KR20080079427A - Light diffusion resin composition and light diffusion plate using the same - Google Patents

Abstract

A light diffusion resin composition is provided to ensure low moisture absorption and excellent heat resistance, and to produce a light diffusion plate having small deformations caused by heat and moisture. A light diffusion resin composition includes 0.001-40 parts by weight of a light diffusion agent based on 100 parts by weight of styrene-based copolymer resin. The styrene-based copolymer resin is prepared by copolymerizing 70-99.5 parts by weight of at least one monomer selected from styrene and styrene-based derivatives and 0.5-30 parts by weight of a vinyl-based monomer. A light diffusion plate includes a diffusion base material layer formed by using the light diffusion resin composition as a base resin, and a functional layer formed on at least one surface of the diffusion base material layer.

Description

Light Diffusion Resin Composition And Light Diffusion Plate Using The Same

1A to 1C are cross-sectional schematic diagrams of a light diffusion plate according to an embodiment of the present invention.

Figure 2 is a schematic diagram of a method for measuring the heat deflection of the diffusion plate according to an embodiment of the present invention.

** Description of the major symbols in the drawings **

1: Inorganic Particles Containing Ultraviolet Absorber

20: diffusion substrate layer

21: light diffusing agent

30: functional layer

The present invention relates to a resin composition having excellent heat resistance and hygroscopicity and a light diffusion plate having improved heat resistance and small warpage deformation due to moisture absorption.

The light diffusion plate has a function of uniformly distributing light of a light source in light scattering or light diffusion. The expression of such a function is used in a cover unit of a lamp or a backlight unit such as a liquid crystal TV or a monitor. In particular, in the case of a liquid crystal display using a backlight unit, a light diffusion plate is provided directly above the light source to uniformly emit the light of the backlight light source, thereby preventing a difference in contrast due to the position of the light source on the entire display screen. . Such a light diffusion plate must maintain high brightness performance for efficient use of light as well as concealment performance or light diffusion performance, and relatively high light transmittance and light diffusion efficiency must be maintained to express such performance.

As the main substrates used in the light diffusion plate, acryl-based, polystyrene-based, and MS-based, cycloolefin-based, and polycarbonate-based resins, which are copolymers of acryl and polystyrene, have been used. Ghana has added light diffusing agents to adjust light diffusion efficiency and light transmission efficiency.

In recent years, due to the increase in size of liquid crystal displays, liquid crystal TVs of a direct type backlight unit type have become mainstream. The performance of the diffuser plate which is required with the enlargement of such a display is low hygroscopicity and high heat resistance.

In the case of hygroscopicity, the light diffusing plate has a large amount of warpage deformation of the light diffusing plate due to the heating and drying at the time of lamp lighting due to the hygroscopic property of the substrate. In many cases, it acts as a stain, and a diffusion plate using a substrate having a lower hygroscopicity is required. Accordingly, many diffusion plates using polystyrene having low hygroscopicity as a substrate have been developed and applied to actual products. However, polystyrene has a low hygroscopic property, but has a relatively low heat resistance. Therefore, a large display of 40 inches or more has a disadvantage such as long-term deformation due to heat of a light source in the backlight.

On the other hand, a method of using a high-brightness light source such as an LED has been proposed to increase the number of lamps and to improve luminance by increasing the size of a liquid crystal TV, but in this case, the temperature in the backlight unit rises, and thermal deformation of the diffusion plate easily occurs. do. Accordingly, there is a demand for a diffusion plate having high heat resistance due to uneven brightness and unevenness of the screen. Recently, in order to achieve this object, a polycarbonate diffusion plate having excellent heat resistance is used, but a polycarbonate diffusion plate is expensive despite high heat resistance and has a relatively high hygroscopicity.

The present invention is to solve the above problems, an object of the present invention is to minimize the deformation of the diffusion plate by the change in humidity and temperature by using a light diffusion plate using a substrate having a low hygroscopicity and excellent heat resistance.

The present invention for achieving the above object,

The light diffusing agent comprises 0.001 to 40 parts by weight based on 100 parts by weight of the styrene copolymer resin, wherein the styrene copolymer resin is 70 to 99.5 parts by weight of at least one monomer selected from styrene and styrene derivatives and 0.5 to 30 vinyl monomers. It provides a light diffusion resin composition prepared by copolymerization, including parts by weight.

