Laminated Polyester Film

Abstract

To provide a laminated polyester film which is excellent in handleability when being wound in a roll shape due to formation of a fine uneven structure.SOLUTION: A laminated polyester film has a polyester film and a resin layer formed on at least one surface of the polyester film using a resin composition, and satisfies all of the following requirements (1) to (4). (1) The resin layer has an uneven structure. (2) The resin composition contains the following compounds (A) and (B): (A) one or more selected from the group consisting of a binder resin and a crosslinking agent, and (B) particles. (3) A ratio of the content of the particles (B) occupying in the total non-volatile component in the resin composition is 20 mass% or more. (4) Kurtosis (Sku) of the surface of the resin layer is less than 3.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminated polyester film. [Background technology]

[0002] Polyester films, such as polyethylene terephthalate films and polyethylene naphthalate films, are used in a variety of applications because they have excellent properties such as mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and also have excellent cost performance.

[0003] Furthermore, polyester films are suitable for various applications, such as release films for forming green sheets for multilayer ceramic capacitors, substrates for releasing interlayer insulating resins, and substrates for dry film resists, taking advantage of the smoothness of the film surface.

[0004] Polyester films for sheet molding having excellent surface smoothness for the above-mentioned applications and other uses are required to be wrinkle-free and have a good roll appearance when wound into a roll. However, increasing the surface smoothness reduces the slipperiness and makes it difficult for air to escape when wound into a roll or when unwound from the roll, resulting in slippage during winding and blocking, which reduces the handleability. In particular, in recent years, with the improvement in productivity, there has been a trend toward thinner and longer polyester films, which requires a higher level of roll appearance quality.

[0005] Therefore, in order to ensure ease of handling, the non-smooth side (back side) is sometimes designed to be rougher than the smooth side by incorporating particles (for example, Patent Document 1). Furthermore, Patent Document 2 discloses a slippery composite polyester film in which a continuous coating layer having a fine mesh uneven structure is provided on at least one surface of a polyester film for the purpose of improving handling properties. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-33811 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-211082 Summary of the Invention [Problem to be solved by the invention]

[0007] However, with the conventional particle-incorporated film manufacturing method disclosed in Patent Document 1, it is difficult to control the formation of unevenness, making it difficult to form a fine uneven structure. Furthermore, the film disclosed in Patent Document 2 has insufficient unevenness, so that it is prone to wrinkles when wound into a roll, which can impair the appearance of the roll.

[0008] Therefore, the present invention has been made in consideration of the above-mentioned situation, and the problem to be solved is to provide a laminated polyester film that has excellent handling properties when winding the film into a roll, etc., by forming a fine uneven structure. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by the following configuration. The present invention has the following aspects.

[0010] [1] A laminated polyester film comprising a polyester film and a resin layer formed from a resin composition on at least one side of the polyester film, the laminated polyester film satisfying all of the following requirements (1) to (4): (1) The resin layer has an uneven structure. (2) The resin composition contains the following compounds (A) and (B): (A) one or more members selected from the group consisting of binder resins and crosslinking agents (B) Particles (3) The content of the (B) particles is 20% by mass or more as a proportion of the total nonvolatile components in the resin composition. (4) The kurtosis (Sku) of the surface of the resin layer is less than 3.0. [2] The laminated polyester film according to the above [1], wherein the arithmetic mean roughness (Ra) of the surface of the resin layer is 10 nm or more when measured with a scanning probe microscope. [3] The laminated polyester film according to the above [1] or [2], wherein the ten-point average roughness (Rzjis) of the surface of the resin layer measured with a scanning probe microscope is 60 nm or more. [4] The laminated polyester film according to any one of the above [1] to [3], wherein the load length ratio (Rmr(70)) of the roughness curve at a cutting level of 70% of the surface of the resin layer measured with a scanning probe microscope is 82% or less. [5] The laminated polyester film according to any one of the above [1] to [4], wherein the root mean square gradient (Sdq) of the surface of the resin layer is 0.1 or more. [6] The laminated polyester film according to any one of the above [1] to [5], wherein the developed interface area ratio (Sdr) of the resin layer surface is 0.5% or more. [7] The laminated polyester film according to any one of the above [1] to [6], which has an air leakage index of 130,000 seconds or less. [8] The laminated polyester film according to any one of the above [1] to [7], wherein the (B) particles have an average particle size of 1 to 100 nm. [9] The laminated polyester film according to any one of the above [1] to [8], wherein the (A) binder resin comprises at least one resin selected from the group consisting of polyester resins, (meth)acrylic resins, and polyurethane resins.

[10] The laminated polyester film according to any one of the above [1] to [9], wherein the (B) particles contain at least one kind selected from the group consisting of zirconium oxide, titanium oxide, and silica. [Effects of the Invention]

[0011] According to the present invention, a laminated polyester film having a fine uneven structure formed thereon is provided which has excellent handling properties when the film is wound into a roll.

[0012] Furthermore, since the laminated polyester film of the present invention can form a fine uneven structure on the surface of the resin layer, when used for sheet molding, for example, it has the advantage that the extremely smooth film exhibits good winding properties and is less likely to wrinkle when wound into a roll.

[0013] Furthermore, since the resin layer of the laminated polyester film of the present invention can be made thin, it can also accommodate thin, long polyester films, which can contribute to improving productivity by reducing the frequency of changing product rolls during processing. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an image obtained by observing the surface of a resin layer in Example 1. [Figure 2] 1 is an image of the surface of the resin layer of Example 8. [Figure 3] 10 is an image of the surface of the resin layer of Example 19. DETAILED DESCRIPTION OF THE INVENTION

[0015] Next, an example of an embodiment of the present invention will be described, but the present invention is not limited to the embodiment described below.

[0016] In this specification, when the expression "(meth)acrylic" is used, "(meth)acrylic" means one or both of "acrylic" and "methacrylic". Similarly, "(meth)acrylic acid" means one or both of "acrylic acid" and "methacrylic acid", "(meth)acrylate" means one or both of "acrylate" and "methacrylate", and "(meth)acryloyl" means one or both of "acryloyl" and "methacryloyl". The same applies to other terms.

[0017] <<<Laminated polyester film>>> The laminated polyester film of the present invention (hereinafter also referred to as "the present laminated polyester film") comprises a polyester film (hereinafter also referred to as "the present polyester film") and a resin layer (hereinafter also referred to as "the present resin layer") formed from a resin composition on at least one side of the polyester film.

[0018] The laminated structure of the present laminated polyester film may be a structure in which a resin layer is formed on one side of a polyester film and the surface of the polyester film is left as is on the other side, or a structure in which another layer is formed on the other side. Alternatively, the film may have a resin layer formed on both sides of a polyester film. Furthermore, the resin layer may be formed directly on the polyester film, or another layer may be provided between the polyester film and the resin layer.

[0019] <<Polyester film>> The polyester film serves as the substrate of the laminated polyester film. The polyester film may have a single layer structure or a multilayer structure. When the polyester film has a multilayer structure, the polyester film may have a two-layer structure, a three-layer structure, or a four-layer structure or more, without departing from the gist of the present invention. The number of layers is not particularly limited. When the polyester film has a multilayer structure of two or more layers, a two-kind three-layer structure or a three-kind three-layer structure is particularly preferred. When the polyester film has a multilayer structure, it is also preferred that the polyester film has a structure in which surface layers are provided on both sides of an intermediate layer.

[0020] In particular, when utilizing the smoothness of the present laminated polyester film, it is preferable that at least one side of the present polyester film has excellent smoothness. Examples of such design methods include a method in which the present polyester film has a single layer, a two-kind three-layer, or a three-kind three-layer structure, and both sides of the present polyester film have excellent smoothness, and a method in which the present polyester film has a three-kind three-layer structure, and one side of the present polyester film has excellent smoothness and the other side has a different roughness.

[0021] The polyester film may be either an unstretched film (sheet) or a stretched film. A uniaxially or biaxially stretched film is preferred. A biaxially stretched film is more preferred because of its excellent balance of mechanical properties and flatness.

[0022] <Polyester> The polyester, which is the raw material of the polyester film, refers to a polymer compound having continuous ester bonds in the main chain, and may be a homopolyester or a copolymer polyester. Specific examples include polyesters obtained by polycondensation of a dicarboxylic acid component and a diol component. Furthermore, it is preferable to use a polyester containing more than 50 mol% of an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid, based on 100 mol% of the dicarboxylic acid component.

[0023] Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfonedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and ester derivatives thereof.

[0024] Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol.

[0025] When the polyester is a homopolyester, it is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic diol. Preferred examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and preferred examples of the aliphatic diol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative examples of homopolyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with polyethylene terephthalate being preferred.

[0026] On the other hand, the copolymer polyester is preferably a polycondensation polymer of, for example, a dicarboxylic acid component and an aliphatic diol. The dicarboxylic acid component preferably includes one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (e.g., p-oxybenzoic acid). The aliphatic diol preferably includes one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol. The copolymer polyester preferably includes terephthalic acid as the dicarboxylic acid component and ethylene glycol as the aliphatic diol. When the polyester is a copolymer polyester, it is preferably a copolymer containing 30 mol % or less of a third component. The third component is a component other than the compound that is the main component (i.e., the component with the highest content) of the dicarboxylic acid component constituting the polyester and the compound that is the main component of the diol component, such as a component other than terephthalic acid and ethylene glycol in the case of copolymer polyethylene terephthalate. The copolymer polyester may also contain structural units derived from difunctional compounds other than dicarboxylic acid components and aliphatic diols. The structural units derived from difunctional compounds other than dicarboxylic acid components and aliphatic diols are preferably 20 mol% or less, more preferably 10 mol% or less, based on the total moles of all structural units constituting the polyester. Examples of the difunctional compound include various hydroxycarboxylic acids and aromatic diols.

