JP2012188504A - Resin composition for light guide plate, and light guide plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin composition for a light guide plate, suitable for fabrication of the light guide plate whose yellowness degree is sufficiently suppressed and whose light emission efficiency is excellent.SOLUTION: The resin composition for a light guide plate includes a transparent resin and a silicone resin microparticle, which is preferably contained in a proportion of 0.1 to 200 ppm with respect to the total weight of the resin composition. A molded body from the resin composition has an average light-ray transmittance of 25 to 85%, in the wavelength region of 300 nm to 800 nm as measured at an optical length of 200 mm.

Description

  The present invention relates to a resin composition for a light guide plate that is suitable for preparing a light guide plate in which yellowness is sufficiently suppressed and light emission efficiency is excellent.

  As backlights for liquid crystal display devices and lighting devices, for example, a light source such as a cold cathode tube or an LED is disposed on the side of the light guide plate, and light from the light source is formed on the back surface of the light guide plate with a dot pattern or prism And the like so that light can be uniformly emitted from the front surface of the light guide plate.

  As a light guide plate for backlight, a light guide plate in which fine particles are dispersed in a transparent resin such as an acrylic resin is known. A light guide plate in which fine particles are dispersed in a transparent resin tends to have a yellowish transmitted light (that is, a large yellow index (YI) value), and a liquid crystal display device using such a light guide plate has a slight image. It is yellowish and high-quality images cannot be obtained.

As a light guide plate that suppresses yellowness of transmitted light, Patent Document 1 discloses that the product of the absolute value of the difference between the refractive index of the transparent resin and the refractive index of the fine particles and the cumulative 50% particle size of the fine particles has a predetermined range. A filling light guide plate is disclosed.
However, in the light guide plate of Patent Document 1, yellowness may not be sufficiently suppressed, and light emission efficiency may not be sufficient.

JP 2010-92755 A

  The objective of this invention is providing the resin composition for light-guide plates suitable for producing the light-guide plate which yellowness was fully suppressed and was excellent in the light emission efficiency.

The resin composition for a light guide plate of the present invention has the following configuration.
(1) A resin composition for a light guide plate comprising a transparent resin and silicone resin fine particles,
The resin composition for light-guide plates whose average light transmittance in the wavelength range of 300 nm-800 nm measured by the optical path length of 200 mm when the said resin composition is made into a molded object is 25-85%.
(2) The resin composition according to (1), wherein the silicone resin fine particles are contained at a ratio of 0.1 to 200 ppm with respect to the total weight of the resin composition.
(3) The resin composition according to (1) or (2), wherein the transparent resin is a methacrylic resin.
(4) A light guide plate comprising the resin composition according to any one of (1) to (3).
(5) The light guide plate according to (4), which is used in a liquid crystal display provided with an LED light source.
(6) A surface light source device comprising the light guide plate according to (4) or (5).
(7) A liquid crystal display device, wherein the surface light source device according to (6) is disposed on the back side of the liquid crystal panel.

  According to the present invention, it is possible to provide a resin composition for a light guide plate suitable for producing a light guide plate in which yellowness is sufficiently suppressed and light emission efficiency is excellent.

It is a typical side view which shows one embodiment of the liquid crystal display device of this invention. It is a figure explaining the measuring method of the average light transmittance in the wavelength range of 300 nm-800 nm in optical path length 200mm. It is a figure explaining the measuring method of the total luminous flux.

<Resin composition for light guide plate>
The resin composition for a light guide plate of the present invention (hereinafter sometimes simply referred to as “resin composition”) contains a transparent resin and silicone resin fine particles, and when the resin composition is used as a molded body, The average light transmittance in a wavelength region of 300 nm to 800 nm measured with an optical path length of 200 mm is 25 to 85%.

  The transparent resin contained in the resin composition of the present invention is not particularly limited as long as it is transparent, such as composition and weight average molecular weight. For example, methacrylic resin (polymethyl methacrylate (PMMA), etc.), polycarbonate resin, acrylonitrile-styrene-butadiene copolymer resin (ABS resin), polystyrene resin, acrylonitrile-styrene copolymer resin (AS resin), polyolefin resin (polyethylene) And polypropylene). Among these, methacrylic resin is preferable.

  The silicone resin fine particles contained in the resin composition of the present invention are used for diffusing light transmitted through the light guide plate.

  The silicone resin fine particles are not particularly limited, such as an average particle diameter and a weight average molecular weight. In order to diffuse light more efficiently, the silicone resin fine particles preferably have an average particle diameter of 1 to 12 μm, and more preferably have an average particle diameter of 2 to 6 μm.

