JP2010092755A - Light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate for emitting light in which the degree of yellow is sufficiently controlled while it contains particulates for scattering light. <P>SOLUTION: The light guide plate 3 includes particulates scattered in a transparent resin, and when the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the particulates is made [Δn], and the accumulated 50% particle diameter of the particulates is made [D<SB>50</SB>] (μm), a relation formula of 0.30≤Δn×D<SB>50</SB>≤0.70 is satisfied, and the average light transmittance of visible light as measured by optical path length of 300 mm is 35% or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light guide plate that contains fine particles for light scattering and has sufficiently suppressed yellowness.

  As a backlight of a liquid crystal display device or a lighting device, for example, a cold cathode lamp is disposed on the side of a light guide plate, and light from the cold cathode lamp is reflected by a dot pattern or a prism portion formed on the back surface of the light guide plate. It is known that the light can be uniformly emitted from the front surface of the light guide plate.

As such a light guide plate for a backlight, a light guide plate in which fine particles are dispersed in a transparent resin such as an acrylic resin is known, and this light guide plate can scatter light by containing fine particles. Excellent brightness uniformity (see Patent Document 1).
JP 2001-76522 A

  However, the light guide plate in which the fine particles are dispersed in the transparent resin as described above, the transmitted light is slightly yellowish (large YI value), and the liquid crystal display device configured using this light guide plate is There was a problem that the image was slightly yellowish and a high-quality image could not be obtained. That is, there is a problem that a natural and high-quality color display cannot be realized.

  The present invention has been made in view of such technical background, and includes a light guide plate capable of emitting light with sufficiently suppressed yellowness while containing fine particles for light scattering, and high whiteness. An object of the present invention is to provide a surface light source device capable of emitting light and a liquid crystal display device capable of realizing a natural and high-quality color display.

In order to achieve the above object, the present inventor has intensively studied,
1) Accumulation of fine particles 50% Particle diameter D ₅₀ (μm)
2) Absolute value Δn of difference between refractive index of transparent resin and refractive index of fine particles
3) YI (yellow index) with an optical path length of 300 mm
As a result of finding that there is a relationship between them and paying close attention to this relationship, when a relational expression of 0.30 ≦ Δn × D ₅₀ ≦ 0.70 holds, The inventors have found that the YI value can be sufficiently reduced, thus completing the present invention. That is, the present invention provides the following means.

[1] A light guide plate in which fine particles are dispersed in a transparent resin,
When the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the fine particles is “Δn” and the cumulative 50% particle diameter of the fine particles is “D ₅₀ ” (μm), 0.30 ≦ Δn × D The relational expression ₅₀ ≦ 0.70 holds,
A light guide plate, wherein an average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more.

[2] The light guide plate according to item 1 above, wherein the cumulative 50% particle diameter (D ₅₀ ) of the fine particles is in the range of 3 to 7 μm.

  [3] The light guide plate according to item 1 or 2, wherein the absolute value (Δn) of the difference between the refractive index of the transparent resin and the refractive index of the fine particles is 0.08 to 0.13.

  [4] The light guide plate according to any one of items 1 to 3, wherein the content of the fine particles in the light guide plate is 0.2 to 20 ppm.

  [5] The light guide plate according to any one of items 1 to 4, wherein the transparent resin is PMMA, and the fine particles are styrenic polymer fine particles.

  [6] A surface light source device comprising the light guide plate according to any one of items 1 to 5.

  [7] A liquid crystal display device, characterized in that the surface light source device according to item 6 is disposed on the back side of the liquid crystal panel.

In the invention of [1], the relational expression of 0.30 ≦ Δn × D ₅₀ ≦ 0.70 is established. That is, the fine particles satisfying such a relational expression are not limited to any wavelength of visible light. Since it can be scattered to the same extent, the yellowness of the light emitted from the light exit surface of the light guide plate is sufficiently reduced, and light with high whiteness that is not substantially yellowish can be emitted. Further, since the average light transmittance of visible light measured with an optical path length of 300 mm is 35% or more, high luminance can be achieved.

