JP5785046B2 - Styrenic resin composition for light guide and light guide - Google Patents

Description

  The present invention relates to a styrenic resin composition for a light guide and a light guide formed from the composition. More specifically, the present invention relates to a technique for improving optical characteristics in a styrenic resin composition for a light guide.

  The light guide, for example, diffuses light incident from the end face and emits it from the surface, and is capable of surface light emission. Therefore, the light guide is used in backlights of display devices, lighting fixtures, and the like. As a material for forming such a light guide, acrylic resin such as polymethyl methacrylate is used because of its high visible light transmittance (see, for example, Patent Documents 1 and 2).

  In recent years, with the reduction in thickness and size of display devices, the light guide is also required to have improved heat resistance and moldability. Therefore, conventionally, a light guide body that has improved heat resistance by using a polycarbonate resin has been proposed (see, for example, Patent Documents 3 and 4). It has also been proposed to use a styrenic resin that is superior in heat resistance and moisture resistance as compared to an acrylic resin and cheaper than an acrylic resin or a polycarbonate resin as a light guide material (for example, Patent Documents). 5 and 6).

Japanese Patent Laid-Open No. 10-265530 JP 2006-298966 A JP 2008-0514141 A JP 2010-037380 A JP 2007-106991 A JP 2007-204535 A

  However, the above-described conventional resin materials for light guides have the following problems. That is, the light guide using acrylic resin has problems such as low heat resistance and high hygroscopicity. These problems can be improved to some extent by using a polycarbonate resin or a styrene resin, but for example, when a polycarbonate resin is used, the heat resistance can be improved, but it is necessary to perform molding at a high temperature. Further, there is a problem in terms of hygroscopicity, and the dimensional stability is inferior. In addition, since the techniques described in Patent Documents 5 and 6 use acrylonitrile-styrene resin, there is a problem that the resin is easily colored yellow, and a problem that an expensive material such as organic crosslinked fine particles is required to be added. There is a point.

  Therefore, the main object of the present invention is to provide a styrenic resin composition from which a high-intensity light guide capable of uniform surface emission can be obtained.

The styrenic resin composition for a light guide according to the present invention contains methyl methacrylate-styrene copolymer resin as a main component, and contains 75 to 140 ppb of a blue dye with respect to the total mass of the resin component.
In this styrene resin composition, an anthraquinone compound may be added as a blue dye.
Further, the luminance can be 90 to 95% of the state where no blue dye is added, and the chromaticity variation can be 0.004 or less.

The light guide according to the present invention is formed by the styrene resin composition described above.
In this light guide, when a light source is arranged at one end and the chromaticity is measured at any two points, the chromaticity ya when the distance from the light source is _a and the distance from the light source is b The difference (Δy = y _a −y _b , where a> b) from the chromaticity y _{b at the} time can be set to 0 to 0.004.

  According to the present invention, since the unevenness of the light emitting surface is reduced while minimizing the decrease in luminance, it is possible to realize a high-intensity light guide that can uniformly emit light.

In the Example of this invention, it is a side view which shows typically the structure of the planar light source used for evaluation. It is a figure which shows the measurement position of a brightness | luminance and chromaticity.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

(First embodiment)
First, the styrene resin composition according to the first embodiment of the present invention will be described. The styrenic resin composition of the present embodiment is a light guide material, containing methyl methacrylate-styrene copolymer resin as a main component, and containing 75 to 140 ppb of a blue dye with respect to the total mass of the resin component.

[Methyl methacrylate-styrene copolymer resin]
The methyl methacrylate-styrene copolymer resin, which is the main component of the styrene-based resin composition of the present embodiment, is a copolymer of styrene and methyl methacrylate, and has excellent transparency, moisture absorption resistance and heat resistance, and is suitable for optical applications. It is a suitable resin material. The proportion of each monomer in the methyl methacrylate-styrene copolymer resin is not particularly limited, but from the viewpoint of water absorption and moldability, the styrene content is preferably 10 to 70% by mass, more Preferably it is 40-60 mass%.

