JP2001246713A - Laminated polyester film and magnetic recording material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film excellent in heat resistance and dimentional stability at a high temperature. SOLUTION: In the laminated polyester film wherein heat-resistant resin layers are provided on both surfaces of a biaxially oriented polyester film, curl quantity at the time of heat treatment at 180 deg.C is set to 10 mm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated polyester film which is excellent in heat resistance and does not deteriorate in flatness even when subjected to heat treatment in a processing step, and a magnetic recording medium which can exhibit high characteristics.

[0002]

2. Description of the Related Art Polyester films are used for capacitors and packaging by utilizing their excellent mechanical properties, thermal properties, electrical properties, surface properties, optical properties, heat resistance and chemical resistance. Are widely used for various purposes such as magnetic recording media.

[0003] Above all, the form of the magnetic recording medium includes a tape form, a card form, and a disc form. In any of these forms, studies for increasing the recording density are rapidly progressing. There is great expectation for higher density magnetic recording media.

[0004] Typical examples of the magnetic disk include a hard disk having a magnetic layer formed on a glass substrate or an aluminum substrate, and a floppy disk having a magnetic layer formed on an organic polymer such as a polyester film. Of these, inexpensive,
From the viewpoint of portability and convenience, demand for floppy disks is particularly expected to increase significantly.

[0005] However, in order to expand the floppy disk widely, it is necessary to increase the recording density to increase the capacity. Therefore, many attempts have been made to improve the recording density. One direction is to provide a magnetic layer composed of a thin film magnetic layer containing a ferromagnetic powder or a hexagonal ferrite and a functional non-magnetic layer. For example, JP-A-10-334457, JP-A-10-320744, JP-A-10-3
02243, JP-A-10-334664,
JP-A-10-320754 and the like. In the other direction, a metal thin film type magnetic layer is provided by a method such as sputtering, vapor deposition, or ion plating.
Japanese Patent Application Laid-Open Nos. 0-269947, 10-198944, 10-143854, and 10-1989.
No. 40542, and the like.

Conventionally, a film made of polyester typified by polyethylene terephthalate or polyethylene naphthalate has been used as a support for a floppy disk. However, it cannot be said that the film is necessarily sufficient for the above-mentioned high recording density. ing. Further, when a metal thin film type magnetic layer is provided to improve the recording density, the temperature applied to the support is high, and the heat resistance of the polyester film may be insufficient. When a magnetic layer consisting of a thin-film magnetic layer containing ferromagnetic powder or hexagonal ferrite and a functional non-magnetic layer is provided by coating, the drying step is often performed at high speed and high temperature to improve productivity. May be insufficient.

Therefore, studies have been made on the use of an aromatic polyamide or polyimide having excellent heat resistance as a support for a disk (for example, Japanese Patent Application Laid-Open No. H11-25445,
JP-A-10-21529). However, since aromatic polyamides and polyimides are expensive in raw materials, it has been difficult to use them frequently for floppy disks having a large thickness.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and to provide a laminated polyester film which is excellent in heat resistance and has a small form change when exposed to heat.

[0009]

The laminated polyester film of the present invention which achieves the above object has a heat-resistant resin layer provided on both sides of a biaxially oriented polyester film.
A laminated polyester film having a curl amount of 10 mm or less during heat treatment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the polyester in the laminated polyester film of the present invention include polyethylene terephthalate, polyethylene naphthalate, polypropylene terephthalate, polybutylene terephthalate, and polypropylene naphthalate. In particular, polyethylene terephthalate is preferable for the availability of raw materials and for reducing coarse projections on the surface, but is not particularly limited. Further, a mixture of two or more of these may be used. Further, those obtained by copolymerizing these and other dicarboxylic acid components or diol components may be used. Further, a composite film having two or more layers of an inner layer and a surface layer may be used. For example, a composite film having substantially no particles in the inner layer portion and having a layer containing the particles in the surface layer portion, a laminate film having coarse particles in the inner layer portion and containing fine particles in the surface layer portion And the like. In the composite film, the inner layer portion and the surface layer portion may be of different polymers or of the same type. When the above-mentioned polyester is used, its intrinsic viscosity (measured in o-chlorophenol at 25 ° C.) is preferably 0.4 to 1.2 dl / g.
More preferably, it is 5 to 0.8 dl / g.

