JP2009265613A - Lens sheet, surface light source device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens sheet which prevents a glaring phenomenon while maintaining opacifying effect and increases luminance to widen a viewing angle, a surface light source device using the lens sheet, and a liquid crystal display device. <P>SOLUTION: The lens sheet has a lens layer 51 where a lens array 59 is formed on one surface of a translucent base material 55 and a light diffusing layer 53 where an uneven surface is formed on the other surface. The light diffusing layer 53 has a light diffusing material 57 and a translucent resin 56, wherein the light diffusing layer 53 contains ≥10 and ≤70 mass% of the light diffusing material 57, ≥50% by volume of the light diffusing material 57 is a first light diffusing material having a difference in refractive index of ≥0.005 and ≤0.03 from the translucent resin 56, and ≥50% by volume of the light diffusing material 57 has particle sizes of ≥1 μm and ≤4 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lens sheet, a surface light source device, and a liquid crystal display device.

Liquid crystal display devices are widely used in various fields such as notebook computers and mobile phones, and as the amount of information processing increases and the needs diversify, the liquid crystal display devices are becoming larger and more precise. Yes.
In general, a 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. From the viewpoint of downsizing liquid crystal display devices, an edge light type is often used.
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, in order to more efficiently use the light obtained from the light source, a lens sheet for concentrating and emitting the light from the surface light source in a specific direction is used.
In such a lens 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 diffusion layer provided on the surface opposite to the lens array.

In order to increase the size and precision of liquid crystal display devices in recent years, further precision is required for lens sheets. As one of the functions of the surface structure having the light diffusing function of the prism sheet as described above, light is diffused by each protrusion, and desired haze (Haze) is expressed, so that the desired luminance and viewing angle can be obtained. Adjustments can be made. Many prism sheets that improve the diffusion layer for the purpose of improving the luminance at a specific viewing angle have been reported (for example, Patent Documents 1 to 5).
Another one of the functions of the surface structure having the light diffusion function of the prism sheet is due to partial close contact with the light diffusion sheet and the liquid crystal panel located on the upper surface of the prism sheet (surface opposite to the prism row forming surface). It is possible to suppress a phenomenon called sticking that generates interference fringes. As a further function of the surface structure having the light diffusion function of the prism sheet, the mat structure or lens formed on the light emitting surface of the light guide or the back surface on the opposite side can be reduced. A so-called defect concealing property that reduces the visibility of surface structure defects such as a column arrangement structure is exemplified. This defect concealment property is particularly important when a high-luminance light source is used as the primary light source.
Thus, when a surface structure having a light diffusion function is formed on the surface opposite to the prism row forming surface of the prism sheet, the light having a strong directivity emitted from the light guide and internally reflected by the prism row of the prism sheet. May interfere with the surface structure having a light diffusing function, and a glare phenomenon called speckle or sparkling may occur in which fine particles in the coating film and surface irregularities are extremely glazed. In this case, the display image is very difficult to see, and in recent years, there has been a strong demand for solving this glare phenomenon.

Japanese Patent Laid-Open No. 2-84618 Japanese Utility Model Publication No. 3-69187 JP-A-6-324205 JP-A-10-160914 JP 2000-353413 A

However, the conventional technology has not sufficiently prevented the glare phenomenon. In order to suppress the glare phenomenon caused by the surface structure having a light diffusion function, it is conceivable to increase the light diffusion property by increasing the amount of fine particles added to the coating film forming the surface structure. As a result, the glare phenomenon can be reduced to some extent, but the luminance of the surface light source device or the liquid crystal display device is greatly reduced.
Accordingly, the present invention provides a lens sheet that can prevent glare phenomenon while maintaining concealment, and can increase the viewing angle by increasing the brightness, a surface light source device using the lens sheet, and a liquid crystal display device With the goal.

The lens sheet of the present invention has a lens layer in which a lens array is formed on one surface of a translucent substrate, and a light diffusion layer in which an uneven surface is formed on the other surface, The light diffusing layer has a light diffusing material and a translucent resin, and the content of the light diffusing material in the light diffusing layer is 10% by mass or more and 70% by mass or less, and 50 volumes of the light diffusing material. % Or more is a first light diffusing material having a refractive index difference of 0.005 or more and 0.03 or less with respect to the refractive index of the translucent resin, and 50% by volume of the light diffusing material. The above is characterized in that the particle diameter is 1 μm or more and 4 μm or less.
The light diffusing material preferably further includes a second light diffusing material having a refractive index difference with respect to the refractive index of the translucent resin of more than 0.03 and 0.09 or less. The unevenness is preferably such that the local summit average interval S is 40 μm or less and the ten-point average roughness Rz is 4 μm or less.

  The surface light source device of the present invention includes a light source, a light guide having at least one light incident surface facing the light source, a light emitting surface substantially orthogonal to the light incident surface, and light emission of the light guide. It has the lens sheet on which the lens layer is arranged to face the surface.

  The liquid crystal display device of the present invention includes the surface light source device.

  According to the lens sheet of the present invention, it is possible to prevent a glare phenomenon while maintaining concealment and to increase the luminance and widen the viewing angle. According to the surface light source device of the present invention, it is possible to prevent the glare phenomenon while maintaining the concealability, and to increase the luminance and widen the viewing angle. According to the liquid crystal display device of the present invention, it is possible to prevent a glare phenomenon while maintaining concealment and to increase the luminance and widen the viewing angle.

It is a perspective view which shows the liquid crystal display device concerning embodiment of this invention. It is a fragmentary sectional view of the lens sheet concerning the embodiment of the present invention.

