JP7000677B2 - Polyester film - Google Patents

Description

The present invention relates to a polyester film having excellent smoothness and transparency.

Polyester resins, especially polyethylene terephthalate (hereinafter sometimes abbreviated as PET) and polyethylene 2,6-naphthalenedicarboxylate (hereinafter sometimes abbreviated as PEN) have excellent mechanical properties, thermal properties, chemical resistance, and moldability. It is used for various purposes because of its excellent surface control. Polyester film made from the polyester, especially biaxially oriented polyester film, is a variety of industrial materials such as magnetic recording materials and materials for condensers, and dry film resist (DFR) because of its excellent mechanical properties, thermal properties, and surface properties. ) Transparent electrodes for flexible displays, organic EL, etc., taking advantage of the applications of process paper such as mold release / process films for base materials, laminated ceramic condenser manufacturing processes, plate plate release, etc., and excellent transparency. It is used as an optical material such as a substrate.

In recent years, dry film resists (DFRs) using a polyester film as a base material are often used in the manufacture of printed wiring boards, semiconductor packages, flexible substrates and the like. Generally, the DFR has a sandwich structure in which a photosensitive layer (photoresist layer) is sandwiched between a base film made of a polyester film and a protective film (cover film) made of a polyolefin film or the like. In order to manufacture a conductor circuit using this DFR, the following operations are generally performed.

That is, the protective film is peeled off from the DFR and laminated with the substrate / conductive substrate layer so that the surface of the exposed resist layer and the surface of the conductive substrate layer such as copper foil on the substrate are in close contact with each other. .. Next, the reticle on which the conductor circuit pattern is baked is placed on a base material made of a polyester film, and the resist layer mainly composed of a photosensitive resin is irradiated with light rays to expose the resist layer. Then, after peeling off the rectyl and the polyester film, the unreacted component in the resist layer is dissolved and removed with a solvent. Then, etching is performed with an acid or the like to dissolve and remove the exposed portion in the conductive base material layer. As a result, the photoreactive portion in the resist layer and the conductive base material layer portion corresponding to this photoreactive portion remain as they are. After that, if the remaining resist layer is removed, a conductor circuit on the substrate will be formed. Since the conductor circuit is formed by such a method, the polyester film as a support is required to have high light transmittance that can transmit light rays without hindrance.

In particular, in recent years, with the miniaturization and weight reduction of OA equipment and IT equipment, there is a demand for a polyester filler for a dry film resist support which has excellent transparency, low haze, and high resolution.

In addition, with the recent spread of smartphones, monolithic ceramic capacitors are becoming smaller and larger in capacity. Therefore, the release film used for manufacturing a laminated ceramic capacitor has a high smoothness, and the demand for a polyester film having no defects on the film surface and inside is rapidly increasing. As a surface characteristic of the polyester film used as a base material, the quality of the smooth surface tends to easily affect the quality of the processed green sheet product. In addition, the quality of the rough surface tends to easily affect the quality of the processed green sheet product. For example, when the waviness of the smooth surface processed by the green sheet is related to the quality of the laminated ceramic capacitor, which was not a problem with the conventional polyester film, and when the protrusion on the rough surface side winds up the green sheet product. It may be transferred to a green sheet and cause scratches or dents.

Further, the member used for a liquid crystal display or the like includes a polarizing plate, a retardation polarizing plate or a retardation plate, and the polarizing plate is usually composed of a polarizing film, a surface protective film, an adhesive layer and a release film. The polarizing film covers a polarizing element having a polarizing axis and an adsorption axis in which a polarizing element such as iodine or a dichroic dye is adsorbed and oriented on a hydrophilic film such as a polyvinyl alcohol-based film with a cellulose-based film from above and below. Or, it has a structure by coating with an acrylic resin. As the surface protective film, a transparent plastic film such as a polyester film having low moisture permeability and little deformation such as elongation is used. The surface protective film and the polarizing film are adhered to each other with an adhesive, and the adhesive firmly adheres to the surface protective film, but a polarizing film that can be easily peeled off even after a long period of time is used. The pressure-sensitive adhesive layer is made of a pressure-sensitive pressure-sensitive adhesive for adhering the polarizing film to the liquid crystal cell, and the release film is made of a polyester film or the like. In the manufacture of such a polarizing plate, although the optical characteristics such as the light transmittance, the degree of polarization and the haze of the polarizing film as a raw material are inspected and used in advance, the polarizing film in the manufacturing process for the polarizing plate is used. Defects may occur due to mechanical stress on the surface, contamination with foreign matter, or adhesion. For this reason, in the inspection of foreign matter and defects in the final product, the cross Nicol method (two polarizing plates are orthogonal to each other with their polarizing planes orthogonal to each other, and the longitudinal direction and width direction of the film are aligned with the polarizing planes of the polarizing plates which are orthogonal to each other. A method of observing transmitted light while being sandwiched between them) is used for visual inspection of humans. In the actual visual inspection of the polarizing plate, the polarizing plate to be inspected is replaced with the polarizing element and the film in the cross Nicol method so that the polarizing plane is orthogonal to the polarizing plane on the normal analyzer. In principle, defects such as foreign matter contamination and defects appear as bright spots in the polarizing plate, so that the defects can be visually inspected. However, the biaxially oriented polyester film currently used as a release film for a polarizing plate tends to leak light during a polarizing plate inspection by the cross Nicol method, which makes accurate visual inspection difficult and causes foreign matter to be mixed in the polarizing plate. There is a problem of overlooking the bright spot, which is a drawback.

Patent Documents 1 and 2 disclose a film in which the average roughness of the surface of the DFR base material is smoothed. Patent Document 3 discloses a film using specific particles in a three-layer structure as a manufacturing process film for a laminated ceramic capacitor.

Japanese Unexamined Patent Publication No. 2016-78754 JP-A-2015-208939 International Publication No. 2014/0641010

However, in the technique described in the above patent document, when used as a DFR substrate, smoothing and transparency are not sufficient in order to suppress exposure defects. In addition, when used as a manufacturing process film for multilayer ceramic capacitors, the green sheet becomes thinner and thinner, so it is represented by the spatial frequency density of a long wavelength of 10 μm level on the surface to be coated or processed on the film. The surface waviness index to be formed becomes more important, and the smoothness on the rough surface side is not sufficient from the viewpoint of suppressing transfer to the processed surface by the high protrusions on the rough surface side.

The subject of the present invention is that, in view of the background of the prior art, the long-wavelength surface waviness of the surface to be processed for mold removal / process or optical member is small, and the height of the protrusion on the opposite surface is controlled. By doing so, it is an object of the present invention to provide a polyester film having excellent smoothness and transparency.

