JP2013103361A - Biaxially-oriented polyester film and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially-oriented polyester film hardly causing change in dimensions as a magnetic recording medium even with change of the environment, which has superior storage stability, and which is superior in a slit property and a winding posture.SOLUTION: The biaxially-oriented polyester film has a laminated structure of at least two layers including a C layer configuring one surface, wherein the wave center line waviness of the C layer side surface is 0.5 nm or more and less than 10 nm, the air leakage index when the C layer side surface and the surface on the opposite side thereof are overlapped is 3,000-6,000 seconds, the humidity expansion coefficient in the width direction is 0-6 ppm/%RH, and n_bar((nMD+nTD+nZD)/3) indicated by an average of a refractive index nMD in the longitudinal direction, a refractive index nTD in the width direction, and a refractive index nZD in the thickness direction is 1.590-1.680.

Description

  The present invention relates to a biaxially oriented polyester film having excellent heat resistance, dimensional stability, and surface characteristics, and is suitably used for magnetic recording media, electrical insulation, capacitors, circuit materials, solar cell materials, and the like. The present invention relates to a biaxially oriented polyester film that can be used.

  Biaxially stretched polyester film is used for various applications because of its excellent thermal properties, dimensional stability, mechanical properties, and ease of control of surface morphology, and is particularly useful as a support for magnetic recording media. It is known that high density recording is always required for magnetic recording media. In order to achieve higher density recording, the magnetic layer is made thinner and fine magnetic particles are used, and the fine magnetic particles are highly dispersed to increase the smoothness of the magnetic layer surface and shorten the recording wavelength. However, it is effective to reduce the recording track.

  However, if the smoothness is improved by making the substrate film an ultra-high-definition surface in order to improve the smoothness of the magnetic layer surface, the running property, winding, and surface durability become insufficient. Further, when the recording track is made small, there is a problem that the recording track is liable to be displaced due to deformation due to heat during tape running or temperature / humidity change during tape storage.

  Accordingly, there is an increasing demand for improvement in characteristics such as compatibility of winding property and surface smoothness and dimensional stability in the usage environment and storage environment of the tape.

  From this point of view, the support may be made of an aromatic polyamide having high rigidity superior to the biaxially oriented polyester film in terms of strength and dimensional stability. However, aromatic polyamide is expensive and expensive, and is not practical as a support for general-purpose recording media. Even for polyester films using polyethylene terephthalate, polyethylene naphthalate, etc., a support for magnetic recording media has been developed that has both runnability and smoothness, and has been strengthened using a stretching technique. When it is used for a magnetic recording medium support using magnetic hexagonal ferrite powder, it is still insufficient, and it is still difficult to satisfy strict requirements such as dimensional stability against temperature and humidity.

  In order to make the runnability and smoothness of the polyester film compatible, methods such as coating a primer for a magnetic layer on both sides or one side of the polyester film have been studied (for example, Patent Document 1). However, since the magnetic layer itself is intended for a support for a ferromagnetic metal thin film type magnetic recording medium with extremely high dimensional stability, there is not much demand for dimensional stability of the support with respect to temperature and humidity, and the width of the support Humidity expansion coefficient in the direction is insufficient.

  There is also known a polyester film that achieves both excellent winding properties and electromagnetic conversion characteristics by controlling the waviness of the film surface within a specific range (for example, Patent Document 2). However, when it is used for a magnetic recording medium support using a ferromagnetic hexagonal ferrite powder that requires a high-definition surface, the undulation generated on the surface due to the push-up by particles in the polyester film is still large. The current situation is sufficient.

JP 2005-153322 A JP 2004-299057 A

  An object of the present invention is to solve the above-mentioned problems and to obtain a biaxially oriented polyester film excellent in running property, winding property, dimensional stability and electromagnetic conversion characteristics, and smooth when used as a magnetic recording medium. It is an object of the present invention to provide a biaxially oriented polyester film that has a magnetic layer, can reduce environmental changes in temperature and humidity, and can reduce dimensional changes due to storage, and can be a high-density magnetic recording medium with a low error rate.

  The present invention for solving the above-described problems is characterized by the following configurations.

  (1) A biaxially oriented polyester film having a C layer constituting one surface and having a laminated structure of at least two layers, wherein the center line waviness of filtering on the C layer side surface is 0.5 nm or more and less than 10 nm The air leakage index when the C layer side surface and the opposite surface are superimposed is 3,000 to 6,000 seconds, the humidity expansion coefficient in the width direction is 0 to 6 ppm /% RH, and the longitudinal direction The biaxially oriented polyester film has an n_bar ((nMD + nTD + nZD) / 3) of 1.590 to 1.680, which is an average of the refractive index nMD, the refractive index nTD in the width direction, and the refractive index nZD in the thickness direction.

  (2) The biaxially oriented polyester film according to the above (1), wherein the minute melting peak temperature T-meta is 160 to 190 ° C.

  (3) The biaxially oriented polyester film according to (1) or (2), wherein the Young's modulus in the longitudinal direction is 3.0 to 5.0 GPa.

  (4) The C layer is a layer provided by coating, and the center line surface roughness Ra of the C layer side surface is 0.5 nm or more and less than 5 nm, according to any one of (1) to (3) above Biaxially oriented polyester film.

(5) The center line surface roughness Ra of the surface opposite to the C layer side surface is 3 to 15 nm, and the number of protrusions having a height of 300 nm or more on the surface is less than 30 / mm ^2. The biaxially oriented polyester film according to any one of (1) to (4).

  (6) The biaxially oriented polyester according to any one of (1) to (5), wherein the heat shrinkage in the width direction after heat treatment at 100 ° C. for 30 minutes is 0.5 to 1.5%. the film.

  (7) The biaxially oriented polyester film according to any one of (1) to (6), wherein a magnetic layer is provided on the C layer side and used as a base film for a magnetic recording medium.

  (8) The biaxially oriented polyester film according to any one of the above (1) to (7), which is used as a base film for a coating type digital recording magnetic recording medium.

  (9) A magnetic recording medium using the biaxially oriented polyester film according to (7) or (8) as a base film.

  According to the present invention, a biaxially oriented polyester film excellent in running property, winding property, dimensional stability and electromagnetic conversion characteristics is obtained. A biaxially oriented polyester film that can reduce the dimensional change due to environmental changes and storage of humidity and can be used as a high-density magnetic recording medium with a low error rate can be obtained.

It is the schematic of the sheet | seat width measuring apparatus used when measuring a width dimension.

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

  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. Acid, 4,4′-diphenyl ether dicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, and the like can be used. Among them, terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid can be preferably used. . As the alicyclic dicarboxylic acid component, for example, cyclohexane dicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. These acid components may be used alone or in combination of two or more.

  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, , 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 It can be used. These diol components may be used alone or in combination of two or more.

  The polyester may be copolymerized with a monofunctional compound such as lauryl alcohol or phenyl isocyanate, or a trifunctional compound such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, or 2,4-dioxybenzoic acid. A compound or the like may be copolymerized within a range in which the polymer is substantially linear without excessive branching or crosslinking. In addition to the acid component and diol component, the present invention includes aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid, and 2,6-hydroxynaphthoic acid, p-aminophenol, and p-aminobenzoic acid. As long as the effect is not impaired, the copolymerization can be further carried out.

  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).

  Polyester having a glass transition temperature of less than 150 ° C. can be suitably used in order to achieve biaxial stretching and to exhibit the effects of the present invention such as dimensional stability. As the polyester used in the present invention, polyethylene terephthalate and polyethylene naphthalate (polyethylene-2,6-naphthalate) are preferable. In particular, the main component is preferably polyethylene terephthalate because a process for increasing the crystallite size and the degree of crystal orientation is easy to apply. Here, the main component means 80% by mass or more in the film composition. Further, these copolymers and modified products may be used, and polymer alloys with other thermoplastic resins may be used. The polymer alloy here refers to a polymer multi-component system, which may be a block copolymer by copolymerization or a polymer blend by mixing. In particular, a polymer compatible with polyester is preferable, and a polyetherimide resin is preferable. As the polyetherimide resin, for example, those shown below can be used.

(Wherein R ¹ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, R ² is a divalent aromatic residue having 6 to 30 carbon atoms, From the group consisting of alkylene groups having 2 to 20 carbon atoms, cycloalkylene groups having 2 to 20 carbon atoms, and polydiorganosiloxane groups chain-terminated with alkylene groups having 2 to 8 carbon atoms Selected divalent organic group.)
As said R < ¹ >, R < ² >, the aromatic residue shown by the following formula group can be mentioned, for example.

  In the present invention, 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride and m-phenylenediamine from the viewpoint of affinity with polyester, cost, melt moldability, and the like, or A polymer having a repeating unit represented by the following formula, which is a condensate with p-phenylenediamine, is preferred.

Or

(N is an integer of 2 or more, preferably an integer of 20 to 50)
This polyetherimide is available from SABIC Innovative Plastics under the trade name "Ultem" (registered trademark), and is "Ultem 1000", "Ultem 1010", "Ultem 1040", "Ultem 5000", "Ultem 6000" and "Ultem XH6050". ”Series,“ Extreme XH ”, and“ Extreme UH ”registered trademark names.

  In the biaxially oriented polyester film of the present invention, one surface is constituted by a C layer, and the filtering center line undulation on the surface of the C layer is 0.5 nm or more and less than 10 nm. In a magnetic recording / reproducing system that reproduces a signal with a high-sensitivity MR head as a magnetic recording medium containing a ferromagnetic hexagonal ferrite powder when the filtered center line waviness on the surface of layer C is 10 nm or more, errors occur frequently during recording reproduction. High output cannot be obtained. In a magnetic recording medium containing ferromagnetic hexagonal ferrite powder, a non-magnetic layer and a magnetic layer are extremely thin in order to achieve high-density recording, so that a film as a support is required to have a high-definition surface. The smaller the filtering centerline undulation, the better. However, it is preferably 0.8 to 6 nm, more preferably 1 to 4 nm from the viewpoint of compatibility with running performance.

  The biaxially oriented polyester film of the present invention is a film having the C layer and having a laminated structure of at least two layers. Examples of the layer configuration include a two-layer configuration of C layer | A layer and a three-layer configuration of A layer | B layer | C layer. With a single layer film, it is difficult to satisfy the running property, winding property and electromagnetic conversion characteristics of the present invention.