  An example of an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view showing a liquid crystal display device 10 using a lens sheet 50 of the present invention. FIG. 2 is a partial cross-sectional view showing an example of the lens sheet 50 of the present invention. In FIG. 1, the reflection sheet 30, the light guide 40, the lens sheet 50, and the liquid crystal panel 60 are illustrated separately from each other, but in actuality, they are in close contact with each other. In FIG. 2, the lens sheet 50 and the light guide 40 are illustrated separately from each other, but are actually in close contact with each other.

As shown in FIG. 1, the liquid crystal display device 10 includes a surface light source device 100 including a light source 20, a light source reflection sheet 22, a reflection sheet 30, a light guide 40, and a lens sheet 50, and a liquid crystal panel 60. It is configured.
The light source 20 is disposed such that the irradiation surface thereof faces the light incident surface 42 of the light guide 40, and the light source reflection sheet 22 is disposed so as to cover other than the irradiation surface of the light source 20. The reflection sheet 30 is disposed on the surface 44 side of the light guide 40. The lens sheet 50 is disposed so that the surface 52 on which the lens layer is formed faces the light emitting surface 46 of the light guide 40.
The liquid crystal panel 60 is disposed so that the incident surface 62 opposite to the observation surface 64 faces the surface 54 of the lens sheet 50.

(Lens sheet)
The lens sheet 50 will be described with reference to FIG. As shown in FIG. 2, the lens sheet 50 is provided with a light diffusion layer 53 having an uneven surface 54 formed on one surface of a translucent substrate 55. A lens layer 51 in which a plurality of lens rows 59 are formed in parallel at regular intervals is provided on the other surface of the translucent substrate 55. The surface of the lens layer 51 forms a surface 52.

<Light diffusion layer>
The light diffusion layer 53 is formed of a translucent resin 56 and a light diffusion material 57.
The translucent resin 56 can be used without particular limitation as long as it can disperse the light diffusing material 57, 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 considering the adhesiveness to the translucent base material 55 and the light diffusing material 57, and the use of an acrylic resin having a high transmittance is particularly preferable. As the acrylic resin, polymers such as hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, and acrylic acid are preferable. 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 a difunctional monomer of isocyanate and an isocyanate compound such as isocyanurate or melamine, etc. 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 56. Among these, by incorporating a leveling agent, aggregation of the light diffusing material 57 can be suppressed, and irregularities due to the light diffusing material 57 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 Big Chemie Japan Co., Ltd.

Examples of the light diffusing material 57 include inorganic particles such as glass, silica, talc, and barium sulfate. Examples of organic particles include crosslinked 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. The light diffusing material 57 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.
An example of the acrylic crosslinked particles is polymethyl methacrylate crosslinked particles containing 20 to 50% of a crosslinking agent. 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 57 can be appropriately selected and used regardless of the shape such as a sphere, an indeterminate shape, a bowl shape, a spheroid, or a needle shape.

  As a configuration of the light diffusing material 57, a refractive index difference (absolute value) Δn expressed by the following formula is 50% by volume or more of the light diffusing material 57 and the refractive index N 1 of the translucent resin 56. The first light diffusing material having a refractive index N2 of 0.005 or more and 0.03 or less, preferably 0.01 or more and 0.02 or less. This is because if Δn is less than 0.005, the glare phenomenon cannot be sufficiently prevented, and if it exceeds 0.03, a decrease in luminance or a decrease in concealment cannot be effectively prevented. Further, when the content of the first light diffusing material is less than 50% by volume, it is not possible to effectively prevent the glare phenomenon, the decrease in luminance and the decrease in concealability.

  Δn = | N1-N2 | (1)

The light diffusing material 57 has a particle diameter of 1 μm or more and 4 μm or less when the light diffusing material 57 is 50 volume% or more, preferably 60 volume% or more. As the particle size of the light diffusing material 57 is smaller, the effect of preventing the glare phenomenon is higher. When there are many light-diffusion materials 57 whose particle diameter is less than 1 micrometer, the transmitted light will color and it is unpreferable. On the other hand, it is not preferable that the number of the light diffusing material 57 having a particle diameter exceeding 4 μm is not possible because the glare phenomenon cannot be prevented. If the amount of the light diffusing material having a particle size of 1 μm or more and 4 μm or less in the light diffusing material 57 is less than 50% by volume, the effect of preventing the glare phenomenon may be insufficient.
The particle size in the present invention is a value calculated from the particle size distribution measured by various particle size distribution measuring devices. Examples of the particle size distribution measuring apparatus include COULTER MULTISIZER manufactured by Beckman Coulter.

  Further, the light diffusing material 57 has a refractive index difference (absolute value) Δn2 expressed by the following formula larger than 0.03 between the refractive index N1 of the translucent resin 56 expressed by the following formula. It is preferable that the 2nd light-diffusion material which has N3 used as 0.09 or less is contained. If Δn2 is 0.03 or less, the effect due to the addition of the second light diffusing material cannot be obtained, and if it exceeds 0.09, the refraction angle of transmitted light at the interface with the translucent resin increases. This is because the luminance in the front direction of the light source is reduced. The addition of the second light diffusing material can improve the color balance.

  Δn2 = | N1-N3 | (2)

The light diffusion layer 53 preferably has a haze of 40% or more and 95% or less, and more preferably 50% or more and 90% or less. If the haze is less than 40%, the light diffusing property of the light diffusing layer is insufficient, and therefore, when the lens sheet 50 is used in the liquid crystal display device 10, the viewing angle becomes narrow and the image becomes difficult to see. On the other hand, when the haze exceeds 95%, the luminance of the liquid crystal display device 10 is lowered, which is not preferable.
The haze is a value defined according to JIS-K7136 by using a haze meter (for example, product name: NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.) so that the light diffusion layer 53 faces the light receiving side.

