JPS6080125A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a floppy disk which is dimensionally stable to the change of temp. and humidity by laminating a high polymer film having specified surface roughness on both surfaces of a specified biaxially oriented poly-p-phenylene sulfide (PPS) film. CONSTITUTION:The PPS contg. >=70mol% repeating unit shown by the formula and <=10mol% methaphenylene sulfide and diphenyl ether is biaxially oriented to manufacture a film having <=0.04 birefringence, <=2.8X10<-5> deg.C<-1> thermal expansion coefficient at 25 deg.C in the direction of the main orientation axis, 0.001-0.3mu mean surface roughness on both surfaces, and <=0.5 projection/cm<2> coarse projection density. A biaxially oriented high polymer film such as polyethylene terephthalate having >=100 particle/mm.<2> particle density and <=5mu thickness which is <=50% of the PPS film thickness is laminated on both surfaces of said film. A magnetic layer is provided on the laminated film to obtain the floppy disk having less dropouts and high-density tracks which is dimensionally stable to the change of temp. and humidity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetic recording medium, and more particularly to a flexible magnetic disk.

[Prior art]

Flexible magnetic disks (commonly called ``floppy disks''), which are often used as auxiliary storage devices in small computers, are a representative example of this. However, recently, in order to increase the recording capacity, there has been a strong emphasis on increasing the trunk density (the number of tracks per unit length in the radial direction of the disk) (that is, decreasing the trunk width).

Conventional floppy disks use a biaxially oriented polyethylene terephthalate film (hereinafter referred to as PET film) as a base film.

Those with magnetic layers on one side or both sides are widely used.

Further, the use of a biaxially oriented polyP-phenylene sulfide film (hereinafter referred to as PPS film) as a base film for magnetic recording media has been disclosed in Japanese Patent Application Laid-Open No. 55-5531. 3861
It has been proposed in the 3rd prize.

However, conventional floppy disks using PET film.

■ Dimensional changes due to changes in humidity are extremely large.

■ The coefficient of thermal expansion has large in-plane anisotropy, and when the temperature changes, the dimensional change differs depending on the direction of the disk.

■ If left under high temperature and high humidity for a long period of time, permanent shrinkage will be significant.

If the track width is narrowed for reasons such as this, the relative position of the recording/playback head (hereinafter referred to as the head) of the recording/reproducing device (hereinafter referred to as the drive) and the track on the disk may shift due to changes in the environment, causing the L-rack to become narrower. Since the recorded signal cannot be reproduced (so-called "off-track" occurs), it has been impossible to increase the track density.

On the other hand, a floppy disk using a conventional PPS film as a base film has desirable characteristics in that dimensional changes due to changes in humidity and permanent shrinkage under high temperature and high humidity are both small.

- The anisotropy of the coefficient of thermal expansion is greater than that of PET film, and it will off-track even at a track density comparable to that of a PET film-based floppy disk.

■ Signal dropouts are likely to occur because many rough protrusions are formed on the surface of the disc due to the surface condition of the base film.

It had the following drawbacks and was impractical.

[Purpose of the invention]

It is an object of the present invention to be able to record at high track densities (i.e. recording capacity The objective is to provide a large magnetic recording medium.

[Structure of the invention]

The magnetic recording medium of the present invention has a repeating unit with a mole ratio of 70 or more expressed by the structural formula B→-8+, a birefringence of 0.04 or less, and a layer on both sides of the layer at 25° C. in the direction of the main orientation axis. , a magnetic recording medium having a magnetic layer on at least one side of a base film laminated with surface layers made of polymer films each having a thickness of 5 μm or more and 50% or less of the thickness of the center layer.

The particle density of the above polymer film is 100 particles/ml112
The magnetic recording medium described below is characterized in that the average surface roughness and coarse protrusion density of the base film are 0.001 to 0.03 μm and 05 pieces/C1112 or less, respectively.

In the present invention, the center layer is located approximately at the center of the base film and is made of a biaxially oriented polyP-phenylene sulfide film. Refers to the flexible layer that forms the main body of the base film.

Poly P-phenylene sulfide (hereinafter referred to as “
(referred to as P
Refers to those containing 0 molar proportion or more. If the number of such para-bonded phenylene sulfide units is less than 70 moles, the crystallinity of the polymer will decrease, so floppy disks using a film made of such a polymer as a base film will not shrink when used at high temperatures or during storage. This is undesirable as it tends to cause permanent deformation. The remaining 60 molar units or less of the repeating units of the polymer are metafe unit ((◇-o 0), sulfone unit ((■-5O
2(◇-), Hyphenyl unit <% s-),
Naphthyl Uniha (Jikunya s=).

Substituted phenyl sulfide unit (+8-) (herein, R represents an alkyltro group having 1 to 10 carbon atoms, a phenyl group, or an alkoxy group having 1 to 10 carbon atoms -J-), trifunctional phenyl sulfide unit The copolymerization component is preferably 10 molar or less.

The characteristic melt viscosity of PPS in the present invention is at a temperature of 300°C.
, under conditions of an apparent shear rate of 200 esc-'.

500 to 12,000 poise (more preferably 7'00 poise)
~7000 poise) is preferable from the viewpoints of film formability, surface smoothness, etc.

