TWI434074B - A light diffusion plate, a light source device provided with the same, and a transmission type image display device - Google Patents

Description

Light diffusing plate and surface light source device therewith and transmissive image display device

The present invention relates to a light diffusion plate capable of illuminating, for example, a transmitted image display panel, etc., brightly and in a more natural hue.

In the liquid crystal display device, for example, a back light side of a liquid crystal panel (image display unit) including a liquid crystal panel is disposed as a backlight (backlight panel), and a surface light source device is disposed. In the surface light source device for the backlight, a surface light source device in which a plurality of light sources are disposed in a light box (housing) and a light diffusing plate is disposed on the front side of the light source is known (refer to Japan). Patent Publication No. 2004-170937 (Patent Document 1)).

In the above-mentioned light-diffusing sheet, even if the screen size is increased, it is possible to produce a relatively lightweight one, and it is widely used to disperse light-diffusing particles in a transparent resin.

However, such a known light diffusing plate is often in a case where the brightness of the transmissive image display panel or the like is insufficient, or the obtained illumination is not a natural hue. In this case, the liquid crystal formed by the light diffusing plate is used. In a transmissive image display device such as a display device, there is a problem in that the brightness of the displayed image is insufficient or it is difficult to obtain a display image of a natural hue.

The present invention has been made in view of the above circumstances, and aims to provide a light diffusing plate capable of illuminating a transmissive image display panel or the like more brightly. Further, the present invention has an object of providing a light diffusing plate which can illuminate a transmissive image display panel or the like in a brighter and more natural color tone.

As a result of intensive studies to achieve the above object, the present inventors have found that the light transmittance of light having a wavelength of 600 nm affects the brightness of illumination, and the zinc compound added during the manufacturing process of the resin is found. The fact that the color tone of the illumination has an influencer has finally completed the present invention. That is, the present invention provides the following means.

[1] A light diffusing plate formed of a transparent resin and a light diffusion particle, characterized by light transmittance when light having a wavelength of 600 nm is transmitted through a light pass length of 200 mm. (light transmissivity) is more than 65%.

[2] The light-diffusing sheet according to the above [1], wherein the transparent resin contains a composition of a zinc compound, and the content of zinc in the composition is 150 ppm or less.

[3] The light diffusing plate according to [2], wherein the zinc compound is zinc stearate.

[4] The light diffusing plate according to any one of [1] to [3] wherein the transparent resin contains polystyrene.

[5] The light-diffusing sheet according to any one of the above-mentioned [1], wherein the light-diffusing particles are selected from the group consisting of propylene-based polymer particles and siloxane-based polymer particles. One or more kinds of polymer particles.

[6] The light-diffusing sheet according to any one of [1] to [5] wherein the light-diffusing particles have an average particle diameter of 0.5 to 5 μm, a refractive index of the transparent resin, and a refractive index of the light-diffusing particles. The absolute value of the difference in the ratio is 0.05 or more, and the content of the light-diffusing particles per 100 parts by mass of the transparent resin is 0.1 to 10 parts by mass.

[7] A light-diffusing sheet according to any one of [1] to [6], wherein the light-diffusing sheet is disposed on a back side of the light-diffusing sheet.

[8] A light-diffusing sheet according to any one of [1] to [6], wherein the light-diffusing sheet according to any one of [1] to [6], and a plurality of light sources disposed on a back side of the light-diffusing sheet And a transmissive image display panel disposed on a front side of the light diffusing plate.

In the invention of [1], the light diffusing plate is made of a transparent resin and a light diffusing particle, and the transparent resin is a light transmittance of 65% or more when the light having a wavelength of 600 nm is transmitted for an optical path length of 200 mm. It can be used to illuminate a transmissive image display panel more brightly.

In the invention of the above [2], the transparent resin contains a composition of a zinc compound, and since the content of zinc in the composition is set to 150 ppm or less, the transmissive type can be illuminated in a more natural color tone. Image display panel, etc. Here, "ppm" means a unit of mass parts per million.

In the invention of [3], since the zinc compound is zinc stearate, it is more natural under the moldability of the molding process due to the lubricity effect by the zinc stearate lubricant. The tone of the illuminator.

In the invention of [4], since the transparent resin contains a structure of polystyrene, transparency is high and illumination can be performed in a more natural color tone.

In the invention of the above [5], it is possible to use one or more kinds of polymer particles selected from the group consisting of propylene-based polymer particles and siloxane-based polymer particles as the light-diffusing particles. Illuminated in bright, natural tones.

In the invention of [6], the average particle diameter of the light-diffusing particles is 0.5 to 5 μm, and the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the light-diffusing particles is 0.05 or more, and the transparent resin is Since the content of the light-diffusing particles of 100 parts by mass is 0.1 to 10 parts by mass, the light-diffusing particles can be sufficiently uniformly dispersed, and the light-diffusion particles can be sufficiently diffused with a small amount of light-diffusing particles.

In the invention of [7], a surface light source device capable of brighter illumination can be provided. Further, when the light diffusing plate is provided with the configuration [2], it is possible to provide a surface light source device capable of performing illumination with a brighter and more natural color tone.

In the invention of [8], a transmissive image display device capable of obtaining a brighter display image can be provided. Further, when the light diffusing plate has the configuration of [2], a transmissive image display device capable of obtaining a display image of a brighter and more natural hue can be provided.