The present invention for solving the above problems is characterized by the following configurations.
(1) A polyester film having a two-layer or three-layer structure , wherein (M60 / M10) × 100 on at least one side (A side) of the polyester film is 0.1 or more and 5.0 or less, and the A side is The spectral density on the opposite surface (plane B) at a wavelength of 9.65 μm is in the range of 1000 to 50,000 nm ³ .
Two kinds of particles having different particle diameters are contained in the A layer constituting the A surface.
A polyester film containing 0.02 to 0.20% by mass of particles having a particle diameter of 0.05 to 0.15 μm in the B layer constituting the B surface .
(However, M10 is the protrusion density (pieces / mm ² ) at the slice level with a height of 10 nm, and M60 is the protrusion density (pieces / mm ² ) at the slice level with a height of 60 nm.)
(2) The polyester film according to (1) above, wherein the M60 on the A side is 500 pieces / mm ² or less.
(3) The polyester film according to (1) or (2) above, wherein M100 on the A side is 5 pieces / mm ² or less.
(However, M100 is the protrusion density (pieces / mm ² ) at the slice level with a height of 100 nm .)
(4) The polyester film according to any one of (1) to (3) above, wherein M10 on the A side is 1000 pieces / mm ² or more and less than 30,000 pieces / mm ² .
(5) The polyester film according to any one of (1) to (4) above, wherein the average surface roughness Ra of the A surface is 2 to 7 nm.
(6) The polyester film according to any one of (1) to (5) above, wherein the average surface roughness Ra of the A surface is 0.5 to 5 nm.
(7) The polyester film according to any one of (1) to (6) above, wherein the film has a thickness of 10 μm or more and 250 nm or less.
(8) The layer forming the A surface of the polyester film (9) according to any one of (1) to (7) above, which has a laminated structure of three or more layers, contains particles, and is based on the volume of the particles. D (μm) is the particle size of the peak top with the largest particle size among the maximum particles in the particle abundance chart obtained when the particle size distribution is measured and plotted with the horizontal axis as the particle size and the vertical axis as the particle abundance ratio. The polyester film according to any one of (1) to (8) above, wherein the t / D is 0.5 or more and 10 or less when the thickness of the layer forming the A surface is t (μm).
(10) The polyester film according to any one of (1) to (9) above, which is used as a film for mold release or a process.
(11) The polyester film according to (10) above, which is used as a film for a resist substrate.
(12) The polyester film according to (10) above, which is used as a support for forming a green sheet in a process of manufacturing a laminated ceramic capacitor.
(13) The polyester film according to (10) above, which is used as a polarizing plate release film.
(14) The polyester film according to any one of (1) to (9) above, which is used as a film for an optical member.

According to the present invention, the surface smoothness and transparency are excellent, there are few exposure defects when used as a base film for a dry film resist, and there are few defects of a green sheet in the process of manufacturing a laminated ceramic capacitor. Further, it is possible to provide a film for mold release / process, which has few defects causing inspection errors for polarizing plate release, and a film suitable as an optical member having few defects and scratches when a transparent electrode or the like is processed. ..

The present invention will be described in detail below with reference to specific examples.

The polyester used in the polyester film of the present invention is composed of, for example, a polymer having an acid component such as an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid, or a diol component as a constituent unit (polymerization unit). Can be used.

Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-diphenyldicarboxylic acid. Acids, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenylsulfone dicarboxylic acid and the like can be used, and among them, terephthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid can be used. .. As the alicyclic dicarboxylic acid component, for example, cyclohexanedicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecandionic acid and the like can be used. Only one kind of these acid components may be used, or two or more kinds thereof may be used in combination.

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, and 1, , 6-Hexanediol, 1,2-Cyclohexanedimethanol, 1,3-Cyclohexanedimethanol, 1,4-Cyclohexanedimethanol, Diethylene glycol, Triethylene glycol, Polyalkylene glycol, 2,2'-Bis (4'- β-Hydroxyethoxyphenyl) propane and the like can be used, and among them, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like can be preferably used, and ethylene glycol is particularly preferable. Etc. can be used. Only one kind of these diol components may be used, or two or more kinds thereof may be used in combination.

The polyester may be copolymerized with a monofunctional compound such as lauryl alcohol or phenyl isocyanate, or may be trifunctional such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol and 2,4-dioxybenzoic acid. The compound or the like may be copolymerized within a range in which the polymer is substantially linear without excessive branching or cross-linking. Further, in addition to the acid component and the diol component, the present invention comprises aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, and p-aminophenol and p-aminobenzoic acid. If the amount is small enough not to impair the effect of the above, further copolymerization can be performed.

The copolymerization ratio of the polymer can be examined by using an NMR method (nuclear magnetic resonance method) or a microscopic FT-IR method (Fourier transform microinfrared spectroscopy).

As the polyester, a polyester having a glass transition temperature of less than 150 ° C. can be preferably used in order to be able to perform biaxial stretching and to exhibit the effects of the present invention such as surface properties and transparency. The polyester used in the present invention is preferably polyethylene terephthalate or polyethylene naphthalate (polyethylene-2,6-naphthalate), and may be a copolymer or modified product thereof, or may be a polymer alloy with another thermoplastic resin. .. The polymer alloy referred to here is a polymer multi-component system, and may be a block copolymer by copolymerization or a polymer blend by mixing or the like. As the polyester used in the present invention, it is more preferable that the main component is polyethylene terephthalate because a process for increasing the crystallite size and the degree of crystal orientation can be easily applied. Here, the main component means that it is 80% by mass or more in the film composition.

The polyester film of the present invention is a slice having a height of 60 nm with respect to the protrusion density when the slice level is set at intervals of 10 nm from the reference plane in the roughness curve measured by a three-dimensional surface roughness meter on at least one side (A side). As the relationship between the protrusion density at the level (M60 (pieces / mm ² )) and the protrusion density at the slice level with a height of 10 nm (M10 (pieces / mm ² )), (M60 / M10) × 100 is 0.1 or more and 5.0. It is as follows. The value of (M60 / M10) × 100 is preferably 0.3 or more and 3.0 or less, and more preferably 0.5 or more and 2.5 or less. If the lower limit value is small, it is preferable that it leads to suppression of transfer, but if it is too small than 0.1, the running performance is lowered and the processability is lowered. When the upper limit exceeds 5.0, the ratio of protrusions with a height of 60 nm or more to all protrusions becomes high, and transfer is likely to occur, and the surface of the processed layer (such as the resist layer of DFR and the green sheet layer in the manufacturing process of laminated ceramic capacitors) Defects are more likely to occur. By setting the value of the protrusion density ratio (M60 / M10) × 100 within the range of the present invention, it is possible to achieve both runnability and processability and suppression of defects on the surface of the processed layer at a high level. The method of setting the value of the protrusion density ratio (M60 / M10) × 100 in the above range is not particularly limited, and examples thereof include a method of controlling by the particle type and the particle content contained in the polyester film. Details will be described later.

The polyester film of the present invention needs to have a spectral density of 1000 to 50,000 nm ³ at a wavelength of 9.65 μm on the surface (plane B) opposite to the surface satisfying the protrusion density. The spectral density is preferably in the range of 2000 to 40,000 nm ³ , and more preferably in the range of 3000 to 35,000 nm ³ . Spectral density (hereinafter referred to as PSD) is a method in which profile data of surface roughness is subjected to Fourier transform processing and frequency analysis is performed to calculate the intensity at each wavelength. In the present application, PSD measurement was performed using an atomic force microscope (AFM) with a measurement field of view of 125 μm × 125 μm, and the intensity corresponding to a wavelength of 9.65 μm was obtained. The PSD obtained by the above method is a parameter representing the waviness of the film surface. In the present application, the surface where the PSD satisfies the above range is preferable for suppressing defects on the surface of the processed layer, and when the PSD is within the range of the present application, both processing suitability and defect suppression can be achieved at a high level, which is preferable.