[Other resin components]
In the styrene resin composition of the present embodiment, in addition to the above-mentioned methyl methacrylate-styrene copolymer resin, a styrene-maleic anhydride copolymer resin, a styrene-methyl methacrylate-maleic anhydride copolymer resin, as a resin component, Styrene-methyl methacrylate-N-phenylmaleimide copolymer resin, styrene-maleic anhydride-N-phenylmaleimide copolymer resin, and the like may be blended.

[Blue dye: 75-140 ppb]
Various resin compositions may be blended with a bluing agent in order to adjust the color tone when formed into a molded product, in particular to suppress yellowness. In the styrene-based composition of this embodiment, the chromaticity In order to suppress the dispersion of the blue dye, a blue dye is added.

  However, when the addition amount of the blue dye is less than 75 ppb with respect to the total mass of the resin component, variation in chromaticity cannot be sufficiently suppressed. On the other hand, when a blue dye is added in excess of 140 ppb with respect to the total mass of the resin component, the bluish color increases and the luminance decreases, and the optical properties when used as a light guide become insufficient. Therefore, in the styrene resin composition of the present embodiment, the blue dye is added in the range of 75 to 140 ppb with respect to the total mass of the resin component.

  Here, the blue dye added to the styrenic resin composition of the present embodiment is not particularly limited, and for example, anthraquinone compounds, naphthoquinone compounds, triarylmethane compounds, and the like can be used. . In addition, these dyes may be used alone or in combination. Among the blue dyes described above, anthraquinone compounds are particularly preferable from the viewpoints of dispersibility and availability.

[Other ingredients]
In addition to the components described above, the styrene-based resin composition of the present embodiment includes an antioxidant, a weathering agent, a lubricant, a plasticizer, and an antistatic electricity as long as the effects described above are not impaired. Various additives such as agents, mineral oils, and flame retardants may be added.

  In the styrene-based resin composition of the present embodiment, since a specific amount of blue dye is added, variation in chromaticity can be suppressed without reducing luminance. Thereby, it is 90-95% of the state which does not add blue dye, and the dispersion | distribution of chromaticity can implement | achieve the styrene resin composition for light guides of 0.004 or less by this.

(Second Embodiment)
Next, a light guide according to a second embodiment of the present invention will be described. The light guide of the present embodiment is obtained by molding the styrene resin composition of the first embodiment described above. The molding method is not particularly limited, and various molding methods such as injection molding, extrusion molding, compression molding, and vacuum molding can be applied. From the viewpoint of shape stability, injection molding is preferable. is there.

Since the light guide of this embodiment is formed of a styrene-based resin composition containing a specific amount of a blue dye, the chromaticity difference (Δy) on the light emitting surface is maintained while maintaining the same level of brightness as a conventional product. Can be small. Specifically, when a light source is arranged at one end and the chromaticity is measured at any two points, the chromaticity ya when the distance from the light source is _a and the distance from the light source is b The difference (Δy = y _a −y _b , where a> b.) From the chromaticity y _b of can be in the range of 0 to 0.004. Moreover, the brightness | luminance fall by addition of a blue dye can be suppressed to 10% or less.

  Thereby, it is possible to realize a high-intensity light guide that is excellent in heat resistance and moisture absorption resistance and capable of emitting light uniformly.

  Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention. In this example, a plurality of styrene-based resin compositions were prepared by changing the content of the blue dye, and the optical characteristics (luminance / chromaticity) of the light guide were evaluated.

  Specifically, a predetermined amount of anthraquinone blue dye (Diaresin Blue-J, manufactured by Mitsubishi Chemical Corporation) is added to methyl methacrylate-styrene copolymer resin (styrene 53 mass%, methyl methacrylate 47 mass%, molecular weight 160,000). The extruded product was extruded at 220 ° C. by an extruder (F40, manufactured by Ikegai Co., Ltd.) to produce pellets of styrene resin compositions of Examples 1 to 3 and Comparative Examples 1 to 4.

