JP2016095380A - Light-diffusive member and backlight unit having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-diffusive member to be incorporated in backlight units, which exhibits improved light transmissivity (brightness) and light-diffusivity (haze) and minimizes development of scars, especially pressed scars and abrasion scars, on a light guide plate.SOLUTION: A light diffusive member has a first layer on one surface of a support body, and a second layer on the other surface of the support body. The first layer and second layer contains a binder resin and light-diffusive particles, where the first layer contains 50-150 pts.wt., inclusive, of the light-diffusive particles per 100 pts.wt. of the binder resin, and the second layer contains 20-40 pts.wt., inclusive, of nylon particles as the light-diffusive particles per 100 pts.wt. of the binder resin.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light diffusing member used in a backlight unit such as a liquid crystal display device.

  The backlight unit is widely used in color liquid crystal display devices such as personal computers, tablet terminals, mobile phones, PDAs (Personal Digital Assistants), navigation devices, and game machines. The backlight unit includes a direct type in which a light source is arranged directly below the display surface and emits light to the display surface side through a diffusion plate, and a light guide plate in which the light source is arranged in parallel with the display surface of the display device There is an edge light type which is arranged on the side surface and emits light from the light guide plate. In either case, a light diffusing sheet for making the light from the light source uniform and a prism sheet for increasing the front luminance are arranged on the light emitting surface of the diffusing plate or the light guide plate.

  In recent years, in the fields of tablet terminals, mobile phones, and the like, higher-definition images can be visually recognized, and the pixels of liquid crystal cells provided in liquid crystal display devices tend to become smaller. As the pixels become smaller, the transmittance from the light source decreases and the front luminance also decreases.

  In order to improve the decrease in front luminance, proposals have been made such as using a material having a high refractive index as the prism sheet. As for the light diffusive sheet used in combination with the prism sheet, research on a light diffusive sheet suitable for such a high refractive index material has been conducted. For example, Patent Document 1 discloses a light diffusing sheet in which light diffusing layers are provided on both sides of a transparent sheet to improve light diffusibility and to increase brightness.

  Further, in the edge light type backlight unit, the light diffusive sheet is used in close contact with the light guide plate, so that sticking to the light guide plate is prevented or the light diffusive sheet is guided by contacting the light guide plate. In order to prevent scratches generated on the light plate, it has been proposed to provide a sticking prevention layer or a backcoat layer on the surface of the light diffusive sheet that contacts the light guide plate (Patent Documents 2, 3, etc.).

JP 2007-133173 A Japanese Patent No. 4488597 JP 2012-230364 A

  The light diffusing sheet provided with the light diffusing layer on both sides described in Patent Document 1 and the like has a trade-off relationship between luminance improvement and light diffusing property compared to the light diffusing sheet provided with the light diffusing layer only on one side ( Although improvement of haze) is improved, the point of preventing damage to the light guide plate is not taken into consideration, and a problem remains.

  On the other hand, in the techniques described in Patent Documents 2 and 3, etc., the layer provided on the opposite side of the light diffusion layer contains particles that do not affect the optical characteristics, and contributes to the improvement of the light diffusion property. do not do.

  Further, according to the study by the present inventors, the light diffusing layer can damage the light guide plate roughly in two. One is a pressure flaw caused by pressurization at the time of close contact, and the other is a scratch. It is a wear scar that occurs when fitting. Although the back coat layer using the elastic silicone particles described in Patent Document 2 is considered to be effective for pressure flaws, a satisfactory effect for suppressing wear flaws has not been obtained.

  It is an object of the present invention to suppress the occurrence of scratches on the light guide plate, particularly both pressure scratches and wear scratches, while improving both light transmittance (luminance) and light diffusibility (haze).

  In order to solve the above problems, the present inventors have arranged a layer having light diffusibility on both sides of the light diffusive sheet, and the type, content and balance of both sides of the light diffusing material contained in these layers. As a result of diligent research on the light guide plate, the content of the light diffusing material is made different between the layers on both sides, and nylon particles are used as the light diffusing material contained in the layer on the back surface (the surface facing the light guide plate). It is possible to suppress the occurrence of both pressure flaws and wear flaws, and to increase the haze while maintaining high luminance by making the particle size of the light diffusing material contained in the light diffusing layers on both sides into a specific range, respectively. The present inventors have found out what can be done and have arrived at the present invention.

