JP2012102251A - Biaxially oriented polyester film and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film which reduces dimensional changes due to the environmental changes of temperature and humidity and to storage when it is used especially as the base film of a magnetic recording medium and is used to form a high density magnetic recording medium having a low error rate.SOLUTION: The biaxially oriented polyester film has a sea-island structure, wherein the average dispersion diameter of island parts is 30-200 nm, and is characterized in that the coefficient of humidity expansion in at least one of longitudinal direction and the width direction thereof is 0-6 ppm/%RH and the gelation rate after a treatment at 300°C for 2.5 h is 0-15 mass%.

Description

  The present invention relates to a biaxially oriented polyester film excellent in dimensional stability. The biaxially oriented polyester film of the present invention can be suitably used for magnetic recording media, electrical insulation, capacitors, circuit materials and solar cell materials. The biaxially oriented polyester film of the present invention has excellent film-forming stability over a long period of time, has few surface defects, and particularly when used as a base film for a magnetic recording medium, changes in environmental conditions such as temperature and humidity and after storage. A high-density magnetic recording medium with a small dimensional change and a low error rate can be obtained.

  Biaxially oriented polyester film is used for magnetic recording media, for electrical insulation, for capacitors, for packaging and magnetic recording media using its excellent thermal properties, dimensional stability, mechanical properties, electrical properties, heat resistance and surface properties. It is used for various industrial materials. In particular, its usefulness as a support for magnetic recording media is well known.

  In recent years, a magnetic recording medium such as a magnetic tape has been required to have a thin base film and a high density recording in order to reduce the weight, size, and capacity of the equipment. For high density recording, it is useful to shorten the recording wavelength and the recording track.

  However, if the recording track is made small, there is a problem that the recording track is liable to shift due to deformation of the tape due to heat during tape running or temperature / humidity change during tape storage. Therefore, there is an increasing demand for improving the dimensional stability of the base film with respect to the tape usage environment and storage environment. In addition, there is an increasing demand for improvement in running durability when a magnetic tape is used.

  In addition, when the film is thinned, the mechanical strength becomes insufficient and the stiffness of the film becomes weak, and the film tends to stretch in the longitudinal direction and shrink in the width direction. There are problems such as deterioration in conversion characteristics and head and tape scraping.

  From these viewpoints, the support may be made of an aromatic polyamide having high rigidity superior to the biaxially stretched polyester film in terms of strength and dimensional stability. However, aromatic polyamides may be too rigid to cause head scraping. Furthermore, the price is high and it is not practical as a support for general-purpose recording media. Also for polyester films using polyethylene terephthalate, polyethylene naphthalate, etc., a support for a magnetic recording medium that has been strengthened by using a stretching technique has been developed. However, it is still difficult to satisfy strict requirements such as dimensional stability with respect to temperature and humidity.

  In recent years, in order to increase the heat resistance of a polyester film, methods such as blending other thermoplastic resins with polyester have been studied.

  As for a biaxially oriented polyester film in which a polyester and a thermoplastic resin other than polyester are mixed, a film excellent in running property and scratch resistance has been proposed (for example, Patent Document 1). However, this technique is a technique for improving the scratch resistance of the film surface, and has a technical idea different from that of the present application. In fact, the mechanical properties and dimensional stability cannot be improved by the technique described in this document. In addition, when mixing a thermoplastic resin other than polyester in the polyester, as shown in the present application, a mixing technique that is important for improving the dimensional stability of the film, polyimides exemplified in the present application examples, etc. A specific method for forming a film using a three-component resin is not disclosed.

  In addition, in films consisting of polyester and polyimide and polyimide and nano-compatible polymer, a film with improved heat resistance and thermal dimensional stability has been proposed using aromatic polyether ketone as a polymer compatible with polyimide and nano-compatibility. (For example, Patent Document 2). However, this technique involves a large amount of polyimide or a polymer that is nano-compatible with polyimide with respect to polyester, and may not be sufficient for effective molecular chain orientation by stretching or the like. For example, it may not always be sufficient to meet stringent requirements such as temperature and humidity dimensional stability when used in high-density magnetic recording media. Further, foreign matters due to unmelted materials are likely to be generated in the film, and the surface is likely to be rough. For example, when used for a magnetic recording medium, electromagnetic conversion characteristics may be deteriorated.

  Furthermore, a film made of polyester and polyimide tends to easily generate an oxidative degradation product, and an improvement using an antioxidant has been proposed (for example, Patent Document 3), but the antioxidant bleeds out and wettability decreases. There are issues such as.

JP 2001-323146 A JP 2004-123863 A JP 2009-179739 A

  An object of the present invention is to solve the above-described problems, and to obtain a biaxially oriented polyester film having few defects, excellent productivity, and excellent rigidity and dimensional stability. Especially when used as a base film for magnetic recording media, a biaxially oriented polyester film that can reduce temperature and humidity environmental changes and dimensional changes due to storage and can be used as a high-density magnetic recording medium with a low error rate. The purpose is to provide.

  To achieve the above object, the present invention has the following features.

  (1) It has a sea-island structure, the average dispersion diameter of the island portion is 30 to 200 nm, the humidity expansion coefficient in at least one direction in the longitudinal direction or width direction of the film is 0 to 6 ppm /% RH, and 300 ° C. 2 A biaxially oriented polyester film having a gelation rate of 0 to 15% by mass after treatment for 5 hours.

  (2) The biaxially oriented polyester film according to (1) above, wherein the glass transition temperature of the amorphous resin forming the island portion having a diameter of 30 to 200 nm is 230 ° C to 400 ° C.

  (3) Amorphous resin forming an island part having a diameter of 30 to 200 nm is represented by the following formula (1)

The biaxially oriented polyester film according to the above (1) or (2), which is a polyetherimide having a sulfonyl group component represented by

  (4) It has an island part having a diameter of 30 to 200 nm, and the average of the ratio of the major axis to the minor axis (major axis / minor axis) of the island part is 1 to 20, the above (1) to (3) The biaxially oriented polyester film according to any one of the above.

  (5) The biaxially oriented polyester film according to any one of the above (1) to (4), having an island portion having a diameter of 1 nm or more and less than 30 nm.

  (6) The biaxially oriented polyester film according to (5), wherein the island portion having a diameter of 1 nm or more and less than 30 nm contains polyetherimide.

  (7) A magnetic recording medium using the biaxially oriented polyester film according to any one of (1) to (6) above.

  According to the present invention, it can be suitably used for magnetic recording media, electrical insulation, capacitors, circuit materials, solar cell materials, etc., and has few defects, excellent productivity, and excellent rigidity and dimensional stability. An axially oriented polyester film can be obtained. The biaxially oriented polyester film of the present invention is a high-density magnetic recording having a low error rate and a small change in temperature and humidity environment and dimensional change after storage, especially when used as a base film for a magnetic recording medium. It can be a medium.

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

  The biaxially oriented polyester film of the present invention is composed mainly of polyester. Here, “having polyester as a main component” means that 50% by mass or more of polyester is the total amount of all polymers constituting the film. If the polyester content is less than 50% by mass, productivity tends to decrease. The content of the polyester is more preferably 80% by mass or more, and still more preferably 85% by mass or more, based on the total amount of all polymers constituting the film.

  Examples of the polyester constituting the biaxially oriented polyester film of the present invention include polymers having an acid component or a diol component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid as a structural unit (polymerization unit). Preferably there is.

  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, 6,6 ′-(alkyl). Rangeoxy) di-2-naphthoic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, and the like. Among these, terephthalic is preferable. Acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid can be used. As the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, an alkylene having 2 to 10 carbon atoms is preferable, and 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 Examples include '-(trimethylenedioxy) di-2-naphthoic acid and 6,6'-(butyleneoxy) di-2-naphthoic acid. 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.

  The 6,6 '-(alkylenedioxy) di-2-naphthoic acid component can be used as a main component, but is preferably copolymerized with other aromatic polyester components. The preferable copolymerization amount of the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is 5 to 50 mol%, more preferably 10 to 40 mol%, still more preferably 15 to 30 mol%. is there. The melting point of the polyester copolymerized with 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is preferably 220 to 260 ° C. More preferably, it is 230-250 degreeC. More preferably, it is 235-245 degreeC. The glass transition temperature of the polyester copolymerized with 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is preferably 100 to 140 ° C. More preferably, it is 110-130 degreeC. More preferably, it is 115-125 degreeC. The melt crystallization peak temperature of the polyester copolymerized with 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is preferably 140 to 180 ° C. More preferably, it is 150-170 degreeC. More preferably, it is 155-165 degreeC.

  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).

  The biaxially oriented polyester film of the present invention preferably contains a crystalline polyester from the viewpoint that particularly excellent productivity, mechanical properties, thermal properties, electrical properties, surface properties, and heat resistance can be imparted. A group consisting of terephthalate (hereinafter sometimes referred to as PET), poly (ethylene-2,6-naphthalenedicarboxylate (polyethylene-2,6-naphthalate)) (hereinafter sometimes referred to as PEN), and modified products thereof. It is preferable that at least one polyester selected from the group consisting of: Of course, it may be a copolymer of PET or PEN, or may be a polymer alloy with another thermoplastic resin. 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. The biaxially oriented polyester film of the present invention preferably contains at least one of these polymers.

