Laminated polyester film and method for producing the same

Abstract

To provide a laminated film that has easy adhesiveness to surfaces and comprises a resin layer that suppresses the deposition of low-molecular-weight materials such as oligomers and ultraviolet absorbers from a polyester film.SOLUTION: A laminated polyester film comprises a resin layer X at the outermost surface layer on at least one side of the polyester film. The hydrogen bonding force γSh and the dispersion force γSd in the surface free energy of the resin layer X satisfy the formula 1: 0.10≤γSh / (γSh+γSd)≤0.20, and a change in reflected light after heat treatment at 150°C for 1 hour is 0.05 or less, where the change in reflected light is expressed by the formula 2: L(SCI)-L(SCE) / L(SCI).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a laminated polyester film having a resin layer laminated on a polyester film and a method for producing the same, and more particularly to a laminated polyester film which maintains transparency even after undergoing a processing step involving heat treatment and has excellent adhesion to materials to be laminated or attached, an optical film, a vehicle display, and a vehicle electronic part each using the same, and a method for producing the same. [Background technology]

[0002] Thermoplastic resin films, especially biaxially oriented polyester films, are widely used as substrate films in many applications such as magnetic recording materials and packaging materials due to their excellent mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. In particular, in recent years, there has been an increasing demand for them as various optical films, including anti-reflection materials for flat panel displays and display materials related to touch panels. In these applications, coating processes and processes for laminating electrode materials and optical films are often used to impart various functions.

[0003] However, polyester films are sometimes unable to be used as final products because they suffer from whitening and surface contamination due to the precipitation of low molecular weight volatile substances such as oligomers and ultraviolet absorbers during the heat treatment in the above-mentioned processing steps.

[0004] For this reason, various studies have been conducted so far with the aim of suppressing the deposition of low molecular volatiles in polyester films. For example, a method of providing a resin composition coating film containing a resin (A) having a hydroxyl group and an acryloyl group and a melamine compound (B) having a methylol group by an in-line coating method in which a resin composition is applied during the manufacturing process of a polyester film (Patent Document 1) has been considered. In addition, a method of providing a resin layer containing a polyester resin containing a diol component having a tricyclodecane structure and a curing agent on the surface layer (Patent Document 2) and a method of further laminating an oligomer deposition prevention layer and an adhesive layer in sequence on a polyester film to suppress oligomer deposition and provide an easy adhesion function (Patent Document 3) have been considered.

[0005] In addition, in recent years, the number of automobiles equipped with liquid crystal panels has been increasing. Since the liquid crystal panels installed in such automobiles are often exposed to high temperature and high humidity for long periods of time, the adhesive films constituting the liquid crystal panels are also required to have resistance to moisture and heat and durability at high temperatures.

[0006] When an easily adhesive film is exposed to a humid and hot atmosphere, foreign matter precipitates on the surface from inside the film, causing the following problems. For example, the precipitates scatter light and deteriorate the transparency of the film; when used for lamination with a pressure-sensitive adhesive or hard coat, the precipitates accumulate at the interface and reduce adhesion; when used as a protective film to which a polarizing plate containing a polarizing element is attached, the precipitates penetrate into the polarizer resin and cause deterioration of properties such as reduced polarization properties and color loss. As a method for solving such problems, an easily adhesive film that has improved hot water resistance and adhesion under high temperature and high humidity conditions by reducing the amount of crosslinking agent is known (Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2016-55584 A [Patent Document 2] JP 2017-65114 A [Patent Document 3] JP 2012-92314 A [Patent Document 4] JP 2009-214531 A [Patent Document 5] JP 2014-65887 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, the resin layer of Patent Document 1 can prevent the precipitation of low molecular volatiles from the polyester film by forming a dense cured layer, but has almost no easy-adhesion function. The resin layer of Patent Document 2 is insufficient in both easy adhesion and oligomer precipitation suppression effect. In addition, as in Patent Document 3, the method of laminating an oligomer precipitation prevention layer and an easy-adhesion layer sequentially on a polyester film and providing a coating film for the purpose of inhibiting oligomer precipitation and imparting an easy-adhesion function is to laminate an oligomer precipitation prevention layer and an adhesive layer sequentially on a polyester film. Therefore, the manufacturing process becomes multiple, and not only the product yield is reduced, but also the manufacturing cost is increased. In addition, when the oligomer precipitation prevention layer is completely crosslinked and cured, and a coating liquid for forming an easy-adhesion layer is applied thereon, there is a problem that coating repelling is likely to occur due to the difference in surface energy, making it difficult to apply uniformly.

[0009] In addition, the methods disclosed in Patent Documents 4 and 5 improve the transparency and adhesion after a wet heat test to some extent, but the current situation is that an easily adhesive film having both satisfactory performance cannot be obtained. When the present inventors investigated the cause of the decrease in transparency and adhesion after a wet heat test, it was found that the surface precipitates generated under a wet heat atmosphere are residues of the reactive compound contained in the easily adhesive layer, and it was found that these problems can be improved by reducing the amount of the reactive compound. On the other hand, in the study by the present inventors, it was also found that the reactive compound is strongly related to the strength of the easily adhesive layer and the initial adhesion to the target object, and sufficient adhesion cannot be obtained by simply reducing the amount of the reactive compound.

[0010] Therefore, the present invention aims to eliminate the above-mentioned drawbacks and provide a laminated polyester film having a resin layer that combines the contradictory properties of easy adhesion and inhibition of precipitation of low molecular weight volatile matter at high temperatures, and can maintain transparency even in a humid and hot atmosphere. [Means for solving the problem]

[0011] The present invention has the following configuration: A laminated polyester film having a resin layer X on at least one surface of a polyester film, the resin layer X having a hydrogen bonding strength γSh and a dispersion strength γSd in the surface free energy satisfying the following formula 1, and a change in reflected light defined by the following formula 2 after heat treatment at 150° C. for 1 hour is 0.05 or less. Formula 1: 0.10≦γSh / (γSh+γSd)≦0.20 Equation 2: L(SCI)-L(SCE) / L(SCI).

[0012] The laminated polyester film of the present invention may have the following embodiments and may be produced by the following production method. (1) A laminated polyester film having a resin layer X on at least one surface of a polyester film, the resin layer X having a hydrogen bonding strength γSh and a dispersion strength γSd in the surface free energy satisfying the following formula 1, and a change in reflected light defined by the following formula 2 after heat treatment at 150°C for 1 hour is 0.05 or less. Formula 1: 0.10≦γSh / (γSh+γSd)≦0.20 Equation 2: L(SCI)-L(SCE) / L(SCI) (2) The laminated polyester film according to (1), which contains an ultraviolet absorber and has a light transmittance of 10% or less at a wavelength of 380 nm. (3) The laminated polyester film according to (1) or (2), wherein the resin layer X has a laminated structure of two or more layers when observed in cross section by a transmission electron microscope. (4) The laminated polyester film according to (3), wherein, among the resin layers constituting the resin layer X, the resin layer located at the outermost surface is designated as X1, and the resin layer X1 contains a polyester resin. (5) The laminated polyester film according to claim 3 or 4, wherein, among the resin layers constituting the resin layer X, a layer in contact with the polyester film is designated as a resin layer X2, and the resin layer X2 contains a resin having a hydroxyl group and a polyfunctional acryloyl group, and a melamine compound having a methylol group. (6) The laminated polyester film according to any one of (1) to (5), wherein the thickness of the polyester film is from 10 μm to 50 μm. (7) The laminated polyester film according to (4) or (5), wherein the thickness of the resin layer X1 and the thickness of the resin layer X2 are both 30 nm or more and 800 nm or less. (8) The laminated polyester film according to any one of (4) to (7), characterized in that a change in the total value of the polar strength γSp and the hydrogen bonding strength γSh in the surface free energy of the resin layer X1 after a wet heat treatment for 500 hours in an environment having a temperature of 85°C and a humidity of 85% is 0.0 mN / m to 3.0 mN / m. (9) The domain area in the elastic modulus dispersion image of the resin layer X1 of 1 μm square measured by an atomic force microscope (AFM) is 500 nm 2 The laminated polyester film according to any one of (4) to (8), which is: (10) The laminated polyester film according to any one of (1) to (9), which is used as an optical film. (11) The laminate film according to any one of (1) to (9), which is used for a vehicle display. (12) The laminate film according to any one of (1) to (9), which is used for an electronic part for a vehicle. (13) A vehicle display using the laminated polyester film according to any one of (1) to (9). (14) An electronic part for a vehicle, which uses the laminated polyester film according to any one of (1) to (9). (15) A method for producing a laminated polyester film according to any one of (1) to (14), comprising the steps of: coating step 1 of coating a resin composition containing a resin having a hydroxyl group and an acryloyl group, and a melamine compound having a methylol group, on at least one surface of a polyester film; drying step 1 of drying the resin composition at less than 150°C; coating step 2 of coating a polyester resin on the resin composition; stretching step of stretching at least in one axial direction; and drying step 2 of heating to 150°C or higher to form a resin layer X, in this order. Effect of the Invention

[0013] The present invention can provide a laminated polyester film which has good transparency, excellent adhesion to various hard coating agents and pressure-sensitive adhesives, reduces the precipitation of low-molecular-weight volatile substances from the polyester film during heat treatment, and maintains transparency and adhesion even after moist heat resistance treatment. [Brief description of the drawings]

[0014] [Figure 1] 1 is an image showing the elastic modulus variation of a resin layer X1 according to one embodiment (embodiment of Example 1) of the present invention. [Diagram 2] 1 is an image showing the variation in elastic modulus of a laminated polyester film having a problem to be solved by the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The laminated polyester film of the present invention will be described in detail below. The laminated polyester film of the present invention is a laminated polyester film having a resin layer X on at least one surface of the polyester film, characterized in that the hydrogen bonding strength γSh and the dispersion strength γSd in the surface free energy of the resin layer X satisfy the following formula 1, and the change in reflected light defined by the following formula 2 after heat treatment at 150°C for 1 hour is 0.05 or less. Formula 1: 0.10≦γSh / (γSh+γSd)≦0.20 Equation 2: L(SCI)-L(SCE) / L(SCI).

[0016] The laminated polyester film of the present invention has, as the outermost layer on at least one side of the polyester film, a resin layer X. The resin layer X will be described in detail below.

[0017] (Resin layer X) In the laminated polyester film of the present invention, it is necessary that the hydrogen bonding force γSh and the dispersion force γSd in the surface free energy of the resin layer X satisfy the following formula 1. Equation 1: 0.10≦γSh / (γSh+γSd)≦0.20.

[0018] The hydrogen bonding strength γSh, the dispersion strength γSd, and the polar strength γSp described below can be determined by the contact angle (sessile drop method) described in JIS R3257:1999, and the specific numerical range of the contact angle and the measurement method will be described later.

[0019] In the present invention, the dispersion force γSd is one of the forces constituting the surface energy of the resin layer X. This dispersion force γSd is an index representing the degree of intermolecular force generated by a main chain such as a hydrocarbon chain, and indicates the magnitude of hydrophobic interaction. Moreover, the hydrogen bond force γSh is an index representing the degree of intermolecular force due to the electronegativity of the resin layer X. This hydrogen bond force γSh is generated by a polar group having hydrogen such as a hydroxyl group, a carboxyl group, or an amino group, and therefore indicates the magnitude of hydrophilic interaction.

[0020] By setting the value of γSh / (γSh+γSd) to 0.10 or more and 0.20 or less, the initial adhesion with the resin composition for forming a coating layer such as a hard coat layer is at a preferred level. In addition, when the value of formula 1 is 0.15 or more and less than 0.19, the adhesion under moist heat conditions is excellent, which is preferable. When the value of formula 1 is less than 0.10, the reaction activity with the resin composition is low and the adhesion is poor. When the value is greater than 0.20, the reaction between the crosslinking agent and the resin composition proceeds excessively, resulting in poor adhesion. The hydrogen bond strength γSh and the dispersion strength γSd can be adjusted by the type of binder or crosslinking agent of the resin layer and the crosslinking density, the details of which will be described later. In addition, it is also effective to form the resin layer X in the order of coating step 1, drying step, coating step 2, and heat treatment step, which will be described later.

