JP2002050033A - Method for producing polyester film for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a polyester film for a magnetic recording medium suitable for use in the production of a tape for mass data storage having a low error rate. SOLUTION: An aqueous solution containing a water-soluble polymer and fine particles having 5-50 nm average particle diameter as essential components is applied to the surface A of a polyester film melt-extruded, cooled and drawn in one direction at 3-1,000 mg/m2 solid concentration. The polyester film is drawn in a direction perpendicular to the above drawing direction after or while drying the aqueous solution and then the film is heat-treated to produce the objective polyester film for a magnetic recording medium with the surface A side as a ferromagnetic metallic thin film forming face. When the average particle diameter of the fine particles is represented by d (nm), the thickness of a solid material formed by applying the aqueous solution by t (mn) and the draw ratio in the perpendicular direction by s (times), the relation of d/2<=2t/s<d is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for producing a high quality ferromagnetic metal thin film type magnetic recording medium for recording a large amount of digital data, such as a polyester film for a magnetic recording medium, especially for a data storage tape. The present invention relates to a method for producing a polyester film for a magnetic recording medium.

[0002]

2. Description of the Related Art Consumer digital video tapes put into practical use in 1995 are provided by depositing a metal magnetic thin film of Co on a base film having a thickness of 6 to 7 .mu.m by vacuum evaporation and coating the surface with a diamond-like carbon film. In the case of a camera-integrated video using a digital video mini-cassette, the basic specification (SD specification) has a recording time of one hour.

[0003] This digital video cassette (DVC)
Is the world's first digital video cassette for home use, and a. Despite its small body, it can record a huge amount of information,
b. Since the signal does not deteriorate, the image quality and sound quality do not deteriorate even after many years, c. Enjoys high image quality and high sound quality because it is not disturbed by noise. D. It has such advantages that the image does not deteriorate even after repeated dubbing, and is highly evaluated in the market.

[0004] As a method of manufacturing the base film,
As shown in Japanese Patent Publication No. 3-80410, an aqueous solution mainly composed of a water-soluble polymer and fine particles having an average diameter of 5 nm or more is applied to a surface of a polyester film stretched in one direction on which a metal magnetic thin film is to be formed. After drying, the film is stretched in a direction perpendicular to the stretching direction, heat-treated, and a film is formed.

[0005] In addition, a vapor deposition type digital video tape, a DV
The use of C for computer data backup began in 1996, and 8mm tape width 8mm data (Exabyte Mammoth, Sony AIT system) computer data backup devices were put into practical use. It is quickly popular.

Recently, the use of these magnetic recording media for data backup has been increasing. Particularly, when the data is used for compressing and backing up data, as disclosed in Japanese Patent Publication No. 3-80410. A data tape made using a base film manufactured by a conventional manufacturing method has a problem that an error rate (a ratio of data that cannot be accurately recorded) tends to increase.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to produce a polyester film for a magnetic recording medium suitable for producing a data tape having a low error rate, particularly a tape for data storage having a low error rate and a large capacity. With the goal.

[0008]

In order to achieve the above object, a method for producing a polyester film for a magnetic recording medium according to the present invention comprises the steps of melt extruding, cooling, and unidirectionally stretching the surface A of a polyester film. An aqueous solution containing a water-soluble polymer and fine particles having an average particle size of 5 to 50 nm as main components is applied at a solid concentration of 3 to 1000 mg / m ² and then dried or dried. After stretching in a direction perpendicular to the direction, a heat treatment is performed to produce a polyester film for a magnetic recording medium in which the surface A side is a surface on which a ferromagnetic metal thin film is formed, wherein the average particle diameter of the fine particles is d. (Nm), the solid content thickness by application of the aqueous solution is t (nm), and the drawing ratio in the direction perpendicular to the drawing is s (times), and the relationship of d / 2 ≦ 2t / s <d is satisfied. And wherein the door.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION
Any polyester can be used as long as it becomes a high-strength film by molecular orientation, and among them, polyethylene terephthalate or polyethylene-2,6-naphthalate is preferable.
As used herein, polyethylene terephthalate or polyethylene-2,6-naphthalate refers to the component 80
% Or more is ethylene terephthalate or ethylene naphthalate. Ethylene terephthalate,
Examples of the polyester copolymer component other than ethylene naphthalate include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, and 1,4-cyclohexanedimethanol, adipic acid,
Examples include dicarboxylic acid components such as sebacic acid, phthalic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, and p-oxyethoxybenzoic acid.

