JP2005275015A - Light diffusion board, light guiding board and back light using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion board and a light guiding board without generating deflection to be a cause of poor video image. <P>SOLUTION: The light guiding board 3 is constituted by sticking film 2 on both surfaces of the light diffusion board 1 consisting of synthetic resin. Preferably, biaxial stretching polyethylene terephthalate film is used as the film. The light diffusion board 3 and the light guiding board 3 in this invention are suitably used in the light diffusion board 3 and the light guiding board 3 of wide area where a problem of the deflection is easy to be generated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light diffusing plate and a light guide plate, and relates to a light diffusion plate and a light guide plate that do not cause dimensional changes over time and that do not impair optical characteristics, and a backlight using these.

  Backlights used in liquid crystal displays and electric signboards have been used significantly in line with the expansion of shipments of liquid crystal displays such as notebook computers and large liquid crystal televisions.

  As such a backlight, an edge light type or a direct type backlight is mainly used. Edge-light type backlights are used in notebook computers and the like because the thickness of the backlight itself can be reduced, and direct-type backlights are often used in large LCD TVs and the like.

  Such a backlight is an edge light type backlight, in addition to a light source and a light guide plate, a prism sheet, a light diffusion film, a light reflection film, a polarizing film, a reflective polarizing film, a retardation film, an electromagnetic wave Consists of optical members such as shield film. In direct type backlight, in addition to light source and light diffusion plate, prism sheet, light diffusion film, light reflection film, polarizing film, reflection type polarizing film, retardation It is comprised from optical members, such as a film and an electromagnetic wave shield film (refer patent document 1).

  In the liquid crystal display using the backlight as described above, image defects hardly occurred over time, except for the lighting failure of the light source.

JP-A-9-127314 (Claim 1, paragraph number 0034)

  However, as the size of the liquid crystal display increases, a phenomenon in which a portion having a different video state from the surroundings locally appears on the display after several hours have passed since the liquid crystal display was turned on.

  As a result of diligent research to solve the above problems, the present inventors have found that the cause of the image failure is that the light diffusion plate or the light guide plate constituting the backlight is wavy and bent. It came to solve.

  That is, the light diffusing plate of the present invention is a light diffusing plate made of a synthetic resin, and is characterized in that a film is bonded to both surfaces of the light diffusing plate.

  The light diffusion plate of the present invention is characterized in that the film is a biaxially stretched polyethylene terephthalate film.

  The backlight of the present invention is a backlight having a light source and a light diffusing plate disposed on the light source, and the light diffusing plate of the present invention is used as the light diffusing plate. It is characterized by this.

  Further, the backlight of the present invention is characterized by having one or more optical members on the surface of the light diffusion plate of the backlight opposite to the light source. .

  The light guide plate of the present invention is a light guide plate made of a synthetic resin having at least one end as a light incident surface and a light exit surface as a surface substantially orthogonal to the light incident surface, and a film is formed on both surfaces of the light guide plate. It is characterized by being bonded together.

  The light guide plate of the present invention is characterized in that the film is a biaxially stretched polyethylene terephthalate film.

  The backlight of the present invention is a backlight having a light guide plate and a light source disposed at least at one end of the light guide plate, and the light guide plate of the present invention is used as the light guide plate. It is characterized by.

  In addition, the backlight of the present invention has one or more optical members on the light exit surface of the light guide plate of the backlight and / or on the surface opposite to the light exit surface. It is characterized by.

  Hereinafter, “on the light exit surface of the light guide plate and / or on the surface opposite to the light exit surface” may be simply referred to as “on the light guide plate”.

  Since the light diffusing plate or the light guide plate of the present invention is formed by laminating films on both surfaces, there is no deflection, and this causes no image defect in the liquid crystal display.

  In addition, since the backlight of the present invention uses a light diffusion plate or a light guide plate that is formed by bonding films on both sides, the light diffusion plate or the light guide plate is not bent. In addition, it is possible to prevent the deflection of the optical member installed on the light diffusing plate or the light guide plate, and to prevent local image defects of the liquid crystal display.

