JP4832496B2 - Backlight unit - Google Patents

Description

  The present invention relates to a backlight unit incorporated in a liquid crystal display or the like.

  As a light diffusing plate used for a backlight unit or the like, 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 the transparent resin 100 A light diffusing plate having a two-layer structure comprising a resin layer in which 0.1 to 5 parts by weight of a light diffusing agent having an average particle size per part by weight of 2 or more of the light diffusing agent particle size and 5 to 30 μm is dispersed. It is known (see Patent Document 1).

However, in a backlight unit using this light diffusion plate, if the transparent resin of the light diffusion plate is inferior in light resistance, it will deteriorate early due to ultraviolet rays irradiated from the cold cathode tube of the backlight, etc. There is a problem that the luminance is lowered because the light transmittance is changed or the light transmittance is lowered. In addition, the light refractive index of both resin layers is not taken into consideration, and both resin layers contain a light diffusing agent. Therefore, although the haze (light diffusibility) is high, the total light transmittance is low. There was also a problem that the luminance was lowered.
Japanese Patent Application Laid-Open No. 7-100985

  The present invention has been made under the above circumstances, and the problem to be solved is that the light diffusion plate to be incorporated has good light resistance, high haze, and can fully satisfy the total light transmittance. An object of the present invention is to provide a backlight unit that is high in luminance and hardly causes uneven luminance.

To solve the above problems, Ba click light unit of the present invention,
A first resin layer made of a translucent resin containing an ultraviolet absorber and a second resin layer made of a translucent resin are laminated and integrated, and the translucent resin of the first resin layer is integrated into the second translucent resin. A light diffusing plate having a light refractive index smaller than that of the translucent resin of the first resin layer, the translucent resin of the first resin layer being an acrylic resin, and the translucent resin of the second resin layer. The light resin is a polycarbonate resin, and a light diffusing plate having a two-layer structure in which a light diffusing agent is contained in at least the second resin layer ;
A direct light source disposed on the first resin layer side of the light diffusion plate;
It is characterized by including.

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In these backlight unit, which A acrylic resin has a refractive index of 1.49, it is desirable that the polycarbonate resin is one having a refractive index of 1.58. Further, it is desirable to form irregularities having an arithmetic average roughness Ra of 0.5 to 10 μm based on JIS B 0601 on at least one of the light incident surface of the first resin layer and the light output surface of the second resin layer. .

Ba click light unit of the present invention, since the light from the light source is made to contain an ultraviolet absorber in the first resin layer of the light diffusion plate incident, the ultraviolet absorber of the first resin layer, the incident light The ultraviolet rays contained in the light are absorbed, ultraviolet deterioration and yellowing of the light diffusing plate are suppressed, and durability is improved. And since the light diffusing agent is contained in at least the second resin layer , the incident light is sufficiently diffused by this light diffusing agent to increase the haze (haze value), the brightness is high, and the brightness unevenness occurs. Difficult and durable backlight unit is obtained.

Moreover, the backlight unit, light-transmissive resin of the first resin layer on the light incident side, light having a smaller refractive index than the polycarbonate resin is a translucent resin for the light emitting side second resin layer Acrylic Since the difference in the optical refractive index between the air and the first resin layer is smaller than the difference in the optical refractive index between the air and the second resin layer, from the air to the first resin layer The light transmittance that is incident and transmitted is larger 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. Therefore, the light transmittance of the two-layered light diffusion plate as a whole is higher than the light transmittance when light is transmitted only through the second resin layer, and the total light transmittance is further improved accordingly. Therefore, the backlight unit using the light diffusion plate having the two-layer structure is a high-performance unit with extremely high luminance.

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In particular, in the above-mentioned bar click light unit is an acrylic resin translucent resin of the first resin layer on the light incident side has a refractive index of 1.49, the light emission side second resin layer permeable In the case of using a light diffusing plate whose optical resin is a polycarbonate resin having a light refractive index of 1.58, both resins are originally resins with high light transmittance, and acrylic resin has excellent light resistance. In addition to being a resin, the difference in optical refractive index between air and acrylic resin is 0.49, the difference in optical refractive index between acrylic resin and polycarbonate resin is 0.09, and polycarbonate resin and air Is 0.48, so that light is incident on the first resin layer from the air with a light transmittance of 96.1%, and 96 from the first resin layer to the second resin layer. Transmits with a light transmittance of 0% and finally the second resin Is emitted from the light into the air at a transmittance of 91.2%, so that the light transmittance is 90.1% when compared with the final light transmittance (90.1%) in the case where light is transmitted only through the second resin layer. The light transmittance of the entire diffusing plate is improved by 1.1%, and the luminance is increased by that amount, thereby improving the performance of the backlight unit. 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 the above-described server click light unit, the light emitting surface of the light diffusion plate first light incident surface of the resin layer and second resin layer, the arithmetic average roughness Ra based on JIS B 0601 is 0.5 In the case where the unevenness of 10 μm is formed, the unevenness of brightness can be sufficiently prevented by further improving the light diffusibility by the unevenness.

