JP7809964B2 - Polyester film roll and method for producing polyester film roll - Google Patents

Description

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

In recent years, with the increasing use of electrical equipment in automobiles and the increasing functionality of smartphones, multi-layered ceramic capacitors (MLCCs) have become smaller and have higher capacities.
The multilayer ceramic capacitor is manufactured as follows.
First, a ceramic slurry containing ceramic components and a binder resin is applied to a release film and dried to produce a ceramic green sheet (dielectric sheet), which is then printed with electrodes by screen printing or the like to form internal electrodes. After drying, the printed ceramic green sheet is peeled off from the release film and multiple such green sheets are stacked. The stacked green sheets are pressed together and then cut into individual chips.
Thereafter, the internal electrodes and dielectric layers are sintered in a firing furnace to produce a multilayer ceramic capacitor.

As MLCCs become smaller and have higher capacities, ceramic green sheets are becoming thinner. However, when ceramic green sheets are further thinned to 0.5 μm (thickness after drying) or less, any tiny protrusions on the surface of the release film used as a carrier film can cause pinholes and other defects in the ceramic green sheets. For this reason, release films are required to have even higher levels of surface smoothness.

Conventionally, as a support for this type of release film, Patent Document 1 discloses a release film for producing a green sheet, which comprises 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 surface of the smoothing layer opposite the substrate, wherein the smoothing layer is formed by heating and curing a composition for forming a smoothing layer that contains a thermosetting compound having a weight average molecular weight of 950 or less, and wherein 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 having excellent surface smoothness and particularly few fine defects on the film surface, in which the number of depression defects having a depth of 0.5 μm or more is 5/ ^m2 or less, and the center line average roughness SRa of the surface of at least one side 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 obtained by winding a polyester film, in which the number of slack defects present in the polyester film is less than 5 per 100 m ² .

JP 2014-177093 A JP 2013-7054 A JP 2018-90803 A

However, the inventors' investigations have revealed that in the polyester film manufacturing process, particles in the polyester resin sometimes aggregate during the melt extrusion process. In particular, when organic particles are used, the tendency for particles to aggregate is pronounced, and it has been found that the dispersion state of the particles in the polyester raw material prior to the melt extrusion process is not maintained. Furthermore, in conventional film surface design, the formation of fine irregularities on the film surface has been controlled by adjusting the type, average particle size, and amount of particles used. However, as ceramic green sheets become thinner, more precise control is required.
Therefore, there is a need for polyester films that allow for precise design of the film surface texture, minimize loss during raw material changeover, enable long-term continuous production, and contribute to improved productivity.

The object of the present invention is to provide a new polyester film roll and a method for producing the same, in which the fine irregularities on the polyester film surface are precisely controlled, resulting in high smoothness, reduced loss due to raw material switching, long-term continuous production possible, and improved productivity.

In view of the above-mentioned circumstances, the present inventors have conducted extensive research and found that the above-mentioned problems can be easily solved by using a polyester film roll having a specific configuration, and have thus completed the present invention. That is, the present invention provides the following items [1] to [9].
[1] A polyester film roll obtained by winding up 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 300 nm or less.
(3) The average spacing (RSm) of the irregularities 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 materials.
[5] The polyester film roll according to any one of [1] to [4], wherein the polyester film has a release layer on one surface (A).
[6] The polyester film roll according to any one of [1] to [5], which is used as a support for a ceramic green sheet in a manufacturing process of a multilayer ceramic capacitor.
[7] The polyester film roll according to any one of [1] to [6], which is used as a support for a ceramic green sheet in a manufacturing process of an automotive ceramic capacitor.
[8] A method for producing a polyester film roll obtained by winding up a polyester film, wherein the polyester film contains organic particles having an average particle size of 0.05 to 0.4 μm, the polyester film is a three-layer polyester film, and under extrusion conditions for a surface layer (A) of the polyester film, 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)
[9] The method for producing a polyester film roll according to [8], wherein the discharge rate Q of the polyester raw material constituting the surface layer (A) is 180 kg/h or more.

According to the present invention, it is possible to provide a polyester film roll having a high smoothness with precisely controlled fine unevenness on the surface of the polyester film, reducing loss due to raw material switching, enabling long-term continuous production, and improving productivity, and a method for producing the same.
Furthermore, since the polyester film roll of the present invention has extremely excellent surface smoothness, when used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor, for example, it has the advantage that there is little risk of defects occurring in the ceramic green sheet due to fine irregularities on the surface of the polyester film roll of the present invention.

Furthermore, it has been found that the method for producing a polyester film roll of the present invention differs from conventional production methods in that the uneven shape of the film surface can be precisely controlled by adjusting the production conditions.
In particular, in the case of a multi-layer polyester film, it has been found that by increasing the discharge rate of the polyester raw material constituting the surface layer A in the solution extrusion process, the time required for the polyester raw material to move within the extruder during the melt extrusion process (residence time) can be shortened, thereby suppressing the aggregation of particles in the polyester raw material.

Furthermore, the tendency for unevenness to form on the polyester film surface varies 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 as the amount of polyester resin discharged increased.
On the other hand, the inventors' investigations revealed that by using organic particles having a specific particle size, the Sp value of the film surface decreases when the discharge amount of the polyester raw material is increased, which is a behavior completely different from conventional behavior.
Therefore, when producing a multi-layer polyester film, the polyester film manufacturing method of the present invention combines adjustment of the discharge rate of the polyester raw material that constitutes the surface layer in the melt extrusion process as a new elemental technology for controlling the fine unevenness of the film surface, thereby offering the following excellent advantages: 1) it is no longer necessary to use a polyester raw material that contains specially designed particles, and 2) it is no longer necessary to use multiple polyester raw materials whose average particle size and particle addition amount have been adjusted in advance before adjusting the fine unevenness of the film surface.
In particular, by reducing the changeover loss that occurs when different types of raw materials are used in the manufacturing process, further continuous production becomes possible, which greatly contributes to improving productivity.

