JP2002090515A - White film for reflecting member of surface light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflecting member for a surface light source showing only a small deterioration of luminance with the lapse of time even in long-time use and capable of holding high image quality over a long period of time. SOLUTION: A coating layer containing a light stabilizer is disposed on at least one face of a while film containing air bubbles to obtain the objective white film for the reflecting member of a surface light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a white film used for a surface light source reflecting member, and more particularly to a reflector for a surface light source of an edge light and a direct type light for a liquid crystal display, and a reflector. The present invention relates to a white film having a small decrease in luminance even when used for a long time.

[0002]

2. Description of the Related Art A so-called edge light system in which light from an illumination light source (cold cathode ray tube) enters from the edge of a light guide plate is widely used for lighting equipment for a liquid crystal display (Japanese Patent Laid-Open No. 63-62104). No.). In this illumination method, a reflector is provided around the cold cathode ray tube in order to utilize light more efficiently, and further, a light guide plate is provided to efficiently reflect light diffused from the light guide plate toward the liquid crystal screen. A reflector is provided below. Thereby, a function of reducing the loss of light from the cold cathode ray tube and brightening the liquid crystal screen is provided. In recent years, for a large screen such as a liquid crystal television, a direct-type light system has been adopted since high brightness of the screen cannot be expected in the edge light system. In this method, cold cathode ray tubes are provided in parallel at a lower portion of a liquid crystal screen, and the cold cathode ray tubes are arranged in parallel on a reflection plate. As the reflector, a flat plate or a cold cathode ray tube having a semicircular concave shape is used.

[0003] Reflectors and reflectors used in such surface light sources for liquid crystal screens (hereinafter collectively referred to as surface light source reflection members) are required to have a high reflection function. Conventionally, white dyes and white pigments are used. Films to which the added film or a film containing fine bubbles inside are used alone, or a film obtained by laminating such a film with a metal plate, a plastic plate or the like has been used. In particular, when a film containing fine bubbles therein is used, it is widely used because of its excellent brightness improving effect and excellent uniformity. Such a film containing fine bubbles inside is disclosed in JP-A-6-322.
No. 153, Japanese Patent Application Laid-Open No. Hei 7-118433, and the like.

[0004]

In recent years, the use of liquid crystal screens has been remarkably expanding. In addition to the conventional notebook personal computers, they have been widely used in stationary personal computers, liquid crystal televisions, mobile phone displays, various game machines, and the like. Have been. Higher brightness and higher definition of the screen have been demanded in response to such expanded use, and improvements have been made to illumination light sources such as higher output and an increase in the number of light source lamps. Further, in order to meet the demand for long-time use on a large screen such as a liquid crystal television, higher luminance and durability are required. In particular, when a direct-type light source is used, light emitted from the light source is directly applied, and a higher level of durability of the reflector is required. However, in the case of a reflector or reflector using a conventional film, yellowing due to deterioration of the film occurs when used for a long time, and the reflection characteristics are reduced.
As a result, there is a problem that the luminance of the screen is reduced.

The present invention solves the above-mentioned problems and provides a surface light source reflecting member capable of maintaining a high quality image for a long period of time with little decrease in luminance over a long period of use, and a white film for the surface light source reflecting member. It is intended to do so.

[0006]

According to the present invention, there is provided a surface light source reflecting member having a coating film containing a light stabilizer provided on at least one surface of a white film containing bubbles therein. It is to be a white film.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The white film used in the present invention is:
A thermoplastic film to which organic and inorganic dyes and fine particles are added; a resin component constituting the film mixed with a resin incompatible with the resin component and / or organic or inorganic particles and melt-extruded. After that, it is stretched in at least one direction to form fine bubbles inside; foamed by adding foamable particles and melt-extruding; extruding and foaming by injecting a gas such as carbon dioxide gas. The film is not particularly limited as long as it has an apparent whiteness, such as a film. In particular, in the use of the present invention, the reflectance is further improved, and the brightness is improved, as a resin component constituting the film, a resin incompatible with the resin component, and / or organic or inorganic particles. After mixing and melt-extruding, it is preferably stretched in at least one direction to form fine bubbles inside.
Further, on at least one surface of the film in which fine bubbles are formed, a thermoplastic resin to which organic or inorganic fine particles are added is laminated by a method such as co-extrusion, further stretched, and the surface layer is finer than the inner layer. A composite film with air bubbles is particularly preferred.

The thermoplastic resin constituting the film is not particularly limited as long as it can form the film by melt extrusion. Preferred examples include polyester, polyolefin, polyamide, polyurethane, polyphenylene sulfide and the like. . In particular, in the present invention, the dimensional stability and mechanical properties are good,
Polyester is preferred because it hardly absorbs in the visible light region.

Specific examples of polyester include polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalenedicarboxylate (hereinafter abbreviated as PEN), polypropylene terephthalate, polybutylene terephthalate, and poly-1. And 4-cyclohexylene dimethylene terephthalate. Of course, these polyesters may be homopolymers or copolymers, but are preferably homopolymers. Examples of the copolymer component in the case of a copolymer include an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid, and a diol component having 2 to 15 carbon atoms. Examples of these include, for example, isophthalic acid. , Adipic acid, sebacic acid, phthalic acid,
Sulfonate group-containing isophthalic acid and their ester-forming compounds, diethylene glycol, triethylene glycol, neopentyl glycol, molecular weight 400
And 20,000 polyalkylene glycols.