In the invention [2], since the cumulative 50% particle diameter (D ₅₀ ) of the fine particles is in the range of 3 to 7 μm, surface roughness can be suppressed and the surface of the light guide plate can be made smoother.

  In the invention of [3], the absolute value (Δn) of the difference between the refractive index of the transparent resin and the refractive index of the fine particles is 0.08 to 0.13. The content of fine particles required for light scattering is small, and the processability can be improved by reducing the fine particle content.

  In the invention of [4], since the content of the fine particles in the light guide plate is 0.2 to 20 ppm, there is an effect that uneven distribution of the fine particles due to aggregation of the fine particles can be reduced.

  In the invention of [5], the transparent resin is PMMA, the fine particles are styrene polymer fine particles, and both the PMMA and the styrene polymer have low light absorption and high transparency, thereby further improving the luminance. be able to.

  In the invention of [6], it is possible to emit light with high brightness that is substantially yellowish and has high whiteness.

  In the invention of [7], since the light having a high whiteness that is not substantially yellowish is emitted from the surface light source device with high luminance, the color of the liquid crystal panel can be accurately reproduced, and the yellowish Provided is a liquid crystal display device capable of realizing a natural and high-quality bright color display without taking on.

  One embodiment of a liquid crystal display device (1) according to the present invention is shown in FIG. The liquid crystal display device (1) includes a surface light source device (9) and a liquid crystal panel (30) disposed on the front side of the surface light source device (9).

  The liquid crystal panel (30) includes a liquid crystal cell (20) in which a liquid crystal (11) is sealed between a pair of upper and lower transparent electrodes (12) and (13) arranged in parallel and spaced apart from each other. The liquid crystal cell (20) includes polarizing plates (14) and (15) disposed on both upper and lower sides. These constituent members (11), (12), (13), (14), and (15) constitute an image display unit. An alignment film (not shown) is laminated on the inner surfaces (surfaces on the liquid crystal side) of the transparent electrodes (12) and (13).

  The surface light source device (9) is disposed on the lower surface side (rear surface side) of the lower polarizing plate (15). The surface light source device (9) includes a thin box-shaped lamp box (5) having a rectangular shape in plan view and an open upper surface (front surface), and a light guide plate (5) accommodated in the lamp box (5). 3) and a light source (2), and a light diffusing plate (4) mounted and fixed to the lamp box (5) so as to close its open surface. The said light source (2) is arrange | positioned in the side position of the said light-guide plate (3), ie, is arrange | positioned in the contact state with respect to one side surface of the light-guide plate (3). The lamp box (5) is made of a white acrylic resin plate. On the back surface (3a) of the light guide plate (3), a dot printing portion (dot pattern) made of white ink is formed, and light incident from one side surface into the light guide plate (3) from the light source (2) is received. The light is uniformly emitted from the front surface of the light guide plate, that is, the light emitting surface (3b), by being reflected by the dot printing unit.

  The said light-guide plate (3) consists of a plate-shaped body of the resin composition by which microparticles | fine-particles are disperse | distributed in transparent resin.

The light guide plate (3) is configured to satisfy the following relational expression. That is, when the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the fine particles is “Δn” and the cumulative 50% particle diameter of the fine particles is “D ₅₀ ” (μm), 0.30 ≦ Δn XD ₅₀ ≦ 0.70 is established. That is, the light guide plate (3) is composed of transparent resin and fine particles that satisfy such a relational expression.

  Further, the light guide plate (3) has an average light transmittance of 35% or more measured with an optical path length of 300 mm.

The light guide plate (3) according to the above configuration has a configuration in which the relational expression of 0.30 ≦ Δn × D ₅₀ ≦ 0.70 is established, and the fine particles satisfying such a relational expression have any wavelength of visible light. Since the light can be scattered to the same extent, the yellowness of the light emitted from the light emitting surface (3b) of the light guide plate (3) is sufficiently reduced, and the whiteness that is not substantially yellowish is obtained. High light can be emitted. Moreover, since the average light transmittance of visible light measured with the optical path length of 300 mm is 35% or more, high-intensity light can be emitted.

