JP2002011786A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film reduced in the deviation of a recording track when the film is used for a magnetic tape and excellent in running durability as well as preservation stability. SOLUTION: The biaxially oriented polyester film is characterized in that a Poisson's ratio upon loading the load of 50 MPa in the lengthwise direction is within the range of 0.10-0.35 and a creep compliance in the lengthwise direction of the film when 30 minute is elapsed after loading the load of 28 MPa at a temperature of 50 deg.C is within the range of 0.1-0.3 Gpa-1 while a residual stress when 30 minute is elapsed after removing the load is within the range of 0-0.1%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film suitable for high density magnetic recording media.

[0002]

2. Description of the Related Art Biaxially oriented polyester films are used for various applications because of their excellent thermal properties, dimensional stability and mechanical properties, and their usefulness as base films for magnetic tapes and the like is well known. . In recent years, in order to reduce the weight, size, and long-term recording of equipment, magnetic tapes have been required to have a thinner base film and higher recording density. There is an increasing demand for improved stability. However, when the film is thinned, the mechanical strength becomes insufficient and the stiffness of the film becomes weak, or it becomes easy to expand in the longitudinal direction, and it becomes easy to shrink in the width direction.
There are problems such as the occurrence of track deviation, deterioration of head touch and deterioration of electromagnetic conversion characteristics.

[0003] As a base film that can meet the above requirements, an aramid film has been conventionally used in view of strength and dimensional stability. Aramid film is disadvantageous in terms of cost due to its high price, but is currently used because there is no substitute.

On the other hand, as a conventional technique for increasing the strength of a biaxially oriented polyester film, there is known a method in which a film stretched in two directions, longitudinal and transverse, is stretched in the longitudinal direction again to increase the strength in the longitudinal direction ( For example, JP-B-42-9270, JP-B-43-3040, JP-B-46-111
9, JP-B-46-1120, JP-A-50-
No. 133276, Japanese Unexamined Patent Publication No. 55-22915), (1) the tape is cut when used, (2) edge damage occurs due to insufficient rigidity in the width direction, (3)
Large-capacity, high-density magnets have problems such as the occurrence of errors in recording tracks due to deviations in the recording tracks, (4) insufficient strength and difficulty in handling thin films, and the inability to obtain desired electromagnetic conversion characteristics. At present, many problems remain when applied to recording tapes.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a biaxially oriented polyester film excellent in running durability and storage stability.

[0006]

The above object is achieved when the Poisson's ratio when a load of 50 MPa is applied in the longitudinal direction is 0.10 to 0.10.
0.35, temperature 50 ° C, load 28MPa
The creep compliance in the longitudinal direction of the film after 30 minutes is in the range of 0.1 to 0.3 GPa ^-1 and the residual strain after 30 minutes from the removal of the load is -0.05 to
This is achieved by a biaxially oriented polyester film characterized by being in the range of 0.1%.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester used in the present invention is a polyester containing an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main components. As the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-
Use of naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, and the like Of these, terephthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid can be preferably used. As the alicyclic dicarboxylic acid, for example, cyclohexanedicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. One of these acid components may be used alone, or two or more of them may be used in combination. Further, an oxyacid such as hydroxyethoxybenzoic acid may be partially copolymerized.

The diol component includes, for example, ethylene glycol, 1,2-propanediol, 1,3-
Propanediol, neopentyl glycol, 1,3-
Butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-
Cyclohexane dimethanol, 1,3-cyclohexane dimethanol, 1,4-cyclohexane dimethanol,
Diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2′-bis (4′-β-hydroxyethoxyphenyl) propane and the like can be used. Among them, ethylene glycol,
Examples thereof include 1,4-butanediol, 1,4-cyclohexanedimethanol, and diethylene glycol, and particularly preferred is ethylene glycol. These diol components may be used alone or in combination of two or more.

Further, trimellitic acid,
Pyromellitic acid, glycerol, pentaerythritol, 2,4-dioxybenzoic acid, lauryl alcohol,
A polyfunctional compound such as phenyl isocyanate may be copolymerized to the extent that the polymer is substantially linear.

As the polyester of the present invention, polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, a copolymer thereof, and a modified product thereof are preferred.

The polyester used in the present invention may contain a polyetherimide in a range of 5 to 30% by weight. As the polyetherimide used,
Aliphatic, alicyclic or aromatic ether unit and a polymer containing a cyclic imide group as a repeating unit,
The polymer is not particularly limited as long as it is a polymer having melt moldability. For example, U.S. Pat.
No. 22678, Patent No. 2606912, Patent No. 260
No. 6914, Patent No. 2596565, Patent No. 2596
No. 566, No. 2,598,478, polyetherimide, No. 2,598,536, No. 2,599,171.
No., JP-A-9-48852, and Patent No. 256555
No. 6, Patent No. 2,564,636, Patent No. 2,564,637
No. 2,563,548, Patent No. 2,563,547
No. 2,558,341, Patent No. 2,558,339
No. 2,834,580.
As long as the effects of the present invention are not impaired, the main chain of the polyetherimide contains a cyclic imide, a structural unit other than an ether unit, for example, an aromatic, aliphatic, alicyclic ester unit, or an oxycarbonyl unit. May be. In the present invention, a polyetherimide having a glass transition temperature of 350 ° C. or lower, more preferably 250 ° C. or lower is preferable.
Condensates of -bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride with m-phenylenediamine or p-phenylenediamine are compatible with polyester, cost, melt moldability, etc. Is most preferred. This polyetherimide is available under the trade name "Ultem" (registered trademark) under the name General Electric.
Available from the company.

