JPS61107530A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium which has a long repetitive running life under low humidity and is less deteriorated under high humidity by forming a thin layer contg. a fluoro-polymer having the side chain of which the terminal is a fluoroalkyl group and the side chain of which the terminal is mercapto group on a thin ferromagnetic metallic film contg. oxygen. CONSTITUTION:The fluoro-polymer having the side chain of which the terminal is a fluoroalkyl group and the side chain of which the terminal is a mercapto group is made to present on the thin ferromagnetic metallic film contg. oxygen. The polymer of the structure united with the stable lubricating effect possessed by the side chain contg. the fluoroalkyl group and the powerful adhesive strength of the mercapto group side chain to the oxide layer on the surface of the thin ferromagnetic metallic film is made to exist as a surface coating layer on the thin ferromagnetic metallic film which is improved in the surface hardness and corrosion resistance as well as the adhesiveness of the surface coating material, etc. by the oxygen incorporated therein. The stable repetitive running durability is thus maintained under the low humidity environment where the sticking of the ferromagnetic metal to a magnetic head is liable to arise.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is suitable for magnetic recording media such as magnetic tapes and magnetic disks, and particularly relates to a magnetic recording medium suitable for rotary head type video tape recorders.

Structures of conventional examples and their problems Iron, cobalt, nickel, or alloys containing these as main components are used to form polymer films such as polyester films and polyimide films using vacuum film forming methods such as vacuum evaporation, sputtering, and ion blating. Ferromagnetic metal thin film magnetic recording media formed on a substrate made of non-magnetic metal thin plates can dramatically improve recording density compared to conventional coated magnetic recording media. In order to increase the density, it is necessary to make the surface of the magnetic recording medium as flat as possible to reduce the spacing loss between the magnetic head and the magnetic recording medium as much as possible. However, if the surface is too flattened, head touch and running performance will be affected, so it is necessary to solve this problem by making the surface finely rough and at the same time providing a surface coating made of various organic lubricants, resins, etc.

Conventionally, as such surface coating materials, lubricants such as various fatty acids, fatty acid esters, fatty acid amides, silicone oil, fluorine oil, etc., and resins such as polyamide resins and epoxy resins have been used singly or in various composite forms. Ta. However, none of these products have any problems with running performance at normal temperature and humidity (for example, 20°C and 60% RH) and durability under repeated running. As a result of studies conducted by the present inventors, it became clear for the first time that when the RH decreases below %RH, the durability in repeated running significantly decreases. To explain in concrete numbers, at 60% R, f (at 60% R, f), it could be used without any problems after 50 or more repeated runs, but at 25% R, H, the output decreased after 10 to 30 repeated runs, The output fluctuation increased, and such a state occurred after 5 to 20 times at 20% R and H. This phenomenon occurs very conspicuously in ferromagnetic metal thin films without surface coating, so low humidity This is thought to be due to the fact that adhesion tends to occur between the ferromagnetic metal thin film and the magnetic head when the head is running inside.

In addition, ferromagnetic metal thin films tend to rust when they are left in high humidity for long periods of time or when exposed to condensation due to humidity cycles, and to prevent this, ferromagnetic metal In addition to making the ferromagnetic metal thin film contain oxygen by introducing oxygen gas during thin film production, improvements have been made by adding a rust preventive agent that reacts with the magnetic metal to the surface coating material. However, since the latter rust preventive agent generally has poor lubricity, by adding it, part of the running performance of the surface coating has to be sacrificed.

Purpose of the Invention The present invention solves the above-mentioned problems at once, and aims to provide a ferromagnetic metal thin film type magnetic recording medium that has excellent durability against repeated running in low humidity and is also corrosion resistant. It is something to do.

