JP2024056103A - Laminated Polyester Film - Google Patents

Abstract

[Problem] To provide a laminated polyester film that has excellent handleability when winding the film into a roll by forming a fine uneven structure. [Solution] 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 kinds of (B) particles selected from the group consisting of binder resins and crosslinking agents. (3) The content of the (B) particles is 20 mass % or more as a proportion of the total non-volatile components in the resin composition. (4) The kurtosis (Sku) of the surface of the resin layer is less than 3.0. [Selected Figures] None

Description

The present invention relates to a laminated polyester film.

Polyester films, such as polyethylene terephthalate film and polyethylene naphthalate film, have excellent mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc., and are cost-effective, so they are used for a variety of purposes.

In addition, polyester films are suitable for a variety of 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.

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 reduces the ability of the film to escape air when wound into a roll or when unwound from the roll, resulting in slippage and blocking, which reduces the handling properties.
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.

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 kneading particles into it (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.

JP 2015-33811 A JP 2000-211082 A

However, in the conventional method of manufacturing a particle-incorporated film as disclosed in Patent Document 1, it is difficult to control the formation of unevenness, making it difficult to form a fine uneven structure, and in the film disclosed in Patent Document 2, the unevenness is insufficient, so wrinkles tend to occur when the film is wound into a roll, which can impair the appearance of the roll.

The present invention has been made in consideration of the above-mentioned circumstances, 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.

As a result of intensive research, the present inventors have found that the above problems can be solved by the following configuration.
The present invention has the following aspects.

[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.
(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) The content of the (B) particles is 20 mass% or more as a ratio of the total non-volatile 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 resin layer has a surface having an arithmetic average roughness (Ra) of 10 nm or more as measured by 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 as measured by 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 cut 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 resin layer surface 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], having 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 average particle size of the (B) particles is 1 to 100 nm.
[9] The laminated polyester film according to any one of the above [1] to [8], wherein the binder resin (A) 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 particles (B) contain at least one selected from the group consisting of zirconium oxide, titanium oxide, and silica.

According to the present invention, a laminated polyester film is provided that has excellent handling properties when winding the film into a roll, etc., due to the formation of a fine uneven structure.

In addition, since the laminated polyester film of the present invention can form a fine uneven structure on the resin layer surface, when used for forming a sheet, for example, the extremely smooth film has the advantage of exhibiting good winding properties and being less prone to wrinkles when wound into a roll.

Furthermore, since the resin layer of the laminated polyester film of the present invention can be made thin, it is also possible to make the polyester film thin and long, which can contribute to improving productivity by reducing the frequency of changing product rolls during processing.

1 is an image obtained by observing the surface of a resin layer in Example 1. 1 is an image obtained by observing the surface of a resin layer in Example 8. 1 is an image obtained by observing the surface of a resin layer in Example 19.

Next, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

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 the other terms.

<<<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.

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 laminate may have a structure in which a resin layer is 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.

<<Polyester film>>
The polyester film serves as a substrate for 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 multi-layer 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 multi-layer 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.

In particular, when utilizing the smoothness of the laminated polyester film, it is preferable that at least one side of the polyester film has excellent smoothness. Examples of such design methods include a method of designing the polyester film to have a single layer, two-type three-layer, or three-type three-layer structure so that both sides of the polyester film have excellent smoothness, and a method of designing the polyester film to have a three-type three-layer structure so that one side of the polyester film has excellent smoothness and the other side has a different roughness.

The polyester film may be either an unstretched film (sheet) or a stretched film. Of these, a stretched film stretched uniaxially or biaxially is preferred. Of these, a biaxially stretched film is more preferred in terms of excellent balance of mechanical properties and flatness.

<Polyester>
The polyester, which is the raw material of the polyester film, refers to a polymeric compound having continuous ester bonds in the main chain, and may be a homopolyester or a copolymer polyester. Specifically, a polyester obtained by polycondensation reaction of a dicarboxylic acid component and a diol component can be mentioned. In addition, it is preferable to use a polyester containing more than 50 mol% of an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid when the dicarboxylic acid component is taken as 100 mol%.

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.

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.

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 homopolyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with polyethylene terephthalate being preferred.

On the other hand, the copolymer polyester is preferably, for example, a polycondensation polymer of a dicarboxylic acid component and an aliphatic diol. As the dicarboxylic acid component, preferably, 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, etc.) are mentioned. As the aliphatic diol, preferably, one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol are mentioned. The copolymer polyester preferably contains terephthalic acid as the dicarboxylic acid component and ethylene glycol as the aliphatic diol.
When the polyester is a copolymer polyester, it is preferable that the polyester is 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 largest content) of the dicarboxylic acid component constituting the polyester and the compound that is the main component of the diol component, and for example, in the case of copolymerized polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol.
The copolymer polyester may also contain a structural unit derived from a difunctional compound other than the dicarboxylic acid component and the aliphatic diol. The structural unit derived from the difunctional compound other than the dicarboxylic acid component and the aliphatic diol is 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 bifunctional compound include various hydroxycarboxylic acids and aromatic diols.

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 further 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 further preferably 90 mol % or more.
The upper limit of the content of terephthalic acid and ethylene glycol is 100 mol %.

The polyester may be recycled polyester or may be biomass-derived polyester.

<Polycondensation catalyst>
The polycondensation catalyst used in polycondensing the polyester is not particularly limited, and any conventionally known compound can be used. Examples of the polycondensation catalyst include titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds.
Among these, at least one of titanium compounds and antimony compounds is preferred, and it is particularly preferred to use a polyester obtained by using a titanium compound.
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.

By using the titanium compound, the amount of antimony compound used can be reduced, which reduces the risk of new protrusions being formed due to the precipitation of the antimony compound on the film surface, and allows 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 polyester constituting at least one of the surface layers contains a titanium compound.

