JP5221880B2 - White polyester film for reflector - Google Patents

Description

  The present invention relates to a white polyester film for a reflector.

  The liquid crystal display may entrap dust and dust during its assembly, which may cause quality problems such as a decrease in brightness and color spots. In order to prevent this problem, the film used for the reflecting plate is required to be resistant to dust and dirt.

  By the way, a backlight system has been adopted as a light source installation system for liquid crystal displays, but in recent years, a sidelight system as disclosed in JP-A-63-62104 has been widely used. Yes. This sidelight system has an advantage of obtaining a uniform display surface, but the reflector used in this application is required to have high reflectivity.

JP 63-62104 A Japanese Patent Publication No. 8-16175 JP 2001-226501 A JP 2002-90515 A

  A cold cathode tube is generally used as a light source for a liquid crystal display. Since this cold cathode tube generates heat, the amount of heat to which the film is exposed changes depending on whether the cold cathode tube is turned on or off, and the film expands or contracts in accordance with this change. There is a case where an unpleasant sound is generated. This tendency is particularly large in the current liquid crystal display which has been increased in screen size. Moreover, the same problem also arises in the reflection plate for internally illuminated signboards by turning on and off the light source.

  It is an object of the present invention to solve the problems of the prior art, has a practically sufficient visible light region reflection performance, can be stably formed, is difficult to be attached to dust and dirt, and other members An object of the present invention is to provide a white polyester film for a reflector, which can be suitably used as a reflector for a liquid crystal display or an interior-illuminated electric signboard, in which the generation of a squeaking sound is suppressed.

That is, the present invention comprises a white polyester film and a coating layer provided on at least one side thereof, the white polyester film is composed of at least three layers, and the coating layer contains an antistatic agent and a silicone compound having a reactive group. A white polyester film for a reflector of a liquid crystal display or internally illuminated signboard .

  According to the present invention, a liquid crystal that has a practically sufficient visible light region reflection performance, can form a film stably, is less likely to get dust and dirt, and is less likely to slid with other members. A white polyester film for a reflector that can be suitably used as a reflector for a display or an internally illuminated signboard can be provided.

Hereinafter, the present invention will be described in detail.
[White polyester film]
In this invention, a white polyester film is a polyester film which exhibits white by containing a pigment or a void forming substance. As the void-forming substance, inorganic particles and / or organic particles can be used.

  The white polyester film in the present invention is composed of at least 3 layers, preferably 3 to 49 layers, more preferably 3 to 11 layers, and particularly preferably 3 layers. Particularly preferred is a white polyester film in which a polyester A layer containing relatively few particles and a polyester B layer containing relatively many particles are laminated in the order of A / B / A. All the layers need not necessarily be white, and the white film as a whole may be white.

  The polyester constituting each layer is a polymer obtained by condensation polymerization from a diol component and a dicarboxylic acid component. As the dicarboxylic acid, for example, terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid, and sebacic acid can be used. As the diol, for example, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol can be used.

  As the polyester, polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are particularly preferable. The polyester may be a homopolyester or a copolyester. Examples of copolymer components in the case of copolymer polyester include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium. Mention may be made of dicarboxylic acid components such as sulfoisophthalic acid.

  Polyester is preferably polyethylene terephthalate or polyethylene naphthalate. Copolymerized polyethylene terephthalate or copolymerized polyethylene naphthalate is preferable because it can be stably formed even when inorganic particles and / or organic particles are added at a high concentration. The melting point of the polyester is preferably 250 ° C. or lower, more preferably 245 ° C. or lower, particularly preferably 240 ° C. or lower. Examples of the polyester include isophthalic acid copolymerized polyethylene terephthalate and cyclohexanedimethanol copolymerized polyethylene terephthalate. In particular, 2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate is preferable in order to obtain high heat resistance and film forming properties.

  The polyester A layer constituting this white polyester film preferably contains 1 to 30% by weight, more preferably 1 to 15% by weight of particles. If it is less than 1% by weight, the slipping property is lowered and winding becomes difficult, and if it exceeds 30% by weight, the film is easily broken and the film forming property is lowered, which is not preferable. On the other hand, the layer B contains 31 to 60% by weight, more preferably 31 to 55% by weight of particles. If it is less than 31% by weight, the reflectance is lowered, which is not preferable, and if it exceeds 60% by weight, the film-forming property as a film is extremely lowered, and the productivity is extremely lowered.