  Accordingly, in the liquid crystal display device (1), light having a high whiteness that is not substantially yellowish is emitted from the surface light source device (9) toward the liquid crystal panel (30) with high brightness. The color of the panel (30) can be accurately reproduced, and a natural and high-quality bright color display can be realized without being yellowish.

In addition, when the relational expression Δn × D ₅₀ <0.30 or 0.70 <Δn × D ₅₀ is satisfied, the emitted light is tinged with yellow and the whiteness level is high from the surface light source device (9). Diffuse light cannot be emitted. Therefore, in this case, a liquid crystal display device capable of realizing a natural and high-quality color display cannot be configured.

Among them, the configuration in which the relational expression of 0.35 ≦ Δn × D ₅₀ ≦ 0.65 is satisfied is preferable in that light with higher whiteness can be emitted.

  The light guide plate (3) is not particularly limited as long as it is a plate-shaped body of a resin composition in which fine particles are dispersed in a transparent resin. Any light guide plate can be used.

  Examples of the transparent resin include methacrylic resin (PMMA, etc.), polycarbonate resin, ABS resin (acrylonitrile-styrene-butadiene copolymer resin), MS resin (methyl methacrylate-styrene copolymer resin), polystyrene resin, AS resin. (Acrylonitrile-styrene copolymer resin), polyolefin resin (polyethylene, polypropylene, etc.) and the like.

  The fine particles are not particularly limited as long as they are fine particles having a refractive index different from that of the transparent resin constituting the light guide plate (3) and can diffuse transmitted light. For example, inorganic particles such as glass beads, silica particles, aluminum hydroxide particles, calcium carbonate particles, barium sulfate particles, titanium oxide particles, talc, styrene polymer particles, acrylic polymer particles, siloxane polymer particles, etc. Resin particles and the like.

The cumulative 50% particle diameter (D ₅₀ ) of the fine particles is preferably in the range of 3 to 7 μm. When it is 3 μm or more, the transmitted light can be sufficiently scattered, and when it is 7 μm or less, the surface of the light guide plate (3) such as the light exit surface (3b) can be made smoother.

  The absolute value Δn of the difference between the refractive index of the transparent resin and the refractive index of the fine particles is preferably set to 0.08 to 0.13. If the absolute value Δn of the difference in refractive index is within such a range, the content of fine particles required to obtain desired light scattering is small, and the workability can be improved by reducing the fine particle content. There are advantages.

  The content of the fine particles in the light guide plate (3) is preferably set to 0.2 to 20 ppm. By setting the concentration to 0.2 ppm or more, the transmitted light can be sufficiently scattered, and by setting the concentration to 20 ppm or less, uneven distribution of fine particles due to aggregation of the fine particles can be reduced. Especially, it is more preferable that the content rate of the microparticles | fine-particles in the said light-guide plate (3) is set to 0.5-10 ppm.

  The light guide plate (3) may contain various additives such as an ultraviolet absorber, a heat stabilizer, an antioxidant, a weathering agent, a light stabilizer, a fluorescent brightening agent, and a processing stabilizer. Further, fine particles other than the fine particles satisfying the specific relational expression can be added as long as the effects of the present invention are not impaired.

  Although the thickness of the said light-guide plate (3) is not specifically limited, Usually, it is 0.05-15 mm, Preferably it is 0.1-10 mm, More preferably, it is 0.5-5 mm.

  In the present invention, since the light guide plate (3) has an average light transmittance of visible light measured at an optical path length of 300 mm of 35% or more, high brightness can be achieved. The light guide plate (3) preferably has an average visible light transmittance of 50% or more measured at an optical path length of 300 mm, particularly preferably 60% or more.

  As a manufacturing method of the said light-guide plate (3), a well-known shaping | molding method can be used as a shaping | molding method of a resin plate, Although it does not specifically limit, For example, a hot press method, a melt extrusion method, an injection molding method etc. are mentioned.

  In the present invention, the light guide plate (3) may be subjected to the following processing. That is, for example, the peripheral side surface (51) may be polished, the light emitting surface (3b) may be subjected to light diffusion processing to make uniform light, and the back surface (3a) may be white. Light diffusion processing such as dot printing using ink or the like, formation of a prism, or the like, or light such as a silver-deposited sheet or film on a surface other than the light exit surface (3b) of the light guide plate A reflective layer may be provided.

