JP7830966B2 - Polyester film roll and method for manufacturing polyester film roll - Google Patents

Description

This invention relates to a polyester film roll suitable as a support for a process release film used in the manufacturing process of multilayer ceramic capacitors.

In recent years, with the increasing electrification of automobiles and the sophistication of smartphones, multilayer ceramic capacitors (MLCCs) have become smaller and have higher capacitance.
Multilayer ceramic capacitors are manufactured as follows:
First, a ceramic slurry containing ceramic components and binder resin is applied to a release film and dried to create a ceramic green sheet (dielectric sheet). Electrodes are then printed onto this sheet using screen printing or the like to form internal electrodes. After drying, the printed ceramic green sheet is peeled off the release film, and multiple such ceramic green sheets are stacked. The stacked ceramic green sheets are then pressed together to form a single unit, and finally cut into individual chips.
Subsequently, the internal electrodes and dielectric layers are sintered in a firing furnace to manufacture a multilayer ceramic capacitor.

As MLCCs become smaller and larger in capacity, the thickness of the ceramic green sheet is being reduced. If the thickness of the ceramic green sheet is further reduced to 0.5 μm (thickness after drying) or less, even minute protrusions on the surface of the release film (carrier film) can cause pinholes and other defects in the ceramic green sheet. Therefore, the release film requires even higher surface smoothness.

Conventionally, as a support for this type of release film, Patent Document 1 discloses a release film for manufacturing ceramic green sheets, comprising a substrate having a first surface and a second surface, a smoothing layer provided on the first surface side of the substrate, and a release agent layer provided on the side of the smoothing layer opposite to the substrate, wherein the smoothing layer is formed by heating and curing a smoothing layer forming composition containing a thermosetting compound with a weight-average molecular weight of 950 or less, the arithmetic mean roughness Ra ₁ of the outer surface of the release agent layer is 8 nm or less, and the maximum protrusion height Rp ₁ of the outer surface of the release agent layer is 50 nm or less.

Furthermore, Patent Document 2 discloses a release polyester film that has excellent surface smoothness and, in particular, few fine defects on the film surface, wherein the number of depression defects with a depth of 0.5 μm or more is 5 or less per ^m² , and the centerline average roughness SRa of at least one side of the surface is 15 to 35 nm, and the ten-point average roughness SRz is 1000 nm or less.

Furthermore, Patent Document 3 discloses a polyester film roll made by winding up a polyester film, wherein the polyester film has fewer than 5 slack defects per 100 ^m² .

Japanese Patent Publication No. 2014-177093 Japanese Patent Publication No. 2013-7054 Japanese Patent Publication No. 2018-90803

However, the inventors' research revealed that in the polyester film manufacturing process, particles in the polyester resin sometimes aggregated during the melt extrusion process. In particular, when organic particles were used, the tendency for particle aggregation was significant, and it was found that the dispersion state of the polyester raw material particles before the melt extrusion process was not maintained.
Furthermore, conventionally, in film surface design, the formation of fine irregularities on the film surface was controlled by adjusting the type of particles used, the average particle size, and the amount added. However, with the thinning of ceramic green sheets, even more precise control is required.

Therefore, the objective of the present invention is to propose a new polyester film roll and a method for manufacturing the same, in which the polyester film surface has fine irregularities, the occurrence of scratches and other damage can be suppressed, losses due to raw material changes can be reduced, continuous production for long periods of time is possible, and the roll can be made into longer lengths.

In view of the above circumstances, the inventors of the present invention have conducted extensive research and found that the above problems can be easily solved by using a polyester film roll having a specific configuration, and have completed the present invention. That is, the present invention provides the following [1] to [8].
[1] A polyester film roll formed by winding a polyester film, wherein the polyester film contains organic particles having an average particle size of 0.05 to 0.4 μm, and one surface (A) of the polyester film satisfies the following (1) to (3).
(1) The average surface roughness (Sa) is 5 to 20 nm.
(2) The maximum peak height (Sp) is 310 nm or more.
(3) The average spacing between irregularities (RSm) is 0.016 mm or less.
[2] The polyester film roll according to [1], wherein the polyester film is a three-layer polyester film.
[3] The polyester film roll according to [1] or [2], wherein one surface layer A of the polyester film contains the particles.
[4] The polyester film roll according to [2] or [3], wherein the intermediate layer of the polyester film contains 50% by mass or more of recycled polyester raw material.
[5] A polyester film roll according to any one of [1] to [4], having a release layer on one surface (A) of the polyester film.
[6] A polyester film roll according to any one of [1] to [5], used as a support for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor.
[7] A polyester film roll according to any one of [1] to [6], used as a support for a ceramic green sheet in the manufacturing process of an automotive ceramic capacitor.
[8] A method for manufacturing a polyester film roll obtained by winding up a polyester film,
The polyester film contains organic particles with an average particle size of 0.05 to 0.4 μm.
The aforementioned polyester film is a three-layer polyester film.
A method for manufacturing a polyester film roll, wherein, in the extrusion conditions for the surface layer (A) of the polyester film, the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) is 150 kg/h or less, and the ratio Q/N of the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) to the screw rotation speed N rpm satisfies the following formula (A).
2.5≦Q/N≦3.0 (A)

According to the present invention, it is possible to provide a polyester film roll and a method for manufacturing the same, in which the surface of the polyester film has fine irregularities, the occurrence of scratches and the like can be suppressed, losses due to raw material changes can be reduced, continuous production for long periods of time is possible, and the roll can be made into a long length.
Furthermore, since one surface (A) of the polyester film roll of the present invention satisfies the above (1) to (3), it has the advantage of suppressing the occurrence of defects and enabling the thinning of the ceramic green sheet when used, for example, as a support for a ceramic green sheet.

Furthermore, we have found that, unlike conventional manufacturing methods, the polyester film roll manufacturing method of the present invention allows for precise control of the uneven surface shape of the film by adjusting the manufacturing conditions.
In particular, in the case of multilayer polyester films, we found that increasing the discharge amount of polyester raw material constituting the surface layer A during the elution extrusion process shortens the time required for the polyester raw material to move within the extruder (residence time) during the melt extrusion process, thereby suppressing the aggregation of particles in the polyester raw material.

Furthermore, the tendency for uneven surface formation on the polyester film differs depending on the type of particles in the polyester raw material. For example, when conventional inorganic particles were used, the maximum peak height (Sp) on the polyester film surface tended to increase with increasing polyester resin discharge rate.
On the other hand, the inventors' research has shown that by using organic particles with a specific particle size, the amount of polyester raw material discharged is reduced, which conversely increases the Sp value while keeping the Sa value of the film surface low, exhibiting behavior that is completely different from conventional methods.
Therefore, the present invention provides excellent advantages in the manufacturing method of polyester film, when manufacturing a multilayer polyester film, by combining the adjustment of the discharge amount of polyester raw material constituting the surface layer in the melt extrusion process as a new elemental technology for controlling the fine unevenness shape of the film surface. These advantages include: 1) eliminating the need to use polyester raw material containing specially modified particles, and 2) eliminating the need to use multiple polyester raw materials with pre-adjusted average particle size and particle addition amount before adjusting the fine unevenness shape of the film surface.
In particular, reducing changeover losses due to different types of raw materials in the manufacturing process enables further continuous production, significantly contributing to improved productivity.