Structure of the Invention The present invention is characterized in that a fluorine-containing polymer having a side chain whose terminal is a fluoroalkyl group and a side chain whose terminal is a mercapto group is present on a ferromagnetic metal thin film containing oxygen. A polymer with a structure that combines the stable lubricity of the fluoroalkyl group-containing side chain and the strong adhesion to the oxide layer on the surface of the ferromagnetic metal thin film due to the mercapto group side chain. By making it exist as a surface coating layer on a ferromagnetic metal thin film that has improved surface hardness and corrosion resistance by containing oxygen, the adhesion of the surface coating material is improved. It is intended to maintain stable repeated running durability in the environment, and also has high water repellency due to the water repellency of the fluoroalkyl group-containing side chain and the reaction between the mercapto group-containing side chain and the surface of the ferromagnetic metal thin film. The purpose is to improve corrosion resistance by preventing the generation of free ions in humid conditions.

DESCRIPTION OF EMBODIMENTS Two embodiments of the present invention will be described below with reference to the drawings.

The figure is a diagram showing the basic configuration of a magnetic recording medium in an embodiment of the present invention. In the figure, 1 is a substrate, 2 is a ferromagnetic metal thin film, and 3 is a surface coating.

The surface coating 3 is constituted by the presence of a fluorine-containing polymer having a side chain whose terminal is a fluoroalkyl group and a side chain whose terminal is a mercapto group. A specific example will be explained below.

This fluorine-containing polymer is obtained, for example, by substituting a terminal hydroxyl group contained in a radical copolymer of a fluoroalkyl group-containing acrylic compound and a hydroxyl group-containing acrylic compound with a mercapto group. In this case, the fluoroalkyl group-containing acrylic compound is
For example, (1) C) et al=CHCoo(CH2) nR
1n:○～11(2)CH2=C(CH3)Coo(
CH2)nRf n:○~11(3)0M2=CHC0
0C)(2C)I(OH)Rf(4)CH2=C(CH
3) COOCH2CH(OH), R.

(5) CH2=CHCOOCH2CH(OH)CH2R
f(6)CH2=C(CH3)COOCH2CH(OH
)CH2Rf(7)CH2=CHCOOCH2CH2N
(CH3)So2Rf(8)CH2=C(CH3)CO
OCH2CH2N(CH3)SQ)R4(9)CH2=
CHCOOCH2CH2N(C2H5)So2R.

(10) CH2=C(C) (3) COOCH2CH
2N(C2H5)SQ? R.

(11) CH2=CHCOOCH2CH2N(C3H7
)SQ2R6(12)CH2=C(CH3)Co0CH
2CH2N(C3H5O)Rf(13)CH2=CH
COOCH2CH2N(C2H5)ooCRfHowever,
Rf represents a fluoroalkyl group having 4 to 20 carbon atoms. In addition, as Rf, CF3CF2CF2CF2CF2-
In addition to perfluoroalkyl groups such as
Fluoroalkyl groups containing, for example, HCF2CF2
CF2CF2CF2- is also included.

Examples of hydroxyl group-containing acrylic compounds include:

(101] CH2=CHC○○C2H40H(102
) CH2=C(CH3)C00C2H40H(10
3) CH2=CHC00CH2CH(CH3)OH
(104) CH2=CHC0NHCH20H(10
5) CH2=CHC0N(OH5)CH2CH20
There are H etc. The copolymer can be easily obtained by solution polymerization using a radical initiator, emulsion polymerization, or a known vinyl polymerization method. The terminal hydroxyl group of the obtained copolymer can be substituted with a mercapto group by a conventional method using pentasulfide.

Content of fluoroalkyl end groups in the copolymer,
The content of mercapto end groups can be determined by appropriately selecting combinations of the above-mentioned various acrylic compounds and their blending ratios. The molecule and amount of the polymer can be adjusted within an appropriate range by selecting the type and concentration of the polymerization initiator and chain transfer agent using known methods. In addition to the fluoroalkyl group and mercapto group, the fluorine-containing polymer has CH3-.

It may have non-polar terminals such as C2H5"1□H35-, and this can be achieved by adding an acrylic compound having these terminals during polymerization.

