KR20100070580A - Multi-layered light diffuser plate with excellent impact resistance and crack, back light unit and lcd using the light diffuser plate - Google Patents

Abstract

PURPOSE: A multi-layered light diffuser plate with excellent impact resistance, a back light unit and a liquid crystal display apparatus using the same are provided to prevent a delamination phenomenon between a base material layer and a coating layer by forming the coating layer with a methyl methacrylate-based resin in which a styrene resin is copolymerized. CONSTITUTION: A base material layer(110) is formed with a first resin composition. A coating layer(120) is formed with a second resin composition. The coating layer is stacked on the base material layer. The first resin composition includes 0.1 to 10 parts by weight of siloxane-based light-diffusing agent, 0.01 to 20 parts by weight of acryl-based light-diffusing agent, and 0.01 to 20 parts by weight of ultraviolet-absorbing agent, with respect to 100 parts by weight of styrene-based resin. The second resin composition includes 0.1 to 30 parts by weight of acryl-based light-diffusing agent, with respect to 100 parts by weight of a methyl methacrylate-based resin.

Description

 Multi-layered light diffuser plate with excellent impact resistance and crack, back light unit and LCD using the light diffuser plate}

The present invention relates to a light diffusing plate for a backlight unit, and more particularly, based on a styrene-based resin having excellent water absorption and warpage characteristics but having low impact resistance, and having compatibility with a styrene-based resin for strengthening impact and cracking. In order to prevent peeling of the base layer to which the excellent acrylic optical acid is added and the base layer, a multilayer light diffusing plate comprising a coating layer using a methyl methacrylate resin copolymerized with a styrene resin as a base resin and It relates to a used backlight unit and a liquid crystal display device.

Among the thermoplastic resins used as the base resin of the light diffusion plate for the backlight unit of the liquid crystal display device, transparent thermoplastic resins such as methacryl resin, styrene resin, cyclic olefin resin, and polycarbonate resin that transmit light are used. Can be mentioned.

However, when only basic resin is used and no light diffusing agent is added, there is a problem in that light transmittance and light diffusing property are not sufficient. Therefore, in general, a light diffusing agent is added to a basic resin to prepare a light diffusing plate. The light diffusing agent transmits light such as direct light or fluorescent light with high transmittance and hiding power such that the light source is not visually discernible. And light diffusion effect to diffuse light.

The light diffusing agent is an inorganic material or an organic material. The inorganic fine particles include calcium carbonate, barium sulfate, titanium dioxide, aluminum hydroxide, silica, glass, talc, mica, white carbon, magnesium oxide, zinc oxide, and the like.

In Japanese Laid-Open Patent Publication No. 1997-031288 (published on Feb. 4, 1997), 0.2-10 parts by weight of precipitated calcium carbonate was added as a methacrylic resin, and the shape was hexahedral, and the average particle diameter was 1-15 μm. A composition added as a diffusing agent is disclosed.

In Japanese Patent Laid-Open No. 1999-035779 (published on February 9, 1999), barium sulfate, calcium carbonate, talc, and the like were used as a methacrylic resin, and a composition in which a small amount of additives such as an ultraviolet absorber and a light stabilizer were added. Is disclosed.

Most of the thermoplastic resins used for the light diffusion plate for the backlight unit of the conventional liquid crystal display device are methacryl-based, methacryl-based copolymers with unsaturated monomers, and polycarbonate-based resins.

However, these base resins are expensive in comparison with styrene resins and have a disadvantage in that moisture and heat deformation easily occur. Nevertheless, the use of styrene resins has been limited because impact resistance and cracking are superior to styrene resins.

When the styrene resin is used as the base resin of the light diffusion plate, cracks are more likely to occur during the impact and vibration tests of the diffusion plate than transparent thermoplastic resins such as methacrylic resin and polycarbonate resin during extrusion molding. Therefore, due to such a problem, conventionally, methacryl-based resins having relatively little impact and cracking are used as the base resins in addition to styrene-based resins, and many siloxane-based crosslinked particles are added as light diffusing agents.

