JP5871474B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a laminated polyester film having no particle feeling, good transparency, good scratch resistance, and good adhesion to a hard coat layer when used as, for example, a hard coat polyester film. In particular, the present invention relates to a film suitable for optical applications that require a higher degree of transparency, for example, touch panel manufacturing, liquid crystal polarizing plate manufacturing, etc., with emphasis on so-called visibility that transmits light. .

  Polyester film has excellent electrical properties, mechanical properties, thermal properties, processability and chemical resistance, so packaging materials, electrical insulation materials, metal insulation materials, metal deposition materials, plate making materials, magnetic recording materials, It is used in many applications such as display materials, transfer materials, and window paste materials. Especially recently, for base films for prism panels used in touch panels, liquid crystal display devices, cathode ray tubes, LCD panels, front panel glass surfaces of flat panel displays such as LCDs, PDPs, antistatic, antireflection, electromagnetic shielding, etc. It is widely used in various optical applications such as a protective film base film provided with a functional layer.

  As a problem in using the polyester film, a scratch on the surface of the film, which is not a problem at all in ordinary applications, is liable to deteriorate the appearance and optical characteristics, and may become a fatal defect (Patent Document 1).

  Therefore, the polyester film corresponding to the optical application needs to satisfy both transparency and slipperiness. In general, a method for adjusting the amount of particles added in the film is generally used. However, when the amount of added particles is extremely reduced, the slipperiness of the film itself is lowered and the winding property is reduced. Since it may be lowered, forming a slippery / scratch resistant layer on at least one side of the film is performed (Patent Document 2). There is also an example in which a polyester film having minute protrusions on the surface is used. In this case, in order to form protrusions on the film surface, inorganic or organic fine particles are added to the polyester layer constituting the film (Patent Document 3). The purpose is to improve the scratch resistance by incorporating particles in the film, forming fine irregularities (microprojections) on the film surface with the particles, and reducing the coefficient of friction on the film surface.

  However, when particles are added to the film to prevent scratches, the particles become an internal scattering factor, the transparency of the film is lowered, and it may be difficult to achieve both transparency and scratch resistance. Moreover, since the polyester film used conventionally has the protrusion by inorganic or organic microparticles | fine-particles, it has the problem that a scratch is easy to produce at the time of film forming, for example. Since the light is irregularly reflected by the scratches generated, it becomes a bright spot, so it is difficult to obtain a polyester film that requires high transparency, and improvement is required.

JP-A-11-157036 Japanese Patent No. 4097534 Japanese Patent Laid-Open No. 3-175034

  The present invention has been made in view of the above circumstances, and the problem to be solved is, for example, when it is used as a polyester film for hard coat, it has high transparency without particle feeling and good scratch resistance. An object of the present invention is to provide a laminated polyester film having good adhesion to a coating layer.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the use of a laminated polyester film having a specific configuration can easily solve the above-described problems, and have completed the present invention.

That is, the gist of the present invention is a coating layer comprising a urethane resin having a polycarbonate structure on one film surface and a glass transition roll of −15 ° C. or less, comprising a laminated polyester film composed of at least three polyester layers. And having a solvent- less active energy ray-curable resin layer on the coating layer of the laminated polyester film having a film haze of 2% or less.

  According to the present invention, it is possible to suppress the occurrence of scratches occurring in the polyester film production process, and it is possible to produce a laminated polyester film having good scratch resistance, transparency and good adhesion to the hard coat layer at a low cost. Industrial value is high.

  In the present invention, the polyester film constituting the laminated polyester film is characterized in that it is composed of at least three layers. Besides the three-layer structure, the polyester film has four or more layers as long as the gist of the present invention is not exceeded. There is no particular limitation.

  The polyester used in the present invention is preferably obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol, and may be a polyester comprising one kind of aromatic dicarboxylic acid and one kind of aliphatic glycol. It may be a copolyester obtained by copolymerizing one or more other components. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Typical polyester includes polyethylene terephthalate and the like. On the other hand, examples of the dicarboxylic acid used as a component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, and sebacic acid. As the glycol component, ethylene glycol, diethylene glycol , Propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like. Oxycarboxylic acids such as p-oxybenzoic acid can also be used.

