JPH0566651B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 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, polyimide films, and non-woven materials using vacuum film forming methods such as vacuum evaporation, sputtering, and ion plating. A ferromagnetic metal thin film magnetic recording medium formed on a substrate made of a magnetic thin plate or the like 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 runnability 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, such surface coating materials include lubricants such as various fatty acids, fatty acid esters, fatty acid amides, silicone oils, fluorine oils,
Resins such as polyamide resins and epoxy resins have been used singly or in various composite forms. However, all of these products have no 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 inventors, it became clear for the first time that when the temperature decreases below RH, durability under repeated running significantly decreases. To explain in concrete numbers, at 60% RH it could be used for more than 50 repeated runs without any problem, but at 25% RH it would run 10 times.
After ~30 repeated runs, a decrease in output and an increase in output fluctuation occurred, and when the RH reached 20%RH, such a state occurred after 5 to 20 times. This phenomenon occurs very markedly in ferromagnetic metal thin films without surface coating, and is thought to be caused by the tendency for adhesion to occur between the ferromagnetic metal thin film and the magnetic head when running in low humidity. It is believed that there is. 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.To prevent this, ferromagnetic metal thin films In addition to making the ferromagnetic metal thin film contain oxygen by introducing oxygen gas during manufacturing, 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, its addition necessitates sacrificing a portion of the running performance of the surface coating. 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 repeated running durability in low humidity and also has excellent corrosion resistance. It is something. Structure of the Invention The present invention forms a thin layer containing a fluorine-containing polymer having a side chain whose terminal is a perfluoroalkyl group and a side chain whose terminal is a polar group on a ferromagnetic metal thin film containing oxygen. It is a magnetic recording medium characterized by the stable lubricity of the perfluoroalkyl group-containing side chain and the strong adhesion to the oxide layer on the surface of the ferromagnetic metal thin film due to the polar group-containing side chain. By making a polymer with an integrated structure exist as a surface coating layer on a ferromagnetic metal thin film, which has improved surface hardness, corrosion resistance, adhesion of surface coating material, etc. by containing oxygen, It is intended to maintain stable repeated running durability in a low humidity environment where adhesion to the magnetic head is likely to occur. The purpose is to improve corrosion resistance by preventing the generation of free metal ions in high humidity due to the reaction between the chains and the surface of the ferromagnetic metal thin film. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described 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 the substrate, 2
3 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 perfluoroalkyl group and a side chain whose terminal is a polar group. Specific examples of this fluorine-containing polymer will be explained below. This fluorine-containing polymer is obtained, for example, by radical copolymerization of a perfluoroalkyl group-containing acrylic compound and a polar group-containing acrylic compound. In this case, the perfluoroalkyl group-containing acrylic compound is, for example, (1) CH ₂ = CHCOO (CH ₂ ) _o R _f n: 1 to 11 (2) CH ₂ = C (CH ₃ ) COO (CH ₂ ) _o R _f n: 1 to 11 (3) CH ₂ = CHCOOCH ₂ CH(OH)R _f (4) CH ₂ = C(CH ₃ ) COOCH ₂ CH(OH)R _f (5) CH ₂ = CHCOOCH ₂ CH (OH)CH ₂ R _f (6) CH ₂ =C(CH ₃ )COOCH ₂ CH(OH)CH ₂ R _f (7) CH ₂ =CHCOOCH ₂ CH ₂ N(CH ₃ )SO ₂ R _f (8) _CH2 =C _{( CH3} ) _COOCH2CH2N ( _CH3 ) _SO2
R _f (9) CH ₂ = CHCOOCH ₂ CH ₂ N (C ₂ H ₅ ) SO ₂ R _f (10) CH ₂ = C (CH ₃ ) COOCH ₂ CH ₂ N (C ₂ H ₅ )
SO ₂ R _f (11) CH ₂ = CHCOOCH ₂ CH ₂ N (C ₃ H ₇ ) SO ₂ R _f (12) CH ₂ = C (CH ₃ ) COOCH ₂ CH ₂ N (C ₃ H ₇ )
SO ₂ R _f (13) CH ₂ =CHCOOCH ₂ CH ₂ N(C ₂ H ₅ )OCR _f where R _f represents a perfluoroalkyl group having 4 to 20 carbon atoms. etc., and polar group-containing acrylic compounds have one end consisting of an unsaturated carbon bond and the other end consisting of a carboxyl group, hydroxyl group, amino group, amide group, phosphoric acid group, sulfonic acid group, or cyano group. It consists of at least one kind, for example, (101) CH ₂ =CHC00H (102) CH ₂ =C(CH ₃ )COOH (104) CH ₂ ＝CHCOOC ₂ H ₄ OH (105) CH ₂ ＝C(CH ₃ )COOC ₂ H ₄ OH (106) CH ₂ ＝CHCOOCH ₂ CH(CH ₃ )OH (107) CH ₂ ＝CHCONHCH ₂ OH (108) CH ₂ = CHCON(CH ₃ ) CH ₂ CH ₂ OH (109) CH ₂ = CHCOOCH ₂ CH ₂ NH ₂ (110) CH ₂ = CONH ₂ (111) CH ₂ = C(CH ₃ ) CONH ₂ ( 112) (CH ₂ =CHCOOCH ₂ CH ₂ O) _o PO(OH) _3
-o n:1~2 (113) ( _CH2 =C( _CH3 ) _COOCH2CH2O ) _{o PO}
(OH) _3-o n: 1-2 (114) CH ₂ =CHCOOCH ₂ CH (CH ₂ Cl) OPO
(OH) ₂ (115) CH ₂ = CHCOOC ₂ H ₄ SO ₃ H (116) CH ₂ = CHCOONH−C(CH ₃ ) ₂ CH ₂ SO ₃
