JP4246602B2 - Light diffusion plate - Google Patents

Description

  The present invention relates to a light diffusing plate used for a backlight unit of a liquid crystal display, an electric signboard, a lighting cover, an arcade, a daylighting plate, a blindfolding plate of a balcony, and the like.

  As this type of light diffusing plate, for example, a resin layer in which 0.1 to 20 parts by weight of a light diffusing agent having an average particle diameter of 1 to 10 μm is dispersed per 100 parts by weight of the transparent resin, and an average particle per 100 parts by weight of the transparent resin. A light diffusing plate having a two-layer structure is known which comprises a resin layer in which 0.1 to 5 parts by weight of a light diffusing agent having a diameter of at least twice the particle size of the light diffusing agent and 5 to 30 μm is dispersed ( Patent Document 1).

However, this light diffusing plate has a problem that when the transparent resin is inferior in light resistance, it is quickly deteriorated by ultraviolet rays and yellowed, or the light transmittance is lowered. Moreover, since the light diffusing agent is contained in both resin layers, there is a problem that the total light transmittance is low although the haze (light diffusibility) is high.
Japanese Patent Application Laid-Open No. 7-100985

  The problem to be solved by the present invention is to provide a high-performance light diffusing plate having good light resistance, high haze, and sufficiently satisfying the total light transmittance.

In order to solve the above-described problems, a first light diffusion plate having a two-layer structure according to the present invention includes a first resin layer on the light emitting side obtained by adding a UV absorber to a light-transmitting resin, and a light-transmitting property. The light emitting side second resin layer made of resin is laminated and integrated, and the light transmitting resin of the first resin layer on the light incident side is lighter than the light transmitting resin of the second resin layer on the light emitting side. A resin having a small refractive index, a light diffusing agent is contained in the first resin layer, and an arithmetic average roughness Ra based on JIS B 0601 is formed on the light incident surface of the first resin layer and the light output surface of the second resin layer. Is formed with irregularities of 0.5 to 10 μm .

And the light diffusion plate of the second two-layer structure of the present invention includes a first resin layer on the light incident side made of a light transmissive resin containing an ultraviolet absorber, and a light emitting side made of the light transmissive resin. The second resin layer is laminated and integrated, and the light-transmitting resin of the first resin layer on the light incident side is made to have a lower refractive index than the light-transmitting resin of the second resin layer on the light emitting side. The second resin layer contains a light diffusing agent, and the arithmetic average roughness Ra based on JIS B 0601 is 0.5 to 10 μm on the light incident surface of the first resin layer and the light emitting surface of the second resin layer. This is characterized in that the unevenness is formed .

Furthermore, the light diffusion plate of the third two-layer structure of the present invention includes a first resin layer on the light incident side in which an ultraviolet absorber is contained in a translucent resin, and a light output side made of the translucent resin. The second resin layer is laminated and integrated, and the light-transmitting resin of the first resin layer on the light incident side is made to have a lower refractive index than the light-transmitting resin of the second resin layer on the light emitting side. The first resin layer and the second resin layer contain a light diffusing agent, and the light incident surface of the first resin layer and the light output surface of the second resin layer have an arithmetic average roughness Ra based on JIS B 0601. Is formed with irregularities of 0.5 to 10 μm .

In these light diffusion plates, it is desirable that the translucent resin of the first resin layer is an acrylic resin, and the translucent resin of the second resin layer is a polycarbonate resin. are those having a refractive index of 49, it is not to desired polycarbonate resin and has a refractive index of 1.58.

In the first light diffusion plate of the present invention, since the first resin layer on the light incident side contains an ultraviolet absorber, the first resin layer is used for light such as sunlight, fluorescent lamps and cold cathode tubes. When the light diffusing plate is used so as to be on the incident surface side, the ultraviolet ray is absorbed by the ultraviolet absorbent of the first resin layer, the ultraviolet ray deterioration of the light diffusing plate is suppressed, and yellowing hardly occurs. And since the light diffusing agent is contained only in the first resin layer, the content of the light diffusing agent is reduced as compared with the case where the light diffusing agent is contained in the entire light diffusing plate, and the total amount of light is reduced accordingly. While the transmittance is improved, incident light is sufficiently diffused by the light diffusing agent contained in the first resin layer, and has a high haze (haze value).

