JPS59191129A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a thin film type medium which has good adhesion to a substrate film and excellent durability by composing the medium of an org. polymer film which is composed essentially of a polymer having >=30 deg.C glass transition temp. of which the satd. amt. of water absorption at a specific temp. is a specific weight % or below and a thin film layer of a ferromagnetic metal. CONSTITUTION:A medium consists of an org. polymer film which is composed essentially of a polymer having >=30 deg.C glass transition temp. and of which the satd. amt. of water absorption at 23 deg.C is <=0.3wt% and a thin film layer of a ferromagnetic metal. The org. polymer film is enumerated by polymers such as polyphenylene sulfide, polystyrene, PVA, polychlorotrifluoroethylene, etc. and a copolymer of these polymer components and other copolymer components. The thin film layer of a ferromagnetic metal refers to a ferromagnetic layer formed by a vacuum deposition method. The ferromagnetic layer contains a ferromagnetic metal as represented by Co, Ni or Fe, a ferromagnetic metallic alloy such as Co-Ni, Co-Cr, Co-Fe or Co-V, or a ferromagnetic metallic oxide such as iron oxide, Co-doped iron oxide, chromium oxide, barium ferrite, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and more specifically, to a thin film type magnetic recording medium.

Magnetic recording media are made by dispersing oxide-based ferromagnetic powder represented by γ-Fe, O, or metal-based ferromagnetic powder represented by Fe in an organic polymer as a binder. It was applied onto a plastic film substrate typically made of terephthalate. So-called coated magnetic recording media have been mainly used in this field.

In this case, the organic polymer as a binder is necessary to coat the biferromagnetic powder as a strong coating film with wear resistance, adhesion, and durability, but it also improves magnetic properties and recording density. From this point of view, it is rather an unnecessary additive. For this reason, recently, two ferromagnetic thin film layers are formed directly on a substrate without using a binder by vacuum evaporation, sputtering, ion blasting, or the like. So-called thin-film magnetic recording media have been developed and some have been put into practical use.

However, in thin-film magnetic recording media (4), since no binder is used, the adhesion between the polyethylene terephthalate film or polyimide film, which is mainly used as a substrate, and the ferromagnetic thin film layer is poor, and the magnetic Due to sliding contact with the mechanical parts of heads and recording/reproducing devices, the magnetic layer may come off or be scratched, resulting in poor wear resistance and durability, which is an important practical problem. For type 9 magnetic recording media, the ferromagnetic thin film layer is vacuum deposited.

By so-called vacuum thin film formation methods such as sputtering,
Because the method is used to deposit the magnetic layer while evaporating the magnetic atoms, the magnetic properties of the deposited ferromagnetic thin film layer may deteriorate or fluctuate depending on the conditions during evaporation, the atmosphere in the vacuum system, the state of the substrate surface, etc. There were some easy drawbacks. For this reason, there was an important manufacturing problem in that it was difficult to form a continuous and uniform magnetic layer on a wide plastic film.

The inventors of the present invention have conducted extensive studies on the manufacturing process of magnetic recording media using vacuum evaporation and sputtering.

Durability due to the adhesion of the ferromagnetic thin film layer to the substrate,
We have arrived at the present invention by discovering that the factors that vary the magnetic percentage are closely related to the water absorption properties of the substrate film and the glass transition temperature of the polymer constituting the substrate film.

That is, an object of the present invention is to provide a thin film magnetic recording medium that has good adhesion to a substrate film, excellent durability, and good magnetic properties.

In order to achieve this object, the present invention mainly consists of a polymer having a glass transition temperature of 60'c or higher.

The present invention is characterized by a magnetic recording medium comprising an organic polymer film having a saturated water absorption of 0.3 weight coefficient or less at a temperature of 23'a and nine ferromagnetic metal thin film layers.

In the present invention, examples of the organic polymer film mainly composed of a polymer having a glass transition temperature of 30°C or higher and having a saturated water absorption of 0.3% by weight or less at a temperature of 26°C include polyphenylene sulfide, polystyrene, and polyvinyl chloride. Among them, homopolymers such as polychlorotrifluoroethylene and copolymers of these with other copolymer components are mentioned.

In order to satisfy the flexibility, two-dimensional stability, and mechanical properties required for a magnetic recording medium, a biaxially stretched crystalline organic polymer film is preferred. Furthermore, among the characteristics indicating the surface physical properties of the organic polymer film, it is preferable that a portion consisting of a monomer having a solubility parameter of 8.0 or more is contained in an amount of 50 or more moles.

