KR100635152B1 - Light-diffusion plate - Google Patents

Abstract

The present invention relates to a light diffusion plate used for a backlight unit, an illumination device, and the like of a liquid crystal display, and more particularly, a base layer containing a first base resin and a light diffusion agent made of a polycarbonate resin; It relates to a light diffusion plate comprising a second base resin containing an acrylic resin, comprising a surface layer formed on one side or both sides of the base layer, and has high dimensional stability with high heat resistance and high humidity resistance, high temperature, high humidity environment Even in the warpage does not occur, excellent optical properties including the total light transmittance, and provides a light diffusion plate with a low yellowing degree even when exposed to a light source for a long time.

Liquid crystal display, polycarbonate resin, dimensional stability, light diffusing plate, light diffusing agent

Description

Light-diffusion plate             

1 is a side cross-sectional view of one form of a light diffusion plate according to the present invention;

2 is a side cross-sectional view of another form of the light diffusing plate according to the present invention;

3 is a side cross-sectional view of another form of light diffusing plate according to the present invention;

4 is a side cross-sectional view of another form of light diffusing plate according to the present invention.

<Code Description of Main Parts of Drawing>

Reference Signs List 1 light diffusion plate 10

11: first base resin 20: surface layer

21: second base resin 30: light diffusing agent

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusion plate used for a backlight unit, an illumination device, or the like of a liquid crystal display.                         

Conventionally used light diffusing plates include (1) a light diffusing plate (Japanese Patent Application Laid-Open No. 4-275501) obtained by performing a process of imparting physical concavities and convexities to a surface, and (2) a transparent material containing fine particles on a transparent substrate such as a polyester resin. Optical diffuser plate obtained by coating a light diffusing layer made of resin (Japanese Patent Application Laid-Open No. 6-59108), and a light diffusing plate obtained by melt-mixing beads in a transparent resin and extruding them (Japan, Patent Application Laid-Open Patent No. 6-59108). 123802) and (4) disclose a light diffusion plate (Japanese Patent Application Laid-open No. 9-311205) having a sea island structure formed by melt kneading two or more kinds of transparent thermoplastic resins.

The light diffusing plates 1 and 2 are surface diffusing plates, that is, light diffusing effects are obtained by the uneven or coated light diffusing layer formed on the surface. On the other hand, the light diffusing plates 3 and 4 are light diffusing plates having a light diffusing component at least inside the substrate.

The light diffusion plate made of the existing methyl methacrylate resin, which is mainly used as the light diffusion plate, has excellent optical properties such as total light transmittance, but has low dimensional stability, so it is used together with cold cathode fluorescent lamps and light sources such as LEDs to light and When the temperature is changed by turning off, the water absorption rate of the light diffusing plate can be easily changed, so there are problems such as warpage, wrinkles, deformations such as cracking, and the like. That is, there is a problem that deformation such as bending phenomenon occurs in a high temperature and high humidity environment (Japanese Patent Application Laid-Open No. 07-100985, Japanese Patent Application Laid-open No. 08-198976).

In order to solve this problem, a multi-layered sheet (Japanese Patent Application Laid-Open No. 2004-37483, Korean Patent Publication No. 2003-95262) to which methyl methacrylate-styrene resin is applied to reduce the absorption capacity has been proposed. Inherently, the light resistance is not sufficient, and depending on the conditions of use, there may be a problem of deterioration such as coloring. One of the known methods for improving the light resistance of the resin is the addition of an ultraviolet absorber, but the effect is not sufficient in some cases where the light resistance of the resin is low.

In addition, a light diffusion plate using a polycarbonate resin having excellent dimensional stability due to relatively high light transmittance and high heat resistance and high water absorption is proposed, but in the case of a light diffusion plate to which a polycarbonate resin is applied, high heat resistance and water absorption resistance of the resin By the high dimensional stability but low light resistance there is a problem that yellowing phenomenon occurs when exposed to a light source for a long time.

The present inventors have confirmed through experiments that the present invention can provide a light diffusion plate that does not generate yellowing even when exposed to a light source for a long time due to the light resistance of the surface layer while showing high dimensional stability due to high heat resistance and low absorption even at high temperature and humidity The present invention has been completed.