As described above, the polyester film roll and polyester film roll manufacturing method of the present invention not only take a conventional approach to controlling the surface shape of polyester film from the perspective of materials such as polyester raw materials, but also combine it with a new elemental technology, namely, adjusting the discharge rate of the polyester raw materials that make up the surface layer during the melt extrusion process, thereby enabling more precise control of the uneven shape of the film surface. In particular, the present invention proposes a film with a fine yet precise uneven shape and a manufacturing method thereof that can be used even in situations where thin-film green sheets with a thickness (after drying) of 0.5 μm or less are required to be molded in the manufacture of multilayer ceramic capacitors.

The graph shows the relationship between shear stress calculated from the intrinsic viscosity (IV) of the polyester and shear rate. The image diagram shows the (estimated) particle dispersion mechanism in polyester resin. 1 shows the particle distribution on one surface (A) of the polyester film obtained in Example 2. 1 shows the particle distribution on one surface (A) of the polyester film obtained in Comparative Example 1. 1 shows the particle distribution on one surface (A) of the polyester film obtained in Comparative Example 2.

The present invention is described in detail below. In this specification, the term "A to B" used to describe numerical values means "A or more and B or less" (when A<B) or "A or less and B or more" (when A>B). Furthermore, in the present invention, a combination of preferred 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 up a polyester film, characterized in that 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 300 nm or less.
(3) The average spacing (RSm) of the irregularities is 0.016 mm or less.

In the polyester film roll of the present invention, one surface (A) of the polyester film refers to the side on which a ceramic green sheet is laminated when the polyester film is used as a support for the ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor. By simultaneously satisfying the above (1) to (3) on one surface (A) of the polyester film, multilayer capacitors can be manufactured in an optimal state. Furthermore, from the perspective of using the polyester film as a support for the ceramic green sheet, one surface (A) of the polyester film is also suitable as a surface on which a release layer, described below, is provided.

The polyester film roll of the present invention (hereinafter also referred to as "the present roll") is obtained by winding up a polyester film (hereinafter also referred to as "the present film").
The roll is a polyester film roll wound around a core such as a paper tube, metal tube, or plastic tube, and has a width of preferably 0.2 m or more, more preferably 0.3 m or more, particularly preferably 1.0 m or more, and most preferably 1.5 m or more. The upper limit of the film width is not particularly limited, but from the viewpoint of handleability, it is preferably 2.3 m or less, more preferably 2.0 m or less.
The length of the present film wound onto the present 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 the present film is preferably 19 μm or more and 38 μm or less, more preferably 25 μm or more and 32 μm or less.

<Polyester film>
(Surface properties)
In the present invention, 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 is required to satisfy the following (1) to (3):
(1) The average surface roughness (Sa) is 5 to 20 nm.
(2) The maximum peak height (Sp) is 300 nm or less.
(3) The average spacing (RSm) of the irregularities 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.
If the average surface roughness (Sa) of one surface (A) of the polyester film is greater than 20 nm, defects such as pinholes are likely to occur due to minute irregularities on the polyester film surface. On the other hand, if the average surface roughness (Sa) is less than 5 nm, the film surface becomes too flat, reducing the film's slipperiness and making it more susceptible 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 viewpoints of enabling thinning of ceramic layers in the production of multilayer ceramic capacitors and the like, suppressing the occurrence of pinholes, and suppressing a decrease in the slipperiness of the film.

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. It is obtained by dividing the volume of the area enclosed by the surface shape curve and the average surface by the measured area, and is calculated using the following formula (1):
When the surface is the XY plane and the height direction is the Z axis, A is the defined area (the entire image), and Z(x, y) is the height of the image point (x, y) from the surface at height 0, it can be expressed as in the following equation (1).

(2) Maximum peak height on film surface (Sp)
In the present invention, the maximum peak height (Sp) of one surface (A) of the polyester film must be 300 nm or less. If the maximum peak height (Sp) of one surface (A) of the polyester film is greater than 300 nm, defects such as pinholes are likely to occur due to minute irregularities on the polyester film surface.
In the present invention, the maximum peak height (Sp) on one surface (A) of the polyester film is preferably 250 nm or less, more preferably 200 nm or less, from the viewpoint of suppressing the occurrence of pinholes. The lower limit of the maximum peak height (Sp) is not particularly limited, but is preferably 50 nm or more, more preferably 80 nm or more, even more preferably 100 nm or more, and even more preferably 120 nm or more, from the viewpoint of improving the winding property of the polyester film.

The maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178) and represents the maximum height from the mean plane of the surface, and is expressed by the following formula (2):

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 less, more preferably 18 or less, and even more preferably 16 or less.
By setting the relationship Sp/Sa between the average surface roughness (Sa) and the maximum peak height (Sp) to 20 or less, the average surface roughness (Sa) can be adjusted to a high state while the maximum peak height (Sp) is relatively low, making it easy to form thin film green sheets.
Furthermore, the lower limit of the relationship Sp/Sa between the average surface roughness (Sa) and the maximum peak height (Sp) is not particularly limited, but from the viewpoint of adjusting the balance between high Sa and low Sp, it is preferably 5 or more, and more preferably 8 or more.