It is preferable to add a compatibilizer if necessary, since the dispersion diameter can be controlled. In this case, the type of the compatibilizer differs depending on the type of the polymer, but the amount of addition is preferably 0.01 to 10% by weight.

The biaxially oriented polyester film of the present invention preferably contains inert particles. Examples of inert particles include clay, mica, titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, aluminum silicate, alumina and zirconia, and the like, and acrylic acid. And organic particles containing styrene or the like as a constituent component, so-called internal particles precipitated by a catalyst or the like added at the time of the polyester polymerization reaction. Among them, particularly preferred are polymer crosslinked particles, alumina, spherical silica, and aluminum silicate.

The biaxially oriented polyester film of the present invention may contain other various additives such as a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a pigment within a range not to impair the present invention. Organic lubricants such as dyes, fatty acid esters, and waxes can also be added.

The average particle size of the inert particles contained in the biaxially oriented polyester film of the present invention is 0.001 to 2 μm.
It is preferably 0.005 to 1 μm, and more preferably 0.01 to 0.5 μm. 0.001
When it is smaller than μm, it does not play a role as a film surface protrusion, and when it is larger than 2 μm, it is not preferable because it easily falls off as coarse protrusion.

The content of the inert particles contained in the biaxially oriented polyester film of the present invention is 0.01 to 3% by weight.
Is more preferable, more preferably 0.02 to 1% by weight, and still more preferably 0.05 to 0.5% by weight. 0.01
If it is less than 3% by weight, it is not effective because it is not effective for the running characteristics of the film.
It is not preferable because it aggregates into coarse projections and easily falls off.

The biaxially oriented polyester film of the present invention may be a single layer or a laminated structure of two or more layers. In the present invention, it is particularly preferable to adopt a two-layer structure in which a film layer having a role of improving the running property and the handling property of the film is laminated on one side of the base layer portion of the film. Note that the base layer portion is a layer having the largest thickness in the layer thickness, and the other portion is a laminated portion. Physical properties such as elastic modulus and dimensional stability, which are important for magnetic material applications, are determined mainly by the physical properties of the base layer.

In the laminated part of the film layer of the present invention, when the relation between the average particle diameter d (nm) of the inert particles and the laminated thickness t (nm) is 0.2d ≦ t ≦ 10d, the laminated part is uniform. This is preferable because a projection having a height can be obtained.

The biaxially oriented polyester film of the present invention has a Poisson's ratio of 0.10 to 0.35 when a load of 50 MPa is applied in the longitudinal direction, and has a temperature of 50 to 50.
C., creep compliance in the longitudinal direction of the film after 30 minutes at a load of 28 MPa is 0.1 to 0.3 GPa ^-1.
And the residual strain 30 minutes after the removal of the load is required to be in the range of -0.05 to 0.1%.

In recent magnetic material applications, further thinning of the base film and high-density recording for long-time recording are required. In the present invention, the most important characteristics for satisfying the requirements are a processing step on a magnetic tape, a longitudinal elongation deformation of the tape under conditions of temperature, humidity, tension, etc. of a tape use environment, and a width direction. We paid attention to the dimensional stability of. By setting the Poisson's ratio, creep compliance and residual strain within the above ranges as indicators of the dimensional stability, the temperature, humidity,
It was found that a highly rigid biaxially oriented polyester film having excellent dimensional stability and little deformation in the longitudinal and width directions due to tension was obtained.

The Poisson's ratio is the ratio of the contraction rate in the width direction to the elongation rate in the longitudinal direction when a tension is applied in the longitudinal direction. When Poisson's ratio is greater than 0.35,
Shrinkage in the width direction increases during tape processing, and dimensional stability deteriorates. Also, during recording and reproduction when using a magnetic tape, shrinkage in the width direction occurs due to stress elongation deformation in the longitudinal direction, and a recording track shift occurs. In addition, dropouts occur frequently, and the storage stability of the data deteriorates. A value where the Poisson's ratio is less than 0.10 is a region that is difficult to reach with a polyester film. The Poisson's ratio is more preferably 0.12 to 0.32, even more preferably 0.14.
０．３0.30.

The creep compliance of the present invention is 5
Measured at 0 ° C. The temperature of 50 ° C. is the maximum temperature at which the temperature around the tape increases due to friction with the magnetic head during recording and reproduction of the magnetic tape, and is a condition assuming the environment in which the tape is used. Creep compliance is 0.
When it is 3 GPa ^-1 or more, the magnetic tape is liable to elongate and deform due to the tension at the time of recording / reproducing, causing deterioration in running durability and track deviation. 0.1 GPa ^-1
Below, the tape is likely to break. The creep compliance is more preferably 0.13 to 0.27.
GPa ^-1 , more preferably 0.16 to 0.24 GPa
It is in the range of ^-1 .

The residual strain after a lapse of 30 minutes from the removal of the load is 0.
When it is 1% or more, a part of the elongation deformation due to the tension at the time of recording and reproduction of the magnetic tape tends to remain as permanent distortion,
This causes track deviation. If it is less than -0.05%, when the recording / reproduction of the magnetic tape is stopped, it expands easily in the longitudinal direction, which causes wrinkles and turbulence. The residual strain is more preferably -0.02 to 0.08.
%, More preferably in the range of 0 to 0.06%.