[0011] The polyester film of the present invention comprises:
It is biaxially oriented. Biaxially oriented refers to unstretched, that is, a polyester film before completion of crystal orientation, which is stretched about 2.5 to 5 times in the longitudinal direction and width direction, respectively, and then crystal orientation is completed by heat treatment. And those showing biaxial orientation patterns in wide angle X-ray diffraction. When the polyester film is not biaxially oriented, the heat resistance, dimensional stability, and mechanical strength of the laminated polyester film become insufficient, and a laminated film suitable for the present invention cannot be obtained. The polyester film of the present invention may contain various additives, a resin composition, a cross-linking agent, and the like as long as the effects of the present invention are not impaired. For example, antioxidants, heat stabilizers, ultraviolet absorbers, organic and inorganic particles, pigments, dyes, antistatic agents, nucleating agents, flame retardants, acrylic resins, polyester resins, urethane resins, polyolefin resins, polycarbonate resins, alkyd resins , Epoxy resin, urea resin, phenolic resin, silicone resin, rubber resin, wax composition, melamine crosslinker, oxazoline crosslinker, methylolated, alkylolated urea crosslinker, acrylamide, polyamide, epoxy resin , Isocyanate compounds, aziridine compounds, various silane coupling agents, various titanate coupling agents, and the like.

The laminated film of the present invention is obtained by laminating a heat-resistant resin layer on both sides of a biaxially oriented polyester film. In the case of a film having only one side laminated, not only the amount of curl when heat-treated is increased, but also the flatness is deteriorated when used under high humidity.

The heat-resistant resin to be laminated has a glass transition point of 170 ° C. or higher due to its heat resistance.
Those having no melting point or decomposition point at 0 ° C. or lower are preferred.
The heat-resistant resin selected from the above requirements is not particularly limited as long as the resin satisfies the requirements, but examples thereof include aromatic polyamide resins, aromatic polyimide resins and precursors thereof, and polyamideimide resins. , Polyethersulfone-based resins, polyetherimide-based resins, polybenzimidazoles and their precursors, polybenzoxazoles and their precursors, polybenzthiazoles and their precursors, and polysulfone-based resins. Among these, those which can be dissolved in a dipolar aprotic solvent are particularly preferred, and aromatic polyamide resins are particularly preferred. Examples of the dipolar aprotic solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide and the like. In the present invention, dissolving the heat-resistant resin in these dipolar aprotic solvents has a very important meaning in the adhesion between the polyester film and the heat-resistant resin layer. Is difficult. That is, a solvent that dissolves the heat-resistant resin and whitens or swells the polyester film before the completion of the crystal orientation is particularly preferable, and among the above, N-methyl-2-pyrrolidone is particularly preferable. The aromatic polyamide suitable in the present invention refers to a repeating unit represented by the following general formula (1) and / or general formula (2) alone or in a copolymerized form in an amount of 50 mol% or more, preferably 7 mol% or more.
It is desirable that the content be 0 mol% or more.

Embedded image

Embedded image Here, as Ar ₁ , Ar ₂ and Ar ₃ , for example, those shown in (a) to (e) of the general formula (3) are used.
_{Is, -O -, - CH 2 -} , - CO -, - SO 2 -, - S
—, —C (CH ₃ ) ₂ — or the like, but is not limited thereto. Furthermore, some of the hydrogen atoms on these aromatic rings are halogen groups such as chlorine, fluorine and bromine (especially chlorine), and alkyl groups such as nitro, methyl, ethyl and propyl (especially methyl groups). ), Methoxy group, ethoxy group, those substituted with a substituent such as an alkoxy group such as a propoxy group,
Also included are those in which the hydrogen in the amide bond constituting the polymer is replaced by another substituent.

Embedded image In particular, the polymer in which the aromatic ring of the above general formula (2) is bonded at the para position accounts for 50 mol% or more, more preferably 70 mol% or more of the whole aromatic ring, in terms of reducing the curl amount during heat treatment. preferable. Some of the hydrogen atoms on the aromatic ring are chlorine,
Halogen groups such as fluorine and bromine (especially chlorine), alkyl groups such as nitro group, methyl group, ethyl group and propyl group (preferably methyl group), and alkoxy groups such as methoxy group, ethoxy group and propoxy group. 30% by mole or more of the aromatic ring substituted with the substituent of
Preferably, the content is 50 mol% or more, because it becomes easier to obtain a laminated film having a small curl amount at the time of heat treatment. In the present invention, it is desirable that the repeating unit represented by the general formula (1) and / or the general formula (2) is at least 50 mol%, preferably at least 70 mol%, and copolymerization of other compounds with less than this amount. And other polymers may be mixed.