[0021] The laminated polyester film of the present invention must have a change in reflected light, as defined by the formula 2, of 0.05 or less after being heat-treated at 150° C. for 1 hour. Equation 2: L(SCI)-L(SCE) / L(SCI).

[0022] L(SCI) represents the brightness including the specular reflected light (total reflected light) measured by the SCI method, L(SCE) represents the brightness excluding the specular reflected light measured by the SCE method, and L(SCI)-L(SCE) represents the brightness of only the specular reflected light. L(SCI)-L(SCE) / L(SCI) in formula 2 represents the ratio of the specular reflected light to the total reflected light. That is, the value of formula 2 being 0.05 or less after heat treatment at 150°C for 1 hour indicates that there is little precipitate on the laminated polyester film surface due to heating, and the laminated polyester film maintains transparency even after heating, and laminated polyester films with a low value can be suitably used for various optical films. In order to maintain higher transparency before and after heating, the value of formula 2 is preferably 0.03 or less, more preferably 0.02 or less, and even more preferably 0.01 or less. From the above viewpoint, the smaller the value of formula 2, the more preferable it is, and there is no particular limit to the lower limit, but the lower limit is theoretically 0.00.

[0023] L(SCI) and L(SCE) can be measured by a known spectrophotometer, the details of which will be described later. As a measuring device, for example, a spectrophotometer CM-3600A or CM-3700A manufactured by Konica Minolta can be used. In addition, as a method for making the value of formula 2 0.05 or less or within the above-mentioned preferable range, for example, a method of making the resin layer X described later have a laminated structure of two or more layers and increasing the thickness of the resin layer X (particularly the resin layer X2 described later). In addition, it is also effective to suppress the amount of ultraviolet absorber contained in the laminated polyester to a preferable level described later. The resin layer X2 will be described later in detail.

[0024] The laminated polyester film of the present invention preferably contains an ultraviolet absorbing agent. When the laminated polyester film contains an ultraviolet absorbing agent, ultraviolet rays that deteriorate liquid crystal panels and organic EL devices can be cut. The content of the ultraviolet absorbing agent is preferably 2.5% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less, when the total components constituting the laminated polyester film are taken as 100% by mass. By suppressing the content of the ultraviolet absorbing agent in the laminated polyester film to 2.5% by mass or less, it is possible to reduce the white turbidity (haze value) caused by the decrease in light transmittance, and good visibility can be maintained when the laminated polyester film is mounted on a liquid crystal image display device or the like.

[0025] The laminated polyester film of the present invention preferably has a light transmittance of 10% or less at a wavelength of 380 nm. The wavelength of 380 nm is located at the boundary between ultraviolet light and visible light, and if light longer than this wavelength is reflected or absorbed, it may cause a change in the hue of the screen when mounted on an image display device. In addition, since ultraviolet light deteriorates liquid crystal panels and organic EL, when the laminated polyester film is used in a liquid crystal image display device or the like, it is required that the transmission of ultraviolet light is low. From the above viewpoint, the light transmittance at a wavelength of 380 nm is preferably 8% or less, more preferably 5% or less. The light transmittance at a wavelength of 380 nm can be adjusted by the amount of ultraviolet absorber added and the film thickness, and the value can be lowered by increasing the amount of ultraviolet absorber added and increasing the film thickness.

[0026] Examples of ultraviolet absorbents that can be suitably used in the laminated polyester film of the present invention include benzotriazole-based, benzophenone-based, benzoate-based, and triazine-based ultraviolet absorbents having a molecular weight of 300 g / mol or more. The ultraviolet absorbent may be selected from these, or two or more types may be used in combination. There is a relationship between the molecular weight and the sublimation property of additives such as ultraviolet absorbents, and generally, when an additive with a large molecular weight is used, sublimation is less likely to occur. In addition, many ultraviolet absorbents with a high molecular weight have long alkyl chains attached to the basic aromatic ring skeleton, which inhibits stacking between ultraviolet absorbents. Therefore, using an ultraviolet absorbent with a high molecular weight is also preferable in terms of reducing problems such as crystallization in the resin and an increase in haze.

[0027] The benzotriazole-based ultraviolet absorber is not particularly limited, but examples thereof include 2-(2'-hydroxyphenyl)benzotriazoles such as 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-dicumylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-carboxyphenyl)benzotriazole, and 2,2'-methylenebis(4-tert-octyl-6-benzotriazolyl)phenol.

[0028] Benzophenone-based ultraviolet absorbers are not particularly limited, but examples thereof include 2-hydroxybenzophenones such as 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 5,5'-methylenebis(2-hydroxy-4-methoxybenzophenone).

[0029] Benzoate-based ultraviolet absorbers include, but are not limited to, phenyl salicylate, resorcinol monobenzoate, 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate, 2,4-di-tert-amylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate, hexadecyl-3,5-di-tert-butyl-4-hydroxybenzoate, and the like.

[0030] Examples of triazine-based ultraviolet absorbers include, but are not limited to, triaryltriazines such as 2-(2-hydroxy-4-octoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-s-triazine, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-s-triazine, 2-(2-hydroxy-4-propoxy-5-methylphenyl)-4,6-bis(2,4-dimethylphenyl)-s-triazine, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diviphenyl-s-triazine, 2,4-bis(2-hydroxy-4-octoxyphenyl)-6-(2,4-dimethylphenyl)-s-triazine, 2,4,6-tris(2-hydroxy-4-octoxyphenyl)-s-triazine, and 2-(4-isooctyloxycarbonylethoxyphenyl)-4,6-diphenyl-s-triazine.

[0031] Other ultraviolet absorbing agents that can be used include salicylic acid-based agents such as phenyl salicylate, t-butylphenyl salicylate, and p-octylphenyl salicylate, as well as natural products (such as oryzanol, shea butter, and baicalin) and biological systems (such as keratinocytes, melanin, and urocanin). These ultraviolet absorbing agents can also be used in combination with hindered amine compounds as stabilizers. Inorganic ultraviolet absorbing agents have low compatibility with the base resin, which can lead to an increase in haze in the laminated polyester film and can deteriorate visibility when an image is displayed.

[0032] In the laminated polyester film of the present invention, the resin layer X preferably has a laminated structure of two or more layers when observed in cross section by a transmission electron microscope. By having a laminated structure of two or more layers, it is possible to impart different functions to the layer in contact with air and the layer in contact with the polyester film surface. In a preferred embodiment of the present invention, the layer in contact with air is preferably easily adhesive, and the layer in contact with the polyester film surface is preferably capable of suppressing the deposition of low molecular weight volatile substances.

[0033] When different resin layers are laminated, contrast appears depending on the electron density when observed with a transmission electron microscope. Whether or not resin layer X has a laminated structure of two or more layers can be determined by the fact that, when observed with a transmission electron microscope at a magnification of 50,000 times or more, fine shades of lamellar structure due to biaxial orientation in which crystalline and amorphous parts are mixed are observed in the polyester film, but such fine shades are not observed in resin layer X.

[0034] (Resin layer x1) In the laminated polyester film of the present invention, when the resin layer located at the outermost surface of the resin layers constituting the resin layer X is designated as X1, the resin layer X1 preferably contains a polyester resin. By containing a polyester resin in the resin layer X1, the adhesiveness to the hard coat layer and the adhesive layer at room temperature is excellent. In particular, the proportion of naphthalene dicarboxylic acid in the polyester resin is preferably 20 mol% or more and 90 mol% or less as an acid component, more preferably 30 mol% or more and 80 mol% or less, and even more preferably 30 mol% or more and 70 mol% or less. Note that "naphthalene dicarboxylic acid in the polyester resin" refers to a structural unit derived from naphthalene dicarboxylic acid that constitutes the molecular chain of the polyester resin. The acid component in the resin can be interpreted in the same manner hereinafter.

[0035] When the ratio of naphthalenedicarboxylic acid in the acid component in the polyester resin is 20 mol% or more and 90 mol% or less, the X1 layer has excellent adhesion (humid heat adhesion) with the hard coat layer under high temperature and high humidity. In addition, in addition to naphthalenedicarboxylic acid, aromatic, aliphatic, and alicyclic dicarboxylic acids and polyvalent carboxylic acids having three or more valences can be used as the acid component of the polyester resin, as long as the effect of the present invention is not impaired. As the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 2,5-dimethylterephthalic acid, biphenyl dicarboxylic acid, 1,2-bisphenoxyethane-p,p'-dicarboxylic acid, phenylindanedicarboxylic acid, etc. can be used. Examples of aliphatic and alicyclic dicarboxylic acids that can be used include succinic acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and ester-forming derivatives thereof.

[0036] When the polyester resin is used as a water-based coating agent, it is preferable to copolymerize a compound containing a carboxylate group or a compound containing a sulfonate group in order to improve the adhesiveness of the polyester resin or to facilitate the water solubility of the polyester resin. In particular, in applications requiring adhesiveness under wet heat, it is preferable to copolymerize a compound containing a carboxylate group as the polyester resin constituting the coating layer, without copolymerizing a compound exhibiting strong basicity such as a sulfonate group.

[0037] From the viewpoint of whitening and adhesion to an object, the laminated polyester film of the present invention is preferably such that the change in the total value of the polar force γSp and the hydrogen bonding force γSh in the surface free energy of the resin layer X1 after 500 hours of wet heat treatment in an environment of a temperature of 85° C. and a humidity of 85% is 0.0 mN / m to 3.0 mN / m (hereinafter, the "change in the total value of the polar force γSp and the hydrogen bonding force γSh in the surface free energy of the resin layer X1 after 500 hours of wet heat treatment in an environment of a temperature of 85° C. and a humidity of 85%" may be simply referred to as the "change in the total value of the polar force γSp and the hydrogen bonding force γSh of the resin layer X1"). Here, the polar force γSp is a parameter that indicates the strength of the interaction between polar groups. The resin layer X1 preferably contains a reactive compound having a polar group or hydrogen bond in order to enhance adhesion to an object, and such a reactive compound precipitates on the outermost surface of the resin layer X1 by storing the laminated polyester film in an atmosphere under wet heat conditions for a long period of time.

[0038] Therefore, we have focused on the change in the surface free energy of the resin layer X1 and have found that there is a correlation between the amount of precipitates on the surface and the change in the total value of the polar strength γSp and the hydrogen bonding strength γSp of the resin layer X1. We have found that when the change in the resin layer X1 is in the range of 0.0 mN / m to 3.0 mN / m, whitening in a moist heat atmosphere is suppressed. By setting the change in the resin layer X1 to 3.0 mN / m or less, the amount of precipitates on the surface can be suppressed and whitening can be reduced. From the above viewpoint, the change in the resin layer X1 is more preferably 0.0 mN / m to 2.3 mN / m, and particularly preferably 0.0 mN / m to 1.4 mN / m. The change in the resin layer X1 being 0.0 mN / m means that the total value of the polar strength γSp and the hydrogen bonding strength γSh does not change before and after 500 hours of moist heat treatment in an environment with a temperature of 85°C and a humidity of 85%.

[0039] The amount of change in the total value of the polar strength γSp and the hydrogen bonding strength γSp of the resin layer X1 can be controlled by the components contained in the resin layer X1, the method of forming the resin layer X1, and the combination thereof. Specifically, it can be adjusted by the type of functional group that the resin or compound that is the component has on the side chain, the molecular weight of the unit structure when a polymer is used, the progress of the crosslinking reaction, etc. The details of the preferred constituent materials and manufacturing method will be described later.