The molecular weight of the fluoropolymer applied to the present invention is as follows:
2,000 or more, more preferably 5,000 or more. When the molecular weight is less than 2,000, it is difficult to obtain the effect of improving low-humidity running durability. In addition, the content of fluoroalkyl end groups in the fluoropolymer is 2 in terms of molecular weight ratio.
0 to 80 inches is desirable.

If it is less than 20%, the slipperiness and corrosion resistance will be poor, and if it is more than 80%, the low humidity running durability will be reduced. The content of mercapto groups in the fluoropolymer is 1 to 3o% in terms of molecular weight ratio.
is desirable. If it is less than 1 inch, the adhesion to the ferromagnetic metal thin film will be poor, resulting in no improvement in low humidity running durability. If it is 30 inches or more, the slipperiness during running is poor and stick-slip occurs.
:, 1 The amount of fluorine-containing polymer on the ferromagnetic metal thin film is 1 m' per surface, 1
A suitable range is ˜200 WF, more preferably O,S˜200 WF. The surface coating on the ferromagnetic metal thin film is as follows:
It is also possible to use not only the fluoropolymer alone but also various known organic lubricants.

Examples of ferromagnetic gold thin films include metal thin films mainly made of Co, Ni, Fe, etc. formed by oblique or vertical vapor deposition, metal thin films mainly made of alloys thereof (e.g. C
oNi, CoCr, etc.) containing oxygen, which can be obtained when the atmosphere during film formation is dominated by oxygen gas. The oxygen content is suitably at least 3% or more, preferably 5% or more in terms of atomic ratio to the ferromagnetic metal. If it is 3% or less, running durability and corrosion resistance in low humidity will deteriorate.

Example Wave-like protrusions (surface roughness: 100 Co 1'J'i ferromagnetic metal thin film (Ni
= 20% film thickness (1000 layers) was formed in the presence of a trace amount of oxygen. The oxygen content in the film was 5% in terms of atomic ratio. This sample is designated as A.

There are several granular protrusions (average height to human average diameter 1 μm) with a gentle slope created by fine silica particles added to the polyester film per 100 μm2 of the surface, and relatively large protrusions caused by fine particles caused by polymerization catalyst residue. 1 diameter on the surface of the polyester film, which has been reduced as much as possible.
C under the same conditions as above on a substrate on which approximately 10 million steep mountain-like protrusions were formed using silica colloid particles as cores and ultraviolet-curable epoxy resin as a binder.

Ni film (Ni = 20%, film thickness 1000, oxygen content 7%
) is formed as B. In addition, as a comparative example, B was not introduced with oxygen during vapor deposition (
B) with only the oxygen content being 2% or less is designated as C. Two kinds of fluorine-containing polymer solutions prepared in advance were coated on these vapor-deposited films, and then cut into predetermined widths to make magnetic tapes.
Repeated running tests were conducted on a prototype video recorder in an H0 atmosphere, and the number of runs until the playback output decreased by 16 dB compared to the initial state was determined. Also, 20'Cao%
The media recorded in R,H was heated at 30°C at 80% in R,H.
After leaving it for 0 days, the stability of the image (clogging) when reproduced in 20'C60 inch R, H was examined. The results are summarized in the table below.

As a comparative example, a fluoropolymer with a low degree of polymerization
...No, 2. Those without mercapto group...
・No. 8 etc. are added.

Effects of the Invention As is clear from the above results, the magnetic recording medium of the present invention has a long repeated running life in low humidity, and has little deterioration in high humidity, making it very useful industrially. It is.

[Brief explanation of the drawing]

The drawing is a sectional view of a first embodiment of the magnetic recording medium of the present invention. 1...Substrate, 2...Ferromagnetic metal thin film,
3...Surface coating.

Claims (1)

[Claims] A magnetic field characterized in that a thin layer containing a fluorine-containing polymer having a side chain whose terminal end is a fluoroalkyl group and a side chain whose terminal end is a mercapto group is formed on a ferromagnetic metal thin film containing oxygen. recoding media.