The titanium element content derived from the titanium compound in the surface layer is preferably 3 ppm to 40 ppm, more preferably 4 ppm to 35 ppm, based on mass. When the surface layer contains at least one of an antimony compound and a titanium compound, the antimony element content in the surface layer is preferably 0 ppm to 100 ppm. Within this range, it is possible to reduce the amount of foreign matter caused by the catalyst without reducing the 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, it is possible to obtain a polyester film having excellent smoothness. In addition, when the polyester film is made into a laminated polyester film having the resin layer, the laminated polyester film can be suitably used for forming a sheet or the like.

<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. If it is in such a range, there is an advantage that the particles are highly dispersed by increasing the shear stress during kneading. In addition, the intrinsic viscosity (IV) of the polyester is, for example, 1.00 dL/g or less.
In addition, when two or more polyesters having different intrinsic viscosities (IV) are used, the "intrinsic viscosity (IV) of the polyester constituting the present polyester film" means the intrinsic viscosity (IV) of the mixed polyesters.

When the polyester film has a multi-layer structure, it is preferable that the intrinsic viscosity (IV) of the polyester constituting the surface layer is within the above range.

<Particles>
The polyester film may contain particles, which imparts slipperiness to the polyester film and prevents scratches during each process, improving the handling properties.
The type of particles contained in the polyester film is not particularly limited as long as it is a particle capable of imparting slipperiness, and 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, 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. Of these, organic particles, silica, aluminum oxide, and the like are preferred. Among these, it is preferred to include aluminum oxide 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.

The shape of the particles to be used is not particularly limited, and any of spherical, block, rod-like, flat, etc. may be used.
There is also no particular restriction on the hardness, specific gravity, color, etc. Two or more kinds of these particles may be used in combination as necessary.

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. If it is 5 μm or less, the surface roughness of the film does not become too rough, and no problems occur when forming a resin layer and various surface functional layers other than the resin layer in a later process, which is preferable. If the average particle size is within this range, the haze is kept low, and the transparency of the present laminated polyester film as a whole is easily ensured.
The average particle size of the particles can be determined by measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and averaging the 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.

When the polyester film contains particles, it is preferable to provide a surface layer and an intermediate layer and contain particles in the surface layer. When the polyester film has a three-type three-layer structure with different front and back layers, it is also possible to contain particles in at least one of the surface layers.
The content of the particles depends on the average particle size, but is usually 5000 ppm or less, preferably 3000 ppm or less, more preferably 1000 ppm or less, based on mass in the layer containing the particles. When the particles are not contained or the content of the particles is small, the slipperiness cannot be sufficiently imparted, and the transparency of the polyester film is high, but the slipperiness may be insufficient. Therefore, it is necessary to improve the slipperiness by laminating the present resin layer described later. In addition, if it is 5000 ppm or less, the transparency of the polyester film can be sufficiently guaranteed. In addition, in the layer containing the resin, the content of the particles is not particularly limited, and is, for example, 50 ppm or more, preferably 100 ppm or more.

The resin layer described later may be provided on a layer of the polyester film containing particles, or may be provided on a layer that does not substantially contain particles. In addition, the surface (opposite surface) of the polyester film opposite to the surface on which the resin layer is provided 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 later. In addition, by making one or both of the surface on which the resin layer is provided and the opposite surface into layers that contain particles, the winding properties are further improved.
In order to impart excellent smoothness 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, but in order to obtain an extremely smooth film, it is preferable that the surface layer be substantially free of particles.
Incidentally, "substantially not contained" means that it is not intentionally contained, 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 opposite side to the smooth surface, the handling properties when the film is wound into a roll can be improved. In particular, from the viewpoint of improving the handling properties while maintaining the smoothness of the film, it is preferable to make at least one side smooth and laminate the present resin layer on the opposite side.

The method of 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, the particles can be added at any stage in the production of the polyester constituting each layer, but it is preferable to add the particles after the esterification or transesterification reaction is completed.

＜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 of performing solid phase polymerization after the production of a polyester.
The amount of precipitation of oligomer components may be suppressed by forming the present polyester film into a three or more layer structure and forming a surface layer of the present polyester film using a polyester raw material having a low content of oligomer components.
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.

In addition to the above-mentioned particles, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. can be added to the polyester film as necessary.

The thickness of the polyester film is not particularly limited as long as it is within the range in which it can be formed into a film, but from the viewpoints of mechanical strength, handling properties, productivity, etc., it 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 preferably 200 μm or less, more preferably 125 μm or less, even more preferably 80 μm or less, particularly preferably 50 μm or less.

<Method of producing polyester film>
Next, a production example of the polyester film will be specifically described, but the production example is not limited to the following production example. For example, when producing a biaxially stretched film, a method is preferred in which the dried pellets of the polyester raw material described above are extruded as a molten sheet from a die using a melt extrusion device such as an extruder, and cooled and solidified with 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 in order to improve the flatness of the sheet, and an electrostatic application adhesion method and/or a liquid application adhesion method are preferably used.

The unstretched sheet is then stretched in biaxial directions. In this case, the unstretched sheet is first stretched in one direction by 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 this case, the stretching temperature is usually 70 to 170° C., and the stretch ratio is usually 3.0 to 7.0 times, preferably 3.5 to 6.0 times.
Then, the film is subsequently 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 with 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, is preferably in the range of 100 to 160° C. This cooling may be performed in two or more steps with different temperatures.
In the above stretching, a method of stretching in one direction in two or more stages can be adopted. In that case, it is preferable to perform the stretching so that the final stretch ratios in both directions are each within the above range.

