JP6518057B2 - Light diffusing member and backlight unit using the same - Google Patents

Description

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

  Backlight units are widely used in color liquid crystal display devices such as personal computers, tablet terminals, mobile phones, PDAs (Personal Digital Assistants), navigation devices, and game devices. The backlight unit has a light source disposed directly below the display surface, and a direct light type in which light is emitted to the display surface side through the diffusion plate, and a light guide plate in which the light source is disposed parallel to the display surface of the display device There is an edge light type which is disposed on the side surface of the light guide plate so as to emit light from the light guide plate. In any case, a light diffusive sheet for equalizing the light from the light source and a prism sheet for enhancing the front luminance are disposed on the light exit surface of the diffusion plate or the light guide plate.

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

  In order to improve the reduction in frontal brightness, proposals have also been made to use a material having a high refractive index as the prism sheet. With respect to a light diffusing sheet used in combination with a prism sheet, research on a light diffusing sheet suitable for such a high refractive index material has been made. For example, Patent Document 1 discloses a light diffusion sheet in which light diffusion layers are provided on both sides of a transparent sheet to enhance light diffusion and to achieve high brightness.

  Further, in the edge light type backlight unit, the light diffusing sheet is used in a state of being in close contact with the light guide plate, so that sticking to the light guide plate can be prevented or the light diffusing sheet is guided by contacting the light guide plate. It has been proposed to provide an anti-sticking layer or a back coat layer on the surface of the light diffusing sheet in contact with the light guide plate in order to prevent a scratch generated on the light plate (Patent Documents 2, 3 and the like).

JP, 2007-133173, A Patent No. 4885895 gazette JP 2012-230364 A

  The light diffusion sheet provided with the light diffusion layer on both sides described in Patent Document 1 etc. has a trade-off relationship with the improvement of the luminance and the light diffusivity as compared with the light diffusion sheet provided with the light diffusion layer only on one side However, the problem 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 and the like, the layer provided on the opposite side of the light diffusion layer contains particles to such an extent that optical properties are not affected, which contributes to the improvement of light diffusion. do not do.

  Further, according to the study of the present inventors, the causes of the light diffusion layer damaging the light guide plate are roughly divided into two, one is a pressure damage caused by the pressure at the time of close contact, and the other one is both. It is an abrasion wound that occurs when fitting. The backcoat layer using elastic silicone particles described in Patent Document 2 is considered to be effective for pressure damage, but a satisfactory effect is not obtained for suppression of abrasion damage.

  An object of the present invention is to suppress generation of a scratch of a light guide plate, in particular, both a pressure scratch and a wear scratch while improving both light transmittance (brightness) and light diffusivity (haze).

  In order to solve the above-mentioned subject, the present inventors arrange the layer which has light diffusivity on both sides of a light diffusive sheet, and the kind of the light diffusion material contained in these layers, content, balance of both sides, etc. As a result of earnestly researching the light guide plate, it is possible to make the light guide plate different by making the content of the light diffusing material different in the layers on both sides and using nylon particles as the light diffusing material contained in the layer on the back surface (surface facing the light guide) side. The haze can be increased while maintaining high brightness by suppressing the generation of both pressure and abrasion scratches and setting the particle diameter of the light diffusing material to be contained in the light diffusing layer on both sides to a specific range. It is found out what can be done and is the result of 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, wherein 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, as the light diffusing particles, 20 parts by weight or more and 40 parts by weight or less of nylon particles with respect to 100 parts by weight of the binder resin.

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

  The light diffusing member of the present invention is a thin sheet-like material, and is a different category of material from the light diffusing plate having a thickness of more than 1 mm.

  According to the light diffusing member of the present invention, the light diffusing layer is disposed 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 diffusivity can be obtained, the total thickness of the light diffusion layer including both light diffusion layers can be reduced, and a decrease in the amount of light passing through the light diffusion layer can be reduced. The brightness 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 includes a predetermined amount of nylon particles, the nylon particles have resistance to In addition to wear and scratch resistance, pressure scratch resistance can be imparted.

  Conventionally, nylon particles have been added to the backcoat layer for imparting anti-scratch properties, but at an amount usually added to the backcoat layer, the anti-abrasion effect is obtained but the anti-abrasion effect is not obtained. . On the other hand, elastic silicone particles are considered to be effective in preventing pressure damage, and in order to achieve both wear and damage prevention and pressure damage prevention, it is conceivable to use nylon particles and silicone particles in combination. However, silicone particles tend to come off the layer when the amount of particles added is large. In the present invention, by using a relatively large number of nylon particles, an unexpected pressure scratch preventing effect can be obtained, and there is no detachment from the layer, and further it can contribute to the improvement of the light diffusion without inhibiting the light transmission. .

