JP2008185655A - Light diffusion plate, surface light source apparatus and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion plate lightweight, having sufficient strength and low hygroscopic property and excellent heat resistance to be free from deformation due to moisture absorption and heat. <P>SOLUTION: The light diffusion plate 3 contains a resin component and light diffusion particles wherein a propylene resin and a methacrylate resin are contained as the resin component and the content of propylene resin is ≥40 pts.mass and ≤100 pts.mass per 100 pts.mass in total of the propylene resin and the methacrylate resin. A liquid crystal display device 30 is provided with the light diffusion plate 3, a plurality of the light sources 2 arranged in the back side of the light diffusion plate 3 and a liquid crystal panel 20 arranged on the front side of the light diffusion plate 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light diffusing plate that is lightweight, has sufficient strength, and has low hygroscopicity, and a surface light source device and a liquid crystal display device that are configured using the light diffusing plate.

As a liquid crystal display device, for example, a configuration in which a surface light source device is disposed as a backlight on the back side of a liquid crystal panel (image display unit) including a liquid crystal cell is known. As the surface light source device for the backlight, a surface light source device having a configuration in which a plurality of light sources are disposed in a lamp box (housing) and a light diffusion plate is disposed on the front side of these light sources is known. (See Patent Document 1). In many cases, the light diffusion plate is made of methacrylic resin.
JP 2004-170937 A

  However, a lighter light diffusing plate is required. Moreover, the light diffusing plate made of the methacrylic resin has a problem that it is easily deformed by moisture absorption or heat, and the strength is not sufficient.

  The present invention has been made in view of such a technical background, and is lighter and lighter, has sufficient strength, has low hygroscopicity and excellent heat resistance, and does not deform due to moisture absorption or heat. It is an object of the present invention to provide a plate, a surface light source device including the light diffusion plate, and a liquid crystal display device.

  In order to achieve the above object, the present invention provides the following means.

[1] In a light diffusing plate comprising a resin composition containing a resin component and light diffusing particles,
A light diffusion plate containing propylene resin and methacrylic resin as the resin component, wherein the propylene resin content per 100 parts by mass of the total amount of propylene resin and methacrylic resin is 40 parts by mass or more and less than 100 parts by mass .

  [2] A surface light source device comprising: the light diffusing plate according to the preceding item 1; and a plurality of light sources arranged on the back side of the light diffusing plate.

  [3] The light diffusing plate according to item 1 above, a plurality of light sources arranged on the back side of the light diffusing plate, and a liquid crystal panel arranged on the front side of the light diffusing plate. Liquid crystal display device.

  In the invention of [1], since it contains a propylene resin in addition to a methacrylic resin, it can be reduced in weight, and has a reduced hygroscopicity and improved heat resistance, compared to a conventional light diffusion plate made of a methacrylic resin. And can sufficiently prevent moisture absorption and heat deformation. Moreover, since the same mechanical strength is obtained as compared with a conventional light diffusion plate made of methacrylic resin, it is difficult to break.

  In the invention of [2], the light diffusing plate which is a constituent member is lightweight, has sufficient strength, has low hygroscopicity and excellent heat resistance, and is not deformed by moisture absorption or heat. A surface light source device is provided. That is, in this surface light source device, the light diffusing plate is not deformed by heat generated when the light source is turned on, and the light diffusing plate is not deformed by moisture absorption.

  In the invention of [3], the light diffusing plate as a constituent member is lightweight, has sufficient strength, has low hygroscopicity and excellent heat resistance, and is not deformed by moisture absorption or heat. A liquid crystal display device is provided. That is, in this liquid crystal display device, the light diffusing plate is not deformed by heat generated when the light source is turned on, and the light diffusing plate is not deformed by moisture absorption, so that high-quality image display can be realized.

  An embodiment of a liquid crystal display device according to the present invention is shown in FIG. In FIG. 1, (30) is a liquid crystal display device, (11) is a liquid crystal cell, (12) and (13) are polarizing plates, and (1) is a surface light source device (backlight). Polarizing plates (12) and (13) are respectively arranged on the upper and lower sides of the liquid crystal cell (11), and a liquid crystal panel (20) as an image display unit is constituted by these constituent members (11), (12) and (13). Yes. In addition, as the liquid crystal cell (11), those capable of displaying a color image are preferably used.

  The said surface light source device (1) is arrange | positioned at the lower surface side (back side) of the polarizing plate (13) below the said liquid crystal panel (20). That is, the liquid crystal display device (30) is a direct liquid crystal display (display) device.

