JP2715436B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic disk in which a metal magnetic thin film is formed on a non-magnetic support, and particularly to a fluorine-based lubricating medium. The present invention relates to a magnetic recording medium in which a lubricant and an organic compound having a hydroxyl group are used in combination as a lubricant.

[Summary of the Invention]

The present invention provides a magnetic recording medium comprising a metal magnetic thin film formed on a non-magnetic support, by using a fluorine-based lubricant and an organic compound having a hydroxyl group in combination as a lubricant, under various use conditions. , Especially under high temperature and low humidity conditions, the dynamic friction coefficient can be reduced, and excellent running stability,
An object of the present invention is to provide a magnetic recording medium exhibiting abrasion resistance, durability and the like.

[Conventional technology]

For example, in the case of a so-called metal thin film type magnetic recording medium in which a ferromagnetic metal material is deposited on a nonmagnetic support by a method such as vapor deposition and the magnetic layer is used as a magnetic layer, the surface smoothness of the magnetic layer is extremely good. In addition, there are many problems such as a substantial contact area with a sliding member such as a magnetic head and a guide roller, a large friction coefficient, an adhesive phenomenon (so-called sticking) easily occurring, and a lack of running property and durability.

Therefore, it has been studied to use various lubricants in order to improve these problems. Conventionally, higher fatty acids or esters thereof are internally added to the magnetic layer of the magnetic recording medium or top coated. Attempts have been made to reduce the coefficient of friction.

Incidentally, lubricants used for magnetic recording media are required to have extremely strict characteristics due to their properties, and it is difficult for conventional lubricants to cope with them.

In other words, the lubricant used for the magnetic recording medium has an excellent low-temperature characteristic so that a predetermined lubricating effect is ensured even when used in a cold region, and the spacing with the magnetic head becomes a problem. It is required to be able to be applied thinly, to exhibit sufficient lubricity even in such a case, to be able to withstand long-term or long-term use, and to maintain the lubricating effect.

However, higher fatty acids and their esters, which have been conventionally used, tend to freeze and solidify under low-temperature conditions such as 0 ° C. or lower, impairing the function as a lubricant, or lacking long-term durability. is there.

Conventionally, as a method for solving this problem, for example, in JP-A-57-198541, ammonium perfluorocarboxylate and ammonium perfluorosulfonate are used as a surface treatment agent for the magnetic layer, and the surface treatment is performed on the magnetic layer. A method for improving the lubricating effect by forming a film on a surface treatment layer has been proposed.

In this method, although there is an effect of improving lubricity under certain conditions of use, in actual use conditions of a so-called metal thin film type magnetic recording medium, for example, a hard disk, a high temperature is generated due to heat generation of a motor mounted in a drive device. ,
Under such high-temperature and low-humidity conditions, the surface treatment with the ammonium perfluorocarboxylate and ammonium perfluorosulfonate alone is sufficient for improving the lubricity of the magnetic recording medium. No effect.

[Problems to be solved by the invention]

As described above, in the field of magnetic recording media, practical properties such as running properties, wear resistance, durability, and corrosion resistance remain unsatisfactory due to insufficient capacity of the lubricant used.

Therefore, the present invention maintains excellent lubricity under various use conditions, particularly under high-temperature and low-humidity conditions, maintains a lubricating effect for a long period of time, and is excellent in running properties, wear resistance, durability and the like. It is an object to provide a magnetic recording medium.

[Means for solving the problem]

The present inventors have conducted intensive studies with the achievement of the above-mentioned object, and as a result, have a hydroxyl group at a predetermined ratio to ordinary fluorine-based lubricants such as perfluorocarboxylate and perfluorosulfonate. It has been found that the addition of an organic compound can improve running stability, abrasion resistance and durability under all use conditions, especially under high temperature and low humidity conditions.

That is, in the magnetic recording medium of the present invention, a metal magnetic thin film is formed on a non-magnetic support, and a lubricating agent mainly composed of a perfluorocarboxylate and an organic compound having two or more hydroxyl groups is formed on the metal magnetic thin film. Characterized by being coated with an agent.

Further, the magnetic recording medium of the present invention is characterized in that a metal magnetic thin film is adhered and formed on a non-magnetic support, and a lubricant mainly composed of a perfluorosulfonic acid salt and an organic compound having two or more hydroxyl groups is formed on the metal magnetic thin film. Characterized by being coated with an agent.