  The average particle size of the particles is preferably 0.3 to 3.0 μm, more preferably 0.4 to 2.5 μm, and particularly preferably 0.5 to 2.0 μm. If the average particle size is less than 0.3 μm, the dispersibility becomes extremely poor, and the particles are aggregated, so that troubles in the production process are likely to occur, and the film has coarse protrusions, resulting in a film with poor gloss. In addition, a filter used at the time of melt extrusion may cause clogging due to coarse particles, which is not preferable. On the other hand, if the average particle size exceeds 3.0 μm, the surface of the film becomes rough and the gloss decreases, and it becomes difficult to control the gloss to an appropriate range, which is not preferable.

  As particles, inorganic particles and / or organic particles can be used. Examples of the inorganic particles include barium sulfate, calcium carbonate, silicon dioxide, and titanium oxide particles. Examples of the organic particles include silicone and acrylic particles. The particles may be used alone or in combination of two or more.

  As the particles, it is preferable to use inorganic particles because high reflectivity and heat resistance can be obtained. In particular, the particles can be stably dispersed in the polyester polymer, have good film forming properties, and have good reflection. In particular, it is preferable to use barium sulfate particles because the rate can be obtained.

As a method of incorporating the particles into the polyester, it is preferable to take any one of the following methods, and it is particularly preferable to take the method (c) or (d).
(A) A method of adding before transesterification or esterification reaction at the time of polyester synthesis or adding before polycondensation reaction.
(A) A method of adding to polyester and melt-kneading.
(C) A method of producing master pellets in which a large amount of particles are added in the method (a) or (b) above, and kneading these with a polyester not containing an additive to contain a predetermined amount of additive.
(D) A method of using the master pellet of (c) as it is.

  In the present invention, it is preferable to filter the molten polymer by using a nonwoven fabric type filter having an average opening of 10 to 100 μm, preferably an average opening of 20 to 50 μm made of a stainless steel fine wire having a wire diameter of 15 μm or less as a filter during film formation. . By performing this filtration, it is possible to obtain a film with few coarse foreign matters by suppressing aggregation of particles that are generally agglomerated and become coarse agglomerated particles.

  In the present invention, a fluorescent whitening agent may be added to the white polyester film. When the fluorescent whitening agent is blended, for example, 0.005 to 0.2% by weight, preferably 0.01 to 0.1% by weight with respect to 100% by weight of the polyester composition in the blended polyester layer. is there. If the fluorescent whitening agent is less than 0.005% by weight, the reflectance in the wavelength region near 350 nm is not sufficient, so it makes little sense to add it. If it exceeds 0.2% by weight, the specific color of the fluorescent whitening agent is present. Appears, which is not preferable.

As the fluorescent brightening agent, for example, OB-1 (manufactured by Eastman), Uvitex-MD (manufactured by Ciba Geigy), or JP-Conc (manufactured by Nippon Chemical Industry Co., Ltd.) can be used.
You may add antioxidant, a ultraviolet absorber lubricant, etc. as needed.

  The polyester B layer is a layer containing particles at a higher concentration than the polyester A layer, and the thickness thereof is preferably 40 to 90%, more preferably 100% with respect to 100% of the total thickness of the polyester A layer and the polyester B layer. 50-85%. If it is less than 40%, the reflectance may be inferior, which is not preferable. If it exceeds 90%, the stretchability is lowered, which is not preferable.

[Antistatic agent]
In the present invention, the coating layer contains an antistatic agent and a silicone compound.
The antistatic agent is an agent that imparts antistatic properties, and a cationic polymer is preferably used. This cationic polymer is preferably a compound made of a vinyl polymer, having a cationic group in the side chain, and the cationic group being a quaternary ammonium salt. Examples of the quaternary ammonium salt include quaternary ammonium sulfonate, quaternary ammonium sulfate, and quaternary ammonium nitrate. Specifically, the cationic polymer is preferably a cationic polymer containing a unit represented by the following formula in the main chain.

  When the cationic polymer is a vinyl polymer, it is preferable to have a reactive monomer component as the monomer component. In this case, film cohesion can be improved and durability of the coating layer can be improved.