  In addition, in the polyester film constituting the laminated polyester film of the present invention, due to the thermal history during film processing, etc., in order to reduce the amount of oligomers contained in the film deposited and crystallized on the surface of the film, It is also possible to use low oligomerized polyester for the outermost layer of the multilayer structure film. As a method for reducing the amount of oligomer in the polyester, for example, a solid phase polymerization method or the like can be used.

  It is preferable to mix | blend particle | grains with the polyester film which comprises the lamination | stacking polyester film of this invention for the main objective of provision of slipperiness and prevention of a crack | wound generation | occurrence | production in each process. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples of the particles include magnesium, kaolin, aluminum oxide, and titanium oxide. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. Two or more kinds of these particles may be used in combination as required.

  In the present invention, the average particle size of the particles used is usually 0.5 μm or less, preferably 0.3 μm or less. The lower limit of the average particle diameter is preferably 0.01 μm in consideration of film slipperiness. When outside this range, the particles tend to aggregate and the dispersibility may be insufficient. On the other hand, when the thickness exceeds 0.5 μm, the surface roughness of the film becomes too rough, which may cause problems when various surface functional layers are applied in a subsequent process.

  Furthermore, the particle content in the polyester layer is usually in the range of 0.5 to 5% by weight, preferably 0.5 to 3% by weight. When the particle content is less than 0.5% by weight, the slipperiness of the film may be insufficient, while when it exceeds 5% by weight, the transparency of the film may be insufficient.

  The method for adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but it is preferably added after completion of esterification or transesterification.

  Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known UV absorbers, antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film in the present invention as necessary. Can do.

  The thickness of the polyester film constituting the laminated polyester film in the present invention is not particularly limited as long as it can be formed as a film, but is usually 25 to 250 μm, preferably 38 to 188 μm, more preferably 50. It is in the range of ˜188 μm.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all. That is, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the film is stretched in the direction perpendicular to the first stretching direction. In that case, the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. is there. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  In the present invention, a simultaneous biaxial stretching method can also be employed for producing a polyester film. The simultaneous biaxial stretching method is a method in which the above-mentioned unstretched sheet is usually stretched and oriented in the machine direction and the width direction at a temperature controlled normally at 70 to 120 ° C., preferably 80 to 110 ° C. Is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be employed.

  Furthermore, a so-called coating stretching method (in-line coating) in which the film surface is treated during the above-described polyester film stretching step can be applied. When a coating layer is provided on a laminated polyester film by a coating stretching method, coating can be performed simultaneously with stretching, and the thickness of the coating layer can be reduced according to the stretching ratio. Can be manufactured.

Next, formation of the coating layer in the present invention will be described.
When the coating layer constituting the laminated polyester film in the present invention is provided, it may be provided on the polyester film in the film production process such as the above-described coating stretching method (in-line coating), and it may be provided outside the system once produced. So-called off-line coating, which is applied by the above method, may be employed, and any method may be employed. The coating stretching method (in-line coating) is not limited to the following, but for example, in sequential biaxial stretching, the first stage of stretching may be completed and the coating treatment may be performed before the second stage of stretching. it can. When a hard coat layer is provided on a polyester film by a coating stretching method, the film can be applied simultaneously with stretching, and the thickness of the hard coat layer can be reduced according to the stretching ratio, and is a film suitable as a polyester film. Can be manufactured.

The coating layer constituting the laminated polyester film in the present invention will be described below.
In the present invention, the coated layer of the laminated polyester film includes an urethane resin having a polycarbonate structure in order to improve the adhesion to the hard coat layer. The urethane resin having a polycarbonate structure refers to a urethane resin in which one of the polyols, which are main components of the urethane resin, is a polycarbonate polyol.

  Polycarbonate polyols are obtained from a polyhydric alcohol and a carbonate compound by a dealcoholization reaction. Polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, trimethylolpropane, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, , 5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, , 10-decanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylol heptane and the like. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, and ethylene carbonate. Examples of polycarbonate polyols obtained from these reactions include poly (1,6-hexylene) carbonate, poly (3- And methyl-1,5-pentylene) carbonate.