  The surface light source device (1) is a thin box-shaped lamp box (5) having a rectangular shape in plan view and having an upper surface side (front surface side) opened, and the lamp box (5) spaced apart from each other. A plurality of linear light sources (2), and a light diffusing plate (3) disposed on the upper side (front side) of the plurality of linear light sources (2). The said light diffusing plate (3) is mounted and fixed with respect to the said lamp box (5) so that the open surface may be block | closed. A light reflecting layer (not shown) is provided on the inner surface of the lamp box (5). Although it does not specifically limit as said light source (2), For example, a cold cathode ray tube, a light emitting diode (LED), etc. are used.

  The light diffusing plate (3) is made of a resin composition containing a resin component and light diffusing particles (light diffusing agent). The resin composition contains a propylene resin and a methacrylic resin as resin components. In the resin composition, the propylene resin content per 100 parts by mass of the total amount of propylene resin and methacrylic resin is 40 parts by mass or more and 100 parts by mass. Less than part by mass.

  Since the light diffusing plate (3) according to the above structure contains a propylene resin in addition to the methacrylic resin, the light diffusing plate can be reduced in weight as compared with a conventional light diffusing plate made of methacrylic resin, and has a low hygroscopicity. Heat resistance can be improved and deformation due to moisture absorption or heat can be sufficiently prevented. Further, since mechanical strength equivalent to that of a conventional light diffusion plate made of methacrylic resin is obtained, it is difficult to break. Further, since the light diffusing particles are contained, a sufficient light diffusing function can be obtained. Therefore, in the surface light source device (1) and the liquid crystal display device (30) of the present invention configured using the light diffusing plate (3), the light diffusing plate (3) is caused by heat generated when the light source (2) is turned on. It does not deform, and the light diffusing plate (3) is not deformed by moisture absorption.

  In this invention, the propylene resin content in the resin composition constituting the light diffusion plate (3) is such that the propylene resin content per 100 parts by mass of the total amount of propylene resin and methacrylic resin is 40 parts by mass or more and less than 100 parts by mass. Set to be in range. If the amount is less than 40 parts by mass, the weight cannot be reduced, the hygroscopicity is increased, the heat resistance is also lowered, and the film is easily deformed by moisture absorption or heat. Especially, in the said resin composition, the preferable upper limit of the propylene resin content per 100 mass parts of total amounts of a propylene resin and a methacryl resin is 97 mass parts or less, and a more preferable upper limit is 95 mass parts or less. That is, in the resin composition, a preferable lower limit value of the methacrylic resin content per 100 parts by mass of the total amount of the propylene resin and the methacrylic resin is 3 parts by mass or more, and a more preferable lower limit value is 5 parts by mass or more. Thus, when the content of the methacrylic resin per 100 parts by mass of the total amount of the propylene resin and the methacrylic resin is 5 parts by mass or more, the light resistance can be improved.

  In the present invention, the propylene resin may be homopolypropylene obtained by polymerizing propylene alone, or may be a copolymer of propylene and a copolymerizable component capable of copolymerizing therewith. Among these, the propylene resin is preferably a polymer containing 50% by mass or more of propylene units. Furthermore, the content of the propylene unit in the propylene resin is particularly preferably 98% by mass or more in that sufficient rigidity is obtained. The copolymer component is not particularly limited, and examples thereof include α-olefins such as ethylene and 1-butene.

  The methacrylic resin may be a methyl methacrylate homopolymer (with a methyl methacrylate unit content of 100%) obtained by polymerizing methyl methacrylate units alone. It may be a copolymer with another monomer that can be copolymerized. Among them, the methacrylic resin is preferably a polymer containing 50% by mass or more of methyl methacrylate units.

  The monomer that can be copolymerized with methyl methacrylate is not particularly limited. For example, a monofunctional monomer having one double bond copolymerizable with methyl methacrylate in the molecule. Examples of such monofunctional monomers include methacrylic acid esters other than methyl methacrylate. Examples of the methacrylic acid esters include ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate and the like. Further, other specific examples of the monomer copolymerizable with methyl methacrylate include, for example, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, acrylic acid Acrylic esters such as 2-ethylhexyl, unsaturated acids such as acrylic acid and methacrylic acid, halogenated styrenes such as chlorostyrene and bromostyrene, and substituted styrenes such as alkylstyrenes such as vinyltoluene and α-methylstyrene. Styrene, acrylonitrile, methacrylonitrile, maleic anhydride, phenylmaleimide, cyclohexylmaleimide and the like. These monomers may be used alone or in combination of two or more.