  The silicone resin fine particles are preferably contained in a proportion of 0.1 to 200 ppm, more preferably 1 to 90 ppm, and still more preferably 1 to 50 ppm with respect to the total weight of the resin composition.

  The resin composition of the present invention has an average light transmittance of 25 to 85%, preferably 40 to 70% in a wavelength region of 300 nm to 800 nm measured with an optical path length of 200 mm when formed into a molded body. Brightness can be increased while suppressing the yellowness of the obtained light guide plate.

<Light guide plate>
The light guide plate of this invention is comprised from the said resin composition. Specifically, the light guide plate of the present invention is obtained, for example, by molding the above resin composition by an extrusion molding method, an injection molding method, a hot press molding method, or the like.

  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 may be added to the light guide plate.

  Although the thickness of a light-guide plate 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.

<Surface light source device and liquid crystal display device>
Next, FIG. 1 shows one embodiment of a surface light source device using a light guide plate composed of the resin composition of the present invention and a liquid crystal display device using the same.

  The liquid crystal display device 1 includes a surface light source device 9 and a liquid crystal panel 30, and the surface light source device 9 is disposed on the back side of the liquid crystal panel 30.

  The liquid crystal panel 30 includes a liquid crystal cell 20 in which the liquid crystal 11 is sealed between a pair of upper and lower transparent electrodes 12 and 13 disposed in parallel and spaced apart from each other, and polarized light disposed on both upper and lower sides of the liquid crystal cell 20. Plates 14 and 15 are provided. The liquid crystal 11, the transparent electrodes 12 and 13, and the polarizing plates 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 (back surface side) of the 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 side), a light guide plate 3 and a light source 2 housed in the lamp box 5, and a lamp box. 5 and a light diffusing plate 4 arranged and fixed so as to close the open surface. The light source 2 is an LED (light emitting diode) light source, for example, and is disposed at a side position 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 reflected by the dot printing portion. The light guide plate 3 is configured so that light can be uniformly emitted from the front surface (that is, the light emission surface 3b).

  In addition, the light guide plate 3 to be used may have a peripheral side surface 51 polished as shown in FIG. 2, for example, or the light emitting surface 3b may be subjected to a light diffusion process for making uniform light. good. The back surface 3a of the light guide plate 3 may be subjected to light diffusion processing such as prism formation instead of dot printing using white ink or the like, or a surface other than the light exit surface 3b of the light guide plate. Further, a light reflecting layer such as a silver-deposited sheet or film may be provided.

  With this configuration, in the liquid crystal display device 1 of the present invention, 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 luminance. Therefore, the color of the liquid crystal panel 30 can be accurately reproduced. Therefore, a natural and high-quality bright color display can be realized without being yellowish.

  In the liquid crystal display device 1 illustrated in FIG. 1, a configuration in which the light source 2 is disposed on one side surface among the four side surfaces of the light guide plate 3 is employed, but the configuration is not particularly limited thereto. For example, you may employ | adopt the structure by which the light source 2 is each arrange | positioned to a pair of side surface which the light-guide plate 3 opposes.

  The light source 2 is not particularly limited, and examples thereof include a linear light source such as a cold cathode tube, a hot cathode tube, and an external electrode fluorescent lamp (EEFL), and a point light source such as a light emitting diode (LED).

  According to the present invention, it is possible to provide a resin composition for a light guide plate suitable for producing a light guide plate in which yellowness is sufficiently suppressed and light emission efficiency is excellent. Therefore, the present invention is useful in fields such as liquid crystal display devices. The light guide plate of the present invention is particularly preferably used for a liquid crystal display including a large screen LED light source such as a television.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to these Examples.

Example 1
(Preparation of plate sample (light guide plate))
PMMA (“SUMIPEX EXN” manufactured by Sumitomo Chemical Co., Ltd., refractive index: 1.49), crosslinked silicone fine particles (“Tospearl 145” manufactured by Momentive Performance Materials Japan LLC), refractive index: 1.42, average Particle size: 4 μm) was mixed at a ratio of 10 ppm. Next, using a single screw extruder (screw diameter: 20 mm), melt-kneaded so that the resin temperature becomes 250 ° C., extruded into a strand, cooled with water, and cut with a strand cutter to form a pellet-shaped methacrylic resin composition The thing (resin composition for light-guide plates) was obtained.
160 g of the obtained pellet-shaped resin composition was subjected to heat compression molding to prepare a 210 mm square plate sample (light guide plate) having a thickness of 3 mm.

(Example 2)
A methacrylic resin composition was obtained in the same manner as in Example 1 except that “Tospearl 145” was mixed at a ratio of 1 ppm to prepare a plate sample.