In addition, the styrene derivative provides a copolymerized light diffusion resin composition, characterized in that the α-methylstyrene monomer.

In addition, the vinyl monomer provides a light-diffusion resin composition, characterized in that at least one selected from acryl, imide, and olefin.

In addition, the light diffusing agent provides a light diffusing resin composition, characterized in that at least one selected from silica, silicone rubber, acrylic and polystyrene resin.

In addition, with respect to 100 weight of the styrene-based copolymer resin, 0.01 to 10 parts by weight of an antioxidant is further included, wherein the antioxidant provides a light-diffusion resin composition, characterized in that at least one selected from phosphoric acid and phenolic. .

The present invention also provides a light diffusion plate comprising a diffusion base layer formed by using the light diffusion resin composition as a base resin, and a functional layer formed on at least one surface of the diffusion base layer.

In addition, the functional layer provides a light diffusion plate, characterized in that formed using a light diffusion resin composition defined as being used for the diffusion substrate layer as a base resin.

In addition, the functional layer provides a light diffusing plate, characterized in that the inorganic particles containing the ultraviolet absorber is included.

In addition, the thickness of the diffusion substrate layer is 0.1mm to 3.0mm, the thickness of the functional layer provides a light diffusion plate, characterized in that 0.01mm to 0.5mm.

In addition, with respect to a total of 100 weight of the inorganic particles containing the ultraviolet absorber, there is provided a light diffusion plate characterized in that 0.1 to 85 parts by weight of the ultraviolet absorber.

In addition, the ultraviolet absorber provides a light diffusion plate, characterized in that at least one selected from benzotriazole-based, malonic ester-based and benzophenone-based ultraviolet absorber.

The present invention also provides a backlight device having the light diffusion plate.

The present invention also provides a liquid crystal display device having the backlight device.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings and examples. The following description is a description of some embodiments of the present invention, and the present invention is not limited by the following detailed description, and the scope of the present invention is determined by the matters described in the claims.

The light-diffusion resin composition according to the present invention comprises 0.001 to 40 parts by weight of a light diffusing agent based on 100 weights of styrene-based copolymer resin, wherein the styrene-based copolymer resin is selected from at least one monomer selected from styrene and styrene derivatives. 99.5 parts by weight and vinyl monomers, including 0.5 to 30 parts by weight, characterized in that produced by copolymerization.

When using the light diffusion resin composition as a base resin to form a diffusion base layer of the light diffusion plate, the heat resistance is improved compared to the conventional polystyrene resin, and the hygroscopicity is lower than that of PMMA or polycarbonate. Excellent stability, heat resistance stability, and has the advantage of low hygroscopicity.

The styrene copolymer resin is prepared by copolymerizing styrene, styrene derivatives and vinyl monomers.

As said styrene derivative, (alpha) -methyl styrene etc. are mentioned preferably.

      In the present invention, the vinyl monomer copolymerizable with the styrene monomer may be selected from acryl, imide, and olefin, and acrylic and imide compounds are particularly advantageous in terms of heat resistance and strength improvement. Examples of such vinyl monomers include methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate and methacrylic acid; Acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, butyl acrylate and acrylic acid; Methacrylic acid cycloalkyl esters such as cyclohexyl methacrylate, 2-methylcyclohexyl methacrylate and dicyclopentanyl methacrylate; Acrylic acid cycloalkyl esters such as cyclohexyl acrylate and 2-methylcyclohexyl acrylate; Methacrylic acid aryl esters such as phenyl methacrylate and benzyl methacrylate; And acrylic acid aryl esters such as phenyl acrylate and benzyl acrylate, maleimide monomers such as maleimide, N-methyl maleimide and N-phenyl maleimide.

Regarding the total weight of styrene-based copolymer resins used in the present invention, at least one monomer selected from the above styrene and styrene derivatives is preferably 70 to 99.5 parts by weight, and suitably 80 to 98 parts by weight. The composition of vinyl monomers such as acrylic and imide copolymerized is preferably 0.5 to 30 parts by weight, and more preferably 2 to 20 parts by weight.

In the case of the copolymerized vinyl monomers, particularly acrylic and imide monomers, when the amount is less than 0.5 parts by weight, the heat resistance may be difficult to express. If the content is 30 parts by weight or more, the hygroscopicity may be increased.

        The method for producing the styrene-based copolymer resin is not particularly limited, but may be appropriately prepared by bulk polymerization, suspension polymerization, and emulsion polymerization.

