JPH0679844B2 - Polyester film for magnetic recording medium and method for producing the same - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk,
In particular, it relates to a base film for a magnetic recording medium having a ferromagnetic thin film as a recording layer.

[Conventional technology]

A base film for a magnetic recording medium, particularly for a ferromagnetic thin film, is a composite film in which a layer A made of a thermoplastic resin and a thermoplastic resin B to which fine particles are added are laminated.
On the outer surface of which a discontinuous coating having a height of 50 to 1000Å is formed, for example, JP-A-58-153640, 58-155940, granular, wrinkle-shaped, and earthworm-shaped protrusions are formed, and A plastic film having ridges higher than the height of 10 to 10,000 pieces / mm ² formed on the surface thereof, for example, JP-A-58-68225.
A polyester film having a height of 100 to 2000Å and an average of 10,000 to 1 million mountain projections per 1 mm ^2;
58-100221 publication.

Average height of 1 x 10 ⁵ to 1 x 10 ⁸ per 1 mm ² at heights of 50 to 600 Å
A polyester film having a mountain-shaped projection is known, for example, JP-A-60-93636.

[Problems to be solved by the invention]

In the film of the above item, if a ferromagnetic thin film is provided on the surface of the discontinuous coating, a high density magnetic recording medium can be produced. The ferromagnetic thin film provided on the surface has good head touch and head running properties. However, there was a problem that the head clogging phenomenon was not sufficiently improved.

In the film of the above item, a relatively high ridge is provided on the magnetic recording medium, and head clogging is prevented by using a kind of polishing action. There was a problem that the performance of the head clogging prevention effect deteriorates after repeated running.

In the film of the above item, if a ferromagnetic thin film is provided on the surface where the mountain projections are formed, a high density magnetic recording medium can be produced, but since the mountain projections are abrupt, contact with various rolls in the magnetic recording medium manufacturing process. The magnetic recording medium is easily scratched by scratches, and the head does not clog when running under normal temperature and humidity conditions.However, the mountain-shaped protrusions of the ferromagnetic thin film may not come into contact with the magnetic head. It has a drawback that it is easily scraped, and scratches occur on the vapor deposition surface during repeated running for a long time under severe conditions such as high temperature and high humidity conditions, and the tape performance deteriorates.

[Means for solving problems]

The present invention is a composite stretched film in which a layer made of polyester A and a layer made of polyester B to which fine particles are added are laminated, and an average of fine particles are provided on the outer surface of the layer made of polyester B. Height is 50Å or more, 200
Characterized by a polyester film for magnetic recording media in which surface protrusions having a maximum height of 1.1 times or more and a maximum height of 1.1 times or more and 1.5 or less are formed at 10 ³ pieces / mm ² or more and 10 ⁷ pieces / mm ² or less. To do.

The polyester A forming the film of the present invention may be any as long as it is mainly composed of linear polyester. For example, polyethylene terephthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-
Typical examples are naphthalene dicarboxylate and polyethylene-p-oxybenzoate.

Further, the above polyester may be a homopolyester or a copolyester. In the case of copolyester, examples of components to be copolymerized include diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, diol components such as 1,4-cyclohexanedimethanol, adipic acid, sebacic acid, Dicarboxylic acid components such as phthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 5-sodium sulfoisophthalic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, p-
Examples thereof include oxyethoxybenzoic acid. In the case of copolymerization, the component to be copolymerized is 20 mol% or less.

Further, in addition to the above polyester, at least one of an alkali metal salt derivative of sulfonic acid which is non-reactive with the polyester and a polyalkylene glycol which is substantially insoluble in the polyester is mixed in an amount not exceeding 5% by weight. You may.

The polyester A forming the film of the present invention is
The following fine particles are preferably added in an amount of less than 0.01% by weight, and more preferably substantially not added.

The polyester B to which the fine particles forming the film of the present invention are added is the above polyester A to which the following fine particles are added.

Fine particles in the present invention, the particle size before addition to polyester is 10mμ ~ 300mμ, specifically, CaCO ₃ , Si
Inorganic particles such as O ₂ and Al ₂ O ₃ are used, but not limited thereto.