  In particular, in order to make the filtering center line undulation within the scope of the present invention, the layer adjacent to the C layer can be efficiently obtained the filtering center line undulation of the present invention if it is made of a polyester layer containing no inert particles. Although it is preferable because it is easy, particles having an average particle size of 0.1 μm or less may be contained as long as they have a proportion of 0.2% by mass or less, preferably 0.1% by mass or less. When the particle size of the particles in the adjacent layer is large, waviness is generated on the surface of the C layer due to the pushing up of the particles, and therefore the filtered centerline waviness may not be controlled within the scope of the present invention.

  The air leak index when the biaxially oriented polyester film of the present invention is superposed on the surface of the C layer and the surface on the opposite side (A layer in the example of the layer configuration described above) is 3,000 to 6,000 seconds, Preferably, it is 4,000 to 5,000 seconds. If the air leakage index of the film is less than 3,000 seconds, the air layer trapped between the film / film when it is wound up as a roll is reduced, and the magnetic layer is provided on the side where the magnetic layer is provided by pushing up or transferring by particles in the film. The surface property is lowered, and the filtered center line waviness cannot be within the scope of the present invention. Also, if the air leakage index is longer than 6,000 seconds, the air trapped between the films cannot be discharged, causing vertical wrinkles and uneven roll end surfaces, resulting in poor winding characteristics. Become. Since the air leak index becomes smaller as the surface roughness of the film surface increases, the air leak index can be easily controlled by setting the surface roughness of the front and back surfaces of the film within a range described later. In particular, in order to set the air leakage index to 3,000 seconds or more, it is effective to set the number of protrusions having a height of 300 nm or more on the surface opposite to the surface of the C layer within the range described later. Can be controlled by fine protrusions formed at a high density by coating the C layer and surface protrusions of the A layer.

  The biaxially oriented polyester film of the present invention has a humidity expansion coefficient in the width direction of 0 to 6 ppm /% RH. When the humidity expansion coefficient is larger than 6 ppm /% RH, when used for a magnetic recording medium, deformation due to a change in humidity increases, and dimensional stability deteriorates. A more preferred upper limit is 5.5 ppm /% RH, and even more preferred is 5 ppm /% RH. A more preferred range is 0 to 5.5 ppm /% RH, and even more preferably 0 to 5 ppm /% RH. The humidity expansion coefficient is a physical property affected by the degree of tension of the molecular chain, and can be controlled by the ratio of TD stretching 1 and TD stretching 2 as described later. Control is also possible by the ratio. The greater the ratio of TD stretching 1 and TD stretching 2 (TD1 / TD2), the smaller the coefficient of humidity expansion. Further, the higher the TD stretch total magnification, the smaller the humidity expansion coefficient.

  In the present invention, MD indicates the longitudinal direction of the film, and TD indicates the width direction or the lateral direction of the film.

  The biaxially oriented polyester film of the present invention has an average refractive index n_bar of 1.590 to 1.680. The average refractive index n_bar is preferably 1.590 to 1.615. When n_bar is smaller than 1.590, crystallinity and orientation are insufficient, and storage stability and slit property deteriorate. When n_bar is larger than 1.680, crystallinity is too advanced due to orientation relaxation, and the dimensional stability is deteriorated. n_bar can be controlled by the heat setting temperature, and can also be controlled by the conditions of TD stretching 1 and 2 described later. Note that n_bar is a value calculated by ((nMD + nTD + nZD) / 3) where nMD is the refractive index in the longitudinal direction, nTD is the refractive index in the width direction, and nZD is the refractive index in the thickness direction. The lower n_bar is, the lower the heat setting temperature is. Moreover, n_bar becomes small, so that the ratio (TD1 / TD2) of TD extending | stretching 1 and TD extending | stretching 2 is large.

  The fine melting peak temperature T-meta of the biaxially oriented polyester film of the present invention is preferably 160 to 190 ° C. When the temperature is lower than 160 ° C., the structural fixation due to insufficient heat quantity is insufficient, and the dimensional stability and the heat shrinkage rate deteriorate. When it is higher than 190 ° C., orientation relaxation occurs due to an excessive amount of heat, and the dimensional stability deteriorates. A more preferred upper limit is 188 ° C, and even more preferred is 185 ° C. A more preferred lower limit is 170 ° C, and even more preferred is 175 ° C. A more preferable range is 170 to 188 ° C, and further preferably 175 to 185 ° C. T-meta can be controlled by the heat setting temperature. When the heat setting temperature is high, T-meta is high.

  The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the longitudinal direction of 3 to 5 GPa. When the Young's modulus in the longitudinal direction is within the above range, when used for a magnetic recording medium, the storage stability due to the tension during storage of the magnetic recording medium is good. In order to make it larger than 5 GPa, the MD magnification is increased, and the film forming property tends to be lowered. A preferable range of Young's modulus in the longitudinal direction is 3.4 to 4.5 GPa, and a more preferable range is 3.8 to 4.4 GPa. The Young's modulus in the longitudinal direction can be controlled by the MD stretching ratio. The MD Young's modulus increases as the MD magnification increases.

  The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the width direction of 6 to 12 GPa from the viewpoint of controlling the humidity expansion coefficient in the width direction. When the Young's modulus in the width direction is within the above range, when used for a magnetic recording medium, the dimensional stability due to environmental changes during recording / reproduction of the magnetic recording medium becomes good. The upper limit of the Young's modulus in the width direction is more preferably 10 GPa, still more preferably 9 GPa. The lower limit of the Young's modulus in the width direction is more preferably 6.2 GPa, and even more preferably 6.5 GPa. A more preferable range is 6.2 to 10 GPa, and a further preferable range is 6.5 to 9 GPa. The Young's modulus in the width direction can be controlled by the temperature and magnification of TD stretching 1 and 2 described later. In particular, the total TD magnification is affected, and the higher the total TD magnification, the higher the TD Young's modulus.

  The C layer constituting one side of the biaxially oriented polyester film of the present invention is preferably a layer coated by coating. In particular, it is preferable to coat a C layer containing a water-soluble polymer for the purpose of making the running property, winding property and surface roughness within the scope of the present invention. Examples of water-soluble polymers are those obtained by dissolving an ion-modified polymer such as polyester, polyurethane, polyacryl, polyvinyl alcohol, polyvinyl pyrrolidone, polyamide, polyolefin, or a salt thereof, tragacanth rubber, gelatin, cellulose, and a modified product thereof in water. These blends can also be used. Moreover, it can also bridge | crosslink using crosslinking agents, such as a silane coupling agent, a melamine resin, and an epoxy compound, as needed.

  For example, examples of the polyester constituting the C layer include a polyester copolymer composed of a dicarboxylic acid and a polyhydric alcohol in which 0.5 to 40 mol% of the total dicarboxylic acid component is a sulfonic acid metal group-containing dicarboxylic acid. Can do. Examples of the sulfonic acid metal base-containing dicabonic acid include metals such as sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and 5 [4-sulfophenoxy] isophthalic acid. Examples of the salt include 5-sodium sulfoisophthalic acid and sodium sulfoterephthalic acid. Alternatively, an aqueous polyester resin having at least one free carboxylic acid and carboxylic acid group in the molecule, a crosslinking agent having two or more epoxy groups, and, if necessary, a compound containing a reaction promoting compound can be exemplified. In order to introduce a carboxylic acid group into the molecule of this aqueous polyester resin, for example, trimellitic anhydride, trimellitic acid, pyromellitic anhydride, pyromellitic acid, trimesic acid, cyclobutanetetracarboxylic acid, dimethylolpropionic acid, etc. It is preferable to use the polyvalent compound as one of the raw materials for producing the polymer. The carboxylate can be introduced by neutralizing the carboxylic acid group introduced into the polymer with an amino compound, ammonia, alkali metal or the like.

Although it does not specifically limit as urethane, The polyurethane by which the affinity to water was improved with the carboxylate group, the sulfonate group, or the sulfuric acid half ester base can be mentioned. However, the amount of base such as carboxylate base, sulfonate base or sulfuric acid half ester base is preferably 0.5 to 15% by mass. Alternatively, a polyurethane resin having an anionic group or a polyurethane resin according to them can be used. Here, main components of the polyurethane-forming component are polyisocyanate, polyol, chain extender, cross-linking agent, and the like. Further, a resin composed of a polyol having a molecular weight of 300 to 20,000, a polyisocyanate, a chain extender having a reactive hydrogen atom, a group that reacts with an isocyanate group, and a compound having at least one anionic group is preferable. The anionic group in the polyurethane-based resin is preferably used as —SO ₃ H, —SO ₂ H, —COOH and ammonium salts, lithium salts, sodium salts, potassium salts or magnesium salts thereof. The amount of the anionic group in the polyurethane resin is preferably 0.05 to 8% by mass.

  Polyacrylic includes 40 mole% acrylic and / or methacrylic monomers, 0.1-20 mole% of other functional group-containing monomers and one or more halogen-free ethylenically unsaturated monomers of about 0-49.9. Mol% and copolymer, or at least 25 mol% of acrylic acid, methacrylic acid or an alkyl ester of methacrylic acid alkyl ester and 1 to 50 mol% of vinyl sulfonic acid and p-styrene sulfonic acid and their Copolymers derived from comonomers selected from acids are preferred.

  The solid content concentration in these aqueous solutions is preferably 0.1 to 2% by mass, particularly 0.3 to 1% by mass. If the solid content concentration is less than 0.1% by mass, fine protrusions are not efficiently formed by the water-soluble polymer resin, and the surface becomes smooth, resulting in an increase in the air leakage index and a decrease in winding characteristics. There is. On the other hand, if the solid content concentration exceeds 2% by mass, fine protrusions due to the water-soluble resin become large, and the filtered center line waviness and surface roughness may not be controlled within the scope of the present invention. In addition, the durability of the fine protrusions themselves due to the water-soluble polymer resin may decrease due to the stress applied during the manufacturing process.

