WO2006080798A1

WO2006080798A1 - Light-diffusion plate

Info

Publication number: WO2006080798A1
Application number: PCT/KR2006/000279
Authority: WO
Inventors: Jun Kil Doo; Yoon Hee Cho; Hee Cheong Lee; Dong Hyun Kim; Byeong Heui Han; Tae Yong Ryu; Chung Seock Kang
Original assignee: Kolon Ind. Inc./Kr
Priority date: 2005-01-25
Filing date: 2006-01-25
Publication date: 2006-08-03
Also published as: JP4857286B2; JP2008532058A

Abstract

Disclosed is a light-diffusion plate for use in a backlight unit of a liquid crystal display or an illumination apparatus. Specifically, this invention provides a light-diffusion plate including a substrate layer prepared by using a polycarbonate resin as a base resin. Thus, such a light-diffusion plate exhibits high dimensional stability thanks to high heat resistance and moisture resistance, and seldom causes a bending phenomenon even under conditions of high temperature and high humidity. Further, even if the light-diffusion plate is exposed to a light source for a long period of time, it has a low yellowing index.

Description

LIGHT-DIFFUSION PLATE

Technical Field

The present invention relates to a light-diffusion plate for use in a backlight unit of a liquid crystal display (LCD) or an illumination apparatus .

Background Art

As conventional light-diffusion plates, there are disclosed © a light-diffusion plate having surface protrusions through a physical process (Japanese Patent Laid- open Publication No. Hei . 4-275501) , © a light-diffusion plate obtained by coating a transparent substrate of a polyester resin with a light-diffusion layer containing transparent resin particles (Japanese Patent Laid-open Publication No . Hei . 6-59108) , (S) a light-diffusion plate obtained by melt-mixing beads with a transparent resin and then extruding a mixture of beads and resin, (Japanese Patent Laid-open Publication No. Hei . 6-123802) , and ® a light- diffusion plate having a sea-island structure formed by melt- kneading at least two kinds of transparent thermoplastic resins (Japanese Patent Laid-open Publication No . Hei . 9- 311205) .

The light-diffusion plates of φ and CD are a surface light-diffusion plate exhibiting a light-diffusing effect by the surface protrusions or coated light-diffusion layer . In addition, the light-diffusion plates of (3) and ® are a light- diffusion plate having the light-diffusing component even in the substrate . Typically, a light-diffusion plate prepared mainly using a methylmethacrylate resin is advantageous because it has excellent light properties, such as total luminous transmittance . However, since such a light-diffusion plate has low dimensional stability, when it is used along with a light source such as a cold cathode fluorescent lamp or an LED and a change in temperature is caused by turn on and off of the light source, the water absorption rate of the light- diffusion plate may easily vary, therefore causing problems including deformation, leading to bending, corrugations, or cracking . That is, under conditions of high temperature and high humidity, deformation such as a bending phenomenon may be caused (Japanese Patent Laid-open Publication Nos . Hei . 07-100985 and 08-198976) .

In order to solve such problems, a multi-layer sheet including methylmethacrylate-styrene capable of decreasing absorption ability is proposed (Japanese Patent Laid-open Publication No . 2004-37483 and Korean Patent Laid-open Publication No . 2003-95262 ) . However, the resin used essentially has insufficient light resistance, and may entail a problem of deterioration such as coloration . As a known process to improve light resistance of the resin, a UV absorbent may be added. However, in some of resins having low light resistance, such improvement effects are not sufficient .

Disclosure of the Invention

Leading to the present invention, intensive and thorough research on light-diffusion plates, carried out by the present inventors aiming to avoid the problems encountered in the related art, led to the development of a light-diffusion plate having high dimensional stability thanks to high heat resistance and low absorption performance even under conditions of high temperature and high humidity, without a yellowing phenomenon even upon exposure to a light source for a long period of time by virtue of light resistance of a surface layer.

Therefore, it is an object of the present invention to provide a light-diffusion plate having high dimensional stability, thus generating less of a bending phenomenon even under conditions of high temperature and high humidity.

Another obj ect of the present invention is to provide a light-diffusion plate which can be inexpensively manufactured while maintaining high dimensional stability.