Furthermore, the above-mentioned polyester does not exceed 5% by weight of at least one of an alkali metal salt derivative of sulfonic acid which is not reactive with the polyester and a polyalkylene glycol which is substantially insoluble in the polyester. It may be mixed in the degree.

In the method of the present invention, an aqueous solution containing a water-soluble polymer and fine particles as main components is applied to a polyester film at a stage where it is melt-extruded, cooled and stretched in one direction. Is a film at the time when the polyester is melted, extruded into a sheet or cylindrical shape, cooled, and stretched in one direction,
The stretching direction is usually the longitudinal direction. The stretching ratio is preferably 2 times or more, and the upper limit is not particularly limited, but is about 6 times.

The water-soluble polymer used in the aqueous solution may be a polar polymer such as polyvinyl alcohol, tragacanth rubber, casein, gelatin, a cellulose derivative, a water-soluble polyester, polyurethane, or a blend thereof, but is not limited thereto. Not done.

The fine particles used in this aqueous solution are fine particles having an average particle size of 5 to 50 nm, more preferably 10 to 30 nm.
Inorganic compounds such as alumina, organic compounds such as polyacrylic acid spheres and polystyrene spheres, and inorganic particles such as silica, alumina and calcium carbonate as nuclei, and particles coated with an organic polymer can be used, but are not limited thereto. .

If the average particle size of the fine particles is less than 5 nm, the surface of the ferromagnetic metal thin film layer formed by vacuum deposition on the surface A of the polyester film produced by the method of the present invention becomes too smooth, It is not suitable because the ferromagnetic metal thin film layer is worn by the magnetic head during recording and reproduction in the data 8 mm backup device. If the average particle size of the fine particles exceeds 50 nm, the ferromagnetic metal thin film layer formed on the surface A is too rough, and the output characteristics of the magnetic recording tape are deteriorated.

The amount of the fine particles contained in the aqueous solution is 0.5 to 12.0% by weight based on the solid content, and 0.6 to 1% by weight.
An aqueous solution containing a water-soluble polymer and fine particles as main components is preferably 0.03% by weight.
mg / m ² . The application surface is the surface A on the side where the ferromagnetic metal film is formed, and this surface A is
It is preferable that the film is made of polyester from which the polyester film-containing particles are removed as much as possible.

If the amount of the aqueous solution applied to the surface A is less than 3 mg / m ² in terms of the solid content, the strength of the aqueous solution formed by vacuum deposition on the surface A of the polyester film produced by the method of the present invention is reduced. Magnetic metal thin film layer, data 8m
This method is not suitable because the durability of the recording / reproducing operation in the backup device becomes poor in a large number of times. When the coating amount exceeds 1000 mg / m ² in solid content, the surface A
It is not suitable because the ferromagnetic metal thin film layer formed thereon is roughened and the error rate of the magnetic recording tape is extremely increased.