As the light diffusing agent, organic and / or inorganic diffusing agents may be used alone or in combination. For example, silicone-based crosslinked fine particles, acrylic-based crosslinked fine particles, styrene-based crosslinked fine particles, methyl methacrylate-styrene copolymerized crosslinked fine particles (MS-based crosslinked fine particles), calcium carbonate, barium sulfate, polycarbonate-based resins, olefinic resins, titanium dioxide (TiO ₂ ) silica and the like can be used. Although not limited, the particle size is in the range of 0.1-50 μm, more suitably 0.5-20 μm. The amount used is preferably 0.001 to 40 parts by weight, more preferably 0.005 to 10 parts by weight relative to the styrene-based copolymer resin. In addition, the light diffusing agent of the present invention includes not only the material but also all the constitutions applied for light diffusion, such as forming a porosity in the diffusion base layer.

In the present invention, there is no particular limitation on the mixing method of the styrene copolymer resin and the light diffusing agent, but after premixing using a known mixing device such as a Hansel mixer, etc., mixing by melt kneading by a single screw or twin screw extruder. The method is suitable. In such blending, after producing a master batch having a high concentration of the light diffusing agent, it is suitable to manufacture the optical sheet by secondary blending by the extrusion process of the master batch and the styrene copolymer resin.

In addition, the light diffusion resin composition may further include additives such as antioxidants and antistatic agents described below.

1A to 1C are cross-sectional schematic diagrams of a light diffusion plate according to an embodiment of the present invention. As shown, it comprises a diffusion base layer formed by using the above-described light-diffusion resin composition as a base resin. A functional layer may be formed on at least one surface of the diffusion substrate layer.

It is preferable to use the light-diffusion resin composition mentioned above as a base resin of the said diffusion base material layer. A light diffusing agent is included in the diffusion substrate layer to diffuse the light. In addition, an phenolic or phosphoric acid-based antioxidant may be added to the diffusion base layer to prevent thermal decomposition of the resin due to high temperature conditions during extrusion. In some cases, an ultraviolet absorber or an ultraviolet absorber may be used to prevent degradation by ultraviolet rays. Inorganic particles containing may be added.

The thickness of the diffusion substrate layer is not limited but is preferably in the range of about 0.1 mm to 3 mm. Since the diffusion base layer has a certain thickness, the stiffness and heat resistance required as the diffusion plate are obtained, and the light is partially absorbed in the diffusion base layer, whereby the transmittance can be adjusted.

As the base resin of the functional layer, a polystyrene resin or an acrylic resin may be used, and more preferably, the above-described styrene copolymer resin is used. In addition, a light diffusing agent may be used for the functional layer separately from the base layer, and an inorganic particle including an ultraviolet absorber or an ultraviolet absorber may be used to prevent degradation by ultraviolet rays.

The thickness of the functional layer is preferably in the range of 0.01 mm to 0.5 mm, and more appropriately in the range of 0.04 mm to 0.15 mm.

As the light diffusing agent that can be used in the diffusion substrate layer and the functional layer, the above-described light diffusing agent may be used and description thereof will be omitted.

Examples of the ultraviolet absorber used for the diffusion base layer and the functional layer include cyanoacryl, salicylate, malonic ester, oxalanilide, diketone, hydroxy benzophenone, hydroxy benzotriazole, and organometallic. These ultraviolet absorbers can be directly mixed with each resin and used. The concentration range of the ultraviolet absorber is preferably 0.1 to 2 parts by weight relative to the base resin, more preferably 0.5 to 1.2 parts by weight.

Preferably, for ultraviolet absorption, inorganic particles containing ultraviolet absorbers contained in inorganic particles such as silica may be used. Inorganic particles containing the ultraviolet absorber may solve the thermal stability problem of the ultraviolet absorber by the inorganic material containing the ultraviolet absorber. In addition, the light diffusion function may be performed. In addition, other additives may be incorporated to add additional functionality. In the present invention, the inorganic particles containing the ultraviolet absorber, as well as the form of the inorganic material coating the outer surface of the ultraviolet absorber, as well as the form containing the ultraviolet absorber in the inorganic material and the form in which the ultraviolet absorber is impregnated in the porous portion of the surface of the inorganic material, such as porous It is a broad meaning to include.