Sectional view schematically showing the light diffusing member of the present invention Sectional view schematically showing the backlight unit of the present invention

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

  The support 20 is not particularly limited 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, acryl, polyvinyl chloride, norbornene compounds and the like can be used. Among them, a polyethylene terephthalate film subjected to a stretching process, particularly a biaxial stretching process is preferable in that it is excellent in mechanical strength and dimensional stability.

  The support 20 can be subjected to corona discharge treatment on the surface or provided with an easy adhesion layer in order to improve the adhesion to 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.

  The materials of the binder resin constituting the first light diffusion layer 21 and the second light diffusion layer 22 are common, and therefore will be collectively described.

  The binder resin is made of a polymeric material having high optical transparency as in the case of 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 which can be cross-linked and cured by irradiation of ionizing radiation (ultraviolet ray or electron beam) can be used. As this photopolymerizable prepolymer, it is possible to use 2 per molecule. Particularly preferred is an acrylic prepolymer which has three or more acryloyl groups and forms a three-dimensional network structure by crosslinking and curing. As the acrylic prepolymer, urethane acrylate, polyester acrylate, epoxy acrylate, melamine acrylate, polyfluoroalkyl acrylate, silicone acrylate and the like can be used. Furthermore, although these acrylic prepolymers can be used alone, it is preferable to add a photopolymerizable monomer in order to improve the crosslinking curability and further improve the hardness of the light diffusion layer.

  Examples of photopolymerizable monomers include monofunctional acrylic monomers such as 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and butoxyethyl acrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol Bifunctional acrylic monomer such as diacrylate, polyethylene glycol diacrylate, hydroxypivalic acid ester neopentyl glycol diacrylate, etc. or polyfunctional acrylic monomer such as dipentaerythritol hexaacrylate, trimethylpropane triacrylate, pentaerythritol triacrylate etc. Two or more are used.

  In addition to the photopolymerizable prepolymer and the photopolymerizable monomer described above, in the case of curing by ultraviolet irradiation, it is preferable to use an additive such as a photopolymerization initiator or a photopolymerization accelerator.

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

  Further, the photopolymerization accelerator is capable of reducing the polymerization trouble due to air at the time of curing and accelerating the curing rate, and for example, p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester and the like It can be mentioned.

  As thermosetting resins, silicone resins, phenol resins, urea resins, melamine resins, furan resins, unsaturated polyester resins, epoxy resins, diallyl phthalate resins, guanamine resins, ketone resins, Amino alkyd resins, urethane resins, acrylic resins, polycarbonate resins and the like can be mentioned. Although these can be used alone, it is desirable to add a curing agent in order to further improve the crosslinkability and the hardness of the crosslinked cured coating.

  As the curing agent, compounds such as polyisocyanate, amino resin, epoxy resin, carboxylic acid and the like can be appropriately used in accordance with a compatible resin.

  The thermoplastic resin includes 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 Alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethylene glycol and the like can be mentioned.

  Among these thermosetting resins or thermoplastic resins, the thermosetting resin or thermoplastic resin of acrylic resin is used from the viewpoint that the coating film strength in forming the light diffusion layer and the good transparency can be obtained. Is preferred. Moreover, these thermosetting resins or thermoplastic resins can also be used as composite resin which combined multiple types of thermosetting resins or thermoplastic resins, respectively.

  The binder resin may be the same or different for the first light diffusion layer 21 and the second light diffusion layer 22. However, it is preferable to select the material in consideration of "warpage" 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 and inorganic particles generally used as a light diffusing material can be used, but organic particles excellent in transparency and optical properties are preferable. Specific examples of the organic particles include (meth) acrylic resins such as poly (meth) acrylates, 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 combination of two or more.

  The first light diffusion layer 21 is preferably a layer on the light emission side when the light diffusion member of the present invention is used for a backlight unit, and has a surface shape and a haze that can obtain good light emission characteristics. Is preferred. Specifically, the surface shape is preferably 0.2 to 1.0 μm in average surface roughness Ra. The haze is preferably adjusted to 85 to 95% in the state where the second light diffusion layer is provided.

  In order to obtain such optical properties, the average particle size of the light diffusing particles contained in the first light diffusing 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.

