KR20110070999A

KR20110070999A - Light guide plate

Info

Publication number: KR20110070999A
Application number: KR1020117010433A
Authority: KR
Inventors: 아키요시 가네미츠
Original assignee: 수미토모 케미칼 컴퍼니 리미티드
Priority date: 2008-10-09
Filing date: 2009-10-08
Publication date: 2011-06-27
Also published as: CN102171506A; TW201033661A; JP2010092755A; CN102171506B; JP4933512B2; WO2010041768A1; TWI434080B

Abstract

In the light guide plate 3 of this invention, microparticles | fine-particles are disperse | distributed in transparent resin, The absolute value of the difference of the refractive index of the said transparent resin and the refractive index of the said microparticles | fine-particles is made into "(DELTA) n", and the cumulative 50% particle diameter of the said microparticles is " When D ₅₀ ″ (μm), a relationship of 0.30 ≦ Δn × D ₅₀ ≦ 0.70 is established, and the average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more.

Description

Light guide plate {LIGHT GUIDE PLATE}

The present invention relates to a light guide plate in which yellowness is sufficiently suppressed while containing fine particles for light scattering.

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 the light guide plate, and the 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 to uniform the light from the side of the light guide plate. It is known to be configured so that it can exit.

As such a light guide plate for backlight, the light guide plate which microparticles | fine-particles disperse | distribute in transparent resins, such as an acrylic resin, is known, This light guide plate can be made to scatter light by containing microparticles | fine-particles, and is excellent in uniformity of brightness (Japanese Patent Laid-Open No. 2001). -76522 (Patent Document 1)).

Japanese Patent Laid-Open No. 2001-76522

However, the light guide plate in which the fine particles are dispersed in the transparent resin as described above tends to have a slightly yellowish transmitted light (YI value is large), and the liquid crystal display device constructed by using the light guide plate has a slightly yellowish image and has a high quality image. There was a problem that this was not obtained. That is, there existed a problem that a natural and high quality color display could not be implement | achieved.

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

The present invention provides the following means.

[1] A light guide plate in which fine particles are dispersed in a transparent resin,

A relational expression of 0.30 ≦ Δn × D50 ≦ 0.70 when the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the fine particles is set to “Δn” and the cumulative 50% particle size of the fine particles is set to “D ₅₀ ” (μm). Is established,

A light guide plate having an average light transmittance of 35% or more of visible light measured at an optical path length of 300 mm.

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

[3] The light guide plate according to item 1 or 2, wherein an absolute value Δn 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 a content rate 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 styrene 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, wherein the surface light source device according to item 6 is arranged on the back side of the liquid crystal panel.

In the invention of [1], the relationship of 0.30 ≦ Δn × D ₅₀ ≦ 0.70 holds. Since the fine particles satisfying the relational expression can scatter the light of any wavelength of visible light to the same degree, the yellow group of the light emitted from the light exit surface of the light guide plate is sufficiently reduced, and the light having high whiteness that is not substantially yellow is emitted. can do. In addition, since the average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more, high luminance can be achieved.

In the invention of [2], since the cumulative 50% particle size (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], since 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, if the refractive index is in this range, the content of the fine particles required for the desired light scattering is at least sufficient. By reducing such fine particle content, workability can be improved.

In the invention of [4], since the content rate of the fine particles in the light guide plate is 0.2 to 20 ppm, the effect of reducing the ubiquity of the fine particles due to the aggregation of the fine particles is exhibited.

In the invention of [5], the transparent resin is PMMA, the fine particles are styrene polymer fine particles, and both of these PMMA and styrene polymers have low light absorption and high transparency, so that the luminance can be further improved.

In the invention [6], light having a high whiteness which is not substantially yellow can be emitted with high luminance.

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

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.

1 embodiment of the liquid crystal display device 1 which concerns on this invention is shown in FIG. This liquid crystal display device 1 is provided with the surface light source device 9 and the liquid crystal panel 30 arrange | positioned at the front side of the said surface light source device 9. As shown in FIG.

