JP2012048015A - Reflection sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection sheet having a metal thin film layer and a white film, which protects the metal thin film layer, prevents the deterioration of the white film, and has an excellent reflection property.SOLUTION: A reflection sheet includes a polyester film 1, a metal thin film layer 2, and a white film 3, which are laminated in this order. The polyester film 1 has ultraviolet light absorbing capability, haze of 1.8% or less, and surface roughness at the side of the metal thin film layer 2 of 0.020 μm or less.

Description

  The present invention relates to a reflection sheet, particularly to a reflection sheet used for a backlight used in a surface light source device of a liquid crystal display device. Specifically, it is a reflective sheet with a metal thin film layer, which prevents the corrosion of the metal thin film layer due to adsorbed water by laminating a polyester film having ultraviolet absorbing ability, and further prevents the white film from deteriorating. The present invention relates to a reflective sheet with little deterioration in characteristics.

  In a liquid crystal display device, the sidelight type backlight method generally has a laminated structure in the order of a reflection sheet, a light guide plate, a diffusion plate, a prism sheet, and a liquid crystal cell in a casing, and the side of the light guide plate. A light source (lamp) such as a cold cathode tube or LED (light emitting diode) and a lamp reflector are arranged, and a backlight is mainly composed of a laminated structure from a reflection sheet to a diffusion plate or a prism sheet, a light source and a lamp reflector. Has been. On the other hand, in a direct backlight type liquid crystal display device, a reflective sheet, a light source (lamp), a diffuser plate, a prism sheet, and a liquid crystal cell are laminated in this order in a casing, and a laminated structure from the reflective sheet to the prism sheet And the backlight is mainly composed.

  The reflection sheet is required to have a high front reflection ratio (also referred to as mirror reflection) in order to efficiently allow the light emitted from the light source to reach the liquid crystal cell. As such a reflective sheet, a reflective sheet such as a white film containing a white pigment, a foamed white film containing a cavity, or a film having a metal deposited layer such as a silver deposited layer or an aluminum layer is used. . In particular, a metal thin film layer such as a metal vapor deposition layer has a high reflectance. In particular, when the metal thin film layer is provided by a vapor deposition method, a defect may be manifested depending on the shape of the film surface serving as the base material, or the reflection characteristics may be deteriorated. Moreover, since light may leak from the metal thin film layer to the back surface, a configuration in which a white film having a high light shielding property is disposed on the back surface of the metal thin film layer is employed as the reflective sheet.

  On the other hand, the metal thin film layer has a defect that is weak against oxidation and corrosion due to adsorbed water. Therefore, many proposals have been made to protect the metal thin film layer. For example, Document 1 proposes that after forming a metal vapor deposition layer such as silver on transparent polyethylene terephthalate, the vapor deposition layer is applied with a polyester-based resin to provide a protective layer. Further, Document 2 proposes that a silver vapor deposition layer is formed on one side of a synthetic film, and a titanium oxide protective layer formed by applying a titanium alkoxide and heat-treating thereon is provided.

Japanese Patent Publication No. 37-12931 Japanese Patent Laid-Open No. 4-45821

  However, in Reference 1, the gas is not sufficiently blocked by the protective layer, and corrosion of the metal thin film layer cannot be prevented. Further, in Document 2, since the number of steps is increased because a protective layer is provided, workability is poor and costs are increased.

  Further, in long-term use, the white film is deteriorated or yellowed by ultraviolet rays emitted from a light source such as a cold cathode tube. In recent years, the brightness of displays has been improved, and the amount of ultraviolet rays emitted from a light source is increasing. Therefore, the problem of deterioration of the white film due to ultraviolet rays is becoming obvious.

  The present invention relates to a reflection sheet, and in the reflection sheet having a metal thin film layer and a white film, an object is to provide a reflection sheet that protects the metal thin film layer, prevents the deterioration of the white film, and has good reflection characteristics. And

The above-described problem can be achieved by the following solution means.
(1) A reflective sheet obtained by laminating a polyester film, a metal thin film layer, and a white film in this order, the polyester film has an ultraviolet absorbing ability, has a haze of 1.8% or less, and has a metal thin layer side. A three-dimensional center plane average roughness (SRa) of 0.020 μm or less.
(2) The reflective sheet, wherein the polyester film has a laminated structure of three or more layers, and contains an ultraviolet absorber in at least the intermediate layer.
(3) The said reflective sheet whose light transmittance of wavelength 380nm of the said polyester film is 20% or less.
(4) A polyester film used for the reflection sheet.