The inorganic particles including the ultraviolet absorber are not limited but 0.001 to 50 parts by weight, preferably 0.005 to 20 parts by weight, based on 100 parts by weight of the base resin. If the amount of the inorganic particles including the ultraviolet absorber is less than the above range, the ultraviolet absorber and the light diffusing property are disadvantageous.

Inorganic particles containing the ultraviolet absorber are usually used to have a different refractive index from the base resin, it is good to increase the diffusion rate. When the difference in refractive index with the base resin is large, the light diffusion effect is exerted in a small amount, and when the difference in refractive index is small, a relatively large amount should be included. Although not limited, the inorganic particles containing the ultraviolet absorber preferably have a refractive index of 1.3 to 1.6, specific gravity of 1.5 to 2.5, and thermal stability of 300 ° C or higher.

The content of the ultraviolet absorber is 0.1 to 85 parts by weight, preferably 1 to 80 parts by weight, and more preferably 10 to 50 parts by weight based on 100 parts by weight of the total of inorganic particles including the ultraviolet absorber. Yellowing phenomenon due to ultraviolet rays does not occur in the above range, and good transmittance can be obtained.

As said ultraviolet absorber, what can absorb the light of 300-400 nm ultraviolet range is preferable. Examples thereof include organometallic, cyanoacrylic, salicylate, oxalanilide, diketone, benzophenone, benzotriazole and malonic acid esters. One or more selected from these can be used in combination, and benzophenone series, benzotriazole series or malonic acid ester series are most preferred.

For benzophenone ultraviolet absorbers, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-benzyl Oxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, and the like.

As the benzotriazole ultraviolet absorber, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole and 2- (5-methyl-2-hydroxyphenyl) benzo Triazole, 2- (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2- (2'-hydroxy-5'-t-octylphenyl) benzotriazole, 2- ( 3-t-butyl-5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3,5-di-t-butyl-2-hydroxyphenyl) -5-chlorobenzotriazole , 2- (3,5-di-t-amyl-2-hydroxyphenyl) benzotriazole, 2- (2'-hydroxy-5'-t-octylphenyl) benzotriazole, and the like.

Among them, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole and 2- (5-methyl-2-hydroxyphenyl) benzotriazole are preferable. Do.

Dimethyl malonate, diethyl malonate, dibenzyl malonate, diallyl malonate, etc. are mentioned as a malonic acid ester ultraviolet absorber. Especially, dimethyl malonate is preferable.

On the other hand, examples of the inorganic material of the inorganic particles containing such ultraviolet absorbers are not limited, but at least one may be selected from the group consisting of silica, calcium carbonate, silicon and silsesquioxane, and silica particles are particularly preferable.

The inorganic particles containing the ultraviolet absorber are sol-gel method (W. Stober et al., J. colloid and Interface Science, 26, 62-69 (1968), microemulsion method (Patent Publication 10-2002-0096118), spray drying method) , Spray pyrolysis, etc., may be prepared by methods known in the art.

As an example of the sol-gel process, a mixed solution is prepared by mixing a partially hydrolyzed silane compound, an ultraviolet absorber and tetraethylorthosilicate (TEOS). Then, the mixed solution prepared above is emulsified in 10% to 20% by weight of ammonia water using a stirrer to form an emulsion, and a polyvinyl alcohol solution is added to prevent aggregation of capsule particles during sol-gel solidification. can do. The prepared emulsion containing the ultraviolet absorber may be reacted for 2 hours while stirring at 500 rpm using a mechanical stirrer to prepare silica particles containing the ultraviolet absorbent. The silica particles in the aqueous solution are recovered by centrifugation at 4000 rpm for 10 minutes using a centrifuge, and dried at room temperature to obtain silica particles containing a powdery ultraviolet absorber.

As an example of the microemulsion method, silica particles having a pore size of 0.05 to 20 nm, prepared by the method described in Patent Publication No. 10-2002-0096118, are subjected to pretreatment of a silane coupling agent as necessary, and a solvent in which an ultraviolet absorber is dissolved, preferably Preferably, after impregnating the pretreated silica particles in a non-polar solvent, the solvent is removed to adsorb the ultraviolet absorber to the pretreated silica particles to prepare silica particles (inorganic particles) containing the ultraviolet absorber. If necessary, the surface of the silica particles to which the ultraviolet absorber is adsorbed is modified with a silane compound.

