JPH1196542A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a medium which keeps a lubricating effect under various use conditions, which has a small coefft. of friction, excellent travelling property, wear resistance and durability by holding a lubricant comprising a diester monocarboxylic acid compd. in a magnetic layer on a nonmagnetic supporting body. SOLUTION: Relating to a magnetic record medium having a carbon film on a magnetic layer, a lubricant is applied on the carbon film by coating. When a diester monocarboxylic acid compd. is applied as a lubricant on the carbon film, the carboxylic acid or ester of the polar groups of the lubricant is adsorbed on the carbon film while aggregation force between long-chain hydrocarbon groups in the hydrophobic part form a lubricant. Therefore, the lubricant is firmly held on the carbon film and is made extremely thin, and an enough lubricating effect can be kept for a long time. The diester monocarboxylic acid compd. is preferably a compd. expressed by the chemical formula (wherein R<1> , R<2> are hydrophobic functional groups).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk.

[0002]

2. Description of the Related Art For example, a so-called metal magnetic thin film type magnetic recording medium in which a ferromagnetic metal material is deposited on a non-magnetic support by a method such as vapor deposition and a magnetic layer is used, In a so-called coating type magnetic recording medium in which a magnetic coating material containing a binder and a resin binder is applied on a non-magnetic support and this is used as a magnetic layer, the surface of the magnetic layer is extremely smooth to improve the electromagnetic conversion characteristics. As a result, a substantial contact area with a sliding member such as a magnetic head or a guide roller is large, so that the friction coefficient is large, so that an adhesion phenomenon (so-called sticking) easily occurs, and the running property and durability are lacking. There are many problems.

[0003] In order to solve these problems, use of various lubricants has been studied. Conventionally, higher fatty acids and esters thereof have been internally added to the magnetic layer of the magnetic recording medium. Alternatively, attempts have been made to suppress the coefficient of friction by top coating.

[0004]

By the way, lubricants used for magnetic recording media are required to have very strict characteristics due to their properties, and it is difficult for conventional lubricants to respond. It is.

[0005] Lubricants used in magnetic recording media include (1) excellent low-temperature characteristics so as to ensure a predetermined lubricating effect when used in cold regions, and (2) lubricants for magnetic heads. Since pacing poses a problem, it is required that the coating be able to be applied extremely thinly and that sufficient lubrication properties be exhibited even in such a case, and (3) that it can withstand long-term use or long-term use and that the lubrication effect be maintained. Is done.

However, it is difficult to say that a lubricant such as a higher fatty acid or an ester thereof sufficiently satisfies the performance required for the above-mentioned lubricant, and in the field of magnetic recording media, Due to the lack of capacity, they are dissatisfied with the practical characteristics such as the level reduction of the reproduction output in the shuttle running test.

Accordingly, the present invention provides a magnetic recording medium which maintains excellent lubricity under various use conditions, maintains a lubricating effect for a long time, and exhibits excellent running properties, abrasion resistance and durability. It is intended to provide.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies on achieving the above object, and as a result, a magnetic recording medium comprising at least a magnetic layer on a nonmagnetic support, The inventors have found that an excellent lubricating effect can be obtained by holding a diester monocarboxylic acid compound as a lubricant in this magnetic recording medium, and have completed the present invention.

That is, the present invention provides a magnetic recording medium having a magnetic layer on a nonmagnetic support, wherein a lubricant comprising a diester monocarboxylic acid compound is held. (Hereinafter referred to as a magnetic recording medium of the present invention).

According to the magnetic recording medium of the present invention, since the diester monocarboxylic acid compound is held as a lubricant, excellent lubricity is maintained under various use conditions, and the lubricating effect is maintained for a long time. As a result, the friction coefficient is small, and excellent running properties, wear resistance, and durability can be exhibited.

That is, the diester monocarboxylic acid compound according to the present invention has a carboxyl group having a large polarity and an ester having a relatively small polarity as a polar group (hydrophilic group). It is considered that the reduction of the coefficient is realized, and the still traveling property and the shuttle traveling property are improved mainly by the ester moiety.

[0012] In particular, the diester monocarboxylic acid compound has one carboxyl group and two esters, so that a reduction in the coefficient of friction and an improvement in running properties are both achieved in a well-balanced manner.

The conventional fluorine-containing lubricant dissolves only in a fluorinated solvent and can only be applied using this solvent. On the other hand, the lubricant comprising the diester monocarboxylic acid compound is, for example, toluene, acetone or the like. Can be dissolved in a hydrocarbon solvent, and the load on the environment is small.