The liquid crystal panel 30 includes a liquid crystal cell 20 in which a liquid crystal 11 is enclosed between a pair of upper and lower transparent electrodes 12 and 13 spaced apart from each other and arranged in parallel to each other, and the liquid crystal cell 20. And polarizing plates 14 and 15 disposed on both upper and lower sides. The image display part is comprised by these structural members 11, 12, 13, 14, and 15. As shown in FIG. On the other hand, an alignment film (not shown) is laminated on the inner surface (surface on the liquid crystal side) of the transparent electrodes 12 and 13, respectively.

The surface light source device 9 is disposed on the lower surface side (back side) of the lower polarizing plate 15. The surface light source device 9 includes a thin box-shaped lamp box 5 having an upper surface side (front side) opened in a rectangular shape in plan view, a light guide plate 3 and a light source (housed in the lamp box 5); 2) and a light diffusing plate 4 which is placed and fixed to the lamp box 5 so as to block its open surface. The light source 2 is disposed at a side position of the light guide plate 3. That is, it 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 part (dot pattern) by white ink is formed, and the light incident from the one side from the light source 2 into the light guide plate 3 is applied to the dot printing part. By reflecting by the light source, light can be uniformly emitted from the entire surface of the light guide plate, that is, from the light exit surface 3b.

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

The light guide plate 3 is configured such that the following relational expression holds. That is, the absolute value of a difference between the refractive index of the refractive index and the fine particles of the transparent resin as "Δn" and, when the cumulative 50% particle diameter of the fine particles as "D _50" _{(μm), 0.30≤Δn × D 50} ≤ The relation of 0.70 holds. That is, the light guide plate 3 is made of transparent resin and fine particles satisfying such a relational expression.

In the light guide plate 3, the average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more.

The light guide plate 3 according to the above structure is a configuration in which a relational expression of 0.30 ≦ Δn × D ₅₀ ≦ 0.70 is established, and since the fine particles satisfying such a relation can scatter light of any wavelength of visible light to the same degree, The yellow group of the light radiate | emitted from the light output surface 3b of (3) is fully reduced, and the light with high whiteness which is not substantially yellowish can be emitted. In addition, since the average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more, high luminance light can be emitted.

Therefore, in the liquid crystal display device 1, since the light having high whiteness, which is not substantially yellowish, can be emitted from the surface light source device 9 toward the liquid crystal panel 30 with high brightness, the liquid crystal panel 30 The color can be accurately reproduced, and a natural high quality bright color display can be realized without having a yellowish tinge.

It is that in particular, 0.35≤Δn configuration that the relation of ₅₀ ≤ 0.65 × D is satisfied, it is preferable in that it can emit a high brightness than light.

As said light guide plate 3, if it is a plate-shaped object of the resin composition by which microparticles | fine-particles are disperse | distributed in transparent resin, it will not specifically limit, Any can be used.

As said transparent resin, methacryl resin (PMMA etc.), polycarbonate resin, ABS resin (acrylonitrile- styrene-butadiene copolymer resin), MS resin (methyl methacrylate styrene copolymer resin, for example) ), Polystyrene resin, AS resin (acrylonitrile-styrene copolymer resin), polyolefin resin (polyethylene, polypropylene, etc.), etc. are mentioned.

The fine particles are not particularly limited as long as the transparent resin constituting the light guide plate 3 is different from the refractive index and can diffuse the transmitted light, and any one can be used. For example, inorganic particles such as glass beads, silica particles, aluminum hydroxide particles, calcium carbonate particles, barium sulfate particles, titanium oxide particles, talc, resin particles such as styrene polymer particles, acrylic polymer particles, and siloxane polymer particles, etc. may be used. Can be mentioned.

The cumulative 50% particle size (D ₅₀ ) of the fine particles is preferably in the range of 3 to 7 μm. Transmitted light can be scattered sufficiently by being 3 micrometers or more, and the surface, such as the light output surface 3b of the light guide plate 3, can be made smoother by being 7 micrometers or less.

It is preferable that absolute value (DELTA) n of the difference of the refractive index of the said transparent resin and the refractive index of the said microparticles | fine-particles is set to 0.08-0.13. If absolute value (DELTA) n of the difference of refractive index is this range, content of microparticles | fine-particles required in order to obtain desired light scattering will be at least sufficient, and there exists an advantage that processability can be improved by reducing such microparticle content.