  Further, the second light diffusion plate of the present invention also contains an ultraviolet absorber in the first resin layer, so that the first resin layer is incident on light such as sunlight, a fluorescent lamp, a cold cathode tube, etc. When the light diffusing plate is used so as to be on the surface side, the ultraviolet ray is absorbed by the ultraviolet absorbent, the ultraviolet deterioration of the light diffusing plate is suppressed, and yellowing hardly occurs. And in this second light diffusing plate, since the light diffusing agent is contained only in the second resin layer, the content of the light diffusing agent as compared with the case where the light diffusing agent is contained in the entire light diffusing plate. And the total light transmittance is improved by that amount, and the incident light is sufficiently diffused by the light diffusing agent contained in the second resin layer, resulting in high haze (haze value).

Furthermore, since the third light diffusion plate of the present invention also contains an ultraviolet absorber in the first resin layer, the first resin layer is incident on light such as sunlight, fluorescent lamps and cold cathode tubes. When the light diffusing plate is used so as to be on the surface side, the ultraviolet ray is absorbed by the ultraviolet absorbent, the ultraviolet deterioration of the light diffusing plate is suppressed, and yellowing hardly occurs. In the third light diffusing plate, since the light diffusing agent is contained in the first resin layer and the second resin layer, the incident light is further diffused by the light diffusing agent contained in these resin layers. In addition, it has a higher haze (haze value).

In any of the first, second, and third light diffusion plates, the translucent resin of the first resin layer on the light incident side is the translucent resin of the second resin layer on the light exit side . is a resin refractive index is less than, since the difference in refractive index between air and the first resin layer is smaller than the difference in refractive index between air and the second resin layer, first from the air The light transmittance that is incident on and transmitted through the resin layer is greater than the light transmittance that is directly incident and transmitted from the air to the second resin layer without the first resin layer. And since the difference in the optical refractive index between the first resin layer and the second resin layer is slight, the light transmitted through the first resin layer hardly decreases its light transmittance and the second resin layer. When the layer also passes through and is emitted from the second resin layer into the air, the light transmittance decreases according to the difference in the optical refractive index between the second resin layer and air. Accordingly, the light transmittance of the entire light diffusing plate is higher than the light transmittance when light is transmitted only through the second resin layer, and the total light transmittance is improved by that much, resulting in luminance. Can be improved.

In particular, the translucent resin of the first resin layer on the light incident side is an acrylic resin having a light refractive index of 1.49 , and the translucent resin of the second resin layer on the light exit side is 1.58. The light diffusing plate, which is a polycarbonate resin having a photorefractive index, is a resin with high light transmittance, and both the resin and the acrylic resin are excellent in light resistance. The difference in optical refractive index between the resin and the acrylic resin and the polycarbonate resin is 0.09, and the difference in optical refractive index between the polycarbonate resin and the air is 0.48. Therefore, light enters the first resin layer from the air with a light transmittance of 96.1%, and transmits from the first resin layer to the second resin layer with a light transmittance of 96.0%. to be emitted 91.2% transmission into the air from the second resin layer Since, compared to the final light transmittance when the light is transmitted through only the second resin layer (90.1%), light transmittance of the entire light diffusion plate is improved. In addition, the above-mentioned numerical value of the specific light transmittance does not take into account light absorption by acrylic resin, polycarbonate resin, ultraviolet absorber or light diffusing agent, and when light is incident vertically using the Fresnel formula. A theoretical value is calculated.

In addition, any of the first, second, and third light diffusing plates of the present invention has an arithmetic average roughness based on JIS B 0601 on the light incident surface of the first resin layer and the light output surface of the second resin layer. since Ra forms irregularities 0.5~10μm is, it is possible to further improve the light diffusion properties by this unevenness.

  Hereinafter, representative embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these embodiments.

  FIG. 1 is a cross-sectional view showing an embodiment of a light diffusing plate according to the present invention.

This light diffusing plate P1 is formed by laminating a light incident side first resin layer 1 made of a light transmissive resin containing an ultraviolet absorber and a light emitting side second resin layer 2 made of a light transmissive resin. The laminated plate has an integrated two-layer structure, and the first resin layer 1 contains a light diffusing agent 3 in a uniformly dispersed state in addition to the ultraviolet absorber.

  As the translucent resin of the first resin layer 1 and the second resin layer 2, polycarbonate, polyester, polyethylene, polypropylene, polyolefin copolymer (for example, poly-4-methylpentene-1 etc.) having a high total light transmittance ), Thermoplastic resins such as polyvinyl chloride, cyclic polyolefin, acrylic resin, polystyrene, and ionomer are preferably used. The first resin layer 1 and the second resin layer 2 may use the same translucent resin or different translucent resins.