In addition, the diffusion base layer or / and the functional layer may further include an antioxidant, for example, phenolic antioxidants, phosphorus antioxidants, sulfur-based antioxidants and the like, among these phenolic antioxidants and phosphorus antioxidants Preference is given to phenolic antioxidants, which can be prevented without lowering the transparency, heat resistance and the like, without reducing the coloration or physical properties of the molded body due to heat or oxidation deterioration generated during coating. Although not limited, it is preferable to further include 0.01 to 10 parts by weight of antioxidant based on 100 parts by weight of the styrene-based copolymer resin.

Types of phenolic antioxidants are octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate and n-octadecyl 3- (3,5-di-t-butyl- 4-hydroxyphenyl) -acetate, n-octadecyl 3,5-di-t-butyl-4-hydroxybenzoate, n-hexyl 3,5-di-t-butyl-4-hydroxyphenylbenzoate , n-dodecyl 3,5-di-t-butyl-4-hydroxyphenylbenzoate, neo-dodecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, Phenolic antioxidants formed with the structure of dodecylβ (3,5-di-t-butyl-4-hydroxyphenyl) propionate are exemplified, and trisonoylphenylphosphite, triphenylphosphite, tris (2) Phosphorus antioxidant formed from the structure of 4-4-di-tert-butylphenyl) phosphite, dilauryl-3,3'- thiodipropionate, dimythyl-3,3'- thiodipropionate, and dis Tearyl-3,3'-thiodipropionate, pentaerythritol tetrakis (3-laurylthiopropionate) And the formed sulfur-based antioxidants, and the like, it is preferred to use a dual-1 or more.

In addition, the diffusion substrate layer and / or the functional layer may further include an additive such as an antistatic agent.

In the case of the antistatic agent, metal oxide particles, conductive polymers, surfactants, hydrophilic monomers, ion conductive monomers, and the like may be generally considered, and preferably, surfactants, conductive polymers, and water-soluble polymers may be used. Representative conductive polymers include polyaniline, polypyrrole and polythiophene, and are easy to polymerize, and have excellent conductivity and oxidative stability. It is excellent in water solubility and solubility, and can be used preferably.

The light diffusing plate according to the present invention is produced by molding the styrene copolymer resin, and can be preferably applied to a backlight device for LCD TVs. The light source of the backlight device may be used without limitation, such as a hot cathode tube, a cold cathode tube, a light emitting diode (LED), an organic electroluminescent element (OLED), and the like.

The present invention also provides a liquid crystal display device having a backlight device having the light diffusing plate of the present invention. The backlight device may be preferably applied to a reflective, transmissive, transflective LCD, or a liquid crystal display device of various driving methods such as TN type, STN type, OCB type, HAN type, VA type, and IPS type. The configuration of the liquid crystal display device is well known in the art, and thus description thereof is omitted. Through the following examples will be described in detail the present invention.

EXAMPLE

The manufacturing method of a styrene copolymer resin is the same as the following Example and a comparative example.

Example 1

A reaction mixture obtained by adding 7 parts by weight of ethylbenzene and 200 ppm of t-butylperoxy-2-ethylhexyl carbonate as a reaction regulator to a monomer mixture having a weight ratio of 66% styrene monomer, 30% α-methylstyrene, and 4% methacrylic acid Was continuously added to the first of two completely mixed polymerization units connected in series. The temperature of the first reactor was adjusted to 135 ° C., the temperature of the second reactor was set to 145 ° C., and the residence time was adjusted so that the final conversion rate was 60%. Subsequently, the temperature of the reaction mixture was raised to 250 ° C., degassed under a vacuum condition of 20 torr, and a pellet-like styrene copolymer resin product was obtained by a continuous extrusion process. The produced resin was measured by the softening temperature (VICAT) and heat distortion temperature (HDT) by a heat deflection temperature measuring device (manufactured by Tosei Sangsa, model name: 3M-2), respectively. This evaluation method was evaluated in accordance with the provisions of Japanese Industrial Standards (JIS) K7206. In addition, by using the evaluation of the water absorption rate of absorption by the deposition in water at room temperature (23 ℃) was measured as follows. After drying the resin, a specimen was prepared by injection molding. At this time, the size of the specimen was 100x100x3.2mm, and the prepared specimen was stored in a drying oven at 50 ° C. for 24 hours, and then the specimen was again stored in a desiccator at room temperature for 2 hours to cool down and then weighed (A1). Was weighed. Thereafter, the sample was deposited in a water bath at 23 ° C. and left for 24 hours, then taken out to remove moisture from the surface, and the weight (A2) thereof was measured. Based on the above results, the water absorption was calculated as follows. Absorption (%) = (A2-A1) / A1 * 100.