[Best Embodiment of the Invention]

A liquid crystal display device according to an embodiment of the transmissive image display device (30) of the present invention is shown in Fig. 1. In Fig. 1, (30) is a liquid crystal display device, (11) is a liquid crystal cell, (12) (13) is a polarizing plate, and (1) is a surface light source device. A polarizing plate (12) (13) is disposed on each of the upper and lower sides of the liquid crystal panel (11), and a liquid crystal as a transmissive image display portion is formed using the constituent members (11) (12) and (13). Panel (20).

Further, the liquid crystal cell (11) is formed by sealing a liquid crystal compound between a pair of transparent electrodes. The liquid crystal panel (20) is preferably provided with a color filter or the like to display a color image. Further, the liquid crystal panel (20) may be configured to include a phase difference plate for adjusting contrast, color tone, and the like when viewed from an oblique direction.

The surface light source device (1) is disposed on the lower surface side (back surface side) of the polarizing plate (13) on the lower side of the liquid crystal panel (20). That is, such a liquid crystal display device (30) is a direct type liquid crystal display device.

The surface light source device (1) includes a thin box-shaped lamp holder (5) having a rectangular shape when viewed in plan and a top cover (front side) having no cover, and is spaced apart from each other in the lamp holder (5). A plurality of linear light sources (2) arranged in a manner, and a light diffusing plate (3) disposed on an upper side (front side) of the plurality of linear light sources (2). The light diffusing plate (3) is placed and fixed to the lamp holder (5) so as to be able to cover the coverless surface. Further, a light reflecting layer (not shown) is provided on the inner surface of the lamp cymbal (5).

The light source (2) is not particularly limited, but may be, for example, a linear light source such as a cold cathode tube (CCFL), an external electrode fluorescent tube (EEFL), or a flat fluorescent lamp (FFL). A point light source such as a light emitting diode (LED) is used.

The light diffusing plate (3) is made of a transparent resin and a light diffusing plate, and light diffusing particles are dispersed in the transparent resin. In the present invention, as the transparent resin, a transparent resin having a light transmittance of 65% or more when the light having a wavelength of 600 nm is transmitted for an optical path length of 200 mm is used.

Therefore, if the above-described surface light source device (1) is used, the liquid crystal panel (20) can be illuminated more brightly. Therefore, if the liquid crystal display device (30) is used, the effect of obtaining a brighter display image can be exhibited.

In the present embodiment, the transparent resin contains a composition of a zinc compound, and the content of zinc (Zn atom) in the composition is set to 150 ppm or less.

Therefore, if the above-described surface light source device (1) is used, the liquid crystal panel (20) can be illuminated with a more natural color tone. Therefore, if the liquid crystal display device (30) is used, the effect of obtaining a display image with a more natural hue can be exhibited.

Further, in the liquid crystal display device (30), another light diffusion plate may be disposed between the light diffusion plate (3) and the liquid crystal panel (20). Further, an optical member for brightly illuminating the front side may be disposed between the light diffusing plate (3) and the liquid crystal panel (20). The optical member may be, for example, "DBEF" (trade name) manufactured by 3M Company of the United States.

For the aforementioned transparent resin, it is suitable for use without coloring. The transparent resin is not particularly limited, and examples thereof include polystyrene, methyl methacrylate-styrene copolymer, methacrylic-styrene copolymer, and maleic anhydride-styrene copolymer. Polymethyl methacrylate, methyl methacrylate-acrylate copolymer, polycarbonate, polypropylene, polycycloolefin, cycloolefin-α-olefin copolymer, and the like. Among them, polystyrene, polypropylene, polycycloolefin, and cycloolefin-α-olefin copolymer are suitable for use from the viewpoint of low hygroscopicity.

Further, the transparent resin is a transparent resin having a light transmittance of 65% or more when a light having a wavelength of 600 nm is transmitted through an optical path length of 200 mm. In this way, the illuminance obtained by the transmitted light can be improved. In particular, the transparent resin is preferably a transparent resin having a light transmittance of 70% or more when a light having a wavelength of 600 nm is transmitted through an optical path length of 200 mm.

For example, when a raw material monomer is produced into a transparent resin by a method such as suspension polymerization or dispersion polymerization in a liquid phase, the solvent remaining in the obtained transparent resin, or The catalyst component, the additive, and the like added to the solvent may also affect the light transmittance of light having a wavelength of 600 nm as an impurity. Alternatively, an additive or the like added in a small amount for various purposes due to polymerization of the transparent resin may also affect the light transmittance of light having a wavelength of 600 nm as an impurity. Therefore, the "transparent resin having a light transmittance of 65% or more in the optical path length of 200 mm when the light having a wavelength of 600 nm is used in the present invention" is used, for example, the amount of the catalyst or the additive used in the production process is selected. In the case where the amount of the additive to be added to the transparent resin obtained by the polymerization is small, the amount of the additive to be added to the transparent resin obtained by the polymerization is not sufficient, and it can be obtained.

Further, the transparent resin may be a composition containing a zinc compound, but in this case, the zinc content (the content of Zn atoms rather than the content of the zinc compound) in the composition is preferably set. Below 150ppm. When the content of zinc is 150 ppm or less, the transmission type image display panel (20) can be irradiated with a more natural color tone because the content of zinc which is generally considered to have an influence on the color tone is suppressed. In particular, the content of zinc in the composition is preferably set to 90 ppm or less, more preferably 50 ppm or less, and particularly preferably 10 ppm or less.