  The reflective sheet of the present invention has little deterioration due to adsorbed water or ultraviolet rays, and has stable reflection characteristics over a long period of time.

Reflection sheet configuration diagram

(1) Polyester film The present invention is characterized in that a polyester film having an ultraviolet absorbing performance is laminated on a metal thin layer surface of a reflective sheet having a metal thin film layer and a white film. Thereby, not only can the metal thin film layer be simply and easily protected, but also the white film can be protected from ultraviolet rays, whereby the deterioration of the reflection characteristics in the long-term use can be suitably suppressed.

  The thickness of the polyester film used in the present invention is not particularly limited, but can be arbitrarily determined in the range of 10 to 250 μm according to the standard of the application to be used. The upper limit of the thickness of the polyester film is preferably 150 μm, particularly preferably 125 μm. On the other hand, the lower limit of the film thickness is preferably 15 μm, more preferably 25 μm, and particularly preferably 50 μm. When the film thickness is less than 10 μm, the protection of the metal thin film layer tends to be insufficient. On the other hand, when the film thickness exceeds 250 μm, the manufacturing cost increases.

  As the polyester resin constituting the polyester film, polyethylene terephthalate, polyethylene-2, 6 naphthalate, polypropylene terephthalate, polybutylene terephthalate, or a copolymer mainly composed of these resin components is preferable, and in particular, polyethylene terephthalate. Is preferred.

  When a polyester copolymer having polyethylene terephthalate as a basic skeleton is used as the resin for forming the polyester film, the ratio of the copolymer component is preferably less than 20 mol%. If it is 20 mol% or more, the film strength, transparency, and heat resistance may be inferior. Examples of the dicarboxylic acid component that can be used as a copolymerization component include aliphatic dicarboxylic acids such as adipic acid and sebacic acid, aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid, and trimellilot acid And polyfunctional carboxylic acids such as pyromellilottic acid. Examples of the glycol component that can be used as a copolymer component include fatty acid glycols such as diethylene glycol, 1,4-butanediol, propylene glycol, and neopentyl glycol; aromatic glycols such as p-xylene glycol; 1,4-cyclohexane Examples include alicyclic glycols such as dimethanol; polyethylene glycol having an average molecular weight of 150 to 20,000.

  The polyester film of the present invention may be a single layer or a laminated structure of two or more layers. In the case of a multilayer structure of three or more layers, if the layer having an ultraviolet absorber is an A layer, and the other surfaces are a B layer and a C layer, the layer structure in the film thickness direction is B / A / B, B / Configurations such as A / C, B / A / C / B, or B / A / C / A / B are conceivable. Each of the A to C layers may have the same or different configuration of the polyester resin, but preferably has a B / A / B configuration (two types and three layers). In any case, by including an ultraviolet absorber in the intermediate layer, bleeding out of the additive can be suitably prevented, and deterioration of adhesion due to bleeding out of the additive can be suppressed.

  It is important that the polyester film of the present invention contains an ultraviolet absorber. A well-known substance can be used for a ultraviolet absorber. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency. Examples of the organic ultraviolet absorber include benzotoazole, benzophenone, cyclic imino ester, and combinations thereof, but are not particularly limited as long as the absorbance is within the range defined by the present invention. However, from the viewpoint of durability, benzotoazole and cyclic imino ester are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved.

  Examples of the benzophenone ultraviolet absorber, benzotriazole ultraviolet absorber, and acrylonitrile ultraviolet absorber include 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole, 2- [2 ′. -Hydroxy-5 '-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2'-hydroxy-5'-(methacryloyloxypropyl) phenyl] -2H-benzotriazole, 2,2'-dihydroxy- 4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2- ( 2'-hydroxy-3'-tert-butyl-5'-methylphenyl)- 5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol, 2,2'-methylenebis (4- (1,1 , 3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, etc. Examples of cyclic imino ester UV absorbers include 2,2 ′-(1,4-phenylene). Bis (4H-3,1-benzoxazinon-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, 2-phenyl -3,1-benzoxazin-4-one, etc. However, it is not particularly limited thereto.