A biaxially oriented pps film is a film obtained by melt-molding the above pps to form a sheet, biaxially stretching it, and heat-treating it, and its thickness ranges from 10 to 100 μm (more preferably from 10 to 70 μm). preferable.

The birefringence of the biaxially oriented PPS film must be 0.04 or less (preferably 0.06 or less).

If the birefringence exceeds 0.04, off-track is likely to occur due to temperature changes, making it impossible to achieve the second object of the present invention.

In addition, the biaxially oriented PPS film has two directions in the main orientation axis direction.
Thermal expansion coefficient (α11) at 5℃ is 28×10-5℃
-1 or less (preferably 2.4 x 10-5°C or less). If the coefficient of thermal expansion is too large, the final floppy disk will be

Off-track is more likely to occur due to temperature changes.

Average surface roughness of the biaxially oriented PPS film.

0001 to 0.03 μm (more preferably) on both sides.

The thickness is preferably in the range of 0.003 to 0.02 μm).

In addition, the density of coarse protrusions was 3.0 pieces/cm2 or less on both sides.

(preferably 20 pieces/cm2 or less).

In the present invention, the 9 surface layers are layers that are located on both sides of the center layer and form the surface of the base film before the magnetic layer is applied.

The thickness of each of the surface layers must be at least 5 μm and at most 50 times (preferably at most 60%) the thickness of the center layer. A surface layer that is too thin will increase dropout due to the surface condition of the center layer, while a surface layer that is too thick will be susceptible to off-track due to environmental changes.

The average surface roughness Ra of the outer surface of the surface layer is 0.001 to 0.
．． 03 μm (preferably 0.001-0.02 μm
) must be within the range. If Ra is too small, one surface layer may be used alone or in layers to form a base film.

The surface becomes easily scratched, which causes dropouts. On the other hand, if Ra is too large, the electromagnetic conversion characteristics of the disk will be impaired. The "outer surface" herein refers to the surface that becomes the surface of the base film after lamination.

Furthermore, the particle density of the surface layer is 100 particles/=2 or less (
(preferably 30 pieces/mm2 or less).

If the particle density is too thick, no matter how the method of laminating the center layer and surface layer is devised, coarse protrusions in the base film will increase and dropouts will increase.

The average in-plane coefficient of thermal expansion of the surface layer is 3.0x10°C.
The following is desirable.

The polymer film forming the surface layer is not particularly limited, but examples thereof include PET film, wholly aromatic polyamide film, wholly aromatic polyimide film, and polyethylene 2.6 naphthalate film.

Examples include polyethylene α, β bis(2-chlorophenoxy)ethane 4.4 dicarboxylate film, and preferably biaxially oriented PET film, biaxially oriented polyethylene 2.6 naphthalate film, and dicarboxylate film. Preferably, it is a polyester film such as an axially oriented polyethylene alpha, beta bis(2-chlorophenoxy)ethane 4,4' dicarboxylate film.

From the viewpoint of disk curling, it is desirable that the two surface layers located on both sides of the center layer have substantially the same composition.

Here, "substantially the same" means that the difference in copolymer composition, blend composition, etc. is about 5 factors or less, and the presence or absence or amount of organic and/or inorganic additives, etc. It does not matter if a difference exists between both surface layers.

Further, from the viewpoint of disk curling, it is desirable that the thicknesses of the two surface layers be substantially equal to each other. here,"
"Almost equal" means that the difference in thickness between the two surface layers is about 20 Lf) or less, which is the arithmetic mean thickness of the two surface layers.

The base film in the present invention is a flexible support on which a magnetic layer is provided, and is composed of a center layer made of the above-mentioned biaxially oriented PPS film and surface layers laminated on both sides of the center layer.

The thickness of the base film is preferably in the range of 20 to 150 μm (more preferably 20 to 100 μm) in terms of shape retention as a floppy disk, head touch, etc.

between the center layer and the surface layer of the base film.

For the purpose of fixing both layers to each other, an adhesive layer (thickness 1 to 5 μm
m) may be interposed.

The coarse protrusion density Pd of the base film is 05 on both sides of 9.
It must be less than 06 pieces/cm2 (preferably less than 06 pieces/cm2). A floppy disk made of such a base film with a high protrusion density has a high frequency of dropouts, making it impossible to achieve the two objects of the present invention.

Furthermore, the dimensional stability index Ds of the base film.

5.2 x I D-' or less (preferably 4.Ox
10-' or less), the floppy disk will have a higher track density.

The product of the present invention has a magnetic recording layer on one or both sides of the base film, and a polymer is added between the base film and the magnetic layer for the purpose of improving dimensional stability and adhesion of the magnetic recording layer. There is no problem in interposing an intermediate layer made of metal or the like, or providing a protective layer on the magnetic layer for the purpose of improving durability. The magnetic recording medium of the present invention can be used for tapes, floppy disks, etc., but it is preferable to use it as a floppy disk. In the case of a floppy disk, it is generally placed in a case called a "jacket". is used, but is not particularly limited to this.