Here, examples of the salt constituting the perfluorocarboxylate or perfluorosulfonate include metal salts such as alkali metals such as Na and K and alkaline earth metals, and ammonium salts.

Or the general formula Or (Where n represents 1-3, R ₁ , R ₂ , and R ₃ represent hydrogen or a hydrocarbon group, and R _f represents a perfluoroalkyl group having 3 or more carbon atoms.) It may be a perfluorocarboxylic acid amine salt.

The perfluorocarboxylic acid amine salt is synthesized from a perfluorocarboxylic acid and an organic amine.

Here, the number n of the perfluorocarboxylic acid and the organic amine salt in the above formula is preferably 1 to 3. When n is 0, no lubricant is formed. When n is 4 or more, practical problems such as handling of the lubricant occur. For example, it becomes difficult to apply a very thin coating.

Further, in the above formula, R ₁ , R ₂ , and R ₃ represent a hydrogen or a hydrocarbon group. In this case, the hydrocarbon may be an alkyl, alkene, aryl, or the like, and in some cases, may be a heterocyclic compound. The hydrocarbon group preferably has 1 or more carbon atoms, and _one of R ₁ , R ₂ , and R ₃ has 10 carbon atoms.
More preferably, it is the above.

Similarly, perfluorosulfonic acid has the general formula Or (Where n is an integer of 1 to 3, R _f is a perfluoroalkyl group having 3 or more carbon atoms, and at least one of R ₄ , R ₅ and R ₆ is a hydrocarbon group having 6 or more carbon atoms, respectively) ) May be used.

The perfluorosulfonic acid amine salt is synthesized from perfluorosulfonic acid and an organic amine.

Here, the number n of the perfluorosulfonic acid and the amine in the above formula is preferably 1 to 3. When n is 0, no lubricant is formed. When n is 4 or more, practical problems such as handling of the lubricant occur. For example, it becomes difficult to apply a very thin coating.

In the above formula, R ₄ , R ₅ and R ₆ constituting the amine represent hydrogen or hydrocarbon. In this case, the hydrocarbon is alkyl,
It may be an alkene, an aryl or the like, and in some cases, a heterocyclic compound. Further, the hydrocarbon group preferably has 1 or more carbon atoms, and more preferably one of R ₄ , R ₅ , and R ₆ has 10 or more carbon atoms.

It is preferable that the perfluoroalkyl group constituting the above-mentioned perfluorocarboxylate or perfluorosulfonate has 3 or more carbon atoms. If the number of carbon atoms in the perfluoroalkyl group is less than 3, the lubricating effect due to the introduction of fluorine will be insufficient. There is no particular upper limit, but if the number of carbon atoms exceeds 12, there is a problem in handling as a lubricant. The perfluoroalkyl group may be linear or branched.

The perfluoroalkyl group does not need to have all of the hydrogens of the alkyl group replaced with fluorine, and may be partially substituted with fluorine and partially left with hydrogen.

On the other hand, the organic compound having two or more hydroxyl groups used simultaneously with the fluorine-based lubricant such as the perfluorocarboxylate and the perfluorosulfonate according to the present invention includes two or more hydroxyl groups in one molecule. Any organic compound can be used. However, since the effect is more remarkable as the content ratio of the hydroxyl group is higher, it is preferable that the compound has at least one hydroxyl group per 5 carbon atoms, more preferably at least one hydroxyl group per 3 carbon atoms. .

Specific examples of the compound having two or more hydroxyl groups include aromatic polyols and aliphatic polyols, and certain polyvinyl alcohols.

As the aromatic polyol, for example, (Where R ₇ represents a substituent), (Wherein R ₈ and R ₉ represent substituents), (Wherein R ₁₀ and R ₁₁ represent substituents), and the like. The same applies to those having a heterocyclic ring as the aromatic ring.

Examples of the aliphatic polyol include a compound represented by the general formula (Cn _{+ LH2n + L} (OH) _{2 + L} (l ≧ 0,4> n−10)
What is represented by More specifically, the general formula C _{n + 1} H _{2n +} having a hydroxyl group at a terminal of alkenediol such as butylene glycol, ethylene glycol, and propylene glycol having a hydroxyl group at a terminal represented by HOCH _{2 n} OH or a branched hydrocarbon. Triol represented by ₁ (OH) ₃ .

For example, glycerin (m = 2, n = 1) having a hydroxyl group other than the terminal represented by.

And the like.

Further, for example And polyvinyl alcohol having a saponification degree of 58% or more.