A further object of the present invention is to provide a light-diffusion plate which generates less of a yellowing phenomenon . In order to achieve the above objects, the present invention provides a light-diffusion plate comprising a substrate layer containing a polycarbonate resin as a base resin .

In addition, the present invention provides a light- diffusion plate comprising a substrate layer containing a mixture including a polycarbonate resin and a polystyrene resin as a base resin .

The polycarbonate resin may be selected from the group consisting of linear and branched aromatic polycarbonate homopolymers prepared by reacting dihydroxyphenol with phosgene or reacting dihydroxyphenol and a carbonate precursor .

The base resin may comprise a mixture including a polycarbonate resin and a polystyrene resin mixed at a weight ratio of 1 : 9-9 : 1.

The polycarbonate resin may have a melt index of 8~30 g/10min at 300°C under a load of 1.2 kg according to ASTM D1238.

The polystyrene resin may have a melt index of 0.5-3 g/10min at 200⁰C under a load of 5 kg according to ASTM D1238.

The light-diffusion plate may further comprise a surface layer formed on either or both surfaces of the substrate layer and including an acrylic resin or a styrene- acrylic copolymer resin as a base resin.

The acrylic resin may be a homopolymer, a copolymer, or mixtures thereof obtained from at least one monomer selected from the group consisting of methacrylic acid alkylester, acrylic acid alkylester, methacrylic acid cycloalkylester, acrylic acid cycloalkylester, methacrylic acid arylester, and acrylic acid arylester. The styrene-acrylic copolymer resin may be a copolymer of at least one acrylic monomer selected from the group consisting of methacrylic acid alkylester, acrylic acid alkylester, methacrylic acid cycloalkylester, acrylic acid cycloalkylester, methacrylic acid arylester, and acrylic acid arylester and at least one styrene monomer selected from the group consisting of. styrene, α-methylstyrene, m- methylstyrene, p-methylstyrene and p-methoxystyrene .

The styrene-acrylic copolymer resin may be obtained by reacting the acrylic monomer with the styrene monomer at a weight ratio of 6 : 4-2 : 8.

The surface layer may further comprise a fluorine resin or fluorine resin particles .

The substrate layer or surface layer may further comprise 0.1-35 wt% of a light-diffusing agent, based on the total weight of the composition of the substrate layer or surface layer.

The light-diffusing agent may have a particle size of 0.2-50 μm.

The surface layer may have an embossed shape through protrusion of the light-diffusing agent, with a surface roughness of 1-50 μm. The substrate layer or surface layer may further comprise 0.01-5 wt% of a light stabilizer, based on the total weight of the composition of the substrate layer or surface layer.

Best Mode for Carrying Out the Invention

Hereinafter, a detailed description will be given of the present invention.

In the present invention, a light-diffusion plate comprises a substrate layer including only a polycarbonate resin or a mixture composed of a polycarbonate resin and a polystyrene resin as a base resin.

The polycarbonate resin has excellent impact resistance, light transmittance, cold resistance and electrical properties, and in particular has high heat resistance and absorption resistance, and thus is outstanding in dimensional stability and has a wide temperature range . Hence, this resin is mainly used for optical lenses , optical disk materials, helmets, guards, covers, etc. The polycarbonate resin used in the present invention is a general aromatic polycarbonate resin, which includes linear and branched carbonate homopolymers, polyester copolymers or mixtures thereof resulting from the reaction of dihydroxyphenol and phosgene or of dihydroxyphenol and a . carbonate precursor. As such, dihydroxyphenol is exemplified by 2, 2-bis ( 4-hydroxyphenyl) propane (bisphenol A) , bis ( 4-hydroxyphenyl) methane, 2, 2-bis ( 4-hydroxy-3, 5- dimethylpheny1) propane and 1, 1-bis (4-hydroxyphenyl) cyclohexane, and the carbonate precursor is exemplified by diphenylcarbonate, carbonyl halide, and diarylcarbonate .

The polycarbonate resin preferably has a melt index (MI) of 7-30 g/10min at 300°C under a load of 1.2 kg according to ASTM D1238.