The magnetic layer in the present invention includes + (1) Fe2O,
Ferromagnetic fine powder such as lFe3O4, Cry□, Fe, Ni, Go, etc. is coated on a base film together with an organic binder (hereinafter referred to as "coated type"); (2) Methods such as plating, vapor deposition, and sputtering. However, in the case of a metal thin film type, it is preferable to provide the above-mentioned intermediate layer and protective layer. More preferred.

The thickness of the magnetic recording layer is 0.2 to 0.02 in the case of coating type.
5 μm, and in the case of metal thin film type, the range of 0.05 to 2 μm is the magnetic recording property and dimensional stability of the disk.

This is preferable in terms of head touch, etc.

Further, there are two types of magnetization of the magnetic layer: horizontal magnetization and perpendicular magnetization, and the present invention is applicable to both of them.

Next, a method for manufacturing a magnetic recording medium, particularly a floppy disk, according to the present invention will be described.

First, as a method for polymerizing PPS used in the present invention, a method is used in which alkali sulfide and P dino-lobenzene are reacted in a polar solvent at high temperature and high pressure. In particular, it is preferable to react sodium sulfide and P-dichlorobenzene in an amide-based high-boiling polar solvent such as N-methyl-pyrrolidone. In this case, in order to adjust the degree of double polymerization, a so-called polymerization aid such as a caustic alkali or an alkali metal carboxylic acid salt is added.

Most preferably, the reaction is carried out between 250'C and 280C.

The pressure within the polymerization system and the polymerization time are appropriately determined depending on the type and amount of the auxiliary agent used, the desired degree of polymerization, and the like.

The PPS thus obtained is supplied to a well-known melt extrusion device such as an extruder and melted.

At any stage before the melt extrusion process, for the purpose of adjusting the surface roughness of the film, an average primary particle size of 5.
It is preferable to uniformly disperse fine particles of ~300 nm (more preferably 6~10100 nm).

The molten resin is continuously extruded from a so-called T-die, cast onto a cooled metal drum, and rapidly solidified to form an unoriented amorphous sheet.

The surface of the metal drum is preferably finished into a mirror surface with a roughness of about 0.4S or less.

Also for melting films on metal drums.

Preferably, a positive or negative electrostatic charge is applied to bring the film into close contact with the drum.

Next, the sheet thus obtained is biaxially stretched.

Conventionally, various methods have been known for stretching plastic films, such as sequential biaxial stretching and simultaneous biaxial stretching.
pps used as the center layer of the base film of the product of the present invention
In order to stably obtain a film, the sheet is rapidly stretched in the longitudinal direction by a group of rolls, and then stretched in the width direction by a tenter. A so-called longitudinal and transverse sequential biaxial stretching method is used.

Like the simultaneous biaxial stretching method and the horizontal and vertical sequential biaxial stretching method.

In the first stretching method using a tenter, not only the physical properties of the film become different and non-uniform between the center and the edges, but even the center part does not meet the above-mentioned properties required for the pps film used in the product of the present invention. I can't satisfy you.

Stretching in the longitudinal direction (longitudinal stretching) is performed by rapid stretching between two rolls having different circumferential speeds, and the film temperature immediately before stretching is in the range of 95 to 105°C.

and the temperature difference in the middle direction (of the part that will be later effectively stretched laterally)
(difference between maximum and minimum temperature) should be 3°C or less.

The stretching speed should still be 30,000% or more than 7 min. If the temperature difference in the middle direction is large or the stretching speed is slow, not only will the obtained biaxially stretched film lack uniformity in thickness, but also it will not be possible to obtain an in-plane coefficient of thermal expansion. The stretching ratio is determined as follows. That is, the magnification is selected so that the degree of optical orientation immediately before lateral stretching is in the range of 0.145 to 0.165.

The term "immediately before transverse stretching" as used herein does not necessarily mean immediately after the end of longitudinal stretching. For example, if the tenter has a preheating section for transverse stretching.

This means immediately after preheating. In any case, it refers to the state immediately before the film is stretched in the width direction.

The actual magnification varies depending on the stretching temperature and the degree of polymerization of the polymer, but is approximately in the range of 6.9 to 4.9 times.

In addition, the density of the film immediately before horizontal stretching was set to 1°617 to 1
．． The longitudinal stretching temperature (1x) and the preheating conditions for the transverse stretching are selected so as to be in the range of 330°C. If the density is too low, it will be difficult to stretch the film to a uniform thickness.

If it is too large, the film will have a large anisotropy of thermal expansion coefficient.

The longitudinally-axially stretched film whose degree of orientation has been accurately controlled in this way is stretched horizontally nine times using a tenter. The stretching temperature was 95 to 110°C, and the stretching speed V was.

When the stretching temperature is T°C, at least V=40T-
3200 [unit H%/m1n3 or more].

If the stretching temperature is too low or too high, the film will tear during stretching. The same applies when the stretching speed is slow. The stretching ratio is selected in the range of 6.5 to 6.9 times.

Next, the stretched film thus obtained is subjected to fixed length heat treatment. Such heat treatment is usually carried out by providing a heat treatment chamber after the stretching chamber in the same tenter as that used for stretching.

