KR100781687B1 - 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 including a first base resin made of a polycarbonate resin; And a surface diffuser plate formed on one or both surfaces of the substrate layer, the surface layer including a second base resin of acrylic resin and fluorine resin, and having high dimensional stability with high heat resistance and high moisture resistance. Almost no warping occurs even in a high humidity environment, and provides a light diffusion plate having a very low yellowing degree even when exposed to a light source for a long time.

Liquid Crystal Display, Polycarbonate Resin, Acrylic Resin, Fluorine Resin, Dimensional Stability, Light Diffusion Plate

Description

Light-diffusion plate

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 multilayer sheet to which methyl methacrylate-styrene resin is applied (Japanese Patent Application Laid-Open No. 2004-37483, Korean Patent Publication No. 2003-95262) has been proposed. Inherently, the light resistance is not sufficient, and depending on the use conditions, 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 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 humid conditions. The present invention has been completed.

Accordingly, the present invention provides a light diffusing plate having a high dimensional stability and low warpage even in an environment of high temperature and high humidity, a yellowing phenomenon occurring very low, and providing a light diffusing plate having a low reflection property on a matt surface. Its purpose is.

The present invention for achieving the above object is a base layer comprising a first base resin of a polycarbonate resin; And a surface layer formed on one or both surfaces of the substrate layer, the surface layer including a second base resin made of an acrylic resin and a fluorine resin.

The first base resin of the base layer is selected from the group consisting of linear and branched aromatic polycarbonate homopolymers prepared by reacting dihydroxy phenol with phosgene or by reaction of dihydroxy phenol with a carbonate precursor. It is characterized by.

The acrylic resin of the surface layer is selected from homopolymers and copolymers obtained from monomers selected from alkyl methacrylate, alkyl acrylate, cycloalkyl methacrylate, cycloalkyl acrylate, aryl methacrylate and aryl acrylate. It is characterized by one or more.

The fluorine-based resin of the surface layer is characterized in that it contains 0.5 to 30 parts by weight based on 100 parts by weight of acrylic resin.

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 prepared by reacting dihydroxy phenol with phosgene or by reaction of dihydroxy phenol with a carbonate precursor. And polyester 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, acrylic resin and fluorine resin are used as 2nd base resin of a surface layer.
The acrylic resin has excellent properties in light transmittance, light resistance, etc., and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate and 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 to use what is a homopolymer or copolymers of any of acrylic acid aryl esters, such as phenyl acrylate and benzyl acrylate.

On the other hand, the surface layer of the present invention contains a fluorine resin in addition to the acrylic resin.

Fluorine-based resins have excellent thermal stability and electrical properties, and are excellent in chemical durability, weather resistance, light resistance and oxygen resistance, and in particular, have almost no water absorption rate, high heat resistance, high use temperature of 250 ~ 300 ℃, and excellent surface friction. Currently, it is applied to various valves, pumps, tanks, filters, pipes, cables, computers, and aerospace industries.

In particular, the fluorine resin used in the present invention is a tetrafluoroethylene (TFE) homopolymer, a copolymer of tetrafluoroethylene and perfluoropropyl ether (PFA), tetrafluoroethylene (TFE) and hexafluoro At least one selected from a copolymer of propylene (HFP), a copolymer of tetrafluoroethylene and ethylene (ETFE), and a copolymer of vinylidene fluoride (VDF) and tetrafluoroethylene (TFE) is preferable. The fluorine resin is applied to exhibit excellent water repellency. That is, by including the fluorine-based resin in the surface layer, the dimensional stability is further improved, so that warpage does not occur even in a high temperature and high humidity environment.

The content of the fluorine-based resin contained in the surface layer is in the range of 0.5 to 50 parts by weight relative to 100 parts by weight of the acrylic resin in consideration of dimensional stability and permeability, preferably 5 to 20 parts by weight.

The base layer may further include a light diffusing agent, which 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. In this case, 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.

Representative organic particles 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 used in combination.

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 suitably about 0.1 ~ 50㎛, if the roughness is more than 50㎛ surface impact strength is insufficient, if the roughness is less than 0.1㎛ the matt effect.

The content of the light diffusing agent used in the base 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 acrylic resin of the first base resin or the surface layer of the base layer. to be. 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 combination can be used.

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 acrylic 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.

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 20 and Comparative Examples 1 to 10 are as shown in Table 1 below. Examples 1 to 10 and Comparative Examples 1 to 5 form surface layers on one surface of the substrate layer, and examples. 11-20 and Comparative Examples 6-10 are surface layers formed on both surfaces of a base material layer.

At this time, the 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 10 and Comparative Examples 1 to 5 each had a thickness of the substrate layer of 1.9 mm and a surface layer. The thickness of was 0.1 mm, Examples 11 to 20 and Comparative Examples 6 to 10 were the thickness of the substrate layer 1.8mm, the thickness of the surface layer was both 0.1mm.

