JPH0624061B2 - Micro floppy disk - Google Patents

Description

The present invention relates to a micro floppy disc, and more particularly to a micro floppy disc improved to withstand use in a high temperature atmosphere.

[Conventional technology]

In recent years, it has become general to use a floppy disk drive device as an external storage device of a personal computer or a word processor and a floppy disk as a magnetic recording medium thereof. Further, miniaturization of the floppy disk has been attempted in order to systematize these devices and make them portable, and efforts have been made to expand the range of environmental conditions that can be used.

As a non-magnetic substrate for these magnetic recording media, biaxially oriented polyethylene terephthalate (hereinafter abbreviated as PET).
The film is used. As a Floppy disk to be miniaturized, the Micro Floppy disk that stores a magnetic recording medium with an outer diameter of 3.5 inches in a cartridge case is easy to carry because dust does not easily adhere,
It has the effect of expanding the usage environment in terms of heat resistance and humidity resistance, and can design the storage capacity to be almost equal to that of the conventional 51/4 inch floppy disk, which maintains software compatibility. Promising because of its promise.

However, it is necessary to increase the linear density and the track density in order to reduce the size of the floppy disk to a diameter of 3.5 inches and increase the storage capacity to be equal to or higher than that of the 51/4 inch floppy disk. In order to increase the linear density, it is necessary to increase not only the coercive force of the magnetic layer but also the rotation speed of the magnetic recording medium. However, when the PET film is used as a non-magnetic substrate, the Young's modulus is low and the Frotpie disk (magnetic recording medium) causes a flatter ring as the number of revolutions increases, and contact with the magnetic head under certain conditions cannot be maintained. There was a problem that caused a recording error and a reproduction error. In order to increase the track density, the coefficient of thermal expansion (hereinafter abbreviated as αt) of the magnetic recording medium is set to the floppy disk drive device (hereinafter FDD).
(Hereinafter abbreviated as)), further improvement has been made to further reduce the direction difference of αt in the plane. In addition, even if these αt are improved at the time of use at a high temperature, there is a problem that permanent shrinkage occurs due to a large heat shrinkage rate, resulting in a recording error or a reproducing error.

Further, in JP-A-59-127730, it is proposed to use a biaxially oriented polyethylene naphthalate film having "low anisotropy" as a substrate of a magnetic recording medium, though it is suitable as a magnetic tape, When used as a floppy disc, there is no consideration for downsizing, and the Young's modulus is too high.As a result, wear due to contact with the magnetic head is generated in the magnetic layer, and the heat shrinkage rate of the substrate is 2.5 to 3.5%. Since it is very large, the thermal deformation easily becomes permanent strain, and there is a problem that adaptability as a micro floppy disc is not recognized.

[Object of the Invention]

An object of the present invention is to solve the above problems and to provide a small-sized magnetic recording medium which has a large storage capacity and can be used even in a high temperature atmosphere of 60 to 70 ° C. when used as a micro floppy disc. .

[Structure of Invention]

The present invention has a heat shrinkage rate of 0.05% or less when heated at 70 ° C. for 1 hour and a heat shrinkage rate when heated at 150 ° C. for 1 hour in the range of 0.1 to 1.5% in all in-plane directions. And a biaxially oriented polyethylene naphthalate film having a Young's modulus in the range of 600 to 750 kg / mm ² as a non-magnetic substrate, and a magnetic layer is provided on one or both surfaces of the substrate. At the same time, it is a micro floppy disc with an outer diameter of 90 mm or less.

The polyethylene naphthalate in the present invention is polyethylene-2,6-naphthalenedicarboxylate itself or a polymer, copolymer or mixture containing 70% by weight or more of polyethylene-2,6-naphthalenedicarboxylate, The polyester composition essentially does not impair the properties of polyethylene-2,6-naphthalenedicarboxylate.

The surface roughness of the polyethylene naphthalate (hereinafter abbreviated as PEN) film is preferably 0.012 μm or less as measured by the centerline average method, and the inert solid particles are PEN. It may be formed by being contained in the polymer, or may be formed by another surface treatment.