  In the said embodiment (FIG. 1), the structure by which the light source (2) was arrange | positioned in one side surface among the four side surfaces (51) of a light-guide plate (3) was employ | adopted, but it is limited especially in such a structure. For example, a configuration in which the light source (2) is disposed on each of a pair of opposing side surfaces of the light guide plate (3) may be employed.

  The light source (2) is not particularly limited. For example, in addition to a linear light source such as a cold cathode tube, a hot cathode tube, or an EEFL (external electrode fluorescent lamp), a light emitting diode (LED) or the like is used. A point light source or the like is used.

  The light guide plate (3), the surface light source device (9) and the liquid crystal display device (1) according to the present invention are not particularly limited to those of the above-described embodiment, and the spirit thereof is within the scope of the claims. Any design changes are allowed as long as they do not deviate.

  Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.

<Example 1>
PMMA (polymethyl methacrylate) (“SUMIPEX EXN” manufactured by Sumitomo Chemical Co., Ltd., refractive index: 1.49) and polystyrene resin fine particles (“SBX-4” manufactured by Sekisui Plastics Co., Ltd.), refractive index: 1.59 ) Is mixed with a Henschel mixer so that the content is 0.5 ppm, melt-kneaded with a single screw extruder with a screw diameter of 40 mm, and extruded from a T die at a resin temperature of 265 ° C. A light guide plate of 4 mm and a width of 20 cm was produced. The cumulative 50% particle diameter (D ₅₀ ) of the polystyrene resin fine particles was 3.7 (μm).

<Example 2>
A light guide plate was produced in the same manner as in Example 1 except that the content of the polystyrene resin fine particles was set to 1 ppm.

<Example 3>
A light guide plate was produced in the same manner as in Example 1 except that the content of the polystyrene resin fine particles was set to 3 ppm.

<Example 4>
A light guide plate was produced in the same manner as in Example 1 except that the content of the polystyrene resin fine particles was set to 10 ppm.

<Example 5>
PMMA (polymethyl methacrylate) (“SUMIPEX EXN” manufactured by Sumitomo Chemical Co., Ltd., refractive index: 1.49) and polystyrene resin fine particles (“SBX-6” manufactured by Sekisui Plastics Co., Ltd.), refractive index: 1.59 ) Is mixed with a Henschel mixer so that the content is 0.5 ppm, melt-kneaded with a single screw extruder with a screw diameter of 40 mm, and extruded from a T die at a resin temperature of 265 ° C. A light guide plate of 4 mm and a width of 20 cm was produced. The cumulative 50% particle diameter (D ₅₀ ) of the polystyrene resin fine particles was 5.8 (μm).

<Example 6>
A light guide plate was produced in the same manner as in Example 5 except that the content of the polystyrene resin fine particles was set to 1 ppm.

<Example 7>
A light guide plate was produced in the same manner as in Example 5 except that the content of the polystyrene resin fine particles was set to 5 ppm.

<Comparative Example 1>
A light guide plate was produced in the same manner as in Example 5 except that the content of the polystyrene resin fine particles was set to 21 ppm.

<Comparative example 2>
Polystyrene resin fine particles (“XX52K” manufactured by Sekisui Plastics Co., Ltd., refractive index: 1.59) are added to PMMA (polymethyl methacrylate) (“SUMIPEX EXN” manufactured by Sumitomo Chemical Co., Ltd., refractive index: 1.49). After mixing with a Henschel mixer so that the content is 0.5 ppm, melt kneading with a single screw extruder with a screw diameter of 40 mm and extruding from a T die at a resin temperature of 265 ° C., a thickness of 4 mm, A light guide plate with a width of 20 cm was produced. The cumulative 50% particle diameter (D ₅₀ ) of the polystyrene resin fine particles was 2.8 (μm).

<Comparative Example 3>
A light guide plate was produced in the same manner as in Comparative Example 2 except that the content of the polystyrene resin fine particles was set to 1 ppm.