The polyester film of the present invention has a protrusion density (M60) of 500 pieces / mm ² or less at a slice level 60 nm in height from the reference plane in the roughness curve measured by the three-dimensional surface roughness meter of the A surface. Is preferable. More preferably, it is 300 pieces / mm ² or less. If the protrusion density (M60) exceeds 500 pieces / mm ² , it may be transferred to the processing layer and cause defects such as pinholes when used for mold release / processing, or exposure defects may occur for DFR. Sometimes. Further, the polyester film of the present invention has a protrusion density (M10) of 1000 to 30,000 pieces / mm ² at a slice level 10 nm in height from the reference plane in the roughness curve measured by the three-dimensional surface roughness meter of the A surface. Is preferable. More preferably, it is 3000 to 25000 / mm ² . If the protrusion density (M10) is less than 1000 pieces / mm ² , the runnability may be insufficient and the workability may be lowered, or the stress of the A-plane protrusion may not be dispersed and transfer may easily occur. If the upper limit of 30,000 pieces / mm ² is exceeded, the distance between the protrusions will be narrowed, and the protrusions will be densely formed, and coarse protrusions will be easily formed. Therefore, transfer to a smooth surface may increase when the film is wound as a film roll. Further, since it is difficult to obtain a value of the protrusion density ratio (M60 / M10) × 100 specified above, the PSD on the opposite surface may not be controlled within the scope of the present invention. By controlling M10 within a specific range, the reference plane of the roughness curve rises and the height of the protrusions becomes apparently low, which has the effect of reducing transfer to a smooth surface and the stress caused by the tightening of the film roll. It is considered that the transfer to the smooth surface is reduced by the synergistic effect of the effect of dispersing the stress without concentrating it on the high protrusions.

The polyester film of the present invention has a protrusion density at a slice level of 100 nm in height with respect to the protrusion density when the slice level is set at intervals of 10 nm from the reference plane in the roughness curve measured by the three-dimensional surface roughness meter of the A side. (M100 (pieces / mm ² )) is preferably 5 or less. If the protrusion density (M100) is out of this range, when it is used for mold release / process, transfer to the surface of the processed layer occurs, which causes defects and may deteriorate the characteristics. When the characteristic surface having the respective characteristics (values) of the protrusion density ratio (M60 / M10) × 100 and the protrusion density (M100) specified above is the B layer surface, the running performance and workability are improved and the surface of the processed layer is smooth. It is preferable because the effect of suppressing sexual defects is sufficiently exhibited.

The polyester film of the present invention preferably has a laminated structure of two or more layers having at least one layer (A layer) containing inert particles having an average particle size of 0.050 to 0.50 μm. In this case, when the layer having the A surface is the A layer, the A layer functions as a layer responsible for handleability and processability, and is provided as one outermost layer of the film. At this time, at least the other outermost layer (layer having the B surface) is provided with a layer (B layer) having an average particle size of 0.05 to 0.20 μm and containing inert particles and having smoothness. A laminated structure of two or more layers is preferable for obtaining the effect of the present invention. More preferably, a laminated structure of three or more layers in which an intermediate layer (C layer) is provided between the A layer and the B layer is exemplified. In this case, in order to control the spectral density (PSD) at the wavelength of 9.65 μm on the B surface and the protrusion density on the A surface within the range of the present invention, it is preferable that the C layer contains substantially no particles.

In the polyester film of the present invention, in the layer (A layer) forming the A surface, the ratio (t / D) of the thickness (t) of the layer to the maximum particle size (D) of the layer of the layer is 0.5. It is preferably ~ 10. More preferably, it is 1 to 5. If (t / D) is less than 0.5, the particles may fall off the film and it may be difficult to form a surface, and if t / D is greater than 10, the particles are buried in the film. Therefore, it may be difficult to set the protrusion density ratio (M60 / M10) × 100 within the above range. The maximum particle size (D) is the maximum of the particle abundance ratio chart obtained when the volume-based particle size distribution of the particles is measured and plotted with the horizontal axis as the particle size and the vertical axis as the particle abundance ratio. The particle size of the peak top having the largest particle size was defined as D (μm).

As the method for controlling the protrusion density (M60, M100) described above, it is possible to control the particle size, content, and layer thickness of the contained particles in the A layer (for example, when applied to the A layer). In particular, it is preferable that the particle size of the particles contained in the A layer does not exceed 0.5 μm. When the particle size of the maximum particles (L) that can be contained in the layer A is 0.3 μm or more and 0.5 μm or less, the content of the particles is preferably 0.05 to 0.25% by mass. When the particle size of the particles (L) exceeds 0.4 μm, the content of the particles is preferably 0.05 to 0.20% by mass. Further, the ratio (t / D) of the layer thickness (t) to the maximum particle diameter (D) contained in the layer is set to 0.5 to 10, preferably 1 to 5, and more preferably 1 to 3.

The above-mentioned protrusion density (M10) control method can be achieved by controlling the particle size, content, and layer thickness of the particles contained in the A layer. Particles having a particle size of 0.03 to 0.5 μm are contained in an amount of 0.1 to 0.5% by mass, and the ratio (t / d) of the laminated thickness (t) to the average particle size (d) contained in the layer. ) Is set to 0.5 to 10, preferably 1 to 5. In particular, in addition to containing 0.1 to 0.3% by mass of particles (M) having a particle size of 0.1 μm or more and less than 0.3 μm, particles having a particle size of 0.03 μm or more and less than 0.1 μm (S). ) Is contained in an amount of 0.15 to 0.3% by mass, the desired protrusion density (M10) can be efficiently obtained without increasing the surface roughness Ra and the protrusion density (M60). As a result, the contact area with the in-process roll in the manufacturing process and the film at the time of winding is reduced, and the running performance is improved. Further, controlling M10 within a specific range increases the surface area of the A layer because fine irregularities are formed on the surface of the A layer, so that the air that is caught when the film roll is wound is escaped. It is considered that it becomes easier to secure, the winding deviation is less likely to occur, and the slit property is improved.

As a method for controlling the value of the density ratio (M60 / M10) × 100 described above, it is preferable to use at least two kinds of particles (L and M, S) having different particle diameters in combination in the A layer, and the particles (L). ) And the content of the particles (M) and t / D can be adjusted. The particle size (L) is 0.3 μm or more and 0.5 μm or less, and the particle size of the particle (M) is 0.1 μm or more and less than 0.3 μm. At this time, the particle (L) is a particle having a larger particle diameter than the particle (M). Further, by adding 0.15 to 0.3% by mass of particles (S) having a particle size of 0.03 μm or more and less than 0.1 μm, the protrusion density (M10) of the present invention is not increased. ) Can be increased efficiently, which is preferable.

The particles preferably contained in the polyester film A layer of the present invention are not particularly limited, but either inorganic particles or organic particles can be used. It is preferable to use two or more kinds of particles in combination in order to obtain the characteristic surface of the present invention. Specific types include inorganic particles such as clay, mica, titanium oxide, calcium carbonate, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina silicate, kaolin, talc, montmorillonite, alumina, and zirconia. , Acrylic acids, styrene resin, silicone, imide and other organic particles, core-shell type organic particles and the like can be exemplified. However, in order to control the protrusion density and PSD of the present invention, single dispersed spherical particles can be exemplified. Organic particles and colloidal silica are particularly preferable.

Further, as the particles preferably contained in the A layer of the polyester film of the present invention, spherical particles having a single dispersion are preferable.

In the polyester film of the present invention, the surface roughness Ra of the center line of the A surface is preferably 2 to 10 nm, and more preferably 2 to 7 nm. The 10-point average roughness Rz is 30 to 200 nm, preferably 40 to 180 nm, and more preferably 80 to 160 nm. If the surface roughness Ra and Rz are less than the lower limit values, the runnability and slitting property are likely to be poor, and if the surface roughness Ra and Rz exceed the upper limit values, they are processed to the B layer side when used for mold release / process. Transfer marks are likely to occur on the layer, and defects may be likely to occur.

Further, in the polyester film of the present invention, the surface roughness Ra of the center line of the B surface is preferably 0.5 to 5 nm, and more preferably 1 to 4 nm. If the surface roughness Ra is less than the lower limit value, the running performance and the slit property are likely to be poor, and if the Ra exceeds the upper limit value, defects are likely to occur in the processed layer when used for mold release / process. Sometimes.