Although the polycarbonate resin has excellent impact resistance, absorption resistance and light transmittance, it is disadvantageously expensive . Thus, the polycarbonate resin may be mixed with the polystyrene resin having a similar refractive index and being relatively inexpensive, in order to reinforce stiffness of the polycarbonate resin, decrease material expense in preparation cost, and maintain and improve optical and mechanical properties .

Since the polystyrene resin used to prepare the base resin of the substrate layer is hard, colorless, transparent, inexpensive (thanks to mass production) , and has excellent electrical properties, it has been widely used for daily necessities such as kitchen utensils, writing materials, furniture, etc . , and electrochemical articles , such as large automobile molds, television cabinets, etc .

The polystyrene resin used in the present invention has a melt index (MI) of 0.5-3 g/10min at 200⁰C under a load of 5 kg according to ASTM D1238. With the intention of mixing the polycarbonate resin with the polystyrene resin, these resins may be melt-kneaded at 200~300°C, preferably 25O⁰C, and at a motor speed of 250 rpm using a twin-screw extruder having a screw diameter of 30 mm.

As such, the polycarbonate resin and polystyrene resin may be mixed at a ratio of 1 : 9-9 : 1. Each of these resins should be added in an amount of at least 10% to exhibit advantages of polycarbonate, for example, flexibility and dimensional stability, and advantages of polystyrene, for example, high absorption resistance and strength .

The light-diffusion plate of the present invention may be a single-layered light-diffusion plate composed of only the substrate layer including the above base resin, or a multi-layered light-diffusion plate composed of the substrate layer and a surface layer formed on either or both surfaces thereof.

In the case of the multi-layered light-diffusion plate, in addition to the above-mentioned substrate layer, the surface layer may be further formed on either or both surfaces of the substrate layer . As such, although the base resin of the surface layer is not particularly limited, an acrylic resin or a styrene-acrylic copolymer resin may be used. The acrylic resin is preferably a homopolymer or copolymer obtained from at least one monomer selected from the group consisting of methacrylic acid alkylester, such as methylmethacrylate, ethylmethacrylate, butylmethacrylate, 2- ethylhexylmethacrylate, etc . ; acrylic acid alkylester, such as methylacrylate, ethylacrylate, butylacrylate, etc . ; methacrylic acid cycloalkylester, such as cyclohexylmethacrylate, 2-methylcyclohexylmethacrylate, dicyclopentanylmethacrylate, etc . ; acrylic acid cycloalkylester, such as cyclohexylacrylate, 2- methylcyclohexylacrylate, etc . ; methacrylic acid arylester, such as phenylmethacrylate, benzylmethacrylate, etc . ; acrylic acid arylester, such as phenylacrylate, benzylacrylate, etc.

The styrene-acrylic copolymer resin is prepared using the above-mentioned resin as the acrylic monomer and styrene or substituted styrene as the styrene monomer . Examples of substituted styrene include alkylstyrene, such as α- methylstyrene, halogenated styrene such as chlorosytrene, and vinyl styrene . In addition, two or more styrene monomers may be used, if necessary .

In particular, in the styrene-acrylic copolymer resin used in the present invention, the acrylic monomer and styrene monomer are copolymerized at a ratio of 9 : 1-1 : 9, preferably at a ratio of 6 : 4-1 : 9. In consideration of adhesion to the substrate layer, these monomers are preferably used in the above ratio .

In addition, the surface layer of the present invention may further include a fluorine resin or fluorine resin particles . The fluorine resin has excellent thermal stability and electrical properties, and is superior in chemical durability, weatherability, light resistance and oxygen resistance, and in particular, has a very low water absorption rate and high heat resistance, and thus has a high service temperature of 250~300°C. Also, since this resin has outstanding surface friction resistance, it is presently applied to various valves, pumps, tanks, filters, pipes, cables, and computers and is widely used in the aerospace industry.

Particularly, the fluorine resin or fluorine resin particles used in the present invention comprise at least one selected from among a tetrafluoroethylene (TFE) homopolymer, a tetrafluoroethylene and perfluoropropylether copolymer (PFA) , a tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) copolymer, a tetrafluoroethylene and ethylene copolymer (ETFE) , and a vinylidenefluoride (VDF) and tetrafluoroethylene (TFE) copolymer . The use of the fluorine resin or fluorine resin particles results in superior water repellent properties . That is, the fluorine resin is included in the surface layer, whereby dimensional stability is further improved. Thus, a bending phenomenon does not occur even under conditions of high temperature and high humidity.