After the application of the aqueous solution, the film is dried. After or while drying, the film is stretched in a direction perpendicular to the previous stretching direction. Thereafter, if necessary, the film is redrawn. The stretching in the perpendicular direction is usually a stretching in the transverse direction, preferably at 90 to 145 ° C and 3.0 to 7.0.
Done in times. Further, if necessary, the re-stretching is performed by 1
It is preferable to carry out the stretching in the longitudinal direction at 1.1 to 3.0 times at 00 to 150 ° C. Thereafter, heat treatment is performed at a temperature of 190 to 220C. Next, at a temperature of 130 to 190 ° C.
It is preferable that a relaxation treatment in the lateral direction of about 2 to 2.5% is performed to reduce the film width. If it is necessary to further increase the lateral strength, it is preferable to perform the stretching by 1.1 to 2.0 times in the lateral direction simultaneously with the heat fixing.

When the average diameter of the fine particles is d (nm), the solid content thickness of the aqueous solution coating is t (nm), and the stretching ratio in the perpendicular direction is s (times), d / 2 ≦ 2t / s <d,
More preferably, the relationship of d / 1.5 ≦ 2t / s <d must be satisfied. The value of 2 t / s is an estimated value representing the average coating film thickness after stretching in the direction at right angles,
If the value is smaller than d / 2, the fine particles are liable to be scraped by the contact of the roll in the subsequent film forming process, and the surface of the film is easily damaged. Not suitable because it becomes easier.
When 2 t / s is d or more, it is difficult to form projections due to fine particles on the surface of the film after stretching, the surface of the film becomes too smooth, and a ferromagnetic metal formed by vacuum evaporation during tape processing on surface A. The thin film is also too smooth, and is not suitable because the magnetic head wears the magnetic recording tape during recording and reproduction of the magnetic tape in the data 8 mm backup device.

In order to further increase the durability of the magnetic recording tape by the magnetic head, the average particle diameter of the polyester film layer A forming the surface A side of the polyester film is 50 to 150 nm, more preferably 55 to 100 nm. Fine particles may be contained in an amount of 0.01 to 1.0% by weight, more preferably 0.02 to 0.8% by weight.

An A / B laminated film is extruded by using a raw material for the layer A and a raw material for the layer B in which fine particles are positively contained. An aqueous solution mainly composed of a polymer may be applied. Examples of the fine particles used in the layer B include calcium carbonate, silica, alumina, and polystyrene. The fine particles preferably have an average particle diameter of 100 to 1000 n.
m, more preferably 150 to 900 nm, and the amount of addition is preferably 0.05 to 1.0% by weight, more preferably 0.08 to 0.8% by weight.

Instead of using the layer B, a coating solution containing a lubricant may be applied to the side B of the polyester film opposite to the side A to facilitate the lubrication.

The SRa value of the surface A of the polyester film for a magnetic recording medium to be manufactured is such that the ferromagnetic metal thin film layer formed on the surface A by vacuum evaporation is minimized in the abrasion of the magnetic head during recording and reproduction. And 2 to 5 nm, more preferably 2 to 4 nm, in order to maintain good output characteristics of the magnetic tape. If the SRa value is less than 2 nm, the surface of the ferromagnetic metal thin film formed by vacuum evaporation on the surface A is too smooth, and the magnetic recording tape is worn by the magnetic head during recording and reproduction in a data 8 mm backup device. It is not preferable. If the SRa value exceeds 5 nm, the ferromagnetic metal thin film layer on the surface A is too rough,
The output characteristics of the magnetic recording tape are undesirably deteriorated.

The SRa value of the surface B (the surface opposite to the surface A) of the polyester film produced by the method of the present invention is such that when the polyester film is formed and then slit to a predetermined width, After providing a ferromagnetic thin film on the surface A of the polyester film to make it easier to collect a good product, the roughness of the surface B is transferred to the surface A side by roll-up winding, and the undulation is formed on the ferromagnetic thin film layer. 8-35 nm, more preferably 10-35 nm to minimize the occurrence of
25 nm is desirable. The SRz value of the surface B is determined by forming a polyester film into a film, keeping the rolled product in a good roll after slitting, and adjusting the surface A of the polyester film.
After the ferromagnetic metal thin film layer is provided thereon, in order to minimize the occurrence of undulating deformation of the ferromagnetic metal thin film layer due to the transfer of the roughness of the surface B to the surface A side by roll-up winding. ,
100 to 700 nm, more preferably 140 to 550 n
m is desirable.