In these polyesters, various additives such as heat stabilizers, oxidation stabilizers, organic lubricants, organic and inorganic fine particles, as long as the effects of the present invention are not impaired.
A light stabilizer, an antistatic agent, a nucleating agent, a coupling agent and the like may be added.

Hereinafter, as a preferred example of the present invention, a case where polyester is used as a white film substrate will be described in detail.
Using polyester as a base material and whitening it include various white dyes, a method of adding a white pigment, a method of containing fine bubbles in the above-mentioned method, etc., but the effect of the present invention is more remarkable. In order to allow the fine particles to be expressed, it is preferable to use a method in which fine bubbles are contained inside. Examples of the method for containing such fine bubbles include: (1) a method in which a foaming agent is contained and foamed by heat during extrusion or film formation, or foamed by chemical decomposition; (2) carbonic acid is formed during extrusion or after extrusion. (3) a method of adding a gas such as a gas or a vaporizable substance and foaming it, (3) a method of adding a thermoplastic resin incompatible with the polyester, and extruding the mixture after melt extrusion and uniaxially or biaxially; (4) A method in which organic or inorganic fine particles are added, melt-extruded, and monoaxially or biaxially stretched can be used. In the present invention, it is preferable to increase the reflection interface by forming fine bubbles, and from this point, it is preferable to use the method (3) or (4).

The size of bubbles obtained by the above method
(Cross-sectional area size in the thickness direction) is 0.5 μm ^{2 to} 50 μm ² ,
Preferably it is preferable in view of the brightness enhancement is 1μm ² ~30μm ^2. The cross-sectional shape of the bubbles may be any of a circular shape and an elliptical shape, but a structure in which at least one bubble is present in all the surfaces from the upper surface to the lower surface of the film is particularly preferable. That is, when used as a reflector, light enters from the surface into the inside of the film as the reflector, and it is the most preferable form that all of the entered light is reflected by bubbles inside. Actually, some light passes through the inside of the film, and this part causes light loss. To reduce this, metal such as aluminum or silver is placed on the film surface opposite to the side where light enters (light source side). Preferably, evaporation is performed.

It is preferable to provide a layer containing fine bubbles of organic or inorganic fine particles on the surface of the bubble-containing polyester film in order to reduce the light loss of the film containing fine bubbles therein. . The surface layer is formed by compounding a resin composition containing organic or inorganic fine particles in a polyester resin by co-extrusion during the production of the internal bubble-containing film, and then stretching the resin composition in at least one direction. Things.
In this composite film, it is preferable that the bubbles in the surface layer (surface layer) are smaller than the bubbles in the inner layer in view of improving the brightness. The ratio (size of bubbles in the surface layer / size of bubbles in the inner layer) is not particularly limited, but is preferably 0.05 to 0.8, more preferably 0.07 to 0.7,
Most preferably, it is 0.1 to 0.6. The size of the bubbles can be controlled by the size of the particles to be added.

Here, components added to form air bubbles, that is, a resin incompatible with the polyester resin, and organic or inorganic fine particles added to the inner layer and the surface layer will be described. The resin incompatible with the polyester resin (hereinafter abbreviated as the incompatible resin) is a thermoplastic resin other than the polyester and can be dispersed in the polyester in the form of particles. For example, polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, polystyrene resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, and fluorine resins are preferable. These may be a homopolymer or a copolymer, and two or more of them may be used in combination. Particularly, a resin having a large difference in critical surface tension from polyester and hardly deformed by heat treatment after stretching is preferable, and a polyolefin resin, particularly, polymethylpentene is particularly preferable. The content of the incompatible resin in the white film is not particularly limited, and may be selected in consideration of the brightness at the time of film formation, the formation of bubbles with the incompatible resin as a nucleus,
Usually, it is preferably 3 to 35% by weight, more preferably 4 to 35% by weight.
Most preferably, it is in the range of 30% by weight, more preferably 5 to 25% by weight. If it is less than 3% by weight, the effect of improving brightness is small, and if it exceeds 35% by weight, the film tends to be broken during film formation.

The inorganic fine particles to be added to the inner layer and / or the surface layer are preferably those capable of forming bubbles by themselves as nuclei. For example, calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide (anatase type, rutile type) ), Zinc oxide, barium sulfate, zinc sulfide, basic lead carbonate, titanium mica, antimony oxide, magnesium oxide, calcium phosphate, silica, alumina, mica, talc, kaolin and the like. Among these, it is particularly preferable to use calcium carbonate and barium sulfate, which have low absorption in the visible light region of 400 to 700 nm. If absorption occurs in the visible light range, there is a problem that the luminance is reduced. In the case of organic fine particles, those which do not melt by melt extrusion are preferable, and cross-linked fine particles made of cross-linked styrene, cross-linked acryl and the like are particularly preferable. The organic fine particles may be hollow ones.

