JP2006116801A - Laminated resin plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a resin plate which keeps optical properties necessary for a diffusion plate such as high transmittance and high diffusion and exhibits small warpage when its surface and back are exposed to different environments. <P>SOLUTION: In the diffusion plate, a laminated resin plate is incorporated into a direct bottom type back light unit used in a liquid crystal monitor or a liquid crystal television unit. The laminated resin plate is composed of a substrate resin layer containing at least two methyl methacrylate-styrene copolymers different in monomer ratio and a membrane resin layer. The constitution ratio between methyl methacrylate and styrene of the copolymers in the substrate resin layer is 5:95-40:60. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

Description

The present invention relates to a laminated resin plate.
More specifically, the present invention relates to a resin plate that diffuses light emitted from a light source.

In recent years, with the spread of notebook computers, thin monitors, and thin televisions, the opportunity to see liquid crystal screens has increased.
Since the liquid crystal is not a self-luminous device such as a cathode ray tube, a light source called “backlight” is required on the back of the liquid crystal, and the light source is roughly classified into two types.
One is called an “edge-light” or “side-light” backlight unit. This is a method in which a light source is provided on the side surface of the light guide plate, and the liquid crystal side surface of the light guide plate is caused to emit light uniformly by light irradiated to the light guide plate. It has the features of being thin and lightweight and having relatively low power consumption, and is used for mobile phones, notebook computers, personal computer monitors, car navigation system monitors, and the like.

The other is called a “direct type” backlight unit. In this method, a plurality of lamps (cold cathode tubes), LEDs, and the like are caused to emit light, and this light is passed through a diffusion plate and a diffusion film to obtain uniform surface emission on the back side of the liquid crystal. The diffusion plate used here is often a milky white resin plate and has a function of scattering and diffusing light.
The direct-type backlight unit has a simple structure, but it has an edge in the display market due to the disadvantage that the backlight unit is thicker and consumes more power than the edge-lit backlight unit. The share of the light type was large.

However, when the edge type backlight unit is used for a large liquid crystal, there is a problem that the amount of light is insufficient on the whole, particularly the amount of light at the center portion is insufficient. On the other hand, the direct type backlight unit is easy to obtain a sufficient amount of light although the unit itself is thick. For this reason, it is common in recent years to use a direct type backlight unit in a liquid crystal television having a size exceeding 20 inches.
FIG. 1 shows a schematic diagram of a direct type backlight unit.
A direct backlight unit generally has a structure in which a diffusion plate, a light diffusion sheet, a brightness enhancement film, and the like are installed in order to scatter and diffuse light from a lamp (cold cathode tube).

The diffusing plate diffuses and scatters the light of the lamp, so that the shape of the lamp is not seen through, and the light is uniformly scattered and diffused to reduce unevenness in brightness on the liquid crystal screen. However, there is a problem that the liquid crystal screen becomes dark because the transmitted light is reduced only by scattering and diffusing the light. The performance that has been demanded of the diffusion plate until now has been a contradictory optical characteristic of higher light transmittance (high transmission) and more light diffusion (high diffusion).
Various methods have been disclosed so far for this high transmission and high diffusion technology. (For example, see Patent Documents 1 to 4)
However, recently, with the progress of thinning of liquid crystal televisions, the problem of warping of the diffusion plate incorporated in the direct type backlight unit has become a problem.

When the backlight is continuously lit, the warp gradually becomes convex toward the liquid crystal unit. Since the clearance between the diffusion plate and the liquid crystal panel is slight, the diffusion plate and the diffusion sheets are pressed against the liquid crystal panel due to warping, which may cause screen distortion and breakage of the liquid crystal panel.
The diffusion plate incorporated in the direct type backlight unit is in a state of containing some moisture, but the backlight side is easily dried due to the temperature rise caused by the lighting of the lamp (cold cathode tube), while the liquid crystal The unit side is more easily absorbed than the backlight side.