  The biaxially oriented polyester film of the present invention preferably contains at least two types of polyetherimide. Since the biaxially oriented polyester film of the present invention contains at least two kinds of polyetherimides, it becomes easy to simultaneously impart excellent heat resistance, high orientation, and excellent surface properties to the biaxially oriented polyester film of the present invention. is there. Specific types of polyetherimide will be described later.

  The biaxially oriented polyester film of the present invention has a sea-island structure.

  When the sea-island structure is used, a high orientation can be imparted in the longitudinal direction and the width direction while maintaining dimensional stability, so that the mechanical properties can be enhanced at the same time. For this reason, use as a base film for a magnetic recording medium is particularly suitable because it has the advantage of reducing environmental changes in temperature and humidity, dimensional changes during storage, error rate, and the like.

  In order to further enhance the effects as described above, it is important to cause the island portion to function as a restraint point during stretching and to exhibit the effect of increasing the molecular chain orientation of the sea portion. For this reason, it is preferable that the average dispersion diameter of an island part is 30-200 nm. More preferably, it has an island component having a dispersion diameter of 30 to 200 nm. As a result, the above-described effects, i.e., during stretching, the island part functions as a restraint point or nodal point, stress is likely to rise at a low magnification in the stress-strain curve, and the molecular chains of the film structure are stretched uniformly. The effect that it is easy to be made can be expressed more. That is, it is possible to further enhance the effect of developing the effect of uniformly increasing the molecular chain orientation in the sea portion.

  When the dispersion diameter of the island portion is less than 30 nm, the island portion is difficult to function as a restraint point with respect to the sea portion, and the molecular chain orientation in the film longitudinal direction and / or the width direction cannot be increased during film stretching. is there. Therefore, the dimensional stability and mechanical properties of the biaxially oriented polyester film are reduced, and when the film is used for magnetic recording media, the temperature and humidity environment changes, the dimensional changes after storage, and the error rate increase. There is.

  For example, in a sea-island structure in which polyester is the sea part and a resin different from the sea part forms the island part, the glass transition temperature of the resin that forms the island part (below) as the average dispersion diameter of the island part becomes smaller May be lower than the Tg when the resin is present alone. If the dispersion diameter of the island portion is less than 30 nm, the Tg of the island portion becomes sufficiently low, and the island portion may not function as a restraint point with respect to the sea portion. Moreover, an island part may receive a stress at the time of extending | stretching of a film, and may deform | transform.

  On the other hand, if the average dispersion diameter of the island portion of the biaxially oriented polyester film of the present invention is larger than 200 nm, film breakage due to the island portion frequently occurs during film formation, and the productivity tends to decrease. In addition, when the film is stretched, sufficient molecular chain orientation cannot be provided, the film surface becomes rough, or voids are generated. For example, when used for a magnetic recording medium, the electromagnetic conversion characteristics are low. It becomes difficult to obtain the effect of the present invention.

  The average dispersion diameter of the island portion of the biaxially oriented polyester film of the present invention is more preferably 50 to 150 nm.

  In the biaxially oriented polyester film of the present invention, the average of the ratio of the major axis to the minor axis (major axis / minor axis) of the island part having a diameter of 30 to 200 nm is preferably 1 to 20.

  When the average of the ratio of the major axis to the minor axis (major axis / minor axis) is 1 to 20, this island part functions as a restraint point during stretching, and the stretching stress is uniformly and efficiently transmitted to the sea part. It becomes possible. By uniformly and efficiently transmitting the stretching stress to the sea part, the film longitudinal direction and the width direction can be more easily oriented. As a result, the dimensional stability and mechanical properties of the biaxially oriented polyester film of the present invention are dramatically improved. When the film is used as a base film of a magnetic recording medium, the temperature and humidity are changed due to environmental changes and storage. Changes and error rates can be made very small. Moreover, it is easy to control the 10-point average roughness Rz of the film surface within a preferable range by suppressing the formation of coarse protrusions, and it is easy to control the film surface roughness Ra within a preferable range. Furthermore, it is possible to suppress a decrease in electromagnetic conversion characteristics after storing the cartridge. In order to further enhance these effects, the average of the ratio of the major axis to the minor axis (major axis / minor axis) is more preferably 1 to 15, and further preferably 1 to 10.

  In the biaxially oriented polyester film of the present invention, the island portion having a diameter of 30 to 200 nm is preferably made of an amorphous resin.

  When the island portion having a diameter of 30 to 200 nm is an amorphous resin, the processability with the polyester is improved and the surface of the film is easily smoothed. Further, when used as a base film for a magnetic recording medium, excellent running durability and electromagnetic conversion characteristics can be imparted.

  Here, the amorphous resin refers to a resin having such a characteristic that, when a sample is measured using differential scanning calorimetry (DSC) or the like, only the glass transition temperature is detected and the melting point and the melting peak are not detected.

  The glass transition temperature of the above amorphous resin is preferably 230 to 400 ° C. When the glass transition temperature is 230 to 400 ° C., the island portion in the film is likely to function as a restraint point during stretching or heat treatment, and the molecular chain orientation of the sea portion in the stretching process is easily enhanced. When the molecular chain orientation is increased, it becomes easier to obtain the effect of the present application by strengthening and improving dimensional stability. Furthermore, there are few defects on the surface of the biaxially oriented polyester film of the present invention, and there is an effect of forming a film. For example, when the biaxially oriented polyester film of the present invention is produced by the melt casting method, when the amorphous resin is extruded simultaneously with the polyester, the higher the glass transition temperature of the amorphous resin, the more the oxidative degradation of the polyester. The film surface defects can be reduced.

  From the viewpoint of extruding the polyester and amorphous resin for a long time by the melt film-forming method of the biaxially oriented polyester film of the present invention, and from the viewpoint of suppressing molecular chain orientation relaxation in the heat treatment step after film stretching, The glass transition temperature of the amorphous resin forming the island portion having a thickness of 30 to 200 nm is more preferably 232 to 300 ° C, and further preferably 235 to 250 ° C. The glass transition temperature of the amorphous resin forming the island portion having a diameter of 30 to 200 nm is 230 to 400 ° C., and the glass transition temperature is higher than the stretching temperature and heat treatment temperature of the film, so that the island portion in the film is stretched. It is easy to function as a restraint point at the time of heat treatment or heat treatment, and deformation of the island component is less likely to occur, and the average of the ratio of the major axis to the minor axis (major axis / minor axis) is easily in the range of 1 to 20. It becomes easy to increase the molecular chain orientation of the sea component, which is an effect. The higher the glass transition temperature, the lower the oxidative degradation of the polyester.

  In the biaxially oriented polyester film of the present invention, the amorphous resin constituting the island portion is polyetherimide (hereinafter sometimes referred to as PEI), polyimide (hereinafter sometimes referred to as PI), polyethersulfone (hereinafter referred to as PIEI). , PES) is preferred, and polyetherimide containing a sulfonyl group is more preferred.

  Here, PEI is a resin containing an ether bond in a polyimide constituent component composed of an imide group, and is represented by the following general formula.

(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.

  From the viewpoints of affinity with the polyester constituting the biaxially oriented polyester film of the present invention, cost, melt moldability, and the like, PEI is preferably a polymer having a repeating unit represented by the following formula containing a sulfonyl group.

(N is an integer of 2 or more, preferably an integer of 20 to 50)
This PEI is a trade name of “Ultem” (registered trademark), which is available from SABIC Innovative Plastics, Inc., and is known by a registered trademark name of “UltemXH6050-1000” series.

  In the present invention, the various PEIs described above are preferably included in at least two types. By including two types of PEI, the melt processability of PEI is improved and it becomes easy to mix in PET. Furthermore, since the entanglement of the molecular chain with the polymer that forms the sea portion increases, the force from the restraint point can be more effectively transmitted to the sea portion during the stretching process, and the molecular chain orientation of the sea portion can be changed. Can be increased. Moreover, since Tg is high, the thermal stability at the time of melt extrusion is improved.

  In the biaxially oriented polyester film of the present invention, the total mass of island portions having a diameter of 30 to 200 nm is preferably 0.1 to 30% by mass of the total mass of the film. When the total mass of the island portion is 0.1 to 30% by mass of the total film mass, the mechanical properties, thermal properties, electrical properties, surface properties, heat resistance, and workability of the biaxially oriented polyester film of the present invention are improved. Can be increased. Furthermore, the frequency of film breakage due to stretching during film formation is reduced, and the biaxially oriented polyester of the present invention can be manufactured at a lower cost and with higher productivity.