As described above, the polyester film roll and method for manufacturing the polyester film roll of the present invention, in controlling the surface shape of the polyester film, combines not only the conventional approach from the material side, such as the polyester raw material, but also a new elemental technology: adjustment of the discharge amount of the polyester raw material constituting the surface layer in the melt extrusion process. This allows for more precise control of the uneven shape of the film surface. In particular, this invention proposes a film with a fine yet precise uneven shape and a method for manufacturing the same, which can be used in situations where ceramic green sheets with a thickness (after drying) of 0.5 μm or less are required in the manufacturing of multilayer ceramic capacitors.

The graph shows the relationship between shear stress and shear rate, calculated from the intrinsic viscosity (IV) of polyester. This diagram illustrates the estimated particle dispersion mechanism in polyester resin. This shows the particle distribution on one surface (A) of the polyester film obtained in Example 1. (The surface of the sample, which had been pre-coated with aluminum, was photographed using a Keyence digital high-definition camera (magnification: 400x)). This shows the particle distribution on one surface (A) of the polyester film obtained in Comparative Example 4. (The surface of the sample, which had been pre-coated with aluminum, was photographed using a Keyence digital high-definition camera (magnification: 400x)). This shows the particle distribution on one surface (A) of the polyester film obtained in Comparative Example 5. (The surface of the sample, which had been pre-coated with aluminum, was photographed using a Keyence digital high-definition camera (magnification: 400x)).

The present invention will be described in detail below. In this specification, the term "A to B" in relation to numerical values means "A or greater and B or less" (when A < B) or "A or less and B or greater" (when A > B). Furthermore, in this invention, a preferred combination of embodiments is a more preferred embodiment.

[Polyester film roll]
The polyester film roll of the present invention is a polyester film roll obtained by winding a polyester film, wherein the polyester film contains organic particles with an average particle size of 0.05 to 0.4 μm, and one surface (A) of the polyester film satisfies the following (1) to (3).
(1) The average surface roughness (Sa) is 5 to 20 nm.
(2) The maximum peak height (Sp) is 310 nm or more.
(3) The average spacing between irregularities (RSm) is 0.016 mm or less.

In the polyester film roll of the present invention, one surface (A) of the polyester film refers to, for example, the surface on which the ceramic green sheet is laminated when used as a support for the ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor. By satisfying conditions (1) to (3) above simultaneously on one surface (A) of the polyester film, a multilayer capacitor can be manufactured in a suitable condition. Furthermore, from the viewpoint of using it as a support for the ceramic green sheet, the surface of one surface (A) of the polyester film is suitable as the surface on which the release layer described later is provided.

The polyester film roll of the present invention (hereinafter also referred to as "this roll") is made by winding up a polyester film (hereinafter also referred to as "this film").
This roll is a polyester film roll wound onto a core such as a paper tube, metal tube, or plastic tube, and is preferably 0.2 m or wider, more preferably 0.3 m or wider, particularly preferably 1.0 m or wider, and most preferably 1.5 m or wider. The upper limit of the film width is not particularly limited, but from the viewpoint of handling, it is preferably 2.3 m or less, and more preferably 2.0 m or less.
Furthermore, the length of the film wound onto the roll is not particularly limited, but is preferably 1,000 m or more, more preferably 6,000 m or more, and even more preferably 12,000 m or more.
Furthermore, the thickness of this film is preferably 19 μm to 38 μm, and more preferably 25 μm to 32 μm.

<Polyester film>
(Surface properties)
In the present invention, the polyester film contains organic particles with an average particle size of 0.05 to 0.4 μm, and one surface (A) of the polyester film must satisfy the following conditions (1) to (3).
(1) The average surface roughness (Sa) is 5 to 20 nm.
(2) The maximum peak height (Sp) is 310 nm or more.
(3) The average spacing between irregularities (RSm) is 0.016 mm or less.

(1) Average surface roughness (Sa) of the film surface
In the present invention, the average surface roughness (Sa) of one surface (A) of the polyester film must be 5 to 20 nm.
When the average surface roughness (Sa) of one surface (A) of a polyester film exceeds 20 nm, the fine irregularities on the surface of the polyester film make it more susceptible to defects such as pinholes. On the other hand, when the average surface roughness (Sa) is less than 5 nm, the film surface becomes excessively flat, reducing the film's slipperiness and making it more prone to scratches.
In the present invention, the average surface roughness (Sa) of one surface (A) of the polyester film is preferably 7 to 18 nm, more preferably 9 to 16 nm, and even more preferably 10 to 14 nm, from the viewpoint of improving scratch resistance, suppressing a decrease in the slipperiness of the polyester film, and thinning the ceramic green sheet.

Average surface roughness (Sa) is one of the surface roughness parameters (ISO 25178), and is an extension of the two-dimensional Ra to three dimensions. It is calculated by dividing the volume of the area enclosed by the surface shape curve and the average surface by the measured area, and can be obtained from the following formula (1).
When the surface is the XY plane and the height direction is the Z axis, if A is the defined region (the entire image) and Z(x,y) is the height of the image point (x,y) from the plane with height 0, then it can be expressed as shown in equation (1) below.

(2) Maximum peak height (Sp) on the film surface
In this invention, the maximum peak height (Sp) of one surface (A) of the polyester film must be 310 nm or more. If the maximum peak height (Sp) of one surface (A) of the polyester film is less than 310 nm, it becomes difficult for air to escape between the films when the polyester film is wound up, which makes it easier for wrinkles and other defects to occur in the polyester film, making it difficult to produce long rolls of polyester film.
In the present invention, the maximum peak height (Sp) of one surface (A) of the polyester film is preferably 350 nm or more from the viewpoint of extending the length of the polyester film roll and improving handling. Furthermore, there is no particular upper limit to the maximum peak height (Sp), but from the viewpoint of improving the winding properties of the polyester film, it is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less.

Maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178), representing the maximum height from the average surface level, and is expressed by the following equation (2).

Furthermore, in the present invention, the relationship Sp/Sa between the average surface roughness (Sa) and the maximum peak height (Sp) of one surface (A) of the polyester film is preferably 20 or more, more preferably 25 or more, and even more preferably 30 or more.
The relationship between average surface roughness (Sa) and maximum peak height (Sp), Sp/Sa, is 20 or higher. This allows for a balance between low average surface roughness (Sa) and high maximum peak height (Sp), making it easier to lengthen polyester film rolls and thin ceramic green sheets.
Furthermore, while there are no particular limitations on the lower limit of the relationship between average surface roughness (Sa) and maximum peak height (Sp), Sp/Sa, a value of 25 or higher is preferred, and a value of 30 or higher is more preferred, from the viewpoint of adjusting for a balance between high Sa and low Sp.