  As this reactive monomer component, hydroxy-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxypropyl methacrylate; epoxy groups such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether Monomers: carboxy groups such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene sulfonic acid and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.) or salts thereof Monomers containing: acrylamide, methacrylamide, N-alkyl acrylamide, N-alkyl methacrylamide, N, N-dialkyl acrylamide, N, N-dialkyl methacrylate (Alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, cyclohexyl, etc.), N-alkoxyacrylamide, N-alkoxymethacrylamide, N, N-dialkoxyacrylamide, N, N-dialkoxymethacrylamide (alkoxy groups include methoxy, ethoxy, butoxy, isobutoxy, etc.), acryloylmorpholine, N-methylolacrylamide, Monomers containing amide groups such as N-methylol methacrylamide, N-phenyl acrylamide, N-phenyl methacrylamide; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; Isocyanates such as vinyl isocyanate and allyl isocyanate And the like containing monomers.

  Furthermore, when the cationic polymer is a vinyl polymer, it is preferable to have a non-reactive monomer component as the monomer component. In this case, the adhesion to the polyester film and the film forming property of the coating layer can be improved.

  As non-reactive monomer components, alkyl acrylate, alkyl methacrylate (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, Cyclohexyl group, etc.), styrene, and α-methylstyrene.

  The antistatic agent is contained in the coating layer, preferably 20 to 80% by weight, more preferably 30 to 70% by weight, per 100% by weight of the composition of the coating layer. If it is less than 20% by weight, the antistatic property becomes insufficient and dust or the like tends to adhere to the film surface, which is not preferable. If it exceeds 80% by weight, the lubricant component decreases, the antistatic component increases, and the slipperiness decreases. It is not preferable.

[Silicone compound]
In the present invention, the silicone compound is a compound having an organosiloxane skeleton, and examples thereof include dimethyl silicone, methylphenyl silicone, methyl hydrogen silicone, fluorosilicone, silicone polyether copolymer, alkyl-modified silicone, and higher fatty acid-modified silicone. be able to.

  As the silicone compound, a silicone compound having a reactive group is preferably used. The use of a silicone compound that does not contain a reactive group is not preferred because it may result in a decrease in slipperiness due to a missing coating layer, a decrease in antistatic properties, and contamination of the production process due to a missing component.

  Examples of the silicone compound having a reactive group include a reactive group directly bonded to a silicon atom, an organic group including an amino group, an organic group including an epoxy group, an organic group including a carboxylic acid group, a silanol group, or a hydrolized group. It is preferable to use one containing at least one reactive group selected from organic groups that generate silanol groups by decomposition. For example, the reactive group possessed by this silicone is a primary aminoalkyl group such as a 3-aminopropyl group, a 3-amino-2-methyl-propyl group, or a 2-aminoethyl group as an organic group containing an amino group, 2) Examples thereof include organic groups having primary and secondary amino groups such as N- (2-aminoethyl) -3-aminopropyl group and N- (2-aminoethyl) -2-aminoethyl group.

  Examples of the organic group containing an epoxy group include glycidoxyalkyl groups such as γ-glycidoxypropyl group, β-glycidoxyethyl group, γ-glycidoxy-β-methyl-propyl group, and 2-glycidoxycarbonyl-ethyl. And a glycidoxycarbonylalkyl group such as a 2-glycidoxycarbonyl-propyl group.

  Examples of organic groups that generate silanol groups by hydrolysis include alkoxy groups such as methoxy, ethoxy, butoxy, and 2-ethylhexyloxy, methoxy-β-ethoxy, ethoxy-β-ethoxy, and butoxy-β-. Alkoxy-β-ethoxy groups such as ethoxy groups, acyloxy groups such as acetoxy groups and propoxy groups, N-alkylamino groups such as methylamino groups, ethylamino groups and butylamino groups, N, N-dialkyl groups such as dimethylamino groups and diethylamino groups Examples include nitrogen-containing heterocyclic groups such as amino groups, imidazole groups, and pyrrole groups.

  The silicone compound may be a mixture of silicone compounds having different types of reactive groups. Such a silicone compound preferably has a molecular weight of 1,000 to 500,000. If it is less than 1000, the cohesive force of the coating layer is undesirably lowered, and if it exceeds 500,000, the viscosity becomes high and handling is difficult, which is not preferred.