Another tenter or a heating roll may be used. In either case, the heat treatment must be carried out over a constant length in both the longitudinal and width directions. The constant length mentioned here means that the change in width and length during heat treatment is 1 inch or less. The heat treatment temperature is 200-250°C (more preferably 210-250°C
After heat treatment for a selected length in the range of 40° C.), it is permissible to relax by a few percent or less in the longitudinal direction and/or width direction at a temperature below the heat treatment temperature.

Note that controlling the birefringence to 0.04 or less can be easily done by finely adjusting the transverse stretching ratio as long as the film immediately before transverse stretching satisfies the above-mentioned conditions. It is difficult if the condition ゛ is not met.

The thermal expansion coefficient in the direction of the main orientation axis is 2.8 x 10-"c-' or less, provided that the above-mentioned manufacturing conditions are satisfied.

The PPS film thus obtained is used as the middle upper layer of the base film.

Next, a method for preparing the surface layer will be described.

The particle density and average surface roughness of the polymer film forming the surface layer are each 100 particles/m [02 or less, l:1. o[1
The method for adjusting the diameter to 1 to 0.05 μm varies depending on the type of polymer, so it cannot be generalized, but in general.

0.01 inorganic powder consisting of fine particles with a primary particle size of 5 to 10 Dnm that does not produce inorganic or organic foreign matter, gel, etc. during polymerization.
~Q, by adding 5 wt% and uniformly dispersing it.

For example, in the case of PET, monopolymerization occurs in the process of (1) polycondensation by extending direct esterification of terephthalic acid and ethylene glycol, or (2) polycondensation through transesterification of dimethyl terephthalate and ethylene glycol. Phosphoric acid and antimony trioxide are used as catalysts, and before polymerization, a slurry of silicon oxide fine powder with an average primary particle size of 10 to 50 nm uniformly dispersed in water or ethylene glycol is added from outside the system. PET can be used to form the surface layer used in the present invention.

Biaxially oriented P, which is more desirable as a surface layer used in the present invention
To obtain an ET film, etc., first heat and melt PET etc. above its melting point, extrude it into a sheet, rapidly cool it to make an amorphous unstretched sheet, and then lower the glass transition point to
A method is used in which the film is stretched 6 to 5 times in the longitudinal direction and the width direction at a temperature of 'rg + 30°C, and further heat-treated at 180 to 250°C.

Next, one surface layer is laminated on both sides of the center layer.

The common method for laminating the surface layer is to bond the separately prepared center layer and surface layer together using an adhesive.
A method of coextruding a surface layer composition during the production of a pps film (center layer), a method of extrusion lamination on a PPS film (including cases where it is carried out unstretched or after -axial stretching), a method of coating a pps film, etc. It can be argued that one surface layer is formed by this.

In order to keep the coarse protrusion density on the film surface after lamination (i.e., the surface of the base film) to 0.5 pieces/cJn2 or less, it goes without saying that the average surface roughness and particle density of the surface layer used should be within the above range. However, in general, this alone is insufficient, and a method must be taken to keep the coarse protrusion density below the above value depending on the method of laminating one surface layer. For example, when bonding the surface layer and center layer together using an adhesive, 1. Filter the adhesive through a filter.

After that, make sure that no foreign matter gets mixed in from the outside.

■The processes of applying adhesive, drying, and bonding should be carried out in a clean environment. ■The press rolls used for bonding and other rolls that come into direct contact with the surface of the base film should be sufficiently smooth.

Next, a method for forming the magnetic layer will be explained.

As already mentioned, in the present invention, the magnetic layer formed on the base film may be either a coated type or a metal thin film type, but the method for manufacturing a coated type disk will be described here as an example.

Coating-type discs are manufactured by applying a magnetic paint containing magnetic powder dispersed in a solution of a polymeric binder to a base film, drying it, and punching it out into a disc shape.

The composition of the binder used does not need to be particularly limited, but
A thermosetting type material such as urethane type material is suitable. Such a binder is dissolved in an organic solvent such as methyl isobutyl ketone, ethyl acetate, toluene, or the like. Furthermore, magnetic powder is added to the solution and mixed and dispersed. The type of magnetic powder is not limited, but generally γ-Fe20
．． , CrO2°Fe, Ni, Go, etc. are used. Also suitable is a composite magnetic powder in which cobalt is epitaxially grown on the surface of fine iron powder. The composition of the paint is 60 to 7 parts by weight of magnetic powder per 100 parts by weight of solvent.
0 parts by weight, and about 15 to 40 parts by weight of the binder.

It is also effective to add lubricants such as stearic acid, hardness modifiers such as fine alumina powder, etc. to the paint.

The paint thus obtained is applied to one or both sides of the base film and dried to form a magnetic recording layer having a thickness of 02 to 511 m (more preferably 0 to 3.0 m).

Thereafter, if necessary, the surface is smoothed by calendering, polishing, etc., and then heated to crosslink the coating film.

Next, the sheet-like product thus obtained is punched out into a disk shape, and polished as necessary to give a mirror finish to the surface.

Furthermore, if necessary, the above-mentioned disk is inserted into a protective case called a jacket to obtain a floppy disk.