The polyester film may also be produced by a simultaneous biaxial stretching method, which involves simultaneously stretching and orienting the unstretched sheet in the machine direction (longitudinal direction) and width direction (transverse direction) under temperature control usually at 70 to 120° C., preferably 80 to 110° C., and the stretching ratio is preferably 4 to 50 times, more preferably 7 to 35 times, and even more preferably 10 to 25 times in terms of area ratio.
Then, the film is subsequently heat-treated under tension or under relaxation of 30% or less at a temperature of usually 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.

<<Resin layer>>
The laminated polyester film of the present invention comprises a resin layer formed from a resin composition on at least one side of a 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 a concave-convex structure.

<Uneven structure>
The uneven structure of the present resin layer is a fine shape. The shape of the uneven structure may be an uneven shape and/or a mesh shape.
The uneven shape is a surface uneven structure formed by fine protrusions formed by particles described later. The mesh shape is a surface uneven structure formed by coating film cracks caused by intentionally making the composition poor in stretchability and forming a film with poor stretchability. The mesh shape and the uneven shape 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).

<Resin Composition>
The present composition contains the following compounds (A) and (B).
(B) Particles containing one or more selected from the group consisting of (A) binder resins and crosslinking agents. In the present composition, the content of the (B) particles is 20 mass % or more as a proportion of the total non-volatile components in the present composition.

The composition has a low stretchability due to the above composition, and is prone to forming a fine uneven structure due to coating film cracking, which will be described later. 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 total content is not particularly limited in terms of its upper limit, and may be 100% by mass or less.

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

((Binder resin))
The binder resin selected as (A) is defined as a polymer compound having a number average molecular weight (Mn) of 1000 or more as measured by gel permeation chromatography (GPC) in accordance with the "Flow Scheme for Safety Evaluation of Polymer Compounds" (November 1985, sponsored by the Chemical Substances Council), and having film-forming properties.
Such a binder resin (A) is not particularly limited, and conventionally known binder resins such as polyester resins, (meth)acrylic resins, polyurethane resins, polyvinyl resins (polyvinyl alcohol, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycols, polyalkyleneimines, methyl cellulose, hydroxycellulose, starches, etc. can be used. Among them, polyester resins, (meth)acrylic resins, and polyurethane resins are preferred from the viewpoint of film-forming properties and adhesion to polyester films. In the present composition, the binder resin (A) may be used alone or in combination of two or more kinds.

By containing the binder resin (A), the composition is able to form a film (resin layer) that holds and fixes the particles (B).

(Polyester resin)
The polyester resin may be composed of, as main components, for example, the following polyvalent carboxylic acids and polyvalent hydroxy compounds.
That is, examples of polyvalent carboxylic 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, potassium dimethylolpropionate, etc. One or more of these compounds may be appropriately selected from each of them, and a polyester resin may be synthesized by a conventional polycondensation reaction.

As part of the polycarboxylic acid, a product is preferably used in which sulfoisophthalic acids such as 5-sodium sulfoisophthalic acid are copolymerized to introduce sulfonic acid groups into the polyester skeleton, and the polyester skeleton is neutralized to make it hydrophilic. The amount of copolymerization is usually 1 to 13 mol %, preferably 3 to 10 mol %, and more preferably 5 to 9 mol % of the total polycarboxylic acid. By introducing an appropriate amount of sulfonic acid groups, the hydrophilicity of the resin can be increased, making it easier to form an uneven structure. Furthermore, the water dispersion stability can be improved.

((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 a structural unit derived from (meth)acrylic acid or a (meth)acrylic acid alkyl ester. The (meth)acrylic polymer may be at least one polymer selected from (meth)acrylic acid and a (meth)acrylic acid alkyl ester, or may be a copolymer of at least one selected from these and at least one monomer other than these, 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, in some cases) obtained by polymerizing a polymerizable monomer in a polyester solution or polyester dispersion. Similarly, it also includes a polymer (or a mixture of polymers, in some cases) obtained by polymerizing a polymerizable monomer in a polyurethane solution or polyurethane dispersion. Similarly, it also includes a polymer (or a mixture of polymers, in some cases) obtained by polymerizing a polymerizable monomer in another polymer solution or dispersion, and these are also referred to as (meth)acrylic-modified polyester resins and (meth)acrylic-modified polyurethane resins in this specification. The above-mentioned polyesters and polyurethanes used in the (meth)acrylic resins can be appropriately selected from those exemplified as polyesters and polyurethanes used in the binder resins described later.
The (meth)acrylic resin may also contain a hydroxy group or an amino group in order to further improve adhesion to the polyester film.

The above-mentioned 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, citraconic acid, and their salts; 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. These include various alkyl (meth)acrylic acid esters; various nitrogen-containing monomers such as (meth)acrylamide, diacetone acrylamide, or (meth)acrylonitrile; hydroxyl group-containing nitrogen-containing monomers 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.

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 esters.
In addition, the present composition containing the (meth)acrylic resin is preferably diluted with a solvent to prepare a coating liquid as described below, and the solvent is preferably water as the main solvent (50 mass% or more). That is, from the viewpoint of facilitating dissolution or dispersion when the coating liquid is made water-based, the polymerizable monomer preferably has a hydrophilic group such as a hydroxyl group or a carboxyl group. In addition, from the viewpoint of effectively obtaining a concave-convex structure, it is preferable that the polymerizable monomer has a hydrophilic group such as a hydroxyl group or a carboxyl group.
Therefore, the acrylic resin is preferably a polymer obtained by polymerizing an alkyl (meth)acrylic acid ester and a polymerizable monomer 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.

(Polyurethane resin)
The polyurethane resin is a polymeric compound having a urethane bond in the molecule, and is preferably water-dispersible or water-soluble. In the present invention, the polyurethane resin may be used alone or in combination of two or more kinds.

In order 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 the polyurethane resin. Among the hydrophilic groups, carboxyl groups and sulfonic acid groups are particularly preferable 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.