<Comparative example 4>
A light guide plate was produced in the same manner as in Comparative Example 2 except that the content of the polystyrene resin fine particles was set to 3 ppm.

<Comparative Example 5>
A light guide plate was produced in the same manner as in Comparative Example 2 except that the content of the polystyrene resin fine particles was set to 10 ppm.

<Comparative Example 6>
PMMA (polymethyl methacrylate) (“SUMIPEX EXN” manufactured by Sumitomo Chemical Co., Ltd., refractive index: 1.49) and polystyrene resin fine particles (“SBX-8” manufactured by Sekisui Plastics Co., Ltd.), refractive index: 1.59 ) Is mixed with a Henschel mixer so that the content is 0.5 ppm, melt-kneaded with a single screw extruder with a screw diameter of 40 mm, and extruded from a T die at a resin temperature of 265 ° C. A light guide plate of 4 mm and a width of 20 cm was produced. The cumulative 50% particle diameter (D ₅₀ ) of the polystyrene resin fine particles was 7.9 (μm).

<Comparative Example 7>
A light guide plate was produced in the same manner as in Comparative Example 6 except that the content of the polystyrene resin fine particles was set to 10 ppm.

<Comparative Example 8>
PMMA (polymethyl methacrylate) (“SUMIPEX EXN” manufactured by Sumitomo Chemical Co., Ltd., refractive index: 1.49) and acrylic resin fine particles (“Epaster MA1002” manufactured by Nippon Shokubai Co., Ltd., refractive index: 1.492) After mixing with a Henschel mixer so that the content rate becomes 1000 ppm, the mixture is melt-kneaded with a single screw extruder with a screw diameter of 40 mm and extruded from a T die at a resin temperature of 265 ° C., thereby having a thickness of 4 mm and a width of 20 cm. A light guide plate was produced. The 50% cumulative particle diameter (D ₅₀ ) of the acrylic resin fine particles was 2.0 (μm).

<Measurement method of 50% cumulative particle size of fine particles>
The cumulative 50% particle size (D ₅₀ ) of the fine particles was measured by the Fraunhofer diffraction method of the laser light source forward scattered light using a Nikkiso Co., Ltd. Microtrac particle size analyzer (model 9220FRA). In the measurement, about 0.1 g of fine particles are dispersed in methanol to obtain a dispersion, and the dispersion is irradiated with ultrasonic waves for 5 minutes, and then the dispersion is introduced into the sample inlet of the microtrack particle size analyzer. The measurement was carried out. The cumulative 50% particle diameter (D ₅₀ ) is determined by measuring the particle diameter and volume of all particles, and integrating the volume sequentially from the smallest particle diameter, and the accumulated volume is 50% of the total volume of all particles. The particle diameter of the particles to be

  Each light guide plate obtained as described above was evaluated according to the following evaluation method. The results are shown in Tables 1 and 2.

<Measurement method of average light transmittance of visible light at optical path length of 300 mm>
As shown in FIG. 2, the obtained light guide plate was cut into a size of 50 mm in width and 300 mm in length, and then the four side surfaces (51) were polished with a polishing machine (“Pura Beauty 1000” manufactured by Asahi Megaro). A test specimen (50) was prepared. Each of these measurement specimens was measured in increments of 5 nm in a wavelength range of 380 to 780 nm with an optical path length of 300 mm using a plastic property measurement system manufactured by Hitachi, Ltd. (consisting of a U-3410 type spectrophotometer and a large sample chamber integrating sphere accessory) The light transmittance for each wavelength was measured, and the arithmetic average value of the light transmittance thus obtained was defined as “average light transmittance of visible light”.

<YI (Yellow Index) Evaluation Method>
As shown in FIG. 2, the obtained light guide plate was cut into a size of 50 mm in width and 300 mm in length, and then the four side surfaces (51) were polished with a polishing machine (“Pura Beauty 1000” manufactured by Asahi Megaro). A test specimen (50) was prepared. Each of these measurement specimens was measured in increments of 5 nm in a wavelength range of 380 to 780 nm with an optical path length of 300 mm using a plastic property measurement system manufactured by Hitachi, Ltd. (consisting of a U-3410 type spectrophotometer and a large sample chamber integrating sphere accessory) The light transmittance for each wavelength was measured, and YI (yellow index) was calculated from this. In addition, the thing whose YI is 2.0 or less was set as the pass.