  The silicone compound is contained in the coating layer, preferably 5 to 50% by weight, more preferably 10 to 30% by weight, per 100% by weight of the composition of the coating layer. If it is less than 5% by weight, the slipperiness with other contacting members is low, which is not preferable. If it exceeds 50% by weight, the amount of the antistatic agent is reduced, the antistatic property is poor, and dust and dust are involved. It is not preferable.

[Crosslinking agent]
It is preferable to add a crosslinking agent to the coating layer in order to improve the cohesive strength of the coating layer. As a crosslinking agent, an epoxy compound, an oxazoline compound, a melamine compound, an isocyanate compound can be illustrated, and another coupling agent can also be used. Epoxy compounds and oxazoline compounds are preferably used because of easy handling and the pot life of the coating liquid, and a coupling agent is also preferably used.

More specifically, it can be exemplified as follows.
Examples of the epoxy compound include polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, etc. Examples of the polyepoxy compounds include sorbitol, polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diester. Glycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, diepoxy compounds include, for example, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl Ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol As diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, monoepoxy compound, for example, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, glycidyl amine compound N, N, N ′, N ′,-tetraglycidyl-m-xylylenediamine, 1,3-bis (N, N-diglycidylamino) cyclohexane.

  The oxazoline is preferably a polymer containing an oxazoline group. It can be prepared by polymerization with addition polymerizable oxazoline group-containing monomers alone or with other monomers. Addition polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and the like can be mentioned, and one or a mixture of two or more thereof can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer is not limited as long as it is a monomer copolymerizable with an addition-polymerizable oxazoline group-containing monomer, such as alkyl acrylate, alkyl methacrylate (the alkyl group includes a methyl group, an ethyl group, an n-propyl group, an isopropyl group, (meth) acrylic acid esters such as n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, Unsaturated carboxylic acids such as styrenesulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); Unsaturated nitriles such as acrylonitrile, methacrylonitrile; acrylamide, methacrylamide, N-alkyl Acrylamide, N-alkyl methacrylate N, N-dialkylacrylamide, N, N-dialkylmethacrylate (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl Group, cyclohexyl group, etc.); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; vinyl chloride and vinylidene chloride , Halogen-containing α, β-unsaturated monomers such as vinyl fluoride; α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and the like, one or more of these Monomers can be used.

  The melamine compound is preferably a compound obtained by reacting methylol melamine derivative obtained by condensing melamine and formaldehyde with ether such as methyl alcohol, ethyl alcohol or isopropyl alcohol as a lower alcohol and a mixture thereof. Examples of the methylol melamine derivative include monomethylol melamine, dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, and hexamethylol melamine.

  Isocyanate compounds include, for example, tolylene diisocyanate, diphenylmethane-4,4′-diisocyanate, metaxylylene diisocyanate, hexamethylene-1,6-diisocyanate, 1,6-diisocyanate hexane, an adduct of tolylene diisocyanate and hexane triol, Tolylene diisocyanate and trimethylolpropane adduct, polyol-modified diphenylmethane-4,4'-diisocyanate, carbodiimide-modified diphenylmethane-4,4'-diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-vitrylene- Examples include 4,4 'diisocyanate, 3,3' dimethyldiphenylmethane-4,4'-diisocyanate, and metaphenylene diisocyanate.

Coupling agents such as silane coupling agents and the like, a compound represented by the general formula YRSiX _3. Here, Y is an organic functional group such as vinyl group, epoxy group, amino group, and mercapto group, R is an alkylene group such as methylene, ethylene, and propylene group, and X is a hydrolyzable group such as methoxy group and ethoxy group, and an alkyl group. It is particularly preferred that the Y moiety is an epoxy group.

  Preferred silane coupling agents are γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane.

  As the coupling agent, an organometallic compound containing a metal such as zirconium, titanium, or aluminum can be used. For example, those classified into alkoxides, chelates, and acylates are preferable. Specifically, zirconium tetraacetylacetonate, zirconium acetate, titanium acetylacetonate, triethanolamine titanate, and titanium lactate can be exemplified.

