly limited, and examples thereof include existing coating methods such as a screen printing method, a die coating method, a gravure coating method, a spin coating method, a dip coating method, a bar coating method, and a spray coating method. .

The coating amount of the coating solution may be an amount that can obtain the light diffusion layer 34 having a desired thickness, and is preferably about ² to 100 g / m ² , for example.

  The method for volatilizing the dispersion medium is not particularly limited as long as the performance of the optical sheet 30 is not deteriorated. For example, the dispersion medium can be volatilized by heat treatment at 80 to 180 ° C.

Next, the lens layer 32 is formed on the surface of the translucent substrate 33 opposite to the surface on which the light diffusion layer 34 is formed. The method for forming the lens layer 32 is not particularly limited, and an existing method can be used. For example, the active energy ray-curable composition is filled in a known heat press method or a roll-shaped mold in which the shape of the lens array is engraved, and then coated with the translucent substrate 33 through the composition liquid. A method for continuously producing a translucent substrate 33 provided with a lens layer 32 by irradiating ultraviolet rays or the like as it is, and an active energy ray-curable composition liquid on a mold corresponding to the shape of a lens array A method of manufacturing the translucent base material 33 provided with the lens layer 32 by a batch method by pouring and irradiating ultraviolet rays or the like in a state where the translucent base material 33 is laminated.
In this way, an optical sheet in which the lens layer 32 is formed on one surface (first surface) of the translucent substrate 33 and the light diffusion layer 34 is formed on the other surface (second surface) is obtained. Can do.

Next, an attenuation structure that attenuates light rays is formed on the side end face 31 of the optical sheet.
The light attenuation effect by the attenuation structure can be evaluated by measuring the light transmittance for the light shielding layer and by measuring the haze for the light diffusion layer. About the light transmittance and haze of the end surface 31, since the thickness of an optical sheet is small, sufficient area required for a measurement cannot be ensured. Therefore, a process similar to the process of applying the attenuation structure to the side end surface is applied to one surface of the translucent base material 33 on which neither the lens layer 32 nor the light diffusion layer 34 is formed, and the light transmittance and The haze was measured and the light attenuation effect by the attenuation structure was evaluated.

The haze is measured when a haze meter (for example, manufactured by Murakami Color Research Laboratory, trade name: HM-150) is used and measured so that the processed portion applied to the translucent substrate 33 faces the light receiving side. It is a value specified according to JIS-K7136, and light transmittance is a value measured using a haze meter (Murakami Color Research Co., Ltd. HM-150) in accordance with method B of JISK-7105.
As the attenuation structure, the light transmittance is preferably 50% or less, and more preferably 20% or less. When the light transmittance is 50% or less, the light attenuation effect is high and luminance unevenness tends not to occur.

  When the attenuation structure is a light shielding layer, the method for forming the light shielding layer is not particularly limited, and for example, there is a method of applying black ink or spray. Further, it is not necessary to form a light shielding layer for each optical sheet. For example, 100 optical sheets may be stacked and black ink may be applied to the side end surfaces at once.

When the attenuation structure is a light diffusing layer, the method for forming the light diffusing layer is not particularly limited. For example, the side end surface of the optical sheet 30 is rubbed several times with a file or the like to roughen and diffuse incident light. There is a method of making it, and coating of a paint with a diffusing material. Further, when the optical sheet 30 is cut into a desired shape, the cutting surface is roughened by cutting a portion corresponding to the side end face 31 using a blade with minute irregularities on the side of the blade. The method may be used.
For example, as a method of forming a light diffusion layer as shown in FIG. 5 or FIG. 6, it can be formed by punching using a blade processed into a target shape. As such a cutter, for example, Pinnacle Die (registered trademark) of Tsukaya Cutlery Co., Ltd. can be cited.

  When the optical sheet is stacked on the surface light source device, it is processed into a desired shape by die cutting or the like. For example, in the case of a surface light source device for a backlight of a notebook personal computer, the optical sheet is processed into a rectangle according to the dimensions of the surface light source device. If the above Pinnacle Dye (registered trademark) is used, it is possible to form a light diffusion layer on the side end face of the optical sheet at the same time as processing into an appropriate shape by die-cutting, and no additional process is required. This is a particularly useful processing method.