The organic polymer film that best satisfies these requirements is a rough enylene sulfide film in which the constituent units have a mole ratio of 90 or more.

Among these, if it is less than 10 mol%, it is considered as other copolymerization.
It means that the polymer has a mole percentage of 90 mol% or more, preferably 95 mol% or more.

Conventionally, polyethylene terephthalate, polyimide, aromatic polyimide, etc., which have excellent properties such as toughness, dimensional stability, and heat dissipation, have been mainly used as organic polymer films for coated magnetic recording media. It's coming.

However, when producing thin-film magnetic recording media using these organic polymer films by vacuum deposition, the adhesion of the ferromagnetic layer is poor, and the magnetic properties and crystal structure of the 9-year-old ferromagnetic layer, for example, There were problems with variations in magnetic force, squareness, orientation, crystal size, etc. Even when such an organic polymer film is used, it is known that stable magnetic properties can be obtained by subjecting the surface of the bipolymer film to a glow discharge treatment and heating it to a temperature of 500'a or higher before use. . However, heat-resistant films that can withstand heat treatment pressure at high temperatures are expensive, and the flatness and mechanical properties are significantly impaired by heat treatment.

With the organic polymer film according to the invention.

A stable ferromagnetic thin film can be obtained with little or significantly simplified pretreatment. The reason for this is not clear, but when the particles constituting the ferromagnetic layer adhere to the organic polymer film in a vacuum system, water molecules evaporate and scatter from the base film, which has been heated by latent heat of condensation, radiant heat, etc. It is estimated that this will adversely affect adhesive properties and magnetic properties. From this point of view, the saturated water absorption amount of the organic polymer film at a temperature of 26"C is 0.6% by weight or less, preferably 0.25% or less, most preferably 0.2%.
% or less is desirable. Furthermore, the lower the glass transition temperature of the polymer, the faster the release rate of water molecules at the same saturated water content, and the greater the adverse effect on durability and magnetic properties. The glass transition temperature of the polymer constituting the organic polymer film is 0°C or higher, preferably 50°C or higher.
The temperature is preferably 70°C or higher, most preferably 70°C or higher.

Due to the limited use of an organic polymer film having such saturated water content properties and a glass transition temperature, the magnetic properties and adhesive properties of the thin film magnetic recording medium are excellent even with simplified pretreatment. It's stable.

Regarding only the adhesive property, it is further improved if the organic polymer film contains a monomer having a solubility parameter of 80 or more in a mole ratio of 50 or more.

The thickness of such an organic polymer film is not particularly limited, but from the viewpoint of flexibility, flatness, toughness, etc., it is 4μ to 2μ.
00μ, preferably in the range of 8μ to 100μ.

Prior to forming a ferromagnetic layer on such an organic polymer film, various pretreatments such as heat treatment, surface roughening treatment, and discharge treatment may be performed as appropriate.

The ferromagnetic metal thin film layer in the present invention is a ferromagnetic layer formed by a vacuum deposition method, and is of various types such as primary.

The vacuum deposition method refers to a method in which the pressure within the vacuum system is maintained at 1 Torr or less prior to or during the formation of the two ferromagnetic layers. Specifically, vacuum evaporation methods using resistance heating, electron beam heating, induction heating, laser beam heating, etc., or direct current bipolar methods.

High frequency bipole, DC magnetron, high frequency magnetron,
A sputtering method using opposing two poles, an ion brating method using cathode heating, radio frequency excitation, a cluster ion beam, etc., or a molecular beam crystal growth method (M
B E ), glow discharge method, etc. Among these, the vacuum evaporation method, the S/ζ sintering method, and the ion blating method are preferably used in the present invention.

ij as ferromagnetic layer: + c, o, Nl, Fe
Ferromagnetic metals represented by Co-Ni, C
o-Cr, Co-Fe, Co-V.

Co-Rh, Co-Ru, Co-Mn,
Co-W, Go-3n, Ni-Fe+Co-Ni
-Ferromagnetic metal alloys such as At, iron oxide, C.

It contains ferromagnetic metal oxides such as doped iron oxide, chromium oxide, and barium ferrite.

In addition, other component elements may be included in the ferromagnetic material within a range of 20% by weight or less.