In the polyester film of the present invention, the method for controlling the spectral density (PSD) at a wavelength of 9.65 μm on the B surface can be controlled by the particle size and content of the particles contained in the polyester film and the layer thickness. For example, the polyester film has a laminated structure of three or more layers, and 0.02 to 0.20% by mass of particles having a particle diameter of 0.05 to 0.15 μm are contained as particles contained in the B layer forming the B surface. Moreover, a method in which an intermediate layer (C layer) is provided between the A layer and the B layer and the C layer contains substantially no particles is exemplified.

In the present invention, MD indicates the longitudinal direction (longitudinal direction) of the polyester film, and TD indicates the width direction (horizontal direction) of the polyester film.

The thickness of the polyester film of the present invention is preferably 10 μm or more and 250 μm or less. When the thickness of the film exceeds 250 μm, the polyester itself constituting the film also absorbs light, so that the exposure property is lowered when it is used as a DFR base material, and the transparency is lowered when it is used as an optical member. It may happen. If the film thickness is less than 10 μm, the handleability and transportability of the film may deteriorate. When the thickness of the polyester film is within the above range, the transparency, exposure, handleability, and transportability are good, and the film for mold release / process such as for DFR base material, laminated ceramic capacitor manufacturing process, and polarizing plate release. Further, it can be suitably used as a film for an optical member such as a transparent electrode substrate of a flexible display. The film thickness is more preferably 15 μm or more and 100 μm or less, and further preferably 15 μm or more and 50 μm or less.

The method for producing the polyester film of the present invention as described above is not particularly limited, but is produced, for example, as follows.

First, polyester pellets are melted using an extruder, discharged from a mouthpiece, then cooled and solidified to form a sheet. At this time, it is preferable to filter the polymer with a fiber-sintered stainless metal filter in order to remove unmelted matter in the polymer.

Various additives such as compatibilizers, plasticizers, weather resistant agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, and colorants, as long as they do not interfere with the characteristic aspects of the present invention. , Conductive agents, crystal nucleating agents, ultraviolet absorbers, flame retardants, flame retardants, pigments, dyes, etc. may be added.

Subsequently, the sheet is stretched biaxially in the longitudinal direction and the width direction, and then heat-treated. The stretching step for controlling the protrusion density ratio (M60 / M10) on the A surface and the spectral density (PSD) on the B surface within the scope of the present invention is preferably divided into two or more steps in the width direction.

As a stretching type, a sequential biaxial stretching method such as stretching in the longitudinal direction and then stretching in two steps in the width direction is preferably exemplified. Further, a method of simultaneously stretching in the longitudinal direction and the width direction by the simultaneous biaxial stretching method and then stretching in the width direction is also preferably exemplified.

Hereinafter, the method for producing a polyester film of the present invention will be described as a representative example in which polyethylene terephthalate (PET) is used as the polyester. The present invention is not limited to the PET film, and may be one using another polymer. For example, when a polyester film is formed using polyethylene-2,6-naphthalenedicarboxylate having a high glass transition temperature or melting point, extrusion or stretching may be performed at a temperature higher than the temperature shown below.

First, PET pellets are produced. PET is manufactured by one of the following processes. That is, (1) a process in which terephthalic acid and ethylene glycol are used as raw materials, a low molecular weight PET or oligomer is obtained by a direct esterification reaction, and then a polymer is obtained by a polycondensation reaction using an antimony trioxide or a titanium compound as a catalyst. , (2) A process in which a low molecular weight substance is obtained by a transesterification reaction using dimethyl terephthalate and ethylene glycol as raw materials, and then a polymer is obtained by a polycondensation reaction using an antimony trioxide or a titanium compound as a catalyst.

In order to contain the particles in the PET constituting the film, it is preferable to disperse the particles in ethylene glycol in a predetermined ratio in the form of a slurry and add the ethylene glycol at the time of polymerization. When adding the particles, for example, if the particles in the water sol or alcohol sol state obtained at the time of synthesizing the particles are added without being dried once, the dispersibility of the particles is good. It is also effective to directly mix the aqueous slurry of particles with PET pellets and knead them into PET using a vent type twin-screw kneading extruder. As a method for adjusting the particle content, a master pellet of high-concentration particles is prepared by the above method, and the master pellet is diluted with PET which does not substantially contain particles at the time of film formation to adjust the particle content. The method is effective. At this time, it is effective to adjust the intrinsic viscosity of the PET containing no particles higher than the intrinsic viscosity of the pellets containing particles in order to control the above-mentioned value of protrusion density ratio (M60 / M10) × 100 and M100. be.

Next, the obtained PET pellets are dried under reduced pressure at 180 ° C. for 3 hours or more, and then supplied to an extruder heated to 270 to 320 ° C. under a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease. , Extruded from a slit-shaped die and cooled on a casting roll to obtain an unstretched film. At this time, it is preferable to use various filters, for example, filters made of materials such as sintered metal, porous ceramics, sand, and wire mesh, in order to remove foreign substances and altered polymers. Further, it is extremely preferable to provide a gear pump in order to improve the quantitative supply property and obtain a desired t / D in order to form the above-mentioned characteristic surface. To laminate the films, a plurality of different polymers may be melt-laminated using two or more extruders and manifolds or merging blocks.

Next, the unstretched film thus obtained was stretched in the vertical direction (MD stretching) using a longitudinal stretching machine in which several rolls were arranged, utilizing the difference in peripheral speed between the rolls, followed by A biaxial stretching method in which lateral stretching is performed in two stages using a stenter (TD stretching 1, TD stretching 2) will be described.

First, the unstretched film is MD-stretched. The stretching temperature of MD stretching varies depending on the type of polymer used, but can be determined by using the glass transition temperature (Tg) of the unstretched film as a guide. It is preferably in the range of Tg-10 to Tg + 20 ° C, more preferably Tg ° C to Tg + 15 ° C. When the stretching temperature is lower than the above range, the film may be torn frequently and the productivity may be lowered, and it may be difficult to stably stretch the film by the two-step TD stretching after the MD stretching. The MD draw ratio is 3 to 6 times, preferably 3.3 to 5.5 times.

Next, TD stretching is performed using a stenter. In order to efficiently form a film having the protrusion density (M60 and M10) on the A surface and the spectral density (PSD) on the B surface of the present invention, it is preferable to stretch the film in two stages in the TD direction in zones having different temperatures. .. First, the draw ratio of the first-stage stretching (TD stretching 1) is preferably 3.0 to 6.0 times, more preferably 3.3 to 5.8 times. The stretching temperature of the TD stretching 1 is preferably in the range of (longitudinal stretching temperature +5) to (longitudinal stretching temperature +20) ° C.

Next, the second stage stretching (TD stretching 2) is performed in the stenter. The draw ratio of TD stretch 2 is preferably 1.2 to 2 times, more preferably 1.3 to 1.8 times, still more preferably 1.3 to 1.6 times. Setting the TD stretch ratio (TD stretch 1) / (TD stretch 2) in the range of 2 to 3 is an effective means for setting the protrusion density and the surface spectral density within the range of the present invention. The stretching temperature of TD stretching 2 is preferably in the range of (TD stretching 1 temperature +20) ° C. or higher (TD stretching 1 temperature +50) ° C., and more preferably (TD stretching 1 temperature +30) ° C. or higher (TD stretching 1 temperature +50). ) Perform in the range of less than ℃. By providing stretching in the width direction (TD stretching 2) higher than the stretching temperature of the previous step (TD stretching 1), the flatness can be improved, that is, the spectral density (PSD) of the B plane is set to the present. It is preferable because it can be controlled within the scope of the invention.