Hereinafter, representative embodiments and reference 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 a reference form of a backlight unit according to the present invention.

  As shown in FIG. 1, the backlight unit includes a light diffusing plate P1, a plurality of light sources 5, and a light reflecting plate 5a of each light source. The light diffusing plate P1 is a light having a two-layer structure in which a first resin layer 1 made of a light transmissive resin containing an ultraviolet absorber and a second resin layer 2 made of a light transmissive resin are laminated and integrated. The light transmitting resin of the first resin layer 1 is a resin having a light refractive index smaller than that of the light transmitting resin of the second resin layer 2. In addition to the ultraviolet absorber, the light diffusing agent 3 is also contained in a uniformly dispersed state. Each light source 5 is disposed on the first resin layer 1 side (lower side in FIG. 1) of the light diffusion plate P1, and each light reflection plate 5a is on the opposite side of the light diffusion plate P1 of each light source 5. It is arranged.

  As the translucent resin of the first resin layer 1 and the second resin layer 2 of the light diffusion plate P1, polycarbonate, polyester, polyethylene, polypropylene, polyolefin copolymer (for example, poly-4- A thermoplastic resin such as methylpentene-1), polyvinyl chloride, cyclic polyolefin, acrylic resin, polystyrene, ionomer or the like is preferably used, but the translucent resin of the first resin layer 1 on the light incident side is It is necessary to select a resin having a light refractive index smaller than that of the translucent resin of the second resin layer 2 on the light emitting side. 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. Since the light transmittance is higher than that when only the second resin layer 2 is transmitted, and the total light transmittance is improved by that amount, a backlight unit having high luminance can be obtained. .

  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 is transmitted through only the second resin layer 2. 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.

  Although content of the ultraviolet absorber in the 1st resin layer 1 is not specifically limited, In order to provide favorable light resistance to the light diffusing plate P1, an ultraviolet absorber is 0 with respect to 100 mass parts of translucent resin. It is preferable to contain 1-5 mass parts. When the content of the UV absorber is less than 0.1 parts by mass, the light resistance is insufficient. When the content is more than 5 parts by mass, not only the light resistance improvement effect corresponding to the content is not obtained but also the light transmission 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. On the other hand, when the ultraviolet absorber is not substantially contained in the second resin layer 2, the light incident on the second resin layer 2 from the first resin layer 1 is released into the air without being absorbed. Therefore, there is an advantage that the luminance (total light transmittance) is improved. Note that “substantially not contain” means that the ultraviolet absorbent is 0.1 parts by mass or less, preferably 0.05 parts by mass or less with respect to 100 parts by mass of the translucent resin of the second resin layer 2. Say that.

  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 mass of the light diffusing agent 3 with respect to 100 parts by mass 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 mass, 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.

  The light diffusing plate P1 as described above can be easily manufactured, for example, by the following method. 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.

On the other hand, the light source 5 can be any known light source used in a conventional backlight unit, such as a straight or U-shaped cold cathode tube, and the light reflecting plate 5a is also an aluminum plate or white. All known light reflecting plates used in conventional backlight units, such as resin plates, can be used. The light source 5 is a direct light source arranged in a predetermined number on the first resin layer 1 side of the light diffusing plate P1 with an appropriate mutual space where luminance unevenness does not occur and a space to the light diffusing plate P1. Yes , and supported and fixed to a rear case (not shown) of the backlight unit by a support tool (not shown).