  Subsequently, each of the resin composition pellets of Examples, Comparative Examples, and Conventional Examples was molded at 230 ° C. with an injection molding machine (J140AD-180H, manufactured by Nippon Steel Works, Ltd.) having a length of 127 mm, a width of 127 mm, and a thickness of 4 mm. Each plate molded body was obtained. Next, each molded body was cut to have a length of 115 mm, a width of 85 mm, and a thickness of 4 mm, and then the end surface was polished. Furthermore, a circular dot pattern was printed on one surface of the obtained cutting body so that the area increased as the distance from the surface on which the incident light source was installed at the time of evaluation, and a light guide was obtained.

  For comparison, a light guide of a conventional example was prepared in the same manner using methyl methacrylate-styrene copolymer resin (TX-800LF manufactured by Denki Kagaku Kogyo Co., Ltd.) to which no blue dye was added.

  Evaluation of each light guide in Examples, Comparative Examples, and Conventional Examples was performed by the following method. FIG. 1 is a side view schematically showing a configuration of a planar light source used for evaluation. FIG. 2 is a diagram showing measurement positions of luminance and chromaticity. First, as shown in FIG. 1, a white LED (Light Emitting Diode) is arranged as a light source 2 on the small side of the dot pattern for each light guide 1 produced by the method described above. Further, the reflection sheets 3 and 4 are disposed on the surface side on which the dot pattern of each light guide 1 is printed and the end surface side on which the light source 2 is not disposed, and the diffusion sheet 5 is disposed on the surface side on which the dot pattern is not printed. Was used as a planar light source for evaluation.

  And all the white LED which is the light source 2 was lighted, and the brightness | luminance and chromaticity in the normal line direction of 3 in-plane totals of a planar light source were measured with the luminance meter (BM-7 by Topcon Corporation). At that time, the distance between the luminance meter and the planar light source was 1 m, and the viewing angle of the luminance meter was 1 °. Further, as shown in FIG. 2, the measurement point was at the center in the width direction and at a distance of 29 mm, 58 mm, and 86 mm from the light source 2.

“Chromaticity difference (Δy)” was determined as a difference (y _{86 mm−} y _{29 mm} ) between chromaticity y ₈₆ mm at a point having a distance of 86 mm from light source 2 and chromaticity y ₂₉ mm at a point having a distance of 29 mm. The “luminance ratio (%)” is the average luminance of the luminance values measured at the three points shown in FIG. 2 and expressed as (average luminance of the light guides of Examples and Comparative Examples) / (blue dye The average brightness of the conventional light guide without addition) × 100 was calculated. These results are summarized in Table 1 below.

  As shown in Table 1 above, the light guides of Examples 1 to 3 to which the blue dye was added within the scope of the present invention had a small chromaticity difference Δy and a high luminance ratio. In contrast, the light guides of Comparative Examples 1 and 2 in which the amount of blue dye added was less than the range of the present invention had a large chromaticity difference Δy. In addition, the light guides of Comparative Examples 3 and 4 in which the amount of blue dye added exceeded the range of the present invention was colored blue and the luminance ratio was greatly reduced.

  From the above results, it was confirmed that by using the styrenic resin composition of the present invention, a high-intensity light guide capable of uniform surface emission can be obtained.

DESCRIPTION OF SYMBOLS 1 Light guide 2 Light source 3, 4 Reflection sheet 5 Diffusion sheet

Claims (3)

Mainly methyl methacrylate-styrene copolymer resin,
A styrenic resin composition for a light guide containing 75 to 140 ppb of a blue dye with respect to the total mass of the resin component.   The styrenic resin composition for a light guide according to claim 1, wherein an anthraquinone compound is added as a blue dye. Claim 1 or 2 styrenic resin composition lightguide obtained by molding according to.

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