Up to now, acrylic resins that have been widely used for diffusion plates are resins that undergo a relatively large dimensional change due to water absorption, and have the problem of causing warpage when the amount of water absorption is imbalanced on the front and back of the plate. It was.
The cause of the warp occurring in the diffuser plate described above can be considered to be two points that when the front and back of the plate are compared, a difference in water absorption amount and a difference in surface temperature occur.
As for the countermeasures against the warping of the diffuser, the improvement of the backlight unit, such as how to attach the diffuser to the backlight unit, clearance, heat dissipation, etc., is conspicuous, and the improvement of the diffuser material is not progressing You can say that.

Japanese Patent Laid-Open No. 1-172801 JP-A-2-194058 Japanese Patent Laid-Open No. 11-5241 Japanese Patent Laid-Open No. 2004-9524

  An object of this invention is to provide the resin board with a small curvature amount also in the environment where front and back differ.

The present inventor is a resin having a small amount of water absorption and a small amount of warpage even in different environments on the front and back sides without impairing optical performance required as a diffusion plate, such as high transmittance and high diffusion. We studied to make it possible to obtain a board.
As a result, there is a laminated resin plate comprising a base resin layer and a film resin layer containing at least two types of methyl methacrylate / styrene copolymers having different composition ratios of methyl methacrylate and styrene, The laminated resin plate is characterized in that the composition ratio of methyl methacrylate and styrene of the methyl methacrylate / styrene copolymer component is in the range of 5:95 to 40:60. It has been found that the resin plate has a small amount of water absorption and has a small amount of warpage even under different environments, without impairing the optical performance required as a diffusion plate, and the present invention has been completed. .

That is, the present invention
1. The laminated resin plate is a diffusion plate incorporated in a direct type backlight unit used in a liquid crystal monitor or a liquid crystal television unit, and at least two types of methyl methacrylates having different composition ratios of methyl methacrylate and styrene. A laminated resin plate comprising a base resin layer containing a styrene copolymer and a film resin layer, wherein the constituent ratio of the methyl methacrylate / styrene copolymer component of the base resin layer is 5:95. To 40:60, a laminated resin plate,
2. 2. The laminated resin plate according to 1 above, wherein the composition ratio of methyl methacrylate and styrene of the methyl methacrylate / styrene copolymer component of the film resin layer is in the range of 70:30 to 95: 5,
3. The laminated resin plate according to 1 or 2 above, wherein the laminated resin plate has a two-layer structure in which a coating resin layer is laminated on one side of the base resin layer,
4). The laminated resin plate according to 1 or 2 above, wherein the laminated resin plate has a three-layer structure in which a coating resin layer is laminated on both surfaces of a base resin layer,
5. 5. The methyl methacrylate / styrene copolymer used in the base resin layer is a methyl methacrylate / styrene copolymer containing an organic and / or inorganic light diffusing agent. Laminated resin plate,
6). The laminated resin according to any one of 1 to 5 above, wherein the methyl methacrylate / styrene copolymer used for the resin layer is a methyl methacrylate / styrene copolymer containing an organic and / or inorganic light diffusing agent. Board,
It is.

  The resin plate of the present invention has a high transmittance, a high diffusion, etc. without impairing the optical performance required as a diffusion plate, has a small amount of water absorption, and a warping amount in different environments on the front and back sides. Has small features.

The present invention will be specifically described below.
In the present invention, the backlight unit refers to a device that generates uniform surface light emission on the back side of the liquid crystal in order to visualize a liquid crystal screen that is not a self-lighting screen such as a cathode ray tube. Furthermore, the direct type backlight unit is a device that generates uniform surface light emission on the back side of the liquid crystal, such as a plurality of lamps (cold cathode tubes), LEDs, etc., and the light emitted by these lamps is a diffusion plate, a diffusion film, A backlight unit that obtains uniform surface emission on the back side of the liquid crystal by passing a brightness enhancement film. The diffusion plate used here is often a milky white resin plate and has a function of scattering and diffusing light. Here, the light source of the apparatus for generating uniform surface light emission on the back side of the liquid crystal is not limited.