  From the viewpoint of reducing the frequency of film breakage due to stretching during film formation, the total mass of the island portion having a diameter of 30 to 200 nm is more preferably 0.5 to 15% by mass, and further preferably 1 to 10% by mass. is there. More preferably, it is 1-5 mass%.

  The biaxially oriented polyester film of the present invention preferably has an island portion having a diameter of 1 nm or more and less than 30 nm. By having an island portion having a diameter of 1 nm or more and less than 30 nm, excellent heat resistance can be easily imparted to the biaxially oriented film of the present invention.

  In the biaxially oriented polyester film of the present invention, it is preferable that an island portion having a diameter of 1 nm or more and less than 30 nm contains polyetherimide (PEI). By including PEI, the heat resistance excellent in the biaxially oriented polyester film of the present invention can be imparted.

  In addition, the measuring method of the island part whose diameter is 1 nm or more and less than 30 nm will be described later.

  The biaxially oriented polyester film of the present invention has a humidity expansion coefficient of 0 to 6 ppm /% RH in at least one direction in the longitudinal direction or width direction of the film when the humidity is changed from 40% RH to 80% RH at 30 ° C. It is.

  In order to make the above-mentioned humidity expansion coefficient less than 0 ppm /% RH, it is usually necessary to extremely increase the draw ratio of the film. As a result, stretching tears frequently occur during film formation, and productivity is lowered, so that the film tends to be expensive. Further, the obtained biaxially oriented film has a very small elongation at break, so it tends to break, and handling properties tend to decrease. For example, the workability when the film is used for a magnetic recording medium tends to be lowered. .

  On the other hand, if the humidity expansion coefficient is larger than 6 ppm /% RH, for example, when the film is used for a magnetic recording medium, environmental changes in temperature and humidity, dimensional changes after storage, error rates, and the like increase. There are many.

  When used as a base film for a magnetic recording medium, from the viewpoint of improving dimensional stability due to humidity change during recording and reproduction of the obtained magnetic recording medium and dimensional stability after storage under high humidity conditions, at least the above-mentioned The upper limit of the unidirectional humidity expansion coefficient is preferably 5.5 ppm /% RH, and more preferably 5 ppm /% RH. A preferred range is 0 to 5.5 ppm /% RH, and a more preferred range is 0 to 5 ppm /% RH.

  When the biaxially oriented polyester film of the present invention is used for magnetic recording medium applications, the dimensional stability in the width direction of the film may be particularly important. The coefficient is preferably 0 to 6 ppm /% RH. The humidity expansion coefficient in the width direction is more preferably 0 to 5.5 ppm /% RH, and further preferably 0 to 5 ppm /% RH.

  The biaxially oriented polyester film of the present invention preferably has a gelation rate of 0 to 15% by mass after treatment at 300 ° C. for 2.5 hours. When the gelation rate is 0 to 15% by mass, long-term extrusion stability becomes possible. The gelation rate is more preferably 0 to 13% by mass. More preferably, it is 0-10 mass%.

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

  In order to produce a biaxially oriented polyester film, for example, polyester pellets are melted using an extruder, discharged from a die, cooled and solidified, and formed into 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, in order to impart easy slipping, abrasion resistance, scratch resistance, etc. to the surface of the polyester film, inorganic particles and organic particles such as clay, mica, titanium oxide, calcium carbonate, carion, talc, wet silica, dry type Inorganic particles such as silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, organic particles containing acrylic acid, styrene resin, thermosetting resin, silicone, imide compound, etc., added during polyester polymerization reaction It is also preferable to add particles precipitated by a catalyst or the like (so-called internal particles).

  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.

  Subsequently, the sheet is biaxially stretched (stretched biaxially in the longitudinal direction and the width direction) and heat-treated. The stretching process is preferably divided into two or more stages in each direction. That is, the method of performing re-longitudinal and re-lateral stretching is preferable because a high-strength film optimum for a magnetic tape for high-density recording can be easily obtained.

  As the stretching method, a sequential biaxial stretching method such as stretching in the width direction after stretching in the longitudinal direction, a simultaneous biaxial stretching method in which the longitudinal direction and the width direction are simultaneously stretched using a simultaneous biaxial tenter, etc. Further, a method of combining a sequential biaxial stretching method and a simultaneous biaxial stretching method is included.

  It is particularly preferable to use a simultaneous biaxial stretching method. Compared with the sequential biaxial stretching method, the simultaneous biaxial stretching method is easy to stretch stably at a high magnification because crystals grow uniformly in the longitudinal direction and the width direction in the film forming process. In other words, in the present invention, it is important to function the island portion in the polyester film as a knot point, and in order to increase the molecular chain tension of the sea portion by using such an action in the stretching process, sequential biaxial stretching is performed. Rather than gradually tensioning the molecular chain in each step, it is particularly effective to stretch the molecular chain uniformly in the longitudinal direction and the width direction by using simultaneous biaxial stretching because it becomes easy to stretch at a high magnification. Here, the simultaneous biaxial stretching is a stretching method including a step in which stretching in the longitudinal direction and the width direction is performed simultaneously. The longitudinal direction and the width direction do not necessarily have to be stretched at the same time in all sections, the longitudinal stretching starts first, and the stretching is performed in the width direction from the middle (simultaneous stretching). A method may be adopted in which the process is terminated first and the rest is stretched only in the width direction. As the stretching apparatus, for example, a simultaneous biaxial stretching tenter is preferably exemplified, and among them, a linear motor driven simultaneous biaxial tenter is particularly preferable as a method of stretching a film without breaking.

  The heat treatment after the stretching process may be carried out in one stage, but it is effective to control the temperature expansion coefficient and humidity expansion coefficient within the scope of the present invention without causing relaxation of molecular chain orientation by excessive heat treatment. Therefore, it is preferable to carry out the heat treatment in multiple stages by controlling the heat treatment temperature. Multi-stage means that the heat treatment temperature is changed and the process is carried out in two or more stages.

  The heat treatment temperature can be determined based on the melting point of the polyester. The heat treatment temperature is preferably [melting point of polyester constituting film (Tm) -100] to (Tm-50) ° C., and the heat treatment time is preferably 0.5 to 10 seconds. In particular, the heat treatment temperature for the first stage is preferably set to (Tm-75) to (Tm-50) ° C., more preferably (Tm-75) to (Tm-60) ° C. May be set to a lower temperature than the first stage. The heat treatment temperature of the second stage is preferably set to (Tm-100) to (Tm-75) ° C, more preferably (Tm-100) to (Tm-85) ° C. Further, it is more preferable to perform a relaxation treatment at a relaxation rate of 1 to 5% in the width direction in the first stage and / or second stage heat treatment step.

  And the polyester film manufactured in this way is wound up by a roll. Furthermore, in order to improve dimensional stability and storage stability, it is also preferable to heat-treat the wound film together with the roll under a certain temperature condition. “Constant temperature condition” means that the film is placed together with a roll in a hot air oven or zone set to a certain temperature condition. By heat-treating the film while it is in a roll, distortion of the internal structure of the film can be easily removed, and dimensional stability such as creep characteristics can be improved. For example, when the film is wound and stored, or when used for a magnetic recording medium such as a magnetic tape, the film is stored when wound on the tape, or when the tape is run and used. Although tension is applied in the longitudinal direction and creep deformation or the like may occur in the longitudinal direction, storage stability is significantly improved when dimensional stability such as creep characteristics is improved.

  In the present invention, the polyester film and the polyester film roll are subjected to any processing such as heat treatment, microwave heating, molding, surface treatment, lamination, coating, printing, embossing, etching, etc., as necessary. May be.

  Hereinafter, for the method for producing a biaxially oriented polyester film of the present invention, polyethylene terephthalate (PET) is used as a film constituent, PEI (A) having a glass transition temperature of 215 ° C., and a glass transition temperature as a component that forms an island part. An example using PEI (B) having a temperature of 245 ° C. will be described as a representative example. Of course, the present application is not limited to a support using PET as a constituent component, and may be one using another polymer. For example, when a polyester film is formed using polyethylene-2,6-naphthalene dicarboxylate (polyethylene-2,6-naphthalate) having a high glass transition temperature or a melting point, it can be extruded at a temperature higher than the temperature shown below. What is necessary is just to extend | stretch.

  First, PET is prepared. PET 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.

  When the inert particles are contained in the polyester which is a constituent component of the biaxially oriented polyester film of the present invention, the inert particles are dispersed in a predetermined proportion in the form of slurry in ethylene glycol, and this ethylene glycol is added during polymerization. Is preferred. 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.

  As a method of mixing PET and PEI, the composition obtained by (1) pre-melt kneading (pelletizing) a mixture of PEI (A) and PEI (B) and then (2) (1) before melt extrusion. A two-stage melt kneading is preferably exemplified in which a mixture of a product and PET is pre-melted and kneaded (pelletized) to form a master chip. In that case, a method of pre-kneading into a master chip using a high-shear mixer with high shear stress such as a twin screw extruder is preferred. When mixing with a twin screw extruder, from the viewpoint of reducing poor dispersion, a screw equipped with a triple twin screw type or a double twin screw type is preferable. By using two-stage melt-kneading, PEI (B), which is originally difficult to be mixed with PET and has a high glass transition temperature, is easily mixed into PET by interposing PEI (A).