(3) Average spacing of irregularities on the film surface (RSm)
In the present invention, the average spacing (RSm) of the irregularities on one surface (A) of the polyester film is required to be 0.016 mm or less. In the present invention, by having an average spacing (RSm) of the irregularities on one surface (A) of the polyester film of 0.016 mm or less, the polyester film roll can be made longer, and the ceramic green sheet can be made thinner.
In the present invention, the average spacing (RSm) of the irregularities on one surface (A) of the polyester film is preferably 0.015 mm or less, and more preferably 0.014 mm or less. Furthermore, there is no particular lower limit to the average spacing (RSm) of the irregularities, but from the viewpoint of extending the length of the polyester film and handling it, and from the viewpoint of thinning the ceramic green sheet, it is preferably 0.010 mm or more, more preferably 0.012 mm or more, and even more preferably 0.013 nm or more.

In this invention, the average spacing between irregularities (RSm) is measured in accordance with JIS B0601:2013 and is expressed as the average length Xs of the contour curve elements at a given length, as shown in equation (3) below.

In recent years, as ceramic green sheets have become even thinner, there has been a trend towards making the release surface highly smooth. However, if the surface is made too smooth, it can be difficult to control the release properties of the green sheet from the release surface.
The present invention ensures that the average surface roughness (Sa), maximum peak height (Sp), and average spacing (RSm) of one surface (A) of the polyester film simultaneously satisfy the above-mentioned ranges. When manufacturing a ceramic green sheet, for example, by providing a release layer on the surface (A) of the polyester film and using the surface of the release layer to form the ceramic green sheet, the contact area between the polyester film and the green sheet can be increased. This prevents the ceramic green sheet from unintentionally peeling off the polyester film in situations where peeling is not necessary.
In other words, the polyester film roll of the present invention adjusts the maximum peak height (Sp) and average spacing (RSm) of the polyester film surface, thereby arranging protrusions (convex portions) of appropriate height at appropriate intervals. This increases the contact area with the ceramic green sheet, allowing for adjustment of the adhesion between the polyester film and the ceramic green sheet. This enables the smooth peeling of the thinned (for example, 0.5 μm (after drying) or less) ceramic green sheet from the surface of the polyester film only when peeling is necessary.

The surface characteristics of one surface (A) of the polyester film in the present invention described above can be adjusted, for example, by incorporating particles into the polyester layer constituting the film surface, adjusting the average particle size, particle type, and content of those particles, and further by controlling the discharge amount of the polyester raw material of the surface layer during the manufacturing of the polyester film roll.

(Organic particles contained in polyester film)
In the present invention, the polyester film must contain organic particles with an average particle size of 0.05 to 0.4 μm. By containing organic particles with an average particle size of 0.05 to 0.4 μm, it becomes possible to ensure the surface smoothness of the ceramic green sheet when manufacturing a ceramic green sheet or the like using the polyester film roll of the present invention.
The average particle size of the organic particles is preferably 0.1 to 0.4 μm, more preferably 0.15 to 0.35 μm, and even more preferably 0.2 to 0.3 μm, from the viewpoint of ensuring the surface smoothness of the ceramic green sheet when manufacturing the ceramic green sheet.

The average particle size can be determined by measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and calculating the average value. In the case of non-spherical particles, the average of the longest and shortest diameters can be used as the diameter of each individual particle.

Examples of organic particles include crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles, as well as organic particles such as calcium oxalate and ion exchange resins.
Specific examples of organic particles include crosslinked polymer particles. Examples of crosslinked polymer particles in terms of composition include divinylbenzene polymer, ethyl vinylbenzene-divinylbenzene copolymer, styrene-divinylbenzene copolymer, styrene-ethyl vinylbenzene-divinylbenzene copolymer, ethylene glycol dimethacrylate polymer, styrene-ethylene glycol dimethacrylate copolymer, and methyl methacrylate-divinylbenzene copolymer. Furthermore, crosslinked polymer particles composed of three or more components may also be used.

Furthermore, it is preferable to use organic particles that have a narrow particle size distribution and a nearly uniform average particle size (so-called monodisperse organic particles).
By incorporating monodisperse organic particles, it is possible to obtain a polyester film that maintains the handling properties of the polyester film roll while exhibiting high surface smoothness, particularly a low average surface roughness (Sa) on one surface (A) of the polyester film (forming fine irregularities), and yet having a large maximum peak height (Sp).

As organic particles having a narrow and nearly uniform average particle size distribution, when D10 is the particle size at which the cumulative number of particles accounts for 10% of the particle size distribution, D50 is the particle size at which the cumulative number of particles accounts for 50%, and D90 is the particle size at which the cumulative number of particles accounts for 90%, particles in which (D90 - D10) / D50 is 0.4 or less are preferred, and particles in which it is 0.2 or less are particularly preferred.
The relational expression (D90 - D10)/D50 indicates the variation in particle size relative to D50. Particles with (D90 - D10)/D50 of 0.4 or less have a sharp particle size distribution with a small difference between D90 and D10, and can impart fine irregularities to the polyester surface of the polyester film while maintaining excellent handling properties.
The particle size distribution of the aforementioned particles is measured using a laser diffraction measuring device.

In this invention, the organic particle content in the polyester film is preferably 900 ppm or more by mass, more preferably 2000 ppm to 10000 ppm, even more preferably 2500 ppm to 9500 ppm, and even more preferably 3000 ppm to 9000 ppm, from the viewpoint of extending the length of the polyester film roll and improving handling.

(polyester)
In the present invention, polyester refers to polyester used as a raw material for polyester film, and is a polymer compound having ester bonds continuously in its main chain. In the present invention, polyester may be homopolyester or copolymer polyester, and specifically, polyester obtained by polycondensation reaction of a dicarboxylic acid component and a diol component can be mentioned.

Furthermore, in this invention, it is preferable to use a polyester containing more than 50 mol% of aromatic dicarboxylic acid or aliphatic dicarboxylic acid when the dicarboxylic acid component is considered to be 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'-diphenylsulfondicarboxylic acid, as well as aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedionic acid, cyclohexanedicarboxylic acid, and their ester derivatives.

Examples of the aforementioned 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 above polyester consists of a homopolyester, it is preferable to obtain one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol.
Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol.
Typical examples of polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN).

On the other hand, if the polyester is a copolymerized polyester, it is preferable that it 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 of the dicarboxylic acid component that constitutes the polyester and the compound that is the main component of the diol component, and in the case of polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol.
Examples of dicarboxylic acid components in copolymerized polyesters include one or more types of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid.
Examples of glycol components in copolymerized polyesters include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol.