  The content (phr: per hundred resin) of the light diffusing particles in the first light diffusing layer 21 is preferably 50 parts by weight or more, and more preferably 70 parts by weight or more with respect to 100 parts by weight of the binder resin. Moreover, 150 weight parts or less are preferable with respect to 100 weight parts of binder resin, and 120 weight parts or less are more preferable. By setting the content of the light diffusion particles to 50 parts by weight or more, light diffusibility can be obtained, and by setting the content to 150 parts by weight or less, it is possible to prevent a decrease in luminance. In addition, 100 weight part of binder resin here is the quantity which united the resin component and the hardening 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 diffusion layer 22 gives the light diffusion member of the present invention a light diffusion property (a property to compensate for the light diffusion property of the first light diffusion layer 21), and the surface of this layer is another member such as a light guide plate When it contacts, it is a layer which prevents damaging other members.
In order to impart such a function, nylon particles are used as the light diffusing particles of the second light diffusing layer 22. As nylon particles, fine particles of nylon 12 which are easy to obtain true spherical particles are preferable. Specifically, amilan SP-500 (average particle size 5 μm, Toray Industries, Inc.), amilan SP-10 (average particle size 10 μm, Toray Industries, Inc.), Gantz pearl GPA-550 (average particle size 4.0 to 6.0 μm, Aika Kogyo Co., Ltd., MW-330 (average particle size 5-8 μm, Sumika Enviro-Sciences Co., Ltd.), MSP-100 (average particle size 5 μm, Daicel Evonik) and the like.

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

  The content (phr) of nylon particles 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 parts or less are preferable with respect to 100 weight parts of binder resin, and 40 weight parts or less are more preferable. By setting the content of the nylon particles to 20 parts by weight or more, in addition to the wear and scratch prevention effect, a pressure and scratch prevention effect can be obtained. Further, by setting the amount to 60 parts by weight or less, the light transmittance is maintained, and it is possible to prevent the haze from becoming too high.

  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 configuration of the light diffusing layer provided on both sides. Generally, when the layers are arranged on both sides of the support, if the thickness of the layers is not uniform, the support tends to warp, but in the light diffusion 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, by making the type of resin contained in the first light diffusion layer 21 different and the type and content of light diffusion particles different, the rigidity of both is made approximately equal. It is possible to prevent the occurrence of warpage in the light diffusing member.

  In the light diffusion layer, in addition to the binder resin and the particles described above, an additive such as a surfactant such as a leveling agent and an antifoamer, an antioxidant, and an ultraviolet absorber may be added.

  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 layer and the layer Alternatively, it is possible to provide another layer on the surface of the first light diffusion layer or the second light diffusion layer 22 as long as the functions of these layers are not impaired. For example, an antistatic layer (AS) layer may be provided on the surface of the second light diffusion layer 22. In addition, 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 subjecting both sides of the support to a treatment for facilitating adhesion as necessary, a coating solution for the first light diffusion layer and a coating for the second light diffusion layer, each containing a binder resin, light diffusing particles and an appropriate solvent Apply the coating solution and dry it. In the case where the binder resin is a thermosetting resin, heating is performed, and in the case of an ionizing radiation curable resin, radiation such as UV or electron beam is irradiated to cure the layer. 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 sides, it is possible to enhance the light diffusing property without increasing the thickness of the light diffusing layer. Also, when incorporated into a backlight device, relatively high brightness can be realized. Further, according to the light diffusing member of the present invention, by using nylon particles as light diffusing particles of the light diffusing layer on the side in contact with the light guiding plate, scratches of the light guiding plate due to the light diffusing member The occurrence of a bruise can be prevented.
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 light diffusing member of the present invention described above, and as shown in FIG. 2, the light guide plate 1 and the light guide plate 1 are mainly used as main elements. A light diffusing member 2 placed on top, and prism sheets 3 and 3 placed on the light diffusing member. A light source 5 is disposed on at least one side surface of the light guide plate 1. The light source 5 mainly uses a cold cathode tube, an LED light source or the like. The shape of the light source may be point-like, linear or L-like.

  Although FIG. 2 shows the case where one light diffusion member 2 and two prism sheets 3 are used, the number of these members is not limited to that illustrated.

  The light guide plate 1 is formed of a substantially flat plate shaped so that the side on which the light source is disposed is a light incident surface and one surface substantially orthogonal to the light incident surface is a light flat surface. It is made of a matrix resin selected from highly transparent resins such as polycarbonate and amorphous olefin resin. If necessary, resin particles different in refractive index from the matrix resin may be added. Each surface of the light guide plate may have a complex 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 one having a refractive index exceeding 1.60. The refractive index is higher than the refractive index (1.50 to 1.60) of the conventional prism sheet, and light from the light guide plate can be efficiently raised in the front direction. When two prism sheets 3 are used, the directions of the structural rows of these prism sheets are arranged to cross each other.