In the biaxially oriented polyester film of the present invention, the heat shrinkage in the width direction at 100 ° C. for 30 minutes is from the viewpoint of suppressing the generation of wrinkles due to the heat history in the tape processing step.
It is preferably 0.2% or more. Suppression of frictional heat between the magnetic tape and the magnetic recording head, shrinkage in the width direction due to heat history in the tape processing process, durability of the film surface, data storage stability, etc. From the viewpoint of, it is preferable that it is 0.5% or less. More preferably -0.1 to 0.4
%, Most preferably in the range of 0 to 0.3%. Here, a minus sign indicates that it is expanding.

In the biaxially oriented polyester film of the present invention, the elastic modulus in the longitudinal direction is preferably 6 GPa or more from the viewpoint of suppression of elongation and deformation of the magnetic tape due to tension and electromagnetic conversion characteristics. From 15G
It is preferably Pa or less. More preferably, 6.
5-14.5 GPa range, most preferably 7-14 G
Pa range. The elastic modulus in the width direction is 4 GPa from the viewpoint of suppressing the contraction in the width direction due to the tension in the longitudinal direction.
It is preferably at least 13 GPa from the viewpoint that the strength in the longitudinal direction is not suppressed. More preferably 4.5 to 12 GPa, even more preferably 5 G
The range is from Pa to 11 GPa.

In the biaxially oriented polyester film of the present invention, the surface roughness Ra _A of one film surface (A surface) is:
The thickness is preferably 3 nm or more from the viewpoint of reducing friction with the magnetic head, and is preferably 10 nm or less from the viewpoint of electromagnetic conversion characteristics. Further, the surface roughness Ra _B of the film surface (Side B) opposite to the A side is preferably 5 nm or more from the viewpoint of handling properties in the processing step, and the transfer by pressing force when wound as a tape. From the viewpoint of reduction, the thickness is preferably 17 nm or less. More preferably, Ra _A is in the range of 3 to 9 nm and Ra _B is in the range of 6 to 16 nm, and further preferably, Ra _A is in the range of 4 to 8 nm and Ra _{B is}
Is in the range of 7 to 15 nm.

The biaxially oriented polyester film of the present invention has a coefficient of thermal expansion (α) of −10 from the viewpoint of the process of forming a magnetic tape and the dimensional stability under high temperature conditions during recording and reproduction of the magnetic tape. It is preferably in the range of × 10 ^-6 to 10 × 10 ^-6 (/ ° C.). Where-(minus)
Indicates contraction. More preferably,-
8 × 10 ^{−6 to} 9 × 10 ⁻⁶ (/ ° C.), most preferably −
The range is from 6 × 10 ⁻⁶ to 8 × 10 ⁻⁶ (/ ° C.).

The biaxially oriented polyester film of the present invention has a coefficient of humidity expansion (β) of 1 from the viewpoint of processing steps into a magnetic tape and dimensional stability under high humidity conditions during recording and reproduction of the magnetic tape. It is preferably in the range of × 10 ^{-6 to} 12 × 10 ^-6 (/% RH). More preferably, 2 × 1
0 ^{-6 to} 11 × 10 ^-6 (/% RH), most preferably 3
The range is from × 10 ⁻⁶ to 10 × 10 ⁻⁶ (/% RH).

In the biaxially oriented polyester film of the present invention, when a magnetic tape having a width of 1/2 inch is processed and run under temperature, humidity and tension load conditions, the track deviation in the width direction is caused by the appearance of the tape. From the viewpoint of dropout suppression, the thickness is preferably in the range of 0 to 1 μm. The maximum dimensional change width is preferably in the range of 0 to 3 μm from the viewpoint of running durability of the tape and storage stability of data. For track deviation, more preferably 0 to
0.8 μm, most preferably in the range of 0 to 0.5 μm. The maximum dimension change width is more preferably 0.
２2 μm, most preferably in the range of 0-1.5 μm.

The biaxially oriented polyester film of the present invention is preferably used for magnetic recording tapes, capacitors, heat-sensitive transfer ribbons, heat-sensitive stencil sheets, and the like.
A particularly preferred application is a high-density magnetic recording medium such as for data storage that requires a uniform and fine surface morphology. The data recording capacity is preferably 30 GB
(Gigabytes) or more, more preferably 70 GB or more, and still more preferably 100 GB or more. The thickness of the base film for a high-density magnetic recording medium is preferably 3 to 7 μm. More preferably, it is 3.5 to 6.5 μm, further preferably 4 to 6 μm.

When used as a high-density magnetic recording medium, the magnetic layer is preferably a ferromagnetic metal thin film, a magnetic layer obtained by dispersing a ferromagnetic metal fine powder in a binder, or a magnetic layer formed by coating a metal oxide. An example is given. As the ferromagnetic metal thin film, iron, cobalt, nickel and other alloys are preferable. Further, as the ferromagnetic metal fine powder, ferromagnetic hexagonal ferrite fine powder, iron, cobalt, nickel and other alloys are preferable. As the binder, a thermoplastic resin, a thermosetting resin, a reactive resin, a mixture thereof, or the like is preferable.

The magnetic layer is formed by kneading the magnetic powder with a binder such as thermoplastic, thermosetting or radiation curable,
Any of a dry method in which a magnetic metal thin film layer is directly formed on a base film by a coating method of coating and drying, a metal or alloy vapor deposition method, a sputtering method, an ion pre-coating method, or the like can be employed.