The thickness of the polyester film produced by the method of the present invention is preferably 7.0 μm or less, more preferably 3.0 to 6.8 μm. 7.
If it exceeds 0 μm, the data tape to be produced is too thick, and the recording capacity after being incorporated in a specified cassette is less than 20 GB for mammoth and 25 GB for AIT, which is not preferable.

On the surface B of the polyester film obtained by the present invention, a coarser coating layer containing a lubricant such as silicone is provided, or a polyester film layer containing larger fine particles is formed by lamination. However, it is preferable that the coating layer is further provided thereon, but it is not particularly limited thereto.

When manufacturing a magnetic recording tape for data backup, a ferromagnetic metal thin film layer is provided by vacuum evaporation on the surface A of the polyester film according to the present invention, and a known metal thin film can be used. Although not particularly limited, a ferromagnetic material of iron, cobalt, nickel, or an alloy thereof is preferable. The thickness of the metal thin film layer is preferably from 100 to 300 nm. It is preferable that a diamond-like carbon film having a thickness of about 10 nm is coated on the metal thin film layer, and a lubricant treatment is further performed thereon. Further, on the surface B, it is preferable to provide a back coat layer formed by applying a solution composed of solid fine particles and a binder to which various additives are added as necessary. Can be used, and is not particularly limited. The thickness of the back coat layer is about 0.3 to 1.5 μm.

[0027]

EXAMPLE The measuring method used in this example is shown below.

(1) Average particle size of fine particles (d) Fine particle powder is dispersed on an electron microscope (electron microscope) test table so that the particles do not overlap as much as possible. (Microscope) at a magnification of about 1,000,000, the area circle equivalent diameter was obtained for at least 100 particles, and the number average value was used as the particle diameter.

When the particle size is determined from the film, it can be determined by the following method a). a) A gold thin film deposition layer is provided on the surface of the film A with a thickness of 20 to 30 nm (χ nm) by a gold sputtering apparatus, and observed at an magnification of about 100,000 by an electron microscope (preferably a scanning electron microscope). , The diameter equivalent to the area circle is determined, and the value obtained by subtracting 2 nm from the number average value is defined as the particle diameter.

(2) Solid concentration at the time of application of aqueous solution (unit:
mg / m ² ) When the aqueous solution is applied to the surface A of the film by the method of the present invention, the amount of the aqueous solution consumed by the application within a certain time is determined. The area where the aqueous solution was applied within the fixed time was calculated from the application width, the film speed, and the application time, the aqueous solution consumption during application was divided by the application area, and further, the solid content ratio in the applied aqueous solution was Then, the solid concentration (unit: mg / m ² ) at the time of applying the aqueous solution is calculated. This solid content concentration is a value indicating how many mg of solid content is applied per 1 m ² of the application area.

(3) Thickness of solid content by application of aqueous solution (t) The value of the solid content concentration obtained in (2) above is divided by the specific gravity and area of the aqueous solution solid to calculate the solid content thickness (tnm).
The specific gravity is calculated by a weighted average of the specific gravities of the components of the coating solution.

(4) SRa value, SRz value Optical stylus type (critical angle focus error detection system) manufactured by Kosaka Laboratory
Was measured using a three-dimensional roughness meter (ET-30HK). SRa value: A center line average roughness corresponding to JIS B0601 Ra. SRz value: Ten-point average surface roughness corresponding to JIS B0601 Rz. Enter the distance between the average of the highest to fifth peak elevations and the average of the deepest to fifth valley bottoms, using the average surface of the part extracted by the reference area from the roughness surface as the reference surface. What was converted.

