JPS63161516A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve stability of running performance and durability by forming a Langmuir-Blodgett layer (LB layer) consisting of a fluorine-contg. lubricative compd. having a hydrophilic group on the surface of a magnetic layer. CONSTITUTION:The LB layer to be formed on the magnetic layer consists of the fluorine-contg. lubricative compd. having the hydrophilic group. The respective molecules of said compd. attain the dense and highly oriented state of the shape in which said molecules are adsorbed on the metal surface of the magnetic layer via the hydrophilic group and rise perpendicularly on the surface of the magnetic layer with the atomic groups contg. the fluorine to make important contribution to the lubricity as the uppermost layer. The lubricating effect of the fluorine-contg. lubricative compd. is, therefore, exhibited to the max. extent in this embodiment and the coefft. of wear on the surface of the magnetic layer side is considerably decreased. The stable running performance and good durability are thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape having a magnetic layer made of a ferromagnetic metal thin film.

[Prior Art] This type of magnetic recording medium is made by depositing Co, N, etc. on a substrate such as a polyester film by a vacuum deposition method such as vacuum evaporation.
It has a magnetic layer made of a thin film of ferromagnetic metal such as i1Fe or an alloy of these, and has a significantly higher recording density than conventional general-purpose magnetic recording media that have a magnetic layer made of magnetic powder bound with a binder. It has the advantage of being able to achieve However, in such magnetic recording media, the surface smoothness of the magnetic layer is very high, and it comes into sliding contact with the magnetic head and guide part over a large area during recording and reproduction.
The frictional resistance is large and running stability is difficult, and since the thickness of the magnetic layer is usually very thin (0.1 to 0.5 tones), it is easy to wear and scratch due to the above-mentioned sliding contact and has poor durability. There were drawbacks.

Therefore, conventionally, a lubricant layer made of saturated fatty acids and their esters, liquid paraffin, fluorine-based lubricants, etc. is formed as a protective film on the surface of the magnetic layer by coating, dipping, or spraying to reduce the coefficient of friction. Attempts have been made to improve durability (documents unknown). It has also been proposed to provide lubricity by forming a monomolecular layer of higher fatty acids or their metal salts on the surface of the magnetic layer by the Langmiuer Blodget method.
6-30609, JP-A-61-148623).

[Problem that the invention seeks to solve]

However, in magnetic recording media that have a lubricant layer formed by a coating method or a dipping method, it is difficult to control the orientation of lubricant compound molecules when forming the layer, and these molecules are randomly distributed on the surface of the magnetic layer. It is inevitable that a considerable proportion of high-energy polar groups such as carboxyl groups will be located on the surface side of the lubricant layer.
For this reason, there was a problem in that the coefficient of friction on the surface of the magnetic layer could not be significantly reduced.

On the other hand, according to the Langmuir-Blodget method, a monomolecular layer in which each constituent molecule is highly oriented can be formed on the substrate surface, and this is used to form the lubricant layer in the magnetic recording medium proposed above. A higher lubrication effect can be obtained compared to those having a lubricant layer formed by coating or dipping. However, even with such a lubricant layer consisting of a monomolecular layer, it cannot be said that the coefficient of friction is sufficiently reduced, and there is a desire for improved durability through a higher level of lubricating effect.

This invention was made in order to meet the above-mentioned needs, and an object of the present invention is to provide a magnetic recording medium that has a very small coefficient of friction on the surface of the magnetic layer side, exhibits stable running performance, and has extremely high durability. It is said that

[Means for solving problems]

As a result of extensive studies to achieve the above object, the inventors found that when a Langmuir block layer made of a specific compound is provided on the surface of a magnetic layer made of a ferromagnetic metal thin film, the magnetic layer The friction coefficient of the side surface is significantly reduced,
It was discovered that even when this magnetic recording medium is repeatedly run, the surface maintains good lubricity, low friction prevents the occurrence of scratches, and extremely excellent durability is achieved. I arrived at the eggplant.

That is, the present invention provides a magnetic recording medium having a magnetic layer made of a ferromagnetic metal thin film on a substrate, in which a Langmuir brodget layer made of a fluorine-containing lubricating compound having a hydrophilic group is provided on the surface of the magnetic layer. It relates to a magnetic recording medium characterized in that it is formed.