  The centerline surface roughness Ra of the surface of the C layer of the biaxially oriented film of the present invention is 0.5 nm or more and less than 5 nm, preferably 0.5 to 4 nm. In order to control the center line surface roughness Ra of the surface of the C layer within the range of the present invention, the solid content concentration in the aqueous solution is adjusted to 0.1 to 2% by mass, particularly 0.3 to 1% by mass. Can be preferably exemplified.

  The C layer does not need to contain inert particles, but may be contained as long as it does not interfere with the control of the surface roughness Ra of the present invention. Examples of the inert particles include colloidal silica particles, acrylic particles, and polystyrene particles having an average particle size of 10 to 30 nm.

  The center line surface roughness Ra of the surface opposite to the C layer of the biaxially oriented polyester film of the present invention (hereinafter sometimes referred to as the A layer surface. The layer constituting the A layer surface is also referred to as the A layer) is It is 3-15 nm, Preferably it is 5-12 nm.

  When the surface roughness Ra of the A layer is out of the range of 3 to 15 nm, the running property and the winding property tend to be poor. As a method for controlling the surface roughness of the A layer, it is possible to control it by the particle size and content of the particles contained in the A layer. Further, the relationship (t / d) between the layer thickness (t) of the A layer and the average particle size (d) of the particles contained in the A layer is set to 0.1 to 10, preferably 0.5 to 5. Can also be controlled.

From the viewpoint of electromagnetic conversion characteristics, it is important that the number of protrusions having a height of 300 nm or more is formed on the surface of the A layer of the biaxially oriented polyester film of the present invention at a frequency of less than 30 / mm ² . The number is preferably 20 pieces / mm ² or less, and more preferably 10 pieces / mm ² or less. Protrusions having a height of 300 nm or more on the surface of the A layer not only form protrusions on the surface of the A layer, but also form protrusions with a small protrusion height but a large protrusion diameter on the surface of the opposite C layer. Reduces the smoothness of the layer surface. As a result, the filtered centerline waviness on the surface of the C layer may not be controlled within the scope of the present invention. In addition, even after the backcoat layer is coated on layer A, protrusions due to the protrusions are formed on the surface of the backcoat layer, which is transferred to the surface of the magnetic layer during roll aging, thereby reducing the smoothness of the magnetic layer and electromagnetic conversion. The characteristics may be deteriorated.

  In order to control protrusions having a height of 300 nm or more in the A layer within the above-mentioned number density range, it is effective to contain inert particles having an average particle diameter of 0.05 to 0.5 μm. Preferably it is 0.1-0.45 micrometer. The content is preferably 0.05 to 0.3% by mass, more preferably 0.08 to 0.25% by mass. The inert particles are not particularly limited, and inorganic particles and organic particles can be used. Of course, one kind of particles or two or more kinds of particles may be used in combination. Specific types include, for example, clay, mica, titanium oxide, calcium carbonate, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina silicate, kaolin, talc, montmorillonite, alumina, zirconia, and the like. Organic particles containing particles, acrylic acid, styrene resin, silicone, imide and the like as constituent components may be added.

  The biaxially oriented polyester film of the present invention has a heat shrinkage in the width direction of 0.5 to 1.5%, and further 0.8 to 1.2% after heat treatment at 100 ° C. for 30 minutes. It is preferable. It is desirable that the thermal contraction rate in the width direction is small because problems such as width shrinkage and wrinkles are less likely to occur in the manufacturing process of the magnetic recording medium. Generally, heat shrinkage is caused by a large strain in the film. Therefore, in order to reduce the heat shrinkage, it is possible to increase the heat treatment temperature or reduce the strain by reducing the stretching ratio in the width direction. It is valid. However, in the above-described method, it becomes difficult to achieve the humidity expansion coefficient in the width direction of the present invention. Therefore, in order to achieve both a heat shrinkage ratio and a humidity expansion coefficient that are in a trade-off relationship, It is important to control the stretching temperature condition. That is, the preheating temperature of TD stretching 1 is set between (cold crystallization temperature of the film after MD stretching (hereinafter referred to as Tcc.BF) −5 ° C.) to (Tcc.BF + 5 ° C.), and the TD1 stretching temperature is set to the preheating temperature. Set as follows.

  In the present invention, the thickness of the biaxially oriented polyester film can be appropriately determined according to the use, but usually 1 to 7 μm is preferable for the linear magnetic recording medium. When this thickness is smaller than 1 μm, electromagnetic conversion characteristics may be deteriorated when a magnetic tape is used. On the other hand, when the thickness is larger than 7 μm, the tape length per one tape is shortened, so that it may be difficult to reduce the size and increase the capacity of the magnetic tape. Therefore, in the case of high-density magnetic recording medium applications, the lower limit of the thickness is preferably 2 μm, more preferably 3 μm, and the upper limit is preferably 6.5 μm, more preferably 6 μm. A more preferable range is 2 to 6.5 μm, and a further preferable range is 3 to 6 μm.

  When the biaxially oriented polyester film of the present invention is used as a base film for a magnetic recording medium, it is important to provide a magnetic layer on the C layer side in order to obtain a high-density magnetic recording medium. Excellent electromagnetic conversion characteristics can be exhibited when a magnetic recording medium using hexagonal ferrite powder is used.

  The biaxially oriented polyester film of the present invention as described above is produced, for example, as follows.

  First, a polyester film constituting a biaxially oriented polyester film is manufactured. In order to produce a polyester film, for example, polyester pellets are melted using an extruder, discharged from a die, and 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 material in the polymer.

  In addition, it is preferable to add inert particles in order to impart slipperiness, abrasion resistance, scratch resistance and the like while controlling the surface properties of the polyester film. Inert particles are inorganic particles, organic particles such as clay, mica, titanium oxide, calcium carbonate, carion, talc, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, etc., acrylic Examples thereof include organic particles containing acid, styrene resin, thermosetting resin, silicone, imide compound and the like, particles precipitated by a catalyst added at the time of polyester polymerization reaction (so-called internal particles), and the like.

  Furthermore, various additives such as compatibilizers, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, and the like, provided that they do not inhibit the present invention. Conductive agents, crystal nucleating agents, ultraviolet absorbers, flame retardants, flame retardant aids, pigments, dyes, and the like may be added.

  Then, after extending | stretching the said sheet | seat to the biaxial of a longitudinal direction and the width direction, it heat-processes. In order to improve the dimensional stability in the width direction, the stretching step is preferably divided into two or more stages in the width direction. That is, the method of performing re-lateral stretching is preferable because it is easy to obtain a high-strength film optimal as a high dimensional stability magnetic tape.

  As the stretching method, a sequential biaxial stretching method such as stretching in the width direction and then stretching in the width direction is preferable.

  Hereinafter, the production method of the film of the present invention will be described as an example in which polyethylene terephthalate (PET) is used as polyester. Of course, the present application is not limited to a PET film, and other polymers may be used. For example, when a polyester film is formed using polyethylene-2,6-naphthalenedicarboxylate having a high glass transition temperature or a high melting point, it may be extruded or stretched at a temperature higher than the following temperature.

  First, polyethylene terephthalate is prepared. Polyethylene terephthalate is manufactured by one of the following processes. (1) Using terephthalic acid and ethylene glycol as raw materials, a low molecular weight polyethylene terephthalate or oligomer is obtained by direct esterification reaction, and then a polymer is obtained by polycondensation reaction using antimony trioxide or titanium compound as a catalyst. Process (2) A process in which dimethyl terephthalate and ethylene glycol are used as raw materials, a low molecular weight product is obtained by transesterification, and then a polymer is obtained by polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. Here, the reaction proceeds even without a catalyst, but the transesterification usually proceeds using a compound such as manganese, calcium, magnesium, zinc, lithium, titanium as a catalyst, and the transesterification reaction is carried out. After the completion of the reaction, a phosphorus compound may be added for the purpose of inactivating the catalyst used in the reaction.

  In order to contain the inert particles in the polyester constituting the film, a method in which the inert particles are dispersed in a predetermined proportion in the form of a slurry in ethylene glycol and this ethylene glycol is added during polymerization is preferable. When adding inert particles, for example, water sol or alcohol sol particles obtained at the time of synthesis of the inert particles are added without drying once, the dispersibility of the particles is good. It is also effective to mix an aqueous slurry of inert particles directly with PET pellets and knead them into PET using a vented biaxial kneading extruder. As a method for adjusting the content of the inert particles, a master pellet of a high concentration of inert particles is prepared by the above method, and this is diluted with PET that does not substantially contain inert particles during film formation. A method for adjusting the content of the active particles is effective.

  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. The film is 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 types of 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. In addition, providing a gear pump for improving the quantitative supply capability as required is extremely preferable in forming the characteristic surface of the present invention. To laminate the film, a plurality of different polymers may be melt laminated using two or more extruders and manifolds or merge blocks.

  Next, the unstretched film thus obtained is stretched in the machine direction using the difference in peripheral speed of the roll (MD stretching) using a longitudinal stretching machine in which several rolls are arranged, and subsequently A biaxial stretching method in which transverse 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 for MD stretching varies depending on the type of polymer used, but can be determined using the glass transition temperature Tg of the unstretched film as a guide. It is preferable that it is the range of Tg-10-Tg + 15 degreeC, More preferably, it is TgC-Tg + 10 degreeC. When the stretching temperature is lower than the above range, film tearing frequently occurs and the productivity is lowered, and it may be difficult to stably stretch in the two-stage TD stretching after MD stretching, which is a feature of the present application. . The MD draw ratio is preferably 2.5 to 4.0 times. More preferably, it is 2.8 to 3.8 times, and still more preferably 3.0 to 4.0 times. In order to stably perform the two-stage TD stretching, the polymer structure in the film after MD stretching is important. If the film is oriented too much in the MD direction, the molecular chains are entangled during TD stretching and local stress is generated, so that the film is broken. In order to prevent the local generation of stress, it is important to generate a microcrystalline state that acts as a stress propagation part and to impart an appropriate MD orientation. Microcrystals can be easily determined by crystallinity analysis by thermal analysis (DSC). The crystallinity is preferably 20 to 30%, more preferably 23 to 28%. Moreover, it can judge by birefringence (DELTA) n as an orientation parameter after MD extending | stretching, and it is preferable that (DELTA) n is 0.011-0.015. Moreover, it is preferable that cold crystallization temperature is 90-100 degreeC.