[0027] The content of terephthalic acid in all dicarboxylic acid components constituting the present polyester film is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more. The content of ethylene glycol in all diol components constituting the present polyester film is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more. The upper limit of the content of terephthalic acid and ethylene glycol is 100 mol %.

[0028] The polyester may be a recycled polyester or a biomass-derived polyester.

[0029] <Polycondensation catalyst> The polycondensation catalyst used in polycondensing the polyester is not particularly limited, and any conventionally known compound can be used, such as a titanium compound, a germanium compound, an antimony compound, a manganese compound, an aluminum compound, a magnesium compound, and a calcium compound. Among these, at least one of titanium compounds and antimony compounds is preferred, and it is particularly preferred to use polyesters obtained using titanium compounds. Therefore, the present polyester film preferably contains at least one of a titanium compound and an antimony compound, and more preferably contains a titanium compound.

[0030] Use of the titanium compound can ultimately reduce the amount of antimony compound used, thereby reducing the risk of new protrusions being formed due to the antimony compound precipitating on the film surface, and allowing a high level of surface smoothness to be maintained. Therefore, in a particularly preferred embodiment, when the present polyester film has a multi-layer structure, the titanium compound is used as the polyester constituting at least one of the surface layers.

[0031] The content of titanium element derived from the titanium compound in the surface layer is preferably 3 ppm to 40 ppm, more preferably 4 ppm to 35 ppm, by mass. Furthermore, when the surface layer contains at least one of an antimony compound and a titanium compound, the content of antimony element in the surface layer is preferably 0 ppm to 100 ppm. Within this range, catalyst-induced foreign matter can be reduced without reducing production efficiency. From the viewpoint of productivity and cost, it is also preferable that the polyester constituting the layers other than the surface layer does not contain a titanium compound. As described above, by including a titanium compound in the polyester film, the polyester film can have excellent smoothness. If the polyester film is then formed into a laminated polyester film having the resin layer, the laminated polyester film can be suitably used for forming sheets, etc.

[0032] <Intrinsic viscosity> The intrinsic viscosity (IV) of the polyester constituting the present polyester film is preferably 0.50 dL / g or more, more preferably 0.55 dL / g or more, and even more preferably 0.60 dL / g or more. This range has the advantage of increasing the shear stress during kneading, thereby enabling high particle dispersion. The intrinsic viscosity (IV) of the polyester is, for example, 1.00 dL / g or less. In addition, when two or more polyesters with different intrinsic viscosities (IV) are used, the "intrinsic viscosity (IV) of the polyester constituting the present polyester film" refers to the intrinsic viscosity (IV) of the mixed polyesters.

[0033] When the polyester film has a multilayer structure, the intrinsic viscosity (IV) of the polyester constituting the surface layer is preferably within the above range.

[0034] <particle> The polyester film may contain particles, which impart slipperiness to the polyester film and prevent scratches during each process, improving handling properties. The type of particles contained in the polyester film is not particularly limited as long as they are capable of imparting lubricity. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide; crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles; and organic particles such as calcium oxalate and ion exchange resins. Among these, organic particles, silica, aluminum oxide, and the like are preferred. Among these, aluminum oxide is preferred from the viewpoint of hardening the layer to prevent scratches on the film surface and maintaining smoothness. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

[0035] There is no particular limitation on the shape of the particles used, and any of spherical, blocky, rod-like, flat, etc. may be used. There are also no particular limitations on the hardness, specific gravity, color, etc. Two or more types of particles of this series may be used in combination as needed.

[0036] The average particle size of the particles used is usually 5 μm or less, preferably 0.01 to 3 μm, more preferably 0.02 to 1 μm, and even more preferably 0.03 to 0.5 μm. A particle size of 5 μm or less is preferable because it prevents the surface roughness of the film from becoming too rough, which is effective in preventing problems when forming a resin layer and various surface functional layers other than the resin layer in subsequent processes. Furthermore, an average particle size within this range keeps haze low, making it easier to ensure transparency for the entire laminated polyester film. The average particle size of particles can be determined by measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and averaging the measured diameters. In the case of non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each particle.

[0037] When particles are incorporated into the polyester film, it is preferable to incorporate particles into the surface layer, for example, by providing a surface layer and an intermediate layer. Also, when the film has a three-type, three-layer structure with different front and back layers, it is possible to incorporate particles into only one of the surface layers. The particle content, depending on the average particle size, is usually 5000 ppm or less, preferably 3000 ppm or less, and more preferably 1000 ppm or less, by mass in the layer containing the particles. When particles are not contained or when the particle content is low, sufficient slippage cannot be imparted, and although the transparency of the polyester film is high, the slippage may be insufficient. Therefore, measures such as laminating the present resin layer described below to improve the slippage are necessary. Furthermore, if the content is 5000 ppm or less, the transparency of the polyester film can be sufficiently ensured. Furthermore, the particle content in the layer containing the resin is not particularly limited and is, for example, 50 ppm or more, preferably 100 ppm or more.

[0038] The resin layer described below may be provided on a layer of the polyester film that contains particles, or on a layer that does not substantially contain particles. Furthermore, the surface of the polyester film opposite to the surface on which the resin layer is provided (the opposite surface) may be a layer that does not substantially contain particles, or may be a layer that contains particles. In the present invention, even if both the surface on which the resin layer is provided and the opposite surface are layers that do not substantially contain particles, the winding properties can be improved by the resin layer having the uneven structure described below. Furthermore, by providing one or both of the surface on which the resin layer is provided and the opposite surface with a layer that contains particles, the winding properties are further improved. When excellent smoothness is to be imparted to at least one surface of the present polyester film, the surface layer on the smooth side may contain particles or may be substantially free of particles. However, when an extremely smooth film is to be obtained, it is preferable that the surface layer be substantially free of particles. Note that "substantially not containing" means not containing intentionally, and specifically refers to the particle content (particle concentration) being less than 50 ppm by mass, more preferably 40 ppm or less, and even more preferably 30 ppm or less. In this case, by laminating the present resin layer on the surface layer on the smooth surface side and / or on the surface layer on the side opposite the smooth surface, the handleability of the film when wound into a roll can be improved. In particular, from the viewpoint of improving the handleability while maintaining the smoothness of the film, it is preferable to make at least one surface smooth and to laminate the present resin layer on the opposite surface.

[0039] The method for adding particles to the polyester film is not particularly limited, and any conventionally known method can be used. For example, in the case of a multi-layer polyester film, particles can be added at any stage in the production of the polyester constituting each layer, but it is preferable to add particles after the completion of the esterification or transesterification reaction.

[0040] <Other> In order to suppress the amount of precipitation of oligomer components, the film may be produced using a polyester having a low content of oligomer components as the raw material. As a method for producing a polyester having a low content of oligomer components, various known methods can be used, such as a method in which solid-state polymerization is carried out after the polyester is produced. The amount of oligomer component precipitation may be suppressed by forming the polyester film into a three-layer or more layer structure and using a polyester raw material with a low content of oligomer components as the surface layer of the polyester film. The polyester may also be obtained by carrying out the esterification or transesterification reaction, followed by melt polycondensation at a higher reaction temperature under reduced pressure.

[0041] In addition to the above-mentioned particles, conventionally known additives such as ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film as needed.

[0042] The thickness of the polyester film is not particularly limited as long as it is within the range that allows it to be formed into a film. From the viewpoints of mechanical strength, handleability, productivity, etc., the thickness is preferably 1 μm or more, more preferably 10 μm or more, even more preferably 19 μm or more, particularly preferably 25 μm or more, and is preferably 200 μm or less, more preferably 125 μm or less, even more preferably 80 μm or less, particularly preferably 50 μm or less.

[0043] <Polyester film manufacturing method> Next, specific examples of the production of the polyester film will be described, but the production method is not limited to the following examples. For example, when producing a biaxially stretched film, a preferred method is to extrude dried pellets of the polyester raw material described above as a molten sheet from a die using a melt extrusion device such as an extruder, and then cool and solidify the molten sheet on a cooling roll such as a rotating cooling drum to obtain an unstretched sheet. In this case, it is preferable to increase the adhesion between the sheet and the cooling roll to improve the flatness of the sheet, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably used.

[0044] The unstretched sheet is then stretched biaxially. In this case, the unstretched sheet is first stretched in one direction using a roll or tenter type stretching machine. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7.0 times, preferably 3.0 to 6.0 times. Next, the film is stretched in a direction perpendicular to the first-stage stretching direction, in which case the stretching temperature is usually 70 to 170° C., and the stretching ratio is usually 3.0 to 7.0 times, preferably 3.5 to 6.0 times. Subsequently, the film is heat-treated under tension or relaxation of 30% or less at a temperature of 180 to 270°C to obtain a biaxially stretched film. This heat treatment is also called a heat setting step. The heat treatment may be performed in two or more steps at different temperatures. After the heat treatment, the film may be cooled in a cooling zone. The cooling temperature is preferably higher than the glass transition temperature (Tg) of the polyester constituting the film, and more specifically, preferably in the range of 100 to 160° C. This cooling may be performed in two or more steps at different temperatures. In the above stretching, a method of stretching in one direction in two or more stages can be adopted, in which case it is preferable to perform the stretching so that the final stretching ratios in both directions are each within the above ranges.

[0045] The polyester film can also be produced by simultaneous biaxial stretching, which involves simultaneously stretching and orienting the unstretched sheet in the machine direction (longitudinal direction) and width direction (transverse direction) under temperature control, typically at 70 to 120°C, and preferably at 80 to 110°C, with the area stretch ratio being preferably 4 to 50 times, more preferably 7 to 35 times, and even more preferably 10 to 25 times. Subsequently, the film is subjected to a heat treatment under tension or relaxation of 30% or less at a temperature of typically 170 to 250°C to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching device employing the above-mentioned stretching method, any conventionally known stretching method such as a screw method, a pantograph method, or a linear drive method can be employed.