  That is, the light diffusing member of the present invention is a light diffusing member having a first layer on one side of a support and a second layer on the other side of the support, And the second layer contains a binder resin and light diffusing particles, and the first layer contains 50 parts by weight or more and 150 parts by weight or less of the light diffusing particles with respect to 100 parts by weight of the binder resin. The second layer contains nylon particles as the light diffusing particles in an amount of 20 to 40 parts by weight with respect to 100 parts by weight of the binder resin.

  The backlight unit of the present invention includes a light guide plate, a light diffusing member placed on the light guide plate, and a prism sheet placed on the light diffusing member, The light diffusing member of the present invention is characterized in that the second layer is disposed so as to be in contact with the light guide plate.

  The light diffusing member of the present invention is a sheet-like material having a small thickness, and is a material in a category different from that of a light diffusing plate having a thickness exceeding 1 mm.

  According to the light diffusing member of the present invention, the light diffusing layers are arranged on both sides, so that the light diffused by the light diffusing layer on the light incident side is further diffused by the light diffusing layer on the light emitting side. The light diffusion function can be enhanced. In addition, since high light diffusibility can be obtained, the total thickness of the light diffusing layer including both light diffusing layers can be reduced, and the reduction in the amount of light transmitted through the light diffusing layer can be reduced. The luminance when used can be improved.

  Further, according to the light diffusing member of the present invention, when the layer (second layer) on the side in contact with the light guide plate when incorporated in the backlight unit contains a predetermined amount of nylon particles, the nylon particles have a resistance to resistance. In addition to wear and scratch resistance, pressure scratch resistance can be imparted.

  Conventionally, there is an example in which nylon particles are added to a backcoat layer for imparting scratch resistance. However, an amount added to the backcoat layer usually provides an abrasion scratch prevention effect, but a pressure scratch prevention effect cannot be obtained. . On the other hand, elastic silicone particles are considered to have an effect of preventing pressure flaws, and in order to prevent wear flaws and pressure flaws, it is conceivable to use nylon particles and silicone particles in combination. However, silicone particles easily fall off the layer when the amount of added particles is large. In the present invention, by using a relatively large amount of nylon particles, an unexpected pressure flaw prevention effect can be obtained, and there is no dropout from the layer, and it can contribute to an improvement in light diffusivity without impairing light transmittance. .

Sectional drawing which shows the light diffusable member of this invention typically Sectional drawing which shows the backlight unit of this invention typically

Hereinafter, embodiments of the light diffusing member of the present invention will be described.
As schematically shown in FIG. 1, the light diffusing member of the present invention includes a support 20, a first layer (hereinafter referred to as a first light diffusion layer) 21 provided on both sides of the support 10, and And a second layer (hereinafter referred to as a second light diffusion layer) 22. The first light diffusion layer 21 and the second light diffusion layer 22 each include a binder resin and light diffusing particles. In the following description, the first light diffusion layer 21 and the second light diffusion layer 22 are collectively referred to as a light diffusion layer as appropriate.

  The support 20 can be used without particular limitation as long as it is a plastic film having high optical transparency. For example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polystyrene, triacetyl cellulose, acrylic, polyvinyl chloride, norbornene compound and the like can be used. Of these, a stretched polyethylene terephthalate film, particularly a biaxially stretched film, is preferred because of its excellent mechanical strength and dimensional stability.

  The support 20 can be subjected to a corona discharge treatment on its surface or an easy-adhesion layer in order to improve the adhesion with the light diffusion layers 21 and 22. The easy-adhesion layer is a material that enhances the adhesion between the material of the support 20 and the binder resin that constitutes the light diffusion layers 21 and 22. For example, the support 20 is a polyethylene terephthalate film, and the binder resin of the light diffusion layer is In the case of an acrylic resin, polyurethane or the like is used. In addition, it is preferable that the thickness of a support body is about 10-400 micrometers normally.

  Since the materials of the binder resin constituting the first light diffusion layer 21 and the second light diffusion layer 22 are common, they will be described together.

  The binder resin is made of a polymer material having high optical transparency like the support. Any of known ionizing radiation curable resins, thermosetting resins, thermoplastic resins and the like can be used.