When different translucent resins are used as the translucent resins of the first and second resin layers 1 and 2, the translucent resin of the first resin layer 1 on the light incident side is the first translucent resin on the light emitting side . It is desirable to select a resin having a smaller light refractive index than the translucent resin of the second resin layer 2. If it does in this way, the difference of the light refractive index of air and the translucent resin of the 1st resin layer 1 is smaller than the difference of the optical refractive index of air and the translucent resin of the 2nd resin layer 2 Therefore, as described above, the light transmittance of the entire light diffusion plate P1 when light passes through the first resin layer 1 and the second resin layer 2 from the air and is emitted into the air on the opposite side. The light transmittance is higher than that in the case of transmitting only through the second resin plate, and the total light transmittance is improved by that amount. As a result, the luminance can be improved.

  The most suitable combination of the translucent resins of the first and second resin layers 1 and 2 is that the translucent resin of the second resin layer 2 is a polycarbonate resin, and the translucent resin of the first resin layer 1 is used. The resin is a combination of acrylic resins having a light refractive index (1.49) smaller than that of polycarbonate resin (1.58). In such a combination, as described above, both the resins are originally high light transmittance resins, and the acrylic resin is a resin excellent in light resistance. Since the difference in optical refractive index is 0.49, the optical refractive index difference between acrylic resin and polycarbonate resin is 0.09, and the optical refractive index difference between polycarbonate resin and air is 0.48, the light diffusion plate P1 The light transmittance as a whole is 91.2% (theoretical value), which is 1.1% higher than the light transmittance (90.1%) when light passes only through the second resin layer 2. The luminance can be improved.

  As the UV absorber to be contained in the first resin layer 1, conventionally known benzotriazole UV absorbers, benzophenone UV absorbers, and the like are preferably used. Also used. In particular, when the translucent resin of the first resin layer 1 is a polyester-based resin such as polycarbonate, a benzotriazole-based or benzophenone-based one having a carboxyl group, hydroxyl group, or amino group reactive group at the molecular end. And a benzotriazole-based or benzophenone-based ultraviolet absorber having an ester bond in the molecule are preferably used. When these reactive ultraviolet absorbers are used, when the light diffusing plate P1 is produced by means of two-layer extrusion molding as described later, the reactive ultraviolet absorber is in a molten state with polymer molecules of the polyester resin. Since the transesterification is carried out by ester linkage to the polymer molecule and fixed, the ultraviolet absorber does not move to the surface of the first resin layer 1 over time and scatters from the surface, and over a long period of time. There exists an advantage which can exhibit a favorable ultraviolet-ray absorption effect.

  Examples of reactive ultraviolet absorbers include 2- (2'-hydroxy-5'-carboxyphenyl) benzotriazole, 2-hydroxybenzophenone-4-oxyacetic acid having a carboxyl group at the molecular end, or 2-hydroxy-4- (2'-hydroxyethoxy) benzophenone having a hydroxyl group, 2,2 ', 4,4', 6,6'-hexahydroxybenzophenone, 2- (2 ', 4'-hydroxyphenyl) benzo Triazole, 2-hydroxy-4- (2′-hydroxyethoxy) benzotriazole, 2-hydroxy-5- (2′-hydroxyethyl) benzotriazole, or 2- (2′-hydroxy having an amino group at the molecular terminal -3'-amino-5'-t-butyl) benzotriazole or ester in the molecule 2-hydroxy-4- (2′-methacryloyloxyethoxy) benzophenone having a bond, 2,4-di-t-butylphenyl (3 ′, 5′-di-t-butyl-4′-hydroxy) benzophenone, 2 -Methyl hydroxybenzophenone-4-oxyacetate, 2- (2'-acryloyloxy-5'-methyl) benzotriazole and the like.

  Examples of the non-reactive ultraviolet absorber include 2-hydroxy-4-n-octoxybenzophenone, 2- (2-hydroxy-5-methylphenyl) benzotriazole, and 2- (2-hydroxy-5- tert-octylphenyl) benzotriazole and the like.

  The content of the ultraviolet absorber in the first resin layer 1 is not particularly limited, but in order to impart good light resistance to the light diffusion plate P1, the ultraviolet absorber is added to 100 parts by weight of the translucent resin. It is preferable to contain 1-5 weight part. When the content of the UV absorber is less than 0.1 parts by weight, the light resistance is insufficient. When the content is more than 5 parts by weight, not only the light resistance improvement effect corresponding to the content is not obtained but also the light transmittance is lowered. Inconvenience occurs.