In the present invention, the diffuser plate incorporated in the direct type backlight unit is composed of at least two types of methyl methacrylate / styrene copolymers (hereinafter referred to as “MMA”) and styrene having different composition ratios (hereinafter referred to as “MMA”). It is characterized in that it is a laminated resin plate comprising a base resin layer and a coating resin layer containing MS resin ”. Here, MS resin is a resin component obtained by copolymerizing an MMA component and a styrene component. Even if it is a copolymer containing 3rd components other than a MMA component and a styrene component, it can be implemented. Here, the composition ratio of the third component to the MMA component and the styrene component is not limited.
Further, the MS resin used in the present invention can be implemented even if it is a resin composition and / or polymer alloy blended with other different resin components. Further, the present invention can be carried out even with a resin composition and / or a polymer alloy blended with a copolymer containing a third component other than the MMA component and the styrene component and another different resin component.
In the present invention, the MS resin is a laminated resin plate made of two types of MS resins having different composition ratios of MMA and styrene. This is because the characteristics required for the base resin layer and the coating resin layer are different. It is.

For the base resin layer, it is generally preferable to use a resin having a small amount of water absorption.
This is because a resin plate placed in a different temperature environment on the front and back, such as a diffusion plate incorporated in a direct type backlight unit, generates a warp that protrudes on the side with a lower surface temperature. This is because the amount of water absorption of the base resin layer is affected.
Usually, the resin plate is in a state of containing water to some extent. The same applies to the diffusion plate incorporated in the direct type backlight unit. Therefore, in the state before the backlight is lit, the moisture content is uniform between the front and back of the diffuser, but the surface temperature on the side facing the backlight rises at the same time when the backlight is lit, Evaporate moisture. On the other hand, the surface on the side not facing the backlight has a lower temperature than the surface on the side facing the backlight, and the diffusion plate is in a state where a difference in surface temperature occurs. This temperature difference is considered to cause non-uniformity in the water content in the resin. For this reason, on the surface with a high surface temperature, the shrinkage of the resin occurs as the moisture content decreases, and as a result, a dimensional difference from the surface with a low surface temperature occurs. As a result, it is considered that a warp is formed on the surface having a low surface temperature. In the case of a laminated resin plate, the amount of warpage is affected by the amount of water absorbed by the base resin layer.

  In the present invention, the composition ratio of the MMA component and the styrene component of the MS resin used for the base resin layer is in the range of 5:95 to 40:60, more preferably 5:95 to 30:70. And most preferably in the range of 10:90 to 25:75. The composition ratio of the MMA component and the styrene component of the MS resin used in the base resin layer is within this range, so that it is possible to obtain a resin plate with a small amount of water absorption and a small amount of warpage that occurs even under different temperature environments. It becomes. In addition, by including the MMA component, the adhesiveness with the resin used for the coating material is improved, and the characteristics required as a diffusion plate such as optical performance are easily maintained.

On the other hand, it is generally preferable to use a resin excellent in light resistance and scratch resistance for the coating resin layer.
This is because the diffusion plate incorporated in the direct type backlight unit is not easily discolored even when exposed to light emitted from the light source used (cold cathode tube, LED, etc.) for a long time. This is because it is preferable that no scratch is caused by rubbing with the films disposed therebetween. In the case of a laminated resin plate, these characteristics depend on the resin used for the coating layer.

  The composition ratio of the MMA component and the styrene component of the MS resin used in the coating resin layer is preferably in the range of 70:30 to 95: 5, more preferably in the range of 70:30 to 90:10. And most preferably in the range of 75:25 to 85:15. The composition ratio of the MMA component and the styrene component of the MS resin used for the base resin layer is within this range, so that the light resistance and scratch resistance are excellent, the adhesiveness with the base resin layer is good, the optical performance, etc. It is easy to maintain the characteristics required for a diffusion plate. The base resin layer of the laminated resin plate has a low MMA ratio of MMA component to styrene component ratio of 5:95 to 40:60, and the coating resin layer has a MMA component to styrene component ratio of 70. By using MS resin with a high MMA ratio of 30 to 95: 5, even when a temperature difference occurs between the front and back of the laminated resin plate, there is little warpage, and yellowing and deterioration due to light emitted from the light source It is possible to obtain a laminated resin plate that progresses slowly.

