JPH0626015B2 - Magnetic recording flexible disk - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording flexible disk having a track density of 96 tracks / inch or more, and more specifically, the roundness of the central hole is increased to bend the edge of the central hole. The present invention relates to a magnetic recording flexible disk which eliminates breakage and high-edging, does not increase module even after heat history, enables recording with a high track density, and has excellent durability such as repeated use.

[Prior art]

The magnetic recording flexible disk is widely used for office automation and the like, but in recent years, high density recording has been demanded.

A magnetic recording flexible disk is generally manufactured by applying a magnetic layer on a support film, smoothing the film, and punching the disk into a desired size. The following points are raised as problems that need to be solved in order to achieve a high track density of a magnetic recording flexible disk.

 Tracking mistakes due to the anisotropy of the coefficient of thermal expansion.

Due to the distortion of the central hole, there is a mistake in checking due to bending or damage of the disk edge portion during checking.

Signal loss due to increased module after heat history.

On the other hand, it has been conventionally known that the recording / reproducing apparatus of a magnetic recording flexible disk is provided with a mechanism for suppressing a temperature change and a special circuit for detecting a track (track servo etc.) to prevent a tracking error. ing.
In addition, since these means complicate the recording / reproducing apparatus, they are not versatile. Therefore, in general, a base material film or a magnetic material has a thermal expansion coefficient as close as possible to that of a disk drive, and a magnetic flexible disk is selected by selecting a material having a small humidity expansion coefficient. Means have been taken to prevent manufacturing and tracking mistakes.

However, even such a magnetic recording flexible disk has a high temperature (40 to 60 ° C.) and / or a high humidity (about 80% R).
When used in H), tracking mistakes occur. Particularly, a magnetic recording flexible disk recorded under conditions of low temperature (about 10 ° C.) to low humidity (about 20% RH) has high temperature (about 40 to 60 ° C.) and high humidity (60 to 80% RH).
There is a drawback that a tracking mistake occurs when playing in an atmosphere. In addition, there is a drawback that a tracking mistake occurs when a magnetic recording flexible disk recorded at low temperature and high humidity is reproduced at high temperature and low humidity. The problem that the output envelope is lowered due to such a tracking mistake and the S / N ratio is deteriorated is still unsolved.

In addition, since the precision (roundness) of the inner diameter of the punched central hole of the magnetic recording flexible disk is as bad as about 50 μm, the inner edge of the central hole is partially high-edged or bent during checking. It is damaged and causes a tracking mistake.

Furthermore, in the high-density flexible disk, the module (JISC 6291) becomes large even if the disk is slightly deformed after receiving heat of about 60 ° C., which causes a signal error.

[Object of the Invention]

As a result of repeated studies to solve the above problems, the present inventor can solve these problems by setting the internal residual strain and the in-plane anisotropy of the coefficient of thermal expansion of the magnetic recording flexible disk to specific values. And has reached the present invention.

INDUSTRIAL APPLICABILITY The present invention has a wide range of usable temperatures, and magnetic recording excellent in durability such that a tracking error does not occur even when continuously used and a tracking error due to distortion of a central hole does not occur. The purpose is to provide a flexible disk.

[Constitution / Effect of Invention]

According to the present invention, there is provided a magnetic recording flexible disk comprising a polyester film and a magnetic layer provided thereon, the internal residual strain of the film being within 0.02%, and the thermal expansion of the disk. In-plane anisotropy of the ratio is 6 × 1
The track density is 9-6, which is characterized by being within 0 ^-6 / ° C.
This is achieved with a magnetic recording flexible disk of 6 tracks / inch or more.

Here, "internal residual strain is within 0.02%" means
It means that the rate of change (shrinkage rate and elongation rate) of the film is 0.02% or less in any direction when the film is held in an unloaded state for 72 hours in an atmosphere of 60 ° C. and 80% RH. .