  The apex angle of the substantially triangular structural 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 a structural sequence exists in the range of 10-40 micrometers. Moreover, it is preferable that the peak height of a structural row is in the range of 5-20 micrometers.

  The prism sheet 3 may be formed of a resin layer single layer in which substantially triangular structural rows are formed, or may be formed by laminating the resin layer in which the structural rows are formed on a flat support. As the support, a plastic film having high optical transparency can be used. The same support as the support of the light diffusing member of the present invention can be used, but among these, a polyethylene terephthalate film subjected to stretching, particularly biaxial stretching, is excellent in mechanical strength and dimensional stability. It is preferably used in order to As such a support, it is preferable to use a support on which an easy adhesion treatment such as plasma treatment, corona discharge treatment, deep ultraviolet irradiation treatment, formation of an undercoat easily adhesion layer, or the like is performed.

  The backlight unit of the present invention is a unit in which the light diffusing member 2 and the prism sheet 3 are sequentially stacked on the light guide plate 1 as a unit, and the light source and the light guide plate 1 are It is set and used so that the sides match. At this time, the light diffusion member 2 is disposed such that the second light diffusion layer (a layer containing a binder and nylon particles) is on the light guide plate 1 side. In addition, a reflective plate or the like may be provided between the backlight unit and the chassis bottom as needed. In addition, an electromagnetic wave shielding film or the like is provided on the upper side of the backlight as required.

  The back light unit of the present invention uses the light diffusion member 2 in which a specific layer (second light diffusion layer) is formed on the surface in contact with the light guide plate 1 so that the light guide plate 1 and the light diffusion member Even if a pressure is applied between 2 and a lateral force is applied, the light guide plate 1 is unlikely to be scratched (stressed scratch or abrasion scratch). In addition, 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 a display device with high brightness and high definition Etc can be obtained.

  Hereinafter, examples of the present invention will be described. In the following examples, "%" and "parts" are based on weight unless otherwise specified.

1. Production of Light Diffusing Member <Example 1>
The coating liquid for the first light diffusion layer of the following formulation was applied to one side of a transparent plastic support (Lumirror T60: Toray Industries, 25 μm thick) and dried to form a first light diffusion layer with a thickness of 4 μm. Next, on the surface of the support opposite to the surface on which the first light diffusion layer is formed, a coating solution for the second light diffusion layer according to the following formulation is applied and dried to form a second light diffusion layer having a thickness of 7 μm. The light diffusing member of Example 1 was manufactured.

<Coating solution for first light diffusion layer>
Acrylic resin 10 parts (Acrydic A 807: Dainippon Ink and Chemicals, 50% solid content)
・ Polymethyl methacrylate particles 5.6 parts (90 phr)
(Spherical particles, average particle diameter 2 μm)
・ Isocyanate curing agent 2 parts (Takenate D110N: Mitsui Chemical Polyurethanes Co., Ltd., solid content 60%)
・ 32 parts of solvent

<Coating liquid for second light diffusion layer>
Acrylic resin 10 parts (Acrydic A 807: Dainippon Ink and Chemicals, 50% solid content)
-1.9 parts of nylon particles (30 phr)
(Spherical particles, average particle size 5 μm)
・ Isocyanate curing agent 2 parts (Takenate D110N: Mitsui Chemical Polyurethanes Co., Ltd., solid content 60%)
・ 20 parts of solvent

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

Comparative Examples 1 and 2
In the same manner as in Example 1 except that the content of nylon particles in the coating solution for the second light diffusion layer of Example 1 was changed to 10 phr and 60 phr, respectively, the light diffusive members of Comparative Examples 1 and 2 were used. Made.

Comparative Example 3
The same coating solution for the light diffusion layer as the coating liquid for the first light diffusion layer of Example 1 is applied to one side of the same transparent plastic support as in Example 1 and dried 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 in the same manner as in Example 1 except that the content of the light diffusing material (polymethyl methacrylate particles) in the coating liquid for the first light diffusing layer of Example 1 was changed to 40 phr and 160 phr, respectively. A light diffusing member of 5 was produced.

Comparative Example 6
The light diffusivity of Comparative Example 6 in the same manner as in Example 1 except that the nylon particles in the second light diffusion layer of Example 1 were changed to silicone particles (Tospearl 145, average particle size 4.5 μm: Momentive Performance, Inc.) A member was produced.

2. Evaluation The following items were evaluated about the light-diffusing member of Examples 1-3 and Comparative Examples 1-6. The results are shown in Table 1.

<Light diffusing property>
The haze was measured based on JIS K 7105: 2000 as an index of light diffusivity.