  Next, TD stretching is performed using a stenter. In order to improve the dimensional stability in the width direction, and to obtain a biaxially oriented polyester film with good storage stability, slitting properties, and winding shape, it is important to stretch in two stages in zones with different temperatures in the width direction. . First, the draw ratio of the first-stage drawing (TD drawing 1) is preferably 3.0 to 5.0 times, more preferably 3.2 to 4.5 times, and even more preferably 3.3 to 3. It is 4.0 times. The stretching temperature of TD stretching 1 is preferably in the range of (Tcc.BF-5) to (Tcc.BF + 5) ° C., more preferably in the range of (Tcc.BF-3) to (Tcc.BF + 5) ° C. Do. Next, the second stage stretching (TD stretching 2) is performed in the stenter as it is. The draw ratio of TD stretch 2 is preferably 1.05 to 2 times, more preferably 1.1 to 1.8 times, and still more preferably 1.2 to 1.5 times. The stretching temperature of TD stretching 2 is preferably in the range of (TD stretching 1 temperature + 50) to (TD stretching 1 temperature + 100) ° C., more preferably (TD stretching 1 temperature + 60) to (TD stretching 1 temperature + 90) ° C. Do in range. By raising the temperature higher than the stretching temperature in the previous step, the mobility of the molecular chain is improved, and it becomes possible to stretch while appropriately untangling the molecular chain due to stretching in the previous step. In particular, since TD stretching 1 and TD stretching 2 are stretched in the same direction, it is preferable to increase the temperature difference. Furthermore, in order to increase the crystal orientation degree and crystallite size of the biaxially oriented polyester film of the present invention and to achieve both the thermal shrinkage rate and the dimensional stability in the width direction, the preheat temperature of TD stretching 1 is the film after MD stretching. (Tcc.BF-2) ° C. to (Tcc.BF + 15) ° C. and 3 to 8 ° C. higher than the stretching temperature of the TD stretching 1 are preferable. More preferably, it is (Tcc.BF) to (Tcc.BF + 10) ° C. or less. By applying heat above the cold crystallization temperature of the film after MD stretching by the preheating of TD stretching 1, microcrystals generated by MD stretching further grow in the film, and the microcrystals serve as a knot and function of stretching. In addition, since the stress propagates more uniformly, the molecular chain can be oriented uniformly with less distortion. When the temperature is higher than (Tcc.BF + 15) ° C., the produced microcrystals grow and the stretchability tends to deteriorate. Further, when the heat setting treatment is performed through the stretching process of the present invention, the crystal orientation is high, and the crystallite size grows in the width direction. The degree of crystal orientation greatly contributes to dimensional stability, and the higher the degree of crystal orientation, the better the dimensional stability. However, if the degree of crystal orientation is increased by simply increasing the draw ratio or the like, the molecular chains are distorted and shrinkage due to heat tends to occur. Therefore, problems such as width shrinkage and wrinkles are likely to occur in the process of forming the magnetic tape.

  Subsequently, the stretched film is heat-set under tension or while relaxing in the width direction. As for heat setting treatment conditions, the heat setting temperature is preferably 160 to 200 ° C. The upper limit of the heat setting temperature is more preferably 190 ° C., still more preferably 185 ° C. The lower limit of the heat setting temperature is more preferably 170 ° C, and even more preferably 175 ° C. A more preferable range is 170 to 190 ° C, and further preferably 175 to 185 ° C. The heat setting treatment time is preferably in the range of 0.5 to 10 seconds, and the relaxation rate is preferably 0 to 2%. After the heat setting treatment, the gripping clip is released to rapidly cool to room temperature while reducing the tension applied to the film. Thereafter, the film edge is removed and wound on a roll to obtain the biaxially oriented polyester film of the present invention.

  In order to achieve the electromagnetic conversion characteristics, dimensional stability, storage stability, slit property, and winding shape of the present application, the ratio of the total TD stretch ratio and MD stretch ratio is important. The value of total TD stretch ratio / MD stretch ratio is preferably 1.2 to 2.0. More preferably, it is 1.3-1.8, More preferably, it is 1.4-1.6. The value of the total TD stretch ratio / MD stretch ratio serves as an index for controlling the balance of molecular chain orientation, and in particular, it is necessary to increase the TD orientation in order to increase the dimensional stability. However, even if only the TD stretching ratio is simply increased, the effect is limited, and the effect of the subsequent TD stretching can be maximized by appropriately controlling the MD stretching. This is because the degree of molecular chain entanglement required for maximizing the effect of TD orientation by maximizing the degree of molecular chain entanglement required to maximize the TD orientation effect by TD stretching It means to control by. Since the optimum value of the MD stretch ratio is related to the total TD stretch ratio in the subsequent stage, it becomes possible to control to a preferable state with the ratio of the stretch ratio as described above.

  Moreover, in order to perform stable film formation, the draw ratio of TD stretch 1 and TD stretch 2 is important. The value of TD stretching 1 magnification / TD stretching 2 magnification is preferably 1.8 to 4.1. More preferably, it is 2.2-3.5, More preferably, it is 2.5-3.0. TD stretching is performed in two stages, but it is preferable that the stretching ratio is relatively high in TD stretching 1. Usually, in order to increase the TD orientation, the higher the magnification in the final stretching, the higher the orientation. However, the TD stretching 2 is preferably stretched at a higher temperature than the TD stretching 1, and the high temperature facilitates the formation of crystals. It is important for the dimensional stability of the present application that the orientation of the amorphous part is high, not the orientation including the crystal generally referred to. When the TD stretch 2 is stretched at a high magnification, the orientation of the amorphous part is relaxed. It becomes easy. That is, it is preferable that the TD stretch 1 is stretched to a high degree to a certain degree and highly oriented, and the TD stretch 2 is stretched to such an extent that the high orientation is not relaxed.

  A heat setting treatment is performed after the TD stretching, but it is preferable to perform a heat treatment at a temperature substantially equal to that of the TD stretching 2 in order to suppress the relaxation of orientation of the film. The heat setting treatment is preferably TD stretching 2 stretching temperature-5 to TD stretching 2 stretching temperature + 5 ° C., more preferably TD stretching 2 stretching temperature-3 to TD stretching 2 stretching temperature while relaxing the film in tension or in the width direction. The heat setting treatment is performed at + 3 ° C., more preferably at the same temperature as TD stretching 2. By bringing the stretching temperature of TD stretching 2 close to the heat setting temperature, the molecular structure can be fixed in the stretched state, and while maintaining high orientation, the molecular chains are distorted and the storage stability and slitting properties deteriorate. Can be suppressed. In addition, there is a difference between the stretching temperature and the heat setting temperature of TD stretching 2, and if the heat setting temperature is too high, it tends to relax and the dimensional stability tends to decrease. If the heat setting temperature is too low, the crystallinity tends to be low. The slit property is likely to deteriorate.

  In the present application, a biaxially oriented polyester film having good electromagnetic conversion characteristics, dimensional stability, storage stability, slitting properties, and winding shape can be obtained by performing a stretching process of MD-TD1-TD2. In a stretching process such as MD1-TD1-MD2-TD2, it is difficult to obtain a biaxially oriented polyester film having good physical properties.

  In the present invention, as a method of coating the C layer, when the sequential biaxial stretching method of the film manufacturing process is adopted, the C layer is first stretched in the longitudinal direction and then stretched in the width direction before starting to stretch. It is preferable to coat. Moreover, when using the simultaneous biaxial stretching method, it is preferable to apply before simultaneous biaxial stretching. Although any stretching method may be used, it is preferable to perform a corona discharge treatment for coating. Coating the C layer during the above-described continuous manufacturing process is cost effective.

  Next, a method for manufacturing a magnetic recording medium will be described.

  The magnetic recording medium support (biaxially oriented polyester film) obtained as described above is slit into, for example, a width of 0.1 to 3 m, and conveyed at a speed of 20 to 300 m / min and a tension of 50 to 300 N / m. On the other hand, a magnetic paint and a non-magnetic paint are applied successively or simultaneously on one surface (C layer surface) with an extrusion coater. A magnetic paint is applied to the upper layer with a thickness of 0.1 to 0.3 μm, and a nonmagnetic paint is applied to the lower layer with a thickness of 0.5 to 1.5 μm. Thereafter, the support coated with the magnetic coating material and the nonmagnetic coating material is magnetically oriented and dried at a temperature of 80 to 130 ° C. Next, a back coat is applied to the opposite surface (the surface of the A layer) with a thickness of 0.3 to 0.8 μm, calendered, and then wound up. The calendering is performed using a small test calender (steel / nylon roll, 5 stages) at a temperature of 70 to 120 ° C. and a linear pressure of 0.5 to 5 kN / cm. Thereafter, the film is aged at 60 to 80 ° C. for 24 to 72 hours, slit to a width of 1/2 inch (1.27 cm), and a pancake is produced. Next, a specific length from this pancake is incorporated into a cassette to obtain a cassette tape type magnetic recording medium.

  Here, examples of the composition of the magnetic paint include the following compositions.

(Composition of magnetic paint)
Ferromagnetic metal powder: 100 parts by weight Modified vinyl chloride copolymer: 10 parts by weight Modified polyurethane: 10 parts by weight Polyisocyanate: 5 parts by weight 2-ethylhexyl oleate: 1.5 parts by weight Palmitic acid: 1 Mass parts-Carbon black: 1 part by mass-Alumina: 10 parts by mass-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass (composition of back coat)
Carbon black (average particle size 20 nm): 95 parts by mass Carbon black (average particle size 280 nm): 10 parts by mass Alumina: 0.1 parts by mass Modified polyurethane: 20 parts by mass Modified vinyl chloride copolymer: 30 Mass parts: Cyclohexanone: 200 parts by mass Methyl ethyl ketone: 300 parts by mass Toluene: 100 parts by mass Magnetic recording media are, for example, data recording applications, specifically computer data backup applications (for example, linear tape recording media (LTO4 And LTO5))) and digital image recording applications such as video.

(Methods for measuring physical properties and methods for evaluating effects)
The characteristic value measurement method and effect evaluation method in the present invention are as follows.