Furthermore, the polyester should preferably consist of 80 mol% or more, preferably 90 mol% or more, of polyethylene terephthalate units, such as polyethylene terephthalate, or polyethylene-2,6-naphthalate units, such as polyethylene-2,6-naphthalate.

Polyester polycondensation catalyst
Examples of polycondensation catalysts used when polycondensing the above-mentioned polyester include antimony compounds, germanium compounds, aluminum compounds, and titanium compounds. Among these, at least one of antimony compounds and titanium compounds is preferred, and in particular, polyester obtained using a titanium compound is preferred.
Therefore, the polyester film preferably contains at least one of an antimony compound and a titanium compound, and more preferably contains a titanium compound.
By using the aforementioned titanium compound, the number of metal-containing aggregates derived from the titanium compound, so-called coarse foreign matter, in the film can be reduced, and a film with high surface smoothness, in particular, a small maximum peak height (Sp) on at least one side, can be obtained.

It is preferable that the polyester constituting the outermost layer of this film (also called the "surface layer," for example, one surface (A) of a polyester film, or the surface layer on which the release layer is laminated) uses a titanium compound as its polycondensation catalyst.
Preferably, the titanium element content in the outermost layer derived from the titanium compound is 3 ppm to 40 ppm, and more preferably 4 ppm to 35 ppm.
Within the above range, catalyst-induced foreign matter can be reduced without decreasing the manufacturing efficiency of polyester.
Furthermore, in the case of a polyester film with a laminated structure, from the viewpoint of productivity, it is preferable not to use a titanium compound as the polycondensation catalyst for the polyester constituting the intermediate layer described later.
Furthermore, from a similar viewpoint, it is preferable that the antimony compound content in the outermost layer of this film be 100 ppm or less.
For example, the surface layer A described later contains at least one of an antimony compound and a titanium compound, and it is preferable that the antimony compound content in the surface layer A is 100 ppm or less. In this case, the surface layer A does not have to contain an antimony compound.

≪Intrinsic viscosity (IV) of polyester≫
The intrinsic viscosity (IV) of the polyester constituting the polyester film of the present invention is preferably 0.50 dL/g or higher, more preferably 0.55 dL/g or higher, and even more preferably 0.60 dL/g or higher.
In the present invention, by using a polyester with an intrinsic viscosity (IV) of 0.50 dL/g or higher as the polyester constituting the polyester film, the shear stress during the kneading of the polyester increases, making it easier for particles in the polyester resin to be highly dispersed, and making it easier to bring the surface properties of one surface (A) of the polyester film within the above range. Furthermore, from the viewpoint of particle fluidity, the upper limit of the intrinsic viscosity (IV) of the polyester is preferably 1.00 dL/g or less, more preferably 0.85 dL/g or less, and even more preferably 0.75 dL/g or less.

Furthermore, from the same viewpoint as above, when the polyester film of the present invention has a laminated structure, the intrinsic viscosity (IV) of the polyester constituting the surface layer, specifically the outermost layer of the film (for example, one surface (A) of the polyester film, or the surface layer on which the release layer is laminated), is preferably 0.50 dL/g or higher, more preferably 0.55 dL/g or higher, and even more preferably 0.60 dL/g or higher. Also, from the viewpoint of particle fluidity, the upper limit of the intrinsic viscosity (IV) of the polyester constituting the surface layer is preferably 1.00 dL/g or less, more preferably 0.85 dL/g or less, and even more preferably 0.75 dL/g or less.

Furthermore, "the intrinsic viscosity (IV) of the polyester constituting the polyester film of the present invention" refers to the intrinsic viscosity (IV) of the mixed resin when two or more polyesters with different intrinsic viscosities (IV) are used.

(Composition of polyester film)
In the present invention, the polyester film may be a single-layer polyester film or a laminated polyester film having two or more layers.
In the present invention, the polyester film is preferably a laminated polyester film having two or more layers, and more preferably a polyester film with a three-layer structure, from the viewpoint of easily controlling the surface properties of one surface (A) within the above range.

In the present invention, when the polyester film is a laminated polyester film having two or more layers, it is preferable that one of the surface layers A contains the above-mentioned organic particles. Here, the one surface layer A is the surface layer that forms one of the surfaces (A) of the polyester film in the present invention, and in a laminated polyester film, by having one surface layer A contain the above-mentioned particles, it is easier to control the surface properties of one of the surfaces (A) of the polyester film within the above range. Furthermore, the film may have both sides as surface layer A containing particles, or one side may be surface layer A and the other side as surface layer C described later. It is preferable that surface layer C contains particles.

≪Laminated structure of polyester film≫
In the present invention, when the polyester film is a laminated polyester having two or more layers, a three-layer configuration of A/B/C, consisting of an intermediate layer B, a surface layer A, and a surface layer C, or an A/B/A, consisting of an intermediate layer B and a surface layer A, is preferred, and a three-layer configuration of A/B/A is more preferred.

Furthermore, in the case of a polyester film with a three-layer structure of A/B/C, it is preferable that the surface layer C has an average surface roughness (Sa) and maximum peak height (Sp) equal to or less than that of surface layer A, and it is preferable that the average surface roughness (Sa) of surface layer C is 5 nm or more, or the maximum peak height (Sp) is 220 nm or less. In this case, the average surface roughness (Sa) of surface layer C may be around 20 nm or less.
By adopting this laminated structure, the surface layer C can be provided with the rough surface necessary to improve handling, and the surface layer A can be provided with the smoothness necessary to provide a thin ceramic layer.

In the above-mentioned A/B/C and A/B/A three-layer structures, it is preferable that surface layer A and surface layer C contain particles to ensure handling.
Furthermore, in the above-mentioned A/B/C and A/B/A three-layer structures, the particles used in the surface layer A, intermediate layer B, and surface layer C can preferably be the same as the organic particles contained in the polyester film described above, and the same applies to the preferred ranges of average particle size and particle size distribution.

From the viewpoint of suppressing the occurrence of pinholes, suppressing the decrease in the slipperiness of the polyester film, and thinning the lamic green sheet, the content of the particles in the surface layer A is preferably 900 ppm to 6000 ppm by mass, more preferably 900 ppm to 4000 ppm, and even more preferably 900 ppm to 3000 ppm.
Furthermore, from the viewpoint of improving the handling of the polyester film roll, the content of the particles in the surface layer C is preferably less than 5,000 ppm by mass, and more preferably 2,000 ppm or more and 4,000 ppm or less.

The intermediate layer B is preferably configured to function as the thickest main layer, and in order to reduce costs, it is preferable that it contains substantially no particles or particles at a lower concentration than the surface layer A.
Furthermore, "substantially absent" means intentionally absent, and specifically refers to a particle content (particle concentration) of 200 ppm or less, more preferably 150 ppm or less.