In the magnetic recording medium of the present invention, a protective film may be provided on the ferromagnetic metal thin film. With this protective film, running durability and corrosion resistance can be further improved. Examples of the protective film include oxide protective films such as silica, alumina, titania, zirconia, cobalt oxide, and nickel oxide; nitride protective films such as titanium nitride, silicon nitride, and boron nitride; silicon carbide, chromium carbide, and boron carbide. A carbon protective film made of carbon such as a carbide protective film, graphite, and amorphous carbon may be used.

The carbon protective film is a carbon film having an amorphous structure, a graphite structure, a diamond structure, or a mixture thereof formed by a plasma CVD method, a sputtering method, or the like, and particularly preferably a hard carbon film generally called diamond-like carbon. It is a membrane.

For the purpose of further improving the adhesion with the lubricant to be provided on the hard carbon protective film, the surface of the hard carbon protective film may be subjected to a surface treatment with plasma of an oxidizing or inert gas.

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

Next, the method for producing the biaxially oriented polyester film of the present invention will be described. However, the present invention is not limited to the following method.

The biaxially oriented polyester film of the present invention is a film in which a sheet obtained by melt-molding a polyester resin is stretched in the longitudinal direction and the width direction by successive biaxial stretching and / or simultaneous biaxial stretching. After performing one-stage biaxial stretching in the width direction, fine stretching is performed in multiple stages in the width direction, and further stretching is performed in the longitudinal and width directions to obtain a high degree of orientation.

Hereinafter, a specific production method will be described by taking a case of sequential biaxial stretching of a polyethylene terephthalate (PET) film as an example.

First, terephthalic acid and ethylene glycol are esterified, or dimethyl terephthalate and ethylene glycol are transesterified according to a conventional method to obtain bis-β-hydroxyethyl terephthalate (BHT). Next, this BHT was transferred to a polymerization tank, and the BHT was placed under vacuum for 28 hours.
Heat to 0 ° C. to advance the polymerization reaction. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. The obtained polyester is subjected to solid-state polymerization in a pellet form under reduced pressure. In the case of solid-phase polymerization, after preliminarily crystallizing at a temperature of 180 ° C. or lower, solid-phase polymerization is performed at 190 to 250 ° C. under a reduced pressure of about 1 mmhg for 10 to 50 hours. Also, in order to contain particles in the polyester, during the above polymerization,
A method is also preferable in which particles are dispersed in a predetermined ratio in a form of slurry in ethylene glycol, and this ethylene glycol is polymerized with terephthalic acid. When the particles are added, for example, a water sol or an alcohol sol obtained at the time of synthesizing the particles is added without drying once, so that the particles have good dispersibility. It is also effective to mix a water slurry of particles with polyester pellets and knead the polyester with a vent-type twin-screw extruder. As a method for adjusting the content and the number of particles, a high-concentration particle master is prepared by the above-described method, and it is made into a polyester or other thermoplastic resin substantially free of particles during film formation or a mixture thereof. Is effective to adjust the content of the particles by diluting the particles. The polyester pellet containing high-concentration inert particles is mixed with the polyester pellet containing substantially no particles, dried at 180 ° C. for 3 hours or more under vacuum, and then melt-extruded at 270 to 300 ° C. After passing through the filter, it is discharged in a sheet form from a T-shaped base. The melted sheet is brought into close contact with a drum cooled to a surface temperature of 25 to 30 ° C. by electrostatic force to be cooled and solidified to obtain a substantially non-oriented unstretched polyester film.

Next, this unstretched film is biaxially stretched,
Biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. here,
Using a longitudinal stretching machine in which several rolls are arranged, stretching is performed in the machine direction using the peripheral speed difference of the rolls (MD stretching 1), and then transverse stretching is performed by a stenter (TD stretching 1). A biaxial stretching method in which longitudinal stretching is performed again by a roll longitudinal stretching machine (MD stretching 2) and transverse stretching is again performed by a stenter (TD stretching 2) will be described.

First, the unstretched polyester film is heated by a group of heating rolls, and is 1.1 to 5.0 times, preferably 1.5 to 4.0 times, more preferably 2.0 to 2.0 times in the longitudinal direction.
It is stretched 3.5 times (MD stretching 1). The stretching temperature is (Tg
(Glass transition temperature of polyester) -100) to (Tg)
+100) ° C., more preferably (Tg)
−50) to (Tg + 50) ° C., more preferably (Tg−30) to (Tg + 30) ° C. Thereafter, the film is cooled with a group of cooling rolls at 20 to 50 ° C., and both ends of the film are gripped with clips, guided to a tenter, and stretched in the width direction (TD stretching 1-1). The stretching temperature is (Tg
-100) to (Tg + 100) ° C, more preferably (Tg-50) to (Tg + 50) ° C, and still more preferably (Tg-30) to (Tg + 30) ° C. The stretching ratio is preferably 2.0 to 6.0 times, more preferably 3.0 to 5.0 times, and still more preferably 3.5 to 5.0 times.
The range is 4.5 times. Furthermore, fine stretching in the width direction (TD
Stretching 1-2) is performed. Stretching temperature is Tg ~ (Tg + 50) ℃
The stretching ratio is preferably in the range of 1.1 to 1.3 times. Most preferably, the fine stretching in the width direction is performed in multiple stages of two or more stages within the range of the stretching ratio while the temperature is increased stepwise within the stretching temperature range.
By performing this fine stretching, the degree of orientation in the width direction is improved, the structure is fixed, and the biaxially oriented polyester film of the present invention is easily obtained, which is preferable.