As the polyester in the present invention, polyethylene terephthalate and polyethylene-2,6-naphthalate are mainly targeted. This polyethylene terephthalate is a polyester in which 80 mol% or more of the dibasic acid component is terephthalic acid and 90 mol% or more of the glycol component is ethylene glycol. Dibasic acid components other than terephthalic acid include isophthalic acid, phthalic acid,
Dibasic acids such as adipic acid, sebacic acid, succinic acid, oxalic acid, naphthalene-2,6-dicarboxylic acid and the like are exemplified. Examples of glycol components other than ethylene glycol include chain-like aliphatic glycols such as trimethylene glycol, tetramethylene glycol and hexamethylene glycol. Polyethylene-2,6-naphthalate is a polyester in which 80 mol% or more of the dibasic acid component is 2,6-naphthalenedicarboxylic acid and 90 mol% or more of the glycol component is ethylene glycol. Examples of dibasic acid components other than 2,6-naphthalenedicarboxylic acid include dibasic acids such as isophthalic acid, terephthalic acid, phthalic acid, adipic acid, sebacic acid, succinic acid, and oxalic acid. Examples of glycol components other than ethylene glycol include chain-like aliphatic glycols such as trimethylene glycol, tetramethylene glycol and hexamethylene glycol.

In such polyesters, for example, stabilizers such as phosphoric acid, phosphorous acid and their esters, titanium dioxide,
Fine particles of silica, matting agents such as kaolin, calcium carbonate and calcium phosphate, lubricants and the like may be included.

The polyester film in the present invention basically has
The polyester can be produced by a known method. That is, the melted polyester is extruded into a sheet by an extruder, cooled and solidified, then sequentially or simultaneously biaxially stretched, and further heat-treated under tension or under contraction. If necessary, the heat-treated film can be manufactured by a method of re-heat-treating. In the production of the film, in order to make the internal residual strain of the film 0.02% or less and the coefficient of thermal expansion anisotropy 6 × 10 ⁻⁶ / ° C. or less,
The conditions such as the draw ratio in the machine direction and the transverse direction, the heat setting temperature, the amount of heat shrinkage applied under restriction, etc. are appropriately selected, and these conditions are combined. Specifically, the draw ratio is 3.6 to 3.8 in the machine direction.
Double, lateral direction 3.7 to 3.9 times, the heating and fixing temperature is selected from the range of 180 to 240 ° C., and the lateral limiting shrinkage rate (toe-in) is 0 to 2%, and the vertical direction is To 1
It is recommended to relax by applying tension of 6 to 9 kg / cm ² at a temperature of 00 to 120 ° C. It is recommended to avoid applying strong tension that changes the shrinkage characteristics of the base film during the magnetic layer coating process and calendering process. Further, even if the film obtained in the production of the film has some longitudinal shrinkage, the present invention can be achieved by adding a step corresponding to the above-mentioned longitudinal relaxation treatment in the magnetic layer coating step.

As one guideline for manufacturing a base film having an internal residual strain of 0.02% or less, the absolute value of the difference between the longitudinal direction and the lateral direction of the heat shrinkage ratio when held at 70 ° C. for 72 minutes under no load is 0. It is preferable to suppress it within 0.035%. When the absolute value of the difference in the heat shrinkage ratio exceeds 0.035%, the internal residual strain of the obtained magnetic recording flexible disk exceeds 0.02%, and as a result, the inner edge portion of the central hole is partially It is connected to a high edge or bent to form a seaweed, which is damaged, and the thermal history increases the amount of module and causes a defect in recording and reproduction. Further, if the in-plane anisotropy of the coefficient of thermal expansion is too large, the tracking shift during use of the disk becomes significant, and high density cannot be achieved.

The magnetic recording flexible disk of the present invention comprises a magnetic layer and the above-mentioned polyester film.
The magnetic layer is made of magnetic powder or metal. Examples of the ferromagnetic powder or metal used in the present invention include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and Co-containing Fe ₃ O ₄ , CrO ₂ , Co- Examples include ferromagnetic materials such as Ni-P alloy, Co-Ni-Fe alloy, Co-Cr alloy, Co-Ni alloy, and barium ferrite.