  The polyester film of the present invention preferably has a transmittance at a wavelength of 380 nm of 20% or less, more preferably 10% or less. In order to reduce the transmittance of the polyester film of the present invention at a wavelength of 380 nm to 20% or less, it is preferable to appropriately adjust the concentration of the ultraviolet absorber and the thickness of the polyester film. In addition, the transmittance | permeability in this invention is measured by the perpendicular | vertical method with respect to the plane of a polyester film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type).

  In addition to the ultraviolet absorber, the polyester resin constituting the polyester film can contain various additives in addition to the catalyst as long as the effects of the present invention are not hindered. Examples of additives include inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light proofing agents, flame retardants, thermal stabilizers, antioxidants, and antigelling agents. And surfactants.

  In the reflection sheet of the present invention, since the light beam that has passed through the polyester film is reflected on the metal thin film layer on the back surface, the reflected light passes through the polyester film twice or more. Therefore, it is preferable that the polyester film has high transparency. The polyester film of the present invention preferably has a haze of 1.8% or less. Furthermore, it is preferable that it is 1.0% or less. If the haze of the polyester film is higher than 1.8%, the brightness of the liquid crystal display screen is lowered, which is not preferable.

  In the present invention, the metal thin film layer is preferably provided on the polyester film surface by vapor deposition. In order to maintain good reflection characteristics in the metal thin film layer, the polyester film surface is preferably smooth. When the film surface is rough, the surface brightness may decrease due to surface scattering, and it may be visually recognized as a defect in appearance. Therefore, the three-dimensional center plane average roughness (SRa) of the polyester film of the present invention is preferably 0.020 μm or less, more preferably 0.015 μm or less. The ten-point average roughness (SRz) is preferably 1.0 μm or less, and more preferably 0.5 μm or less. When the surface roughness of the polyester film exceeds the above range, the surface quality of the metal vapor-deposited surface is rough and the gloss is lost.

  In order to control the haze and surface roughness of the polyester film within the above ranges, it is desirable that the polyester film does not substantially contain particles that cause a decrease in transparency. When it is contained in the polyester film, it is desirable to provide an outermost layer and minimize the influence on transparency.

  The above-mentioned “substantially contain no particles” means, for example, in the case of inorganic particles, a content of 50 ppm or less, preferably 10 ppm or less, most preferably less than the detection limit when inorganic elements are quantified by fluorescent X-ray analysis. Means quantity. This means that even if particles are not actively added to the polyester film, contaminants derived from foreign substances and raw material resin or dirt adhering to the lines and equipment in the film manufacturing process are peeled off and mixed into the film. This is because there are cases.

  Moreover, in order to provide easy slipperiness | lubricity, it is preferable to control the density | concentration and average particle diameter of particle | grains, even when it is a case where particle | grains are included in a polyester film. The average particle size of the particles added to the film is preferably 3 μm or less, and more preferably 2.5 μm or less. In the case of a laminate structure of three or more layers, it is preferable to add the particles only to the outermost layer from the viewpoint of transparency. In that case, the additive concentration of the particles is preferably 0.03% by mass or less, and more preferably 0.025% or less.

  The particles include calcium carbonate, calcium phosphate, amorphous silica, spherical silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, Inorganic particles such as zeolite, molybdenum sulfide and mica, crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate particles, benzoguanamine / formaldehyde condensate particles, melamine / formaldehyde condensate particles, polytetrafluoroethylene particles, etc. Examples include heat-resistant polymer fine particles. In particular, from the viewpoint of transparency, silica particles, particularly amorphous silica, having a refractive index relatively close to that of the resin component are suitable.

  Although the manufacturing method of the polyester film of this invention is not specifically limited, It is as follows when it illustrates.

  As a method of blending a UV absorber with a polyester film, a known method can be used in combination. For example, a master batch is prepared by blending a dried UV absorber and a polyester raw material in advance using a kneading extruder. In addition, it can be blended by a method of mixing the predetermined master batch and the polyester raw material at the time of forming the polyester film.

  At this time, the concentration of the UV absorber in the master batch is preferably 5 to 30% by weight in order to uniformly disperse the UV absorber and economically blend it. As a condition for producing the master batch, it is preferable to use a kneading extruder and to extrude it at a temperature not lower than the melting point of the polyester raw material and not higher than 290 ° C. for 1 to 15 minutes. Above 290 ° C, the weight loss of the UV absorber is large, and the viscosity of the master batch is greatly reduced. When the extrusion temperature is 1 minute or less, uniform mixing of the UV absorber becomes difficult. At this time, if necessary, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added.