It is preferable that the content rate of the said microparticles | fine-particles in the said light guide plate 3 is set to 0.2-20 ppm. By setting it as 0.2 ppm or more, transmitted light can be scattered fully, and since it is 20 ppm or less, uneven distribution of microparticles | fine-particles by aggregation of microparticles | fine-particles etc. 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 further contain, for example, various additives such as ultraviolet absorbers, heat stabilizers, antioxidants, weathering agents, light stabilizers, fluorescent brighteners, and processing stabilizers. Moreover, as long as it is a range which does not significantly inhibit the effect of this invention, you may add other microparticles other than the microparticle which satisfy | fills the said specific relationship.

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, the light guide plate 3 can achieve high luminance because the average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more, but the light guide plate 3 is a 300 mm optical path. It is preferable that the average light transmittance of visible light measured in length is 50% or more, and especially preferable is 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 main side surface 51 may be polished, or the light diffusing process may be performed on the light exit surface 3b for uniform light, and dot printing using white ink or the like on the back surface 3a, A light diffusion process such as the formation of a prism may be performed, or a light reflection layer such as a silver-deposited sheet or a film may be provided on a surface other than the light exit surface 3b of the light guide plate.

In the said embodiment (FIG. 1), although the structure which the light source 2 was arrange | positioned at the one side surface side among the four side surfaces 51 of the light guide plate 3 is employ | adopted, it is not specifically limited to such a structure, For example, light guide plate The structure in which the light source 2 is arrange | positioned at the pair of opposing side surfaces in (3), respectively can also be employ | adopted.

On the other hand, the light source 2 is not particularly limited, but for example, a point light source such as a light emitting diode (LED) or the like can be used in addition to linear light sources such as a cold cathode tube, a hot cathode tube, and an EEFL (external electrode fluorescent lamp).

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 embodiments, and are within the scope of the claims unless otherwise departed from the spirit thereof. Design changes are also allowed.

Example

Next, although the specific Example of this invention is described, this invention is not specifically limited to these Examples.

&Lt; Example 1 >

0.5 ppm of polystyrene resin microparticles | fine-particles ("SBX-4" made by Sekisui Plastic Co., Ltd., refractive index: 1.59) to PMMA (polymethyl methacrylate) ("Semipex EXN" made by Sumitomo Chemical Co., Ltd., refractive index: 1.49) After mixing so that it might be mixed with the Henschel mixer, it melt-kneaded with the screw diameter 40mm single screw extruder, and extruded from the T die at the resin temperature of 265 degreeC, and the light guide plate of thickness 4mm and width 20cm was produced. On the other hand, the cumulative 50% particle size (D ₅₀ ) of the polystyrene resin fine particles was 3.7 (μm).

The light guide plate was produced like Example 1 except having set the content rate of polystyrene resin microparticles | fine-particles to 1 ppm.

The light guide plate was produced like Example 1 except having set the content rate of polystyrene resin microparticles | fine-particles to 3 ppm.

The light guide plate was produced like Example 1 except having set the content rate of polystyrene resin microparticles | fine-particles to 10 ppm.

0.5 ppm of polystyrene resin microparticles | fine-particles ("SBX-6" made by Sekisui Plastic Co., Ltd., refractive index: 1.59) to PMMA (polymethyl methacrylate) ("Semipex EXN" made by Sumitomo Chemical Co., Ltd., refractive index: 1.49) After mixing so that it might be mixed with the Henschel mixer, it melt-kneaded with the screw diameter 40mm single screw extruder, and extruded from the T die at the resin temperature of 265 degreeC, and the light guide plate of thickness 4mm and width 20cm was produced. On the other hand, the cumulative 50% particle size (D ₅₀ ) of the polystyrene resin fine particles was 5.8 (μm).

The light guide plate was produced like Example 5 except having set the content rate of polystyrene resin microparticles | fine-particles to 1 ppm.

The light guide plate was produced like Example 5 except having set the content rate of polystyrene resin microparticles | fine-particles to 5 ppm.