Here, as described above, the organic compound having a hydroxyl group in the molecule is used together with a usual lubricant for the following reason. That is, for example, in a magnetic recording medium such as a hard disk, a motor generates heat by driving in a drive device. Due to this heat generation, the use conditions of the magnetic recording medium are high temperature and low humidity. Normally, a slight amount of water exists on the surface of the magnetic recording medium, which contributes to the effect of reducing friction during driving. However, when extremely low humidity conditions are caused by heat generated by driving the motor, a trace amount of water existing on the surface of the magnetic recording medium is lost, and the durability is deteriorated. Therefore, the durability under low humidity can be improved by introducing a hydroxyl group into the molecules constituting the binder instead of the trace water present on the surface of the magnetic recording medium.

The magnetic recording medium of the present invention has a perfluorocarboxylate and an organic compound having two or more hydroxyl groups or a perfluorosulfonate and an organic compound having two or more hydroxyl groups as a lubricant.

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

Also in this case, the non-magnetic support and the metal magnetic thin film of the applicable metal thin film type magnetic recording medium are not limited at all, and any conventionally known ones can be used.

For example, as the non-magnetic support, a polymer support formed of a polymer material represented by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates and the like And a metal substrate made of an aluminum alloy, a titanium alloy or the like, a ceramic substrate made of alumina glass or the like, a glass substrate, or the like. In this case, the non-magnetic support
When a rigid substrate such as an alloy plate or a glass plate is used, an oxide film such as alumite treatment or Ni-P
A film or the like may be formed to harden the surface.

Metal magnetic thin films are formed as continuous films by PVD techniques such as plating, sputtering, and vacuum evaporation.
e, Co, metals such as Ni, Co-Ni alloys, Co-Pt alloys, Co
-Ni-Pt alloy, Fe-Co alloy, Fe-Ni alloy, Fe-Co
-Ni alloy, Fe-Ni-B alloy, Fe-Co-B alloy, Fe
Examples thereof include an in-plane magnetization recording metal magnetic thin film made of a -Co-Ni-B alloy or the like, and a perpendicular magnetization recording metal magnetic thin film such as a Co-Cr alloy thin film or a Co-O thin film.

In particular, in the case of an in-plane magnetized recording metal magnetic thin film, a base film of a low-melting nonmagnetic material such as Bi, Sb, Pb, Sn, Ga, In, Ge, Si, or Tl is formed on a nonmagnetic support in advance. Each metal magnetic material is deposited or sputtered from the vertical direction to diffuse these low-melting non-magnetic materials into the metal magnetic thin film, thereby eliminating orientation and ensuring in-plane isotropy and improving coercive force. You may do so.

When a hard disk as described above is used, a hard protective film such as a carbon film, a diamond-like carbon film, a chromium oxide film, and a SiO ₂ film may be formed on the surface of the metal magnetic thin film.

As a method of causing such a metal thin film type magnetic recording medium to hold a lubricant composed of the perfluorocarboxylate and a compound having two or more hydroxyl groups or a perfluorosulfonate and a lubricant composed of a compound having two or more hydroxyl groups, As shown in FIG. 1, there is a method of top-coating a lubricant layer (3) on the surface of a metal magnetic thin film (magnetic layer) (2) formed on a non-magnetic support (1) or on the surface of the protective film. .
In this case, the coating amount of perfluoro carboxylate and compounds hydroxyl containing two or more or perfluoroalkyl sulfonate and hydroxyl groups consists of those compounds having two or more lubricants, it is 0.5 to 100 mg / m ² Preferably 1
More preferably, it is 2020 mg / m ² .

The above-mentioned lubricant comprising a perfluorocarboxylate and a compound having two or more hydroxyl groups or a lubricant comprising a perfluorosulfonate and a compound having two or more hydroxyl groups may be used alone as a lubricant for a magnetic recording medium. It may be used in combination with a conventionally known lubricant. Or,
It is also possible to use in combination with a perfluoroalkyl carboxylic acid ester, a carboxylic acid perfluoroalkyl ester, a perfluoroalkyl carboxylic acid perfluoroalkyl ester, or a derivative thereof.

Further, in order to cope with more severe conditions and maintain the lubricating effect, an extreme pressure agent may be used in combination at a weight ratio of about 30:70 to 70:30.