(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 must be 0.016 mm or less. By having the average spacing (RSm) of the irregularities on one surface (A) of the polyester film be 0.016 mm or less, a film surface with good reproducibility of the irregularities can be obtained.
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, more preferably 0.014 mm or less. Although there is no particular lower limit for the average spacing (RSm) of the irregularities, from the viewpoint of compatibility with thin film green sheet forming processing, it is preferably 0.010 mm or more, more preferably 0.012 mm or more, and even more preferably 0.013 mm or more.

In the present invention, the average spacing between irregularities (RSm) is measured in accordance with JIS B0601:2013 and is expressed as the average of the lengths Xs of the profile curve elements over the reference length, as shown in the following formula (3).

The surface properties of one surface (A) of the polyester film of the present invention can be adjusted, for example, by incorporating particles into the polyester layer that constitutes the film surface and adjusting the average particle size, particle type, and content of the particles, and further by controlling the amount of polyester raw material extruded for the surface layer during the production of the polyester film roll.

(Organic particles contained in polyester film)
In the present invention, the polyester film must contain organic particles having an average particle size of 0.05 to 0.4 μm. By containing organic particles having an average particle size of 0.05 to 0.4 μm, it is possible to ensure the surface smoothness of a ceramic green sheet when producing 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 it is produced.

The average particle size of particles can be determined by measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and taking the average value. In the case of non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each 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, and organic particles such as calcium oxalate and ion exchange resins.
Specific examples of organic particles include crosslinked polymer particles, and examples of crosslinked polymer particles by composition include crosslinked polymer particles such as divinylbenzene polymer, ethylvinylbenzene-divinylbenzene copolymer, styrene-divinylbenzene copolymer, styrene-ethylvinylbenzene-divinylbenzene copolymer, ethylene glycol dimethacrylate polymer, styrene-ethylene glycol dimethacrylate copolymer, methyl methacrylate-divinylbenzene copolymer, etc. Furthermore, crosslinked polymer particles composed of a system of three or more components may also be used.

As the organic particles, it is preferable to use organic particles having a narrow particle size distribution and a substantially uniform average particle size (so-called monodispersity).
By containing monodisperse organic particles, it is possible to obtain a polyester film having high surface smoothness, in particular, a high average surface roughness (Sa) of one surface (A) of the polyester film (moderately roughened), and yet a small maximum peak height (Sp), while maintaining the handleability of the polyester film roll.

As the organic particles having a narrow particle size distribution and a substantially uniform average particle size, when the particle size distribution is such that the particle size at which the cumulative number is 10% is D10, the particle size at which the cumulative number is 50%, and the particle size at which the cumulative number is 90%, D90, the ratio (D90-D10)/D50 is preferably 0.4 or less, and particularly preferably 0.2 or less.
The relational expression (D90-D10)/D50 indicates the variation in particle size based on D50, and particles with a (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 extremely high smoothness to the present film while maintaining excellent handleability.
The particle size distribution of the particles is measured by a laser diffraction measuring device.

In the present invention, from the viewpoint of improving handleability, the organic particle content in the polyester film is preferably 900 ppm or more by mass, more preferably 2000 ppm or more and 10000 ppm or less, even more preferably 2500 ppm or more and 9500 ppm or less, and even more preferably 3000 ppm or more and 9000 ppm or less.

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

In the present invention, it is preferable to use a polyester that contains more than 50 mol% of aromatic dicarboxylic acid or aliphatic dicarboxylic acid, assuming the dicarboxylic acid component is 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 polycondensing an aromatic dicarboxylic acid with an aliphatic glycol.
Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol.
Typical examples of polyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN).

On the other hand, when the polyester is a copolymer polyester, it is preferably a copolymer containing 30 mol % or less of a third component, which is a component other than the compound that is the main component of the dicarboxylic acid component constituting 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 the dicarboxylic acid component of the copolymer polyester include one or more of isophthalic acid, terephthalic acid phthalate, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid.
Examples of the glycol component of the copolymer polyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

Furthermore, the above-mentioned polyester is preferably polyethylene terephthalate, in which 80 mol % or more, preferably 90 mol % or more, is ethylene terephthalate unit, or polyethylene-2,6-naphthalate, in which ethylene-2,6-naphthalate unit is.

<Polyester polycondensation catalyst>
Examples of polycondensation catalysts used in polycondensing the polyester include antimony compounds, germanium compounds, aluminum compounds, titanium compounds, etc. Among these, at least one of antimony compounds and titanium compounds is preferred, and it is particularly preferred to use a polyester obtained using a titanium compound.
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 titanium compound, the number of metal-containing aggregates, so-called coarse foreign matter, derived from the titanium compound in the film can be reduced, and a film having high surface smoothness, particularly 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 the present film (also called the "surface layer", for example, one surface (A) of the polyester film, or the surface layer onto which the release layer is laminated) uses a titanium compound as its polycondensation catalyst.
The content of titanium element derived from the titanium compound in the outermost layer is preferably 3 ppm or more and 40 ppm or less, and more preferably 4 ppm or more and 35 ppm or less.
Within the above range, the amount of catalyst-induced foreign matter can be reduced without reducing the production efficiency of polyester.
When the polyester film is a laminated polyester film, it is preferable from the viewpoint of productivity that the polyester constituting the intermediate layer described below does not use a titanium compound as a polycondensation catalyst.
From the same viewpoint, the content of antimony compounds in the outermost layer of the present film is preferably 100 ppm or less.
For example, the surface layer A described below preferably contains at least one of an antimony compound and a titanium compound, and the content of the antimony compound in the surface layer A is preferably 100 ppm or less. In this case, the surface layer A does not necessarily need to contain the 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 more, more preferably 0.55 dl/g or more, and even more preferably 0.60 dl/g or more.
In the present invention, by using a polyester having an intrinsic viscosity (IV) of 0.50 dL/g or more as the polyester constituting the polyester film, the shear stress during kneading of the polyester is increased, particles in the polyester resin are easily dispersed, and the surface properties of one surface (A) of the polyester film can be easily adjusted to 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.