  As the ionizing radiation curable resin, a photopolymerizable prepolymer that can be crosslinked and cured by irradiation with ionizing radiation (ultraviolet ray or electron beam) can be used. An acrylic prepolymer having at least one acryloyl group and having a three-dimensional network structure by crosslinking and curing is particularly preferably used. As the acrylic prepolymer, urethane acrylate, polyester acrylate, epoxy acrylate, melamine acrylate, polyfluoroalkyl acrylate, silicone acrylate and the like can be used. Furthermore, these acrylic prepolymers can be used alone, but it is preferable to add a photopolymerizable monomer in order to improve the cross-linking curability and further improve the hardness of the light diffusion layer.

  As photopolymerizable monomers, monofunctional acrylic monomers such as 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, butoxyethyl acrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol One kind of bifunctional acrylic monomer such as diacrylate, polyethylene glycol diacrylate, hydroxypivalate ester neopentyl glycol diacrylate, etc., or polyfunctional acrylic monomer such as dipentaerythritol hexaacrylate, trimethylpropane triacrylate, pentaerythritol triacrylate or the like Two or more are used.

  In addition to the above-described photopolymerizable prepolymer and photopolymerizable monomer, it is preferable to use additives such as a photopolymerization initiator and a photopolymerization accelerator when curing by ultraviolet irradiation.

  Examples of the photopolymerization initiator include acetophenone, benzophenone, Michler's ketone, benzoin, benzylmethyl ketal, benzoylbenzoate, α-acyloxime ester, thioxanthone and the like.

  Further, the photopolymerization accelerator is capable of reducing the polymerization obstacle due to air at the time of curing and increasing the curing speed. For example, p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester, etc. Can be mentioned.

  Thermosetting resins include silicone resins, phenolic resins, urea resins, melamine resins, furan resins, unsaturated polyester resins, epoxy resins, diallyl phthalate resins, guanamine resins, ketone resins, Examples include amino alkyd resins, urethane resins, acrylic resins, and polycarbonate resins. These can be used alone, but it is desirable to add a curing agent in order to further improve the crosslinkability and the hardness of the crosslinked cured coating film.

  As the curing agent, a compound such as polyisocyanate, amino resin, epoxy resin, or carboxylic acid can be appropriately used in accordance with a suitable resin.

  As thermoplastic resins, ABS resin, norbornene resin, silicone resin, nylon resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, polybutylene terephthalate, polyethylene terephthalate, sulfone resin, imide resin, fluorine resin Resin, styrene resin, acrylic resin, vinyl chloride resin, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer resin, polyester resin, urethane resin, nylon resin, rubber resin, polyvinyl ether, polyvinyl Examples include alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and polyethylene glycol.

  Of these thermosetting resins or thermoplastic resins, acrylic resin thermosetting resins or thermoplastic resins are used from the viewpoint of obtaining coating strength when the light diffusing layer is used and good transparency. It is preferable. Moreover, these thermosetting resins or thermoplastic resins can also be used as thermosetting resins or composite resins in which a plurality of types of thermoplastic resins are combined.

  The binder resin may be the same or different between the first light diffusion layer 21 and the second light diffusion layer 22. However, it is preferable to select a material in consideration of “warping” that may occur in the light diffusing member described later.

  As the light diffusing particles contained in the first light diffusing layer 21, organic particles or inorganic particles generally used as a light diffusing material can be used, but organic particles having excellent transparency and optical properties are suitable. Specific examples of organic particles include (meth) acrylic resins such as poly (meth) acrylate, styrene resins, amino resins such as melamine and benzoguanamine, polyurethane resins, polyester resins, silicone resins, and fluorine resins. And synthetic resin particles. These synthetic resin particles can be used alone or in admixture of two or more.

  When the light diffusing member of the present invention is used in a backlight unit, the first light diffusing layer 21 is preferably a layer on the light emitting side, and has a surface shape and a haze that can provide good light emitting characteristics. It is preferable. Specifically, the surface shape is preferably 0.2 to 1.0 μm in terms of average surface roughness Ra. Moreover, it is preferable that haze is adjusted so that it may become 85 to 95% in the state which provided the 2nd light-diffusion layer.

  In order to obtain such optical characteristics, the average particle diameter of the light diffusing particles contained in the first light diffusion layer 21 is preferably 1 to 5 μm, more preferably 2 to 4 μm, although it depends on the thickness of the layer. is there.