  Examples of the polyisocyanates constituting the urethane resin having a polycarbonate structure in the present invention include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate, α, α, Aliphatic diisocyanates having aromatic rings such as α ', α'-tetramethylxylylene diisocyanate, methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate and other aliphatic diisocyanates, cyclohexane diisocyanate, methylcyclohexane diisocyanate , Isophorone diisocyanate Over DOO, methylenebis (4-cyclohexyl isocyanate), dicyclohexylmethane diisocyanate, alicyclic diisocyanates such as isopropylidene dicyclohexyl diisocyanates. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates from the viewpoint of improving adhesion to the active energy ray-curable coating material and preventing yellowing due to ultraviolet rays.

  A chain extender may be used when synthesizing the urethane resin, and the chain extender is not particularly limited as long as it has two or more active groups that react with an isocyanate group. Alternatively, a chain extender having two amino groups can be mainly used.

  Examples of the chain extender having two hydroxyl groups include aliphatic glycols such as ethylene glycol, propylene glycol, butanediol and pentanediol, aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene, neopentyl glycol and neopentyl. Examples include glycols such as ester glycols such as glycol hydroxypivalate. Examples of the chain extender having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine, ethylenediamine, propylenediamine, hexanediamine, 2,2-dimethyl-1,3- Propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10- Aliphatic diamines such as decane diamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, isoprobilitincyclohexyl-4,4′-diamine, 1,4-diaminocyclohexane, 1 , 3-Bisaminomethylcyclohexa And alicyclic diamines such as isophorone diamine.

  The urethane resin used in the present invention may use a solvent as a medium, but preferably uses water as a medium. In order to disperse or dissolve the urethane resin in water, there are a forced emulsification type using an emulsifier, a self-emulsification type in which a hydrophilic group is introduced into the urethane resin, and a water-soluble type. In particular, a self-emulsification type in which an ionic group is introduced into the skeleton of a urethane resin to form an ionomer is preferable because of excellent storage stability of the liquid and water resistance, transparency, and adhesion of the resulting coating layer.

Examples of the ionic group to be introduced include various groups such as a carboxyl group, sulfonic acid, phosphoric acid, phosphonic acid, quaternary ammonium salt, and the like, and a carboxyl group is preferable. As a method for introducing a carboxyl group into a urethane resin, various methods can be taken in each stage of the polymerization reaction. For example, there are a method of using a carboxyl group-containing resin as a copolymer component during prepolymer synthesis, and a method of using a component having a carboxyl group as one component such as polyol, polyisocyanate, and chain extender. In particular, a method in which a desired amount of carboxyl groups is introduced using a carboxyl group-containing diol depending on the amount of this component charged is preferred. For example, dimethylolpropionic acid, dimethylolbutanoic acid, bis- (2-hydroxyethyl) propionic acid, bis- (2-hydroxyethyl) butanoic acid and the like are copolymerized with a diol used for polymerization of a urethane resin. Can do. The carboxyl group is preferably in the form of a salt neutralized with ammonia, amine, alkali metal, inorganic alkali or the like. Particularly preferred are ammonia, trimethylamine and triethylamine.
The urethane resin having a polycarbonate structure in the present invention has a glass transition point (hereinafter sometimes referred to as Tg) of preferably 0 ° C. or less, more preferably −15 ° C. or less, and further preferably −30 ° C. or less. When Tg is higher than 0 ° C., easy adhesion may be insufficient. Tg said here refers to the temperature which created the dry film | membrane of the urethane resin and measured using the differential scanning calorimeter (DSC).

  The coating layer in the present invention preferably contains an isocyanate compound for the purpose of improving the durability of the coating film. The isocyanate compound referred to in the present invention is a compound derived from an isocyanate derivative typified by isocyanate or blocked isocyanate. Examples of the isocyanate include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate, and aromatics such as α, α, α ′, α′-tetramethylxylylene diisocyanate. Aliphatic diisocyanates having a ring, methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, etc., cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylenebis (4-cyclohexyl isocyanate), isopropylidene Alicyclic diisocyanates such as emissions dicyclohexyl diisocyanates. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates in order to avoid yellowing due to ultraviolet rays.