Further, in the case of the light diffusion layer as shown in FIG. 7, for example, cutting with a cutting tool having a fine shape or a mold having a shape in which the unevenness of the target diffusion layer shape is reversed, the end face on the side of the optical sheet is formed. Curing on the end face of the optical sheet by so-called thermal transfer method, where the shape is transferred by pressing against the mold after plasticizing by heating, or by curing with a curable resin filled between the end face of the optical sheet and the mold A method of forming a light diffusion layer made of a resin can be used.
As a damping structure, the haze is preferably 50% or more, and more preferably 70% or more. When the haze is 50% or more, the light attenuation effect is high, and brightness unevenness tends not to occur.

  Furthermore, as a method of forming the inclined surface on the side end face as shown in FIG. 8, it can be formed with a cutter knife capable of cutting at an inclined angle with respect to the direction in which the blade is inserted. It is also possible to form a desired slope on the side end face by setting the optical sheet at a desired angle and punching it.

  Moreover, as a method of forming the through hole in the vicinity of the side end face as shown in FIG. 9, it can be formed by punching using a blade processed into a target shape. As such a cutter, for example, Pinnacle Die (registered trademark) of Tsukaya Cutlery Co., Ltd. can be cited.

  Thus, the optical sheet 30 can be obtained. In addition, the manufacturing method of the optical sheet 30 is not limited to the above. For example, after the lens layer 32 is formed on one surface of the translucent substrate 33, the light diffusion layer 33 is formed on the other surface of the translucent substrate 33. After forming, an attenuation structure may be formed on the side end face.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, it is not limited to an Example.
The evaluation methods used in the examples are described below.

<Total haze of light diffusion layer formed on second surface of optical sheet (H1 + H2)>
Using a haze meter (Murakami Color Research Laboratory, trade name: HM-150), the laminate X or laminate Y, which will be described later, is attached so that the light diffusion layer of the laminate X or laminate Y faces the light receiving side. By measuring the total haze (JIS-K7136), the total haze (H1 + H2) of the light diffusion layer formed on the second surface of the optical sheet was determined.

<Internal haze (H2) of light diffusion layer formed on second surface of optical sheet>
A thickness obtained by spreading a transparent ultraviolet curable resin having a refractive index of 1.52 after curing on a light diffusing layer of a laminate X or a laminate Y, which will be described later, and then providing an easy adhesion layer only on one side A surface without an easy-adhesion layer of a 188 μm PET film (trade name Cosmo Shine A4100, manufactured by Toyobo Co., Ltd.) is overlaid on an ultraviolet curable resin, and the excess resin is removed by squeezing with a rubber roll. ) Irradiating ultraviolet rays from the side to cure, then releasing the PET film, and having a UV curable resin layer having a thickness of 15 μm and a smooth surface on the light diffusion layer of the laminate X or laminate Y And the haze of this film was measured in the same manner as the total haze, thereby determining the internal haze (H2) of the light diffusion layer formed on the second surface of the optical sheet.

<Ratio of internal haze (H2) to total haze (H1 + H2)>
The internal haze (H2) determined above was obtained by dividing by the total haze (H1 + H2).

<Light transmittance and haze of attenuation structure>
The same processing as the processing for forming the attenuation structure on the side end face is performed by using a PET film (Toyobo Co., Ltd., trade name: Cosmo Shine A4300, thickness 125 μm, on both sides) on which the lens layer and the light diffusion layer are not formed. It was applied to one surface (with an easy adhesion layer), and the light transmittance and haze were measured to evaluate the light attenuation effect by the attenuation structure.
The haze is measured according to JIS-K7136 when a haze meter (for example, manufactured by Murakami Color Research Laboratory, trade name: HM-150) is used and measured so that the processed part applied to the PET film faces the light receiving side. The light transmittance is a value measured using a haze meter (HM-150 manufactured by Murakami Color Research Co., Ltd.) in accordance with JIS K-7105 Method B.

<Luminance and half-value angle>
A luminance meter (trade name: BM-7, manufactured by Topcon Co., Ltd.) is placed at a position 50 cm away from the center of the surface light source device in the normal direction without placing the liquid crystal panel on the surface light source device. Was turned on, and the normal luminance and half-value angle were measured using the center of the effective screen as the luminance measurement region.

<Luminance unevenness>
The luminance unevenness observed on the optical sheet of the surface light source device was evaluated by visual observation, and the length from the optical sheet side end surface of the peak tip portion of the bright portion in the luminance unevenness was measured. Moreover, it measured from every angle and determined as follows by making the maximum length of the brightness nonuniformity which can be confirmed into a criterion.

