JP2005163020A - Biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare a biaxially oriented polyester film having excellent dimensional stability in all of temperature and humidity ranges comprising a low temperature and low humidity range, a low temperature and high humidity range, a high temperature and low humidity range, and a high temperature and high humidity range, and especially useful as a high-density magnetic recording medium. <P>SOLUTION: This biaxially oriented polyester film has a thermal expansion coefficient (a) (ppm/°C) in the transverse direction of the film, a moisture expansion coefficient (b) (ppm/%RH) in the transverse direction, and a temperature variation coefficient (c) (ppm/°C) of shrinkage in the transverse direction, when measured by applying a load of 10 MPa to the film in the longitudinal direction, so that the coefficients (a), (b), and (c) satisfy following inequalities: -3≤a≤15; 0≤b≤10; 0≤c≤15; a-2b-c≥-15; and a+2b-c≤30. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a biaxially oriented polyester film.

  Biaxially oriented polyester films are used in various applications because of their excellent thermal properties, dimensional stability, mechanical properties, and ease of control of surface morphology, and are particularly well-known for their usefulness as base films for magnetic tapes. It has been. In recent years, magnetic tapes have been required to have high density recording in order to reduce the weight, size, and recording time of equipment. In order to achieve high density recording, it is effective to shorten the recording wavelength and downsize the track.

  Due to the miniaturization of the track, slight thermal and mechanical dimensional changes during tape running and storage, and the difference in temperature and humidity environment during recording and reading data on magnetic tape, data reproduction failure The problem that causes

  Accordingly, a high-density magnetic recording medium base film is required to have high dimensional stability against stresses such as temperature and humidity changes and heat and tape tension. Needless to say, high productivity is required to supply products to the market at a low price in accordance with the recent price reduction of recording media in general.

  Conventionally, an aramid film is known as a base film that can meet the above-mentioned requirements for heat resistance and dimensional stability (Patent Document 1). Aramid film is disadvantageous in terms of cost because it is expensive, and it is also disadvantageous in that production efficiency is low because it cannot be molded by melt extrusion like conventional polyethylene terephthalate film. Development of a base film with high productivity is eagerly desired.

  As a technique for improving the dimensional stability of a polyester film, a biaxially oriented polyester film made of polyethylene terephthalate and polyetherimide is known (Patent Document 2). Furthermore, a polyethylene-2,6-naphthalate film is known in which the temperature expansion coefficient in the film width direction, the humidity expansion coefficient, and the dimensional change in the width direction when a load is applied in the longitudinal direction are reduced (Patent Document 3, Patent). Reference 4).

However, the dimensional change of the film width with respect to the temperature and humidity environment change cannot be accurately grasped only by the temperature expansion coefficient and the humidity expansion coefficient. That is, even if the above method is used, a stable film can be obtained with respect to temperature and humidity changes under normal temperature and high temperature and humidity conditions, but it is possible to suppress the dimensional change of the film when the temperature and humidity environment changes greatly. The present situation is that it is difficult to obtain a film that can withstand use in all temperature and humidity ranges of low temperature and low humidity, low temperature and high humidity, high temperature and low humidity, and high temperature and high humidity.
JP-A-10-114038 JP 2000-141475 A JP 2003-132523 A JP 2003-132524 A

  An object of the present invention is to provide a polyester film having excellent dimensional stability in all temperature and humidity ranges of low-temperature and low-humidity, low-temperature and high-humidity, high-temperature and low-humidity, and high-temperature and high-humidity, and particularly useful for high-density magnetic recording media. There is.

  In order to achieve the above object, the present invention provides a film having a temperature expansion coefficient in the width direction of a (ppm / ° C.), a film having a humidity expansion coefficient in the width direction of b (ppm /% RH), and the longitudinal direction of the film. A biaxially oriented polyester film in which a, b and c satisfy the following ranges, where c (ppm / ° C.) is the temperature change coefficient of the amount of shrinkage in the width direction when a load of 10 MPa is applied to .

-3 ≦ a ≦ 15
0 ≦ b ≦ 10
0 ≦ c ≦ 15
a-2b-c ≧ −15
a + 2b-c ≦ 30

  According to the present invention, as described below, the temperature expansion coefficient of the polyester film, the humidity expansion coefficient, and the temperature change in the width dimension when a load is applied in the longitudinal direction of the film are defined in a specific range, thereby reducing the temperature. A polyester film for magnetic recording media having excellent dimensional stability in all temperature and humidity ranges of low humidity, low temperature and high humidity, high temperature and low humidity, and high temperature and high humidity can be obtained.

  The film of the present invention is a biaxially oriented polyester film. In the case of a laminated film having two or more film layers, it is sufficient that at least one layer constituting the film layer is biaxially oriented. If all the layers are non-oriented or uniaxially oriented, it is difficult to satisfy the characteristics of the present invention.

  The film of the present invention is a polyester film containing 60% by weight or more of polyester. Preferably, it is a polyester film containing 80% by weight or more of polyester. It may consist of a single polyester or two or more polyesters, 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 or the like.

  The polyester used in the biaxially oriented polyester film of the present invention may be a polymer composed of an acid component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid and a diol component.

  As the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and the like can be used. As alicyclic dicarboxylic acid, cyclohexane dicarboxylic acid etc. can be used, for example. As the aliphatic dicarboxylic acid, for example, adipic acid, sebacic acid, dodecanedioic acid and the like can be used. Of these, terephthalic acid, 2,6-naphthalenedicarboxylic acid and the like can be preferably used, and terephthalic acid can be particularly preferably used. These acid components may be used alone or in combination of two or more.

  Examples of the diol component include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, Triethylene glycol, 2,2′-bis (4′-β-hydroxyethoxyphenyl) propane and the like can be used, and ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol are particularly preferable. Diethylene glycol or the like can be used, and ethylene glycol can be used particularly preferably. These diol components may be used alone or in combination of two or more.

  Preferred examples of the polyester used in the present invention include polyethylene terephthalate (PET) and poly (ethylene-2,6-naphthalenedicarboxylate) (PEN). Among these, polyethylene terephthalate (PET) is particularly preferable because the temperature change coefficient c of the shrinkage in the width direction when a load is applied in the longitudinal direction of the film, which will be described later, can be easily controlled within the preferred range of the present application.

  When the polyester used in the present invention is a polyester having ethylene terephthalate as a main constituent, the polyester may be either a direct weight method or a DMT method, but calcium acetate may be used as a transesterification catalyst in the DMT method. preferable. In the polymerization stage, although not particularly limited, it is preferable to use a germanium compound as a polymerization catalyst in order to reduce coarse protrusions due to foreign matters. Examples of germanium catalysts include (1) amorphous germanium oxide, (2) crystalline germanium oxide of 5 μm or less, and (3) germanium oxide dissolved in glycol in the presence of an alkali metal, an alkaline earth metal, or a compound thereof. And a solution of germanium oxide prepared by dissolving (4) germanium oxide in water, adding glycol to the solution and distilling off the water, and the like.

  Polyesters include trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, polyfunctional compounds such as 2,4-dioxybenzoic acid, monofunctional compounds such as lauryl alcohol and phenyl isocyanate, p-hydroxybenzoic acid, Copolymerization of aromatic hydroxycarboxylic acid such as m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, p-aminophenol, p-aminobenzoic acid, etc., in an amount that does not impair the effects of the present invention. May be.

  As described above, the biaxially oriented polyester film of the present invention may be a polymer alloy of polyester and another thermoplastic resin. In this case, the thermoplastic resin preferably has good affinity with the polyester and preferably has melt moldability, and has a glass transition temperature higher than that of the polyester from the viewpoint of improving thermal dimensional stability. A thermoplastic resin is preferred. Examples of such a thermoplastic resin include polyimide (including polyetherimide), polysulfone, polyethersulfone and the like, and polyimide is particularly preferable from the viewpoint of affinity. Here, having good affinity (compatibility) means, for example, using a polymer alloy made of polyester and a thermoplastic resin, creating an unstretched or biaxially stretched film, When observed with a microscope at a magnification of 30,000 to 500,000 times, it means that a structure having a diameter of 200 nm or more (for example, a polymer domain having poor dispersion) that is not caused by additives such as organic and inorganic particles is not observed. However, the method for determining affinity is not particularly limited to this, and if necessary, there is good affinity by observing a single glass transition point by a temperature modulation type DSC (MDSC). May be determined.

  As said polyimide, what contains a structural unit as shown by the following general formula is preferable, for example.

However, R ₁ in the formula is

Represents one or more groups selected from an aliphatic hydrocarbon group such as, an alicyclic hydrocarbon group, an aromatic hydrocarbon group,
R ₂ in the formula is

Represents one or two or more groups selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group.

  Such a polyimide dehydrates one or more compounds selected from the group consisting of tetracarboxylic acid and / or its anhydride and an aliphatic primary monoamine, aromatic primary monoamine, aliphatic primary diamine and aromatic primary diamine. It can be obtained by condensation.

  From the viewpoints of melt moldability and affinity with polyester, a polyetherimide containing an ether bond in the polyimide component as shown by the following general formula is particularly preferred.

(Wherein R ₃ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, R ₄ 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.)
Examples of R ₃ and R ₄ include aromatic residues represented by the following formula group:

Can be mentioned.

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

Or

(N is an integer of 2 or more, preferably an integer of 20 to 50)
This polyetherimide is available from GE Plastics under the trade name “Ultem” (registered trademark).

  Moreover, it is preferable that content of the said polyimide exists in the range of 30 weight% or less in a polymer alloy. More preferably, it is 15 weight% or less. When the polyimide content exceeds 30% by weight, it may be difficult to perform extrusion molding or stretching, which may cause troubles in film formation such as film tearing or die lines during extrusion. There is.