  In the present invention, PEI (A) and PEI (B) are mixed in the first stage of kneading. At this time, when 1 to 5% by mass of PET is added, the melt viscosity of the resulting master chip can be reduced, and the difference in melt viscosity from the second-stage PET is reduced, thereby improving dispersibility. When the amount is more than 5% by mass, PET is likely to deteriorate and the gelation rate may increase. More preferably, it is 2-4 mass%. As PET to be used, high viscosity PET having an IV of 0.8 or more, preferably 1.0 or more, and a melting temperature in the range of 300 to 380 ° C., preferably in the range of 320 to 350 ° C., PEI (B ) Is preferably mixed at a high concentration, and in particular, the mixing mass ratio of PEI (A) / PEI (B) is preferably 90/10 to 10/90, more preferably 80. / 20 to 20/80. A more preferred range is 80/20 to 50/50. Further, the composition obtained by the first stage kneading is mixed with PET by the second stage kneading. The blend chip obtained by the first stage kneading is dried under reduced pressure at 150 ° C. for 3 hours to carry out the second stage kneading. In the first stage kneading, by controlling the mixing mass ratio of PEI (A) / PEI (B) in the range of 80/20 to 50/50, PET and PEI are phase separated in the second stage kneading. It can prevent mixing failure. In the second stage kneading, the mixing mass ratio of PET / (PEI (A) and PEI (B) blend composition) is preferably 70/30 to 30/70, more preferably 70/30 to The range is 40/60. In this method, the shear stress is increased by high-viscosity PET to increase the mixing force, and the mixing amount of PEI (B) is adjusted to improve the dispersibility of PEI (B) relative to PET. This is important because coarse foreign matters can be reduced and deterioration of stretchability can be suppressed, and the surface roughness can be prevented from becoming extremely large. In the two-stage melt-kneading, the heat history increases, so that the higher the glass transition temperature of PEI (B), the higher the thermal stability, the longer the extrusion stability in film formation, and the deterioration Disadvantages are reduced.

  On the other hand, a composition raw material obtained by pre-melting (pelletizing) a mixture of PET and PEI (A) having a low glass transition temperature to prepare a master chip is prepared, and the content of PEI (A) in the film is appropriately determined. Can be adjusted. Moreover, when mixing PET and PEI (A), there is a difference in melt viscosity, so it is preferable to prepare a master chip in which PEI (A) is mixed at a high concentration, and in particular, PET / PEI (A) The mixing mass ratio is preferably 10/90 to 70/30, more preferably 30/70 to 60/40.

  When kneading PET and PEI (A), the processing temperature is important from the viewpoint of favorably dispersing PEI in PET. It is important that the temperature range is such that PET does not thermally decompose and exhibits sufficient fluidity to process PEI (A). Specifically, for example, 280 ° C to 320 ° C is preferable. From the viewpoint of imparting excellent mechanical properties and dimensional stability to the resulting film when the biaxially oriented polyester film of the present invention is produced using master pellets made of PET and PEI (A), PET and PEI ( The processing temperature of A) is more preferably 290 to 315 ° C.

  When forming into a film, the mixed master chip raw material may be put into a normal single-screw extruder to form a melt, or may be directly sheeted without being converted into a master chip in a state where high shear is applied. Good.

  Moreover, when pelletizing with a twin-screw extruder, it is preferable to make screw rotation into 100-500 rotation / min, More preferably, it is the range of 200-400 rotation / min. Even when the screw rotation speed is set within a preferable range, high shear stress is easily applied, and defective dispersion is easily reduced. Further, the ratio of (screw shaft length / screw shaft diameter) of the twin screw extruder is preferably in the range of 20 to 60, more preferably in the range of 30 to 50.

  Further, in the twin screw, in order to increase the kneading force, it is preferable to provide a kneading part by a kneading paddle or the like, and the kneading part is preferably two or more, more preferably three or more, particularly four or more. Shape it. At this time, the mixing order of the raw materials is not particularly limited, and a method in which all raw materials are blended and then melt-kneaded by the above method, a part of the raw materials are blended and melt-kneaded by the above method, and the remaining raw materials are further blended Any method may be used such as a method of melt kneading or a method of mixing a part of raw materials and mixing the remaining raw materials using a side feeder during melt kneading with a single or twin screw extruder. Further, a method using a supercritical fluid described in Journal of Plastics Processing Society of Japan, “Molding”, Vol. 15, No. 6, pp. 382 to 385 (2003) can be preferably exemplified.

  When four or more kneading parts are provided, the kneading time tends to be long, so it is preferable to knead the screw at a rotational speed of 300 to 700 rotations / minute, and more preferably to knead at 400 to 600 rotations / minute, It is preferable for improving the dispersibility while reducing the thermal deterioration of the polymer and obtaining the effects of the present invention.

  Next, after drying the above-mentioned pellets under reduced pressure at 180 ° C. for 3 hours or more, in order to sufficiently melt the blended chips under a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease, comparison is made more than usual. An unstretched film is obtained by feeding to an extruder heated to 300 to 330 [deg.] C. set to a relatively high temperature, extruding from a slit-shaped die, and cooling on a casting roll. 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. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. When laminating films, a plurality of different polymers are melt laminated using two or more extruders and manifolds or merging blocks.

  Next, the obtained unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used.

  For example, when the sequential biaxial stretching method is used, stretching is first performed in the longitudinal direction and then in the width direction. Stretching in the longitudinal direction is usually performed using a roll. The stretching temperature may be appropriately determined depending on the type of polymer used, but can be determined using the glass transition temperature Tg of the polyester of the unstretched film as a guide. Further, when the glass transition temperature (Tg) is unclear or a plurality of Tg exists, the Tg of the polyester having the highest content among all the polyesters constituting the film is set as the Tg of the unstretched film. .

  The temperature in the longitudinal stretching step is preferably in the range of (Tg-10 ° C.) to (Tg + 25 ° C.), more preferably (Tg) to (Tg + 10 ° C.) in one step or in multiple steps of two or more steps. Do. When the stretching temperature is lower than the above range, film tearing frequently occurs and productivity is lowered, or redrawability is lowered, and it may be difficult to stably stretch at a high magnification. . In addition, when the stretching temperature is higher than the above range, the molecular orientation does not proceed sufficiently, and the Young's modulus of the produced film may decrease.

  The film of the present invention can be stretched at a stretching ratio of 2 to 8 times, preferably 2.5 to 7 times, more preferably 3 to 4 times, and most preferably 3 to 3.5 times. It is preferable because it is easy. That is, in the film structure of the present invention, the island portion exists as a nodal point, so that stress tends to rise at a low magnification in the stress strain curve. Therefore, if the stretching ratio in the longitudinal direction is too high, the tension and crystallization of the molecular chain may proceed excessively and subsequent stretching may not be performed. Therefore, the stretching ratio in the longitudinal direction should be set in the above range. Is preferred.

  Stretching in the width direction is preferably performed with a temperature gradient in two or more stages using a tenter. In the first stage, the temperature is in the range of (longitudinal stretching temperature) to (longitudinal stretching temperature + 30 ° C.), more preferably (longitudinal stretching temperature + 5 ° C.) to (longitudinal stretching temperature + 20 ° C.). In the second stage, the film is preferably stretched at (stretching temperature in the first stage in the width direction + 60 ° C.) to (stretching temperature in the first stage in the width direction + 100 ° C.). It is preferable to stretch at a stretching temperature of the first stage in the width direction + 80 ° C.) to (stretching temperature of the first stage in the width direction + 100 ° C.).

  When the stretching temperature is out of the above range, the film is frequently broken due to insufficient heat amount or excessive crystallization, resulting in a decrease in productivity or a sufficient decrease in orientation and a decrease in strength. There is a case.

  Among these, the biaxially oriented polyester film of the present invention is preferably stretched by increasing the temperature stepwise because the island portion becomes a node. In particular, the temperature condition of the second step in the width direction is preferably set to (stretching temperature of the first step in the width direction + 60 ° C.) to (stretching temperature of the first step in the width direction + 100 ° C.), more preferably (one step in the width direction). It is effective to obtain the effect of high dimensional stability of the present invention by setting the stretching temperature of the eye + 80 ° C) to (stretching temperature of the first step in the width direction + 100 ° C).

  You may perform longitudinal direction extending | stretching by a roll extending machine etc. between the extending | stretching of the width direction of the 1st step and the 2nd step. The temperature in that case is preferably (stretching temperature in the first step in the width direction + 30 ° C.) to (stretching temperature in the first step in the width direction + 60 ° C.).