Surface layer A and surface layer C are different layers. Specifically, examples include variations in particle type, average particle size, and blending ratio, as well as variations in layer thickness.

In the present invention, the intermediate layer B of the polyester film preferably contains 50% by mass or more of recycled polyester raw material, more preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass. By containing recycled polyester raw material in the intermediate layer B within the above range, for example, _CO2 emissions can be reduced, and the burden on the environment can be reduced.

Furthermore, in the polyester film roll of the present invention, a configuration in which the polyester film comprises surface layer A and/or surface layer C as shown in (X) and (Y) below is particularly preferred.
By adopting this configuration, the polyester film can be endowed with excellent handling properties and surface smoothness.

(X) Particularly Preferred Embodiment 1
(1) In the configuration of A/B/C described above, surface layer A contains organic particles and a titanium compound, and surface layer A contains organic particles with an average particle size of 0.05 μm to 0.4 μm. (2) In the configuration of (1), surface layer C contains organic particles. (3) In either of (1) or (2), surface layer C contains an antimony compound and/or a titanium compound, and the antimony compound content is 100 ppm or less. (4) In any of (1) to (3), the particles are configured such that when the particle diameter at which the cumulative number reaches 10% is D10, the particle diameter at which the cumulative number reaches 50% is D50, and the particle diameter at which the cumulative number reaches 90% is D90, (D90 - D10) / D50 is 0.4 or less. (5) In the configuration of (4), the organic particles are configured to be divinylbenzene-styrene particles.

In (X) above, by using polyester polycondensed with a titanium compound as a catalyst in both surface layer A and surface layer C, catalyst-induced impurities can be reduced, resulting in high surface smoothness.

(Y) Particularly Preferred Embodiment 2
(1) In the A/B/A configuration, the surface layer A contains particles such that when the particle size at which the cumulative number of particles reaches 10% is D10, the particle size at which the cumulative number of particles reaches 50% is D50, and the particle size at which the cumulative number of particles reaches 90% is D90, (D90 - D10) / D50 is 0.4 or less. (2) In the above (1), the surface layer A contains an antimony compound and/or a titanium compound, and the content of the antimony compound is 100 ppm or less. (3) In the above (1) or (2), the intrinsic viscosity (IV) of the polyester constituting the surface layer A is 0.55 dL/g or more, preferably 0.60 dL/g or more. (4) In any of the above (1) to (3), the particles are organic particles.

In the above (Y), the surface layer A contains particles having a substantially uniform average particle size. More specifically, when D10 is the particle size at which the cumulative number of particles reaches 10%, D50 is the particle size at which the cumulative number of particles reaches 50%, and D90 is the particle size at which the cumulative number of particles reaches 90%, the film can be obtained with high surface smoothness, particularly a small maximum peak height (Sp) on at least one side, while maintaining handling properties.

(Method for manufacturing polyester film)
The following is an example of a method for manufacturing this film.
First, raw materials, such as polyester chips, are supplied to an extruder by known methods, heated to a temperature above the melting point of each polymer, the molten polymer is extruded from the die, and cooled and solidified on a rotating cooling drum to a temperature below the glass transition point of the polymer, thereby obtaining a substantially amorphous, unoriented sheet.

Next, the unoriented sheet is stretched in one direction using a roll or tenter type stretcher. At this time, the stretching temperature is typically 25 to 120°C, preferably 35 to 100°C, and the stretching ratio is typically 2.5 to 7 times, preferably 2.8 to 6 times.

Next, the material is stretched in a direction perpendicular to the first stretching direction. During this stretching, the stretching temperature is typically 50 to 140°C, and the stretching ratio is typically 3.0 to 7 times, preferably 4.5 times or more, and more preferably 4.5 to 5.0 times.

Then, a heat-setting treatment is carried out at a temperature of 180 to 220°C under tension or under relaxation of 30% or less to obtain the polyester film of the present invention as a biaxially oriented film. This heat-setting treatment may be carried out in two or more steps at different temperatures.
Furthermore, cooling may be performed in a cooling zone after the heat-setting treatment. The cooling temperature is preferably higher than the glass transition temperature (Tg) of the polyester resin constituting the polyester film, and more specifically, it is preferably in the range of 100 to 160°C. This cooling may be carried out in two or more stages at different temperatures.
Furthermore, in the aforementioned extension, a method can be adopted in which the extension is carried out in two or more stages in one direction.

In this invention, when the polyester film is a polyester film with the three-layer structure described above, the extruder used for the surface layer (A) is preferably a vented twin-screw extruder having a raw material supply port and a vent opening in the cylinder, and having at least one reduced-pressure vent section. The bore diameter (cylinder inner diameter) D mm of the twin-screw extruder used in this invention is not particularly limited. The length L mm of the twin-screw extruder used in this invention is preferably 20 × D to 50 × D, and more preferably 25 × D to 45 × D. When the length L of the twin-screw extruder is 50 D or less, the residence time of the polyester raw material in the twin-screw extruder does not become too long, and thermal degradation of the polyester raw material is easily suppressed. Furthermore, when L is 20 D or more, the plasticization of the polyester raw material is sufficient, enabling stable melt extrusion.

Furthermore, in the present invention, when the polyester film is a polyester film having the three-layer structure described above, in the method for manufacturing a polyester film roll of the present invention, the polyester film contains organic particles having an average particle size of 0.05 to 0.4 μm, and when the polyester film is a polyester film having the three-layer structure described above, the extrusion conditions for the surface layer (A) of the polyester film are characterized in that the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) is 150 kg/h or less, and the ratio Q/N of the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) to the screw rotation speed N rpm satisfies the following formula (A).
2.5≦Q/N≦3.0 (A)
By keeping the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) within the above range, the aggregation of particles in the polyester raw material can be adjusted, and the surface properties of the surface layer (A) (the surface properties of one surface (A) of the polyester film) can be set to a desired range.
Furthermore, by satisfying the range of formula (A) above, the screw rotation speed can be set to an appropriate range with respect to the amount of polyester resin extrusion, the degree of renewal of the molten resin surface under vacuum can be appropriately performed, and sufficient degassing can be achieved, making it possible to mold the desired polyester film.

The discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) is preferably 145 kg/h or less, and more preferably 140 kg/h or less, from the viewpoint of preventing damage to the polyester film roll and extending its length. Also, from the same viewpoint, the ratio Q/N of the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) to the screw rotation speed N rpm is more preferably satisfied by the following formula (B).
2.8≦Q/N≦3.0 (B)

In this invention, the dispersion mechanism of particles in the polyester raw material during the melt extrusion process is presumed to be as follows.
As shown in Figure 1, the inventors focused on the relationship between shear stress and shear rate calculated from the intrinsic viscosity (IV) of polyester. As a result, it was found that shear stress tends to decrease as the shear rate decreases.
Next, we considered the particle dispersibility in the melt extrusion process. First, the polyester resin is subjected to moderate shear stress by the extruder screw in a semi-molten state, and furthermore, as the amount of polyester raw material discharged decreases, the shear rate decreases. As a result, moderate shear stress can be applied to the particles in the polyester resin, so as shown in Figure 2, the particles are dispersed in the polyester resin (matrix resin), which is thought to regulate particle aggregation in the melt extrusion process and allow the material to be extruded from the die while maintaining a good dispersion state.