Example 2

A monomer mixed solution was prepared in the same manner as in Example 1 except that the composition of the monomer mixture was adjusted to a weight ratio of 78% of styrene monomer, 15% of α-methylstyrene, and 7% of methacrylic acid.

Example 3

A monomer mixed solution was prepared in the same manner as in Example 1 except that the composition of the monomer mixture was adjusted to a weight ratio of 79% of styrene monomer, 20% of α-methylstyrene, and 1% of acrylic acid.

Example 4

A monomer mixed solution was prepared in the same manner as in Example 1 except that the composition of the monomer mixture was adjusted to a weight ratio of 74.5% of styrene monomer, 25% of α-methylstyrene, and 0.5% of methacrylic acid.

Example 5

A monomer mixed solution was prepared in the same manner as in Example 1 except that the composition of the styrene monomer was adjusted to a weight ratio of 87% of styrene monomer, 3% of methacrylic acid, and 10% of maleic anhydride.

Example 6

A monomer mixed solution was prepared in the same manner as in Example 1 except that the composition of the monomer mixture was adjusted to a weight ratio of 94% styrene monomer, 1% methacrylic acid, and 5% N-phenylmaleimide.

Comparative Example 1

In Comparative Example 1, the thermal characteristics and the water absorption of HRM40 of Toyo Sterren, Japan, were evaluated as a typical GPPS resin.

Comparative Example 2

The thermal properties and water absorption of Sumitomo Chemical's LG-25 resin were compared and evaluated as conventional PMMA resins.

Table 1

Monomer composition (% by weight) Softening Temperature (VICAT) (℃) Heat Deflection Temperature (HDT) (℃) Absorption rate (%) Styrene α-methyl styrene Methacrylic acid Maleic anhydride N-phenyl maleimide Example 1 66 30 4 - - 124 103 0.05 Example 2 78 15 7 - - 127 104 0.09 Example 3 79 20 1 ^b - - 116 94 0.04 Example 4 74.5 25 0.5 - - 114 93 0.03 Example 5 87 - 3 10 - 121 100 0.1 Example 6 94 - One - 5 117 96 0.06 Comparative Example 1 100 - - - - 99 92 0.04 Comparative Example 2 100 ^a - - - - 97 90 0.19

^{a For} Comparative Example 2, it is PMMA of 100% methyl methacrylate but not a styrene monomer. ^b For example 3 1% acrylic acid was added.

In Table 1, the heat deformation characteristics and the water absorption rate of the styrene-based copolymer resins according to the compositions and the examples of each composition are shown. Compared with the heat deflection temperatures of the polystyrene resins and the PMMA resins of Comparative Examples 1 and 2, the resins of Examples 1 to 6 were all improved in heat resistance and at least 1 to 14 degrees in the case of HDT. This tendency was stronger as the content of acrylic acid or methacrylic acid increased. The absorption rates of Examples 1 to 6 were significantly improved compared to the absorption rates of PMMA of Comparative Example 2. In particular, in the case of Examples 1-4, the higher the content of methacrylic acid, the lower the absorption rate, and the closer the absorption rate of the polystyrene of Comparative Example 1 was. However, since the heat resistance is improved at the same time according to the proper content of acrylic acid or methacrylic acid, it is considered that the balance of the proper content of alphamethyl styrene and methacrylic acid or acrylic acid is an important factor. In Examples 5 to 6 using maleimide instead of alphamethyl styrene, the heat resistance was improved, and in the case of heat resistance, in Example 5 using maleic anhydride, and in Example 6 using N-phenylmaleimide for water absorption Each physical property was improved.

In the present invention, using the resins of Examples 1 and 2 having low water absorption and excellent heat resistance among the copolymer resins of the six compositions, the light diffusion plate was manufactured and evaluated for physical properties through the following Examples and Examples. .