(1) Filter centerline swell Wc
In accordance with ISO 4287-1997, the filtered centerline swell Wc was measured using a surf-order ET-4000A manufactured by Kosaka Laboratory. The conditions were as follows, and the average value of 10 measurements was taken as the value.

・ Device: “surf-order ET-4000A” manufactured by Kosaka Laboratory
・ Analysis software: i-star
・ Tip radius of stylus: 0.5μm
・ Measurement length: 0.5mm
・ Needle pressure: 50μN
Cut-off value: High range -0.08mm, Low range -0.8mm
・ Leveling: Straight line (entire area)
-Filter: Gauss-Magnification Vertical x 200,000 times Horizontal x 500 times (2) Air Leakage Index Measurement was performed at 25 ° C and 65% RH using a Digibeck smoothness tester manufactured by Toyo Seiki Co., Ltd. First, two films are overlapped so that the upper surface is on the C layer side, a hole with a diameter of 10 mmφ is made in one of the lower sheets, and the film is set on a sample stage. At this time, the center of the hole is set at the center of the sample stage. In this state, a load of 1 kg / cm ² is applied to set the degree of vacuum at 383 mmHg. After reaching 383 mmHg, air flows between the film and the sample stage in order to return to normal pressure. At this time, the time during which the degree of vacuum was from 381 mmHg to 379 mmHg was measured and used as the air leakage index.

(3) Humidity expansion coefficient in the width direction Measurement is performed under the following conditions in the width direction of the film, and an average value of three measurement results is defined as a humidity expansion coefficient in the present invention.

Measuring device: Thermomechanical analyzer TMA-50 manufactured by Shimadzu (humidity generator: humidity control device HC-1 manufactured by ULVAC-RIKO)
Sample size: 10 mm in the film longitudinal direction x 12.6 mm in the film width direction
・ Load: 0.5g
・ Number of measurements: 3 times ・ Measurement temperature: 30 ° C.
・ Measurement humidity: Measured dimensions by holding at 40% RH for 6 hours, increasing the humidity to 80% RH in 40 minutes and holding at 80% RH for 6 hours, and then measuring the dimensional change ΔL (mm) in the width direction of the support. taking measurement. The humidity expansion coefficient (ppm /% RH) is calculated from the following equation.

Humidity expansion coefficient (ppm /% RH) = 10 ⁶ × {(ΔL / 12.6) / (80-40)}
(4) Refractive index It measured using the following measuring device according to JIS-K7142 (2008).

・ Device: Abbe refractometer 4T (manufactured by Atago Co., Ltd.)
-Light source: Sodium D line-Measurement temperature: 25 ° C
・ Measurement humidity: 65% RH
-Mount solution: methylene iodide. When the refractive index is 1.74 or more, use sulfur methylene iodide.

Average refractive index n_bar = ((nMD + nTD + nZD) / 3)
Birefringence Δn = (nMD−nTD)
nMD: Refractive index in the film longitudinal direction nTD: Refractive index in the film width direction nZD: Refractive index in the film thickness direction (5) Melting point (Tm), minute melting peak temperature (T-meta), heat of fusion (ΔHm)
According to JIS-K7121 (1987), using a DSC (RDC220) manufactured by Seiko Instruments Inc. as a differential scanning calorimeter and a disk station (SSC / 5200) manufactured by Seiko Instruments Inc. The temperature was raised from 0 ° C. to 300 ° C. at a heating rate of 20 ° C./min. At that time, the peak temperature of the endothermic peak of melting observed was defined as the melting point (Tm), and the minute endothermic peak temperature appearing slightly on the low temperature side of Tm was defined as T-meta. The amount of heat calculated from the peak area of Tm is defined as the heat of fusion ΔHm.

(6) Glass transition temperature (Tg)
Specific heat is measured with the following equipment and conditions, and determined according to JIS-K7121 (1987).

・ Device: Temperature modulation DSC manufactured by TA Instrument
-Measurement conditions-Heating temperature: 270-570K (RCS cooling method)
・ Temperature calibration: Melting point of high purity indium and tin ・ Temperature modulation amplitude: ± 1K
・ Temperature modulation period: 60 seconds ・ Temperature increase step: 5K
・ Sample mass: 5mg
Sample container: Aluminum open container (22 mg)
Reference container: Aluminum open container (18mg)
The glass transition temperature is calculated by the following formula.

Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
(7) Young's modulus The Young's modulus of the film is measured according to ASTM-D882 (1997). Instron type tensile tester is used and the conditions are as follows. The average value of the five measurement results is defined as the Young's modulus in the present invention.

・ Measuring device: Model 5848, an ultra-precision material testing machine manufactured by Instron
・ Sample size:
When measuring Young's modulus in the film width direction Film length direction 2 mm x film width direction 12.6 mm
(The gripping distance is 8mm in the film width direction)
When measuring Young's modulus in the longitudinal direction of the film 2 mm in the film width direction × 12.6 mm in the film longitudinal direction
(Grip interval is 8mm in the longitudinal direction of the film)
・ Tensile speed: 1 mm / min ・ Measurement environment: Temperature 23 ° C., humidity 65% RH
-Number of measurements: 5 times.

(8) Surface roughness SRa of the C layer surface, 10-point average roughness SRz
Ten fields of view were measured at different locations using an atomic force microscope. 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. About the obtained image, three-dimensional surface roughness was computed by Off-Line function Roughness Analysis, and SRa and SRz were measured. The conditions are as follows.

  In the measurement apparatus described below, the X-axis direction of the obtained image is the cantilever scanning direction, which corresponds to the width direction of the film, and the Y-axis direction corresponds to the longitudinal direction of the film.

Measuring device: NanoScope III AFM
(Manufactured by Digital Instruments)
Cantilever: Silicon single crystal Scanning mode: Tapping mode Scanning range: 5μm
Scanning speed: 0.5Hz
Flatten Auto: Order 3
(9) Surface roughness SRa on the surface of layer A, 10-point average roughness SRz, number of protrusions Using the apparatus described in (8) above, the scanning range was changed to 125 μm □, and measurement was performed. About the image obtained by changing a place, surface roughness SRa and SRz were measured by the method similar to said (8). With respect to the number of protrusions, the number of protrusions of 300 nm or more was obtained by setting Grain Height to 300 nm using the Grain Size of the Off-Line function.

(10) Heat shrinkage rate The film is cut in the MD direction or TD direction to a width of 10 mm and a length of 300 mm, marked at intervals of 150 mm, fixed to the support plate under a constant tension (5 g), and then the original length of the marking interval a (mm) Measure. Next, it is allowed to stand for 30 minutes in a hot air oven at 100 ° C. under no load, and the marking interval b (mm) is measured in the same manner as the original length measurement. The thermal shrinkage rate is obtained by the following formula, and an average value of 5 is used.

Thermal contraction rate (%) = (a−b) / a × 100
(11) Average particle diameter of inert particles The cross section of the film is observed at a magnification of 10,000 using a transmission electron microscope (TEM). At this time, when 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 was about 100 nm, 100 fields of view were measured at different locations, the equivalent circle equivalent diameter was obtained for all monodispersed particles photographed in the photograph, and the average was taken as the average particle diameter of the inert particles. Here, when irregular aggregated particles can be confirmed on a photograph observed at a magnification of 10,000, this is not included in the average particle diameter of the particles.

  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 defined as the average particle diameter of each particle.

(12) Content of inert particles 1 g of the polymer was put into 200 ml of 1N-KOH methanol solution and heated to reflux to dissolve the polymer. 200 ml of water was added to the solution after dissolution, and the liquid was then centrifuged to settle the particles, and the supernatant was removed. Water was further added to the particles, and washing and centrifugation were repeated twice. The particles thus obtained were dried, and the content of the particles was calculated by measuring the mass of the particles.

(13) Winding form A film is wound at a speed of 200 m / min. When the rolled film roll is seen, there are no wrinkles or the like. Rolls with no problems, rolls, good, wrinkles, etc. were generated.

(14) Width dimensional stability A film slit to a width of 1 m is conveyed at a tension of 200 N, and a magnetic paint and a non-magnetic paint are applied to one surface of the support (the surface of the C layer) in accordance with the following and 1/2 inch ( 12.65 mm) to make a pancake. Next, a length of 200 m from this pancake is incorporated into a cassette to obtain a magnetic tape.

(Hereinafter, “parts” means “parts by mass.”)
Magnetic layer forming coating solution Barium ferrite magnetic powder 100 parts [plate diameter: 20.5 nm, plate thickness: 7.6 nm, plate ratio: 2.7, Hc: 191 kA / m (≈2400 Oe) saturation magnetization: 44 Am ² / kg, BET specific surface area: 60 m ² / g]
12 parts polyurethane resin Mass average molecular weight 10,000
Sulfonic acid functional group 0.5 meq / g
α-alumina HIT60 (manufactured by Sumitomo Chemical Co., Ltd.) 8 parts Carbon black # 55 (manufactured by Asahi Carbon Co., Ltd.) Particle size 0.015 μm 0.5 parts Stearic acid 0.5 parts Butyl stearate 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 100 parts Nonmagnetic Coating liquid for layer formation Non-magnetic powder α iron oxide 100 parts Average major axis length 0.09 μm, specific surface area by BET method 50 m ² / g
pH 7
DBP oil absorption 27-38ml / 100g
Surface treatment layer Al ₂ O ₃ 8% by mass
Carbon black 25 parts CONDUCTEX SC-U (manufactured by Colombian Carbon)
Vinyl chloride copolymer MR104 (manufactured by Nippon Zeon) 13 parts Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 5 parts Phenylphosphonic acid 3.5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 205 parts Cyclohexanone 135 parts Each component was kneaded with a kneader. The coating solution was pumped through a horizontal sand mill filled with 1.0 mmφ zirconia beads in an amount of 65% with respect to the volume of the dispersed portion, and the liquid was pumped at 2,000 rpm for 120 minutes (substantially residence time in the dispersed portion). ), Dispersed. To the obtained dispersion, polyisocyanate is added to 5.0 parts of the coating for the non-magnetic layer, 2.5 parts to the coating of the magnetic layer, and further 3 parts of methyl ethyl ketone to add a filter having an average pore size of 1 μm. Then, coating solutions for forming the nonmagnetic layer and for forming the magnetic layer were prepared.