From the same viewpoint as above, when the polyester film of the present invention has a laminate structure, the intrinsic viscosity (IV) of the polyester constituting the surface layer, specifically the outermost layer of the present film (for example, one surface (A) of the polyester film, the surface layer on which a release layer is laminated) 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. Furthermore, 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.

Note that when two or more polyesters with different intrinsic viscosities (IV) are used, the "intrinsic viscosity (IV) of the polyester constituting the film" refers to the intrinsic viscosity (IV) of the mixed resins.

(Structure 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, more preferably a three-layer polyester film, 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 has a laminated structure having two or more layers, it is preferable that one surface layer A contains the above-mentioned organic particles. Here, the one surface layer A is the surface layer that forms one surface (A) of the polyester film of the present invention, and in a laminated polyester film, by having one surface layer A contain the above-mentioned particles, it is easy to control the surface characteristics of one surface (A) of the polyester film within the above-mentioned range. Furthermore, the present film may have surface layers A containing particles on both surfaces, or one surface may be surface layer A and the other surface may be surface layer C, described below. It is preferable that surface layer C contains particles.

<Polyester film laminate structure>
In the present invention, when the polyester film is a laminated polyester having two or more layers, a three-layer structure, such as an A/B/C structure consisting of an intermediate layer B and a surface layer A and a surface layer C, or an A/B/A structure consisting of an intermediate layer B and a surface layer A, is preferred, and a three-layer structure, such as an A/B/A structure, is more preferred.

When the polyester film has a three-layer structure of A/B/C, the surface layer C preferably has an average surface roughness (Sa) and a maximum peak height (Sp) equal to or less than those of the surface layer A. Preferably, the surface layer C has an average surface roughness (Sa) of 5 nm or more or a maximum peak height (Sp) of 220 nm or less. In this case, the surface layer C may have an average surface roughness (Sa) of approximately 20 nm or less.
By adopting such a laminated structure, the surface layer C can be provided with a rough surface necessary for improving handling, and the surface layer A can be provided with the smoothness necessary for providing a thin ceramic layer.

In the three-layer structure of A/B/C and A/B/A, the surface layer A and the surface layer C preferably contain particles to ensure ease of handling.
In the above-mentioned three-layer structure of A/B/C and A/B/A, the particles used in each of the surface layer A, intermediate layer B, and surface layer C can be similar to the organic particles contained in the polyester film described above, and the preferred ranges of the average particle size, particle size distribution, etc. are also similar.

The content of the particles in the surface layer A is preferably 900 ppm or more and 6000 ppm or less, more preferably 900 ppm or more and 4000 ppm or less, and even more preferably 900 ppm or more and 3000 ppm or less, in terms of responding to thinning of ceramic layers during the production of multilayer ceramic capacitors and the like, suppressing the occurrence of pinholes, and suppressing a decrease in the slipperiness of the film, in terms of mass ratio.
The content of the particles in the surface layer C is preferably less than 5000 ppm, more preferably 2000 ppm to 4000 ppm by mass, from the viewpoint of improving the handleability of the polyester film roll.

The intermediate layer B preferably functions as the thickest main layer, and in order to reduce costs, it preferably contains substantially no particles or at least a lower concentration of particles than the surface layer A.
The phrase "substantially not containing" means that the particles are not intentionally contained, 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, and specific examples include layers with different particle types, average particle sizes, and blending amounts, as well as layers with different layer thicknesses.

In the present invention, the intermediate layer B of the polyester film preferably contains recycled polyester raw materials in an amount of 50% by mass or more, 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 materials in the intermediate layer B in the above range, for example, _CO2 emissions can be reduced, which can contribute to reducing the burden on the environment.

In the polyester film roll of the present invention, it is particularly preferable that the polyester film has a surface layer A and/or a surface layer C shown in the following (X) and (Y).
By adopting such a configuration, the polyester film can have excellent handling properties and surface smoothness.

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

In the above (X), by using polyester polycondensed using a titanium compound as a catalyst in both surface layer A and surface layer C, it is possible to reduce catalyst-induced foreign matter and achieve high surface smoothness.

(Y) Particularly preferred embodiment 2
(1) In the A/B/A structure, the surface layer A contains particles such that (D90-D10)/D50 is 0.4 or less, where D10 is the particle diameter at which the cumulative number is 10%, D50 is the particle diameter at which the cumulative number is 50%, and D90 is the particle diameter at which the cumulative number is 90%. (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 polyester constituting the surface layer A has an intrinsic viscosity (IV) of 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 (Y) above, the surface layer A contains particles with a substantially uniform average particle size, more specifically, particles such that (D90-D10)/D50 is 0.4 or less, where D10 is the particle size at which the cumulative number reaches 10%, D50 is the particle size at which the cumulative number reaches 50%, and D90 is the particle size at which the cumulative number reaches 90%. This allows the film to maintain handleability while maintaining high surface smoothness, and in particular, a small maximum peak height (Sp) on at least one side.