Further, the film is heated by a group of heating rolls,
1.1 to 4.0 times, preferably 1.3 to 3.0 times in the longitudinal direction.
It is stretched again by 0 times, more preferably by 1.5 to 2.5 times, and cooled by a group of cooling rolls at 20 to 50 ° C (MD stretching 2). Stretching temperature is (Tg-50)-(Tg + 100) ° C
The range of (Tg-20)-is more preferable.
(Tg + 80) ° C., more preferably (Tg−1)
0) to (Tg + 50) ° C. Next, stretching in the width direction is performed again using a stenter (TD stretching 2). The stretching temperature is preferably in the range of Tg to 250 ° C, more preferably in the range of (Tg + 20) to 240 ° C, still more preferably in the range of (Tg + 40) to 220 ° C, and the stretching ratio is 1.1.
To 2.5 times, more preferably 1.15 to 2.
It is carried out at 2 times, more preferably at 1.2 to 2.0 times. The stretched film is heat-set under tension or while relaxing in the width direction. A preferred heat setting temperature is 150 to 250 ° C, more preferably 170 to 240 ° C, and still more preferably 16 to 250 ° C.
The range is from 0 to 220 ° C. In addition, this film
It is preferable to cool while relaxing in the width direction in a temperature zone of ~ 180 ° C. At this time, the range of 120 to 180 ° C and 4
It is preferable to perform slow cooling in two or more stages in the range of 0 to 120 ° C. Thereafter, the film edge is removed, and the film is wound up on a roll. Further, if necessary, the film may be heat-treated in a hot-air oven with the film wound around a core (roll-shaped film). The preferred processing temperature is (Tg-10)
To (Tg-60) ° C, more preferably (Tg-1)
5) to (Tg-55) ° C, more preferably (Tg-55) ° C.
g-20) to (Tg-50) ° C. A preferred treatment time is in the range of 10 to 360 hours, more preferably in the range of 24 to 240 hours, even more preferably 72 to 16 hours.
8 hours. Further, the heat treatment with the roll-shaped film can be performed in two or more stages by changing the temperature and the time within the above-mentioned temperature and time ranges. Performing the roll-shaped heat treatment is preferable because dimensional stability such as creep characteristics is improved.

[Method for Measuring Physical Properties and Method for Evaluating Effect] The method for measuring characteristic values and the method for evaluating effect are as follows.

(1) Poisson's Ratio Sampling was performed at a width of 20 mm with respect to the longitudinal direction of the film, and a 10 mm square grid was written at the center of the film. 2
In an atmosphere of 3 ° C. and 65% RH, the sample length was set to 110 mm in a sheet width measuring device manufactured by Ayaha Engineering Co., Ltd., and two high-performance laser dimension measuring devices manufactured by KEYENCE CORPORATION were used. The longitudinal and width dimensions of the grid were each read. 50 in the longitudinal direction of the film
When a load of MPa is applied, the dimensional change rate in the longitudinal direction of the lattice (ΔL _MD %) and the dimensional change rate in the width direction (ΔL _TD)
%), And the Poisson's ratio was determined from the following equation: Poisson's ratio = (ΔL _TD / ΔL _MD ).

(2) Creep Compliance and Residual Strain The film was sampled to a width of 4 mm, and TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. was set to a sample length of 15 mm.
And heating control section TA-1500, 50 ℃,
The condition was adjusted to 65% RH. The length of the film at that time was defined as L ₀ (μm). Thereafter, a load of 28 MPa was applied to the film, and the length of the film when held for 30 minutes was defined as L ₃₀ (μm). Further, the load was removed, and the length of the film when held for 30 minutes was defined as L ₆₀ (μm).
The time-dependent change in the amount of film expansion / contraction was measured, and the following equation was used. Creep compliance (GPa ^-1 ) = (L ₃₀ −
L ₀ ) /15000/0.028 Residual strain (%) = (L ₆₀ −L ₀ ) / 15000 × 100 The creep compliance and the residual strain were calculated. Here, creep is a phenomenon in which strain increases with time under a constant stress, and creep compliance is a ratio of this strain to a constant stress, and is described in "Introduction to Polymer Chemistry (Second Edition)". (Published by Kagaku Dojin) p1
50.

(3) Heat shrinkage rate According to the method specified in JIS-C2318, a width of 10
mm, a sample with a mark interval of about 100 mm
Heat treatment was performed at a load of 0.5 g for 30 minutes. The distance between the marked lines before and after the heat treatment was measured using a thermal shrinkage rate measuring device manufactured by Techno-Needs Co., Ltd., and the following equation: Heat shrinkage rate (%) = [(L0−L) / L0] × 100 L0: Heat treatment Previous mark line interval L: Heat shrinkage was calculated from mark line interval after heat treatment.

(4) Elastic modulus According to the method specified in ASTM-D882, a sample having a width of 10 mm and a test length of 100 mm was measured using an automatic film strength and elongation measuring device “Tensilon AMF / RTA-100” manufactured by Orientec Co., Ltd. At a temperature of 23 ° C. and a humidity of 65% R
H, an average value of five measurements performed under the conditions of a tensile speed of 200 mm / min.

(5) Surface Roughness Ra Using a high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory, a stylus tip radius is 0.5 m, a stylus load is 5 mg, and a measurement length is 1
mm, center line average roughness R at a cutoff value of 0.08 mm
a was taken as the average value of 20 measurements made by scanning in the film width direction.