  The ultraviolet absorber may be contained in the second resin layer 2, but it is desirable not to contain it substantially. When it contains, there exists an advantage which light resistance improves further. Further, when the ultraviolet absorber is not substantially contained, the light incident on the second resin layer 2 is released into the air without being absorbed, so that there is an advantage that the luminance (total light transmittance) is improved. is there. “Substantially not contain” means that the ratio is 0.1 parts by weight or less, preferably 0.05 parts by weight or less, with respect to 100 parts by weight of the translucent resin of the second resin layer 2.

  On the other hand, as the light diffusing agent 3 to be contained in the first resin layer 1, inorganic particles, metal oxide particles, and organic polymer particles having a light refractive index different from that of the translucent resin are used alone or in combination. . Examples of inorganic particles include glass, silica, mica, synthetic mica, calcium carbonate, magnesium carbonate, barium sulfate, talc, montmorillonite, kaolin clay, bentonite, hectorite, and metal oxide particles include titanium oxide. Particles such as zinc oxide and alumina are used, and organic polymer particles such as acrylic beads, styrene beads, and benzoquamine are used.

  The light diffusing agent 3 has a distribution average particle size of 0.1 to 100 μm, preferably 0.5 to 50 μm, more preferably 1 to 15 μm. If the particle size is smaller than 0.1 μm, the particles are easily aggregated and thus dispersibility is poor. Even if the particles can be uniformly dispersed, the light wavelength is larger and the scattering efficiency is deteriorated. Therefore, particles having a size of 0.5 μm or more, and further 1.0 μm or more are preferable. On the other hand, if the particle size is larger than 100 μm, light scattering becomes non-uniform, light transmittance is reduced, and particles are visible. Therefore, particles with a size of up to 50 μm and even up to 15 μm are preferred.

  The content of the light diffusing agent 3 in the first resin layer 1 is 0.1 to 20 parts by weight of the light diffusing agent 3 with respect to 100 parts by weight of the translucent resin in order to give an excellent light diffusing effect. It is preferable to contain. When the light diffusing agent 3 is contained in the first resin layer 1 in such a ratio in a uniform dispersion state, the average distance between the dispersed particles is reasonably short, so that the mean free path in which the incident light particles collide. Becomes shorter, a large diffusion effect can be obtained even though the content of the light diffusing agent 3 is relatively small, and a sufficient light transmittance can be maintained. When the content of the light diffusing agent 3 is less than 0.1 parts by weight, it becomes difficult to obtain a sufficient diffusion effect because the average distance between dispersed particles becomes long. The average distance between the particles is too short, and there is a disadvantage that the light transmittance decreases due to light scattering, reflection and refraction by the light diffusing agent 3.

  Although the thickness of the 1st resin layer 1 and the 2nd resin layer 2 is not specifically limited, When the 1st resin layer 1 is made to contain a ultraviolet absorber and a light-diffusion agent by the said content rate, sufficient light resistance improvement In order to obtain the effect and the light diffusion effect, the thickness of the first resin layer 1 is preferably about 0.1 to 1.5 mm. The thickness of the second resin layer 2 is preferably about 1 to 3 times that of the first resin layer 1.

  Further, as shown in FIG. 1, fine irregularities 4 are formed on the surface (lower surface) of the first resin layer 1 and the surface (upper surface) of the second resin layer 2, and the light diffusibility is further improved by the irregularities 4. It is desirable to make it. As for this unevenness | corrugation 4, arithmetic mean roughness Ra (value measured based on JISB0601) of the surface of the 1st and 2nd resin layers 1 and 2 is 0.5-10.0 micrometers, Especially 0.6- It is desirable that the irregularities be fine enough to be 8.0 μm.

  This light diffusing plate P1 can be easily manufactured by the following method, for example. That is, using a multilayer coextrusion molding machine, the above-mentioned ultraviolet absorber and light diffusing agent are uniformly contained in the above-mentioned translucent resin in the above-mentioned proportions, and the above-mentioned material for molding a resin layer, An extrudate of this two-layer structure is formed by simultaneously extruding a second resin layer molding material made of a translucent resin (sometimes containing a trace amount of an ultraviolet absorber) in two layers. The light diffusing plate P1 can be mass-produced efficiently by a method in which fine irregularities are formed on both the upper and lower surfaces by passing the film between a pair of upper and lower embossing rolls.

