JP2007086098A - Optical sheet and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet suitable for a high-brightness direct backlight liquid crystal display device capable of preventing a linear light source from being seen through and improving a light-condensing function by a concave and convex lens shape part, and to provide a liquid crystal display device provided with the optical sheet. <P>SOLUTION: The optical sheet 7 is constituted by integrally laminating a resin layer 1 in which light-scattering fine particles are compounded, to a transparent resin layer 2 which has the linear concave and convex lens shape part 2a formed on the surface thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical sheet and a liquid crystal display device, and more particularly to an optical sheet suitable for a direct backlight type liquid crystal display device and a liquid crystal display device including the same.

  In recent years, liquid crystal display devices are rapidly expanding as large-sized and thin display devices replacing CRTs. Since the liquid crystal itself does not emit light, a back light source called a backlight is always integrated.

  There are two types of backlights. One of them is a so-called edge light type backlight in which a linear light source represented by a cold cathode tube is disposed on an end face of a transparent resin plate called a light guide plate, and the light guide plate surface is illuminated to make a liquid crystal back light source. The other is a large number of linear light sources, on which a milk semi-resin plate (milk-white translucent resin plate) containing light scattering fine particles called a diffusion plate or a light-scattering optical sheet is placed. This is a so-called direct type backlight in which the light source directly becomes the back light source of the liquid crystal.

  Edge-light type backlights are widely used in connection with downsizing and thinning required for notebook computer screens, LCD monitors, mobile phone screens, etc., but light passes through a transparent resin plate called a light guide plate. It is difficult to increase the screen size and brightness, and it is difficult to apply when the size is 20 inches, 30 inches, or 40 inches like TV (television).

  On the other hand, direct-type backlights have not been able to meet the demands for miniaturization and thinning, but the market has been growing in recent years because it is very easy to handle large screens and high brightness by increasing the number of linear light sources. It is growing rapidly as a backlight for large LCD TVs that are expanding.

  Diffusers used in direct type backlights often scatter light from a linear light source and are not required to be seen through the light source. Various developments have been made in response to the rapid increase in type backlights. Many of them aim at high transmission and high diffusion, and control the kind, particle size, and blending amount of the light scattering fine particles (see, for example, Patent Documents 1 to 3).

On the other hand, technical development has been actively performed in which a diffusion plate is regarded as an optical sheet and a prism-shaped portion is formed on the surface (see, for example, Patent Documents 4 to 8).
Japanese Patent Laid-Open No. 01-172801 Japanese Patent Laid-Open No. 02-194058 Japanese Patent Application Laid-Open No. 07-100755 Japanese Patent Laid-Open No. 02-257188 JP 05-0455505 A Japanese Patent Application Laid-Open No. 06-018707 JP 07-294709 A Japanese Patent Laid-Open No. 08-211230

  However, in the diffusion plate technique using light scattering fine particles disclosed in Patent Documents 1 to 3, the linear light source is seen through when aiming at high luminance, and the luminance decreases when the transparent light from the linear light source is turned off. However, the high transmission and diffusion performance was limited.

  Further, even with the techniques of the above-mentioned Patent Documents 4 to 8, it has not been possible to achieve prevention of see-through of the linear light source and high luminance at the same time.

  The present invention solves the above-mentioned problems, and an object of the present invention is to provide a high-brightness direct-type backlight type liquid crystal display device that prevents the linear light source from being seen through and enhances the light collecting function by the concave-convex lens shape portion. A suitable optical sheet and a liquid crystal display device including the same are provided.

  In order to solve the above problems, the present inventor has divided a diffusion layer made of a resin layer in which light scattering particles are blended and a light collecting functional layer made of a transparent resin layer having a concave-convex lens forming portion formed on the surface. It has been found that by laminating the layers and controlling the layer thickness of the light condensing function layer, it is possible to design a high-brightness optical sheet that prevents the transmission of the linear light source and has completed the present invention. It is.

  That is, the first configuration of the optical sheet according to the present invention for achieving the above object is an optical sheet in which the transparent resin layer (2) is laminated on the surface of the resin layer (1) in which the light scattering fine particles are blended. In addition, a linear concavo-convex lens-shaped portion is formed on the surface of the transparent resin layer (2).