The heat-resistant resin layer may contain various additives, a resin composition, a cross-linking agent and the like as long as the effects of the present invention are not impaired. For example, antioxidants, heat stabilizers, ultraviolet absorbers, organic, inorganic particles such as spherical silica, pigments,
Dyes, antistatic agents, nucleating agents, acrylic resins, polyester resins, urethane resins, polyolefin resins, polycarbonate resins, alkyd resins, epoxy resins, urea resins, phenol resins, silicone resins, rubber resins, wax compositions, melamine crosslinks Agents, oxazoline-based crosslinking agents, methylolated, alkylolated urea-based crosslinking agents, acrylamide, polyamide, epoxy resins, isocyanate compounds, aziridine compounds, various silane coupling agents, various titanate coupling agents, and the like. it can.

The heat-resistant resin layer is preferably made of the same resin on both sides in terms of flatness, but is not particularly limited, and may be different resins. The ratio of the thickness of both surfaces is not particularly limited, but is 1: 2 to
A ratio of 2: 1 is preferable in terms of flatness.

The method of laminating the heat-resistant resin layer on the polyester film is not particularly limited, and any method such as a method of bonding a film made of the heat-resistant resin via an adhesive layer, a method of applying and drying the heat-resistant resin, and the like can be used. However, a method in which a heat-resistant resin layer is provided by coating and drying is preferable because a surface form suitable for use as a magnetic recording medium can be easily obtained. In order to more effectively exhibit the effects of the present invention, it is preferable that the heat-resistant resin layer is laminated on both surfaces of the biaxially oriented polyester film without substantially interposing an adhesive layer. Here, "substantially not through the adhesive layer" means that a layer made of a substance other than the base material and the laminated film forming substance is substantially formed at the interface between the base material and the laminated film in a state where the heat resistant resin layer is laminated on the polyester film. That is, even if there is a layer mainly composed of a substance other than the base material and the laminated film, the thickness thereof is 10 n
When it is not more than m, it can be considered that no adhesive layer is interposed. However, it is particularly preferable that a mixed layer of a base material and a heat-resistant resin layer is formed at the interface because the adhesiveness is further improved, and the layer is out of the definition of the adhesive layer.

The laminated polyester film of the present invention comprises:
The curl amount at the time of heat treatment at 80 ° C. needs to be 10 mm or less, preferably 5 mm or less. If the curl amount at the time of heat treatment at 180 ° C. is greater than 10 mm, a step of providing a magnetic layer by a method such as evaporation or sputtering when subjected to a heat treatment in a film processing step, particularly when used as a high-density magnetic recording medium, After coating the thin film magnetic layer containing powder or hexagonal ferrite, there is a problem that the flatness is deteriorated in the step of heating and drying.

The laminated film of the present invention has a humidity of 80% RH.
Is preferably 15 mm or less, and more preferably 10 mm or less. If the curl amount at a relative humidity of 80% RH is larger than 15 mm, not only the flatness tends to deteriorate when stored and used at high humidity, but also when the film is subjected to a heat treatment in a film processing step, it is heated during dehumidification. Deterioration of flatness is likely to occur due to the difference in moisture absorption between the front and back before and after the treatment.

The heat shrinkage of the laminated film of the present invention at 150 ° C. in the longitudinal and width directions of the film is preferably 2% or less, more preferably 1.5% or less. If the heat shrinkage at 150 ° C. in the longitudinal direction or width direction of the film is more than 2%, the flatness and the reliability of recording when heat treatment is performed in the film processing step are likely to occur, which is not preferable.

In the laminated film of the present invention, the ratio of the thickness of the heat-resistant resin layer to the total thickness of the film (TL)
Is 0.4% or more and 10% or less, preferably 1% or more and 5% or less. If the thickness of the heat-resistant resin layer is less than 0.4% of the total thickness of the film, heat resistance and flatness are likely to deteriorate, which is not preferable. On the other hand, if the thickness of the heat-resistant resin layer is set to be larger than 10% of the total thickness of the film, undulations and coarse protrusions are likely to be generated on the film surface, which is not preferable particularly when used as a magnetic recording medium.