Subsequently, the stretched film is heat-fixed under tension or while relaxing in the width direction. As the heat fixing treatment condition, the heat fixing temperature is preferably 180 to 240 ° C. The upper limit of the heat fixing temperature is more preferably 230 ° C., still more preferably 220 ° C. The lower limit of the heat fixing temperature is more preferably 185 ° C, still more preferably 190 ° C. The heat fixing treatment time is preferably in the range of 0.5 to 10 seconds, and the relaxation rate is preferably 0.3 to 2%. After the heat fixing process, the clip is opened to quench the film to room temperature while reducing the tension applied to the film. Then, the film edge can be removed and wound on a roll to obtain the polyester film of the present invention. Further, the heat fixing temperature is more preferably in the range of (TD stretching 2 temperature +20) ° C. or higher (TD stretching 2 temperature +80) ° C. or lower. There is a difference between the stretching temperature and the heat fixing temperature of the TD stretching 2, and if the heat fixing temperature is higher than the above range, the film is easily relaxed and the surface protrusions may become large. On the other hand, if the heat fixing temperature is too low, the crystallinity tends to be low, so that the flatness of the base film tends to be lowered in the manufacturing process used for mold release / process or as an optical member. Further, heat fixing is performed in two or more steps, and in the first step, the film is slightly stretched in the range of 1.01 to 1.2 times in the lateral direction to improve the flatness of the film, and the A-side protrusion density and the B-side spectral density. It is more preferable to control (PSD) within the scope of the present invention.

The polyester film of the present invention can also be used as a mold release / process film. The release / process film is formed by using a polyester film as a base material and applying a releaseable resin layer such as a silicone resin or an epoxy resin. In particular, for dry film resists (DFR) to which photoresist is applied, for multilayer substrates to which insulating resin is applied, for manufacturing green sheets for laminated ceramic capacitors, for mold release for liquid crystal polarizing plates, for mold release for liquid crystal protective films, etc. It is used for various mold release and process applications. In polyester film, it is common to mix an appropriate amount of particles in order to improve processability, such as slipperiness and winding characteristics, to form fine protrusions on the film surface, but in recent years, various applications have been refined. As a result, the release film used is also required to have a smooth surface and runnability without surface defects. Since the polyester film of the present invention has high-definition surface smoothness and runnability, it can be suitably used as a release film for various purposes.

The polyester film of the present invention can also be used as a transparent electrode film and a film for an optical member such as a polarizing plate and an optical compensation film for a liquid crystal display device. With the recent development of thin and lightweight notebook computers and thin electronic mobiles, the demand for thinning optical compensation films for liquid crystal displays has become extremely strict, and thin optical films with excellent transparency and running performance have become particularly strict. Can be suitably used as.

(Measurement method of physical properties and evaluation method of effect)
The method for measuring the characteristic value and the method for evaluating the effect in the present invention are as follows.

(1) Protrusion density (M100, M60, M10)
Three-dimensional surface roughness was measured under the following conditions using a surf-coder ET-4000A manufactured by Kosaka Laboratory, and then particle analysis (multiple levels) was performed using the built-in analysis software. The measurement conditions were as follows. The slice levels were set at equal intervals of 10 nm, the average diameter and density of each slice level were changed in different locations, and measurements were taken 5 times, and the average value was used as the value. The sample set was set on the sample table so that the X direction of the visual field measurement was the width direction of the polyester film.

(However, the protrusion density at the slice level of M100: 100 nm, the protrusion density at the slice level of M60: 60 nm,
M10: Protrusion density at 10 nm slice level)
Equipment: "surf-corder ET-4000A" manufactured by Kosaka Research Institute
Analysis software: i-Face model TDA31 Ver 2.2.0.4 JSGIS
Radius of stylus tip: 0.5 μm
Measurement field of view: X direction: 380 μm Pitch: 1 μm
Y direction: 280 μm Pitch: 5 μm
Needle pressure: 50 μN
Measurement speed: 0.1 mm / s
Cutoff value: Low range-0.8mm, High range-None Leveling: Whole area filter: Gaussian filter (2D)
Magnification: 100,000 times Particle analysis (multiple levels) Condition Output content setting: Mountain particle Hysteresis width: 5 nm
Slice level equal spacing: 10 nm
(2) Center line surface roughness Ra, 10-point average roughness Rz
Using the device described in (1) above, the three-dimensional roughness is measured 10 times at different locations under the measurement conditions described above, and the average value is the center line surface roughness Ra and the 10-point average roughness Rz, respectively. And said.

(3) Spectral density (PSD)
Using an atomic force microscope (AFM), 10 visual field measurements were performed at different locations. In the sample set, the sample is set in the piezo so that the direction perpendicular to the scanning direction of the cantilever (Y-axis direction) is the longitudinal direction of the sample film (the longitudinal direction is the direction in which the film travels in the film manufacturing process). And measure. For the obtained image, 1D PSD in the Y-axis direction (longitudinal direction of the film) in the Power Spectral Densityy of the Off-Line function was obtained, and the average value was defined as PSD.

Measuring device: NanoScope (R) IIIa Version 5.31R1
(Manufactured by Digital Instruments)
Cantilever: Silicon single crystal Scanning mode: Tapping mode Scanning range: 125 μm □
Scanning speed: 0.5Hz
Samples line: 256
Flatten Auto: Order 3
(4) Laminated thickness Under the following conditions, cross-sectional observation was performed in 10 different places, and the average value of the obtained thickness [nm] was calculated and used as the thickness [nm] of the A layer or the B layer.

Measuring device: Transmission electron microscope (TEM) Hitachi H-7100FA type Measuring conditions: Acceleration voltage 100 kV
Measurement magnification: 10,000 times Sample preparation: Ultra-thin section section Observation surface: TD-ZD cross section (TD: width direction, ZD: thickness direction)
(5) Maximum particle diameter (D), average particle diameter (d) of the laminated portion,
The cross section of the film is observed at a magnification of 10,000 using a transmission electron microscope (TEM). At this time, if particles of 1 cm or less can be confirmed on the photograph, the TEM observation magnification is changed to 50,000 times for observation. The section thickness of the TEM is about 100 nm, 100 field measurements are taken at different locations, the equivalent circle equivalent diameter is obtained for all the dispersed particles photographed, the horizontal axis is the equivalent circle equivalent diameter, and the vertical axis is the particle. The number distribution of particles was plotted as the number, and the equivalent circle equivalent diameter of the peak value was taken as the average particle diameter of the particles. Here, if aggregated particles can be confirmed on the photograph observed at 10,000 times, they are not included in the above plot. When two or more kinds of particles having different particle diameters are present in the film, the number distribution of the equivalent circle equivalent diameter is a distribution having two or more peaks. In this case, each peak value is used as the average particle size of each particle. The maximum particle size is the particle size of the particle having the maximum particle size in a 100-field photograph observed at a magnification of 10,000.
For the average particle diameter of the laminated portion, the volume average diameter is obtained by the following equation from each equivalent sphere equivalent diameter obtained above and its volume fraction, and this value is taken as the average particle diameter (d) of the laminated portion.

d = Σ (di ・ Nvi)
Here, di is the equivalent sphere equivalent diameter, and Nvi is the volume fraction thereof.

(6) Particle Content In the examples, the particle content was calculated from the particle content in polyester, which is a raw material for the film, and is shown in the table.

It can also be calculated by analyzing the film according to the following method.

(6) -1 Elemental analysis of particles Polyester is removed from the film by a plasma ashing treatment method to expose the particles. Select a treatment condition in which the polymer is incinerated but the particles are not damaged as much as possible. The particles are observed with a scanning electron microscope (SEM) and the particle images are processed with an image analyzer. According to the particle size distribution obtained in (6) above, the magnification of SEM is increased to 30,000 times, observation is performed in 20 fields at different observation points, and elemental analysis is performed on all observed particles using energy dispersive X-ray spectroscopy (EDX). To clarify the relationship between particles and elements.