The polyester film of the present invention means a layer made of polyester A (hereinafter abbreviated as layer A) and a layer made of polyester B to which fine particles are added (hereinafter abbreviated as layer B).
And are laminated, and is a biaxially stretched composite stretched film, the mechanical properties of which are the normal balance type, the type strengthened to the uniaxial orientation in the machine axis direction or its orthogonal direction, the biaxial direction It should be one of the enhanced types.

On the outer surface of the layer B of the composite stretched polyester film of the present invention, surface protrusions formed by the fine particles are formed, and the average height is 50Å or more and 200Å or less (more preferably 1
00 Å or more and 180 Å or less), and the maximum height is 1.1 times or more and 1.5 times or more of the average (more preferably 1.1 times or more and 1.4 times or less), and 10 ³ pieces / mm ² or more, 10 ⁷ pieces or more of the number. / mm ² or less (more preferably 10 ³ cells / mm ² or more and 10 ⁶ cells / mm ² or less).

The polyester film of the present invention is a magnetic recording medium in which a ferromagnetic thin film is provided on the outer surface of the layer B, and the average height of the surface protrusions is less than 50Å, or the number thereof is 10 ³ /
If it is less than mm ² , the running property of the ferromagnetic thin film on the magnetic head deteriorates. It has no effect on the head clogging phenomenon. The average height exceeds 200Å and the number is 10 ⁷ pieces / m
If it exceeds m ² , the shape of the ferromagnetic thin film becomes rough and the electromagnetic conversion characteristics deteriorate. When the maximum height exceeds 1.5 times the average height, the electromagnetic conversion characteristics also deteriorate. In addition, scratching occurs in a rough portion due to scratching in a rough portion after repeated running for a long time under high temperature and high humidity conditions, and scratches occur. If the maximum height is less than 1.1 times the average height, the projection height becomes too uniform and the effect of preventing head clogging decreases.

When the projection height H and the diameter are D, the ratio H / D of the two is
0.1-0.01 is preferable and 0.1-0.02 is more preferable. H / D
Within this range, the fine protrusions cannot be scraped off by various guide rolls during the processing of the base film, and the protrusions formed on the tape surface after table formation cannot be scraped off, and after the metal thin film is provided. The effect of preventing head clogging is further improved.

The surface roughness of the outer surface of the layer B, that is, the surface on which the ferromagnetic metal thin film is provided, has a Ra value (DIN4
When the ferromagnetic metal thin film is provided on the surface, the surface becomes smooth and the electromagnetic conversion characteristics are further improved.

On the surface of the layer B, Japanese Patent Publication No. 5183/1985, Japanese Patent Publication No.
The earthworm-like coating structure seen in Japanese Patent Publication No. 50150 may be formed. Further, a discontinuous coating as disclosed in JP-B-60-5015 may be formed.

The ferromagnetic metal thin film may be a known thin film and is not particularly limited, but the thickness is 0.01 to 1 μm, more preferably 0.1 to 1 μm.
It is about 0.5 μ and is preferably made of a ferromagnetic material of iron, cobalt, nickel, or an alloy thereof. The film is formed directly on the base film by vacuum vapor deposition ion plating, sputtering or the like, or through an underlying thin film of aluminum, titanium, chromium or the like.

The polyester film for a magnetic recording medium of the present invention,
It can be obtained by the following manufacturing method.

That is, polyester A and polyester B containing 0.01 to 1 wt% of fine particles having a particle size of 10 to 300 mμ are melted at a temperature of 260 ° C. or higher and 300 ° C. or lower, respectively, and both are joined to form a sheet from a slit-shaped die. And coextruded, and the sheet is cooled and solidified on a moving cooling body at a temperature of 5 to 40 ° C. to obtain an unstretched sheet in which polyesters A and B are laminated,
In the method for producing a polyester film, the sheet is biaxially stretched, and then re-stretched if necessary, and then heat-treated.
10 to 300 mμ, the thickness of the polyester B layer of the unstretched sheet is 5 times or more and 100 times or less the particle size of the added fine particles, and the biaxial stretching is 70 to 150 ° C. in the uniaxial direction. At a temperature of 70 to 150 [deg.] C. in the direction orthogonal to the above direction, and at a temperature of 70 to 150 [deg.] C. at a temperature of 3 to 5 times.