[0014]

According to the present invention, in a magnetic recording medium having a carbon film (carbon film) provided on the magnetic layer, the lubricant may be provided on the carbon film by coating. desirable.

When the diester monocarboxylic acid compound is applied as a lubricant on a carbon film, the carboxylic acid or ester of the polar group of the lubricant molecule is adsorbed on the carbon film, and the hydrocarbon group has a long-chain hydrocarbon group. A lubricant is formed by the cohesive force between them. Therefore, the lubricant is firmly held on the carbon film and can be applied very thinly, and at the same time, can maintain a sufficient lubricating effect for a long time.

The carbon film (carbon film) may be formed by a physical film forming method (PVD method) such as a sputtering method, or may be formed by a chemical vapor deposition (CVD) method using a hydrocarbon gas. Method). Further, the carbon film may be a hard carbon film or an amorphous carbon film in which a diamond structure and a graphite structure are mixed, which is called diamond-like carbon.

In the magnetic recording medium of the present invention, the diester monocarboxylic acid compound is preferably a compound represented by the following general formula 1. General formula 1: R ¹ —OCOCH ₂ CH (COOH) CH ₂ COO-R
² (However, in the general formula 1, R ¹ and R ² are hydrophobic functional groups.)

That is, the diester monocarboxylic acid compound having such a structure can stably exist under various environmental conditions because of its good structural symmetry, and has a large polar carboxyl group at the center thereof. It has an ester on both sides thereof, and is arranged such that a polar group always exists on its surface when forming a lubricant or a lubricant layer.

In the magnetic recording medium of the present invention, the hydrophobic functional group [long-chain (fluorinated) hydrocarbon group] represented by R ¹ is a group represented by the following general formula A; The hydrophobic functional group [long-chain (fluorinated) hydrocarbon group] represented by R ² is preferably a group represented by the following general formula B.

Embedded image (However, in the general formula A, l, m, and n are integers selected from the following ranges: l = 3 to 28, m = 0 to 24, n = 1 to 15)

Embedded image (In the general formula B, p, q, and r are integers selected from the following ranges: p = 3 to 28, q = 0 to 24, and r = 1 to 15)

In particular, when each of the hydrophobic functional groups [long-chain (fluorinated) hydrocarbon group] is a polar group containing a fluorine atom, it is effective in reducing the friction coefficient and further improving the running property. is there.

In the general formula A, l, m, n
Is more preferably an integer selected from the following range. l = 6 to 22, m = 0 to 18, n = 1 to 10

Similarly, in the general formula B, p, q,
More preferably, r is an integer selected from the following range. p = 6-22, q = 0-18, r = 1-10

That is, in the case of the long-chain hydrocarbon group (or fluorinated hydrocarbon group) of the hydrophobic functional group site in the diester monocarboxylic acid compound, if the number of carbon atoms is 6 or more, the alkyl group has an appropriate length. And the durability against friction and wear is improved. When the carbon number is 22 or less, the solubility of the lubricant comprising the diester monocarboxylic acid compound in the solvent is good.

In the present invention, when a carbon film is provided on the magnetic layer, and a lubricant comprising a diester monocarboxylic acid compound is applied on the carbon film,
It is desirable that the amount of the lubricant applied is 0.5 to 100 mg / m ² .

If the coating amount is less than 0.5 mg / m ² , the performance of the lubricant cannot be sufficiently exhibited,
On the other hand, if it exceeds 100 mg / m ² , the amount of the lubricant may become too large and the friction coefficient may be increased.

In the magnetic recording medium of the present invention, the magnetic layer may be a metal magnetic thin film type magnetic recording medium comprising a metal magnetic thin film.

In general, in a magnetic recording medium of a so-called metal magnetic thin film type in which a ferromagnetic metal material is deposited on a non-magnetic support by a method such as vapor deposition and a magnetic layer is used, the magnetic layer is formed by depositing a magnetic material. In addition, since no binder is used in the magnetic layer, the magnetic layer is vulnerable to the sliding operation. To compensate for this, a protective film such as a carbon film is provided.

The lubricant according to the present invention can be applied very thinly on such a protective film, and in this case, sufficient lubricating properties can be exhibited, and the lubricant can withstand long-term use. The obtained lubrication effect can be maintained.