  In addition, in the second configuration of the optical sheet according to the present invention, in the first configuration, the thickness of the transparent resin layer (2) is 1.1 times or more the height of the concave-convex lens-shaped portion, and It is 0 times or less.

  The third configuration of the optical sheet according to the present invention is characterized in that, in the first and second configurations, the total light transmittance of the transparent resin layer (2) is 80% or more.

  Moreover, the 4th structure of the optical sheet which concerns on this invention is the said 1st-3rd structure. WHEREIN: The total light transmittance of the said resin layer (1) is set to the total light transmittance of the said transparent resin layer (2). It is characterized by being 60% or more and 90% or less.

  Moreover, the liquid crystal display device according to the present invention is a direct-type backlight type liquid crystal display device that is installed in the order of a linear light source, the optical sheet according to any one of claims 1 to 4, and a liquid crystal panel sheet. The concave-convex lens surface of the concave-convex lens-shaped portion of the optical sheet is installed toward the linear light source side.

  According to the first configuration of the optical sheet according to the present invention, a diffusion layer composed of a resin layer in which light scattering particles are blended, and a condensing functional layer composed of a transparent resin layer having a concave-convex lens forming portion formed on the surface, By separately stacking layers and controlling the layer thickness of the light collecting functional layer, it is possible to obtain a high-brightness optical sheet that prevents the linear light source from being seen through.

  Moreover, according to the 2nd structure of the optical sheet which concerns on this invention, the thickness of the transparent resin layer (2) was set to 1.1 times or more and 3.0 times or less of the height of an uneven | corrugated lens shape part. Thus, the luminance can be improved while effectively preventing the linear light source from being seen through.

  Further, according to the third configuration of the optical sheet according to the present invention, the total light transmittance of the transparent resin layer (2) is set to 80% or more, thereby preventing light loss and contributing to luminance improvement. I can do it.

  Moreover, according to the 4th structure of the optical sheet which concerns on this invention, the total light transmittance of the said resin layer (1) is 60% or more with respect to the total light transmittance of a transparent resin layer (2), and 90%. By setting as follows, it is possible to further prevent the linear light source from being seen through and to obtain high luminance.

  In addition, according to the liquid crystal display device according to the present invention, the above-described optical sheet is installed in the direct-type backlight type liquid crystal display device, so that the linear light source can be prevented from being transparent and high brightness can be realized.

  An embodiment of an optical sheet and a liquid crystal display device according to the present invention will be specifically described with reference to the drawings. 1 and 2 are a side view and a perspective explanatory view showing a configuration of a liquid crystal display device including an optical sheet according to the present invention.

  1 and 2, reference numeral 1 denotes a resin layer in which light scattering fine particles are blended, and a transparent resin layer 2 is laminated on the surface of the resin layer 1 to constitute an optical sheet 3. On the surface of the transparent resin layer 2, a linear concavo-convex lens shape portion 2 a is formed.

  The liquid crystal display device 6 is configured as a direct-type backlight liquid crystal display device that is installed in the order of the linear light source 4, the optical sheet 3, and the liquid crystal panel sheet 5, and the unevenness of the uneven lens shape portion 2 a of the transparent resin layer 2. The lens surface is installed toward the linear light source 4 side.

  Examples of the resin used for the resin layer 1 and the transparent resin layer 2 of the optical sheet 3 include the following. For example, acrylic resin, MS resin (methacrylic ester and styrene copolymer resin), polystyrene resin, polycarbonate resin, polyethylene, polypropylene, AS resin (polystyrene, copolymer resin of acrylonitrile and styrene), ABS resin (acrylonitrile, butadiene) Styrene copolymer resin), PET (polyethylene terephthalate; polyester), COP (cycloolefin polymer), alpha methyl styrene, polylactic acid, fluororesin, phenol resin, epoxy resin, polyurethane, etc. Resin. The resin used for the resin layer 1 and the transparent resin layer 2 may be the same or different depending on the function.