  Further, the content of light diffusing particles (phr: per hindered resin) in the first light diffusion layer 21 is preferably 50 parts by weight or more, more preferably 70 parts by weight or more with respect to 100 parts by weight of the binder resin. Moreover, 150 weight part or less is preferable with respect to 100 weight part of binder resin, and 120 weight part or less is more preferable. When the content of the light diffusing particles is 50 parts by weight or more, light diffusibility is obtained, and when the content is 150 parts by weight or less, a decrease in luminance can be prevented. In addition, 100 weight part of binder resin here is the quantity which match | combined the resin component and the hardening | curing agent component (Hereinafter, it is the same about content based on binder resin.).

  The thickness of the first light diffusion layer 21 is preferably 2 to 7 μm, more preferably 3 to 6 μm. The thickness of the light diffusion layer is the thickness of the portion where the particles are present (hereinafter the same).

The second light diffusing layer 22 imparts light diffusibility (a property to supplement the light diffusibility of the first light diffusing layer 21) to the light diffusing member of the present invention, and the surface of this layer is another member such as a light guide plate. It is a layer that prevents other members from being damaged when contacted.
In order to have such a function, nylon particles are used as the light diffusing particles of the second light diffusion layer 22. Nylon particles are preferably nylon 12 fine particles that are easy to obtain true spherical particles. Specifically, Amilan SP-500 (average particle size 5 μm, Toray Industries, Inc.), Amilan SP-10 (average particle size 10 μm, Toray Industries, Inc.), Gantzpearl GPA-550 (average particle size 4.0-6.0 μm, Aika Kogyo Co., Ltd.), MW-330 (average particle size of 5-8 μm, Sumika Enviro Science Co., Ltd.), MSP-100 (average particle size of 5 μm, Daicel Evonik) and the like.

  The average particle diameter of the nylon particles contained in the second light diffusing layer 22 is preferably larger than the light diffusing particles contained in the first light diffusing layer 21. Specifically, although it depends on the thickness of the layer, it is preferably 2 to 10 μm, more preferably 4 to 8 μm. By using nylon particles having the above particle diameter range as the light diffusing particles of the second light diffusing layer 22, a high scratch prevention effect can be obtained while imparting light diffusibility.

  The nylon particle content (phr) in the second light diffusion layer 22 is preferably 20 parts by weight or more, and more preferably 30 parts by weight or more with respect to 100 parts by weight of the binder resin. Moreover, 60 weight part or less is preferable with respect to 100 weight part of binder resin, and 40 weight part or less is more preferable. By setting the content of nylon particles to 20 parts by weight or more, in addition to the abrasion scratch preventing effect, a pressure scratch preventing effect can be obtained. Moreover, by setting it as 60 weight part or less, light transmittance is maintained and it can prevent that haze becomes high too much.

  The thickness of the second light diffusion layer 22 is preferably 2 to 10 μm, more preferably 4 to 8 μm. The total thickness of the first light diffusion layer 21 and the second light diffusion layer 22 is preferably 10 μm or more and 14 μm or less.

  As described above, the light diffusing member of the present invention is different in the structure of the light diffusing layer provided on both sides. In general, when the layers are arranged on both sides of the support, if the thickness of the layers is uneven, the support is likely to warp, but in the light diffusing member of the present invention, the thickness of the first light diffusion layer 21 and Even if the thickness of the second light diffusion layer 22 is different, the rigidity of the two is made substantially equal by changing the type of resin and the type and content of the light diffusing particles contained in the first light diffusion layer 21. It is possible to prevent the light diffusing member from being warped.

  In addition to the binder resin and particles described above, additives such as surfactants such as leveling agents and antifoaming agents, antioxidants, and ultraviolet absorbers may be added to the light diffusion layer.

  The light diffusing member of the present invention is mainly composed of the support 10, the first light diffusing layer 21 and the second light diffusing layer 22 described above, but if necessary, between the layers. Alternatively, another layer can be provided on the surface of the first light diffusion layer or the second light diffusion layer 22 as long as the function of these layers is not hindered. For example, an antistatic layer (AS) layer may be provided on the surface of the second light diffusion layer 22. Further, hard coat (HC) layers may be provided on both sides of the support 10.

  Although the manufacturing method of the light diffusable member of this invention is not specifically limited, For example, it can manufacture by the following methods.

  After applying an easy adhesion treatment or the like to both surfaces of the support as necessary, the first light diffusion layer coating solution and the second light diffusion layer coating solution each containing a binder resin, light diffusing particles, and an appropriate solvent are provided. Apply and dry the working solution. When the binder resin is a thermosetting resin, it is heated, and when it is an ionizing radiation curable resin, the layer is cured by irradiation with radiation such as UV or electron beam. Thereafter, an AS agent is applied to the surface of the second light diffusion layer as necessary to form an AS layer.