[0046] <<Resin layer>> The present laminated polyester film comprises a polyester film and a resin layer formed from a resin composition on at least one side of the polyester film. The resin layer may be a cured resin layer. As described above, the present resin layer is formed from a resin composition (hereinafter also referred to as "the present composition") and has an uneven structure.

[0047] <Uneven structure> The uneven structure of the present resin layer is a fine shape, and examples of the shape of the uneven structure include an uneven shape and / or a mesh shape. The uneven surface structure is formed by fine protrusions formed by particles described later. The network structure is formed by coating film cracks that occur when the composition is intentionally made to have poor stretchability to form a film with poor stretchability. The network structure and the uneven surface structure may be mixed on the resin layer surface. The structure can be confirmed by various surface analysis techniques, such as an atomic force microscope (scanning probe microscope).

[0048] <Resin composition> The composition contains the following compounds (A) and (B): (A) one or more members selected from the group consisting of binder resins and crosslinking agents (B) Particles In addition, the content of the (B) particles in the present composition is 20% by mass or more as a proportion of the total nonvolatile components in the present composition.

[0049] The composition has the above-described composition, which reduces its suitability for stretching and makes it more likely to form a fine uneven structure due to coating film cracking, as described below. The total content of compounds (A) and (B) contained in the composition is preferably 80% by mass or more as non-volatile components. More preferably, it is 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass. If the total content is within this range, it becomes easier to obtain the desired fine uneven structure. The upper limit of the total content is not particularly limited, and it is sufficient if it is 100% by mass or less.

[0050] (((Compound (A)))) The present composition contains (A) one or more members selected from a binder resin and a crosslinking agent.

[0051] ((binder resin)) The binder resin selected as (A) is defined as a polymer compound having a number average molecular weight (Mn) of 1,000 or more as measured by gel permeation chromatography (GPC) and having film-forming properties, in accordance with the "Flow Scheme for Safety Evaluation of Polymeric Compounds" (November 1985, sponsored by the Chemical Substances Council). The binder resin (A) is not particularly limited, and conventionally known binder resins such as polyester resins, (meth)acrylic resins, polyurethane resins, polyvinyl resins (such as polyvinyl alcohol and vinyl chloride vinyl acetate copolymers), polyalkylene glycols, polyalkyleneimines, methyl cellulose, hydroxycellulose, and starches can be used. Among these, polyester resins, (meth)acrylic resins, and polyurethane resins are preferred from the viewpoints of film-forming properties and adhesion to polyester films. In the present composition, one type of binder resin (A) may be used alone, or two or more types may be used in combination.

[0052] By including the binder resin (A) in the present composition, it becomes possible to form a film (resin layer) that holds and fixes the particles (B).

[0053] (polyester resin) The polyester resin may be composed of, for example, the following polycarboxylic acids and polyhydroxy compounds as main components. That is, examples of polycarboxylic acids that can be used include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt, and ester-forming derivatives thereof. Examples of polyhydric hydroxy compounds that can be used include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, and potassium dimethylolpropionate. One or more of these compounds can be appropriately selected and used to synthesize a polyester resin by a conventional polycondensation reaction.

[0054] As part of the polycarboxylic acid, a product obtained by copolymerizing sulfoisophthalic acids such as 5-sodium sulfoisophthalic acid, introducing sulfonic acid groups into the polyester skeleton, and neutralizing the copolymer to make it hydrophilic is preferably used. The amount copolymerized is usually 1 to 13 mol %, preferably 3 to 10 mol %, and more preferably 5 to 9 mol % of the total polycarboxylic acid. Introducing an appropriate amount of sulfonic acid groups can increase the hydrophilicity of the resin and facilitate the formation of an uneven structure. Furthermore, aqueous dispersion stability can be improved.

[0055] ((Meth)acrylic resin) The (meth)acrylic resin is a polymer made of polymerizable monomers including acrylic and methacrylic monomers. These may be homopolymers or copolymers, or copolymers with polymerizable monomers other than acrylic and methacrylic monomers. The (meth)acrylic polymer is a polymer having structural units derived from (meth)acrylic acid or (meth)acrylic acid alkyl esters. The (meth)acrylic polymer may be a polymer of at least one selected from (meth)acrylic acid and (meth)acrylic acid alkyl esters, or may be a copolymer of at least one selected from these and at least one other monomer, such as styrene or a styrene derivative, or a monomer containing a hydroxyl group. Also included are copolymers of these polymers with other polymers (e.g., polyester, polyurethane, etc.), such as block copolymers and graft copolymers. That is, the (meth)acrylic resin may be a (meth)acrylic-modified polyester resin or a (meth)acrylic-modified polyurethane resin. Alternatively, it also includes a polymer (or a mixture of polymers, as the case may be) obtained by polymerizing a polymerizable monomer in a polyester solution or polyester dispersion. Similarly, it also includes a polymer (or a mixture of polymers, as the case may be) obtained by polymerizing a polymerizable monomer in a polyurethane solution or polyurethane dispersion. Similarly, it also includes a polymer (or a mixture of polymers, as the case may be) obtained by polymerizing a polymerizable monomer in another polymer solution or dispersion, and these are also referred to herein as (meth)acrylic-modified polyester resins and (meth)acrylic-modified polyurethane resins. The above-mentioned polyesters and polyurethanes used in the (meth)acrylic resins can be appropriately selected from the polyesters and polyurethanes exemplified for use in the binder resins described below. The (meth)acrylic resin may also contain a hydroxy group or an amino group in order to further improve adhesion to the polyester film.

[0056] The polymerizable monomer is not particularly limited, but particularly representative compounds include various carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid, and salts thereof; various hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutylhydroxyfumarate, and monobutylhydroxyitaconate; and various hydroxyl group-containing monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and lauryl (meth)acrylate. Examples of suitable alkyl (meth)acrylates include various nitrogen-containing monomers such as (meth)acrylamide, diacetone acrylamide, and (meth)acrylonitrile; nitrogen-containing monomers containing a hydroxyl group such as N-methylol (meth)acrylamide; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, and vinyltoluene; various vinyl esters such as vinyl propionate; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and vinylidene chloride; and various conjugated dienes such as butadiene.

[0057] Among the above (meth)acrylic resins, polymers obtained by polymerizing polymerizable monomers including acrylic and methacrylic monomers are preferred, and it is more preferred that the polymerizable monomers include alkyl(meth)acrylic acid esters. Furthermore, the present composition containing a (meth)acrylic resin is preferably diluted with a solvent to form a coating solution, as described below, and the solvent preferably contains water as the main solvent (50% by mass or more). That is, from the viewpoint of facilitating dissolution or dispersion in an aqueous coating solution, the polymerizable monomer preferably has a hydrophilic group such as a hydroxyl group or a carboxyl group. Furthermore, from the viewpoint of effectively obtaining a concave-convex structure, the polymerizable monomer preferably has a hydrophilic group such as a hydroxyl group or a carboxyl group. Therefore, the acrylic resin is also preferably a polymer obtained by polymerizing alkyl (meth)acrylates and polymerizable monomers including a hydroxyl group-containing monomer and a hydrophilic group-containing monomer such as a carboxyl group-containing monomer. The acrylic resin may also be an emulsion polymer obtained by polymerizing a polymerizable monomer in the presence of a surfactant.

[0058] (Polyurethane resin) The polyurethane resin is a polymer compound having a urethane bond in the molecule, and is preferably water-dispersible or water-soluble. In the present invention, a single type of polyurethane resin may be used, or two or more types of polyurethane resins may be used in combination.

[0059] To impart water dispersibility or water solubility, it is common and preferable to introduce hydrophilic groups such as hydroxyl groups, carboxyl groups, sulfonic acid groups, sulfonyl groups, phosphate groups, and ether groups into polyurethane resins. Among these hydrophilic groups, carboxyl groups and sulfonic acid groups are particularly preferred in terms of adhesion between the resin layer and the polyester film. For example, the introduction of carboxyl groups can be carried out using carboxyl group-containing polyhydric alcohols such as dimethylolpropionic acid and dimethylolbutanoic acid.

[0060] One method for producing polyurethane resins involves the reaction of a hydroxyl group-containing compound with an isocyanate. Polyols are preferably used as raw materials for the hydroxyl group-containing compound, including polyester polyols, polyether polyols, polycarbonate polyols, polyolefin polyols, and acrylic polyols. Among these, polyester polyols are preferred because of their excellent adhesion to polyester films. These compounds may be used alone or in combination.

[0061] Polyester polyols include those obtained by reacting polycarboxylic acids or their acid anhydrides with polyhydric alcohols. Examples of polycarboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, and isophthalic acid. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-methyl-2-propyl-1,3-propanediol, and 1,6-hexanediol. ,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyldialkanolamines, lactonediols, and the like.

[0062] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, and polyhexamethylene ether glycol.

[0063] Examples of polycarbonate polyols include polycarbonate diols obtained by dealcoholization reaction of polyhydric alcohols with dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, etc., such as poly(1,6-hexylene) carbonate and poly(3-methyl-1,5-pentylene) carbonate. Among the above, polyester polyols are preferred.

[0064] Examples of polyisocyanate compounds used to obtain polyurethane resins include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate; aliphatic diisocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and isopropylidenedicyclohexyl diisocyanate. These may be used alone or in combination.

[0065] A chain extender may be used when synthesizing the polyurethane resin. The chain extender is not particularly limited as long as it has two or more active groups that react with isocyanate groups, and generally, a chain extender having two hydroxyl groups or two amino groups can be mainly used.

[0066] Examples of chain extenders having two hydroxyl groups include glycols such as aliphatic glycols such as ethylene glycol, propylene glycol, and butanediol; aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene; and ester glycols such as neopentyl glycol hydroxypivalate.