  When using a crosslinking agent, the addition amount of the crosslinking agent is preferably 5 to 30% by weight per 100% by weight of the composition of the coating layer. If it is less than 5% by weight, the cohesive force of the coating layer is lowered, and the durability may be deteriorated. If it exceeds 30% by weight, the film forming property of the coating layer is deteriorated, and the antistatic performance is lowered, which is not preferable.

In this invention, although an application layer is provided on a white polyester film, an application layer may be provided in the single side | surface of a white polyester film, and may be provided in both surfaces.
The thickness of the coating layer is preferably 0.005 to 0.5 μm, more preferably 0.005 to 0.2 μm, as the thickness after drying. When the thickness is less than 0.005 μm, the antistatic property is insufficient, which is not preferable. When the thickness exceeds 0.5 μm, the coating layer becomes conspicuous and the coating appearance is deteriorated.

[Surfactant]
The coating solution for forming the coating layer preferably contains a composition that is chemically inert to the composition of the coating layer. When the surfactant is blended, it is blended, for example, 1 to 20% by weight, preferably 1 to 10% by weight, and more preferably 5 to 10% by weight per 100% by weight of the composition of the coating layer. By mix | blending in this range, wetting of the aqueous coating liquid to a polyester film can be accelerated | stimulated, and stability of a coating liquid can be improved. Examples of surfactants include anionic and nonionic surfactants such as polyoxyethylene-fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters, fatty acid metal soaps, alkyl sulfates, alkyl sulfonates, and alkyl sulfosuccinates. Can be mentioned.

[Production method]
Hereafter, the method to manufacture the white polyester film for reflectors of this invention is demonstrated.
The polymer melted from the die is extruded into an unstretched sheet. In the case of obtaining a laminated film, a polymer melt forming the A layer and a polymer melt forming the B layer are laminated so as to be, for example, A layer / B layer / A layer using a feed block. And is extruded to obtain an unstretched laminated sheet. At this time, the polymer laminated by the feed block maintains the laminated form. In this configuration, the B layer contains particles at a higher concentration than the A layer.

  The unstretched sheet extruded from the die is cooled and solidified by a casting drum to form an unstretched film. This unstretched film is heated by roll heating, infrared heating or the like, and stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The stretching temperature is preferably a temperature equal to or higher than the glass transition point (Tg) of the polyester, and more preferably a temperature higher by Tg to 70 ° C.

  The draw ratio is preferably 2.2 to 4.5 times, more preferably 2.3 to both the longitudinal direction and the direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction), although it depends on the required characteristics of the application. 3.9 times. When it is less than 2.2 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and when it exceeds 4.5 times, breakage tends to occur during film formation, which is not preferred.

  Subsequently, the film after longitudinal stretching is subjected to lateral stretching, heat setting, and thermal relaxation in order to form a biaxially oriented film. These processes are performed while the film is running. The transverse stretching process starts from a temperature higher than the glass transition point (Tg) of the polyester. And it is performed while raising the temperature to (5 to 70) ° C. higher than Tg. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone. The transverse stretching ratio is preferably 2.2 to 4.5 times, more preferably 2.8 to 3.9 times, although it depends on the required characteristics. If it is less than 2.2 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.5 times, breakage tends to occur during film formation.

  The film after transverse stretching is preferably heat treated at a constant width or a width reduction of 10% or less at a temperature (Tm-20 to 100) while holding both ends to reduce the thermal shrinkage. When the temperature is higher than this, the flatness of the film is deteriorated, and the thickness unevenness becomes large, which is not preferable. On the other hand, if the heat treatment temperature is lower than (Tm-80) ° C., the thermal shrinkage rate may increase. Moreover, in order to adjust the thermal shrinkage in the region of (Tm-20 to 100) ° C. or lower in the process of returning the film temperature to room temperature after heat setting, both ends of the film being gripped are cut off, and the take-up speed in the film vertical direction Can be adjusted and relaxed in the vertical direction. As a means for relaxing, the speed of the roll group on the tenter exit side is adjusted. As the rate of relaxation, the speed of the roll group is reduced with respect to the film line speed of the tenter, preferably 0.1 to 1.5%, more preferably 0.2 to 1.2%, particularly preferably 0.3. The film is relaxed by performing a speed reduction of ˜1.0% (this value is referred to as “relaxation rate”), and the longitudinal heat shrinkage rate is adjusted by controlling the relaxation rate. Further, the width of the film in the horizontal direction can be reduced in the process until both ends are cut off, so that a desired heat shrinkage rate can be obtained.