  First, the light diffusion plate and the light guide plate of the present invention will be described. The light diffusing plate of the present invention is a light diffusing plate made of synthetic resin, and is characterized in that films are bonded to both surfaces of the light diffusing plate. Moreover, the light guide plate of the present invention is a light guide plate made of a synthetic resin, and is characterized in that films are bonded to both surfaces of the light guide plate.

  FIG. 1 is a cross-sectional view showing an embodiment of a light diffusion plate 3 and a light guide plate 3 according to the present invention, in which a film 2 is bonded to both surfaces of the light diffusion plate 1 or the light guide plate 1. The light diffusing plate 3 and the light guide plate 3 of the present invention can prevent the occurrence of deflection by such a configuration.

  The reason that the occurrence of deflection can be prevented by such a configuration will be described together with the cause of the occurrence of deflection.

  First, most of the light diffusing plate and the light guide plate are made of synthetic resin from the viewpoint of optical characteristics, weight, and the like. And synthetic resin tends to absorb moisture with high water vapor permeability. When such a light diffusing plate or light guide plate that easily absorbs moisture is left in a high humidity environment for a long time, the light diffusing plate or the light guide plate sufficiently absorbs moisture. Then, when the backlight is turned on in a state where the light diffusion plate and the light guide plate are sufficiently absorbed in this way, sudden moisture release is started by the heat of the light source. This moisture release does not occur uniformly in the light diffusion plate or the light guide plate, and is likely to occur in the vicinity of the light source of the light diffusion plate or the light guide plate. Insufficient and non-uniform moisture absorption occurs. In such a state, the part that has been dehumidified (near the light source) is in a state of being contracted and bent as compared with the part that has been absorbed. In summary, the cause of the deflection is considered to be partially non-uniform moisture absorption in the light diffusion plate or the light guide plate. FIG. 2 shows a state where the light diffusion plate is bent in the direct type backlight.

  In a state where the light diffusing plate and the light guide plate are deflected, local image defects slightly occur on the display screen of the liquid crystal display. This local image failure is caused by the fact that optical films such as a prism sheet, a light diffusion film, a light reflection film, a polarizing film, a reflective polarizing film, a retardation film, and an electromagnetic wave shielding film are formed on the light diffusion plate and the light guide plate where the deflection occurs. When the member is placed, it becomes very prominent. That is, the optical member disposed on the light diffusion plate or the light guide plate tries to follow the bent shape of the light diffusion plate and the light guide plate, but cannot follow up, and causes deflection due to its own weight. And the local image defect becomes very remarkable by the deflection of the optical member. The deflection of the optical member becomes conspicuous with the increase in the area of the backlight due to the increase in the size of the liquid crystal display and the increase in the area of the optical member.

  Here, in the present invention, the movement of the light diffusing plate or the light guide plate can be suppressed by attaching films to both surfaces of the light diffusing plate and the light guide plate made of synthetic resin. Thereby, in the light diffusing plate and the light guide plate of the present invention, the occurrence of deflection can be prevented, and also the deflection of the optical member disposed on the light diffusing plate and the light guide plate can be prevented, and the liquid crystal display It is possible to prevent the occurrence of local image defects.

  Once the light diffusion plate, the light guide plate, and the optical member are bent, it is difficult to make them completely flat as in the beginning. In other words, once a deflection occurs in the optical member or the like, a video defect is permanently generated. Therefore, the present invention that can prevent the occurrence of deflection is extremely useful.

The light diffusing plate is installed on the light source of the direct type backlight, has a role of erasing the pattern of the light source, and is mainly made of synthetic resin. Since such a light diffusing plate is used for erasing the pattern of the light source, the thickness needs to be as thick as 1 to 10 mm, in order to give a suitable viewing angle while improving the front luminance. It is different from the light diffusion film which is used and has a thickness of 12 to 350 μm. Further, the area of the light diffusing plate is not particularly limited, but in the present invention, the light diffusing plate having an area of 900 cm ² or more where the problem of deflection is likely to occur is particularly effective.

  Synthetic resins constituting the light diffusion plate include polyester resins, acrylic resins, acrylic urethane resins, polyester acrylate resins, polyurethane acrylate resins, epoxy acrylate resins, urethane resins, epoxy resins, polycarbonate resins. , Cellulosic resin, Acetal resin, Polyethylene resin, Polystyrene resin, Polyamide resin, Polyimide resin, Melamine resin, Phenol resin, Silicone resin and other thermoplastic resins, Thermosetting resin, Ionizing radiation curing Resin. Among these, acrylic resins having excellent optical properties are preferably used.