[Structure and operation of the invention]

The above-mentioned Langmuir Blossom layer (hereinafter referred to as LB layer) is a monomolecular layer formed by the Langmuir Blosget method, and is generally a layer in which a water-insoluble compound is dissolved in a volatile solvent. is dropped onto the water surface to develop it, and the monomolecular layer of the compound formed on the water surface by volatilization of the solvent is transferred to the surface of the substrate by pulling up a clean substrate immersed in water.

When the above compound has a hydrophilic group, when surface pressure is applied from the side to the monomolecular layer on the water surface to reduce the area above the water surface, each molecule of the compound changes from a random state to a hydrophilic group. A densely oriented state is formed in which the molecule stands perpendicular to the water surface with the surface facing the water, and the monomolecular layer is transferred onto the substrate while maintaining this oriented state. In addition, monomolecular layers can be formed by repeating this operation, so
The layer thickness on the substrate can be set arbitrarily.

The LB layer in the magnetic recording medium of this invention is made of a fluorine-containing compound having a hydrophilic group as described above, and each molecule of this compound is adsorbed to the metal surface of the magnetic layer via the hydrophilic group, and It has a dense and highly oriented state in which the atomic group containing fluorine, which greatly contributes to lubricity, stands at the top and stands perpendicular to the surface of the magnetic layer. Therefore, in the magnetic recording medium of the present invention, the lubricating action of the above-mentioned fluorine-containing lubricating compound is maximized,
The coefficient of friction on the surface of the magnetic layer is significantly reduced, exhibiting stable running properties, and each molecule of the above compound strongly adsorbs to the surface of the magnetic layer and is difficult to fall off, maintaining an excellent lubricating effect even after repeated running. This prevents wear and scratches, resulting in extremely good durability.

Various types of fluorine-containing lubricating compounds can be used as the above-mentioned fluorine-containing lubricating compound, but those having a fluorine-containing atomic group on at least one end of the chain-like molecule and a hydrophilic group on the other end are preferred. suitable. Examples of the hydrophilic group include polar groups such as a carboxyl group, a hydroxyl group, an alkyl ester residue, a phosphoric acid ester residue, and a sulfonic acid ester residue.

Suitable examples of such compounds include the following structural formula;
2 is a hydrogen atom or an alkyl group, n is an integer of 1 or more, m
is an integer of 0 or more), and among these, those in which n+m in the above formula is 8 or more are particularly suitable.

Moreover, as the above-mentioned fluorine-containing lubricating compound, compounds having a group that can be polymerized by radiation irradiation can also be used. This polymerizable group may be included in the hydrophilic group.

That is, the LB layer made of a fluorine-containing lubricating compound having such a polymerizable group is formed on the magnetic layer and then irradiated with radiation such as an electron beam or ultraviolet rays, thereby forming the LB layer in the highly oriented state. The molecules of the compound mutually polymerize while maintaining this orientation, and the entire layer is uniformly integrated, making it strong and highly wear resistant, further improving the durability of the magnetic recording medium.

A suitable example of the fluorine-containing lubricating compound having the above-mentioned radiation polymerizable group is the following structural formula % formula % () (wherein L I R5 and R6 are methylene groups, R4
is an alkenyl group or an alkynyl group, R7 is a hydrogen atom or an alkyl group, l, j and k are integers of 0 or more, and n is the same as above.
+l is 8 or more, and (n+ in the surface formula
It is optimal that j0k is 6 or more.

In this invention, in order to form the LB layer made of the above-mentioned fluorine-containing lubricating compound, 0.05-0.5% by weight of the compound is added to a volatile solvent such as 1,1,2-trichlorotrifluoroethane or chloroform. A solution dissolved at a certain level is dropped onto the water surface in an aquarium, a monomolecular layer of the above compound is developed on the water surface, and the area on the water surface is reduced by compressing it with a barrier from the side to form a monomolecular layer. is brought into a highly oriented state, and a substrate on which a magnetic layer made of a thin ferromagnetic metal film has been previously formed is passed through the water and pulled up above the water surface. At this time, in order to continuously form the LB layer, it is sufficient to introduce the long tape-shaped substrate into water at a constant speed and pull it up, while continuously supplying the solution above the water surface. An LB layer consisting of a plurality of monomolecular layers can be formed by repeatedly introducing and pulling out the LB layer into water.