Accordingly, the present invention provides a light diffusion plate having excellent optical properties and no yellowing phenomenon without warping in high temperature and high humidity conditions with high dimensional stability, and also having low reflection properties on a matt surface. The purpose is to provide a version.

The present invention for achieving the above object is a base layer comprising a first base resin and a light diffusing agent made of a polycarbonate resin; It is formed on at least one surface of the substrate layer, and provides a light diffusion plate comprising a surface layer comprising a second base resin containing an acrylic resin.

Linear and branched aromatic polycarbonate homopolymers prepared by reacting a dihydroxy phenol with a phosgene or by reacting a dihydroxy phenol with a carbonate precursor; Polyester copolymers; Or a mixture of one or more thereof.

The acrylic resin of the second base resin of the surface layer is any one selected from alkyl methacrylate, alkyl acrylate, methacrylic acid cycloalkyl ester, acrylic acid cyclic alkyl ester, methacrylic acid aryl ester and acrylic acid aryl ester. It is a homopolymer or any 1 or more types of copolymers, It is characterized by the above-mentioned.

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The surface layer further includes a light diffusing agent, characterized in that the surface of the surface layer has an embossed shape by the protrusion of the light diffusing agent. The surface layer is characterized in that the surface roughness is 1 ~ 50㎛.

The light diffusing agent of the base layer or the surface layer is characterized in that it comprises 0.1 to 50 parts by weight based on 100 parts by weight of the base resin of the base layer or surface layer.

The light diffusing agent of the substrate layer or the surface layer is characterized in that the particle diameter is 0.2 ~ 50㎛.

Each of the base layer and the surface layer further comprises 0.01 to 5 parts by weight of an optical stabilizer based on 100 parts by weight of the base resin of the base layer or the surface layer.

Hereinafter, the present invention will be described in more detail.                     

The polycarbonate resin used as the first base resin of the base material layer of the present invention has excellent impact resistance and light transmittance, good cold resistance and electrical characteristics, and particularly has high heat resistance and water absorption resistance, and thus has excellent dimensional stability and a high temperature range. As a wide resin, it is used for optical lenses, optical disc materials, helmets, protective equipment, covers, and the like.

The polycarbonate resins used in the present invention are aromatic polycarbonate resins which are generally used, and linear and branched carbonate homopolymers and polys prepared by reacting dihydroxy phenol with phosgene or by reaction of dihydroxy phenol with a carbonate precursor. Ester copolymers or mixtures of one or more thereof. The dihydroxy phenol is 2,2-bis (4-hydroxyphenyl) propane (ie bisphenol A), bis (4-hydroxy phenyl) methane, 2,2-bis (4-hydroxy-3,5 -Dimethylphenyl) propane and 1,1-bis (4-hydroxyphenyl) cyclohexane and the like, and the carbonate precursors include diphenyl carbonate, carbonyl halide and diaryl carbonate.

On the other hand, as a 2nd base resin of a surface layer, the acrylic resin which shows the outstanding characteristic in light transmittance, light resistance, etc. is included.

In particular, the acrylic resin used as the second base resin in the present invention is an alkyl methacrylate such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate; Alkyl acrylates such as methyl acrylate, ethyl acrylate and butyl acrylate; 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; It is preferable that it is any one homopolymer selected from acrylic acid aryl esters, such as phenyl acrylate and benzyl acrylate, or a copolymer thereof.

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The light diffusing agent included in the base layer is usually the same refractive index as the base resin, is used to increase the light diffusion rate, various organic and inorganic particles are used. At this time, the light diffusing agent exhibits a light diffusing effect even in a small amount when the refractive index with the base resin is large, and a relatively large amount should be included when the refractive index difference is small.

Examples of organic particles typically used include methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid and hydroxyethyl methacrylate. , Hydroxypropyl methacrylate, hydroxy ethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer Or acrylic polymer particles such as copolymers or terpolymers thereof; Olefin polymer particles such as polyethylene and polypropylene; Multi-layered multicomponent particles, siloxane-based polymer particles, tetrafluoroethylene-based particles formed by forming copolymer particles of acryl and olefin, particles of the homopolymer, copolymer or terpolymer, and then covering the layers with other monomers. Particles and the like.

