JP2010284943A - Polyester film optical use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for optical use having high transparency wherein the polyester film for optical use comprising polyethylene naphthalene dicarboxylate as a main ingredient does not decrease visibility by interference stigma upon hard coat lamination. <P>SOLUTION: In a polyester film for optical use, a coating layer is formed on at least one surface of a biaxial oriented polyester film comprising polyethylene naphthalene dicarboxylate as the main ingredient, wherein at least one ingredient of the coating layer is a copolymerized polyester resin composition comprising a dicarboxylic acid ingredient containing 40-99 mol% of 2,6-naphthalene dicarboxylic acid relative to the total repeating units, a glycol ingredient containing 20-60 mol% of a glycol ingredient having a specific fluorene structure and 30-80 mol% of a glycol ingredient containing ethylene glycol, and further wherein the thickness of the coating layer is 0.05-0.20 um. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical polyester film for use in a flexible display and the like, and more specifically, an optical polyester that suppresses interference spots generated when a hard coat layer is provided on an optical polyester film and has high transparency. Related to film.

  Polyester films, especially biaxially oriented films such as polyethylene terephthalate and polyethylene naphthalene dicarboxylate, have excellent mechanical properties, heat resistance, and chemical resistance, so magnetic tape, ferromagnetic thin film tape, photographic film, packaging film It is widely used as a material for films for electronic parts, electrical insulating films, films for metal laminates, films to be attached to the surface of glass displays, and protective films for various members.

  Conventionally, a glass substrate has been used for an image display device represented by a liquid crystal display. In recent years, however, image display devices have been required to be thinner, lighter, larger in screen, more flexible in shape, curved display, and the like. Therefore, instead of a heavy and easily broken glass substrate, a highly transparent polymer film substrate has been studied. Moreover, since a liquid crystal display must employ a backlight, it is necessary to use many members.

  In contrast, electroluminescent (EL) display elements, especially self-luminous elements such as organic EL elements, and displays with a self-printing function using electronic ink such as electronic paper can be handled with fewer members than liquid crystal displays. Therefore, development is being actively promoted for applications that require thinning, portability, and flexibility.

  Polymer films are being studied as substrate materials for these organic EL and electronic papers, and development of portable applications and rollable flexible displays using the flexibility of polymer films is also underway. . Accordingly, further thinning of the polymer substrate film is required, while high dimensional stability around 200 ° C., which is the heat treatment temperature of the TFT layer laminated on the substrate film, is required.

  As a polymer film material having high dimensional stability, a biaxially oriented polyester film using polyethylene naphthalene dicarboxylate as a resin material is often used (for example, Patent Document 1 and Patent Document 2).

  On the other hand, in general, a display having a self-printing function using an electroluminescence (EL) display element, particularly a self-luminous element such as an organic EL element, or an electronic ink such as electronic paper is inferior in durability to humidity. The formation of a gas barrier layer is indispensable when preparing the film. When such a gas barrier layer is formed, it may be laminated directly on the resin film, but in many cases, a hard coat layer is laminated on the resin film because gas barrier performance deteriorates due to minute defects. Later, a method of laminating a gas barrier layer is used.

  When a hard coat layer is laminated on a resin film, if the refractive index of the hard coat layer differs from that of the resin film, interference spots due to interface reflection occur, and this affects the display. Yes.

  As a method for reducing the interfacial reflection generated between the hard coat layer and the film, for example, in Patent Document 3, as an easy-adhesion layer provided on a polyethylene terephthalate film, the refractive index of both the polymer binder and the fine particles is 1.50-1. A method has been proposed in which the haze value is small and the interface reflection is suppressed by using one in the range of 60.

  Furthermore, for example, Patent Document 4 proposes to provide a coating layer using fine particles having a high refractive index on a polyethylene terephthalate film in order to suppress interface reflection with a hard coat having a high refractive index. However, in the method of adding fine particles having a high refractive index, a large amount of fine particles must be added, resulting in an increase in film haze and a decrease in transparency.

  In addition, in the case of a biaxially oriented polyester film using polyethylene naphthalene dicarboxylate having excellent heat resistance as a resin material, the refractive index of the polyester film is a high refractive index of 1.7 or more. Interference spots are more likely to occur between the two and the case of polyethylene terephthalate, leading to a reduction in visibility. In order to reduce interference spots generated when a hard coat layer is provided on such a high refractive index polyester film, for example, in Patent Document 2, a low melting point polyester is formed on a polyethylene naphthalene dicarboxylate layer by coextrusion. A method has been proposed in which a layer is provided, the refractive index is controlled by heat treatment, and the average refractive index in the in-plane direction of the entire film is 1.70 or less.

  On the other hand, studies have been made on providing a coating layer on a polyester film according to various purposes. However, a method in which an adhesive coating layer is provided on a polyethylene naphthalene dicarboxylate film is used to provide a layer between a high haze characteristic and a hard coat layer. At present, no film suitable for optical applications with improved interference spots has been proposed.

JP 2003-334912 A JP 2004-98324 A JP 2004-284331 A JP 2004-54161 A JP 2007-268711 A

  An object of the present invention is an optical polyester film mainly composed of polyethylene naphthalene dicarboxylate, but does not cause a decrease in visibility due to interference spots when laminating a hard coat and has high transparency. Is to provide.

  As a result of intensive studies to solve the above problems, the present inventors have found that a copolyester containing 2,6-naphthalenedicarboxylic acid as a dicarboxylic acid component and a copolymer component having a specific fluorene structure as a glycol component. When the refractive index characteristic of the coating layer of the conventional optical polyester film was 1.60 or less, the coating layer having a high refractive index exceeding 1.60 was converted to polyethylene naphthalene dicarboxylate. It can be provided on a rate film, and if the coating layer thickness is controlled, an optical film can be obtained that is highly transparent and eliminates interference spots when laminating a hard coat layer without using high refractive index particles. As a result, the present invention has been completed.