The test piece was subjected to Al evaporation on the measurement surface. The measurement direction is the width direction, the cutoff value is 0.08 mm, the measurement length is 0.1 to 0.25 mm, and the feed pitch is 0.2 μm.
m, the measurement speed was 20 μm / s, and the number of measurement was 100. The unit was nm.

(5) Magnetic recording tape (data tape)
The evaluation was performed by determining the error rate of the magnetic recording tape using a commercially available 8 mm data device manufactured by Exabyte and a mammoth. The error rate was measured by obtaining the ratio of write errors when backing up 20 GB data from a hard disk to a tape at a compression ratio of 2: 1 and the ratio of read errors when reading. The error rate was obtained at the time of first use after the tape was manufactured, and the value after 100 times of recording and storage and reading. It is preferable that the error rate has a small absolute value. Expressed in the form of minus a power of 10,
A larger negative multiplier is more preferable. Ten minus tenth power is much more preferable than ten minus fiveth power.

Next, the present invention will be described based on examples.

Example 1 The same polyethylene terephthalate as raw material A in which 0.03% by weight of silica having an average particle size of 60 nm was added to polyethylene terephthalate substantially containing no inert particles, and silicic acid having an average particle size of 300 nm Raw material B containing 0.20% by weight of aluminum was co-extruded at a thickness ratio of 5: 1, closely adhered to a cooling drum to form a sheet, and longitudinally stretched 3.0 times at 110 ° C. by a roll stretching method. In a process after the longitudinal stretching, an aqueous solution having the following composition was applied to the outside of one surface A so as to have a coating concentration (solid content concentration) of 30 mg / m ² .

Aqueous solution applied to the outside of side A: methyl cellulose 0.10% by weight Water-soluble polyester (= 70 mol% of terephthalic acid, 30 mol% of 5-sodium sulfoisophthalic acid, 1: 1 mixture of acid component and ethylene glycol) Copolymer) 0.32% by weight Aminoethylsilane coupling agent 0.01% by weight Ultrafine silica having an average particle size of 18 nm 0.04% by weight Then, it is stretched 4.0 times at 102 ° C. in the lateral direction by a stenter. Then, it was heat-treated at 215 ° C., wound around an intermediate spool, slit into a small width with a slitter, and wound up in a roll shape around a cylindrical core to obtain a 6.3 μm-thick roll-like polyester film.

In this aqueous solution application, d = 18 nm,
The specific gravity of the solid content is 1.27, the solid content thickness (t) by applying the aqueous solution is 23.6 nm, and the transverse stretching ratio (s) is 4.0, which satisfies the relational expression of d / 2 <2t / s <d. did.

On the surface A of this polyester film, a cobalt-oxygen thin film having a thickness of 80 nm
Formed in layers. Next, a diamond-like carbon film is formed on the cobalt-oxygen thin film layer by sputtering to a thickness of 10 nm.
And a fluorine-containing fatty acid ester-based lubricant was applied to a thickness of 3 nm. Subsequently, a back coat layer made of carbon black, polyurethane, and silicone was provided on the surface B to a thickness of 500 nm, slit to a width of 8 mm by a slitter, wound up on a reel, assembled into a mammoth cassette, and magnetic recording tape (data Tape). Table 1 shows the properties of the obtained polyester film and magnetic recording tape.

Example 2 A magnetic recording tape having a width of 8 mm was prepared in the same manner as in Example 1 except that silica having an average particle diameter of 60 nm was removed from the raw material A in the production of the base film of Example 1. Table 1 shows the properties of the obtained polyester film and magnetic recording tape.