One method for producing polyurethane resin is by reacting a hydroxyl group-containing compound with an isocyanate. As the hydroxyl group-containing compound used as a raw material, polyols are preferably used, such as polyester polyols, polyether polyols, polycarbonate polyols, polyolefin polyols, and acrylic polyols. Among these, polyester polyols are preferred from the viewpoint of excellent adhesion to polyester films. These compounds may be used alone or in combination.

Examples of polyester polyols include those obtained by reacting polyvalent carboxylic acids or their acid anhydrides with polyhydric alcohols. Examples of polyvalent carboxylic 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, 1, Examples include 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, and lactonediols.

Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, etc.

Examples of polycarbonate-based 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.

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'-tetramethyl xylylene 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.

A chain extender may be used when synthesizing the polyurethane resin. There are no particular limitations on the chain extender as long as it has two or more active groups that react with isocyanate groups, and generally, chain extenders having two hydroxyl groups or two amino groups can be mainly used.

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.

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.

(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 more, preferably in the range of 300 to 40,000. When the degree of polymerization is 100 or more, the water resistance of the resin layer is easily improved. In addition, the degree of saponification of polyvinyl alcohol is not particularly limited, but a polyvinyl acetate saponification product having a degree of saponification of usually 70 mol % or more, preferably in the range of 70 to 99.9 mol %, more preferably 80 to 97 mol %, and particularly preferably 86 to 95 mol % is practically used.

((Crosslinking Agent))
The crosslinking agent selected as the compound (A) is not particularly limited, and a conventionally known crosslinking agent can be used. For example, a melamine compound, an oxazoline compound, an epoxy compound, a carbodiimide compound, an isocyanate compound, a silane coupling compound, etc. can be mentioned. Among them, it is preferable to include a melamine compound from the viewpoint of increasing the strength of the coating film and improving the adhesion with the polyester film. In addition, the resin layer is easily made into a cured resin layer by using a crosslinking agent.

(Melamine compounds)
The melamine compound refers to a compound having a melamine skeleton in the compound, and for example, alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohol to partially or completely etherify them, and mixtures thereof can be used.
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 in the etherification, methanol, ethanol, isopropanol, n-butanol, isobutanol, etc. are preferably used, and among these, methanol is more preferred.
The melamine compound may be either a monomer or a dimer or higher polymer, or a mixture of these may be used. Furthermore, a product obtained by co-condensing melamine with urea or the like may also be used, and a catalyst may also be used in the present composition to increase the reactivity of the melamine compound.

(Oxazoline Compounds)
The oxazoline compound is a compound having an oxazoline group in the molecule, and in particular a polymer containing an oxazoline group is preferred, and can be prepared by polymerization of 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, and one or a mixture of two or more of these can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer is not limited as long as it is a monomer copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include (meth)acrylic acid esters such as alkyl(meth)acrylates (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and salts thereof (sodium salts, potassium salts, ammonium salts, tertiary amine salts, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl(meth)acrylates, etc. Examples of the monomer include unsaturated amides such as (t)acrylamide and N,N-dialkyl(meth)acrylamide (the alkyl group can be, for example, 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, etc.); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; 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. 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.

(Epoxy Compound)
The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include condensations 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 the polyepoxy compound include sorbitol polyglycidyl ether, 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 the monoepoxy compound include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, and examples of the glycidylamine compound 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 more preferable than a polyfunctional compound having two functional groups.

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

The carbodiimide compound can be synthesized by a conventionally known technique, and generally, a condensation reaction of a diisocyanate compound is used. The diisocyanate compound is not particularly limited, and both aromatic and aliphatic compounds can be used. Specific examples of the diisocyanate compound 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 hydroxyalkylsulfonate may be added.

(Isocyanate Compounds)
The isocyanate compound is 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'-tetramethyl xylylene 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, methylene bis(4-cyclohexyl isocyanate), and isopropylidenedicyclohexyl diisocyanate.
In addition, polymers and derivatives such as biuretized products, isocyanurate products, uretdione products, and carbodiimide modified products of these isocyanates are also included. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates in order to prevent yellowing due to ultraviolet rays.

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 isobutanoyl methyl acetate, 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, which may be used alone or in combination of two or more.

(Silane coupling compound)
A silane coupling compound is an organosilicon compound having 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, N-2-(aminoethyl)-3 -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, N-phenyl-3-aminopropyltriethoxysilane and other amino group-containing compounds; isocyanurate group-containing compounds such as tris(trimethoxysilylpropyl)isocyanurate and tris(triethoxysilylpropyl)isocyanurate; mercapto group-containing compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropylmethyldiethoxysilane.

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 percentage of the total non-volatile components in the composition. By making the content 10% by mass or more, a film having film-forming properties and containing particles can be obtained. In addition, by making the film have adhesion to the polyester film, it is possible to prevent the coating film from falling off. In addition, by making the content 80% by mass or less, a high particle content is obtained, and the coating film hardness is increased, making it possible to form unevenness in the coating film.

Compound (A) contains one or more selected from a binder resin and a crosslinking agent, and from the viewpoint of obtaining better film-forming properties, it is preferable that the compound contains a binder resin. Furthermore, from the viewpoint of further improving the coating film strength and adhesion to the polyester film, it is more preferable that the compound contains a binder resin and a crosslinking agent.

((Compound (B)))
The present composition contains particles (B). By containing particles (B) in the present composition, the stretchability of the coating film is reduced, and an uneven structure is easily formed. In addition, the hardness of the uneven structure formed is increased, and therefore, air escape property can be effectively improved.

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.

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).

The average particle size of the (B) particles is preferably 1 to 100 nm, more preferably 4 to 60 nm, and further preferably 8 to 40 nm. When the average particle size is within this range, the generation of coarse protrusions due to particle aggregation and process contamination due to particle dropout can be suppressed, and the desired fine uneven structure can be easily obtained.
The average particle size of the microparticles can be measured by a method that calculates the particle size 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 with a transmission electron microscope (TEM) or a scanning electron microscope (SEM), or a method that determines the particle size by measurement using a dynamic light scattering method. The average particle size of the microparticles can be measured by a method that is more suitable for the particle size.