  Examples of the blocking agent for the blocked isocyanate in the present invention include phenol compounds such as bisulfites, phenol, cresol and ethyl phenol, alcohol compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol and ethanol, and malonic acid. Active methylene compounds such as dimethyl, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, mercaptan compounds such as butyl mercaptan, dodecyl mercaptan, lactam compounds such as ε-caprolactam, δ-valerolactam, diphenylaniline, Amine compounds such as aniline and ethyleneimine, acetanilide, acid amide compounds of acetic acid amide, formaldehyde, acetoaldoxime, Examples include oxime compounds such as acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime, and these may be used alone or in combination of two or more.

  In addition, the isocyanate compound in the present invention may be used alone, or may be used as a mixture or bond with various polymers. In the sense of improving the dispersibility and crosslinkability of the isocyanate-based compound, it is preferable to use a mixture or a bond with a urethane resin or a polyester resin, and in the sense of further improving the adhesion, a urethane resin is more preferable. .

  In order to improve slipperiness and blocking, it is preferable to contain particles as a constituent component of the coating layer. The content of the particles is preferably in the range of 3 to 25%, more preferably in the range of 5 to 15%, and in the range of 5 to 10% in terms of the weight ratio of the entire coating layer. Further preferred. If it is less than 3%, the effect of imparting slipperiness or preventing blocking may be insufficient. On the other hand, when it exceeds 25%, there is a concern that the transparency of the coating layer is decreased, the coating film strength of the coating layer is decreased, or the easy adhesion is decreased.

  Examples of the particles used include inorganic particles such as silica, alumina, and metal oxide, or organic particles such as crosslinked polymer particles. In particular, silica particles are preferred from the viewpoint of dispersibility in the coating layer and transparency of the resulting coating film.

  In the coating layer of the film of the present invention, a binder polymer other than the above-described urethane resin is used in combination for improving the coated surface, improving the visibility when a hard coat layer is laminated on the coated surface, or improving the transparency. It is also possible.

  In the present invention, the “binder polymer” is a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) according to a polymer compound safety evaluation flow scheme (sponsored by the Chemical Substances Council in November 1985). Is defined as a polymer compound having a film forming property of 1000 or more.

Specific examples of the binder polymer include polyester resin, acrylic resin, urethane resin having no polycarbonate structure, polyvinyl (polyvinyl alcohol, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycol, polyalkyleneimine, methylcellulose. , Hydroxycellulose, starches and the like.
Furthermore, as long as it does not impair the gist of the present invention, the coating layer has an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, an antioxidant, foaming as necessary. Agents, dyes and the like may be contained.

  In the present invention, the content of the urethane resin in the coating layer constituting the laminated polyester film is usually 5 to 90% by weight, preferably 10 to 80% by weight, and more preferably 30 to 75% by weight. If the amount is less than 5% by weight, the adhesiveness may not be sufficient due to the small amount of the urethane resin component. If the amount exceeds 90% by weight, the coating layer becomes brittle due to the small amount of the isocyanate compound, and the adhesiveness is not sufficient. In some cases, the heat and humidity resistance may not be sufficient.

  In the present invention, the content of the isocyanate compound in the coating layer is usually 5 to 90% by weight, preferably 10 to 85% by weight, and more preferably 20 to 70% by weight. When the amount is less than 5% by weight, the coating layer becomes brittle due to the small amount of isocyanate compound, and the adhesion or heat and humidity resistance may be insufficient. On the other hand, when the amount exceeds 90% by weight, the adhesion decreases. There is a case.