  The obtained non-magnetic layer-forming coating solution is coated and dried on a polyethylene terephthalate base so that the thickness after drying is 1.0 μm, and then the magnetic layer-forming coating solution is dried to the thickness of the magnetic layer. Are successively applied so that the magnetic layer is 0.10 μm, and while the magnetic layer is still wet, a cobalt magnet having a magnetic force of 6,000 G (600 mT) and a solenoid having a magnetic force of 6,000 G (600 mT) are used. Oriented and dried. Next, the treatment was performed at a temperature of 90 ° C. and a linear pressure of 300 kg / cm (294 kN / m) using a seven-stage calendar. Thereafter, a 0.4 μm-thick back layer (carbon black average particle size: 17 nm 100 parts, calcium carbonate average particle size: 40 nm 80 parts, α alumina average particle size: 200 nm 5 parts on nitrocellulose resin, polyurethane resin, polyisocyanate Dispersion) was applied. A non-woven fabric and a razor blade were attached to a device having a slit product feeding and winding device so as to press against the magnetic surface, and the surface of the magnetic layer was cleaned with a tape cleaning device to obtain a magnetic tape.

  The tape is taken out from the cartridge of the magnetic tape, and the sheet width measuring device produced as shown in FIG. 1 is put into the following constant temperature and humidity chamber to measure the width dimension. The sheet width measuring device shown in FIG. 1 is a device that measures the width dimension using a laser, and fixes the magnetic tape 9 to the load detector 3 while setting it on the free rolls 5 to 8, and the end portion A weight 4 serving as a load is hung on. When this magnetic tape 9 is irradiated with the laser beam 10, the laser beam 10 oscillated linearly in the width direction from the laser oscillator 1 is blocked only by the portion of the magnetic tape 9, enters the light receiving unit 2, and the blocked laser beam The width is measured as the width of the magnetic tape. The average value of the three measurement results is defined as the width in the present invention.

・ Measuring device: Sheet width measuring device manufactured by Ayaha Engineering Co., Ltd. ・ Laser oscillator 1, light receiving unit 2: Laser dimension measuring device LS-5040 manufactured by Keyence Corporation
-Load detector 3: Load cell CBE1-10K manufactured by NMB
・ Constant temperature and humidity chamber: SE-25VL-A manufactured by Kato Corporation
・ Load 4: Weight (longitudinal direction)
・ Sample size: width 1/2 inch x length 250 mm
-Retention time: 5 hours-Number of measurements: 3 measurements.

(Width dimensional change rate: dimensional stability)
The width dimension (l _A , l _B ) is measured under two conditions, and the dimensional change rate is calculated by the following equation. Specifically, dimensional stability is evaluated according to the following criteria.

By measuring the lapse of 24 hours after _{l A} in A conditions, measuring the _{l B} after a lapse of 24 hours then B conditions. Three points were measured: a sample cut from the 30 m point from the beginning of the tape cartridge, a sample cut from the 100 m point, and a sample cut from the 170 m point. X is rejected.

A condition: 10 ° C, 10% RH, tension 0.8N
B condition: 29 ° C, 80% RH, tension 0.5N
Width dimensional change rate (ppm) = 10 ⁶ × ((l _B -l _A ) / l _A )
◎: The maximum width dimension change rate is less than 450 (ppm) ◎: The maximum width dimension change rate is 450 (ppm) or more and less than 500 (ppm) ○: The maximum width dimension change rate is 500 (ppm) Or more and less than 600 (ppm) Δ: the maximum value of the width dimensional change rate is 600 (ppm) or more and less than 700 (ppm) ×: the maximum value of the width dimensional change rate is 700 (ppm) or more (15) Electromagnetic conversion characteristics ), A recording head (Gap = 0.15 μm, 1.8T) was attached to a drum tester using the produced cassette tape, and noise was measured at a head-medium relative speed of 10 m / sec. SN represents Example 3 as 0 dB, 1.5 dB or more was evaluated as ◯, less than 1.5 to 0 dB as Δ, and less than 0 dB as ×. ○ is desirable, but Δ can be used practically.

(16) Storage stability In the same manner as in (14) above, the tape is taken out from the produced cassette tape cartridge, and the width dimensions (l _C , l _D ) are measured under the following two conditions. Calculate the rate of change.

  Specifically, dimensional stability is evaluated according to the following criteria.

After 24 hours at 23 ° C. and 65% RH, 1 _C is measured. After storing the cartridge for 10 days in an environment of 40 ° C. and 20% RH, 1 _D is measured after 24 hours at 23 ° C. and 65% RH. Three points were measured: a sample cut from the 30 m point from the beginning of the tape cartridge, a sample cut from the 100 m point, and a sample cut from the 170 m point. X is rejected.

Width dimensional change rate (ppm) = 10 ⁶ × (| l _C −l _D | / l _C )
A: Maximum value of width dimension change rate is less than 50 (ppm) ○: Maximum value of width dimension change rate is 50 (ppm) or more and less than 100 (ppm) Δ: Maximum value of width dimension change rate is 100 (ppm) or more Less than 150 (ppm) ×: The maximum value of the rate of change in width dimension is 150 (ppm) or more. (17) Slit property As in (14) above, the tape is taken out from the produced magnetic tape cartridge, and its end is observed. The beard generated at the time of slitting was evaluated by the following method. The slitter speed was 80 m / min. The evaluation of beard was performed by observing the end face of the film with a scanning electron microscope and evaluating the occurrence of beard according to the following criteria. In addition, the beard here means the film piece which peeled in the fiber form.

  A: There is almost no generation of beard.

  ○: There is little generation of beard.

  Δ: There are many whiskers, but slitting is possible.

  X: The generation of whiskers is severe, the slits are torn frequently, and the slits are difficult.

  Based on the following examples, embodiments of the present invention will be described. Here, polyethylene terephthalate is expressed as PET, polyethylene naphthalate is expressed as PEN, and polyetherimide is expressed as PEI.

  (1) Preparation of PET pellets: 194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reaction apparatus, and the contents were heated to 140 ° C. and dissolved. Thereafter, 0.3 parts by mass of magnesium acetate tetrahydrate and 0.05 parts by mass of antimony trioxide were added while stirring the contents, and a transesterification reaction was performed while distilling methanol at 140 to 230 ° C. Next, 1 part by mass of a 5% by mass ethylene glycol solution of trimethyl phosphate (0.05 parts by mass as trimethyl phosphate) was added.

  Addition of trimethyl phosphoric acid in ethylene glycol reduces the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling excess ethylene glycol. In this way, after the temperature of the reaction contents in the transesterification reactor reached 230 ° C., the reaction contents were transferred to the polymerization apparatus.

  After the transition, the reaction system was gradually heated from 230 ° C. to 290 ° C. and the pressure was reduced to 0.1 kPa. The time to reach the final temperature and final pressure was both 60 minutes. After reaching the final temperature and the final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the agitation torque of the polymerization apparatus was a predetermined value (specific values differ depending on the specifications of the polymerization apparatus. The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.62 was 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 form, and immediately cut to obtain polyethylene terephthalate PET pellets having an intrinsic viscosity of 0.62 (raw material-1).

  (2-a) Preparation of particle-containing PET pellets: 80 parts by mass of PET pellets (raw material-1) and an average particle size of 0 were added to a bent biaxial kneading extruder of the same direction rotation type heated to 280 ° C. 20 mass parts (2 mass parts as crosslinked polystyrene particles) of 10 mass% water slurry of 3 μm crosslinked polystyrene particles is supplied, moisture is removed while maintaining the vent hole at a reduced pressure of 1 kPa or less, and Particle-containing pellets (raw material-2a) having an intrinsic viscosity of 0.62 contained in mass% were obtained.

  (2-b) Production of particle-containing PET pellets: 80 parts by mass of PET pellets (raw material-1) described above and an average particle size of 0 were placed in a co-rotating vent type biaxial kneading extruder heated to 280 ° C. 20 parts by mass (2 parts by mass as crosslinked polystyrene particles) of 10 mass% water slurry of .45 μm crosslinked polystyrene particles was supplied, the vent hole was kept at a reduced pressure of 1 kPa or less, moisture was removed, and the crosslinked polystyrene particles 2 A particle-containing pellet (raw material-2b) having an intrinsic viscosity of 0.62 and contained by mass was obtained.

  (2-c) Preparation of particle-containing PET pellets: 80 parts by mass of PET pellets (raw material-1) described above and an average particle size of 0 were placed in a co-rotating vent type biaxial kneading extruder heated to 280 ° C. 20 mass parts (2 mass parts as crosslinked polystyrene particles) of 10 mass% water slurry of .8 μm crosslinked polystyrene particles are supplied, the moisture is removed while maintaining the vent hole at a reduced pressure of 1 kPa or less, and A particle-containing pellet (raw material-2c) having an intrinsic viscosity of 0.62 and contained by mass was obtained.

  (2-d) Preparation of particle-containing PET pellets: 95 parts by mass of the PET pellets (raw material-1) and an average particle diameter of 60 nm were added to a bent biaxial kneading extruder of the same direction rotation type heated to 280 ° C. 5 mass parts (0.5 mass parts as colloidal silica particles) of 10 mass% water colloidal silica particles was supplied, the vent hole was maintained at a reduced pressure of 1 kPa or less, moisture was removed, and the colloidal silica particles were reduced to 0. A particle-containing pellet (raw material-2d) having an intrinsic viscosity of 0.62 and containing 5% by mass was obtained.

  (2-e) Preparation of particle-containing PET pellets: 90 parts by mass of the PET pellets (raw material-1) and an average particle diameter of 100 nm were added to a bent biaxial kneading extruder of the same direction rotation type heated to 280 ° C. 10 parts by weight (1 part by weight as colloidal silica particles) of a 10% by weight water colloidal silica particle is supplied, the vent hole is kept at a reduced pressure of 1 kPa or less, moisture is removed, and the colloidal silica particles are 1% by weight. A particle-containing pellet (raw material-2e) having an intrinsic viscosity of 0.62 was obtained.