[0040] The laminated polyester film of the present invention is, from the viewpoint of reducing the amount of change in the total value of the polar force γSp and the hydrogen bonding force γSh in the surface free energy of the resin layer X1 after 500 hours of wet heat treatment in an environment of a temperature of 85° C. and a humidity of 85%, and from the viewpoint of suppressing a decrease in adhesion after the wet heat treatment, a domain area in an elastic modulus variation image of the resin layer X1 in a 1 μm square measured by an atomic force microscope (AFM) is 500 nm 2 It is preferable that the elastic modulus of the resin layer X1 is equal to or less than the above. The elastic modulus of the resin layer X1 can be measured and calculated by performing analysis based on the JKR contact theory after measurement by a force curve method using an AFM (Atomic Force Microscope), and detailed measurement methods and conditions will be described later. Note that hereinafter, "elastic modulus of the resin layer X1 of 1 μm square measured by an atomic force microscope (AFM)" and "elastic modulus variation image of the resin layer X1 of 1 μm square measured by an atomic force microscope (AFM)" may be referred to as "elastic modulus of the resin layer X1" and "variation image of elastic modulus of the resin layer X1", respectively.

[0041] There is a preferred form in the distribution of the elastic modulus of the resin layer X1, in other words, there is a preferred form in the "elastic modulus variation image of the resin layer X1" obtained by smoothing the elastic modulus image of the resin layer X1 (i.e., the data of the DMT Modulus channel) measured by the measurement method described below in the Flatten mode of the analysis software "NanoScope Analysis V1.40" in Order: 3rd and offsetting the average value to 0 MPa. Specifically, in the elastic modulus variation image of the resin layer X1 described above, it is preferable that the elastic modulus variation width is small, and it is particularly preferable that there are no coarse domains, because this keeps the surface adhesion uniform and minimizes the decrease in adhesion after moist heat treatment.

[0042] The elastic modulus variation image of the resin layer X1 will be described below with reference to the drawings. FIG. 1 is an elastic modulus variation image of the resin layer X1 according to one embodiment of the present invention, and FIG. 2 is an elastic modulus variation image of a laminated polyester film having a problem to be solved by the present invention. In FIGS. 1 and 2, the "black part in the elastic modulus variation image" (reference number 1) represents a region with a relatively low elastic modulus, and the "white part in the elastic modulus variation image" (reference number 2) represents a region with a relatively high elastic modulus. Each domain in the elastic modulus variation image of the resin layer is formed by local aggregation of the binder resin and reactive compound used, and when the domain becomes coarse as shown in FIG. 2, that is, when aggregation of the constituent materials is observed, it tends to lead to whitening after moist heat treatment.

[0043] The elastic modulus variation width of the resin layer X1 corresponds to the Image Rmax obtained by analyzing the above-mentioned "elastic modulus variation image" in Roughness mode, and is preferably less than 5 GPa, and particularly preferably less than 2 GPa. The smaller the elastic modulus variation width of the resin layer X1, the more preferable it is, and there is no particular lower limit, but from the viewpoint of feasibility, 0.05 GPa is preferable. On the other hand, the domain area in the elastic modulus variation image of the resin layer X1 is represented by the average area of ​​each domain colored with Bearing Area Percent: 10% in Bearing Analysis mode, and is 500 nm 2 It is preferable that the thickness is less than 300 nm. 2More preferably, it is 100 nm or less. 2 The domain area in the elastic modulus variation image of the resin layer X1 is preferably as small as possible, and is not particularly limited. 2 The details of the method for measuring the variation width of the elastic modulus of the resin layer X1 and the domain area in the elastic modulus variation image of the resin layer X1 will be described later.

[0044] The domain area in the elastic modulus variation image of the resin layer X1 can be adjusted by the resin constituting the resin layer X1, the type of reactive compound, the progress of the crosslinking reaction (which can be increased by thermally curing the coating composition at 170° C. or higher), etc. Details of the preferred coating composition and the production method from the above viewpoint will be described later.

[0045] (Coating composition for forming resin layer X1) The coating composition for forming the resin layer X1 of the laminated polyester film of the present invention will be described below. The resin layer X1 of the laminated polyester film of the present invention is preferably formed from a coating composition containing at least one reactive compound selected from various binder resins such as polyester resins, urethane resins, and acrylic resins, oxazoline compounds, carbodiimide compounds, and melamine compounds.

[0046] In the resin layer X1 of the present invention, the reactive compound plays a role of sufficiently advancing the crosslinking reaction and enhancing the adhesion with the layer to be laminated by processing. As the reactive compound, an oxazoline compound, a carbodiimide compound, a melamine compound, an isocyanate compound, etc. can be used alone or in any combination. However, from the viewpoint of easily lowering the amount of change in the total value of the polar force γSp and the hydrogen bonding force γSh in the surface free energy of the resin layer X1 after 500 hours of wet heat treatment in an environment of a temperature of 85°C and a humidity of 85%, it is preferable that the resin layer X1 is formed from a coating composition that satisfies all of the following characteristics 1 to 3. Feature 1: Contains binder resin, melamine compound, and carbodiimide compound. Feature 2: When the content of the binder resin in the coating composition is taken as 100 parts by mass, the content A of the melamine compound is 10 parts by mass or less, and the content B of the carbodiimide compound is 5 parts by mass to 30 parts by mass. Feature 3: A / B is less than 0.50.

[0047] In this case, when there are a plurality of components corresponding to the binder resin, the melamine compound, and the carbodiimide compound, the content of each component is treated as the total content of all the components.

[0048] The reactive compound is essential for increasing the strength of the resin layer X1 and for increasing the adhesion with the layer laminated during processing, while an excessive amount of the reactive compound may precipitate on the outermost surface in a high-temperature, high-humidity atmosphere, thereby deteriorating transparency and adhesion. Therefore, by setting the amount of the reactive compound within the range that satisfies the above requirements, precipitation on the outermost surface in a high-temperature, high-humidity atmosphere can be reduced, and deterioration of transparency and adhesion can be suppressed. In particular, since melamine compounds are more likely to precipitate than other reactive compounds and are more likely to affect the domain area in the elastic modulus variation image of the resin layer X1, in consideration of the balance between the adhesion with the layer laminated during processing and the strength of the resin layer X1, it is more preferable to set A / B to 0.05 or more and 0.35 or less, and even more preferably 0.18 or more and 0.35 or less.

[0049] In order to improve the coating property and adhesion of the coating composition, the domain area in the elastic modulus variation image of the resin layer X1 of 1 μm square measured by atomic force microscope (AFM) was easily reduced to 500 nm 2 From the viewpoints below, it is also preferable not to use a melamine compound, but to use an oxazoline compound or a carbodiimide compound alone or in combination in an amount of 5% by mass to 40% by mass of the total components of the coating composition.

[0050] The oxazoline compound is preferably an oxazoline group-containing copolymer obtained by copolymerizing at least one monomer containing an oxazoline group and at least one other monomer, the oxazoline compound having an oxazoline group as a functional group in the compound.

[0051] In the oxazoline compound, at least one other monomer used for the monomer containing an oxazoline group is a monomer copolymerizable with the monomer containing an oxazoline group, and examples thereof include acrylic acid esters or methacrylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid; unsaturated carboxylic acids such as acrylonitrile and methacrylonitrile; Examples of the monomer include nitriles, unsaturated amides such as acrylamide, methacrylamide, N-methylol acrylamide, and N-methylol methacrylamide, vinyl esters such as vinyl acetate and vinyl propionate, vinyl ethers such as methyl vinyl ether and ethyl vinyl ether, olefins such as ethylene and propylene, halogen-containing α,β-unsaturated monomers such as vinyl chloride, vinylidene chloride, and vinyl fluoride, and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene. These may be used alone or in combination as long as the scope of the present invention is satisfied.

[0052] Specific examples of monomers containing an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. These may be used alone or in combination as long as they satisfy the scope of the present invention.

[0053] A carbodiimide compound is a compound having at least one carbodiimide group or a cyanamide group in a tautomeric relationship therewith as a functional group in the compound in the molecule. Specific examples of such carbodiimide compounds include dicyclohexylmethane carbodiimide, dicyclohexyl carbodiimide, tetramethylxylylene carbodiimide, and urea-modified carbodiimide, which may be used alone or in combination as long as they satisfy the scope of the present invention. Specific examples of polycarbodiimide compounds include "Carbodilite" (registered trademark) V-02, "Carbodilite" (registered trademark) V-02-L2, "Carbodilite" (registered trademark) SV-02, and "Carbodilite" (registered trademark) V-04 (all manufactured by Nisshinbo Co., Ltd.), which are less colored and have excellent adhesion. In particular, "Carbodilite" (registered trademark) V-02-L2 has high crosslinking properties and is excellent in the effect of suppressing the precipitation of the crosslinking agent on the outermost surface under a high-temperature and high-humidity atmosphere.

[0054] As a melamine compound that can be suitably used in the laminated polyester film of the present invention, for example, a melamine compound having one or more triazine rings and one or more methylol groups in one molecule can be mentioned. By using such a melamine compound, a crosslinked structure between methylol groups can be provided in the resin layer X1.

[0055] Examples of the melamine compound include melamine, methylolated melamine derivatives obtained by condensing melamine with formaldehyde, compounds obtained by reacting methylolated melamine with a lower alcohol to partially or completely etherify the melamine, and mixtures thereof. The melamine compound may be either a condensate of a monomer or a dimer or higher polymer, or a mixture thereof. Examples of the lower alcohol used for etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. Examples of the functional group include an imino group, a methylol group, or an alkoxymethyl group such as a methoxymethyl group or a butoxymethyl group in one molecule, and examples of the methylated melamine compound include an imino group type methylated melamine compound, a methylol group type melamine compound, a methylol group type methylated melamine compound, and a fully alkylated methylated melamine compound. In particular, examples of methylol melamine compounds include monomethylol melamine, dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, and hexamethylol melamine. These may be used alone or in combination as long as they satisfy the scope of the present invention.

[0056] In particular, since melamine compounds are materials that are compatible with water, they tend to precipitate on the surface under high temperature and high humidity conditions. When the coating composition contains a melamine compound, the content is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of the binder resin. By making the content of the melamine compound 10 parts by mass or less relative to 100 parts by mass of the binder resin, it is easy to keep low the amount of change in the total value of polar force and hydrogen bond force in the surface free energy of the resin layer X after the moist heat treatment.

[0057] (Resin layer x2) In the laminated polyester film of the present invention, when the layer in contact with the polyester film is the resin layer X2 among the resin layers constituting the resin layer X, it is preferable that the resin layer X2 contains a resin having a hydroxyl group and a polyfunctional acryloyl group (hereinafter, sometimes simply referred to as resin A) and a melamine compound having a methylol group (hereinafter, sometimes simply referred to as melamine compound B). The resin A and the melamine compound B form a crosslinked structure by heating (the resin obtained by forming the crosslinked structure is sometimes referred to as resin α). By containing the resin A and the melamine compound B, a dense crosslinked structure is formed in the resin layer X2 by a part of them, and the precipitation of low molecular weight substances such as oligomers and ultraviolet absorbers from the polyester film side can be suppressed. Most ultraviolet absorbers have a low molecular weight, and problems such as precipitation on the surface of the film occur during the heat treatment process and reliability test. Therefore, by providing the resin layer X2 on the outermost layer on at least one side, the amount of precipitates on the surface generated during heating is reduced, and the transparency of the laminated polyester film can be maintained.

[0058] Resin α is preferably a resin obtained by heating a resin composition made of a resin having a hydroxyl group and an acryloyl group (resin A) and a melamine compound having a methylol group (melamine compound B) to 150°C or higher. When a resin composition made of resin A and melamine compound B is heated to 150°C or higher, a crosslinked structure formed by crosslinking between the acryloyl groups of resin A and a crosslinked structure formed by crosslinking between the hydroxyl groups of resin A and the methylol groups of melamine compound B can be efficiently formed. At the same time, a crosslinked structure formed by crosslinking between the methylol groups of melamine compound B can also be efficiently formed. The crosslinking reactions between the acryloyl groups of resin A, between the hydroxyl groups of resin A and the methylol groups of melamine compound B, and between the methylol groups of melamine compound B are highly reactive. Therefore, resin α becomes a resin having many crosslinked structures.