  When providing a coating layer by in-line coating, the above-mentioned series of compounds is applied as an aqueous solution or dispersion, and the coating solution adjusted to a solid content concentration of about 0.1 to 50% by weight as a guide is applied onto the polyester film. It is preferable to produce a laminated polyester film. Moreover, in the range which does not impair the main point of this invention, a small amount of organic solvents may be contained in the coating liquid for the purpose of improving dispersibility in water, improving film-forming properties, and the like. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

The coating amount of the coating layer provided on the laminated polyester film of the present invention is usually 0.002 to 1.0 g / m ² , more preferably 0.005 to 0.5 g / m ² , still more preferably 0.01 to The range is 0.2 g / m ² . If the coating amount is less than 0.002 g / m ^2, sufficient adhesion may not be obtained, and if it exceeds 1.0 g / m ² , the appearance, transparency, and film blocking properties may be deteriorated. There is sex.

  In the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  In the present invention, the drying and curing conditions for forming the coating layer on the polyester film are not particularly limited. For example, when the coating layer is provided by off-line coating, it is usually 3 to 40 at 80 to 200 ° C. The heat treatment may be performed for 2 seconds, preferably 100 to 180 ° C. for 3 to 40 seconds.

  In addition, a small amount of an organic solvent may be contained in the coating solution for the purpose of improving the dispersibility in water, improving the film forming property, and the like within a range not exceeding the gist of the present invention. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

The coating amount (after drying) of the coating layer constituting the laminated polyester film in the present invention is usually 0.005 to 0.1 g / m ² , preferably 0.005 to 0.05 g / m ² , and more preferably 0.00. The range is from 005 to 0.01 g / m ² . When the coating amount is less than 0.005 g / m ² , the uniformity of the coating thickness may be insufficient, and the coating layer may be eluted by a solvent when the release layer is applied. On the other hand, in the case of application exceeding 0.1 g / m ² , problems such as deterioration of the applied surface may occur.

  In the present invention, as a method of providing each coating layer on the polyester film, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, spray coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  The film haze of the laminated polyester film of the present invention needs to be 2% or less, preferably 1.5% or less, more preferably 0.9% or less. If the film haze exceeds 2%, the transparency in optical applications such as diffusion, prism, and touch panel member is lacking, which makes it unsuitable for applications requiring high transparency.

  In the laminated polyester film of the present invention, it is preferable that the image clarity transmittance at an optical comb width of 0.125 mm is 90% or more as an additional requirement at the same time. The image clarity transmittance is preferably 92% or more, and more preferably 94% or more. If the image clarity transmittance is less than 90%, it may be unsuitable as an optical member such as a protective sheet for display or a touch panel member that requires a higher degree of image clarity.

  In the laminated polyester film of the present invention, the intermediate layer preferably contains substantially no particles. In the present invention, “substantially not containing particles” specifically means that the content of particles is 100 ppm or less. When the amount of particles added to the intermediate layer exceeds 100 ppm, voids may be formed around the particles depending on the stretching conditions, and it may be difficult to ensure the desired transparency.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. The measurement method and evaluation method used in the present invention are as follows.

(1) Measuring method of intrinsic viscosity of polyester 1 g of polyester was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and the measurement was performed at 30 ° C.

(2) Measuring method of average particle size (d ₅₀ : μm) Integration (weight basis) 50 in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type, manufactured by Shimadzu Corporation) % Was defined as the average particle size.

(3) Measurement of film haze (H0) of laminated polyester film According to JIS-K-7136, the film haze was measured by “HM-150” manufactured by Murakami Color Research Laboratory, and transparency was evaluated according to the following criteria. Standard.
(Criteria)
○: Film haze is 1.0% or less ×: Film haze exceeds 1.0%

(4) Measurement of glass transition point A water dispersion of urethane resin was dried in a petri dish to obtain a resin film. The obtained film was heated at a rate of 10 ° C./min in a temperature range of −100 ° C. to 100 ° C. using a DSC 204F Phoenix manufactured by NETZSCH, and further a glass transition from a change in heat capacity. Points were measured.

(5) Thickness (μm) measurement A sample film is embedded in an epoxy resin, sectioned with an ultramicrotome, and the obtained flakes are observed with a scanning electron microscope. The thickness is measured using the region where the particles are concentrated as a surface layer, and the thickness obtained by subtracting the thickness of each surface layer from the total thickness is defined as the thickness of the intermediate layer.