(6) Thermal Expansion Coefficient (/ ° C.) A film was sampled to a width of 4 mm, and TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. was set to a sample length of 15 mm.
And the heating controller TA-1500. 15%
Under RH conditions, a load of 0.5 g was applied to the film to raise the temperature from room temperature (23 ° C.) to 50 ° C., and then the temperature was once returned to room temperature. Thereafter, the temperature was increased again from room temperature to 50 ° C. At that time, 30 ° C to 40 ° C
The displacement (ΔL μm) of the film up to the following was measured, and the following equation was used. Temperature expansion coefficient (/ ° C.) = {ΔL / (15 × 1000)}
/ (40-30) was used to calculate the thermal expansion coefficient.

(7) Humidity expansion coefficient (/% RH) The film was sampled to a width of 10 mm, and the sample length was 200 m.
m, set in a tape elongation tester manufactured by Okura Industry, change the humidity from 40% RH to 80% RH at a temperature of 30 ° C., measure the displacement (ΔL mm), and calculate the following equation. Coefficient (/% RH) = (ΔL / 200) / (80
−40) to calculate the humidity expansion coefficient.

(8) Glass transition temperature Tg DSC2920 manufactured by TA Instruments
Using (2), a specific heat measurement was performed under the following conditions, and JIS
Determined according to K7121. Measurement conditions Heating temperature: 270 to 540K (RCS cooling method) Temperature calibration: Melting point of high-purity indium and tin Temperature modulation amplitude: ± 1K Temperature modulation cycle: 60 seconds Average heating rate: 1K / min Sample weight: Approx. 10mg Sample container : Open aluminum container (33 mg) The glass transition temperature was calculated from the following equation: glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2.

(9) Intrinsic Viscosity η From the solution viscosity (dl / g) and the solvent viscosity (dl / g) measured in orthochlorophenol at 25 ° C. using an Ostwald viscometer, the following equation η _sp / C = [ η] + K [η] ² · C was used to calculate the intrinsic viscosity.

Here, η _sp = (solution viscosity / solvent viscosity) −
1, C is the weight of the dissolved polymer per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (0.343).

(10) Running Durability and Storage Stability of Magnetic Tape A magnetic paint having the following composition is applied to the surface of the biaxially oriented polyester film of the present invention so as to have a coating thickness of 2.0 μm, and is magnetically oriented. ,dry. Then, a back coat having the following composition was applied to the opposite surface and calendered.
Cure at 0 ° C. for 48 hours. The raw tape was slit into a 1/2 inch width, and a 670 m long magnetic tape was assembled into a cassette to form a cassette tape. (Magnetic paint composition)-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 (composition of the back coat)-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 part 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 A cassette tape that was created amount part, IBM made Magstar3
Using the 590 MODELB1A Tape Drive for 100 hours, the following criteria: ○: no tape end surface elongation, no bend, no scraping mark △: no tape end surface elongation, no bend mark, but some cut off marks are seen X: A part of the tape end face was elongated, wakame-like deformation was observed, and abrasion marks were observed. The running durability of the tape was evaluated.

Further, the cassette tape created above is inserted into the IB
M Magstar 3590 Model B1A T
After reading the data using the ape drive, the cassette tape was placed in an atmosphere of 60 ° C. and 80% RH for 100 hours.
After the time was stored, the data was reproduced and the following criteria were used. ○: There was no abnormality in the tape width and there was no track shift, and the data was reproduced normally. △: There was no abnormality in the tape width, but some parts could not be read. × : The tape storage stability was evaluated because the tape width changed and reading was impossible.

(11) Track deviation, maximum dimensional change width The dimensional change in the width direction when the above-prepared cassette tape is run sequentially under the following conditions 1 to 5 is always read, and Dimensional change width and track deviation before and after running were determined. The dimensional change in the width direction was measured by changing the distance (about 1.5 mm) from the servo to the tape. The initial value of the distance from the servo to the tape under the conditions of 20 ° C. and 50% RH is L0 (μm), the distance from the servo to the tape after running under the following condition 3 is L1 (μm),
The distance from the servo to the tape after running under the following condition 5 was L2 (μm).

The cassette tape created above is transferred to IBM
Magstar 3590 Model B1A Ta
Using pe Drive, the dimensional change in the width direction when the vehicle is run sequentially under the following conditions 1 to 5 is always read by a laser size measuring device, and the maximum dimensional change width and the track deviation before and after running are as follows. I asked. The dimensional change in the width direction is represented by a change in the distance from the servo to the tape (about 1.5 mm) before and after running.

Condition 1: 25 ° C., 60% RH, tension 90 g, 3 times of running conditions 2: 25 ° C., 60% RH, 150 g of tension, 3 times of running conditions 3: Condition 3: 50 ° C., 60% RH, 150 g of tension, 100 times of running times Times Condition 4: 25 ° C, 60% RH, tension 150g Number of runs 3 times Condition 5: 25 ° C, 60% RH, tension 90g Number of runs 3 times Distance from servo to tape under 25 ° C, 60% RH conditions: L0 Distance from servo to tape after running under condition 3:
L1 Distance from servo to tape after running under condition 5:
L2 Track deviation (μm) = | L0−L2 | Maximum dimensional change width (μm) = | L0−L1 | (12) Suitability of film processing A film wound up to a width of 500 mm is transported while being unwound from an unwinder. At a speed of 20 m / min, the mixture was supplied to an oven treatment device manufactured by Inoue Metal Industry Co., Ltd.
, And wound up in a length of 100 m. At this time, the end of the wound film is 1
“×” indicates that the projections were more than 0 mm and became irregular.
Those whose end protrusion is 5 mm or more and 10 mm or less,
A mark of less than 5 mm but wrinkles observed during processing was marked as “△”, and a mark with a protrusion at the end of less than 5 mm and no wrinkles observed during processing was marked as “○”.