<Abrasion wound>
A light diffusive member and a polycarbonate plate with a load weight of 300 g / cm ² and 15 reciprocations in accordance with JIS H-8682-1 using a wear tester (NUS-ISO-1, Suga tester) The abrasion test with (thickness: 1.0 mm) was conducted, and the occurrence of scratches on the surface of the polycarbonate plate was visually observed. Wear marks appear thin, but when incorporated into a backlight device, those that can not be identified as “○” are those that have wear marks and those that can be identified when incorporated into a backlight device are “×” did.

<Pressure wound>
Using a surface tester (HEIDON-14, Shinto Science), stack the second light diffusion layer of the light diffusion member so that the polycarbonate plate (thickness: 1.0 mm) comes in contact, and from the light diffusion member side A load was applied and the occurrence of scratches on the surface of the carbonate plate 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 .
Those that do not can be confirmed pressurized pressure scars under a load of 1500g / cm ² "○", but 1000g / cm ² in the pressurized pressure scars can not be confirmed, what was confirmed at 1500g / cm ² "△", at 500g / cm ² The thing which can confirm a pressurization flaw was made into "x".

<Brightness and light source unevenness>
The luminance when each of the light diffusing members of Examples 1 to 3 and Comparative Examples 1 to 6 is incorporated into a backlight device (for a smartphone) is measured, and the relative luminance when the luminance of Example 1 is 100. I asked for. All of the light diffusing members were arranged such that the first light diffusing layer (the light diffusing layer in Comparative Example 3) faced the light guide plate. Furthermore, in the same backlight device as the above in which the light diffusing member was incorporated, the light source unevenness was visually confirmed. Those in which the light source unevenness can not be confirmed are "○", those in which the light source unevenness can be slightly confirmed are "Δ", and those in which the light source unevenness is remarkable are "X".

  As can be seen from the results shown in Table 1, in Examples 1 to 3 in which the content of nylon particles in the second light diffusion layer is 20 to 40 phr, there are no visible abrasion and pressure scarring in any cases, and they are high. It was confirmed that light diffusivity and light transparency can be obtained.

  In the light diffusing member of Comparative Example 1, the content of nylon particles was as low as 10 phr, so that the generation of wear and tear could be suppressed, but a visible pressure damage was generated. In the light diffusing member of Comparative Example 2, although the nylon particle content was 60 phr, it was possible to suppress the occurrence of both an abrasion scratch and a pressure scratch, but the haze as a whole becomes high, and the light combined with the high refractive index prism sheet Satisfactory characteristics were not obtained as the diffusing member.

  The light diffusing member of Comparative Example 3 had the light diffusing layer of the same composition as that of Example 1 formed only on one side, and in addition to the fact that the scratch (abrasion scratch) preventing effect was not obtained, the haze as a whole As a light diffusing member combined with a high refractive index prism sheet, satisfactory characteristics were not obtained.

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

  The light diffusing member of Comparative Example 6 has the same performance as that of the embodiment with respect to luminance and light source unevenness, but the layer in contact with the carbonate plate contains silicone particles instead of nylon particles. The effect of suppressing pressure blemish was obtained, but a visible abrasion blemish occurred.

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

Reference Signs List 1 light guide plate 2 light diffusive member 3 prism sheet 5 light source 20 support 21 first layer (first light diffusion layer)
22 ··· Second layer (second light diffusion layer)

Claims (6)

A light diffusing member comprising a first layer on one side of a 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 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,
20 parts by weight or more and 40 parts by weight or less of nylon particles having an average particle size (volume average particle size) of 4 μm or more and 8 μm or less as the light diffusing particles, with respect to 100 parts by weight of the binder resin Including
The thickness of the second layer is thicker than the thickness of the first layer,
The total of the thickness of said 1st layer and said 2nd layer is 10 micrometers or more and 14 micrometers or less, The light-diffusion member characterized by the above-mentioned. The light diffusing member according to claim 1, wherein
A light diffusing member characterized in that an average particle diameter of the light diffusing particles contained in the first layer is smaller than an average particle diameter of nylon particles contained in the second layer. The light diffusing member according to claim 2,
A light diffusing member characterized in that an average particle diameter (volume average particle diameter ) of nylon particles contained in the second layer is 6 μm or less. The light diffusing member according to claim 1, wherein
The light diffusing member is characterized in that the thickness of the second layer is 2 μm or more and 10 μm or less. A backlight unit comprising: a light guide plate; a light diffusing member placed on the light guiding plate; and a prism sheet placed on the light diffusing member,
The light diffusive member is the light diffusive member according to any one of claims 1 to 4, wherein the second layer is disposed in contact with the light guide plate. Light unit. The backlight unit according to claim 5, wherein
A back light unit characterized in that 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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