Hereinafter, a configuration example of the magnetic recording medium of the present invention will be described in more detail.

When the diester monocarboxylic acid compound according to the present invention is coated on a carbon film as a lubricant, the carboxylic acid or ester of the polar group of the lubricant molecule is adsorbed on the carbon film and the long chain (fluorine) of the hydrophobic group is formed. Chemical formula) A lubricating film is formed by the cohesive force between hydrocarbon groups.

In a conventional lubricant, a compound having a relatively large polarity, such as a carboxylic acid or an amine, reduces the friction coefficient, but tends to deteriorate still durability and the like.
Further, compounds having relatively low polarity such as esters are excellent in still durability and the like, but tend to have a large friction coefficient. Accordingly, since the diester monocarboxylic acid compound has one carboxylic acid and two esters in the polar group, these characteristics are compatible with a good balance, the coefficient of friction is small, and excellent characteristics such as still durability are exhibited.

As described above, the conventional fluorine-containing lubricant can be applied only with a fluorine-based solvent, whereas the lubricant comprising the diester monocarboxylic acid compound is
In particular, even when the hydrophobic group contains fluorine, it can be dissolved in a hydrocarbon-based solvent such as toluene or acetone, and can be applied using the solvent, and the burden on the environment in the solvent treatment is small.

The magnetic recording medium to which the present invention is applied can be applied to a so-called metal thin film type magnetic recording medium in which a magnetic film is formed as a magnetic layer on the surface of a nonmagnetic support by a method such as vapor deposition. is there. Further, a carbon film may be formed as a protective film on the magnetic layer. The metal thin film type magnetic recording medium may have a configuration in which an underlayer is interposed between the nonmagnetic support and the magnetic layer.

In this case, the applicable non-magnetic support of the metal thin film type magnetic recording medium, the metal magnetic thin film, etc. are not limited at all without departing from the gist of the present invention. Can be used.

For example, as the non-magnetic support, those similar to a coating type magnetic recording medium can be used. When a rigid substrate such as an Al alloy plate or a glass plate is used for the nonmagnetic support, an oxide film such as alumite treatment or a Ni-P film is formed on the surface of the substrate, and the surface is hardened. You may make it.

The metal magnetic thin film is formed as a continuous film by a PVD technique such as plating, sputtering, or vacuum deposition, and is made of a metal such as Fe, Co, Ni or the like.
Ni-based alloy, Co-Pt-based alloy, Co-Pt-Ni-based alloy, Fe-Co-based alloy, Fe-Ni-based alloy, Fe-Co
-Ni-based alloy, Fe-Ni-B-based alloy, Fe-Co-B
An in-plane magnetization recording metal magnetic thin film or a Co-Cr alloy thin film made of a base alloy, a Fe-Co-Ni-B alloy, or the like is exemplified.

In particular, in the case of an in-plane magnetization recording metal magnetic thin film,
Bi, Sb, Pb, Sn, Ga,
A base layer of a low-melting non-magnetic material such as In, Ge, Si, or Tl is formed, and a metal magnetic material is vapor-deposited or sputtered from a vertical direction to diffuse the low-melting non-magnetic material into the metal magnetic thin film. Orientation may be eliminated to ensure in-plane isotropy and also to improve coercivity.

As a method for forming a protective film, particularly a carbon film on the surface of such a magnetic recording medium, sputtering is generally used, but the method is not particularly limited, and any method can be used. In this case, the thickness of the protective film is 2 to 10
0 nm, more preferably 5 to 30 nm.
nm.

As a method for retaining the lubricating film structure on a protective film, particularly a carbon film, on the surface of a magnetic recording medium, a solution obtained by dissolving the diester monocarboxylic acid compound in a solvent such as toluene or acetone is used. A method of top-coating the surface of the carbon film may be used. In this case, the amount of the lubricant applied is 0.5 to 100 m
g / m ² , more preferably 1 to ²⁰ mg / m ² .

The above-mentioned lubricant may be used together with a rust preventive, if necessary.

As the rust preventive, any one can be used as long as it is usually used as a rust preventive for this type of magnetic recording medium. Examples thereof include phenols, naphthols, quinones, and heterocycles containing a nitrogen atom. Examples include a formula compound, a heterocyclic compound containing an oxygen atom, and a heterocyclic compound containing a sulfur atom.

This rust preventive may be used in combination with the above-mentioned lubricant. However, after a rust preventive layer is applied on the carbon film, a lubricant layer is applied. The effect is high if they are applied separately.