  When the polymer constituting the biaxially oriented polyester film of the present invention is a polymer alloy, a compatibilizer may be used in combination with the polymer alloy as necessary in order to control the dispersion diameter. In this case, although the kind of compatibilizer varies depending on the kind of polymer, the addition amount is preferably 0.01 to 10% by weight.

  When the polymer constituting the biaxially oriented polyester film of the present invention is a polymer alloy, the time when the thermoplastic resin is added to the polyester may be added before the polymerization of the polyester, for example, before the esterification reaction. It may be added later. Further, the polymer 1 and the polymer 2 may be mixed and pelletized before melt extrusion.

  Moreover, when the polymer which comprises the biaxially-oriented polyester film of this invention is a polymer alloy, as another method of adjusting a polymer alloy to a more preferable dispersion state, for example, the method of mixing using a tandem extruder, two types A method of finely dispersing a thermoplastic resin using the above polyester, a method of mixing after pulverizing the thermoplastic resin with a pulverizer, a method of mixing by dissolving both in a solvent and coprecipitation, one of which is a solvent Although the method of mixing in the other after making it into the solution form melt | dissolved in is mentioned, it is not this limitation. Particularly preferably, two or more kinds of polyesters are used. First, a high molecular weight polyester and a thermoplastic resin are pelletized, and once the thermoplastic resin is in a high concentration (for example, 35 to 65% by weight, more preferably 40 to 60% by weight). ) After preparing the master pellets to be contained and further diluting with a relatively low molecular weight polyester before melt extrusion, and using a method of adjusting to a predetermined concentration, the dispersibility between the polymers improves, and a preferable dispersion state May be indicated. In addition, this method is preferable because the melt viscosity of the polymer alloy as a whole can be kept low, so that melt moldability is improved and productivity is improved.

  The biaxially oriented polyester film of the present invention may be a single layer film, but when used as a magnetic tape, it preferably has a laminated structure of at least two layers. By having a laminated structure of two or more layers, the surfaces on both sides of the film have different characteristics such as a certain degree of roughness for improving transportability and runnability and smoothness for improving electromagnetic conversion characteristics. be able to. Furthermore, you may have the coating layer which consists of a 1-50 nm-thick water-soluble polymer etc. on the film surface.

  When the biaxially oriented polyester film of the present invention is a laminated film of two or more layers, the base layer portion (film layer having the thickest thickness in the film) is preferably the above-mentioned polymer. When the same polymer as that used for the base layer part is used for the laminated part (film layer other than the base layer part and is thinner than the base layer part), the polymer species used in the base part and the laminated part Since the difference in the heat shrinkage rate is unlikely to occur, it is preferable because troubles in the production process such as stacking spots and base lines are less likely to occur, and problems such as “warping” of the film when heat is applied to the film.

  In the biaxially oriented polyester film of the present invention, when used as a magnetic recording medium, the running durability of the magnetic tape, the running property with the magnetic head is improved, or the handling property such as winding property is improved. Inactive particles may be included. The inert particles referred to in the present invention are inorganic or organic particles having an average particle diameter of about 10 nm to 1 μm and do not cause a chemical reaction in the polymer of the present invention or adversely affect magnetic recording due to electromagnetic influence. Say things. Inactive particles include titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, and other inorganic particles, acrylic acids, styrene, silicone, imide, etc. Organic particles, particles precipitated by a catalyst added during the polyester polymerization reaction (so-called internal particles), surfactants, and the like. The content of inert particles is preferably 0.01 to 3% by weight.

  A terminal cross-linking agent may be added to the biaxially oriented polyester film of the present invention from the viewpoint of reducing the terminal carboxyl group concentration and decreasing the moisture absorption rate of the film. As a method for reducing the humidity expansion, it is common to increase the molecular orientation. In this case, however, the temperature expansion simultaneously decreases. Since the degree of expansion of the expansion coefficient is higher due to the higher orientation, the temperature expansion is larger, so if the humidity expansion is reduced to some extent, the temperature expansion coefficient may become too small (shrink). The above-described method for reducing the moisture absorption rate (addition of a terminal cross-linking agent) is effective in that only the humidity expansion coefficient can be reduced.

  Preferred examples of the terminal cross-linking agent include compounds having a carbodiimide group, an epoxy group, and an oxazoline group. .

  Examples of preferable monofunctional carbodiimide compounds include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, di-β-naphthylcarbodiimide and the like. Among these, dicyclohexylcarbodiimide or diisopropylcarbodiimide is particularly preferable.

  The polyfunctional carbodiimide is preferably a carbodiimide having a degree of polymerization of 3 to 15, specifically 1,5-naphthalenecarbodiimide, 4,4′-diphenylmethanecarbodiimide, 4,4′-diphenyldimethylmethanecarbodiimide, 1,3-phenylene carbodiimide, 1,4-phenylene diisocyanate, 2,4-tolylene carbodiimide, 2,6-tolylene carbodiimide, mixture of 2,4-tolylene carbodiimide and 2,6-tolylene carbodiimide, hexamethylene Carbodiimide, cyclohexane-1,4-carbodiimide, xylylene carbodiimide, isophorone carbodiimide, isophorone carbodiimide, dicyclohexylmethane-4,4′-carbodiimide, methylcyclohexanecarbodiimide, tetra Chill xylylene carbodiimide, 2,6-diisopropylphenyl carbodiimide, 1,3,5-triisopropylbenzene-2,4 is a carbodiimide and the like can be exemplified, but not of course limited to the above compounds.

  Preferred examples of the epoxy compound include glycidyl ester compounds and glycidyl ether compounds.

  Specific examples of the glycidyl ester compound include benzoic acid glycidyl ester, t-Bu-benzoic acid glycidyl ester, P-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, and lauric acid glycidyl ester. , Glycidyl palmitate, glycidyl behenate, glycidyl versatate, glycidyl oleate, glycidyl linoleate, glycidyl linolein, glycidyl behenol, glycidyl stearol, diglycidyl terephthalate, isophthalic acid Diglycidyl ester, phthalic acid diglycidyl ester, naphthalenedicarboxylic acid diglycidyl ester Ter, methylterephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, adipic acid diglycidyl ester, succinic acid diglycidyl ester, sebacic acid diglycidyl ester, dodecane Examples thereof include diglycidyl diacid, octadecanedicarboxylic acid diglycidyl ester, trimellitic acid triglycidyl ester, pyromellitic acid tetraglycidyl ester, and the like. One or more of these can be used.

  Specific examples of the glycidyl ether compound include phenyl glycidyl ether, O-phenyl glycidyl ether, 1,4-bis (β, γ-epoxypropoxy) butane, 1,6-bis (β, γ-epoxypropoxy). ) Hexane, 1,4-bis (β, γ-epoxypropoxy) benzene, 1- (β, γ-epoxypropoxy) -2-ethoxyethane, 1- (β, γ-epoxypropoxy) -2-benzyloxyethane 2,2-bis- [р- (β, γ-epoxypropoxy) phenyl] propane, 2,2-bis- (4-hydroxyphenyl) propane, 2,2-bis- (4-hydroxyphenyl) methane, etc. Bisglycidyl polyether obtained by the reaction of bisphenol and epichlorohydrin, and the like are used. It is possible.

  Further, the oxazoline compound is preferably a bisoxazoline compound, specifically, 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-2-oxazoline), 2,2′-. Bis (4,4-dimethyl-2-oxazoline), 2,2′-bis (4-ethyl-2-oxazoline), 2,2′-bis (4,4′-diethyl-2-oxazoline), 2, 2'-bis (4-propyl-2-oxazoline), 2,2'-bis (4-butyl-2-oxazoline), 2,2'-bis (4-hexyl-2-oxazoline), 2,2 ' -Bis (4-phenyl-2-oxazoline), 2,2'-bis (4-cyclohexyl-2-oxazoline), 2,2'-bis (4-benzyl-2-oxazoline), 2,2'-p -Phenylenebis (2-oxazo ), 2,2′-m-phenylenebis (2-oxazoline), 2,2′-o-phenylenebis (2-oxazoline), 2,2′-p-phenylenebis (4-methyl-2-oxazoline) ), 2,2′-p-phenylenebis (4,4-dimethyl-2-oxazoline), 2,2′-m-phenylenebis (4-methyl-2-oxazoline), 2,2′-m-phenylene Bis (4,4-dimethyl-2-oxazoline), 2,2′-ethylenebis (2-oxazoline), 2,2′-tetramethylenebis (2-oxazoline), 2,2′-hexamethylenebis (2 -Oxazoline), 2,2'-octamethylenebis (2-oxazoline), 2,2'-decamethylenebis (2-oxazoline), 2,2'-ethylenebis (4-methyl-2-oxazoline), , 2′-tetramethylenebis (4,4-dimethyl-2-oxazoline), 2,2′-9,9′-diphenoxyethanebis (2-oxazoline), 2,2′-cyclohexylenebis (2- Oxazoline), 2,2′-diphenylenebis (2-oxazoline), and the like. Among these, 2,2′-bis (2-oxazoline) is preferable from the viewpoint of reactivity with polyester. Most preferred. Furthermore, the bisoxazoline compounds listed above may be used singly or in combination of two or more as long as the object of the present invention is achieved.

  When adding a terminal cross-linking agent to the biaxially oriented polyester film of the present invention, the preferable content of the terminal cross-linking agent is 0.1 to 5% by weight based on the total weight of the film. If the content of the terminal cross-linking agent is 0.1% by weight or more, the effect of reducing moisture absorption can be easily obtained. However, if the content exceeds 5% by weight, the cross-linking reaction easily proceeds and a gel-like foreign matter is generated. Sometimes. A more preferable range is 0.2 to 2% by weight, and a most preferable range is 0.3 to 1% by weight.