According to the light diffusing member of the present invention, by providing the light diffusing layer on both surfaces, the light diffusing property can be enhanced without increasing the thickness of the light diffusing layer. Further, when incorporated in a backlight device, a relatively high luminance can be realized. Further, according to the light diffusing member of the present invention, by using nylon particles as the light diffusing particles of the light diffusing layer on the side in contact with the light guide plate, scratches on the light guide plate caused by the light diffusive member, particularly abrasion scratches and damages. Can prevent the occurrence of pressure wounds.
The light diffusing member of the present invention can be suitably used for a backlight unit, and is particularly suitable for a backlight unit of a high-definition display device in which a light diffusing member and a prism sheet are combined.

  Next, the backlight unit of the present invention will be described.

  The backlight unit of the present invention is characterized by using the above-described light diffusing member of the present invention. As shown in FIG. 2, as the main elements, the light guide plate 1 and the light guide plate 1 A light diffusing member 2 placed on top and prism sheets 3 and 3 placed on the light diffusing member are provided. A light source 5 is disposed on at least one side surface of the light guide plate 1. As the light source 5, a cold cathode tube, an LED light source or the like is mainly used. Examples of the shape of the light source include a dot shape, a line shape, and an L shape.

  2 shows a case where one light diffusing member 2 and two prism sheets 3 are used, the number is not limited to that shown in the figure.

  The light guide plate 1 is formed of a substantially flat plate shape so that a side surface on which a light source is disposed is a light incident surface and one surface substantially orthogonal thereto is a light emission surface. It consists of matrix resin chosen from highly transparent resin, such as a polycarbonate and an amorphous olefin resin. If necessary, resin particles having a refractive index different from that of the matrix resin may be added. Each surface of the light guide plate may have a complicated surface shape instead of a uniform plane, or may be provided with diffusion printing such as a dot pattern.

  The prism sheet 3 is configured such that a plurality of structural rows having a substantially triangular cross section are arranged in parallel on one surface, and preferably has a refractive index exceeding 1.60. This refractive index is higher than the refractive index (1.50 to 1.60) of the conventional prism sheet, and the light from the light guide plate can be efficiently launched in the front direction. When two prism sheets 3 are used, they are arranged so that the directions of the structural rows of these prism sheets intersect.

  The apex angle of the substantially triangular structure row of the prism sheet 3 is preferably in the range of 80 to 105 °. The shape of the substantially triangular structure row may be a shape having a sharp peak, or may have a slight R at the tip of the structure row. Moreover, it is preferable that the pitch between the peaks of the structure row is in the range of 10 to 40 μm. Moreover, it is preferable that the peak height of a structure row | line | column is in the range of 5-20 micrometers.

  The prism sheet 3 may be composed of a single resin layer in which a substantially triangular structure row is formed, or may be formed by laminating a resin layer in which a structure row is formed on a flat support. As the support, a plastic film having high optical transparency can be used. Although the same thing as the support body of the light diffusing member of the present invention can be used, among these, a polyethylene terephthalate film stretched, particularly biaxially stretched, is excellent in mechanical strength and dimensional stability. Therefore, it is preferably used. It is preferable to use a support that has been subjected to an easy adhesion treatment such as a plasma treatment, a corona discharge treatment, a far-ultraviolet irradiation treatment, or an undercoat easy adhesion layer.

  The backlight unit of the present invention is a unit in which a light diffusing member 2 and a prism sheet 3 are sequentially stacked on a light guide plate 1, and the light source and the light guide plate 1 are placed in the chassis of the display device to which the light source is attached. It is set and used so that the side faces match. At this time, the light diffusing member 2 is disposed such that the second light diffusing layer (a layer containing a binder and nylon particles) is on the light guide plate 1 side. Further, a reflector or the like is provided between the backlight unit and the chassis bottom as required. Further, an electromagnetic wave shielding film or the like is provided on the upper side of the backlight as necessary.