The above fine particles may be used alone or in combination of two or more. The particle size of the fine particles is not particularly limited, but is usually 0.05 to 15 μm, preferably 0.1 to 10 μm,
More preferably, the thickness is 0.3 to 5 μm.
When the thickness is less than 0.05 μm, the bubble-forming property is insufficient, and when it exceeds 15 μm, the surface is unnecessarily roughened, which is not preferable. In the case where the fine particles are contained in the surface layer portion and the incompatible resin is contained in the inner layer portion, it is preferable that the bubble diameter having the fine particles as a nucleus is smaller than the bubble diameter formed in the inner layer portion in terms of improving brightness. . Further, the content of the fine particles in the white film is preferably 1 to 30% by weight, more preferably 2 to 25% by weight, and further preferably 3 to 2% by weight.
0% by weight is most preferred. When the content is less than 1% by weight, the effect of improving the brightness is small, and when it exceeds 30% by weight, the film tends to be broken during the film formation.

The specific gravity, which is a measure of the bubble content of the white film containing such bubbles, is preferably 0.1 or more and 1.3 or less. When the specific gravity is less than 0.1, problems such as insufficient mechanical strength of the film, breakage and poor handling properties may occur. On the other hand, when the ratio exceeds 1.3, the bubble content is too low, the reflectance is reduced, and the luminance tends to be insufficient. Also,
When polyester is used as the thermoplastic resin constituting the film, the lower limit of the specific gravity is preferably 0.4.
If the specific gravity is less than 0.4, there may be a problem that the content of the foam is too high and the film is likely to be broken during film formation.

The surface light source reflecting member is a plate-like material incorporated in a surface light source for light reflection as described above, and specifically, a reflection plate of an edge light for a liquid crystal screen and a reflector of a direct type light. It means a reflector of a surface light source, a reflector around a cold cathode ray tube, and the like.When used for this surface light source reflection member, it is preferable that the reflector has higher whiteness in terms of the color tone of the screen, and A bluish tint is more preferable than a yellow tint. Considering this point, it is preferable to add a fluorescent whitening agent to the white film. Commercially available fluorescent whitening agents may be used as appropriate, for example, “Ubitek” (manufactured by Ciba-Geigy), OB-1 (manufactured by Eastman), TBO (manufactured by Sumitomo Seika), “Kaycoal” (Manufactured by Nippon Soda Co., Ltd.), "Kayalite" (manufactured by Nippon Kayaku), "Ryukopua" EGM (manufactured by Client Japan) and the like can be used. The content of the fluorescent whitening agent in the white film is preferably from 0.005 to 1% by weight, more preferably from 0.007 to 0.7% by weight, and even more preferably from 0.01 to 0.7% by weight.
Most preferably, it is in the range of 0.5% by weight. 0.
If the content is less than 005% by weight, the effect is small, and if it exceeds 1% by weight, yellowing is unfavorably caused. When the white film is a composite film, it is more effective to add the optical brightener to the surface layer.

In the present invention, it is necessary to provide a coating layer containing a light stabilizer on at least one side of such a white film. Light stabilizers include organic light stabilizers such as hindered amine, salicylic acid, benzophenone, benzotriazole, cyanoacrylate, triazine, benzoate and oxalic anilide, or inorganic light stabilizers such as sol-gel. Agents can be used. Specific examples of the light stabilizer preferably used are shown below, but are not limited thereto.

Hindered amines: bis (2,2,
6,6-tetramethyl-4-piperidyl) sebacate,
Dimethyl succinate 1- (2-hydroxyethyl) -4
-Hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, salicylic acid: pt-butylphenyl salicylate, p-octylphenyl salicylate, benzophenone: 2,4-dihydroxybenzophenone, 2-hydroxy-4 -Methoxybenzophenone, 2
-Hydroxy-4-methoxy-5-sulfobenzophenone, 2,2'-4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'- Dimethoxybenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenyl) methane,

Benzotriazoles: 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-t-butylphenyl) benzotriazole, 2- (2'-hydroxy −
3 ', 5'-di-t-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-butyl-
5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2-
(2′-hydroxy-5′-t-octylphenol)
Benzotriazole, 2- (2′-hydroxy-3 ′,
5′-di-t-amylphenyl) benzotriazole,
2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazole-
2-yl) phenol], 2 (2'hydroxy-5'-
(Methacryloxyphenyl) -2H-benzotriazole, 2- [2′-hydroxy-3 ′-(3 ″, 4 ″,
5 ", 6" -tetrahydrophthalimidomethyl) -5 '
-Methylphenyl] benzotriazole, 2- (2′-
Hydroxy-5-acryloyloxyethylphenyl)
-2H-benzotriazole, 2- (2'-hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole, 2- (2'-hydroxy-3'-t-
Butyl-5'-acryloylethylphenyl) -5-chloro-2H-benzotriazole cyanoacrylate: ethyl-2-cyano-3,3'-diphenylacrylate;

Other than the above: nickel bis (octylphenyl) sulfide, [2,2'-thiobis (4-t-octylphenolate)]-n-butylamine nickel, nickel complex-3,5-di-t-butyl- 4-hydroxybenzyl phosphate monoethylate, nickel dibutyl dithiocarbamate, 2,4-di-t
-Butylphenyl-3 ', 5'-di-t-butyl-4'
-Hydroxybenzoate, 2,4-di-t-butylphenyl-3 ', 5'-di-t-butyl-4'-hydroxybenzoate, 2-ethoxy-2'-ethyloxac acid bisanilide, 2- ( 4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol. In the present invention, among the above specific examples, at least hindered amines, benzophenones, benzo It is preferable to use any of the triazole-based light stabilizers, and it is more preferable to use them in combination.