In the present invention, the inert solid fine particles are preferably silicon dioxide (including hydrate, diatomaceous earth, silica sand, quartz, etc.); alumina; silicate containing 30% by weight or more of SiO ₂ ( For example, amorphous or crystalline clay minerals,
Aluminosilicate (including calcined products and hydrates), warm asbestos, zircon, fly ash, etc.); Ng, Zn, Zr and Ti
Oxides; Ca and Ba sulfates; Li, Na, and Ca phosphates (including monohydrogen and dihydrogen salts); Li, Na, and K
Benzoate of Ca; Ba, Zn, and Mn terephthalate;
Mg, Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, Co and Ni titanates; Ba and Pb chromates; Carbon (eg carbon black, graphite) etc .; Glass (eg glass powder) , Glass beads, etc.); Ca and Mg carbonates; fluorspar and ZnS. More preferably, silicic acid anhydride, hydrous silicic acid, aluminum oxide, aluminum silicate (including calcined products and hydrates), 1 lithium phosphate, 3 lithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, titanium oxide, Examples include lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay etc.), talc, diatomaceous earth, calcium carbonate and the like. Particularly preferably,
Examples include silicon dioxide, titanium oxide, and calcium carbonate. These inert solid fine particles have an average particle size of 0.05 to 0.
6 μm, more preferably 0.08 to 0.4 μm, and the addition amount is 0.01 to 1.5% by weight (relative to polyester), further 0.03
It is preferably from 1.0 to 1.0% by weight, particularly from 0.05 to 0.6% by weight.

If the surface roughness (Ra) of the film exceeds 0.012 μm, the surface of the magnetic surface cannot maintain the electromagnetic conversion characteristics required for a high-quality Flotpies disk, which is not preferable. The preferable surface roughness (Ra) is 0.010 μm or less.

The PEN film as the non-magnetic substrate of the present invention needs to have a heat shrinkage rate of 0.05% or less when heated at 70 ° C. for 1 hour, and particularly preferably 0.03% or less.

If the heat shrinkage exceeds 0.05%, it is impossible to construct a microdisk magnetic recording medium that can be used in a high temperature atmosphere of 60 ° C. or higher.

Furthermore, the heat shrinkage rate of the PEN film when heated at 150 ° C. for 1 hour must be in the range of 0.1 to 1.5%. It is preferably 0.5 to 1.2%.

If the heat shrinkage ratio exceeds 1.5%, the film shrinks in the processing (running) direction during the process of coating or vapor depositing the magnetic layer on the PEN film, causing anisotropy in the film, and thus the micro floppy disk magnetic field. Not only cannot the outer diameter and inner diameter of a perfect circle be formed as a recording medium, but the surface of the magnetic recording medium is curled, which makes it difficult to increase the rotational speed of the FDD and increase the linear density. Further, if the heat shrinkage ratio is less than 0.1%, the film undergoes thermal expansion in the process of vapor deposition or sputtering of the PEN film, which makes it difficult to form a uniform magnetic layer.

The Young's modulus of the PEN film is 600 to 7
It must be in the range of 50 kg / mm ² . If the Young's modulus is less than 600 kg / mm ² , increasing the FDD rotation speed causes the magnetic recording medium to flutter, failing to maintain uniform contact with the magnetic head, causing recording errors and reproducing errors, making it difficult to increase the linear density. . On the other hand, Young's modulus is 750 kg / mm
^When it exceeds ² , the contact between the magnetic recording medium and the magnetic head becomes too strong and the magnetic layer of the magnetic recording medium is worn.

As the magnetic layer in the present invention, γ-Fe ₂ O ₃ , Co-containing γ-
Fe ₂ O ₃ , fine needle-shaped iron powder or barium ferrite powder may be applied, and Co, Ni, Cr, Fe or their alloys may be formed by plating, vapor deposition or sputtering. It may be a boiled one. Co-containing γ
A magnetic layer for in-plane recording by coating with —Fe ₂ O ₃ or perpendicular recording by sputtering of a Co—Ni alloy is preferable.

As the floppy disc, a micro floppy disc of 90 mm or less is targeted. The 51/4 inch and 8 inch disks over 90 mm are inserted in a vinyl chloride jacket with insufficient heat resistance and are open type, so the effect of expanding the usage environment cannot be expected.

The PEN film used in the present invention has αt of 30.
It is preferably × 10 ^-6 / ° C or less. The iron and aluminum that compose the FDD have an αt of about 25 to 30 × 10 ^-6.
/ ° C, and αt is 30 × depending on the combination and structure of the constituent villages.
Easy to design below 10 ^-6 / ° C, but αt is 30 × 10
^{Above -6} / ° C, it becomes difficult to design a precise and robust structure.

Further, it is preferable that the difference in αt is 5 × 10 ⁻⁶ / ° C. or less in all directions of the PEN film. That is, α
If the difference between the maximum value and the minimum value of t is 5 × 10 ⁻⁶ / ° C. or more, a track difference occurs when the temperature difference between recording and reproducing is large, and it becomes difficult to increase the track density.
It is necessary to incorporate an expensive servo mechanism into the DD,
It becomes difficult to design a small FDD corresponding to the micro floppy disk.