The content of compound (B) in the composition is 20% by mass or more as a percentage of the total non-volatile components in the composition. The 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 making the content 20% by mass or more, it becomes easier to form an uneven structure, and the hardness of the uneven structure formed is increased, making it possible to effectively improve air escape properties. In addition, by making the content 90% by mass or less, it is possible to include the necessary amount of other components, and it is possible to form an uneven film and obtain adhesion to the polyester film. In addition, by making the content of compound (B) a certain value or less, it becomes easier to prevent the coating film from falling off.

(Other ingredients)
In addition to the above-mentioned components, additives such as crosslinking catalysts, defoamers, coatability improvers, surfactants, thickeners, organic lubricants, ultraviolet absorbers, antioxidants, foaming agents, dyes, and pigments may be appropriately added within the scope of the present invention.

((solvent))
The present composition may be diluted with a solvent to form a coating liquid, that is, the present composition may be applied as a liquid coating liquid to, for example, the present polyester film, and then dried and cured as necessary to form a resin layer.
Each of 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 the total non-volatile components of the composition 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 a 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 suppressed, thereby improving the appearance of the resin layer and increasing the stability in the coating solution.

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 use water as the main solvent (50% by mass or more of the total solvent) to prepare an aqueous coating liquid. 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 an organic solvent. The specific amount of the organic solvent is preferably 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 in 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 liquid as necessary, the stability and coatability of the coating liquid may be improved.

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

It can be assumed that the resin layer contains unreacted components of the present 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.

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

The resin layer can be formed by in-line coating or off-line coating. The method of 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 usually performed at 80 to 200° C. for 3 to 40 seconds, preferably at 100 to 180° C. for 3 to 40 seconds. On the other hand, when the resin layer is formed by in-line coating, the heat treatment is usually performed at 70 to 280° C. for 3 to 200 seconds.
The heat treatment may be performed in two or more steps at different temperatures within the above temperature range. At least a part of the heat treatment may be performed by heating during stretching. Drying and curing may be performed together by heating in the heat treatment.

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, coating at any stage from melt extrusion of polyester to stretching, heat setting and winding up. Usually, 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.

For example, but not limited to, in sequential biaxial stretching, a method in which a uniaxially stretched film that has been stretched in the longitudinal direction (machine direction) is coated and then stretched in the transverse direction is particularly advantageous. This method has the advantage of being able to simultaneously form the film and the resin layer, and is advantageous in terms of production costs. In addition, because stretching is performed after coating, the thickness of the resin layer can be changed by changing the stretch ratio, and thin film coating can be performed more easily than with offline coating films.

In addition, 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.

Furthermore, in the production of biaxially stretched polyester film, the film can be stretched while holding the ends of the film with clips or the like, thereby restraining the film in both the vertical and horizontal directions, and in the subsequent heat treatment (heat setting process), high temperatures can be applied without wrinkles or the like and while maintaining flatness.
Therefore, the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, so that the film-forming properties of the resin layer are improved and the resin layer and the polyester film can be more firmly attached to each other. 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.

In particular, in the present invention, this method is optimal as a manufacturing method for forming coating cracks. The contents of the compounds (A) and (B) in the present composition are adjusted to intentionally make the composition less suitable for stretching. In this way, by adopting a manufacturing method in which the present composition is coated and then stretched, a coating crack caused by stretching a film with poor stretchability can form an uneven structure on the surface of the resin layer. Those skilled in the art have traditionally considered coating cracks to be one form of coating defect, and have required 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 inventor has come to use such coating cracks as one of the means for forming a fine uneven structure on the surface of the resin layer.

Regardless of whether offline 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 necessary. 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.

The coating amount of the non-volatile components of the present resin layer is preferably 0.005 to 0.95 g/m ² , more preferably 0.02 to 0.5 g/m ² , even 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 is the coating amount in the present laminated polyester film, and in the case where drying and stretching are performed, for example, it is the coating amount after drying and stretching.

<<<<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 unevenness, with Sku = 3 being a normal distribution, and if Sku > 3, the height distribution is sharp, i.e., the surface has many sharp unevennesses, and if Sku < 3, the height distribution of the surface unevenness 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 projection apex is not easily crushed when the film is stacked, and air escape can be efficiently maintained. From this viewpoint, 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.

Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) and can be used to evaluate the peakiness (kurtosis) of a histogram of height distribution, and is calculated by the following formula (1).
If 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), then it can be expressed as follows:

The arithmetic mean roughness (Ra) of the resin layer surface of the 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. There is no particular upper limit, but it is preferably 600 nm, more preferably 400 nm, and even more preferably 200 nm. If the arithmetic mean roughness (Ra) is 10 nm or more, it can be said that the resin layer has a fine uneven structure, and the handleability of the laminated polyester film is good. Also, if the arithmetic mean roughness (Ra) is 600 nm or less, it can be said that the uneven structure of the resin layer has a sufficiently fine shape.

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

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. There is no particular upper limit, but 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.

The ten-point average roughness (Rzjis) is one of the line roughness parameters (JIS B 0601), and represents the sum of the average of the maximum peak height (Zp) to the fifth largest peak on the profile curve and the average of the maximum valley depth (Zv) to the fifth largest valley on the profile curve over the reference length L, and is calculated using the following formula (3).

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

Here, the inventors considered that the load length ratio (Rmr(70)) is effective as an index representing the unevenness distribution of the uneven structure. For example, a load length ratio (Rmr(70)) with a large concave distribution will have a small value, and a load length ratio (Rmr(70)) with a large convex distribution will have a large value.
If the load length ratio (Rmr(70)) is 82% or less, an appropriate fine uneven structure is formed, and the gaps between the films when the film is wound into a roll become larger, which makes it easier for air to escape and improves the winding characteristics, etc.

