JP2002040214A - White film for surface light source reflection plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a member for surface light source reflection excellent in initial reflective characteristics, small in reduction with lapse of time of reflectance and luminance in long time usage and capable of maintaining high quality image for a long term. SOLUTION: A white film for surface light source reflection plate is characterized in that a coating layer containing a substance having UV absorbing ability and a fluorescent whitening agent is provided on at least one surface of a white film having bubbles in its internal part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a white film used for a surface light source reflector, 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 high initial luminance and 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 a cold cathode ray tube is used as an illumination light source from the edge of a light guide plate is widely used as an illumination device for a liquid crystal display (Japanese Patent Laid-Open No. 63-62).
No. 104). In this illumination method, a reflector is provided around the cold cathode ray tube in order to utilize light more efficiently, and furthermore, a reflector is provided under the light guide plate to efficiently reflect the light diffused from the light guide plate toward the liquid crystal screen. Is provided with a reflection plate. This reduces the loss of light from the cold cathode ray tube and provides a function of brightening the liquid crystal screen. 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.

A high reflection function is required for a reflector or a reflector used for such a surface light source for a liquid crystal screen. Conventionally, a film containing a white dye or a white pigment or a fine bubble contained therein is used. Films which have been used alone or in which these films are bonded to a metal plate, a plastic plate or the like have 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-6-322153 and JP-A-7-11843.
No. 3 discloses this.

[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 the illumination light source 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 conventional collector or reflector using a film, if used for a long time, yellowing occurs due to the deterioration of the film, which causes a problem that the reflection characteristics are reduced and the luminance of the screen is reduced.

[0005] In the conventional reflector, the luminance of the screen depends on the amount of light emitted from the light source. If the luminance is insufficient, it is necessary to increase the number of light source lamps or increase the output of the light source. There were problems such as insufficient durability of the reflector and energy loss due to an increase in the output of the light source.

The present invention solves the above-mentioned problems, improves the luminance without increasing the amount of incident light, can obtain high luminance without increasing the light source output more than necessary, and can be used for a long time. It is an object of the present invention to provide a surface light source reflecting member capable of maintaining a high-quality image for a long time with little decrease in luminance over time.

[0007]

In order to solve the above-mentioned problems, the present invention provides a coating film containing a substance having an ultraviolet absorbing ability and a fluorescent whitening agent on at least one surface of a white film containing bubbles therein. The main feature is a white film for a surface light source reflector, wherein

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The white film of the present invention is a thermoplastic film in which organic and inorganic dyes, fine particles, etc. are added;
The resin component is mixed with an incompatible resin and / or organic or inorganic particles, melt-extruded, and then stretched in at least one direction to form fine bubbles inside; It is not particularly limited as long as it has an apparent whiteness, such as foamed by adding and melt-extrusion; foamed by injection of a gas such as carbon dioxide gas. In particular, in the use of the present invention, as the reflectance is further improved, as the brightness is improved,
The resin component constituting the film is mixed with a resin incompatible with the resin component, and / or organic or inorganic particles, melt-extruded, and then stretched in at least one direction to form fine bubbles inside. Are preferred. Further, on at least one side of the film in which fine bubbles are formed inside, a thermoplastic resin to which organic and inorganic particles are added is laminated by a method such as co-extrusion, stretched, and air bubbles finer than the inner layer in the surface layer portion. Are 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,
Examples thereof include polybutylene terephthalate and poly-1,4-cyclohexylene dimethylene terephthalate. Of course, these polyesters may be homopolymers or copolymers, but are preferably homopolymers. When the copolymer component is a copolymer component, aromatic dicarboxylic acid, aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, a diol component having 2 to 15 carbon atoms, for example, isophthalic acid, adipic acid, sebacic acid,
Phthalic acid, sulfonic acid group-containing isophthalic acid, and ester-forming compounds thereof, diethylene glycol,
Examples thereof include triethylene glycol, neopentyl glycol, and polyalkylene glycol having a molecular weight of 400 to 20,000.