In the laminated film of the present invention,
Roughness of at least one surface of the
The number of large projections (H1) is 0 / 100cm^TwoMore than 100
Pieces / 100cm^TwoHereinafter, more preferably 0/100
cm^TwoMore than 50 pieces / 100cm ^TwoLess than magnetic
Error caused by missing recording when used as a recording medium
This is preferable because it makes it easy to obtain a magnetic recording medium with a small amount. Coarse
The number of large projections is 100 / 100cm^TwoBigger and bigger
-It became difficult to obtain a magnetic recording medium with less occurrence
Not preferred.

The method for producing the laminated film of the present invention is described below, but is not limited thereto.

A sufficiently dried polyester chip is supplied to an extruder, melt-extruded at 280 to 300 ° C., and formed into a sheet on a mirror cooling drum at 20 to 70 ° C. The sheet is stretched in the longitudinal direction at a temperature of 80 to 120 ° C. for 2.5 to
Stretch 4.5 times. Apply a heat-resistant resin dissolved in a solvent to be laminated on both sides of the uniaxially oriented polyester film,
Then, hold both ends of the film with clips and
1. After a preheating step of 20 ° C, at 80 to 120 ° C in the width direction.
Stretch 5 to 4.5 times. 180 to 25 more continuously
Heat treatment is performed at 0 ° C. to complete the crystal orientation of the base polyester film. Here, in the case of stretching in the width direction, it is preferable that the solvent is stretched together with the substrate before being completely dried, and thereafter the solvent is evaporated to complete the crystal orientation of the substrate,
It is preferable from the viewpoint of adhesion to the substrate that most of the solvent to be used is left in the preheating step and the stretching step after the coating and before the stretching and evaporates in the heat treatment step after the stretching.

When the laminated film of the present invention is used as a magnetic recording medium, the method for forming the magnetic layer is as follows.
A coating method of kneading and drying with a binder such as thermoplastic or radiation-curable, or a dry method of forming a magnetic metal thin film layer directly on a substrate film by vapor deposition of metal or alloy, sputtering, ion plating, etc. Any of the above methods can be adopted, but a dry method requiring heat resistance at a higher temperature is preferable.

The ferromagnetic metal thin film serving as a magnetic film in the magnetic recording medium of the present invention can be formed by a conventionally known vacuum evaporation method, ion plating method, or sputtering method.

When the magnetic film is formed by the sputtering method, the composition may be a conventionally known metal or alloy mainly composed of cobalt, and specifically, Co-Cr, Co-Ni
-Cr, Co-Cr-Ta, Co-Cr-Pt, Co-
Cr-Ta-Pt, Co-Cr-Pt-Si, Co-C
r-Pt-B or the like can be used. Particularly, Co-Cr-Ta and Co-Cr-Pt are preferable for improving the electromagnetic conversion characteristics. The thickness of the magnetic layer is desirably 10 to 300 nm. In this case, it is preferable to provide a base film for improving the magnetostatic characteristics of the magnetic film. Examples of the composition of the base film include a conventionally known metal or alloy, and specifically, Cr, V, Ti, Ta, W, Si and the like or alloys thereof can be used. Among them, Cr, Cr-Ti,
Cr-Si is particularly preferred. The thickness of the base film is 5 to 500 nm, preferably 10 to 200 nm. When a magnetic film is formed by a sputtering method, it is preferable to form the film while the support is heated. The temperature at that time is usually 200 ° C. or lower, but a temperature of about 250 ° C. is suitable for forming a dense magnetic film. Since the film of the present invention is excellent in heat resistance and rigidity and does not lose heat even at such a high temperature, it can be used very preferably.

Further, the ferromagnetic metal thin film may have a multilayer structure for improving the electromagnetic conversion characteristics, or may have a nonmagnetic underlayer or an intermediate layer.

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. As the protective film, silica, alumina, titania,
Oxide protective films such as zirconia, cobalt oxide, and nickel oxide; nitride protective films such as titanium nitride, silicon nitride, and boron nitride; carbide protective films such as silicon carbide, chromium carbide, and boron carbide; graphite, amorphous carbon, and the like. And a carbon protective film made of carbon.

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

In the magnetic recording medium of the present invention, in order to improve running durability and corrosion resistance, it is preferable to add a lubricant or a rust inhibitor to the magnetic film or the protective film. As the lubricant, known hydrocarbon-based lubricants, fluorine-based lubricants, extreme pressure additives and the like can be used.