An object of the present invention is to use a styrene-based resin having a relatively low cost and excellent light scattering and light transmittance as a base resin of the base layer, while adding an acrylic light-diffusing agent having excellent adhesion and compatibility with the styrene-based resin as a light diffusing agent To provide a multilayer light diffusion plate that can enhance impact resistance and cracking, and can prevent peeling from the base layer by using methyl methacrylate resin copolymerized with styrene resin as the base resin of the coating layer. will be.

Another object of the present invention is to provide a backlight unit including the multilayer light diffusion plate.

Another object of the present invention is to provide a liquid crystal display device including the backlight unit.

Multilayer light-diffusing plate according to the present invention for achieving the above one object consists of a base layer and a coating layer laminated on at least one surface of the base layer.

The base layer includes 0.1 to 10 parts by weight of a siloxane light diffusing agent having an average particle diameter of 1 to 20 μm, 0.01 to 20 parts by weight of an acrylic light diffusing agent, and 0.1 to 10 parts by weight of an ultraviolet absorber based on 100 parts by weight of a styrene resin. It is formed of a first resin composition. The coating layer is formed of a second resin composition containing 0.1 to 30 parts by weight of an acrylic light diffusing agent having an average particle diameter of 1 to 50 µm with respect to 100 parts by weight of methyl methacrylate resin copolymerized with styrene resin.

According to another aspect of the present invention, there is provided a backlight unit including the multilayer light diffusing plate.

According to another aspect of the present invention, there is provided a liquid crystal display device including the multilayer backlight unit.

The multilayer light diffusing plate according to the present invention has a low cost and excellent light scattering property and light transmittance, and by using a styrene resin which is advantageous for heat and moisture absorption as the base resin of the base layer, and adding an acrylic diffusing agent having excellent compatibility and adhesion It is possible to obtain a multilayer light diffusing plate excellent in impact strength.

In addition, the multilayer light diffusion plate according to the present invention can obtain the effect of preventing the peeling phenomenon with the base layer by using the methyl methacrylate resin copolymerized with the styrene resin as the base resin of the coating layer.

Hereinafter, a multilayer light diffusing plate, a backlight unit including the same, and a liquid crystal display according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The inventors of the present invention have studied light diffusion plates for backlight units of liquid crystal displays, in particular, multi-layer light diffusion plates in which cracking characteristics, which have been a problem in the past, can be enhanced while using styrene resin as the substrate layer. Using a styrene resin as the base resin, and adding a siloxane light diffusing agent and an acrylic light diffusing agent to the base resin, it was confirmed that the warpage phenomenon, crack characteristics and the like of the light diffusion plate are reinforced. In this case, styrene resin can be used as the base resin of the substrate layer to show excellent light transmittance and light scattering properties, and the warpage phenomenon and weather resistance of the light diffusion plate can be improved, and an acrylic optical acid agent is added to the styrene resin. It can reinforce shocks and cracks.

In addition, by using the methyl methacrylate resin copolymerized with styrene resin as the base resin of the coating layer, the peeling phenomenon with the base layer can be significantly improved.

1 is a perspective view schematically showing a multilayer light diffuser plate for a backlight unit of a liquid crystal display according to the present invention.

Referring to FIG. 1, the multilayer light diffusion plate 100 according to the present invention includes a base layer 110 formed of a first resin composition and an application layer 120 formed of a second resin composition. The coating layer 120 is laminated on at least one surface of the base layer 110.

Substrate layer

The 1st resin composition which forms the base material layer of this invention is 0.1-10 weight part of (a2) siloxane-type light-diffusion agents, and 0.01-20 weight part of (a3) acrylic light-diffusion agents with respect to 100 weight part of (a1) styrene-type resins. Part and (a4) 0.1 to 10 parts by weight of an ultraviolet absorber.