The fluorine resin is preferably contained in the surface layer in an amount of 0.5-35 wt%, preferably 5-15 wt%, in consideration of dimensional stability and transmittance, based on the total composition of the surface layer .

In addition, the substrate layer or surface layer may further include a light-diffusing agent, which has a refractive index different from the base resin and is used to increase the diffusion rate of light . To this end, various organic and inorganic particles may be used. As such, if the light-diffusing agent has a large difference in refractive index from the base resin, even though it is used in a small amount, desired light-diffusing effects may be exhibited. On the other hand, if a difference in refractive index is small, this material should be used in a relatively larger amount .

Typically, examples of the organic particles include acrylic polymer particles, such as methylmethacrylate, ethylmethacrylate, isobutylmethacrylate, n-butylmethacrylate, n-butylmethylmethacrylate, acrylic acid, methacrylic acid, hydroxyethylmethacrylate, hydroxypropylmethacrylate, hydroxyethylacrylate, acrylamide, methylolacrylamide, glycidylmethacrylate, ethylacrylate, isobutylacrylate, n- butylacrylate, 2-ethylhexylacrylate polymers, or copolymers or terpolymers thereof; olefin polymer particles, such as polyethylene and polypropylene; acryl-olefin copolymer particles, multi-layered multicomponent particles obtained by forming a layer of the homopolymer, copolymer or terpolymer particles and then applying another monomer layer onto the above polymer particle layer, siloxane polymer particles, tetrafluoroethylene particles, etc. Examples of the inorganic light-diffusion particles include calcium carbonate, barium sulfate, silicon oxide, aluminum hydroxide, titanium oxide, zirconium oxide, magnesium fluoride, talc, glass, mica, etc. Commonly, the organic particles have superior light-diffusibility to inorganic particles . Also, at least two kinds of light- diffusion particles may be mixed, if necessary.

When the light-diffusing agent is further included in the surface layer, light-diffusing effects may be more increased. As well, the light-diffusion particles protrude from -'the surface of the surface layer such that they are embossed, thereby exhibiting a non-glossy surface and low reflectivity. As such, the surface layer preferably has a surface roughness of about 0.1-50 μm. If the roughness exceeds 50 μm, surface impact strength becomes insufficient . On the other hand, if the roughness is less than 0.1 μm, non- glossy effects are deteriorated.

The light-diffusing agent is contained in the substrate layer or surface layer of the present invention in an amount of 0.01-35 wt%, preferably 0.5-15 wt%, based on the total weight of the composition of the base resin of the substrate layer or surface layer. When the amount of light- diffusing agent is less than 0.01 wt%, it is difficult to expect sufficient light-diffusing effects and masking effects . On the other hand, when the above amount exceeds 35 wt%, light transmittance becomes bad. As such, the amount of light-diffusing agent may be determined depending on the difference in refractive index from the base resin.

In addition, the substrate layer or surface layer may further include a light stabilizer . Examples of the light stabilizer include a UV absorbent having a maximum absorption wavelength of 250-380 run, or a radical scavenger such as a hindered amine UV stabilizer capable of maximizing a light stabilizing effect . This component should exhibit such effect for a long period of time, and should not be separated or removed from the sheet due to evaporation or extraction.

An absorbent having high compatibility with the substrate should be selected.

The UV absorbent may be selected from the group consisting of cyanoacryl, salicylate, malonic acid ester, oxalic anilide, diketone, hydroxyl benzophenone, hydroxy benzotriazole, organic metals, and mixtures thereof .

The UV stabilizer may be selected from the group consisting of piperidinyl ester, oxazolidine and piperidino- oxazolidine, piperidispiroacetal, diazacycloalkanone, and mixtures thereof.

The light stabilizer may be used in an amount of 0.01~5 wt%, preferably 0.1~2 wt%, based on the total weight of the resin composition of the substrate layer or surface layer . In particular, this component is contained in the surface layer, thereby obtaining a light stabilizing effect, without a decrease in total luminous transmittance or physical properties of the substrate layer . In addition, the preparation cost may be reduced.