[0059] Increasing the number of hydroxyl groups and acryloyl groups in resin A and the number of methylol groups in melamine compound B makes it possible to obtain resin α with a denser crosslinked structure. Here, resin A may be a resin having a polymer with a hydroxyl group and a polymer with an acryloyl group, or a resin having a polymer with a hydroxyl group and an acryloyl group in a repeating unit. Among them, resin A is preferably a resin having a polymer obtained by using an acrylic acid ester compound and / or a methacrylic acid ester compound a (hereinafter sometimes simply referred to as compound a), an ethylenically unsaturated compound b having a hydroxyl group (hereinafter sometimes simply referred to as compound b), and a compound c having a urethane structure and a polyfunctional acryloyl group (hereinafter sometimes simply referred to as compound c), and polymerizing them. In terms of forming a dense crosslinked structure, it is more preferable to have a polymer in which b and c are randomly graft-polymerized to the hydrocarbon chain formed from a. Resin A polymerized using these monomers can be heated with melamine compound B to form the above-mentioned resin α. Hereinafter, compounds a, b, and c will be described.

[0060] Compound a is a monomer that forms the main skeleton of resin A. Specific examples of compound a include alkyl esters of acrylic acid and / or methacrylic acid having 1 to 18 carbon atoms, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, n-octyl acrylate, i-octyl acrylate, t-octyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, i-octyl methacrylate, t-octyl methacrylate, and 2-ethylhexyl methacrylate, as well as cycloalkyl esters having 5 to 12 cyclocarbons, such as cyclohexyl acrylate, and aralkyl esters having 7 to 12 carbon atoms, such as benzyl acrylate.

[0061] Compound b must have a hydroxyl group. By using such compound b as a monomer, resin A can have a hydroxyl group. Specific examples of compound b include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 3-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, 2-hydroxyethyl allyl ether, 2-hydroxypropyl allyl ether, 2-hydroxybutyl allyl ether, allyl alcohol, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 3-hydroxybutyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, 2-hydroxyethyl methallyl ether, 2-hydroxypropyl methallyl ether, 2-hydroxybutyl methallyl ether, and other unsaturated compounds containing one or more hydroxyl groups in the molecule. Compound b may also have a carboxyl group.

[0062] When the resin A is polymerized using the compounds a, b, and c, the mass of the compound b is preferably 1% by mass or more and 30% by mass or less when the total mass of the compounds a to c is 100% by mass. By making the mass (charged amount) of the compound b 1% by mass or more, the resin A can have a sufficient amount of hydroxyl groups. In addition, by making the mass of the compound b 30% by mass or less, the resin A can be efficiently polymerized. If the compound b exceeds 30% by mass, when preparing a coating liquid containing the resin composition by the method described below, the resin A dispersed or dissolved in the aqueous solvent E may gel or aggregate, making it difficult to use it suitably.

[0063] Compound c has an acryloyl group, and if the acryloyl group is polyfunctional, it is preferable because a dense crosslinked structure can be formed in resin α. The number of acryloyl groups in compound c is preferably 2 or more and 15 or less. In the present invention, the acryloyl group includes a methacryloyl group. By using such compound c as a monomer, resin A can have an acryloyl group. In addition, compound c preferably has a urethane structure in the molecule in addition to the polyfunctional acryloyl group. By using such compound c as a monomer, resin A can have an acryloyl group and a urethane structure.

[0064] Specifically, compound c is preferably a urethane acrylate compound obtained by reacting a compound obtained by reacting a polyhydric alcohol with an isocyanate monomer and / or an organic polyisocyanate with an acrylate monomer having a hydroxyl group and / or a methacrylate monomer having a hydroxyl group in the absence of a solvent or in the presence of an organic solvent.

[0065] Examples of polyhydric alcohols include acrylic polyols, polyester polyols, polycarbonate polyols, ethylene glycol, and propylene glycol. Examples of isocyanate monomers include tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. Examples of organic polyisocyanates include adduct type, isocyanurate type, and biuret type polyisocyanates synthesized from isocyanate monomers. Examples of acrylate monomers having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, isocyanuric acid ethylene oxide modified diacrylate, pentaerythritol tri- and tetraacrylate, and dipentaerythritol pentaacrylate. Examples of methacrylate monomers having a hydroxyl group include 2-hydroxyethyl methacrylate and hydroxypropyl methacrylate. Compound c may also contain a methylol group.

[0066] When polymerizing resin A using compounds a, b, and c, the mass of compound c is preferably 1 part by mass or more and 15 parts by mass or less when the total mass of compounds a to c is 100% by mass. By setting the mass of compound c to 1% by mass or more, a sufficient amount of acryloyl groups and urethane structures can be imparted to resin A. On the other hand, when the mass of compound c exceeds 15% by mass, the following phenomena may occur, which is not preferable. When the mass of compound c exceeds 15% by mass, since resin A has an excessive amount of acryloyl groups, when resin A is heated to obtain resin α, a very large number of cross-linked structures between acryloyl groups are formed. As a result, significant curing shrinkage is caused, and cracks may occur in the resin layer.

[0067] In the laminated polyester film of the present invention, the thickness of resin layer X1 and the thickness of resin layer X2 are both preferably 30 nm or more and 800 nm or less. By setting the thicknesses of resin layers X1 and X2 to both 30 nm or more, it becomes possible to impart the respective functions of easy adhesiveness and suppression of low molecular weight substance precipitation. Also, if the thicknesses of resin layers X1 and X2 are too thick, curl occurs in the polyester film. Therefore, by setting the thicknesses of resin layers X1 and X2 to both 800 nm or less, preferably 750 nm or less, more preferably 100 nm or less, and particularly preferably 80 nm or less, the curl resistance can be enhanced. Also, considering the viewpoint of lowering L(SCI) - L(SCE) / L(SCI) of the above formula 2, the thicknesses of resin layers X1 and X2 are preferably such that X1 < X2.

[0068] (Method for Producing Resin A Having Hydroxyl Group and Acryloyl Group) The method for producing the resin A used in the present invention is not particularly limited and known techniques can be applied, but it is preferable to use compounds a, b and c as monomers. Furthermore, the method for producing the resin A is preferably produced by emulsion polymerization in an aqueous solvent E using compounds a, b and c. By using the aqueous solvent E, it becomes easy to prepare a coating liquid containing a resin composition using the aqueous solvent E. In addition, it is preferable to produce the resin A by emulsion polymerization because the mechanical dispersion stability of the resin A is excellent. The emulsifier used in the present invention is not particularly limited and may be any of anionic emulsifiers and nonionic emulsifiers, which may be used alone or in combination of two or more types.

[0069] Examples of the anionic emulsifier include higher fatty acid salts such as sodium oleate, alkylarylsulfonates such as sodium dodecylbenzenesulfonate, and alkyl sulfates such as sodium laurate, etc. Examples of the nonionic emulsifier include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, and polyoxyethylene octylphenyl ethers, etc.

[0070] In emulsion polymerization, polymerization initiators such as persulfates such as sodium persulfate, potassium persulfate, ammonium persulfate, etc., organic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, etc., hydrogen peroxide, etc., are usually used. These polymerization initiators can be used either alone or in combination.

[0071] In emulsion polymerization, a reducing agent can be used in combination with the polymerization initiator if desired. Examples of such reducing agents include reducing organic compounds such as ascorbic acid, tartaric acid, citric acid, glucose, and formaldehyde sulfoxylate metal salts; and reducing inorganic compounds such as sodium thiosulfate, sodium sulfite, sodium bisulfite, sodium metabisulfite, and ammonium bisulfite.

[0072] Furthermore, a chain transfer agent can be used in the emulsion polymerization. Examples of such a chain transfer agent include n-dodecyl mercaptan, t-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, trichlorobromomethane, etc. The polymerization temperature preferably used in the emulsion polymerization of the resin A of the present invention is about 30 to 100°C.

[0073] (Melamine compound B having a methylol group) A melamine compound having a methylol group that can be used in the laminated polyester film of the present invention must have at least one triazine ring and at least one methylol group in one molecule (hereinafter, a melamine compound having a methylol group may be referred to as melamine compound B). By using such a melamine compound B, it is possible to provide resin α with a crosslinked structure between methylol groups.

[0074] Specifically, the melamine compound B is preferably a compound obtained by etherifying a methylolmelamine derivative obtained by condensing melamine with formaldehyde through a dehydration condensation reaction with a lower alcohol such as methyl alcohol, ethyl alcohol, or isopropyl alcohol. Examples of the methylol melamine derivative include monomethylolmelamine, dimethylolmelamine, trimethylolmelamine, tetramethylolmelamine, pentamethylolmelamine, and hexamethylolmelamine.

[0075] The resin composition forming the X2 layer of the laminated polyester film of the present invention preferably has a content of the melamine compound B of 10 parts by mass or more and 60 parts by mass or less, based on 100 parts by mass of the resin A. More preferably, the content of the melamine compound B is 20 parts by mass or more and 50 parts by mass or less.

[0076] (Crosslinking agent C containing at least one selected from an isocyanate compound, a carbodiimide compound, and an oxazoline compound) In the laminated polyester film of the present invention, the resin composition forming the resin layer X2 may contain, in addition to the resin A and the melamine compound B, a crosslinking agent C (hereinafter sometimes simply referred to as crosslinking agent C) containing at least one selected from an isocyanate compound, a carbodiimide compound, and an oxazoline compound.

[0077] Examples of compounds having an isocyanate group include aromatic polyisocyanate compounds such as 1,3- or 1,4-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4-diphenylmethane diisocyanate, 3,3-dimethyldiphenylmethane-4,4-diisocyanate, and 1,3-xylylene diisocyanate, as well as 1,4-tetramethylene diisocyanate and 1,6- Examples of the isocyanate include aliphatic polyisocyanate compounds such as hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,8-octamethylene diisocyanate, and 1,10-decamethylene diisocyanate, as well as dimers or trimers of these isocyanates and adducts of these isocyanates with divalent or trivalent polyols such as ethylene glycol and trimethylolpropane.

[0078] The compound having an oxazoline group is not particularly limited as long as it has at least one oxazoline group or oxazine group per molecule, but an addition-polymerizable oxazoline group-containing monomer is preferred, and examples thereof include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0079] The compound having a carbodiimide group is not particularly limited as long as it has at least one carbodiimide structure (-N=C=N-) per molecule, but a polycarbodiimide compound having two or more per molecule is particularly preferred in terms of moisture-resistant heat adhesion, etc. Among them, when a polymeric isocyanate compound having multiple carbodiimide groups at the end or side chain of a polymer such as a polyester resin or an acrylic resin is used, it is preferable that the laminated polyester film of the present invention is made from the viewpoints of not only improving the hardness of the resin layer and suppressing oligomer precipitation, but also improving adhesion to various hard coat agents and pressure-sensitive adhesives, moisture-resistant heat adhesion, flexibility, and toughness.

[0080] A known technique can be applied to the production of a carbodiimide compound, and generally, the carbodiimide compound is obtained by polycondensing a diisocyanate compound in the presence of a catalyst. As the diisocyanate compound, which is the starting material of the polycarbodiimide compound, aromatic, aliphatic, alicyclic diisocyanates, etc. can be used, and specifically, tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, etc. can be used. Furthermore, within the range that does not eliminate the effects of the present invention, in order to improve the water solubility or water dispersibility of the polycarbodiimide compound, a surfactant may be added, or a hydrophilic monomer such as a polyalkylene oxide, a quaternary ammonium salt of a dialkylamino alcohol, or a hydroxyalkylsulfonate may be added.

[0081] Other compounds, for example, aziridine compounds, amide epoxy compounds, titanate coupling agents such as titanium chelate, methylolated or alkylolated urea compounds, acrylamide compounds, and the like, can also be used arbitrarily.