On the other hand, examples of the inorganic light diffusing particles include calcium carbonate, barium sulfate, silicon oxide, aluminum hydroxide, titanium oxide, zirconium oxide, magnesium fluoride, talc, glass, mica and the like. Normally, the organic particles have excellent light diffusivity compared to the inorganic particles, and if necessary, two or more kinds of light diffusing particles can be combined.

In addition, the light diffusing agent included in the base layer may be further included in the surface layer. The light diffusing agent is further included in the surface layer to further increase the light diffusing effect, and the light diffusing particles protrude to the surface of the surface layer to have an embossed shape, thereby achieving an effect of having a matte surface and a low reflectance. At this time, the surface roughness of the surface layer is about 0.1 ~ 50㎛ suitable, if the roughness is more than 50㎛ surface impact strength is insufficient, if the roughness is less than 0.1㎛ matt effect.

The content of the light diffusing agent used in the substrate layer or the surface layer of the present invention is 0.01 to 50 parts by weight, preferably 0.5 to 20 parts by weight, based on 100 parts by weight of the first base resin or the second base resin of the surface layer. Parts by weight. If the amount of the light diffusing agent is less than 0.01 part by weight, it is difficult to expect sufficient light diffusing effect and concealability, and if it is more than 50 parts by weight, light transmittance is not good. At this time, the content of the light diffusing agent may be determined according to the difference in refractive index with the base resin.

On the other hand, in the present invention, a light stabilizer may be added to the base layer or the surface layer, the light stabilizer that can be added as a UV absorber and a radical scavenger having a maximum absorption wavelength in the range 250nm ~ 380nm can maximize the light stabilizer effect Ultraviolet stabilizers of hindered amines are preferred. They must be effective for a long time, must not be evaporated or extracted to be freed or removed from the sheet, and an absorbent with good compatibility with the substrate should be selected.

Examples of the ultraviolet absorber include cyanoacrylic, salicylate, malonic ester, oxalanilide, diketone, hydroxy benzophenone, hydroxy benzotriazole, organometallic, and the like. The above can be used in combination.

Examples of ultraviolet stabilizers include piperidinyl esters, oxazolidines and piperidino oxazolidines, piperidisspiroacetals, diazacycloalkanones, and the like, and two or more selected from these may be used in combination.

The content of the light stabilizer is 0.01 parts by weight to 5 parts by weight, and preferably 0.1 parts by weight to 2 parts by weight, based on 100 parts by weight of the base resin of the base layer or the surface layer. In particular, by including them in the surface layer, it is possible to obtain the expected light stability effect without lowering the total light transmittance and physical properties of the substrate layer, and also bring about the effect of cost reduction.

Hereinafter, with reference to the accompanying drawings the present invention will be described in more detail.

1 to 4 show various forms of the light diffusing plate according to the present invention. FIG. 1 is a side cross-sectional view when a surface layer containing no light diffusing agent is formed on one surface of a base layer, and FIG. 2 is a base layer. 3 is a side cross-sectional view when the surface layer containing the light diffusing agent is formed on one surface of the substrate, and FIG. 3 is a side cross-sectional view when the surface layer without the light diffusing agent is formed on both surfaces of the substrate layer, and FIG. The side cross-sectional view at the time of forming the surface layer containing a light-diffusion agent is shown.

The light diffusing plate 1 of the present invention can be manufactured by a method such as coextrusion molding, lamination, thermal bonding, surface coating, etc., which are known techniques.

The base layer 10 includes a first base resin 11 and a light diffusing agent 30, and as shown in FIGS. 2 and 4, light is applied to the second base resin 21 of the surface layer 20. When the diffusing agent 30 is contained, the light diffusing agent 30 in the form of particles protrudes from the surface of the surface layer 20 to have an embossed shape to provide a matte surface and low reflectance. In this case, the roughness of the surface layer 20 is suitably 0.1 to 50 µm as described above. If the roughness exceeds 50 µm, the surface impact strength is insufficient. If the roughness is less than 0.1 µm, the matte effect is inferior.