If the fluorine-containing lubricating compound used has a group that can be polymerized by radiation irradiation, LB
After forming the layer, the above compounds may be polymerized by irradiation with electron beams, ultraviolet rays, or the like.

The surface pressure during compression by the above barrier is 10 to 40
mNm, more preferably 20 to 35 mNm-
' is better. In addition, the number of monomolecular layers constituting the LB layer is 1 to
It is preferable to have about 50 layers, especially about 3 to 15 layers. Further, the total thickness of the LB layer is about 20 to 1,000A, preferably 30 to 300A.

In addition, in order to improve the film forming property of a monomolecular layer, the above water contains an alkali metal salt or an alkaline earth metal salt at a molar concentration of 1 x 10 to 1 x 10, and the pH is adjusted to 5.0. ~
It is recommended to adjust it to 8.0, especially in the range of 5.5 to 6.5.

The ferromagnetic metals constituting the magnetic layer of the magnetic recording medium of the present invention include conventional ferromagnetic metals such as Co, Ni, Fe%Cr, alloys thereof, and alloys containing these and other metals or small amounts of nonmetallic elements. Any known material for magnetic layers made of thin metal films can be used. Moreover, various methods such as vacuum evaporation, sputtering, ion blating, electroplating, electroless plating, and vapor phase plating can be adopted as the formation method. Note that the thickness of such a magnetic layer is preferably about 0.1 to 0.3p.

〔Effect of the invention〕

In the magnetic recording medium of the present invention, since the LB layer made of a fluorine-containing lubricating compound having a hydrophilic group is formed on the surface of the magnetic layer made of a ferromagnetic metal thin film, the coefficient of friction on the surface of the magnetic layer side is extremely low. , and the adhesion between the LB layer and the magnetic layer is good, and the surface maintains good lubricity even after repeated running, providing stable running performance with low friction and preventing wear and sliding contact. It does not easily cause scratches and exhibits extremely high durability.

[Example] Hereinafter, this invention will be specifically explained based on examples.

Example 1 A polyester film with a thickness of 12/'' was loaded into a vacuum deposition apparatus, and metal cobalt was heated and evaporated under a vacuum of 5×10 Torr to form a magnetic layer consisting of a ferromagnetic metal thin film with a thickness of 0.2p. .

On the other hand, prepare a solution in which C3F17CH2CH20COoH is dissolved at a ratio of 100 to 100 chloroform, and drop this solution onto the water surface of pH 6.0 water to which 5 x 10 molar concentration of CuC1 has been added. After developing a monomolecular layer of the chemical compound, the area above the water surface is reduced by a barrier, and the surface pressure is reduced to 28 mNm.
-' to orient the monolayer.

Next, the polyester film having the magnetic layer was introduced into the water and passed through the monomolecular layer three times, thereby forming an LB layer with a thickness of 60A consisting of three monomolecular layers on the surface of the magnetic layer. was formed to produce a magnetic tape.

Example 2 C3F17CH2CH2 as a fluorine-containing lubricating compound
After forming an LB layer in the same manner as in Example 1 except that 100 q of COOCH=CH2 was used, the LB layer was polymerized by irradiation with a 3 megarad electron beam to produce a magnetic tape.

Example 3 C3F17CH2CH as a fluorine-containing lubricating compound,
A magnetic tape having a polymerized LB layer was prepared in the same manner as in Example 2, except that 100 cm of CH=CHCH2CH2C0OH was used.

Comparative example 1 0.1% by weight (D Ca F 17cHz cH20
In a methyl ethyl ketone solution containing COOH, Example 1
A polyester film on which a magnetic layer was formed in the same manner as above was immersed, taken out and dried to produce a magnetic tape having a 100A thick lubricant layer made of the above-mentioned fluorine-containing lubricant compound on the magnetic layer.

Comparative Example 2 Stearic acid was used in place of the fluorine-containing lubricating compound.
A magnetic tape was produced in the same manner as in Example 1 except that ~ ~ was used.