  Next, this stretched film is heat-treated. The heat treatment in this case is preferably performed at a temperature of 180 to 250 ° C., particularly 190 to 220 ° C. for 1 to 20 seconds. Subsequently, after intermediate cooling at 100 to 180 ° C., the film is cooled and wound up to room temperature, if necessary, in the longitudinal and lateral directions, to obtain a desired biaxially oriented polyester film. At this time, when it is desired to further increase the strength in the vertical or horizontal direction, it is preferable to redraw in the vertical or horizontal direction before the heat treatment. The stretching conditions in this case are preferably a stretching temperature of 110 to 150 ° C. and a stretching ratio of 1.1 to 1.8.

  Next, a production example using a simultaneous biaxial stretching apparatus will be described. In this case, it is preferable that the clip driving method is a linear motor type stretching device.

  For example, it is led to a simultaneous biaxial stretching tenter, and biaxial stretching is performed simultaneously in the longitudinal and width directions. The stretching speed is preferably 100 to 20,000% / min in both the longitudinal and width directions. More preferably, it is 500-10,000% / min, More preferably, it is 2,000-7,000% / min. When the stretching speed is less than 100% / min, the film is exposed to heat for a long time. In particular, the edge portion is crystallized to cause stretching breakage, and the film-forming property is lowered. However, mechanical properties such as Young's modulus of the manufactured film may be deteriorated without progressing. On the other hand, if it is higher than 20,000% / min, entanglement between molecules is likely to occur at the time of stretching, and the stretchability may be lowered, making it difficult to stretch at a high magnification.

  The stretching temperature may be appropriately determined depending on the type of polymer used. For example, the stretching temperature can be determined based on the glass transition temperature Tg of the polyester of the unstretched film. The temperature in the first stretching step in each of the longitudinal direction and the width direction is preferably in the range of Tg to Tg + 30 ° C, more preferably Tg + 5 ° C to Tg + 20 ° C. When the stretching temperature is lower than the above range, film tearing frequently occurs and the productivity is lowered, or the redrawing property is lowered, and it may be difficult to stably stretch at a high magnification. In addition, when the stretching temperature is higher than the above range, particularly the edge portion is crystallized to cause stretching breakage, the film forming property is lowered, or the Young's modulus of the produced film is lowered without sufficient molecular orientation. Sometimes.

  And when the manufacturing process of a polyester film includes multistage stretching, that is, a re-stretching process, the first stage stretching temperature is as described above, but the second stage stretching temperature is preferably Tg + 40 ° C. to Tg + 120 ° C., more preferably. Is Tg + 60 ° C. to Tg + 100 ° C. Most preferably, it is Tg + 80 degreeC-Tg + 100 degreeC. When the stretching temperature is out of the above range, the film is frequently broken due to insufficient heat or crystallization, resulting in a decrease in productivity or a decrease in strength due to insufficient orientation. There is.

  The draw ratio may be appropriately determined depending on the type of polymer to be used, the drawing temperature, and the drawing method (multistage drawing, etc.). For example, the total area draw ratio (total longitudinal draw ratio × total transverse draw ratio) is 20 to 40. It is preferable to be in the double range. More preferably, it is 25 to 35 times. The total draw ratio in one direction of the longitudinal direction and the width direction is preferably 2.5 to 8 times, and more preferably 3 to 7 times. If the draw ratio is smaller than the above range, uneven drawing or the like may occur and the processability of the film may be reduced. Moreover, when a draw ratio is larger than the said range, stretch breaks occur frequently and productivity may fall.

  When stretching is performed in multiple stages with respect to each direction, the stretching ratio in each of the longitudinal and width directions of the first stage is preferably 2 to 4 times, more preferably 3 to 3.8 times. Moreover, the preferable area draw ratio in the first stage is 4 to 18 times, and more preferably 7 to 15 times. These stretch ratio values are particularly suitable when the simultaneous biaxial stretching method is employed, but can also be applied to the sequential biaxial stretching method. In the film structure of the present invention, the island portion exists as a nodal point, so that stress tends to rise at a low magnification in the stress strain curve. Therefore, if the first stage draw ratio is too high, the tension and crystallization of the molecular chain may proceed excessively and the second stage stretch may not be performed. It is preferable to set to.

  Moreover, 1.05-2.5 times are preferable and, as for the draw ratio in one direction in the case of performing redrawing, More preferably, it is 1.2-1.8 times. The area stretching ratio for re-stretching is preferably 1.4 to 4 times, more preferably 1.9 to 3 times.

  Subsequently, this stretched film is heat-treated under tension or while relaxing in the width direction. Of the heat treatment conditions, the heat treatment temperature is preferably 155 to 205 ° C., and the heat treatment time is preferably 0.5 to 10 seconds. It is preferable to perform the heat treatment process in two or more stages. In particular, the heat treatment temperature of the first stage is preferably set to 180 to 205 ° C., more preferably 180 to 195 ° C. The temperature is lower than that of the first stage, preferably 155 to 180 ° C, more preferably 155 to 170 ° C. Further, it is more preferable that only the second heat treatment step is relaxed at a relaxation rate of 1 to 5% in the width direction. According to the above-mentioned multi-step heat treatment process, the mechanical properties such as Young's modulus and the dimensional stability against temperature / humidity changes are enhanced while the molecular chain relaxation effectively proceeds, so when stored under load It becomes easy to improve the storage stability that represents the dimensional change.

  Thereafter, the film edge is removed and wound on the core. And in order to further improve the effect of dimensional stability and storage stability, it is also preferable to heat-process with a hot air oven etc. in the state which wound the film around the core (roll-shaped film). The atmospheric temperature of the heat treatment can be determined with reference to the glass transition temperature (Tg) of the film, and is in the range of (Tg-80) to (Tg-30) ° C., more preferably (Tg-75) to ( It is in the range of Tg-35) ° C., more preferably in the range of (Tg-70) to (Tg-40) ° C. A preferable treatment time is in the range of 10 to 360 hours, more preferably in the range of 24 to 240 hours, and still more preferably in the range of 72 to 168 hours. It is preferable that the total time of the heat treatment of the roll film performed in multiple stages is within the above range.

  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 coating and a non-magnetic coating are applied on one surface (A) by 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 (B) with a thickness of 0.3 to 0.8 μm, and after calendar treatment, it is 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) Average dispersion diameter of island portion The film is (a) parallel to the longitudinal direction and perpendicular to the film surface, (b) parallel to the width direction and perpendicular to the film surface, and (c) parallel to the film surface. The sample was cut in various directions, and a sample was prepared by an ultrathin section method. In order to clarify the contrast of the dispersed phase, it may be stained with osmic acid, ruthenic acid, phosphotungstic acid, or the like. The cut surface was observed with a transmission electron microscope (Hitachi H-7100FA type) under the condition of an acceleration voltage of 100 kV, and a photograph was taken at 20,000 times. The obtained photograph is taken into an image analyzer as an image, 100 disperse phases (island portions) having a diameter of 30 nm or more are selected, and image processing is performed as necessary. The phase size was determined. The maximum thickness (la) and the maximum length (lb) in the film thickness direction of each dispersed phase appearing on the cut surface of (a), and the maximum thickness (lb) in the longitudinal direction of each disperse phase appearing on the cut surface of (a). The maximum length (lc), the maximum length (ld) in the width direction, the maximum length (le) in the film longitudinal direction and the maximum length (lf) in the width direction of each dispersed phase appearing on the cut surface of (c). Asked. Next, the shape index I of the dispersed phase I = (number average value of lb + number average value of le) / 2, shape index J = (number average value of ld + number average value of lf) / 2, shape index K = (of la Number average value + number average value of lc) / 2, the average dispersion diameter of the dispersed phase was (I + J + K) / 3. Further, from I, J, and K, the maximum value was determined as the average major axis L, and the minimum value was determined as the average minor axis D.

  A method for performing image analysis will be described.

  Transmission electron micrographs of each sample were taken into a computer with a scanner. Thereafter, image analysis was performed with dedicated software (Image Pro Plus Ver. 4.0, manufactured by Planetron). Adjust the brightness and contrast by manipulating the tone curve, and then observe 100 points with a dispersion diameter of 30 nm or more at random from the equivalent circle diameter of the high-contrast component of the image obtained using the Gaussian filter. The average dispersion diameter was calculated according to the method. Here, when using a negative photograph of a transmission electron microscope photograph, Leafscan 45 Plug-In manufactured by Nippon Cytex Co., Ltd. is used as the scanner, and when using a positive transmission electron microscope, the scanner is used as the scanner. Although a Seiko Epson GT-7600S is used, an equivalent value can be obtained with either of them.