  Further, the biaxially oriented polyester film of the present invention includes a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a pigment, a dye, a fatty acid ester, a wax and the like within a range not inhibiting the present invention. Organic lubricants and the like may be added.

  The intrinsic viscosity of the polymer constituting the film of the present invention is preferably in the range of 0.55 to 3.0 (dl / g) from the viewpoint of controlling the stability of the film forming process and the terminal carboxyl group concentration, More preferably, it is 0.55-2.0 (dl / g), More preferably, it is 0.60-2.0 (dl / g), Most preferably, it is 0.60-1.0 (dl / g). . In addition, the intrinsic viscosity of the film after film formation varies depending on the type of polyester, but in the range of 0.50 to 2.0 (dl / g) from the viewpoint of film forming stability and dimensional stability. It is preferable that it is in the range of 0.55 to 1.0 (dl / g). In particular, when the polyester is PET, it is most preferably 0.60 to 0.80 (dl / g). When the intrinsic viscosity is smaller than the above range, the terminal carboxyl group concentration becomes high, and the entanglement of the molecular chain decreases, so that it is easy to cause expansion due to temperature and humidity, or the viscosity is too low to cause bubbles and the like. Extrusion failure may occur. On the other hand, if it is larger than the above range, extrusion defects such as streaks may occur due to high viscosity. In the case of a PET film, when the film is stretched under the same stretching conditions, when the intrinsic viscosity of the film increases by 0.10, the temperature expansion coefficient a decreases by about 2 ppm / ° C. and the humidity expansion coefficient b decreases by about 1 ppm /% RH.

  The temperature expansion coefficient a in the width direction of the biaxially oriented polyester film of the present invention is in the range of −3 to 15 ppm / ° C., preferably 0 to 12 ppm / ° C., more preferably 4 to 9 ppm / ° C. Generally, the temperature expansion coefficient of a magnetic head used in a magnetic recording apparatus is 5 to 10 ppm / ° C. When the temperature expansion coefficient a in the film width direction is larger than 15 ppm / ° C., the temperature expansion of the film is too much larger than the temperature expansion of the magnetic head, so the environment for recording and reproducing magnetic data has changed from low to high. At the same time, the film expands in the tape width direction, which tends to cause a reproduction failure. Further, when the temperature expansion coefficient a is smaller than −3 ppm / ° C., the temperature expansion of the film is too smaller than the temperature expansion of the magnetic head, so that the film shrinks in the tape width direction when the temperature is changed from low to high. , Prone to poor playback.

  The humidity expansion coefficient b in the width direction of the biaxially oriented polyester film of the present invention is in the range of 0 to 10 ppm /% RH, preferably 2 to 8 ppm / ° C. Since the polyester swells when humidity, that is, moisture is added, generally, in a polyester film, b often has a positive value. In addition, when the orientation is so high that the humidity expansion takes a negative value, the temperature expansion coefficient becomes too small (shrinkage), and when the temperature changes from low to high, the film shrinks in the tape width direction and regenerates. It tends to cause defects. Further, when the humidity expansion coefficient b is larger than 10 ppm /% RH, when the environment for recording / reproducing magnetic data is changed from low humidity to high humidity, the film expands in the tape width direction and is likely to cause a reproduction failure. .

  The temperature change coefficient c of the amount of shrinkage in the width direction when a load of 10 MPa is applied in the longitudinal direction of the biaxially oriented polyester film of the present invention is in the range of 0 to 15 ppm / ° C, preferably 0 to 7 ppm / ° C. Preferably it is 0-4 ppm / degrees C. When a film is tensioned in the longitudinal direction, the film instantaneously undergoes elastic deformation in the longitudinal direction and stretches. At this time, the film width contracts due to the Poisson effect. As a result of intensive studies, we have found that the width shrinkage amount depends on temperature. It was also found that this effect greatly affects the dimensional stability in the width direction with respect to changes in temperature and humidity of the film, particularly when the film is used with a magnetic tape or the like loaded in the longitudinal direction. It is difficult to industrially manufacture a biaxially stretched film in which the temperature change coefficient c of the amount of shrinkage in the width direction is 0 or less. If the temperature change coefficient c of the amount of shrinkage in the width direction is greater than 15 ppm / ° C., the recording / reproducing environment for magnetic data is too small for the film to shrink when the environment changes from low temperature to high temperature. It becomes easy to cause.

  In order to reduce the temperature and humidity change between all temperature and humidity environments, that is, low temperature and low humidity-low temperature and high humidity-high temperature and low humidity-high temperature and high humidity, the above-mentioned temperature expansion coefficient a, humidity expansion coefficient b, and 10 MPa in the longitudinal direction It is important that the temperature change coefficient c of the amount of contraction in the width direction when a load is applied satisfies the relationship of a−2b−c ≧ −15 and a + 2b−c ≦ 30. More preferably, a−2b−c ≧ −7 and a + 2b−c ≦ 21, and most preferably a−2b−c ≧ 0 and a + 2b−c ≦ 14.

  Each coefficient a, b, c is a coefficient representing the degree of reversible change in the magnetic tape width when the temperature and humidity environment where the magnetic tape is placed changes. Conventionally, it was thought that only the temperature expansion coefficient and humidity expansion coefficient (ie, a and b) were involved in changes in the temperature and humidity environment. It was found that the influence of the temperature dependence (c) of the width shrinkage when applied was very large. That is, unless the three factors a, b, and c are controlled simultaneously, it is difficult to control the dimensional change of the magnetic tape. Among the above three factors, a and c have temperature dependence, and b has humidity dependence. In the usage environment of the magnetic tape, a temperature change of about 0 to 40 ° C. should be considered, whereas a humidity change of 10 to 90% RH needs to be taken into consideration, which is almost twice as much. Moreover, it is necessary to consider the possibility that temperature and humidity change independently. Considering these influences, we have found that the reversible dimensional change with respect to the temperature and humidity environment change of the magnetic tape can be expressed as a ± 2b-c.

  When both the temperature and humidity increase or decrease, this corresponds to “a + 2b−c” in the above formula, and when the temperature increases and the humidity decreases, or vice versa, This corresponds to the expression “a-2b-c”. As shown above, the values of a and b are positive when the width expands, but the value of c is positive when the width contracts. It takes the form of subtracting.

  Here, when a-2b-c is smaller than -15, when the environment for recording / reproducing magnetic data is changed from low temperature and high humidity to high temperature and low humidity, the dimensional change in the tape width direction becomes large and reproducibility is liable to occur. Become. When a + 2b-c is larger than 30, when the environment for recording / reproducing magnetic data is changed from low temperature and low humidity to high temperature and high humidity, the dimensional change in the tape width direction becomes large, and reproduction failure is likely to occur.

  The dimensional change in the width direction is preferably 0 to 200 ppm, more preferably 0 when a load of 10 MPa is applied to the longitudinal direction of the biaxially oriented polyester film of the present invention and the treatment is performed at 45 ° C. and 30% RH for 24 hours. ~ 100 ppm. This deformation is an irreversible width shrinkage due to creep elongation due to a load in the longitudinal direction. When it is larger than 200 ppm, when used as a magnetic tape, when used for a long time, a reproduction failure occurs, or a long-term Storage stability is reduced.

  When the load applied to the longitudinal direction of the biaxially oriented polyester film of the present invention is changed from 10 MPa to 20 MPa, the dimensional change rate in the width direction of the film is preferably 0 to 300 ppm, more preferably 0 to 150 ppm. This deformation is a reversible width shrinkage accompanying elastic deformation and elongation due to a load in the longitudinal direction. When it is larger than 300 ppm, when used as a magnetic tape, when the tension applied to the tape fluctuates in the drive, Playback failure may occur when used between different drives.

  When the environmental condition is changed from 10 ° C. and 10% RH to 30 ° C. and 90% RH with a 10 MPa load applied to the longitudinal direction of the biaxially oriented polyester film of the present invention, and from 10 ° C. and 90% RH to 50 ° C. When changed to 10% RH, the dimensional change rate in the width direction of the film is preferably 500 ppm or less, more preferably 250 ppm or less. When the dimensional change rate in the width direction of the film due to environmental changes from 10 ° C 10% RH to 30 ° C. 90% RH or 10 ° C. 90% RH to 50 ° C. 10% RH is greater than 500 ppm, magnetic data is recorded / reproduced. When the temperature / humidity environment changes, it becomes easy to cause a reproduction failure, and it becomes easy to cause wrinkles when storing the tape.

  The preferred surface roughness Ra of the biaxially oriented polyester film of the present invention varies depending on the presence or absence of a single layer, a laminated structure, a coating, or the like. When the surface roughness of the film front and back is the same, 5-20 nm is preferable, More preferably, it is 7-15 nm. When Ra is smaller than 5 nm, sufficient handling properties cannot be obtained in the film forming and processing steps, and productivity is reduced. When used as a magnetic tape, running property and wear resistance are reduced, It is not preferable because sufficient characteristics cannot be obtained. Further, when Ra is larger than 20 nm, for example, when used as a magnetic tape, electromagnetic conversion characteristics are deteriorated or dropout is caused, which is not preferable.

  When the biaxially oriented polyester film of the present invention is used as a magnetic tape, the surface roughness on both sides is preferably different. In this case, the surface roughness of the smoother surface is preferably 1 to 15 nm, more preferably 3 to 7 nm, from the viewpoint of improving electromagnetic conversion characteristics. Further, the surface roughness of the relatively rough surface on the opposite side is preferably 5 to 20 nm, more preferably 7 to 15 nm, from the viewpoints of improving transportability and running properties and suppressing transfer to a smooth surface.