The light-diffusion plate of the present invention may be used for various indoor or outdoor purposes . That is, the light-diffusion plate may be applied to signboards, illuminated signboards, illuminated covers, glass display cases, etc . , and may be preferably used as light-diffusion plates for displays . The light-diffusion plate for a display is typically exemplified by light-diffusion plates for backlight units of LCDs or edge-light-type backlight units .

A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention . In the examples , in which PC and PS were used as the base resin of the substrate layer, they were uniformly added as shown in composition ratios of Table 1 and then melt- kneaded at 250⁰C using a twin-screw extruder .

As such, the polycarbonate resin had a melt index of 22 g/10min at 300°C under a load of 1.2 kg according to ASTM D1238 , while the polystyrene resin had a melt index of 1.5 g/10min at 200⁰C under a load of 5 kg according to ASTM D1238.

In addition, as the base resin of the surface layer, polymethylmethacrylate, polystyrene or a styrene-acrylic copolymer resin copolymerized using an acrylate monomer and a styrene monomer according to a typical process was used. The light-diffusion plate was formed at 25O⁰C through a co-extruding process using an extruder having screws having diameters of 135 mm and 60 mm. In the light-diffusion plate composed of only a substrate layer, the substrate layer was 2.0 mm thick. In the light-diffusion plate further including the surface layer, the surface layer was formed on one surface of the substrate layer. As such, the substrate layer was 1.0 mm thick and the surface layer was 0.1 mm thick.

TABLE 1

Substrate Layer

Pv NFn

Base Resin

1 PC, 100 wt parts + PS, 100 wt parts

2 PC, 100 Wt parts + PS, 300 wt parts

3 PC, 100 Wt parts + PS, 500 wt parts

4 PC, 100 Wt parts + PS, 900 wt parts

5 PC, 300 wt parts + PS, 100 Wt parts

6 PC, 500 Wt parts + PS, 100 Wt parts

7 PC, 900 wt parts + PS, 100 Wt parts

TABLE 2

T?v NIn Substrate Layer Surface Layer

Base Resin Base I ^esin Fluorine Resin

8 PC, 100 Wt parts PMMA, 100 Wt parts

TFE Resin Particles,

9 PC, 100 wt parts PMMA, 100 Wt parts 0.2 wt parts

TFE Resin Particles,

10 PC, 100 wt parts PMMA, 100 Wt parts 0.5 wt parts

TFE Resin Particles,

11 PC, 100 Wt parts PMMA, 100 wt parts 10 wt parts

TFE Resin Particles,

12 PC, 100 wt parts PMMA, 100 Wt parts 25 wt parts

13 PC, 100 Wt parts PMMA, 100 Wt parts TFE-HFP Resin , 10 wt parts

TFE-HFP Resin,

14 PC, 100 Wt parts PMMA, 100 Wt parts 20 wt parts

TFE-HFP Resin,

15 PC, 100 wt parts PMMA, 100 Wt parts 50 wt parts

TFE-HFP Resin,

16 PC, 100 Wt parts PMMA, 100 Wt parts 60 wt parts

17 PC, 100 wt parts PC, 100 wt parts

TABLE 3

TABLE 4

TABLE 5

In the compositions of the light-diffusion plates of the examples and comparative examples, the substrate layer was comprised by mixing the base resin shown in Table 1 with 0.2 parts by weight of silicone resin beads (average particle size : 2 μm) as a light-diffusing agent and 0.05 parts by weight of B-cap (tetra-ethyl-2, 2 ' - ( 1, 4-phenylene- dimethylidene) -bismalonate) as a UV absorbent in a light stabilizer, and the surface layer was comprising the base resin for a surface layer or by mixing the base resin with the fluorine resin or fluorine resin particles as shown in the above tables , 2 parts by weight of silicone resin beads (average particle size : 2 μm) as a light-diffusing agent and 0.5 parts by weight of B-cap (tetra-ethyl-2 , 2' - ( 1, 4-phenylene- dimethylidene) -bismalonate) as a UV absorbent in a light stabilizer .

The light-diffusion plates manufactured in the examples and comparative examples were measured for water absorption rate, bending, total luminous transmittance, haze, yellowing index and thermal deformation temperature . The results are given in Tables 5 to 8.