Substrate layer Surface layer 1st base resin Light diffusing agent Light stabilizer 2nd base resin Light diffusing agent Light stabilizer Example 1 and Example 11 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 0.2 part by weight of TFE resin 10 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 2, Example 12 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 0.5 part by weight of TFE resin 10 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 3, Example 13 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 20 parts by weight of TFE resin 10 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 4, Example 14 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 50 parts by weight of TFE resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 5, Example 15 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 60 parts by weight of TFE resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 6, Example 16 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 10 parts by weight of TFE-HFP resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 7 and Example 17 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 15 parts by weight of TFE-HFP resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 8, Example 18 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 20 parts by weight of TFE-HFP resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 9, Example 19 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 50 parts by weight of TFE-HFP resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Example 10, Example 20 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 60 parts by weight of TFE-HFP resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Comparative Example 1, Comparative Example 6 PC 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight - 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Comparative Example 2, Comparative Example 7 MS 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight PMMA 100 parts by weight 15 parts by weight of TFE resin 2 parts by weight of silicon beads Tinuvin P 0.2 parts by weight Comparative Example 3, Comparative Example 8 PMMA 100 parts by weight 1 part by weight of silicon beads Tinuvin P 0.2 parts by weight MS 100 parts by weight 15 parts by weight of TFE resin 2 parts by weight of silicon beads 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 15 parts by weight of TFE resin 2 parts by weight of silicon beads 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 15 parts by weight of TFE resin 2 parts by weight of silicon beads 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 (6-4) copolymerization Resin * Silicon Bead: Silicon Resin Bead, Particle Size 2㎛ * TFE Resin: Tetrafluoroethylene Resin * TFE-HFP Resin: Tetrafluoroethylene-hexafluoropropylene Copolymer Resin * 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 10 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 leaving it 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 10, 20 and Comparative Examples 5, 10 and the like were measured at 80 ° C. and 75% relative humidity for 96 hours, and then the degree of floating of four corners from the bottom was measured.

Haze was measured by the ASTM D1003 method.

The yellowing degree after exposure was measured by ASTM D1003 method after performing lamp at 40 degreeC and 240 hours in the Q-UV tester equipped with FS-40313 / 280 according to ASTM D1925 standard.

division Water absorption rate (%) Deflection (mm) Haze (%) Yellowness after exposure (△ YI) Surface layer formation on one side of the base layer Example 1 0.25 0.27 99 1.20 Example 2 0.25 0.27 99 1.19 Example 3 0.21 0.24 99 1.20 Example 4 0.18 0.23 99 1.20 Example 5 0.17 0.23 99 1.19 Example 6 0.23 0.26 99 1.20 Example 7 0.23 0.25 99 1.18 Example 8 0.22 0.24 99 1.19 Example 9 0.20 0.22 99 1.20 Example 10 0.19 0.23 99 1.18 Comparative Example 1 0.26 0.28 99 1.21 Comparative Example 2 0.24 0.32 99 1.19 Comparative Example 3 0.25 0.40 99 1.22 Comparative Example 4 0.30 0.40 99 1.18 Comparative Example 5 0.20 0.20 99 2.20 Surface layer formation on both sides of the base layer Example 11 0.21 0.27 99 1.20 Example 12 0.21 0.27 99 1.19 Example 13 0.19 0.26 99 1.20 Example 14 0.18 0.24 99 1.21 Example 15 0.18 0.24 99 1.19 Example 16 0.20 0.25 99 1.21 Example 17 0.19 0.25 99 1.19 Example 18 0.19 0.24 99 1.20 Example 19 0.17 0.22 99 1.18 Example 20 0.16 0.22 99 1.19 Comparative Example 6 0.23 0.28 99 1.21 Comparative Example 7 0.21 0.30 99 1.19 Comparative Example 8 0.22 0.40 99 1.22 Comparative Example 9 0.27 0.40 99 1.18 Comparative Example 10 0.25 0.20 99 2.20

As a result of the physical property evaluation, in Examples 1 to 20 in which the acrylic resin and the fluorine-based resin were included in the surface layer, the water absorption rate was lower than that of Comparative Examples 1 and 6, and the warpage phenomenon was also low.

In addition, in the case of Examples 1-20 whose base resin of a base material layer is a polycarbonate resin, even if the surface layer contains fluorine-type resin, the base resin of a base material layer is not a polycarbonate resin, Comparative Examples 2, 3, 4, 7, 8 , 9, the warpage is lower than the case.

In addition, in the case of Examples 1-20 whose base resin of a surface layer is an acrylic resin and a fluorine resin, in the yellowing degree after exposure compared with Comparative Examples 5 and 10 which do not use acrylic resin for a surface layer even if it contains a fluorine resin in a surface layer, It can be seen that excellent.

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 its water absorption resistance, so that warpage is very low even in a high temperature and high humidity environment, and has provided excellent light diffusing plate with low yellowing even when exposed to a light source for a long time. .

Claims (5)

A base layer comprising a first base resin of polycarbonate resin; And A light diffusion plate formed on one surface or both surfaces of the substrate layer, and including a surface layer containing a second base resin of acrylic resin and fluorine resin. The method of claim 1, The first base resin of the base layer is selected from the group consisting of linear and branched aromatic polycarbonate homopolymers prepared by reacting dihydroxy phenol with phosgene or by reaction of dihydroxy phenol with a carbonate precursor. Light diffusion plate, characterized in that. The method of claim 1, The acrylic resin of the surface layer is selected from homopolymers and copolymers obtained from monomers selected from alkyl methacrylate, alkyl acrylate, cycloalkyl methacrylate, cycloalkyl acrylate, aryl methacrylate and aryl acrylate. Light diffusion plate, characterized in that at least one. The method of claim 1, The fluorine-based resin of the surface layer is a light diffusion plate, characterized in that contained 0.5 to 30 parts by weight based on 100 parts by weight of acrylic resin. The method of claim 1, The fluororesin is a tetrafluoroethylene (TFE) homopolymer, a copolymer of tetrafluoroethylene and perfluoropropyl ether (PFA), tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) Light diffusion plate, characterized in that at least one selected from copolymers, copolymers of tetrafluoroethylene and ethylene (ETFE), copolymers of vinylidene fluoride (VDF) and tetrafluoroethylene (TFE).