Example 3 In the production of the base film of Example 2, the polyethylene terephthalate was changed to polyethylene-2,6-naphthalate, the content of aluminum silicate in the raw material B was set to 1.1% by weight, The stretching temperature and magnification were set to 5.0 times at 135 ° C., the solid concentration at the time of application of the aqueous solution was set to 45 mg / m ² , and the lateral stretching temperature and magnification were set to 1
The temperature was changed to 35 ° C. and 6.5 times, and the heat treatment was changed to 200 ° C., and the other conditions were the same to obtain a 4.2 μm thick polyester film roll. Otherwise, the width is 8 in the same manner as in the first embodiment.
mm magnetic tape was prepared. Table 1 shows the properties of the obtained polyester film and magnetic recording tape. In addition,
The solid content thickness (t) by application of the aqueous solution was 35.4 nm, the transverse stretching ratio (s) was 6.5, and d / 2 <2t / s <d.
Was satisfied.

Comparative Example 1 In the production of the base film of Example 1, the average particle size of silica in the aqueous solution was 4 nm. Otherwise, a polyester film roll having a thickness of 6.3 μm was obtained in the same manner as in Example 1, and a magnetic recording tape having a width of 8 mm was prepared. Table 1 shows the properties of the obtained polyester film and magnetic recording tape.

Comparative Example 2 In the production of the base film of Example 1, the average particle size of silica in the aqueous solution was set to 60 nm. Otherwise, a polyester film roll having a thickness of 6.3 μm was obtained in the same manner as in Example 1, and a magnetic recording tape having a width of 8 mm was prepared. Table 1 shows the properties of the obtained polyester film and magnetic recording tape.

Comparative Example 3 In the production of the base film of Example 1, the coating concentration (solid content concentration) of the aqueous solution was set to 2
mg / m ² . Otherwise, in the same manner as in Example 1, a polyester film roll having a thickness of 6.3 μm was obtained, and the width was 8 m.
m of magnetic recording tape was prepared. Table 1 shows the properties of the obtained polyester film and magnetic recording tape. The solid content thickness (t) by application of the aqueous solution was 1.6 nm.

Comparative Example 4 In the production of the base film of Example 1, the solid concentration at the time of application of the aqueous solution was 1500 mg.
/ M ² . Otherwise, the thickness is the same as in Example 1.
A 3 μm polyester film roll was obtained, and a magnetic recording tape having a width of 8 mm was prepared. Table 1 shows the properties of the obtained polyester film and magnetic recording tape. In addition, solid content thickness (t) by application of an aqueous solution = 1181.2 nm,
The transverse stretching ratio (s) was 4.0, and 2 t / s> d.

Comparative Example 5 In the production of the base film of Example 1, the solid content concentration at the time of applying the aqueous solution was 20 mg / m 2.
It was m ^2. Otherwise, the thickness is 6.3 as in Example 1.
A polyester film roll of μm was obtained, and a magnetic recording tape having a width of 8 mm was prepared. Table 1 shows the properties of the obtained polyester film and magnetic recording tape. The solid content thickness (t) by application of the aqueous solution was 15.7 nm, the transverse stretching ratio (s) was 4.0, and d / 2> 2 t / s.

When the surface A of the polyester film was observed at a magnification of 3000 times with a scanning electron microscope (SEM), a scratch having a width of about 50 to 100 nm and a diameter of 50 to 100 nm were obtained.
Several amorphous materials such as dust having a size of about nm were adhered to the surface, and several were observed per visual field.

[Comparative Example 6] In the production of the base film of Example 1, the solid content concentration of the aqueous solution applied was 52 mg / mm.
^{And 2} . Otherwise, the thickness is 6.3 μm as in Example 1.
m, and a magnetic recording tape having a width of 8 mm was prepared. Table 1 shows the properties of the obtained polyester film and magnetic recording tape. The solid content thickness (t) by application of the aqueous solution (t) was 40.9 nm, the transverse stretching ratio (s) was 4.0, and 2t / s> d.

When the surface A of the polyester film was observed with a scanning electron microscope (SEM) at a magnification of 30,000, almost no surface protrusions due to fine particles were observed.