Although the form of the surface 54 of the light-diffusion layer 53 is not specifically limited, It is preferable that the local peak top average space | interval S is 40 micrometers or less, More preferably, it is 35 micrometers or less, More preferably, it is 30 micrometers or less. This is because the glare phenomenon worsens when the thickness exceeds 40 μm. In addition, the local peak sum average space | interval S means the average of the distance of the vertex of an adjacent convex part.
Further, the surface 54 preferably has a ten-point average roughness Rz of 4 μm or less, and more preferably 3.5 μm or less. This is because the glare phenomenon worsens when Rz exceeds 4 μm. Further, from the viewpoint of preventing sticking with the liquid crystal panel, Rz is preferably 0.5 μm or more, and more preferably 1.0 μm or more.
The local peak-top average interval S and the ten-point average roughness Rz of the unevenness are measured according to JIS-B0601 using a surface roughness meter (for example, manufactured by Tokyo Seimitsu Co., Ltd., trade name: Surfcom 1500DX-3DF). Value.

  Content of the light-diffusion material 57 in the light-diffusion layer 53 is 10-70 mass%, and 15-65 mass% is preferable. If it is less than 10% by mass, the light transmitted without being refracted at the interface between the translucent resin 56 and the light diffusing material 57 may increase and concealment may decrease, and if it exceeds 70% by mass, the luminance may decrease. is there.

A plurality of fine particles such as the light diffusing material 57 may aggregate and aggregate in the coating liquid to form secondary particles. This aggregation is caused by differences in affinity due to differences in SP values (solubility parameters) between the light diffusing material 57, the translucent resin 56 and the solvent, the surface potential of the light diffusing material 57, and the viscosity of the dope during coating. The leveling time (the time from coating to drying) varies depending on the length of the leveling agent. The average local summit spacing S of the unevenness tends to increase as the aggregation in the coating film in-plane direction becomes significant. Further, the ten-point average roughness Rz of the concavo-convex surface tends to increase when the aggregation in the coating thickness direction becomes significant.
In the circular region of 70 μm radius at an arbitrary position of the light diffusion layer 53, the number of secondary particles having a major axis of 30 μm or more is 3 or less, preferably 2 or less, more preferably 1 or less. It is desirable to suppress the glare phenomenon. More preferably, the major axis of 20 μm or less is in the above number range. The planar shape of secondary particles formed by aggregating a plurality of light diffusing materials 57 is generally not circular. Therefore, the size of the secondary particles is represented by the major axis.
When the aggregated secondary particles are regarded as primary particles, this is the same as adding very large particles, and it is very important to suppress aggregation for the reasons described above.

  The thickness of the light diffusion layer 53 is not particularly limited, and is preferably determined in the range of 1 to 20 μm, for example. This is because the concealability decreases when the thickness is less than 1 μm, and the brightness decreases when the thickness exceeds 20 μm.

<Translucent substrate>
Although it does not specifically limit as the translucent base material 55, The thing which permeate | transmits an active energy ray is preferable, for example, acrylic resins, such as a polymethylmethacrylate, polycarbonate resin, polyester resins, such as a polyethylene terephthalate and a polyethylene naphthalate, diacetylcellulose, Cellulose resins such as 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, nylon and aromatic A film, a sheet, a plate, or the like made of a polyamide-based resin such as an aromatic polyamide, a vinyl chloride resin, or a polymethacrylimide resin can be used. In addition, other treatments such as antistatic, antireflection, and adhesion prevention between substrates can be performed.

Although the thickness of the translucent base material 55 is not specifically limited, For example, 10-500 micrometers is preferable, 20-400 micrometers is more preferable, and 30-300 micrometers is especially preferable from points, such as workability | operativity, such as intensity | strength and a handleability.
Further, the translucent substrate 55 may have a surface treatment portion for improving the adhesion with the lens layer 51. Examples of the surface treatment include those having easy adhesion made of polyester resin, acrylic resin, urethane resin, and the like. Further, the surface of the translucent substrate 55 may be roughened. Furthermore, an antistatic agent may be contained in the easy-adhesion layer as necessary, and the antistatic performance can be imparted to the lens sheet 50. Accordingly, when the lens sheet 50 is used in the liquid crystal display device 10, the lens sheet 50 and the liquid crystal panel 60, the light guide 40, and other members can be prevented from being adhered due to static electricity. It is for improving. In addition, foreign matter adsorption due to static electricity can be prevented in the manufacturing process, and the yield is improved.

<Lens layer>
The material of the lens layer 51 is not particularly limited, and is made of, for example, an active energy ray curable resin, and the refractive index is about 1.52 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, (meth) acrylate resins are particularly preferable from the viewpoint of optical characteristics and the like. The active energy ray-curable composition used for such a cured resin is a polyfunctional acrylate and / or a polyfunctional methacrylate (hereinafter referred to as polyfunctional (meth) acrylate) in terms of handleability and curability. , Monoacrylate and / or monomethacrylate (hereinafter referred to as mono (meth) acrylate), and a photopolymerization initiator by active energy rays are preferred. Typical polyfunctional (meth) acrylates include polyol poly (meth) acrylate, polyester poly (meth) acrylate, epoxy poly (meth) acrylate, urethane poly (meth) acrylate, and the like. These are used alone or as a mixture of two or more. Examples of mono (meth) acrylates include mono (meth) acrylates of monoalcohols and mono (meth) acrylates of polyols.