  As is apparent from Table 1, the light guide plates of Examples 1 to 7 of the present invention have a sufficiently reduced YI, and thus can emit light with high whiteness that is not substantially yellowish. Moreover, since the average light transmittance of visible light measured with the optical path length of 300 mm is 35% or more, sufficient luminance can be ensured.

  On the other hand, YI was a large value in the light guide plates of Comparative Examples 1 to 8 that deviated from the specified range of the present invention.

From the comparison between Examples 1 and 5 and Comparative Examples 2 and 6, when (Δn × D ₅₀ ) is smaller than 0.30, YI increases, and (Δn × D ₅₀ ) is larger than 0.70. It can be seen that YI becomes large while YI is sufficiently small when (Δn × D ₅₀ ) is in the range of 0.30 to 0.70.

From the comparison between Examples 2 and 6 and Comparative Example 3, YI increases when (Δn × D ₅₀ ) is smaller than 0.30, whereas (Δn × D ₅₀ ) is 0.30 to 0. It can be seen that YI is sufficiently small in the range of .70.

From the comparison between Example 3 and Comparative Example 4, YI increases when (Δn × D ₅₀ ) is smaller than 0.30, whereas (Δn × D ₅₀ ) is 0.30 to 0.70. In this range, it can be seen that YI is sufficiently small.

Further, from the comparison between Example 4 and Comparative Examples 5 and 7, when (Δn × D ₅₀ ) is smaller than 0.30, YI increases, and when (Δn × D ₅₀ ) is larger than 0.70. It can be seen that while YI increases, YI decreases sufficiently when (Δn × D ₅₀ ) is in the range of 0.30 to 0.70.

  Further, from the comparison between Examples 5 to 7 and Comparative Example 1, when the content ratio of the fine particles in the light guide plate exceeds 20 ppm, the average light transmittance of visible light measured at an optical path length of 300 mm is smaller than 35%. It can also be seen that YI also increases.

Further, from the comparison between Example 6 and Comparative Example 8, even when the average light transmittance is substantially equal, YI increases when (Δn × D ₅₀ ) is smaller than 0.30, whereas (Δn × D ₅₀₎ it can be seen that the YI is sufficiently small as long as the range of 0.30 to 0.70.

  The light guide plate according to the present invention is suitably used as a light guide plate for a surface light source device, but is not particularly limited to such applications. Further, the surface light source device of the present invention is suitably used as a backlight for a liquid crystal display device, but is not particularly limited to such applications, for example, for other display devices, lighting devices, signboards. Etc.

1 is a schematic side view showing an embodiment of a liquid crystal display device according to the present invention. It is explanatory drawing of the measuring method of the average light transmittance of visible light in optical path length 300mm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 2 ... Light source 3 ... Light guide plate 9 ... Surface light source device 30 ... Liquid crystal panel

Claims (7)

A light guide plate in which fine particles are dispersed in a transparent resin,
When the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the fine particles is “Δn” and the cumulative 50% particle diameter of the fine particles is “D ₅₀ ” (μm), 0.30 ≦ Δn × D The relational expression ₅₀ ≦ 0.70 holds,
A light guide plate, wherein an average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more. 2. The light guide plate according to claim 1, wherein the cumulative 50% particle diameter (D ₅₀ ) of the fine particles is in the range of 3 to 7 μm.   The light guide plate according to claim 1 or 2, wherein an absolute value (Δn) of a difference between a refractive index of the transparent resin and a refractive index of the fine particles is 0.08 to 0.13.   The light guide plate according to any one of claims 1 to 3, wherein the content of the fine particles in the light guide plate is 0.2 to 20 ppm.   The light guide plate according to claim 1, wherein the transparent resin is PMMA, and the fine particles are styrene polymer fine particles.   A surface light source device comprising the light guide plate according to claim 1.   A liquid crystal display device, wherein the surface light source device according to claim 6 is arranged on the back side of the liquid crystal panel.

Images