The zinc compound is not particularly limited, and may, for example, be zinc stearate, zinc laurate, zinc tributyl benzoate, zinc 1,2-hydroxystearic acid or zinc myristate ( Zinc miristate) and so on.

Due to the use of the above-mentioned zinc stearate, the lubricity-improving effect can be obtained, and the friction between the transparent resin and the metal surface of the molding machine is lowered by the inclusion of the zinc stearate, and the molding machine is metal-resistant. The prevention of the adhesion of the surface and the improvement of the mold release property are helpful.

The content of zinc described above is a value obtained by the following method (the content of zinc in the examples is also the same). That is, the composition containing the zinc compound is taken on a platinum dish, heated with sulfuric acid to heat the organic matter, and then the obtained carbide is ashed at 550 ° C in an electric furnace, and alkali fusion is added to the ash. The agent is heated to melt. Then, the obtained melt was dissolved in nitric acid and water, and adjusted to a predetermined volume to serve as a test solution, and Zn (element) in the test solution was subjected to ICP-AES (Inductive Formula manufactured by Thermo Fisher Scientific Co., Ltd.). The coupled plasma atomic emission spectrometer "iCAP6500" was used for measurement.

The light-diffusing particles are incompatible with the transparent resin and exhibit a refractive index different from that of the transparent resin, and have a function of diffusing light that passes through the light-diffusing sheet (3). The powder (including the powder) is not particularly limited. For example, it may be an inorganic particle made of an inorganic material or an organic particle made of an organic material. Such a light-diffusing particle may be subjected to surface treatment by a surface treatment agent such as a coupling agent.

The inorganic material constituting the inorganic particles is not particularly limited, and examples thereof include cerium oxide, calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, inorganic glass, mica, talc, and white carbon black (white). Carbon), magnesium oxide, zinc oxide, and the like.

The organic material constituting the organic particles is not particularly limited, and examples thereof include a propylene-based polymer, a siloxane-based polymer, and a styrene-based polymer.

Among these, from the viewpoint that the light diffusing plate can be made lighter while the illuminance is increased due to less impurities, it is preferable to use organic particles, and particularly suitable are propylene-based polymer particles and helium oxygen. Alkane polymer particles.

The propylene-based polymer particles may be a polymer having a propylene-based monofunctional monomer unit as a main component, that is, a polymer containing 50% by mass or more of a propylene-based monofunctional monomer unit. . The particles containing the polymer of 50% by mass or more of the propylene-based monofunctional monomer unit may be particles of a polymer of all (100% by mass) of the monomer unit, which is a propylene-based monofunctional monomer unit. It may be a particle of a copolymer of a propylene-based monofunctional monomer and a monofunctional monomer copolymerizable therewith.

The propylene-based monofunctional monomer may, for example, be acrylic acid, methacrylic acid, acrylate or methacrylate. The acrylate is not particularly limited, and may, for example, be methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate or 2-ethylhexyl acrylate. 2-hydroxyethyl acrylate or the like. Further, the methacrylate is not particularly limited, and examples thereof include methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, and benzene methacrylate. Ester, benzyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, and the like. These propylene-based monofunctional monomers may be used singly or in combination of two or more.

The monofunctional monomer copolymerizable with the above-mentioned propylene-based monofunctional monomer has one double bond capable of radical polymerization in the molecule, and can be carried out by the double bond and the propylene-based monofunctional monomer. Copolymerized compound. Specifically, for example, in addition to styrene, substituted styrene such as halogenated styrene such as chlorostyrene or bromostyrene, alkylstyrene such as vinyltoluene or α-methylstyrene, and the like may be mentioned. . Further, acrylonitrile can also be mentioned. These monofunctional monomers may be used singly or in combination of two or more.

When the propylene-based polymer particles are all particles of a polymer of a monomer unit (100% by mass) of a propylene-based monofunctional monomer unit, and a propylene-based monofunctional monomer and can be carried out therewith In the case of particles of a copolymer of a copolymerized monofunctional monomer, the weight average molecular weight thereof is preferably from 500,000 to 5,000,000.

Further, the propylene-based polymer particles may be particles of a copolymer of a propylene-based monofunctional monomer and a polyfunctional monomer copolymerizable therewith. Such a polyfunctional monomer means two or more double bonds capable of copolymerizing with a propylene-based monofunctional monomer in the molecule, and can be copolymerized with the propylene-based monofunctional monomer by such a double bond. The meaning of the compound. Examples of such a polyfunctional monomer include methacrylates of polyhydric alcohols, acrylates of polyhydric alcohols, and aromatic polyfunctional groups similar to those described for the styrene polymer particles. Compounds, etc. These polyfunctional monomers may be used singly or in combination of two or more.

A copolymer of a propylene-based monofunctional monomer and a polyfunctional monomer copolymerizable therewith, which is a copolymer of a bridge structure, and preferably has a gel fraction of 10% by mass. More than %.

Further, the propylene-based polymer particles may be obtained by copolymerizing a propylene-based monofunctional monomer/a monofunctional monomer copolymerizable therewith/a polyfunctional monomer which can be copolymerized in the same manner. A particle such as a ternary copolymer.