In these polyesters, various additives such as heat stabilizers, oxidation-resistant 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, a preferred example of the present invention in which polyester is used as a white film substrate will be described in detail.
Using polyester as a base material and whitening, there are various white dyes, a method of adding a white pigment, a method of including fine bubbles in the above-mentioned method, and the effects of the present invention are more remarkably exhibited. For this purpose, it is preferable to use a method in which fine bubbles are contained inside. As a method of containing such fine bubbles, a method of containing a foaming agent and foaming by heat at the time of extrusion or film formation, or foaming by chemical decomposition, a method of adding a gas or a vaporizable substance at the time of extrusion A method in which a thermoplastic resin incompatible with polyester is added, and after melt extrusion, it is monoaxially or biaxially stretched,
A method in which organic and inorganic fine particles are added, melt-extruded, and then uniaxially or biaxially stretched can be used. In the present invention, it is preferable to increase the reflection interface by forming fine bubbles, and the above method or the above method is preferable.

[0013] sectional area size 0.5μm ² ~50μm ² bubble thickness method obtained by the above method, preferably in terms those 1 [mu] m ² 30 .mu.m ² of brightness enhancement. The cross-sectional shape of the bubbles may be any of a circular shape and an elliptical shape. In particular, 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 preferable. That is, the light emitted from the light source is incident on the film surface when it is used as a reflector, and it is the most preferable form that all the incident light is reflected by the bubbles inside. Actually, there is light passing through the inside of the film, and this part is lost, but in order to cover this, metal deposition of aluminum, silver, etc. is applied to the film side opposite to the incident light side (light source side). It is preferable to apply.
In order to reduce light loss of the film containing fine bubbles therein, it is preferable to provide a layer containing fine bubbles of organic and inorganic particles on the surface of the bubble-containing polyester film. This surface layer can be obtained by incorporating organic and inorganic fine particles into a polyester resin, coextruding and compounding during the production of the internal bubble-containing film, and then stretching the film in at least one direction. The bubbles in the surface layer are preferably smaller than the bubbles in the inner layer in terms of luminance. The size of the bubbles can be controlled by the size of the particles to be added.

Here, the resin which is incompatible with the polyester resin and which is added for forming bubbles and the particles which are added to the inner layer portion and the surface layer portion will be described. The resin incompatible with the polyester 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 amount of the incompatible resin to be added is not particularly limited, and may be selected in consideration of the breakage during film formation and the luminance due to the formation of bubbles using the incompatible resin as a nucleus. Usually, the range is 3 to 35% by weight, 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, breakage during film formation is liable to occur.

The 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, anatase type, rutile type titanium oxide, and sulfuric acid. Barium, magnesium oxide, calcium phosphate, silica, alumina, mica, talc, kaolin and the like can be mentioned. Of these, addition of calcium carbonate and barium sulfate, which have low absorption in the visible light region of 400 to 700 nm, is particularly preferred. If absorption occurs in the visible light range, there is a problem that the luminance is reduced. In addition to the above, organic hollow particles and the like can also be preferably used. In the case of organic particles, those that do not melt by melt extrusion are preferable,
Crosslinked particles are particularly preferred. The above particles may be used alone or in combination of two or more. Although the particle size is not particularly limited, usually,
It is desirable that the thickness be 0.05 to 15 μm, preferably 0.1 to 5 μm, and more preferably 0.3 to 3 μm. 0.
When the thickness is less than 05 μm, the bubble formation property is insufficient,
If it exceeds μm, the surface is unnecessarily roughened, which is not preferable. In the case where particles are contained in the surface layer portion, it is preferable that the bubble diameter having the particles as a nucleus is smaller than the bubble diameter formed in the inner layer portion in terms of luminance.

The density of the white film containing such bubbles, which is a measure of the bubble content, is preferably 0.4 or more and less than 1.3. If the density is less than 0.4, the content of air bubbles is too high, and frequent tearing during film formation is likely to occur.
Problems such as insufficient mechanical strength and easy breakage may occur. When the ratio exceeds 1.3, the content of bubbles is too low, the reflectance is lowered, and the luminance tends to be insufficient.