  The light diffusing particle (light diffusing agent) is a particle having a refractive index different from that of the resin component (mixed resin) constituting the resin composition, and diffuses the light transmitted through the light diffusing plate by the dispersion inclusion of the particle. If it can do, it will not specifically limit. For example, the particles may be inorganic particles such as glass particles, glass fibers, silica particles, aluminum hydroxide particles, calcium carbonate particles, barium sulfate particles, titanium oxide particles, talc, styrene polymer particles, acrylic polymers. Organic particles such as particles and siloxane polymer particles may be used.

As the light diffusing particles, those having a volume average particle diameter in the range of 0.5 to 25 μm are usually used. Among these, a preferable lower limit value of the volume average particle diameter is 0.7 μm or more, and a preferable upper limit value of the volume average particle diameter is 20 μm or less, and a particularly preferable upper limit value is 10 μm or less. The volume average particle size (D ₅₀ ) is determined by measuring the particle size and volume of all particles, and integrating the volume sequentially from the smallest particle size, and the integrated volume is 50% of the total volume of all particles. The particle diameter of the resulting particles.

  The content of the light diffusing agent in the resin composition constituting the light diffusing plate (3) is preferably set in the range of 0.1 to 20 parts by mass with respect to 100 parts by mass of the total amount of the resin components. When the amount is 0.1 parts by mass or more, the light diffusion effect can be sufficiently obtained, and when the amount is 20 parts by mass or less, sufficient mechanical strength can be secured.

  If necessary, the resin composition constituting the light diffusing plate (3) may include a nucleating agent, an ultraviolet absorber, a heat stabilizer, an antioxidant, a weathering agent, a light stabilizer, a fluorescent whitening agent, and processing stability. You may contain additives, such as an agent. Examples of the nucleating agent are compatible with resin components (mixed resins) such as sorbitol nucleating agents, organophosphate nucleating agents, metal salt nucleating agents for carboxylic acids, and rosin nucleating agents. Good one can be used.

  Moreover, if it is a range which does not inhibit the effect of this invention, you may make resin other than a propylene resin and a methacryl resin contain in the resin composition which comprises the said light diffusing plate (3).

  The light diffusing plate (3) of this invention can be manufactured as follows, for example. That is, an extrusion molding method for extrusion molding, an injection molding method for injection molding, and a hot press method for hot pressing a resin composition (for example, a resin composition containing a propylene resin, a methacrylic resin, and a light diffusing agent) according to the above configuration. It can manufacture by well-known forming methods, such as. The said manufacturing method is only what showed the example, and the light diffusing plate (3) of this invention is not limited to what was manufactured with such a manufacturing method.

  In addition, the structure by which the surface layer was laminated | stacked on the single side | surface or both surfaces may be sufficient as the light diffusing plate (3) of this invention.

  Moreover, the thickness of the said light diffusing plate (3) is normally set to the range of 1-3 mm.

  The size of the light diffusing plate (3) is not particularly limited, and is appropriately set according to the size of the target surface light source device (1) or liquid crystal display device (30), for example. However, among them, it is particularly suitable as a light diffusing plate designed to have a size of 20 type (length 30 cm, width 40 cm) or more.

  The light diffusing plate (3), the surface light source device (1), and the liquid crystal display device (30) according to the present invention are not particularly limited to those of the above-described embodiment, and the spirit thereof is within the scope of the claims. Any design changes are allowed as long as they do not deviate from.

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

<Example 1>
90 parts by mass of a propylene resin (“D101” manufactured by Sumitomo Chemical Co., Ltd., a propylene-ethylene copolymer resin, a propylene unit content of 99% by mass or more and an ethylene unit content of 1% or less), a methacrylic resin (manufactured by Sumitomo Chemical “ EXN ", methyl methacrylate unit content 94% by mass) 10 parts by mass, siloxane polymer particles (light diffusion particles) (" DY33-719 "manufactured by Toray Dow Corning Co., Ltd., volume average particle diameter 2 to 3 m) 1 mass Part, 0.3 part by mass of a nucleating agent (“NA11” manufactured by ADEKA) was dry blended, then supplied to an extruder with a screw diameter of 40 mm and melt-kneaded at 210 to 250 ° C., then a feed block and a T die The light diffusion plate (3) having a thickness of 2 mm was manufactured by performing extrusion molding at a T-die temperature of 245 to 260 ° C.

<Examples 2 and 3 and Comparative Example 1>
A light diffusing plate (3) was produced in the same manner as in Example 1 except that the composition of the resin composition supplied to the extruder was as shown in Table 1.

  Each light diffusion plate obtained as described above was evaluated according to the following evaluation method. The evaluation results are shown in Table 1.