The refractive index of the propylene-based polymer particles is usually about 1.46 to 1.55, and the larger the content of the benzen skeleton or the halogen atom, the higher the refractive index tends to be. Further, such propylene-based polymer particles can be produced, for example, by a general polymerization method such as a suspension polymerization method, a micro suspension polymerization method, an emulsion polymerization method, or a dispersion polymerization method.

The azeosiloxane-based polymer particles are, for example, polymers produced by a method in which a chlorodecane is hydrolyzed and condensed. The chlorodecanes may, for example, be dimethyldichlorodecane, diphenyldichlorodecane, phenylmethyldichlorodecane, methyltrichlorodecane or phenyltrichlorodecane. The aforementioned siloxane-based polymer may be a cross-linker. For example, when it is crosslinked, for example, a paraxane-based polymer, such as benzammonium peroxide, 2,4-dichlorobenzidine peroxide, p-chlorobenzothymidine peroxide, or bismuth peroxide The peroxide such as a base or dibutyl butyl-2,5-dimethyl-2,5-di(t-butylperoxy)hexane may be used. Further, in the case where a structure having a stanol group at the terminal is to be formed, it is subjected to condensation bridging with an alkyl decane. The crosslinked naphthenic polymer is preferably one having two or three organic groups bonded to each of the ruthenium atoms. Such a decane-based polymer is also referred to as a polymer of a polyoxyxene rubber or a polyoxymethylene resin. The siloxane model is preferably one which is solid at normal temperature.

The azeosiloxane-based polymer particles can be obtained, for example, by pulverizing the above-described siloxane-based polymer. A curable polymer having a linear organosiloxane block or a composition thereof may be hardened in a spray state to form a granulated particle (refer to Japanese Patent Laid-Open No. 59). -68333 bulletin). Further, an alkyltrialkoxide or a partially hydrolyzed condensate thereof may be obtained by subjecting it to a hydrolytical condensation in an aqueous solution of ammonia or an amine to prepare a granulated particle (refer to Japanese Patent Special). Kai-kai 60-13813).

The above siloxane polymer particles preferably have a weight average molecular weight of from 500,000 to 5,000,000. In the case where the azeosiloxane-based polymer has a crosslinked structure, the gel fraction is preferably 10% by mass or more. The refractive index of the above siloxane polymer particles is usually about 1.40 to 1.47.

The styrene polymer particles may be a polymer containing a styrene-based monofunctional monomer unit as a main component, that is, a polymer containing 50% by mass or more of a styrene-based monofunctional monomer unit. . The particles containing the polymer of 50% by mass or more of the styrene-based monofunctional monomer unit may be particles of a polymer of a styrene-based monofunctional monomer unit (100% by mass) of the monomer unit. It may be a particle of a copolymer of a styrene-based monofunctional monomer and a monofunctional monomer copolymerizable therewith.

The styrene-based monofunctional monomer has a styrene skeleton and has a compound having one double bond capable of undergoing radical polymerization in the molecule. Specifically, for example, in addition to styrene, a substituted styrene is also mentioned. The substituted styrene may, for example, be a halogenated styrene such as chlorostyrene or bromostyrene, an alkylstyrene such as vinyltoluene or α-methylstyrene, or the like.

The monofunctional monomer copolymerizable with the styrene-based monofunctional monomer has one double bond capable of radical polymerization in the molecule, and can be co-polymerized with the styrene-based monofunctional monomer. Polymerized compound. Specifically, methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, methacrylic acid 2- Ethyl acrylate such as ethyl hexyl ester or 2-hydroxyethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethyl acrylate An acrylate such as hexyl ester or 2-hydroxyethyl acrylate, acrylonitrile or the like. These monofunctional monomers may be used singly or in combination of two or more. Among them, a monofunctional monomer copolymerizable with the styrene-based monofunctional monomer is preferably a methacrylate.

When the styrene polymer particles are all particles of a polymer of a monomer unit (100% by mass) of a styrene-based monofunctional monomer unit, and a styrene-based monofunctional monomer and can be carried out therewith In the case of particles of a copolymer of a copolymerized monofunctional monomer, the weight average molecular weight thereof is preferably from 500,000 to 5,000,000.

Further, the styrene polymer particles may be particles of a copolymer of a styrene-based monofunctional monomer and a polyfunctional monomer copolymerizable therewith. These polyfunctional monomers mean a compound having two or more double bonds capable of undergoing radical polymerization in the molecule and capable of copolymerizing the double bond with a styrene monofunctional monomer. Such a polyfunctional monomer may, for example, be 1,4-butanediol dimethacrylate, neopentyl glycol methacrylate, ethylene glycol dimethacrylate or diethylene glycol dimethacrylate. Acrylate, tetraethylene glycol dimethacrylate, propylene glycol dimethacrylate, tetrapropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, isopentaerythritol tetramethacrylate, etc. Polyol methacrylates, 1,4-butanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate Polyacrylate acrylates such as ester, propylene glycol diacrylate, tetrapropylene glycol diacrylate, trimethylolpropane triacrylate, and isopentaerythritol tetraacrylate, divinylbenzene, diallyl phthalate An aromatic polyfunctional compound such as an acid ester. These polyfunctional monomers may be used singly or in combination of two or more.