The stretching in each direction in the biaxial stretching may be either one-stage stretching or multiple-stage stretching. Further, re-stretching may be at least uniaxially re-stretching, when re-stretching only in the uniaxial direction, 1.1-2.0 times at 90-170 ℃, when re-stretching in the biaxial direction, It is preferable to set 1.1 to 1.8 times at 90 to 170 ° C. in each axial direction. The heat treatment is not particularly limited as long as it is a known condition, but is preferably 180 to 240 ° C. for 5 to 180 seconds.

In the method for producing the above film, the particle size of the fine particles is
When it is less than 10 mμ, the average height of the fine projections formed on the outer surface of the layer B of the laminated film is less than 50Å. Also,
If the particle size exceeds 300 mμ, the average height of fine protrusions is 200.
Go above Å. When the amount of the fine particles added is less than 0.001 wt%, the effect of surface fine protrusions is less than 10 ³ pieces / mm ² . If the amount added exceeds 1 wt%, the number of fine protrusions will increase to 10 ⁷
Ke / mm ² is exceeded.

When the thickness of the layer B of the coextruded sheet is less than 5 times the diameter of the fine particles, the fine projections formed by the subsequent stretching process easily come off from the surface. In addition, this makes the surface very likely to come off. When the thickness of the layer B exceeds 100 times the fine particle diameter, the maximum height of the fine projections formed exceeds 1.5 times the average height.

Further, if the draw ratio in the biaxial direction is lower than each of the above draw ratios, the mechanical strength of the film decreases, which is not preferable. When the ratio is increased, the added fine particles are likely to fall off the film.

The re-stretching ratio is arbitrarily selected according to the strength required for the film and is not particularly limited.

In the above stretching, after the uniaxial stretching, the Japanese Patent Publication No.
The layer A may be subjected to slipperiness treatment disclosed in Japanese Patent Publication No. 050, Japanese Patent Publication No. 59-39308, etc., and Japanese Patent Publication No. 60-5183, Japanese Patent Publication No. 60-50150, Japanese Patent Publication No. 60- Layer B may be subjected to the earthworm-like coating or the discontinuous coating forming treatment disclosed in Japanese Patent No. 50151.

[Operation] The laminated stretched polyester film of the present invention has an average height of 50 to 200Å and a maximum height of 1.1 to 1.5 on one surface.
Since 10 ³ to 10 ⁷ pieces / mm ^{2 of} projections that are doubled are formed, providing a ferromagnetic thin film layer on the surface side improves the running property for the magnetic head and the head clogging prevention effect.
The electromagnetic conversion characteristics are good and the shift resistance is secured.

Further, in the production direction of the laminated film of the present invention, in order to make the thickness of the particle addition layer of the laminated unstretched sheet formed by coextrusion 5 to 100 times the added particle diameter,
The fine protrusions formed by stretching have uniform maximum heights of 1.1 to 1.5 times the average height.

[Evaluation Method / Measurement Method] The height of the surface protrusions of the film of the present invention is measured by a highly accurate stylus type surface roughness measuring device. Measure a distance of at least 500μ and obtain the cross-section curve. Each unevenness that appears in the cross-sectional curve is due to an individual surface protrusion, and the value displayed by calculating the distance from the peak to the valley bottom of each unevenness is the height of each surface protrusion, and the average value is the average of the surface protrusions. Let it be the height. The maximum height of each surface protrusion is the maximum height.

The diameter and number of the surface protrusions of the film of the present invention can be observed by a differential interference optical microscope and an electron microscope, but they are measured by observation with an electron microscope at a magnification of 5000 times or more. For the diameter, 10 or more protrusions are observed and the average value is calculated. Take the number of ordinary photographs and calculate the number per 1 mm ² from the number in the photograph.