The resin layer 1 is mixed with light scattering fine particles. Examples of the light scattering fine particles include the following. For example, acrylic crosslinked fine particles, styrene crosslinked fine particles, silicone crosslinked fine particles, fluorine fine particles, glass fine particles, SiO ₂ fine particles, calcium carbonate, barium sulfate, titanium oxide, alumina, talc (inorganic powder obtained by finely pulverizing ore called talc) Mica and the like, and these may be used alone or in combination.

  The particle size of the light scattering fine particles may be arbitrarily selected between an average particle size of 0.01 μm and 100 μm, and the shape is also a true sphere, an ellipse, a sphere, an indeterminate shape, a needle shape, a flake shape (petal) shape Any of a hollow shape, a cubic shape, a triangular pyramid shape, and the like may be used.

  The blending amount of the light scattering fine particles to be blended in the resin layer 1 varies depending on the particle size of the fine particles and the thickness of the resin layer 1, but is preferably 0.001% by weight or more and 30% by weight or less, more preferably 0.01% by weight. Above and 20% by weight or less.

  If the resin layer 1 is thick, it is better to have less light diffusing fine particles in order to increase the luminance. Conversely, if the resin layer 1 is thin, it is necessary to increase the amount of light scattering fine particles in order to prevent the linear light source from being seen through. The total light transmittance of the entire optical sheet 3 is preferably 50% or more and 90% or less, and the total light transmittance can be adjusted by the blending amount of the light scattering fine particles blended in the resin layer 1 as necessary. .

  On the other hand, it is important that the transparent resin layer 2 on which the concave and convex lens-shaped portion 2a is formed is transparent. The concave / convex lens-shaped portion 2a has a function as a prism or a lens, and needs to be transparent in order to condense, reflect or refract light. The low transmittance of the transparent resin layer 2 means that light is lost. In the present invention, the total light transmittance of the transparent resin layer 2 must be 80% or more. At that time, the total light transmittance of the resin layer 1 is adjusted to 60% or more and 90% or less with respect to the total light transmittance of the transparent resin layer 2 in order to prevent the bright light and the linear light source from being seen through. More preferably.

  You may mix | blend an additive with the transparent resin layer 2 in the range which can maintain 80% or more of total light transmittance. For example, ultraviolet absorbers, light stabilizers, antioxidants, lubricants, antistatic agents, colorants, fluorescent whitening agents, matting agents, and the like.

  The transparent resin layer 2 is laminated on the surface of the resin layer 1 and may be a single-area layer or a double-sided laminate. Examples of a method for laminating the resin layer 1 and the transparent resin layer 2 include a coextrusion method, a film-like laminating method, a coating method, and a thermocompression bonding method. The coextrusion method is a method in which a plurality of types of resins (in the case of the present invention, the resin of the resin layer 1 and the resin of the transparent resin layer 2) are melt-extruded with an extruder, and the molten resins are joined and fused in a mold. This is a general method for producing a laminated sheet.

  The film-like laminating method is a method in which the resin of the resin layer 1 and the resin of the transparent resin layer 2 are processed in advance into a film shape and bonded together with heat or an adhesive.

  The optical sheet 3 of the present invention is characterized in that a linear concavo-convex lens-shaped portion 2 a is formed on the surface of the transparent resin layer 2. The concave-convex lens shape portion 2a has functions of condensing, reflecting, and refraction, and the shape thereof is, for example, a triangular prism lens shape having an apex angle θ of 40 degrees or more and 150 degrees or less, as shown in FIG. Although not shown, a cylindrical lens shape having a curvature radius of 3 μm or more and 500 μm or less, a polygonal prism lens shape, a wave shape having a curvature radius of 3 μm or more and 500 μm or less, or a combination lens shape in which these lens shapes are superimposed. It is desirable that the lens-shaped portions are arranged in a straight line in parallel with the linear light source 4 of the direct type backlight at a pitch of 0.1 μm or more and 500 μm or less. 1 and 2 show an example in which a plurality of linear light sources 4 are arranged in a straight line, and the concavo-convex lens-shaped portion 2 a is arranged in a straight line in parallel with the linear light source 4.

  The thickness t of the transparent resin layer 2 in the present invention needs to be 1.1 times or more and 3.0 times or less of the height h of the concavo-convex lens shape portion 2a. The height h of the concave-convex lens shape portion 2a here means the lens height, the lens thickness, or the wave height of the corrugated lens, and in the case of a combination lens, it means the maximum height or the maximum thickness. .