  The backlight unit configured as described above is incorporated behind the liquid crystal panel of the liquid crystal display. When the power source for the light source is turned on, the light emitted from the light source 5 is diffused by the irregularities 4 on the surface (lower surface) of the first resin layer 1 and enters the light diffusion plate P1, and the incident light is the first light. Strongly diffused by the light diffusing agent 3 contained in the resin layer 1 and further diffused by the irregularities 4 on the surface (upper surface) through the second resin layer 2 to uniformly illuminate the liquid crystal panel from behind, The brightness unevenness of the liquid crystal panel can be eliminated. In addition, the backlight unit contains the ultraviolet absorber and the light diffusing agent in the entire light diffusing plate P1 by containing the ultraviolet absorber and the light diffusing agent 3 only in the first resin layer 1 of the light diffusing plate P1. By improving the total light transmittance as compared with the case of making the resin, the light-transmitting resin of the first resin layer 1 is a resin having a smaller light refractive index than the light-transmitting resin of the second resin layer 2, As described above, since the light transmittance of the entire light diffusion plate P1 is further improved, the brightness is extremely high. And since the ultraviolet-ray which injects from the light source 5 with the ultraviolet absorber contained in the 1st resin layer 1 is absorbed, and yellowing and deterioration of the light-diffusion board P1 are suppressed, durability is also favorable.

Figure 2 is a sectional view showing the implementation form of the backlight unit according to the present invention.

In this backlight unit, the configuration of the light diffusion plate P2 is different from the light diffusion plate P1 of the reference embodiment . That is, the light diffusing plate P2 of the backlight unit is composed of the first resin layer 1 in which the ultraviolet absorbing agent is contained in the translucent resin and the translucent resin, like the light diffusing plate P1. Light having a two-layer structure in which the second resin layer 2 is laminated and integrated, and the light-transmitting resin of the first resin layer 1 is a resin having a lower refractive index than the light-transmitting resin of the second resin layer 2. Although it is a diffusing plate, it is different from the light diffusing plate P1 in that the light diffusing agent 3 is not contained in the first resin layer 1 and is contained in the second resin layer 2 in a uniform dispersed state. Yes.

  When the first resin layer 1 and the second resin layer 2 have the same thickness, the content of the light diffusing agent 3 in the second resin layer 2 is 100 mass of the translucent resin as described above. Although it is preferable to contain 1-20 mass parts of light diffusing agents 3 with respect to a part, when the 2nd resin layer 2 is thicker than the 1st resin layer 1, light diffusing agent 3 is more than said content. The amount is preferably 0.1 to 10 parts by mass. 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.

Since the other structure of this backlight unit is the same as that of the backlight unit of the reference embodiment , the same members are assigned the same reference numerals in FIG.

  In this backlight unit, the light emitted from the light source 5 is diffused by the unevenness 4 on the surface (lower surface) of the first resin layer 1 of the light diffusion plate P2, and enters the first resin layer 1, and the second Since it is strongly diffused by the light diffusing agent 3 when passing through the resin layer 2 and further diffused by the unevenness 4 on the surface (upper surface) of the second resin layer 2, the liquid crystal panel is illuminated uniformly from the back. Brightness unevenness can be eliminated. In addition, the backlight unit includes the light diffusing agent 3 only in the second resin layer 2 of the light diffusing plate P2, so that the total light transmittance is higher than the case where the entire light diffusing plate P2 contains the light diffusing agent. In addition, the light transmissive resin of the first resin layer 1 is made a resin having a light refractive index smaller than that of the light transmissive resin of the second resin layer 2, so that the light transmission of the entire light diffusion plate P2 is achieved. Since the rate is further improved, the brightness is extremely high. Then, ultraviolet rays incident on the first resin layer 1 from the light source 5 are absorbed by the ultraviolet absorber contained in the first resin layer 1 of the light diffusion plate P2, and ultraviolet deterioration and yellowing of the light diffusion plate P2 are suppressed. Therefore, durability is also good.

FIG. 3 is a sectional view showing another embodiment of the backlight unit according to the present invention.

In this backlight unit, the configuration of the light diffusion plate P3 is different from the light diffusion plate P1 of the reference embodiment . That is, the light diffusing plate P3 of the backlight unit is composed of the first resin layer 1 made of a light transmissive resin containing an ultraviolet absorber and the light transmissive resin, like the light diffusing plate P1. Light having a two-layer structure in which the second resin layer 2 is laminated and integrated, and the light-transmitting resin of the first resin layer 1 is a resin having a lower refractive index than the light-transmitting resin of the second resin layer 2. Although it is a diffusion plate, it is different from the light diffusion plate P1 in that the light diffusing agent 3 is contained in the first resin layer 1 and the second resin layer 2 in a uniformly dispersed state.