For this reason, it can be said that it has an excellent property as a diffusion plate incorporated in a direct type backlight unit.
The MS resin used in the present invention preferably contains a light diffusing agent in order to ensure good light diffusibility as a diffusing plate used in a direct type backlight unit. The light diffusing agent to be blended is not particularly limited, and is preferably an organic and / or inorganic light diffusing agent. Specifically, acrylic crosslinked fine particles, styrene crosslinked fine particles, methyl methacrylate / styrene copolymer crosslinked fine particles, silicone crosslinked fine particles, calcium carbonate, barium sulfate, titanium oxide, alumina, talc, mica, etc. These can be used alone or in combination of two or more. By blending these light diffusing agents into the resin composition, the viewing angle can be arbitrarily set.

The kind and blending ratio of the light diffusing agent blended in the MS resin used in the present invention are not particularly limited, and can be implemented by any combination and blending ratio.
The particle size of the light diffusing agent is not limited, but the average particle size is preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 20 μm, and most preferably Is in the range of 1 μm or more and 10 μm or less.
This is because when the average particle diameter of the light diffusing agent is in the range of 1 μm or more and 50 μm or less, the effect as the light diffusing agent is efficiently expressed, and fine adjustment of the total light transmittance is easy. .

Further, the shape of the light diffusing agent is not limited, and a fiber shape, a plate shape, a scale shape, a spherical shape, a tube shape, a confectionery shape and the like can be arbitrarily selected, and a light diffusing agent having a hollow portion inside is also used. be able to.
The particle diameter of the light diffusing agent blended in the MS resin used for the coating resin layer is an acrylic crosslinked fine particle having a particle diameter equal to or larger than that of the light diffusing agent blended in the MS resin used for the base resin layer, Styrene-based crosslinked fine particles and methyl methacrylate / styrene copolymer-based crosslinked fine particles are preferable.
Moreover, the surface of the diffusion plate can be formed into a mat with a large unevenness by adding talc, mica or the like to the MS resin used for the coating resin layer.

Moreover, other additives can be mix | blended with MS resin as needed. The kind of additive is not limited, The additive used for a normal thermoplastic resin can be used. Specific examples include ultraviolet absorbers, selective wavelength absorbers, antioxidants, light stabilizers, antistatic agents, various dyes, pigments, fluorescent brighteners, lubricants, and flame retardants. These can also be used independently like a light-diffusion agent, or 2 or more types can be used together, and arbitrary addition amounts can be mix | blended.
The total light transmittance of the laminated resin plate of the present invention can be arbitrarily set by adjusting the amount of the light diffusing agent to be blended. Generally, the total light transmittance of the diffuser used in the direct type backlight unit is in the range of 40 to 90%. Also in the present invention, it is relatively easy to obtain a diffuser plate having an arbitrary total light transmittance by adjusting the type and addition amount of the light diffusing agent.

On the other hand, the thickness of the laminated resin plate is not limited, but is generally in the range of 1 to 5 mm. At present, the thickness of the diffusion plate incorporated in the direct type backlight unit is often 2 to 3 mm. When the screen size is large, it tends to be thick, and conversely, when the screen size is small, it tends to be thin.
The laminated resin plate according to the present invention may have a two-layer structure in which the base material layer and the coating layer are in close contact, or may have a three-layer structure in which the base material layer is sandwiched between the coating layers.
In the case of a two-layer structure, it is preferable that the coating layer is disposed on the backlight unit side. This is to slow down the progress of yellowing and deterioration due to the backlight light source.

The thickness of the coating resin layer is not limited, but is preferably 300 μm or less, and more preferably 100 μm or less. When the thickness of the coating resin layer is 300 μm or less, the lamination itself is easy, and a laminated resin plate having a good appearance can be easily obtained.
The method for producing the laminated resin plate is not limited, and examples thereof include a coextrusion method, a film laminating method, and a coating method.
Considering that the structure of the apparatus is simple and that a continuous and stable quality laminated resin plate can be produced, the coextrusion method is preferred.
In the co-extrusion method, the MS resin that becomes the base resin layer and the MS resin that becomes the coating resin layer are heated and melt-extruded by separate extruders, and are expanded in a mold (hereinafter abbreviated as “die”). It is a method of joining, laminating, and forming into a sheet shape via a polishing roll or the like.