Less than 1mm: ◎
Within 1-10mm: ○
10 mm or more: ×

The compounds used in the examples are abbreviated as follows.
Methyl ethyl ketone: MEK
Methyl methacrylate: MMA
Ethyl acrylate: EA
2-Hydroxyethyl methacrylate: HEMA
Methacrylic acid: MAA
Azobisisobutyronitrile: AIBN

(Preparation Example 1) Production of translucent resin In a 2 L separable flask of a polymerization reaction vessel, 106 parts by mass of toluene, 71 parts by mass of MEK, 69 parts by mass of MMA, 25 parts by mass of EA, 5 parts by mass of HEMA, and 1 part by mass of MAA were weighed. While stirring with a stirring blade, bubbling with nitrogen was performed for 30 minutes. Thereafter, 0.45 parts by mass of AIBN was added as a radical polymerization initiator, and then the reaction vessel was heated to 90 ° C. and kept in that state for 5 hours. Further, 1 part by mass of AIBN was added and held for 4 hours, and then cooled to room temperature to complete the reaction, whereby an acrylic resin X solution was obtained. The acrylic resin X has a molecular weight (MW) of 75,100, a hydroxyl value of 21.6 mgKOH / g, an acid value of 2.1 mgKOH / g, Tg of 61 ° C., and a refractive index of 1.49. It was 36.0 mass%.

Example 1
An optical sheet, a surface light source device, and a liquid crystal display device were produced as follows.
As the translucent substrate, a 125 μm thick PET film (manufactured by Toyobo Co., Ltd., trade name: Cosmo Shine A4300) having an easy-adhesion layer on both sides was used.

  Acrylic resin X having a refractive index of 1.49 obtained in Preparation Example 1 as a translucent resin, and resin fine particles having a refractive index of 1.49 and a volume average particle diameter of 5 μm as a light diffusing material (manufactured by Sekisui Plastics Co., Ltd., Tech. Polymer SSX-105), resin fine particles having a refractive index of 1.49 and a volume average particle diameter of 8 μm (manufactured by Sekisui Plastics Co., Ltd., Techpolymer SSX-108), duranate TPA-100 (manufactured by Asahi Kasei Chemicals Corporation) as a cross-linking agent ), MEK and toluene as diluent solvents were weighed in a container and stirred with a stirring blade to prepare a coating solution X for forming a light diffusion layer in which the light diffusion material was uniformly dispersed. .

  Using the reverse gravure coating method, the coating liquid X was applied onto a PET film so that the average thickness after solvent drying was 7 μm and dried. Thereby, the laminated body X which has a light-diffusion layer in the single side | surface of PET film was obtained.

  The appearance of the obtained laminate X was very good with no generation of coating spots such as streaks. For the light diffusion layer, the ratio of internal haze (H2) to total haze (H1 + H2) was 6.0%. The results are shown in Table 2.

  On the other hand, a shape transfer surface corresponding to the shape of the prism row forming surface was formed on the surface of three types of JIS brass thin plates having a thickness of 1.0 mm and 400 mm × 690 mm to obtain a mold member. Here, the target prism array forming surface has a shape in which a large number of prism arrays having a pitch P = 50 μm and an apex angle of 65 ° are arranged in parallel.

  Next, a stainless steel cylindrical roll having a diameter of 220 mm and a length of 450 mm was prepared, and a mold member was wound around and fixed to the outer peripheral surface to obtain a roll-shaped mold (roll mold). The laminate X was supplied along the roll mold between the roll mold and the rubber roll, and the laminate X was nipped between the rubber roll and the roll mold by a pneumatic cylinder connected to the rubber roll.

The viscosity was adjusted to 300 mPa · s / 25 ° C. using an ultraviolet curable composition having the following composition.
Phenoxyethyl acrylate (Biscoat # 192, manufactured by Osaka Organic Chemical Industry Co., Ltd.): 50 parts by mass Bisphenol A-diepoxy-acrylate (epoxy ester 3000A, manufactured by Kyoeisha Chemical Co., Ltd.): 50 parts by mass 2-hydroxy-2-methyl-1 -Phenyl-propan-1-one (Darocur 1173, manufactured by Ciba Geigy Corporation of Japan): 1.5 parts by mass

  This ultraviolet curable composition was supplied to the surface on the opposite side of the surface to which the light-diffusion layer of the laminated body X nipped by the rubber roll to the roll type | mold was provided. While rotating the roll mold, in a state where the ultraviolet curable composition is sandwiched between the roll mold and the translucent substrate, ultraviolet rays are irradiated from an ultraviolet irradiation device to polymerize and cure the ultraviolet curable composition. The prism row pattern on the shape transfer surface of the mold was transferred. Then, it released from the roll type | mold and the prism sheet X was obtained.