In the method for manufacturing polyester film rolls of the present invention, by setting the extrusion conditions of the polyester raw material constituting the surface layer (A) as described above, it is possible to achieve a maximum peak height (Sp) that was previously difficult to reach, while maintaining a low and constant average surface roughness (Sa).

(Release layer)
The polyester film roll of the present invention can be used in a form having a release layer on at least one side.
The release layer is preferably laminated on one of the surfaces (A) of the polyester film.
In other words, in the polyester film roll of the present invention, it is preferable to have a release layer on one surface (A) of the polyester film.
Therefore, for example, in the case of an A/B/C configuration, a release layer is laminated on the surface of surface layer A, resulting in a release layer/A/B/C configuration. Also, in the case of an A/B/A configuration, a release layer is laminated on the surface of one of the surface layers (A), resulting in a release layer/A/B/A configuration.
By laminating a release layer on one surface (A) of the polyester film, it is expected that when forming a ceramic green sheet by laminating an ultrathin ceramic layer on the release layer, the ceramic green sheet will not unintentionally peel off from the release surface in situations where peeling is not necessary.

The release layer is laminated onto the polyester film either directly or via another layer.
Other layers include, for example, an easy-adhesion coating layer to improve adhesion to the film, as well as an antistatic layer and an anti-blocking layer.

The aforementioned release layer is formed from a release agent composition containing a release agent. From the viewpoint of obtaining good release performance, it is particularly preferable that the release agent composition contains a silicone resin. Specifically, it is preferable to include a type mainly composed of a curable silicone resin, a modified silicone type formed by graft polymerization with organic resins such as urethane resin, epoxy resin, or alkyd resin, or a fluorosilicone resin.

As the curable silicone resin, any existing curing reaction type can be used, such as addition-type, condensation-type, or other thermosetting types, or electron beam-curing types such as ultraviolet-curing types, and multiple types of curable silicone resins may be used in combination.
Furthermore, there are no particular restrictions on the coating form of the curable silicone resin used to form the release layer; it may be in the form of a solution in an organic solvent, an aqueous emulsion, or a solvent-free form.

The mold release agent composition forming the aforementioned release layer may also contain, as needed, a binder, defoaming agent, coating properties improver, thickener, inorganic/organic particles, organic lubricant, antistatic agent, conductive agent, ultraviolet absorber, antioxidant, foaming agent, dye, and pigment.

The release layer is formed by coating the film with a release agent composition. This can be achieved through either in-line coating performed during the film manufacturing process, or so-called off-line coating applied to a pre-manufactured film outside the system.

Methods for applying a release layer to this film include conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating.

The curing conditions for forming the release layer are not particularly limited. When providing a release layer by offline coating, it is generally recommended to perform heat treatment at 80°C or higher for 10 seconds or more, preferably at 100-200°C for 3-40 seconds, and more preferably at 120-180°C for 3-40 seconds.

Furthermore, if necessary, heat treatment may be used in combination with irradiation using active energy rays such as ultraviolet irradiation.
Furthermore, known devices and energy sources can be used as the energy source for curing by activated energy ray irradiation.

The amount of release layer applied (after drying) is typically in the range of 0.005 to 5 g/ ^m² , preferably 0.005 to 1 g/ ^m² , and more preferably 0.005 to 0.1 g/ ^m² , from the standpoint of coatability. If the amount of application (after drying) is less than 0.005 g/ ^m² , the coating may lack stability from the standpoint of coatability, making it difficult to obtain a uniform coating film.

On the other hand, if the coating is applied thickly, exceeding 5 g/ ^m² , the adhesion and curing properties of the release layer itself may decrease.

The coating amount is calculated based on the liquid mass per unit of time applied (before drying), the non-volatile content concentration of the coating solution, the coating width, the stretching ratio, the line speed, etc.

(Application)
The polyester film roll of the present invention can be suitably used for various release applications.
For example, it can be used for various release and process applications such as dry film resist (DFR), multilayer circuit boards, and the manufacture of ceramic green sheets for multilayer ceramic capacitors. In release and process applications, this film can be used, for example, as a support, and various materials such as ceramic slurry can be applied or laminated onto the support.

In particular, as mentioned above, the polyester film roll of the present invention has fine irregularities, excellent scratch resistance, and can contribute to improved productivity. Therefore, it can be suitably used as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

Furthermore, in the future, as multilayer ceramic capacitors for automobiles become increasingly electrified, it is predicted that the thickness of the ceramic green sheets used will continue to decrease, particularly as the size and capacitance of these capacitors increase.
Therefore, in particular, the polyester film roll of the present invention can be suitably used as a support for ceramic green sheets used in multilayer ceramic capacitors for automobiles.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

<Polyester Manufacturing>
(1) Production of polyester A 100 parts by mass of dimethyl terephthalate and 65 parts by mass of ethylene glycol were charged into a transesterification reactor equipped with a stirring device, a heating 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 to the resulting polyester was 0.09% by mass.
Subsequently, the temperature was raised to 225°C over 3 hours under atmospheric pressure, and the transesterification reaction was carried out at 225°C for 1 hour and 15 minutes while stirring and distilling off methanol, thereby effectively completing the transesterification reaction and obtaining a low-polymer polyester (oligomer).

Next, the oligomer was transferred to a polycondensation reactor 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 relative to the resulting polyester resin was 0.09% by mass.
Subsequently, 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 to the oligomer as a polycondensation catalyst in such a concentration of titanium atoms as 4.5 ppm by mass relative to the resulting polyester.
Subsequently, 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 held at 280°C for 1.5 hours to carry out a melt polycondensation reaction, yielding polyester A with an intrinsic viscosity (IV) of 0.63 dL/g.

(2) Production of Polyester B Polyester A was subjected to solid-phase polymerization to obtain Polyester B having an intrinsic viscosity (IV) of 0.70 dL/g.

(3) Production of Polyester C Polyester C was obtained in the same manner as Polyester A, except that instead of adding tetrabutyl titanate to Polyester A, antimony trioxide was added as a polycondensation catalyst so that the amount of antimony atoms was 300 ppm by mass relative to the resulting polyester resin, and the intrinsic viscosity (IV) was 0.63 dL/g.

(4) Production of Polyester D Polyester D was obtained in the same manner as Polyester A, except that tetrabutyl titanate was added to the obtained polyester in a quantity of 210 ppm by mass of titanium atoms, with an intrinsic viscosity (IV) of 0.63 dL/g.