(3) Preparation of two-component composition (PET / PEI) pellets: Bent twin-screw kneading extruder of the same direction rotation type provided with three kneading paddle kneading sections heated to a temperature of 280 ° C. (manufactured by Nippon Steel Works) , Screw diameter 30 mm, screw length / screw diameter = 45.5), PET pellet (raw material-1) obtained by the above method and polyetherimide (PEI) "Ultem 1010" manufactured by SABIC Innovative Plastics Co., Ltd. The mixture was melt-extruded at a shear rate of 100 sec ⁻¹ and a residence time of 1 minute to obtain a two-component composition pellet containing 50% by mass of polyetherimide. In addition, the glass transition temperature of the produced two-component composition pellet was 150 ° C. (raw material-3).

  (4) Preparation of PEN pellets: To a mixture of 128 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, 0.025 parts by mass of manganese acetate tetrahydrate salt and sodium acetate trihydrate 0 0.005 part by mass was added, and the ester exchange reaction was carried out while gradually raising the temperature from 150 ° C to 240 ° C. In the middle, when the reaction temperature reached 170 ° C., 0.024 parts by mass of antimony trioxide was added. When the reaction temperature reached 220 ° C., 0.042 parts by mass of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt (corresponding to 2 mmol%) was added. Thereafter, a transesterification reaction was carried out, and 0.023 parts by mass of trimethyl phosphoric acid was added. Next, the reaction product is transferred to a polymerization apparatus, heated to a temperature of 290 ° C., subjected to a polycondensation reaction under a high vacuum of 30 Pa, and the stirring torque of the polymerization apparatus is a predetermined value (specifically depending on the specifications of the polymerization apparatus). The value indicated by polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.6 in the present polymerization apparatus was a predetermined value). Accordingly, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain PEN pellets (raw material-4) having an intrinsic viscosity of 0.6.

  (5-a) Preparation of particle-containing PEN pellets: Colloidal silica particles having 95 parts by mass of PEN pellets (raw material 4) and an average diameter of 60 nm in a co-rotating vent type twin-screw kneading extruder heated to 280 ° C. 10 parts by mass of water slurry (0.5 parts by mass as colloidal silica particles) is supplied, the vent hole is maintained at a reduced pressure of 1 kPa or less to remove moisture, and the colloidal silica particles having an average diameter of 60 nm are reduced to 0. A particle-containing PEN pellet (raw material 5-a) having an intrinsic viscosity of 0.6 and containing 5 parts by mass was obtained.

  (5-b) Preparation of particle-containing PEN pellets: Colloidal silica particles having 90 parts by mass of PEN pellets (raw material 4) and an average diameter of 100 nm in a bent biaxial kneading extruder of the same direction rotation type heated to 280 ° C. 10 parts by weight of water slurry (1 part by weight as colloidal silica particles) is supplied, the vent hole is maintained at a reduced pressure of 1 kPa or less, moisture is removed, and 1 part by weight of colloidal silica particles having an average diameter of 100 nm is contained. A particle-containing PEN pellet (raw material 5-b) having an intrinsic viscosity of 0.6 was obtained.

  (5-c) Preparation of particle-containing PEN pellets: 80 parts by mass of PEN pellets (raw material-4) and an average diameter of 0.3 μm were added to a biaxial kneading extruder of the same direction rotation type heated to 280 ° C. Supply 20 parts by mass of water slurry of 10 parts by mass of spherical cross-linked polystyrene particles (2 parts by mass as spherical cross-linked polystyrene), keep the vent holes at a reduced pressure of 1 kPa or less, remove water, and form spherical cross-links with an average diameter of 0.3 μm. A particle-containing PEN pellet (raw material 5-c) having an intrinsic viscosity of 0.65 containing 2 parts by mass of polystyrene particles was obtained.

Example 1
Extruder E1 heated at 280 ° C. using two extruders E1 and E2 contains 90 parts by mass of PET pellets (raw material-1) and cross-linked polystyrene particles having an average particle size of 0.3 μm as the A layer raw material. 10 parts by mass of pellets (raw material-2a) were dried under reduced pressure at 180 ° C. for 3 hours and then supplied. Similarly, 100 parts by mass of PET pellets (raw material-1) was blended as the raw material for layer B into the extruder E2 heated to 280 ° C., and was supplied after drying under reduced pressure at 180 ° C. for 3 hours. In order to laminate these two layers, the lamination thickness ratio (A layer | B layer) = 1 | 10 is combined in the T die, and the B layer side is merged so that it becomes the cast drum surface side. While applying an electric charge, the film was closely cooled and solidified to produce a laminated unstretched film.

  This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 87 ° C. with a roll-type stretching machine. This stretching was performed using the difference in peripheral speed between two sets of rolls. After performing corona discharge treatment on the B layer of this uniaxially stretched film, the following aqueous solution was applied.

[B layer side (C layer) coating solution]
Methylcellulose 0.15 parts by mass Silane coupling agent 0.045 parts by mass (3- (2-aminoethylamino) fluorotrimethoxysilane)
Solid content coating concentration 12mg / m ²
While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 95 ° C. in the tenter, and then continuously in the heating zone at a temperature of 90 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. Then, the film was stretched 3.5 times (TD stretch 1), and further stretched 1.3 times in the width direction in a heating zone at a temperature of 170 ° C. (TD stretch 2). Subsequently, a heat treatment was performed for 5 seconds at a temperature of 180 ° C. in a heat treatment zone in the tenter, and a relaxation treatment was further performed in the 1% width direction at a temperature of 180 ° C. Subsequently, after uniformly cooling to 25 ° C., the film edge was removed, and the film was wound on a core to obtain a biaxially stretched polyester film having a thickness of 4.8 μm. When the obtained biaxially oriented polyester film was evaluated, as shown in Table 3, when it was used as a magnetic tape, it had excellent electromagnetic conversion characteristics, dimensional stability, storage stability, winding shape, and slit property. Was.

(Example 2, Example 3)
As shown in Table 1, the coating liquid for the C layer was as follows, and the biaxial thickness of 4.8 μm was the same as in Example 1 except that the lamination thickness of the A layer and the magnification of TD stretching 2 were changed. A stretched polyester film was obtained.

[B layer side (C layer) coating solution]
Methyl cellulose 0.093 parts by mass Water-soluble polyester 0.28 parts by mass Silane coupling agent 0.013 parts by mass (3- (2-aminoethylamino) fluorotrimethoxysilane)
Solid content coating concentration 19mg / m ²
Example 4
As layer A raw material, 97.5 parts by mass of PET pellets (raw material-1) and 2.5 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2b) with an average particle size of 0.45 μm were dried under reduced pressure at 180 ° C. for 3 hours. It was supplied after. Similarly, 100 parts by mass of PET pellets (raw material-1) was blended as the raw material for layer B into the extruder E2 heated to 280 ° C., and was supplied after drying under reduced pressure at 180 ° C. for 3 hours. In order to laminate these two layers, the lamination thickness ratio (A layer | B layer) = 1 | 10 is combined in the T die, and the B layer side is merged so that it becomes the cast drum surface side. While applying an electric charge, the film was closely cooled and solidified to produce a laminated unstretched film. The stretching conditions are as shown in Table 1, and the aqueous solution used in Example 1 was applied onto the B layer as the coating solution for the C layer.

(Example 5)
As shown in Table 1, the coating solution for the C layer was as follows, and the biaxial thickness of 4.8 μm was the same as in Example 4 except that the lamination thickness of the A layer and the magnification of TD stretching 2 were changed. A stretched polyester film was obtained.

[B layer side (C layer) coating solution]
Water-soluble polyester 0.39 parts by mass Silane coupling agent 0.012 parts by mass (3- (2-aminoethylamino) fluorotrimethoxysilane)
Melamine resin crosslinking agent 0.12 parts by weight Solid content concentration 12 mg / m ²
(Example 6)
As shown in Table 1, the coating liquid for layer C was as follows, and the thickness was 4.8 μm in the same manner as in Example 4 except that the thickness of layer A and the temperature and magnification of TD stretching 2 were changed. A biaxially stretched polyester film was obtained.

[B layer side (C layer) coating solution]
Water-soluble polyester 0.39 parts by mass Silane coupling agent 0.012 parts by mass (3- (2-aminoethylamino) fluorotrimethoxysilane)
Melamine resin cross-linking agent 0.15 parts by mass Cross-linked styrene / acrylic copolymer particles (average particle size φ20 nm) 0.09 parts by mass PH regulator 0.01 parts by mass (Plus Coat RY-2 manufactured by Kyosei Chemical Industry Co., Ltd.)
Solid content coating concentration 15 mg / m ²
(Example 7)
Two extruders E1 and E2 were used, and the extruder E1 heated to 280 ° C. had a cross-linked polystyrene having 94.5 parts by mass of PET pellets (raw material-1) and an average particle size of 0.3 μm as the A layer raw material. 5 parts by mass of particle-containing pellets (raw material-2a) and 0.5 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2b) having an average particle size of 0.45 μm were supplied after drying under reduced pressure at 180 ° C. for 3 hours. Similarly, 100 parts by mass of PET pellets (raw material-1) was blended as the raw material for layer B into the extruder E2 heated to 280 ° C., and was supplied after drying under reduced pressure at 180 ° C. for 3 hours. In order to laminate these two layers, the lamination thickness ratio (A layer | B layer) = 1 | 10 is combined in the T die, and the B layer side is merged so that it becomes the cast drum surface side. While applying an electric charge, the film was closely cooled and solidified to produce a laminated unstretched film.

  This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 87 ° C. with a roll-type stretching machine. This stretching was performed using the difference in peripheral speed between two sets of rolls. After performing corona discharge treatment on the B layer of this uniaxially stretched film, the following aqueous solution was applied, and TD stretching was performed under the conditions shown in Table 1.

[B layer side (C layer) coating solution]
Methyl cellulose 0.093 parts by mass Water-soluble polyester 0.28 parts by mass Silane coupling agent 0.013 parts by mass (3- (2-aminoethylamino) fluorotrimethoxysilane)
Colloidal silica with an average particle size of 18 nm 0.1 parts by weight Solid content coating concentration 19 mg / m ²
(Example 8)
A biaxially oriented polyester film was obtained in the same manner as in Example 7 except that the layer A lamination thickness and the heat setting temperature were changed as shown in Table 1.