  When the diffusing agent 3 is contained in both the resin layers 1 and 2 of the light diffusing plate P3 as in this backlight unit, the content of the light diffusing agent in the first resin layer 1 described above. It is preferable to contain less than (0.1-20 mass parts), and to contain a light-diffusion agent in the range of 0.1-10 mass parts with respect to 100 mass parts of translucent resin. The content 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.

Other configurations of the backlight unit is the same as the backlight unit of the reference embodiment, and the description thereof is omitted here denoted by the same reference numerals to the same members in FIG.

  In this backlight unit, the light emitted from the light source 5 is diffused by the unevenness 4 on the surface (lower surface) of the first resin layer 1 of the light diffusion plate P3 and is incident on the first resin layer 1. When passing through the resin layer 1 and the second resin layer 2, it is strongly diffused by the light diffusing agent 3, and further diffused by the irregularities 4 on the surface (upper surface) of the second resin layer 2, so that the liquid crystal panel is uniform from the back As a result, the luminance unevenness of the liquid crystal panel can be eliminated. In addition, the backlight unit uses the light-transmitting resin of the first resin layer 1 as a resin having a smaller refractive index than the light-transmitting resin of the second resin layer 2. Since the light transmittance is improved, the luminance is high, and ultraviolet rays incident on the first resin layer 1 from the light source 5 are absorbed by the ultraviolet absorber contained in the first resin layer 1 of the light diffusion plate P3. Since it absorbs and suppresses UV degradation and yellowing of the light diffusion plate P3, durability is also good.

In the backlight unit of the above reference embodiment and embodiment, the unevenness 4 is formed on both surfaces of the light diffusion plates P1, P2, P3, but at least one surface (preferably the light emitting surface of the second resin layer). It is only necessary to form the unevenness 4 on the surface, and the unevenness may not be formed on both sides.

Next, specific examples and reference examples of the light diffusion plate used in the backlight unit of the present invention and the performance thereof will be described.

[ Reference example 1 of light diffusing plate]
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 the multi-layer co-extrusion molding machine at a cylinder temperature of 240 to 260 ° C., a die temperature of 260 ° C., holding the vacuum degree of the vent portion 200 mmHg, also the thickness of the first resin layer and second resin layer is either By co-extrusion 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 1 mm, the total thickness is 2 mm. A light 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.

[ Reference example 2 of light diffusing plate]
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 Reference Example 1 , these materials were coextruded into two upper and lower layers to produce a light diffusing plate having an overall 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 Reference Example 1, and the results are shown in Table 1 below.

[ Reference example 3 of light diffusing plate]
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 Reference Example 1 , these materials were coextruded into two upper and lower layers to produce a light diffusing plate having an overall 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 Reference Example 1, and the results are shown in Table 1 below.

[Comparative example 1 of light diffusing plate]
As the first resin layer molding material and the second resin layer molding material, 100 parts by weight of polycarbonate resin used in Reference Example 1, an acrylic polymer infusible used in Reference 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 Reference Example 1 , these materials were coextruded into two upper and lower layers to produce a light diffusing plate having an overall 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 Reference Example 1, and the results are shown in Table 1 below.

[Comparative example 2 of light diffusing plate]
And a first resin layer molded timber fees, to 100 parts by weight of polycarbonate resin used in Reference Example 1, and the acrylic polymer fine particles infusible used in Reference Example 1 as a light diffusion agent mixed 1 part by weight I prepared something. On the other hand, 100 parts by weight of the polycarbonate resin used in Reference Example 1 was prepared as the second resin layer molding material. Then, in the same manner as in Reference Example 1 , these materials were coextruded into two upper and lower layers to produce a light diffusing plate having an overall 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 Reference Example 1, and the results are shown in Table 1 below.

[ Example of light diffusion plate]
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 the multi-layer co-extrusion molding machine at a cylinder temperature of 240 to 260 ° C., a die temperature of 260 ° C., holding the vacuum degree of the vent portion 200 mmHg, the thickness of the first resin layer and second resin layer, 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 0.3 mm and 1.7 mm, A light diffusing plate having a thickness of 2 mm was prepared.

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

[ Reference example 4 of light diffusing plate]
As a first resin layer molding material, 100 parts by weight of polycarbonate resin [PC-1250 manufactured by Teijin Chemicals Ltd.] was mixed with 0.3 part by weight of UV absorber [LA-31 manufactured by Asahi Denka Co., Ltd.]. I prepared something. 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 Reference Example 1, and the results are shown in Table 2 below.