(5) Production of polyester E 1.0% by mass of monodisperse spherical silica with an average primary particle size of 0.5 μm ((D90 - D10) / D50 = 0.27) was added to the above substantially particle-free polyester D, and the mixture was kneaded using a vented twin-screw kneader to obtain polyester E.

(6) Production of polyester F 0.75% by mass of alumina particles with an average primary particle size of 0.05 μm was added to the above-mentioned polyester D which is substantially free of particles, and the mixture was kneaded using a vented twin-screw kneader to obtain polyester F.

(7) Production of polyester G Polyester G was obtained by mixing 2.0% by mass of calcium carbonate particles with an average primary particle size of 0.7 μm into the above-mentioned polyester D which is substantially free of particles, and kneading it using a vented twin-screw kneader.

(8) Production of polyester H 1.0% by mass of organic particles ((D90-D10)/D50 = 0.46: divinylbenzene-ethylstyrene-methacrylic acid-styrene copolymer) with an average primary particle size of 0.3 μm was added to the above-mentioned polyester D which is substantially free of particles, and the mixture was kneaded using a vented twin-screw kneader to obtain polyester H.

[Example 1]
A raw material blend of 70% polyester D and 30% polyester H was used as the raw material for the surface layer A, and a raw material of 100% polyester D was used as the raw material for the intermediate layer B. These materials were supplied to a vented extruder, melt-extruded at 290°C, and then the raw material for the surface layer A was divided into two layers to form the outermost layer (surface layer), and the intermediate layer B was used as the intermediate layer, resulting in a two-layer, three-layer structure (A/B/A). An amorphous film was obtained by co-extrusion using an electrostatically applied adhesion method, cooling and solidifying on a cooling roll with a surface temperature set to 40°C, so that the thickness composition ratio of A/B/A = 1.4/28.2/1.4 under the extrusion conditions. At this time, the extrusion conditions for the polyester raw material of layer A during melt extrusion were set to a discharge rate of 140 kg/h and a screw rotation speed of 50 rpm.

Next, utilizing the difference in roll peripheral speed, the film was stretched 3.4 times in the longitudinal direction (MD direction) at a film temperature of 85°C. This longitudinally stretched film was then guided to a tenter and stretched 4.6 times in the transverse direction (TD direction) at 120°C. After heat treatment in the tenter's heat treatment (fixing) zones 1 and 2, and cooling zones 3 and 4 at 215°C, 205°C, 150°C, and 110°C, respectively, the film was wound into a roll on a 6-inch plastic core to obtain a polyester film roll with a thickness of 31 μm.

[Comparative Example 1]
In Example 1, the extrusion conditions for the polyester raw material of the surface layer A in melt extrusion were set to a discharge rate of 200 kg/h and a screw rotation speed of 71 rpm, and the product was co-extruded so that the thickness composition ratio was A/B/A = 2/27/2. Otherwise, the product was manufactured in the same manner as in Example 1 to obtain a polyester film roll.

[Comparative Example 2]
In Example 1, the extrusion conditions for the polyester raw material of the surface layer A in melt extrusion were set to a discharge rate of 250 kg/h and a screw rotation speed of 90 rpm, and the material was co-extruded so that the thickness composition ratio was A/B/A = 2.5/26/2.5. Otherwise, the manufacturing process was carried out in the same manner as in Example 1 to obtain a polyester film roll.

[Comparative Example 3]
In Example 1, the extrusion conditions for the polyester raw material of the surface layer A in melt extrusion were set to a discharge rate of 160 kg/h and a screw rotation speed of 57 rpm, and the extrusion was carried out in the same manner as in Example 1, except that the thickness composition ratio was A/B/A = 1.6/27.8/1.6. A polyester film roll was obtained.

[Comparative Example 4]
In Example 1, a raw material blend of polyester B at a mass ratio of 75% and polyester E at 25% was used as the raw material for surface layer A, and a raw material of 100% polyester C was used as the raw material for intermediate layer B. These materials were supplied to a vented extruder, and the extrusion conditions for the polyester raw material of surface layer A in melt extrusion were set to a discharge rate of 160 kg/h and a screw rotation speed of 56 rpm. Except for co-extrusion being performed so that the thickness composition ratio was A/B/A = 1.6/27.8/1.6, a polyester film roll was obtained in the same manner as in Example 1.

[Comparative Example 5]
In Comparative Example 4, the extrusion conditions for the polyester raw material of the surface layer A in melt extrusion were set to a discharge rate of 320 kg/h and a screw rotation speed of 110 rpm, and the co-extrusion was performed in the same manner as in Example 1, except that the thickness composition ratio was A/B/A = 3.1/24.8/3.1. A polyester film roll was obtained.

[Comparative Example 6]
In Example 1, a raw material blend of polyester A at a mass ratio of 87% and polyester F at a mass ratio of 13% was used as the raw material for surface layer A, a raw material of 100% polyester D was used as the raw material for intermediate layer B, and a raw material blend of polyester C at a mass ratio of 28%, polyester G at 22%, and polyester H at 50% was used as the raw material for surface layer C. These materials were supplied to a vented extruder and melt-extruded at 290°C. After melt-extrusion, an amorphous film was obtained by cooling and solidifying on a cooling roll set to a surface temperature of 40°C using a co-extrusion electrostatic application adhesion method, with surface layers A and C as the outermost layers (surface layers) and intermediate layer B as the intermediate layer. The thickness composition ratio of A/B/C was set to 4/25/2 under the extrusion conditions. At this time, the extrusion conditions for the polyester raw material of layer A during melt extrusion were set to a discharge rate of 160 kg/h and a screw rotation speed of 56 rpm.

Next, using the difference in roll peripheral speed, the film was stretched 3.4 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 85°C. This longitudinally stretched film was then guided to a tenter and stretched 4.6 times in the transverse direction, i.e., the TD direction, at 120°C. Heat treatment was then performed in heat treatment (fixing) zones 1 and 2 and cooling zones 3 and 4 within the tenter at 215°C, 205°C, 150°C, and 110°C, respectively. Finally, the film was wound into a roll on a 6-inch plastic core to obtain a polyester film roll with a thickness of 31 μm, which is the comparative example 6.
Table 1 shows the characteristics of the polyester film rolls obtained for each example and comparative example.

<Measurement and Evaluation Methods>
The measurement and evaluation methods used in the examples and comparative examples are as follows. The measurement and evaluation results are summarized in Table 1.

(1) Intrinsic viscosity (IV)
One g of polyester was accurately weighed, dissolved in 100 mL of a phenol/tetrachloroethane mixed solvent (50/50 by mass ratio), and its viscosity (IV) was measured at 30°C using a viscosity (IV) measuring device (VMS-022UPC-F10, manufactured by Rigosha Co., Ltd.).