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).

The root-mean-square gradient (Sdq) of the resin layer surface of this laminated polyester film is preferably 0.1 or more, more preferably 0.25 or more, and even more preferably 0.45 or more. On the other hand, the root-mean-square gradient (Sdq) is preferably 3 or less, more preferably 1.0 or less. If the root-mean-square gradient (Sdq) is 0.1 or more, the difference between the peaks and valleys of the uneven structure is clear, which can improve air escape properties. Furthermore, if the root-mean-square gradient (Sdq) is 3 or less, coarse protrusions can be suppressed.

The root mean square gradient (Sdq) is one of the surface roughness parameters (ISO 25178) and is calculated by the following formula (5).
The root mean square gradient (Sdq) represents the average magnitude of the local gradient (slope) of the uneven shape of the surface, and a larger value indicates a steeper surface.

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 the winding characteristics. If the developed interface area ratio (Sdr) is 60% or less, the undulations are appropriately suppressed, and coarse protrusions can be prevented.

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, and the value increases as the surface shape becomes denser and more rugged.

The above 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 in the composition, the method of forming the resin layer, and various conditions in the formation process.

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. Measurements using an atomic force microscope (scanning probe microscope) can capture finer surface structures, making it possible to obtain values that strongly reflect the effects of the resin layer.

The surface arithmetic mean roughness (Sa) of the resin layer surface of the 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. If the arithmetic mean roughness (Sa) is in this range, extremely large irregularities can be reduced while maintaining a fine irregular shape. Therefore, for example, the handleability of the laminated polyester film can be ensured, and wrinkles when wound into a roll can be suppressed. When the film is used as a support for a ceramic green sheet in the manufacturing process of a laminated ceramic capacitor, and a release layer or ceramic layer is provided on the film surface opposite to the surface on which the resin layer is provided, the projections on the surface of the resin layer can be prevented from transferring to the ceramic layer or from destroying the ceramic layer.

The 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 obtained by dividing the volume of the area enclosed by the surface shape curved surface and the average surface by the measured area, and is calculated using the following formula (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 surface with height 0, it can be expressed as follows.

In addition, 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. On the other hand, the maximum peak height (Sp) is preferably 10 nm or more, more preferably 20 nm or more. If the maximum peak height (Sp) is 800 nm or less, protrusions can be reduced. Therefore, for example, when the laminated polyester film is used as a support for a ceramic green sheet in the manufacturing process of a laminated ceramic capacitor, and a release layer or ceramic layer is provided on the film surface opposite to the surface on which the resin layer is provided, protrusion transfer to the ceramic layer or destruction of the ceramic layer due to protrusions on the surface of the resin layer can be prevented. In addition, if the maximum peak height (Sp) is 10 nm or more, the handleability of the laminated polyester film can be ensured, and wrinkles when wound into a roll can be suppressed.

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

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

The maximum peak height (Sp) of the surface opposite 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 the handling of the film, it is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more.

When the laminated polyester film is used as a release film for forming green sheets for laminated ceramic capacitors, as a substrate for interlayer insulating resin release, as a substrate for dry film resist, etc., the smoothness of the film is utilized for processing. In this case, it is preferable that at least one side of the laminated polyester film is smooth, and if the arithmetic mean roughness (Sa) and maximum peak height (Sp) of the side opposite to the side on which the resin layer is formed are within the above ranges, the transfer of unevenness and protrusions on the film surface is small, and good processing is possible. In particular, when the laminated polyester film is used as a support for ceramic green sheets in the manufacturing process of a laminated ceramic capacitor, and a release layer or ceramic layer is provided on the film surface opposite to the side on which the resin layer is provided, if the arithmetic mean roughness (Sa) and maximum peak height (Sp) are within the above ranges, the film becomes extremely smooth, and it is possible to accommodate the thinning of ceramic green sheets when miniaturizing and increasing the capacity of laminated ceramic capacitors.

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.

The arithmetic mean roughness (Sa) and maximum peak height (Sp) of the resin layer surface and the surface opposite the resin layer surface can be measured using a non-contact surface roughness meter that utilizes optical interference, specifically, using the method described in the Examples. Measurements using this method can provide values that reflect a larger area of the laminated polyester film.

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 the fallen coating can be suppressed.
The coating retention rate can be measured by the method described in the Examples.

The static friction coefficient 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 further preferably 0.6 or less.
When the present laminated polyester film is wound into a roll, the resin layer surface and the opposite surface come into contact with each other, and therefore the coefficient of friction between the resin layer surface and the opposite surface is important.
Therefore, when the static friction coefficient is within this range, the uneven structure of the present resin layer provides good slipperiness, improving the handleability of the present laminated polyester film.
The static friction coefficient can be measured by the method described in the Examples.

The air leakage index can be used as an index for evaluating the handling properties, such as the winding properties, of the present laminated polyester film. If the air leakage index is low, the air trapped when the present laminated polyester film is wound up can be easily released, preventing defects in the roll appearance, such as wrinkles and uneven edges. On the other hand, if the air leakage index is high, the trapped air can escape after a sufficient amount of time has passed, especially during transport, causing problems such as the film shifting in the direction of the winding core or scratches due to the shifting.

The air leakage index may 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 handleability.
In addition, when the surface opposite to the surface on which the resin layer is formed, i.e., when used as a release film for forming a green sheet of a multilayer ceramic capacitor, a substrate for interlayer insulating resin release, a substrate for dry film resist, etc., as described above, the arithmetic mean roughness (Sa) of the smooth surface of the film used for processing is more preferably 9 nm or less, or the maximum peak height (Sp) is 500 nm or less. 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. In this way, when the smooth surface of the film is extremely smooth, more precise processing can be performed by utilizing the smoothness of the film, and the uneven structure of the resin layer improves the air leakage index to the above range, improving the winding property, and improving the handling property of the laminated polyester film.
The air leakage index can be measured by the method described in the Examples.