The copolymer of a styrene-based monofunctional monomer and a polyfunctional monomer copolymerizable therewith is a copolymer of a crosslinked structure, and the gel fraction thereof is preferably 10% by mass or more.

Further, the styrene polymer particles may be obtained by copolymerizing a styrene monofunctional monomer/a monofunctional monomer copolymerizable with the same/copolymerizable polyfunctional monomer. A particle such as a ternary copolymer.

The refractive index of the styrene polymer particles is usually about 1.53 to 1.61, and the larger the content ratio of the benzene skeleton or the halogen atom, the higher the refractive index tends to be. Further, such styrene polymer particles can be produced, for example, by a general polymerization method such as a suspension polymerization method, a microsuspension polymerization method, an emulsion polymerization method, or a dispersion polymerization method.

The average particle diameter of the light-diffusing particles is preferably from 0.5 μm to 5 μm, more preferably from 0.6 μm to 3 μm, from the viewpoint of being able to sufficiently uniformly disperse the light in the transparent resin while diffusing light.

Further, the average particle diameter of the light-diffusing particles is a value measured as follows (the average particle diameter of the light-diffusing particles of the examples is also the same). In other words, first, a light diffusing agent (light diffusing particles) is press-fitted to a sample stage, and carbon deposition is performed to prepare a sample piece. This test piece was subjected to a field emission scanning electron microscope "FE-SEM S-4200" manufactured by Hitachi, Ltd., and the SEM of the light diffusing agent was performed at a magnification of 10,000 times to 20,000 times. Microscope) observation and photography. In the photographic image of the obtained light-diffusing particles, 40 light-diffusing particles were randomly selected (randomly), and the particle diameters of the 40 light-diffusing particles were measured from each image by a three-point circular radius method. The average value of the particle diameters of the 40 light-diffusing particles obtained in this manner is referred to as "average particle diameter". That is, after the total particle diameters of the 40 light-diffusing particles are totaled, the total value is divided by the value obtained by 40.

Moreover, the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the light-diffusing particle is obtained from the viewpoint of sufficiently diffusing light even when the amount of use of the light-diffusing particles is relatively small. Preferably, the absolute value of the difference in refractive index is preferably 0.10 or more, and the absolute value of the difference in refractive index is set to 0.50. The following way.

The amount of use of the light-diffusing particles varies depending on the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the light-diffusing particles, or the degree of diffusion of the intended light, but the transparent resin 100 The parts by mass are usually from 0.01 to 20 parts by mass, preferably from 0.1 to 10 parts by mass.

The light-diffusing sheet (3) of the present invention may contain additives such as an antistatic agent, an antioxidant, a processing stabilizer, an ultraviolet absorber, and a flame retardant, within a range not inhibiting the effects of the present invention. These additives may be used alone or in combination of two or more.

In the embodiment of Fig. 2, the light diffusing plate (3) is formed of a single layer, but it may be formed of two or more layers.

For example, as shown in FIG. 3, the light diffusing plate (3) may be formed by laminating the surface layer (9) (9) by double-sided surface of the base layer (base layer) (8). The composition. The base layer (8) is made of a transparent resin and light-diffusing particles, and a layer of a transparent resin having a light transmittance of 65% or more when the light having a wavelength of 600 nm is transmitted for an optical path length of 200 mm is used as the transparent resin. It is also possible to adopt a configuration in which the surface layer (9) is laminated and integrated on one side of the base layer (8).

The transparent resin constituting the surface layer (9) is, for example, a suitable one for the transparent resin constituting the base layer (8). The transparent resin is not particularly limited, and polystyrene is exemplified. , methyl methacrylate-styrene copolymer, methacrylic acid-styrene copolymer, maleic anhydride-styrene copolymer, polymethyl methacrylate, methyl methacrylate-acrylate copolymer, polycarbonate Ester, polypropylene, polycycloolefin, cycloolefin-α-olefin copolymer, and the like. The transparent resin constituting the surface layer (9) may have a light transmittance of 65% or more when the light having a wavelength of 600 nm is transmitted for an optical path length of 200 mm, or for example, the thickness (T) of the surface layer (9) is higher than the base layer. (8) In the case of a thin condition, the light transmittance when the light having a wavelength of 600 nm is transmitted for an optical path length of 200 mm may be 65% or less.

In the case where the surface layer (9) contains an ultraviolet absorber, the ultraviolet absorber is not particularly limited, and examples thereof include a benzotriazole-based ultraviolet absorber and a diphenylketone-based ultraviolet absorber. An absorbent, a cyanoacrylate ultraviolet absorber, a malonate ultraviolet absorber, an oxalic anilide ultraviolet absorber, or the like. As a result of containing the ultraviolet absorber in the surface layer (9), deterioration of the light diffusing plate (3) due to ultraviolet rays or the like contained in the light from the external light and the light (2) can be prevented.

The surface layer (9) may contain, in addition to the ultraviolet absorber, a matt agent, a light diffusing agent (light diffusing particles), an antistatic agent, an antioxidant, a processing stabilizer, Additives such as flame retardants and lubricants.

The thickness (T) of the aforementioned surface layer (9) is usually from 10 μm to 200 μm, more preferably from 20 μm to 200 μm, particularly preferably from 50 μm to 100 μm (refer to Fig. 3).