  The light diffusing plate P1 as described above is used by being incorporated in a backlight unit of a liquid crystal panel so that the first resin layer 1 is on the light source 5 side, for example. When the light diffusing plate P1 is incorporated in this way, the light emitted from the light source 5 behind is diffused by the unevenness 4 on the surface (lower surface) of the first resin layer 1 and is incident on the light diffusing plate P1. Is strongly diffused by the light diffusing agent 3 contained in the first resin layer 1 and further diffused by the unevenness 4 on the surface (upper surface) through the second resin layer 2 to uniformly illuminate the liquid crystal panel from behind. To do. Therefore, the luminance unevenness of the liquid crystal panel can be eliminated. In addition, since the light diffusion plate P1 contains only the first resin layer 1 with the ultraviolet absorber and the light diffusion agent 3, compared with the case where the entire light diffusion plate P1 contains the ultraviolet absorber and the light diffusion agent. In addition, the total light transmittance can be improved by the amount of the content of the light diffusing agent or the ultraviolet absorber, and the luminance can be increased. In particular, the light refractive index of the translucent resin of the first resin layer 1 is increased. If it is smaller than the light refractive index of the translucent resin of the second resin layer 2, since the light transmittance of the entire light diffusion plate P1 is improved as described above, it is possible to increase the luminance from this point as well. It becomes. And since the ultraviolet rays which are incident from behind are absorbed by the ultraviolet absorber contained in the first resin layer 1, it is possible to suppress the yellowing and deterioration of the light diffusion plate P1 due to the ultraviolet rays and to enhance the durability. .

  FIG. 2 is a cross-sectional view showing another embodiment of the light diffusing plate according to the present invention.

  This light diffusion plate P2 has a two-layer structure in which a first resin layer 1 made of a light-transmitting resin containing an ultraviolet absorber and a second resin layer 2 made of a light-transmitting resin are laminated and integrated. It is a laminated board, and the light diffusing agent 3 is contained in the second resin layer 2. When the first resin layer 1 and the second resin layer 2 have the same thickness, the content of the light diffusing agent 3 is as described above with respect to 100 parts by weight of the translucent resin. 3 is preferably contained in an amount of 1 to 20 parts by weight. However, when the second resin layer 2 is thicker than the first resin layer 1, the light diffusing agent 3 is reduced from the above content rate to 0. .1 to 10 parts by weight. Even if it reduces in this way, since the 2nd resin layer 2 is thick, the total content of the light diffusing agent 3 is hardly changed, and the transmitted light can be sufficiently diffused. On the other hand, since the first resin layer 1 does not contain the light diffusing agent 3, the thickness thereof can be reduced to 30 to 200 μm. Therefore, the thickness of the second resin layer 2 is set to 1. It can be as thick as 0.0 to 5.0 mm. When the second resin layer 2 is thus thickened, the light diffusing agent 3 contained in the second resin layer 2 repeats light scattering, reflection, and refraction many times. It is preferable that the second resin layer 2 is not substantially contained. The other configuration is the same as that of the light diffusing plate P1, and the description thereof is omitted.

  Since such a light diffusion plate P2 also contains the ultraviolet absorber in the first resin layer 1, the first resin layer 1 becomes the incident surface side of sunlight or other light from the light source 4 in the sky. When the light diffusing plate P2 is used as described above, the ultraviolet light is absorbed by the ultraviolet absorber, the deterioration of the ultraviolet light of the light diffusing plate P2 is suppressed, and yellowing hardly occurs. And since the light diffusing agent 3 is contained only in the second resin layer 2, the content of the light diffusing agent is reduced compared to the case where the light diffusing agent is contained in the entire light diffusing plate P 2. As a result, the total light transmittance is improved and incident light is sufficiently diffused by the light diffusing agent 3 contained in the second resin layer 2 and the fine irregularities 4 and 4 on both sides, and a high haze value is obtained. .

  FIG. 3 is a sectional view showing still another embodiment of the light diffusing plate according to the present invention.

  The light diffusing plate P3 has a two-layer structure in which a first resin layer 1 made of a light-transmitting resin containing an ultraviolet absorber and a second resin layer 2 made of a light-transmitting resin are laminated and integrated. It is a laminated board, and the light diffusing agent 3 is contained in both the first resin layer 1 and the second resin layer 2. As described above, when the diffusing agent 3 is contained in both the resin layers 1 and 2, the content is reduced from the content of the light diffusing agent in the first resin layer 1 described above. It is preferable to contain the light diffusing agent in the range of 0.1 to 10 parts by weight with respect to parts by weight. The content ratio of the light diffusing agent 3 may be the same for both the first resin layer 1 and the second resin layer 2, but may be different depending on the case. The other configuration is the same as that of the light diffusing plate P1, and the description thereof is omitted.