<<<<Applications of laminated polyester film>>>
The resin layer is characterized in that it 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 characteristic is that it focuses on the sharpness (kurtosis), which allows the tip shape of the unevenness to be evaluated, as an index of the roughness structure.
This design concept has made it possible to precisely control the fine uneven structure, which was difficult to achieve with conventional particle-kneading film manufacturing methods. In addition, the specific roughness structure has made it possible to improve the ease of air escape even in a thin film, making it possible to provide a laminated polyester film with excellent handling properties.

The present laminated polyester film can be used for various applications for the purpose of improving the handleability, and the applications are not particularly limited.
Among them, as described above, since it has a fine uneven structure, when used for sheet molding, it has an advantage that it exhibits good winding properties and is less likely to cause wrinkles even when a highly smooth film is wound into a roll, and it can be suitably used as a polyester film for sheet molding. Examples of polyester films for sheet molding include various release and process 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 process applications, the laminated polyester film is used, for example, as a support.
The polyester film for sheet molding may be used, for example, in a process of forming various sheets such as green sheets by applying or laminating various materials on at least one side of the film. When the resin layer is provided only on one side, the various materials are preferably applied or laminated on the film side opposite the side on which the resin layer is provided, but may be applied or laminated on the film side on which the resin layer is provided. In addition, in the polyester film for sheet molding, a release layer or the like may be appropriately provided on the film side opposite the side on which the resin layer is provided.

In particular, when this laminated polyester film is used as a support for ceramic green sheets in the manufacturing process of MLCCs, it is possible to form a uniform thin dielectric layer, and it can 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.

<<<<Terminology 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 described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as the meaning of "preferably larger than X" or "preferably smaller than Y".
In addition, 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.

The present invention will now be described in further detail with reference to examples.
However, the present invention is not limited to the following examples as long as it does not deviate from the gist of the present invention.

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

(2) 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 diameters of the particles, and averaging the diameters (average primary particle size). In this case, in the case of non-spherical particles, the average of the longest and shortest diameters was measured as the diameter of each particle.

(3) Uneven Structure of Resin Layer Measurement was carried out under the following conditions using a scanning probe microscope (SPM-9700, manufactured by Shimadzu Corporation).
Probe: Silicon cantilever Scanning mode: Dynamic mode Scanning range: 25 μm x 25 μm
Scan speed: 0.8Hz
Number of pixels: 512 × 512 data points From the obtained data, a cross-sectional shape with a width of 25 μm was observed. If there were multiple protrusions or recesses with a step difference exceeding 10 nm in 80% or more of the positions, it was determined that a concave-convex structure was “present,” and if multiple protrusions or recesses could not be confirmed, it was determined that a concave-convex structure was “absent.”

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

(5) Load length ratio of resin layer surface (Rmr(70))
The cross-sectional analysis was performed using a scanning probe microscope in the same manner as in (4) above, and the load length ratio at a cutting level of 70% (Rmr(70)) was determined. Cross-sectional analysis data was obtained at 10 points at equal intervals in the film formation direction (i.e., the machine direction) of the film, and the data was averaged.

(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 in (3) above was analyzed using image analysis software SPIP6.2.5 Image Metrology to calculate kurtosis (Sku), root mean square gradient (Sdq), and developed interface area ratio (Sdr).

(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 (registered trademark) 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, and the arithmetic average roughness (Sa) and maximum peak height (Sp) were calculated as an average of 10 points using the output from a fourth-order polynomial correction.

(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 on the surface of the resin layer of the sample film with an arm load of 680 g. The surface of the resin layer before and after the treatment was measured by X-ray fluorescence analysis (XRF) to measure the amount of components derived from the resin layer. The coating retention rate was calculated by the following formula.
Coating retention rate (%) = resin layer component amount after treatment / resin layer component amount before treatment × 100

(9) Static Friction Coefficient 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 having a width of 10 mm and a length of 100 mm so that the surface opposite to the surface on which the resin layer was provided was the upper surface. A film cut to a width of 18 mm and a length of 120 mm was placed on the film so that the surface on which the resin layer was provided was the lower surface, and a metal pin having a diameter of 8 mm was pressed against the film, and the metal pin was slid in the longitudinal direction of the glass plate with a load of 30 g and at 40 mm/min to measure the friction force, and the maximum value immediately after the sliding was evaluated as the static friction coefficient. The measurement was performed in an atmosphere of room temperature 23±1°C and humidity 50±0.5% RH. The number of measurements (N) was 10, and the average value was adopted.
Static friction coefficient (μs) = Fs / deadweight load (in the above formula, Fs and Fd are in g-force, and the deadweight load is in g-force)

(10) Air Leakage Index Using a Digibec smoothness tester (manufactured by Toyo Seiki Co., Ltd., "DB-2"), measurements were taken in accordance with JIS P8119 under an atmosphere of temperature 23°C and humidity 50% RH. The pressure of the pressurizing device was 100 kPa, and the vacuum container was a container with a volume of 38 ml. The time for 1 mL of air to flow, that is, the time (seconds) until the pressure in the container changed from 50.7 kPa to 48.0 kPa, was measured, and the air leakage index was 10 times the number of seconds obtained. The sample size of the test film was 70 mm square, and 20 sheets of the test film were laminated so that the front and back of the test film overlapped to form a test laminated film.
A hole with a diameter of 5 mm was opened in the center of the test laminate film, and the air leakage index was measured as described above. The larger the value of this air leakage index, the longer it takes for air to leak through the gap between the films, indicating that the films are in closer contact with each other, and therefore indicating a greater risk of wrinkles occurring when the film is rolled up.