Comparative Example 1

The light guide plate was produced like Example 5 except having set the content rate of polystyrene resin microparticles | fine-particles to 21 ppm.

Comparative Example 2

PMMA (polymethyl methacrylate) ("Semipex EXN" manufactured by Sumitomo Chemical Co., Ltd., refractive index: 1.49), and polystyrene resin fine particles ("XX52K" made by Sekisui Plastics Co., Ltd., refractive index: 1.59) so that the content rate is 0.5 ppm. After mixing and mixing by a Henschel mixer, melt-kneading with the screw diameter 40mm single screw extruder and extruding from T die at resin temperature of 265 degreeC produced the light guide plate of thickness 4mm and width 20cm. On the other hand, the cumulative 50% particle size (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 rate of the polystyrene resin fine particles was set to 1 ppm.

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

Comparative Example 6

0.5 ppm of polystyrene resin microparticles | fine-particles ("SBX-8" made by Sekisui Plastics Corporation, refractive index: 1.59) to PMMA (polymethyl methacrylate) ("Semipex EXN" made by Sumitomo Chemical Co., Ltd., refractive index: 1.49) After mixing so that it might be mixed with the Henschel mixer, it melt-kneaded with the screw diameter 40mm single screw extruder, and extruded from the T die at the resin temperature of 265 degreeC, and the light guide plate of thickness 4mm and width 20cm was produced. On the other hand, the cumulative 50% particle size (D ₅₀ ) of the polystyrene resin fine particles was 7.9 (μm).

&Lt; Comparative Example 7 &

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

&Lt; Comparative Example 8 >

To PMMA (polymethyl methacrylate) ("Sumipex EXN" made by Sumitomo Chemical Co., Ltd., refractive index: 1.49), the acrylic resin fine particle ("Eposuta MA1002" made by Nippon Shokubai Co., Ltd., refractive index: 1.492) has the content rate of 1000 ppm. The mixture was mixed as much as possible, mixed with a Henschel mixer, melt-kneaded with a screw diameter of 40 mm, and extruded from a T die at a resin temperature of 265 ° C. to produce a light guide plate having a thickness of 4 mm and a width of 20 cm. On the other hand, the cumulative 50% particle size (D ₅₀ ) of the acrylic resin fine particles was 2.0 (μm).

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 microtrack particle size analyzer (model 9220FRA) manufactured by Nikkiso Corporation. In the measurement, about 0.1 g of fine particles were dispersed in methanol to obtain a dispersion, and the dispersion was irradiated with ultrasonic waves for 5 minutes, and then the dispersion was introduced into the sample inlet of the microtrack particle size analyzer for measurement. On the other hand, the cumulative 50% particle size (D ₅₀ ) measures the particle diameter and volume of all particles, and accumulates the volumes sequentially from those of small particle diameters, so that the cumulative volume becomes 50% of the total volume of all particles. Is the particle diameter of.

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

As shown in Fig. 2, the obtained light guide plate was cut into a size of 50 mm in width x 300 mm in length, and then the four side surfaces 51 were polished with a polishing machine ("Pla-Beauty 1000" manufactured by Asahi Mega Corporation). The measurement test piece 50 was produced. This measurement test piece is made by Hitachi, Ltd., a plastics characteristic measurement system (consisting of a U-3410 type spectrophotometer and a large sample chamber integrating apparatus), each wavelength having a wavelength of 380 to 780 nm and a wavelength of 380 to 780 nm at a wavelength of 300 mm. The light transmittance was measured, and the arithmetic mean value of the light transmittance thus obtained was defined as "average light transmittance of visible light."

As shown in FIG. 2, after cutting the obtained light guide plate into the size of width 50mm x length 300mm, four side surfaces 51 were polished with the grinder ("flavor 1000" by Asahi Mega Corporation), and the measurement test piece 50 Made. This measurement test piece is made by Hitachi, Ltd., a plastics characteristic measurement system (consisting of a U-3410 type spectrophotometer and a large sample chamber integrating apparatus), each wavelength having a wavelength of 380 to 780 nm and a wavelength of 380 to 780 nm at a wavelength of 300 mm. The light transmittance was measured and YI (yellow index) was computed from this. On the other hand, the thing whose YI is 2.0 or less was made into the pass.