(13) Electromagnetic conversion characteristics (C / N) A magnetic paint and a non-magnetic paint having the following compositions are applied on the film surface in layers by an extrusion coater (the upper layer is a magnetic paint, the coating thickness is 0.1 μm, and the non-magnetic lower layer is Was appropriately changed in thickness.), Magnetically oriented, and dried. Next, after forming a back coat layer having the following composition on the opposite surface, a small test calender (steel / nylon roll,
After performing calendering at a temperature of 85 ° C. and a linear pressure of 200 kg / cm, curing is performed at 60 ° C. for 48 hours. The raw tape was slit into a width of 8 mm to prepare a pancake. Then, from this pancake, length 200
m was incorporated into a cassette to form a cassette tape.

For this tape, a commercially available VT for Hi8
R (EV-BS3000 manufactured by Sony Corporation)
The C / N at MHz ± 1 MHz was measured. This C / N
Was compared with a commercially available MP video tape for Hi8 as follows.

+3 dB or more: ◎ + 1 dB or more and less than +3 dB: ○ less than +1 dB: ×

[0063]

EXAMPLES Examples and comparative examples will be described below to clarify the effects of the present invention.

Example 1 Using two extruders A and B, extruder A heated to 280 ° C. was provided with polyethylene terephthalate (PET) -I
The pellets (comprising 0.4% by weight of spherical silica particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm) were vacuum-dried at 180 ° C. for 3 hours and then supplied to the extruder B, which was also heated to 280 ° C. After pellets of PET-II (containing 1.0% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm and 0.1% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm) were vacuum-dried at 180 ° C. for 3 hours, and then dried. Supplied. The molten PET-I and PET-II are combined in a T-die,
The layer is adhered on a cast drum having a surface temperature of 25 ° C. by an electrostatic application method to be cooled and solidified, and the ratio of the lamination thickness is PET-I / P.
A laminated unstretched film of ET-II = 14/1 was obtained. This unstretched film was stretched under the conditions shown in Table 1. First, using a longitudinal stretching machine in which several rolls were arranged, stretching was performed in the longitudinal direction (MD stretching 1) by utilizing the peripheral speed difference between the rolls, and the roll was cooled. Both ends of this film are gripped by clips, guided to a tenter, and stretched in the width direction (TD stretch 1-
1), and finely stretching in two steps in the width direction (TD stretching 1).
-2, 1-3). This film is subjected to re-longitudinal stretching (MD stretching 2) by a roll longitudinal stretching machine, then to transverse stretching (TD stretching 2) by a stenter, and heat set at a temperature of 209 ° C.
2.5% in the width direction in the cooling zone of 123 ° C., and further 10%
After relaxing in the zone of 5 ° C. at a relaxation rate of 0.5% in the width direction, the film was gradually cooled to room temperature and wound up. As for the film thickness, a polyester film of 4.5 μm was obtained by adjusting the extrusion amount.

Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film. As shown in Table 3, the film had running durability, storage stability, track deviation,
Excellent in maximum dimensional change width, workability, and electromagnetic conversion characteristics.

[0066]

[Table 1]

[0067]

[Table 2]

[0068]

[Table 3]

Comparative Example 1 A PET (average diameter of 0.3) was placed in an extruder heated to 280 ° C.
Pellets containing 1.0% by weight of spherical crosslinked polystyrene particles having a diameter of 0.1 μm and 0.1% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm are supplied after being vacuum-dried at 180 ° C. for 3 hours. A single-layer unstretched film was obtained by bringing it into close contact with a cast drum at a temperature of 25 ° C. by an electrostatic application method to cool and solidify, and the stretching conditions were changed as shown in Table 1, and the second stage of fine stretching (TD) in the width direction was performed. Except not having performed stretching 1-3), it carried out similarly to Example 1. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Example 2 A laminated unstretched film was obtained in the same manner as in Example 1. The unstretched film was stretched, heat-set, and relaxed in the same manner as in Example 1 except that the conditions shown in Table 1 were changed, and the film was slowly cooled and wound up to obtain a polyester film having a thickness of 5.0 μm. Obtained. The obtained film was subjected to a heat treatment for 24 hours in a hot-air oven controlled at 50 ° C. in a roll form.

Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film. As shown in Table 3, the film had running durability, storage stability, track deviation,
Excellent in maximum dimensional change width, workability, and electromagnetic conversion characteristics.

Comparative Example 2 The stretching conditions were changed as shown in Table 1 and fine stretching in the width direction (TD) was performed.
Except not performing stretching 1-2, 1-3), it carried out similarly to Example 2. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Example 3 Polyethylene terephthalate was converted to polyethylene-2,6-
A laminated unstretched film was obtained in the same manner as in Example 1 except that naphthalenedicarboxylate (PEN) was changed. The unstretched film was stretched, heat-set, and relaxed in the same manner as in Example 1 except that the conditions shown in Table 1 were changed to obtain a polyester film having a thickness of 4.5 μm.

Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film. As shown in Table 3, the film had running durability, storage stability, track deviation,
Excellent in maximum dimensional change width, workability, and electromagnetic conversion characteristics.