The lens array 59 formed in the lens layer 51 is not limited to a substantially triangular prism 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. A prism having a substantially triangular shape in cross section parallel to the XZ plane (FIG. 1) is particularly preferable.
When the lens array 59 is a prism, the apex angle θ (FIG. 2) of the prism is not particularly limited, but is preferably in the range of about 40 to 75 °, more preferably in the range of 45 to 70 °.
These prism surfaces may be optically sufficiently smooth surfaces (mirror surfaces) or rough surfaces. In the present invention, the prism surface is preferably a mirror surface from the viewpoint of maintaining desired optical characteristics by the prism sheet.
The pitch P (FIG. 2) for arranging the prisms is not particularly limited, but is preferably 10 to 500 μm, and more preferably 10 to 60 μm. The height of the prism is not particularly limited, but is preferably 5 to 70 μm.
By setting it as such a shape, the light radiate | emitted with the radiation | emission angle (alpha) from the light-projection surface 46 of the light guide 40 is aligned in the thickness direction of the lens sheet 50. FIG.

  The thickness of the lens layer 51 is not particularly limited, and is preferably determined according to the shape of the formed lens array 59 and the like, for example, preferably in the range of 10 to 80 μm.

(Light source and reflection sheet for light source)
The light source 20 is not particularly limited, and can be determined according to the desired surface light source device 100 and the liquid crystal display device 10. For example, it is possible to use a line light source in which a fluorescent lamp or a generation source is located at a distance.
The light source reflection sheet 22 that covers the light source 20 is not particularly limited as long as the loss of light from the light source 20 can be reduced and led to the light guide 40, and a plastic film or a diffusion material having a metal-deposited reflection layer on the surface. A contained plastic film or the like can be used.

(Reflective sheet)
The reflection sheet 30 is not particularly limited as long as it reflects the light emitted from the surface 44 of the light guide 40 and enters the light guide 40 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 30 is a white sheet containing a pigment. Examples of the pigment include titanium oxide, barium sulfate, calcium carbonate, and magnesium carbonate. Instead of the reflective sheet 30, a reflective layer may be formed on the surface 44 of the light guide 40 by metal vapor deposition or the like.
The thickness of the reflection sheet 30 is not specifically limited, For example, it is preferable to determine in the range of 30-300 micrometers.

(Light guide)
The light guide 40 can be composed 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, methacrylic resins are optimal because of their high light transmittance, heat resistance, mechanical properties, and molding processability. As such a methacrylic resin, it is resin which has methyl methacrylate as a main component, and the thing whose methyl methacrylate is 80 mass% or more is preferable.

(LCD panel)
The liquid crystal panel 60 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)
The manufacturing method of the lens sheet 50 is a method performed by apply | coating the coating liquid which has the light-diffusion material 57 and the translucent resin 56 on the surface of the translucent base material 55. FIG.
Below, an example of the manufacturing method of the lens sheet 50, the surface light source device 100, and the liquid crystal display device 10 is demonstrated.

First, the light diffusing material 57, the translucent resin 56, and other additives are added to and mixed with the dispersion medium to form a coating solution, and the coating solution is applied to one surface of the translucent substrate 55. As the dispersion medium, it is preferable to select a dispersion medium in which the light diffusing material 57 is dispersed and the translucent resin 56 is well dissolved, and is determined according to the type of the light dispersing material 57 and the translucent resin 56. 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 57 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 53 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 lens sheet 50 is not deteriorated. For example, the dispersion medium can be volatilized by heat treatment at 80 to 180 ° C.

Next, the lens array 59 is formed on the surface of the translucent substrate 55 opposite to the surface on which the light diffusion layer 53 is formed. The method for forming the lens array 59 is not particularly limited, and an existing method can be used. For example, a known hot press method or a roll-shaped mold in which the shape of the lens array 59 is engraved is filled with an active energy ray-curable resin, and then covered with a translucent substrate 55 via a resin liquid, ultraviolet rays, etc. The method of continuously manufacturing the translucent substrate 55 provided with the lens layer 51, the resin liquid being poured into a mold corresponding to the shape of the lens array 59, and the translucent substrate 55 The method of manufacturing the translucent base material 55 in which the lens layer 51 was provided by a batch system by laminating | stacking on is mentioned.
In this way, the lens sheet 50 can be obtained. The manufacturing method of the lens sheet 50 is not limited to the above. For example, after the lens row 59 is formed on one surface of the translucent substrate 55, the light diffusion layer 53 is formed on the other surface of the translucent substrate 55. May be formed.

  Using the lens sheet 50 obtained as described above, the reflective sheet 30, the light guide 40, and the lens sheet 50 are placed in this order as shown in FIG. The surface light source device 100 can be obtained by disposing the light source reflection sheet 22. Further, the liquid crystal panel 60 is mounted so that the surface 54 of the surface light source device 100 on the light diffusion layer 53 side of the lens sheet 50 and the incident surface 62 of the liquid crystal panel 60 face each other, whereby the liquid crystal display device 100 is placed. Obtainable.