  The preferred range of the Young's modulus in the longitudinal direction of the biaxially oriented polyester film of the present invention varies depending on the type of polyester used in the film. For example, when the polyester is polyethylene terephthalate (PET), it is preferably 4.5 to 9 GPa, more preferably 5 to 8.5 GPa, and most preferably 6 to 8 GPa. Although it is the same polyester, poly (ethylene-2,6-naphthalenedicarboxylate) (PEN) is more susceptible to deformation in the longitudinal direction than PET, so the Young's modulus in the longitudinal direction is 6 to 10 GPa is preferable, and 7.5 to 9 GPa is more preferable. If the Young's modulus in the longitudinal direction is smaller than the above range, the elastic deformation elongation and creep elongation when applying a load in the longitudinal direction are likely to increase, and the dimensional stability in the width direction when applied in the longitudinal direction is reduced, Storage stability is reduced. If the Young's modulus in the longitudinal direction is larger than the above range, tearing frequently occurs in the production process and the productivity decreases, the strength in the width direction decreases, and the dimensional stability in the width direction decreases, When used as a magnetic tape, it tends to be bent with respect to the traveling guide roll.

  The preferred range of Young's modulus in the width direction of the biaxially oriented polyester film of the present invention varies depending on the type of polyester used in the film. In general, the higher the Young's modulus, the smaller the temperature and humidity expansion coefficient (a, b) tends to be. When polyester is PET, 4.5-9GPa is preferable, More preferably, it is 5-8GPa, Most preferably, it is 5.5-7GPa. When polyester is PEN, PEN has a Young's modulus in the width direction of preferably 6 to 10 GPa because the temperature and humidity expansion coefficient (values of a and b) cannot be reduced unless the Young's modulus is increased compared to PET. More preferably, it is 7.5-9 GPa. If the Young's modulus in the width direction is smaller than the above range, the temperature-humidity expansion coefficient (a and b values) in the width direction becomes high, making it difficult to control within the preferred range of the present application, and dimensional stability and storage stability. May decrease. Also, when the Young's modulus in the width direction is larger than the above range, the temperature expansion coefficient (a) becomes too small and it becomes difficult to control to the preferred range of the present application, and the environment changes from low temperature to high temperature. In addition, width shrinkage occurs, tearing frequently occurs in the manufacturing process, resulting in a decrease in productivity, and a deterioration in creep characteristics due to a decrease in strength in the longitudinal direction.

  It is preferable that the terminal carboxyl group density | concentration of the biaxially-oriented polyester film of this invention is 0.1-10 equivalent / t, More preferably, it is 1-5 equivalent / t. When the terminal carboxyl group concentration of the film is larger than 10 equivalent / t, the moisture absorption rate and the humidity expansion of the film are increased, so that the preferable range of the present invention is not satisfied, and the dimensional stability against the change in temperature and humidity environment may be lowered. Moreover, when the terminal carboxyl group concentration of the film is less than 0.1 equivalent / t, not only is it difficult to produce industrially, but a gel-like defect caused by a crosslinking reaction is likely to occur in the film production process. There is.

  The glass transition start temperature (Tg) of the polymer of the biaxially oriented polyester film of the present invention is preferably 80 to 150 ° C, more preferably 82 to 130 ° C, and still more preferably 85 to 120 ° C. . When Tg is higher than the above range, productivity may be reduced, and when it is lower than the above range, dimensional stability and storage stability when used as a magnetic tape may be reduced.

  The total thickness of the biaxially oriented polyester film of the present invention is 3 to 8 μm. Preferably it is 4-7 micrometers, More preferably, it is 4.5-6.5 micrometers. When the thickness is smaller than 3 μm, the tape becomes dull and electromagnetic conversion characteristics deteriorate. When the thickness is larger than 8 μm, the tape length per tape is shortened, which makes it difficult to reduce the size and increase the capacity of the magnetic tape.

  In the biaxially oriented polyester film of the present invention, other polymer layers such as polyolefin, polyamide, polyvinylidene chloride and acrylic polymer may be laminated directly or via a layer such as an adhesive. Moreover, you may perform arbitrary processes, such as heat processing, shaping | molding, surface treatment, lamination, coating, printing, embossing, and etching, as needed.

  By providing a magnetic layer on at least one surface of the biaxially oriented polyester film of the present invention, it can be used as a magnetic recording medium. The surface on which the magnetic layer is provided may be any surface of the film or both surfaces, but if the surface roughness is different on both surfaces of the film, the magnetic layer should be provided on the surface with the smaller surface roughness. Is preferred.

  Suitable examples of the magnetic layer include a magnetic layer formed by dispersing a ferromagnetic metal thin film or fine powder of ferromagnetic metal in a binder, a magnetic layer coated with a metal oxide, and the like. As the metal used for the ferromagnetic metal thin film, iron, cobalt, nickel, alloys thereof, and the like are preferable. The ferromagnetic metal fine powder used in the magnetic layer in which the ferromagnetic metal fine powder is dispersed in a binder includes ferromagnetic hexagonal ferrite fine powder, powder made of iron, cobalt, nickel and alloys thereof. preferable. The binder is preferably a thermoplastic resin, a thermosetting resin, a reactive resin, or a mixture thereof.

  As a method for forming the magnetic layer, magnetic powder is kneaded with a binder such as thermosetting, thermoplastic or radiation curable, and coating and drying are performed. Metal or alloy is deposited, sputtering, ion plating, etc. Thus, any of dry methods in which a magnetic metal thin film layer is directly formed on a substrate film can be employed.

  In the magnetic recording medium, a protective film may be provided on the magnetic layer. This protective film can further improve running durability and corrosion resistance. As protective films, oxide protective films such as silica, alumina, titania, zirconia, cobalt oxide, nickel oxide, nitride protective films such as titanium nitride, silicon nitride, boron nitride, silicon carbide, chromium carbide, boron carbide, etc. Examples thereof include a carbon protective film made of carbon such as a carbide protective film, graphite, and amorphous carbon.

  The carbon protective film is a carbon film made of amorphous, graphite, a diamond structure, or a mixture thereof prepared by a plasma CVD method, a sputtering method, or the like, and particularly preferably a hard carbon film generally called diamond-like carbon.

  Further, the surface of the hard carbon protective film may be surface-treated with plasma of oxidizing or inert gas for the purpose of further improving the adhesion with the lubricant applied on the hard carbon protective film.

  In the present invention, in order to improve running durability and corrosion resistance of the magnetic recording medium, it is preferable to apply a lubricant or a rust preventive agent on the magnetic layer or the protective film.

  The use of the biaxially oriented polyester film of the present invention is preferably used as a digital recording magnetic recording medium requiring high dimensional stability. Among them, it is particularly suitable for a base film such as a high density magnetic recording tape for data storage or a digital video tape.

  Hereinafter, the example of the manufacturing method of the biaxially-oriented polyester film of this invention is demonstrated. Here, an example of a biaxially oriented polyester in which PET is used as the polyester and polyetherimide “Ultem” is added as the thermoplastic resin will be mainly shown.

  First, bis-β-hydroxyethyl terephthalate (BHT) is obtained by esterifying terephthalic acid and ethylene glycol or by transesterifying dimethyl terephthalate and ethylene glycol according to a conventional method. Next, while transferring this BHT to the polymerization tank, the polymerization reaction is advanced by heating to 280 ° C. under reduced pressure. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. The obtained polyester is pelletized and placed under reduced pressure to undergo solid phase polymerization. In the case of solid-phase polymerization, the pelletized polyester is preliminarily crystallized at a temperature of 180 ° C. or lower, and then solid-phase polymerized at 190 to 250 ° C. under a reduced pressure of about 1 mmHg for 10 to 50 hours. Moreover, when making the polyester which comprises a film contain an inert particle, the method to which an inert particle is disperse | distributed in the form of a slurry in ethylene glycol in a predetermined ratio, and adding this ethylene glycol at the time of superposition | polymerization is preferable. When the inert particles are added, for example, when the water sol or alcohol sol obtained at the time of synthesis is added without drying, the particles have good dispersibility. Also effective is a method in which a water slurry of inert particles is directly mixed with polyester pellets and kneaded into polyester using a vented twin-screw kneading extruder. As a method for adjusting the content of the inert particles, a master of a high concentration of inert particles is prepared by the above method, and this is diluted with a polyester that does not substantially contain inert particles at the time of film formation. A method of adjusting the content of the particles is effective.

Next, the pellets of polyethylene terephthalate and the pellets of polyetherimide are mixed, supplied to a vent type twin-screw kneading extruder heated to 270 to 300 ° C., and melt extruded. The shear rate at this time is preferably 50 to 300 sec ⁻¹ , more preferably 100 to 200 sec ⁻¹ , and the residence time is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. The mixing ratio is preferably 20 to 80%, more preferably 40 to 60%. If the mixing ratio of the polyetherimide is too high or too low, the two may not be sufficiently compatible by kneading. Furthermore, when both are not compatible on the said conditions, the obtained chip | tip may be thrown into a biaxial extruder again, and extrusion may be repeated until it is compatible.

  The obtained polyetherimide-containing polyester pellets, inert particle master pellets, and polyester pellets were mixed at a predetermined ratio and dried under reduced pressure at 180 ° C. for 3 hours or more. An unstretched film is obtained by supplying to an extruder heated to 280 to 320 ° C. under a nitrogen stream or under reduced pressure so as not to decrease, extruding from a slit-shaped die, and cooling on a casting roll.