(6) -2 Particle content The surface of each laminated portion is scraped off with a single blade, o-chlorophenol is added to 100 g of the shavings, and the polymer is dissolved at 100 ° C. for 1 hour with stirring. Next, the rotor RP30 is mounted on the ultracentrifuge 40P type for separation manufactured by Hitachi, Ltd., and after injecting 30 cc of the above-mentioned solution per cell, the speed is gradually increased to 30,000 rpm. Particle separation is completed 60 minutes after reaching 30,000 rpm. Then, the supernatant is removed and the separated particles are collected. O-Chlorophenol at room temperature is added to the collected particles to make them uniformly turbid, and then an ultracentrifugal separation operation is performed. This operation is repeated for the separated particles described later using a differential scanning calorimetry device (DSC) until the melting peak corresponding to the polymer is no longer detected. The separated particles thus obtained are vacuum dried at 120 ° C. for 16 hours, and then the measured value is taken as the total content of the particles, and the ratio (% by mass) to this is taken as the content of the particles.

(7) Runnability Two films in which the A side and the B side of the film are overlapped are placed on a glass plate, and a weight of 200 g (contact area 40 cm ² ) is placed on the film. One end of the lower film (moving direction side) and the glass were fixed, and one end of the upper film (opposite the moving direction) was fixed to the detector. The coefficient of static friction (μs) when the glass plate was moved 5 mm at a speed of 2 mm / sec was calculated from the following formula.

The judgment of runnability was as follows.

μs = (tension at start) / (load 200g)
A: μs = 0.4 or less B: μs = 0.4 or more, 0.5 or less C: μs = 0.5 or less (8) Resist characteristic evaluation or less a. From c. Evaluation is performed by the method of.
a. A negative resist "PMERN-HC600" manufactured by Tokyo Ohka Co., Ltd. is applied on a single-sided mirror-polished 6-inch Si wafer and rotated with a large spinner to prepare a resist layer having a thickness of 7 μm. Next, a preheat treatment is performed for about 20 minutes under a temperature condition of 70 ° C. using a ventilation oven with a nitrogen cycle.
b. The B side of the polyester film is layered so as to be in contact with the resist layer, the polyester film is laminated on the resist layer using a rubber roller, and a reticle patterned with chrome metal is placed on the reticle. Exposure is performed from above using an I-line (ultraviolet ray having a peak at a wavelength of 365 nm) stepper.
c. After peeling the polyester film from the resist layer, the resist layer is placed in a container containing the developer N-A5 and developed for about 1 minute. After that, remove it from the developer and add about 1 with water.
Perform a minute of washing. 30 states of L / S (μm) (Line and Space) = 10/10 μm of the resist pattern created after development were observed using a scanning electron microscope SEM at a magnification of about 800 to 3000, and the pattern was chipped. Evaluate as follows with a certain number.

A; The number of chips is 0 to 8 B; The number of chips is 9 to 15 C; The number of chips is 16 or more A has the best resistability and C is the worst.

In the above measurement, when the longitudinal direction and the width direction of the film to be measured are not known, the direction having the maximum refractive index in the film is regarded as the longitudinal direction, and the direction orthogonal to the longitudinal direction is regarded as the width direction. Further, the direction of the maximum refractive index in the film may be obtained by measuring the refractive index in all directions of the film with a refractive index meter, and the slow axis direction may be determined by a phase difference measuring device (birefringence measuring device) or the like. It may be obtained by deciding.

(9) Evaluation of green sheet characteristics The following a. From b. Evaluation is performed by the method of.
a. Application of release layer
A coating solution prepared by adjusting a crosslinked primer layer (trade name BY24-846 manufactured by Toray Dow Corning Silicone Co., Ltd.) to a solid content of 1% by weight is applied / dried on the B surface of the biaxially oriented polyester film, and after drying. It was coated with a gravure coater so that the coating thickness was 0.1 μm, and dried and cured at 100 ° C. for 20 seconds. Within 1 hour after that, 100 parts by weight of an addition reaction type silicone resin (trade name: LTC750A manufactured by Toray Dow Corning Silicone Co., Ltd.) and 2 parts by weight of a platinum catalyst (trade name: SRX212 manufactured by Toray Dow Corning Silicone Co., Ltd.) were applied. The coating liquid adjusted to have a solid content of 5% by weight was applied with a gravure coat so that the coating thickness after drying was 0.1 μm, dried and cured at 120 ° C. for 30 seconds, and then wound to obtain a release film.
b. Evaluation of the coating state of the green sheet (applicability of ceramic slurry)
Barium titanate (trade name HPBT-1 manufactured by Fuji Titanium Industry Co., Ltd.) 100 parts by weight, polyvinyl butyral (trade name BL-1 manufactured by Sekisui Chemical Co., Ltd.) 10 parts by weight, dibutyl phthalate 5 parts by weight and toluene-ethanol (Weight ratio 30:30) Glass beads having a number average particle size of 2 mm were added to 60 parts by weight, mixed and dispersed in a jet mill for 20 hours, and then filtered to prepare a paste-like ceramic slurry. The obtained ceramic slurry was applied onto a release film with a die coater so that the thickness after drying was 2 μm, dried, and wound to obtain a green sheet. The green sheet wound up above is unwound and visually observed in a state where it is not peeled off from the release film, and the presence or absence of pinholes and the coating state of the sheet surface and edges are confirmed. The area to be observed is 300 mm in width and 500 mm in length. While illuminating the green sheet molded on the release film with a backlight unit of 1000 lux from the back surface, observe pinholes due to coating omission or dented state due to surface transfer on the back surface of the release film.
A: There are no pinholes or dents.

B: There are no pinholes and no more than 3 dents are found.
C: There are pinholes, and 4 or more dents are recognized.

(10) Visual inspection of polarizing plate
The sample was cut out from an arbitrary position in the film width direction so that the longitudinal direction of the A4 cut sample and the longitudinal direction of the film coincided with each other. As a cross Nicol method, a Fuji Color Lightbox 100V8W (manufactured by Shinko Co., Ltd.) is used for the light source, and the normal detector and the absorber are placed so that the absorption axis planes are orthogonal to each other, and polyester is placed between them. The film was placed so that the B surface was in contact with the polarizing element with the film sandwiched between them, and a visual inspection was performed from the polarizing element side. At this time, the absorption axis of the polarizing element having a dimension width of 28 cm and a length of 34 cm on the observation surface side was aligned with the longitudinal direction of the film of the A4 cut sample. In the visual inspection, first, 50 positions and numbers of foreign substances and defects of the polarizing element appearing as bright spots without sandwiching the polyester film were confirmed. Next, it was evaluated by how many foreign substances and defects could not be recognized with the polyester film sandwiched between them. The interference color was also observed at the same time. The evaluation criteria were as follows.
A: The number of bright spots that cannot be confirmed is less than 5.
B: The number of bright spots that cannot be confirmed is 5 or more and less than 15.
C: The number of bright spots that cannot be confirmed is 15 or more.

Embodiments of the present invention will be described based on the following examples. Here, polyethylene terephthalate is referred to as PET.

(1-a) Preparation of PET pellets: 194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged in a transesterification reaction apparatus, and the contents were heated to 140 ° C. and dissolved. Then, while stirring the contents, 0.3 parts by mass of magnesium acetate tetrahydrate and 0.05 parts by mass of antimony trioxide were added, and a transesterification reaction was carried out while distilling methanol at 140 to 230 ° C. Next, 0.5 parts by mass of a 5% by mass ethylene glycol solution of trimethyl phosphate (0.025 parts by mass as trimethyl phosphate) and 0.3 parts of a 5% by mass ethylene glycol solution of monosodium dihydrogen phosphate dihydrate. By mass (0.015 parts by mass as sodium dihydrogen phosphate dihydrate) was added.