(Comparative Examples 1 and 2)
Instead of the crosslinked silicone fine particles “Tospearl 145”, polystyrene fine particles (“SBX-12” manufactured by Sekisui Plastics Co., Ltd., refractive index: 1.59, average particle size: 12 μm) were mixed at the ratio shown in Table 1. Except for this, a methacrylic resin composition was obtained in the same manner as in Example 1 to prepare a plate sample.

  Using the plate-like samples obtained in Example 1 and Comparative Examples 1 and 2, evaluation of average light transmittance, yellow index (YI), and total luminous flux was performed. The evaluation method is as follows.

<Measurement of average light transmittance of visible light in optical path length of 200 mm>
The obtained plate-like sample was cut into a size of 50 mm width × 200 mm length as shown in FIG. Next, the four side surfaces 51 were polished by a polishing machine (“Pura Beauty PB-500” manufactured by Megaro Technica Co., Ltd.), and a test piece 50 was obtained.
The light transmittance of the test piece 50 at an optical path length of 200 mm was measured using a plastic property measurement system (consisting of a U-4000 type spectrophotometer and a large sample chamber integrating sphere accessory) manufactured by Hitachi, Ltd. In addition, measurement was performed every 5 nm in the wavelength range of 300 nm to 800 nm, and the arithmetic average value of the obtained light transmittance was defined as “average light transmittance of visible light”. The results are shown in Table 1.

<Evaluation of Yellow Index (YI)>
The light transmittance in the optical path length of 200 mm of the test piece 50 is measured every 5 nm in the wavelength range of 300 nm to 800 nm using the plastic property measuring system, and described in JIS Z-8722 from the obtained measurement values. The XYZ values were determined according to the method described above, and the yellowness (YI) was calculated according to the method described in JIS K-7105. When YI was less than 10, it was evaluated that yellowness was suppressed. The results are shown in Table 1.

<Measurement of total luminous flux>
The obtained plate-like sample was cut into a size of 60 mm wide × 80 mm long as shown in FIG. Next, the four side surfaces 611, 612, 613, and 614 were polished with a polishing machine (“Pura Beauty PB-500” manufactured by Megaro Technica Co., Ltd.) to obtain a test piece 60.
Among the four side surfaces of the test piece 60, six LEDs 62 are irradiated so that light enters only from one side 611, and the remaining side surfaces 612, 613, and 614 are black on the inside and white on the outside. A tape having a surface (reflective / light-shielding film single-sided tape 6370 manufactured by Teraoka Seisakusho Co., Ltd.) was bonded. By sticking the tape in this way, the amount of light emitted from the side surface 611 in the surface direction of both surfaces of the test piece 60 can be measured.
Next, the test piece 60 was set in a spherical photometer (model 1500, diameter 1500 mm) manufactured by Nemtech Co., Ltd., and using the SLMS software of Labsphere's Diode Array Spectrometer (Model DAS-1100 / 2100), The amount of light flux in the wavelength region of 350 to 800 nm was measured. The results are shown in Table 1.

  As shown in Table 1, the plate-like samples (light guide plates) of Examples 1 and 2 using the resin composition of the present invention are sufficiently suppressed in yellowness and excellent in light emission efficiency. Recognize. On the other hand, it can be seen that the plate-like sample (light guide plate) of Comparative Example 1 has low light emission efficiency. Moreover, it turns out that the yellowness of the plate-like sample (light guide plate) of Comparative Example 2 is not suppressed.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Light source 3 Light guide plate 4 Light diffusing plate 5 Lamp box 9 Surface light source device 11 Liquid crystal 12, 13 Transparent electrode 14, 15 Polarizing plate 20 Liquid crystal cell 30 Liquid crystal panel 50 Test piece (light guide plate)
51 Side surface of test piece (light guide plate) 60 Test piece (light guide plate)
611, 612, 613, 614 Side surface of test piece (light guide plate) 62 LED

Claims (7)

A resin composition for a light guide plate containing a transparent resin and silicone resin fine particles,
The resin composition for light-guide plates whose average light transmittance in the wavelength range of 300 nm-800 nm measured by the optical path length of 200 mm when the said resin composition is made into a molded object is 25-85%.   The resin composition according to claim 1, wherein the silicone resin fine particles are contained in a proportion of 0.1 to 200 ppm with respect to the total weight of the resin composition.   The resin composition according to claim 1 or 2, wherein the transparent resin is a methacrylic resin.   The light-guide plate comprised from the resin composition of any one of Claims 1-3.   The light-guide plate of Claim 4 used for the liquid crystal display provided with the LED light source.   A surface light source device comprising the light guide plate according to claim 4.   7. A liquid crystal display device, wherein the surface light source device according to claim 6 is disposed on the back side of the liquid crystal panel.

Images