GB2261104A - Magnetic recording medium - Google Patents

Abstract

A magnetic recording medium comprising a non-magnetic substrate, a ferromagnetic metal film formed on the substrate and a lubricating layer formed on the ferromagnetic film with a protective layer interposed therebetween, wherein the lubricating layer contains at least one compound selected from the group consisting of compounds of the following formulas (I) and (II): <IMAGE> wherein each of R<1>, R<2>, R<3>, R<4> and R<5> is an organic group having at its terminal an alkyl group having at least 12 carbon atoms, each of X and X' is a hydrophilic group which contains no Si-O bond, A is an organic group connecting R<1> and R<2> to X, A' is an organic group connecting R<3>, R<4> and R<5> to X', and each of k and 1 is an integer of from 1 to 3.

Description

MAGNETIC RECORDING MEDIUM The present invention relates to a magnetic recording medium, particularly to a thin film type magnetic recording medium which is excellent in the durability not only under a usual operational condition but also under a high temperature and high humidity condition.

A thin film type magnetic recording medium is usually prepared by coating a magnetic metal or its alloy on a non-magnetic substrate by plating, vapor deposition or sputtering. In the actual use, it is abraded and damaged by sliding contact of the magnetic recording medium with a magnetic head. As a result, there will be an increase in the friction coefficient or a deterioration of the magnetic properties. As a method for solving such a problem, it has been proposed to provide a protective film or a lubricating film on the magnetic layer, and such a proposal has been actually in use. As the protective film, a carbon film, an oxide film, a carbide film, a nitride film or a boride film is employed. As the lubricating film, a liquid lubricant or a solid lubricant is employed.For example, a perfluoropolyether, or a higher fatty acid or its metal salt, is employed (Japanese Unexamined Patent Publications No. 208622/1986 and No. 64628/1988).

At the time of using a magnetic recording medium, a disc medium is rotated and accelerated rapidly from a stationary state, whereby a lifting power is given to a head slider and the head is lifted. When the electric power is switched off after the use, the motor driving the disk medium for rotation will stop, and the head and the medium will be physically in contact with each other.

Such an operation is repeated to test the durability.

Such a test is called a contact-start-stop test (hereinafter referred to simply as a CSS test).

Conventional magnetic recording media have a problem that in such a CSS test, the friction coefficient increases as CSS is repeated, whereby the surface tends to be damaged by abrasion, or no lifting power tends to be given to the head slider for some reason and sliding contact is likely to take place even during the high speed rotation to cause a phenomenon so-called head crash whereby the head and the medium will be destroyed.

A liquid lubricant is very effective to reduce a dynamic friction coefficient. However, as the thickness of the liquid lubricant film increases, there appears a phenomenon such that the head and the disc stick to each other in a stationary state (so-called sticking), whereby the static friction coefficient increases. Such a sticking phenomenon is believed to be caused by a meniscus formed by the surface tension of the liquid lubricant between the head and the disc, and such sticking tends to be remarkable as the average roughness of the substrate becomes small. To avoid such a sticking phenomenon, it has been proposed to employ a solid lubricant, but the solid lubricant has a problem that the lubricating performance is poor as compared with a liquid lubricant, and when applied in a thick film, it is likely to stain the head or the medium surface.Further, in a thick film, it is likely that crystallization takes place at a part of the coated surface. Such partial crystallization impairs the lubricating performance and the water resistance, since such a portion differs in orientation from the rest. Therefore, there is a limitation in an attempt to increase the film thickness in order to increase the lubricating performance. To obtain adequate durability with a thin film, a method has been proposed in which an alkylsilane is polymerized to increase the bond strength of molecules in the lubricating layer (Japanese Unexamined Patent Publications No. 103721/1990 and No. 103722/1991).

However, the lubricating layer in such a method is polymerized, whereby movement of molecules is restricted and the lubricating performance is inadequate.

Linear fatty acids and their derivatives or metal salts which have long been known as solid lubricants, exhibit excellent lubricating performance, but have a drawback that the stability against heat is so poor that they undergo evaporation or decomposition even by heating at a relatively low temperature, and the lubricating performance deteriorates under a high temperature and high humidity condition.

It is an object of the present invention to solve the above problems and to provide a magnetic recording medium which is durable for use for a long period of time irrespective of the environment in which it is used, by preventing a substantial increase of the friction coefficient not only under a normal condition for use but also under a high temperature and high humidity condition.