H (117) CH ₂ = CHCOCN (118) CH ₂ = CHCOOC ₂ H ₄ OCH ₂ CHCN (119) CH ₂ = CHCOOC ₄ H ₈ OCH ₂ CHCN, etc. The copolymer can be easily obtained by known vinyl polymerization methods such as solution polymerization and emulsion polymerization using a radical initiator. The content of perfluoroalkyl end groups and the type and content of polar end groups in the copolymer can be determined by appropriately selecting combinations of the various acrylic compounds and their blending ratios. The molecular weight of the polymer can be adjusted to an appropriate range by selecting the type and concentration of the polymerization initiator and chain transfer agent using a known method. In addition to the perfluoroalkyl group and both ends of the above-mentioned various polar groups, the fluorine-containing polymer may have a nonpolar end such as CH ₃ −, C ₂ H ₅ −, C ₁₇ H ₃₅ −, etc. This can be achieved by adding an acrylic compound having these terminals during polymerization. The molecular weight of the fluorine-containing polymer applied to the present invention is desirably 3,000 or more, more preferably 10,000 or more. When the molecular weight is less than 3000, it is difficult to obtain the effect of improving low-humidity running durability. Further, the content of perfluoroalkyl end groups in the fluorine-containing polymer is preferably 20 to 80% in terms of molecular weight ratio. If it is less than 20%, lubricity and corrosion resistance will deteriorate, and if it is more than 80%, low humidity running durability will be reduced. The content of polar end groups in the fluorine-containing polymer is 1 to 1 in terms of molecular weight ratio.
30% is desirable. If it is less than 1%, the adhesion to the ferromagnetic metal thin film will be poor, resulting in no improvement in low humidity running durability. If it exceeds 50%, the slipperiness during running will be poor, resulting in stick slip. The amount of the fluorine-containing polymer present on the ferromagnetic metal thin film is suitably 0.1 to 500 mg, more preferably 0.5 to 200 g ^per square meter of surface. In addition, as a method for making it exist, in addition to the method of diluting the fluorine-containing polymer solution obtained by solution polymerization or emulsion polymerization with a solvent and applying it on a ferromagnetic metal thin film by the usual method, It is also possible to apply a method in which a monomer mixture of an alkyl group-containing compound and a polar group-containing compound or an oligomer polymer thereof is directly deposited on a ferromagnetic metal thin film and then irradiated with electron beams, ultraviolet rays, etc. for polymerization. In addition, as a surface coating on the ferromagnetic metal thin film, it is also possible to use not only the fluorine-containing polymer alone but also various known organic lubricants. The ferromagnetic metal thin film may be, for example, a metal thin film mainly made of Co, Ni, Fe, etc. formed by oblique or vertical vapor deposition, or a metal thin film mainly made of an alloy thereof (e.g. CoNi, CoCr, etc.). A suitable material is one 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. More specific examples will be demonstrated below. Wavy protrusions (surface roughness 100 Å periodic A CoNi ferromagnetic metal thin film (Ni = 20%, film thickness 1000 Å) was formed on the film (0.5 μm) by continuous vacuum oblique evaporation 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. Fine silica particles added to the polyester film create gradual granular protrusions (average height
Ultraviolet curing epoxy with silica colloidal particles of 150 Å in diameter as cores is applied to the surface of the polyester film, which has several particles of 70 Å (average diameter 1 µm) per 100 µm ² of the surface and minimizes relatively large protrusions caused by fine particles caused by polymerization catalyst residue. ^A CoNi film (Ni
=20% film thickness: 1000 Å, oxygen content: 7%) is designated as B. In addition, as a comparative example, in B, no oxygen was introduced during vapor deposition (B
(in which only the oxygen content is 2% or less) is C
shall be. Various fluorine-containing polymer solutions pre-synthesized and prototyped are coated on these vapor-deposited films, and then cut into predetermined widths to make magnetic tapes.
We conducted repeated running tests on a prototype video recorder in an atmosphere of 20% RH, and determined the number of runs until the playback output decreased by -5 dB compared to the initial state.
In addition, media recorded at 20℃ 60% RH at 30℃ 80%
After being left in RH for 10 days, the stability of the image (clogging) was investigated when it was played back at 20°C and 60% RH. The results are summarized in Table 1. As comparative examples, a fluorine-containing polymer with a low degree of polymerization, No. 2, and one without a polar group, No. 15, were added.

[Table] 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 less deterioration in high humidity, making it very useful industrially. It is something.

[Brief explanation of the drawing]

The figure is a diagram showing the structure of a magnetic recording medium according to an embodiment of the present invention. 1...Substrate, 2...Ferromagnetic metal thin film, 3...Surface coating.

Claims (1)

[Claims] 1. Forming a thin layer containing a fluorine-containing polymer having a side chain whose terminal is a perfluoroalkyl group and a side chain whose terminal is a polar group on a ferromagnetic metal thin film containing oxygen. A magnetic recording medium characterized by: 2. The magnetic recording medium according to claim 1, wherein the polar group is at least one of a carboxyl group, a hydroxyl group, an amino group, an amide group, a phosphoric acid group, a sulfonic acid group, and a cyano group. .