Comparative Example 3 The same procedure as in Example 3 was carried out except that the stretching conditions were changed as shown in Table 1 and the second-stage fine stretching (TD stretching 1-3) in the width direction was not performed. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Example 4 A laminated unstretched film was obtained in the same manner as in Example 3. The unstretched film was stretched, heat-set, and relaxed in the same manner as in Example 3 except that the conditions shown in Table 1 were changed to obtain a 4.2 μm-thick polyester film. The obtained film was subjected to a heat treatment for 72 hours in a hot-air oven adjusted to 90 ° C. in a roll form.

Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film. As shown in Table 3, the film had running durability, storage stability, track deviation,
Excellent in maximum dimensional change width, workability, and electromagnetic conversion characteristics.

Comparative Example 4 The procedure of Example 4 was repeated, except that the stretching conditions were changed as shown in Table 1 and the two-stage fine stretching (TD stretching 1-2, 1-3) in the width direction was not performed. went. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Example 5 PET (intrinsic viscosity: 0.85) pellets (50% by weight) and polyetherimide (PEI) pellets ("Ultem" 1010 (General)
Electric (registered trademark)) (50% by weight)
The mixture was fed to a vented twin-screw kneading extruder heated to 80 ° C., and was melt-extruded at a shear rate of 100 sec ⁻¹ and a residence time of 1 minute to obtain a pellet (I) containing 50% by weight of PEI. Using two extruders A and B, the obtained PEI-containing pellets (I) and PE
Pellets (II) of T (containing 0.4% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm) dry-blended at a weight ratio of 10:90 (PET)
/ PEI-III) was supplied after being vacuum-dried at 180 ° C. for 3 hours, and extruder B also heated to 280 ° C.
A pellet (IV) of ET (containing 0.7% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm and 0.1% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm) was mixed at 180 ° C. Supplied after vacuum drying for 3 hours.
These are merged in a T-die, adhered tightly to a cast drum having a surface temperature of 25 ° C. by an electrostatic application method, and cooled and solidified, and the laminate thickness ratio is (PET / PEI-III) / PET.
A PEI-containing laminated unstretched film having -IV = 18/1 was obtained. Under the conditions shown in Table 1, the obtained film was stretched, heat-set, and relaxed in the same manner as in Example 1, and was gradually cooled to room temperature and wound up. The film thickness was adjusted to 5.1 μm by adjusting the extrusion amount.

The physical properties of the obtained biaxially oriented polyester film are shown in Tables 2 and 3. As shown in Table 3, the film had running durability, storage stability, track deviation,
Excellent in maximum dimensional change width, workability, and electromagnetic conversion characteristics.

Example 6 A laminated unstretched film was obtained in the same manner as in Example 1. This unstretched film was stretched under the conditions shown in Table 1. First, both ends of the film are gripped with clips, guided to a simultaneous biaxial stretching tenter, and subjected to simultaneous biaxial stretching (MD stretching 1 × TD stretching 1-1) in the longitudinal direction and width direction, and then only in the width direction. Fine stretching (TD stretching 1-2, 1-3) was performed in two stages. Further, re-simultaneous biaxial stretching (MD stretching 2 × TD stretching 2) is performed in the longitudinal direction and the width direction, and heat setting is performed at a temperature of 215 ° C., and then 2.1% in the width direction in a cooling zone of 120 ° C. 0.6% in the width direction in the 102 ° C zone
The film was slowly cooled to room temperature and wound up. The film thickness was adjusted to 5.2 μm by adjusting the extrusion amount.

The physical properties of the obtained biaxially oriented polyester film are shown in Tables 2 and 3. As shown in Table 3, the film had running durability, storage stability, track deviation,
Excellent in maximum dimensional change width, workability, and electromagnetic conversion characteristics.

[0083]

The biaxially oriented film of the present invention has a small Poisson's ratio when a load of 50 MPa is applied in the longitudinal direction,
By making the creep compliance and the residual strain in the longitudinal direction of the film at 50 ° C. within the range of the present invention, the film becomes particularly suitable for a base film of a high-density magnetic recording medium, has good dimensional stability at the time of film processing, and has good magnetic properties. When a tape is used, recording track misalignment is unlikely to occur, and the film has excellent running durability, storage stability, and electromagnetic conversion characteristics, and its industrial value is extremely high.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F071 AA43 AA46 AF13Y AF20Y AF53Y AF61Y AH14 BB08 BC01 BC10 BC12 BC16 BC17 4F210 AA24 AG01 AH38 QA02 QA03 QC06 QG01 5D006 CB01 CB07

Claims (5)

[Claims] 1. The film has a Poisson's ratio in the range of 0.10 to 0.35 when a load of 50 MPa is applied in the longitudinal direction, and has a creep compliance of 0 in the longitudinal direction of the film after 30 minutes at a temperature of 50 ° C. and a load of 28 MPa. .1 to 0.3 GP
a- ¹ and a residual strain after a lapse of 30 minutes from the load removal is in a range of -0.05 to 0.1%. 2. The biaxially oriented polyester film according to claim 1, wherein the heat shrinkage in the width direction at 100 ° C. for 30 minutes is in the range of −0.2 to 0.5%. 3. The biaxially oriented polyester film according to claim 1, wherein the elastic modulus in the longitudinal direction is in the range of 6 to 15 GPa. 4. The surface roughness R of one film surface (A surface)
a _A is in the range of 3 to 10 nm, the biaxial according to claim 1, the surface roughness Ra _B of the opposite side of the film surface of the A-side (B side) is in a range of 5~17nm Oriented polyester film. 5. The method according to claim 1, wherein the thickness is in the range of 3 to 7 μm.
4. A high-density magnetic recording medium using the biaxially oriented polyester film according to any one of 4 as a base film.