The magnetic recording medium to which the present invention is applied is a so-called coating type magnetic material in which a magnetic paint containing fine magnetic particles and a resin binder is applied on a non-magnetic support, and this is used as a magnetic layer. It may be a recording medium.

The magnetic particles are preferably ferromagnetic powders, for example, γ-Fe ₂ O ₃ and Co-containing γ-Fe
Oxide magnetic powders such as ₂ O ₃ , Co-coated γ-Fe ₂ O ₃ , CrO ₂ , ferrites represented by magnetite,
Further, for example, Fe-Al based, Fe-Al-Ni based, F
e-Al-Ca system, Fe-Al-Co system, Fe-Al-
Zn-based, Fe-Al-Co-based, Fe-Ni-based, Fe-N
i-Si-Al-Mn system, Fe-Ni-Si-Al-Z
As in the case of n-based, Fe-Mn-Zn-based, and Ni-Co-based alloy powders, metal magnetic powders mainly containing Fe, Co, Ni, and the like can be used.

The binder is typically a polyester resin, a polyurethane resin, or a vinyl chloride resin such as a vinyl chloride copolymer. Further, for the purpose of improving the dispersibility of these binders magnetic powder to the resin, these _{resins, -SO 3 M, -OSO 3 M} , -CO
OM, -PO (OM ') ₂ (where M is Na, K, Li
And M ′ is a hydrogen atom or an alkali metal or an alkyl group. ) And at least one polar group selected from sulfopetine groups as a repeating unit.

The magnetic layer comprising the binder and the magnetic powder may contain known additives such as abrasives, lubricants, hardeners, and antistatic agents.

As the non-magnetic support used for the above-described metal magnetic thin film type magnetic recording medium and coating type magnetic recording medium, known materials can be appropriately used. For example, polyethylene terephthalate, polyethylene naphthalate, etc. Polyesters, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, aramid resins such as polyaramid, and plastics such as polycarbonate.

These non-magnetic supports may have a single-layer structure or a multilayer structure. Further, a corona discharge treatment or the like may be performed. Further, it can be formed into any shape such as a film, a sheet, a disk, and a card.

Although the preferred embodiments of the magnetic recording medium of the present invention have been described above, the present invention is not limited to the above-described embodiments.

For example, when a coating type magnetic recording medium is used as the magnetic recording medium of the present invention, a predetermined amount of the lubricant may be contained in a magnetic layer composed of a magnetic powder and a binder. The lubricant may be applied on the magnetic layer with or without a protective film. When the lubricant is contained in the magnetic layer of the coating type magnetic recording medium, the content is preferably 0.5 to 10 parts by weight based on 100 parts by weight of the magnetic powder.

When a magnetic recording medium of the metal magnetic thin film type is used as the magnetic recording medium of the present invention, it is preferable to coat the magnetic recording medium on a carbon film as described above. Alternatively, it may be applied indirectly.

Further, in addition to the above-mentioned carbon film, a quartz (SiO ₂ ) film, a zirconia (ZrO ₂ ) film, or the like may be used as a protective film.

In the magnetic recording medium of the present invention,
A back coat layer may be provided on the surface of the non-magnetic support on which the magnetic layer is not provided. This back coat layer can be formed according to a usual method. Further, the lubricant may be internally added or applied to the back coat layer.

[0054]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Examples 1 to 20 Using a compound having the composition shown in Table 1 below as a lubricant comprising a diester monocarboxylic acid compound, a metal magnetic thin film type magnetic recording medium having the following structure was prepared.

<Example of Making Sample Tape> A Co—Ni alloy was applied to a 10 μm thick polyethylene terephthalate film by an oblique evaporation method to form a 100 nm-thick ferromagnetic metal thin film. A film in which a carbon film having a thickness of 15 nm was formed by sputtering was cut into a width of 8 mm to obtain a sample tape.

In Examples 1 to 20, Compounds 1 to 20 having the composition shown in Table 1 as a lubricant were dissolved in a toluene solvent, and then applied to the sample tapes to obtain samples. The amount of the lubricant applied is 10 mg / m ² (film thickness of 5 to 10 nm) in terms of the amount after drying.
And

FIG. 1 shows a schematic sectional view of the magnetic tape thus manufactured. That is, the magnetic recording medium of this embodiment is a magnetic recording medium 5 in which a magnetic layer 3, a carbon film 4, and a lubricant layer 1 are sequentially provided on a nonmagnetic support 2.