<Total light transmittance measurement method>
Based on JIS K7361-1997, the total light transmittance (%) of the light diffusing plate was measured.

<Diffusion light transmittance measurement method>
Based on JIS K7136-2000, the diffused light transmittance (%) of the light diffusing plate was measured.

<Haze value measuring method>
The haze (%) of the light diffusion plate was measured according to JIS K7136-2000.

<Measurement of yellowness YI, chromaticity x, chromaticity y by spectral transmittance measurement>
Using a self-recording spectrophotometer equipped with an integrating sphere (“UV-4000” manufactured by Hitachi, Ltd.), the spectral transmittance in the wavelength range of 380 to 780 nm of the light diffusing plate was measured, and based on this, yellowness YI, chromaticity x and chromaticity y were calculated respectively.

<Measurement method of water absorption rate (Method A)>
The obtained light diffusion plate was cut into a size of 150 mm × 150 mm to obtain a test piece. The test piece was placed in an oven at 80 ° C. for 4 days and dried, and then the mass of the test piece was measured. This measured value is defined as dry mass W ₀ . Next, the test piece was placed in a constant temperature and humidity chamber of 60 ° C. × 95% RH for 4 days to absorb water, and the mass of the test piece was immediately measured. This measured value is defined as W ₁ .

Water absorption rate (%) = {(W ₁ −W ₀ ) / W ₀ } × 100 Equation 1
The water absorption rate (%) was calculated by the above formula 1.

<Measurement method of water absorption rate (Method B)>
The obtained light diffusion plate was cut into a size of 150 mm × 150 mm to obtain a test piece. The test piece was placed in an oven at 80 ° C. for 4 days and dried, and then the mass of the test piece was measured. This measured value is defined as dry mass W ₀ . Next, the test piece was immersed in water at 23 ° C. for 24 hours, and the mass of the test piece was immediately measured. This measurement and W _2.

Water absorption rate (%) = {(W ₂ −W ₀ ) / W ₀ } × 100 Equation 2
The water absorption (%) was calculated by the above formula 2.

<Load deflection temperature measurement method>
The deflection temperature under load (° C.) of the obtained light diffusion plate was measured in accordance with JIS K7207-1995. Moreover, the obtained light diffusing plate was annealed at 80 ° C. for 16 hours, and the deflection temperature (° C.) under load was measured in accordance with JIS K7207-1995 for the light diffusing plate after the annealing treatment.

<Vicat softening point measurement method>
The Vicat softening point (° C.) of the obtained light diffusion plate was measured according to JIS K7206-1999. The obtained light diffusion plate was annealed at 80 ° C. for 16 hours, and the Vicat softening point (° C.) of the light diffusion plate after the annealing treatment was measured in accordance with JIS K7206-1999.

<Tensile fracture strength measurement method>
The tensile break strength (MPa) of the obtained light diffusion plate was measured according to JIS K7113-1994.

<Bending stiffness measurement method>
The bending stiffness (MPa) of the obtained light diffusion plate was measured according to JIS K7203-1995.

<Lightness evaluation method>
The lightness was evaluated by calculating the mass (kg / m ² ) per unit area of the obtained light diffusion plate having a thickness of 2 mm.

  As is apparent from Table 1, the light diffusion plates of Examples 1 to 3 of the present invention were lightweight, had sufficient mechanical strength, had low hygroscopicity, and were excellent in heat resistance.

  On the other hand, the light diffusing plate of Comparative Example 1 in which the content of the propylene resin deviates from the specified range of the present invention is poor in light weight, has high hygroscopicity, and is not sufficient in heat resistance.

  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 applications. The surface light source device of the present invention is preferably used as a backlight for a liquid crystal display device, but is not particularly limited to such applications.

1 is a schematic view showing an embodiment of a liquid crystal display device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface light source device 2 ... Light source 3 ... Light diffusing plate 20 ... Liquid crystal panel 30 ... Liquid crystal display device

Claims (3)

In a light diffusing plate comprising a resin composition containing a resin component and light diffusing particles,
A light diffusion plate containing propylene resin and methacrylic resin as the resin component, wherein the propylene resin content per 100 parts by mass of the total amount of propylene resin and methacrylic resin is 40 parts by mass or more and less than 100 parts by mass .   A surface light source device comprising: the light diffusing plate according to claim 1; and a plurality of light sources arranged on a back side of the light diffusing plate.   A liquid crystal display comprising: the light diffusing plate according to claim 1; a plurality of light sources arranged on a back side of the light diffusing plate; and a liquid crystal panel arranged on the front side of the light diffusing plate. apparatus.

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