[0082] In the laminated polyester film of the present invention, the mass of the crosslinking agent C containing at least one selected from an isocyanate compound, a carbodiimide compound, and an oxazoline compound in the resin composition forming the resin layer X2 is preferably 10 parts by mass or more and 80 parts by mass or less when the mass of the resin A is 100 parts by mass. More preferably, it is 15 parts by mass or more and 50 parts by mass or less. By making the crosslinking agent C 10 parts by mass or more, the resin layer X can exhibit good adhesion to various hard coating agents and pressure-sensitive adhesives. On the other hand, by making the crosslinking agent C 80 parts by mass or less, the resin layer X can exhibit the precipitation suppression property of the resin α while maintaining good adhesion to various hard coating agents and pressure-sensitive adhesives.

[0083] In addition, the resin composition forming the resin layer X2 of the laminated polyester film of the present invention preferably has a total content of the resin A having a hydroxyl group and an acryloyl group and the melamine compound B having a methylol group of 70% by mass or more based on the total content of the resin forming the resin layer. By making the total content of the resin A and the melamine compound B in the resin forming the resin layer 70% by mass or more, precipitation from the polyester film can be suppressed.

[0084] When a resin composition made of resin A having a hydroxyl group and an acryloyl group and melamine compound B having a methylol group is heated to 150°C or higher, the acryloyl groups of resin A crosslink with each other, or the hydroxyl groups crosslink with the methylol groups of melamine compound B to form a crosslinked structure. Increasing the number of hydroxyl groups and acryloyl groups of resin A and the number of methylol groups of melamine compound B makes it possible to form a denser crosslinked structure. Such a dense crosslinked structure reduces the precipitation of oligomers and ultraviolet absorbers contained in the laminated polyester film after heating, and can improve transparency.

[0085] (Polyester film) The polyester film serving as the base film in the laminated polyester film of the present invention will be described in detail. Polyester is a general term for polymers having an ester bond as the main bond in the main chain, and those having at least one component selected from ethylene terephthalate, propylene terephthalate, ethylene-2,6-naphthalate, butylene terephthalate, propylene-2,6-naphthalate, ethylene-α,β-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate as the main component (main structural unit) can be preferably used. Among them, in the laminated polyester film of the present invention, it is preferable to use polyethylene terephthalate as the polyester film. In addition, when heat or shrinkage stress acts on the polyester film, it is particularly preferable to use polyethylene-2,6-naphthalate, which has excellent heat resistance and rigidity, as the polyester film.

[0086] The polyester film is preferably biaxially oriented. A biaxially oriented polyester film is generally a polyester sheet or film that is stretched about 2.5 to 5.0 times in the longitudinal direction and in the width direction perpendicular to the longitudinal direction, and then heat-treated to complete crystal orientation, and shows a biaxially oriented pattern in wide-angle X-ray diffraction. If the polyester film is a biaxially oriented film, the laminated polyester film is preferably improved in thermal stability, particularly dimensional stability and mechanical strength, and improved flatness.

[0087] In addition, various additives such as antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, antistatic agents, nucleating agents, etc. may be added to the polyester film to the extent that they do not deteriorate its properties.

[0088] The thickness of the polyester film is not particularly limited and is appropriately selected according to the application and type, but is preferably 10 μm or more and 50 μm or less. In particular, when used as an optical film, it is preferably 15 μm or more and 38 μm or less from the viewpoint of the trend of thinning panels, reduction of rainbow unevenness, reduction of precipitation of ultraviolet absorbers and the like during heating, and light resistance. If it is desired to make the light transmittance of the polyester film at a wavelength of 380 nm 10% or less, the concentration of the ultraviolet absorber added needs to be increased as the thickness decreases, and precipitation of the ultraviolet absorber during heating becomes more problematic. Therefore, by making the thickness of the polyester film 10 μm or more, it is possible to reduce the precipitation of the ultraviolet absorber while maintaining light resistance. On the other hand, by suppressing the thickness of the polyester film to 50 μm or less, it is possible to suppress rainbow unevenness of the laminated polyester film. Rainbow unevenness occurs due to the magnitude of the phase difference of the biaxially oriented film, and the phase difference is expressed as the product of the refractive index difference in the longitudinal direction and the width direction and the thickness, so that rainbow unevenness of the laminated polyester film can be reduced by making the polyester film thinner.

[0089] The laminated polyester film of the present invention is preferably used for optical films. Here, the optical film refers to a film used in display devices such as LCD, OLED, and touch panels, and specific examples include films used for anti-reflection films, hard coat films, circular polarizing plates, polarizing plate protective films, retardation films, backlight units, diffusion sheets, prism sheets, microlens sheets, brightness enhancement films, QD sheets, etc. Since there is little change in formula 2 even when heat-treated at 150°C for 1 hour, the laminated polyester film of the present invention is preferably used for applications requiring heating and transparency. Specifically, it can be used for applications in which a hard coat layer or a conductive layer such as indium tin oxide (hereinafter referred to as ITO) is provided on the laminated polyester film of the present invention (for example, touch panel applications). It is also used for films that have both the prevention of precipitation of ultraviolet absorbers and the easy adhesion function required for ultraviolet ray cutting functions such as liquid crystal and OLED displays.

[0090] (Production method of polyester film) The method for producing the polyester film constituting the laminated polyester film of the present invention will be described in more detail with an example in which polyethylene terephthalate (hereinafter referred to as PET) is used as the polyester resin. First, PET pellets are thoroughly vacuum-dried to reduce the moisture content to 100 ppm or less, and then fed to an extruder. The extruder performs melt extrusion into a sheet at about 280°C, and the sheet is cooled and solidified by a cast drum with a surface temperature of 5 to 40°C to produce an unstretched (unoriented) PET film (A film). The A film is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120°C to obtain a uniaxially oriented PET film (B film). The end of the B film is held by a clip and introduced into a tenter, where it is heated to 80 to 130°C and then stretched 1.1 to 5.0 times in the width direction. The film is then introduced into a heat treatment zone at 150 to 250°C and heat-treated for 1 to 30 seconds to complete the crystal orientation. In this heating step (heat treatment step), a relaxation treatment of 3 to 15% may be carried out in the width direction or the length direction as required. In this manner, the polyester film constituting the laminated polyester film of the present invention can be obtained.

[0091] (Method of forming resin layer X) In the method for forming a resin layer of the present invention, it is preferable to have a coating step 1 of coating a resin composition containing a resin (resin A) having a hydroxyl group and an acryloyl group and a melamine compound (melamine compound B) having a methylol group on at least one surface of a polyester film, a drying step 1 of drying the resin composition at less than 150°C, a coating step 2 of coating a polyester resin on the resin composition, a stretching step of stretching at least in one axial direction, and a drying step 2 of heating in the range of 100 to 250°C to form a resin layer X in this order. Each drying step may be performed in parallel with the transverse stretching or heat treatment step of the polyester film. In this case, the drying temperature in the drying step 1 is the highest temperature until the coating step 2.

[0092] If the drying temperature in the drying step 1 is 150°C or higher, the crosslinking reaction between the resin having an acryloyl group (resin A) and the melamine compound having a methylol group (melamine compound B) proceeds, and when the polyester resin is applied, the liquid is easily repelled, which may make it difficult to apply it uniformly. As a result, since a highly uniform X1 layer is not formed on the outermost surface, it may not be possible to set "γSh / (γSh+γSd)" in formula 1 within a preferred range. On the other hand, if the drying temperature in the coating step 1 is less than 150°C, the resin composition is in a state in which only water has evaporated, so that the polyester resin can be applied uniformly, and the adhesion between the resin layer X2 formed in the coating step 1 and the resin layer X1 formed in the coating step 2 and the subsequent drying step 2 can also be increased.

[0093] In the drying step 2 following the coating step 2, drying is continued at a temperature range of 100°C to 250°C, preferably at a temperature range of 150°C to 240°C, since the curing of the resin layer X proceeds. The resin composition used in each coating step is as described above. The temperature setting for each drying step may be changed stepwise, but the final highest temperature in each drying step shall be the drying temperature in that step.

[0094] When the resin composition containing the resin A and the melamine compound B is provided on the polyester film, a solvent may be used, but it is preferable to use an aqueous solvent. By using an aqueous solvent, the solvent can be prevented from evaporating rapidly during the heating process, and a uniform resin layer can be formed. In addition, the aqueous solvent is superior in terms of environmental load compared to organic solvents. Here, the aqueous solvent refers to a mixture of water, or water and an organic solvent soluble in water, such as alcohols such as methanol, ethanol, isopropyl alcohol, and butanol, ketones such as acetone and methyl ethyl ketone, and glycols such as ethylene glycol, diethylene glycol, and propylene glycol, in a ratio of 0.1% by mass to 40% by mass in the entire solvent.

[0095] In the laminated polyester film of the present invention, there are two methods for coating the polyester film. One is an off-coating method, specifically, after fixing the four sides of a biaxially oriented polyester film cut into a sheet shape by a known method with a metal frame or the like so as not to move, a resin composition containing a resin having a hydroxyl group and an acryloyl group and a melamine compound having a methylol group is coated on the polyester film, and then dried within a range of 100°C to 150°C to form a resin layer X2. Then, a polyester resin composition is coated and dried within a temperature range of 150°C to 240°C to form a resin layer X1.

[0096] Another method is an in-line coating method, in which a resin composition containing a resin having a hydroxyl group and an acryloyl group and a melamine compound having a methylol group is applied onto a substantially amorphous film A obtained by melt extruding a polyester resin and then quenching it, and a film B stretched in the longitudinal direction, and then the film is stretched in the width direction while being held laterally by a tenter, and finally dried within a temperature range of 150°C to 240°C to form a resin layer X2 and wound up. Thereafter, a polyester resin composition is applied onto the wound film, and dried within a temperature range of 100°C to 250°C, preferably 150°C to 240°C, to form a resin layer X1.

[0097] The resin composition can be applied to the polyester film by any known coating method, such as bar coating, reverse coating, gravure coating, die coating, or blade coating.

[0098] The laminated polyester film thus obtained has good transparency and can suppress the occurrence of scratches during the transportation and processing steps. Furthermore, it can also suppress the precipitation of oligomers, ultraviolet absorbers, and the like from the polyester film during processing steps involving heat treatment. EXAMPLES

[0099] The laminated polyester film of the present invention will be described more specifically below with reference to examples, but the laminated polyester film of the present invention is not limited thereto.

[0100] (Methods for measuring characteristics and evaluating effects) The methods for measuring the characteristics and evaluating the effects of the present invention are as follows.

[0101] (1) Calculation method of dispersion force γSd, hydrogen bond force γSh, and polar force γSp First, the laminated polyester film was left in an atmosphere of room temperature 23°C and relative humidity 65% ​​for 24 hours. Then, in the same atmosphere, the contact angle of each of the four solutions of pure water, ethylene glycol, formamide, and diiodomethane was measured at five points on the resin layer using a contact angle meter CA-D type (manufactured by Kyowa Interface Science Co., Ltd.). The average value of the three measured values ​​excluding the maximum and minimum values ​​of the five measured values ​​was taken as the contact angle of each solution. Next, using the contact angles of the four types of solutions obtained, the surface energy of the present invention, which is the dispersion force, polar force, hydrogen bond force, and the sum of the dispersion force and polar force, was calculated by the geometric mean method based on the formula proposed by Hata et al., which separates the surface free energy (γ) of a solid into three components, the dispersion force component (γSd), the polar force component (γSp), and the hydrogen bond force component (γSh), and expands the Fowkes formula (extended Fowkes formula).