Among these ferromagnetic materials, - C with large axial high anisotropy
Ol or Co-based alloys are particularly preferred in terms of exhibiting the effects of the present invention.

These ferromagnetic layers may be formed from a single layer having the same composition, or may be formed from two or more layers having different trench compositions.

As a ferromagnetic layer, it is preferable that after being saturated magnetized by an external magnetic field, a magnetic field in the opposite direction is applied to increase the residual magnetic flux and the magnetic density. Coercive force is measured by applying an external magnetic field in a direction parallel to the substrate surface in the case of a longitudinal magnetic recording medium, and by applying an external magnetic field in a direction perpendicular to the substrate surface in the case of a perpendicular magnetic recording medium.

The thickness of the ferromagnetic layer can be selected in an optimal range depending on the purpose of use, but the thickness range is 0.05 to 6μ, preferably 0.08 to 2μ, most preferably o, i to 1μ.
is desirable.

The magnetic recording medium thus obtained had good adhesion between the substrate and the ferromagnetic layer, was excellent in durability, and exhibited uniform magnetic properties in both the width and length directions.

The magnetic recording medium according to the present invention is suitable for audio tapes, video tapes, recording disks, data tapes, magnetic cards, etc., and is particularly suitable for floppy disk applications that require uniformity and durability. . Of course, the uses of the magnetic recording medium are not limited to those described above, and can also be effectively used as magnetic recording media for other purposes such as facsimiles, cameras, and magnetic recording printing materials.

Various measurement methods and examples used in the examples will be described below.

(1) Coercive force Until the magnetization or magnetic flux density of the sample is saturated.

The external magnetic field when the magnetization or magnetic flux density of the sample becomes zero in the process of applying an external magnetic field to the sample, then subtracting this magnetic field, and then reversing the direction of the magnetic field to reverse the magnetization or magnetic flux direction of the sample. The magnitude of is called the coercive force. At this time, the coercive force when an external magnetic field is applied perpendicular to the substrate surface is the coercive force perpendicular to the substrate surface, and the coercive force when an external magnetic field is applied in a direction parallel to the substrate surface is parallel to the substrate surface. is the coercive force in the direction.

In this case, a vibrating sample magnetometer (model BHv-30) manufactured by Riken Denshi Co., Ltd. was used to measure the coercive force.

(2) Δθso(..2) Δθ50([102) is an index indicating how much the (002) plane of the crystal is dispersed in the direction parallel to the substrate surface.Δθso(..2 The smaller the value of ., the better the vertical orientation of the (002) plane of the crystal and the better the perpendicular magnetization.Δθ50(002) II”j
:, can be measured by 7-ray diffraction. That is, it is oriented parallel to the substrate surface according to X-ray diffraction (002)
Find the plane and fix the incident direction of the X-rays and the position of the X-ray detector. Next, only the sample is rotated and the diffraction intensity distribution to the X-ray detector is measured. The half width of this distribution is assumed to be Δθ50([+02).

In this case, Δθ5o(oo2) was measured using a DSC type X-ray generator manufactured by Rigaku Denki Co., Ltd.

(3) Using a surface roughness meter using the film thickness stylus method (manufactured by Kosaka Laboratories, universal surface profile measuring device model 5E-3K), measure the height difference between the surface to which the thin film is attached and the surface to which it is not attached. did.

(4) After cutting the durable magnetic thin film sheet into a 5-inch diameter floppy disk and storing it in a jacket.

Record the sine wave signal of
, /vo) xI Do is used as the durability index. The larger this value is, the more excellent the durability is.

(5) Saturated water absorption The organic polymer film sample was thoroughly dried and dehydrated in a hot air oven at 110°C for over 1 hour,
Measure W, (mg). This sample.

After being stored for 24 hours in distilled water maintained at 26°C, the dew condensation adhering to the surface was measured with blotting paper to determine the saturated water absorption amount of the organic polymer film (according to ASTM D570).

(6) Glass transition temperature organic polymer pellets were measured using a scanning differential calorimeter (DSC,
The glass transition temperature is determined from the change in the amount of heat absorption (heat generation) during temperature rise.

Example 1 Sodium sulfide (nase hydrate) 1 mol, sodium hydroxide 0.1
mole + vinegar k ”Thium (dihydrate) 0.99 mole.