[0067] Examples of chain extenders having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine; aliphatic diamines such as ethylenediamine, propanediamine, hexanediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine; and alicyclic diamines such as 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, 1,4-diaminocyclohexane, and 1,3-bisaminomethylcyclohexane.

[0068] (Polyvinyl alcohol) Polyvinyl alcohol is a compound having a polyvinyl alcohol moiety. For example, conventionally known polyvinyl alcohols can be used, including modified compounds in which polyvinyl alcohol is partially acetalized or butyralized. The degree of polymerization of polyvinyl alcohol is not particularly limited, but is usually 100 or higher, preferably in the range of 300 to 40,000. A degree of polymerization of 100 or higher facilitates improving the water resistance of the resin layer. Furthermore, the saponification degree of polyvinyl alcohol is not particularly limited, but saponified polyvinyl acetates having a degree of saponification of usually 70 mol % or higher, preferably in the range of 70 to 99.9 mol %, more preferably 80 to 97 mol %, and particularly preferably 86 to 95 mol % are practically used.

[0069] ((Crosslinking agent)) The crosslinking agent selected as the compound (A) is not particularly limited, and conventionally known crosslinking agents can be used. Examples include melamine compounds, oxazoline compounds, epoxy compounds, carbodiimide compounds, isocyanate compounds, and silane coupling compounds. Among these, it is preferable to include a melamine compound from the viewpoint of increasing the strength of the coating film and improving adhesion to the polyester film. Furthermore, the resin layer can be easily cured by using a crosslinking agent.

[0070] (melamine compounds) The melamine compound is a compound having a melamine skeleton within the compound, and examples thereof include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohol to partially or completely etherify them, and mixtures thereof. Examples of alkylolation include methylolation, ethylolation, isopropylolation, n-butylolation, isobutyrolation, etc. Among these, methylolation is preferred from the viewpoint of reactivity. As the alcohol used for etherification, methanol, ethanol, isopropanol, n-butanol, isobutanol, etc. are preferably used, and among these, methanol is more preferred. The melamine compound may be a monomer or a dimer or higher polymer, or a mixture thereof. Furthermore, melamine may be partially co-condensed with urea or the like, and a catalyst may be further added to the composition to increase the reactivity of the melamine compound.

[0071] (Oxazoline compounds) An oxazoline compound is a compound having an oxazoline group in the molecule. A polymer containing an oxazoline group is particularly preferred. The compound can be prepared by polymerizing an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of the addition-polymerizable oxazoline group-containing monomer 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 monomers can be used alone or in combination. Among these, 2-isopropenyl-2-oxazoline is preferred because it is readily available industrially. The other monomer is not limited as long as it is copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include (meth)acrylic acid esters such as alkyl(meth)acrylate (the alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl(meth)acrylate, N-methyl-N ... Examples of suitable monomers include unsaturated amides such as t)acrylamide and N,N-dialkyl(meth)acrylamide (the alkyl group can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, a cyclohexyl group, and the like); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and one or more of these monomers can be used. The oxazoline compound may have a polyalkylene oxide chain such as a polyethylene oxide chain, and for example, a (meth)acrylate having a polyalkylene oxide chain may be used as another monomer.

[0072] (epoxy compounds) Epoxy compounds are compounds having an epoxy group in the molecule, and examples thereof include condensation products of epichlorohydrin, ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc. with a hydroxyl group or an amino group, polyepoxy compounds, diepoxy compounds, monoepoxy compounds, and glycidylamine compounds. Examples of polyepoxy compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl)isocyanate, glycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Examples of diepoxy compounds include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether. Examples of monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, and examples of glycidylamine compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylamino)cyclohexane, etc. From the viewpoint of improving the adhesion of the resin layer to the polyester film, polyether-based epoxy compounds are preferred. In terms of the amount of epoxy groups, a polyepoxy compound having three or more functional groups is preferred over a difunctional compound.

[0073] (Carbodiimide compounds) A carbodiimide compound is a compound having a carbodiimide structure, and is a compound having one or more carbodiimide structures in the molecule. However, for better adhesion between the resin layer and the polyester film, a polycarbodiimide compound having two or more carbodiimide structures in the molecule is more preferred.

[0074] Carbodiimide compounds can be synthesized by conventionally known techniques, and generally involve the condensation reaction of a diisocyanate compound. The diisocyanate compound is not particularly limited, and both aromatic and aliphatic diisocyanates can be used. Specific examples include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate. Furthermore, within the scope 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 hydroxyalkyl sulfonate may be added.

[0075] (Isocyanate compounds) The isocyanate compound refers to a compound having an isocyanate or an isocyanate derivative structure, such as a blocked isocyanate. Examples of the isocyanate include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanates having an aromatic ring, such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexyl isocyanate), and isopropylidenedicyclohexyl diisocyanate. Further examples include polymers and derivatives of these isocyanates, such as biuretized products, isocyanurated products, urethodionated products, and carbodiimide-modified products. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferred than aromatic isocyanates in order to prevent yellowing due to ultraviolet rays.

[0076] When used in the form of a blocked isocyanate, examples of the blocking agent include bisulfites; phenolic compounds such as phenol, cresol, and ethylphenol; alcohol compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol; active methylene compounds such as methyl isobutanoylacetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone; mercaptan compounds such as butyl mercaptan and dodecyl mercaptan; lactam compounds such as ε-caprolactam and δ-valerolactam; amine compounds such as diphenylaniline, aniline, and ethyleneimine; acid amide compounds such as acetanilide and acetic acid amide; and oxime compounds such as formaldehyde oxime, acetaldoxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime, and these may be used alone or in combination of two or more.

[0077] (Silane coupling compounds) A silane coupling compound is an organosilicon compound that contains an organic functional group and a hydrolyzable group such as an alkoxy group in one molecule. For example, epoxy group-containing compounds such as 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; vinyl group-containing compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing compounds such as p-styryltrimethoxysilane and p-styryltriethoxysilane; (meth)acrylic group-containing compounds such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and N-2-(aminoethyl)-3 amino group-containing compounds such as N-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane; isocyanurate group-containing compounds such as tris(trimethoxysilylpropyl)isocyanurate and tris(triethoxysilylpropyl)isocyanurate; and mercapto group-containing compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane.

[0078] The content of compound (A) in the composition is preferably 10 to 80% by mass, more preferably 25 to 70% by mass, and even more preferably 40 to 60% by mass, as a proportion of all nonvolatile components in the composition. By setting the content to 10% by mass or more, it is possible to obtain a film that has film-forming properties and contains particles. Furthermore, by providing adhesion to polyester films, it is possible to prevent the coating film from peeling off. Furthermore, by setting the content to 80% by mass or less, a high particle content is achieved, which increases the coating film hardness and enables the formation of unevenness in the coating film.

[0079] Compound (A) contains one or more selected from a binder resin and a crosslinking agent, and preferably contains a binder resin from the viewpoint of obtaining better film-forming properties, and more preferably contains a binder resin and a crosslinking agent from the viewpoint of further improving coating film strength and adhesion to polyester film.

[0080] ((Compound (B))) The present composition contains (B) particles. By including (B) particles in the present composition, the stretchability of the coating film is reduced, making it easier to form a concave-convex structure. Furthermore, the hardness of the formed concave-convex structure is increased, making it possible to effectively improve air release properties.

[0081] Examples of the (B) particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, zirconium oxide, aluminum oxide, and titanium oxide, as well as crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles, and organic particles such as calcium oxalate and ion exchange resins. Among these, zirconium oxide, titanium oxide, and silica are preferred. The (B) particles may be used alone or in combination of two or more types.

[0082] The shape of the (B) particles used may be spherical, blocky, rod-like, flat, chain-like, etc. Among these, spherical is preferred from the viewpoint of facilitating uniform distribution in the compound (A).

[0083] The average particle size of the (B) particles is preferably 1 to 100 nm, more preferably 4 to 60 nm, and even more preferably 8 to 40 nm. When the average particle size is within this range, the generation of coarse protrusions due to particle aggregation and contamination of the process due to particle dropout can be suppressed, and the desired fine uneven structure can be easily obtained. The average particle size of microparticles can be measured by a method that calculates it from the specific surface area measured by a specific surface area measuring device and the particle density, a method that calculates the particle diameter by observing it with a transmission electron microscope (TEM) or a scanning electron microscope (SEM), or a method that determines it from measurements using dynamic light scattering.The average particle size of microparticles can be measured by a method that is more suitable for the method.

[0084] The content of compound (B) in the composition is 20% by mass or more, as a proportion of all nonvolatile components in the composition. This content is preferably 90% by mass or less, more preferably 30 to 75% by mass, and even more preferably 40 to 60% by mass. By setting this content to 20% by mass or more, it becomes easier to form a concave-convex structure, and the hardness of the formed concave-convex structure increases, thereby effectively improving air release properties. Furthermore, by setting this content to 90% by mass or less, it becomes possible to include the necessary amounts of other components, thereby forming a concave-convex film and achieving adhesion to the polyester film. Furthermore, by setting the content of compound (B) to a certain value or less, it becomes easier to prevent the coating film from peeling off.

[0085] ((Other ingredients)) In addition to the above components, additives such as crosslinking catalysts, antifoaming agents, coatability improvers, surfactants, thickeners, organic lubricants, ultraviolet absorbers, antioxidants, foaming agents, dyes, and pigments may be further blended as appropriate within the scope of the present invention.

[0086] ((solvent)) The present composition may be diluted with a solvent to form a coating solution, that is, the present composition may be applied as a liquid coating solution to, for example, the present polyester film, and then dried and cured as necessary to form a resin layer. The components constituting the present composition (compounds (A) and (B), other components, etc.) may be dissolved in a solvent or dispersed in a solvent. When the composition is used as a coating solution, the concentration of all nonvolatile components in the coating solution is preferably 0.1 to 50% by mass. If the concentration is 0.1% by mass or more, a resin layer of the desired thickness can be efficiently formed. On the other hand, if the concentration is 50% by mass or less, the viscosity during coating can be reduced, thereby improving the appearance of the resin layer and increasing the stability in the coating solution.