The characteristics of the magnetic recording medium in which the film of the present invention is provided with a ferromagnetic thin film, that is, the magnetic tape, is measured using a commercially available 8 mm video tape recorder. As the electromagnetic conversion characteristics, the video S / N ratio, dropout, and the number of repetitions until the occurrence of image disturbance due to head clogging were obtained. To measure the S / N ratio and dropout, a signal was supplied from a TV test signal generator, and a video noise meter and dropout counter were used. Video S / N ratio is 8 on the market
Milli-video metal tape was compared and measured as zero decibel (dB). Dropout has a playback signal attenuation of -16 dB
As mentioned above, the length of 15 microseconds or more was obtained. The S / N ratio and dropout were at room temperature and normal humidity (25 ° C, 60% RH), and the initial characteristics after tape production were observed. To prevent head clogging, leave the magnetic tape for 1 month at 60 ° C and 90% RH, and slightly generate rust that causes clogging on the surface, then at 25 ° C and 90%. Repeatedly record and reproduce video under RH, and determine the number of repetitions until the start of image distortion due to head clogging. so
Both tapes after 100 times of reproduction running were evaluated and evaluated. In addition, the surface of the tape after 100 times of reproduction and running was observed under the conditions of 60 ° C and 90% RH, and the occurrence of scratches was observed.

In the production method of the present invention, the particle size of the fine particles is determined by measuring the particles by observation with an electron microscope. Ten
Observe more than one particle and calculate the average diameter.

In the production method of the present invention, the layer thickness of the coextruded sheet is determined by cutting the unstretched sheet with a microtome and observing the section with a microscope.

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

Example 1 Substantially non-oriented, non-crystalline polyethylene terephthalate raw material (A) containing as little as possible fine particles formed on the basis of a polymerization catalyst residue, and SiO 2 having a particle diameter of 10 mμ as raw material (A).
Melt so that the thickness of the raw material (B) layer is 1μ (9 times the particle size) and the thickness of the raw material (A) layer is 137μ using the raw material (B) containing 0.02% by weight of ₂ particles. After coextrusion and solidification by cooling, longitudinal stretching with a draw ratio of 3.4 was performed at a temperature of 100 ° C., and then the surface of the raw material (A) layer was coated with the following aqueous emulsion at a solid content concentration of 20 mg / m ² .

Epoxidized polydimethylsiloxane emulsion: 0.40w
t% Silane coupling agent [N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane]: 0.050wt% Alkylphenol nonionic surfactant: 0.20wt% After that, pass through a stenter and dry at 115 ° C, preheat, It was laterally stretched. The transverse stretching ratio was 3.4 times. Next, heat treatment at 200 ℃ for 1 second, average diameter 0.2μ, average height 150Å, maximum height
A biaxially stretched polyester having a thickness of 12 μ, in which a layer B having a surface with 180Å surface protrusions formed in a range of 3.0 to 10 ⁴ pieces / mm ² and a layer A having a surface having a lubricant-based coating layer formed thereon are laminated. A laminated film was obtained.

A cobalt-iron alloy thin film having a thickness of 1500 Å was formed on the surface of the layer A of the polyester film by vacuum vapor deposition. Subsequently, a protective film layer made of epoxy resin, silicone, and a silane coupling agent was formed on the surface of the cobalt-iron alloy thin film.
A 1 μm thin film is provided on the reverse side of layer B, which is a back coat layer containing carbon black and made of an epoxy resin, silicone, and a silane coupling agent to a thickness of 1 μm, and then cut to a predetermined width in the longitudinal direction. , Magnetic tape.

The characteristics of the film and magnetic tape are shown in Table 1.