Moreover, it can also manufacture by the simultaneous biaxial stretching method of extending | stretching simultaneously to the vertical direction and a horizontal direction.
The white polyester film thus obtained should have a heat shrinkage rate of 85 ° C. of 0.5% or less, more preferably 0.4% or less, and most preferably 0.3% or less in two orthogonal directions. Can do.

  The thickness of the white polyester film after biaxial stretching is preferably 25 to 250 μm, more preferably 40 to 250 μm, and particularly preferably 50 to 250 μm. If the thickness is less than 25 μm, the reflectivity is lowered, and if it exceeds 250 μm, the increase in the reflectivity cannot be expected even if the thickness is further increased.

  In the present invention, the coating liquid for forming the coating layer is preferably used in the form of an aqueous coating liquid, for example, an aqueous solution, an aqueous dispersion, or an emulsion. In order to form the coating layer, other resins than the above-described composition, such as a colorant, a surfactant, and an ultraviolet absorber, may be added as necessary.

  The solid content concentration of the aqueous coating solution used in the present invention is usually 20% by weight or less, preferably 1 to 10% by weight. If it is less than 1% by weight, the coating properties on the polyester film may be insufficient, and if it exceeds 20% by weight, the stability of the coating liquid and the appearance of the coating layer may be deteriorated.

  Application of the aqueous coating solution to the polyester film can be carried out at any stage, but it is preferably carried out during the production process of the polyester film, and is further applied to the polyester film before the completion of orientational crystallization. Is preferred.

  Here, the polyester film before the crystal orientation is completed is an unstretched film, a uniaxially oriented film in which the unstretched film is oriented in either the longitudinal direction or the transverse direction, and further in two directions, the longitudinal direction and the transverse direction. And the like that have been oriented at a low magnification (biaxially stretched film before being finally re-stretched in the machine direction or the transverse direction to complete orientation crystallization). In particular, it is preferable to apply the aqueous coating liquid of the above composition to an unstretched film or a uniaxially stretched film oriented in one direction, and perform longitudinal stretching and / or lateral stretching and heat setting as it is.

  When applying an aqueous coating solution to a film, as a pretreatment for improving the coatability, the film surface is subjected to physical treatment such as corona surface treatment, flame treatment, plasma treatment, or when no pretreatment is performed. In the coating solution, a surfactant that is chemically inert to the composition of the coating layer is preferably blended.

  As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, and a curtain coating method can be applied. These can be used alone or in combination.

  The white polyester film of the present invention thus obtained has a reflectance of at least one surface of 90% or more, more preferably 92% or more, more preferably 94% or more, with an average reflectance of a wavelength of 400 to 700 nm. is there. If it is less than 90%, it is not preferable because sufficient screen brightness cannot be obtained.

Hereinafter, the present invention will be described in detail by way of examples. Each characteristic value was measured by the following method.
(1) Film thickness Ten-point thickness was measured for the film with an electric micrometer (K-402B manufactured by Anritsu), and the average value was defined as the film thickness.

(2) Thickness of each layer The film was cut into a triangle, fixed in an embedded capsule, and then embedded in an epoxy resin. Then, after embedding the sample with a microtome (ULTRACUT-S) into a thin film section having a thickness of 50 nm in parallel with the microtome, the specimen was observed and photographed with a transmission electron microscope at an acceleration voltage of 100 kv. The thickness of each layer was measured and the average thickness was determined.

(3) Glass transition point (Tg), melting point (Tm)
Using a differential scanning calorimeter (TA Instruments 2100 DSC), the measurement was performed at a heating rate of 20 m / min.

(4) Reflectance A spectrophotometer (UV-3101PC manufactured by Shimadzu Corporation) is attached with an integrating sphere, and the reflectance when BaSO ₄ white plate is 100% is measured over 400 to 700 nm. From the obtained chart, the interval is 2 nm. The reflectance was read. When the film was a laminated film, the measurement was performed from the side of the layer having a large particle content. An average value is obtained within the above range, and a reflectance of 90% or more is preferable in the entire measurement region.