The present invention provides a magnetic recording medium comprising a non-magnetic substrate, a ferromagnetic metal film formed on the substrate and a lubricating layer formed on the ferromagnetic film with a protective layer interposed therebetween, wherein the lubricating layer contains at least one compound selected from the group consisting of compounds of the following formulas (I) and (II):

wherein each of R1, R2, R3, R4 and R5 is an organic group having at its terminal an alkyl group having at least 12 carbon atoms, each of X and X' is a hydrophilic group which contains no Si-O bond, A is an organic group connecting R1 and R2 to X, A' is an organic group connecting R3, R4 and R5 to X', and each of k and 1 is an integer of from 1 to 3.

Now, the present invention will be described in further detail with reference to the preferred embodiments.

In the formulas (I) and (II), each of R1, R2, R3, R4 and R5 is an organic group having at its terminal an alkyl group having at least 12 carbon atoms. The organic group may have at such an alkyl group a bonding chain such as an ether bond, an ester bond, an amide bond, an urea bond or an urethane bond, for linkage with A or A'.

The carbon number of the terminal alkyl group is at least 12, usually from 12 to 30, preferably from 16 to 22.

Specific examples of R1 to R5 may preferably be an alkyl group such as C161133-, C171135-, C18H37-, C19H39-, C20H41- or C22H45-, an alkoxy alkyl group of the formula C#H2m+iO(CH2)n such as Cl4H29O(CH2) n-, C15H31O(CH2)### 16H33 (CH2)n~t 7H350(CH2)n C18H37o(cH2) C19H39O(CH2)# or an alkylcarbonyloxyalkyl group of the formula CrnH2rn+iCOO(CH2)n such as CllH23coo(cH2)n~ C12H25COO(CH2)n## , C13H27COO(CH2) C14H29COO(CH2)# or Cl5H3lCOO(CH2) n~' an alkylcarbamoylalkyl group of the formula C,H,,,,NHCO(CH2), such as Cl6H33NHC (CH2) Cl7R35NHco(cH2)n-r C18H37NHCO(CH2)# or Cl9H39NHco(cH2) ~, an alkylureidoalkyl group of the formula CmH2m+lNHCONH(CH2)n~ such as C16H33NHCONK(CH2), , C17H35NHCONH(CH2)n- C18H37NHCONH ( CH2) # or ClgH39NHCONH(CH2)n- and an alkylcarbamoyloxyalkyl group of the formula CmH2n+lNHCOO(CH2)n- such as C16H33NHCOO(CH2)n-, C17H35NHCOO(CH2)n-, C18H37NHCOO(CH2)n- or Cl19H39NHCOO(CH2)- (wherein m is an integer of at least 12, usually an integer of from 12 to 30, preferably an integer of from 12 to 22, and n is an integer of from 0 to 5, preferably an integer of from 0 to 2).

Each of X and X' is a hydrophilic group, but a highly reactive group such as a metal alkoxide or a halide is not desirable. Specifically, it is at least one group selected from the group consisting of -OH, -COOH, -CONH2, -NH2, =CO, -SO3H and a heterocyclic group containing nitrogen or oxygen as a hetero atom. The heterocyclic group is usually a 5- or 6-membered ring. A is an organic group connecting R1 and R2 to X, and A' is likewise an organic group connecting R3, R4 and R5 to X'.

Such an organic group may, for example, be

or

wherein each of p and q is an integer of from 0 to 5. When k or 1 is 2 or 3, each of p and q is an integer of from 1 to 5, and the number of hydrogen atoms bonded to the carbon at the terminal of the bond with X or X' decreases in proportion to the number of bonded X or X'. Further, in the interior of the lubricating layer, if polymerization takes place due to e.g.

hydrolysis, the lubricating performance will be impaired.

Accordingly, the one which bonds to X or X' to form Si-O is undesirable. Namely, the compounds of the above formulas (I) and (II) have both hydrophobic moieties (R1 to R5) and hydrophilic moieties (X and X') in their molecules. Accordingly, these compounds are believed to maintain the mutual affinity with the protective layer by means of the hydrophilic moieties, while the hydrophobic moieties are oriented towards the surface. If polymerization due to e.g. hydrolysis takes place at the mutual affinity portion with the protective layer in the interior of the lubricating layer, the lubricating performance will be impaired, and accordingly, it is undesirable that X or X' has a Si-O bond.