Further, the thickness (S) of the light diffusing plate (3) is usually set to 1 mm or more (refer to Figs. 2 and 3). If the thickness is 1 mm or more, sufficient mechanical strength can be ensured. Further, in order to ensure the light weight of the light diffusing plate (3), the thickness (S) of the light diffusing plate (3) is preferably set to 5 mm or less.

In the case where the light-diffusing sheet (3) of the present invention has a single-layer structure as shown in Fig. 2, for example, it can be produced by a method such as extrusion molding or injection molding. For example, the transparent resin and the light-diffusing particles are dry blended, and after being heated, they are melted, and then molded by a usual molding method such as an extrusion molding method or an injection molding method. Alternatively, a pellet master-like master batch may be prepared by melt-kneading the light-diffusing particles together with a relatively small amount of a transparent resin, and then the transparent resin and the master batch may be dry-blended and molded. Moreover, in the case of the multi-layer structure as shown in FIG. 3, coextrusion molding, lamination, hot gluing, solvent gluing may be employed. It is produced by methods such as polymerization gluing, cast polymerization, and surface coating. These manufacturing methods are merely examples, and the light diffusing plate (3) of the present invention is not limited to the manufacturer of the manufacturing method.

Further, the light diffusing plate (3) of the present invention may be coated with an antistatic agent on its surface. Since the surface is coated with an antistatic agent to prevent the adhesion of dust due to static electricity to prevent the light transmittance due to dust from being lowered, the transmissive image display panel (liquid crystal panel) can be brightly illuminated for a longer period of time. Etc) (20).

Further, the size of the light diffusing plate (3) of the present invention is not particularly limited, and may be appropriately set in accordance with, for example, the size of the intended surface light source device (1) or the transmissive image display device (30). Among them, a light diffusing plate designed to have a size of 20 (length 30 cm, width 40 cm) or more is particularly suitable.

The light diffusing plate (3) of the present invention, the surface light source device (1) and the transmissive image display device (30) are not limited by the above embodiments, and are intended to be within the scope of the patent application. Any design changes may be tolerated without departing from the gist of the invention.

[Examples]

Next, the specific embodiments of the present invention will be described, but the present invention is not particularly limited by the examples.

First, the first extruder, the second extruder, and the T-dies used are as follows.

The first extruder: screw diameter 40mm, single-axis type, with vents (vent), made by Tanabe Plastics Co., Ltd.

2nd extruder: screw diameter 40mm, single-axis type, with vent hole, made by Tanabe Plastic Co., Ltd.

T-type die: 2 kinds of 3-layer multi-tubular T-die, lip width 250mm, manufactured by Sangao Engineering Co., Ltd.

<raw material>

(light diffusing agent masterbatch)

84 parts by mass of polystyrene ("HRM40" manufactured by Toyo Phenol Co., Ltd.) and light-diffusing particles ("Barra Route EXL 5766" manufactured by Roma and Haas, and crosslinked propylene-based polymer particles) 14 parts by mass 1 part by mass of ultraviolet ray absorbing agent ("Biotech spectroscopy 520" manufactured by Kyoritsu Co., Ltd.) and 1 part by mass of a processing stabilizer ("Summer Chemical GP" manufactured by Sumitomo Chemical Co., Ltd.), and a screw diameter of 65 mm was used. The twin-screw extruder was kneaded at 80 to 250 ° C to pelletize it to obtain a pellet-shaped light diffusing agent master batch.

(surface compound (compound))

90.9 parts by mass of a methyl methacrylate-styrene copolymer ("MS200NT" manufactured by Nippon Steel Chemical Co., Ltd.), a matting agent (XC1A manufactured by Sumitomo Chemical Co., Ltd., crosslinked propylene-based polymer particles, and an average particle diameter of 25 μm) 1 part by mass, a UV absorber ("Akasdav LA-31" manufactured by ADEKA Co., Ltd.), 1 part by mass, and a processing stabilizer ("Summer Chemicals GP" manufactured by Sumitomo Chemical Co., Ltd.), 0.1 part by mass, dry blended Thereafter, the mixture was kneaded at 180 to 250 ° C using a twin-screw extruder having a screw diameter of 65 mm to obtain a pellet-like surface layer compound.

<Example 1>

The polystyrene (zinc is contained in polyethylene zinc) adjusted to a zinc content of 10 ppm or less by a manufacturer of the company "STYRON 648" manufactured by Dow Chemical Co., Ltd., and placed in a 260 mm × In a mold of 110 mm × 5 mm in thickness, a hot press ("New Channel type ASF type hydraulic press machine" manufactured by Shinto Metal Industry Co., Ltd.) was used, and hot press molding was performed at a molding temperature of 230 ° C ( Pressing at 0.3 MPa for 5 minutes, pressing at 2.0 MPa for 3 minutes, pressing at 13.0 MPa for 1 minute, cooling for 5 minutes), and then cutting to obtain a transparent resin sheet having a width of 50 mm, a length of 200 mm, and a thickness of 5 mm (refer to the fourth In the transparent resin sheet, T ₆₀₀ , T ₄₀₀ , Tt (spectrum), chromaticity x, chromaticity y, and chromaticity difference were obtained according to the measurement method described later.