Examples of the rust preventive usable in the present invention include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, derivatives having an alkyl side chain or the like introduced into their mother nucleus, benzothiazole, 2-benzothiazole, Nitrogen- and sulfur-containing heterocycles such as mercapton benzothiazole, tetrazaindene ring compounds and thiouracil compounds, and derivatives thereof.

Although the laminated polyester film of the present invention is suitable for a high-density magnetic recording medium, it is subjected to a heat treatment at a high temperature when the film is processed or used as a processed product, for example, a thermal transfer type printer ribbon or a vapor deposition process. And FPC applications.

[0033]

[Method for measuring characteristics and method for evaluating effects] The method for measuring characteristics and the method for evaluating effects in the present invention are as follows.

(1) Curling amount at the time of heat treatment at 180 ° C. The film is cut into a width of 10 mm and a length of 120 mm. The cut sample is clipped at a position of 20 mm from the end, and the clip is suspended from the support and supported vertically. The sample is placed in a 180 ° C. oven with a support and heat treated for 30 minutes.

The support table taken out after the heat treatment was cooled to 25 ° C.
The temperature is adjusted for 6 hours in an atmosphere at a temperature of 65 ° C and a humidity of 65% RH. With respect to the position of the lower end of the film after the adjustment, the amount of lifting from a line vertically lowered from the film supporting portion was measured, and the amount of curling was determined. The measurement was performed on five samples in each of the longitudinal direction and the width direction of the film, and the average value of ten points was defined as the curl amount.

(2) Curling amount at a humidity of 80% RH The film is cut into a width of 10 mm and a length of 120 mm. The cut sample is clipped at a position of 20 mm from the end, and the clip is suspended from the support and supported vertically. Sample with support at temperature 40 ℃, humidity 80%
Place in a constant temperature and humidity chamber of RH and treat for 30 minutes. The support taken out after the treatment is adjusted for 6 hours in an atmosphere of a temperature of 25 ° C. and a humidity of 65% RH. With respect to the position of the lower end of the film after the adjustment, the amount of lifting from a line vertically lowered from the film supporting portion was measured, and the amount of curling was determined. The measurement was performed on five samples in each of the longitudinal direction and the width direction of the film, and the average value of ten points was defined as the curl amount.

(3) Heat resistance The film is cut into a square of 10 cm on each side, and 10 films are stacked. The top and bottom of the stacked film is 1mm thick, 15cm on each side
And a heating and pressing treatment is performed at a temperature of 250 ° C. under a load of 100 kg for 1 minute using a heating and pressing press. After the heat treatment, remove the sample at a temperature of 2
After adjusting for 6 hours in an atmosphere of 5 ° C. and a humidity of 65% RH, observation was made and judgment was made. When all the films are heat-sealed to each other: Poor When each of the five films is easily peeled off: Good.

(4) Change in flatness under high temperature The film is cut into a square having a side of 15 cm, and is left on a heat-resistant glass plate having a smooth thickness of 5 mm. The film and the glass plate are placed in an oven at 180 ° C. and heat-treated for 1 hour. The film and the glass plate taken out after the heat treatment are adjusted for 6 hours in an atmosphere at a temperature of 25 ° C. and a humidity of 65% RH. The film was observed from right beside, and the height of the portion (the distance from the upper surface of the glass to the lower surface of the film) of the portion most protruding from the glass plate due to undulation was measured to make a judgment. Height less than 3 mm: excellent 3 mm or more and less than 5 mm: good 5 mm or more and less than 7 mm: acceptable 7 mm or more: bad.

(5) Heat Shrinkage The heat shrinkage in the longitudinal direction of the film was measured according to the method specified in JIS C-2318. However, the oven temperature and the holding time were set to 150 ° C. and 30 minutes, and the average of the results of 20 measurements was used while changing the samples.

(6) Ratio of thickness of heat-resistant resin layer to total thickness of film (TL) A cross section is cut out from the laminated polyester film, and the cross section is observed with a transmission electron microscope. Was measured for the thickness (t2) of the heat-resistant resin layer and the thickness (t3) of the entire film. When there is a mixed phase, the thickness including the mixed phase was defined as the thickness of the heat-resistant resin layer. TL (%) = 100 × (t1 + t2) / t3.