Examples of the binder used with the magnetic powder in the present invention include known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. Specifically, for example, vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinylidene chloride copolymer, vinyl chloride / acrylonitrile copolymer, acrylic ester / acrylonitrile copolymer, acrylic ester / vinylidene chloride copolymer , Acrylic acid ester / styrene copolymer, methacrylic acid ester / acrylonitrile copolymer, methacrylic acid ester / vinylidene chloride copolymer, methacrylic acid ester / styrene copolymer, urethane elastomer, polyvinyl chloride, vinylidene chloride / acrylonitrile copolymer Polymer, butadiene-acrylotolyl copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propio Over DOO, nitrocellulose), styrene-butadiene copolymer, polyester resin, chlorovinyl ether-
Acrylic ester copolymers, amino resins, various synthetic rubber thermoplastic resins, and mixtures thereof can be used.

Examples of the method for coating the above magnetic layer on a polyester film include air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, A spray coat can be used. The metal layer can be provided by a physical vapor deposition method such as a vacuum vapor deposition method or a sputtering method.

Magnetic layer of 0.1 to 3.0 μm on polyester film
It is preferable to provide the same thickness.

When providing the magnetic layer on the polyester film,
It is carried out under the condition that the internal residual strain of the film can be maintained at 0.02% or less, or under the condition that the internal residual strain becomes 0.02% or less. The in-plane anisotropy of the coefficient of thermal expansion is 6 × 10 ⁻⁶ / ° C.
Conditions that can be maintained below, or the in-plane anisotropy is 6 × 10 ^-6
/ ° C or less.

The polyester film provided with the magnetic layer is calendered according to a conventional method and punched into a disk shape to obtain a magnetic recording flexible disk. The flexible disk is
This average coefficient of thermal expansion is close to the coefficient of thermal expansion of the disk drive, and the circularity of the central hole is excellent, so that the edge of the hole is not bent, damaged, or has a high edge. Furthermore, the in-plane anisotropy of the coefficient of thermal expansion is as small as 6 × 10 ⁻⁶ / ° C. or less. For this reason, the flexible disk does not cause tracking mistakes even if the track density is increased to 96 tracks / inch or more, does not cause deformation or damage of the central hole due to checking mistakes, and even after a thermal history. It has the characteristics of a high-density flexible disk without an increase in module.

The method of measuring the characteristics in the present invention is as follows.

(1) Thermal expansion coefficient Measured using a thermomechanical analyzer TMA-3000 manufactured by Vacuum Riko Co., Ltd. The sample size is 15 mm in length, and when the difference between the maximum value and the minimum value of the thermal expansion coefficient is to be obtained, the sample is placed in the plane of the flexible disk medium, for example, at an angle of 3.
It was cut out at every 0 degree, the coefficient of thermal expansion of each was determined, and the maximum value and the minimum value were determined. The difference between the maximum value and the minimum value is displayed as the in-plane anisotropy of the coefficient of thermal expansion. The coefficient of thermal expansion was determined by reading the dimensional change at a temperature of 10 ° C. and a humidity of 0% RH and a temperature of 40 ° C. and a relative humidity of 0%.

(2) Tracking deviation test (temperature change) A magnetic layer was applied onto a polyester film, and a magnetic recording flexible disk punched into a disk shape by applying a calendar roll was recorded at a temperature of 15 ° C. and a humidity of 60% RH.
At that time, the maximum output and the output envelope of the magnetic sheet are measured. Next, maintain the ambient temperature at 40 ° C and 60% RH, check the maximum output and output envelope at that temperature, and check the output envelope at 15 ° C and 60% RH and 40 ° C and 60% RH. The output envelopes of are compared to determine the state of tracking deviation. The smaller this difference is, the better the tracking property is. When this difference was 3 db or more, the tracking was poor, and the evaluation was x. When the difference was within 3 db, the evaluation was o.