The coextrusion method has a configuration in which an extruder for a resin serving as a coating layer is added to a general resin plate extrusion manufacturing facility, and can be said to be a simple method for forming a laminated resin plate in terms of structure.
The conditions for coextrusion molding are the same as the molding conditions for resin plates that are generally performed, and the temperature conditions may be set appropriately depending on the resin to be extruded.
Specifically, the temperature of the extruder for the base resin, the extruder for the coating material resin, and the lamination die is preferably set in the range of 200 to 300 ° C, and more preferably in the range of 220 to 250 ° C. preferable. Moreover, it is preferable to set the temperature of the polishing roll used 3-6 in the range of 60-120 degreeC, and it is further more preferable that it is the range of 80-100 degreeC.
The thickness adjustment of the laminated diffusion plate can be freely set by adjusting the gap between the polishing rolls at the time of the extrusion molding.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to the following.
[Reference Examples 1 to 4]
Four types of MS resins, “Estyrene MS200, MS300, MS600, MS800” (registered trademark) manufactured by Nippon Steel Chemical Co., Ltd., were prepared.
The MMA ratio of these four types of MS resins was measured by pyrolysis-gas chromatography. At this time, “GC5890” manufactured by Agilent was used for gas chromatography, and “JHP-3S” manufactured by Nippon Analytical Industries, Ltd. was used as the Curie Point pyrolyzer. The measurement results are shown in Table 1.
Hereinafter, MMA ratio shows the ratio of the methyl methacrylate component in the methyl methacrylate / styrene copolymer component.

[Example 1]
As a base resin, MS resin (“Estyrene MS200” (registered trademark) manufactured by Nippon Steel Chemical Co., Ltd.) having an MMA ratio of 20 is used as a light diffusing agent. 5% by weight of pearl 120 "(registered trademark)), as a coating material resin, MS resin with a MMA ratio of 80 (" Estyrene MS800 "(registered trademark) manufactured by Nippon Steel Chemical Co., Ltd.) 15wt. % Blended was prepared.
Using these, a three-layer laminated resin plate having a plate thickness of 2 mm and a coating layer of 50 μm on one side was obtained by coextrusion molding.
At this time, the temperature of the substrate extruder was adjusted to 220 ° C., the temperature of the coating material extruder was adjusted to 220 ° C., and the temperature of the polishing roll was adjusted to 80 ° C.
After cutting to fit the dimensions of the backlight unit shown in Fig. 2 and drying for 72 hours in a hot air dryer at 80 ° C, it is in a constant temperature and humidity chamber adjusted to 40 ° C and humidity of 95% for 20 hours. It was adjusted. This was fixed in the backlight unit, and the backlight was turned on. The amount of warp deformation of the diffusion plate was continuously measured with a displacement sensor (product name “Eddy current displacement sensor EX-022” manufactured by Keyence Corporation). The displacement measured by the displacement sensor was taken into a personal computer through an amplifier or recorder and processed. The amount of displacement 2 hours after the backlight was turned on was defined as the amount of warpage 1.
In addition, a laminated resin plate having the same dimensions was prepared, dried in a hot air dryer at 80 ° C. for 72 hours, and then conditioned for 70 hours in a constant temperature and humidity chamber adjusted to 40 ° C. and humidity of 95%. This was fixed in the backlight unit, and the backlight was turned on. The amount of displacement 8 hours after the backlight was turned on was defined as the amount of warpage 2.
Table 2 shows the measurement results of the warpage amounts 1 and 2.

[Example 2]
Example 1 except that 5 wt% of a light diffusing agent was blended with MS resin (“Estyrene MS300” (registered trademark) manufactured by Nippon Steel Chemical Co., Ltd.) having an MMA ratio of 30 as the base resin. A three-layer laminated resin plate was obtained by coextrusion molding in the same manner as described above.
The amount of warpage 1 and the amount of warpage 2 were measured in the same manner as in Example 1. The results are shown in Table 2.