  At that time, it is preferable to use various filters, for example, a filter made of a material such as sintered metal, porous ceramic, sand, and wire mesh, as a method for removing foreign substances, altered polymer, unmelted material, etc. in the polymer. . In particular, it is preferably exemplified that the polymer is filtered with a fiber sintered stainless metal filter having a cut of 1.2 μm or less. More preferably, the filter is 0.8 μm or less. The filter of 1.2 μm cut here means a filtration accuracy of 1.2 μm, and the filtration accuracy is the maximum glass bead particle size that has passed through the filter media by the method of JIS-B8356-8 (2002). means.

  Moreover, it is preferable to provide a gear pump in order to improve the quantitative supply as required.

  In the case of laminating films, the method is preferably a method of melt laminating a plurality of different polymers using two or more extruders and a manifold or merging block.

  Next, this 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. In order to highly align the molecular chain and sufficiently reduce the values of a, b, and c, and to control within the preferred range of the present invention, stretching in at least two stages in both the longitudinal direction and the width direction is required. preferable.

  For example, in the case of the sequential biaxial stretching method in which stretching is first performed in the longitudinal direction and then in the width direction, the unstretched film is heated with a heating roll group, and stretched 3 to 8 times in one or more stages in the longitudinal direction (re-longitudinal stretching). Is used, it is 2.5 to 5 times) and cooled by a cooling roll group of 20 to 50 ° C. The longitudinal stretching speed is preferably in the range of 1,000 to 50,000% / min. Subsequently, stretching in the width direction is performed. As a stretching method in the width direction, a method using a tenter is common. The stretching ratio in the width direction is preferably 3 to 8 times (in the case of performing relateral stretching, the first stage stretching is 2 to 4 times), and the stretching speed is preferably in the range of 1,000 to 20,000% / min. .

  When the simultaneous biaxial stretching method is used, the unstretched film is guided to a simultaneous biaxial stretching tenter, and biaxial stretching is performed simultaneously in the longitudinal and width directions. When simultaneous biaxial stretching is performed, the stretching speed is preferably in the range of 1,000 to 20,000% / min in both the longitudinal and width directions. The draw ratio is the same as the sequential biaxial drawing.

  The stretching temperature varies depending on the type of polymer used, but can be determined using the glass transition temperature Tg as a guide. In the case of sequential biaxial stretching, it is preferably performed in the range of Tg to Tg + 50 ° C. in the longitudinal direction and in the range of Tg + 10 ° C. to Tg + 30 ° C. in the width direction. In the case of simultaneous biaxial stretching, it is preferable to stretch in the range of Tg to Tg + 30 ° C. in both the longitudinal and width directions. When the stretching temperature is lower than the above range, film breakage frequently occurs and the productivity is lowered, or the redrawability is lowered, and the orientation cannot be sufficiently increased, and the values of a, b, and c are It may become difficult to control within the preferred range of the present invention. In addition, when the stretching temperature is higher than the above range, the molecular orientation is not sufficiently obtained, and the values of a, b, and c are increased, and it may be difficult to control to the preferable range of the present invention. .

  In order to produce the biaxially oriented polyester film of the present invention, it is preferable to perform re-longitudinal stretching and re-lateral stretching. As the stretching conditions in that case, when performing the second stage by sequential biaxial stretching, the stretching in the longitudinal direction is a heating roll group having a temperature of Tg to Tg + 100 ° C., and a stretching ratio of 1.1 to 2.5 times. As the stretching method in the width direction, a method using a tenter is preferable, and the stretching is preferably performed at a temperature Tg + 50 ° C. to Tg + 150 ° C. and a stretching ratio of 1.1 to 2.5 times. In the case of simultaneous biaxial stretching, it is preferable to perform the stretching at a stretching temperature Tg + 50 ° C. to Tg + 150 ° C. in both the longitudinal direction and the width direction at a stretching ratio of 1.1 to 2.5 times. When the stretching temperature is lower than the above range, film breakage frequently occurs and the productivity is lowered or the orientation cannot be sufficiently increased, and the values of a, b and c are increased, which is preferable in the present invention. It may be difficult to control the range. In addition, when the stretching temperature is higher than the above range, the molecular orientation is not sufficiently obtained, and the values of a, b, and c are increased, and it may be difficult to control to the preferable range of the present invention. .

  Subsequently, the stretched film is heat-treated while being stretched under tension or in the width direction. Preferably, it is preferable to perform heat treatment while performing fine stretching at a magnification of 1.05 to 1.2 times, because relaxation is suppressed, the values of a and b are reduced, and the range of the present invention is easily controlled. For example, in the case of PET, the heat treatment temperature is preferably 190 ° C. to 230 ° C., and the heat treatment time is preferably 3 to 10 seconds. On the other hand, for example, in the case of a polymer alloy in which polyimide is added to PET, the relaxation of the molecular chain is accelerated, so that the heat treatment temperature is preferably 180 ° C. to 220 ° C., and the heat treatment time is preferably 2 to 7 seconds. In addition, for example, in the case of PEN, since the creep characteristics are poor as the polymer characteristics and it is better to sufficiently fix the structure, the heat treatment temperature ranges from 200 ° C. to 250 ° C., and the heat treatment time ranges from 5 seconds to 12 seconds. It is preferable to carry out with. When the heat treatment temperature is made higher than the above range or the heat treatment time is made longer than the above range, the molecular chain is relaxed and the values of a and b become large, which may be difficult to control within the preferred range of the present invention. In addition, when the heat treatment temperature is made lower than the above range or the heat treatment time is made shorter than the above range, the structure of the molecular chain is insufficiently fixed and the creep characteristics are deteriorated. Since a value becomes large, it may become difficult to control within a preferable range of the present invention.

(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) Temperature expansion coefficient a
The film was sampled to a width of 4 mm, and set to TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. and a heating controller TA-1500 so that the test length was 15 mm. Atmospheric conditions were 23 ° C. and 65% RH as starting conditions. A load of 0.5 g was applied to the film, the temperature was raised from the ambient temperature (23 ° C.) to 50 ° C., and then cooled to 25 ° C. Thereafter, the temperature was increased from 25 ° C. to 50 ° C. at a temperature rising rate of 1 ° C./min. The displacement amount ΔL (mm) of the film from 30 ° C. to 40 ° C. at that time was measured, and the temperature expansion coefficient a (ppm / ° C.) was calculated from the following equation.
Thermal expansion coefficient a (ppm / ° C.) = {(ΔL / 15) / (40-30)} × 1,000,000
(2) Humidity expansion coefficient b
The film was sampled to a width of 10 mm, and set in a tape elongation tester made by Okura Industry, which was installed in a constant temperature and humidity chamber so that the test length was 200 mm (load of 0.5 g was applied). Atmosphere conditions were set to a temperature of 30 ° C. and a humidity of 40% RH, and after standing for 2 hours, the film length was measured (L ₄₀ ). Thereafter, at a constant temperature, by varying the humidity from 40% RH to 80% RH, after standing for 2 hours, (and L ₈₀₎ the film length was measured. The displacement (L ₈₀ -L ₄₀ ) between these two points was ΔL (mm), and the humidity expansion coefficient b (ppm /% RH) was calculated from the following equation.

Humidity expansion coefficient b (ppm /% RH) = {(ΔL / 200) / (80-40)} × 1,000,000
(3) Dimensional change rate in the width direction of the film with respect to the load in the longitudinal direction ΔW ₃₀ ° C
The film is slit to a width of 12.65 mm (1/2 inch) (the width direction of the film is the same as the width direction of the slit piece), and gold is deposited on the surface by sputtering. This film sample is set in a film dimension measuring apparatus (FIG. 1) installed in a constant temperature and humidity chamber.

Using a thermostatic chamber, the atmospheric conditions are set to a temperature of 30 ° C. and a humidity of 65% RH. Loads of 10 MPa, 20 MPa, and 30 MPa are applied to the film, and the width (unit: mm) of the sample is measured in each case. The change rate Δw (mm / MPa) of the film width with respect to the load is obtained from the inclination of the load-film width straight line consisting of these three points, and the dimensional change rate ΔW _{30 in} the width direction of the film with respect to the load in the longitudinal direction from ° C (ppm) was calculated.

ΔW ₃₀ ° C. (ppm) = {Δw / 12.65} × 1,000,000
(4) Temperature change coefficient c of widthwise shrinkage when a load of 10 MPa is applied in the longitudinal direction
ΔW is calculated in exactly the same manner as in (3) except that the humidity is fixed at 65% RH and the temperature is changed to 10 ° C. and 50 ° C. to be ΔW ₁₀ ° C. and ΔW ₅₀ ° C., respectively.

Temperature (10, 30, 50 ° C.) and [Delta] W ₁₀ ° C., [Delta] W ₃₀ ° C., from the relationship of [Delta] W ₅₀ ° C., and calculates an inclination of temperature -ΔW straight, a material obtained by 10 times, a load of 10MPa in the longitudinal direction The temperature change coefficient c (ppm / ° C.) of the amount of shrinkage in the width direction at the time was determined.

(5) Dimensional change in the width direction when a load of 10 MPa is applied in the longitudinal direction and treated for 24 hours at 45 ° C. and 30% RH A sample is prepared in the same manner as in (3), and described in (3) A sample was set in the measuring device. After applying a 10 MPa load to the sample, the atmospheric condition was set to 45 ° C. and 30% RH using a constant temperature and humidity chamber. The film width (mm) after standing for 1 hour and the film width (mm) after standing for 24 hours were measured, and the difference between the two was divided by 12.65 (mm) and converted to ppm units. It was set as the dimensional change (ppm) in the width direction when the treatment was performed for 24 hours at 45 ° C. and 30% RH.