  Fine particles are added to the light diffusing plate in order to impart light diffusibility. In addition to inorganic fine particles such as silica, clay, talc, calcium carbonate, calcium sulfate, barium sulfate, aluminum silicate, titanium oxide, synthetic zeolite, alumina, smectite, styrene resin, urethane resin, benzoguanamine resin, silicone resin, Organic fine particles made of acrylic resin and the like can be mentioned.

The light guide plate has a substantially flat plate shape formed so that at least one end portion is a light incident surface and one surface substantially orthogonal to the light incident surface is a light emission surface, and is mainly made of synthetic resin. Each surface of such a light guide plate may have a complicated surface shape instead of a uniform plane, or may be provided with diffusion printing such as a dot pattern. The thickness of the light guide plate is about 1 to 10 mm. In addition, the area of the light guide plate is not particularly limited, but in the present invention, the light guide plate having a large area with an area of 900 cm ² or more in which a problem of deflection is likely to occur is particularly effective.

  As resin which comprises a light-guide plate, the thing similar to what was illustrated as resin which comprises a light-diffusion board can be used, and especially acrylic resin excellent in an optical characteristic is used suitably. Moreover, you may add an organic fine particle in a light-guide plate as needed. As the organic fine particles, those similar to those added to the light diffusion plate can be used.

  The film to be bonded to both sides of the light diffusing plate and the light guide plate is formed by pressing the light diffusing plate and the light guide plate from above and below, and making the light diffusing plate and the light guide plate difficult to absorb moisture. It has a role to prevent bending. In order to press the light diffusion plate and the light guide plate from above and below with equal force, it is preferable to use the same type of film.

  Examples of such films include films made of synthetic resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, and acrylic. Among these, a biaxially stretched polyethylene terephthalate film that is excellent in dimensional stability and can effectively prevent the deflection of the light diffusion plate or the light guide plate is preferably used.

Moreover, as a film bonded on both surfaces of a light-diffusion plate or a light-guide plate, a thing with low water vapor permeability is preferable. If the water vapor transmission rate of the film is low, the light diffusion plate and the light guide plate can absorb moisture in advance, and even if they absorb a little moisture, they can be prevented from suddenly releasing moisture, and the light diffusion plate and the light guide plate can be prevented from bending. It can prevent more effectively. The upper limit of the water vapor permeability of the film is preferably 15 [g / (m ² · 24 h)] or less, more preferably 5 [g / (m ² · 24 h)] or less, and 1 [g / (m ² · 24 h)]. The following is more preferable. The lower limit of the water vapor permeability of the film is about 0.01 [g / (m ² · 24h)].

  As such a film having a low water vapor permeability, first, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-acrylic copolymer, biaxially oriented polypropylene (OPP), none Water vapor permeation of expanded polypropylene (CPP), cyclic polyolefin, polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), etc. A film made of a low-grade synthetic resin can be mentioned.

  As a film having a low water vapor permeability, secondly, a film having a moisture-proof layer made of a substance having a low water vapor permeability on a synthetic resin film can be mentioned. As a substance having a low water vapor transmission rate constituting the moisture-proof layer, a synthetic resin having a low water vapor transmission rate such as the above-mentioned vinylidene chloride-vinyl chloride copolymer, silicon, aluminum, titanium, selenium, magnesium, barium, zinc, Examples thereof include inorganic metal compounds such as tin, indium, calcium, tantalum, zirconium, thorium, thallium, and other oxides or halides alone or as a mixture, and ceramics such as glass. Among these substances constituting the moisture-proof layer, it is preferable to use an inorganic material from the viewpoint of the moisture-proof property of the obtained moisture-proof layer, and in particular, optical properties such as transparency, light transmittance, and color, heat resistance, and surface hardness. In view of physical properties such as the above, handling properties, and price, it is preferable to use silica. As the synthetic resin film, a biaxially stretched polyethylene terephthalate film that is excellent in dimensional stability and can effectively prevent the deflection of the light diffusion plate or the light guide plate is preferably used.