〔Effect of the invention〕

By having the magnetic recording medium of the present invention configured as described above, the positional stability of the trunk against changes in temperature and humidity is significantly improved, and the output due to the excellent flatness and smoothness of the surface is improved. The magnetic recording medium is capable of achieving high trunk density recording, and as a result, it has a large capacity and is suitable for magnetic recording media for various uses, especially floppy disks.

The following nine were used in the description of the present invention. Polymer.

The definition, measurement and evaluation methods of film and floppy disk characteristic values will be explained.

(1) Birefringence nr-nβ Insert the sample film into a polarizing microscope equipped with crossed nicols so that the film surface is perpendicular to the optical axis, and insert the compensator at an azimuth angle of 45 degrees with respect to the analyzer axis. do. continue.

The sample is rotated by one axis of the optical axis, and the phase reduction position is located in the plus or minus 45 direction from the extinction position (the position on the side where the phase difference generated by the sample is reduced by the compensator).
At this time, the optical path difference P caused by the birefringence of the sample is
From the compensation value of the compensator, the birefringence n, -nβ is defined using F/d. (Here d represents the thickness of the sample). At this time, for trial purposes, the direction perpendicular to the rotation axis of the co/pensator is the γ direction (main orientation axis direction) of the sample, and the parallel direction is the β direction.

In the present invention.

Measurement was carried out using a Nippon Kogaku polarizing microscope POH type Leitz universal stage Leitz compensator using a single monochromatic light beam having a wavelength of 05896.

[Cut out a section with a thickness of 70-200 mm and a width of 10 mm from the sample (base film or floppy disk) for measuring the coefficient of thermal expansion at 2125°C.2. It was placed in a constant temperature and humidity chamber without any load, and the temperature was raised from 18°C to 35°C at a rate of 1°C/min at a constant humidity of 35% RH, and then returned to 18°C.

Next, this sample piece was placed in a tension measuring device with a constant tension and minute displacement side (manufactured by Japan Automatic Control) in a constant temperature and humidity chamber at a tension of 1.
0 [! ; 7mm2. Initial length. Set it with

The temperature was raised from 18°C to 65°C with constant tension and constant humidity (35% RH). At this time, displacement meter output X1 at 20°C and 30°C. and X2, (X2-X
, ) converted to the change in sample length is Δ/? , then.

The coefficient of thermal expansion at 25° C. in the longitudinal direction of the sample is defined by the formula “−”a/ (10x j'.).

(3) Particle Density The sample (surface layer on one side of the base film) is observed under transmitted light using a phase contrast microscope, and the number of particles with a particle diameter of 10 μm or more is counted and expressed as the number per 2 plates per area. The measurement conditions are as follows.

Observation magnification: 100 times Count: QTM-20 model Image analyzer (4) Average surface roughness Ra Measurement was carried out by connecting a signal analysis device (all manufactured by Koita Research Institute) to a high-precision thin film step measuring instrument KT-10 model. The measurement conditions are as follows.

Vertical magnification: 100,000 times Lateral magnification: 500 times Measurement length: 4゜Cut-off value: 0.08 m+n (5) Coarse protrusion density Pd The coarse protrusion density is the number of protrusions on the film surface with a height of 116 μm or more per 1 cm2. It is defined as Pd. The measurement method is to push the film onto a smooth glass surface and observe the Newtonian rings that form around the protrusions when monochromatic light (sodium D rays) is irradiated, and calculate the number of protrusions that produce Newtonian rings on vM weight. , 10 on the film
Count over CI1+2.

Convert it to per 1 m2.

(6) Dimensional stability index Ds What is the dimensional stability index Ds in the present invention?

Ds-q+ (I ab 2 x 10-51+Δab
/2)→-q2βb, max here q, = 41.
7°C q2 = 72 coefficient RH (Lb = average coefficient of thermal expansion at 25°C of the base film (°C-”) Δ(1b', thermal expansion anisotropy of the base film at 25°C ('C') βゎ, max 'Maximum humidity expansion coefficient of base film (
%RH').

(7) Average coefficient of thermal expansion of the base film (Ib- Let O be any direction of the base film, and measure the azimuth angle θ clockwise from O.

The thermal expansion coefficients ab1 to aba were each measured by the method (2) above in 8 directions every 225 times from 0 to 1575.

ab=　(Σαゎ,)/8 1=1 Define ib using the formula.

(8) Thermal expansion anisotropy Δαゎ of the base film (6
) is defined as the difference between the maximum value and the minimum value of αb1 to αb8 measured at Δαb.

(9) Humidity expansion coefficient β Cut a section with a length of 70 to 200 mm and a width of 10 mm from the sample, and place it in the extensibility measuring device used in (2) above at a tension of 10 mm.
87mm2. Initial length l! Set the temperature at o, and keep the tank atmosphere at 20°C and 65% RH for several hours until the displacement meter output stabilizes. The displacement word 1 output at this time is assumed to be X3.

Next, the temperature is changed to t″ii with constant tension and constant humidity at 5% RH, and the displacement meter output is maintained for several hours at a point where it becomes stable.The so-called displacement output at this time is assumed to be X4.

Converting (X4-X5) into a change in length, the difference is Δlβ
As.