The water absorption rate was measured from a difference in weight by cutting the light-diffusion plate to 10 x 10 cm and then dipping it into water at 25⁰C for 24 hours . The bending was determined in such a manner that the light-diffusion plate was mounted on a 20" sized backlight unit and then allowed to stand at 6O⁰C with a relative humidity of 75% for 96 hours, and a distance between four corners of the light-diffusion plate which were warped upwards and the surface of the backlight unit was measured. The thermal deformation temperature was measured according to ASTM D648.

The yellowing index was measured according to ASTM D1003 after exposure was conducted at 40⁰C for 240 hours using a Q-UV tester equipped with an FS-40 313/280 lamp under conditions of ASTM D1925, and the total luminous transmittance and haze were measured according to ASTM D1003.

TABLE 6

From the results of the above properties, the light- diffusion plate having only the substrate layer comprising the mixture of polycarbonate resin and polystyrene resin as the base resin can be confirmed to have relatively high dimensional stability even under conditions of high temperature and high humidity, with the exception of high yellowing index.

TABLE 7

From the results of the above properties, the light- diffusion plate having the substrate layer comprising the polycarbonate resin as the base resin and the surface layer formed on one surface of the substrate layer or the surface layer further including the fluorine resin or fluorine resin particles can be confirmed to have high dimensional stability.

Thus, when the polycarbonate resin is used as the base resin for the substrate layer, light properties including dimensional stability can be seen to be excellent, regardless of the kinds of base resin used for the surface layer.

TABLE 8

From the results of the above properties, the light- diffusion plate having the substrate layer comprising the mixture of polycarbonate resin and polystyrene resin as the base resin and the surface layer formed of PMMA resin as the base resin on one surface of the substrate layer can be confirmed to have excellent dimensional stability and anti- yellowing. Further, the light-diffusion plate having the surface layer further including the fluorine resin or fluorine resin particles has superior dimensional stability to the light- diffusion plate having no fluorine resin or fluorine resin particles . As well, as the amount of fluorine resin or fluorine resin particles is increased, dimensional stability becomes more and more excellent .

Therefore, in the case where the mixture of polycarbonate resin and relatively inexpensive polystyrene resin is used as the base resin of the substrate layer, dimensional stability is equal or superior to the case where only the polycarbonate resin is used as the base resin of the substrate layer, and thus, the preparation cost may be decreased.

TABLE 9

From the results of the above properties, the light- diffusion plate including the substrate layer comprising the mixture of polycarbonate r^*esin and polystyrene resin as the base resin and the surface layer formed of the base resin of MS resin on one surface of the substrate layer can be confirmed to have excellent dimensional stability.

Hence, even though the relatively inexpensive polystyrene resin is mixed with the polycarbonate resin and used as the base resin of the substrate layer, excellent dimensional stability can be exhibited, resulting in decreased preparation cost .

TABLE 10

From the results of the above properties, in the light-diffusion plate in which the polycarbonate resin or mixture of polycarbonate resin and polystyrene resin was not contained in the substrate layer all the properties, including dimensional stability and anti-yellowing, can be confirmed to decrease .

Therefore, since the light-diffusion plate of the present invention comprises the substrate layer formed of the polycarbonate resin or the mixture of polycarbonate resin and polystyrene resin, it has excellent total luminous transmittance and light diffusibility, in particular, high heat resistance and absorption resistance, and thus has superior dimensional stability. Also, polystyrene resin is used, which is relatively inexpensive compared to polycarbonate resin, thereby decreasing the preparation cost .

In addition, the light-diffusion plate of the present invention further includes the surface layer, thereby providing anti-yellowing upon exposure to a light source for a long period of time . Moreover, the surface layer of the light-diffusion plate of the present invention further includes the fluorine resin or fluorine resin particles, whereby dimensional stability is further increased and a yellowing index is further decreased upon exposure to a light source for a long period of time, resulting in light-diffusion plates having more improved properties . Industrial Applicability

As previously described herein, the present invention provides a light-diffusion plate . According to the present invention, since the light-diffusion plate includes a substrate layer having a polycarbonate resin as a base resin, it has high dimensional stability thanks to high absorption resistance, and thus it generates less of a bending phenomenon . even under conditions of high temperature and high humidity. In addition, a surface layer is further included or such a surface layer further includes a fluorine resin or fluorine resin particles, thereby providing a light-diffusion plate having further increased dimensional stability and further decreased yellowing even upon exposure to a light source for a long period of time .