(2) Average particle size and particle size distribution The powder was observed from the surface of the surface layer A side of the polyester film of the example and comparative example using a scanning electron microscope (HITACHI, "S3400N").
The size of a single particle was measured from the obtained image data, and the average value of 10 points was defined as the average primary particle size.
Furthermore, a dispersion with a solid content of 0.03 g/mL was prepared by adding a mixed solvent of phenol/tetrachloroethane = 2/3 (mass ratio) to the particles. Using a Microtrac-Bel "MT3300EXII" laser diffraction scattering method, the particle sizes D10 (where the cumulative number of particles reaches 10%), D50 (where the cumulative number of particles reaches 50%), and D90 (where the cumulative number of particles reaches 90%) were measured for this dispersion, and (D90 - D10) / D50 was calculated.

(3) Average surface roughness (Sa), maximum peak height (Sp), and average spacing between irregularities (RSm)
Using a surface roughness measuring instrument (AMETEK Co., Ltd., "NewView" registered trademark), the surface of the surface layer A of the polyester film rolls in the examples and comparative examples was measured, and the average surface roughness (Sa), maximum peak height (Sp), and average spacing between irregularities (RSm) were determined from the obtained surface profile curves.

(4) Measurement of the number of protrusions Using a white light interferometer (Contour), the surface of the surface layer A of the polyester film rolls of the examples and comparative examples was measured under the following measurement conditions, and the number of protrusions with a height of less than 50 nm, the number of protrusions with a height of 50 nm or more and less than 100 nm, and the number of protrusions with a height of 100 nm or more were measured.
(Measurement conditions)
• Measurement mode: VXI mode • Objective lens: 20x • Internal lens: 0.55x • Field of view: 586 μm × 460 μm

(5) Scratch Resistance Regarding scratches and defects on the film surface, the polyester rolls of the examples and comparative examples were used as A4-sized sample films, and it was checked whether scratches (fine scratches, scratch-like defects, granular patterns, etc.) could be visually recognized under "transmitted light under indoor three-wavelength fluorescent lamps" and "reflected light from a halogen lamp in a dark room". If scratches were found, their number was determined and judged according to the evaluation criteria below.
<Evaluation Criteria>
A: 0 to 4 scratches with a depth of 0.3 μm or more, which can be seen under transmitted light from a three-wavelength fluorescent lamp indoors or reflected light from a halogen lamp.
B: Five or more scratches with a depth of 0.3 μm or more that can be seen under transmitted light from a three-wavelength fluorescent lamp indoors or reflected light from a halogen lamp.

(6) Handling of lengthening of polyester film rolls When the polyester film rolls of the examples and comparative examples were wound into 12,000 m rolls, cases where no wrinkles or other defects occurred and lengthening was possible were judged as good "A", and cases where wrinkles or other defects occurred and lengthening was difficult were judged as poor "B".

The polyester film roll of Example 1, which contains organic particles with an average particle size of 0.05 to 0.4 μm, and whose average surface roughness (Ra), maximum peak height (Sp), and average spacing between irregularities (RSm) of one surface (A) of the polyester film satisfy the range of the present invention, has a fine irregular structure and, while maintaining the average surface roughness (Ra), has a large maximum peak height (Sp). Therefore, despite using relatively soft organic particles, it has good scratch resistance and allows for the production of longer polyester film rolls. Furthermore, since the polyester film roll of Example 1 satisfies the range of the present invention in terms of average surface roughness (Ra), maximum peak height (Sp), and average spacing between irregularities (RSm), when used in the manufacture of ceramic green sheets, it can prevent the green sheet from unintentionally peeling off from the polyester film in situations where peeling is not necessary, due to the increased contact area with the green sheet.
On the other hand, the polyester film rolls of Comparative Examples 1 to 6 did not meet the requirements of the present invention in terms of average surface roughness (Ra), maximum peak height (Sp), and average spacing of irregularities (RSm). Therefore, they were found to be inferior in at least one of the following aspects: scratch resistance and suitability for long-length polyester film rolls, making them unsuitable for use in the manufacture of ceramic green sheets.

Furthermore, in Example 1, where the extrusion conditions for surface layer A were such that the discharge rate Q kg/h was 150 kg/h or less and Q/N satisfied the range of formula (A) described above, the average surface roughness (Ra), maximum peak height (Sp), and average spacing between irregularities (RSm) satisfied the range of the present invention, and the resulting polyester film roll exhibited excellent scratch resistance and could be made into a long roll.
On the other hand, in the extrusion conditions for surface layer A, the polyester film rolls of Comparative Examples 1 to 6, where the discharge rate Q kg/h exceeded 150 kg/h, could not achieve the average surface roughness (Ra), maximum peak height (Sp), and average spacing between irregularities (RSm) within the range of the present invention, resulting in polyester film rolls that were inferior in scratch resistance and suitability for long lengths.

The polyester film roll of the present invention has fine irregularities, providing excellent scratch resistance, and offers the advantage of being able to accommodate longer lengths of polyester film rolls as productivity improves. Furthermore, when used as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, it is possible to form a uniform thin dielectric layer. In particular, it can be suitably used as a support for ceramic green sheets used in multilayer ceramic capacitors for automobiles.

Claims (8)

A polyester film roll made by winding up polyester film,
The polyester film is a polyester film having a laminated structure with two or more layers.
The polyester film contains organic particles with an average particle size of 0.05 to 0.4 μm.
A polyester film roll in which one surface (A) of the polyester film satisfies the following conditions (1) to (3).
(1) The average surface roughness (Sa) is 5 to 20 nm.
(2) The maximum peak height (Sp) is 310 nm or more.
(3) The average spacing between irregularities (RSm) is 0.016 mm or less. The polyester film roll according to claim 1, wherein the polyester film is a three-layer polyester film. The polyester film roll according to claim 1 or 2, wherein the surface layer (A) forming one surface ( A ) of the polyester film contains the particles. The polyester film roll according to claim 2 or 3, wherein the intermediate layer of the polyester film contains 50% by mass or more of recycled polyester raw material. A polyester film roll according to any one of claims 1 to 4, wherein the polyester film has a release layer on one surface (A). A polyester film roll according to any one of claims 1 to 5, used as a support for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor. A polyester film roll according to any one of claims 1 to 6, used as a support for a ceramic green sheet in the manufacturing process of an automotive ceramic capacitor. A method for manufacturing a polyester film roll obtained by winding up a polyester film,
The polyester film contains organic particles with an average particle size of 0.05 to 0.4 μm.
The aforementioned polyester film is a three-layer polyester film.
A method for manufacturing a polyester film roll, wherein, in the extrusion conditions for the surface layer (A) that forms one surface (A) of the polyester film, the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) is 150 kg/h or less, and the ratio Q/N of the discharge rate Q kg/h of the polyester raw material constituting the surface layer (A) to the screw rotation speed N rpm satisfies the following formula (A).
2.5≦Q/N≦3.0 (A)