[Comparative Example 1]
Example 1 except that 5 wt% of a light diffusing agent was blended with MS resin (“Estyrene MS400” (registered trademark) manufactured by Nippon Steel Chemical Co., Ltd.) having an MMA ratio of 40 as the base resin. A three-layer laminated resin plate was obtained by coextrusion molding in the same manner as described above.
The amount of warpage 1 and the amount of warpage 2 were measured in the same manner as in Example 1. The results are shown in Table 2.

[Comparative Example 2]
As a base material resin, PMMA acrylic resin ("Delpet LP-1" (registered trademark) manufactured by Asahi Kasei Chemicals Corporation) is blended with 5 wt% of a light diffusing agent, and PMMA acrylic resin (Asahi Kasei Chemicals) A three-layer laminated resin plate was obtained by coextrusion molding in the same manner as in Example 1 except that 15% by weight of talc was blended with “Delpet LP-1” (registered trademark) manufactured by Co., Ltd. .
At this time, the temperature of the substrate extruder was adjusted to 250 ° C., the temperature of the coating material extruder was adjusted to 250 ° C., and the temperature of the polishing roll was adjusted to 90 ° C.
The amount of warpage 1 and the amount of warpage 2 were measured in the same manner as in Example 1. The results are shown in Table 2.

[Comparative Example 3]
The same method as in Example 1 except that PMMA acrylic resin ("Delpet LP-1" (registered trademark) manufactured by Asahi Kasei Chemicals Corporation) blended with 5 wt% of the light diffusing agent was used as the substrate resin. A three-layer laminated resin plate was obtained by coextrusion molding.
At this time, the temperature of the substrate extruder was adjusted to 250 ° C., the temperature of the coating material extruder was adjusted to 220 ° C., and the temperature of the polishing roll was adjusted to 80 ° C.
The amount of warpage 1 and the amount of warpage 2 were measured in the same manner as in Example 1. The results are shown in Table 2.

  The laminated resin plate according to the present invention is a laminated resin plate that has a small amount of water absorption and a small amount of warpage even under different environments. Therefore, the laminated resin plate can be effectively used for members in which the amount of warpage is regarded as important. In particular, it can be effectively used as a diffusion plate of a direct type backlight unit used for a light source of a liquid crystal screen.

Schematic diagram of direct type backlight unit Schematic of warpage evaluation method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Brightness improvement film 3 Diffusion plate 4 Lamp 5 Reflective film 6 Case 7 Backlight unit 8 Displacement sensor 9 Recorder 10 Personal computer 10

Claims (6)

  The laminated resin plate is a diffusion plate incorporated in a direct type backlight unit used in a liquid crystal monitor or a liquid crystal television unit, and at least two types of methyl methacrylates having different composition ratios of methyl methacrylate and styrene. A laminated resin plate comprising a base resin layer containing a styrene copolymer and a film resin layer, wherein the constituent ratio of the methyl methacrylate / styrene copolymer component of the base resin layer is 5:95. To 40:60, a laminated resin plate.   2. The laminated resin plate according to claim 1, wherein the composition ratio of methyl methacrylate and styrene of the methyl methacrylate / styrene copolymer component of the film resin layer is in the range of 70:30 to 95: 5.   The laminated resin plate according to claim 1 or 2, wherein the laminated resin plate has a two-layer structure in which a coating resin layer is laminated on one side of a base resin layer.   The laminated resin plate according to claim 1 or 2, wherein the laminated resin plate has a three-layer structure in which a film resin layer is laminated on both surfaces of a base resin layer.   The methyl methacrylate / styrene copolymer used for the base resin layer is a methyl methacrylate / styrene copolymer containing an organic and / or inorganic light diffusing agent. Laminated resin plate.   The methyl methacrylate / styrene copolymer used for the coating resin layer is a methyl methacrylate / styrene copolymer containing an organic and / or inorganic light diffusing agent. Laminated resin plate.

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