  That is, an object of the present invention is an optical polyester film in which a coating layer is provided on at least one side of a biaxially oriented polyester film mainly composed of polyethylene naphthalene dicarboxylate, and at least one component of the coating layer is a copolymer polyester. A dicarboxylic acid component containing 40 to 99 mol% of 2,6-naphthalenedicarboxylic acid based on all repeating units, and 20 to 60 mol% of a fluorene structure represented by the following formula (I): And a glycol component containing 30 to 80 mol% ethylene glycol, and is achieved by an optical polyester film having a coating layer thickness of 0.05 μm or more and 0.20 μm or less. The

（Ｒ₁は炭素数２から４のアルキレン基、Ｒ₂、Ｒ₃、Ｒ₄、及びＲ₅は水素、炭素数１から４のアルキル基、アリール基またはアラルキル基であり、それぞれ同じであっても異なっていてもよい）

(R ₁ is an alkylene group having 2 to 4 carbon atoms, R ₂ , R ₃ , R ₄ , and R ₅ are hydrogen, an alkyl group having 1 to 4 carbon atoms, an aryl group, or an aralkyl group, and each is the same. May be different)

  In the optical polyester film of the present invention, as a preferred embodiment, the glycol component having a fluorene structure represented by the formula (I) is 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene. The polymerized polyester further comprises an aromatic dicarboxylic acid having 0.1 to 5 mol% of a sulfonate group and 0 to 60 mol% of another aromatic dicarboxylic acid based on the total repeating units, coating The particle content of the layer is 1% or less based on the weight of the coating layer, the haze value of the film is 0% or more and 1.0% or less, and a hard coat layer is further provided on the coating layer. The thermal contraction rate in the longitudinal direction of the film and the thermal contraction rate in the width direction after heating at 200 ° C. for 10 minutes are each 0.1% or less, flexible display Be used for the substrate, it flexible display is an organic EL display or electronic paper, also those comprising at least any one embraces.

  The optical polyester film of the present invention is excellent in high dimensional stability at around 200 ° C. by using a film mainly composed of polyethylene naphthalene dicarboxylate, and a hard coat layer is laminated by having a coating layer of a specific component. The generation of interference spots can be suppressed, and haze characteristics are excellent and highly transparent. Therefore, when used as a flexible display substrate such as an organic EL display or electronic paper, a flexible display excellent in visibility is provided. be able to.

The present invention will be described in detail below.
<Biaxially oriented polyester film>
The optical polyester film of the present invention has a layer structure in which a coating layer is provided on at least one side of a biaxially oriented polyester film containing polyethylene naphthalene dicarboxylate as a main component.

Hereinafter, the components constituting the biaxially oriented polyester film will be described.
<Polyester>
The main component of the biaxially oriented polyester film of the present invention is polyethylene naphthalene dicarboxylate. Such polyethylene naphthalene dicarboxylate is synthesized from naphthalene dicarboxylic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof. Here, the “main component” means 90% by weight or more, preferably 95% by weight or more, particularly preferably 99% by weight or more based on the weight of the film layer containing polyethylene naphthalene dicarboxylate. Examples of naphthalenedicarboxylic acid include 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and 1,5-naphthalenedicarboxylic acid. Among these, 2,6-naphthalenedicarboxylic acid is particularly preferable. .

  The polyethylene naphthalene dicarboxylate may be a homopolymer or a copolymer. Such copolymer component is preferably 10 mol% or less, more preferably 5 mol% or less, and particularly preferably 1 mol% or less of all repeating units constituting polyethylene naphthalene dicarboxylate.

  As the copolymer component, diol components such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexane dimethanol, diethylene glycol, polyethylene oxide glycol, and an ethylene oxide adduct of bisphenol sulfone can be used. As copolymerization components, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4,4′- Dicarboxylic acid components such as diphenyldicarboxylic acid and 5-sodium sulfoisophthalic acid can be used. These compounds may be used alone or in combination of two or more.

  Among these copolymer components, isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, and 2,7-naphthalenedicarboxylic acid are used as the acid component, and diethylene glycol, trimethylene glycol, and hexamethylene glycol are used as the glycol components. Preferred examples include ethylene oxide adducts of neopentyl glycol and bisphenol sulfone.

  Polyethylene naphthalene dicarboxylate can be produced by applying a known method. For example, it can be produced by a method in which a diol and a dicarboxylic acid are esterified, and then a reaction product obtained is subjected to a polycondensation reaction to obtain a polyester. Alternatively, these raw material monomer derivatives may be transesterified, and then the resulting reaction product may be subjected to a polycondensation reaction to obtain a polyester.

  The intrinsic viscosity of polyethylene naphthalene dicarboxylate is preferably 0.40 dl / g or more, more preferably 0.40 dl / g or more and 0.90 dl / g or less at 35 ° C. in o-chlorophenol. . If the intrinsic viscosity is less than the lower limit, cutting may occur frequently during film formation, or the strength of the product after forming may be insufficient. On the other hand, when the intrinsic viscosity exceeds the upper limit, the melt viscosity is high, so that melt extrusion is difficult, and a long time is required for the polymerization, and productivity may deteriorate.

<Other ingredients>
In addition to the polyethylene naphthalene dicarboxylate component, the biaxially oriented polyester film mainly composed of the polyethylene naphthalene dicarboxylate of the present invention may contain a small amount of a resin component within a range not impairing the problems of the present invention. The content of components other than polyethylene naphthalene dicarboxylate is preferably 10% by weight or less, more preferably 5% by weight or less, particularly preferably 1% by weight or less based on the weight of the film layer. is there.

  The polyethylene naphthalene dicarboxylate film layer of the present invention can contain particles preferably in the range of 0.0005 to 0.01% by weight based on the weight of the film layer. If the particle content of the base material layer is within such a range, the total light transmittance of the film exceeds 85%, and the haze value is 1.0% or less, so that the transparency can be maintained. The particles can be added at the time of film formation, or may be particles contained in the recovered film. The type of particle is not particularly limited.

<Method for forming biaxially oriented film>
In the biaxially oriented polyester film of the present invention, polyethylene naphthalene dicarboxylate is melt-extruded into a film shape, cooled and solidified with a casting drum to form an unstretched film, and this unstretched film is longitudinally at a temperature of Tg to (Tg + 60) ° C. (Hereinafter sometimes referred to as continuous film forming direction, longitudinal direction, MD direction) and width direction (hereinafter, sometimes referred to as lateral direction, TD direction) are biaxial at a magnification of 3.1 to 4.5 times. It is preferable to stretch. The difference between the draw ratio in the longitudinal direction and the draw ratio in the width direction is preferably 0.3 or less. Here, Tg represents the glass transition point of polyethylene naphthalene dicarboxylate, and Tm represents the melting point of polyethylene naphthalene dicarboxylate.
Stretching can be performed by a generally used method, for example, a method using a roll or a method using a stenter. The stretching may be performed simultaneously in the longitudinal direction and the width direction, or may be sequentially performed in the longitudinal direction and the width direction.

The biaxially stretched film is then preferably heat-set for 1 to 100 seconds at a temperature of (Tm-100) to (Tm-5) ° C, more preferably 200 to 250 ° C, particularly preferably heat. The fixing temperature is 220-240 ° C. By carrying out heat relaxation treatment at a relaxation rate of 0.5 to 3% on the biaxially stretched film subjected to such heat setting treatment, the heat shrinkage rate at 200 ° C. can be reduced to 0.1% or less. it can. Here, the heat setting treatment is a method of performing heat treatment in a fixed state in which both ends of the film are held.
The refractive index of the polyethylene naphthalene dicarboxylate film layer obtained in this way exceeds 1.70 in both the longitudinal direction and the width direction in the in-plane direction of the film.