[0087] The solvent is not particularly limited, and either water or an organic solvent can be used. From the viewpoint of environmental protection, it is preferable to prepare an aqueous coating liquid using water as the main solvent (50% by mass or more of the total solvent). The water content is preferably 60% by mass or more, more preferably 70% by mass or more. The aqueous coating liquid may contain a small amount of organic solvent. The specific amount of organic solvent should be equal to or less than the amount of water on a mass basis, for example, 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less of the solvent. Examples of organic solvents used in combination with water include alcohols such as ethanol, isopropanol, ethylene glycol, and glycerin; ethers such as ethyl cellosolve, t-butyl cellosolve, propylene glycol monomethyl ether, and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; and amines such as dimethylethanolamine. These can be used alone or in combination. By appropriately selecting and adding these organic solvents to the aqueous coating solution as needed, the stability and coatability of the coating solution can sometimes be improved.

[0088] Furthermore, when only an organic solvent is used as the solvent, examples of such organic solvents include aromatic hydrocarbons such as toluene, aliphatic hydrocarbons such as hexane, heptane, isooctane, esters such as ethyl acetate, butyl acetate, ketones such as ethyl methyl ketone, isobutyl methyl ketone, alcohols such as ethanol, 2-propanol, ethers such as diisopropyl ether, dibutyl ether, etc. These may be used alone or in combination, taking into consideration solubility, coatability, boiling point, etc.

[0089] It is assumed that the resin layer contains unreacted components of the composition (compounds (A) and (B), other components, etc.), reacted compounds, or a mixture thereof. The components in the resin layer can be analyzed by, for example, TOF-SIMS, ESCA, fluorescent X-rays, or the like.

[0090] <Method for forming resin layer> Next, a method for forming the resin layer constituting the present laminated polyester film will be described. The resin layer may be formed by applying the composition to a polyester film and, if necessary, subjecting the applied composition to treatments such as drying, curing, heat treatment, etc., preferably at least heat treatment. The method for applying the resin composition is not particularly limited, and any conventionally known coating method can be used, such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, etc.

[0091] The resin layer can be formed by in-line coating or off-line coating. The method for heat-treating the applied resin composition is not particularly limited, and when the resin layer is formed by off-line coating, the heat treatment is typically carried out at 80 to 200°C for 3 to 40 seconds, preferably at 100 to 180°C for 3 to 40 seconds. When the resin layer is formed by in-line coating, the heat treatment is typically carried out at 70 to 280°C for 3 to 200 seconds. The heat treatment may be carried out in two or more steps at different temperatures within the above temperature range. At least a part of the heat treatment may be carried out by heating during stretching. Drying and curing may be carried out together by heating in the heat treatment.

[0092] In the present invention, the resin layer is preferably formed by in-line coating, which treats the surface of a polyester film during the film-forming process. In-line coating is a method of coating within the polyester film production process, specifically, at any stage from melt extrusion of polyester to stretching, heat setting, and winding up. Typically, coating is performed on any of the following: an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, or a film after heat setting and before winding up.

[0093] Although not limited to the following, for example, in sequential biaxial stretching, a method in which a uniaxially stretched film stretched in the longitudinal direction (machine direction) is coated and then stretched in the transverse direction is particularly advantageous. This method has advantages in terms of production costs because film production and resin layer formation can be carried out simultaneously. In addition, because stretching is carried out after coating, the thickness of the resin layer can be changed by adjusting the stretch ratio, and thin film coating can be carried out more easily than with offline coating films.

[0094] Furthermore, by providing a resin layer on the film before stretching, the resin layer can be stretched together with the polyester film, thereby allowing the resin layer to be firmly adhered to the polyester film.

[0095] Furthermore, in the production of biaxially stretched polyester film, the film can be stretched while holding the edges with clips or the like, thereby restraining the film in both the longitudinal and transverse directions, and in the subsequent heat treatment (heat setting process), high temperatures can be applied while maintaining flatness and preventing wrinkles. Therefore, the heat treatment after coating can be performed at a high temperature that cannot be achieved by other methods, improving the film-forming properties of the resin layer and enabling stronger adhesion between the resin layer and the polyester film.Furthermore, a strong resin layer can be formed, and the performance such as migration resistance and moist heat resistance of various functional layers that can be formed on the resin layer can be improved.

[0096] In particular, in the present invention, this method is optimal as a manufacturing method for forming coating cracks. The contents of compounds (A) and (B) in the composition are adjusted to intentionally reduce the stretchability of the composition. Then, by employing a manufacturing method in which the composition is coated and then stretched, a textured structure can be formed on the surface of the resin layer due to coating cracks caused by stretching a film with poor stretchability. Those skilled in the art have traditionally considered coating cracks to be a form of coating defect, and have emphasized the need for uniform coating film formation that minimizes the occurrence of coating cracks. One cause of coating cracks is insufficient stretchability of the resin composition, so the resin composition is designed to have sufficient stretchability. However, the present inventors have come up with the idea of ​​utilizing such coating cracks as one means for forming a fine textured structure on the surface of a resin layer.

[0097] Regardless of whether off-line coating or in-line coating is used, heat treatment and irradiation with active energy rays such as ultraviolet light may be used in combination as needed. The polyester film constituting the present laminated polyester film may be previously subjected to a surface treatment such as a corona treatment or a plasma treatment.

[0098] The coating amount of the nonvolatile component of the resin layer is preferably 0.005 to 0.95 g / m 2 , more preferably 0.02 to 0.5 g / m 2 , and more preferably 0.04 to 0.3 g / m 2 , and particularly preferably 0.06 to 0.2 g / m 2 If the coating amount is within this range, a fine uneven structure can be formed by coating film cracking or the like. The coating amount can be calculated from the concentration of nonvolatile components in the coating solution, the coating amount before drying derived from the consumption amount of the coating solution, the transverse stretching ratio, etc. The coating amount of the nonvolatile components refers to the coating amount in the present laminated polyester film, and, for example, in the case where drying and stretching are performed, refers to the coating amount after drying and stretching.

[0099] <<<Physical properties of laminated polyester film>>> The kurtosis (Sku) of the resin layer surface of the present laminated polyester film is less than 3.0. Kurtosis (Sku) is a parameter related to the tip shape of the irregularities, with Sku=3 being a normal distribution, and if Sku>3, the height distribution is sharp, i.e., the surface has many sharp irregularities, while if Sku<3, the height distribution of the surface irregularities is flat, i.e., the surface is relatively flat. Therefore, if the kurtosis (Sku) is less than 3.0, the projections have a flat surface, so that the tops of the projections are less likely to be crushed when the films are stacked, and air escape properties can be efficiently maintained. From this perspective, the kurtosis is preferably 2.9 or less, more preferably 2.8 or less, even more preferably 2.6 or less, particularly preferably 2.4 or less, and especially preferably 2.2 or less. The lower limit is not particularly limited, and is 0.1.

[0100] Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) that can be used to evaluate the peakedness (kurtosis) of the height distribution histogram, and can be calculated using the following formula (1). When the surface is the XY plane and the height direction is the Z axis, A is the defined area (the entire image), Z(x,y) is the height of the image point (x,y) from the surface at height 0, and Sq is the root mean square height (equivalent to the standard deviation of the height distribution), it can be expressed as follows.

[0101]

number

[0102] The arithmetic mean roughness (Ra) of the resin layer surface of the present laminated polyester film is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 50 nm or more, and particularly preferably 80 nm or more. While there is no particular upper limit, it is preferably 600 nm, more preferably 400 nm, and even more preferably 200 nm. When the arithmetic mean roughness (Ra) is 10 nm or more, the present resin layer can be said to have a fine uneven structure, and the present laminated polyester film can be easily handled. Furthermore, when the arithmetic mean roughness (Ra) is 600 nm or less, the present resin layer can be said to have a sufficiently fine uneven structure.

[0103] The arithmetic mean roughness (Ra) is one of the line roughness parameters (JIS B 0601) and represents the average value of the average height difference from the average surface. That is, when a portion of the reference length L is sampled and the roughness curve is expressed as y = Z(x) with the average line of this sampled portion as the x-axis and the direction of the vertical magnification as the y-axis, the following formula (2) can be used to determine the roughness.

[0104]

number

[0105] The ten-point average roughness (Rzjis) of the resin layer surface is preferably 60 nm or more, more preferably 150 nm or more, and even more preferably 250 nm or more. While there is no particular upper limit, it is preferably 800 nm, more preferably 600 nm, and even more preferably 450 nm. If the ten-point average roughness (Rzjis) is 60 nm or more, it can be said that the resin layer has a sufficient uneven structure. If the ten-point average roughness (Rzjis) is 800 nm or less, it can be said that the uneven structure of the resin layer has a sufficiently fine shape.

[0106] Ten-point average roughness (Rzjis) is one of the line roughness parameters (JIS B 0601), and represents the sum of the average of the five largest peaks (Zp) and the five largest valleys (Zv) on the profile curve over a reference length L, and is calculated using the following formula (3):

[0107]

number

[0108] The load length ratio (Rmr(70)) of the roughness curve at a cutting level of 70% on the surface of the resin layer is preferably 82% or less, more preferably 65% ​​or less, and even more preferably 60% or less. The lower limit is not particularly limited, but is about 1%, preferably 10% or more, and more preferably 15% or more.