(7) Number of coarse protrusions having a height of 0.27 μm or more (H1) Foreign matter is observed and marked under polarized light on a film surface of 10 cm ² or more by a stereoscopic microscope. The height of the marked foreign matter is observed at a wavelength of 546 nm using a multiple interferometer, and the number of interference fringes having a single ring or more is converted into the number per 100 cm ² .

(8) Error Rate A signal was recorded on the obtained magnetic disk by the (2, 7) RLL modulation method, and each surface was measured. The signal to be recorded has a linear recording density of 200 kbpi and a track density of 7500 tpi.
And

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

Example 1 N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), which had been passed through a sintered metal filter having a filtration accuracy of 1.2 μm and a polypropylene filter having a filtration accuracy of 0.6 μm in advance, had an aromatic diamine content of 90%. 2 mol% of 2-chloroparaphenylenediamine and 10 mol% of 4,4′-diaminodiphenyl ether are dissolved,
To this, 2-chloroterephthalic acid chloride corresponding to 100 mol% was added, and the mixture was stirred for 2 hours to complete the polymerization, thereby obtaining an aromatic polyamide solution having a polymer concentration of 10% by weight. Since hydrochloric acid was contained in this polyamide solution, this solution was reprecipitated with a large amount of water to isolate the polymer, and further washed with running water at 40 ° C. for 60 minutes to remove hydrochloric acid. After drying the obtained polymer at 150 ° C., NM
P was gradually dissolved at 50 ° C. to obtain an aromatic polyamide solution (hereinafter referred to as solution A) having a polymer concentration of 10% by weight.

A polyethylene terephthalate (intrinsic viscosity: 0.60 dl / g) chip containing 0.005% by weight of colloidal silica having an average particle diameter of 0.05 μm was sufficiently vacuum-dried at 180 ° C., and then supplied to an extruder. After melting at 0 ° C., the mixture was passed through a sintered metal filter having a filtration accuracy of 2 μm, extruded into a sheet shape from a T-shaped die, wound around a mirror surface cast drum having a surface temperature of 20 ° C. using an electrostatic application casting method, and cooled and solidified. . The unstretched sheet was stretched 3.5 times in the longitudinal direction with a group of rolls heated to 95 ° C. to obtain a uniaxially stretched film. After passing the solution A through a sintered metal filter having a filtration accuracy of 5 μm and 0.9 μm on both sides of the film, the final lamination thickness per side is 0.1 mm by a die coating method.
It was applied so as to have a thickness of 5 μm. The coated film was guided to a preheating zone at 100 ° C. while holding both ends with clips, and subsequently stretched 3.5 times in the width direction in a heating zone at 110 ° C. Further, a heat treatment was continuously performed with a heat treatment soak at 230 ° C. for 5 seconds to completely dry the NMP. This laminated film has a thickness of 50 μm and a laminated thickness of 0.5
μm.

Comparative Example 1 0.005 of colloidal silica having an average particle size of 0.05 μm
A polyethylene naphthalate (intrinsic viscosity: 0.60 dl / g) chip containing 1.0% by weight is sufficiently vacuum-dried at 180 ° C., fed to an extruder, melted at 285 ° C., and passed through a sintered metal filter having a filtration accuracy of 2 μm. After that, the resultant was extruded into a sheet shape from a T-shaped die, wound around a mirror-surface cast drum having a surface temperature of 20 ° C. by an electrostatic application casting method, and cooled and solidified. The unstretched sheet is stretched 3.5 times in the longitudinal direction with a group of rolls heated to 140 ° C., guided to a preheating zone of 100 ° C. while holding both ends of the film with clips, and then in a width direction in a heating zone of 140 ° C. The film was stretched 3.5 times. Further, a heat treatment was continuously performed for 5 seconds using a 230 ° C. heat treatment sone. This polyester film has a thickness of 50
μm.

Example 2 A laminated polyester film having a thickness of 50 μm was obtained in exactly the same manner as in Example 1 except that the thickness of the heat-resistant resin on the upper surface of the film was 0.20 μm and the thickness of the heat-resistant resin layer on the lower surface was 0.25 μm. .

Example 3 A laminated polyester film having a thickness of 50 μm was obtained in exactly the same manner as in Example 1, except that the thickness of the heat-resistant resin on the upper surface of the film was 2.0 μm and the thickness of the heat-resistant resin layer on the lower surface was 2.5 μm. .