(5) Sounding Acrylic plate (Acrylite L N865) is placed on top of the film, and a weight is placed on it, and the film is pulled at a constant speed (10 cm / min). It was measured.
A: No sound with 5 kg weight.
Δ: Sounds with a 5 kg weight.
X: Sounds with a 3 kg weight.
Δ or more has practical performance.

(6) Surface resistance The surface specific resistance of the coating layer surface of the film was measured by using a specific resistance measuring instrument manufactured by Takeda Riken Co., Ltd., with a measurement temperature of 23 ° C. and a measurement humidity of 60%. The surface resistivity (Ω / □) after 1 minute at 100 V was measured. The surface resistivity is preferably 1 × 10 ¹² (Ω / □) or less, and more preferably 1 × 10 ¹¹ or less.

(7) Strength of coating layer The surface of the coating layer of the film was rubbed once by reciprocating with a weight of 200 g using a Gakushin abrasion tester and using gauze. The surface resistivity of the rubbed portion was measured by the measurement method (6) above. In addition, compared with the initial surface specific resistance value, it is preferably up to an increase in the square of ten, and beyond that, the coating layer strength is weak, which is not preferable. More preferably, it is up to an increase within the tenth power.

(8) Average particle diameter The particle size was measured using a CP-50 centrifugul particle size analyzer manufactured by Shimadzu Corp. (centrifugal particle size analyzer). A particle size corresponding to 50 mass percent is read from an integrated curve of particles of each particle size calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is used as the average particle size (see “Particle Size Measurement Technology”). "See Nikkan Kogyo Shimbun, 1975, pages 242-247).

[Examples 1-3, Comparative Examples 1-3]
A rectifying column and a distillation condenser are 58 parts by weight of dimethyl terephthalate, 5 parts by weight of dimethyl isophthalate, 37 parts by weight of ethylene glycol, 0.4 parts by weight of diethylene glycol, 0.05 parts by weight of manganese acetate and 0.012 parts by weight of lithium acetate. Was heated to 150 to 235 ° C. while stirring to distill methanol to conduct a transesterification reaction. After the methanol was distilled off, 0.03 part by weight of trimethyl phosphate and 0.04 part by weight of germanium dioxide were added, and the reaction product was transferred to the reactor. Subsequently, while stirring, the pressure in the reactor was gradually reduced to 0.5 mmHg and the temperature was raised to 290 ° C. to carry out a polycondensation reaction. The obtained copolymer polyester had an isophthalic acid component amount of 8 mol%, a diethylene glycol component amount of 3 mol%, a glass transition point of 75 ° C, and a melting point of 228 ° C. This copolymer polyester was blended with 5% by weight of barium sulfate having an average particle diameter of 1.4 μm to obtain a polyester composition for the A layer. Further, 45% by weight of barium sulfate having an average particle size of 1.4 μm was blended with the same copolyester to obtain a polyester composition for the B layer.

  These A layer polyester and B layer polyester are respectively supplied to two extruders heated to 285 ° C., and the A layer and the B layer are A / B / A (= 15/70/15, layer thickness). The three-layer feed block device having a ratio) was merged and formed into a sheet shape from the die while maintaining the laminated state. Further, an unstretched film obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 20 ° C. was heated at 95 ° C., stretched in the longitudinal direction (longitudinal direction), and cooled with a 20 ° C. roll group. A coating solution (2% by weight) shown in Table 1 was uniformly applied on one side by a roll coater. Subsequently, the film was stretched in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 120 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Then, heat-fixed in a tenter at a temperature of 210 ° C., then relaxed by 0.5% in the vertical direction and 2.0% in the horizontal direction, cooled to room temperature, and biaxially stretched white polyester film having a thickness of 200 μm. Got. The film obtained had a thermal shrinkage of 85% at 30 ° C., a longitudinal direction of 0.3%, a width direction of 0.3%, and a reflectance of 95% in the entire measurement region. The composition of the coating layer was as shown in Table 1, and the evaluation result of the coating layer of the obtained white polyester film was as shown in Table 1.