  The thickness t of the transparent resin layer 2 is less than 1.1 times the height h of the concave-convex lens-shaped portion 2a, that is, the transparent resin layer 2 is thin and immediately joined with the resin layer 1 containing light scattering fine particles. Then, the linear light source 4 can be seen through, and the condensing, reflection and refraction effects as a lens are small, and the luminance improvement effect is small. Conversely, when the thickness t of the transparent resin layer 2 exceeds 3.0 times the height h of the concave-convex lens-shaped portion 2a and the transparent resin layer 2 becomes thicker, light scattering in the transparent resin layer 2 becomes stronger and the resin layer 1 The reflection at the laminated interface increases, and the effect of improving the brightness is reduced.

  The method for forming the concave / convex lens shape portion 2a on the transparent resin layer 2 is, for example, by pressing a sheet in which the transparent resin layer 2 and the resin layer 1 are laminated onto a mold in which the shape of the concave / convex lens shape portion 2a is engraved in advance. There are a method of transferring the shape, a so-called UV molding using a UV (ultraviolet) curable resin, a method of directly engraving with a laser, an engraving machine, etching or the like. There is also a method in which only the transparent resin layer 2 is formed into a film and the concave / convex lens-shaped portion 2a is formed by the above-described method, and then the resin layer 1 is joined.

  The optical sheet 3 on which the concavo-convex lens shape portion 2a is formed is incorporated as a diffuser in a direct type backlight, and at that time, the concavo-convex lens shape portion 2a is placed with the concavo-convex lens surface facing the linear light source 4 side. Is more preferable.

  When the concave / convex lens surface of the concave / convex lens shape portion 2a is placed toward the linear light source 4 side, the light emitted from the linear light source 4 first enters the concave / convex lens shape portion 2a. The light is efficiently condensed (upward in FIG. 1), that is, toward the liquid crystal panel sheet 5 side. Compared to a smooth diffuser plate, the amount of light returning to the linear light source 4 side by total reflection is reduced, so that the brightness is clearly increased. In addition, a plurality of apparent linear light sources 4 are formed by the refraction and reflection functions of the lens. Therefore, the transparency of the linear light source 4, that is, the brightness becomes small and the transparency is not visible.

  The light collected by the concave-convex lens-shaped portion 2a is scattered by the light scattering fine particles blended in the resin layer 1, whereby the transparency of the linear light source 4 can be reduced. Conversely, when the optical sheet 3 is placed with the concave / convex lens surface of the concave / convex lens shape portion 2a facing the liquid crystal panel sheet 5, the light emitted from the linear light source 4 is first scattered by the light scattering fine particles of the resin layer 1, The light enters the concave-convex lens-shaped portion 2 a of the transparent resin layer 2. In this case, when the scattered light enters the concavo-convex lens shape portion 2a, the light is not emitted but dark because it is totally reflected on the lens surface. Therefore, it is preferable that the concavo-convex lens surface of the concavo-convex lens shape portion 2a of the optical sheet 3 is installed facing the linear light source 4 side.

  The following description is based on specific examples and comparative examples.

  As the linear light source 4, 12 cold cathode tubes having a diameter of 3 mm and a length of 450 mm are arranged at intervals of 20 mm, and a diffusion plate made of the optical sheet 3 is installed on the cold cathode tube with a 15 mm gap therebetween. A liquid crystal panel composed of the liquid crystal panel sheet 5 was installed with a gap of 2 mm, and a direct backlight type liquid crystal display device 6 for evaluation was produced.

  The cold cathode tube is turned on by applying a voltage of 16 V, and the luminance at the center of the diffusion plate made of the optical sheet 3 is measured with a luminance meter (BM-7 manufactured by Topcon Corporation) from a position 500 mm away. The evaluation performed in each of the following Examples and Comparative Examples is to visually check the presence or absence of bright and dark streaks of the cold cathode tube, determine that there is no show as `` ○ '', and show through as `` X '', As shown in Table 1.