Example 2 In the production of the laminated film of Example 1, after the longitudinal stretching, the surface of the raw material (A) layer was coated with an aqueous emulsion, and at the same time, the surface of the raw material (B) layer was treated with the following aqueous solution in a solid content concentration of 20 mg. / m ^{2 was} applied. Methylcellulose 0.1 as an aqueous solution
5 wt%, silane coupling agent N-β (aminoethyl)
γ-Aminopropylomethyldimethoxysilane 0.05 wt% was prepared. Others are the same as in Example 1, Ra value at a cutoff value of 0.25 mm is 0.005μ, a discontinuous coating is formed on the surface, average diameter 0.2μ, average height 140Å, maximum height
A biaxially stretched polyester laminated film having a thickness of 12 μ was obtained, which was composed of a layer B having 170 Å surface projections formed by 2.9 × 10 ⁴ pieces / mm ² and a layer A having a lubricant-based coating layer formed thereon. The height of the surface protrusion was determined by focusing only on the height higher than that of the discontinuous coating. More specifically, the unevenness of the cross-section curve of the roughness meter was determined by focusing on those with a height higher than 100Å. Using this base film, a magnetic tape was obtained in the same manner as in Example 1.

The characteristics of the film and magnetic tape are shown in Table 1.

Comparative Example 1 A base film was prepared in the same manner as in Example 1 except that the raw material (B) layer and the raw material (A) layer were coextruded at a ratio of 17 μ / 121 μ in the production of the base film of Example 1. And made a magnetic tape.

The characteristics of the film and magnetic tape are shown in Table 1.

Comparative Example 2 A base film was prepared in the same manner as in Example 1 except that the raw material (B) layer and the raw material (A) layer were coextruded at a ratio of 0.4 μ / 138β in the production of the base film of Example 1. And made a magnetic tape.

The characteristics of the film and magnetic tape are shown in Table 1.

Comparative Example 3 In the production of the base film of Example 1, the same except that the particle diameter of SiO ₂ added to the raw material (B) was changed to 500 mμ and the thickness of the raw material B layer and the raw material A layer was 4 μ / 134 μ. I chose Using this base film, a magnetic tape was obtained in the same manner as in Example 1.

The characteristics of the film and magnetic tape are shown in Table 1.

Comparative Example 4 A 12 μm-thick base film was obtained in the same manner as in the production of the base film of Example 1 except that the particle diameter of the SiO ₂ particles added to the raw material (B) was changed to 5 mμ. Using this base film, a magnetic tape was obtained in the same manner as in Example 1.

The characteristics of the film and magnetic tape are shown in Table 1.

Comparative Example 5 A 12 μm-thick base film was obtained in the same manner as in the production of the base film of Example 1, except that the amount of SiO ² added in the raw material (B) was 2 wt%. A magnetic tape was prepared in the same manner as in Example 1 except that this base film was used.

The characteristics of the film and magnetic tape are shown in Table 1.

[Effects of the Invention] The effect of preventing the clogging of the head of the ferromagnetic metal thin film provided on the surface of the layer B of the composite film of the present invention, the scratch resistance to the magnetic head, and the S / N ratio and dropout of the magnetic tape are excellent. Has the effect of being good.

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Claims (2)

[Claims] 1. A composite stretched film obtained by laminating a layer made of polyester A and a layer made of polyester B to which fine particles are added, wherein the fine particles are formed on the outer surface of the layer made of polyester B by the fine particles. Average height is 50Å or more, 20
A polyester film for a magnetic recording medium, wherein surface protrusions having a height of 0 Å or less and a maximum height of 1.1 times or more and 1.5 times or less of the average height are formed in a number of 10 ³ / mm ² or more and 10 ⁷ / mm ² or less. 2. Polyester A and fine particles in an amount of 0.001 to 1 wt%
The added polyester B is melted, and the two are joined together to form a sheet from a slit-shaped die and coextruded. The sheet is cooled and solidified on a moving cooling body at a temperature of 5 to 40 ° C. to form polyesters A and B. In the method for producing a polyester film, the particle size of the fine particles is added to the polyester in the method for producing a polyester film, which is a non-stretched sheet in which and are laminated, the sheet is biaxially stretched, and then re-stretched if necessary The particle size before is 10 to 300 mμ, the thickness of the layer made of polyester B of the unstretched sheet is 5 times or more and 100 times or less the particle size of the added fine particles, and the biaxial stretching is uniaxial. 2 to 4 times at a temperature of 70 to 150 ° C., and 3 to 5 times at a temperature of 70 to 150 ° C. in the direction orthogonal to the above direction, the method for producing a polyester film for a magnetic recording medium.