<Coating layer>
In the present invention, a coating layer (hereinafter sometimes referred to as “coating film”) is provided on at least one surface of the biaxially oriented polyester film, and the coating layer is a high-concentration polyester resin composition comprising at least one component. Contains a molecular binder.

<Polymer binder>
It is necessary that at least one component of the polymer binder constituting the coating layer of the present invention is a copolyester. As a polymer binder constituting the coating layer, an acrylic resin, a urethane resin, and a modified body thereof can be further added as necessary. By using a small amount of these resins in addition to the copolyester, the adhesion with the hard coat layer can be enhanced in addition to the refractive index characteristics.

  Further, from the viewpoint of suppression of interference spots, the refractive index of the polymer binder is preferably in the range of more than 1.60 and less than 1.66, and more preferably 1.63 or more and 1.65 or less. The polymer binder having such a refractive index is achieved by including 70 to 100% by weight of a copolymer polyester comprising the copolymer component of the present invention in the polymer binder.

The proportion of the polymer binder in the coating layer is preferably 85 to 100% by weight based on the weight of the coating layer. The content of the polymer binder is preferably 85 to 95% by weight.
The polymer binder of the present invention is preferably one that is soluble or dispersible in water, but one that contains some organic solvent and is soluble in water can also be preferably used.

(Copolymerized polyester)
The copolymer polyester of the present invention contains 40 to 99 mol% of 2,6-naphthalenedicarboxylic acid as a dicarboxylic acid component based on all repeating units constituting the copolymer polyester, and constitutes the copolymer polyester as a glycol component. It is a copolyester containing 20 to 60 mol% of a glycol component having a fluorene structure represented by the following formula (I) on the basis of all repeating units and 30 to 80 mol% of ethylene glycol.

（Ｒ₁は炭素数２から４のアルキレン基、Ｒ₂、Ｒ₃、Ｒ₄、及びＲ₅は水素、炭素数１から４のアルキル基、アリール基またはアラルキル基であり、それぞれ同じであっても異なっていてもよい）

(R ₁ is an alkylene group having 2 to 4 carbon atoms, R ₂ , R ₃ , R ₄ , and R ₅ are hydrogen, an alkyl group having 1 to 4 carbon atoms, an aryl group, or an aralkyl group, and each is the same. May be different)

  The copolymer polyester further comprises 0.1 to 5 mol% of an aromatic dicarboxylic acid having a sulfonate group based on the total repeating units constituting the copolymer polyester, and 0 to 60 mol of another aromatic dicarboxylic acid. % Content is preferable. By containing an aromatic dicarboxylic acid having a sulfonate group as a copolymer component of the dicarboxylic acid, the copolymerized polyester can be easily dispersed in water.

  In the acid component of the copolymer polyester, the lower limit of the proportion of the 2,6-naphthalenedicarboxylic acid component is preferably 50 mol%, more preferably 60 mol%, and even more preferably 70 mol%. The upper limit of the proportion of the 2,6-naphthalenedicarboxylic acid component is preferably 95 mol%.

  When the proportion of the 2,6-naphthalenedicarboxylic acid component is less than the lower limit, the refractive index of the copolyester is lowered, leading to a decrease in the refractive index of the coating layer. On the other hand, if the proportion of the 2,6-naphthalenedicarboxylic acid component exceeds the upper limit, it becomes difficult to dissolve the copolymerized polyester in the hydrophilic organic solvent, which makes it difficult to disperse in water. In particular, if it exceeds 99 mol%, even if the non-crystalline improved glycol component is copolymerized, it is no longer dissolved in the hydrophilic organic solvent, making it difficult to disperse in water.

  In the acid component of the copolyester, the lower limit of the proportion of the aromatic dicarboxylic acid having a sulfonate group is preferably 1 mol%, more preferably 2 mol%, still more preferably 3 mol%. When the ratio of the aromatic dicarboxylic acid having a sulfonate group is less than the lower limit, the hydrophilicity of the copolyester is lowered, and water dispersion may not be sufficient. On the other hand, when the ratio of the aromatic dicarboxylic acid having a sulfonate group exceeds the upper limit, the hydrophilicity of the film increases, and as a result, the blocking resistance may decrease.

  Preferred examples of the aromatic dicarboxylic acid having a sulfonate group include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 5-lithium sulfoisophthalic acid, and 5-phosphonium sulfoisophthalic acid. In order to improve water dispersibility, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, and 5-lithium sulfoisophthalic acid are more preferable, and 5-sodium sulfoisophthalic acid is most preferable.

  As an acid component of the copolyester, 2,6-naphthalenedicarboxylic acid is used from the viewpoint of refractive index characteristics, and an aromatic dicarboxylic acid having a sulfonate group is used from the viewpoint that the copolyester can be easily dispersed in water. Preferably, other aromatic dicarboxylic acids can be used with them. Examples of other aromatic dicarboxylic acids include isophthalic acid, terephthalic acid, and biphenyl dicarboxylic acid. Of these, isophthalic acid is particularly preferred.

  The lower limit of the proportion of other aromatic dicarboxylic acids is preferably 3 mol%, more preferably 5 mol%. Moreover, the upper limit of the ratio of the other aromatic dicarboxylic acid is preferably 50 mol%, more preferably 40 mol%, still more preferably 30 mol%.

  The glycol component having a fluorene structure used as one of the glycol components of the copolyester is a compound represented by the following formula (I).

（Ｒ₁は炭素数２から４のアルキレン基、Ｒ₂、Ｒ₃、Ｒ₄、及びＲ₅は水素、炭素数１から４のアルキル基、アリール基またはアラルキル基であり、それぞれ同じであっても異なっていてもよい）

(R ₁ is an alkylene group having 2 to 4 carbon atoms, R ₂ , R ₃ , R ₄ , and R ₅ are hydrogen, an alkyl group having 1 to 4 carbon atoms, an aryl group, or an aralkyl group, and each is the same. May be different)

  Specifically, 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-methylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3,5-dimethylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-ethylphenyl] fluorene, 9,9-bis [4- ( 2-hydroxyethoxy) -3,5-diethylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-propylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) ) -3,5-dipropylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-isopropylphenyl] fluorene, 9,9-bis [ -(2-hydroxyethoxy) -3,5-diisopropylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-n-butylphenyl] fluorene, 9,9-bis [4- ( 2-hydroxyethoxy) -3,5-di-n-butylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-isobutylphenyl] fluorene, 9,9-bis [4- ( 2-hydroxyethoxy) -3,5-diisobutylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3- (1-methylpropyl) phenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3,5-bis (1-methylpropyl) phenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-fur Nylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3,5-diphenylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3-benzylphenyl] fluorene, 9,9-bis [4- (2-hydroxyethoxy) -3,5-dibenzylphenyl] fluorene, 9,9-bis [4- (3-hydroxypropoxy) phenyl] fluorene 9,9-bis [4- (4-Hydroxybutoxy) phenyl] fluorene is exemplified.