[Example 1]
As a resin for the resin layer 1, an acrylic resin (trade name “Delpet LP-1” manufactured by Asahi Kasei Chemicals Co., Ltd.) is blended with 1% by weight of polymethylsilsesoxane fine particles having an average particle diameter of 2 μm as silicone-based crosslinked fine particles. Resin layer 1 using a resin having a light transmittance of 70% and an acrylic resin having a total light transmittance of 93% as a resin for transparent resin layer 2 (trade name “Delpet LP-1” manufactured by Asahi Kasei Chemicals Corporation) A two-type two-layer laminated sheet in which the transparent resin layer 2 was laminated on one side was molded by a coextrusion method.

  At this time, the coextrusion molding conditions were adjusted so that the thickness of the resin layer 1 was 1.8 mm, and the thickness t of the transparent resin layer 2 was 200 μm, for a total of 2.0 mm. The total light transmittance of the entire laminated sheet was 65%. The laminated sheet is heated to about 150 ° C., and a mold in which a triangular prism lens shape having a vertex angle of 60 degrees and a pitch of 100 μm is linearly formed on the surface side of the transparent resin layer 2 is thermocompression bonded. An optical sheet 3 was obtained in which a triangular prism lens shape having an apex angle of 60 degrees and a pitch of 100 μm was formed in a linear shape on the surface of the concave-convex lens shape portion 2a.

  Since the height h of the concave / convex lens shape portion 2a is 86.6 μm and the thickness t of the transparent resin layer 2 is 200 μm, the thickness t of the transparent resin layer 2 is just 2.3 of the height h of the concave / convex lens shape portion 2a. Set to double. Further, the total light transmittance was measured with the optical sheet 3 on which the concave / convex lens shape portion 2a was formed, but it was 65% as before the formation of the concave / convex lens shape portion 2a.

  The optical sheet 3 is installed as a diffusion plate of the above-described liquid crystal display device 6 for evaluation so that the concavo-convex lens surface of the concavo-convex lens shape portion 2a faces the linear light source 4 side. confirmed. The evaluation results are shown in Table 1 below together with comparative examples.

[Example 2]
The same procedure as in Example 1 was performed except that the laminated sheet was prepared so that the thickness t of the transparent resin layer 2 was 100 μm and 1.15 times the height h of the concave-convex lens-shaped portion 2a. The evaluation results are shown in Table 1 below.

[Example 3]
The same procedure as in Example 1 was performed except that the laminated sheet was prepared so that the thickness t of the transparent resin layer 2 was 150 μm and the height h of the concave-convex lens-shaped portion 2a was 1.7 times. The evaluation results are shown in Table 1 below.

[Comparative Example 1]
As in Example 1 above, an acrylic resin (trade name “Delpet LP-1” manufactured by Asahi Kasei Chemicals Corporation) as a resin for the resin layer 1 and polymethylsilsesoxane fine particles having an average particle diameter of 2 μm as silicone-based crosslinked fine particles 1% by weight of resin and acrylic resin having a total light transmittance of 93% (trade name “Delpet LP-1” manufactured by Asahi Kasei Chemicals Corporation) as a resin for the transparent resin layer 2, A two-type two-layer laminated sheet in which the transparent resin layer 2 was laminated on one side was molded by a coextrusion method.

  Similarly to Example 1, the coextrusion molding conditions were adjusted so that the thickness of the resin layer 1 was 1.8 mm, and the thickness t of the transparent resin layer 2 was 200 μm, for a total of 2.0 mm. The total light transmittance of the entire laminated sheet was 65% as in Example 1. The laminated sheet on which the concave / convex lens-shaped portion 2a is not formed is placed on the evaluation liquid crystal display device 6 in the same manner as in Example 1 so that the transparent resin layer 2 faces the linear light source 4 side. The presence or absence of see-through of the linear light source 4 was confirmed. The evaluation results are shown in Table 1 below.

[Comparative Example 2]
The same procedure as in Example 1 was conducted, except that the laminated sheet was prepared so that the thickness t of the transparent resin layer 2 was 90 μm and 1.04 times the height h of the concave-convex lens-shaped portion 2a. The evaluation results are shown in Table 1 below.