  The obtained prism sheet X was cut into a 11.1 inch W (wide) size, and one side end surface of the long side was painted with black ink to form a light shielding layer, whereby a prism sheet A was produced. The light transmittance of the light shielding layer with the black ink was 28.7%.

As shown in FIG. 1, the lens array forming surface faces the light guide made of resin on the light exit surface of the 11.1 W inch (wide) size light guide with the light source arranged on the side surface, and is blackened. The prism sheet A was placed so that the side end face that was made was close to the stepped portion of the light guide, and the other side face and the back face were covered with a reflective sheet to obtain a surface light source device. The thickness of the light guide on the light incident surface is 0.75 mm, and the thickness of the light guide on the light exit surface is 0.60 mm, that is, the height of the stepped portion is 0.15 mm. Further, the step portion has a stepped shape with a width of 2.5 mm in which 25 steps with a height of 0.006 mm and a width of 0.1 mm are formed at equal intervals.
The obtained surface light source device was evaluated for luminance, half-value angle, and luminance unevenness according to the evaluation method. The results are shown in Table 2.

(Example 2)
Using the prism sheet X cut out in the 11.1 inch W (wide) size manufactured in Example 1, one side end surface of the long side was rubbed 10 times with a # 1000 paper file to prepare a prism sheet B. The haze when processed with a paper file was 73.1%.
Using this prism sheet B, a surface light source device was produced in the same manner as in Example 1, and the luminance, half-value angle, and luminance unevenness were evaluated. The results are shown in Table 2.

(Example 3)
Using the prism sheet X cut out in the 11.1 inch W (wide) size manufactured in Example 1 and using the Pinnacle Die (registered trademark) manufactured by Tsukaya Seisakusho on one side end surface of the long side, it is shown in FIG. A prism sheet C was prepared by forming a microlens having a semi-elliptical cross section. Here, in the semi-elliptical shape of the cross section of the microlens, one of the two axes of the semi-ellipse is arranged perpendicular to the extending direction of the side end face, and the other axis is arranged parallel to the extending direction of the side end face. ing. The ratio of the length of the axis perpendicular to the extending direction of the side end face to the length of the axis parallel to the extending direction of the side end face is 1.5 to 1, and the pitch P is 800 μm. Here, the lengths of the two axes are the lengths when the half ellipse is a complete ellipse.
Using this prism sheet C, a surface light source device was produced in the same manner as in Example 1, and the luminance, half-value angle, and luminance unevenness were evaluated. The results are shown in Table 2.

Example 4
Using the prism sheet X cut out in the 11.1 inch W (wide) size produced in Example 1 and using the Pinnacle Die (registered trademark) manufactured by Tsukaya Seisakusho on one side end surface of the long side, it is shown in FIG. A prism sheet having an isosceles triangle in cross section was formed to prepare a prism sheet D. Here, the apex angle β of the prism is 60 °, both sides sandwiching the apex angle are 250 μm, and the pitch P is 250 μm.
Using this prism sheet D, a surface light source device was produced in the same manner as in Example 1, and the luminance, half-value angle, and luminance unevenness were evaluated. The results are shown in Table 2.

(Example 5)
By using the prism sheet X cut out to the 11.1 inch W (wide) size produced in Example 1, one side end surface of the long side is cut obliquely with NT NT cutter (product number MAT-45P). As shown in FIG. 8, a prism sheet E having a slope portion on the side end face was produced. Here, the apex angle γ is 45 °.
Using this prism sheet E, a surface light source device was produced in the same manner as in Example 1, and the luminance, half-value angle, and luminance unevenness were evaluated. The results are shown in Table 2.

(Comparative Example 1)
Using the prism sheet X produced in Example 1 cut into a 11.1 inch W (wide) size as it is without forming an attenuation structure on the side end surface thereof, a surface light source is produced in the same manner as in Example 1. A device was fabricated and evaluated for luminance, half-value angle, and luminance unevenness. The results are shown in Table 2.

(Comparative Example 2)
A polyester resin solution (trade name: Byron 20SS, manufactured by Toyobo Co., Ltd.) having a refractive index of 1.55 and a heating residue of 29.7% by mass as a light-transmitting resin, and a volume average particle having a refractive index of 1.49 as a light diffusing material. Resin fine particles having a diameter of 5 μm (manufactured by Sekisui Plastics Co., Ltd., Techpolymer SSX-105) and resin fine particles having a refractive index of 1.49 and a volume average particle diameter of 8 μm (manufactured by Sekisui Chemicals Co., Ltd., Techpolymer SSX-108) ), Takenate D-110N (manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) as a cross-linking agent, MEK and toluene as diluent solvents in a container, measure the amount shown in Table 1 and stir with a stirring blade, the light diffusing material is uniform A coating liquid Y for forming a light diffusion layer dispersed in was prepared.