[0109] Here, the inventors considered that the load length ratio (Rmr(70)) is an effective index for expressing the unevenness distribution of the uneven structure. For example, a large concave distribution will result in a small load length ratio (Rmr(70)), and a large convex distribution will result in a large load length ratio (Rmr(70)). If the load length ratio (Rmr(70)) is 82% or less, an appropriate fine uneven structure is formed, which increases the gaps between the film when it is wound into a roll, making it easier for air to escape and improving winding characteristics.

[0110] The load length ratio (Rmr(c)) is one of the line roughness parameters (JIS B 0601) and represents the ratio of the load length ML(c) of the profile curve element at the cutting level c (height % or μm) to the evaluation length Ln, and is calculated using the following formula (4):

[0111]

number

[0112] The root-mean-square gradient (Sdq) of the resin layer surface of the present laminated polyester film is preferably 0.1 or more, more preferably 0.25 or more, and even more preferably 0.45 or more. Meanwhile, the root-mean-square gradient (Sdq) is preferably 3 or less, more preferably 1.0 or less. When the root-mean-square gradient (Sdq) is 0.1 or more, the difference between the peaks and valleys of the uneven structure is clear, thereby improving air release properties. Furthermore, when the root-mean-square gradient (Sdq) is 3 or less, coarse protrusions can be suppressed.

[0113] The root mean square gradient (Sdq) is one of the surface roughness parameters (ISO 25178) and is calculated using the following formula (5). The root mean square gradient (Sdq) represents the average magnitude of the local gradient (slope) of the surface irregularities, with a larger value indicating a steeper surface.

[0114]

number

[0115] Furthermore, the developed interface area ratio (Sdr) of the resin layer surface is preferably 0.5% or more, more preferably 3% or more, and even more preferably 9% or more. On the other hand, the developed interface area ratio (Sdr) is preferably 60% or less, more preferably 50% or less. If the developed interface area ratio (Sdr) is 0.5% or more, a fine uneven structure can be formed, thereby improving winding properties. Furthermore, if the developed interface area ratio (Sdr) is 60% or less, undulations are appropriately suppressed, and coarse protrusions can be prevented.

[0116] The developed interface area ratio (Sdr) is one of the surface roughness parameters (ISO 25178) and is calculated by the following formula (6). The developed interface area ratio (Sdr) represents the degree to which the developed area (surface area) of a defined region has increased relative to the area of ​​the defined region, i.e., the rate of increase in surface area; the denser and more uneven the surface shape, the larger the value.

[0117]

number

[0118] The above-mentioned kurtosis (Sku), arithmetic mean roughness (Ra), ten-point mean roughness (Rzjis), load length ratio (Rmr(70)), root mean square gradient (Sdq) and developed interface area ratio (Sdr) can be adjusted by the composition and content of the composition, the method for forming the resin layer, and various conditions in the forming process.

[0119] The kurtosis (Sku), arithmetic mean roughness (Ra), ten-point mean roughness (Rzjis), load length ratio (Rmr(70)), root mean square gradient (Sdq), and developed interface area ratio (Sdr) of the resin layer surface are measured using an atomic force microscope (scanning probe microscope) by the method described in the Examples. Measurement using an atomic force microscope (scanning probe microscope) makes it possible to capture finer surface structures and obtain values ​​that strongly reflect the effects of the resin layer.

[0120] The surface arithmetic mean roughness (Sa) of the resin layer surface of the present laminated polyester film is preferably in the range of 1 to 70 nm, more preferably 2 to 50 nm, and even more preferably 3 to 30 nm. When the arithmetic mean roughness (Sa) is within this range, it is possible to reduce extremely large irregularities while maintaining a fine irregular shape. Therefore, for example, the handleability of the present laminated polyester film can be ensured, and wrinkles during winding into a roll can be suppressed. Furthermore, when the present laminated polyester film is used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor, and a release layer or ceramic layer is provided on the film surface opposite to the surface on which the present resin layer is provided, it is possible to prevent protrusions on the surface of the present resin layer from transferring to the ceramic layer or destroying the ceramic layer.

[0121] Average surface roughness (Sa) is one of the surface roughness parameters (ISO 25178), and is a three-dimensional extension of the two-dimensional Ra (arithmetic mean roughness of lines). It is calculated by dividing the volume enclosed by the surface shape curve and the average surface by the measured area, and is calculated using the following equation (7). When the surface is the XY plane and the height direction is the Z axis, A is the defined area (the entire image), and Z(x,y) is the height of the image point (x,y) from the plane with height 0, it can be expressed as follows.

[0122]

number

[0123] Furthermore, the maximum peak height (Sp) of the resin layer surface is preferably 800 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less. Meanwhile, the maximum peak height (Sp) is preferably 10 nm or more, more preferably 20 nm or more. A maximum peak height (Sp) of 800 nm or less can reduce protrusions. Therefore, for example, when the present laminated polyester film is used as a support for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor, and a release layer or ceramic layer is provided on the film surface opposite to the surface on which the present resin layer is provided, protrusions on the surface of the present resin layer can be prevented from transferring to the ceramic layer or damaging the ceramic layer. Furthermore, a maximum peak height (Sp) of 10 nm or more can ensure the handleability of the present laminated polyester film and suppress wrinkling when wound into a roll.

[0124] The maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178), and represents the maximum value of the height from the mean plane of the surface, and is expressed by the following formula (8).

[0125]

number

[0126] On the other hand, the surface arithmetic mean roughness (Sa) of the surface opposite to the resin layer surface of the present laminated polyester film is preferably 15 nm or less, more preferably 9 nm or less, and even more preferably 5 nm or less, and from the viewpoint of film handling, the arithmetic mean roughness (Sa) is preferably 0.3 nm or more.

[0127] The maximum peak height (Sp) on the surface opposite to the resin layer surface is preferably 800 nm or less, more preferably 500 nm or less, and even more preferably 100 nm or less. On the other hand, the lower limit of the maximum peak height (Sp) is not particularly limited, but from the viewpoint of film handleability, it is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more.

[0128] When the present laminated polyester film is used as a release film for forming green sheets for multilayer ceramic capacitors, as a substrate for interlayer insulating resin release, or as a substrate for dry film resist, the film's smoothness is utilized for processing. In this case, it is preferable that at least one side of the present laminated polyester film is smooth. If the arithmetic mean roughness (Sa) and maximum peak height (Sp) of the side opposite the side on which the resin layer is formed are within the above-mentioned ranges, transfer of irregularities and protrusions to the film surface is minimized, enabling good processing. In particular, when the present laminated polyester film is used as a support for ceramic green sheets in the manufacturing process of a multilayer ceramic capacitor, and a release layer or ceramic layer is formed on the film side opposite the side on which the resin layer is formed, if the arithmetic mean roughness (Sa) and maximum peak height (Sp) are within the above-mentioned ranges, the film will be extremely smooth, enabling the use of thinner ceramic green sheets to achieve smaller and higher-capacity multilayer ceramic capacitors.

[0129] The arithmetic mean roughness (Sa) and maximum peak height (Sp) of the resin layer surface can be adjusted by the composition and content of the present composition. The arithmetic mean roughness (Sa) and maximum peak height (Sp) of the surface opposite to the resin layer surface can be adjusted by the type, average particle size, and content of particles contained in the surface layer of the polyester film.

[0130] The arithmetic mean roughness (Sa) and maximum peak height (Sp) of the resin layer surface and the surface opposite to the resin layer surface can be measured using a non-contact surface roughness meter that utilizes optical interference, specifically, by the method described in the Examples. Measurement by this method allows obtaining values ​​that reflect a larger area of ​​the present laminated polyester film.

[0131] The coating retention rate of the resin layer is preferably 60% or more, more preferably 70% or more, and even more preferably 90% or more. The upper limit of the coating retention rate is not particularly limited, and is 100% or less. If the coating retention rate is within this range, process contamination due to peeled coating can be suppressed. The coating retention rate can be measured by the method described in the Examples.

[0132] The coefficient of static friction between the resin layer surface and the opposite surface of the present laminated polyester film is preferably 1.0 or less, more preferably 0.7 or less, and even more preferably 0.6 or less. When the present laminated polyester film is wound into a roll, the surface of the resin layer and the opposite surface come into contact with each other, and therefore the coefficient of friction between the surface of the resin layer and the opposite surface is important. Therefore, when the static friction coefficient is within this range, the uneven structure of the resin layer provides good slip properties, improving the handling properties of the laminated polyester film. The static friction coefficient can be measured by the method described in the examples.

[0133] The air leakage index can be used as an index to evaluate the handling properties, such as the winding properties, of the present laminated polyester film. If the air leakage index is low, the air trapped during winding of the present laminated polyester film is easily released, preventing poor roll appearance such as wrinkles and uneven edge surfaces. On the other hand, if the air leakage index is high, the trapped air will escape after a sufficient amount of time has passed, especially during transport, causing problems such as film misalignment toward the core or scratches due to the misalignment.

[0134] The air leakage index should be, for example, 130,000 seconds or less. If it is 130,000 seconds or less, it can be said that the tire has a certain level of handling ability. Furthermore, when the surface opposite the surface on which the resin layer is formed, i.e., when used as a release film for molding green sheets for multilayer ceramic capacitors, a substrate for interlayer insulating resin release, or a substrate for dry film resist, the smooth surface of the film used for processing preferably has an arithmetic mean roughness (Sa) of 9 nm or less, or a maximum peak height (Sp) of 500 nm or less, as described above. In this case, the air leakage index is preferably 130,000 seconds or less, more preferably 50,000 seconds or less, and even more preferably 30,000 seconds or less. Thus, when the smooth surface of the film is extremely smooth, more precise processing can be achieved by utilizing the film's smoothness. Furthermore, the uneven structure of the resin layer improves the air leakage index to within the above range, improving windability and improving the handleability of the laminated polyester film. The air leakage index can be measured by the method described in the Examples.