Example 9
A biaxially oriented polyester film was obtained in the same manner as in Example 7 except that the layer A lamination thickness, MD stretch ratio, TD2 stretch ratio, and heat setting temperature were changed as shown in Table 1. In addition, the aqueous solution similar to Example 5 was apply | coated as the coating liquid of C layer.

(Example 10)
In the extruder E1 heated to 280 ° C. using two extruders E1 and E2, 76.5 parts by mass of the raw material-1 as the A layer raw material, 6 masses of the two-component composition pellet (raw material-3) 10 parts by mass of a colloidal silica particle-containing pellet (raw material-2e) having an average particle size of 0.1 μm and 7.5 parts by mass of a crosslinked polystyrene particle-containing pellet (raw material-2a) having an average particle size of 0.3 μm are blended. It supplied after drying under reduced pressure at 3 degreeC for 3 hours. Similarly, in the extruder E2 heated to 280 ° C., 94 parts by mass of PET pellets (raw material-1) and 6 parts by mass of two-component composition pellets (raw material-3) were blended as B layer raw materials at 180 ° C. for 3 hours. It supplied after drying under reduced pressure. In order to laminate these two layers, the lamination thickness ratio (A layer | B layer) = 1 | 10 is combined in the T die, and the B layer side is merged so that it becomes the cast drum surface side. While applying electric charge, it was closely cooled and solidified to produce a laminated unstretched film.

  This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 90 ° C. with a roll-type stretching machine. This stretching was performed using the difference in peripheral speed between two sets of rolls. The uniaxially stretched film was subjected to a corona discharge treatment, and the aqueous solution prepared in Example 2 was applied on the B layer. Then, TD stretching was performed under the conditions shown in Table 1 to obtain a biaxially oriented polyester film.

(Example 11)
The extruder E1 heated to 280 ° C. using two extruders E1 and E2 contains 75 parts by mass of PEN pellets (raw material-4) and colloidal silica particles having an average particle size of 0.1 μm as the A layer raw material. 10 parts by weight of pellets (raw material-5b) 15 parts by weight of crosslinked polystyrene particle-containing pellets (raw material-5c) having an average particle size of 0.3 μm were blended, dried at 180 ° C. for 3 hours under reduced pressure, and then supplied. Similarly, in the extruder E2 heated to 280 ° C., 80 parts by mass of raw material-4 and 20 parts by mass of colloidal silica particle-containing pellets (raw material-5a) having an average particle diameter of 60 nm are blended as B layer raw materials. It supplied after drying under reduced pressure at 3 degreeC for 3 hours. In order to laminate these two layers, the lamination thickness ratio (A layer | B layer) = 1 | 10 is combined in the T die, and the B layer side is merged so that it becomes the cast drum surface side. While applying electric charge, it was closely cooled and solidified to produce a laminated unstretched film.

  This laminated unstretched film was stretched 4 times in the longitudinal direction at 115 ° C. by a roll-type stretching machine. This stretching was performed using the difference in peripheral speed between two sets of rolls. The uniaxially stretched film was subjected to corona discharge treatment, and then the aqueous solution prepared in Example 2 was applied onto the B layer, and TD stretching was performed under the conditions shown in Table 1.

(Comparative Example 1)
As the A layer raw material, 86.5 parts by mass of PET pellets (raw material-1), 13 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2a) having an average particle size of 0.3 μm, and crosslinked polystyrene having an average particle size of 0.8 μm Particle-containing pellets (raw material-2c) were supplied after drying 0.5 parts by mass at 160 ° C. for 8 hours under reduced pressure. Similarly, in the extruder E2 heated to 280 ° C., 60 parts by mass of PET pellets (raw material-1) are blended as B layer raw materials, and 40 colloidal silica particle-containing pellets (raw material-2d) having an average particle diameter of 60 nm are used. It was supplied after being dried under reduced pressure at 160 ° C. for 8 hours. In order to laminate these two layers, the layer thickness ratio (A layer | B layer) = 1 | 14 is combined in the T die, and the A layer side is merged with the cast drum surface side. While applying an electric charge, the film was closely cooled and solidified to produce a laminated unstretched film. This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 110 ° C. (MD stretching 1) using a roll-type stretching machine, and this stretching was performed using the difference in peripheral speed between two sets of rolls.

  While holding both ends of the obtained uniaxially stretched film with a clip, it is guided to a preheating zone at a temperature of 95 ° C. in the tenter, and continuously 3.2 times in the width direction (TD direction) perpendicular to the longitudinal direction at 95 ° C. Stretched (TD stretch 1). Subsequently, the film was re-stretched 1.7 times in the longitudinal direction at 140 ° C. (MD stretching 2). Heat treatment was performed for 3 seconds at a temperature of 210 ° C. under a constant length, and relaxation treatment was performed in the width direction. A biaxially stretched polyester film having a thickness of 6 μm was obtained.

(Comparative Example 2)
As the A layer raw material, 79.5 parts by mass of PEN pellets (raw material-4), 13 parts by mass of colloidal silica particle-containing pellets (raw material-5b) having an average particle size of 0.1 μm, containing crosslinked polystyrene particles having an average particle size of 0.3 μm 7.5 parts by mass of pellets (raw material-5c) were blended, dried at 180 ° C. for 3 hours under reduced pressure, and then supplied. As B layer raw material, 100 parts by mass of PEN pellets (raw material-4) were supplied after drying under reduced pressure at 180 ° C. for 3 hours. In order to laminate these two layers, the lamination thickness ratio (A layer | B layer) = 2 | 8 is combined in the T die, and the B layer side is merged so as to be on the cast drum surface side. While applying an electric charge, the film was closely cooled and solidified to produce a laminated unstretched film. This laminated unstretched film was stretched 5.4 times (MD stretching 1) in the longitudinal direction at 135 ° C. with a roll-type stretching machine and quenched. This stretching was performed using the difference in peripheral speed between two sets of rolls. The uniaxially stretched film was subjected to a corona discharge treatment, and the following aqueous solution was applied onto the B layer.

[B layer side (C layer) coating solution]
Water-soluble polyester 1.2 parts by mass Average particle size 30 nm Polymethyl methacrylate particles 0.06 parts by mass (Epaster MA, manufactured by Nippon Shokubai Chemical Co., Ltd.)
0.225 parts by mass of polyoxyethylene lauryl ether (n = 7) (Nanoacty N70, manufactured by Sanyo Chemical Industries)
Solid content coating concentration 30 mg / m ²
The both ends of the obtained uniaxially stretched film were guided to a tenter while being held with clips, and stretched 4.2 times in the width direction (TD direction) perpendicular to the longitudinal direction at a temperature of 155 ° C. (TD stretch 1). Subsequently, while performing a heat treatment for 4 seconds at a temperature of 205 ° C. under a constant length, the film was stretched in the 1.08-fold width direction to obtain a biaxially stretched polyester film having a thickness of 8.3 μm.

(Comparative Example 3)
The raw materials used for the A layer and the B layer were the same as in Comparative Example 1. Moreover, the aqueous solution which used the coating liquid of C layer in Example 7 was apply | coated, and it changed into the film forming conditions shown in Table 1, and obtained the biaxially stretched polyester film.

(Comparative Example 4)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the preheating temperature condition of TD stretch 1 was changed as shown in Table 1.

(Comparative Example 5)
A biaxially stretched polyester film was obtained under the same conditions as in Example 1 except that the A layer and B layer materials were the same as those used in Example 1, except that the surface of the B layer was not coated.

(Comparative Example 6)
As the A layer raw material, 78.5 parts by mass of PET pellets (raw material-1) and 22.5 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2a) having an average particle size of 0.3 μm are blended to obtain the B layer raw material. 80 parts by mass of PET pellets (raw material-1), 20 parts by mass of colloidal silica particle-containing pellets (raw material-2d) having an average particle size of 60 nm, and the particles of layer A and layer B shown in Table 1 A biaxially stretched polyester film was obtained in the same manner as in Example 6 except that the formulation was changed and no coating was applied to the surface of the B layer.

(Comparative Example 7)
A biaxially stretched polyester film was obtained in the same manner as in Example 10 except that the TD stretching 2 was not performed and the magnification of the TD stretching 1 and the heat setting temperature were changed as shown in Table 1.

1: Laser oscillator 2: Light receiving unit 3: Load detector 4: Load 5: Free roll 6: Free roll 7: Free roll 8: Free roll 9: Magnetic tape 10: Laser light

Claims (9)

A biaxially oriented polyester film having a C layer constituting one surface and having a laminate structure of at least two layers, wherein the waviness center line waviness on the C layer side surface is 0.5 nm or more and less than 10 nm. When the side surface and the opposite surface are overlapped, the air leak index is 3,000 to 6,000 seconds, the humidity expansion coefficient in the width direction is 0 to 6 ppm /% RH, and the refractive index in the longitudinal direction A biaxially oriented polyester film in which n_bar ((nMD + nTD + nZD) / 3) represented by an average of nMD, a refractive index nTD in the width direction, and a refractive index nZD in the thickness direction is 1.590 to 1.680. The biaxially oriented polyester film according to claim 1, wherein the minute melting peak temperature T-meta is 160 to 190 ° C. The biaxially oriented polyester film according to claim 1 or 2, wherein Young's modulus in the longitudinal direction is 3.0 to 5.0 GPa. The biaxially oriented polyester film according to any one of claims 1 to 3, wherein the C layer is a layer provided by coating, and the center line surface roughness Ra of the C layer side surface is 0.5 nm or more and less than 5 nm. The center line surface roughness Ra of the surface opposite to the C layer side surface is 3 to 15 nm, and the number of protrusions having a height of 300 nm or more on the surface is less than 30 / mm ² . 4. The biaxially oriented polyester film according to any one of 4 above. The biaxially oriented polyester film according to any one of claims 1 to 5, wherein the heat shrinkage in the width direction after heat treatment at 100 ° C for 30 minutes is 0.5 to 1.5%. The biaxially oriented polyester film according to claim 1, wherein a magnetic layer is provided on the C layer side and used as a base film for a magnetic recording medium. The biaxially oriented polyester film according to any one of claims 1 to 7, which is used as a base film for a magnetic recording medium of a coating type digital recording system. A magnetic recording medium using the biaxially oriented polyester film according to claim 7 or 8 as a base film.

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