Using a 125 μm thick PET film (trade name: Cosmo Shine A4300, manufactured by Toyobo Co., Ltd.) having an easy-adhesion layer on both sides as a translucent substrate, light diffusion was performed in the same manner as in Example 1. A layer was formed on one side of the PET film to produce a laminate Y. Next, using this laminate Y, a prism sheet Y was obtained in the same manner as in Example 1 using a mold member having a pitch P = 50 μm.
This prism sheet Y is cut into a 11.1 inch W (wide) size, and is used as it is without forming an attenuation structure on the side end surface thereof, and a surface light source device is manufactured in the same manner as in Example 1 to obtain luminance. , Half-value angle and luminance unevenness were evaluated. The results are shown in Table 2.

As shown in Table 2, the ratio of internal haze to the total haze of the light diffusing layer is 50% or less, and the light shielding layer is provided on the prism sheet side end surface. In Examples 2 to 5, luminance unevenness was reduced. Furthermore, since the luminance was maintained at 11787 cd / m ² or more and the half-value angle was 18.5 °, it was found that the luminance necessary for the liquid crystal display device was maintained and a wide viewing angle was obtained. It was.

On the other hand, in the comparative example 1 having no attenuation structure on the side end face, the degree of luminance unevenness was large. Moreover, the said brightness nonuniformity was visually recognized also in the effective screen of the liquid crystal display device produced by mounting a liquid crystal panel on a surface light source device.
In Comparative Example 2 using the light diffusion layer in which the ratio of the internal haze to the total haze exceeds 50%, although the luminance unevenness and the half-value angle are not a problem, the luminance is 11353 cd / m ² , which is about 200 cd / m as compared with Examples 1 to 5. m ² decreased.

DESCRIPTION OF SYMBOLS 10 Light guide 11 Light incident surface 12 Light output surface 13 Step part 20 Light source 21 Light source reflection sheet 30 Optical sheet 31 Side end surface 32 Lens layer 33 Translucent base material 34 Light diffusion layer 35 Translucent resin 36 Light diffusion material 40 Reflective sheet

Claims (10)

An optical sheet having a first surface on which a plurality of lens rows are formed in parallel, a second surface on which a light diffusion layer is formed, and a side end surface substantially orthogonal to the first surface and the second surface Because
An optical sheet characterized in that an attenuation structure for attenuating light incident on the optical sheet from the outside of the optical sheet through the side end surface is formed on or near at least one side end surface.   The optical sheet according to claim 1, wherein the attenuation structure is a light shielding layer.   The optical sheet according to claim 1, wherein the attenuation structure is a light diffusion layer.   4. The optical sheet according to claim 3, wherein the light diffusion layer is formed of a microlens.   The microlens is a prism array having an apex angle of 50 to 90 °, and the prism array is arranged in parallel so that the extending direction thereof is parallel to the optical sheet thickness direction and the apex angle is directed to the outside of the optical sheet side end surface. The optical sheet according to claim 4, wherein the optical sheet is arranged.   4. The optical sheet according to claim 3, wherein the light diffusion layer is formed of a slope or a through hole.   The total haze of the light diffusion layer formed on the second surface of the optical sheet is 60% or less, and the proportion of the internal haze in the total haze is 50% or less. The optical sheet according to -6. The optical sheet according to any one of claims 1 to 7,
A primary light source composed of a plurality of point light sources; at least one light incident surface facing the primary light source; and a light emitting surface from which light incident from the light incident surface exits substantially orthogonal to the light incident surface. A light guide;
In the surface light source device having
In the light guide, the thickness of the light guide on the light incident surface is larger than the thickness of the light guide on the light output surface, and the light guide is between the light incident surface and the light output surface. It has a step part where the thickness of the body gradually decreases,
The surface light source device, wherein the optical sheet is arranged such that a side end surface of the attenuation structure formed on or near the surface thereof is close to the stepped portion.   The surface light source device according to claim 8, wherein the first surface of the optical sheet is disposed so as to face a light emitting surface of the light guide.   A liquid crystal display device comprising the surface light source device according to claim 8.