  Specifically, a polyester film having a three-layer structure containing an ultraviolet absorber in the intermediate layer can be produced as follows. PET pellets alone for the outer layer, and master batches containing UV absorbers for the intermediate layer and PET pellets are mixed at a predetermined ratio, dried and then fed to a known melt laminating extruder, Extruded into a sheet form from a die and cooled and solidified on a casting roll to make an unstretched film. That is, using two or more extruders, a three-layer manifold or a merging block (for example, a merging block having a square merging portion), a film layer constituting both outer layers and a film layer constituting an intermediate layer are laminated, An unstretched film is formed by extruding a three-layer sheet from the die and cooling with a casting roll. In the present invention, it is preferable to perform high-precision filtration during melt extrusion in order to remove foreign substances contained in the raw material polyester that cause optical defects. The filter particle size (initial filtration efficiency 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. When the filter particle size of the filter medium exceeds 15 μm, removal of foreign matters of 20 μm or more tends to be insufficient.

  The unstretched film obtained above is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120 ° C. to obtain a uniaxially oriented polyester film. A coating solution is applied to one side or both sides of a uniaxially oriented polyester film as described below. Next, both ends of the film are gripped with clips, guided to a hot air zone heated to 80 to 180 ° C., and stretched 2.5 to 5.0 times in the width direction after drying. Subsequently, it is guided to a heat treatment zone of 220 to 240 ° C., and heat treatment is performed to complete crystal orientation. In this heat treatment step, a relaxation treatment of 1 to 12% may be performed in the width direction or the longitudinal direction as necessary.

  The polyester film is a surface activation treatment such as a corona discharge treatment, a glow discharge treatment, a flame treatment, an ultraviolet irradiation treatment, an electron beam irradiation treatment, and an ozone treatment within a range not impairing the object of the present invention. May be applied.

  Furthermore, the film of the present invention may be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion of the film surface when the curable resin is laminated.

  In the present invention, in order to improve the adhesiveness with the curable resin, an adhesive modification layer mainly comprising at least one of a polyester resin, a polyurethane resin or a polyacrylic resin is formed on at least one surface of the film of the present invention. It is preferable to have. Here, the “main component” refers to a component that is 50% by mass or more of the solid components constituting the adhesive modified layer. The coating liquid used for forming the adhesion modified layer is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymerized polyester resin, acrylic resin and polyurethane resin. Examples of these coating liquids include water-soluble or water-dispersible co-polymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The adhesive modification layer can be obtained by applying the coating solution on one or both sides of a uniaxially stretched film in the longitudinal direction, drying at 100 to 150 ° C., and further stretching in the transverse direction. It is preferable to manage the final coating amount of the adhesion modified layer at 0.05 to 0.20 g / m ² . If the coating amount is less than 0.05 g / m ² , adhesion with the resulting curable resin may be insufficient. On the other hand, when the coating amount exceeds 0.20 g / m ² , blocking resistance may be lowered. When the adhesive property modification layer is provided on both sides of the polyester film, the coating amount of the adhesive property modification layer on both surfaces may be the same or different, and can be independently set within the above range. it can.

  It is preferable to add particles to the adhesion modified layer in order to impart easy slipping. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle diameter of the particles exceeds 2 μm, the particles easily fall off from the adhesion modified layer. Examples of the particles to be contained in the adhesion modified layer include the same particles as those described above.

  Moreover, a well-known method can be used as a method of apply | coating a coating liquid. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, etc. can be mentioned. Or it can carry out in combination.

(2) Metal thin film layer In this invention, in order to provide favorable light reflectivity, it is preferable to provide a metal thin film layer. The metal which comprises a metal thin film layer should just be a metal with little light absorption, for example, aluminum, silver, gold | metal | money, platinum, stainless steel, and those alloys can also be tried. Aluminum is superior in terms of economy. On the other hand, it is preferable to use silver or a silver alloy in the light reflection characteristics. What is necessary is just to select a metal material suitably by market demand. Further, the metal thin film may contain a small amount of a nonmetallic element to the extent that the reflectance is not impaired. The metal thin film may have a single layer configuration or a stacked configuration.