The carbon number of the terminal alkyl group of each of R1 to R5 as the hydrophobic portion of each compound, is at least 12. If the carbon number of this terminal alkyl group is less than 12, the durability tends to be inadequate. Further, if the carbon number exceeds 22, the solubility in a solvent tends to be poor, such is not desirable in the case of a coating method wherein a solvent is employed. However, in a case where a coating method requiring no solvent, such as vapor deposition is employed, there is no such a problem. In the case of coating, the film thickness is preferably up to 80 A. If the film thickness is small, the lubricating performance tends to be poor, and if the film thickness is large, a stain is likely to result during the sliding contact.

Therefore, the film thickness is more preferably from 10 to 50 A.

Preferred specific examples of the lubricants of the formula (I) or (II) to be used in the present invention include (C14H29OCH2) 2CHOH, (C15H31OCH2) 2CHOH, (C16H33OCH2 2)2CHOH, (C17H35OCH2)2CHOH, (C18H37OCH2)2CHOH, (Cl9H39OCH2)2CHOH, (C14H29OCH2)2CHCH2OH, (C16H33OCH2) 2CHCH2OH, (C18H37OCH2) 2CHCH2OH, (C11H23COOCH2 ) 3CNH2, (C13H27COOCH2) 3CNH2 (C15H31COOCH2) 3CNH2, (C16H33)2NCO(CH2) 2COOH, (C17H35)2NCO(CH2)2COOH, (C18H37)2NCO(CH2)2COOH, (C19H3s)2NCO(CH2)2COOH, (C16H33)2NCO(CH2)3COOH, (C17H35)2NCO(CH2)3COOH, (C18H37)2NCO(CH2)3COOH, (C1gH39)2NCO(CH2)3COOH, (C16H33)2NCO(CH2)2CONH2, (C17H35)2NCO(CH2)2CONR2, (C18H37)2NCO(CH2)2CONH2, (C19H39)2NCO(CH2)2CONH2, (C13H27OCH2)2CHO(CH2)2OCH2COOH, (C15H31OCH2)2CHO(CH2)2OCH2COOH, (C17H35OCH2)2CHO(CH2)2OCH2COOH, (Cl6H33)2N(CH2)2COOH, (C16H33)2N(CH2)2COOH, (C18H37)2N(CH2)2COOH, (C16H33)2N(CH2)2CONH2, (C18H37) 2N(CH2) 2CONH2, (C16H33NHCOCH2) 2CHOH, (C17H35NHCOCH2) 2CHOH, (C18H37NHCOCH2) 2CHOH, (C16H33) 2NCOC6H4COOH, (C16H33NHCONHCH2)2CHOH, (C18H37NHCONHCH2) 2CHOH, (C16H33) 2NCOC6H4CH2COOH, (C16H33NHCOOCH2) 3CNH2, (C18H37NHCOOCH2) 3CNH2, (C16fl33)2N(CH2)2CH(COOH)2 and (C18H37)2NCH2CH(CONH2)2.

In addition to the above lubricants, (C16H33) (C17H35) (C18H37)C(CH2)2COOH, (C16H33)(C17H35)NCO(CH2)2COOH, (C1#H35) (C18H37)NCO(CH2)2COOH and (C16H33)2(C17H35)C(CH2)2OH may be mentioned.

However, selection of the lubricant is by no means restricted to the above-mentioned specific lubricants, and any other lubricant may be employed within the scope of the present invention.

In the present invention, after coating the lubricant, the product may be used as it is, as a magnetic recording medium. However, by an application of heat treatment to the lubricant layer, the water repellency can be increased, whereby the lubricating performance will be improved and the effect for water resistance will be remarkable. The heat treatment may be conducted usually by maintaining the coated product in an atmosphere of from 80 to 1500C for from 30 minutes to 2 hours. The contact angle to water of the surface after coating of the lubricant (prior to the heat treatment) is about 600. For example, by the heat treatment at l300C for one hour, the contact angle to water of such a surface can be increased to a level of from 90 to 950.

This phenomenon may be explained in such a way that irregularity in the orientation of the lubricant molecules after coating the lubricant has been mended by the heat treatment to present uniform orientation, whereby the density of the hydrophobic groups at the surface of the lubricant has increased.

It is usually effective to increase the film thickness in order to improve the performance of the lubricant film. However, in the case of a solid lubricant, some irregularity in the orientation is likely to result due to partial crystallization. Further, crystallization will be promoted in a high humidity atmosphere. From further studies, the present inventors have found it possible to control this crystallization and thereby to improve the performance by property selecting and combining the compounds having different terminal alkyl groups in R1 to R5 among the compounds of the formulas (I) and (II).

That is, the lubricating layer may, for example, (i) contain at least two compounds of the formula (I) wherein the terminal alkyl groups of R1 and R2 are the same, and the carbon numbers of the terminal alkyl groups of R1 or R2 of the respective compounds are mutually continuous, (ii) contain at least two compounds of the formula (II) wherein the terminal alkyl groups of R3, R4 and R5 are the same, and the carbon numbers of the terminal alkyl groups of R3, R4 or R5 of the respective compounds are mutually continuous, (iii) contain at least two compounds of the formula (I) wherein the terminal alkyl groups of R1 and R2 are different from each other, and the carbon numbers of the terminal alkyl groups of at least one of R1 and R2 of the respective compounds are mutually continuous, or (iv) at least two compounds of the formula (II) wherein the terminal alkyl groups of R3 and R4 are the same, and the carbon numbers of the terminal alkyl groups of R3 or R4 of the respective compounds are mutually continuous.

Specifically, the lubricating layer may, for example, contain (i) a mixture of (C171135)2NCO(CH2)2COOH and (C18H37)2NCO(CH2)2COOH, (ii) a mixture of (C171135)3C(CH2)2OtI and (Cl8H37)3C(CH2)2OH, (iii) a mixture of (C14H29) (C16H33)N(CH2)2CONH2 and (C22H45)(C17H35)N(CH2)2CONH2, or (iv) a mixture of (C17H35)2(C16H33)C(CH2)2COOH and (C18H37)2(C20H41)C(CH2)2COOH. In such a mixture, it is preferred that the proportion of a compound wherein the carbon numbers of the terminal alkyl groups are even numbers is substantially equal by mol to the proportion of a compound wherein the carbon numbers of the terminal alkyl groups are odd numbers, among the terminal groups of R1 to R5 of the compounds to be mixed.

Heretofore, it has been known by experience that crystallization may sometimes be suppressed by mixing different types of compounds. However, in such a case, unless the mixed compounds have sufficient compatibility, they tend to be separated when left to stand under a high humidity condition or for a long period of time, and no adequate control of crystallization can be accomplished by such a mixture. However, compounds having different alkyl chain lengths only by one or two carbon atoms, as in the present invention, usually maintain limitless compatibility, whereby the effect for controlling crystallization by mixing will sufficiently be performed.

When the number of compounds to be mixed is larger, for example, three compounds rather than two compounds, the effect will be higher. In such a case, groups X and X' as well as A and A' in the compounds should be preferably the same.

The melting point of the mixture of lubricants is lower than the melting point of a single lubricant. From the inventors' experience, a slight sticking phenomenon is likely to be observed when the melting point of a solid lubricant is less than 700C. This is believed attributable to the fact that partial fusion is caused by the sliding heat, but the actual mechanism is not clearly understood. There is no clear upper limit for the melting point, but the initiation of thermal decomposition is at a level of 2000C. Accordingly, with respect to selection of lubricants when compounds of the formulas (I) and (II) are used in combination, it is advisable to select the compounds so that the melting point of the mixture will be at least 700C and usually at most 2000C, preferably at most 1500C,.

By the use of the compounds of the formulas (I) and (II), according to the present invention, not only the durability under a normal condition for use but also the durability under a high temperature and high humidity condition, can be remarkably improved. This is believed due to a fact that when the compounds are coated on the protective layer, the density of the hydrophobic moieties of the compounds becomes high. Namely, the hydrophobic moiety of each compound is composed of two or three alkyl groups each having at least twelve carbon atoms.

Therefore, as compared with a case of a linear fatty acid having only one alkyl chain, the compound of the present invention presents a higher density of the hydrophobic moieties in an oriented state. The degree of this orientation can be improved by the heat treatment.

Further, when the organic group A or A' linking the hydrophobic terminal alkyl groups of R1 to R5 to the hydrophilic group X or X', has a polarity, such a polarity is expected to serve to enhance the orientation by creating an electrostatic interaction between adjacent molecules when the molecules are oriented.

Accordingly, by the use of compounds of the formulas (I) and (it), a dense lubricating film with a uniform orientation can be obtained. It is believed that as a result, the orientation is hardly disturbed even at a high temperature, and a structure can be obtained whereby even under a high humidity condition, water molecules can hardly penetrate into the lubricating film as blocked by the dense hydrophobic moieties. Thus, the lubricating performance undergoes no deterioration even under a high temperature and high humidity atmosphere, and it is possible to obtain a remarkable effect to prevent corrosion. Further, if the molecule contains a metal as in the case of a metal salt of a fatty acid, the orientation will be disturbed by swelling under a high humidity condition.However, the compounds of the formulas (I) and (II) used in the present invention have no such a problem, since they contain no such a metal.

Further, by properly selecting and combining specific compounds wherein the alkyl chain lengths of the terminal alkyl groups of R1 to R5 are different among said compounds, it is possible to form a thick film having crystallization controlled and it is thereby possible to further improve the lubricating performance and the water resistance.

In the present invention, there is no particular restriction as to the non-magnetic substrate. It is usually common to employ an aluminum alloy plate having a nickel-phosphorus layer formed by electroless plating.

However, a metal substrate made of e.g. copper or titanium, a glass substrate, a ceramic substrate, a carbon substrate or a resin substrate may also be employed. The magnetic recording layer is formed by such a method as electroless plating, electroplating, sputtering or vapor deposition. As the magnetic layer, a ferromagnetic metal film of such an alloy has Co-P, Co Ni-P, Co-Ni-Cr, Co-Ni-Pt, Co-Cr-Pt or Co-Cr-Pt-Ta, is formed, and the film thickness is usually from 300 to 700 A. On this magnetic recording layer, as a protective layer, a carbon film, an oxide film such as SiO2, At203 or ZrO2, a carbide film such as TiC or SiC, or a nitride film such as Si3N4 or TiN, is formed by such a method as vapor deposition, sputtering, plasma CVD, ion plating or a wet system method. On this protective layer, a lubricant containing at least one compound selected from the group consisting of compounds of the formula (I) and (II), is laminated. Specifically, such a lubricant is dissolved in an organic solvent such as an alcohol, a ketone, an ester, an aromatic hydrocarbon or a halogenated hydrocarbon, and such a solution is coated by a common method such as a dip coating method, a spin coating method, a spray coating method or an LB method.

Otherwise, it may be formed by vapor deposition.

Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted by such specific Examples.

COMPARATIVE EXAMPLE 1 On an aluminum alloy substrate having an average roughness of from 50 to 60 A and having a diameter of 3.5 inches, 200 A of cbromium, 500 A of a magnetic film of a cobalt alloy and 300 A of a carbon protective film were sequentially formed by sputtering to obtain a magnetic disc. On this magnetic disc, a lubricating layer having a thickness of 30 A was formed by a dip coating method using a solution having sodium stearate dissolved in a solvent mixture of methanol and Furon 113.

Using the obtained disc, a CSS test was conducted.

As the head, a thin film head with AW203-TiC slider with a load of 9.5 g, was employed. The motor for rotating the disc was switched on to rotate the disc at 3,600 rpm for 5 seconds, and then the power was switched off and left for 25 seconds. This operation was taken as one cycle of CSS. The test was started under a normal temperature and normal humidity condition (250C, 40%), and after 2,000 cycles of CSS, the temperature and the humidity were raised, and CSS was conducted for further 2,000 cycles in an atmosphere of 600C under a relative humidity of 80%. Then, the temperature and humidity were lowered to the normal temperature and normal humidity condition, and the test was continued. In this manner, the test environment was alternately changed between 250C under 40% and 600C under 80% every 2,000 cycles of CSS.

the test cycle was every 20,000 cycles of CSS, and the friction coefficient after 20,000 cycles of CSS was measured. Further, after the test, the surface of the disc was inspected to see the presence or absence of scratch marks or stain on the disc surface.

The test results are shown in Table 1. With the disc of Comparative Example 1, the sliding scratch marks were observed on the surface after the test.

COMPARATIVE EXAMPLE 2 In the same manner as in Comparative Example 1, a disc was prepared up to the formation of the carbon protective film. On this disc, a lubricating layer of magnesium stearate was formed by spin coating in a film thickness of 40 A. Using the obtained disc, a CSS test was conducted in the same manner as in Comparative Example 1.

The test results are shown in Table 1. The disc in Comparative Example 2 underwent head crash at the point of 12,000 cycles of CSS. Accordingly, the friction coefficient of this disc shown in Table 1 is the one measured at the point of 12,000 cycles of CSS.

EXAMPLES 1 to 15 In the same manner as in Comparative Example 1, the disc was prepared up to the carbon protective film. On this disc, a lubricating layer having a film thickness of 30 A was formed by a dipping method using a solution having the lubricant as identified in Table 1 dissolved in chloroform, followed by the CSS test. The test results indicating the friction coefficients and the presence or absence of the scratch marks or stain on the disc surface are shown in Table 1.

It is evident that the durability under a high temperature and high humidity condition is remarkably improved by using the lubricants of the formulas (I) and (if).

Table 1

Friction Surface Example No. Lubricant coefficient inspection Comparative Sliding scratch Example 1 C17H35COONa 0. 42 marks observed Deep Deep sliding Comparative Example 2 (C17H35C0O)2Mg (0.63) scratch marks observed Slight sliding Example 1 (Cl4H29OCH2)2CHOH 0.32 scratch marks observed Example 2 (Cl6H33OcH2)2cHOH 0.24 No scratch mark or 2 (C16H33OCH2) 2CHOH 0.24 or stain observed No scratch mark Example 3 (C11H23COOCH2)3CNH2 0.25 or stain observed Example 4 (C15H31COOCH2)3CNH2 0. 24 No scratch mark or stain observed No scratch mark Example 5 (C16H33)2NCO(CH2)2COOH 0. 21 or stain observed No scratch mark Example 6 (C18H37)2NCO(CH2)2COOH 0. 23 or stain observed (C15H31OCH2)2CHO(CH2)2- No scratch mark Example 7 15312 222 0. or No stain observed OCH2COOH No 8 (C H NHCOCH )2CHOH 0.26 No scratch mark Example 8 (C16H33NHCOCH2)2CHOH 0.26 or stain observed No scratch mark Example 9 (C16H33NHCONHCH2)2CHOH 0.26 or stain observed Table 1 (continued)

Friction Surface Example No. Lubricant coefficient inspection Example 10 (C16H33NHCOOCH2) 3CH22 0.30 No scratch Example 10 (C16H33NHCOOCH2) 3CNH2 0.30 or stain observed No scratch mark Example 11 (C18H37)2NCO(CH2)3COOH 0.22 or stain observed No scratch mark Example 12 (C18H37)2NCO(CH2)2CONH2 0.20 or stain observed No scratch mark Example 13 (C18H37)2N(CH2)2COOH 0.25 or stain observed Example 14 (C18H37)2N(CH2)2CONH2 0.26 No scratch mark or on stain observed No 8H37)2NCH2CH(CONH2\ 0.25 No scratch mark Example 15 (C18H37)2NCH2CH(CONH2)2 0.25 or stain observed EXAMPLES 16 to 19 In the same manner as in Comparative Example 1, a disc was prepared up to the carbon protective film.On this disc, a lubricating layer having a film thickness of 50 A was formed by a dip coating method using a solution having the lubricant as identified in Table 2 dissolved in chloroform, and then the disc was left to stand for 7 days in a high humidity atmosphere (250C, 80%), whereupon the presence or absence of crystal precipitation was inspected by an optical microscope. Then, a CSS test was conducted in the same manner as in Comparative Example 1, and the friction coefficient was measured, and the surface was inspected. The results are shown in Table 2.

Table 2

Crystal Friction Surface Example No. Lubricant precipi- coefficient inspection No scratch Example 16 (C16H33)2NCO(CH2)2COOH Observed 0.35 mark or stain observed Equimolar mixture of No scratch Example 17 (C16H33)2NCO(CH2)2COOH Slightly and 17 and observed 0.22 mark or stain observed (C17H35)2NCO(CH2)2COOH Mixture of (C16H33)2NCO(CH2)2COOH, Not No scratch Example 18 (C17H35)2NCO(CH2)2COOH observed observed 0.21 mark or stain and observed observed and (C18H37) 2NCO ( CH2) 2COOH Equimolar mixture of No scratch Example 19 (C17H35)2N(CH2)2CONH2 Not 0.23 mark or stain and observed observed (C18H37)2N(CH2)2CONH2 With the magnetic recording medium of the present invention, not only the durability under a normal condition for use but also the durability under a high temperature and high humidity condition can be remarkably improved by the use of the compounds of the formulas (I) and (II).

Further, this effect can be remarkably improved by heat treatment of the lubricating layer.

Further, by properly selecting and combining certain specific compounds having different alkyl chain lengths of the terminal alkyl groups of R1 to R5 among the compounds of the formulas (I) and (II), it is possible to suppress the partial crystallization of the lubricant and to further improve the lubricating performance and the water resistance.

Thus, the present invention has a significant industrial value.

Claims (25)

CLAIMS:

1. A magnetic recording medium comprising a non-magnetic substrate, a ferromagnetic metal film formed on the substrate and a lubricating layer formed on the ferromagnetic film with a protective layer interposed therebetween, wherein the lubricating layer contains at least one compound selected from the group consisting of compounds of the following formulas (I) and (II):

wherein each of R1, R2, R3, R4 and R5 is an organic group having at its terminal an alkyl group having at least 12 carbon atoms, each of X and X' is a hydrophilic group which contains no Si-O bond, A is an organic group connecting R1 and R2 to X, A' is an organic group connecting R3, R4 and R5 to X', and each of k and 1 is an integer of from 1 to 3.

2. The magnetic recording medium according to Claim 1, wherein each of R1, R2, R3, R4 and R5 in the formulas (I) and (II) is an organic group having at its terminal an alkyl group having from 12 to 30 carbon atoms.

3. The magnetic recording medium according to Claim 1, wherein each of R1, R2, R3, R4 and R5 in the formulas (I) and (II) is an organic group selected from the group consisting of an alkyl group, an alkoxyalkyl group, an alkylcarbonyloxyalkyl group, an alkylcarbamoylalkyl group, an alkylureidoalkyl group and an alkylcarbamoyloxyalkyl group.

4. The magnetic recording medium according to Claim 1, wherein each of X and X' is a hydrophilic group selected from the group consisting of -OH, -COOH, -CONH2, -NH2, =CO, 503 and a heterocyclic group containing nitrogen or oxygen as a hetero atom.

5. The magnetic recording medium according to Claim 1, wherein each of A and A' is an organic group selected from the group consisting of

and

wherein each of p and q is an integer of from 0 to 5.

6. The magnetic recording medium according to Claim 1, wherein the lubricating layer has a thickness of from 10 to 50 A.

7. The magnetic recording medium according to Claim 1, wherein the compounds of the formulas (I) and (II) are (C14H29OCH2)2CHOH, (C15H31OCH2)2CHOH, (C16H33OCH2)2CHOH, (C17H350CH2) 2CHOH, (C18H37OCH2) 2CHOH, (C19H39OCH2) 2CHOH, (C14H29OCH2) 2CHCH2OH, (C16H33OCH2 ) 2CHCH2OH, (C18H37OCH2) 2CHCH2OH, (C11H23COOCH2) 3CNH2, (C13H27COOCH2) 3CNH2, (C15H31COOCH2) 3CNH21 (C16H33)2NCO(CH2)2COOH, (C17H35)2NCO(CH2)2COOH, (C18H37)2NCO(CH2)2COOH, (C19H39)2NCO(CH2)2COOH, (C1#H33)2NCO(CH2)3COOH, (C171135)2NCO(CH2)3COOH, (C18H37)2NCO(CH2)3COOH, (C19H39)2NCO(CH2)3COOH, (C16H33)2NCO(CH2)2CONH2, (C17H35)2NCO(CH2)2CONH2, (C18H37)2NCO(CH2)2CONH2, (C19H39)2NCO(CH2)2CONH2, (Cl3H27OCH2) 2CHO(CH2)2OCH2COOH, (C15H31OCH2 )2CHO(CR2)2OCH2COOH, (C17H35OCH2)2CHO(CH2)2OCH2COOH, (C16H33)2N(CH2)2COOH, (C18H37)2N(CH2)2COOH, (C16H33)2N(C112)2CONH2, (C18H37) 2N(CH2) 2CONH2, (C16H33NHCOCH2)2CHOH, (C17H35NHCOCH2) 2CHOH, (C18H37NHCOCH2) 2CHOH, (C16H33) 2NCOC6H4COOH, (C16H33NHCONHCH2) 2CHOH, (C18H37NHCONHCH2) 2CHOH, (C15H33 ) 2NCOC6H4CH2COOH, (C15H33NHCOOCH2) 3CNH2, (C18H37NHCOOCH2) 3CNH2, (C16H33)2N(CH2)2CH(COOH)2, (C18H37)2NCH2CH(CONH2)2, (C16H33)(C17H35)(C18H37)C(CH2)2COOH, (C16H33) (C17H35)NCO(CH2)2COOH, (C17H35) (C18H37)NCO(CH2)2COOH and (C16H33)2(C17H35)C(CH2)2OH.

8. The magnetic recording medium according to Claim 1, wherein the lubricating layer is heat-treated after being formed on the ferromagnetic metal film with a protective layer interposed therebetween.

9. The magnetic recording medium according to Claim 8, wherein the heat-treatment is conducted at a temperature of from about 80 to 1500C for from about 30 minutes to 2 hours.

10. The magnetic recording medium according to Claim 8, wherein the contact angle to water of the surface of the lubricating layer after the heat-treatment is within a range of from about 90 to 950.

11. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains at least two compounds of the formula (I) in admixture, the terminal alkyl groups of R1 and R2 in each compound being the same, and the carbon numbers of the terminal alkyl groups of R1 or R2 in the respective compounds being mutually continuous.

12. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains at least two compounds of the formula (II) in admixture, the terminal alkyl groups of R3, R4 and R5 in each compound being the same, and the carbon numbers of the terminal alkyl groups of R3, R4 or R5 in the respective compounds being mutually continuous.

13. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains at least two compounds of the formula (I) in admixture, the terminal alkyl groups of R1 and R2 in each compound are different from. each other, and the carbon numbers of the terminal alkyl groups of at least one of R1 and R2 in the respective compounds are mutually continuous.

14. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains at least two compounds of the formula (II) in admixture, the terminal alkyl groups of R3 and R4 in each compound being the same, and the carbon numbers of the terminal alkyl groups of R3 or R4 in the respective compounds being mutually continuous.

15. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains (C17H35)2NCO(CH2)2COOH and (C18H37)2NCO(CH2)2COOH, as the compounds of the formulas (I) and (II).

16. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains (C17H35)3C(CH2)2OH and (C18H37)3C(CH2)2OH, as the compounds of the formulas (I) and (II).

17. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains (C14H29) (C16H33)N(CH2)2CONH2 and (C22H45)(C17H35)N(CH2)2CONH2, as the compounds of the formulas (I) and (II).

18. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains (C17H35)2(C16H33)C(CH2)2COOH and (C18H37)2(C20H41)C(CH2)2COOH, as the compounds of the formulas (I) and (II).

19. The magnetic recording medium according to any one of Claims 1 to 18, wherein the non-magnetic substrate is an aluminum alloy plate provided with a nickel-phosphorus layer, a glass substrate, a ceramics substrate, a carbon substrate or a resin substrate.

20. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains (C16H33)2NCO(CH2)2COOH and (C17H35)2NCO(CH2)2COOH as the compounds of the formulas (I) and (II).

21. The magnetic recording medium according to Claim 20, wherein (C16H33)2NCO(CH2)2COOH and (C17H35)2NCO(CH2)2COOH are contained substantially in equimolar amounts.

22. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains (C16H33)2NCO(CH2)2COOH, (C17H35)2NCO(CH2)2COOH and (C18H37)2NCO(CH2)2COOH as the compounds of the formulas (I) and (II).

23. The magnetic recording medium according to Claim 22, wherein (C16H33)2NCO(CH2)2COOH, (C17H35)2NCO(C112)2COOH and (C18H37)2NCO(CH2)2COOH are contained substantially in a molar ratio of 1:2:1.

24. The magnetic recording medium according to Claim 1, wherein the lubricating layer contains (C17H35)2N(CH2)2CONH2 and (C18H37)2N(CH2)2CONH2 as the compounds of the formulas (I) and (II).

25. The magnetic recording medium according to Claim 24, wherein (C17H35)2N(CH2)2CONH2 and (C18H37)2N(CH2)2CONH2 are contained substantially in equimolar amounts.