Then, 7.5 parts by mass of the light diffusing agent masterbatch and 100 parts by mass of polystyrene ("STYRON 648" manufactured by DOW Chemical Co., Ltd.) having a zinc content of 10 ppm or less were fed into a raw material tank of the first extruder ( In the hopper, after being melt-kneaded at 200 to 250 ° C while maintaining the vacuum of the vent portion at 100 kPa (gauge), it is supplied to a T-die which is maintained at 245 to 250 ° C. head.

On the other hand, the surface layer compound is fed into the raw material tank of the second extruder, and after being melted and kneaded at 190 to 250 ° C while maintaining the vacuum of the vent hole portion at 100 kPa (gauge pressure), It is supplied to a T-die which is maintained at the aforementioned 245 to 250 °C.

The resin composition supplied from the first extruder can be used as the base layer (8), and the resin composition supplied from the second extruder can be coextruded as the surface layer (9) (9). A light diffusing plate (3) made of a laminate having a thickness of 2.0 mm (1.9 mm of base layer and 0.05 mm × 2 of surface layer) as shown in Fig. 3 was produced.

<Example 2>

In addition to the polyethylene which is adjusted to have a zinc content of 10 ppm or less as the transparent resin, the polyphenylene adjusted by the manufacturer of "STYRON 648" manufactured by DOW Chemical Company, and having a zinc content of 100 ppm can be used. In the same manner as in Example 1, except that ethylene (zinc is contained in zinc stearate), a transparent resin sheet having a width of 50 mm, a length of 200 mm, and a thickness of 5 mm was obtained, and a laminate having a three-layer structure was produced. Light diffusing plate.

<Example 3>

In addition, as a transparent resin, a polyethylene whose zinc content is adjusted to 10 ppm or less is not used, and it is adjusted by a manufacturer of "168N" manufactured by BASF, and the zinc content is 50 ppm. A transparent resin plate having a width of 50 mm, a length of 200 mm, and a thickness of 5 mm was produced in the same manner as in Example 1 except that the zinc stearate was used, and a light-diffusing sheet made of a laminate having a three-layer structure was produced.

<Comparative Example 1>

In addition to polyethylene which is adjusted to have a zinc content of 10 ppm or less as a transparent resin, it is treated by a manufacturer of "Empera 350N" manufactured by INEOS NOVA Chemicals Co., Ltd., and adjusted to have a zinc content of 70 ppm. In the same manner as in Example 1, a transparent resin sheet having a width of 50 mm, a length of 200 mm, and a thickness of 5 mm was produced, and a light-diffusing sheet made of a laminate having a three-layer structure was produced.

With respect to each of the transparent resin sheets obtained as described above, T ₆₀₀ , T ₄₀₀ , Tt (spectrum), chromaticity x, chromaticity y, and chromaticity difference were determined by the following measurement methods. Moreover, the light transmittance (Tt) and the average luminance difference were determined by the following evaluation methods for each of the light-diffusing sheets obtained as described above. These results are shown in Table 1.

<Measurement of light transmittance of light having a wavelength of 600 nm in the optical path length of 200 mm ‧Measurement of light transmittance of light having a wavelength of 400 nm in an optical path length of 200 mm ‧Light transmittance of a transparent resin plate (Tt Determination method>

The four side surfaces (51) of the obtained transparent resin sheet (width: 50 mm, length: 200 mm, thickness: 5 mm) were polished using a grinder ("Purabiti 1000" manufactured by Asahi Kagaku Co., Ltd.) to prepare a test piece (50). (Refer to Figure 4). For the measurement test piece, a plastic property measurement system (manufactured by a U-4000 spectrophotometer and a large-scale integrated sphere attachment device) manufactured by Hitachi, Ltd. was used to measure light having a wavelength of 600 nm and a transmission of 200 mm. Light transmittance (T ₆₀₀ ) when the optical path is long. Further, in the same manner, the light transmittance (T ₄₀₀ ) when the light having a wavelength of 400 nm was transmitted for an optical path length of 200 mm was measured. Further, the light transmittance Tt (the arithmetic mean of the light transmittance of light having a wavelength of 380 to 780 nm) in the optical path length of 200 mm was also measured.

<Measurement of chromaticity x and chromaticity y ‧ Calculation method of chromaticity difference>

For the above measurement test piece, a plastic characteristic measurement system (manufactured by a U-4000 type spectrophotometer and a large sample room integrating sphere attachment device) manufactured by Hitachi, Ltd. was used to measure the chromaticity x and the chromaticity y of the transmitted light. The chromaticity of the source of the spectrophotometer is x=0.3100, y=0.3161, and the chromaticity difference between the “source chromaticity” and the “chromaticity of transmitted light” is {(Δx) ² +(Δy) ² } The chromaticity (whether or not the natural color tone) of the transparent resin was evaluated ^1/2 . That is, as the chromaticity difference is smaller, the light from the light source is illuminated toward the front with a more natural hue.

<Formability Evaluation Method>

When a transparent resin sheet is produced by hot press molding, the resin on the metal surface of the hot press machine is not adhered, and the mold release property is also good as "○", and the metal for the hot press machine is used. The resin on the surface is attached, and those who are not good in the model are referred to as "x".

<Measurement of Light Transmittance (Tt) of Light-Diffusing Plate>

For the obtained light-diffusing sheet, a transmission ‧ reflectance meter HR-100 manufactured by Murakami Color Research Laboratory was used, and the light transmittance (Tt) was measured in accordance with JIS K7136.