As a method for biaxially orienting the PEN film, known sequential biaxial stretching or simultaneous biaxial stretching can be applied. At that time, stretched 3.5 to 4.5 times in the longitudinal direction at a temperature of 115 to 150 ° C.,
Also, it is stretched 3.5 to 5.0 times in the transverse direction at a temperature of 120 to 180 ° C, then heat set at 200 to 250 ° C, and further contracted 3 to 10% in the transverse direction at a temperature of 160 to 230 ° C, followed by 20 ° C. It is preferable to cool to 70 ° C or lower. Furthermore, the biaxially oriented film is 120 to 1
It is relaxed by 0.1 to 3% in the longitudinal direction while being heated to a temperature of 70 ° C and then cooled to 70 ° C or less, or a roll wound with a biaxially oriented film is heated at a temperature of 50 to 90 ° C for 1 to 10 ° C. It may be aged for days. Also, the difference in αt is 5 × 10 ⁻⁶ / ° C. or less P
In order to obtain the EN film, the central portion of the film which is sequentially biaxially stretched may be adopted, or a wide range of materials may be sampled by simultaneously biaxially stretching the film. It is also possible to use the one obtained by re-heat treatment.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The present invention is a biaxially oriented PE having a low thermal shrinkage of 0.05% or less when heated at 70 ° C. for 1 hour in all in-plane directions.
Since N film is used, there is little reversible thermal deformation even when used from room temperature to high temperature environment, there is virtually no permanent distortion of thermal deformation, and Young's modulus is high even when rotated at high speed. Since the PEN film of 600 to 750 kg / mm ² is used, uniform contact with the magnetic head can be maintained, so 60 to 7
It is possible to provide a micro-floppy magnetic recording medium having a large storage capacity and having a high linear density and a high track density even in a high temperature atmosphere of 0 ° C.

Moreover, the heat shrinkage rate when heated at 150 ° C. for 1 hour is 0.1 to
It is in the range of 1.5%, and even if a magnetic layer is formed, a flat and perfect circular micro-floppy magnetic recording medium can be obtained.

Furthermore, as a non-magnetic substrate, αt is less than 30 × 10 ^-6 / ° C.
By setting the difference in t to 5 × 10 ⁻⁶ / ° C. or less, the reversible difference in thermal deformation can be brought close to substantially 0. It can be made as large as or larger than the 8 inch or 51/4 inch floppy disk that is the product.

〔Example〕

A part of the embodiments of the present invention will be described below based on examples.

Incidentally, various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Shrinkage (70 ° C. × 1 hr) Measured in a constant temperature and humidity chamber without tension at 70 ° C. and 65% RH for 1 hour. When the original length is lo and the measured length is l, it is expressed as [(lo-l) / lo] × 100 (%).

(2) Shrinkage rate (150 ° C x 1 hr) Measured by leaving it at 150 ° C for 1 hour in a tension-free state with a gear aging tester. When the original length is lo and the measured length is l, it is expressed as [(lo-l) / lo] × 100 (%).

With respect to items (1) and (2), the film forming running direction was set to 0 ° in the in-plane of the non-magnetic substrate film, and measurements were taken in the directions of 45 °, 90 ° and 135 ° as required.

(3) Temperature expansion coefficient A thermomechanical analyzer TM-3000 manufactured by Vacuum Riko Co., Ltd. is placed in a constant temperature and humidity chamber for measurement. The measurement sample is previously heat-treated under predetermined conditions (for example, 80 ° C., 120 minutes), and this sample is mounted on a tester at a temperature of 20 ° C. and a humidity of 60% RH (relative humidity) and a temperature of 40 ° C. and a humidity of 60% RH. The coefficient of thermal expansion is measured by reading the dimensional change between.

The size of the sample is 15 mm in length and 5 mm in width, and the biaxially oriented film is run in the film forming direction, then 45 ° in the counterclockwise direction by 45 °.
A sample up to 35 ° is cut out and the temperature expansion coefficient αt is obtained for each angle θ.

(4) Young's modulus The film is cut into a sample width of 10 mm and a length of 15 cm, and the space between the chucks is set to 100 mm, the tensile speed is 10 mm / min, and the chat speed is 5
It was pulled at 00 mm / min with an Instron type universal tensile tester. The Young's modulus was calculated from the tangent line of the rising portion of the obtained load-elongation curve.

(5) Dropout 3.5 inch FDDJU-36 manufactured by Matsushita Communication Industrial Co., Ltd.
No. 2 was modified to 600 rpm and placed in a constant temperature and humidity chamber, and connected to a drop-in drop-out counter SK-444B manufactured by Tokyo Engineering Co., Ltd. via an interface to measure a mixing pulse.