  The backlight unit of the present invention uses the light diffusing member 2 in which a specific layer (second light diffusing layer) is formed on the surface in contact with the light guide plate 1, so that the light guide plate 1 and the light diffusing member are assembled at the time of assembly. Even if a pressure is applied between the two or a lateral force is applied, the light guide plate 1 is less likely to be scratched (pressurized or worn). Moreover, since the light diffusing member is excellent in light transmittance and light diffusing property, the pattern of the prism sheet can be hidden without impairing the high front luminance of the high refractive index prism sheet, and the display device has high luminance and high definition. Etc. can be obtained.

  Examples of the present invention will be described below. In the following examples, “%” and “parts” are based on weight unless otherwise specified.

1. Production of Light Diffusing Member <Example 1>
A first light diffusion layer having a thickness of 4 μm was formed on one side of a transparent plastic support (Lumirror T60: Toray Industries Inc., thickness 25 μm) by applying and drying a coating solution for the first light diffusion layer having the following formulation. Next, the second light diffusing layer having a thickness of 7 μm is formed by applying and drying a coating solution for the second light diffusing layer having the following formulation on the surface of the support opposite to the surface on which the first light diffusing layer is formed. Thus, the light diffusing member of Example 1 was produced.

<First light diffusion layer coating solution>
・ Acrylic resin 10 parts (Acridic A807: Dainippon Ink & Chemicals, solid content 50%)
-Polymethyl methacrylate particles 5.6 parts (90 phr)
(Spherical particles, average particle size 2 μm)
・ Isocyanate curing agent 2 parts (Takenate D110N: Mitsui Chemicals Polyurethanes, 60% solid content)
・ Solvent 32 parts

<Coating liquid for second light diffusion layer>
・ Acrylic resin 10 parts (Acridic A807: Dainippon Ink & Chemicals, solid content 50%)
-Nylon particles 1.9 parts (30 phr)
(Spherical particles, average particle size 5 μm)
・ Isocyanate curing agent 2 parts (Takenate D110N: Mitsui Chemicals Polyurethanes, 60% solid content)
・ Solvent 20 parts

<Examples 2 and 3>
The light diffusing members of Examples 2 and 3 were prepared in the same manner as in Example 1 except that the nylon particle content in the coating solution for the second diffusion layer of Example 1 was changed to 20 phr and 40 phr, respectively. did.

<Comparative Examples 1 and 2>
The light diffusing members of Comparative Examples 1 and 2 were prepared in the same manner as in Example 1 except that the nylon particle content in the second light diffusion layer coating solution of Example 1 was changed to 10 phr and 60 phr, respectively. Produced.

<Comparative Example 3>
The same light diffusion layer coating solution as that of Example 1 was applied and dried on one side of the same transparent plastic support as in Example 1 to form a light diffusion layer having a thickness of 4 μm. The light diffusing member of Example 3 was produced.

<Comparative Examples 4 and 5>
Comparative Example 4, except that the content of the light diffusing material (polymethyl methacrylate particles) in the first light diffusing layer coating liquid of Example 1 was changed to 40 phr and 160 phr, respectively. 5 light diffusing members were produced.

<Comparative Example 6>
The light diffusibility of Comparative Example 6 was the same as Example 1 except that the nylon particles of the second light diffusing layer of Example 1 were changed to silicone particles (Tospearl 145, average particle size 4.5 μm: Momentive Performance). A member was prepared.

2. Evaluation The following items were evaluated for the light diffusing members of Examples 1 to 3 and Comparative Examples 1 to 6. The results are shown in Table 1.

<Light diffusion>
As an index of light diffusivity, haze was measured based on JIS K7105: 2000.

<Abrasion scratches>
Using a wear tester (NUS-ISO-1, Suga tester), in accordance with JIS H-8682-1, with a load weight of 300 g / cm ² and 15 reciprocations, a light diffusing member and a polycarbonate plate A wear test (thickness: 1.0 mm) was performed, and the occurrence of scratches on the polycarbonate plate surface was visually observed. Wear scratches appear to be thin, but “○” indicates that scratches cannot be confirmed when incorporated into a backlight device, and “×” indicates that there are wear scratches that can be confirmed when incorporated into a backlight device. did.

<Pressure wound>
Using a surface property tester (HEIDON-14, Shinto Kagaku), stack the light diffusing member so that the second light diffusing layer and the polycarbonate plate (thickness: 1.0 mm) are in contact with each other, from the light diffusing member side. A load was applied, and the occurrence of scratches on the carbonate plate surface was visually observed. The load area was 1 cm ² , the load time was 10 seconds, and the load weight was changed to 500 g / cm ² , 1000 g / cm ² , and 1500 g / cm ² .
“○” indicates that no pressure flaw can be confirmed at a load of 1500 g / cm ² , while “1000” / 500 ² indicates that no flaw can be confirmed at 1000 g / cm ² , while “Δ” indicates that the pressure flaw can be confirmed at 500 g / cm ² . The thing which can confirm a pressurization damage | wound was set as "x".