  Such a moisture-proof layer is formed on the synthetic resin film by using a material having a low water vapor transmission rate, such as a vacuum deposition method, a sputtering method, or an ion plating method, or by dissolving the material having a low water vapor transmission rate in a solvent. Alternatively, it can be formed by dispersing, coating and drying by a known coating method.

The water vapor permeability of such a substance having a low water vapor permeability is about 1 [g / (m) in the case of an inorganic substance (for example, silica deposited on polyethylene terephthalate having a thickness of 12 μm with a thickness of 0.04 μm). ² · 24 h)], and the water vapor permeability is significantly lower than that of 40 μg / (m ² · 24 h)] of polyethylene terephthalate having a thickness of 12 μm alone. In the case of an organic substance (synthetic resin), the thickness is about 0.2 to 1.5 [g / (m ² · 24 h)] at a thickness of 100 μm, and about 6.9 [g / (in a polyethylene terephthalate with a thickness of 100 μm. m ² · 24h)], which is a slight water vapor permeability.

  Although the thickness of the film bonded to both surfaces of the light diffusion plate and the light guide plate is not particularly limited, it is about 4 to 250 μm.

  It is preferable to have an ionizing radiation curable resin layer on the film to be bonded to both surfaces of the light diffusion plate and the light guide plate in order to more effectively suppress the deflection. As the ionizing radiation curable resin composition constituting the ionizing radiation curable resin layer, a photopolymerizable prepolymer that can be crosslinked and cured by irradiation with ionizing radiation (ultraviolet rays or electron beams) can be used. As the prepolymer, an acrylic prepolymer having two or more acryloyl groups in one molecule and having a three-dimensional network structure by crosslinking and curing is particularly preferably used. As the acrylic prepolymer, urethane acrylate, polyester acrylate, epoxy acrylate, melamine acrylate, polyfluoroalkyl acrylate, silicone acrylate and the like can be used. Furthermore, these acrylic prepolymers can be used alone, but it is preferable to add a photopolymerizable monomer in order to improve the cross-linking curability and further improve the hardness of the surface protective film.

  As photopolymerizable monomers, monofunctional acrylic monomers such as 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, butoxyethyl acrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol One kind of bifunctional acrylic monomer such as diacrylate, polyethylene glycol diacrylate, hydroxypivalate ester neopentyl glycol diacrylate, etc., or polyfunctional acrylic monomer such as dipentaerythritol hexaacrylate, trimethylpropane triacrylate, pentaerythritol triacrylate or the like Two or more are used.

  When the ionizing radiation curable resin layer is cured by ultraviolet irradiation in addition to the above-described photopolymerizable prepolymer and photopolymerizable monomer, it is preferable to use additives such as a photopolymerization initiator and a photopolymerization accelerator. .

  Examples of the photopolymerization initiator include acetophenone, benzophenone, Michler's ketone, benzoin, benzylmethyl ketal, benzoylbenzoate, α-acyloxime ester, thioxanthone and the like.

  Further, the photopolymerization accelerator can reduce the polymerization obstacle due to air at the time of curing and increase the curing speed. For example, p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester, and the like. can give.

  Moreover, an ionizing radiation curable organic-inorganic hybrid resin can also be used as the resin constituting the ionizing radiation curable resin layer. Unlike traditional composites typified by glass fiber reinforced plastic (FRP), ionizing radiation curable organic / inorganic hybrid resins are closely mixed with organic and inorganic materials, and the dispersion state is close to or close to the molecular level. Therefore, the film can be formed by the reaction between the inorganic component and the organic component by irradiation with ionizing radiation.

  Examples of the inorganic component of the ionizing radiation curable organic-inorganic hybrid resin include metal oxides such as silica and titania. Among them, those using silica are preferable.

  Examples of such silica include reactive silica in which a photosensitive group having photopolymerization reactivity is introduced on the surface. For example, with respect to powdery silica or colloidal silica as a base, the following general formula is used in the molecule. A compound having four groups of (1) and (2), a hydrolyzable silyl group, and a polymerizable unsaturated group is chemically reacted with the hydrolyzable silyl group via a silyloxy group. Can be used.