The addition of ethylene glycol solution of trimethylphosphoric acid lowers the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling off excess ethylene glycol. In this way, after the temperature of the reaction contents in the transesterification reaction apparatus reached 230 ° C., the reaction contents were transferred to the polymerization apparatus.

After the transition, the temperature of the reaction system was gradually raised from 230 ° C. to 275 ° C., and the pressure was lowered to 0.1 kPa. Both the final temperature and the time to reach the final pressure were set to 60 minutes. After reaching the final temperature and final pressure, the reaction was carried out for 6 hours (5 hours after the start of polymerization), and the stirring torque of the polymerization apparatus became a predetermined value (the specific value varies depending on the specifications of the polymerization apparatus, but the present polymerization apparatus). The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.62 was set as a predetermined value). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand shape, and immediately cut to obtain polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 (raw material-1). .. The glass transition temperature (Tg) was 78 ° C.

(2-a) Preparation of particle-containing PET pellets: The above-mentioned solid-phase polymerized PET pellets (raw material-1k: treatment time 2 hours) were applied to a vent-type twin-screw kneading extruder heated to 280 ° C. and rotating in the same direction. 20 parts by mass (2 parts by mass as cross-linked polystyrene particles) of 10% by mass water slurry of cross-linked polystyrene particles having 80 parts by mass and an average particle size of 0.30 μm is supplied, and the vent holes are maintained at a reduced pressure of 1 kPa or less to retain water. The particles were removed to obtain particle-containing pellets (raw material-2a) having an intrinsic viscosity of 0.62 containing 2% by mass of crosslinked polystyrene particles.

(2-b) Preparation of particle-containing PET pellets: The above-mentioned solid-phase polymerized PET pellets (raw material-1k: processing time 2 hours) were added to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 20 parts by mass (2 parts by mass as cross-linked polystyrene particles) of 10% by mass water slurry of cross-linked polystyrene particles having 80 parts by mass and an average particle size of 0.45 μm is supplied, and the vent holes are maintained at a reduced pressure of 1 kPa or less to retain water. The particles were removed to obtain particle-containing pellets (raw material-2b) having an intrinsic viscosity of 0.62 containing 2% by mass of crosslinked polystyrene particles.

(2-c) Preparation of particle-containing PET pellets: The above-mentioned solid-phase polymerized PET pellets (raw material-1k: processing time 2 hours) were added to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 20 parts by mass (2 parts by mass as cross-linked polystyrene particles) of 10% by mass water slurry of cross-linked polystyrene particles having 80 parts by mass and an average particle size of 0.80 μm is supplied, and the vent holes are maintained at a reduced pressure of 1 kPa or less to retain water. The particles were removed to obtain particle-containing pellets (raw material-2c) having an intrinsic viscosity of 0.62 containing 2% by mass of crosslinked polystyrene particles.

(2-d) Preparation of particle-containing PET pellets: The above-mentioned solid-phase polymerized PET pellets (raw material-1k: processing time 2 hours) were applied to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. Supply 10 parts by mass (1 part by mass as colloidal silica particles) of 10% by mass water slurry of colloidal silica particles having 90 parts by mass and an average particle size of 0.060 μm, and keep the vent holes at a reduced pressure of 1 kPa or less to retain water. The particles were removed to obtain particle-containing pellets (raw material-2d) having an intrinsic viscosity of 0.62 containing 1% by mass of colloidal silica particles.

(2-e) Preparation of particle-containing PET pellets: The above-mentioned solid-phase polymerized PET pellets (raw material-1k: processing time 2 hours) were applied to a vent-type twin-screw kneading extruder heated to 280 ° C. and rotating in the same direction. 20 parts by mass (2 parts by mass as colloidal silica particles) of 10% by mass water slurry of colloidal silica particles having 80 parts by mass and an average particle size of 0.10 μm is supplied, and the vent holes are maintained at a reduced pressure of 1 kPa or less to retain water. The particles were removed to obtain particle-containing pellets (raw material-2e) having an intrinsic viscosity of 0.62 containing 2% by mass of colloidal silica particles.

(2-f) Preparation of particle-containing PET pellets: The above-mentioned solid-phase polymerized PET pellets (raw material-1k: treatment time 2 hours) were applied to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 20 parts by mass (2 parts by mass as colloidal silica particles) of 10% by mass water slurry of colloidal silica particles having 80 parts by mass and an average particle size of 0.20 μm is supplied, and the vent holes are maintained at a reduced pressure of 1 kPa or less to retain water. The particles were removed to obtain particle-containing pellets (raw material-2f) having an intrinsic viscosity of 0.62 containing 2% by mass of colloidal silica particles.

(Example 1)
Using three extruders E1, E2 and E3, the extruder E1 heated to 280 ° C. contains 90 parts by mass of PET pellets (raw material-1) as a raw material for the B layer and a colloidal having an average particle size of 0.06 μm. 10 parts by mass of the silica particle-containing pellet (raw material-2d) was dried under reduced pressure at 180 ° C. for 3 hours before being supplied. Similarly, in the extruder E2 heated to 280 ° C., 82.5 parts by mass of PET pellets (raw material-1) used in the B layer as a raw material for the A layer and colloidal polystyrene particle-containing pellets having an average particle size of 0.20 μm (raw material-1). Raw material-2f) 10 parts by mass and 7.5 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2a) having an average particle size of 0.30 μm were blended and dried under reduced pressure at 180 ° C. for 3 hours before being supplied. Further, PET pellets (raw material-1) as a C layer were supplied to the extruder E3, which was also heated to 280 ° C., after being dried under reduced pressure at 180 ° C. for 3 hours. In order to stack these three layers, the stacking thickness ratio (A layer | C layer | B layer) = 0.5 | 14 | 1.5 was set in the T-die, and the layers were merged so that the B layer side was on the cast drum surface side. A laminated unstretched film was produced by close-contact cooling and solidification while applying a static charge to a cast drum having a surface temperature of 25 ° C.

This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 90 ° C. using a roll-type stretching machine. While grasping both ends of the obtained uniaxially stretched film with clips, the film is guided to a preheating zone having a temperature of 95 ° C. in the tenter, and continuously in a heating zone having a temperature of 110 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. Was stretched 3.4 times (TD stretch 1), and subsequently stretched 1.2 times in the width direction in a heating zone at a temperature of 150 ° C. (TD stretch 2). Subsequently, in the heat treatment zone in the tenter, heat treatment was performed for 10 seconds after microstretching 1.05 times at a temperature of 220 ° C., and further relaxation treatment was performed in the width direction by 0.5% at a temperature of 150 ° C. Then, after cooling uniformly to 25 ° C., the film edge was removed and the film was wound onto a core to obtain a biaxially oriented polyester film having a thickness of 16 μm. The film-forming stability of the obtained biaxially oriented polyester film was good, and when the physical properties were evaluated, it had excellent properties as shown in the table.

(Examples 2 to 7)
As shown in the table, a biaxially oriented polyester film having a thickness of 16 μm was obtained in the same manner as in Example 1 except that the blending amount and the laminated thickness of various particle raw materials were changed so as to have a predetermined concentration. The film-forming stability of the obtained biaxially oriented polyester film was good, and when the physical properties were evaluated, it had excellent properties as shown in the table.