  Among these, 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene is particularly preferable. 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene is obtained, for example, by adding ethylene oxide to 9,9-bis (4-hydroxyphenyl) fluorene.

  Along with 2,6-naphthalenedicarboxylic acid constituting the dicarboxylic acid component, the refractive index of the copolymerized polyester is improved by using such a copolymerized component as an essential component, and the refractive index of the coating layer exceeds 1.6. Become.

  The lower limit of the proportion of the copolymer component having such a fluorene structure is preferably 25 mol%, more preferably 30 mol%. On the other hand, the upper limit of the proportion of the copolymer component having a fluorene structure is preferably 55 mol%, and more preferably 50 mol%.

  If the ratio of this compound is less than the lower limit, the effect of improving the refractive index is small, and in addition, the amorphous property is insufficient, making it difficult to disperse in water. This effect increases as the copolymerization amount of such a compound increases. However, when the upper limit is exceeded, the adhesion to the hard coat layer decreases or the surface becomes rough. On the other hand, if the upper limit is exceeded, the non-crystalline property becomes too large, and not only the blocking resistance of the film is lowered, but also the polymerization rate in the production of the copolyester is lowered.

  In the glycol component of the copolyester, the lower limit of the proportion of ethylene glycol is preferably 35 mol%, more preferably 40 mol%. The upper limit of the proportion of ethylene glycol is preferably 75 mol%. When the ratio of ethylene glycol is less than the lower limit, the blocking resistance of the film is lowered. On the other hand, when the proportion of ethylene glycol exceeds the upper limit, the content of the copolymer component having a fluorene structure is relatively reduced, which leads to a decrease in the refractive index of the coating layer.

As the glycol component of the copolymer polyester, other glycols can be used together with the two components of ethylene glycol and the copolymer component having the fluorene structure.
Examples of other glycol components include aliphatic or alicyclic glycols, and preferred examples include 1,4-butanediol and 1,4-cyclohexanedimethanol. Further, although not added as a monomer component, it may contain diethylene glycol generated in the polymerization process.
The lower limit of the proportion of other glycol components is preferably 5 mol%. On the other hand, the upper limit of the proportion of the other glycol component is preferably 40 mol%, more preferably 20 mol%, and even more preferably 10 mol%.

  The intrinsic viscosity of the copolyester in the present invention is preferably 0.2 to 0.8 dl / g. Such intrinsic viscosity is a value measured at 35 ° C. using orthochlorophenol.

  The copolyester of the present invention can be produced by conventional polyester production techniques. For example, it is produced by a method in which a monomer or oligomer is formed by reacting the above-mentioned acid component or an ester-forming derivative thereof with the above-described glycol component, followed by polycondensation under vacuum to obtain a copolyester having a predetermined intrinsic viscosity. it can. At that time, a catalyst for promoting the reaction, for example, an esterification or transesterification catalyst or a polycondensation catalyst can be used. Various additives such as stabilizers can be added as necessary.

The proportion of the copolymerized polyester in the polymer binder component is preferably 70 to 100% by weight based on the amount of the binder component. The lower limit of the content of the copolyester is preferably 80% by weight, more preferably 90% by weight. Further, the upper limit of the content of the copolyester is more preferably 97% by weight, and further 95% by weight. When the content of the copolyester is within such a range, a refractive index characteristic exceeding 1.60 can be expressed as a coating layer.
The copolymerized polyester of the present invention is mixed with other coating layer components in the state of a polyester aqueous dispersion, and is coated on at least one side of the biaxially oriented polyester film in the state of a coating solution.

The polyester aqueous dispersion is preferably produced by the following method.
The copolyester is preferably dissolved in a hydrophilic organic solvent having a solubility in water of 1 liter at 20 ° C. or more and a boiling point of 100 ° C. or less, or azeotropic with water at 100 ° C. or less. By using a copolyester having such solubility, a polyester aqueous dispersion can be obtained. Examples of the organic solvent include dioxane, acetone, tetrahydrofuran, and methyl ethyl ketone. Smaller amounts of surfactant can also be added to such solutions.

  Then, water is added to the organic solvent in which the copolyester is dissolved, with stirring, preferably with heating and high-speed stirring, to obtain a blue white to milky white dispersion. A blue-white to milky white dispersion can also be obtained by a method of adding the organic solution to water under stirring.

  The target polyester aqueous dispersion is obtained by separating and removing the organic solvent from the obtained dispersion. For example, the desired polyester aqueous dispersion can be obtained from the obtained dispersion by a method of evaporating a hydrophilic organic solvent under normal pressure or reduced pressure. If the copolyester is dissolved in a hydrophilic organic solvent azeotroped with water, the water will azeotropically evaporate when the organic solvent is distilled off. It is desirable to keep it.

  In addition, when the solid content concentration after removal of the organic solvent exceeds 40% by weight, re-aggregation of the copolyester dispersed in water is likely to occur, and the stability of the aqueous dispersion is lowered. The solid content concentration is preferably 40% by weight or less. On the other hand, the lower limit of the solid content concentration is preferably 0.1% by weight or more because the time required for drying becomes longer if the concentration is too small.

(acrylic resin)
As a polymer binder constituting the coating layer, an acrylic resin can be further used in addition to the copolyester. The proportion of the acrylic resin in the polymer binder component is preferably 0 to 30% by weight based on the amount of the binder component. The content of the acrylic resin is more preferably 3 to 20% by weight, and further preferably 5 to 10% by weight. Adhesiveness with a hard-coat layer improves by using an acrylic resin together within this range.

  The acrylic resin is preferably an acrylic resin obtained by copolymerizing monomers exemplified below. That is, as a copolymerization component constituting the acrylic resin, alkyl acrylate, alkyl methacrylate; hydroxy-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate; glycidyl acrylate, Epoxy group-containing monomers such as glycidyl methacrylate and allyl glycidyl ether; acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary salt A monomer having a carboxyl group such as an amine salt) or a salt thereof; acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, , N-dialkylacrylamide, N, N-dialkylmethacrylate, N-alkoxyacrylamide, N-alkoxymethacrylamide, N, N-dialkoxyacrylamide, N, N-dialkoxymethacrylamide, acryloylmorpholine, N-methylolacrylamide, N -Monomers having an amide group such as methylolmethacrylamide, N-phenylacrylamide, N-phenylmethacrylamide; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; 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-methyl -2 Oxazoline group-containing monomers such as oxazoline; methoxydiethylene glycol methacrylate, methoxypolyethylene glycol methacrylate, vinyl isocyanate, allyl isocyanate, styrene, α-methylstyrene, vinyl methyl ether, vinyl ethyl ether, vinyl trialkoxysilane, alkyl maleic acid monoester, alkyl Examples include fumaric acid monoester, alkylitaconic acid monoester, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, and butadiene.