  The metal thin film layer is generally formed by a vacuum vapor deposition method, but can also be formed by an ion plating method, a sputtering method or a CVD method. Moreover, what was prepared by wet methods, such as a plating method, may be used. Preferably, it is preferably provided on one surface of the polyester film by vapor deposition. The thickness of the metal thin film is in the range of 200 to 1100 mm, preferably in the range of 400 to 900 mm in view of the reflectivity. Further, an undercoat layer or a protective layer may be formed in order to improve the adhesion of the metal thin film layer or to suppress deterioration of the metal thin film layer. Moreover, you may form the coating layer which has functions, such as scratch resistance, on the opposite surface of a metal thin film layer.

(3) White film A light-shielding white film is used to prevent the light from the backlight from passing through the metal thin film layer and leaking from the back surface to prevent escape. Here, the white color of the white film means that the average reflectance at a wavelength of 400 nm to 700 nm is 85% or more.

  The material of the white film is not particularly limited, but a thermoplastic resin that can be melt-molded is more preferable. For example, polyesters such as polyethylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, polyolefins such as polyethylene, polypropylene, and polycyclohexanedimethanol , Polyamide, polyurethane, polyphenylene sulfide, and the like. These may be copolymers, and various additives such as heat stabilizers, antioxidants, lubricants, organic, inorganic fine particles, light-proofing agents, antistatic agents, nucleating agents, etc. are harmful to the physical properties of the film. It may be added to such an extent that does not give. Of these, a polyester resin having good mechanical stability and low visible light absorption is more preferable, and polyethylene terephthalate is particularly preferable.

  The method for imparting whiteness is not particularly limited, but it is preferable to add a white pigment such as titanium oxide or barium sulfate to the inside of the film or to contain a cavity. In particular, those containing cavities are suitable in terms of high reflectivity. Preferred examples of such a white film include porous unstretched or biaxially stretched polypropylene film, porous unstretched or stretched polyethylene terephthalate film. These production methods and the like are disclosed in JP-A-8-262208 and JP-A-2004-294611.

(4) Adhesive layer The reflective sheet of the present invention is formed by laminating a polyester film, a metal thin film layer, and a white film in this order. Each of these components may be laminated directly or via other layers. Preferably, a pressure-sensitive adhesive layer such as an acrylic pressure-sensitive adhesive, a hot-melt type polyester-based adhesive, or a silicon-based pressure-sensitive adhesive between these layers can be used.

  As the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, a heat-modified resin composed of an epoxy resin, a fatty acid or a hydroxy-substituted phenol, a polyester polyol obtained by reacting a diol compound and a dicarboxylic acid, or ring-opening polymerization of a lactone, A combination of a polyether polyol obtained by addition of an alkylene oxide or the like of a diol compound and an isocyanate compound is known. An adhesive composition for a composite laminate film, wherein a polybasic acid anhydride having at least two acid anhydride groups in the molecule is added to a polyol component of an adhesive composition comprising a polyol component and a polyisocyanate component. Adhesives for dry laminates, etc., in which a polyisocyanate compound is blended with a modified polyester composition obtained by reacting a product or polyester with an ethylenically unsaturated carboxylic acid or its acid anhydride in the presence of a radical generator. Are known.

  Next, although the polyester film and reflective sheet of this invention are demonstrated using an Example and a comparative example, this invention is naturally not limited to these Examples. Moreover, the physical property and characteristic of the polyester film and the reflective sheet which were described in the Example were evaluated using the following method.

(1) Film thickness A tape-like sample (5 cm in the horizontal direction × 1 m in the vertical direction) continuous in the vertical direction was collected, and 20 thicknesses at a pitch of 1 cm using a Seiko EM electronic micrometer, Millitron 1240. Was measured and obtained as the average value.

(2) Intrinsic Viscosity of Polyester Resin 0.1 g of polyester was dissolved in 25 g of a mixed solution of phenol / tetrachloroethane (volume ratio 3/2) and measured at 30 ° C. using an Ostwald viscometer.

(3) Average particle diameter of the inert particles The inert particles are observed with a scanning electron microscope (S-51O type, manufactured by Hitachi, Ltd.), and the magnification is appropriately changed according to the size of the particles. Copied. Next, the outer circumference of each particle was traced for at least 200 particles selected at random, the equivalent circle diameter of the particles was measured from these trace images with an image analyzer, and the average of these was taken as the average particle diameter.