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims .

Claims

1. A light-diffusion plate, comprising a substrate layer containing a polycarbonate resin as a base resin .

2. A light-diffusion plate, comprising a substrate layer containing a mixture including a polycarbonate resin and a polystyrene resin as a base resin.

3. The light-diffusion plate according to claim 1 or 2, wherein the polycarbonate resin is selected from the group consisting of linear and branched aromatic polycarbonate homopolymers prepared by reacting dihydroxyphenol with phosgene or reacting dihydroxyphenol and a carbonate precursor .

4. The light-diffusion plate according to claim 2, wherein the base resin comprises a mixture including a polycarbonate resin and a polystyrene resin mixed at a weight ratio of 1 : 9-9 : 1.

5. The light-diffusion plate according to claim 1 or 2, wherein the polycarbonate resin has a melt index of 8~30 g/10min at 300°C under a load of 1.2 kg according to ASTM D1238. β . The light-diffusion plate according to claim 2, wherein the polystyrene resin has a melt index of 0.5-3 g/10min at 200°C under a load of 5 kg according to ASTM D1238.

7. The light-diffusion plate according to claim 1 or 2 , further comprising a surface layer formed on either or both surfaces of the substrate layer and including an acrylic resin or a styrene-acrylic copolymer resin as a base resin .

8. The light-diffusion plate according to claim 7 , wherein the acrylic resin is a homopolymer, a copolymer or mixtures thereof, obtained from at least one monomer selected from the group consisting of methacrylic acid alkylester, acrylic acid alkylester, methacrylic acid cycloalkylester, acrylic acid cycloalkylester, methacrylic acid arylester, and acrylic acid arylester .

9. The light-diffusion plate according to claim 7 , wherein the styrene-acrylic copolymer resin is a copolymer of at least one acrylic monomer selected from the group consisting of methacrylic acid alkylester, acrylic acid alkylester, methacrylic acid cycloalkylester, acrylic acid cycloalkylester, methacrylic acid arylester, and acrylic acid arylester and at least one styrene monomer selected from the group consisting of styrene, α-methylstyrene, m- methylstyrene, p-methylstyrene and p-methoxystyrene . 10. The light-diffusion plate according to claim 7, wherein the styrene-acrylic copolymer resin is obtained by reacting an acrylic monomer with a styrene monomer at a weight ratio of 9 : 1-1 : 9.

11. The light-diffusion plate according to claim 7 , wherein the styrene-acrylic copolymer resin is obtained by reacting an acrylic monomer with a styrene monomer at a weight ratio of 6 : 4-2 : 8.

12. The light-diffusion plate according to claim 7 , wherein the surface layer further comprises a fluorine resin or fluorine resin particles .

13. The light-diffusion plate according to claim 1 or 2 , wherein the substrate layer further comprises 0.1-35 wt% of a light-diffusing agent, based on a total weight of a composition of the substrate layer.

14. The light-diffusion plate according to claim 7 , wherein the substrate layer or surface layer further comprises 0.1-35 wt% of a light-diffusing agent, based on a total weight of a composition of the substrate layer or surface layer . 15. The light-diffusion plate according to claim 13, wherein the light-diffusing agent has a particle size of 0.2-50 μm.

16. The light-diffusion plate according to claim 14, wherein the light-diffusing agent has a particle size of 0.2-50 μm.

17. The light-diffusion plate according to claim 14, wherein the surface layer has an embossed shape through protrusion of the light-diffusing agent and has a surface roughness of 1-50 μm.

18. The light-diffusion plate according to claim 1 or 2, wherein the substrate layer further comprises 0.01-5 wt% of a light stabilizer, based on a total weight of a composition of the substrate layer.

19. The light-diffusion plate according to claim 7 , wherein the substrate layer or surface layer further comprises 0.01-5 wt% of a light stabilizer, based on a total weight of a composition of the substrate layer or surface layer.