The surface light source reflector is a plate-like material incorporated in the surface light source for light reflection, and specifically, a reflector of an edge light for a liquid crystal screen, a reflector of a surface light source of a direct type light. , And a reflector around the cold cathode ray tube, and the like, and when used as the surface light source reflector, the reflector preferably has higher whiteness in terms of the color tone of the screen, and is more bluish than yellowish. Darker shades are preferred. Considering this point, it is preferable to add a fluorescent whitening agent to the white film. As the fluorescent whitening agent, a commercially available one may be appropriately used. For example, "Ubitek" (Ciba-Geigy-
OB-1 (manufactured by Eastman), TBO (manufactured by Sumitomo Seika), "Kay Coal" (manufactured by Nippon Soda), "Kayalite" (manufactured by Nippon Kayaku), "Ryukopua" EGM
(Manufactured by Client Japan) can be used. The addition amount of the fluorescent whitening agent is in the range of 0.005 to 1% by weight, preferably 0.03 to 0.5% by weight.
If the amount is less than 0.005% by weight, the effect is small, and if it exceeds 1% by weight, yellowish tint is unfavorably produced. It is effective to add the fluorescent whitening agent to the surface layer when the white film is a composite.

In the present invention, it is important to provide a coating layer containing a substance having an ultraviolet absorbing ability and a fluorescent whitening agent on at least one side of such a white film.
Examples of the compound having an ultraviolet absorbing ability include inorganic ultraviolet absorbing agents such as benzophenone, benzotriazole, triazine, cyanoacrylate, salicylic acid, benzoate, oxalic anilide, and sol-gel. Further, those obtained by copolymerizing these compounds having an ultraviolet absorbing ability can also be suitably used. Furthermore, the combined use of a hindered amine light stabilizer,
More effective.

Specific examples of the compound having the ultraviolet absorbing ability and the light stabilizer are shown below, but are not limited thereto.

[Compound having UV absorbing ability] 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, benzotriazole: 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-benzotriazol-2-yl) phenol], 2 (2'hydroxy-5'-methacryloxyphenyl) -2H -Benzotriazole, 2
-[2'-hydroxy-3 '-(3 ", 4", 5 ",
6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl] benzotriazole, cyanoacrylate: ethyl-2-cyano-3,
3'-Diphenyl acrylate Other than the above: 2-ethoxy-2'-ethyloxazac acid bisanilide, 2- (4,6-diphenyl-1,
3,5-triazin-2-yl) -5-[(hexyl)
[Oxy] -phenol, [light stabilizer] hindered amine type: bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, dimethyl succinate-1- (2-hydroxyethyl) -4-hydroxy-
2,2,6,6-tetramethylpiperidine polycondensate, other than the above: nickel bis (octylphenyl) sulfide, [2-thiobis (4-t-octylphenolate)]-n-butylamine nickel, nickel complex-3 , 5-di-t-butyl-4-hydroxybenzyl-phosphate monoethylate, nickel dibutyldithiocarbamate, 2,4-di-t-butylphenyl-
3 ', 5'-di-t-butyl-4'-hydroxybenzoate, 2,4-di-t-butylphenyl-3', 5 '
-Di-t-butyl-4'-hydroxybenzoate The above compounds may be used alone or in combination of two or more. Particularly, the combined use of a compound having an ultraviolet absorbing ability and a light stabilizer is excellent in durability and is particularly preferable.

The compound having an ultraviolet absorbing ability can be used by being appropriately mixed with other resin components. Mixing is performed by dissolving or dispersing the resin component and the ultraviolet absorbing compound in an organic solvent that respectively dissolves them, and using as a coating liquid.
The resin component to be mixed is not particularly limited, and those dissolved or dispersed in an organic solvent or water can be arbitrarily used. Examples of the resin component include polyester, polyurethane, acrylic, polyamide, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, a fluororesin, and a copolymer of these, or a mixture of two or more thereof. Etc. can be used. In addition, a compound obtained by copolymerizing a compound having an ultraviolet absorbing ability may be used as it is as a coating material.

As a copolymer of a compound having an ultraviolet absorbing ability and another monomer component, for example, a polymer obtained by copolymerizing a benzotriazole-based reactive monomer and an acrylic monomer can be preferably used. The benzotriazole-based 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'-te
rt-butyl-5'-acryloylethylphenyl)-
5-chloro-2H-benzotriazole and the like can be mentioned.