(4) Absorbance Using a spectrophotometer (U-3500, manufactured by Hitachi, Ltd.), the light transmittance in the wavelength region of 300 to 500 nm was measured using the air layer as a standard, and the absorbance at a wavelength of 380 nm was determined.

(5) Haze and total light transmittance The haze and total light transmittance of the polyester film were measured using a turbidimeter (NHD2000, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS-K7105.

(6) Surface three-dimensional surface roughness (SRa, SRz) on the vapor deposition surface side
In Examples and Comparative Examples, the surface on the vapor deposition surface side of the polyester film was measured using a stylus type three-dimensional roughness meter (SE-3AK, manufactured by Kosaka Laboratory Co., Ltd.) with a needle radius of 2 μm and a load of 30 mg. Under the conditions, the cut-off value is 0.25 mm in the longitudinal direction of the film, the measurement length is 1 mm, the needle feed rate is 0.1 mm / second, and it is divided into 500 points at a 2 μm pitch. The sample was taken into a three-dimensional roughness analyzer (SPA-11). The same operation was performed 150 times continuously at intervals of 2 μm in the width direction of the film, that is, over 0.3 mm in the width direction of the film, and the data was taken into the analyzer. Next, the center plane average roughness (SRa) and the ten-point average roughness (SRz) were determined using an analyzer.

(7) Light resistance The accelerated light resistance test is based on continuous UV irradiation treatment at 63 ° C., 50% Rh, irradiation intensity of 100 mW / cm ² for 100 hours using an I-super UV tester SUV-W151 manufactured by Iwasaki Electric Co., Ltd. The test was carried out with the polyester side facing up, and the determination was made with the aim of determining the degree of yellowing of the void-containing film on the opposite side.
No change: ◎
Almost no change: ○
Slightly yellowing: △
Clearly yellowed: ×

(8) Vapor deposition surface appearance evaluation The metal vapor deposition film was cut into A4 size, 10 films were arranged under a fluorescent lamp, observed with the naked eye from the non-metal layer side, and judged according to the following criteria.
A: Appearance was uniform and had a metallic luster.
○: Depending on the observation angle, the gloss was lost, and there was no problem.
(Triangle | delta): The surface was partially rough and gloss was slightly lost, and it was a level without a problem.
X: The surface was rough and the metallic luster was greatly lost, which was a problematic level.

Example 1

(1) Preparation of coating solution A transesterification reaction and a polycondensation reaction are carried out by a conventional method to obtain 46 mol% terephthalic acid, 46 mol% isophthalic acid and 5-sulfonato as the dicarboxylic acid component (relative to the entire dicarboxylic acid component). A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 8 mol% sodium isophthalate, 50 mol% ethylene glycol and 50 mol% neopentyl glycol as a glycol component (based on the entire glycol component) was prepared. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, 0.06 parts by mass of nonionic surfactant were mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer agglomerated, the resin water dispersion is cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A uniform water-dispersible copolymerized polyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (Silicia 310, manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolyester resin solution was mixed with 99.46 parts by mass of the silicia 310. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain a coating solution.

(2) Production of polyester film 10 parts by weight of dried UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinon-4-one), no particles 90 parts by weight of PET resin pellets (intrinsic viscosity 0.62 dl / g) were mixed, and a UV-absorber-containing masterbatch (A) was prepared using a kneading extruder, at which the extrusion temperature was 285 ° C. .

  90 parts by weight of PET resin pellets having an intrinsic viscosity of 0.62 dl / g and no UV-absorbing master batch (A) as a raw material for the polyester film intermediate layer are dried under reduced pressure at 135 ° C. for 6 hours (1 Torr) After that, the polyethylene terephthalate pellets (inherent viscosity is 0.62 dl / g) containing no particles in the extruder 2 (for the intermediate layer B layer) and the extruders 1 (for the outer layer A layer) and 3 (for the outer layer C layer) ) And dissolved at 285 ° C. These two polymers are each filtered through a filter material of stainless steel sintered body (nominal filtration accuracy 10 μm particle 95% cut), laminated in a three-layer confluence block, extruded into a sheet form from the die, and then electrostatically applied. It was wound around a casting drum having a surface temperature of 30 ° C. using a casting method, and solidified by cooling to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the A layer, the B layer, and the C layer was 5: 90: 5.