(a1) styrene resin

In this invention, styrene resin is used as a base resin of a base material layer. The styrene-based resin is a monomer unit containing 50% or more by weight of styrene, and may be substantially a polymer of styrene alone or a copolymer including 50% or more by weight of styrene and 50% or less by weight of unsaturated monomer copolymerizable with styrene.

Substituted styrenes can be used as the styrene monomer, and examples of the substituted styrenes include halogenated styrenes such as chloro styrene and bromo styrene, alkyl styrenes such as vinyltoluene and α-methyl styrene. The styrene-based monomers may be used alone or in combination of two or more as necessary.

(a2) siloxane light diffusing agent

The siloxane-based light diffusing agent used in the present invention is a siloxane-based crosslinked particle, which is a solid silicone resin particle at room temperature, and includes both a silicone rubber having a low crosslinking density and flexibility and a silicone resin having a high crosslinking density and a hard silicone resin. For example, the silicone resin which has a three-dimensional network structure, such as polydialkyl siloxane resin, such as polydimethyl siloxane and polydimethyl siloxane, and the siloxane which has an epoxy in a terminal group, is mentioned.

Since these siloxane crosslinked particles have good weather resistance, yellowing does not occur even when the final resin composition is exposed to light for a long time. In addition, the siloxane-based light diffusing agent has a refractive index of 1.40 ~ 1.42 lower than other organic-based crosslinked particles has an excellent advantage that can be obtained light diffusion and transmittance equal to or higher than a small amount of addition.

The siloxane light diffusing agent according to the present invention is spherical crosslinked fine particles. Here, if the average particle diameter of the siloxane light diffusing agent is less than 1 μm, the concealability of the light source is lowered. If the average particle diameter is more than 20 μm, there is a problem that an excessive amount of the light diffusing agent must be added to ensure proper light diffusing property. Since it arises, it is preferable that the average particle diameter is 1-20 micrometers.

It is preferable that 0.1-10 weight part of siloxane light diffusing agents are added with respect to 100 weight part of styrene resins. If the addition amount of the siloxane light diffusing agent is less than 0.1 part by weight, the light diffusivity of the final resin composition is not sufficient, so it is difficult to see a lamp or to expect light diffusion, and when it is added more than 10 parts by weight, the light transmittance becomes too low. There is a problem of reducing the brightness.

(a3) acrylic light diffusing agent

The acrylic light diffusing agent, which is another light diffusing agent dispersed in the base material layer, is preferably added at a ratio of 0.01 to 20 parts by weight based on 100 parts by weight of the styrene resin. If the acrylic light diffusing agent is added in less than 0.01 part by weight, the scattering degree of light is reduced, there is a problem that the light source itself is visible. On the contrary, when the acrylic light diffusing agent is added in excess of 20 parts by weight, the light transmittance is reduced, thereby causing a problem in that the transparency is weakened.

The average particle size of such an acrylic light diffusing agent varies depending on the amount added, but is preferably formed in a range of about 0.1 to 20 μm. When the average particle size of the acrylic light diffusing agent is less than 0.1 μm, the concealment and light scattering properties of the light source are inferior.

The acrylic light diffusing agent contained in the base material layer and the coating layer has good compatibility and adhesion with the styrene resin contained in the base resin of each layer. Therefore, the acrylic light diffusing agent also serves as an impact reinforcing agent for reinforcing the impact resistance of the light diffusing plate and the like in vibration evaluation.

(a4) UV absorbers

UV absorbers are generally used a material having an absorption wavelength in the range of 250 ~ 800nm. Particularly, in the present invention, a material having a maximum absorption wavelength in the range of 250 to 320 nm is used, which can improve the light resistance of the light diffusion plate and also suppress the coloring of the light diffusion plate by ultraviolet absorption. Such a ultraviolet absorber can be used individually or in mixture of a benzophenone type ultraviolet absorber, a cyanoacrylate type ultraviolet absorber, a sarichireto type | system | group ultraviolet absorber, a nickel complex salt type ultraviolet absorber, etc.