(Evaluation method of average luminance difference (difference from luminance of Comparative Example 1)>

The light-diffusing sheet obtained as described above was cut into a square shape so that the extrusion direction (MD (machine direction) direction) was 110 mm long, and the direction perpendicular thereto was 110 mm wide, and an evaluation test piece was obtained. Next, after removing the liquid crystal panel, various optical films, and the light diffusing plate from the 20-inch type liquid crystal television, the center portion of the light diffusing plate is excavated into a square shape of 110 mm × 110 mm, and the light diffusing is mounted thereon. The evaluation test piece of the plate (the embodiment product and the comparative example) was placed in the state of the front side of the frame portion of the lamp urn after the detachment (the plurality of fluorescent lamps were disposed inside each other) The configuration is fixed to block the uncovered surface of the lamp unit. Then, two commercially available light-diffusing films were laminated on the front side of the light-diffusing sheet, and a brightness-enhancing film ("DBEF (reflective polarizing film)" manufactured by 3M Company, USA) was laminated on the front side. In the state of the bright fluorescent lamp, a brightness meter (Eye Scale-3W, a multipoint luminance meter) manufactured by Ai ‧ Systems Co., Ltd. was used to measure the brightness.

In addition, the aforementioned brightness measurement is carried out as follows. That is, in the floor surface of a dark room with constant temperature and humidity (temperature 25.0 ° C, humidity 50.0%), the LCD TV is placed with the front side as the top surface (the back side can be connected to the floor surface), and The overall way of shooting the front of the LCD TV is at the top of the LCD TV, and the camera is placed in the downward direction. At this time, the distance from the front of the liquid crystal television to the camera is set to 120.0 cm, and the measurement conditions of the luminance meter are set to SPEED (photosensitive speed): 1/250, GAIN (gain): 3, aperture: 16, and the liquid crystal television is set. The full range of the front is specified as a measurement spot to measure the brightness at each measurement spot (51×51=2601), and the average value of these brightnesses is taken as the average brightness (cd/m ² ( New candlelight / meter ² )).

Average luminance difference (%) = {(average luminance of the embodiment) - (average luminance of Comparative Example 1)} / (average luminance of Comparative Example 1)

It was evaluated by the average luminance difference (%) obtained from the above calculation formula.

From Table 1, since the embodiments of the present invention a light diffusing plate 3, based transparent resin T ₆₀₀ at 65%, therefore, more T ₆₀₀ at average brightness of the light diffusion plate of 30.9% of Comparative Example 1 was It is high, and thus, for example, a transmissive image display panel or the like can be illuminated more brightly.

Further, in the light-diffusing sheets of Examples 1 to 3, since the content of zinc in the transparent resin (polystyrene) is 150 ppm or less, the chromaticity difference is small, and it is possible to illuminate, for example, a transmissive image with a more natural color tone. Display panel, etc. In the light diffusing plates of Examples 1 and 3 in which the content of zinc in the transparent resin is 50 ppm or less, the difference in chromaticity is extremely small, and the transmissive image display panel or the like can be illuminated in a more natural color tone.

[Industry use possibility]

The light diffusing plate of the present invention is suitably used as a light diffusing plate for a surface light source device, but is not particularly limited to such use. Further, the surface light source device of the present invention is suitably used as a backlight for a transmissive image display device, but is not particularly limited to such use.

1‧‧‧ surface light source device

2‧‧‧Light source

3‧‧‧Light diffuser

20‧‧‧Transmissive image display panel

30‧‧‧Transmissive image display device (liquid crystal display device)

Fig. 1 is a schematic view showing an embodiment of a transmissive image display device according to the present invention.

Fig. 2 is a cross-sectional view showing an embodiment of a light diffusing plate according to the present invention.

Fig. 3 is a cross-sectional view showing another embodiment of the light diffusing plate of the present invention.

Fig. 4 is an explanatory view showing a method of measuring the light transmittance of light having a wavelength of 600 nm in an optical path length of 200 mm.

Claims (7)

A light diffusing plate comprising a transparent resin and a light-diffusing particle, wherein the transparent resin has a light transmittance of 65% or more when light having a wavelength of 600 nm is transmitted for an optical path length of 200 mm, and the transparent resin contains zinc. The composition of the compound, and the content of zinc in the composition is 90 ppm or less. The light diffusing plate of claim 1, wherein the zinc compound is zinc stearate. The light diffusing plate of claim 1 or 2, wherein the transparent resin contains polystyrene. The light-diffusing sheet of the first or second aspect of the invention, wherein the light-diffusing particles are one or more polymer particles selected from the group consisting of propylene-based polymer particles and siloxane-based polymer particles. The light diffusing plate of claim 1 or 2, wherein the light diffusing particles have an average particle diameter of 0.5 to 5 μm, and an absolute value of a difference between a refractive index of the transparent resin and a refractive index of the light diffusing particles is 0.05 or more The transparent resin is contained in an amount of from 0.1 to 10 parts by mass per 100 parts by mass of the light-diffusing particles. A surface light source device comprising: a light diffusing plate according to any one of claims 1 to 5; and a plurality of light sources disposed on a back side of the light diffusing plate. A transmissive image display device comprising: a light diffusing plate according to any one of claims 1 to 5; and a plurality of light sources disposed on a back side of the light diffusing plate, and Configured before A transmissive image display panel on the front side of the light diffusing plate.