(6) When the environmental condition is changed from 10 ° C. and 10% RH to 30 ° C. and 90% RH with a load of 10 MPa in the longitudinal direction, and from 10 ° C. and 90% RH to 50 ° C. and 10% RH In the case, a sample was prepared in the same manner as the dimensional change rate (3) in the width direction of the film, and the sample was set in the measuring apparatus described in (3). After applying a 10 MPa load to the sample, using a constant temperature and humidity chamber, the atmospheric condition was set to 10 ° C. and 10% RH, and the film was allowed to stand for 1 hour, and then the film width (mm) was measured. Next, the atmosphere condition was changed to 30 ° C. and 90% RH, and the film was allowed to stand for 1 hour, and then the film width (mm) was measured in the same manner. Dimensional change (ppm) in the width direction when the environmental condition is changed from 10 ° C 10% RH to 30 ° C 90% RH by dividing the two differences by 12.65 (mm) and converting to ppm units did.

  In the same manner as described above, the dimensional change (ppm) in the width direction when the atmospheric condition was changed from 10 ° C. 90% RH to 50 ° C. 10% RH was calculated.

(7) Terminal carboxyl group concentration of film The film was dissolved in orthochlorocresol / chloroform (weight ratio 7/3) at 90 to 100 ° C., and the potential difference was measured with an alkali. The unit is equivalent / ton.

(8) Young's modulus It measured using the Instron type tensile tester according to the method prescribed | regulated to ASTM-D882. The measurement was performed under the following conditions.

Measuring device: Orientec Co., Ltd. film strong elongation automatic measuring device
“Tensilon AMF / RTA-100”
Sample size: width 10 mm x test length 100 mm,
Tensile speed: 200 mm / min Measurement environment: temperature 23 ° C., humidity 65% RH
(9) Surface roughness Ra
The center line average roughness Ra was measured using a high precision thin film level difference measuring device ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and an average value obtained by scanning 20 times in the film width direction was used as a value: ・ Tip tip radius: 0.5 μm
-Stylus load: 5mg
・ Measurement length: 1mm
・ Cutoff value: 0.08mm
(10) Average particle diameter of inert particles The cross section of the film is observed at a magnification of 10,000 or more using a transmission electron microscope (TEM). The section thickness of TEM is about 100 nm, and the measurement is performed at 100 fields or more at different locations. The measured weight average of equivalent circle equivalent diameters was defined as the average particle diameter d of the inert particles.

  When two or more kinds of particles having different particle diameters exist in the film, the number distribution of equivalent circle equivalent diameters is a distribution having two or more peaks, and the average particle diameter is calculated separately for each of them. To do.

(11) Content of inert particles in polyester, thermoplastic resin and film layer Dissolve both polyester and thermoplastic resin in a suitable solvent and measure NMR (nuclear magnetic resonance) spectrum of ¹ H nucleus To do. A suitable solvent varies depending on the type of polymer, for example, hexafluoroisopropanol (HFIP) / deuterated chloroform is used. In the obtained spectrum, the peak area intensity of absorption peculiar to polyester and thermoplastic resin (for example, absorption of aromatic protons of terephthalic acid in the case of PET) is obtained, and the molarity of polyester and thermoplastic resin is determined from the ratio and the number of protons. Calculate the ratio. Further, the weight ratio is calculated from the formula amount corresponding to the unit unit of each polymer. The measurement conditions are, for example, the following conditions, but are not limited to this because they differ depending on the type of polymer.

Equipment: BRUKER DRX-500 (Bruker)
Solvent: HFIP / deuterated chloroform Observation frequency: 499.8 MHz
Standard: TMS (tetramethylsilane) (0 ppm)
Measurement temperature: 30 ° C
Observation width: 10 KHz
Data point: 64K
acquisiton time: 4.952 seconds
Pulse delay time: 3.048 seconds Integration count: 256 times In addition, composition analysis may be performed by a microscopic FT-IR method (Fourier transform microscopic infrared spectroscopy) as necessary. In that case, it calculates | requires from ratio of the peak resulting from the carbonyl group of polyester, and the peak resulting from other than that substance. In order to convert the peak height ratio to the weight ratio, a calibration curve is prepared with a sample whose weight ratio is known in advance, and the polyester ratio relative to the total amount of polyester and other substances is determined. The thermoplastic resin ratio is determined from this and the inert particle content. Moreover, you may use together an X-ray microanalyzer as needed.

  In addition, for the content of the inert particles, a solvent that dissolves the polyester and the thermoplastic resin but does not dissolve the inert particles is selected, the polyester and the thermoplastic resin are dissolved, the inert particles are centrifuged, and the weight percentage is obtained. Asked.

  In addition, when polyester is polyester which does not contain nitrogen, such as PET and PEN, and the thermoplastic resin is polyimide, the content of polyimide can be measured by the amount of nitrogen in the film. The nitrogen amount is preferably measured by oxidative decomposition CHN analysis. As the apparatus, for example, a CHN coder MT-3 type manufactured by Yanagimoto Seisakusho or a total nitrogen analyzer TN-10 can be used.

(12) Intrinsic viscosity Calculated from the following equation from the solution viscosity measured at 25 ° C in orthochlorophenol.

η _sp / C = [η] + K [η] ² · C
Here, η _sp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (assuming 0.343). The solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

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

Apparatus: 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 rising step: 5K
Sample weight: 5mg
Sample container: Aluminum open container (22 mg)
Reference container: Aluminum open container (18mg)
The glass transition temperature was calculated by the following formula.

Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
(14) Environmental change stability of magnetic tape A film slit to a width of 1 m is conveyed at a tension of 20 kg / m, and a magnetic coating and a non-magnetic coating having the following composition are applied to the surface of the A layer side of the film by an extrusion coater. (The upper layer is a magnetic paint, the coating thickness is 0.1 μm, and the thickness of the non-magnetic lower layer is appropriately changed), magnetically oriented, and dried at a drying temperature of 100 ° C. Next, a back coat having the following composition is applied to the opposite surface, and calendered at a temperature of 85 ° C. and a linear pressure of 200 kg / cm with a small test calender (steel / nylon roll, 5 steps), and then wound. The original tape was slit into a 1/2 inch width to prepare a pancake (length: 500 m).

(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-Stearic acid: 1.5 parts by weight-Oleic acid: 1 part by weight Carbon black: 1 part by weight Alumina: 10 parts by weight Methyl ethyl ketone: 75 parts by weight Cyclohexanone: 75 parts by weight Toluene: 75 parts by weight (Backcoat composition)
Carbon black (average particle size 20 nm): 95 parts by weight Carbon black (average particle size 280 nm): 10 parts by weight α-alumina: 0.1 parts by weight Modified polyurethane: 20 parts by weight Modified vinyl chloride copolymer: 30 parts by weight ・ Cyclohexanone: 200 parts by weight ・ Methyl ethyl ketone: 300 parts by weight ・ Toluene: 100 parts by weight The above-mentioned magnetic tape is set in the film size measuring apparatus, the load is 10 MPa, and the width of the tape is set under the following temperature and humidity conditions. It was measured.

The temperature and humidity conditions are (a) 10 ° C. 10% RH, (b) 10 ° C. 90% RH, (c) 30 ° C. 90% RH, (d) 50 ° C. 10% RH. The dimensions were measured in the order of (a) → (b) → (c) → (d), and after reaching the respective temperature and humidity, the tape was allowed to stand for 2 hours, and then the width (mm) of the tape was measured (each the respective tape width _{L a, L b, L c} , and L _d).

  The tape width change between each of the above conditions was calculated, and further corrected (subtracting the product of the temperature difference between the 7 conditions) by taking into account the temperature expansion (7 ppm / ° C.) of the magnetic head, as follows: The change in tape width between each condition was determined.

ΔL _ba = | L _b −L _a |
ΔL _ca = | L _c −L _a − (7 × 20) |
ΔL _da = | L _d −L _a − (7 × 40) |
ΔL _cb = | L _c −L _b − (7 × 20) |
ΔL _db = | L _d −L _b − (7 × 40) |
ΔL _dc = | L _d −L _c − (7 × 20) |
Of the above six tape width changes, the largest value divided by 12.65 (mm) and converted to ppm units (1,000,000 times) is the tape width change (temperature and humidity environment change) ppm) and evaluated according to the following criteria.

  Less than 500 ppm: Excellent level for high-density magnetic tape applications (◎).

  500 ppm or more and less than 800 ppm: Can be used as a high-density magnetic tape application (◯).

  800 ppm or more: a level that cannot be used for high-density magnetic tape applications (×).

(15) Long-term storage stability of magnetic tape A pancake prepared in the same manner as in (14) is prepared. After storing for 60 days in an environment of 50 ° C. and 65% RH, the conditions were returned to 25 ° C. and 65% RH, and left for 2 hours. Then, the film width measuring apparatus was used to measure the tape width (W: unit) mm). The tape width change (ppm) after long-term storage is calculated according to the following formula.

Tape width change after long-term storage (ppm) = {(12.65-W) /12.65} × 1,000,000
When this value was less than 150 ppm, it was judged that storage stability was good (◯), when it was 150 ppm or more and less than 300 ppm, it was usable (Δ), and when it was 300 ppm or more, storage stability was poor (x).