[0135] <<<Applications of laminated polyester film>>> This resin layer is made of a resin composition containing a certain amount of a specific compound, and has a specific roughness structure, which allows it to express a fine uneven structure. Another feature is that it focuses on the sharpness (kurtosis), which can be used to evaluate the tip shape of the unevenness, as an index of the roughness structure. This design concept has made it possible to precisely control the fine uneven structure, which is difficult to achieve with conventional particle-kneading film manufacturing methods. Furthermore, the specific roughness structure improves the ease of air escape even in thin films, making it possible to provide laminated polyester films with excellent handling properties.

[0136] The present laminated polyester film can be used in various applications for the purpose of improving the handling properties, and the applications are not particularly limited. In particular, as described above, because of its fine uneven structure, when used for sheet molding, it has the advantage of exhibiting good winding properties and being less prone to wrinkles, even when wound into a roll, making it suitable for use as a polyester film for sheet molding. Examples of polyester films for sheet molding include those for various release and processing applications, such as green sheet molding for multi-layer ceramic capacitors (MLCCs), interlayer insulating resins, dry film resists (DFRs), and multilayer circuit boards. In release and processing applications, this laminated polyester film is used, for example, as a support. The polyester film for sheet molding may be used, for example, in a process for forming various sheets such as green sheets by coating or laminating various materials on at least one side of the film. When the resin layer is provided on only one side, the various materials are preferably coated or laminated on the film side opposite the side on which the resin layer is provided, but may also be coated or laminated on the film side on which the resin layer is provided. In addition, the polyester film for sheet molding may have an appropriate release layer or the like provided on the film side opposite the side on which the resin layer is provided.

[0137] In particular, when this laminated polyester film is used as a support for ceramic green sheets in the manufacturing process of MLCCs, it can form a uniformly thin dielectric layer and contribute to improving productivity by reducing the frequency of changing polyester film rolls due to longer lengths.In particular, it can be suitably used as a support for ceramic green sheets used in MLCCs for automobiles.

[0138] <<<Term Explanation>>> In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film". In the present invention, when it is stated that "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified. [Example]

[0139] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0140] <Evaluation method> Intrinsic viscosity (IV) of polyester 1 g of polyester, from which components incompatible with the polyester had been removed, was precisely weighed and dissolved in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane mixed solvent. The viscosity was measured at 30°C using a viscosity measuring device "VMS-022UPC·F10" (manufactured by Rigo Co., Ltd.).

[0141] Average particle size of particles contained in polyester film The average particle size of particles was determined by observing 10 or more particles with a scanning electron microscope (SEM), measuring the particle diameters, and averaging the results to determine the average particle size (average primary particle size). In the case of non-spherical particles, the average of the longest and shortest diameters was measured as the diameter of each particle.

[0142] (3) Uneven structure of the resin layer Measurements were carried out using a scanning probe microscope (Shimadzu Corporation, SPM-9700) under the following conditions. Probe: Silicon cantilever Scanning mode: Dynamic mode Scanning range: 25 μm x 25 μm Scan rate: 0.8Hz Pixel count: 512 x 512 data points From the obtained data, a 25 μm wide cross-sectional shape was observed, and if there were multiple convex or concave portions with a step height of more than 10 nm at 80% or more of the positions, it was judged as "present" with an uneven structure, and if multiple convex or concave portions could not be confirmed, it was judged as "absent" with an uneven structure.

[0143] (4) Arithmetic mean roughness (Ra) and ten-point mean roughness (Rzjis) of the resin layer surface From the scanning probe microscope data measured by the method (3) above, a cross-sectional analysis of 25 μm width parallel to the tenter stretching direction (i.e., the transverse direction) was performed to determine the arithmetic mean roughness (Ra) and ten-point mean roughness (Rzjis). Cross-sectional analysis data were obtained at 10 equally spaced points in the film formation direction (i.e., the longitudinal direction), and these were averaged to determine the arithmetic mean roughness (Ra) and ten-point mean roughness (Rzjis).

[0144] (5) Load length ratio of the resin layer surface (Rmr(70)) Cross-sectional analysis was performed using a scanning probe microscope in the same manner as in (4) above, and the load length ratio at 70% of the cutting level (Rmr(70)) was calculated. Cross-sectional analysis data were collected at 10 equally spaced points in the film formation direction (i.e., the machine direction), and the average was calculated.

[0145] (6) Kurtosis (Sku), root mean square gradient (Sdq), and developed interface area ratio (Sdr) of the resin layer surface Image data obtained from the scanning probe microscope data measured by the method (3) above was analyzed using the image analysis software SPIP6.2.5 Image Metrology, and the kurtosis (Sku), root mean square gradient (Sdq), and developed interface area ratio (Sdr) were calculated.

[0146] (7) Arithmetic mean roughness (Sa) and maximum peak height (Sp) of the surface of the resin layer and the surface opposite to the resin layer The film surface was measured over an area of ​​640 μm × 480 μm using a non-contact surface / layer cross-sectional shape measurement system, VertScan® R550GML, manufactured by Ryoka Systems Co., Ltd., with a CCD camera: SONY HR-50 1 / 3', objective lens: 20x, lens barrel: 1X Body, zoom lens: No Relay, wavelength filter: 530 white, and measurement mode: Wave. The arithmetic mean roughness (Sa) and maximum peak height (Sp) were calculated as 10-point averages using the output from a fourth-order polynomial correction.

[0147] (8) Coating retention rate A Bemcot (M-3II, manufactured by Asahi Kasei Fibers Corporation) was attached to a rubbing tester (manufactured by Ohira Rika Kogyo Co., Ltd.) and rubbed five times over the resin layer surface of the sample film with an arm load of 680 g. The resin layer surface before and after treatment was measured by X-ray fluorescence analysis (XRF) to determine the amount of components derived from the resin layer. The coating film retention rate was calculated using the following formula. Coating retention rate (%) = amount of resin layer component after treatment / amount of resin layer component before treatment × 100

[0148] (9) Coefficient of static friction The static friction coefficient between the resin layer surface and the opposite surface of the laminated polyester film was determined by the following method. A film was attached to a smooth glass plate measuring 10 mm wide and 100 mm long, with the surface opposite the resin layer facing up. A film cut to a width of 18 mm and a length of 120 mm was placed on top of the film, with the resin layer facing down. An 8 mm diameter metal pin was pressed against the film, and the metal pin was slid longitudinally across the glass plate at a speed of 40 mm / min with a load of 30 g to measure the friction force. The maximum value immediately after sliding was evaluated as the static friction coefficient. Measurements were performed at room temperature (23±1°C) and humidity (50±0.5%). Ten measurements (N) were performed, and the average value was used. Coefficient of static friction (μs) = Fs / weight (In the above formula, the units of Fs and Fd are g-force, and the unit of weight load is g-force)

[0149] (10) Air leakage index Measurements were made using a DigiBec smoothness tester ("DB-2" manufactured by Toyo Seiki Co., Ltd.) in accordance with JIS P8119 at a temperature of 23°C and a humidity of 50%RH. The pressure of the pressure device was 100 kPa, and the vacuum container used was a container with a volume of 38 ml. The time it took for 1 ml of air to flow, i.e., the time (seconds) for the pressure inside the container to change from 50.7 kPa to 48.0 kPa, was measured, and the air leakage index was calculated by multiplying the obtained number of seconds. The test film sample size was 70 mm square, and 20 sheets were stacked so that the front and back of the test film overlapped to create a test laminate film. A 5mm diameter hole was drilled in the center of the test laminate film, and the air leakage index was measured as described above. The higher the air leakage index value, the longer it takes for air to leak through the gaps between the films, indicating that the films are more closely connected, and therefore the greater the risk of wrinkles occurring when the film is rolled up.

[0150] <Materials used> The polyesters used in the examples and comparative examples are as follows:

[0151] [Polyester (A)] 100 parts by mass of dimethyl terephthalate and 65 parts by mass of ethylene glycol were charged into an ester exchange reaction vessel equipped with a stirrer, a temperature raising device, and a distillate separation column, and heated to 150° C. to melt the dimethyl terephthalate.

[0152] Next, an ethylene glycol solution of magnesium acetate tetrahydrate was added so that the amount of magnesium acetate added was 0.09% by mass based on the obtained polyester. The mixture was then heated to 225°C under normal pressure over 3 hours, and then stirred and maintained at 225°C for 1 hour and 15 minutes while distilling off methanol to carry out an ester exchange reaction. The ester exchange reaction was essentially completed, yielding a polyester oligomer.

[0153] The oligomer was then transferred to a polycondensation reactor equipped with a distillation tube and a stirrer. An ethylene glycol solution of magnesium acetate tetrahydrate was added to the transferred oligomer so that the amount of magnesium acetate added would be 0.09% by mass relative to the polyester resin content obtained. Thereafter, an ethylene glycol solution of phosphoric acid was added as a heat stabilizer so that the amount of phosphoric acid added to the resulting polyester was 0.017% by mass.

[0154] Next, an ethylene glycol solution of tetrabutyl titanate was added as a polycondensation catalyst to the oligomer so that the titanium atom content was 4.5 ppm by mass relative to the resulting polyester. The pressure was then reduced from 101.3 kPa to 0.4 kPa over 85 minutes and maintained at 0.4 kPa, while the temperature was increased from 225°C to 280°C over 2 hours and maintained at 280°C for 1.5 hours to carry out a melt polycondensation reaction, yielding polyester A with an intrinsic viscosity (IV) of 0.63 dL / g.

[0155] [Polyester (B)] 0.75% by mass of alumina particles having an average particle size of 0.05 μm were added to polyester (A) and kneaded using a vented twin-screw kneader to obtain polyester (B) having an intrinsic viscosity (IV) of 0.63 dL / g.

[0156] [Polyester (C)] Polyester (C) having an intrinsic viscosity (IV) of 0.63 dl / g was obtained in the same manner as polyester (A), except that antimony trioxide was added as a polycondensation catalyst in an amount of 300 ppm by mass in terms of antimony atoms relative to the polyester resin content obtained, instead of adding tetrabutyl titanate as in polyester (A).