  According to the lens sheet of the present invention, 50 volume% or more of the light diffusing material of the light diffusing layer is the first light diffusing material, and 50 volume% or more of the light diffusing material is 1 μm or more and 4 μm or less in particle diameter. Thus, the glare phenomenon can be prevented while maintaining the concealment property, and the viewing angle can be widened by increasing the luminance. Furthermore, by adding the second light diffusing material, the color tone of light can be prevented from becoming yellow, and the color tone balance can be improved. In addition, the effect of preventing the glare phenomenon can be further improved by setting the local peak-top average interval S of the irregularities on the surface of the light diffusion layer to 40 μm or less and Rz to 4 μm or less.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, it is not limited to an Example.
The compounds used in the examples are abbreviated as follows.
Methyl ethyl ketone: MEK
Methyl methacrylate: MMA
Ethyl acrylate: EA
2-Hydroxyethyl methacrylate: HEMA
Acrylic 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 the reaction vessel was held for 4 hours, and then cooled to room temperature to complete the reaction, whereby an acrylic resin A solution was obtained.
The molecular weight of the acrylic resin A is MW = 75,100, the hydroxyl value is 21.6 mgKOH / g, the acid value is 2.1 mgKOH / g, Tg is 61 ° C., and the heating residue of the acrylic resin A solution is 36.0% by mass. there were.

The volume ratio of the light diffusing material used in Examples and the particles having a particle diameter of 1 to 4 μm in each light diffusing material is shown below.
(1) Techpolymer development product XX-78B (acrylic-styrene resin fine particles): ratio of 1 to 4 μm particles; 99.0% by volume
(2) Techpolymer development product XX-79B (acrylic-styrene resin fine particles): ratio of 1 to 4 μm particles; 99.2% by volume
(3) Techpolymer development product XX-80B (acrylic-styrene resin fine particles): ratio of 1-4 μm particles; 99.2% by volume
(4) Techpolymer SSX-103 (acrylic resin fine particles): ratio of 1-4 μm particles; 96.4% by volume
(5) Techpolymer development product XX-74B (acrylic-styrene resin fine particles): ratio of 1-4 μm particles; 0.7% by volume
(6) Techpolymer development product XX-38B (acrylic resin fine particles): ratio of 1-4 μm particles; 0.7% by volume
(7) Techpolymer development product XX-95B (acrylic-styrene resin fine particles): ratio of 1-4 μm particles; 1 vol%
The particle size distribution measurements (1) to (7) above are based on COULTER MULTISIZER (manufactured by Beckman Coulter, Inc.).
(8) Tospearl 145 (silicone resin fine particles): ratio of 1 to 4 μm particles; 25.4% by volume
The particle size distribution measurement of the above (8) is based on a particle size distribution measuring apparatus (CAPA-700, manufactured by Horiba, Ltd.).

Example 1
A lens sheet, a surface light source device, and a liquid crystal display device similar to those shown in FIGS. 1 and 2 were produced as follows.
A 188 μm thick PET film (manufactured by Toyobo Co., Ltd., trade name: A4300) was used as the translucent substrate.
To 201 parts by mass of the acrylic resin A solution obtained in Preparation Example 1, acrylic-styrene resin fine particles (Sekisui) having a refractive index of 1.51, a volume average particle diameter of 2.5 μm, and a true specific gravity of 1.20 as a first light diffusing material. 22.0 parts by mass of Kasei Chemical Industries, Ltd., techpolymer development product XX-78B) and 5.6 parts by mass of Duranate TPA-100 (manufactured by Asahi Kasei Chemicals Corporation) as a cross-linking agent are weighed in a container and stirred with a stirring blade. As a result, a coating liquid A for forming a light diffusing layer in which the light diffusing material was uniformly dispersed was produced. The total solid content of this coating liquid A is 28% by mass, and the ratio of the diffusing material to the total solid content is 22% by mass.

The mass ratio of the acrylic resin A and the crosslinking agent in the solid content is acrylic resin A solid content: crosslinking agent solid content = 92.8: 7.2. That is, the refractive index N1 of the translucent resin layer is 1.495. Therefore, the refractive index difference Δn between the translucent resin and the light diffusing material is 0.015.
Using the reverse gravure coating method, the coating liquid A was applied onto the PET film so that the average thickness after solvent drying was 7 μm and dried. Thereby, the laminated body A which has the light-diffusion layer with the uneven structure based on a light-diffusion material on the single side | surface of PET film was obtained.
The content of the light diffusing material in the formed light diffusing layer is 22% by mass, the content of the first light diffusing material in the light diffusing material is 100% by volume, and the particle diameter 1 occupied in the light diffusing material is 1%. The ratio of the amount of the light diffusing material of ˜4 μm is 99.0% by volume from the added amount ratio of the light diffusing material.

The appearance of the obtained laminate A was very good with no generation of coating spots such as streaks.
About a light-diffusion layer, it attached so that a light-diffusion layer might face the light-receiving side using a haze meter (the Nippon Denshoku Industries Co., Ltd. make, brand name: NDH2000), total light transmittance (JIS-K7316) Tt, and haze ( JIS-K7136) was measured. As a result, the total light transmittance was 94.9%, and the haze was 63.7%.

  Using a surface roughness meter (trade name Surfcom 1400LCD, manufactured by Tokyo Seimitsu Co., Ltd.), 1 μm, using the surface roughness meter (Tokyo Seimitsu Co., Ltd., trade name Surfcom 1400LCD) (JIS-B0601-1994). As a result, the local summit average interval S was 24 μm, and the ten-point average roughness Rz was 1.5 μm.

  The aggregation state of the light diffusing material in the light diffusion layer of the laminate A was observed with transmitted light at a magnification of 500 times using an optical microscope (manufactured by Olympus Corporation, trade name: MX61L). As a result, the maximum number of secondary particles having a major axis of 30 μm or more in a circular region having a radius of 70 μm of an arbitrary area on the surface of the light diffusion layer was one.