It is preferable that a ultraviolet absorber is added in 0.1-10 weight part with respect to 100 weight part of styrene resins. If the ultraviolet absorber is added in less than 0.1 part by weight, light resistance of the light diffusion plate is not sufficient, and if it is added in excess of 10 parts by weight, the appearance of the light diffusion plate may be damaged by bridging on the surface of the light diffusion plate.

Coating layer

The 2nd resin composition which forms the base material layer of this invention contains 0.1-30 weight part of (b2) acrylic light-diffusion agents with respect to 100 weight part of methyl methacrylate resins which copolymerized (b1) styrene resin.

(b1) Methyl methacrylate resin copolymerized with styrene resin

Methyl methacrylate resin copolymerized with styrene resin as the base resin of the coating layer contains 50 parts by weight or more of methyl methacrylate as a monomer unit with respect to 100 parts by weight of the base resin, and 50 parts by weight or less of the styrene resin. Include.

The methyl methacrylate resin may be methyl methacrylate resin alone, or may include one or more monomers copolymerizable with methyl methacrylate monomers or, if necessary, two or more. Such monomers include iii) ethyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate. Methacrylic acid esters, ii) Methyl acrylate, ethyl acrylate, beta acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, acrylic esters such as 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, iii) methacrylic acid And unsaturated acids such as acrylic acid, (iii) acrylonitrile, methacrylonitrile, maleic anhydride, phenyl maleimide and Shikuroheksilmaleimido. In addition, the methyl methacrylate resin may contain an inorganic glutamic acid unit or a glutarimide unit.

(b2) acrylic light diffusing agent

An acryl-based light diffusing agent is used in a range that does not significantly reduce light transmittance in order to adjust the feel of a matte or the like having a white or irregular surface on the surface of the light diffusion plate of the present invention and to make the surface appearance beautiful. It is preferable that the average particle diameter is about 1 to 50 μm, and in this case, those having different average particle diameters may be mixed and used, such as an acrylic crosslinked particle having an average particle diameter of 30 μm and an acrylic crosslinked particle having an average particle diameter of 30 μm. . The refractive index of the acrylic light diffusing agent has a range of approximately 1.46 to 1.55.

In the multilayer light diffusing plate, the amount added to the coating layer is preferably 0.1 to 30 parts by weight based on 100 parts by weight of the methyl methacrylate resin copolymerized with the styrene resin. If the acrylic light diffusing agent is added to less than 0.1 part by weight to the coating layer, the above effect is hard to be obtained, and if it is added more than 30 parts by weight, there is a concern that the light transmittance is lowered.

As a raw material of the multilayer light diffusion plate according to the present invention, an additive may be further included within a range that does not affect the physical properties of the light diffusion plate. For example, as the light stabilizer, a blowing agent may be added to prevent appearance defects caused by a hindered amine-based and yellowing phenomenon due to deterioration of the resin. In addition, plasticizers, antioxidants, heat stabilizers, lubricants, flame retardants, fillers, mold release agents, dyes, pigments, antibacterial agents, anti-dripping agents and nucleating agents may be further added.

In the manufacture of the multilayer light diffusing plate according to the present invention, all molding methods of thermoplastic resins, such as injection molding, extrusion molding, vacuum molding, hot press molding, and coextrusion molding, may be applied according to the use of the light diffusing plate as a final molded product.

Producing a light diffusion plate by adding an appropriate additive or molding the raw material can be easily carried out by those skilled in the art.

Manufactured light diffuser plate has excellent impact, crack, and impact resistance by adding acrylic light diffuser, so that light diffuser plate can be used during vibration test (30min each for X, Y, Z axis at 300Hz). Less cracking of supporter and guide part, less water absorption and heat deformation by using styrene resin, furthermore, base resin based on low-cost styrene resin instead of methyl methacrylate resin used in conventional diffusion plate Since it is used as, it reduces the manufacturing cost of the light diffusion plate.