(Method for producing polyester film)
An example of a method for producing the present film will be described below.
First, using a known method, raw materials, such as polyester chips, are fed into an extruder and heated to above the melting point of each polymer, the molten polymer is extruded through a die, and cooled and solidified on a rotating cooling drum to a temperature below the glass transition point of the polymer, thereby obtaining an unoriented sheet in a substantially amorphous state.

Next, the unoriented sheet is stretched in one direction using a roll or tenter-type stretching machine. 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.

Then, the film is stretched in a direction perpendicular to the first-stage stretching direction. The stretching temperature is typically 50 to 140°C, and the stretch ratio is typically 3.0 to 7 times, preferably 4.5 times or more, and more preferably 4.5 to 5.0 times.

Subsequently, the polyester film of the present invention is heat-set at a temperature of 180 to 220°C under tension or relaxation of 30% or less to obtain a biaxially oriented film. This heat-set may be performed in two or more steps at different temperatures.
After the heat setting 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 resin constituting the polyester film, more specifically, preferably in the range of 100 to 160° C. This cooling may be performed in two or more steps at different temperatures.
In the above-mentioned stretching, a method of performing unidirectional stretching in two or more stages can also be employed.

In the present invention, when the polyester film is the three-layer polyester film 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. The diameter (cylinder inner diameter) D mm of the twin-screw extruder used in the present invention is not particularly limited. The length L mm of the twin-screw extruder used in the present invention is preferably 20 × D to 50 × D, 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 raw polyester in the twin-screw extruder is not too long, and thermal degradation of the raw polyester is easily suppressed. Furthermore, when L is 20 D or more, the raw polyester is sufficiently plasticized, enabling stable melt extrusion.

In the present invention, when the polyester film is the above-described three-layer polyester film, the method for producing a polyester film roll of the present invention is characterized in that the polyester film contains the above-described organic particles having an average particle size of 0.05 to 0.4 μm, and when the polyester film is the above-described three-layer polyester film, the extrusion conditions for the surface layer (A) of the polyester film are such that 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 satisfying the range of the above formula (A), the screw rotation speed can be set to an appropriate range for the extrusion amount of the polyester resin, the degree of renewal of the molten resin surface under vacuum is appropriately achieved, and sufficient degassing can be performed, thereby enabling the molding of a desired polyester film. From the same viewpoint as above, it is more preferable that the ratio Q/N of the extrusion 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 (B).
2.8≦Q/N≦3.0...(B)

Furthermore, when forming a polyester film, in the step of melt-extruding a polyester raw material, the residence time of the polyester raw material in the melt-extrusion step can be reduced by intentionally increasing the discharge amount Q of the surface layer (A) after satisfying the above formula (A) or formula (B).
Therefore, the discharge rate Q of the polyester raw material constituting the surface layer (A) is preferably 180 kg/h or more, more preferably 200 kg/h or more, even more preferably 220 kg/h or more, and even more preferably 240 kg/h or more.
By setting the discharge rate Q of the polyester raw material constituting the surface layer (A) to 180 kg/h or more, aggregation of particles in the polyester raw material can be suppressed, and the surface properties of one surface (A) of the polyester film can be more easily adjusted to the desired range.
The upper limit of the discharge rate Q of the polyester raw material constituting the surface layer (A) is preferably 300 kg/h or less, more preferably 280 kg/h or less, from the viewpoint of controlling particle dispersibility.

In the present invention, the mechanism by which particles are dispersed in the polyester raw material during the melt extrusion process of the polyester raw material is presumed to be as follows.
The present inventors have focused on the relationship between shear stress calculated from the intrinsic viscosity (IV) of polyester and shear rate, as shown in Figure 1. As a result, it has been found that the shear stress tends to increase as the shear rate increases.
Next, we considered particle dispersibility during the melt extrusion process. First, the polyester resin is subjected to shear stress by the extruder screw while in a semi-molten state. Furthermore, as the discharge rate of the polyester raw material increases, the shear rate also increases. As a result, greater shear stress can be applied to the particles in the polyester resin, which disperses the particles in the polyester resin (matrix resin) as shown in Figure 2. This prevents the particles from agglomerating during the melt extrusion process, and we believe that the particles are extruded from the die while maintaining a good dispersion state.

In the method for producing a polyester film roll of the present invention, by setting the extrusion conditions for the polyester raw material constituting the surface layer (A) as described above, it is possible to achieve a smaller maximum peak height (Sp) that was previously difficult to achieve while maintaining a 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 surface.
The release layer is preferably laminated on one surface (A) of the polyester film.
That is, in the polyester film roll of the present invention, it is preferable that one surface (A) of the polyester film has a release layer.
Therefore, for example, in the case of an A/B/C structure, a release layer is laminated on the surface of the surface layer A, resulting in a structure of release layer/A/B/C. Also, in the case of an A/B/A structure, a release layer is laminated on the surface of one surface layer (A), resulting in a structure of release layer/A/B/A.
By laminating a release layer on one surface (A) of the polyester film, pinholes and the like are less likely to occur when an ultrathin ceramic layer is laminated on the release layer to form a green sheet, which is preferable.

The release layer is laminated to the polyester film directly or via another layer.
Examples of other layers include an easy-adhesion coating layer for improving adhesion to the present film, an antistatic layer, an antiblocking layer, and the like.