The acrylic monomers and / or oligomers copolymerized with these monomers include alkyl acrylates and alkyl methacrylates (where the alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl). Group, t-butyl group,
2-ethylhexyl group, lauryl group, stearyl group, cyclohexyl group, etc.) and a monomer having a crosslinkable functional group, for example, a carboxyl group, a methylol group, an acid anhydride group, a sulfonic acid group, an amide group, a methylolated amide group And a monomer 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 such as a saturated polyester.

The copolymerization ratio of these monomers having an ultraviolet absorbing ability and the monomers copolymerized therewith is not particularly limited, and one or two or more of them can be copolymerized at an arbitrary ratio. Preferably, the ratio of the monomer having an ultraviolet absorbing ability is 10% by weight or more,
Preferably 20% by weight or more, more preferably 35% by weight
It is desirable that this is the case. Of course, a homopolymer of a monomer having an ultraviolet absorbing ability 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, more preferably 20,000
It is preferable that the above is from the viewpoint of the toughness of the coating film. These polymers are used in the state of being dissolved or dispersed in an organic solvent or water. In addition, commercially available hybrid ultraviolet absorbing polymers, for example, "U-double" (manufactured by Nippon Shokubai Co., Ltd.) can also be used.

The coating layer contains the substance having the ability to absorb ultraviolet light and a fluorescent whitening agent. By incorporating the fluorescent whitening agent, the effect of absorbing the wavelength in the ultraviolet region emitted from the light source and improving the apparent reflectance in the visible wavelength range of 400 to 450 nm can be exhibited. The improvement in the reflectance of the wavelength in this region increases the bluishness of the liquid crystal screen, and can provide a more attractive white color on the display.

The fluorescent whitening agent is effective even if it is added to the substrate film, but it is particularly effective to include it in the coating layer in the sense that it is closer to the light source and absorbs ultraviolet light efficiently to emit light.

Known fluorescent brightening agents can be used. For example, "Ubitech" (manufactured by Ciba-Geigy), OB-1 (manufactured by Eastman), TBO (manufactured by Sumitomo Seika), "Kay Coal" (manufactured by Nippon Soda), "Kayalite" (manufactured by Nippon Kayaku) , "Lyukopua" EGM (manufactured by Client Japan) or the like can be used.
These are used by adding to a coating solution in a state of being dissolved or dispersed in various solvents.

The amount of the optical brightener added in the coating layer is 0.0
It is desirably in the range of 0.05 to 1% by weight, preferably 0.01% to 0.5% by weight, more preferably 0.03% to 0.2% by weight. If the amount is less than 0.005% by weight, the effect of improving brightness is small, and if it exceeds 1% by weight, the coating layer becomes yellowish.

The thickness of the coating layer is not particularly limited.
It is desirable that it is 5 to 15 μm, preferably 1 to 10 μm, and more preferably 2 to 7 μm. If it is less than 0.5 μm, the durability may be insufficient, and if it exceeds 15 μm, the luminance may be reduced.

The above-mentioned coating layer may be provided directly on the white film of the base material. However, when the adhesiveness is insufficient, it is preferable to provide the base film with a corona discharge treatment or a subbing treatment. The undercoating treatment may be a method provided in the white film manufacturing process (in-line coating method),
After the white film is manufactured, it may be separately applied. The material applied to the undercoating treatment is not particularly limited and may be appropriately selected, but preferred examples include copolymerized polyester, polyurethane, acrylic, and various coupling agents.

The coating layer can be applied by any method. For example, methods such as gravure, roll, spin, reverse, bar, screen, and dipping can be used. A known method can be used as a curing method after the application. For example, a method using active rays such as heat curing, ultraviolet rays, electron beams, and radiation, and a method using a combination thereof can be applied. The coating may be performed at the time of manufacturing the base film (in-line coating) or may be performed after the completion of the crystal orientation (off-line coating).

Various additives can be appropriately added to the coating layer as long as the effects of the present invention are not impaired. For example, heat stabilizers, oxidation stabilizers, organic lubricants, organic and inorganic fine particles, light stabilizers, antistatic agents, nucleating agents, coupling agents, and the like may be added.