The light diffusion plate of the present invention can be used for various applications indoors and outdoors. That is, it can be used for signage, lighting signage, lighting cover, glass showcase, and preferably used as a light diffusion plate for display. Representative examples of display light diffusers include light diffusers for liquid crystal display backlights or edge light type backlights.

Hereinafter, examples of the present invention will be described in more detail, but the scope of the present invention is not limited to these examples.

Compositions and composition ratios of Examples 1 to 8 and Comparative Examples 1 to 10 are as shown in the following [Table 1], and Examples 1 to 4 and Comparative Examples 1 to 5 form surface layers on one surface of the substrate layer. 5-8 and Comparative Examples 6-10 are surface layers formed on both surfaces of a base material layer.

At this time, molding was coextruded at a screw diameter of 135 mm and 60 mm, respectively, and the molding temperature was performed at 300 ° C., and Examples 1 to 4 and Comparative Examples 1 to 5 were 1.9 mm in thickness of the substrate layer and the surface layer. The thickness of was 0.1 mm, and Examples 5 to 8 and Comparative Examples 6 to 10 were 1.8 mm in thickness of the base layer and 0.1 mm in thickness on both surfaces.

Substrate layer Surface layer 1st base Suzy Light diffusing agent Light stabilizer 2nd base Suzy Light diffusing agent Light stabilizer Example 1, Example 5 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight MM resin bead 10 parts by weight Tinuvin P 0.2 parts by weight Example 2, Example 6 PC 100 parts by weight 0.8 parts by weight of TFE resin beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight MM resin bead 10 parts by weight Tinuvin P 0.2 parts by weight Example 3 and Example 7 PC 100 parts by weight 3 parts by weight of calcium carbonate Tinuvin P 0.2 parts by weight PMMA 100 parts by weight MM resin bead 10 parts by weight Tinuvin P 0.2 parts by weight Example 4, Example 8 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight MM resin bead 10 parts by weight Tinuvin P 0.2 parts by weight Comparative Example 1, Comparative Example 6 PMMA 100 parts by weight 3 parts by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight MM resin bead 10 parts by weight Tinuvin P 0.2 parts by weight Comparative Example 2, Comparative Example 7 MS 100 parts by weight 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight MM resin bead 10 parts by weight Tinuvin P 0.2 parts by weight Comparative Example 4, Comparative Example 9 PMMA 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight MM resin bead 10 parts by weight Tinuvin P 0.2 parts by weight Comparative Example 5, Comparative Example 10 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PC 100 parts by weight MM resin bead 2 parts by weight Tinuvin P 0.2 parts by weight * PMMA: Polymethylmethacrylate * PC: Polycarbonate (polycarbonate obtained by reacting 2,2-bis (4-hydroxyphenyl) propane with phosgene) * MS: Methyl methacrylate-styrene copolymer resin * Silicone beads: Silicone resin beads, particle diameter 2㎛ * MM resin beads: methyl methacrylate resin beads, particle diameter 20㎛ * Tinuvin P: 2- (2'-Hydroxy-5'-methyl-phenyl) benzotriazole, UV absorber

As a result of measuring the water absorption rate, the warpage, the total light transmittance, the haze, and the yellowness after exposure, the light diffusing plates manufactured in the above Examples and Comparative Examples are shown in Table 2 below. In particular, warpage, total light transmittance, haze, and yellowness after exposure of Examples 1 to 4 and Comparative Examples 1 to 5 were measured by setting the surface layer as a reference object.

Here, the water absorption rate was measured by cutting the light diffusion plate into 10 × 10 ㎝ and left in water at 25 ° C. for 24 hours, and then measuring the water absorption from the change in weight. After 96 hours at 75% relative humidity, the four corners were measured from the bottom. However, Examples 4, 8 and Comparative Examples 4, 9 and the like were measured for 96 hours at 80 ° C. and 75% relative humidity, and then the degree of floating of four corners from the bottom was measured.

Total light transmittance and haze were measured by ASTM D1003 method.