[0102] The specific calculation method for each parameter is shown below. The meaning of each symbol is explained below. When γSL is the tension at the interface between a solid and a liquid, formula (A) is established. γSL: Surface energy of the resin layer and the known solution listed in Table 1 γS: Surface energy of the resin layer γL: Surface energy of known solutions listed in Table 1 γSd: Dispersion force component of the surface energy of the resin layer γSp: Polar component of the surface energy of the resin layer γSh: Hydrogen bonding force component of the surface energy of the resin layer γLd: Dispersion force component of the surface energy of the known solutions listed in Table 1 γLp: Polar component of the surface energy of the known solutions listed in Table 1 γLh: Hydrogen bond force component of the surface energy of the known solutions listed in Table 1 γSL=γS+γL-2(γSd・γLd)1 / 2-2(γSp・γLp)1 / 2-2(γSh・γLh)1 / 2...Formula (A) Furthermore, the state when a droplet is in contact with a smooth solid surface at a contact angle (θ) is expressed by the following equation (B) (Young's equation). γS=γSL+γLcosθ...Formula (B) Combining equations (A) and (B), we obtain the following equation (C). (γSd·γLd)1 / 2+(γSp·γLp)1 / 2+(γSh·γLh)1 / 2=γL(1+cosθ) / 2 ····Formula (C).

[0103] In practice, the contact angles (θ) of four types of solutions, namely water, ethylene glycol, formamide, and diiodomethane, and the components of the surface tension of the known solutions listed in Table 1 (γLd, γLp, γLh) are substituted into formula (C) to solve four simultaneous equations. As a result, the surface energy (γ), dispersion force component (γSd), polar force component (γSp), and hydrogen bonding force component (γSh) of the solid are calculated. Note that the dispersion force of the present invention corresponds to the dispersion force component (γSd), and the polar force of the present invention corresponds to the sum of the polar force component (γSp) and the hydrogen bonding force component (γSh).

[0104] (2)L(SCI), L(SCE), L(SCI)-L(SCE) A sample was cut to 5 cm x 5 cm, and the side opposite the coated side of the sample was painted black with magic marker (name), and the L value of the coated side was measured by the SCE method and the SCI method under the condition of a target mask (CM-A106) with a measurement diameter of φ8 mm using a CM-3600A manufactured by Konica Minolta, Inc., and the average value of n=3 was calculated. Note that a CM-A103 was used as the white calibration plate, and a CM-A104 was used as the zero calibration box. Note that if there was no coating layer, no particular measurement surface was specified.

[0105] (3) Transparency after heating A laminated polyester film sample with a side length of 10 cm was fixed to a metal frame on all four sides. Next, the laminated polyester film sample fixed to the metal frame was placed upright against the floor of a hot air oven "HIGH-TEMP-OVEN PHH-200" manufactured by ESPEC Corp., set at 150°C (air flow gauge "7"), and heated for 1 hour. After cooling the removed laminated polyester film sample, the surface opposite to the resin layer surface was wiped with ethyl alcohol and visually evaluated according to the following criteria. Regarding the evaluation, D was a level that was problematic for practical use, C was a practical level, and A and B were considered to be good. A: There was absolutely no difference in transparency before and after heating. B: A slight difference in transparency was observed after heating. C: Clouding was observed after heating. D: Significant clouding was observed after heating.

[0106] (4) Number of resin layers, thickness of resin layer X, thickness of polyester film The laminated polyester film sample was embedded in a visible light curing resin (D-800, manufactured by JEOL Datum Co., Ltd.) and cured by exposing to visible light at room temperature to obtain an embedded block. From the obtained embedded block, an ultrathin section with a thickness of about 70 to 100 nm was prepared using an ultramicrotome equipped with a diamond knife, and this was dyed in ruthenium tetroxide vapor for 30 minutes. The cross section of this sample was appropriately enlarged in the range of 10,000 to 100,000 times with a TEM (transmission electron microscope: H7100FA type manufactured by Hitachi, Ltd.) to obtain a cross-sectional photograph. In Example 1 of the present invention, the magnification was set to 80,000 times (accelerating voltage 200 kv). The measured values ​​of the resin layer thickness of the five samples (five pieces) were averaged to obtain the resin layer X thickness of the laminated polyester film. The number of resin layers was confirmed by the number of interfaces where the shade of dyeing was clearly observed.

[0107] The cross section of the sample was imaged using a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd. The total thickness was calculated from the image obtained, and the total thickness minus the thickness of the resin layer X was determined as the polyester film thickness. The magnification and acceleration voltage can be appropriately adjusted. For example, in Example 1 of the present invention, the magnification was set to 300 times (acceleration voltage 3 kv).

[0108] (5) Confirmation of the structure of the resin that forms the resin layer X The structure of the resin forming the resin layer X can be confirmed by pyrolysis gas chromatography mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy ( 1 Three types of NMR (H-NMR) were performed, and a comprehensive judgment was made based on all the results. The presence or absence of weight peaks due to resins with hydroxyl groups and acryloyl groups, melamine compounds with methylol groups, and polyester structures was confirmed by pyrolysis GC-MS. The presence or absence of peaks due to bonds between atoms in resins with hydroxyl groups and acryloyl groups, melamine compounds with methylol groups, and polyester structures was confirmed by FT-IR. 1 The chemical shift positions and proton absorption line areas derived from the number of hydrogen atoms in the structures of resins having hydroxyl and acryloyl groups, melamine compounds having methylol groups, and polyesters were confirmed by H-NMR. The equipment and conditions used for the measurements are shown below.

[0109] <Pyrolysis GC-MS> Pyrolysis furnace: PY-3030D (manufactured by Frontier Labs) Heating temperature: 600℃ GC-MS (Agilent) conditions Column: "UltraALLOY" (registered trademark)-5 5% diphenyl + 95% dimethylpolysiloxane Column temperature: 40°C (3 min) - 320°C (18 min) at 20°C / min Injection temperature: 300℃ <ft-ir> IR: Nicolet iS5 (Thermo Fisher Scientific) Sample preparation method: KBr Measurement mode: Transmittance Resolution: 8cm -1 Number of times accumulated: 64 < 1 H-NMR> NMR: ECA-400 (JOEL) Resonance wavelength: 399.78MHz Number of scans: 32.

[0110] (6) Adhesion 25 parts by mass of a carboxylic acid group-containing monomer (Toagosei Co., Ltd., "Aronix" (registered trademark) M-5300), 75 parts by mass of cyclohexanone, and 1.2 parts by mass of a photoinitiator (Ciba-Geigy Co., Ltd., "Irgacure" (registered trademark) 184) were mixed and dispersed using a sand grinder mill to obtain a UV-curable resin composition. This was uniformly applied to the resin layer X side of the laminated polyester film using a bar coater so that the film thickness after curing would be 2 μm. Next, a concentrated high-pressure mercury lamp (Eye Graphics Co., Ltd., H03-L31) with an irradiation intensity of 120 W / cm set at a height of 9 cm from the surface to which the UV-curable resin composition was applied was used to illuminate the resin layer X side of the laminated polyester film at an integrated irradiation intensity of 300 mJ / cm. 2 The UV-curable resin composition was cured to form a hard coat layer on the laminated polyester film. The integrated irradiation intensity of the UV rays was measured using an industrial UV checker (UVR-N1, manufactured by Japan Battery Co., Ltd.). The hard coat laminated polyester film thus obtained was then cut by 1 mm 2 100 pieces of cross-cut paper were inserted, and "Sellotape" (registered trademark) (manufactured by Nichiban Co., Ltd., CT405AP) was attached, and the paper was rolled with a hand roller at 1.5 kg / cm. 2 After pressing the sheet with a load of 1000g, it was quickly peeled off in a 90° direction against the hard-coated laminated polyester film, and the number of lattices that remained without peeling was counted. The same measurement was carried out five times, and the adhesion was evaluated according to the following criteria based on the average number of lattices that remained without peeling. D was a level that was problematic for practical use, C was a level that could be used practically, and A and B were considered to be good. A: More than 90 pieces and less than 100 pieces remaining B: 80 to less than 90 remaining C: 50 to less than 80 remaining D: 0 to less than 50 remaining.

[0111] (7) Adhesion to heat and humidity A hard coat layer was laminated on the resin layer X side of the laminated polyester film in the same manner as in (6) to obtain a hard coat laminated polyester film. The obtained hard coat laminated polyester film was then left in a thermohygrostat at a temperature of 85°C and a relative humidity of 85% for 500 hours to obtain a sample for a moist heat adhesion test. The obtained sample for a moist heat adhesion test was subjected to an adhesion test in the same manner as in (6) and evaluated according to the same criteria.

[0112] (8) Rainbow unevenness The laminated polyester film obtained in each Example and Comparative Example was laminated with an adhesive so that the orientation axis was parallel to the absorption axis of the polarizer. After that, the transmitted light when irradiated from the bottom with a white LED backlight was visually observed from all directions at an angle of 50° for the presence or absence of rainbow unevenness, and was evaluated according to the following criteria: C is a level that is problematic for practical use, B is a practical level, and A is good. A: No rainbow unevenness was observed. B: Slight rainbow unevenness was observed. C: Rainbow unevenness was clearly observed.

[0113] (9) Curl The laminated polyester film was cut into a square of 100 mm (longitudinal direction) × 100 mm (width direction), and the degree of curling of the film when the resin layer surface was facing up was evaluated according to the following criteria: D was a level that was problematic for practical use, C was a practical level, and A and B were considered to be good. A: The film was flat and had no lifting whatsoever. B: The lifting of the film edge was 1 mm or more and less than 3 mm. C: The lifting of the film edge was 3 mm or more and less than 20 mm. D: The edge of the film was lifted by 20 mm or more, or curled inward.

[0114] (10) Light resistance The laminated polyester film was cut into a square sample of 50 mm (longitudinal direction) x 50 mm (transverse direction). The sample was left at 60°C for 1000 hours using a Sunshine carbon arc lamp type light fastness tester (Sunshine Weather Meter S80D manufactured by Suga Test Instruments Co., Ltd.) specified in JIS B7753 (1999 edition), and the light fastness test was performed. The laminated polyester film sample before the light fastness test and the laminated polyester film sample after the light fastness test were measured five times for each sample using the SCI method under the target mask condition of a measurement diameter of φ25.4 mm using a CM-3600d manufactured by Konica Minolta, Inc. Based on the average value of the obtained values, ΔE was calculated from the following formula. The white calibration plate was CM-A103, and the zero calibration box was CM-A104. The ΔE at this time was used to judge the light fastness according to the following criteria. Regarding the evaluation, D was a level that was problematic for practical use, C was a level that could be used practically, and A and B were considered to be good. ΔE = {(L* value before test - L* value after test) 2 + (a*value before test - a*value after test) 2 + (b* value before test - b* value after test) 2 } 1 / 2 A: ΔE is 0.0 to 2.0 B: ΔE is 2.1 to 3.0 C: ΔE is 3.1 to 5.0 D: ΔE is 5.1 or more.

[0115] (11) Appearance of coating The appearance of the laminated polyester film was visually evaluated according to the following criteria. ◯: No coating cissing or unevenness in coating thickness was observed. ×: Repelling of coating or unevenness in coating thickness was observed.

[0116] (12) Domain area using elastic modulus variation images obtained by atomic force microscope (AFM) Measurements were performed in PeakForceQNM mode using an AFM (DimensionIcon manufactured by Burker Corporation). Using the attached analysis software "NanoScopeAnalysis V1.40", analysis was performed based on the JKR contact theory from the obtained force curve to obtain the elastic modulus distribution of the resin layer. Specifically, the laminated polyester film was first fixed to the sample stage using double-sided tape so that the measurement surface (resin layer surface) was on the upper side. Next, the cantilever's warp sensitivity, spring constant, and tip curvature were configured according to the manual for PeakForceQNM mode, and then measurements were performed under the following conditions, and the data obtained from the DMT Modulus channel was adopted as the elastic modulus of the resin layer. The measurement conditions are shown below.

[0117] <Measurement equipment and conditions> Measurement equipment: Atomic force microscope (AFM) manufactured by Burker Corporation (model number: DimensionIcon) Measurement mode: PeakForceQNM (force curve method) Cantilever: Bruker AXS RTESPA-300 Measurement atmosphere: 23℃ in air Measurement range: 5 (μm) square Resolution: 512×512 Measurement speed: 0.977 Hz Cantilever movement speed: 10 (μm / s) Pressing load (Setpoint): 40 (nN) Poisson's ratio: 0.4.