(Example 8)
In the extruder E1 heated to 280 ° C. using two extruders E1 and E2, 90 parts by mass of PET pellets (raw material-1) as a raw material for the B layer and colloidal silica particles having an average particle size of 0.06 μm were used. 10 parts by mass of the contained pellet (raw material-2d) was dried under reduced pressure at 180 ° C. for 3 hours before being supplied. Similarly, in the extruder E2 heated to 280 ° C., 82.5 parts by mass of PET pellets (raw material-1) used in the B layer as a raw material for the A layer and colloidal polystyrene particle-containing pellets having an average particle size of 0.20 μm (raw material-1). Raw material-2f) 10 parts by mass and 7.5 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2a) having an average particle size of 0.30 μm were blended and dried under reduced pressure at 180 ° C. for 3 hours before being supplied. In order to stack two layers of these, the stacking thickness ratio (A layer | B layer) = 1 | 15 is set in the T-die, and the layers are merged so that the B layer side is on the cast drum surface side, and the cast drum has a surface temperature of 25 ° C. Adhesion cooling and solidification were performed while applying an electric charge to prepare a laminated unstretched film.

This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 90 ° C. using a roll-type stretching machine. While gripping both ends of the obtained uniaxially stretched film with clips, the film is guided to a preheating zone having a temperature of 95 ° C. in the tenter, and continuously in a heating zone having a temperature of 110 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. Was stretched 3.4 times (TD stretch 1), and subsequently stretched 1.2 times in the width direction in a heating zone at a temperature of 150 ° C. (TD stretch 2). Subsequently, in the heat treatment zone in the tenter, heat treatment was performed for 10 seconds after microstretching 1.05 times at a temperature of 220 ° C., and further relaxation treatment was performed in the width direction by 0.5% at a temperature of 150 ° C. Then, after cooling uniformly to 25 ° C., the film edge was removed and the film was wound onto a core to obtain a biaxially oriented polyester film having a thickness of 16 μm. The film-forming stability of the obtained biaxially oriented polyester film was good, and when the physical properties were evaluated, it had excellent properties as shown in the table.

(Comparative Examples 1 to 5)
As shown in the table, a biaxially oriented polyester film having a thickness of 16 μm was obtained in the same manner as in Example 1 except that the blending amount and the laminated thickness of various particle raw materials were changed so as to have a predetermined concentration. The PSDs on the A side were all larger than 50,000 nm ³ , and the other characteristics were as shown in the table.

(Comparative Example 6)
Using three extruders E1, E2 and E3, the extruder E1 heated to 280 ° C. contains 90 parts by mass of PET pellets (raw material-1) as a raw material for the B layer and a colloidal having an average particle size of 0.06 μm. 10 parts by mass of the silica particle-containing pellet (raw material-2d) was dried under reduced pressure at 180 ° C. for 3 hours before being supplied. Similarly, in the extruder E2 heated to 280 ° C., 82.5 parts by mass of PET pellets (raw material-1) used in the B layer as a raw material for the A layer and colloidal polystyrene particle-containing pellets having an average particle size of 0.20 μm (raw material-1). Raw material-2f) 10 parts by mass and 7.5 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2a) having an average particle size of 0.30 μm were blended and dried under reduced pressure at 180 ° C. for 3 hours before being supplied. Further, PET pellets (raw material-1) as a C layer were supplied to the extruder E3, which was also heated to 280 ° C., after being dried under reduced pressure at 180 ° C. for 3 hours. In order to stack these three layers, the stacking thickness ratio (A layer | C layer | B layer) = 0.5 | 14 | 1.5 was set in the T-die, and the layers were merged so that the B layer side was on the cast drum surface side. A laminated unstretched film was produced by close-contact cooling and solidification while applying a static charge to a cast drum having a surface temperature of 25 ° C.

This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 90 ° C. using a roll-type stretching machine. While gripping both ends of the obtained uniaxially stretched film with clips, the film is guided to a preheating zone having a temperature of 95 ° C. in the tenter, and continuously in a heating zone having a temperature of 110 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. Was stretched 4.3 times (TD stretching), followed by heat treatment at a temperature of 220 ° C. for 10 seconds in the heat treatment zone in the tenter, and further relaxation treatment at a temperature of 150 ° C. in the 0.5% width direction. rice field. Then, after cooling uniformly to 25 ° C., the film edge was removed and the film was wound onto a core to obtain a biaxially oriented polyester film having a thickness of 16 μm. The PSD of the A side was larger than 50,000 nm ³ , and the other characteristics were as shown in the table.

Claims (13)

A two-layer or three-layered polyester film in which (M60 / M10) × 100 on at least one side (A side) of the polyester film is 0.1 or more and 5.0 or less, which is opposite to the A side. The spectral density on the surface (plane B) at a wavelength of 9.65 μm is in the range of 1000 to 50,000 nm ³ , and the particles (L) having the largest particle diameter as two kinds of particles having different particle diameters in the A layer constituting the A plane. ) And particles (M) having different particle diameters, the particle diameter of the particles (L) is 0.3 μm or more and 0.5 μm or less, the content is 0.05 to 0.25 mass%, and the particles (M) The particle size is 0.1 μm or more and less than 0.3 μm, the content is 0.1 to 0.3% by mass, and the volume-based particle size distribution measurement of the particles is performed. The particle size of the peak top having the largest particle size in the maximum of the particle abundance ratio chart obtained when plotted as the abundance ratio was defined as D (μm), and the thickness t (μm) of the layer forming the A plane was defined. When the t / D is 0.5 or more and 10 or less, 0.02 to 0.20% by mass of particles having a particle diameter of 0.05 to 0.15 μm are contained in the B layer constituting the B surface. Polyester film.
(However, M10 is the protrusion density (pieces / mm ² ) at the slice level with a height of 10 nm, and M60 is the protrusion density (pieces / mm ² ) at the slice level with a height of 60 nm. The particle size is transmitted through the cross section of the film. In the volume-based particle size distribution measurement obtained using a type electron microscope (TEM), the equivalent circle equivalent diameter of the peak value obtained when plotting with the horizontal axis as the particle size and the vertical axis as the particle abundance ratio is the particle size. The average particle diameter of the laminated portion was taken as the average particle diameter. The average particle diameter of the laminated portion was obtained by the following formula from the equivalent circle equivalent diameters obtained above and their body integration ratios, and this value was used as the average particle diameter of the laminated portion. (D).
d = Σ (di ・ Nvi)
Here, di is the equivalent circle equivalent diameter, and Nvi is the volume fraction. ) The polyester film according to claim 1, wherein the M60 on the A side is 500 pieces / mm ² or less. The polyester film according to claim 1 or 2, wherein the M100 on the A side is 5 pieces / mm ² or less.
(However, M100 is the protrusion density (pieces / mm ² ) at the slice level with a height of 100 nm.) The polyester film according to any one of claims 1 to 3, wherein the M10 on the A side is 1000 pieces / mm ² or more and less than 30,000 pieces / mm ² . The polyester film according to any one of claims 1 to 4, wherein the average surface roughness Ra of the A surface is 2 to 7 nm. The polyester film according to any one of claims 1 to 5, wherein the average surface roughness Ra of the B surface is 0.5 to 5 nm. The polyester film according to any one of claims 1 to 6, wherein the film has a thickness of 10 μm or more and 250 nm or less. The polyester film according to any one of claims 1 to 7, which has a three-layer laminated structure. The polyester film according to any one of claims 1 to 8 , which is used as a film for mold release or a process. The polyester film according to claim 9 , which is used as a film for a dry film resist substrate. The polyester film according to claim 9 , which is used as a support for forming a green sheet in a process of manufacturing a multilayer ceramic capacitor. The polyester film according to claim 9 , which is used as a polarizing plate release film. The polyester film according to any one of claims 1 to 8 , which is used as a film for an optical member.