β-Δlβ/(50XJo) β is defined by the formula:

(10) Maximum humidity expansion coefficient βゎ of base film, □Measure the humidity expansion coefficients βb1 to βb8 of the base film in the same eight directions as in (6) in Section 11J using the method described in (8) above. The largest value among βb1 to βb8 is βゎ,
Set to max.

(11) Characteristic melt viscosity (μ0) When polymer is extruded at temperature T and pressure P using a Koka-type siro tester having a capillary die with length JL and radius R, the volume discharged is Q. Then, the apparent shear stress τ, apparent shear rate γ, and apparent viscosity μ are defined as follows.

τ-(RP)/(2L) (4Q)/(πR5) μ-τ/'r In this case, the curve μ-f obtained by plotting μ at that time for various n. , : Characteristic melt viscosity μ with the value at r=2oo□−1. Define.

In the present invention, L=10mm, R=0.5
The value measured at 00° C. using a T-rotation die was used.

(12) Evaluation of recording and playback characteristics of floppy disk A commercially available 8-inch floppy disk drive (48 trunks/inch, trunk width approximately 620 μm) was modified, and only the head and drive portions were placed in a constant temperature and humidity chamber, and the control circuit was etc. were conducted using an external test device.

(Test) Track position stability test against changes in temperature and humidity A floppy disk was inserted into the drive section of the above test equipment, left at 10°C and 8% RH for 12 hours, and then tested again under the same conditions. Outer track (trunk OO
) is recorded, and the average signal amplitude when immediately reproduced is Ro.

Thereafter, the atmosphere was changed to 517° C. and 80% RH and maintained for 12 hours, and the average signal amplitude when the outermost trunk was reproduced under the same conditions was set as R1.

Rd=R,/R8 with respect to temperature and humidity changes. It is used as an index of the positional stability of the trunk (the closer Rd is to 1, the better).

Test S: Set the 70 SOBE disk to be tested for permanent deformation under high temperature and high humidity into the above test equipment, leave it at 23℃ and 50% RH for 24 hours, and then apply a 125KHz sine wave signal to the outermost track under the same conditions. The average signal amplitude when recorded and immediately played back is S
. shall be.

Next, the atmosphere was changed to 70°C and 90% RH, held for 2 hours, and returned to 26°C and 50% RH.

Hold for 24 hours. Thereafter, the average signal amplitude when the outermost track is reproduced under the same conditions is defined as Sl.

5d-81/S.

This is used as an index of permanent deformation characteristics under high temperature and high humidity.

(The closer Sd is to 1, the better).

Test T (Initial Output Stability Test) - A floppy disk was set in the drive section of the test equipment described above, and after being left at 26°C and 50% RH for 12 hours, the outermost track was heated at 250 K under the same conditions.
When an H2 sine wave signal was recorded and immediately reproduced, the output fluctuation during one rotation of the disk was measured, and ranked according to the magnitude of the fluctuation.

Note that for both R, S, and T (Tess), the raw output was envelope-detected and then passed through a low-pass filter to detect only components of 3KH2 or less.

Test U Dropout Connect a drop inout counter (manufactured by Tokyo Kogyo/Geneering, 5K-444A) to the above test equipment,
A dropout tester was constructed.

The test is for all tracks on one side of Tisfu (track 00~
76) and calculate the total dropout for 10 sheets of the same type.

Calculated per disc.

The determining conditions are as follows.

Measurement atmosphere: 23℃, 50%RH Recording frequency: 125KHz Detection window: 50% 〔Example〕 Next, the present invention will be explained in more detail by giving examples.

Example 1 (11 Preparation of biaxially oriented PPS film used in the present invention a) Preparation of PPS polymer In an autoclave, 32.6 kg of sodium sulfide (2
50 mol, including 4 Qwt% of crystallization water), 100 g of sodium hydroxide, 36.1 kg of sodium benzoate (250
mole), and N-methyl-2-pyrrolidone (hereinafter referred to as NMP
79.2 kg was charged and the temperature was gradually raised to 205°C while stirring to obtain a distillate containing 6.9 kg of water. O
j? was removed. 67.5 kg (255 mol) of 1,4-dichlorobenzeno (hereinafter abbreviated as DCB) and 20.0 NMP were added to the residual mixture, and the mixture was heated at 265° C. for 4 hours. The reaction product was washed 8 times with boiling water and dried at 80°C for 24 hours using a vacuum dryer to obtain μ, 290
0 Boise, N 1.17. Tg91℃, Tl112
21.1 kg (yield 78%) of high polymerization degree PPS having a temperature of 85°C was obtained (referred to as PPS-A).

b) Melt molding To the composition obtained in (1) above, 31wt% of calcium/umium stearate powder was added as a lubricant, and after stirring and mixing with a mixer, the mixture was poured into the hopper of a 40anφ extruder and Replace the air inside the tank with nitrogen gas. 6
The composition melted at 10°C is taken up by a filter (using metal fiber PI, maximum hole diameter 10°C) at the tip of the extruder.
μmφ) filtered through a trap.