[0118] The obtained data of the DMT Modulus channel was then analyzed using the analysis software "NanoScopeAnalysis V1.40", and the value of Image Raw Mean in the Results tab obtained by processing with Roughness was taken as the elastic modulus of the resin layer. The obtained data of the DMT Modulus channel was then analyzed using the analysis software "NanoScopeAnalysis V1.40". First, the data was smoothed in Flatten mode with Order:3rd to obtain an "elastic modulus variation image". The "elastic modulus variation image" was then analyzed in Roughness mode, and Image Rmax was taken as the variation width of the elastic modulus of the resin layer.

[0119] On the other hand, for the analysis of the domain area, the "elastic modulus variation image" was converted to a grayscale image by selecting Color tabel: 7 from Adjust Image Color Scale in the Commands tab (corresponding to the images shown in Figures 1 and 2). Furthermore, in Bearing Analysis mode, the elastic modulus variation image was colored with Bearing Area Percent: 10%. Next, the colored parts were selected based on the hue using Color Threshold of the image processing software ImageJ / developer: National Institutes of Health (NIH). Furthermore, the average area of ​​each domain was calculated using the Analyze Particles function. Note that the area of ​​noise parts was excluded by setting the Size range to 5-Infinity (Pixel^2) in the measurement condition settings of Analyze Particles. The average area of ​​each domain obtained by the above operations was used as the domain area.

[0120] (13) Change in the total value of polarity and hydrogen bonding strength after moist heat treatment The sample that had been subjected to moist heat treatment under the same conditions as in (7) was left in an atmosphere of 25°C and 65% humidity for a day, and the polar strength γSp and hydrogen bonding strength γSh were calculated under the same conditions as in (2). (Total value of γSp + γSh after moist heat treatment) - (Total value of γSp + γSh before moist heat treatment) was taken as the change in the total value of polar strength and hydrogen bonding strength after moist heat treatment. n was 3, and the average value was used.

[0121] (14) Haze change after wet heat treatment Five square laminated polyester film samples, each 5 cm on a side, were prepared, and the haze was measured using a turbidity meter "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with the JIS "Method of Determining Haze of Transparent Materials" (K7136 2000 edition). Next, the samples were subjected to a moist heat treatment under the same conditions as in (7), and the haze was measured in the same manner. From the measurement results obtained, the "5-point average haze value after moist heat treatment - 5-point average haze value before moist heat treatment" was calculated, and this was defined as the amount of haze change after moist heat treatment.

[0122] Example 1 Resin A1 having hydroxyl groups and multifunctional acryloyl groups: In a stainless steel reaction vessel, methyl methacrylate a, hydroxyethyl methacrylate b, and urethane acrylate oligomer (manufactured by Negami Chemical Industries Co., Ltd., "Art Resin" (registered trademark) UN-3320HA, number of acryloyl groups is 6) c were charged in a ratio of 70:20:5 (mass ratio), and 2 parts by mass of sodium dodecylbenzenesulfonate was added as an emulsifier to a total of 100 parts by mass of a to c, and stirred to prepare mixed solution 1. Next, a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a dropping funnel was prepared. The above mixed solution 1, isopropyl alcohol, and potassium persulfate as a polymerization initiator were charged in a ratio of 60:200:5 (mass ratio) in the reaction apparatus, and heated to 60 ° C. to prepare mixed solution 2, which was kept heated at 60 ° C. for 20 minutes. Next, mixed solution 1, isopropyl alcohol, and potassium persulfate were mixed in a ratio of 40:50:5 (mass ratio) to prepare mixed solution 3. Next, using a dropping funnel, mixed liquid 3 was dropped into mixed liquid 2 over 2 hours to prepare mixed liquid 4, which was heated to 60 ° C and held for 2 hours. The obtained mixed liquid 4 was cooled to 50 ° C or less and then transferred to a container equipped with a stirrer and a pressure reducing device. 60 parts by mass of ammonia water with a concentration of 25% by mass and 900 parts by mass of pure water were added thereto, and isopropyl alcohol and unreacted monomers were recovered under reduced pressure while heating to 60 ° C, and resin A1 dispersed in pure water was obtained.

[0123] Melamine compounds B having methylol groups: Methylol melamine (manufactured by Sanwa Chemical Co., Ltd., "Nicalac" (registered trademark) MX-035) was used.

[0124] ·Resin composition 1 (for X2 layer formation): Resin A1 and melamine compound B were mixed in a mass ratio of resin A1 / melamine compound B=100 / 50. In order to impart slipperiness to the laminated polyester film surface, 2 parts by mass of silica particles (manufactured by Nippon Shokubai Co., Ltd., "Sea Hoster" (registered trademark) KE-W30) having an average particle size of 300 nm were added as inorganic particles per 100 parts by mass of resin A1. Furthermore, in order to improve the applicability of the resin composition onto the polyester film, a fluorine-based surfactant (manufactured by GOO Kagaku Co., Ltd., "Plus Coat" (registered trademark) RY-2) was added so that the content of the resin composition in the coating liquid was 0.06 parts by mass. The solid content was finally adjusted with pure water to 5% by mass, and resin composition 1 was obtained. The average particle size in the liquid can be determined, for example, by a scattering type particle size distribution measuring device Partica mini LA350 manufactured by HORIBA. When the particles are contained in a resin layer on a polyester film, the diameters of 50 particle projections and recesses on the surface are measured at 30,000 to 50,000 magnifications using a scanning electron microscope, and the average value is used to determine the average particle size.

[0125] Easy-adhesion resin composition 1 (for forming X1 layer): An easily-adhesive resin composition 1 was prepared as follows. Water dispersion of polyester resin d: A polyester resin containing the following dicarboxylic acid component and diol component-derived structural units in the following ratios (solid content concentration 15% by mass, glass transition temperature 75°C) (Dicarboxylic acid component) Terephthalic acid: 85 mol% Trimellitic acid: 15 mol% (Diol component) Ethylene glycol: 100 mol% Water dispersion of polyester resin e: A polyester resin containing the following dicarboxylic acid components and diol component-derived structural units in the following ratios (solid content concentration 15% by mass, glass transition temperature 120°C) (Dicarboxylic acid component) Dimethyl 2,6-naphthalenedicarboxylate: 88 mol% Sodium dimethyl 5-sulfoisophthalate: 6 mol% Trimellitic acid: 6 mol% (Diol component) Ethylene glycol: 100 mol% Water dispersion of melamine compound f: "Nicalac" (registered trademark) MW-12LF (solid content concentration 25% by mass) manufactured by Sanwa Chemical Co., Ltd. Water dispersion of carbodiimide compound g: "Carbodilite" (registered trademark) V-04, manufactured by Nisshinbo Chemical Inc., solid content concentration 40% by mass.

[0126] The above d to g were mixed so that the solid content mass ratio became d / e / f / g=30 / 70 / 40 / 30, and the concentration was adjusted by adding pure water so that the solid content concentration of the resin composition α became 2 mass %.

[0127] Polyester film: After thoroughly vacuum drying the PET pellets (intrinsic viscosity 0.65 dl / g) containing substantially no particles, 0.8% by mass of 2,2'-(1,4-phenylene)bisbenzoxazine (Shiraishi Kogyo Co., Ltd. "CYASORB" (registered trademark) UV3638) as an ultraviolet absorber having a molecular weight of 368 g / mol was mixed and fed to an extruder and melted at 285°C. Next, the melted PET was extruded into a sheet from a T-shaped die, and was wrapped around a mirror-finished casting drum with a surface temperature of 25°C using an electrostatic casting method, and cooled and solidified. This unstretched film was heated to 90°C and stretched 3.3 times in the longitudinal direction to obtain a uniaxially stretched film (B film).

[0128] Laminated polyester film: A coating solution containing resin composition 1 was applied to one side of a uniaxially stretched film (above polyester film) with a coating thickness of about 6 μm using a bar coater. Then, while both ends of the uniaxially stretched film were held by clips, the film was passed through a tenter set at a temperature of 120 ° C. to evaporate the moisture in the coating film, and the edge portion was trimmed by tentering out, and the film was wound up. The wound up film was run again, and a coating solution containing easy-adhesion formulation resin composition 1 was applied to a coating thickness of about 3 μm using a bar coater. Then, while both ends of the laminated polyester film were held by clips, the laminated polyester film was passed through a tenter. The atmospheric temperature of the preheating zone was set to 100 ° C., and the solvent of the coating solution containing easy-adhesion formulation resin composition 1 was dried. Then, the film was continuously stretched 3.6 times in the width direction in a stretching zone at 110 ° C., and then heat-treated for 10 seconds in a heat treatment zone at 235 ° C. to obtain a laminated polyester film in which crosslinking of the resin layer X and crystal orientation of the polyester film were completed. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0129] (Examples 2 to 4) A laminated polyester film was obtained in the same manner as in Example 1, except that the coating thickness of the resin composition 1 was increased by changing the bar coating and the thickness of the resin layer X2 was changed as shown in Table 2. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0130] Example 5 Easy-adhesion resin composition 2 (for forming X1 layer): An easily-adhesive resin composition 2 was prepared as follows. Aqueous dispersion of acrylic-urethane copolymer resin: "Sannaron" WG-353 (solids concentration 30% by mass) manufactured by Yamanami Synthetic Chemical Industry Co., Ltd. Water dispersion of polyisocyanate i: "Burnoock" (registered trademark) DNW-5000 (solids concentration 80% by mass) manufactured by DIC Corporation. Aqueous dispersion of oxazoline-containing polymer j: "Epocross" (registered trademark) WS-500 (solids concentration 40% by mass) manufactured by Nippon Shokubai Co., Ltd. Water dispersion of carbodiimide compound g: Nisshinbo Chemical Co., Ltd. "Carbodilite" (registered trademark) V-04) (solid content concentration 40% by mass) The above components were mixed so that the solids weight ratio was h / i / j / g=100 / 60 / 30 / 30, and the concentration was adjusted with pure water so that the solids concentration was 2%, to obtain an easily-adhesive resin composition 2.

[0131] Laminated polyester film: A laminated polyester film was obtained in the same manner as in Example 1, except that the easy-adhesion formulation resin composition 1 was changed to the easy-adhesion formulation resin composition 2. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0132] Example 6 Easy-adhesion resin composition 3 (for forming X1 layer): An easily-adhesive resin composition 3 was prepared as follows. Water dispersion of acrylic-urethane copolymer resin: Sannalon WG-658 (solids concentration 30% by mass) manufactured by Sannan Synthetic Chemical Industry Co., Ltd. Water dispersion of polyester resin l: A polyester resin (solid content concentration 15% by mass) containing the following dicarboxylic acid component and diol component-derived structural units in the following ratios: (Dicarboxylic acid component) Dimethyl 2,6-naphthalenedicarboxylate: 88 mol% Sodium dimethyl 5-sulfoisophthalate: 12 mol% (Diol component) Compound with 2 moles of ethylene oxide added to 1 mole of bisphenol S: 86 mole% 1,3-propanediol: 14 mol% Water dispersion of isocyanate compound m: "Elastron" (registered trademark) E-37 (solid content concentration 28% by mass) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Aqueous dispersion of oxazoline-containing polymer j: "Epocross" (registered trademark) WS-500 (solid content concentration 40% by mass) manufactured by Nippon Shokubai Co., Ltd. The above-mentioned components were mixed so that the solids weight ratio was k / l / m / j = 15 / 85 / 10 / 40, and the concentration was adjusted with pure water so that the solids concentration of the coating composition was 2 mass %, thereby obtaining an easily-adhesive resin composition 3.