<Materials used>
The polyesters used in the examples and comparative examples are as follows.

[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.

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.
Thereafter, the temperature was raised to 225°C over 3 hours under normal pressure, and the mixture was further maintained at 225°C for 1 hour and 15 minutes with stirring while distilling off methanol to carry out an ester exchange reaction, which was essentially completed to obtain a polyester low polymer (oligomer).

The oligomer was then transferred to a polycondensation reaction vessel equipped with a stirrer and a distillation tube.
An ethylene glycol solution of magnesium acetate tetrahydrate was added to the transferred oligomer so that the amount of magnesium acetate added was 0.09% by mass based on the obtained polyester resin content.
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.

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.
Thereafter, the pressure was reduced from 101.3 kPa to 0.4 kPa over 85 minutes and maintained at 0.4 kPa, while the temperature was raised 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, thereby obtaining a polyester A having an intrinsic viscosity (IV) of 0.63 dL/g.

[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.

[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 in polyester (A).

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:

[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%)

[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)

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

[Compound (A): Crosslinking agent (IIA)]
Melamine compound: Hexamethoxymethylolmelamine

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

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

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

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

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

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

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

Example 1
A mixed material obtained by mixing polyesters (A) and (B) at a ratio of 87% by mass and 13% by mass, respectively, was used as the raw material for one side outermost layer (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 side outermost layer (C layer). Each of the raw materials for A layer, B layer, and C layer was fed to three extruders, melted at 280°C, and then co-extruded onto a cooling roll set at 25°C in a layer structure of two kinds and three layers (surface layer/middle layer/surface layer = discharge amount of 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 longitudinal direction while passing through a group of heating rolls at 86 ° C. to obtain a uniaxially stretched film. On one side (surface of layer C) of this uniaxially stretched film, coating solution 1 having the composition shown in Table 1 below was applied in a coating amount (after drying and stretching) of 0.12 g / m ² , and then this film was introduced into a tenter stretching machine, stretched 4.5 times in the width direction at 105 ° C., and further subjected to heat treatment at 230 ° C., and then subjected to 2% relaxation treatment in the width direction to obtain a laminated polyester film with a thickness of 31 μm having a resin layer on the surface of layer C of polyester film A. The evaluation results are shown in Table 2.

(Examples 2 to 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.

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

(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.

(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.

(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.

(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.

Regarding the uneven shapes in Table 2 above, shape 1 indicates a mesh shape (see FIG. 1), shape 2 indicates a shape in which a mesh shape and an uneven shape are mixed (see FIG. 2), and shape 3 indicates an uneven shape (see FIG. 3).
In addition, in Table 2 above, polyester film A is the polyester film of Example 1, and polyester film B is the polyester film of Example 4.

As shown in the results 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 an uneven structure, and have an appropriate uneven shape with a kurtosis (Sku) of less than 3.0, a low static friction coefficient of 1.0 or less, good slipperiness, and excellent air leakage with an air leakage index of 130,000 seconds or less, and therefore are excellent films in productivity such as winding properties. In addition, the arithmetic mean roughness (Sa) and maximum peak height (Sp) of the opposite surface of the resin layer are low, making them excellent films that can be precisely processed.
On the other hand, Comparative Examples 1 and 2 do not have a resin layer, and therefore do not have an uneven structure. Comparative Example 3 contains compound (A) and a certain amount or more of compound (B), but has a high kurtosis (Sku) value and does not have an appropriate uneven structure. Therefore, the static friction coefficient was low, but the air leakage index was high, and the film had poor handleability. Comparative Examples 4 and 5 do not contain a certain amount or more of compound (B), and therefore no uneven structure is formed. Therefore, these comparative examples have a high friction coefficient and air leakage index, and are poor in slipperiness and air escape, and are poor in handleability.

Since the laminated polyester film of the present invention can form a fine uneven structure on the resin layer surface, when used for sheet molding, for example, the extremely smooth film has the advantage of exhibiting good winding properties and being less likely to cause wrinkles 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 is possible to accommodate a thin and long polyester film, 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 of great industrial utility.

Claims (10)

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.
(2) The resin composition contains the following compounds (A) and (B):
(A) one or more types selected from the group consisting of binder resins and crosslinking agents; and (B) particles. (3) The content of the (B) particles is 20 mass% or more as a ratio of the total non-volatile components in the resin composition.
(4) The kurtosis (Sku) of the surface of the resin layer is less than 3.0. The laminated polyester film according to claim 1, wherein the arithmetic mean roughness (Ra) of the resin layer surface is 10 nm or more when measured with a scanning probe microscope. The laminated polyester film according to claim 1 or 2, wherein the ten-point average roughness (Rzjis) of the resin layer surface as measured by a scanning probe microscope is 60 nm or more. The laminated polyester film according to any one of claims 1 to 3, wherein the load length ratio (Rmr(70)) of the roughness curve at a cutting level of 70% of the resin layer surface when measured with a scanning probe microscope is 82% or less. The laminated polyester film according to any one of claims 1 to 4, wherein the root mean square gradient (Sdq) of the resin layer surface is 0.1 or more. The laminated polyester film according to any one of claims 1 to 5, wherein the developed interface area ratio (Sdr) of the resin layer surface is 0.5% or more. The laminated polyester film according to any one of claims 1 to 6, having an air leakage index of 130,000 seconds or less. The laminated polyester film according to any one of claims 1 to 7, wherein the average particle size of the (B) particles is 1 to 100 nm. The laminated polyester film according to any one of claims 1 to 8, wherein the binder resin (A) contains at least one selected from the group consisting of polyester resins, (meth)acrylic resins, and polyurethane resins. The laminated polyester film according to any one of claims 1 to 9, wherein the particles (B) contain at least one selected from the group consisting of zirconium oxide, titanium oxide, and silica.