In particular, when the light diffusing plate according to the present invention is applied to a liquid crystal display device, it is possible to prevent a difference in contrast between planes generated by several lamps, to transmit or diffuse light with uniform brightness, and to yellow the phenomenon even when exposed to light for a long time. Since this does not occur, the screen display quality of the liquid crystal display (LCD) is excellent.

 Manufacturing a liquid crystal display device using the multilayer light diffusing plate according to the present invention can be easily carried out by those skilled in the art.

The present invention may be better understood by the following examples, which are only specific examples of the present invention and are not intended to limit or limit the protection scope of the present invention.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. However, this is presented as a preferred example of the present invention and in no sense can be construed as limiting the present invention.

Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.

Example 1

Preparation of First Resin Composition

1.0 parts by weight of siloxane-based crosslinked particles (GE Toshiba Silicon, 120S) having an average particle diameter of 2 µm and 100 parts by weight of styrene resin (Toyo styrene Co., HRM-40), and an acrylic light diffusing agent having an average particle diameter of 0.6 µm. 0.5 parts by weight of (Sekisui, XX-25CH) and 0.2 parts by weight of an ultraviolet absorber (CIBA, T312) were added to prepare a first resin composition for forming a base layer.

Preparation of Second Resin Composition

3 parts by weight of acrylic crosslinked particles (Ganz, GSM-0854S) having an average particle diameter of 8 µm with a light diffusing agent and an average of 100 parts by weight of methyl methacrylate resin (Denka Co. TX-600XL) copolymerized with styrene resin 5 parts by weight of acrylic crosslinked particles having a particle diameter of 30 μm (Sekisui, MBX-30) were added to prepare a second resin composition for forming a coating layer.

Fabrication of Multi-layer Diffuser Plates

In order to laminate the coating layer formed of the second resin composition on both sides of the substrate layer formed of the first resin composition, the first resin composition and the second resin composition prepared in the above process are added to each extruder and melted. After kneading, it was supplied to a feed block die to form a three-layer structure multilayer light diffusion plate having a thickness of 100 µm / 1800 µm / 100 µm.

Example 2

In preparing the first resin composition, it was the same as in Example 1 except that 0.5 parts by weight of siloxane-based crosslinked particles (GE Toshiba Silicon, 120S) and 1.0 parts by weight of acrylic light diffusing agent (Sekisui, XX-25CH) were added. Was performed.

Comparative Example 1

In the preparation of the first resin composition, 1.5 parts by weight of siloxane-based crosslinked particles (GE Toshiba Silicone, 120S) is added and modified, and the coating layer formed of the second resin composition without adding acrylic crosslinked particles (Sekisui, MBX-30). The same procedure as in Example 1 was conducted except that the preparation was omitted.

Comparative Example 2

In preparing the second resin composition, it was carried out in the same manner as in Example 1, except that 100 parts by weight of pure methyl methacrylate resin (Sumitomo Co. EXN) not copolymerized with styrene resin was used.

Property measurement

Impact strength, flexural strength, toughness and vibration were measured for the molded articles (multilayer light diffusing plates) prepared in Examples and Comparative Examples.

Here, the impact strength (IZOD impact) was measured according to ASTM D256 (1/4 ", 1/8" 23 ° C), respectively. Flexural strength and toughness were measured in accordance with ASTM D790, respectively. Vibration evaluation was performed using a 6200D Vibration Evaluation Equipment 6200D after fastening the 46-inch backlight unit (BLU). 10 ~ 300Hz measurement was taken by photographing the part ground by the friction of the guide.

Measurement result

The measurement results for the impact strength and flexural strength are shown in Table 1, and the results of vibration evaluation are shown in FIG. 2.