(6) Adhesion evaluation of coating layer On the coating layer of the sample film, the active energy ray-curable resin composition shown below is coated so that the thickness after curing is 3 μm, and ultraviolet rays are irradiated from the ultraviolet irradiation device by a mercury lamp. The resin was cured by irradiation with 25 mJ / cm ^{2 at} 80 W to obtain a laminated film having a structure of <polyester film / coating layer / active energy ray curable resin layer>. Next, scratches are made at intervals of 5 mm with a cutter knife, a 24 mm wide tape (Cello Tape (registered trademark) CT-24, manufactured by Nichiban Co., Ltd.) is applied, and then peeled off rapidly at a peeling angle of 180 degrees. Was observed and judged according to the following criteria.
(Active energy ray curable resin composition):
Nippon Kayaku KARAYAD DPHA 80 parts, Nippon Kayaku KARAYAD R-128H 20 parts, Ciba Specialty Chemicals IRGACURE 651 5 parts composition.
(Criteria)
A: Peeling area is 5% or less B: Peeling area is 5-20%
Δ: The peeled area exceeds 20% and is 50% or less ×: exceeds 50%

(7) Evaluation of scratch resistance Using a rubbing tester manufactured by Ohira Rika Kogyo, a 2 mm thick methacrylic resin plate specified in JIS K6718 is fixed to a reciprocating plate with a double-sided adhesive tape. Next, a plate on which a sample film is affixed using 24 sheets of 5 cm × 5 cm gauze as a cushion is placed. Next, a reciprocating motion is performed 10 times in a state where the sample film and the methacrylic plate are rubbed in a state where a load of 50 g of the weight of the jig including the plate is applied. Thereafter, the state of occurrence of scratches on the surface of the sample film is visually observed under a fluorescent lamp. The test was performed three times for each sample, the average number of scratches entering the film surface of the sample film was determined, and the determination was made according to the following criteria.
(Criteria)
○: The number of scratches is 5 or less, and the scratch resistance is excellent (practically no problem level).
Δ: The number of scratches is more than 3 and not more than 10, and scratch resistance is slightly good (a level that may cause a problem in practical use).
X: The number of scratches exceeds 10 and is innumerable, and scratch resistance is poor (practical problem level)

(8) Image clarity (image clarity)
Using an ICM-1T type image clarity measuring device manufactured by Suga Test Instruments Co., Ltd., measurement was performed by a transmission method in accordance with JIS K 7105 “Plastic Optical Properties Test Method” image clarity. The optical comb used was 0.125 mm. As the image clarity measurement value in this evaluation is larger, the laminated polyester film has a smaller particle feeling and the image clarity tends to be better.

(9) Comprehensive evaluation The obtained sample film was subjected to comprehensive evaluation according to the following determination criteria.
○: All of transparency, scratch resistance and adhesion to the hard coat layer are ○
Δ: At least one item of transparency, scratch resistance, and adhesion to the hard coat layer is Δ
×: At least one item of transparency, scratch resistance, and adhesion to the hard coat layer is ×
Among the above judgment criteria, Δ or more is a level that can be used practically without any problem.

The polyester used in the examples and comparative examples was prepared as follows.
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part of ethyl acid phosphate to this reaction mixture, 0.04 part of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (A) was 0.63.

<Method for producing polyester (B)>
In the method for producing polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.3 part of silica particles having an average particle diameter of 1.6 μm dispersed in ethylene glycol and 0.04 part of antimony trioxide are added. In addition, polyester (B) was obtained using the same method as the production method of polyester (A) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.65. The obtained polyester (B) had an intrinsic viscosity of 0.65.

<Method for producing polyester (C)>
In the method for producing polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.5 part of alumina having a primary particle size of 0.05 μm (Mohs hardness 8) dispersed in ethylene glycol, antimony trioxide Polyester (C) was obtained using the same method as the production method of polyester (A) except that 0.04 part was added and the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.65. The obtained polyester (C) had an intrinsic viscosity of 0.65.