  Since such a light diffusion plate P3 also contains the ultraviolet absorber in the first resin layer 1, the first resin layer 2 is on the incident surface side of sunlight or light from another light source 4. When the light diffusing plate P3 is used as described above, the ultraviolet light is absorbed by the ultraviolet absorbent, the ultraviolet light deterioration of the light diffusing plate P3 is suppressed, and yellowing hardly occurs. And since the light-diffusion agent 3 is contained in the 1st resin layer 1 and the 2nd resin layer 2, incident light is further diffused by the light diffusion 3 contained in these resin layers and the fine unevenness | corrugation 4 of both surfaces. Higher haze is obtained.

  The light diffusing plates P1, P2, and P3 of the above embodiment have irregularities formed on both sides, but the irregularities may be formed only on one side or may not be formed on both sides.

  Next, specific examples and comparative examples of the present invention will be described.

  As a first resin layer molding material, polycarbonate resin [PC-1250 manufactured by Teijin Kasei Co., Ltd.] 100 parts by weight, infusible acrylic polymer fine particles [Rohm and Haas Company as a light diffusing agent] 1 part by weight of EXL-5136 manufactured, weight distribution average particle size 7 μm] and 0.3 part by weight of UV absorber [LA-31 manufactured by Asahi Denka Co., Ltd.] were prepared. On the other hand, 100 parts by weight of a polycarbonate resin (PC-1250 manufactured by Teijin Chemicals Ltd.) was prepared as a second resin layer molding material.

  Using a multi-layer coextrusion molding machine, the cylinder temperature is 240 to 260 ° C., the die temperature is 260 ° C., the degree of vacuum of the vent is maintained at 200 mmHg, and the first resin layer and the second resin layer thickness are both 1 mm. By adjusting the discharge amount of the first resin layer molding material and the second resin layer molding material, coextrusion molding into upper and lower two layers is performed so that the total thickness is 2 mm. A diffusion plate was produced.

  About the obtained light diffusing plate, the total light transmittance, haze, and light resistance (yellowing degree) were measured, and the results are shown in Table 1 below. The total light transmittance and haze are measured by a light transmittance measuring device [NDH2000 manufactured by Nippon Denshoku Co., Ltd.], and the light resistance (yellowing degree) is measured by a fade meter [Suga Test Instruments ( The yellowness after the lapse of 500 hours was measured by FAL-5H-B manufactured by Co., Ltd., and the yellowing degree was determined by comparison with the initial yellowness.

  As a first resin layer molding material, 100 parts by weight of polycarbonate resin [PC-1250 manufactured by Teijin Chemicals Ltd.] and 0.3 part by weight of UV absorber [LA-31 manufactured by Asahi Denka Co., Ltd.] are mixed. I prepared what I did. On the other hand, as a second resin layer molding material, 100 parts by weight of a polycarbonate resin [PC-1250 manufactured by Teijin Chemicals Ltd.] and infusible acrylic polymer fine particles [Rohm and Haas; A mixture of 1 part by weight of EXL-5136 manufactured by Company and a weight distribution average particle size of 7 μm was prepared. Then, in the same manner as in Example 1, these materials were coextruded into two upper and lower layers to produce a light diffusion plate having a total thickness of 2 mm.

  About the obtained light diffusing plate, the total light transmittance, haze, and light resistance (yellowing degree) were measured in the same manner as in Example 1. The results are shown in Table 1 below.

  As a first resin layer molding material, 100 parts by weight of a polycarbonate resin (PC-1250 manufactured by Teijin Limited) and infusible acrylic polymer fine particles (manufactured by Rohm and Haas Company) as a light diffusing agent A mixture of 0.5 part by weight of EXL-5136, weight distribution average particle size 7 μm) and 0.3 part by weight of an ultraviolet absorber [LA-31 manufactured by Asahi Denka Co., Ltd.] was prepared. On the other hand, as the second resin layer molding material, 100 parts by weight of polycarbonate resin [PC-1250 manufactured by Teijin Ltd.] and 0.5 weight of the above infusible acrylic polymer fine particles as a light diffusing agent are used. A partial mixture was prepared. Then, in the same manner as in Example 1, these materials were coextruded into two upper and lower layers to produce a light diffusion plate having a total thickness of 2 mm.