  Examples of the alkyl group of the compound include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, and a cyclohexyl group. Examples of the alkoxy group of the compound include a methoxy group, an ethoxy group, a butoxy group, and an isobutoxy group.

(Urethane resin)
As a polymer binder constituting the coating layer, a urethane resin can be used in addition to the copolymer polyester. The proportion of the urethane resin in the polymer binder component is preferably 0 to 10% by weight based on the amount of the binder component. The content of the urethane resin is more preferably 3 to 5% by weight. By using a urethane resin in such a range, the adhesion with the hard coat layer is enhanced.

  Specifically, the urethane resin is a resin composed of a polyol, a polyisocyanate, a chain extender, a crosslinking agent, and the like. Examples of polyols include polyoxyethylene glycol, polyoxypropylene glycol, polyethers such as polyoxytetramethylene glycol, polyethylene adipate, polyethylene-butylene adipate, polycaprolactone, and the like by a dehydration reaction of dicarboxylic acid. Examples include polyesters to be produced, polycarbonates having a carbonate bond, acrylic polyols, and castor oil.

  Examples of polyisocyanates include tolylene diisocyanate, phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and the like.

  Examples of chain extenders or crosslinking agents include ethylene glycol, propylene glycol, diethylene glycol, trimethylolpropane, hydrazine, ethylenediamine, diethylenetriamine, triethylenetetramine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodicyclohexylmethane, Water etc. are mentioned.

<Particle>
The coating layer of the present invention has a particle content in the coating layer of 1 weight based on the weight of the coating layer in order to improve visibility when used as a flexible display substrate such as a display such as an organic EL display or electronic paper. % Or less is preferable. The particle content is more preferably 0.001 to 0.8% by weight, still more preferably 0.1 to 0.5% by weight. The particles in the coating layer are added in a very small amount for the purpose of imparting slipperiness, and the haze value of the film can be reduced by keeping the particle content within this range.

  The present invention is characterized in that interference spots at the time of hard coat lamination can be reduced by a polymer binder having a refractive index exceeding 1.60 using the above-mentioned copolymer polyester as a main polymer binder component. Since it is not necessary to increase the refractive index of the coating layer with particles, the particle content can be reduced within a range that does not impair the slipperiness.

  Such particles preferably have an average primary particle size of 5 to 200 nm. If the average primary particle diameter of the particles exceeds 200 nm, optical scattering may occur, and the transparency of the coating layer may be reduced. On the other hand, if the average primary particle size of the particles is less than 5 nm, the particles are aggregated more and the secondary particle size is increased, so that optical scattering may occur and the transparency of the coating layer may be lowered.

  The type of particle is not particularly limited. For example, calcium carbonate, magnesium carbonate, calcium oxide, zinc oxide, magnesium oxide, silicon oxide, sodium silicate, aluminum hydroxide, iron oxide, zirconium oxide, barium sulfate, titanium oxide, tin oxide Inorganic particles such as antimony trioxide, carbon black, molybdenum disulfide, etc., organic crosslinked polymers such as acrylic crosslinked polymers, styrene crosslinked polymers, silicone resins, fluororesins, benzoguanamine resins, phenolic resins, nylon resins, etc. it can.

<Applied layer thickness>
The thickness of the coating layer of the present invention is 0.05 μm or more and 0.20 μm or less. The coating layer thickness is preferably 0.08 μm or more and 0.15 μm or less. When the coating layer thickness is within such a range, interference spots at the time of laminating the hard coat can be reduced, and when the coating layer thickness deviates from such a range, even if a coating layer composition containing a copolymerized polyester is used, the interference spots can be reduced. The reduction effect is not fully manifested.

<Method for producing coating layer>
The coating layer composition used for coating the coating layer of the present invention is preferably used in the form of an aqueous coating solution such as an aqueous solution, an aqueous dispersion, or an emulsion to form the coating layer. In order to form the coating layer, for example, an antistatic agent, a colorant, a surfactant, an ultraviolet absorber, and a crosslinking agent can be added in addition to the above-described polymer binder component and particles as necessary.

  The solid content concentration of the aqueous coating liquid used in the present invention is usually 20% by weight or less with respect to the weight of the coating liquid, but is preferably 1 to 10% by weight. If this ratio is less than 1% by weight, the coatability to the polyester film may be insufficient. On the other hand, 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 liquid 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 further applied to the polyester film before completion of orientation 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 liquid to a film, as a pretreatment for improving the coating property, the film surface is subjected to physical treatment such as corona surface treatment, flame treatment, plasma treatment, etc., or chemically combined with the composition. It is preferable to use an inert surfactant in combination. Such surfactants promote the wetting of the aqueous coating liquid to the polyester film and improve the stability of the coating liquid. For example, polyoxyethylene-fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal Anionic and nonionic surfactants such as soaps, alkyl sulfates, alkyl sulfonates, and alkyl sulfosuccinates can be mentioned. The surfactant is preferably contained in an amount of 1 to 15% by weight, more preferably 5 to 10% by weight, based on the weight of the coating layer.

The coating amount of the coating liquid is adjusted and used so that the thickness of the coating film is in the range of 0.05 to 0.20 μm. 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, a curtain coating method and the like can be used alone or in combination.
In addition, it is preferable to provide the coating layer of this invention in the side which provides a hard-coat layer, and it may form on only one side or both surfaces of a film.

<Film characteristics>
(Haze value)
The haze of the optical polyester film of the present invention is preferably 0% or more and 1.0% or less. Here, haze is represented by a value measured according to JIS standard K7136.
The haze in the present invention is more preferably 0.1 to 0.8%, particularly preferably 0.1 to 0.5%. Haze is one of the methods for evaluating the visibility of a display. When the haze exceeds the upper limit, the transparency of the film is lowered and the display screen looks white, so the contrast is lowered and the visibility may be lowered. .

  In order to make the haze value in such a range, in the biaxially oriented polyester film and the coating layer containing polyethylene naphthalene dicarboxylate as a main component, particles are not used or, if used, the amount is within the above-described range, Moreover, the method of using the above-mentioned copolymer polyester as a polymer binder which comprises an application layer is mentioned.

(Heat shrinkage)
The optical polyester film of the present invention preferably has a heat shrinkage of 0.1% or less in the longitudinal direction and the width direction when heat-treated at 200 ° C. for 10 minutes. Moreover, it is preferable that the minimum of the thermal contraction rate of each direction is -0.1%.

  The lower limit of the thermal shrinkage is preferably −0.05%, more preferably −0.03%, particularly preferably 0.00% in both the longitudinal direction and the width direction of the film. The upper limit of the thermal shrinkage is preferably 0.08%, more preferably 0.05%, and particularly preferably 0.03% in both the longitudinal direction and the width direction of the film.