  Next, this unstretched film was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction with a roll group having a difference in peripheral speed to obtain a uniaxially oriented PET film. Subsequently, the said coating liquid was apply | coated to the single side | surface of a uniaxially oriented PET film by the roll coat method. Then, it was dried at 135 ° C. for 5 seconds in a drying furnace.

Subsequently, while holding the edge of the film with a clip, the film was guided to a hot air zone having a temperature of 125 ° C. and stretched 4.3 times in the width direction. Next, while maintaining the width stretched in the width direction, the treatment was performed at a temperature of 225 ° C. for 30 seconds, and further 3% relaxation treatment was performed in the width direction, so that the coating amount of the adhesive modified layer was 0.08 g / m. ^2. A polyester film having a film thickness of 75 μm was obtained.

(Production of reflection sheet)
A silver layer of 750 mm was formed by vacuum deposition on the flat smooth surface opposite to the adhesion modified layer surface of the ultraviolet absorbent-containing polyester film obtained above. Next, a toluene solution of a crosslinkable acrylic pressure-sensitive adhesive was applied on one side of a K2323 made by Toyobo Co., Ltd. having a thickness of 188 μm as a void-containing biaxially oriented polyester film, and dried to form a pressure-sensitive adhesive layer having a thickness of 9 μm. This adhesion layer and the silver vapor deposition layer formed in the ultraviolet absorber containing film were bonded together, and the reflective sheet was created.

(Example 2)
The same method as in Example 1 except that 80 parts by weight of PET resin pellets having an intrinsic viscosity of 0.62 dl / g and no UV absorber-containing masterbatch (A) are used as the raw material for the polyester film intermediate layer. A polyester film having a film thickness of 75 μm was prepared to obtain a reflective sheet.

(Example 3)
A polyester film was prepared in the same manner as in Example 2 except that the thickness of the polyester film was 100 μm, and a reflective sheet was obtained.

  Polyethylene terephthalate pellets (inherent viscosity: 0.62 dl / g) containing no particles and polyethylene terephthalate master batch pellets (inherent viscosity: 0.62 dl / g) containing 1000 ppm of irregular bulk silica particles having an average particle size of 2.3 μm Are mixed in a ratio of 80:20 and then fed to the extruders 1 (for the outer layer A layer) and 3 (for the outer layer C layer), respectively, in the same manner as in Example 1 to obtain a polyester having a film thickness of 75 μm A film was created to obtain a reflective sheet.

(Comparative Example 1)
A polyester film was prepared in the same manner as in Example 1 except that 100 parts by weight of PET resin pellets (inherent viscosity was 0.62 dl / g) containing no UV absorber and no particles was used. Obtained.

(Comparative Example 2)
In Example 4, polyethylene terephthalate masterbatch pellets (inherent viscosity 0) containing 1000 ppm of polyethylene terephthalate pellets (inherent viscosity 0.62 dl / g) containing no particles and amorphous bulk silica particles having an average particle size of 4.0 μm. .62 dl / g) at a ratio of 60:40 and then fed to extruders 1 (for outer layer A layer) and 3 (for outer layer C layer) in the same manner as in Example 1 A 75 μm thick polyester film was prepared to obtain a reflective sheet.

  The present invention relates to a reflective sheet for a backlight used in the surface light source device of the liquid crystal display device, and in particular, a reflective sheet having a metal thin film layer such as a silver or aluminum vapor deposition layer. Providing a reflective sheet with less degradation of reflection characteristics by preventing the corrosion of the metal vapor deposition layer due to adsorbed water by using a polyester film as the absorbing polyester film, and further preventing the deterioration of the laminated white film To do.

1. 1. Polyester film 2. Metal thin film layer White film 4. 4. Light guide plate Light source Lamp reflector

Claims (4)

A reflective sheet formed by laminating a polyester film, a metal thin film layer and a white film in this order,
The said polyester film is a reflecting sheet which has ultraviolet absorptivity, a haze is 1.8% or less, and the three-dimensional center plane average roughness (SRa) by the side of a metal thin layer is 0.020 micrometer or less.   The reflective sheet according to claim 1, wherein the polyester film has a laminated structure of three or more layers, and at least an intermediate layer contains an ultraviolet absorber.   The reflective sheet according to claim 1 or 2, wherein the polyester film has a light transmittance of 20% or less at a wavelength of 380 nm.   A polyester film characterized by being used in the reflective sheet according to claim 1.