In the present invention, in order to facilitate the formation of a coating layer containing a light stabilizer, it is preferable to use the light stabilizer by appropriately mixing other resin components. That is, the resin component and the light stabilizer are dissolved in an organic solvent capable of dissolving each of them, water, and two or more kinds of organic solvents to form a mixed liquid, or the organic solvent / water mixed liquid is mixed with the resin component to form a light stable state. It is preferable to form a liquid state in which the agent is dissolved or dispersed, and to use this as a coating liquid. Needless to say, a resin component and a light stabilizer previously dissolved and dispersed separately in an organic solvent, water, an organic solvent mixture, or an organic solvent / water mixture may be arbitrarily mixed and used. It is also preferable to use a copolymer of a light stabilizer component and a resin component in advance as it is as a coating material. in this case,
Of course, the copolymer may be dissolved in an organic solvent, water, a mixture of two or more organic solvents, or an organic solvent / water mixture.

The resin component to be mixed or copolymerized is not particularly limited, and examples thereof include a polyester resin,
Examples include polyurethane resin, acrylic resin, methacrylic resin, polyamide resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, and fluorine resin. These resins can be used alone or
It may be used as a copolymer of two or more kinds or as a mixture. It is preferable to select and use an acrylic resin or a methacrylic resin among the above resin components.

In particular, it is preferable to use an acrylic resin or a methacrylic resin obtained by copolymerizing a light stabilizer component in the coating layer. In the case of copolymerization, it is preferable to copolymerize a light stabilizer monomer component with an acrylic monomer component or a methacryl monomer component.

As the light stabilizer monomer component, for example, benzotriazole-based reactive monomers, hindered amine-based reactive monomers, benzophenone-based reactive monomers, and the like can be preferably used. The benzotriazole-based reactive monomer may be any monomer having benzotriazole in the base skeleton and having an unsaturated bond, and is not particularly limited. For example, 2- (2′-hydroxy-5)
-Acryloyloxyethylphenyl) -2H-benzotriazole, 2- (2′-hydroxy-5′-methacryloxyethylphenyl) -2H-benzotriazole, 2- (2′-hydroxy-3′-t-butyl-5) '
-Acryloylethylphenyl) -5-chloro-2H-
Benzotriazole and the like can be mentioned. Similarly, the hindered amine-based reactive monomer and benzophenone-based reactive monomer may be any monomer having a hindered amine and benzophenone in the base skeleton and having an unsaturated bond, respectively.

Examples of the hindered amine type reactive monomer include, for example, bis (2,2,6,6-tetramethyl-4
-Piperidyl-5-acryloyloxyethylphenyl) sebacate, polycondensate of dimethyl succinate / 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethyl-5-acryloyloxyethylphenylpiperidine , Bis (2,2,6,6-tetramethyl-4-piperidyl-5-methacryloxyethylphenyl) sebacate, dimethyl succinate-1- (2-hydroxyethyl) -4-hydroxy-2,2,6, 6-tetramethyl-5-methacryloxyethylphenylpiperidine polycondensate, bis (2,2,6,6-tetramethyl-4
-Piperidyl-5-acryloylethylphenyl) sebacate, dimethyl succinate / 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethyl-5-acryloylethylphenylpiperidine polycondensate and the like. Can be mentioned.

As the benzophenone-based reactive monomer, for example, 2-hydroxy-4-methoxy-5-
Acryloyloxyethylphenylbenzophenone,
2,2'-4,4'-tetrahydroxy-5-acryloyloxyethylphenylbenzophenone, 2,2'-
Dihydroxy-4-methoxy-5-acryloyloxyethylphenylbenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-5-acryloyloxyethylphenylbenzophenone, 2-hydroxy-4-methoxy-5-methacryloxyethylphenyl Benzophenone, 2,2'-4,4'-tetrahydroxy-5-methacryloxyethylphenylbenzophenone, 2,2 '
-Dihydroxy-4-methoxy-5-acryloylethylphenylbenzophenone, 2,2'-dihydroxy-
4,4'-dimethoxy-5-acryloylethylphenylbenzophenone and the like can be mentioned.