As is apparent from Table 1, since the light guide plates of Examples 1 to 7 of the present invention are sufficiently reduced in YI, light having a high degree of whiteness that is not substantially yellow can be emitted. In addition, since the average light transmittance of visible light measured at an optical path length of 300 mm is 35% or more, sufficient luminance can be ensured.

In contrast, in the light guide plates of Comparative Examples 1 to 8 that deviate from the specified range of this invention, YI was a large value.

On the other hand, from the contrast between Examples 1 and 5 and Comparative Examples 2 and 6, YI becomes large when (Δn × D ₅₀ ) is less than 0.30, and YI becomes large when (Δn × D ₅₀ ) is larger than 0.70. In contrast, it can be seen that YI is sufficiently small when (Δn × D ₅₀ ) is in the range of 0.30 to 0.70.

Further, in Example 2, from the preparation of Comparative Examples 3 and 6, (Δn × D ₅₀₎ with respect to which the case is less than 0.30, the YI significantly, (Δn × D ₅₀₎ is in a range of 0.30~0.70 YI is sufficiently It can be seen that small.

In addition, from the comparison between Example 3 and Comparative Example 4, when (Δn × D ₅₀ ) is smaller than 0.30, YI becomes large. However, when (Δn × D ₅₀ ) is in the range of 0.30 to 0.70, YI is sufficiently small. Able to know.

From the contrast between Example 4 and Comparative Examples 5 and 7, YI becomes large when (Δn × D ₅₀ ) is less than 0.30, and YI becomes large when (Δn × D ₅₀ ) is larger than 0.70. It can be seen that YI is sufficiently small when (Δn × D ₅₀ ) is in the range of 0.30 to 0.70.

Further, from the contrast of Examples 5 to 7 and Comparative Example 1, when the content rate of the fine particles in the light guide plate exceeds 20 ppm, not only the average light transmittance of visible light measured at an optical path length of 300 mm is smaller than 35%, but also YI. It can be seen that the larger.

Further, from the contrast between Example 6 and Comparative Example 8, even if the average light transmittance is almost equal, when (Δn × D ₅₀ ) is less than 0.30, YI becomes large, and (Δn × D ₅₀ ) is 0.30 to 0.70 It can be seen that YI is sufficiently small in the range of.

Although the light guide plate which concerns on this invention is used suitably as a light guide plate for surface light source devices, it is not specifically limited to such a use. In addition, although the surface light source device of this invention is used suitably as a backlight for liquid crystal display devices, it is not specifically limited to such a use, For example, it is used as other display devices, lighting devices, signboards, etc.

1: liquid crystal display
2: light source
3: light guide plate
9: surface light source device
30: liquid crystal panel

Claims

As a light guide plate in which microparticles | fine-particles are disperse | distributed in transparent resin,
When the refractive index and the absolute value of a difference between the refractive index of the fine particles as "Δn", and the fine particle cumulative 50% particle diameter (μm) of the transparent resin by "D _50" of 0.30≤Δn × D ₅₀ ≤ 0.70 The relationship is established,
A light guide plate having an average light transmittance of 35% or more of visible light measured at an optical path length of 300 mm.

The method of claim 1,
A light guide plate having a cumulative 50% particle size (D ₅₀ ) of the fine particles in a range of 3 to 7 μm.

The method according to claim 1 or 2,
The light guide plate whose absolute value (DELTA) n of the difference of the refractive index of the said transparent resin and the refractive index of the said microparticles is 0.08-0.13.

The method according to any one of claims 1 to 3,
The light guide plate whose content rate of the said microparticles | fine-particles in a light guide plate is 0.2-20 ppm.

The method according to any one of claims 1 to 4,
A light guide plate wherein said transparent resin is PMMA and said fine particles are styrene polymer fine particles.

The surface light source device provided with the light guide plate of any one of Claims 1-5.

The surface light source device of Claim 6 is arrange | positioned at the back side of a liquid crystal panel, The liquid crystal display device characterized by the above-mentioned.