If the thermal shrinkage exceeds this range, for example, if the electronic paper substrate is heat treated at a temperature of about 200 ° C., which is the heat treatment temperature of the TFT layer laminated on the substrate film, the pattern will be misaligned, leading to a decrease in resolution. There is.
As a specific method for bringing the thermal shrinkage rate into such a range, a method using the draw ratio, heat setting treatment and heat relaxation treatment described in the method for forming a biaxially oriented polyester film can be mentioned.

(Film thickness)
The thickness of the optical polyester film of the present invention is preferably a thickness suitable for a thin flexible display, and is preferably in the range of 50 to 300 μm. The film thickness is more preferably 100 to 200 μm, particularly preferably 100 to 150 μm. The film thickness is preferably thinner in terms of portability and ease of bending. However, if the lower limit is not reached, it may be difficult to maintain sufficient strength as a substrate film for a flexible display.

<Hard coat layer>
In the optical polyester film of the present invention, it is preferable that a hard coat layer is further provided on the coating layer.
As the hard coat layer, a radiation curable resin or a silane resin can be used, and in particular, a hard coat layer using a radiation curable resin is preferable. Among them, an ultraviolet (UV) curable resin is used. A hard coat layer is preferred. Examples of the UV curable composition used for forming the hard coat layer include UV curable compositions such as urethane-acrylate, epoxy-acrylate, and polyester-acrylate.
In order to laminate the hard coat layer on the coating layer of the optical polyester film of the present invention, the composition constituting the hard coat layer is coated on the coating layer, and the composition is formed by heating, irradiation with radiation (for example, ultraviolet rays) or the like. What is necessary is just to harden a thing. Although the thickness of a hard-coat layer is not specifically limited, The range of 1-15 micrometers is preferable.

<Optical use>
The optical polyester film of the present invention is suitably used as a flexible display substrate such as an organic EL display or electronic paper.
When used in such optical applications, a configuration in which a hard coat layer is provided on the coating layer of the optical polyester film of the present invention and a gas barrier layer, a transparent conductive layer such as ITO, etc. is further laminated thereon is exemplified.
By using the optical polyester film of the present invention as such a display substrate, visibility is improved by improving visibility due to good haze value and improving visibility due to less interference spots when laminating hard coats. Can be increased.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Copolymerization component of polymer binder From the coating layer provided on the polymer binder composition or film, it was specified using ¹ H-NMR measurement.

(2) Coating layer thickness The film is fixed with an embedding resin, the cross section is cut with a microtome, stained with 2% osmic acid at 60 ° C. for 2 hours, and using a transmission electron microscope (JEM2010 manufactured by JEOL Ltd.), The thickness of the coating layer was measured.

(3) Film thickness Film thickness was measured at 30 g of needle pressure using an electronic micrometer (trade name “K-312A type” manufactured by Anritsu Corporation).

(4) Haze value According to JIS K7136, the haze value of the film was measured using the Nippon Denshoku Industries Co., Ltd. haze measuring device (NDH-2000).

(5) Heat shrinkage rate Marks are attached to the film at intervals of 30 cm, heat treatment is carried out for 10 minutes in an oven set at 200 ° C. without applying a load, and after cooling at room temperature, the distance between the marks after heat treatment is measured. The thermal shrinkage rate in the longitudinal direction and the width direction was calculated by the following formula. In addition, each thermal contraction rate evaluated by n = 5, respectively, and used the average value.
Heat shrinkage rate (%) = ((distance between the gauge points before heat treatment−distance between gauge points after the heat treatment) / distance between gauge points before the heat treatment) × 100

(6) Refractive index About the coating layer uncoated surface of the obtained biaxially oriented polyester film, the refractive index in the longitudinal direction (MD direction), the width direction (TD direction), and the film thickness direction (Z direction) is the Abbe refractive index. Measured with a meter. In addition, since the coating layer of the present invention is thin, when the coating layer is formed on both sides, it is not affected by the refractive index of the coating layer even if measured using an Abbe refractometer from above the coating layer. The refractive index of the biaxially oriented polyester film can be determined.

(7) Refractive index of coating layer Coating at a wavelength of 550 nm from the phase difference (delta) and amplitude (psi) measured on the coating layer coating surface of the obtained film with an ellipsometer (M-200) manufactured by JASCO The refractive index of the layer was determined. The refractive index obtained by the method (6) was used as the substrate refractive index.

(8) Center plane average roughness (Ra)
Using a non-contact three-dimensional surface structure analysis microscope (NewView 5022) manufactured by Zygo, measurement was performed under the conditions of a measurement magnification of 25 times and a measurement area of 283 μm × 213 μm (= 0.0603 mm ² ). The center plane average roughness Ra was determined from the following equation using surface analysis software.

上式中、Ｚｊｋは測定方法（２８３μｍ）、それと直行する方法（２１３μｍ）をそれぞれＭ分割、Ｎ分割したときの各方向のｊ番目、ｋ番目の位置における２次元粗さチャート上の高さである。

In the above equation, Zjk is the height on the two-dimensional roughness chart at the jth and kth positions in each direction when the measurement method (283 μm) and the direct method (213 μm) are divided into M and N, respectively. is there.

(9) Adhesion A cross-cut crosscut (100 squares of 1 mm ² ) is applied on the polyester film on which the hard coat layer is formed, and a 24 mm wide cellophane tape (trade name, manufactured by Nichiban Co., Ltd.) is pasted thereon. After peeling off rapidly at a peeling angle of 180 °, the peeled surface was observed and evaluated according to the following criteria.
5: Peeling area is less than 10% …… Adhesion is very good 4: Peeling area is 10% or more and less than 20% …… Adhesion is good 3: Peeling area is 20% or more and less than 30% …… Adhesion is slightly good Area is 30% or more and less than 40% …… Adhesive strength failure 1: Peeling area exceeds 40% …… Adhesive strength is extremely poor

(10) Reflectance amplitude (evaluation on interference spots)
The opposite surface of the polyester film on which the hard coat layer was formed was painted with black magic, the reflected light on the opposite surface was eliminated, and the spectral reflectance was measured using a spectrophotometer (Shimadzu Corporation UV-3101PC). The reflectance at a wavelength of 500 nm to 600 nm was measured, and the amplitude of the reflectance was evaluated according to the following criteria. As the amplitude of the measured reflectance is larger, interference spots are generated, and the visibility as a display is lowered.
◎: Reflectance amplitude ≦ 0.5% …… Very good ○: 0.5% <Reflectance amplitude ≦ 1.0% …… Good ×: 1.0% <Reflectance amplitude …… Poor