（式中、ＸはＮＨ、酸素原子及び硫黄原子から選ばれ、Ｙは酸素原子及び硫黄原子から選ばれる。但し、Ｘが酸素原子のときＹは硫黄原子である。）

(In the formula, X is selected from NH, an oxygen atom and a sulfur atom, and Y is selected from an oxygen atom and a sulfur atom. However, when X is an oxygen atom, Y is a sulfur atom.)

  Examples of the hydrolyzable silyl group include a carboxylylate silyl group such as an alkoxylyl group and an acetoxysilyl group, a halogenated silyl group such as a chlorosilyl group, an aminosilyl group, an oxime silyl group, and a hydridosilyl group.

  Examples of the polymerizable unsaturated group include acryloyloxy group, methacryloyloxy group, vinyl group, propenyl group, butadienyl group, styryl group, ethynyl group, cinnamoyl group, malate group, and acrylamide group.

  In addition, the reactive silica is not particularly limited. However, when the optical member requires transparency, an average particle diameter of 1 nm to 100 nm, preferably 1 nm to 10 nm is preferably used. Is more preferable. By setting the average particle diameter in such a range, transparency can be maintained.

  Next, as the organic component, a compound having a polymerizable unsaturated group polymerizable with the reactive silica, for example, a polyunsaturated organic compound having two or more polymerizable unsaturated groups in the molecule, or a molecule Examples thereof include monounsaturated organic compounds having one polymerizable unsaturated group.

  Specific examples of the polyunsaturated organic compound include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, glycerol di (meth) acrylate, glycerol tri (meth) acrylate, and 1,4- Butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dicyclopentanyl di (meth) acrylate, pentaerythritol Tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol monohydroxypenta (meth) acrylate, ditrimethylo Propane tetra (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate and the like.

  Specific examples of the monounsaturated organic compound include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and isodecyl (meth). Acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, allyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2- Hydroxypropyl (meth) acrylate, glycerol (meth) acrylate, glycidyl (meth) acrylate, benzyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2- (2 Ethoxyethoxy) ethyl (meth) acrylate, butoxyethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, 2 -Methoxypropyl (meth) acrylate, methoxydipropylene glycol (meth) acrylate, methoxytripropylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, etc. It is done.

  The above-mentioned film can be bonded to both surfaces of the light diffusion plate or the light guide plate by using a conventionally known adhesive or by thermally melting the film.

  In addition, as a synthetic resin which comprises a light diffusing plate or a light-guide plate, the means which prevents generation | occurrence | production of a deflection | deviation by using the synthetic resin with the low water vapor permeability | transmittance which was illustrated above is also considered. However, synthetic resins with low water vapor permeability are light transmissive, mechanical strength, heat resistant, and solvent resistant compared to the synthetic resins (acrylic resins) that make up commonly used light diffusion plates and light guide plates. The configuration of the present invention is preferable because the balance of price and the like is inferior.

  The light diffusing plate and the light guide plate of the present invention described above are mainly used as one part of a backlight constituting a liquid crystal display, an electric signboard, and the like. In particular, the light diffusing plate is used as a part of a backlight called a so-called direct type, and the light guide plate is used as a part of a backlight called a so-called edge light type.

  Next, the backlight of the present invention will be described. The backlight of the present invention comprises at least the above-described light diffusion plate or light guide plate of the present invention and a light source.

  First, a backlight having the above-described light diffusion plate of the present invention will be described. A backlight having a light diffusing plate is called a direct-type backlight, and has a basic configuration including a light source and a light diffusing plate disposed on the light source.

  A cold cathode tube is mainly used as the light source. Examples of the shape of the light source include a linear shape and a U-shape.