The results of examining the friction coefficient, sliding damage, and contact angle of the magnetic tapes of the above Examples and Comparative Examples are as shown in the table below. In addition, the coefficient of friction and sliding damage are based on the outer diameter of each tape of 4I+! #l cylindrical bottle (SUS30
Multiply 4) by angle 90, load 21y, feed speed 1.4m
Repeatedly sliding the same part at a speed of 1/sec, measuring the coefficient of friction on the surface of the magnetic layer after each required number of slides, and visually observing the scratches caused by the sliding. Those that were observed were evaluated as B, and those that were recognized as significant were evaluated as C.

Further, the contact angle was measured as follows.

That is, first, on each magnetic tape (the lubricant layer), a diameter of 1
A water droplet of ~2 mff1 is placed on it, the water droplet is enlarged on a monitor TV, and the height h and radius r of the water droplet are actually measured.

This actual measurement was carried out both when the water droplet was made larger with the injection needle, and when it was made smaller, when it was made smaller. From these measurements, the contact angle of the water droplet in each case, that is, the advancing contact angle θa, and the retreating water droplet were calculated. The contact angle θr was determined according to the following formula, and the contact angle θ of the water droplet was determined from these contact angles θa and θr according to the following formula 0.

2 rl r2 h+ : Height of water droplet in #J system h2: Height of water droplet in backward movement rl: Radius of water droplet in forward movement r2: Radius of water droplet in backward movement Note that the contact angle θ of the above water droplet is as follows: As shown in the accompanying drawings, it refers to the contact angle of water droplets to the magnetic tape surface, and the larger the contact angle, the better the orientation of the lubricant layer and the better the lubricating performance. In the figure, 1 is a magnetic tape consisting of a base 1a, a magnetic layer 1b, and a lubricant layer IC, 2 is a water droplet, and θ is the above-mentioned contact angle.

From the above table, LB consisting of a specific fluorine-containing lubricating compound
The magnetic tape of this invention (Examples 1 to 3) having a layer of
It has an extremely low coefficient of friction and excellent running stability.Moreover, even after repeated running many times, the increase in the coefficient of friction is extremely small and good lubricity is maintained.
It is clear that no scratches occur and it has excellent durability. Furthermore, it can be seen that the durability is further improved in the magnetic tapes (Examples 2 and 3) in which the LB layer is polymerized.

On the other hand, magnetic tape (
In Comparative Example 1), the coefficient of friction is large, the running stability is poor, and the lubricating effect is lost due to repeated running, indicating that the durability is insufficient. In addition, the magnetic tape provided with the LB layer made of higher fatty acids (Comparative Example 2) has improved lubricity, running stability, and durability compared to the magnetic tape provided with the lubricant layer formed by the dipping method (Comparative Example 1). However, when compared with the magnetic tape of the present invention, it can be seen that each performance is inferior.

[Brief explanation of the drawing]

The drawing is a cross-sectional view for explaining a method of measuring the contact angle of water regarding the magnetic tapes of Examples and Comparative Examples.

Claims (5)

[Claims] (1) In a magnetic recording medium having a magnetic layer made of a ferromagnetic metal thin film on a substrate, a Langmuir brodget layer made of a fluorine-containing lubricating compound having a hydrophilic group is formed on the surface of the magnetic layer. A magnetic recording medium characterized by: (2) The fluorine-containing lubricating compound has the following structural formula; C_
nF_2_n_+_1-(R_1)-_mCOOR_2
...(I) (wherein R_1 is a methylene group or oxyethylene group, R_2 is a hydrogen atom or an alkyl group, n
is an integer of 1 or more, and m is an integer of 0 or more. (3) The fluorine-containing lubricating compound is a compound having a group that can be polymerized by radiation irradiation.
1) The magnetic recording medium described in item 1). (4) A compound having a group that can be polymerized by radiation irradiation has the following structural formula; C_nF_2_n_+_1-(R_3)-_lCOOR
_4...(II) (In the formula, R_3 is a methylene group, R_4
is an alkenyl group or an alkynyl group, n is the same as above,
1 is an integer of 0 or more) The magnetic recording medium according to claim 3, comprising a compound represented by the following. (5) A compound having a group that can be polymerized by radiation irradiation has the following structural formula; C_nF_2_n_+_1-(R_5)-_jCH=C
H-(R_6)-_kCOOR_7...(III) (In the formula, R_5 and R_6 are methylene groups, R_7 is a hydrogen atom or an alkyl group, n is the same as above, j and k are 0
The magnetic recording medium according to claim (3), comprising a compound represented by: