GB2096920A

GB2096920A - Metallic magnetic recording medium and process for its production

Info

Publication number: GB2096920A
Application number: GB8204395A
Authority: GB
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1981-02-19
Filing date: 1982-02-15
Publication date: 1982-10-27
Also published as: GB2096920B; NL188251B; NL188251C; DE3206109C2; NL8200654A; DE3206109A1

Abstract

A magnetic recording medium comprises a non-magnetic base, e.g. of plastics film, bearing a layer of magnetic metal, preferably vapor deposited; and on either or both surfaces of the medium, a layer of an isocyanic acid ester of formula alkyl- NCO, preferably the alkyl being straight chain and of 8 or more C atoms or a compound having at least 2, preferably at least 3, isocyanate groups per molecule, in a dry weight of 1-100 mg/m<2>. The isocyanic or isocyanate compound can be applied by coating a solution in an organic solvent. A coating of an isocyanate compound may also contain 0.2-30 wt.% of a polymer or a lubricant e.g. an aliphatic acid of 10 or more C atoms. The thin layer of isocyanic ester or isocyanate improves the running properties, wear-resistance and electro-to-magnetic conversion characteristics of the tape, even after repeated use.

Description

SPECIFICATION Metallic magnetic recording medium and process for its production The present invention relates to a magnetic recording medium using a thin magnetic film as a magnetic recording layer and, more particularly, to a magnetic recording medium of the thin metal film type having good running properties, wear resistance and electro-to-magnetic conversion characteristics.

Most of the conventional magnetic recording media are of the coated type. These media are produced by dispersing particles of magnetic oxides such as y-Fe2O3, Co-doped y-Fe203, Fe304, Codoped Fe304, a Berthollide compound of y-Fe203 and Fe304 or CrO2 or ferromagnetic alloy particles, in an organic binder such as a vinyl chloride/vinyl acetate copolymer, a styrene/butadiene copolymer, an epoxy resin or polyurethane resin, applying the resulting coating solution to a non-magnetic base, and drying the coating. However, due to a recently increasing demand for higher density recording, researchers' attention has been drawn to magnetic recording media of thin metal film type that use, as a magnetic recording layer, a thin ferromagnetic metal film.The film is formed by vapor deposition such as vacuum deposition, sputtering or ion plating, or plating such as electroplating or electrolessplating. Various efforts have been made to use such recording media on a commercial basis.

Most of the magnetic recording media of coated type use a metal oxide having a small saturation magnetization as a magnetic material. Therefore, an attempt to achieve high density recording by using a thinner magnetic recording medium results in a decreased signal output. However, with a magnetic recording medium of thin metal film type, a very thin magnetic recording layer can be formed by using a ferromagnetic metal having a greater saturation magnetization than that of the magnetic oxide without using a non-magnetic material such as binder. This thinness is very advantageous for providing good electro-to-magnetic conversion characteristics.However, the thin metal film type magnetic recording medium has its own problems: (1) it deveíops a large amount of friction against the magnetic head, guide poles or other transport means when it is run to record, reproduce or erase magnetic signals, and hence wears easily; (2) it is easily attacked by corrosive environments; and (3) the magnetic recording layer may be damaged on impact during handling.

Some attempts have been made to solve these problems by forming a protective layer on the magnetic recording medium of thin metal film type. One such proposals described in Japanese Patent Application (OPI) No. 75001/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") wherein a thin lubricant layer is formed on the metal film. According to this proposal, the friction coefficient between the magnetic head or guide poles and the metal film is reduced, providing a tape that runs consistently and which is least likely to be abraded. However, these advantages are quickly lost if the tape is used repeatedly.Another method is described in Japanese Patent Applications (OPI) Nos. 39708/78 and 40505/78 wherein a lubricant protective layer made of a metal or metal oxide is formed on the thin metal film. However, even when using this method, the effect of the protective layer does not last long; when the tape is used repeatedly, the friction coefficient is increased rapidly or the thin magnetic metal film breaks. Still another method is described in Japanese Patent Application (OPI) No. 155010/79 wherein an overcoat of a high molecular film is formed on the metal film. However, if the overcoat is made of vinylidene chloride/acrylic ester copolymer and other known high molecular substances, the resulting film thickness is at least about 0.2,u and this causes spacing loss which in turn leads to reduce output in high density recording.

Further, most thin magnetic metal films are supported on a very smooth base to achieve high density recording. However, even when the lubricating methods described above are applied to such a smooth base, running properties, especially in highly humid atmospheres, and wear resistance of the base cannot satisfactorily be improved.

Therefore, one object of the present invention is to provide a magnetic recording medium of the thin metal film type that has good running properties, wear resistance and electro-to-magnetic conversion characteristics, as well as a process for producing the same.

Another object of the present invention is to provide a magnetic recording medium of thin metal film type that retains good running properties and wear resistance for an extended period of time, as well as a process for producing the same.

The present inventors have found that by forming a layer of an isocyanic acid ester or a compound having at least two isocyanate groups in the molecule on either the thin magnetic metal film or the surface of the non-magnetic base opposite the thin magnetic metal film or both, improved results are obtained. The improved results obtained relate to a magnetic recording medium having good electro-to-magnetic conversion characteristics, running properties, wear resistance and great abrasion-proofness. Furthermore, these properties last for an extended period.The inventors have further found that the objects of the present invention can be achieved by forming a layer of an isocyanic acid ester or a compound having at least two isocyanate groups in the molecule on either the thin magnetic metal film or the surface of the non-magnetic base opposite the thin magnetic metal film or both and then heat-treating said layer.

The thin magnetic metal film used in the present invention can be formed by vapor deposition or plating. Vapor deposition is preferred since it forms the desired thin metal film rapidly, is a relatively simple process and requires no treatment of effluents or other additional steps. The vapor deposition is a process in which a substance or its compound is heated in a vacuum enclosure until its vapor or ionized vapor condenses on the surface of a base, and includes vacuum vapor deposition, sputtering, ion plating and chemical vapor phase plating.

The magnetic recording layer used in the present invention is a thin film that is formed by vapor deposition or plating of a ferromagnetic metal such as iron, cobalt or nickel, or a ferromagnetic alloy such as Fe-Co, Fe-Ni, Co-Ni, Fe-Si, Fe-Rh, Co-P, Co-B, Co-Si, Co-V, Co-Y, Co-La, Co-Ce, Co-Pr, Co-Sm, Co-Pt, Co-Mn, Fe-Co-Ni, Co-Ni-P, Co-Ni-B, Co-Ni-Ag, Co-Ni-Na, Co-Ni-Ce, Co-Ni-Zn, Co-Ni-Cu, Co-Ni W, Co-Ni-Re or Co-Sm-Cu. The thickness of the layer as used in a magnetic recording medium is preferably in the range of from 0.05 to 2,um, more preferably from 0.1 to 0.4cm.

The isocyanic acid ester which can be used in the present invention is a compound having the formula RN=C=O, wherein R is an alkyl group, preferably a straight alkyl group, and more preferably a straight chain alkyl group having 8 or more carbon atoms. Specific examples are octyl isocyanate, decyl isocyanate, dodecyl isocyanate and octadecyl isocyanate.

Typical examples of the compound having at least two isocyanate groups in the molecule usable in the present invention are 1 ,6-hexamethylene diisocyanate, 2,2,4-trimethylpentane diisocyanate, decane diisocyanate, w,w'-diisocyanate-1 ,2-dimethylcyclohexane, tolylene diisocyanate, ,a,'- diisocya nate- ,5-dimethylnaphthalene, w,w'-diisocyanate-propylbiphenyl, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane diisocyanate, xylidene diisocyanate, alkyl- or halogen-substituted products of these diisocyanates (e.g., 2,5-dichloro-p-xylylene diisocyanate and tetrachloro-p-phenylene diisocyanate) and divalent diisocyanates such as 2,2'-dinitrodiphenyl diisocyanate; trivalent isocyanates such as triphenylmethane triisocyanate; polyvalent isocyanates such as adducts of diisocyanates, e.g. aliphatic diisocyanates, alicyclic diisocyanates having a cyclic group, tolylene diisocyanate, diphenylmethane diisocyanate and triphenylmethane diisocyanate with trimethylolpropane or pentaerythritol; and polymethylene polyphenylene polyisocyanates (PAPI). Of these, compounds having at least three isocyanate groups in the molecule are preferred. To modify the physical properties of the surface of the layer of the compound having at least two isocyanate groups in the molecule, 0.2 to 30% of a polymer such as cellulosic derivatives, polyurethanes or vinyl polymers may be added as required; if the amount of these polymers is too great, it is not possible to obtain one of the objects of this invention which is a highly wear-resistant tape.

A layer of the isocyanic acid ester and/or the compound having at least two isocyanate groups in the molecule can be formed on either the thin magnetic metal film or the non-magnetic base or both by any suitable method. One such method comprises applying a layer of a solution of said ester or compound in an organic solvent onto the base and drying the same. The concentration of the coating solution is preferably in the range of from 0.05 to 5 wt%, and said solution is applied onto the base in such a manner that the dry weight of the layer is preferably in the range of from 1 to 100 mg/m2, more preferably from 2 to 50 mg/m2. In particular, in the case of using the isocyanic acid ester, satisfactory results can be obtained with a relatively small amount thereof, e.g., I to 50 mg/m2, preferably 2 to 10 m9/m2.

After applying and drying the coating, it is preferably heated to a temperature of at least 300 C, preferably 500C or more, at a relative humidity of 30% or more for at least 3 seconds. The heat treatment is preferred because the effects in running properties and wear resistance of the present invention can be further improved or maintained in a longer period of time. The same result can be achieved by adding to the coating solution one or more compounds having active hydrogen such as water, alcohol, amine, carboxylic acid, phenol or carboxylic acid amide when the compound having at least two isocyanate groups in the molecule is used.

For the purposes of the present invention, the isocyanic acid ester of the compound having at least two isocyanate groups in the molecule may be used in combination with a lubricant. Suitable lubricants include aliphatic acids, metal soaps, aliphatic acid amides, aliphatic acid esters, mineral oils, vegetable oils, animal oils such as whale oil, higher alcohols, and silicone oil; fine, electrically conductive particulate materials such as graphite; fine inorganic particulate materials such as molybdenum disulfide and tungsten disulfide; fine particles of plastics such as polyethylene, polypropylene, polyethylene/vinyl chloride copolymer and polytetrafluoroethylene; a-olefin polymers; unsaturated aliphatic hydrocarbons that are liquid at ordinary temperatures (i.e., those compounds having an n-olefin double bond attached to a terminal carbon atom, with about 20 carbon atoms), fluorocarbons and mixtures thereof. In particular, the compound having at least two isocyanate groups in the molecule is preferably used in combination with aliphatic acids, metal soaps, aliphatic acid amides, aliphatic acid esters, higher alcohols and mixtures thereof, and more preferably with aliphatic acids having 10 or more carbon atoms.

In addition to the lubricant, a conventional corrosion inhibitor or mold inhibitor may be used as desired.

These lubricants are dissolved in an organic solvent together with the isocyanic acid ester or the compound having at least two isocyanate groups in the molecule and the solution is applied onto the base. Alternatively, after the layer of the isocyanic acid ester or the isocyanate-containing compound is formed by the methods described above, a lubricant layer may be formed by applying a solution of the lubricant in an organic solvent onto the layer, or by the vapor deposition process described before.

Examples of solvents used for the application of the isocyanic acid ester or compound containing at least two isocyanate groups in the molecule, as well as the lubricant include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols having 1 to 10 carbon atoms (excluding isocyanate-containing compounds) such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol acetate monoethyl ether; ether and glycol ethers such as glycol dimethyl ether, glycol monoethyl ether (excluding isocyanate containing compounds) and dioxane; hydrocarbons such as pentane, hexane, heptane, octane, nonane and decane; tars (aromatic hydrocarbons) such as benzene, toluene and xylene; and chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene.

The lubricant is generally used in a dry weight of from 2 to 100 mg/m2, preferably from 2 to 50 mg/m2, more preferably from 2 to 20 mg/m2.

The recording medium of the present invention achieves the following advantages: (1) When it is used on a tape deck, it experiences only a small increase in the dynamic friction coefficient. This means the medium is very stable to repeated running and has very high wear resistance; (2) The medium retains high stability to repeated running even when it has a very smooth thin magnetic metal film and base; (3) The medium has small dynamic friction coefficient and runs smoothly in humid atmospheres; (4) The film of the isocyanate acid ester or the compound having at least two isocyanate groups in the molecule is very thin, so it does not reduce the electro-to-magnetic conversion characteristics of the magnetic recording medium; and (5) The medium is scarcely susceptible to corrosive attack under humid conditions and causes no reduction in the electro-to-magnetic conversion characteristics.

The present invention is now described in greater detail by reference to the following examples and comparative examples, wherein all parts are by weight.

Example 1 A magnetic cobalt film (0.2,u thick) was formed on a polyethylene terephthalate (PET) film (20y thick) by oblique deposition to thereby prepare a magnetic tape, wherein electron beams were used to condense the vapor of cobalt (99.95% purity) which was directed onto the PET film at an angle of incidence of 700 at a pressure of 5x 10-5 Torr. An isocyanic acid ester coating solution I of the formulation indicated below was applied onto the Co film and the base film in a dry amount of 10 mg/m2, and was allowed to stand at 500C and 80% RH for 2 hours. The resulting tape was then slit into a video tape 1/2 inch wide, the magnetic surface and the opposite (base) surface of which were referred to as Samples Nos. 1 and 2, respectively.

Isocyanic acid ester coating solution I Octadecyl isocyanate [ CH3(CH2)17NCO ] 1.0 parts Methyl ethyl ketone 200 parts Example 2 A magnetic tape was prepared in the same manner as in Example 1. Thereafter, an isocyanic acid ester coating solution II of the formulation indicated below was applied onto a cobalt film of the magnetic tape in a dry amount of 4 mg/m2, and was allowed to stand at 300C and 60% RH for 30 minutes. The resulting tape was then slit into a video tape 1/2 inch wide, the magnetic surface of which was referred to as Sample No. 3.

Isocyanic acid ester coating solution II Octyl isocyanate [ CH3(CH2)7NCOj 0.4 part Methyl ethyl ketone 200 parts Example 3 A magnetic tape was prepared in the same manner as in Example 1. Thereafter, an isocyanic acid ester coating solution Ill of the formulation indicated below was applied onto a base film of the magnetic tape in a dry amount of 6 mg/m2, and was allowed to stand at 400C and 70% RH for 1 hour.

The resulting tape was then slit into a video tape 1/2 inch wide, the base surface of which was referred to as Sample No. 4.

Isocyanic acid ester coating solution Ill Dodecyl isocyanate [ CH3(CH2)1aNCO ] 0.6 part Methyl ethyl ketone 200 parts Comparative Example 1 A video tape was prepared as in Example 1 except that a Co magnetic film was simply formed on a PET base by oblique deposition without forming a protective layer or a lubricant layer. The magnetic surface and the base surface of the tape were referred to as Sample Nos. C-l and C-3.

Comparative Example 2 A video tape 1/2 inch wide was prepared as in Example 1 except that the isocyanic acid ester coating solution I was replaced by a lubricant coating solution IV of the following formulation. The magnetic surface of the tape was referred to as Sample No. C-2.

Lubricant coating solution IV Stearic acid [ CH3(CH2)16COOH ] 1.0 part Methyl ethyl ketone 200 parts Example 4 A magnetic cobalt film (0.2y thick) was formed on a polyethylene terephthalate film (20y thick) by oblique deposition to prepare a magnetic tape, wherein electron beams are used to condense the vapor of cobalt (99.95% purity) which was directed onto the PET film at an angle of incidence of 700 at a pressure of 5x 10-5 Torr. A coating solution V for the compound having three isocyanate groups in the molecule having the formulation indicated below was applied onto the Co film and the base film of the magnetic tape in a dry amount of 10 mg/m2, and was left to stand at 500C and 80% RH for 2 hours.

Coating solution V Adduct of one mol of trimethylolpropane and 3 mols of toluene diisocyanate 1.0 part Methyl ethyl ketone 200 parts A lubricant coating solution Vl of the formulation indicated below was applied onto the resulting layer in an amount of 10 mg/m2 and dried at 500C for 10 seconds. The dried film was slit into a video tape 1/2 inch wide, the magnetic surface and the base surface of which were referred to as Sample Nos. 5 and 6, respectively.

Lubricant coating solution Vl Myristic acid 1.0 part n-Hexane 200 parts Example 5 A magnetic tape was prepared in the same manner as in Example 1. Thereafter, a coating solution VII for the compound having two isocyanate groups in the molecule having the formulation indicated below was applied to a cobalt film of the magnetic tape in a dry amount of 10 mg/m2 and was allowed to stand at 500C and 80% RH for 2 hours. The resulting tape was then slit into a video tape 1/2 inch wide, the magnetic surface of which was referred to as Sample No. 7.

Coating solution VII 1,6-Hexamethylene diisocyanate 1.0 part Methyl ethyl ketone 200 parts Example 6 The same procedures as in Example 5 were repeated to obtain a magnetic tape having a 1,6hexamethyiene diisocyanate layer formed on a cobalt film. Thereafter, the lubricant coating solution Vl was applied onto the 1,6-hexamethylene diisocyanate layer in the same manner as in Example 4. The dried film was slit into a video tape 1/2 inch wide, the magnetic surface of which was referred to as Sample No. 8.

Example 7 A magnetic tape was prepared in the same manner as in Example 1. Thereafter, a coating solution VIII for the compound having three isocyanate groups in the molecule having the formulation indicated below was applied on a base film of the magnetic tape in a dry amount of 10 mg/m2, and was allowed to stand at 500C and 80% RH for 2 hours.

Coating solution VIII Triphenylmethane triisocyanate 1.0 part Methyl ethyl ketone 200 parts The lubricant coating solution Vl was applied onto the resulting layer in the same manner as in Example 4 and slit into a video tape 1/2 inch wide, the base surface of which is referred to as Sample No. 9.

Comparative Example 3 A video tape 1/2 inch wide was prepared as in Example 4 except that only the lubricant coating solution Vl was applied to a Co magnetic film. The magnetic surface of the tape was referred to as Sample No. C-4.

The samples thus prepared were subjected to the following film durability (wear resistance) test and measurement of dynamic friction coefficient.

(1) Durability Durability of a magnetic thin film was determined when pressing a magnetic tape against a magnetic head at a tension of 90 g/-21 inch and reciprocating at 38 cm/sec 500 times. The number of visually observed abrasions that were formed on the tape surface was counted.

(2) Measurement of dynamic friction coefficient The magnetic tape was reciprocated on a VHS video tape recorder (Maclord 88, Model NV-8800, of Matsushita Electric Industrial Co., Ltd.) once, 20 times, 100 times and 500 times, and the change in the dynamic friction coefficient (y) was examined by the formula T2 IT,=e8'r wherein T, was the tape tension at the supply side of the rotary cylinder and T2 at the takeup side.

The test and measurement results are shown in Tables 1 and 2. As for the surface of the base, only measurement of the dynamic friction coefficient was conducted with the tapes of Examples 1, 3, 4 and 7 and that of Comparative Example 1 (see Sample Nos. 2, 4, 6, 9 and C-3).

Table 1 (2) Change in dvnamic friction coefficient Sample Sliding (1) Durability* after no. face Protective layer 500 passes 1 20 100 500 1 Magnetic CH3(CH2),7NCO No abrasion observed 0.30 0.31 0.33 0.36 surface 2 Base CH3(CH2),7NCO ---- 0.30 0.31 0.33 0.37 surface 3 Magnetic CH3(CH2)7NC0 No abrasion observed 0.31 0.32 0.35 0.41 surface 4 Base CH3(CH2)" NCO 0.30 0.30 0.31 0.34 0.40 surface C-1 Magnetic More than 10 0.48 0.55 0.58 0.67 surface deep abrasions C-2 Magnetic CH3(CH2)16COOH More than 10 0.30 0.33 0.41 0.48 surface deep abrasions C-3 Base - 0.35 0.40 0.57 0.59 surface *The durability was expressed in terms of the number of abrasions which appeared over the whole width of the tape at an optical portion of the tape.

Table 2 (2) Change in dynamic Sample Sliding Lubricant (1) Durability* after friction coefficient no face Polymer layer layer 500 passes 1 20 100 500 5 Magnetic Adduct of 1 mol Myristic No abrasions observed 0.28 0.29 0.31 0.34 surface of trimethylol- acid propane and 3 mols of toluene diisocyanate 6 Base do. Myristic ---- 0.29 0.31 0.33 0.35 surface acid 7 Magnetic 1,6-Hexamethylene ------ No abrasions observed 0.32 0.35 0.38 0.44 surface diisocyanate 8 Magnetic do.Myristic No abrasions observed 0.29 0.31 0.35 0.40 surface acid 9 Base Triphenylmethane Myristic ----- 0.29 0.31 0.34 0.38 surface triisocyanate acid C-1 Magnetic ----- ----- More than 10 0.48 0.55 0.58 0.67 surface deep abrasions C-4 Magnetic ----- Myristic More than 10 0.30 0.33 0.41 0.48 surface acid deep abrasions C-3 Base ----- ----- ----- 0.35 0.40 0.57 0.59 suface *The durability was expressed in terms of the number of abrasions which appeared over the whole width of the tape at an optical portion of the tape.

One can see from Tables 1 and 2 that the magnetic recording medium of thin metal film type according to the present invention has very good running properties and wear resistance. Further, the improvement in these properties is retained for an extended period of time.

While higher fatty acids (RCOOH) have been known as lubricants for reducing the dynamic friction coefficient of metals, such fatty acids do not tend to react with the thin magnetic metal film and are merely physically adsorbed on the metal film. Therefore, they are easilyrubbed off from the metal film, so that the dynamic friction coefficient of the metal film increases upon repeated running and the metal film cannot be prevented from abrasion as shown in Sample Nos. C-2 and C-4. On the other hand, the isocyanic acid esters and the compounds having at least two isocyanate groups in the molecule can effectively maintain the dynamic friction coefficient of the metal film at a low level even after repeated running and provide excellent wear resistance as shown in Sample Nos. 1,3, 5, 7 and 8.

Further, the isocyanic acid esters and the compounds having at least two isocyanate groups in the molecule can also improve the running properties of the base surface of the recording medium as shown in Sample Nos. 2, 4, 6 and 9. Furthermore, it can be seen from the comparison of Sample Nos.

5, 6 and 9 with Sample Nos. 7 and 8 that a compound having three or more isocyanate groups in the molecule provides the superior effect to that of a compound having two isocyanate groups in the molecule in the change in dynamic friction coefficient after repeated running. It is presumed that the former react with water in air or solvent to form a three-dimensional cross-linked structure, whereby the resulting polymer has an increased strength concerning the running properties and wear resistance as compared to the latter. In addition, one can see from Sample Nos. 7 and 8 that the compounds having at least two isocyanate groups of the present invention are preferably used in combination with a lubricant to further reduce the dynamic friction coefficient, while the wear resistance cannot be improved using a lubricant independently as shown in Sample No. C-4.

Claims

1. A magnetic recording medium, comprising: a non-magnetic support base; a thin magnetic metal film formed on a surface of said non-magnetic support base; and a layer of an isocyanic acid ester or a compound having at least two isocyanate groups in the molecule formed on either said thin magnetic metal layer or the surface of said non-magnetic support base opposite said thin magnetic metal layer, or both.

2. A magnetic recording medium as claimed in Claim 1 , wherein said isocyanic acid ester is represented by the formula RN=C=O wherein R is an alkyl group.

3. A magnetic recording medium as claimed in Claim 2, wherein said alkyl group is a straight chain alkyl group having 8 or more carbon atoms.

4. A magnetic recording medium as claimed in Claim 1, wherein said compound contains at least three isocyanate groups in the molecule.

5. A magnetic recording medium as claimed in any of Claims 1 to 4, wherein said layer of isocyanic acid ester or compound having at least two isocyanate groups in the molecule has a dry weight within the range of from 1 to 100 mg/m2.

6. A magnetic recording medium as claimed in Claim 5, wherein said dry weight is within the range of from 2 to 50 mg/rn2.

7. A magnetic recording medium as claimed in any preceding claim, wherein said layer of compound having at least two isocyanate groups in the molecule also contains a lubricant.

8. A magnetic recording medium as claimed in Claim 7, wherein said lubricant is an aliphatic acid having 10 or more carbon atoms.

3. A magnetic recording medium as claimed in Claim 7 or 8, wherein said lubricant is disposed on said medium in a dry weight of from 2 to 100 mg/m2.

10. A magnetic recording medium as claimed in Claim 9, wherein said dry weight is within the range of from 2 to 50 mg/m2.

11. A magnetic recording medium as claimed in Claim 10, wherein said dry weight is within the range of from 2 to 20 mg/m2.

12. A magnetic recording medium as claimed in any preceding claim, wherein said thin magnetic metal film has a thickness within the range of from 0.05 to 2ym.

13. A magnetic recording medium as claimed in Claim 12, wherein said thickness is within the range of from 0.1 to 0.4,us.

14. A magnetic recording medium substantially as hereinbefore described in any of Examples 1 to 7.

15. A process for producing a magnetic recording medium, comprising the steps of: providing a non-magnetic support base surface; applying a thin magnetic metal film to said surface of said non-magnetic support base by means of vapor deposition; forming a layer of an isocyanic acid ester or a compound having at least two isocyanate groups in the molecule on either said thin magnetic metal film or the surface of said non-magnetic support base opposite said thin magnetic metal layer or both: and heat-treating said layer of said compound.

16. A process as claimed in Claim 15, wherein said heat-treatment is carried out at a temperature of at least 300C for a period of at least 3 seconds.

17. A process as claimed in Claim 16, wherein said heat-treatment is carried out at a temperature of at least 500C at a relative humidity of 30% or more.

18. A process as claimed in Claims 1 5, 1 6 or 1 7, wherein said layer of isocyanic acid ester or compound is formed by applying a solution of said isocyanic acid ester or compound whose concentration is in the range of from 0.05 to 5 wt%.

19. A method as claimed in any of Claims 15 to 18, wherein there is produced a medium as claimed in any of Claims 1 to 14.