Image processing procedures and parameters:
Once flattened Contrast +30
Gauss once Contrast +30, Brightness -10
1 Gauss flattening filter: background (black), object width (20 pix)
Gaussian filter: size (7), strength (10)
(2) The diameter of the island part having a dispersion diameter of 30 nm or more, the ratio of the major axis to the minor axis (major axis / minor axis)
The film was cut in a direction parallel to the film surface, and a sample was prepared by an ultrathin section method. In order to clarify the contrast of the disperse phase (island portion), it may be dyed with osmic acid, ruthenic acid, phosphotungstic acid or the like. The cut surface was observed with a transmission electron microscope (Hitachi H-7100FA type) under the condition of an acceleration voltage of 100 kV, and a photograph was taken at 20,000 times. The obtained photograph is taken into an image analyzer as an image, 100 disperse phases having an arbitrary dispersion diameter of 30 nm or more are selected, and image processing similar to the above is performed as necessary. The phase size was determined. The maximum length (lg) in the film longitudinal direction and the maximum length (lh) in the width direction of each dispersed phase appearing on the cut surface were determined.

(Long diameter and short diameter of island part)
The larger value of lg and lh was the major axis (l), and the smaller value was the minor axis (d).

(Diameter of island part)
The diameter of each island portion observed was (lg + lh) / 2.

(Average of ratio of major axis to minor axis (major axis / minor axis) of the island portion having a diameter of 30 to 200 nm)
For the island portion having a diameter of 30 to 200 nm, the ratio of the major axis to the minor axis (major axis / minor axis) was 1 / d, and an average value of 100 1 / d values was obtained.

(3) Humidity expansion coefficient It measured on the following conditions with respect to the width direction of a film, and made the average value of three measurement results the humidity expansion coefficient in this 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: Hold for 6 hours at 40% RH, measure dimensions, increase to 80% RH in 40 minutes, hold for 6 hours at 80% RH, then measure dimensional change ΔL (mm) in the film width direction did. The humidity expansion coefficient (ppm /% RH) was calculated from the following equation.

Humidity expansion coefficient (ppm /% RH) = 10 ⁶ × {(ΔL / 12.6) / (80-40)}
The humidity expansion coefficient in the longitudinal direction is also measured in the same manner as described above with the direction of the sample being changed.

(4) Gelation rate 1 g of the polyester resin composition was freeze-pulverized to form a powder having a diameter of 300 μm or less and dried under reduced pressure. The sample is treated in an oven at 300 ° C. for 2.5 hours in the atmosphere. This is heated and dissolved in 500 ml of orthochlorophenol (OCP) at a temperature of 100 ° C. for 0.5 hours. Subsequently, it is filtered with a Buchner type glass filter (maximum pore size 20-30 μm), washed and dried under reduced pressure. The mass of the OCP insoluble matter remaining on the filter was calculated from the mass increment of the filter before and after filtration, and the mass fraction of the OCP insoluble matter with respect to the amount of the polyester resin composition substance (1 g) was determined as the gelation rate.

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

・ Device: Temperature modulation DSC manufactured by TA Instrument
·Measurement condition:
・ 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 weight: 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
(6) Melting point (Tm)
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. as a data analysis device, about 5 mg of a sample is melted and held at 300 ° C. for 5 minutes on an aluminum tray, and rapidly cooled and solidified. After that, the temperature was raised from room temperature 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).

(7) The number of defects on the surface of the film 10 fields of visual inspection of defects having a size of about 5 to 10 mm in the longitudinal direction through changing the surface of the 5 m long and 1 m wide portions of the film obtained when the film was formed for 48 hours. Observe. Based on the total number of defects (per 50 m ² ), the following criteria were used.

◎: Less than 3 ○: 3 or more and less than 5 △: 5 or more and less than 10 ×: 10 or more (8) Long-term extrusion stability The film obtained when the film was formed for 150 hours was Similarly, the defect was observed and judged according to the following criteria.

◎: Less than or equal to the number of defects at 48 hours ○: Increased from the number of defects at 48 hours, but less than 1.2 times △: Increased by more than 1.2 times, less than 1.5 times from the number of defects at 48 hours X: Increase of 1.5 times or more from the number of defects at 48 hours (9) Measurement of width dimension A film slit to a width of 1 m is conveyed with a tension of 200 N, and a magnetic material having the following composition is formed on one surface (A) of the support. Paint and non-magnetic paint are applied in multiple layers with an extrusion coater (the upper layer is magnetic paint, the coating thickness is 0.2 μm, the lower layer is non-magnetic paint and the coating thickness is 0.9 μm), magnetically oriented, and dried at a drying temperature of 100 ° C. It was. Next, a back coat having the following composition was applied to the opposite surface (B), and then at a temperature of 85 ° C. and a linear pressure of 2.0 × 10 ⁵ N / m with a small test calender device (steel / nylon roll, 5 steps). Wind up after calendaring. The tape stock was slit to a width of 1/2 inch (12.65 mm) to prepare a pancake. Subsequently, a length of 200 m from this pancake was incorporated into a cassette to obtain a cassette tape.

(Composition of magnetic paint)
Ferromagnetic metal powder: 100 parts by mass [Fe: Co: Ni: Al: Y: Ca = 70: 24: 1: 2: 2: 1 (mass ratio)]
[Long axis length: 0.09 μm, axial ratio: 6, coercive force: 153 kA / m (1,922 Oe), saturation magnetization: 146 Am ² / kg (146 emu / g), BET specific surface area: 53 m ² / g, X-ray Particle size: 15 nm]
-Modified vinyl chloride copolymer (binder): 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
Modified polyurethane (binder): 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
Polyisocyanate (curing agent): 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass Carbon black (antistatic agent): 1 part by mass (average primary particle size: 0.018 μm)
Alumina (abrasive): 10 parts by mass (α alumina, average particle size: 0.18 μm)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass (composition of nonmagnetic paint)
Modified polyurethane: 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass-Polyisocyanate: 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
・ 2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass (backcoat composition)
Carbon black: 95 parts by mass (antistatic agent, average primary particle size 0.018 μm)
Carbon black: 10 parts by mass (antistatic agent, average primary particle size 0.3 μm)
Alumina: 0.1 part by mass (α alumina, average particle size: 0.18 μm)
Modified polyurethane: 20 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 30 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
• Cyclohexanone: 200 parts by mass • Methyl ethyl ketone: 300 parts by mass • Toluene: 100 parts by mass Take out the tape from the cassette tape cartridge, put the sheet width measuring device prepared as shown in FIG. Measure. 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
-Holding time: 5 hours-Number of measurements: Measure 3 times.

(Width dimensional change rate: dimensional stability)
The width dimension (1A, 1B) 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.

  The lA is measured after 24 hours under the A condition, and then the lB is measured after 24 hours under the B condition. 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 0.85N
B condition: 29 ° C, 80% RH, tension 0.55N
Width change rate (ppm) = 10 ⁶ × ((1B-1A) / 1A)
A: Maximum width change rate is less than 500 (ppm) ○: Maximum width change rate is 500 (ppm) or more and less than 600 (ppm) Δ: Maximum width change rate is 600 (ppm) or more Less than 700 (ppm) ×: The maximum value of the width dimensional change rate is 700 (ppm) or more. (10) Storage stability In the same manner as in (9) above, the tape is taken out from the produced cassette tape cartridge, and the following two conditions are satisfied. Measure the width dimension (1C, 1D) respectively, and calculate the dimensional change rate by the following equation.

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

  After 24 hours at 23 ° C. and 65% RH, 1C is measured. After storing the cartridge for 10 days in an environment of 40 ° C. and 20% RH, 1D 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 × (| lC−lD | / lC)
A: Maximum value of width dimension change rate is less than 80 (ppm) ○: Maximum value of width dimension change rate is 80 (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) x: The maximum value of the width dimensional change rate is 150 (ppm) or more. (11) Electromagnetic conversion characteristics A cassette tape is prepared in the same manner as in (9) above, and a reel-to-reel tester is used for C / N measurement. And a commercially available MR head was mounted under the following conditions.

Relative speed: 2m / sec
Recording track width: 18 μm
Playback track width: 10μm
Distance between shields: 0.27 μm
Recording signal generator: HP 8118A
Reproduction signal processing: spectrum analyzer Compared with this commercially available LTO4 tape (manufactured by Fuji Film Co., Ltd.), -0.5 dB or more is ◎, -1 dB or more and less than -0.5 dB is ◯, -2 dB or more and -1 dB Less than was judged as Δ, and less than −2 dB was judged as ×. ◎ and ○ are desirable, but Δ can also be used practically.

(12) Measurement of an island portion having a diameter of 1 to 30 nm The film is (a) a direction parallel to the longitudinal direction and perpendicular to the film surface, (b) a direction parallel to the width direction and perpendicular to the film surface, and (c) a film. The sample was cut in a direction parallel to the surface, and a sample was prepared by an ultrathin section method. In order to clarify the contrast of the dispersed phase, it may be stained with osmic acid, ruthenic acid, phosphotungstic acid, or the like. The cut surface was observed under a condition of an acceleration voltage of 100 kV using a transmission electron microscope (Hitachi H-7100FA type), and a photograph was taken at 500,000 times. The obtained photograph was taken into an image analyzer as an image, and image processing was performed as necessary, whereby the diameter of the island portion was determined as follows. The maximum length (La) and the maximum length (Lb) in the film thickness direction of each dispersed phase appearing on the cut surface of (a), and the maximum thickness (Lb) in the longitudinal direction of each disperse phase appearing on the cut surface of (a). The maximum length (Lc), the maximum length in the width direction (Ld), the maximum length in the film longitudinal direction (Le) and the maximum length in the width direction (Lf) of each dispersed phase appearing on the cut surface of (c). Asked. Then, when the shape index I of the dispersed phase I = (Lb + Le) / 2, the shape index J = (Ld + Lf) / 2, and the shape index K = (La + Lc) / 2, the diameter of the island portion was set to (I + J + K) / 3. .

  A method for performing image analysis will be described.

  Transmission electron micrographs of each sample were taken into a computer with a scanner. Thereafter, image analysis was performed with dedicated software (Image Pro Plus Ver. 4.0, manufactured by Planetron). By manipulating the tone curve, the brightness and contrast were adjusted, and then the island portion of the high contrast component of the image obtained using a Gaussian filter was observed, and the diameter of the island portion was calculated according to the above calculation method. Here, when using a negative photograph of a transmission electron microscope photograph, Leafscan 45 Plug-In manufactured by Nippon Cytex Co., Ltd. is used as the scanner, and when using a positive transmission electron microscope, the scanner is used as the scanner. GT-7600S manufactured by Seiko Epson is used, and any of them can obtain an equivalent value.

Image processing procedures and parameters:
Once flattened Contrast +30
Gauss once Contrast +30, Brightness -10
1 Gauss flattening filter: background (black), object width (20 pix)
Gaussian filter: size (7), strength (10)

  Embodiments of the present invention will be described based on the following examples.

(Reference Example 1)
194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reactor, 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 phosphate in ethylene glycol lowers 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 (X) having an intrinsic viscosity of 0.62.

(Reference Example 2)
The PET pellet (X) obtained in Reference Example 1 was dried at 160 ° C. for 4 hours under a reduced pressure of 3 mmHg, and then subjected to a solid-state polymerization reaction at 220 ° C. for 8 hours at a reduced pressure of 133 Pa or less. 2 PET pellets (Y) were obtained.

(Reference Example 3)
50 parts by mass of PEI “Ultem 1010-1000” Pellets manufactured by SABIC Innovative Plastics and PET pellets (Y) were separately dried at 180 ° C. under a reduced pressure of 3 mmHg for 6 hours.

  Extrusion head section from a screw zone of a vent-type twin-screw kneading extruder of the same direction with three kneading paddle kneading sections with a screw diameter of 30 mm and a screw length / screw diameter = 45.5 manufactured by Nippon Steel The temperature gradient was set to 270 ° C to 320 ° C. Pellets dried under reduced pressure are supplied to this extruder, melt extruded at a screw rotation speed of 300 revolutions / minute, and a residence time of 3 minutes, discharged in a strand form, cooled with water at a temperature of 25 ° C., and immediately cut into PET. -PEI (Ul 1010) blend pellets (Z) were made.

Example 1
In Reference Example 2 with 75 parts by mass of PEI “Ultem 1010-1000” (Tg = 215 ° C.) pellets from SABIC Innovative Plastics and 25 parts by mass of PEI “UltemXH6050” (Tg = 245 ° C.) pellets from SABIC Innovative Plastics 3 parts by mass of the obtained PET pellets (Y) were separately dried at 150 ° C. under a reduced pressure of 3 mmHg for 6 hours.

  A Nippon Steel Works screw diameter 30 mm, screw length / screw diameter = 45.5 kneading paddle kneading section with three kneading paddle kneading sections provided in a co-rotating vent type twin-screw kneading extruder set at 340 ° C and reduced pressure The dried pellets are supplied, melt extruded at a screw speed of 300 revolutions / minute, and a residence time of 3 minutes, discharged into a strand, cooled with water at a temperature of 10 ° C., and immediately cut to obtain PEI (Ul1010) -PEI. (XH6050) -PET (mixing ratio 75/25/3) blend pellet (I) was produced.

  Next, 50 parts by mass of the PET pellet (Y) and 50 parts by mass of the blend pellet (I) were separately dried at 180 ° C. under a reduced pressure of 3 mmHg for 3 hours, and then heated to 310 ° C. in the same manner. Supplied to the same direction rotation type bent type twin screw kneading extruder (made by Nippon Steel, 30 mm diameter, screw length / screw diameter = 45.5) with 3 kneading paddle kneading sections It was melt-extruded at 300 rpm and discharged in the form of a strand. After cooling with water at a temperature of 25 ° C., it was immediately cut to produce a PET-PEI (Ul 1010) -PEI (XH6050) blend pellet (II).

  Next, the PET pellet (X), blend pellet (Z) and blend pellet (II) were mixed so as to have the content (mass%) shown in Table 2, and dried at 180 ° C. for 3 hours under a reduced pressure of 3 mmHg. Then, it is put into an extruder, melt-extruded at 310 ° C., passed through a fiber sintered stainless metal filter (14 μm cut), discharged from a T-die into a sheet, and cooled to a surface temperature of 25 ° C. An unstretched film was obtained by solidifying and cooling the drum by electrostatic application. The Tg of the unstretched film was 83 ° C.

  Both ends of the unstretched film were gripped by clips and led to a linear motor type simultaneous biaxial stretching tenter to form a film. The film temperature was heated to 95 ° C., and the film was simultaneously biaxially stretched at an area stretch ratio of 12.25 times (longitudinal magnification: 3.5 times, lateral magnification: 3.5 times). Subsequently, the film temperature was set to 160 ° C., and the film was stretched again at an area stretching ratio of 2.16 times (longitudinal magnification: 1.2 times, lateral magnification: 1.8 times), and heat fixed at a heat fixing temperature of 210 ° C. for 2 seconds. After the treatment, a relaxation heat treatment of 2% in the longitudinal direction and the width direction was performed at the heat setting temperature to obtain a biaxially stretched polyester film having a thickness of 5 μm. The composition, characteristics, and the like of this biaxially oriented polyester film are as shown in Tables 1 to 3, and had excellent characteristics as a base film for a magnetic recording medium.

(Example 2)
80 parts by mass of PEI “Ultem 1010-1000” (Tg = 215 ° C.) made by SABIC Innovative Plastics and 20 parts by mass of PEI “Ultem XH6050” (Tg = 245 ° C.) pellets made by SABIC Innovative Plastic 5 parts by mass of the obtained PET pellet (Y) was separately dried at 150 ° C. under a reduced pressure of 3 mmHg for 6 hours.

  A Nippon Steel Works screw diameter 30 mm, screw length / screw diameter = 45.5 kneading paddle kneading section with three kneading paddle kneading sections provided in a co-rotating vent type twin-screw kneading extruder set at 340 ° C and reduced pressure The dried pellets are supplied, melt extruded at a screw speed of 300 revolutions / minute, and a residence time of 3 minutes, discharged into a strand, cooled with water at a temperature of 10 ° C., and immediately cut to obtain PEI (Ul1010) -PEI. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that (XH6050) -PET (mixing ratio 80/20/3) blend pellet (I) was produced. The composition, characteristics, etc. of these biaxially oriented polyester films were as shown in Tables 1 to 3, and had excellent characteristics as a base film for magnetic recording media.

(Example 3)
In Reference Example 2 with 75 parts by mass of PEI “Ultem 1010-1000” (Tg = 215 ° C.) pellets from SABIC Innovative Plastics and 25 parts by mass of PEI “UltemXH6050” (Tg = 245 ° C.) pellets from SABIC Innovative Plastics 1 part by mass of the obtained PET pellet (Y) was separately dried at 150 ° C. under a reduced pressure of 3 mmHg for 6 hours.

  A Nippon Steel Works screw diameter 30 mm, screw length / screw diameter = 45.5 kneading paddle kneading section with three kneading paddle kneading sections provided in a co-rotating vent type twin-screw kneading extruder set at 340 ° C and reduced pressure The dried pellets are supplied, melt extruded at a screw speed of 300 revolutions / minute, and a residence time of 3 minutes, discharged into a strand, cooled with water at a temperature of 10 ° C., and immediately cut to obtain PEI (Ul1010) -PEI. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that (XH6050) -PET (mixing ratio 75/25/1) blend pellet (I) was produced. The composition, characteristics, etc. of these biaxially oriented polyester films were as shown in Tables 1 to 3, and had excellent characteristics as a base film for magnetic recording media.

Example 4
The same procedure as in Example 1 except that PES “RADEL A Grade A-300A” (Tg = 220 ° C.) manufactured by Solvay Advanced Polymers was used instead of PEI “UltemXH6050” manufactured by SABIC Innovative Plastics. An axially oriented polyester film was obtained. The composition, characteristics, etc. of these biaxially oriented polyester films were as shown in Tables 1 to 3, and had excellent characteristics as a base film for magnetic recording media.