The acrylic monomer component or the methacrylic monomer component copolymerized with these light stabilizer monomer components, or the oligomer component thereof includes alkyl acrylate and alkyl methacrylate (the alkyl group is a methyl group, an ethyl group, an n-propyl group). Isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2
-Ethylhexyl group, lauryl group, stearyl group, cyclohexyl group, etc.), and a monomer having a crosslinkable functional group, such as a carboxyl group, a methylol group, an acid anhydride group, a sulfonic acid group, an amide group, a methylolated amide group, Examples include monomers having an amino group, an alkylolated amino group, a hydroxyl group, an epoxy group, and the like. Further, acrylonitrile, methacrylonitrile, styrene, butyl vinyl ether, maleic acid, itaconic acid and its dialkyl ester, methyl vinyl ketone, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl pyridine, vinyl pyrrolidone, alkoxysilane having a vinyl group, It may be a copolymer with a saturated polyester or the like.

The copolymerization ratio between the light stabilizer monomer component and the monomers to be copolymerized is not particularly limited, and one or more of each can be copolymerized at an arbitrary ratio. Most preferably, the ratio of the light stabilizer monomer component is 10% by weight or more, more preferably 20% by weight or more, and most preferably 35% by weight or more. Of course, a homopolymer of the light stabilizer monomer component may be used. The molecular weight of these polymers is not particularly limited, but is usually 5,000 or more, preferably 10,000 or more, and more preferably 20,000 or more, from the viewpoint of the toughness of the coating layer. These polymers are used in the state of being dissolved or dispersed in an organic solvent, water or an organic solvent / water mixture. Besides these, commercially available hybrid light-stable polymers can also be used. Further, "U-double" (manufactured by Nippon Shokubai Co., Ltd.) containing a copolymer of an acrylic monomer and an ultraviolet absorber as an active ingredient can be used.

The thickness of the coating layer containing the light stabilizer is not particularly limited, but is preferably 0.5 to 15 μm, more preferably 1 to 10 μm, and most preferably 2 to 7 μm. If the thickness is less than 0.5 μm, the durability of the coating layer is insufficient, and if it exceeds 15 μm, the brightness may be reduced.

The coating layer containing the above-mentioned light stabilizer may be provided directly on the white film of the base material. However, when the adhesiveness is insufficient, the surface of the base material film may be subjected to corona discharge treatment or undercoating. It is preferable to provide the coating layer after the drawing treatment. The undercoating treatment may be a method of providing in a white film manufacturing process (in-line coating method), or a method of separately applying and providing a white film after manufacturing (off-line coating method). The material applied to the undercoating treatment is not particularly limited and may be appropriately selected, but preferred examples include a copolymerized polyester resin, a polyurethane resin, an acrylic resin, a methacrylic resin, and various coupling agents. .

When a coating layer containing a light stabilizer is provided, the coating liquid can be applied by any method. For example, gravure coat, roll coat, spin coat, reverse coat, bar coat, screen coat, blade coat,
Methods such as air knife coating and dipping can be used. Also, when the coating layer is cured after coating,
As the curing method, a known method can be used. For example, a method of heat curing, a method of curing using actinic rays such as ultraviolet rays, electron beams, and radiations, and a method of a combination thereof can be applied. At this time, it is preferable to use a curing agent such as a crosslinking agent in combination. The coating liquid for forming the coating layer may be applied (in-line coating) at the time of producing the white film of the substrate, or may be applied (off-line coating) on the white film after the completion of the crystal orientation.

The white film of the present invention has a thickness of 400 to 700 nm measured from the surface provided with the coating layer containing the light stabilizer.
Is preferably 85% or more, more preferably 87% or more, and particularly preferably 9% or more.
Desirably, it is 0% or more. When the average reflectance is less than 85%, the luminance may be insufficient depending on the liquid crystal display to be applied.

The white film of the present invention has a glossiness of 60 measured from the surface provided with the coating layer containing the light stabilizer.
%, More preferably 50% or less, and most preferably 40% or less. When the glossiness is greater than 60%, when applied to a liquid crystal display, the brightness may be reduced depending on the viewing angle.

In the present invention, various additives can be added to the coating layer containing the light stabilizer within a range not to impair the effects of the present invention. As an additive, for example, organic and / or inorganic fine particles, a fluorescent brightener, a crosslinking agent, a heat stabilizer, an oxidation resistant stabilizer, an organic lubricant, an antistatic agent, a nucleating agent, a coupling agent, and the like are used. Can be.

In particular, it is preferable to add organic and / or inorganic fine particles to the coating layer in that the glossiness of the surface on which the coating layer is provided is easily within the above range. Examples of such inorganic fine particles include silica, alumina, titanium oxide (anatase type, rutile type), zinc oxide, barium sulfate, calcium carbonate, zeolite, kaolin, and talc. And cross-linked fine particles of cross-linked acryl. The particle diameter of the organic and / or inorganic fine particles is preferably 0.05 to 15 μm,
More preferably, it is 0.1 to 10 μm. 0.05
If it is less than μm, the effect of gloss reduction is insufficient, and
If it exceeds 5 μm, the surface is unnecessarily roughened or particles are easily dropped off, which is not preferable. Further, the content is preferably 0.5 to 50% by weight, more preferably 1 to 40% by weight, furthermore 2 to 50% by weight.
30% by weight is most preferred. When the content is less than 0.5% by weight, the effect of reducing the glossiness is small, and when the content is more than 50% by weight, application tends to be difficult, and the surface is roughened more than necessary. However, it is not preferable because the particles easily fall off.