[Example 1]
Establish 100 parts of dimethyl naphthalene-2,6-dicarboxylate and 60 parts of ethylene glycol with 0.03 part of manganese acetate tetrahydrate as a transesterification catalyst and gradually raise the temperature from 150 ° C. to 238 ° C. for 120 minutes. An exchange reaction was performed. In the middle, when the reaction temperature reached 170 ° C., trimethyl phosphate (135 ° C. in ethylene glycol, heat-treated at 0.11 to 0.16 MPa for 5 hours: 0.023 part in terms of trimethyl phosphate) ) And 0.024 parts of antimony trioxide was added after the transesterification reaction.
Thereafter, the reaction product is transferred to a polymerization reactor, heated to 290 ° C., and subjected to a polycondensation reaction under a high vacuum of 27 Pa or less, and has an intrinsic viscosity of 0.61 dl / g and substantially no particles. Polyethylene-2,6-naphthalenedicarboxylate was obtained.
The polyethylene-2,6-naphthalenedicarboxylate pellets were dried at 170 ° C. for 6 hours, then fed to an extruder hopper, melted at a melting temperature of 305 ° C., and filtered through a stainless steel fine wire filter having an average opening of 17 μm. The film was extruded through a 2 mm slit die on a rotary cooling drum having a surface temperature of 60 ° C. and rapidly cooled to obtain an unstretched film.

  The unstretched film thus obtained is preheated at 120 ° C., and further heated by a 900 ° C. IR heater from above 15 mm between low-speed and high-speed rolls and stretched 3.1 times in the longitudinal direction. An aqueous coating solution having a coating concentration of 6% shown in Table 1 was uniformly applied to both surfaces with a roll coater. Subsequently, it was supplied to a tenter and stretched 3.3 times in the transverse direction at 145 ° C. The obtained biaxially oriented polyester film was heat-fixed at a temperature of 230 ° C. for 40 seconds and a polyester film having a thickness of 125 μm was wound up. Then, the treatment temperature was 200 ° C. and the relaxation rate was 1.0 using a heating zone with an IR heater. % To give a polyester film. The thickness of the coating film was 0.1 μm. The properties of the obtained polyester film are shown in Table 1.

Furthermore, a UV curable composition having the following composition was uniformly coated on the coating layer using a roll coater so that the film thickness after curing was 5 μm.
[UV curable composition]
Pentaerythritol acrylate: 45% by weight
N-methylolacrylamide: 40% by weight
N-vinylpyrrolidone: 10% by weight
1-hydroxycyclohexyl phenyl ketone: 5% by weight
Then, it hardened by irradiating with an ultraviolet-ray for 30 seconds with the high pressure mercury lamp which has an intensity | strength of 80 W / cm, and formed the hard-coat layer. Table 1 shows the characteristics of the obtained laminated film.

[Example 2]
A polyester film and a laminated film were obtained in the same manner as in Example 1 except that the copolyester 2 was used as the copolyester constituting the coating layer. The obtained characteristics are shown in Table 1.

[Example 3]
A polyester film and a laminated film were obtained in the same manner as in Example 1 except that the coating layer thickness was 0.05 μm. The obtained characteristics are shown in Table 1.

[Example 4]
A polyester film and a laminated film were obtained in the same manner as in Example 1 except that the copolyester 2 was used as the copolyester constituting the coating layer, and the coating layer thickness was 0.20 μm. The obtained characteristics are shown in Table 1.

[Comparative Example 1]
A polyester film and a laminated film were obtained in the same manner as in Example 1 except that the copolyester 3 was used as the copolyester constituting the coating layer. The obtained characteristics are shown in Table 1.

[Comparative Example 2]
Implemented except that 50 parts by weight of copolymer polyester 4 was used as the copolymer polyester constituting the coating layer, based on the weight of the coating layer, and 40 parts by weight of inorganic particles having a refractive index of 2.7, based on the weight of the coating layer. A polyester film and a laminated film were obtained in the same manner as in Example 1. The obtained characteristics are shown in Table 1.

[Comparative Example 3]
A polyester film and a laminated film were obtained in the same manner as in Example 1 except that the coating layer thickness was 0.03 μm. The obtained characteristics are shown in Table 1.

[Comparative Example 4]
A polyester film and a laminated film were obtained in the same manner as in Example 1 except that the coating layer thickness was 0.30 μm. The obtained characteristics are shown in Table 1.

[Comparative Example 5]
A polyester film and a laminated film were obtained in the same manner as in Example 1 except that the copolyester 5 was used as the copolyester constituting the coating layer. The obtained characteristics are shown in Table 1.

[Comparative Example 6]
Molten polyethylene terephthalate ([η] = 0.62 dl / g, Tg = 78 ° C.) is extruded from a die, cooled with a cooling drum by a conventional method to form an unstretched film, and then stretched 3.2 times in the machine direction. Then, an aqueous coating solution having a coating composition concentration of 8% shown in Table 1 was uniformly applied to both surfaces with a roll coater. Subsequently, this coated film was subsequently dried at 95 ° C., stretched 3.5 times at 120 ° C. in the transverse direction, and heat-fixed by shrinking 3% in the width direction at 220 ° C. to obtain a polyester film having a thickness of 125 μm. It was. Furthermore, using a roll coater, a UV curable composition having the same composition as in Example 1 was applied uniformly on the coating layer so that the film thickness after curing was 5 μm, and then in accordance with Example 1. Curing treatment was performed to form a hard coat layer. Table 1 shows the characteristics of the obtained laminated film.

Each component of the aqueous coating liquid is as follows.
(Polyester 1)
2,6-Naphthalenedicarboxylic acid 90 mol% / isophthalic acid 6 mol% / 5-sodium sulfoisophthalic acid 4 mol%, glycol component is ethylene glycol 60 mol% / 9,9-bis [4- (2- Hydroxyethoxy) phenyl] fluorene 30 mol% / diethylene glycol 10 mol% (Tg = 130 ° C., average molecular weight 13000, refractive index 1.65, density 1.2 g / cm ³ ).
Polyester 1 is 100 parts dimethyl 2,6-naphthalenedicarboxylate, 5.3 parts dimethyl isophthalate, 5.4 parts dimethyl 5-sodium sulfoisophthalate, 48 parts ethylene glycol and bis (4- (2-hydroxyethoxy) phenyl. ) Charge 75.3 parts of fluorene to the transesterification reactor, add 0.1 part of tetrabutoxytitanium to this, and control the temperature to 230 ° C under a nitrogen atmosphere and heat to distill off the methanol produced. A transesterification reaction was performed.
Next, 0.5 part of Irganox 1010 (manufactured by Ciba Geigy) was added to this reaction system, the temperature was gradually raised to 255 ° C., and the pressure in the system was reduced to 1 mmHg to carry out a polycondensation reaction. A copolyester of .48 dl / g was obtained. 20 parts of this copolyester was dissolved in 80 parts of tetrahydrofuran, and 180 parts of water was added dropwise to the resulting solution under high-speed stirring at 10,000 rpm to give a bluish milky white dispersion. Subsequently, this dispersion was distilled under a reduced pressure of 20 mmHg to distill off the tetrahydrofuran. Thus, a polyester aqueous dispersion having a solid content concentration of 10 wt% was obtained.