For each of the samples thus prepared, (1) when the temperature is 25 ° C. and the humidity is 60%, (2) when the temperature is 40 ° C. and the humidity is 80%, and (3) when the temperature is −5 ° C. The lower coefficient of friction, still durability, and shuttle durability were measured. In addition, the still durability evaluated the decay time of the output in the pause state to -3 dB.
The shuttle durability was evaluated by the number of shuttles in which the shuttle traveled for 2 minutes each time and the output decreased by -3 dB.

The measurement results are shown in Table 2 below. In addition,
Examples 1 to 9 have a hydrophobic group composed of a hydrocarbon, and Examples 10 to 20 have a hydrophobic group composed of a fluorinated hydrocarbon.

From Table 2, it can be seen that the magnetic recording medium of the present invention forms a carbon film on the surface of the magnetic layer and uses a diester monocarboxylic acid compound as a lubricant to provide a coefficient of friction, still durability and shuttle durability. Very good results were obtained without deterioration in properties and the like even under various conditions.

In particular, it can be seen from Examples 10 to 20 that when a lubricant having a fluorinated hydrocarbon group as a hydrophobic group is used, the friction coefficient is particularly reduced, and the magnetic recording medium has good running properties.

Comparative Examples 1 to 10 Sample tapes having the same structure as those of the examples were prepared, and Compounds 21 to 30 having the compositions shown in Table 3 below were applied to the sample tapes to obtain samples. The amount of the lubricant applied was 10 mg / m ² (film thickness 5 to 10 nm).
Comparative Examples 1 to 5 are sample tapes using higher fatty acids as lubricants, and Comparative Examples 6 to 10 are sample tapes using fatty acid esters.

The friction coefficient, still durability and shuttle durability of each of the samples thus prepared were measured under various conditions in the same manner as in the examples. The measurement results are shown in Table 4 below.

From Table 4, it was found that the sample tapes using higher fatty acids as the lubricant (Comparative Examples 1 to 5) had a temperature of 25.
When the temperature is 60 ° C. and the humidity is 60%, relatively excellent friction coefficient, still durability, and shuttle durability are obtained. However, as the use conditions become stricter, the still durability and shuttle durability particularly decrease.

Further, the sample tapes using fatty acid esters as lubricants (Comparative Examples 6 to 10) have a large coefficient of friction under any conditions, have a problem in running property, and have both still durability and shuttle durability. Not enough.

Table 1A (Composition of diester monocarboxylic acid)

Embedded image

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

According to the magnetic recording medium of the present invention, since a diester monocarboxylic acid compound is held as a lubricant, excellent lubricity is maintained under various use conditions, and lubrication is performed for a long time. The effect is maintained, the coefficient of friction is small, and excellent running properties, wear resistance, and durability can be exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part of a magnetic recording medium according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Lubricant layer, 2 ... Nonmagnetic support, 3 ... Magnetic layer 4 ... Carbon film, 5 ... Magnetic recording medium

Continued on the front page (72) Inventor Kenichi Kurihara 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (6)

[Claims] 1. A magnetic recording medium having a magnetic layer on a nonmagnetic support, wherein a lubricant comprising a diester monocarboxylic acid compound is held. 2. The magnetic recording medium according to claim 1, wherein a carbon film is provided on the magnetic layer, and the lubricant is applied on the carbon film. 3. The magnetic recording medium according to claim 1, wherein the diester monocarboxylic acid compound is represented by the following general formula 1. General formula 1: R ¹ —OCOCH ₂ CH (COOH) CH ₂ COO-R
² (However, in the general formula 1, R ¹ and R ² are hydrophobic functional groups.) 4. The method according to claim 3, wherein the hydrophobic functional group represented by R ¹ is represented by the following general formula A, and the hydrophobic functional group represented by R ² is represented by the following general formula B. The magnetic recording medium described. Embedded image (However, in the general formula A, l, m, and n are integers selected from the following ranges: l = 3 to 28, m = 0 to 24, n = 1 to 15) (In the general formula B, p, q, and r are integers selected from the following ranges: p = 3 to 28, q = 0 to 24, and r = 1 to 15) 5. The coating amount of the lubricant is 0.5 to 100 m.
^{3. The} magnetic recording medium according to claim ^2, which has a g / m ² . 6. The magnetic recording medium according to claim 1, wherein said magnetic layer comprises a metal magnetic thin film.