  Depending on the purpose, one or more optical members may be provided on the surface of the light diffusing plate of the direct type backlight opposite to the light source. Examples of such an optical member include a prism sheet, a light diffusing film, a light reflecting film, a polarizing film, a reflective polarizing film, a retardation film, and an electromagnetic shielding film. Examples of the prism sheet include Sumitomo 3M's trade name BEF, trade name RBEF, trade name wave film, and Mitsubishi Rayon's trade name Diaart. Examples of the light diffusing film include trade name Opulse of Ewasha and trade name D114 of Tsujiden. Examples of the light reflecting film include Eira's brand name Leila and Sumitomo 3M's brand name ESR. Examples of the polarizing film include NPF's trade name NPF and Sumitomo Chemical's trade name Sumikaran. Examples of the reflective polarizing film include DBEF manufactured by Sumitomo 3M Limited. Examples of the retardation film include ELMEC (trade name of Kaneka Chemical Co., Ltd.) and Sumikalite (trade name of Sumitomo Chemical Co., Ltd.). Examples of the electromagnetic wave shielding film include Nitto Denko's trade name ELECRYSTA and Teijin's trade name LEFTEL. Moreover, you may have these optical members in other parts in direct type | mold backlight, such as the opposite side to the light diffusing plate of the light source of direct type | mold backlight.

  One embodiment of the direct type backlight 9 of the present invention is shown in FIG. As shown in the figure, the backlight 9 has a plurality of light sources 7 arranged on a reflective film 6 accommodated in a chassis 8, and the light diffusing film 4 via the light diffusing plate 31 of the present invention described above. The prism sheet 5 is disposed.

  Next, a backlight having the above-described light guide plate of the present invention will be described. A backlight having a light guide plate is referred to as an edge light type backlight, and has a basic configuration including a light guide plate and a light source disposed at at least one end of the light guide plate.

  A cold cathode tube is mainly used as the light source. Examples of the shape of the light source include a linear shape and an L shape.

  Depending on the purpose, one or more optical members may be provided on the light exit surface of the light guide plate of the edge light type backlight and / or on the surface opposite to the light exit surface. . Examples of such an optical member include a prism sheet, a light diffusion film, a light reflection film, a polarizing film, a reflective polarizing film, a retardation film, and an electromagnetic wave shielding film similar to those exemplified in the direct type backlight. Moreover, you may have these optical members in other parts in an edge light type backlight, such as the circumference | surroundings of the light source of an edge light type backlight.

  One embodiment of the edge light type backlight 9 of the present invention is shown in FIG. The backlight 9 has a configuration in which the light source 7 is provided at both ends of the light guide plate 32 of the present invention described above, and the light diffusion film 4 and the prism sheet 5 are disposed on the upper side of the light guide plate 32. The light source 7 is covered with the reflective film 6 except for a portion facing the light guide plate 32 so that the light from the light source 7 is efficiently incident on the light guide plate 32. A reflective film 6 accommodated in the chassis 8 is provided below the light guide plate 32. As a result, the light emitted to the side opposite to the light emitting surface side of the light guide plate 32 is returned to the light guide plate 32 again, and the amount of light emitted from the light emitting surface of the light guide plate 32 is increased.

Since the backlight of the present invention described above uses a light diffusion plate or a light guide plate that is formed by bonding films on both surfaces, the light diffusion plate or the light guide plate does not bend. In addition, it is possible to prevent the deflection of the optical member installed on the light diffusing plate or the light guide plate, and it is possible to prevent local image defects of the display. In particular, it has a remarkable effect in a backlight having a large area where the area of the light emitting surface where the problem of deflection is likely to occur is 900 cm ² or more. Since such a large area backlight is often used in a direct type backlight, the present invention is particularly suitable for a direct type backlight.

  The following examples further illustrate the present invention. “Parts” and “%” are based on weight unless otherwise specified.

[Example 1]
A direct type backlight (area of light emission surface 2090 cm ² ) was taken out from a commercially available 26 type liquid crystal TV using a direct type backlight as a backlight. The direct type backlight has a light diffusing plate, a light diffusing film, a prism sheet, and a polarizing film on a light source.

Next, an acrylic resin light diffusion plate (area 2090 cm ² ) is taken out from the direct type backlight, and a film is attached to both surfaces of the light diffusion plate via an acrylic adhesive (Arontack SCL-200: Toa Gosei Chemical Co., Ltd.). Were bonded together to obtain a light diffusion plate of the present invention. As the film, a biaxially stretched polyethylene terephthalate film (Lumirror T60: Toray Industries, Inc.) having a thickness of 100 μm was used. Subsequently, the light diffusing plate was returned to the backlight to obtain the backlight of the present invention.