(Example 5)
The amount of the PET pellet (X), blend pellet (Z) and blend pellet (II) mixed was changed so as to have the content (mass%) shown in Table 2, the film temperature was 160 ° C., and the area was stretched. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was redrawn at a magnification of 2.16 times (vertical magnification: 1.2 times, lateral magnification: 1.9 times). The composition, characteristics, etc. of these biaxially oriented polyester films were as shown in Tables 1 to 3, and had excellent characteristics as a base film for magnetic recording media.

(Example 6)
Biaxial as in Example 1 except that the amount of the PET pellet (X), blend pellet (Z), and blend pellet (II) mixed so as to have the content (% by mass) shown in Table 2 was changed. An oriented polyester film was obtained. The composition, characteristics, etc. of these biaxially oriented polyester films were as shown in Tables 1 to 3, and had excellent characteristics as a base film for magnetic recording media.

(Comparative Example 1)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PEI “Ultem1010-1000” (Tg = 215 ° C.) and PEI “UltemXH6050” (Tg = 245 ° C.) manufactured by SABIC Innovative Plastics were not used. . The composition, characteristics, etc. of these biaxially oriented polyester films are as shown in Tables 1 to 3, and had inferior characteristics as a base film for magnetic recording media.

(Comparative Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PEI “UltemXH6050” (Tg = 245 ° C.) manufactured by SABIC Innovative Plastics was not used. The composition, characteristics, etc. of these biaxially oriented polyester films are as shown in Tables 1 to 3, and had inferior characteristics as a base film for magnetic recording media.

(Comparative Example 3)
50 parts by mass of pellets of PEI “Ultem 1010-1000” (Tg = 215 ° C.) manufactured by SABIC Innovative Plastics and 50 parts by mass of pellets of PEI “Ultem XH6050” (Tg = 245 ° C.) manufactured by SABIC Innovative Plastics are separately 150 ° C. It dried for 6 hours under the reduced pressure of 3 mmHg.

  A Nippon Steel Works screw diameter 30 mm, screw length / screw diameter = 45.5 kneading paddle kneading section with three kneading paddle kneading sections provided in a co-rotating vent type twin-screw kneading extruder set at 340 ° C and reduced pressure The dried pellets are supplied, melt extruded at a screw speed of 300 revolutions / minute, and a residence time of 3 minutes, discharged into a strand, cooled with water at a temperature of 10 ° C., and immediately cut to obtain PEI (Ul1010) -PEI. (XH6050) (Mixing ratio 50/50) Blend pellet (I) was produced. Next, 50 parts by mass of the PET pellet (Y) and 50 parts by mass of the blend pellet (I) were separately dried at 180 ° C. under a reduced pressure of 3 mmHg for 3 hours, and then heated to a temperature of 320 ° C. in the same manner. Supplied to the same direction rotation type bent type twin screw kneading extruder (made by Nippon Steel, 30 mm diameter, screw length / screw diameter = 45.5) with 3 kneading paddle kneading sections Except that melt-extruded at 300 rpm and discharged into a strand, cooled with water at a temperature of 25 ° C., and immediately cut to produce a PET-PEI (U1010) -PEI (XH6050) blend pellet (II) A biaxially oriented polyester film was obtained in the same manner as in Example 1. The composition, characteristics, etc. of these biaxially oriented polyester films are as shown in Tables 1 to 3, and had inferior characteristics as a base film for magnetic recording media.

(Comparative Example 4)
Separately, 75 parts by mass of pellets of PEI “Ultem 1010-1000” (Tg = 215 ° C.) manufactured by SABIC Innovative Plastics and 25 parts by mass of pellets of PEI “Ultem XH6050” (Tg = 245 ° C.) manufactured by SABIC Innovative Plastics are separately 150 ° C. It dried for 6 hours under the reduced pressure of 3 mmHg.

  A Nippon Steel Works screw diameter 30 mm, screw length / screw diameter = 45.5 kneading paddle kneading section with three kneading paddle kneading sections provided in a co-rotating vent type twin-screw kneading extruder set at 340 ° C and reduced pressure The dried pellets are supplied, melt extruded at a screw speed of 300 revolutions / minute, and a residence time of 3 minutes, discharged into a strand, cooled with water at a temperature of 10 ° C., and immediately cut to obtain PEI (Ul1010) -PEI. (XH6050) (mixing ratio 75/25) Blend pellet (I) was produced. Next, 50 parts by mass of the PET pellet (Y) and 50 parts by mass of the blend pellet (I) were separately dried at 180 ° C. under a reduced pressure of 3 mmHg for 3 hours, and then heated to a temperature of 320 ° C. in the same manner. Supplied to the same direction rotation type bent type twin screw kneading extruder (made by Nippon Steel, 30 mm diameter, screw length / screw diameter = 45.5) with 3 kneading paddle kneading sections Except that melt-extruded at 300 rpm and discharged into a strand, cooled with water at a temperature of 25 ° C., and immediately cut to produce a PET-PEI (U1010) -PEI (XH6050) blend pellet (II) A biaxially oriented polyester film was obtained in the same manner as in Example 1. The composition, characteristics, etc. of these biaxially oriented polyester films are as shown in Tables 1 to 3, and had inferior characteristics as a base film for magnetic recording media.

(Comparative Example 5)
Separately, 75 parts by mass of pellets of PEI “Ultem 1010-1000” (Tg = 215 ° C.) manufactured by SABIC Innovative Plastics and 25 parts by mass of pellets of PEI “Ultem XH6050” (Tg = 245 ° C.) manufactured by SABIC Innovative Plastics are separately 150 ° C. It dried for 6 hours under the reduced pressure of 3 mmHg.

  A Nippon Steel Works screw diameter 30 mm, screw length / screw diameter = 45.5 kneading paddle kneading section with three kneading paddle kneading sections provided in a co-rotating vent type twin-screw kneading extruder set at 340 ° C and reduced pressure The dried pellets are supplied, melt extruded at a screw speed of 300 revolutions / minute, and a residence time of 3 minutes, discharged into a strand, cooled with water at a temperature of 10 ° C., and immediately cut to obtain PEI (Ul1010) -PEI. (XH6050) (mixing ratio 75/25) Blend pellet (I) was produced. Next, 50 parts by mass of the PET pellet (Y) and 50 parts by mass of the blend pellet (I) were separately dried at 180 ° C. under a reduced pressure of 3 mmHg for 3 hours, and then heated to 310 ° C. in the same manner. Supplied to the same direction rotation type bent type twin screw kneading extruder (made by Nippon Steel, 30 mm diameter, screw length / screw diameter = 45.5) with 3 kneading paddle kneading sections Except that melt-extruded at 300 rpm and discharged into a strand, cooled with water at a temperature of 25 ° C., and immediately cut to produce a PET-PEI (U1010) -PEI (XH6050) blend pellet (II) A biaxially oriented polyester film was obtained in the same manner as in Example 1. The composition, characteristics, etc. of these biaxially oriented polyester films are as shown in Tables 1 to 3, and had inferior characteristics as a base film for magnetic recording media.

(Comparative Example 6)
Biaxially oriented polyester film in the same manner as in Example 1 except that the film temperature was 160 ° C. and the film was re-stretched at an area stretch ratio of 2.16 times (longitudinal ratio: 1.2 times, lateral ratio: 1.6 times). Got. The composition, characteristics, etc. of these biaxially oriented polyester films are as shown in Tables 1 to 3, and had inferior characteristics as a base film for magnetic recording media.

(Comparative Example 7)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PEI “Ultem 1010-1000” (Tg = 215 ° C.) manufactured by SABIC Innovative Plastics was not used. The composition, characteristics, etc. of these biaxially oriented polyester films are as shown in Tables 1 to 3, and had inferior characteristics as a base film for magnetic recording media.

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 (7)

It has a sea-island structure, the average dispersion diameter of the island portion is 30 to 200 nm, the humidity expansion coefficient in at least one direction in the longitudinal direction or width direction of the film is 0 to 6 ppm /% RH, and 300 ° C. for 2.5 hours. A biaxially oriented polyester film having a gelation rate after treatment of 0 to 15% by mass. The biaxially oriented polyester film according to claim 1, wherein the glass transition temperature of an amorphous resin forming an island portion having a diameter of 30 to 200 nm is 230 ° C to 400 ° C. An amorphous resin that forms an island portion having a diameter of 30 to 200 nm is represented by the following formula (1).

The biaxially oriented polyester film according to claim 1, which is a polyetherimide having a sulfonyl group component represented by: The island portion having a diameter of 30 to 200 nm is provided, and the average ratio of the major axis to the minor axis (major axis / minor axis) of the island part is 1 to 20. Axial-oriented polyester film. The biaxially oriented polyester film according to any one of claims 1 to 4, comprising an island portion having a diameter of 1 nm or more and less than 30 nm. The biaxially oriented polyester film according to claim 5, wherein the island portion having a diameter of 1 nm or more and less than 30 nm contains polyetherimide. A magnetic recording medium comprising the biaxially oriented polyester film according to claim 1.

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