The product was extruded from a T-die having a linear lip with a length of 250 mm and a gap of 1.0 mm, and was cast onto a metal drum whose surface temperature was maintained at 60° C. and solidified by cooling. At this time, at a position approximately 5 mm away from the point where the extruded melt contacts the drum in the radial direction of the drum, parallel to the tram axis, a thickness of 0.0 mm is placed.
A stainless steel wire with a diameter of 1 mm was stretched, and casting was performed while applying a DC voltage of about 5 kV between the wire and the drum (electrostatic casting). The obtained film was an unstretched film having a width of 9 mm, a thickness of 800 μm, and a density of 1615 mm.

c) Biaxially stretched, heat-treated film A is stretched in the longitudinal direction of the film at a stretching temperature of 98° C., a stretching speed of 100, and a longitudinal stretching device consisting of a roll group.
The film was stretched 4.4 times at a rate of 000%/min, and the film was then fed to the rack at a stretching temperature of 98°C.

It was stretched 37 times in the width direction at a stretching speed of 1000%/min.

Further, in a subsequent heat treatment chamber within the same rank, the film was heat-treated at 0° C. for 10 seconds to obtain a bi-oriented PPS film with a thickness of 50 μm (referred to as film A).

d) When various properties of film A were checked as described above, birefringence: 0.015 Coefficient of thermal expansion at 25°C in the direction of the main orientation axis: 2. Ox
10-50c, -'9, which satisfied the conditions for a biaxially oriented Pps film used as the center layer of the present invention.

Further, other characteristics of this film were as follows.

Dimensional stability index 0xlO-' Average surface roughness, 015 μm Coarse protrusion density, 16 pieces/cm 2 (2) Surface layer As the surface layer, a biaxially oriented PKT film prepared by the following method was used.

A slurry was prepared by kneading 100 parts by weight of terephthalic acid and 46 parts by weight of ethylene glycol. The slurry is continuously added at a constant rate to a reactant of 50 parts by weight of terephthalic acid and 21.5 parts by weight of ethylene glycol stored at 245°C in a reactor, and an esterification reaction is carried out at 245°C under normal pressure to produce the slurry. Water was continuously distilled out of the system from the rectification column.

The supply time of the slurry was completed in 6 hours and 30 minutes, and the esterification reaction was completed in 4 hours. From the obtained reaction product, an esterification reaction product equivalent to 100 parts by weight of terephthalic acid was transferred to a polymerization apparatus, and 0.045 parts by weight of phosphoric acid, 0,026 parts by weight of antimonotrioxide, and an average particle size of 40 nm (average of secondary particles) were added. 0.1 weight M of vapor-phase glue ('Aero/Lu' TT-600, manufactured by Nippon Aerosil Co., Ltd.) with a diameter of 700 nm was added as an ethylene glycol slurry.

Polymerization was carried out according to a conventional method to obtain PET with an intrinsic viscosity of 0615.

The composition was bath-melt extruded at 285°C, cast on a cooling tram at 60°C to form a non-stretched sheet, and then subjected to a conventional sequential biaxial stretching method with a difference in circumferential speed. The film was stretched at 90° C. between a pair of rolled rolls in the longitudinal direction. The refractive index is 1.64 in the vertical and horizontal directions, respectively.
．． 1.54, and the in-plane birefringence Δn was previously 0. Next, it was fed into a tenter, and while holding both ends with clips, it was stretched 65 times in the horizontal (width) direction at 95°C, and also in the tenter.

Heat treatment was performed at 220° C. for 5 seconds to obtain a film with a thickness of 10 μm.

The various properties of this film were as follows.

Particle density: 16 particles/mm2 Average surface roughness: 0.014 μm Birefringence: 0.04 (3) Adjustment of base filtration The above surface layer is pasted on both sides of the above center layer using the following procedure. , base film Toshida.

a) Preparation of Adhesive A commercially available two-component urethane adhesive was used to prepare an adhesive bath solution having the following composition and filtered through a 5 μm cut filter.

"Takelac" A-61580 parts by weight (solid content 75 yen) (manufactured by Takeda Pharmaceutical Co., Ltd.) "Takenate" A-5010 parts by weight (solid content 50%) (
(Manufactured by Takeda Pharmaceutical ■) Butyl acetate 280 parts by weightb) Pre-treatment of the middle layer.Both sides of the biaxially oriented PPS film that will become the center layer.

Each sample was subjected to corona discharge treatment by applying electrical energy of 6,600 joules/m 2 .

C) Adhesive application and bonding Apply the above adhesive using a pass-through reverse type coater in a class 10,000 clean room.

Above: One-sided example of 36 p ps film, coated to a dry thickness of 25 μm, dried with hot air at 90°C for 2 minutes, then heated to room temperature and rolled onto a mirror-finish roll with a surface roughness of 0.2 S. 1.5 kg and the above biaxially oriented PET under a pressure of 42
Pasted with film.

Finally, the same polyester film was bonded to the PPS side of this bonded film in exactly the same manner as described above.

This laminated film was cured at 60°C for 24 hours to form a base film.

d) The surface characteristics of this base film were as follows (patent average surface roughness Ra, characterized by the surface bonded first): A side 0.014 μm B side 0.01
4 μm Coarse protrusion density Pd: A side 02 pieces/cnI2 B side 02 pieces/cm2 Therefore, this film satisfies the one-dimensional properties as a base film used in the present invention.