 Example 7

Into the hopper of the single screw extruder (screw diameter: 135 mm, extrusion amount: 700kg / hr) as the main extruder 1000kg of a resin composition having the following composition was put into a single-layer light diffuser plate. The thickness of the produced light diffusion plate was 1.5 mm. That is, the above composition is 76.9% of the copolymer resin of Example 2, silicon rubber light diffusing agent (Toray Dow Silicon, DY33-719, particle diameter 3? M) 0.3%, PMMA light diffusing agent (Sekisui usability, MBX5H, particle size 5 m) 2.5%, UV absorber (Sumisorb 200, Sumitomo Chem.) 0.15%, and heat stabilizer (Sumilizer GP, Sumitomo Chem.) 0.15% of the composition, these compositions are about 20 before Mix for a minute. Extrusion temperature conditions were in the cylinder temperature of 230-250 ℃, the die portion temperature of 240-250 ℃.

Example 8

1000 kg of the resin mixture having the same composition as in Example 7 was introduced into the main extruder, and 200 kg of the resin mixture having the following composition was added to a sub-extruder (screw diameter 60 mm, extrusion amount 80 kg / min) connected to the main extruder to form a surface layer. To produce a multilayer light diffusing plate. That is, the above composition is 10% of silica particles (particle diameter 5mm, refer to patent application) containing 10% of UV absorber (Hostavin PR-25, Clariant, Japan) in 90% of polystyrene resin (HRM40, Toyo St.). Refers to the composition made up. This resin composition was also stirred well for about 20 minutes with a Hansel mixer before being added to the hopper. The ratio of the upper and lower layers to the main layer was maintained at a ratio of about 1:12.

Example 9

1000 kg of the resin mixture having the same composition as in Example 7 was added to the main extruder, and 200 kg of the copolymerized resin of Example 2 was added to the sub-extruder to prepare a multilayer light diffusion plate.

Example 10

Except for changing from the copolymer resin of Example 1 to the copolymer resin of Example 1 instead of the copolymer resin of Example 2, a single-layer light diffusion plate was produced with the same composition.

Comparative Example 3

In Example 7, except that the polystyrene resin (HRM40, Toyo St.) instead of the copolymer resin of Example 2, all of the single-layer fluorescent plate was prepared with the same composition.

Comparative Example 4

In Example 8, except that the copolymer resin of Example 2 was changed to polystyrene (HRM40, Toyo St.), a single-layer fluorescent plate was manufactured with the same composition.

Comparative Example 5

In Example 7, except that the copolymer resin of Example 2 was changed to PMMA (LG25, Sumitomo Chemical), all single-layer fluorescence diffusers were prepared with the same composition.

The amount of change in warpage due to heat deflection temperature, water absorption, and drying was measured for the diffusion plates produced in Example 7-10 and Comparative Example 3-5. Among them, the method of measuring the heat deformation temperature and the water absorption is the same as the method described in Examples 1-6 and Comparative Examples 1-2, and the method of measuring the amount of change in warpage of the diffusion plate according to drying is as follows.

<Method of measuring the amount of change in warping due to drying>

The light diffusing plates produced in Examples 7 to 10 and Comparative Examples 3 to 5 were cut to 46-inch size (1032 x 584 mm), and left at a relative humidity of 90% and 25 ° C. for about 48 hours, respectively. After the sample was erected vertically as shown in Fig. 1, the initial deflection (l ₁ ) in the horizontal direction from the center thereof was evaluated, and then each diffuser plate was perpendicular to the drying oven for 48 hours in a drying oven at 80 캜 and 90 캜, respectively. After leaving to stand in a standing state, it was taken out and the warpage after drying (l ₂ ) was measured, and the difference in warpage before and after drying was indicated by l to grasp the degree of shrinkage due to drying. The measurement method is shown in FIG.

Table 2 shows the structure of each diffusion plate and its physical property evaluation results according to the Examples and Comparative Examples.

Table 2

Diffusion base layer base resin Functional layer base resin Heat Deflection Temperature (HDT) (℃) Softening Temperature (VICAT) (℃) Absorption rate (%) l (80 ℃) (mm) l (90 ℃) (mm) Example 7 Example 2 - 101 124 0.09 12.6 33 Example 8 Example 2 PS 99 122 0.08 13.5 31 Example 9 Example 2 Example 2 102 124 0.09 13.2 34 Example 10 Example 1 - 101 121 0.06 13.6 35 Comparative Example 3 PS - 92 99 0.05 14 107 Comparative Example 4 PS PS 92 98 0.05 13.5 112 Comparative Example 5 PMMA - 90 97 0.20 25.6 167

In all of Examples 7-10, it can be seen that the heat distortion temperature was significantly increased compared to the polystyrene and the resin of the PMMA center of Comparative Example 3-5. Water absorption also showed a relatively low water absorption (0.06 ~ 0.09%) as the physical properties of the copolymer resin in the conventional Example 1-2.