A shape transfer surface having a shape 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 θ = 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 A was supplied along the roll mold between the roll mold and the rubber roll, and the translucent base material 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 to the surface to which the light-diffusing layer was provided of the translucent base material niped by a rubber roll into a roll mold. 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, the lens sheet A was obtained by releasing from the roll mold. The obtained lens sheet A was evaluated for luminance, glare phenomenon, color tone, and concealment according to the evaluation method described later, and the results are shown in Table 1.

(Example 2)
As a light diffusing material, tech-polymer developed product XX-79B as a first light diffusing material (acrylic-styrene resin fine particles, refractive index: 1.52, volume average particle diameter: 2.5 μm, true specific gravity 1.20, water storage A light diffusion layer having a thickness of 7 μm is formed on a PET film in the same manner as in Example 1 except that the total solid content in the coating solution is 22% by mass. As a result, a laminate B was formed. The appearance of the obtained laminate B was very good with no occurrence of coating spots such as streaks. The content of the light diffusing material in the light diffusing layer of the laminate B is 20% by mass, and the content of the first light diffusing material in the light diffusing material is 100% by volume,
The ratio of the amount of the light diffusing material having a particle diameter of 1 to 4 μm in the total amount of the light diffusing material was 99.2% by volume.
Similarly to Example 1, the local peak-top average interval S, ten-point average roughness Rz, and haze on the surface of the light diffusion layer of the laminate B were measured, and the results are shown in Table 1.
In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
Next, a lens array was formed on the surface of the laminate B opposite to the light diffusion layer in the same manner as in Example 1 to obtain a lens sheet B. With respect to the obtained lens sheet B, evaluation of luminance, glare phenomenon, and concealment was performed according to an evaluation method described later, and the results are shown in Table 1.

(Example 3)
As the light diffusing material, 16.4 parts by mass of XX-78B as the first light diffusing material, Tospearl 145 as the second light diffusing material (silicone resin, refractive index: 1.42, volume average particle diameter: 4.5 μm) , Momentive Performance Materials Japan G.K.), the first light diffusing material is 16.4% by mass and the second diffusing material is 4.1% by mass with respect to the total solid content in the coating liquid. Except that it was prepared as described above, a laminate C in which a light diffusion layer having a thickness of 7 μm was formed was obtained in the same manner as in Example 1. The content of the light diffusion material in the light diffusion layer of the obtained laminate C is 20.5% by mass, the content of the first light diffusion material in the light diffusion material is 80% by volume, and the second light diffusion. The content of the material was 20% by volume, and the ratio of the amount of the light diffusing material having a particle diameter of 1 to 4 μm in the total amount of the light diffusing material was 80.8% by volume.
As in Example 1, Table 1 shows the results of measuring the local peak-top average distance S, ten-point average roughness Rz, and haze on the surface of the light diffusion layer of the laminate C. In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
A lens row was formed on the surface of the laminate C opposite to the light diffusion layer in the same manner as in Example 1 to obtain a lens sheet C. With respect to the obtained lens sheet C, evaluation of luminance, glare phenomenon, color tone, and concealment was performed according to an evaluation method described later, and the results are shown in Table 1.

Example 4
A laminate D was obtained in the same manner as in Example 3 except that the thickness of the light diffusion layer was 10 μm. The content of the light diffusion material in the light diffusion layer of the obtained laminate D is 23% by mass, the content of the first light diffusion material in the light diffusion material is 80% by volume, The content was 20% by volume, and the ratio of the amount of the light diffusing material having a particle diameter of 1 to 4 μm in the total amount of the light diffusing material was 80.8% by volume. Further, as in Example 1, Table 1 shows the results of measuring the local peak-top average distance S, the ten-point average roughness Rz, and the haze on the surface of the light diffusion layer of the laminate D. In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
A lens array was formed on the surface of the laminate D opposite to the light diffusion layer in the same manner as in Example 1 to obtain a lens sheet D. With respect to the obtained lens sheet D, evaluation of luminance, glare phenomenon, and concealment is performed according to an evaluation method described later, and the results are shown in Table 1.

(Example 5)
As the light diffusing material, XX-78B as the first light diffusing material, and XX-38B as the other light diffusing material (acrylic resin fine particles, refractive index: 1.495, volume average particle diameter: 10 μm, true specific gravity 1.20, Sekisui Kasei Kogyo Co., Ltd.), so that the first light diffusing material is 22.6% by mass and the other light diffusing material is 1.4% by mass with respect to the total solid content in the coating liquid. Except having prepared, it carried out similarly to Example 1, and obtained the laminated body E with which the 4.5-micrometer-thick light-diffusion layer was formed in PET film. The appearance of the obtained laminate E was very good with no generation of coating spots such as streaks. The content of the light diffusing material in the light diffusing layer of the laminate E is 24% by mass, the content of the first light diffusing material in the light diffusing material is 94% by volume, and occupies the total amount of the light diffusing material. The ratio of the amount of the light diffusing material having a particle diameter of 1 to 4 μm was 93.1% by volume. Similar to Example 1, Table 1 shows the results of measuring the local peak-top average distance S, the ten-point average roughness Rz, and the haze on the surface of the light diffusion layer of the laminate E. In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
A lens row was formed on the surface of the laminate E opposite to the light diffusion layer in the same manner as in Example 1 to obtain a lens sheet E. The obtained lens sheet E was evaluated for luminance, glare phenomenon, and concealment according to an evaluation method described later, and the results are shown in Table 1.