The addition of a fluorescent whitening agent to the coating layer improves the whiteness and tint, and is more preferable. As the fluorescent whitening agent, the same ones as described above which are added to the white film can be used. Also,
The content of the fluorescent whitening agent in the coating layer is 0.01 to 2% by weight.
Is more preferable, more preferably 0.03 to 1.5% by weight,
Most preferably, it is in the range of 0.05 to 1% by weight. If the content is less than 0.01% by weight, the effect is small, and if it exceeds 2% by weight, on the other hand, yellowishness or durability tends to be lowered, which is not preferable.

In the present invention, the thickness of the white film is 10
It is preferably from 500 to 500 m, more preferably from 20 to 300 m. When the thickness is less than 10 μm, the reflectance, whiteness, and tint are low, and the handleability tends to decrease. On the other hand, when the thickness is larger than 500 μm, when the surface light source reflecting member is used for a liquid crystal display or the like, the weight tends to be heavy, and the cost tends to be high. Also,
When the white film is a composite film, its surface layer /
The ratio of the inner layer portion is preferably from 1/30 to 1/3, and
１ ／ is more preferred. 3 for surface layer / inner layer / surface layer
In the case of a multi-layer composite film, the ratio is represented by the sum of both surface layer parts / the inner layer part.

Next, an example of the method for producing a white film for a surface light source reflecting member of the present invention will be described, but the present invention is not limited to this example.

In the composite film forming apparatus provided with the extruder A and the extruder B, the extruder A had 85 parts by weight of dried PET chips, 15 parts by weight of polymethylpentene, and a molecular weight of about 40.
Then, a material obtained by mixing 1 part by weight of polyethylene glycol of No. 00 is supplied. A material obtained by mixing 90 parts by weight of PET, 10 parts by weight of calcium carbonate having an average particle size of about 1 μm, and 0.03 parts by weight of an optical brightener is supplied to the extruder B. Of course, each component of the raw materials supplied to the extruders A and B may be mixed in advance by a method such as pelletizing. Extruders A and B are heated to 280-300 ° C. and are melt-extruded.
At this time, the extruder A is melt-extruded in a composite state in which the raw material of the extruder B is laminated on both surfaces and the raw material of the extruder B is laminated on both surfaces.
The extruded sheet is solidified on a cooling drum having a surface temperature of 10 to 60 ° C. At this time, in order to obtain a uniform sheet, it is preferable to apply static electricity and bring the sheet into close contact with the drum.
The cooled and solidified sheet is guided to a group of rolls heated to 70 to 120 ° C., stretched about 2 to 5 times in the longitudinal direction, and stretched to 20 to 4 times.
Cool with rolls at 0 ° C. Further, the end of the film is continuously guided into the tenter while being gripped with a clip, and 90 to 1
After preheating to 20 ° C, the film is stretched 3 to 6 times in the width direction. Subsequently, the film is continuously guided to a zone heated to 180 to 230 ° C., heat-treated for about 3 to 20 seconds, and then cooled to 40 ° C. or lower to obtain a white film. On one surface of the obtained white film, a coating liquid in which a compound having an ultraviolet absorbing ability, a light stabilizer and a resin are mixed at a predetermined ratio is applied and dried.

The thus obtained white film for a surface light source reflecting member of the present invention has excellent initial luminance, has little deterioration even during long-term use, and can maintain the luminance of a liquid crystal screen.

[Method of Measuring and Evaluating Properties] (1) Average Bubble Diameter The cross section of the film was observed at a magnification of 3000 to 200,000 times using a transmission electron microscope HU-12 type (manufactured by Hitachi, Ltd.). , Marking a bubble portion in the field of view of the cross-sectional photograph, and using a high-definition image analysis processing device PIAS-IV
Image processing was performed using (Pierce Co., Ltd.), and the average bubble diameter when 100 bubbles were converted into a perfect circle was calculated, and the average value was calculated. (2) Specific gravity A sample sample obtained by cutting a film into a size of 50 mm × 60 mm is used as a high-precision electronic hydrometer SD-120L.
(Made by Mirage Trading Co., Ltd.) using JIS K-71
The measurement was carried out according to Method A (Substitution method in water) of No. 12. The measurement was performed at a temperature of 23 ° C. and a relative humidity of 65%. (3) Gloss Digital angular gloss meter UGV-5B (Suga Test Instruments Co., Ltd.)
JIS Z-8) from the side on which the coating layer is provided.
741 was measured. The measurement conditions were as follows: incident angle = 6
0 ° and the light receiving angle = 60 °. (4) Average reflectance spectral colorimeter SE-2000 (Nippon Denshoku Industries Co., Ltd.)
400-7 according to JIS Z-8722.
The spectral reflectance in the range of 00 nm is measured at 10 nm intervals,
The average value was taken as the average reflectance.