Example 1:
A mixed raw material in which polyesters (A) and (C) are mixed at a ratio of 90% and 10%, respectively, is used as a raw material for the outermost layer (surface layer), and a raw material for polyester (A) is used as a raw material for the intermediate layer. After being melted at 285 ° C. each, it is coextruded in a layer configuration of two types and three layers (surface layer / intermediate layer / surface layer) on a cooling roll set to 40 ° C., and cooled and solidified to form an unstretched sheet. Obtained. Next, after stretching 3.4 times in the machine direction at a film temperature of 85 ° C. using the difference in roll peripheral speed, the coating layer composed of the following coating composition is applied in a predetermined amount (after drying). After coating on both sides of the film, led to a tenter, stretched 4.0 times at 120 ° C in the transverse direction, heat treated at 225 ° C, relaxed 2% in the transverse direction, thickness 125 µm (surface layer 7 µm, intermediate layer) 111 μm), a laminated polyester film provided with a coating layer having a thickness of 0.03 μm (after drying) was obtained. In addition, the example of a compound which comprises an application layer is as follows.

Examples of compounds constituting the coating layer are as follows. However, “part” in the text represents the weight ratio in the resin solid content.
U1: Urethane resin having a polycarbonate structure 400 parts of polycarbonate polyol composed of 1,6-hexanediol and diethyl carbonate having a number average molecular weight of 2000, 10.4 parts of neopentyl glycol, 58.4 parts of cyclohexane diisocyanate, dimethylol butanoic acid An aqueous dispersion of a urethane resin having a polycarbonate structure having a Tg of −30 ° C., obtained by neutralizing a prepolymer consisting of 74.3 parts with triethylamine and extending the chain with isophoronediamine.

U2: Urethane resin having a polycarbonate structure 400 parts of polycarbonate polyol composed of 1,6-hexanediol and diethyl carbonate having a number average molecular weight of 2000, 14 parts of butanediol, 15 parts of pentaethylene glycol, 100 parts of isophorone diisocyanate, dimethylolpropion An aqueous dispersion of a urethane resin having a polycarbonate structure having a Tg of −3 ° C., obtained by neutralizing a urethane resin comprising 75 parts of acid with triethylamine.

C1: Isocyanate compound Block isocyanate obtained by blocking the isocyanate group of polyisocyanate consisting of 158 parts of hexamethylene diisocyanate trimer and 26 parts of methoxypolyethylene glycol having a number average molecular weight of 1400 with 66 parts of methyl ethyl ketone oxime; -Prepolymer consisting of 115 parts of polycarbonate polyol consisting of hexanediol and diethyl carbonate having a number average molecular weight of 2000, 1 part of trimethylolpropane, 40 parts of isophorone diisocyanate and 8 parts of dimethylolpropionic acid, and neutralized with triethylamine and chained with diethylenetriamine Aqueous blocked isocyanate compound containing urethane resin obtained by extension

C2: Isocyanate compound 30% sodium bisulfite containing an isocyanate group of a polyisocyanate composed of 200 parts of a polyester having a number average molecular weight of 2000 consisting of an ethylene oxide 2-mole adduct of bisphenol A and maleic acid and 33.6 parts of hexamethylene diisocyanate Polyester resin-containing blocked isocyanate compound obtained by blocking with 84 parts

C3: Oxazoline compound Polymer type cross-linking agent in which oxazoline group is branched to acrylic resin (manufactured by Nippon Shokubai Co., Ltd., WS-500)
C4: Melamine compound Methoxymethylolmelamine F1: Particle Silica sol having a particle size of 65 nm.

Examples 2-5 and Comparative Examples 1-2:
It manufactured on the conditions shown to the following Tables 1-3, and obtained the laminated polyester film.

  The laminated polyester film of the present invention can be suitably used in applications where a hard coat layer is provided, for example.

Claims (1)

It consists of a laminated polyester film composed of at least three polyester layers, and has a coating layer containing a urethane resin having a polycarbonate structure on one film surface and a glass transition roll of -15 ° C. or less, and a film haze of 2% An optically laminated polyester film having a solventless active energy ray-curable resin layer on the coating layer of the laminated polyester film as described below.