As a result of measurement of dry bending test at 80 ° C and 90 ° C respectively, in Examples 7-10 where the heat-resistant copolymer was centered, a slightly lower amount of warpage change was observed at 80 ° C compared with Comparative Examples 3 to 4 where polystyrene was used as the base layer. It can be seen that, at 90 ° C., the amount of warpage change is reduced to about half or less. This is due to the relatively low absorption of both the heat-resistant copolymer resin base layer (Example 7-10) and the polystyrene base layer (Comparative Example 3-4) at 80 ° C. Compared with drying, the warpage variation due to drying is much smaller and shows similar values.However, as the temperature increases, the difference in heat resistance between the diffusion plate having the heat-resistant copolymer resin and the diffusion plate having the polyester resin as the base layer occurs. It can be explained that the amount of warpage change of the diffusion plate of Example 7-10 in which the heat-resistant copolymer is used as the base layer is relatively small.

In Example 7-10, no significant difference was found in the change in heat resistance and dry warpage according to the difference in surface layer. Therefore, it can be seen that the configuration of the material of the intermediate substrate layer is an important factor influencing these physical properties.

Therefore, by applying the polystyrene-based copolymer resin having improved heat resistance to the diffusion plate, it is possible to develop a diffusion plate having a relatively low heat absorption and relatively low water absorption and deformation due to heat drying and deformation due to heat absorption. .

The light diffusing plate according to the present invention uses a polystyrene-based copolymer resin having improved heat resistance and hygroscopicity in a diffusion base layer or / and a functional layer compared to a conventional polystyrene-based or acrylic resin, so that the lamp is turned on after deformation and absorption by heat. By minimizing the deformation of the diffusion plate by heating and drying by the light diffusion plate can be provided with a uniform image quality. Such a light diffusion plate may be widely applied as a light diffusion plate for a new liquid crystal TV having a light source such as a large-sized liquid crystal TV or a large amount of heat generating LEDs, mainly due to an increase in the number of lamps.

Claims (13)

It comprises 0.001 to 40 parts by weight of a light diffusing agent based on 100 parts by weight of a styrene copolymer resin, wherein the styrene copolymer resin is 70 to 99.5 parts by weight of at least one monomer selected from styrene and styrene derivatives and 0.5 to 30 vinyl monomers. Light diffusion resin composition prepared by copolymerization, including parts by weight. The copolymerized light diffusion resin composition of claim 1, wherein the styrene derivative is an α-methylstyrene monomer. The light diffusing resin composition according to claim 1, wherein the vinyl monomer is at least one selected from acryl, imide and olefin. The light diffusing resin composition of claim 1, wherein the light diffusing agent is selected from at least one of silica, silicone rubber, acrylic resin, and polystyrene resin. The light diffusing resin of claim 1, further comprising 0.01 to 10 parts by weight of an antioxidant, based on 100 parts by weight of the styrene copolymer resin, wherein the antioxidant is selected from at least one of a phosphate and a phenol. Composition. A light diffusion plate comprising a diffusion base layer formed by using the light diffusion resin composition of any one of claims 1 to 5 as a base resin, and a functional layer formed on at least one surface of the diffusion base layer. The light diffusing plate according to claim 6, wherein the functional layer is formed using a light diffusion resin composition defined as being used for the diffusion base layer as a base resin. The light diffusing plate of claim 6, wherein the functional layer comprises an inorganic particle containing an ultraviolet absorber. The light diffusion plate of claim 6, wherein the diffusion substrate layer has a thickness of 0.1 mm to 3.0 mm, and the functional layer has a thickness of 0.01 mm to 0.5 mm. The light diffusing plate according to claim 8, wherein the ultraviolet absorber is contained in an amount of 0.1 to 85 parts by weight based on a total of 100 weights of the inorganic particles containing the ultraviolet absorber. The light diffusing plate of claim 8, wherein the ultraviolet absorber is selected from at least one of a benzotriazole-based, malonic ester-based, and benzophenone-based ultraviolet absorber. A backlight device comprising the light diffusion plate of claim 6. A liquid crystal display device comprising the backlight device of claim 12.

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