  About the obtained light diffusing plate, the total light transmittance, haze, and weather resistance (yellowing degree) were measured in the same manner as in Example 1, and the results are shown in Table 1 below.

[Comparative Example 1]
As the first resin layer molding material and the second resin layer molding material, 100 parts by weight of the polycarbonate resin used in Example 1, and the infusible acrylic polymer used in Example 1 as a light diffusing agent A mixture of 0.5 part by weight of fine particles was prepared. Then, in the same manner as in Example 1, these materials were coextruded into two upper and lower layers to produce a light diffusion plate having a total thickness of 2 mm.

  About the obtained light diffusing plate, the total light transmittance, haze, and light resistance (yellowing degree) were measured in the same manner as in Example 1. The results are shown in Table 1 below.

[Comparative Example 2]
As the first resin layer molding material and the second resin layer molding material, 100 parts by weight of the polycarbonate resin used in Example 1, and the infusible acrylic polymer used in Example 1 as a light diffusing agent What mixed 1 weight part of microparticles | fine-particles was prepared. On the other hand, 100 parts by weight of the polycarbonate resin used in Example 1 was prepared as the second resin layer molding material. Then, in the same manner as in Example 1, these materials were coextruded into two upper and lower layers to produce a light diffusion plate having a total thickness of 2 mm.

  About the obtained light diffusing plate, the total light transmittance, haze, and light resistance (yellowing degree) were measured in the same manner as in Example 1. The results are shown in Table 1 below.

  As a first resin layer molding material, 100 parts by weight of acrylic resin [Acrypet V manufactured by Mitsubishi Rayon Co., Ltd.] and 0.3 part by weight of an ultraviolet absorber [LA-31 manufactured by Asahi Denka Co., Ltd.] were mixed. I prepared something. On the other hand, as a second resin layer molding material, 100 parts by weight of a polycarbonate resin (PC-1250 manufactured by Teijin Chemicals Ltd.) and an infusible acrylic polymer fine particle [Rohm and Haas; A mixture of 1 part by weight of EXL-5136 manufactured by Company and a weight distribution average particle size of 7 μm was prepared.

  Using a multi-layer coextrusion molding machine, the cylinder temperature is 240 to 260 ° C., the die temperature is 260 ° C., the vacuum degree of the vent portion is maintained at 200 mmHg, and the first resin layer and the second resin layer thickness are 0 respectively. By coextrusion molding into upper and lower two layers while adjusting the discharge amount of the first resin layer molding material and the second resin layer molding material so as to be 3 mm and 1.7 mm, A light diffusing plate having a thickness of 2 mm was produced.

  About the obtained light diffusing plate, the total light transmittance, haze, and light resistance (yellowing degree) were measured in the same manner as in Example 1. The results are shown in Table 2 below.

  As a first resin layer molding material, 100 parts by weight of polycarbonate resin [PC-1250 manufactured by Teijin Chemicals Ltd.] and 0.3 part by weight of UV absorber [LA-31 manufactured by Asahi Denka Co., Ltd.] are mixed. I prepared what I did. On the other hand, as a second resin layer molding material, 100 parts by weight of polycarbonate resin (PC-1250 manufactured by Teijin Chemicals Ltd.) and infusible acrylic polymer fine particles [Rohm and Haas as a light diffusing agent] -One part by weight of EXL-5136 manufactured by Company, and a weight distribution average particle size of 7 μm] was prepared.

  Using a multi-layer coextrusion molding machine, the cylinder temperature is 240 to 260 ° C., the die temperature is 260 ° C., the vacuum degree of the vent portion is maintained at 200 mmHg, and the first resin layer thickness and the second resin layer thickness are each 0.00. By coextrusion molding into upper and lower two layers while adjusting the discharge amount of the first resin layer molding material and the second resin layer molding material so as to be 3 mm and 1.7 mm, A light diffusion plate having a length of 2 mm was produced.

  About the obtained light diffusing plate, the total light transmittance, haze, and light resistance (yellowing degree) were measured in the same manner as in Example 1. The results are shown in Table 2 below.