(5) Luminance of Surface Light Source According to the apparatus shown in FIG. 1, a 2 mm-thick acrylic transparent light guide plate 14 which has been subjected to halftone printing 15 is prepared. A film sample was set as the reflection plate 11 on the printing surface side, and a translucent sheet was stacked as the diffusion plate 13 on the opposite side. At this time, when the film provided with the coating layer was set, the films were superposed so that the surface of the coating layer was on the halftone dot printing surface side of the transparent light guide plate.
In the case of the sample, a 6 W fluorescent tube was attached as a cold cathode ray tube 16 from one end face of the transparent light guide plate 14, and the surroundings of the fluorescent tube were covered with a reflector 12 as shown in FIG. The fluorescent tube was turned on, and the luminance (cd / m ² ) was measured from the diffusion plate 13 side using a digital photometer J16 and a luminance measuring probe J6503 (manufactured by Tektronix). The measurement was carried out by pressing the photoreceptor portion of the luminance measuring probe attached to the photometer vertically against the diffusion plate 13. The luminance was measured three times at nine points where the in-plane was uniformly divided into nine parts, and expressed as an average value. (6) Average reflectance and brightness after durability test UV deterioration promotion tester i-super UV tester SUV
Using -W131 (manufactured by Iwasaki Electric Co., Ltd.), a forced ultraviolet irradiation test was performed under the following conditions. “Ultraviolet irradiation conditions” Illuminance: 100 mW / cm ² , temperature: 60 ° C., relative humidity:
50% RH, irradiation time: 8 hours The average reflectance and luminance of the sample after irradiation were measured according to the above methods (4) and (5).

[0045]

EXAMPLES The present invention will be described with reference to the following Examples and Comparative Examples, but it should not be construed that the invention is limited thereto.

Example 1 A composite film forming apparatus having an extruder A and an extruder B was supplied with a raw material having the following composition. Extruder A: 90 parts by weight of PET chips vacuum-dried at 180 ° C. for 4 hours, 10 parts by weight of polymethylpentene, and
1 part by weight of polyethylene glycol having a molecular weight of 4000. Extruder B: 15% by weight of barium sulfate having an average particle size of 1 μm
100 parts by weight of a PET chip containing the compound was vacuum-dried at 180 ° C. for 4 hours, and a PET master chip containing 1% by weight of an optical brightener (OB-1: manufactured by Eastman) was evacuated at 180 ° C. for 4 hours. 3 parts by weight of dried product.

Each of the raw materials was extruded from extruders A and B to 290
The mixture was melt-extruded at a temperature of ° C., and the molten material of the extruder A was joined to the inner layer so that the molten material of the extruder B was formed on both surface layers, and extruded into a sheet shape from a T-die. The thickness composition ratio of the composite film is B
/ A / B (5/90/5). This sheet was cast on a mirror cooling drum having a surface temperature of 20 ° C. to obtain an unstretched sheet. This sheet was preheated by a group of rolls heated to 90 ° C, and stretched 3.5 times in the longitudinal direction at 95 ° C. One surface of the uniaxially stretched sheet was subjected to a corona discharge treatment in air, and a polyurethane emulsion solution (AP-40: manufactured by Dainippon Ink Co., Ltd.) was applied to a thickness of 0.3 μm after drying. Then, the end of the sheet was gripped with a clip and guided into a tenter heated to 105 ° C. to remove water from the coating layer. Thereafter, the film was continuously stretched 3.5 times in the width direction in an atmosphere at 110 ° C. Further, heat treatment was continuously performed in an atmosphere at 215 ° C. for 8 seconds to obtain a white base film having a total thickness of 188 μm.

In order to provide a coating layer containing a light stabilizer on the surface of the polyurethane coating layer of the white base film, a coating liquid was applied so that the thickness after drying was 5 μm. As this coating liquid, "U-double" U in the form of a solution (concentration: 20%) is used.
V6010 (manufactured by Nippon Shokubai Co., Ltd.) was used. Drying after application was performed with hot air drying at 150 ° C. for 2 minutes. As shown in Table 1, the white film for the surface light source reflecting member thus obtained is hardly yellowed in an endurance test, and has an average reflectance,
The decrease in luminance was small.

[Comparative Example 1] The white base film obtained in Example 1 was evaluated as it is as a white film for a surface light source reflecting member. As a result, although the initial luminance was excellent, the durability was insufficient and the yellowness was remarkably yellow. And the average reflectance and luminance were remarkably reduced.

Examples 2 to 5 A white base film was obtained in the same manner as in Example 1. The coating layer containing the light stabilizer was dried on the surface of the polyurethane coating layer of the white base film in the same manner as in Example 1 to have a thickness of 1 μm (Example 2), 3 μm
(Example 3), 7 μm (Example 4) and 10 μm (Example 5) were applied. When the coating thickness is thinner than in Example 1 (Examples 2 and 3), the durability slightly decreases, and when the coating thickness is thicker (Examples 4 and 5), the initial luminance tends to slightly decrease. However, all were superior to Comparative Example 1.