(3) Measurement of internal residual strain A film obtained by coating a magnetic layer on a polyester film and subjecting it to a calendar roll treatment has a temperature of 20 ° C. and a humidity of 60% R.
A magnetic recording flexible disk was made by punching with H in a disk shape. Then, the disk is placed under the above atmosphere for 24 hours.
After holding for at least the time, the outer diameter or punched inner diameter (inner diameter of the central hole) of the disk was measured with a universal projector (Nikon 6C manufactured by Nippon Kogaku Kogyo) and designated as A. After that, the disk is aged in an atmosphere of 60 ° C. and 80% RH for 72 hours, returned to room temperature again and kept for 24 hours, and then the outside diameter or punched inside diameter of the disk is measured by the above method and is designated as B. Then, the internal residual strain is calculated from the measured values A and B by the following formula.

The measuring direction includes the stretching direction of the base film (longitudinal direction and lateral direction), and it is desirable to add 45 ° 135 ° obliquely as a measuring direction based on the longitudinal direction or the lateral direction. More preferably, it is measured at 30 ° pitch.

Usually, the maximum diameter and the minimum diameter of the central hole intersect at right angles to each other, and these directions substantially coincide with the longitudinal direction and the lateral direction of the base film.

〔Example〕

 The present invention will be specifically described below with reference to examples.

Examples 1-6 Polyethylene terephthalate or polyethylene-2,6-
Naphthalate was melt extruded, and heat treated after stretching to prepare a biaxially oriented film having a thickness of 75 μm. These conditions are shown in Table-1.

The biaxially oriented film thus obtained was slit to a predetermined width and then a magnetic coating solution having the following composition was applied to a thickness of 2 μm. At that time, the running tension was 10 kg / cm ² .

(Magnetic coating liquid) γ-Fe ₂ O ₃ 200 parts by weight Vinyl chloride-vinyl acetate copolymer resin (VAGH manufactured by UCC) 30 parts by weight Polyurethane (PP-88 manufactured by Nippon Polyurethane Industry Co., Ltd.) 20 parts by weight Isocyanate compound (Japan Polyurethane Industry Co., Ltd. Coronate HL) 40 parts by weight carbon (average size 0.5 μφ) 20 parts by weight Dimethylsiloxane 2 parts by weight Toluene 70 parts by weight Methyl ethyl ketone 70 parts by weight Cyclohexanone 70 parts by weight The above coating composition was sufficiently mixed and stirred for coating treatment.

Then, the coated surface was subjected to calendar roll treatment. Then, it was punched into a magnetic recording flexible disk having an outer diameter of 13 cm and an inner diameter (central hole) of 2.8 cm.

The disc thus obtained was placed in a recording / reproducing apparatus to perform a recording / reproducing operation. At that time, the sheet recorder was rotated at 300 rpm, and the position of the magnetic head was 6 cm from the center of the desk. The width of the track was 300 μ, and the material of the head was ferrite. A signal of 1F was recorded on the magnetic recording flexible disk under a predetermined condition and was reproduced under a predetermined condition, and the difference in output envelope was measured. Recording on this magnetic recording flexible disk was performed under the conditions of 15 ° C. and 60% RH and two levels of 25 ° C. and 20% RH, and the reproduction envelope of the obtained disk was 0.2 dB or less under each recording condition. It was

Further, the magnetic recording flexible disk was subjected to a temperature / humidity expansion coefficient and a track shift test, and the results are shown in Table-1.

As is clear from the results shown in Table 1, those having a coefficient of thermal expansion and an internal residual strain within the specified ranges were as shown in Examples 1 to 6,
The rounding error of the central hole is good because the tracking mistakes are improved and the internal residual strain is small, and the edge of the central hole is not bent, damaged, or made into a high-edge structure, which is excellent. .

On the other hand, in Comparative Examples 1 to 4, tracking mistakes occurred, internal residual strain was large, and the circularity of the central hole was poor. Further, in Comparative Examples 2 and 4, the module after the thermal history is increased.

As described above, it is understood that the disk of the present invention has a high industrial value as a flexible disk having a high track density.

Claims (1)

[Claims] 1. A magnetic recording flexible disk having a magnetic layer provided on a polyester film, wherein the internal residual strain of the film is within 0.02%, and the thermal expansion coefficient of the disk is in-plane anisotropy. Is a magnetic recording flexible disk with a track density of 96 tracks / inch or more, which is within 6 × 10 ^-6 / ° C.