First, at 25 ° C and 50% RH, write frequency 250KHz, 600rp
The m signal is recorded on the DO track, and the atmosphere in the constant temperature and humidity chamber is changed to 70 ° C and 50% RH, and the reproduction output is 50% or less or 3
The presence or absence of a mixing pulse of 0% or less was measured. The case where there is no mixing pulse of 50% or less is good, the case where there is no mixing pulse of 30% or less but the mixing pulse of 50% or less is acceptable, and the case where there is a mixing pulse of 30% or less is not acceptable. .

Further, in order to further see the effect of the temperature expansion coefficient, the above recording was performed at 5 ° C./10% RH and the reproduction was performed at 60 ° C./10% RH, and the mixing pulse was similarly measured.

Example 1 A pellet of polyethylene 2.6 naphthalene dicarboxylate having an intrinsic viscosity of 0.68 and containing 0.2% by weight of titanium oxide having an average particle diameter of 0.25 μm was dried at 170 ° C. for 5 hours.
This pellet is melt extruded by a T-tie according to a conventional method to prepare an unstretched film having a thickness of 1080 μm,
Biaxial stretching was sequentially performed at 135 ° C in the longitudinal direction at 3.7 times and at 140 ° C in the lateral direction at 3.9 times, and heat setting was further performed at 230 ° C for 30 seconds to prepare a PEN film having a surface roughness of 0.006 µm and a thickness of 75 µm. Table 1 shows various characteristics of the film in each direction.

The biaxially oriented film thus obtained was coated with a magnetic coating liquid having the following composition to a thickness of 2.0 μm.

(Magnetic coating liquid) γ-Fe ₂ O ₃ (containing 20% Co) 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 (Coronate HL manufactured by Nippon Polyurethane Industry Co., Ltd.) 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 is sufficiently mixed and stirred to apply the coating treatment. I went to

Then, the coated surface was subjected to calendar roll treatment. After this, punch out on a flexible disk with an outer diameter of 88.9 mm, and test F
Insert in DD, atmosphere 25 ℃, 50% RH to 70 ℃, 5
The mixing pulse when changing to 0% RH was measured. The presence or absence of a mixing pulse at that time is shown in Table 1.
% Or less mixing pulse was not generated, which was good. Also, the flexible disk surface after the evaluation was observed,
It was good without wear marks.

Example 2 and Comparative Examples 1 to 4 In Example 1, the results are shown in Table 1 when the heat setting temperature was 210 ° C. as Example 2 and 190 ° C. as Comparative Example 1.

Next, in Example 1, the case where the unstretched thickness is 1320 μm and the length × width is stretched 4.1 × 4.3 times is set as Comparative Example 2, and then the PEN film of Comparative Example 1 is rolled at 230 ° C. for 30 seconds in the vertical direction. Table 1 shows Comparative Example 3 in which the relaxation heat treatment was added.

Further, Table 1 shows Comparative Example 4 in which a polyethylene terephthalate pellet having an intrinsic viscosity of 0.65 is used in Example 1.

The results were not satisfactory except for Example 2.

Example 3 The case of using a known stenter for transverse stretching and heat setting in Example 1 is shown in Table 2 as Example 3, but the atmosphere was changed from 5 ° C., 10% RH to 60 ° C., 10% RH. The measurement result of the dropout counter when changed was that there was no mixing pulse with a reproduction output of 30% or less and it was usable.

Example 4 The heat setting temperature in Example 3 was set to 190 ° C., and the PEN film once wound was set to a heat setting temperature of 23 with a stenter.
The results of reheat treatment at 0 ° C for 30 seconds are shown in Example 4-
As shown in FIG. 2, there was no mixing pulse with a reproduction output of 50% or less, which was very good.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junji Kobayashi 3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture Teijin Limited Plastics Laboratory (72) Inventor Tomoyuki Nakamura 3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture Teijin Limited Plastics Research Center

Claims (2)

[Claims] 1. A magnetic recording medium comprising a biaxially oriented polyethylene naphthalate film as a non-magnetic substrate, and a magnetic layer provided on at least one surface of the substrate, wherein the film as the substrate is in any direction within the plane. When heated at 70 ℃ for 1 hour, the heat shrinkage rate is 0.05% or less.
A micro-structure comprising a magnetic recording medium having a diameter of 90 mm or less, characterized by having a heat shrinkage of 0.1 to 1.5% when heated for 1 hour and a Young's modulus of 600 to 750 kg / mm ^2. Flotpies disk. 2. The coefficient of thermal expansion in all directions in the plane is 30 × 10 ⁻⁶ / ° C. or less, and the difference between the coefficient of thermal expansion showing the maximum value and the coefficient of thermal expansion showing the minimum value is 5 × 10 ^−6. /
The microfloppy disk according to claim 1, wherein a biaxially oriented film having a temperature of ℃ or less is used as a non-magnetic substrate.