[Example 2]
An edge light type backlight (light emitting surface area 993 cm ² ) was taken out from a commercially available liquid crystal display for 18 type desktop personal computers using an edge light type backlight as a backlight. The edge light type backlight includes light sources at both ends of the light guide plate, and has a light diffusion film, a prism sheet, and a polarizing film on the light output surface of the light guide plate, and is a surface opposite to the light output surface of the light guide plate. It had a reflective film on it.

Next, an acrylic resin light guide plate (area 993 cm ² ) was taken out from the edge light type backlight, and the same film as in Example 1 was bonded to both surfaces of the light guide plate to obtain the light guide plate of the present invention. Subsequently, the light guide plate was returned to the backlight to obtain the backlight of the present invention.

[Evaluation of deflection]
The backlights obtained in Examples 1 and 2 were left in an environment of 40 ° C. and 90% RH for 24 hours, and then returned to a commercially available 26-inch liquid crystal TV and a commercially available 18-inch desktop personal computer liquid crystal display, respectively. And the liquid crystal display was turned on and the progress of the video state was observed. As a result, in all of Examples 1 and 2, no image defect occurred in the liquid crystal display no matter how many hours elapsed from lighting. Further, when the backlight incorporated in the liquid crystal TV and the liquid crystal display was taken out, no deflection was observed in the light diffusion plate and the light guide plate, and no deflection was observed in the light diffusion film, the prism sheet, the polarizing film, and the reflection film. .

[Comparative Examples 1 and 2]
A backlight of Comparative Example 1 was obtained in the same manner as in Example 1 except that the film was not bonded to the light diffusion plate. Moreover, the backlight of Comparative Example 2 was obtained in the same manner as Example 2 except that the film was not bonded to the light guide plate. When the deflection of the obtained backlights of Comparative Examples 1 and 2 was evaluated in the same manner as in Examples 1 and 2, after 3 hours had elapsed from the lighting of the liquid crystal TV or liquid crystal display, A phenomenon was observed in which parts with different image states occurred locally. This local image defect part gradually became smaller with time, but did not disappear completely even after several days. In addition, when the backlight incorporated in the liquid crystal TV or liquid crystal display was taken out, deflection was observed in the light diffusion plate, light diffusion film, prism sheet, and polarizing film in the former, and the light guide plate and light diffusion film in the latter. Deflection was observed in the prism sheet, the polarizing film, and the reflective film.

Sectional drawing which shows one Example of the light diffusing plate of this invention or the light-guide plate of this invention Diagram explaining the state of deflection Sectional drawing which shows one Example of the backlight of this invention Sectional drawing which shows the other Example of the backlight of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Conventional light diffusing plate or light guide plate 2 ... Film 3 ... Light diffusing plate of the present invention or Light guiding plate 31 of the present invention ... Light diffusing plate 32 of the present invention Light guide plate 4 of the present invention ... Light diffusion film 5 ... Prism sheet 6 ... Reflective film 7 ... Light source 8 ... Chassis 9 ... Backlight of the present invention

Claims (8)

  A light diffusing plate comprising a synthetic resin, wherein a film is bonded to both surfaces of the light diffusing plate.   The light diffusing plate according to claim 1, wherein the film is a biaxially stretched polyethylene terephthalate film.   A backlight comprising a light source and a light diffusing plate disposed on the light source, wherein the light diffusing plate according to claim 1 or 2 is used as the light diffusing plate. Light.   4. A backlight comprising: a light diffusing plate of a backlight according to claim 3; and one or more optical members on a surface opposite to the light source.   A light guide plate made of a synthetic resin having at least one end portion as a light incident surface and a light exit surface as a surface substantially orthogonal to the light incident surface, wherein films are bonded to both surfaces of the light guide plate. Light guide plate.   The light guide plate according to claim 5, wherein the film is a biaxially stretched polyethylene terephthalate film.   A backlight comprising a light guide plate and a light source disposed at least at one end of the light guide plate, wherein the light guide plate according to claim 5 or 6 is used as the light guide plate. Backlight.   8. A backlight comprising one or more optical members on the light exit surface of the light guide plate of the backlight according to claim 7 and / or on the surface opposite to the light exit surface. Light.

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