Example 6 A white base film was obtained in the same manner as in Example 1. A coating layer containing a light stabilizer was provided in the same manner as in Example 1 except that a coating solution having the following composition was applied to the surface of the polyurethane coating layer of the white base film. As shown in Table 1, the white film for a surface light source reflecting member thus obtained was hardly yellowed in a durability test, and had a small decrease in average reflectance and luminance after the durability test. (Coating liquid for forming coating layer) "U-double" UV714 (solution having a concentration of 40%, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g "Sumidur" N3200 (hardening agent, manufactured by Sumitomo Bayern Urethane Co., Ltd.): 0.5 g Ethyl acetate / toluene (weight ratio = 1/1): 12.0 g

[Examples 7, 8, 9] A white base film was obtained in the same manner as in Example 6. As a coating liquid to be applied to the surface of the polyurethane coating layer of the white base film, 20.0 g of the coating liquid used in Example 1 was used, and silica powder as inorganic fine particles (“Siholovic” 1 manufactured by Fuji Silysia Ltd.)
00) with 0.13 g (contents of 3
Wt.), 0.21 g (5 wt.%), 0.3 g
(Same as above, 7% by weight) A coating layer containing a light stabilizer was provided in the same manner as in Example 6, except that a coating liquid added with stirring was used. As shown in Table 1, the thus obtained white film for a surface light source reflecting member has an excellent average reflectance and luminance, is hardly yellowed even in a durability test, and has a reduced average reflectance and luminance after a durability test. Was small.

Comparative Example 2 A PET chip containing 10% by weight of anatase-type titanium oxide having an average particle diameter of 0.15 μm was sufficiently dried under vacuum, and then supplied to an extruder of a single-layer film forming apparatus. The sheet was melt-extruded and cast on a cooling drum at 20 ° C. to form an unstretched sheet. This sheet was stretched in the longitudinal direction and the width direction in the same manner as in Example 1 and heat-treated to produce a white base film having a thickness of 188 μm. A coating layer containing a light stabilizer was provided on the white base film in the same manner as in Example 1. As shown in Table 1, the obtained film hardly contained bubbles inside, and the initial reflectance and luminance were insufficient.

[0054]

[Table 1]

[0055]

According to the white film for a surface light source reflecting member of the present invention, since a coating layer containing a light stabilizer is provided on a white base film containing bubbles, deterioration over time due to a light source is small. The image quality and brightness of the liquid crystal display can be maintained for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic vertical cross-sectional view of a device for measuring the luminance of a surface light source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Reflecting plate 12 Reflector 13 Diffusing plate 14 Transparent light guide plate 15 Halftone printing 16 Cold cathode ray tube

 ────────────────────────────────────────────────── ─── Continuing on the front page F-term (reference) 2H042 BA02 BA12 BA20 DA02 DA04 DA11 DE04 4F100 AA00B AA00H AH03A AH03C AK25A AK25C AK41B AK42B AK51B AL01A AL01C AR00B BA03 BA06 BA10A BA10C J23 CC00BJB JA CC01BJ00 JN21A JN21C YY00A YY00C

Claims (12)

[Claims] 1. A white film for a surface light source reflecting member, wherein a coating layer containing a light stabilizer is provided on at least one surface of a white film containing bubbles therein. 2. The white film for a surface light source reflecting member according to claim 1, wherein the coating layer is made of an acrylic resin or a methacrylic resin obtained by copolymerizing a light stabilizer component. 3. The white film for a surface light source reflecting member according to claim 1, wherein the light stabilizer is at least one of a hindered amine-based, benzotriazole-based, and benzophenone-based light stabilizer. 4. 400 to 400 measured from the surface provided with the coating layer.
The white film for a surface light source reflection member according to any one of claims 1 to 3, wherein the average reflectance at a wavelength of 700 nm is 85% or more. 5. The white film for a surface light source reflecting member according to claim 1, wherein the glossiness measured from the surface provided with the coating layer is 60% or less. 6. The white film for a surface light source reflecting member according to claim 1, wherein the white film is made of a resin composition containing polyester as a main component. 7. An internal bubble is formed by melt-extruding a mixture of a polyester resin and a resin incompatible with the polyester resin and / or organic or inorganic fine particles and stretching the mixture in at least one direction. The white film for a surface light source reflecting member according to any one of claims 1 to 6, wherein 8. The white film for a surface light source reflecting member according to claim 1, wherein the white film is a composite film. 9. The white film for a surface light source reflecting member according to claim 8, wherein the surface layer of the white film contains inorganic fine particles and bubbles formed with the inorganic fine particles as nuclei. 10. The white film is a composite film containing air bubbles in both the surface layer portion and the inner layer portion, and the cross-sectional average diameter of the air bubbles is smaller in the surface layer portion than in the inner layer portion. 4. The white film for a surface light source reflection member according to item 1. 11. The white film for a surface light source reflecting member according to claim 1, wherein the coating layer further comprises a resin composition containing organic and / or inorganic fine particles. 12. The white film for a surface light source reflecting member according to claim 1, wherein the coating layer and / or the white film further comprises a resin composition containing a fluorescent whitening agent. .