4 moles of N-methylpyrrolidone were placed in a No. 11 autoclave, and water and a portion of the N-methylpyrrolidone were distilled off at 200°C. Then, P-dichlorhensefu 1.
After adding 0.01 mol, the system was closed and stirred at 270°C for 4 hours to carry out polymerization. The granular polymer was removed from the contents, washed with water and acetic acid, and returned. The glass transition temperature of this polymer was 90°C.

This dried polymer was pressure pressed at 1500'a and quenched in cold water to obtain an amorphous transparent film with a specific gravity of 1.315° and a thickness of 200 μm. This film,
Using a film stretcher (manufactured by T, M, Long), the film was simultaneously stretched 3.5 x 3.5 times at 95'c.
It was axially stretched and heat-set at 270°C for 30 seconds at a constant length.

A colorless transparent film with a thickness of about 15 μm was obtained.

Approximately 200 cm of this film was dried in an oven at 110°C for 2 hours and weighed, and the weight was 402 mg.The film was then stored in distilled water at 26°C for 24 hours, and the weight was measured again.

402.4 mg, the water absorption rate was 0.1%.

The film was placed in a vacuum chamber, and an alloy target having a weight ratio of cobalt and chromium of 83:17 was used to fabricate a DC red sea bream tron sputtering ferromagnetic layer. After evacuating the vacuum chamber to 1° Tor level in advance, a 2 x 05 μm ferromagnetic layer was formed on the film using argon gas.The coercive force of the ferromagnetic layer in the direction perpendicular to the substrate surface is ←→Oersted, Δθ5o(.

. 2) had a temperature of 3.8C.

This film was cut out and the reproduction output was measured using a floppy disk drive. V. -10,4rn'/V,
= 9.8 mV, and the durability index was 94.

The reproduced waveform observed with a synchroscope was good.

Comparative Example 1 A ferromagnetic layer made of CQ-Cr was formed on the organic polymer film in the same manner as in Example 1, except that a biaxially stretched polyethylene terephthalate film with a thickness of 50 l1I11 was used as the organic polymer film. It was formed. 68 of polyethylene terephthalate film.

The playback output is V. = 3.3mV, V, = 1
．． The durability index was 48 at 6 mV. When I observed the recording area after starting the recording, I found that scratches had occurred at the contact area with the head, and the magnetic layer had come off in some places.

Comparative Example 2 A ferromagnetic layer made of Co--Cr was formed on the organic polymer film in the same manner as in Example 1, except that a 75 μm thick polyimide film was used as the organic polymer film. The saturated water absorption amount of the polyimide film was 2.5, and the ferromagnetic layer in the direction perpendicular to the substrate surface was 60. The contact area with the head was scratched and partially detached.

Example 2 A polyparaphenylene sulfide film having a thickness of approximately 50 μm was prepared using the same method as in Example 1, except that the thickness of the force press was changed. The glass transition temperature of this polymer was 90° C., and the saturated water absorption of the film was 0.1.

Using this film, p
, Co--Ni, (Ni: 30% by weight) were deposited to a thickness of 015 μm in a vacuum system of 1×10). During vapor deposition, the film substrate was tilted so that the angle between the normal direction of the film and the direction of scattering of the evaporated particles was 70 to 80 degrees. The coercive force of the ferromagnetic film thus obtained in the direction parallel to the substrate surface was 700 oersteds. Reproduction output v, = 9.5 mv.

V, = 9.0 mV, and the durability index was 95.

Comparative Example 6 Organic polymer film with glass transition temperature of 118°C
polypropylene was used. Example 2 except that a biaxially stretched polypropylene film with a thickness of 60μ was used.
A ferromagnetic layer made of Co--Ni was formed on the film in the same manner as described above.

The saturated water absorption i of the polypropylene film was 40.01 or less.

The coercive force of the ferromagnetic layer in the direction parallel to the substrate surface was 650 Oersteds. Playback output ■. -5,8 mV.

V, = 0.8 mV, and the durability index was 16. When the recording area was observed after the recording was started, it was found that the magnetic layer had detached from most of the areas that were in contact with the head.

Claims (1)

[Claims] +11 Mainly composed of a polymer with a glass transition temperature of 60°C or higher, with a saturated water absorption of 06% by weight at a temperature of 23°C
A magnetic recording medium comprising the following organic polymer film and two ferromagnetic metal thin film layers.