The yellowing degree after exposure was measured by ASTM D1003 method after the lamp was subjected to 40 ^° C. for 240 hours in a Q-UV tester equipped with FS-40 313/280 according to ASTM D1925 standard.

division Water absorption rate (%) Deflection (mm) Total light transmittance (%) Haze (%) Yellowness after exposure (ΔYI) Surface layer formation on one side of the base layer Example 1 0.24 0.28 64 99.4 1.18 Example 2 0.23 0.28 64 99.4 1.18 Example 3 0.23 0.20 64 99.3 1.19 Example 4 0.24 0.28 64 99.4 1.18 Comparative Example 1 0.32 0.58 65 99.2 1.10 Comparative Example 2 0.27 0.35 64 99.4 1.11 Comparative Example 4 0.32 0.58 64 99.5 1.10 Comparative Example 5 0.20 0.18 66 99.4 2.10 Surface layer formation on both sides of the base layer Example 5 0.25 0.28 64 99.3 1.18 Example 6 0.24 0.28 64 99.4 1.18 Example 7 0.23 0.20 64 99.3 1.19 Example 8 0.25 0.28 64 99.4 1.18 Comparative Example 6 0.32 0.58 66 99.2 1.10 Comparative Example 7 0.26 0.35 63 99.1 1.11 Comparative Example 9 0.32 0.58 64 99.3 1.10 Comparative Example 10 0.20 0.18 64 99.4 2.10

As a result of the evaluation of the physical properties, Examples 1 to 8 including the polycarbonate resin in the base layer, the water absorption rate is lower than that of Comparative Examples 1 to 4 and Comparative Examples 6 to 9 that are not, and warpage is also low. Can be.

In addition, Examples 1 to 8 in which the base layer contains polycarbonate resin and the acrylic resin is included in the surface layer have a yellowing degree after exposure as compared to Comparative Examples 5 and 10 in which both the base layer and the surface layer contain polycarbonate resin. It can be seen that excellent.

Also, in Examples 4 and 8 and Comparative Examples 4 and 9 evaluated at relatively high temperature conditions, Examples 4 and 8 in which the base layer is made of polycarbonate resin are more warped than those in Comparative Examples 4 and 9 that are not. It can be seen that the phenomenon is low.

Therefore, the light diffusing plate of the present invention is excellent in total light transmittance and light diffusivity, in particular, it is excellent in high heat resistance and water absorption rate, excellent in dimensional stability, and low yellowing degree even when exposed to a light source for a long time.

As described above, the light diffusing plate of the present invention has high dimensional stability due to high resistivity and water absorption, and does not cause warpage even in a high temperature and high humidity environment, and has a low yellowing degree even when exposed to a light source for a long time. A light diffusion plate having excellent characteristics was provided.

Claims (9)

A base layer containing a first base resin made of a polycarbonate resin and a light diffusing agent; A light diffusing plate comprising a second base resin containing an acrylic resin and a light diffusing agent, the surface having an embossed shape by the protrusion of the light diffusing agent, and including a surface layer formed on one side or both sides of the base layer. The method of claim 1, Linear and branched aromatic polycarbonate homopolymers prepared by reacting a dihydroxy phenol with a phosgene or by reacting a dihydroxy phenol with a carbonate precursor; Polyester copolymers; Or a light diffusing plate selected from the group consisting of a mixture of one or more thereof. The method of claim 1, The acrylic resin of the second base resin of the surface layer is a homopolymer obtained from a monomer selected from alkyl methacrylate, alkyl acrylate, cycloalkyl methacrylate, cycloalkyl acrylate, aryl methacrylate and aryl acrylate. And light diffusing plate, characterized in that one selected from the copolymer. delete delete The method of claim 1, The surface layer is a light diffusion plate, characterized in that the surface roughness of 1 ~ 50㎛. The method of claim 1, The light diffusing plate of the base layer or the surface layer is 0.1 to 50 parts by weight based on 100 parts by weight of the base resin of the base layer or surface layer, respectively. The method of claim 1, The light diffusing agent of the substrate layer or the surface layer is a light diffusion plate, characterized in that the particle diameter is 0.2 ~ 50㎛. delete

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