[0133] Laminated polyester film: A laminated polyester film was obtained in the same manner as in Example 1, except that the easy-adhesion formulation resin composition 1 was changed to the easy-adhesion formulation resin composition 3. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0134] (Examples 7 and 8) Except for changing the thickness of the polyester film by changing the discharge rate of the extruder, a laminated polyester film was obtained in the same manner as in Example 1. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0135] Example 9 Except for changing the amount of the ultraviolet absorber added to the polyester film to 1.5% by mass, a laminated polyester film was obtained in the same manner as in Example 1. The raw material composition of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0136] Example 10 A laminated polyester film was obtained in the same manner as in Example 1, except that the thickness of the polyester film was changed by adjusting the discharge rate of the extruder as shown in Table 2 and the amount of the ultraviolet absorber added to the polyester film was changed to 1.5% by mass. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0137] Example 11 Resin A2 containing hydroxyl and acryloyl groups: In a stainless steel reaction vessel, methyl methacrylate a, hydroxyethyl methacrylate b, and urethane acrylate oligomer (manufactured by Negami Chemical Industries Co., Ltd., "Art Resin" (registered trademark) UN-3320HA, number of acryloyl groups is 6) c were charged in a mass ratio of 55 / 30 / 15, and 2 parts by mass of sodium dodecylbenzenesulfonate as an emulsifier was added to a total of 100 parts by mass of a to c and stirred to prepare mixed solution 1. Next, a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a dropping funnel was prepared. The above mixed solution 1, isopropyl alcohol, and potassium persulfate as a polymerization initiator were charged in a mass ratio of 60:200:5 in the reaction apparatus and heated to 60 ° C. to prepare mixed solution 2, which was then held in a heated state at 60 ° C. for 20 minutes. Next, mixed solution 1, isopropyl alcohol, and potassium persulfate were mixed in a mass ratio of 40:50:5 to prepare mixed solution 3. Next, using a dropping funnel, mixed liquid 3 was dropped into mixed liquid 2 over 2 hours to prepare mixed liquid 4, which was heated to 60 ° C and held for 2 hours. The obtained mixed liquid 4 was cooled to 50 ° C or less and then transferred to a container equipped with a stirrer and a pressure reducing device. 60 parts by weight of ammonia water with a concentration of 25% by mass and 900 parts by weight of pure water were added thereto, and isopropyl alcohol and unreacted monomers were recovered under reduced pressure while heating to 60 ° C, and resin A2 dispersed in pure water was obtained.

[0138] ·Resin composition 2 (for X2 layer formation): Resin A2 and melamine compound B were mixed in a mass ratio of resin A2 / melamine compound B=100 / 50 to obtain resin composition 2.

[0139] Laminated polyester film: A laminated polyester film was obtained in the same manner as in Example 3, except that Resin Composition 1 was changed to Resin Composition 2. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0140] Example 12 Polyester film, laminated polyester film: After thoroughly vacuum drying the PET pellets (intrinsic viscosity 0.65 dl / g) containing substantially no particles, 0.8% by mass of 2,2'-(1,4-phenylene)bisbenzoxazine (Shiraishi Kogyo Co., Ltd. "CYASORB" (registered trademark) UV3638) as an ultraviolet absorber having a molecular weight of 368 g / mol was mixed and fed to an extruder and melted at 285°C. Next, the melted PET was extruded into a sheet from a T-shaped die, and was wrapped around a mirror-finished casting drum with a surface temperature of 25°C using an electrostatic casting method, and cooled and solidified to obtain an unstretched film. The obtained unstretched film was heated to 90°C and stretched 3.3 times in the longitudinal direction to obtain a uniaxially stretched film. Next, the uniaxially stretched film was passed through a tenter while both ends in the width direction were held with clips, and stretched 3.6 times in the width direction in a stretching zone at 100 ° C to 120 ° C, and then heat-treated for 10 seconds in a heat treatment zone at 235 ° C to obtain a polyester film. This polyester film was cut to A4 size, and the four sides were fixed with a metal frame, and then a coating liquid containing resin composition 1 was applied to one side of the polyester film with a coating thickness of about 1.6 μm using a bar coater, and the coating was placed in a hot air oven at an atmospheric temperature of 120 ° C to evaporate the moisture in the coating film. Next, a coating liquid containing easy-adhesion formulation resin composition 1 was applied to a coating thickness of about 0.8 μm using a bar coater, and the coating was placed in a hot air oven at an atmospheric temperature of 120 ° C to evaporate the moisture in the coating film. Next, the coating was placed in a hot air oven at an atmospheric temperature of 235 ° C and heat-treated for 10 seconds to obtain a laminated polyester film in which the crosslinking of the resin layer X was completed. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0141] (Example 13) A laminated polyester film was obtained in the same manner as in Example 12, except that Resin Composition 1 was changed to Resin Composition 2 and the coating thickness was changed as shown in Table 2. The raw material composition of the resin layer of the obtained laminated polyester film, and the evaluation results, etc. are shown in Tables 1 and 2.

[0142] Example 14 Easy-adhesion resin composition 4 (for forming X1 layer): An easily-adhesive resin composition 4 was prepared as follows. Water dispersion of polyester resin n: A polyester resin containing the following dicarboxylic acid components and diol component-derived structural units in the following ratios (solid content concentration 15% by mass, glass transition temperature 120°C) (Dicarboxylic acid component) Dimethyl 2,6-naphthalenedicarboxylate: 88 mol% Sodium dimethyl 5-sulfoisophthalate: 12 mol% (Diol component) Compound with 2 moles of ethylene oxide added to 1 mole of bisphenol S: 86 mole% 1,3-propanediol: 14 mol% Water dispersion of carbodiimide compound o: "Carbodilite" (registered trademark) V-02L-2, manufactured by Nisshinbo Chemical Inc. (solid content concentration: 40% by mass). Aqueous dispersion of oxazoline-containing polymer j: "Epocross" (registered trademark) WS-500 (solid content concentration 40% by mass) manufactured by Nippon Shokubai Co., Ltd. The above j, n, and o were mixed so that the solid content mass ratio became n / o / j=100 / 30 / 30, and the concentration was adjusted by adding pure water so that the solid content concentration of the resin composition α became 2 mass %.

[0143] Laminated polyester film: A laminated polyester film was obtained in the same manner as in Example 3, except that the easy-adhesion formulation resin composition 1 was changed to the easy-adhesion formulation resin composition 4. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0144] Example 15 Easy-adhesion resin composition 5 (for forming X1 layer): An easily-adhesive resin composition 5 was prepared as follows. The above f, j, n, and o were mixed so that the solid content mass ratio was n / o / j / f = 100 / 30 / 30 / 5, and the concentration was adjusted by adding pure water so that the solid content concentration of resin composition α was 2 mass%.

[0145] Laminated polyester film: A laminated polyester film was obtained in the same manner as in Example 3, except that the easy-adhesion formulation resin composition 1 was changed to the easy-adhesion formulation resin composition 4. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0146] Example 16 Easy-adhesion resin composition 6 (for forming X1 layer): An easily-adhesive resin composition 6 was prepared as follows. The above f, j, n, and o were mixed so that the solid content mass ratio was n / o / j / f = 100 / 30 / 30 / 10, and the concentration was adjusted by adding pure water so that the solid content concentration of resin composition α was 2 mass%.

[0147] Laminated polyester film: A laminated polyester film was obtained in the same manner as in Example 3, except that the easy-adhesion formulation resin composition 1 was changed to the easy-adhesion formulation resin composition 6. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0148] Comparative Example 1 A laminated polyester film was obtained in the same manner as in Example 1, except that the film-forming method of the laminated polyester film was as follows. The easy-adhesion formulation resin composition 1 was applied to one side of the uniaxially stretched film with a coating thickness of about 10 μm using a bar coater. Then, the uniaxially stretched film was passed through a tenter while both ends in the width direction were held with clips. The atmospheric temperature in the tenter preheating zone at this time was set to 100° C., and the solvent of the coating liquid containing the easy-adhesion formulation resin composition 1 was dried. Then, the film was continuously stretched 3.6 times in the width direction in a stretching zone at 110° C., and then heat-treated for 10 seconds in a heat treatment zone at 235° C., to obtain a laminated polyester film in which crosslinking of the resin layer X and crystal orientation of the polyester film were completed. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0149] Comparative Example 2 A uniaxially stretched film coated with resin composition 1 was obtained in the same manner as in Example 3, except that the film-forming method of the laminated polyester film was as follows. Then, the uniaxially stretched film was passed through a tenter while both ends in the width direction were held with clips. The atmospheric temperature in the tenter preheating zone at this time was set to 100°C to dry the solvent of the coating liquid containing resin composition 1. Then, the film was continuously stretched 3.6 times in the width direction in a stretching zone at 110°C, and then heat-treated for 10 seconds in a heat treatment zone at 235°C to obtain a laminated polyester film in which crosslinking of the resin layer X and crystal orientation of the polyester film were completed. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0150] Comparative Example 3 A laminated polyester film was obtained in the same manner as in Example 1, except that the film-forming method of the laminated polyester film was as follows. Resin composition 1 was applied to one side of a uniaxially stretched film with a coating thickness of about 6 μm using a bar coater. Then, the uniaxially stretched film was passed through a tenter while both ends in the width direction were held by clips. The temperature condition in the tenter at this time was a temperature condition in which the temperature was gradually increased from 100° C. to 150° C., and the moisture in the coating film was evaporated, and the edge part was trimmed at the tenter out and the film was wound up. The wound up film was run again, and a coating liquid containing the easy-adhesion formulation resin composition 1 was applied to a coating thickness of about 3 μm using a bar coater. Then, the laminated polyester film was passed through a tenter while both ends in the width direction were held by clips. The atmospheric temperature in the preheating zone was set to 100° C., and the solvent of the coating liquid containing the easy-adhesion formulation resin composition 1 was dried. Subsequently, the film was continuously stretched 3.6 times in the width direction in a 110°C stretching zone, and then heat-treated for 10 seconds in a 235°C heat treatment zone to obtain a laminated polyester film in which crosslinking of the resin layer X and crystal orientation of the polyester film were completed. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0151] Comparative Example 4 A laminated polyester film was obtained in the same manner as in Comparative Example 1, except that resin composition 1 and easy-adhesion resin composition 1 were not applied. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0152] Comparative Example 5 A laminated film was obtained in the same manner as in Comparative Example 1, except that no ultraviolet absorber was added to the polyester film and that no resin composition 1 or easy-adhesion resin composition 1 was applied. The raw material composition of the resin layer of the obtained laminated polyester film and the evaluation results are shown in Tables 1 and 2.

[0153] Comparative Example 6 A laminated polyester film was obtained in the same manner as in Example 1, except that the thickness of the polyester film was changed by adjusting the discharge rate of the extruder as shown in Table 1, and the amount of the ultraviolet absorber added to the polyester film was changed to 4.5% by mass. The evaluation results of the obtained laminated polyester film are shown in Tables 1 and 2.

[0154] [Table 1]

[0155] The symbols of the reactive compounds in the table represent the compound types, and the details are as follows. f: "Nicalac" (registered trademark) MW-12LF (solid content concentration 25% by mass) manufactured by Sanwa Chemical Co., Ltd. g: "Carbodilite" (registered trademark) V-04 manufactured by Nisshinbo Chemical Co., Ltd., solid content concentration 40% by mass i: DIC Corporation's "Burnoock" (registered trademark) DNW-5000 (solid content concentration 80% by mass) j: "Epocross" (registered trademark) WS-500 (solid content concentration 40% by mass) manufactured by Nippon Shokubai Co., Ltd. m: "Elastron" (registered trademark) E-37 (solid content concentration 28% by mass) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. о: "Carbodilite" (registered trademark) V-02L-2, manufactured by Nisshinbo Chemical Inc. (solid content: 40% by mass).

[0156] [Table 2]

[0157] When no layers corresponding to the X1 layer or X2 layer were present, the thickness of each layer was recorded as "-" (Comparative Examples 1, 2, 4, and 5). [Industrial Applicability]

[0158] The present invention relates to a laminate film having a resin layer that suppresses the precipitation of oligomers and ultraviolet absorbers that precipitate from a polyester film during processing steps involving film formation and heat treatment of the polyester film, and has excellent adhesion to a hard coat, and can be used for optical films for displays and touch panels, and for films that require various types of heat processing. [Explanation of symbols]

[0159] 1: Black area in the elastic modulus variation image 2: White area in the elastic modulus variation image

Images