The 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 that the release agent composition contains a type that contains a curable silicone resin as the main component, a modified silicone type obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin, or a fluorosilicone resin.

The curable silicone resin may be any of the existing curing reaction types, such as a heat-curable type (addition type, condensation type, etc.) or an electron beam-curable type (ultraviolet curable type, etc.), and a plurality of types of curable silicone resins may be used in combination.
Furthermore, there are no particular limitations on the form in which the curable silicone resin is applied when forming the release layer, and it may be in the form of a solution in an organic solvent, in the form of a water-based emulsion, or in a solventless form.

The release agent composition that forms the release layer may also contain binders, antifoaming agents, coatability improvers, thickeners, inorganic or organic particles, organic lubricants, antistatic agents, conductive agents, UV absorbers, antioxidants, foaming agents, dyes, pigments, and the like, as needed.

The release layer is formed by coating the film with a release agent composition. This can be done either in-line during the film production process, or off-line, where the release agent composition is applied outside the system onto a film that has already been produced.

Methods for providing a release layer on this film include conventional coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating.

There are no particular restrictions on the curing conditions when forming the release layer. When forming the release layer by offline coating, it is usually 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.

If necessary, the heat treatment may be combined with irradiation with active energy rays such as ultraviolet rays.
As the energy source for curing by irradiation with active energy rays, known devices and energy sources can be used.

From the viewpoint of coatability, the coating amount (after drying) of the release layer is usually in the range of 0.005 to 5 g/m ² , preferably 0.005 to 1 g/m ² , and more preferably 0.005 to 0.1 g/m ^2. If the coating amount (after drying) is less than 0.005 g/m ² , the coating may lack stability from the viewpoint of coatability, making it difficult to obtain a uniform coating film.

On the other hand, if the coating is thicker than 5 g/m ² , the coating adhesion and curing properties of the release layer itself may be reduced.

The coating amount is calculated from the liquid mass per coating time (before drying), the non-volatile concentration of the coating liquid, 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 production of ceramic green sheets for multilayer ceramic capacitors. In release and process applications, the film is used, for example, as a support, onto which various materials such as ceramic slurries can be applied or laminated.

In particular, as mentioned above, the polyester film roll of the present invention has excellent smoothness while also contributing to improved productivity, making it suitable for use as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

Furthermore, in the future, as the use of electrical equipment in automobiles increases, it is predicted that the ceramic green sheets used will become thinner, particularly as the capacitors become smaller and their capacitance increases.
Therefore, 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 explained in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

<Production of Polyester>
(1) Production of 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 polyester obtained.
Thereafter, the temperature was raised to 225°C under normal pressure over 3 hours, and the mixture was further stirred and maintained at 225°C for 1 hour and 15 minutes while distilling off methanol to carry out an ester exchange reaction, which essentially ended the ester exchange reaction and gave a polyester oligomer.

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

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.

(2) Production of Polyester B The above 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 having an intrinsic viscosity (IV) of 0.63 dl/g was obtained in the same manner as Polyester A, except that instead of adding tetrabutyl titanate in Polyester A, antimony trioxide was added as a polycondensation catalyst so that the amount of antimony atoms was 300 ppm by mass based on the polyester resin content obtained.

(4) Production of Polyester D Polyester D having an intrinsic viscosity (IV) of 0.63 dl/g was obtained in the same manner as in Polyester A, except that tetrabutyl titanate was added so that the titanium atom content was 210 ppm by mass relative to the polyester obtained.

(5) Production of Polyester E To the above-mentioned Polyester D containing substantially no particles, 1.0% by mass ((D90-D10)/D50=0.27) of monodispersed spherical silica having an average primary particle size of 0.5 μm was added, and the mixture was kneaded using a vented twin-screw kneader to obtain Polyester E.

(6) Production of Polyester F Polyester F was obtained by adding 0.75% by mass of alumina particles having an average primary particle size of 0.05 μm to the above-mentioned Polyester D containing substantially no particles, and kneading the mixture using a vented twin-screw kneader.

(7) Production of Polyester G Polyester G was obtained by kneading 2.0% by mass of calcium carbonate particles having an average primary particle size of 0.7 μm into the above-mentioned Polyester D containing substantially no particles using a vented twin-screw kneader.

(8) Production of Polyester H 1.0% by mass of organic particles having an average primary particle size of 0.3 μm ((D90−D10)/D50=0.46: divinylbenzene-ethylstyrene-methacrylic acid-styrene copolymer) was added to the above-mentioned Polyester D containing substantially no particles, and the mixture was kneaded using a vented twin-screw kneader to obtain Polyester H.

(9) Production of Polyester I 0.5% by mass of organic particles (divinylbenzene-ethylstyrene-methacrylic acid-styrene copolymer) having an average primary particle size of 2 μm was added to the above-mentioned Polyester D containing substantially no particles, and the mixture was kneaded using a vented twin-screw kneader to obtain Polyester I.

[Example 1]
A raw material for the surface layer A was a blend of 70% Polyester D and 30% Polyester H by mass, and a raw material for the intermediate layer B was a 100% Polyester D raw material. These were fed into a vented extruder and melt-extruded at 290°C. The raw material for the surface layer A was then split into two layers, with the outermost layer (surface layer) and the intermediate layer B as the intermediate layer, resulting in a two-kind, three-layer (A/B/A) layer structure. The extrusion conditions for the thickness composition ratio A/B/A = 2/27/2 were coextrusion using an electrostatically applied adhesion method, and the resulting mixture was cooled and solidified on a cooling roll with a surface temperature set at 40°C to obtain an amorphous film. The extrusion conditions for the polyester raw material for layer A in the melt-extrusion were a throughput of 200 kg/h and a screw rotation speed of 71 rpm.