The white film of the present invention preferably has an average reflectance of 85% or more, more preferably 87% or more, particularly preferably 90% or more, at a wavelength of 400 to 700 nm measured from the surface provided with the coating layer. It is desirable that When the average reflectance is less than 85%, the luminance may be insufficient depending on the liquid crystal display to be applied.

Next, an example of the method for producing a white film for a surface light source reflector 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 includes 85 parts by weight of dried PET chips, 15 parts by weight of polymethylpentene, and a molecular weight of about 40 parts.
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 to 300 ° C. and are melt-extruded.
At this time, the composite is formed such that the raw material of the extruder A is laminated on the inner layer 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 cooled by a group of rolls of 20 to 40 ° C. Further, the end of the film is continuously guided into the tenter while being gripped by clips, preheated to 90 to 120 ° C., and then stretched 3 to 6 times in the width direction. Continuously 18
It is led to a zone heated to 0 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, a resin, and a fluorescent whitening agent are mixed at a predetermined ratio is applied and dried.

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

[Method for Measuring and Evaluating Characteristics] (1) Average Bubble Diameter The cross section of the film was observed at a magnification of 3000 to 200,000 using a transmission electron microscope HU-12 (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) Average Reflectance Spectroscopic Color Difference Meter 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. (3) Luminance of Surface Light Source According to the apparatus shown in FIG. 1, a 2 mm-thick acrylic transparent light guide plate 14 having a halftone dot printed thereon is prepared. A film sample was set as a reflection plate 11 on one side, and a translucent sheet as a diffusion plate 13 was placed on the opposite side. Next, a fluorescent lamp of 6 W was attached to one end face of the transparent light guide plate 14 as a cold cathode ray tube 16, and the area around the fluorescent tube was covered with a reflector 12 as shown in FIG. The fluorescent tube is turned on to allow the light to enter the transparent light guide plate 14, and the light diffused from the diffusion plate 13 side is used for luminance (cd / d) using a digital photometer J16 and a luminance measurement probe J6503 (manufactured by Tektronix). m ² ) was measured. 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. (4) Average reflectance and brightness after durability test UV deterioration promotion tester iSuper 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 Average reflectance of the sample after irradiation according to the above methods (2) and (3) And the brightness were measured.

[0039]

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, 10 parts by weight of polymethylpentene, and 1 part by weight of polyethylene glycol having a molecular weight of 4000, which were vacuum-dried at 180 ° C. for 4 hours. Extruder B: 100 parts by weight of a PET chip containing 15% by weight of barium sulfate having an average particle diameter of 1 μm which was vacuum-dried at 180 ° C. for 4 hours, and an optical brightener (OB-
1: 1% by weight manufactured by Eastman Co., Ltd.), and 3 parts by weight of a PET master chip containing 1% by weight and dried at 180 ° C. for 4 hours under vacuum.

Each raw material 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, hold the sheet end with a clip and
It was led into a tenter heated to 05 ° 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.

On the surface of the polyurethane coating layer of this white base film, "UVITEX-OB" was used as a fluorescent brightener in a toluene / butyl acetate solution of "Utable" UV6010 (manufactured by Nippon Shokubai) as a substance having an ultraviolet absorbing ability.
(CHIBA-GEIGY) was applied so that the solid content ratio in the coating solution was 0.03% by weight, and the coating after drying was 5 μm in thickness. Drying was performed with hot air drying at 150 ° C. for 2 minutes. As shown in Table 1, the white film for a surface light source reflector thus obtained had a high initial luminance, was not easily yellowed in a durability test, and had a small decrease in average reflectance and luminance.

Comparative Example 1 As a result of using the white base film obtained in Example 1 as a white film for a surface light source reflector, the initial luminance was excellent but the durability was insufficient.
The yellowness was remarkably increased, and the average reflectance and the luminance were significantly reduced.

Examples 2 to 5 A white base film was obtained in the same manner as in Example 1. The same coating layer as in Example 1 was dried on the surface of the polyurethane coating layer of the white base film, and the thickness after drying was 1 μm (Example 2), 3 μm (Example 3), and 7 μm.
(Example 4) Coating was performed so as to be 10 μm (Example 5). When the coating thickness is small, the luminance and durability slightly decrease, and when the coating thickness is too large, the initial luminance tends to decrease slightly, but all are superior to Comparative Example 1.