(4) Preparation of floppy disk γ-Fe203 magnetic powder 45 parts by weight VAGH 17 parts by weight (U, C, ], ) Vinyl chloride-vinyl acetate copolymer N 1432J 3.5 parts by weight (Nippon Zeon Co., Ltd. Acrylonitrile-butadiene) Copolymer) Coronate L 1.5 parts by weight (manufactured by Nippon Polyurethane Co., Ltd. Polyynnanate) Methyl inbutyl keto 15' M ft parts Toluene 50 parts by weight Carbon black 4 parts by weight or more A magnetic coating composition was prepared, This was applied to both sides of the above base film to a thickness of 30 μm (after drying) using a spinner, dried, passed between smooth pressure rolls, calendered, and heated at 70°C for 24 hours. Time cured.

Next, in the shape of a disk with a diameter of 8 inches, seven notral holes,
Punched out along with the index ball.

The disc was polished while rotating to a mirror finish, and inserted into the jacket of a commercially available 8-inch floppy disc to create a floppy disc (Disk A).

On the other hand, for comparison, the PPS obtained in (1) (a) above was treated in the same manner as in (1) (b), an unstretched sort sheet with a thickness of 920 μm, and a film strainer (T, M
.

(manufactured by Long Co.) at 95° C., the film was simultaneously biaxially stretched to 65 times in both length and width, and then heat treated at 22+)° C. for 10 seconds.
Thickness 75μ, birefringence 004. Thermal expansion coefficient in the direction of the main orientation axis: 1 x 10-5℃-1, coarse protrusion density: 16 x 1 m
2-2 A floppy disk was prepared in the same manner as in (4) above using the 111II oriented PPS film as a base film (referred to as disk B).
.

(5) Evaluation The evaluation results of the floppy disk prepared in Table 1 were compared with a commercially available floppy disk (an 8-inch single-sided single-density type, referred to as disk C) whose base film is polyethylene terephthalate film. and show.

Table 1 shows that the floppy disk of the present invention has excellent track position stability against changes in temperature and humidity, permanent deformation characteristics under high temperature and high humidity, and dropout characteristics, and is capable of high-density recording. Cal. On the other hand, disk C using PET film as a base film has poor track position stability and permanent deformation characteristics against changes in temperature and humidity, and cannot be used with high density. Disk B, which uses only conventional PPS film as a base film, has excellent permanent deformation properties, but has poor track position stability and many dropouts, making it impractical as a floppy disk.

Table 1 Example 2 (1) Creation of floppy disk In the same manner as in Example 1, by changing only the stretching conditions of PPB, seven types of biaxially oriented pps films with different birefringence and thermal expansion coefficients were prepared. Films D-1 to D-7) were prepared.

Using these films as the center layer, the P used in Example 1
ET films were laminated on both sides in the same manner as in Example 1 to obtain seven types of base films. The coarse protrusion densities of these base films on both sides all satisfied the characteristics of the base films used in the present invention.

Furthermore, in exactly the same manner as in Example 1, seven types of floppy disks (
Discs D-i to D-7) were created.

(2) Evaluation As shown in Table 2, only when the birefringence and thermal expansion coefficient of the center layer meet the requirements of the present invention, the recording and reproducing characteristics are excellent and high trunk density is possible. .

Example 3 (1) Creation of floppy disks Four types of 10 μm thick diskettes with different particle densities and average surface roughness obtained by changing the type and particle size of the particles
Axially oriented PET films were laminated together as a surface layer in exactly the same manner as in Example 1. Furthermore, the steps after applying the magnetic layer were carried out in the same manner as in Example 1, and four secret floppy disks (disks E-1 to -4 were prepared).

(2) Evaluation Table 3 shows the results. It can be seen from this table that if the average surface roughness and particle density of the film with 9 surface layers are too large, recording reliability such as dropout and output stability will deteriorate.

Example 4 (1) Creation of a floppy disk The biaxially oriented pps film (film A) used in Example 1 was used as the central layer, and the biaxially oriented PET film used in Example 1 was placed on both sides of the film. Using six types of adhesives with the same composition as in Example 1 but with different degrees of filtration, they were bonded together in the same manner as in Example 1, and the steps after applying the magnetic layer were carried out in the same manner as in Example 1. , six types of floppy disks (disks, ?F-1 to F-3) were created.

(2) Evaluation Table 4 shows the results. From this table, it can be seen that if the coarse protrusion density of the base film is too high, dropout and output stability will deteriorate.

Claims (1)

[Claims] A repeating unit having a molar ratio of 70 or more is represented by the structural formula 6S÷, has a birefringence of 0.04 or less, and has a film on both sides of a central layer made of a carbide film, each having a thickness of 5 μm or more and equal to the thickness of the central layer. A magnetic recording medium in which the surface layer is made of a polymer film having a thickness of 50% or less and a magnetic layer is provided on at least one side of a laminated Saretaheis film, and the particle density of the polymer film is 100 particles/M2 or less. A magnetic recording medium, wherein the base film has an average surface roughness and a coarse protrusion density of 0.001-0.03 μm and 0.5 μm/cm 2 or less, respectively.