  Referring to Table 1, the light diffusing plates of Examples 1 to 3 containing 0.3 part by weight of the ultraviolet absorber in the first resin layer were comparative examples 1 and 1 containing no ultraviolet absorber in the first resin layer. Compared with the light diffusing plate of 2, the yellowing degree is reduced to 1/3 or less, and it can be seen that the light resistance is remarkably improved. Moreover, since the light diffusing plate of Examples 1 to 3 and the light diffusing plate of Comparative Examples 1 and 2 have the same total content of the light diffusing agent of 1 part by weight, substantially the same haze (92.5 However, the light diffusing plates of Examples 1 and 2 and Comparative Example 2 in which the light diffusing agent is contained in either the first or second resin layer have the light diffusing agent as the first. And compared with the light diffusing plate of Example 3 and Comparative Example 1 contained in both of the second resin layer, the total light transmittance is improved by about 2 to 3%. It can be seen that inclusion of either one of the resin layers at a high concentration is advantageous in increasing the total light transmittance. Further, as can be seen from the comparison between the light diffusing plate of Examples 1 and 2 and the light diffusing plate of Comparative Example 2, and the light diffusing plate of Example 3 and the light diffusing plate of Comparative Example 1 are compared, 0.3 wt. Even when about 1 part of the ultraviolet absorber is contained in the first resin layer, there is almost no possibility of causing a decrease in the total light transmittance.

  Further, when looking at Table 2, the light diffusion plate of Example 4 in which the first resin layer is an acrylic resin having a refractive index smaller than that of the polycarbonate of the second resin layer, the first and second resin layers are both Compared with the light diffusing plate of Example 5 which is polycarbonate, the total light transmittance is improved by about 1%. Therefore, the resin of the first resin layer on which light is incident is refracted from the second resin layer. It can be seen that the use of a resin having a low rate is advantageous in increasing the total light transmittance. Further, the thickness of the first resin layer containing the ultraviolet absorber in the same concentration as the light diffusion plate of Example 5 in Table 2 is as thin as 0.3 mm. Compared with the light diffusion of Example 2 of Table 1 which is as thick as 1 mm, the yellowing degree is the same value as 0.5, although the total light transmittance is improved by about 6%. Thus, it can be seen that it is effective to thinly form the first resin layer containing the ultraviolet absorber in order to improve the total light transmittance while maintaining the equivalent light resistance.

It is sectional drawing which shows one Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows other embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows other embodiment of the light diffusing plate which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st resin layer 2 2nd resin layer 3 Light diffusing agent 4 Fine unevenness 5 Light source

Claims (5)

A first resin layer on the light incident side made of a light transmissive resin containing an ultraviolet absorber and a second resin layer on the light output side made of a light transmissive resin are laminated and integrated, and the first light layer on the light incident side is integrated. The light-transmitting resin of one resin layer is a resin having a lower refractive index than the light-transmitting resin of the second resin layer on the light exit side, and the first resin layer contains a light diffusing agent , Light diffusion of a two-layer structure characterized by forming irregularities having an arithmetic average roughness Ra of 0.5 to 10 μm based on JIS B 0601 on the light incident surface of the resin layer and the light emitting surface of the second resin layer Board. A first resin layer on the light incident side made of a light transmissive resin containing an ultraviolet absorber and a second resin layer on the light output side made of a light transmissive resin are laminated and integrated, and the first light layer on the light incident side is integrated. The light-transmitting resin of one resin layer is a resin having a lower refractive index than the light-transmitting resin of the second resin layer on the light exit side, and a light diffusing agent is contained in the second resin layer . Light diffusion of a two-layer structure characterized by forming irregularities having an arithmetic average roughness Ra of 0.5 to 10 μm based on JIS B 0601 on the light incident surface of the resin layer and the light emitting surface of the second resin layer Board. A first resin layer on the light incident side made of a light transmissive resin containing an ultraviolet absorber and a second resin layer on the light output side made of a light transmissive resin are laminated and integrated, and the first light layer on the light incident side is integrated. The light-transmitting resin of one resin layer is a resin having a lower refractive index than the light-transmitting resin of the second resin layer on the light exit side, and a light diffusing agent is applied to the first resin layer and the second resin layer. And an unevenness having an arithmetic average roughness Ra of 0.5 to 10 μm based on JIS B 0601 is formed on the light incident surface of the first resin layer and the light emitting surface of the second resin layer. Light diffusion plate with a two-layer structure. 4. The light according to claim 1, wherein the translucent resin of the first resin layer is an acrylic resin, and the translucent resin of the second resin layer is a polycarbonate resin. Diffusion plate. The light diffusing plate according to claim 4, wherein the acrylic resin has a light refractive index of 1.49, and the polycarbonate resin has a light refractive index of 1.58.

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