[0050]

[Table 1] Polyester film data tape properties Manufacturing conditions Surface Fine grain Solid 2t / s A Surface B Error rate Average value of the element Write / read uniform diameter d Concentration SRa SRa SRz nm mg / m ² nm nm nm Initial 1 after 100 times Example 1 18 30 11.8 3 20 280 10 ^-11 / 10 ^-11 10 ^-11 / 10 ^-11 〃 2 18 30 11.8 2 19 290 10 ^-11 / 10 ^-11 10 ^-11 / 10 ^-11 ３ 3 18 45 10.9 2 23 295 10 ^-11 / 10 ^-11 10 ^-11 / 10 ^-11 Comparative Example 1 4 30 11.8 1 19 270 10 ^-8 / 10 ^-8 10 ^-7 / 10 ^-7 〃 2 60 30 11.8 6 21 285 10 ^-6 / 10 ^-6 10 ^-6 / 10 ^-6 ３ 3 18 2 0.8 1 22 290 10 ^-8 / 10 ^-8 10 ^-7 / 10 ^-7 〃 4 18 1500 590.6 6 19 280 10 ^-6 / 10 ^-6 10 ^-6 / 10 ^-6 ５ 5 18 20 7.9 2 20 270 10 ^-8 / 10 ^-8 10 ^-7 / 10 ^-7 ６ 6 18 52 20.5 4 20 270 10 ^-11 / 10 ^-11 10 ^-7 / 10 ^-7

As is clear from the characteristics shown in Table 1, the magnetic tape using the polyester film produced by the method of the present invention had a low error rate and was excellent as a large-capacity data storage tape.

[0052]

According to the method of the present invention, a polyester film for a magnetic recording medium suitable for producing a large-capacity data storage tape having a low error rate can be obtained. In particular, a large-capacity data storage tape is produced. Therefore, the method of the present invention is effective.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G11B 5/733 G11B 5/733 5D112 // B29K 67:00 B29K 67:00 B29L 7:00 B29L 7:00 C08L 67: 00 C08L 67:00 F term (reference) 4D075 BB21Z DA04 DB48 DC28 EA06 4F006 AA35 AB03 AB73 AB76 BA06 CA02 DA04 EA05 EA06 4F100 AA03 AA20 AB01C AK01B AK41A AK42A BA02 BA03 BA10A BA10C CA19B CA37EBJB EB12B37E01 EB42B02E01 JM02C YY00B 4F210 AA24 AA26 AG01 AG03 AH38 QC06 QD08 QG01 QG18 5D006 CB01 CB05 CB07 CB08 5D112 AA02 BA01 BA09

Claims (5)

[Claims] 1. An aqueous solution containing a water-soluble polymer and fine particles having an average particle size of 5 to 50 nm as main components on a surface A of a melt-extruded, cooled, and unidirectionally stretched polyester film, After coating at a partial concentration of 3 to 1000 mg / m ² , after drying or while drying, the film is stretched in a direction perpendicular to the stretching direction, and then heat-treated, whereby the surface A side is the ferromagnetic metal thin film forming surface. A method for producing a polyester film for a magnetic recording medium, wherein the average particle diameter of the fine particles is d (nm), the solid content thickness by application of an aqueous solution is t (nm), and the stretching ratio in a perpendicular direction is s (times). ), Wherein a relationship of d / 2 ≦ 2t / s <d is satisfied. 2. The method according to claim 1, wherein the thickness of the polyester film for a magnetic recording medium is 7.0 μm or less. 3. The method for producing a polyester film for a magnetic recording medium according to claim 1, wherein the polyester is polyethylene terephthalate or polyethylene-2,6-naphthalate. 4. The method for producing a polyester film for a magnetic recording medium according to claim 1, wherein the magnetic recording medium is a digital recording type magnetic recording tape. 5. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic recording tape in which a ferromagnetic metal thin film layer is provided on a coating film on the surface A of the polyester film. A method for producing a polyester film.