(16) Temperature expansion coefficient a ′ in an absolutely dry state
The film was sampled to a width of 4 mm, and set to TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. and a heating controller TA-1500 so that the test length was 15 mm. A load of 0.5 g was applied to the film, the temperature was raised from the ambient temperature (23 ° C.) to 50 ° C., and then cooled to 25 ° C. Thereafter, the temperature was increased from 25 ° C. to 50 ° C. at a temperature rising rate of 1 ° C./min. Note that the measurement was performed under a completely dry nitrogen flow (absolute humidity 0% RH). The displacement amount ΔL (mm) of the film from 30 ° C. to 40 ° C. at that time was measured, and the temperature expansion coefficient a (ppm / ° C.) was calculated from the following equation.
Thermal expansion coefficient a ′ (ppm / ° C.) = {(ΔL / 15) / (40-30)} × 1,000,000

  Based on the following examples, embodiments of the present invention will be described.

(Example 1)
50 parts by weight of polyethylene terephthalate (PET) pellets (Tg 80 ° C.) having an intrinsic viscosity of 0.85 (dl / g) obtained by a conventional method and an intrinsic viscosity of 0.68 (dl / g) manufactured by General Electric (GE) "Ultem" 1010 (Tg 216 ° C) 50 parts by weight is supplied to a co-rotating bent type twin-screw kneading extruder heated to 290 ° C, and a PET / PEI blend chip containing 50% by weight of PEI Was made.

  Next, in an extruder heated to 295 ° C., 12 parts by weight of the PET / PEI blend chip prepared by the above pelletizing operation and polyethylene terephthalate having an intrinsic viscosity of 0.62 (dl / g) substantially free of inert particles A mixed raw material of 85 parts by weight of (PET) pellets and 3 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 containing 2% by weight of crosslinked divinylbenzene particles having an average particle size of 0.17 μm is obtained at 180 ° C. It supplied after drying under reduced pressure for the time.

  Subsequently, the mixed raw material was filtered using a 1.2 μm cut fiber sintered stainless metal filter, then discharged from the die, solidified by cooling and solidification while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., and unstretched A film was prepared (Tg of the unstretched film polymer was 85 ° C.).

  This unstretched film was stretched 3.0 times at a speed of 20,000% / min and at a temperature of 110 ° C. in two stages in a longitudinal direction using a roll-type stretching machine, and further, a speed of 3, The film was stretched 3.4 times at 000% / min and at a temperature of 105 ° C. Then, it was re-stretched 1.8 times at a temperature of 140 ° C. in a single step in the longitudinal direction with a roll-type stretching machine, and re-stretched 1.2 times at a temperature of 185 ° C. in the width direction using a tenter. Further, after heat treatment at 205 ° C. for 4.5 seconds while performing fine stretching of 1.1 times, a relaxation treatment of 5% in the width direction was performed to produce a biaxially oriented polyester film having a thickness of about 6 μm. The intrinsic viscosity of the film was 0.60 (dl / g), and the surface roughness Ra of the film was 9 nm on both sides.

  As shown in Table 1, the biaxially oriented polyester film satisfies the preferred range of the present invention, has high dimensional stability against long-term changes in temperature and humidity, and long-term storage stability. It had excellent properties.

(Example 2)
As shown in Table 1, an unstretched film was produced in the same manner as in Example 1 by changing the content of polyetherimide (Tg of the polymer of the unstretched film was 90 ° C.).

  This unstretched film was led to a simultaneous biaxial stretching tenter, and stretched 3.0 times x 3.0 times at a temperature of 110 ° C and a stretching speed of 6,000% at the same time in the longitudinal and width directions, and cooled to 70 ° C. Subsequently, the film was redrawn at 1.7 × 1.3 times at the same time in the longitudinal direction and the width direction at a temperature of 175 ° C. Further, the film was heat treated at 200 ° C. for 2.5 seconds while being stretched 1.2 times in the width direction, and then subjected to a relaxation treatment of 2% in the width direction to produce a biaxially oriented polyester film having a thickness of about 6 μm. The intrinsic viscosity of the film was 0.65 (dl / g).

  As shown in Table 1, the biaxially oriented polyester film satisfies the preferred range of the present invention, has high dimensional stability against long-term changes in temperature and humidity, and long-term storage stability. It had excellent properties.

(Example 3)
When preparing the PET / PEI blend chip, 10% by weight of carbodiimide “Stabilizer 9000” manufactured by Raschig was added to prepare a blend chip of PET / PEI / carbodiimide (40/50/10). Using this chip, the content of carbodiimide in the polymer was adjusted to 0.5% by weight to prepare an unstretched film.

  Other conditions were the same as in Example 2, and a biaxially oriented polyester film having a thickness of about 6 μm was produced.

  As shown in Table 1, the biaxially oriented polyester film satisfies the preferred range of the present invention, has high dimensional stability against long-term changes in temperature and humidity, and long-term storage stability. It had excellent properties.

Example 4
A biaxially oriented polyester film was produced in the same manner as in Example 3 except that the content of carbodiimide in the polymer was changed to 2% by weight.

  As shown in Table 1, the biaxially oriented polyester film satisfies the preferred range of the present invention, has high dimensional stability against long-term changes in temperature and humidity, and long-term storage stability. It had excellent properties.

  However, this film tended to cause streaks in long-time film formation (200 hours).

(Example 5)
An unstretched film consisting only of PET (intrinsic viscosity 0.65 (dl / g)) was prepared without using a PET / PEI blend chip (the polymer Tg of the unstretched film was 78 ° C.).

  This unstretched film was stretched 3.0 times at a speed of 30,000% / min and at a temperature of 100 ° C. in two stages in the longitudinal direction using a roll-type stretching machine, and further, a speed of 5, The film was stretched 4 times at 000% / min and at a temperature of 100 ° C. Subsequently, the film was re-stretched 1.5 times at a temperature of 160 ° C. in a single step in a longitudinal direction with a roll-type stretching machine, and re-stretched 1.6 times at a temperature of 175 ° C. in the width direction using a tenter. Furthermore, it heat-processed for 8 second at the temperature of 215 degreeC, performing 1.1 times fine extending | stretching, and produced the biaxially-oriented polyester film of thickness about 8 micrometers. The intrinsic viscosity of the film was 0.62 (dl / g).

  As shown in Table 1, the biaxially oriented polyester film satisfies the preferred range of the present invention, has high dimensional stability against long-term changes in temperature and humidity, and long-term storage stability. It had excellent properties.

(Example 6)
Except for using high molecular weight PET with an intrinsic viscosity of 0.85 (dl / g) and changing the heat treatment to a temperature of 225 ° C. for 10 seconds while performing fine stretching 1.3 times, the same as in Example 5, A biaxially oriented polyester film having a thickness of about 8 μm was prepared. The intrinsic viscosity of the film was 0.75 (dl / g).

  As shown in Table 1, the biaxially oriented polyester film satisfies the preferred range of the present invention, has high dimensional stability against long-term changes in temperature and humidity, and long-term storage stability. It had excellent properties.

(Example 7)
A film was prepared using PEN as a raw material. To a mixture of 100 parts by weight of 2,6-naphthalenedicarboxylic acid dimethyl ester and 60 parts by weight of ethylene glycol, 0.025 parts by weight of manganese acetate tetrahydrate and 0.005 parts by weight of sodium acetate trihydrate were added, and the internal temperature The ester exchange reaction was carried out while gradually raising the temperature from 150 ° C. Next, 0.02% by weight of calcium carbonate particles having an average particle diameter of 0.6 μm and 0.3% by weight of spherical silica particles having an average particle diameter of 0.1 μm were added as an ethylene glycol slurry, and the transesterification rate was 95%. At that time, 0.069 parts by weight of a phosphorous compound glycol solution obtained by reacting 25 parts by weight of trimethyl phosphate and 75 parts by weight of ethylene glycol in advance as a stabilizer was added, and after sufficient stirring, in 2.5 parts by weight of ethylene glycol. 0.014 parts by weight of a solution obtained by reacting 0.8 parts by weight of trimellitic anhydride and 0.65 parts by weight of tetrabutyl titanate (titanium content: 11% by weight) was added. Next, the reaction product was transferred to a polymerization reactor and subjected to a polycondensation reaction under high temperature and reduced pressure (final internal temperature 295 ° C.) to obtain polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.57 (dl / g). .

  Further, in the same manner as in Example 3, a blend chip of PEN / PEI / carbodiimide (49.5 wt% / 50 wt% / 0.5 wt%) was produced. Using this chip, an unstretched film was prepared by adjusting the PEI in the polymer to 10 wt% and the carbodiimide content to be 0.1 wt% (the polymer Tg of the unstretched film was 135 ° C. Met).

  This unstretched film was stretched four times at a speed of 10,000% / min and a temperature of 140 ° C. in two stages in the longitudinal direction using a roll-type stretching machine, and further, a speed of 5,000% in the width direction using a tenter. / Min, stretched 4 times at a temperature of 145 ° C. Subsequently, the film was re-stretched 1.5 times at a temperature of 170 ° C. in a single stage in the longitudinal direction with a roll-type stretching machine, and re-stretched 1.1 times at a temperature of 175 ° C. in the width direction using a tenter. Furthermore, it heat-processed for 11 seconds at the temperature of 240 degreeC, performing 1.1 times fine extending | stretching, and produced the biaxially-oriented polyester film about 6 micrometers thick.

  As shown in Table 1, this biaxially oriented polyester film satisfied the preferred range of the present invention and had characteristics that could be sufficiently used for high-density magnetic tape applications.

(Example 8)
In the same manner as in Example 5, an unstretched film was produced.

  This unstretched film is led to a simultaneous biaxial stretching tenter and stretched 3.5 times x 3.5 times at a stretching temperature of 95 ° C and a stretching speed of 6,000% at the same time in the longitudinal and width directions, and cooled to 70 ° C. did. Subsequently, the film was re-stretched at 1.2 × 1.6 times in the longitudinal direction and the width direction at a temperature of 155 ° C. at the same time. Further, the film was heat treated at 220 ° C. for 5 seconds while being stretched 1.2 times in the width direction, and then subjected to a relaxation treatment of 2% in the width direction to produce a biaxially oriented polyester film having a thickness of about 6 μm.