(Comparative Example 1)
XX-80B (acrylic-styrene resin fine particles, refractive index: 1.53, volume average particle diameter: 2.5 μm, true specific gravity 1.20, manufactured by Sekisui Plastics Co., Ltd.) is used as a light diffusing material, and coating is performed. Except having prepared so that it might become 17 mass% with respect to the total solid in a liquid, it carried out similarly to Example 1, and obtained the laminated body F of thickness 7 micrometers.
The content of the light diffusing material in the light diffusing layer of the obtained laminate F is 17% by mass, the content of the first light diffusing material in the light diffusing material is 0% by volume, and the total light diffusing material. The ratio of the amount of the light diffusing material having a particle diameter of 1 to 4 μm in the amount was 99.2% by volume. Similar to Example 1, Table 1 shows the results of measuring the local peak-top average distance S, the ten-point average roughness Rz, and the haze on the surface of the light diffusion layer of the laminate F. In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
The laminated lens F was used in the same manner as in Example 1, and the obtained lens sheet F was evaluated for luminance, glare phenomenon, and concealment according to an evaluation method described later. The results are shown in Table 1.
In Table 1, the Δn term describes the difference in refractive index between the translucent resin and XX-80B.

(Comparative Example 2)
As the light diffusing material, techpolymer SSX-103 (acrylic resin fine particles, refractive index: 1.495, volume average particle diameter: 3.0 μm, true specific gravity 1.20, manufactured by Sekisui Plastics Co., Ltd.) is used for coating. Except having prepared so that it might become 19 mass% with respect to the total solid content in a liquid, it carried out similarly to Example 1, and obtained the laminated body G of 7 micrometers in thickness. The content of the light diffusing material in the light diffusing layer of the obtained laminate G is 19% by mass, the content of the first light diffusing material in the light diffusing material is 0% by volume, and the light diffusing material. The light diffusing material having a particle diameter of 1 to 4 μm was 96.4% by volume. Similar to Example 1, Table 1 shows the results of measuring the local peak-top average distance S, the ten-point average roughness Rz, and the haze on the surface of the light diffusion layer of the laminate G. In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
With respect to the lens sheet G obtained in the same manner as in Example 1 using the laminate G, evaluation of luminance, glare phenomenon, and concealment is performed according to an evaluation method described later, and the results are shown in Table 1.
In Table 1, the term Δn describes the difference in refractive index between the translucent resin and the techpolymer SSX-103.

(Comparative Example 3)
XX-74B (acrylic-styrene resin fine particles, refractive index: 1.525, volume average particle size: 6.5 μm, manufactured by Sekisui Plastics Co., Ltd.) is used as the light diffusing material, and the total solid content in the coating liquid A laminate H having a thickness of 7 μm was obtained in the same manner as in Example 1 except that the content was adjusted to 13% by mass. The content of the light diffusion material in the light diffusion layer of the obtained laminate H is 13% by mass, the content of the first light diffusion material in the light diffusion material is 100% by volume, and the light diffusion material The light diffusing material having a particle diameter of 1 to 4 μm was 0.7% by volume. Similar to Example 1, Table 1 shows the results of measuring the local peak-top average distance S, the ten-point average roughness Rz, and the haze on the surface of the light diffusion layer of the laminate H. In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
With respect to the lens sheet H obtained in the same manner as in Example 1 using the laminate H, evaluation of luminance, glare phenomenon, and concealment was performed according to an evaluation method described later, and the results are shown in Table 1.

(Comparative Example 4)
As a light diffusing material, XX-95B (acrylic-styrene resin fine particles, refractive index: 1.545, volume average particle diameter: 5 μm, true specific gravity 1.20, manufactured by Sekisui Plastics Co., Ltd.) and XX-38B PET was used in the same manner as in Example 1 except that XX-95B was adjusted to 17.3% by mass and XX-38B to 0.7% by mass with respect to the total solid content in the coating liquid. A laminate I having a 4.5 μm thick light diffusion layer formed on the film was obtained. The appearance of the obtained laminate I was very good with no generation of coating spots such as streaks. The content of the light diffusing material in the light diffusing layer of the laminate I is 18% by mass, the content of the first light diffusing material in the light diffusing material is 0% by volume, and occupies the total amount of the light diffusing material. The ratio of the amount of the light diffusing material having a particle diameter of 1 to 4 μm was 0.17% by volume. As in Example 1, Table 1 shows the results of measuring the local peak-top average distance S, ten-point average roughness Rz, and haze on the surface of the light diffusing layer of the laminate I. In addition, when the aggregation of particles having a major axis of 30 μm or more in an arbitrary region having a radius of 70 μm of the light diffusion layer was measured, it was 1 or less. From this, it was confirmed that a good light diffusion layer without secondary aggregation of the light diffusion material was formed.
The lens sheet I obtained using the laminate I in the same manner as in Example 1 was evaluated for luminance, glare phenomenon, and concealment according to the evaluation method described later. The results are shown in Table 1.
In Table 1, in the term of Δn, the refractive index difference between the translucent resin and XX-95B is described.

(Evaluation methods)
Using the lens sheets A to I obtained in Examples and Comparative Examples, evaluation of luminance, evaluation of glare phenomenon, hiding property, and evaluation of color tone were performed as described below.
Each prism sheet is cut into a 14.1 W (wide) size, and this is formed on the light emitting surface of a 14.1 W (wide) size acrylic resin light guide having a cold cathode tube arranged on the side surface. As shown in FIG. 2, the prism row forming surface was placed so as to face the acrylic resin light guide, and the other side surface and the back surface were covered with a reflection sheet to obtain a surface light source device.
The color tone was evaluated only in Examples 1 and 3 in order to see the effect of adding the second light diffusing material. For the evaluation of the color tone, the measurement was performed without incorporating the lens sheets A and C into the liquid crystal display device.