Comparative Example 2 In a single-layer film forming apparatus having only an extruder A, a PET chip containing 10% by weight of anatase type titanium oxide having an average particle diameter of 0.15 μm was sufficiently dried in vacuum and supplied to the extruder. Then, it was melt-extruded into a sheet at 290 ° C. 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 by the method of Example 1 and subjected to a heat treatment to obtain a white base film having a thickness of 188 μm. The same coating layer as in Example 1 was provided on this film.

The obtained film was as shown in Table 1.
Contains few bubbles inside, initial reflectance,
The luminance was insufficient.

Comparative Example 3 A paint was prepared by removing the fluorescent whitening agent from the paint for the coating layer used in Example 1, and this paint was
On the white substrate film obtained in Example 1, application was performed in the same manner as in Example 1 to form a coating layer, and a white film for a surface light source reflector was prepared. Although showing sufficient durability, the initial luminance was lower than that obtained by adding a fluorescent whitening agent.

[Examples 6 to 8] The amount of the optical brightener added in the coating material for the coating layer used in Example 1 was 0.01% by weight (Example 6) and 0.1% by weight (Example 7). ) And 0.3% by weight (Example 8), except that the coating layer was formed in the same manner as in Example 1 to prepare a white film for a surface light source reflector. All of these improved initial luminance and were excellent in durability.

[Comparative Example 4] In a toluene solution of a polyester copolymer ("Vylon" 200: manufactured by Toyobo Co., Ltd.), "UVITEX-OB" (CHI) was used as a fluorescent whitening agent.
BA-GEIGY) at a solid content ratio of 0.03 in the coating solution.
A white film for a surface light source reflector was prepared in the same manner as in Example 1, except that a coating material was added so as to have a weight%, and this coating material was used for a coating layer. This film was found to have an effect of improving the initial luminance, but was inferior in durability.

[0050]

[Table 1]

[Table 2]

[0051]

According to the white film for a surface light source reflector of the present invention, a coating layer containing a substance having an ultraviolet absorbing ability and a fluorescent whitening agent is provided on a white base film containing bubbles. In addition, the initial luminance is high, the deterioration over time due to the light source is small, and 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 schematically illustrating the structure 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

 ──────────────────────────────────────────────────の Continued on front page F-term (reference) 2H042 BA02 BA12 BA15 BA20 4F100 AA00A AA00C AH00A AH00C AK41A AK41C BA03 BA05 BA10A BA10B BA21 DE01A DE01C DJ01A DJ01C DJ06A DJ06C EH17A EH17C JH37 EJB37 EH171 EHBJ EH17 EJB37

Claims (8)

[Claims] 1. A white film for a surface light source reflector, wherein a coating layer containing a substance having an ultraviolet absorbing ability and a fluorescent whitening agent is provided on at least one surface of a white film containing bubbles therein. . 2. 400 to 400 measured from the surface provided with the coating layer.
The white film for a surface light source reflector according to claim 1, wherein the average reflectance at a wavelength of 700 nm is 85% or more. 3. The white film for a surface light source reflector according to claim 1, wherein the white film is made of a resin composition containing polyester as a main component. 4. An internal cell obtained by melt-extruding a mixture of a polyester resin and a resin incompatible with the polyester resin and / or organic or inorganic particles and stretching the mixture in at least one direction. The white film for a surface light source reflector according to claim 1, wherein: 5. The white film for a surface light source reflector according to claim 1, wherein the white film is a composite film. 6. The white film for a surface light source reflector according to claim 5, wherein the composite layer of the white film contains inorganic particles and contains bubbles formed with the inorganic particles as nuclei. 7. The method according to claim 5, wherein the white film is a composite film having 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. A white film for a surface light source reflector according to the above. 8. The amount of addition of the fluorescent whitening agent in the coating layer is 0.0
The white film for a surface light source reflector according to any one of claims 1 to 7, wherein the content is 0.5 to 1% by weight.