Comparative Example 2 A laminated polyester film having a thickness of 50 μm was obtained in exactly the same manner as in Example 1, except that the thickness of the heat-resistant resin on the upper surface of the film was 0.10 μm and the thickness of the heat-resistant resin layer on the lower surface was 0.05 μm. .

Comparative Example 3 A laminated polyester film having a thickness of 50 μm was obtained in exactly the same manner as in Example 1 except that the thickness of the heat-resistant resin on the upper surface of the film was 5.0 μm and the thickness of the heat-resistant resin layer on the lower surface was 2.5 μm. .

Comparative Example 4 A laminated polyester film having a thickness of 50 μm was obtained in exactly the same manner as in Example 1, except that the heat-resistant resin thickness on the upper surface of the film was 1.0 μm and the heat-resistant resin layer was not provided on the lower surface.

Table 1 shows the properties of the laminated films of Examples 1 to 3 and Comparative Examples 1 to 4. Examples 1 to 3 were within the scope of the present invention and were excellent in change in flatness under high temperature and heat resistance, while Comparative Examples 1 to 4 were inferior in change in flatness under high temperature and heat resistance. Met.

Example 4 Using the film of Example 1, a metal thin-film magnetic disk was manufactured.

After performing a degassing treatment of heating the film to a temperature of 170 ° C. in the air, the film is set in a sputtering apparatus, and a Cr—Ti base film is formed to a thickness of 60 nm by a DC magnetron sputtering method while the substrate temperature is heated to 180 ° C. Then, a Co-Cr-Pt magnetic film was formed to a thickness of 30 nm, and a hard carbon protective film was formed thereon to a thickness of 20 nm by a plasma CVD method using methane as a raw material. Next, a perfluoropolyether-based lubricant (Audimont FO)
A solution in which MBLIN Z-DOL was dissolved in a fluorinated solvent (FC-77 manufactured by Sumitomo 3M) was applied by a dip coating method to form a lubricating film having a thickness of 1 nm. The magnetic film, protective film and lubricating film were provided on both sides of the film. Next, the disk was punched out to a disk outer diameter of 94 mm to obtain a magnetic disk.

This disk has an error rate of 2.0 × 1.
It was excellent at 0 ^-6 .

Comparative Example 5 Using the film of Comparative Example 1, a metal thin-film magnetic disk was manufactured in the same manner as in Example 4.

This disk has an error rate of 125 × 1.
Were those inferior 0 ^-6.

Comparative Example 6 Using the film of Comparative Example 2, a metal thin-film magnetic disk was manufactured in the same manner as in Example 4.

This disk has an error rate of 72 × 10
^-6 was inferior.

[Table 1]

The laminated polyester film of the present invention has
Excellent heat resistance and morphological stability at high temperatures. Thereby, the film of the present invention can be suitably used for any applications such as a magnetic recording medium field, an electric / electronic field, a packaging field, etc., particularly, a magnetic recording medium, and particularly preferably a magnetic disk field. .

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AK01B AK41A AK42A AK47B AK49B AR00C BA02 BA03 BA07 BA10A BA10B BA10C BA13 EJ38A GB90 JA03 JA20B JG06C JJ03B JK14 JL04 YY00 YY00B 5D006 CB01 CB02 CB01 CB02

Claims (8)

[Claims] 1. A heat-resistant resin layer is provided on both sides of a biaxially oriented polyester film, and the curl amount during heat treatment at 180.degree.
A laminated polyester film having a thickness of 0 mm or less. 2. The laminated polyester film according to claim 1, wherein the curl amount at a humidity of 80% RH is 15 mm or less. 3. 150 ° C. in the longitudinal and width directions of the film
3. The laminated polyester film according to claim 1, wherein the heat shrinkage ratio is 2% or less. 4. The laminated polyester film according to claim 1, wherein the ratio (TL) of the thickness of the heat-resistant resin layer to the total thickness of the film is from 0.4% to 10%. 5. The number of coarse projections (H1) having a height of at least 0.27 μm on at least one surface of the film is 0/1.
Laminated polyester film according to any one of claims 1~4 00cm ² or more and 100 pieces / 100 cm ² or less. 6. The laminated polyester film according to claim 1, wherein the heat-resistant resin layer contains an aromatic polyamide or polyimide as a main component. 7. A magnetic recording medium comprising the laminated polyester film according to claim 1 and a magnetic layer provided on at least one surface. 8. The magnetic recording medium according to claim 7, wherein the magnetic layer is a ferromagnetic metal thin film.