<Evaluation of brightness>
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. The normal luminance and half-value angle were measured with the center on the effective screen as the luminance measurement region.

<Evaluation of glare phenomenon>
A transmissive liquid crystal panel was placed on the prism sheet of the surface light source device. This liquid crystal panel had a 60 ° gloss value of 48.6 on the observation surface measured with a gloss meter (trade name: VGS-300A, manufactured by Nippon Denshoku Industries Co., Ltd.) and a 60 ° gloss value of 31.2 on the incident surface. The size was 14.1 W (wide) liquid crystal panel with the number of pixels XGA. In this liquid crystal display device, the surface light source device was caused to emit light, a white image was displayed on the liquid crystal panel, and the glare was visually observed.
The evaluation criteria for glare are as follows.
○ ・ ・ ・ There is almost no glare phenomenon, and it is easy to see with a very smooth texture. △ ・ ・ ・ A glare phenomenon can be confirmed, and it is a little difficult to see. × ・ ・ ・ The glare phenomenon is very conspicuous. Hard to see images

<Evaluation of color tone>
The light transmittance according to wavelength was measured for the lens sheets A and C using a spectrophotometer (manufactured by Hitachi, Ltd., U-3500). In the light transmittance by wavelength, color tone a = (average transmittance of 450 to 500 nm) / (average transmittance of 700 to 750 nm), and color tone b = (average transmittance of 550 to 600 nm) / (700 to 750 nm) Average transmittance). It can be determined that the closer the color tones a and b are to 100%, the better the tone balance.

<Evaluation of concealment>
The hiding property was evaluated by the image clarity. The image clarity was measured in a transmission measurement mode using a image clarity evaluation apparatus (manufactured by Suga Test Instruments Co., Ltd., model: ICM-1DP) using an optical comb of 0.125 mm (JIS-K7105). Since the image clarity value in the absence of the sample is 96 or more, it can be evaluated that the lower the image clarity value, the higher the concealability. An image clarity value of 25 or less was evaluated as having excellent concealability.

As shown in Table 1, the content of the first light diffusing material in the light diffusing material is 50% by volume or more, and the light diffusing material having a mass average particle diameter of 1 to 4 μm in the light diffusing material is 50 volumes. In Examples 1 to 5 containing at least%, the glare phenomenon could be prevented. Further, the image clarity value indicating the concealing property is 25 or less, which indicates that the concealing property is excellent. Furthermore, in Examples 1-5, it turned out that the brightness | luminance required for the liquid crystal display device whose brightness | luminance is 2500 Cd / m < ² > or more is maintained, and a wide viewing angle is obtained. In particular, in Example 5, since the half-value angle was 22.3 °, it was found that it could be used for a wide viewing angle type liquid crystal display device.
On the other hand, in Comparative Example 1 in which only the light diffusing material having Δn of 0.035 was used, the luminance was lowered and the concealability was poor. Moreover, the comparative example 2 which used the light-diffusion material of the same refractive index as the translucent resin of a light-diffusion layer, and the comparative example 3 whose light-diffusion material with a mass mean particle diameter of 1-4 micrometers was 0.7 volume%. In either case, the glare phenomenon could not be prevented. In addition, even in Comparative Example 4 in which a light diffusing material having Δn of 0.05 and a light diffusing material having Δn of 0 were combined, the glare phenomenon could not be prevented.
Furthermore, in Example 3 to which the second light diffusing material was added, the color tone a was 99.7%, the color tone b was 99.8%, and the difference was 0.1 point. In Example 1, the color tone a was 99.3%, the color tone b was 99.9%, and the difference was 0.6 points. From this result, it was found that the difference between the color tone a and the color tone b is reduced by adding the second light diffusing material, that is, the color tone balance can be improved.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 20 Light source 40 Light guide 42 Light incident surface 46 Light output surface 50 Lens sheet 51 Lens layer 53 Light diffusion layer 56 Translucent resin 57 Light diffusion material

Claims (5)

On one surface of the translucent substrate, it has a lens layer in which a lens array is formed,
On the other surface, it has a light diffusing layer with an uneven surface,
The light diffusion layer has a light diffusion material and a translucent resin,
The content of the light diffusing material in the light diffusing layer is 10% by mass or more and 70% by mass or less,
50% by volume or more of the light diffusing material is a first light diffusing material having a refractive index difference of 0.005 or more and 0.03 or less with respect to the refractive index of the translucent resin,
And 50 volume% or more of the said light-diffusion material is a lens sheet whose particle diameter is 1 micrometer or more and 4 micrometers or less.   The said light-diffusion material further has the 2nd light-diffusion material whose refractive index difference with the refractive index of the said translucent resin is 0.03 or more and 0.09 or less. The lens sheet described in 1.   3. The lens sheet according to claim 1, wherein the unevenness on the surface of the light diffusion layer has a local peak-top average interval S of 40 μm or less and a ten-point average roughness Rz of 4 μm or less. A light source;
A light guide having at least one light incident surface facing the light source, and a light exit surface substantially orthogonal to the light incident surface;
The surface light source device which has the lens sheet of any one of Claims 1-3 with which the said lens layer was arrange | positioned facing the light-projection surface of the said light guide.   A liquid crystal display device comprising the surface light source device according to claim 4.

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