[0157] The resin compositions obtained by stirring and mixing the compositions shown in Table 1 below were diluted with water to prepare coating solutions 1 to 17. The compounds used are as follows.

[0158] [Compound (A): Binder resin (IA)] Aqueous dispersion of polyester resin copolymerized with the following composition Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / / (diol component) ethylene glycol / 1,4-butanediol / diethylene glycol = 56 / 40 / 4 / / 70 / 20 / 10 (mol%)

[0159] [Compound (A): Binder resin (IB)] Aqueous dispersion of acrylic resin polymerized with the following composition Emulsion polymer of ethyl acrylate / n-butyl acrylate / methyl methacrylate / N-methylolacrylamide / acrylic acid = 65 / 21 / 10 / 2 / 2 (mass%) (emulsifier: anionic surfactant)

[0160] [Compound (A): Binder resin (IC)] A water dispersion of polyester-based urethane resin polymerized according to the following composition. It is formed from isophorone diisocyanate units: terephthalic acid units: isophthalic acid units: ethylene glycol units: diethylene glycol units: dimethylolpropionic acid units=12:19:18:21:25:5 (mol %).

[0161] [Compound (A): Crosslinker (IIA)] Melamine compound: hexamethoxymethylolmelamine

[0162] [Compound (B): Particle (IIIA)] Zirconium oxide particles with an average particle size of 14 nm

[0163] [Compound (B): Particle (IIIB)] Titanium oxide particles with an average particle size of 15 nm

[0164] [Compound (B): Particles (IIIC)] Spherical silica particles with an average particle size of 5 nm

[0165] [Compound (B): Particle (IIID)] Spherical silica particles with an average particle size of 11 nm

[0166] [Compound (B): Particle (IIIE)] Spherical silica particles with an average particle size of 25 nm

[0167] [Compound (B): Particle (IIIF)] Chain-like silica particles with an average particle size of 12 nm

[0168] [Compound (B): Particle (IIIG)] Spherical silica particles with an average particle size of 45 nm

[0169] Example 1 A mixed raw material consisting of 87% by mass of polyester (A) and 13% by mass of polyester (B) was used as the raw material for one of the outermost layers (A layer), polyester (A) alone was used as the raw material for the middle layer (B layer), and polyester (A) alone was used as the raw material for one of the outermost layers (C layer). The raw materials for A layer, B layer, and C layer were each fed into three extruders and melted at 280°C. Then, they were coextruded onto a cooling roll set at 25°C in a layer structure of two types and three layers (surface layer / middle layer / surface layer = discharge rate 1.6 / 27.8 / 1.6), and cooled and solidified to obtain an unstretched sheet. Next, this film was stretched 3.5 times in the machine direction while passing through a group of heated rolls at 86°C to obtain a uniaxially stretched film. Coating solution 1 having the composition shown in Table 1 below was applied to one side (surface of layer C) of this uniaxially stretched film in an amount (after drying and stretching) of 0.12 g / m 2 The film was then introduced into a tenter stretching machine and stretched 4.5 times in the width direction at 105°C, and then heat-treated at 230°C, followed by a 2% relaxation treatment in the width direction to obtain a 31 μm-thick laminated polyester film having a resin layer on the surface of Layer C of Polyester Film A. The evaluation results are shown in Table 2.

[0170] (Examples 2 and 3) A laminated polyester film was obtained in the same manner as in Example 1, except that the coating solution shown in Table 1 was used and the coating amount (after drying and stretching) was changed to the coating amount shown in Table 2. The evaluation results are shown in Table 2.

[0171] Example 4 A laminated polyester film having a resin layer on the surface of Layer C of the polyester film B was obtained in the same manner as in Example 1, except that only the polyester (A) was used as the raw material for one outermost layer (Layer A) and only the polyester (C) was used as the raw material for the middle layer (Layer B). The evaluation results are shown in Table 2.

[0172] (Examples 5 to 19) A laminated polyester film was obtained in the same manner as in Example 4, except that the coating solution shown in Table 1 was used and the coating amount (after drying and stretching) was changed to the coating amount shown in Table 2. The evaluation results are shown in Table 2.

[0173] (Comparative Example 1) Except for not providing a resin layer, a polyester film was obtained in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0174] (Comparative Example 2) Except for not providing a resin layer, a polyester film was obtained in the same manner as in Example 4. The evaluation results are shown in Table 2.

[0175] (Comparative Examples 3 to 5) A laminated polyester film was obtained in the same manner as in Example 4, except that the coating solution shown in Table 1 was used and the coating amount (after drying and stretching) was changed to the coating amount shown in Table 2. The evaluation results are shown in Table 2.

[0176] [Table 1]

[0177] [Table 2]

[0178] Regarding the uneven shapes in Table 2 above, Shape 1 indicates a mesh shape (see Figure 1), Shape 2 indicates a shape that is a mixture of mesh and uneven shapes (see Figure 2), and Shape 3 indicates an uneven shape (see Figure 3). In Table 2 above, polyester film A refers to the polyester film of Example 1, and polyester film B refers to the polyester film of Example 4.

[0179] As shown in Table 2, the laminated polyester films of Examples 1 to 19 of the present invention contain compound (A) and a certain amount or more of (B) to form a concave-convex structure, and have a kurtosis (Sku) of less than 3.0, resulting in an appropriate concave-convex shape. They also have a low static friction coefficient of 1.0 or less, good slip properties, and an air leakage index of 130,000 seconds or less, which allows for excellent air release, making them excellent films for productivity, such as winding. In addition, the arithmetic mean roughness (Sa) and maximum peak height (Sp) of the surface opposite the resin layer were low, making them excellent films that could be precisely processed. On the other hand, Comparative Examples 1 and 2 do not have a resin layer and therefore do not have a concave-convex structure. Comparative Example 3 contains compound (A) and a certain amount or more of compound (B), but the kurtosis (Sku) value is high and the film does not have an appropriate concave-convex structure. Therefore, the static friction coefficient is low, but the air leakage index is high, and the film has poor handleability. Comparative Examples 4 and 5 do not contain a certain amount or more of compound (B), and therefore no concave-convex structure is formed. Therefore, these Comparative Examples have a high friction coefficient and air leakage index, and the films have poor slip properties and air release properties, and are poor in handleability. [Industrial Applicability]

[0180] The laminated polyester film of the present invention can form a fine uneven structure on the surface of the resin layer, and therefore, when used for sheet molding, has the advantage that the extremely smooth film exhibits good winding properties and is less likely to wrinkle even when wound into a roll. Furthermore, since the resin layer of the laminated polyester film of the present invention can be made thin, it can also accommodate thin and long polyester films, which can contribute to improving productivity by reducing the frequency of changing product rolls during processing. Therefore, the laminated polyester film of the present invention can be suitably used as a polyester film for sheet molding having excellent surface smoothness, and is highly valuable in industrial applications.

Claims

1. A laminated polyester film comprising a polyester film and a resin layer formed from a resin composition on at least one surface of the polyester film, the laminated polyester film satisfying all of the following requirements (1) to (4): (1) The resin layer has an uneven structure, and the arithmetic mean roughness (Ra) of the surface of the resin layer is 10 nm or more and 600 nm or less. The uneven structure refers to a structure in which a cross section of 25 μm width is observed from data obtained by a scanning probe microscope and there are multiple convex or concave portions with a step height of more than 10 nm at 80% or more of the positions. (2) The resin composition contains the following compounds (A) and (B): (A) One or more members selected from the group consisting of binder resins and crosslinking agents (B) Particles with an average particle size of 60 nm or less (3) The content of the (B) particles is 20% by mass or more as a proportion of the total nonvolatile components in the resin composition. (4) The kurtosis (Sku) of the surface of the resin layer is less than 3.

0.

2. 2. The laminated polyester film according to claim 1, wherein the ten-point average roughness (Rzjis) of the surface of the resin layer measured with a scanning probe microscope is 60 nm or more and 800 nm or less.

3. 3. The laminated polyester film according to claim 1, wherein the load length ratio (Rmr(70)) of the roughness curve at a cutting level of 70% of the surface of the resin layer measured with a scanning probe microscope is 82% or less.

4. The laminated polyester film according to any one of claims 1 to 3, wherein the root mean square gradient (Sdq) of the surface of the resin layer is 0.1 or more.

5. The laminated polyester film according to any one of claims 1 to 4, wherein the developed interface area ratio (Sdr) of the resin layer surface is 0.5% or more.

6. 6. The laminated polyester film according to claim 1, which has an air leakage index of 130,000 seconds or less when measured by the following method. (Method for measuring air leakage index) Measurement is carried out using a Digibec smoothness tester in accordance with JIS P8119 in an atmosphere at a temperature of 23° C. and a humidity of 50% RH. The pressure of the pressure device is 100 kPa, and the vacuum container has a volume of 38 ml. The time it takes for 1 mL of air to flow, i.e., the time (seconds) for the pressure inside the container to change from 50.7 kPa to 48.0 kPa, is measured, and the air leakage index is calculated by multiplying the obtained number of seconds by 10. The test film sample size is 70 mm square, and 20 test films are stacked with the front and back overlapping to form a test laminate film. A hole with a diameter of 5 mm is made in the center of the test laminate film to measure the air leakage index.

7. 7. The laminated polyester film according to claim 1, wherein the particles (B) have an average particle size of 1 to 45 nm.

8. The laminated polyester film according to any one of claims 1 to 7, wherein the binder resin (A) comprises at least one resin selected from the group consisting of polyester resins, (meth)acrylic resins, and polyurethane resins.

9. 9. The laminated polyester film according to claim 1, wherein the particles (B) comprise at least one selected from the group consisting of zirconium oxide, titanium oxide, and silica.

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