Referring to Table 1, the light diffusing plates of Reference Examples 1 to 3 containing 0.3 part by weight of the ultraviolet absorber in the first resin layer are comparative examples 1 and 1 that do not contain the ultraviolet absorber in the first resin layer. Compared with the light diffusing plate of 2, the degree of yellowing is reduced to 1/3 or less, and the light resistance is remarkably improved. Therefore, it turns out that the backlight unit using the light diffusing plate of Reference Examples 1-3 is excellent in durability.

Moreover, when Table 1 is seen, since the light diffusing plate of Reference Examples 1-3 and the light diffusing plate of Comparative Examples 1 and 2 are 1 part by weight with the same total content of the light diffusing agent, they are substantially equivalent. The light diffusing plates of Reference Examples 1 and 2 and Comparative Example 2 having haze (92.5 to 93.0%) but containing a light diffusing agent in either the first or second resin layer, Compared with the light diffusing plates of Reference Example 3 and Comparative Example 1 in which both the first and second resin layers contain the light diffusing agent, the total light transmittance is improved by about 2 to 3%. From this, it can be seen that it is more advantageous to increase the total light transmittance by containing a light diffusing agent in one of the resin layers at a high concentration. Therefore, the backlight units using the light diffusing plates of Reference Examples 1 to 3 can sufficiently prevent uneven brightness, and in particular, the backlight units using the light diffusing plates of Reference Examples 1 and 2 have high luminance. I understand that there is.

As can be seen by comparing the light diffusing plate of Reference Examples 1 and 2 with the light diffusing plate of Comparative Example 2, and comparing the light diffusing plate of Reference Example 3 with the light diffusing plate of Comparative Example 1, 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. Therefore, it can be seen that the addition of such an ultraviolet absorber does not adversely affect the luminance of the backlight unit.

Further, as shown in Table 2, in the light diffusing plate of the example 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, both the first and second resin layers are polycarbonate. Compared with the light diffusing plate of Reference Example 4 , the total light transmittance is improved by about 1%. From this, the refractive index of the first resin layer on which light is incident is higher than that of the second resin layer. It can be seen that the use of a resin having a small value is advantageous in increasing the total light transmittance. Therefore, it can be seen that the backlight unit of the present invention using the light diffusion plate of the example has extremely high luminance.

In addition, the light diffusion plate of Reference Example 4 in Table 2 where the thickness of the first resin layer containing the ultraviolet absorber is as thin as 0.3 mm is the thickness of the first resin layer containing the ultraviolet absorber at the same concentration. Compared with the light diffusion of Reference Example 2 in Table 1 which is as thick as 1 mm, the yellowing degree is the same value as 0.5 even though 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. Therefore, it can be seen that the backlight unit using the light diffusion plate of Reference Example 4 has high luminance and excellent durability.

It is sectional drawing which shows the reference form of the backlight unit which concerns on this invention. It is a cross-sectional view showing the implementation form of the backlight unit according to the present invention. It is sectional drawing which shows other embodiment of the backlight unit which concerns on this invention.

DESCRIPTION OF SYMBOLS 1 1st resin layer 2 2nd resin layer 3 Light diffusing agent 4 Fine unevenness | corrugation 5 Light source P1, P2, P3 Light diffusing plate

Claims (3)

A first resin layer made of a translucent resin containing an ultraviolet absorber and a second resin layer made of a translucent resin are laminated and integrated, and the translucent resin of the first resin layer is integrated into the second translucent resin. A light diffusing plate having a light refractive index smaller than that of the translucent resin of the first resin layer, the translucent resin of the first resin layer being an acrylic resin, and the translucent resin of the second resin layer. The light resin is a polycarbonate resin, and a light diffusing plate having a two-layer structure in which a light diffusing agent is contained in at least the second resin layer ;
A direct light source disposed on the first resin layer side of the light diffusion plate;
A backlight unit comprising: The backlight unit according to claim 1 , wherein the acrylic resin has an optical refractive index of 1.49, and the polycarbonate resin has an optical refractive index of 1.58.   3. The backlight unit according to claim 1, wherein unevenness having an arithmetic average roughness Ra of 0.5 to 10 μm based on JIS B 0601 is formed on at least one surface of the light diffusion plate.

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