(Polyester 2)
The acid component is 90 mol% of 2,6-naphthalenedicarboxylic acid / 6 mol% of isophthalic acid / 5 mol of 5-sodium sulfoisophthalic acid, and the glycol component is 40 mol% of ethylene glycol / 9,9-bis [4- (2- Hydroxyethoxy) phenyl] fluorene 50 mol% / diethylene glycol 10 mol% (Tg = 130 ° C., average molecular weight 13000, refractive index 1.65, density 1.2 g / cm ³ ). A polyester aqueous dispersion having a solid content concentration of 10 wt% was obtained according to the production method of polyester 1.

(Polyester 3)
The acid component is 2,6-naphthalenedicarboxylic acid 70 mol% / isophthalic acid 25 mol% / 5-sodium sulfoisophthalic acid 5 mol%, and the glycol component is ethylene glycol 75 mol% / 9,9-bis [4- (2- Hydroxyethoxy) phenyl] fluorene 15 mol% / diethylene glycol 10 mol% (Tg = 111 ° C., average molecular weight 13000, refractive index 1.59, density 1.2 g / cm ³ ). A polyester aqueous dispersion having a solid content concentration of 10 wt% was obtained according to the production method of polyester 1.

(Polyester 4)
The acid component is composed of 90 mol% of terephthalic acid / 5 mol% of isophthalic acid / 5 mol% of 5-sodium sulfoisophthalic acid, and the glycol component is composed of 90 mol% of ethylene glycol / 10 mol% of diethylene glycol (Tg = 70 ° C., average Molecular weight 13000, refractive index 1.56, density 1.2 g / cm ³ ). A polyester aqueous dispersion having a solid content concentration of 10 wt% was obtained according to the production method of polyester 1.

(Polyester 5)
The acid component is 2,6-naphthalenedicarboxylic acid 70 mol% / isophthalic acid 25 mol% / 5-sodium sulfoisophthalic acid 5 mol%, and the glycol component is ethylene glycol 20 mol% / 9,9-bis [4- (2- Hydroxyethoxy) phenyl] fluorene 70 mol% / diethylene glycol 10 mol% (Tg = 175 ° C., average molecular weight 13000, refractive index 1.66, density 1.2 g / cm ³ ). A polyester aqueous dispersion having a solid content concentration of 10 wt% was obtained according to the production method of polyester 1.

(acrylic)
It is composed of 30% by mole of methyl methacrylate / 2% by mole of 2-isopropenyl-2-oxazoline / 10% by mole of polyethylene oxide (n = 10) methacrylate / 30% by mole of acrylamide (Tg = 50 ° C., molecular weight 350,000, refractive index. 1.50, density 1.2 g / cm ³ ).

  In addition, acrylic is charged in a four-necked flask with 302 parts of ion-exchanged water and heated to 60 ° C. in a nitrogen stream, and then 0.5 parts of ammonium persulfate and 0.2 part of sodium bisulfite are added as a polymerization initiator. In addition, a mixture of 23.3 parts of methyl methacrylate, 22.6 parts of 2-isopropenyl-2-oxazoline, 40.7 parts of polyethylene oxide (n = 10) methacrylic acid, and 13.3 parts of acrylamide, which are monomers, The solution was added dropwise over 3 hours while adjusting the liquid temperature to 60 to 70 ° C. After completion of dropping, the reaction was continued with stirring while maintaining the same temperature range for 2 hours, and then cooled to obtain an acrylic aqueous dispersion having a solid content of 25%.

(Organic particles 1)
Acrylic filler (average particle size: 100 nm, refractive index: 1.50, density 1.2 g / cm ³ ) (MX-100W, manufactured by Nippon Shokubai Co., Ltd.)

(Inorganic particles 1)
Titanium oxide filler (average primary particle size: 30 nm, refractive index: 2.70, density: 4.0 g / cm ³ ) (trade name: titanium oxide slurry manufactured by CI Kasei Co., Ltd.)

(Surfactant)
Polyoxyethylene (n = 7) lauryl ether (trade name NAROACTY N-70, manufactured by Sanyo Chemical Co., Ltd.).

  Since the optical polyester film of the present invention uses a film mainly composed of polyethylene naphthalene dicarboxylate, it is excellent in high dimensional stability at around 200 ° C., and has a hard coat layer by having a coating layer of a specific component. Providing flexible displays with excellent visibility when used as flexible display substrates such as organic EL displays and electronic paper because they can suppress the occurrence of interference spots when laminated and have excellent haze characteristics and high transparency. can do.

Claims (9)

An optical polyester film having a coating layer provided on at least one side of a biaxially oriented polyester film mainly composed of polyethylene naphthalene dicarboxylate, wherein at least one component of the coating layer is a copolyester, and the copolyester Is a dicarboxylic acid component containing 40 to 99 mol% of 2,6-naphthalenedicarboxylic acid based on all repeating units, 20 to 60 mol% of a glycol component having a fluorene structure represented by the following formula (I) and 30 to 30 mol% An optical polyester film characterized in that it is a copolyester composed of a glycol component containing 80 mol% of ethylene glycol, and the thickness of the coating layer is from 0.05 μm to 0.20 μm.

(R ₁ is an alkylene group having 2 to 4 carbon atoms, R ₂ , R ₃ , R ₄ , and R ₅ are hydrogen, an alkyl group having 1 to 4 carbon atoms, an aryl group, or an aralkyl group, and each is the same. May be different)   The optical polyester film according to claim 1, wherein the glycol component having a fluorene structure represented by the formula (I) is 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene.   The copolymerized polyester further comprises 0.1 to 5 mol% of an aromatic dicarboxylic acid having a sulfonate group and 0 to 60 mol% of another aromatic dicarboxylic acid based on all repeating units. 3. The optical polyester film according to 1 or 2.   The optical polyester film according to claim 1, wherein the particle content of the coating layer is 1% or less based on the weight of the coating layer.   The optical polyester film according to any one of claims 1 to 4, wherein the haze value of the film is from 0% to 1.0%.   The optical polyester film according to claim 1, wherein a hard coat layer is further provided on the coating layer.   The optical polyester film according to any one of claims 1 to 6, wherein the thermal shrinkage in the longitudinal direction of the film and the thermal shrinkage in the width direction after heating at 200 ° C for 10 minutes are each 0.1% or less.   The optical polyester film according to claim 1, which is used for a flexible display substrate.   The optical polyester film according to claim 8, wherein the flexible display is an organic EL display or electronic paper.