[Example 4]
Distilling 57 parts by weight of dimethyl terephthalate, 6 parts by weight of dimethyl 2,6-naphthalenedicarboxylate, 36 parts by weight of ethylene glycol, 0.4 parts by weight of diethylene glycol, 0.05 parts by weight of manganese acetate, and 0.012 parts by weight of lithium acetate A flask equipped with a tower and a distillation condenser was charged and heated to 150 to 235 ° C. while stirring to distill methanol to conduct a transesterification reaction. After the methanol was distilled off, 0.03 part by weight of trimethyl phosphate and 0.04 part by weight of germanium dioxide were added, and the reaction product was transferred to the reactor. Subsequently, while stirring, the pressure in the reactor was gradually reduced to 0.5 mmHg and the temperature was raised to 290 ° C. to carry out a polycondensation reaction. The amount of the diethylene glycol component of the obtained copolymer polyester was 3 mol%, the glass transition point was 80 ° C., and the melting point was 230 ° C.
This copolymer polyester was blended with 5% by weight of barium sulfate having an average particle diameter of 1.4 μm to obtain a polyester composition for the A layer. The same copolyester was blended with 45% by weight of barium sulfate having an average particle size of 1.4 μm to obtain a polyester composition for layer B.

  These A layer polyester and B layer polyester are respectively supplied to two extruders heated to 285 ° C., and the A layer and the B layer are A / B / A (= 15/70/15, layer thickness). The three-layer feed block device having a ratio) was merged and formed into a sheet shape from the die while maintaining the laminated state. Further, an unstretched film obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 20 ° C. was heated at 95 ° C., stretched in the longitudinal direction (longitudinal direction), and cooled with a 20 ° C. roll group. A coating solution (2% by weight) shown in Table 1 was uniformly applied on one side by a roll coater. Subsequently, the film was stretched in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 120 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at a temperature of 215 ° C. in a tenter, followed by relaxation by 0.5% in the vertical direction and 2.0% in the horizontal direction, and cooling to room temperature to obtain a biaxially stretched film having a thickness of 175 μm. The film obtained had a heat shrinkage of 85% at 30 ° C., 0.1% in the longitudinal direction, 0.1% in the width direction, and a reflectance of 95% in the entire measurement region. The composition of the coating layer was as shown in Table 1, and the evaluation result of the coating layer of the obtained white polyester film was as shown in Table 1.

Antistatic agent 1:
A structure represented by the following formula is a copolymer composed of 90 mol% / N-methylolacrylamide 10 mol%.

Silicone compound 1:
Epoxy-modified silicone (trade name KF-102, manufactured by Shin-Etsu Chemical Co., Ltd.)
Silicone compound 2:
Amino-modified silicone (trade name KF-8003, manufactured by GE Toshiba Silicone Co., Ltd.)
In addition, about the silicone compounds 1-4, after previously mixing with surfactant, it added to the coating liquid.
Surfactant:
Polyoxyethylene (n = 7) lauryl ether (trade name NAROACTY N-70, manufactured by Sanyo Chemical Co., Ltd.)
Cross-linking agent:
Epoxy (trade name Denacol EX-313, manufactured by Nagase ChemteX Corporation)

The white polyester film for a reflector of the present invention can be optimally used as various reflectors, particularly as a reflector for a liquid crystal display and as a back sheet for a solar cell.
In addition, paper substitutes, ie cards, labels, stickers, home delivery slips, video printer paper, inkjet, barcode printer paper, posters, maps, dust-free paper, display boards, white boards, thermal transfer, offset printing, telephones It can be used as a base material for receiving sheets used for various printing records such as cards and IC cards.

Claims (2)

It consists of a white polyester film and a coating layer provided on at least one side thereof, the white polyester film is composed of at least three layers, and the coating layer contains an antistatic agent and a silicone compound having a reactive group, White polyester film for reflectors for liquid crystal displays or internally illuminated signboards . The white polyester film is a laminated white polyester film in which a polyester A layer and a polyester B layer are laminated in the order of A / B / A, and the film comprises inorganic particles and / or organic particles in the polyester A layer and the polyester B. The reflective plate of a liquid crystal display or an internally illuminated signboard according to claim 1, wherein the total content of inorganic particles and organic particles in the polyester B layer is higher than the content in the polyester A layer. White polyester film.