  As shown in Table 1, this biaxially oriented polyester film satisfied the preferred range of the present invention and had characteristics that could be sufficiently used for high-density magnetic tape applications.

Example 9
In the same manner as in Example 7, an unstretched film was prepared by adjusting the PEN / PEI ratio to 85% by weight / 15% by weight and the carbodiimide content to 2% by weight (polymer of unstretched film). The Tg was 140 ° C.).

  This unstretched film was guided to a simultaneous biaxial stretching tenter, and stretched 3.5 times × 4 times at a stretching temperature of 150 ° C. and a stretching speed of 6,000% simultaneously in the longitudinal direction and the width direction, and cooled to 70 ° C. Subsequently, the film was redrawn at a temperature of 175 ° C. at the same time in the longitudinal direction and the width direction by 1.5 × 1.1 times. Further, the film was heat-treated at a temperature of 245 ° C. for 10 seconds while being stretched 1.2 times in the width direction, and then subjected to a relaxation treatment of 2% in the width direction to produce a biaxially oriented polyester film having a thickness of about 6 μm.

  As shown in Table 1, this biaxially oriented polyester film satisfied the preferred range of the present invention and had characteristics that could be sufficiently used for high-density magnetic tape applications.

  As shown in Table 1, this biaxially oriented polyester film satisfied the preferred range of the present invention and had characteristics that could be sufficiently used for high-density magnetic tape applications.

(Example 10)
A biaxially oriented polyester film was prepared in exactly the same manner as in Example 1 except that high molecular weight PET having an intrinsic viscosity of 0.85 (dl / g) was used and the temperature of the extruder was changed to 275 ° C. The intrinsic viscosity of this film was 0.80 (dl / g).

  As shown in Table 1, this biaxially oriented polyester film satisfied the preferred range of the present invention and had characteristics that could be sufficiently used for high-density magnetic tape applications.

(Example 11)
A biaxially oriented polyester film was prepared in exactly the same manner as in Example 1, except that high molecular weight PET having an intrinsic viscosity of 1.2 (dl / g) was used and the temperature of the extruder was changed to 295 ° C. The intrinsic viscosity of this film was 1.00 (dl / g).

  As shown in Table 1, this biaxially oriented polyester film satisfied the preferred range of the present invention and had characteristics that could be sufficiently used for high-density magnetic tape applications.

  However, this film tended to easily generate a base streak during film formation.

(Comparative Examples 1 and 2)
In the same manner as in Example 1, an unstretched film was produced.

  Stretching conditions were performed in accordance with Example 1, but in Comparative Example 1, re-lateral stretching was not performed, and fine stretching in heat treatment was not performed. In Comparative Example 2, fine stretching was not performed during the heat treatment, the heat treatment temperature was changed to 230 ° C., and the heat treatment time was changed to 8 seconds.

  As shown in Table 2, this biaxially oriented polyester film did not satisfy the preferred range of the present invention and was inferior as a high-density magnetic tape application.

(Comparative Example 3)
A biaxially oriented polyester film having a thickness of about 6 μm was prepared as shown in Table 2 in the same manner as in Example 2 except that the intrinsic viscosity of the raw material PET was changed to 0.53 (dl / g). The intrinsic viscosity of the film was 0.48 (dl / g).

  As shown in Table 2, this biaxially oriented polyester film did not satisfy the preferred range of the present invention and was inferior as a high-density magnetic tape application.

(Comparative Example 4)
To a mixture of 100 parts by weight of 2,6-naphthalenedicarboxylic acid dimethyl ester and 60 parts by weight of ethylene glycol, 0.025 parts by weight of manganese acetate tetrahydrate and 0.005 parts by weight of sodium acetate trihydrate were added, and the internal temperature The ester exchange reaction was carried out while gradually raising the temperature from 150 ° C. Next, 0.02% by weight of calcium carbonate particles having an average particle diameter of 0.6 μm and 0.3% by weight of spherical silica particles having an average particle diameter of 0.1 μm were added as an ethylene glycol slurry, and the transesterification rate was 95%. At that time, 0.069 parts by weight of a phosphorous compound glycol solution obtained by reacting 25 parts by weight of trimethyl phosphate and 75 parts by weight of ethylene glycol in advance as a stabilizer was added, and after sufficient stirring, in 2.5 parts by weight of ethylene glycol. 0.014 parts by weight of a solution obtained by reacting 0.8 parts by weight of trimellitic anhydride and 0.65 parts by weight of tetrabutyl titanate (titanium content: 11% by weight) was added. Next, the reaction product was transferred to a polymerization reactor and subjected to a polycondensation reaction under high temperature and reduced pressure (final internal temperature 295 ° C.) to obtain polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.57.

  This polymer was dried at 170 ° C. for 6 hours, then sent to an extruder, and melt-extruded at 300 ° C. to obtain an unstretched polyester film. The obtained unstretched film was preheated, further stretched 5.8 times at a film temperature of 135 ° C. between low speed and high speed rolls, and rapidly cooled to obtain a longitudinally stretched film. Then, it supplied to the stenter and extended | stretched 5.2 times in the horizontal direction at 155 degreeC. Furthermore, heat treatment was performed at 205 ° C. for 4 seconds to obtain a biaxially oriented polyester film having a thickness of 6.0 μm.

  As shown in Table 2, this biaxially oriented polyester film did not satisfy the preferred range of the present invention and was inferior as a high-density magnetic tape application.

(Comparative Example 5)
A biaxially oriented polyester film was produced in the same manner as in Comparative Example 4 except that the draw ratio was changed to 4.3 × 5.5.

  As shown in Table 2, this biaxially oriented polyester film did not satisfy the preferred range of the present invention and was inferior as a high-density magnetic tape application.

(Comparative Example 6)
0.01% by weight of spherical silica particles having an average particle diameter of 0.1 μm, 0.12% of spherical silica particles having an average particle diameter of 0.3 μm, and polyethylene-2,6-naphthalate having a carboxyl end amount shown in Table 1 The pellets containing 0.13% by weight of spherical silica particles having an average particle size of 0.1% by weight and carboxyl end amounts of polyethylene-2,6-naphthalate shown in Table 1 were dried at 170 ° C. for 6 hours. Supply to each extruder, melt at a melting temperature of 300 ° C, use a multi-manifold coextrusion die, laminate so that the center is a normal polymer, and both surface layers are polymers with high terminal carboxyl concentration, extruded, and stretched A biaxially oriented polyester film having a thickness of 6.0 μm was obtained in the same manner as in Comparative Example 4 under the condition where the magnification was 6.4 × 5.0.

  As shown in Table 2, this biaxially oriented polyester film did not satisfy the preferred range of the present invention and was inferior as a high-density magnetic tape application.

(Comparative Example 7)
A biaxially oriented polyester film was prepared in the same manner as in Example 1 except that high molecular weight PET having an intrinsic viscosity of 0.54 (dl / g) was used. The intrinsic viscosity of this film was 0.53 (dl / g).

  As shown in Table 2, this biaxially oriented polyester film did not satisfy the preferred range of the present invention and was inferior as a high-density magnetic tape application.

(Comparative Example 8)
An attempt was made to produce a film by the same production method as in Example 1 using high molecular weight PET having an intrinsic viscosity of 2.0 (dl / g). However, the extrusion state was poor, film tearing occurred frequently, and a film could not be obtained.

  The present invention is particularly preferably used for high-density recording magnetic tapes for data storage, but is not limited to this, and can be applied to capacitor applications, insulating films, and the like, and its application range is limited to these. It is not a thing.

It is the schematic of a film dimension measuring apparatus.

Explanation of symbols

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)

The temperature expansion coefficient in the width direction of the film is a (ppm / ° C.), the humidity expansion coefficient in the width direction of the film is b (ppm /% RH), and the width direction when a 10 MPa load is applied in the longitudinal direction of the film A biaxially oriented polyester film in which a, b and c satisfy the following ranges when the temperature change coefficient of the shrinkage is c (ppm / ° C.).
-3 ≦ a ≦ 15
0 ≦ b ≦ 10
0 ≦ c ≦ 15
a-2b-c ≧ −15
a + 2b-c ≦ 30 2. The biaxially oriented polyester film according to claim 1, wherein a dimensional change in the width direction is 0 to 200 ppm when a load of 10 MPa is applied in the longitudinal direction and the treatment is performed at 45 ° C. and 30% RH for 24 hours. The biaxially oriented polyester film according to claim 1 or 2, wherein the dimensional change rate in the width direction of the film when the load applied in the longitudinal direction is changed from 10 MPa to 20 MPa is from 0 to 300 ppm. With a 10 MPa load applied in the longitudinal direction, the dimensional change rate in the width direction of the film when the environmental condition is changed from 10 ° C. and 10% RH to 30 ° C. and 90% RH, and a 10 MPa load is applied in the longitudinal direction. The dimensional change rate in the width direction of the film when the environmental conditions are changed from 10 ° C. 90% RH to 50 ° C. 10% RH in a state where the film is in the state of any one of claims 1 to 3. Biaxially oriented polyester film. The biaxially oriented polyester film according to any one of claims 1 to 4, comprising 80% by weight or more of polyethylene terephthalate. The biaxially oriented polyester film according to any one of claims 1 to 5, comprising 3 to 30% by weight of polyimide. The biaxially oriented polyester film according to any one of claims 1 to 6, wherein the terminal carboxyl group concentration is 0.1 to 10 equivalent / t.

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