[Comparative Example 3]
The same procedure as in Example 1 was performed except that the laminated sheet was prepared so that the thickness t of the transparent resin layer 2 was 300 μm and the height h of the concave-convex lens-shaped portion 2a was 3.46 times. The evaluation results are shown in Table 1 below.

[Comparative Example 4]
0.1 weight of polymethylsilsesoxane fine particles having an average particle diameter of 2 μm as silicone-based crosslinked fine particles are added to an acrylic resin (trade name “Delpet LP-1” manufactured by Asahi Kasei Chemicals Corporation) as a resin for the transparent resin layer 2. % Blended. At this time, the total light transmittance of the transparent resin layer 2 was 70%. The same procedure as in Example 1 was performed except that the transparent resin layer 2 was changed. The evaluation results are shown in Table 1 below.

[Example 4]
It carried out similarly to the said Example 1 except having changed to the styrene resin (PS950 Co., Ltd. G9504) instead of an acrylic resin as resin for the resin layer 1 and the transparent resin layer 2. FIG. The evaluation results are shown in Table 1 below.

[Example 5]
The same procedure as in Example 1 was performed except that the concave-convex lens shape portion 2a was changed to a triangular prism lens shape having an apex angle of 90 degrees and a pitch of 200 μm. At this time, the height h of the concave-convex lens shape portion 2a was 100 μm, and the thickness t of the transparent resin layer 2 was twice the height h of the concave-convex lens shape portion 2a. The evaluation results are shown in Table 1 below.

[Example 6]
The same procedure as in Example 1 was performed except that the concave-convex lens shape portion 2a was changed to a lens shape in which two triangular prism lens shapes having an apex angle of 85 degrees were combined to a pitch of 200 μm. At this time, the height h of the concave-convex lens shape portion 2a was 100 μm, and the thickness t of the transparent resin layer 2 was twice the height h of the concave-convex lens shape portion 2a. The evaluation results are shown in Table 1 below.

[Example 7]
The same procedure as in Example 1 was performed except that the concave-convex lens shape portion 2a was changed to a cylindrical lens shape having a curvature of 100 μm and a pitch of 200 μm. At this time, the height h of the concave-convex lens shape portion 2a was 100 μm, and the thickness t of the transparent resin layer 2 was twice the height h of the concave-convex lens shape portion 2a. The evaluation results are shown in Table 1 below.

[Comparative Example 5]
A liquid crystal panel sheet using the optical sheet 3 on which the same concave / convex lens-shaped portion 2a as in Example 1 is formed, with the concave / convex lens surface of the concave / convex lens-shaped portion 2a facing away from the linear light source 4, that is, upward in FIG. The same evaluation as in Example 1 was performed by installing on the 5th side. The evaluation results are shown in Table 1 below.

  As an application example of the present invention, it can be suitably used as a diffusion plate for a direct type backlight type liquid crystal display device.

It is a side view which shows the structure of the liquid crystal display device provided with the optical sheet which concerns on this invention. It is a perspective explanatory view showing the composition of the liquid crystal display device provided with the optical sheet concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Resin layer 2 ... Transparent resin layer 2a ... Concave and convex lens shape part 3 ... Optical sheet 4 ... Linear light source 5 ... Liquid crystal panel sheet 6 ... Liquid crystal display device

Claims (5)

An optical sheet in which a transparent resin layer (2) is laminated on the surface of a resin layer (1) containing light scattering fine particles,
An optical sheet, wherein a linear concavo-convex lens-shaped portion is formed on the surface of the transparent resin layer (2). The optical sheet according to claim 1, wherein the thickness of the transparent resin layer (2) is 1.1 times or more and 3.0 times or less of the height of the concave-convex lens-shaped portion. The optical sheet according to claim 1 or 2, wherein the total light transmittance of the transparent resin layer (2) is 80% or more. The total light transmittance of the resin layer (1) is 60% or more and 90% or less with respect to the total light transmittance of the transparent resin layer (2). The optical sheet according to item 1. It is a direct type backlight type liquid crystal display device installed in the order of a linear light source, the optical sheet according to any one of claims 1 to 4, and a liquid crystal panel sheet,
The liquid crystal display device, wherein the concave-convex lens surface of the concave-convex lens-shaped portion of the optical sheet is installed toward the linear light source side.

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