TABLE 1

As shown in Table 1, in the light diffusing plates manufactured by Examples 1 and 2 of the present invention, it can be seen that the numerical values of impact strength and flexural strength are relatively higher than those of Comparative Examples 1 and 2. . In addition, in terms of toughness, Examples 1 and 2 showed relatively high values, but Comparative Examples 1 and 2 showed relatively low values.

In addition, when the methyl methacrylate resin copolymerized with styrene was used as the base resin of the coating layer, the adhesion to the base layer and the resin adhesiveness were excellent, but pure methacryl as in Comparative Example 2 was used. When the acid methyl-based resin is used, it can be seen that the impact strength and toughness are not excellent because of poor adhesion and adhesion to the base layer.

Figure 2 is a photograph showing the vibration evaluation results of the multilayer light diffusing plate produced by the Examples and Comparative Examples of the present invention, Figure 2 (a), (b) and (c) is Example 1, Example 2 and The vibration evaluation result of the multilayer light-diffusion plate manufactured by the comparative example 1 is shown, respectively.

Referring to (a) and (b) of FIG. 2, it can be seen that the multilayer light diffusing plate manufactured according to the embodiment of the present invention is relatively broken by friction of the guide part of the backlight unit. ), It is relatively broken. This means that the multilayer light diffusing plate manufactured according to the embodiments of the present invention is relatively resistant to cracking.

Therefore, the multilayer light diffusing plate according to the present invention increases impact strength and flexural strength by using a styrene-based resin, which is vulnerable to impact resistance and cracking, and improves the cracking phenomenon caused by the supporter and the guide part during the evaluation of the backlight unit (BLU) vibration. As a result, the amount of warpage change due to heat and moisture absorption is small, and the impact resistance and the crack are excellent.

Although preferred embodiments have been described above by way of example, it is possible to make various modifications or variations without departing from the spirit and scope of the invention, and the appended claims include such modifications and variations that fall within the spirit of the invention.

1 is a perspective view schematically showing a multilayer light diffuser plate for a backlight unit of a liquid crystal display according to the present invention.

Figure 2 is a photograph showing the vibration evaluation results of the multilayer light diffusion plate produced by the examples and comparative examples of the present invention.

Claims (9)

A base layer formed of a first resin composition comprising 0.1 to 10 parts by weight of a siloxane light diffusing agent, 0.01 to 20 parts by weight of an acrylic light diffusing agent and 0.1 to 10 parts by weight of an ultraviolet absorber based on 100 parts by weight of a styrene resin; And A coating layer laminated on at least one surface of the base layer and formed of a second resin composition containing 0.1 to 30 parts by weight of an acrylic light diffusing agent based on 100 parts by weight of methyl methacrylate resin copolymerized with a styrene resin; Multilayer light diffusion plate comprising a. The method of claim 1, wherein the styrene resin of the substrate layer A multi-layer light diffusing plate comprising at least one of polystyrene, halogenated styrene, and alkylated polystyrene as monomer units. The method of claim 1, wherein the siloxane light diffusing agent of the base layer A multilayer light diffusion plate, characterized in that the average particle diameter is 1 ~ 20㎛. The method of claim 1, wherein the acrylic light diffusing agent of the base layer A multilayer light diffusion plate, characterized in that the average particle diameter is 0.1 ~ 20㎛. The method of claim 1, wherein the acrylic light diffusing agent of the coating layer A multilayer light diffuser plate having an average particle diameter of 1 to 50 µm. The method of claim 1, wherein the ultraviolet absorber A multilayer light diffuser plate, characterized in that absorbs a wavelength in the range of 250 ~ 320nm. The method of claim 6, wherein the ultraviolet absorber A multi-layered light diffuser plate comprising at least one of a benzophenone series, cyanoacrylate series, sarichireto series, and nickel complex salt ultraviolet absorbers. The backlight unit for liquid crystal display (LCD) containing the multilayer light-diffusion plate of any one of Claims 1-7. A liquid crystal display device comprising the backlight unit of claim 8.

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