The film was then stretched 3.4 times in the machine direction (MD direction) at a film temperature of 85°C using the difference in roll peripheral speed. After this, the machine-stretched film was introduced into a tenter and stretched 4.6 times in the transverse direction (TD direction) at 120°C. It was then heat-treated at 215°C, 205°C, 150°C, and 110°C in heat treatment (fixing) zones 1 and 2 and cooling zones 3 and 4 within the tenter, respectively. The film was then wound up into a roll around a 6-inch plastic core, yielding a polyester film roll with a thickness of 31 μm.

[Example 2]
A polyester film roll was obtained by the same production method as in Example 1, except that the thickness of each layer was changed and the extrusion conditions of the polyester raw material for the surface layer A in the melt extrusion were a discharge rate of 250 kg/h and a screw rotation speed of 90 rpm.

[Comparative Example 1]
A polyester film roll was obtained by the same production method as in Example 1, except that the thickness of each layer was changed and the extrusion conditions of the polyester raw material for the surface layer A in the melt extrusion were changed to a discharge rate of 160 kg/h and a screw rotation speed of 57 rpm.

[Comparative Example 2]
In Example 1, a raw material for the surface layer A was a blend of 75% Polyester B and 25% Polyester E by mass, and a raw material for the intermediate layer B was a raw material containing 100% Polyester C. These were fed into a vented extruder, and the extrusion conditions for the polyester raw material for the surface layer A in the melt extrusion were a discharge rate of 160 kg/h, a screw rotation speed of 56 rpm, and co-extrusion so that the thickness composition ratio was A/B/A = 1/29/1. A polyester film roll was obtained in the same manner as in Example 1, except that the raw material for the surface layer A was a blend of 75% Polyester B and 25% Polyester E by mass, and the raw material for the intermediate layer B was a 100% Polyester C.

[Comparative Example 3]
In Comparative Example 2, a polyester film roll was obtained in the same manner as in Example 1, except that the extrusion rate of the polyester raw material for the surface layer A in the melt extrusion was set to 320 kg/h and the screw rotation speed was set to 110 rpm.

[Comparative Example 4]
In Example 1, a raw material for surface layer A was a blend of 87% Polyester A and 13% Polyester F by mass, a raw material for intermediate layer B was a blend of 100% Polyester D, and a raw material for surface layer C was a blend of 28% Polyester C, 22% Polyester G, and 50% Polyester H by mass. These raw materials were fed into a vented extruder and melt-extruded at 290°C. A polyester film roll was obtained in the same manner as in Comparative Example 2, except that the raw materials were co-extruded to form a three-type, three-layer (A/B/C) structure in which surface layer A and surface layer C were the outermost layers (surface layers) and intermediate layer B was the intermediate layer, with the thickness composition ratio of A/B/C being 4/25/2 under the extrusion conditions.
The properties of each film roll obtained are shown in Table 1 below.

<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)
1 g of polyester was precisely weighed and dissolved in 100 mL of a mixed solvent of phenol/tetrachloroethane = 50/50 (mass ratio), and the viscosity (IV) was measured at 30°C using a viscosity (IV) measuring device (manufactured by Rigo Co., Ltd., "VMS-022UPC-F10").

(2) Average particle size and particle size distribution of particles Powder was observed from the surface of the surface layer A side of the polyester films of the Examples and Comparative Examples using a scanning electron microscope (manufactured by HITACHI, "S3400N").
The size of each particle was measured from the obtained image data, and the average value of 10 points was taken as the average primary particle size.
Furthermore, a dispersion liquid with a solid content of 0.03 g/mL was prepared by adding a mixed solvent of phenol/tetrachloroethane = 2/3 to the particles, and for this dispersion liquid, the particle diameter D10 at which the cumulative number reached 10%, the particle diameter D50 at which the cumulative number reached 50%, and the particle diameter D90 at which the cumulative number reached 90% were measured by a laser diffraction scattering method using an "MT3300EXII" manufactured by Microtrackbell, and (D90 - D10)/D50 was calculated.

(3) Average surface roughness (Sa), maximum peak height (Sp), and average spacing between irregularities (RSm)
The surfaces of the surface layer A of the polyester film rolls of the Examples and Comparative Examples were measured using a surface roughness measuring device (Ametec Co., Ltd., "NewView" (registered trademark)), 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 protrusion height of less than 50 nm, the number of protrusions with a protrusion height of 50 nm or more but less than 100 nm, and the number of protrusions with a protrusion height of 100 nm or more was measured.
(Measurement conditions)
Measurement mode: VXI mode Objective lens: 20x Internal lens: 0.55x Field of view: 586 μm x 460 μm

(4) Scratch Resistance Regarding scratches and defects on the film surface, the polyester rolls of the examples and comparative examples were used as A4 size sample films, and it was confirmed whether scratches (fine scratches, scratch-like defects, grain-like patterns, etc.) could be visually recognized using "transmitted light under indoor three-wavelength fluorescent lamps" and "reflected light from a halogen lamp in a dark room." If scratches were recognized, the number of scratches was counted and judged according to the following evaluation criteria.
<Evaluation criteria>
A: 0 to 4 scratches with a depth of 0.3 μm or more that can be confirmed by transmitted light under indoor three-wavelength fluorescent light or reflected light from a halogen lamp.
B: Five or more scratches with a depth of 0.3 μm or more that can be confirmed by transmitted light under an indoor three-wavelength fluorescent lamp or reflected light from a halogen lamp.