<Brightness and light source unevenness>
The luminance when the light diffusing members of Examples 1 to 3 and Comparative Examples 1 to 6 were each incorporated in a backlight device (for a smartphone) was measured, and the relative luminance when the luminance of Example 1 was 100 was measured. Asked. All the light diffusing members were arranged so that the first light diffusing layer (the light diffusing layer in Comparative Example 3) faced the light guide plate. Furthermore, in the same backlight apparatus incorporating the light diffusing member as described above, the light source unevenness was visually confirmed. “◯” indicates that the light source unevenness cannot be confirmed, “Δ” indicates that the light source unevenness is slightly confirmed, and “×” indicates that the light source unevenness is significant.

  As can be seen from the results shown in Table 1, in Examples 1 to 3 in which the nylon particle content of the second light diffusion layer is 20 to 40 phr, there are no visible wear scratches and pressure scratches, and they are high. It was confirmed that light diffusibility and light transmittance were obtained.

  Since the light diffusing member of Comparative Example 1 had a nylon particle content as low as 10 phr, the generation of wear flaws could be suppressed, but visible pressure flaws occurred. The light diffusing member of Comparative Example 2 had a nylon particle content of 60 phr and was able to suppress both wear and pressure flaws. However, the haze as a whole increased and light combined with the high refractive index prism sheet. As a diffusive member, satisfactory characteristics were not obtained.

  The light diffusing member of Comparative Example 3 is obtained by forming a light diffusing layer having the same composition as that of Example 1 on only one side, and the effect of preventing scratches (abrasion scratches) was not obtained. Therefore, satisfactory characteristics were not obtained as a light diffusing member combined with a high refractive index prism sheet.

  When the light diffusing member of Comparative Example 4 was used, high brightness was obtained, but the haze was low and the light source was conspicuous. When the light diffusing member of Comparative Example 5 was used, haze was high and light source unevenness could be prevented, but the luminance was low.

  The light diffusing member of Comparative Example 6 had the same performance as that of the Example in terms of luminance and light source unevenness, but the layer in contact with the carbonate plate contained silicone particles instead of nylon particles. Yes, the effect of suppressing the pressure flaw was obtained, but a visible wear flaw occurred.

  According to the present invention, by using together with a high refractive index prism sheet as a light diffusing member for a backlight unit, a high-definition liquid crystal display device having high front luminance and no deterioration in image quality due to scratches on the light guide plate is provided. can do.

DESCRIPTION OF SYMBOLS 1 ... Light guide plate 2 ... Light diffusive member 3 ... Prism sheet 5 ... Light source 20 ... Support body 21 ... 1st layer (1st light-diffusion layer)
22 ... Second layer (second light diffusion layer)

Claims (6)

A light diffusing member having a first layer on one side of the support and a second layer on the other side of the support,
The first and second layers include a binder resin and light diffusing particles,
The first layer includes 50 parts by weight or more and 150 parts by weight or less of the light diffusing particles with respect to 100 parts by weight of the binder resin, and the second layer includes nylon particles as the light diffusing particles. A light diffusing member comprising 20 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the binder resin. The light diffusing member according to claim 1,
The light diffusing member, wherein an average particle diameter of the light diffusing particles contained in the first layer is smaller than an average particle diameter of the nylon particles contained in the second layer. The light diffusing member according to claim 2,
The light diffusing member, wherein an average particle size (volume average particle size) of nylon particles contained in the second layer is 4 μm or more and 6 μm or less. The light diffusing member according to any one of claims 1 to 3,
The light diffusing member, wherein the thickness of the second layer is thicker than the thickness of the first layer. A backlight unit comprising a light guide plate, a light diffusing member placed on the light guide plate, and a prism sheet placed on the light diffusing member,
5. The light diffusing member according to claim 1, wherein the light diffusing member is disposed so that the second layer is in contact with the light guide plate. Light unit. The backlight unit according to claim 5,
The backlight unit, wherein the prism sheet is a high refractive index prism sheet made of a material having a refractive index of 1.6 or more.

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