(5) Thinner Green Sheets In the examples and comparative examples, the polyester film rolls were evaluated as good (A) when the maximum peak height (Sp) of the surface of the surface layer A was 200 nm or less, and as poor (B) when the maximum peak height (Sp) exceeded 200 nm.
For example, in the forming process of a thin film green sheet having a thickness of 0.5 μm or less, if the maximum peak height (Sp) exceeds 200 nm, the high protrusions present tend to increase the risk of pinholes occurring.

(6) Adaptability of Polyester Film Roll to Long Length When the polyester film rolls of the Examples and Comparative Examples were wound into a roll of 12,000 m, if no wrinkles or the like occurred and the film could be extended, the film was evaluated as good "A." If wrinkles or the like occurred and the film could not be extended, the film was evaluated as poor "B."

The polyester film roll of Example 1 had high smoothness, and by using fine organic particles, the maximum peak height (Sp) was made even lower than in the conventional example (Comparative Example 1) while maintaining the average surface roughness (Ra). Despite the use of relatively soft organic particles, the roll exhibited good scratch resistance.

Furthermore, the results of Examples 1 and 2 revealed that in order to adjust the surface of surface layer A to have high Sa and low Sp, the average particle size of the particles used in the surface layer needs to be 0.05 to 0.4 μm, and that the particles used in surface layer A need to be organic particles.
Furthermore, it was found that it is preferable that the surface layer A contains an antimony compound and/or a titanium compound, that the content of the antimony compound is 100 ppm or less, and that the intrinsic viscosity (IV) of the polyester constituting the surface layer A is 0.55 dl/g or more.

Furthermore, the number of protrusions on the surface of the surface layer A in Examples 1 and 2 shows a tendency for this to decrease as the size of the protrusions increases. Furthermore, when the number of protrusions in Examples 1 and 2 is compared with that in Comparative Example 1, in which Q/N and Q do not satisfy the ranges of the present invention, it was confirmed that Comparative Example 1 had a higher number of protrusions less than 50 nm, protrusions between 50 nm and 100 nm, and protrusions 100 nm or more. Furthermore, it was confirmed that Comparative Example 1 had a higher maximum peak height (Sp) than Examples 1 and 2.
From this, it was confirmed that by increasing the discharge amount of polyester raw material used for the surface layer of the polyester film, particle aggregation can be suppressed and the smoothness of the polyester film surface can be increased.

On the other hand, when comparing the number of protrusions in Comparative Example 2 and Comparative Example 3, which used inorganic particles, it was confirmed that Comparative Example 3, which had a larger amount of polyester raw material discharged into the surface layer, had a larger number of protrusions of all sizes. It was also confirmed that Comparative Example 3 had a larger maximum peak height (Sp) than Comparative Example 2. In other words, when organic particles were used, the trend differed from when inorganic particles were used, and it was found that the above-mentioned effect was a phenomenon unique to the use of organic particles.

In addition, in Example 4, which used alumina with an average particle size of 0.05 nm, the average surface roughness (Sa) and maximum peak height (Sp) of the polyester film surface could not be made sufficiently large, making it difficult to handle, prone to wrinkling, and difficult to produce in long lengths, making it impossible to improve production efficiency.

The polyester film roll of the present invention has the advantage of being highly smooth and, as productivity improves, capable of producing longer polyester film rolls. Furthermore, when used as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, a uniform, thin dielectric layer can be formed. In particular, it is suitable for use as a support for ceramic green sheets used in multilayer ceramic capacitors for automobiles.

Claims (6)

A polyester film roll obtained by winding up a polyester film,
the polyester film is a three-layer polyester film having an A/B/A structure composed of an intermediate layer B and a surface layer A,
the surface layer A contains organic particles having an average particle size of 0.05 to 0.4 μm,
The surface (A) of the surface layer A of the polyester film roll satisfies the following (1) to (3):
(1) The average surface roughness (Sa) is 5 to 20 nm.
(2) The maximum peak height (Sp) is 300 nm or less.
(3) The average spacing (RSm) of the irregularities is 0.016 mm or less. The polyester film roll according to claim 1 , wherein the intermediate layer of the polyester film contains 50% by mass or more of recycled polyester raw materials. The polyester film roll according to claim 1 or 2 , further comprising a release layer on the surface (A) of the surface layer A. 4. The polyester film roll according to claim 1 , which is used as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor. The polyester film roll according to any one of claims 1 to 4 , which is used as a support for a ceramic green sheet in the process of producing an automotive ceramic capacitor. A method for producing a polyester film roll by winding a polyester film, comprising:
the polyester film is a three-layer polyester film having an A/B/A structure composed of an intermediate layer B and a surface layer A,
the surface layer A contains organic particles having an average particle size of 0.05 to 0.4 μm,
The polyester raw materials for the surface layer A and the intermediate layer B are melt-extruded, and then the raw material for the surface layer A is divided into two parts and co-extruded in a layer structure in which the surface layer and the intermediate layer B are the intermediate layer to obtain a polyester film;
a melt extrusion condition for the surface layer A , in which a ratio Q/N of a discharge rate Q kg/h of a polyester raw material constituting the surface layer A to a screw rotation speed N rpm satisfies the following formula (A) , and the discharge rate Q is 180 kg/h or more and 300 kg/h or less :
2.5≦Q/N≦3.0...(A)