The extreme pressure agent reacts with the metal surface due to the frictional heat generated when partial metal contact occurs in the boundary lubrication region, and performs a friction / wear prevention effect by forming a reaction product film. Any of phosphorus-based extreme-pressure agents, sulfur-based extreme-pressure agents, halogen-based extreme-pressure agents, organometallic-based extreme-pressure agents, and complex-type extreme-pressure agents can be used.

Further, in addition to the above-mentioned lubricant and extreme pressure agent, a rust preventive may be used in combination as needed.

As the rust inhibitor, any one which is usually used as a rust inhibitor for this type of magnetic recording medium can be used, for example, phenols, naphthols, quinones, heterocyclic compounds containing a nitrogen atom, oxygen atoms And heterocyclic compounds containing a sulfur atom.

The rust inhibitor is composed of a perfluorocarboxylate and a hydroxyl group.
It may be used in combination with a compound having at least one compound or a lubricant containing a perfluorosulfonate and a compound having at least two hydroxyl groups. However, as shown in FIG. The effect is high when the layer (2) is formed, the rust preventive layer (4) is applied thereon, and then the lubricant layer (3) is applied.

Incidentally, in the above-described metal thin film type magnetic recording medium, a back coat layer, an undercoat layer, and the like may be formed as necessary in addition to the metal magnetic thin film as the magnetic layer.

For example, the back coat layer is formed by adding a carbon-based fine powder for imparting conductivity or an inorganic pigment for controlling surface roughness to the same resin binder as the magnetic coating film.

In the present invention, the above-mentioned perfluorocarboxylate and the compound having two or more hydroxyl groups or the perfluorosulfonate and the compound having two or more hydroxyl groups are internally added to the back coat layer as a lubricant, or by a top coat. May be included. Alternatively, a perfluorocarboxylate and a compound having two or more hydroxyl groups or a perfluorosulfonate and a compound having two or more hydroxyl groups are internally added to both the metal magnetic thin film and the back coat layer as a lubricant, and top-coated. Various combinations are also possible.

[Action]

A lubricant comprising a perfluorocarboxylate and an organic compound having two or more hydroxyl groups or a lubricant comprising a perfluorosulfonate and an organic compound having two or more hydroxyl groups exerts a good lubricating action under all use conditions, and exhibits a friction coefficient. To reduce. Further, since this lubricant contains a hydroxyl group, it is highly effective especially under high temperature and low humidity.

Therefore, in the magnetic recording medium using the fluorine-based lubricant and the organic compound having two or more hydroxyl groups as a lubricant, the running property is improved by the lubricating action of the fluorine-based lubricant and the organic compound having two or more hydroxyl groups. As a result, the durability is improved.

〔Example〕

Hereinafter, specific examples of the present invention will be described,
It goes without saying that the present invention is not limited to this embodiment.

An embodiment applied to a metal thin-film type magnetic recording medium (with a hard disk and a base film) will be described.

Example 1 First, an Al-Mg alloy substrate (1.5 mm in thickness, 95 m in outer diameter) on which a 15 μm-thick Ni—P plating layer was formed as a nonmagnetic metal underlayer.
m, inner diameter 25 mm), and apply a pressure of 1 × 10
Bi was deposited by electron beam evaporation under the conditions of ^-5 Torr and a substrate temperature of 150 ° C. to form a low-melting metal underlayer having a thickness of 200 °.

Next, Co was electron beam deposited on the underlayer under the conditions of a pressure of 1 × 10 ⁻⁵ Torr and a substrate temperature of 150 ° C.
A metal magnetic thin film was formed, and a carbon protective film was formed on the metal magnetic thin film by a vacuum evaporation method.

Finally, on the surface of the carbon protective film, a lubricant made of a combination of a fluorine-based lubricant and a compound having two or more hydroxyl groups shown in Lubricant 1 in Table 1 was applied to prepare a sample disk. did.

Examples 2 to 11 Sample disks were prepared in the same manner as in Example 1 except that the lubricant 1 used as the lubricant in Example 1 was changed to the lubricants 2 to 11 shown in Table 1. .

For each of the sample disks obtained as described above, the friction coefficient after 20,000 times was determined by the contact start / stop (CSS) test at 25 ° C, 60RH and 70 ° C, 20% RH.
Under the following conditions. Further, Comparative Examples 1 to 11 were performed on the lubricants 1 to 11 shown in Table 1 using only a fluorine-based lubricant to which no compound having a hydroxyl group was added as a lubricant.

 Table 2 shows the results.

As is clear from Table 2, a carbon protective film is formed on the surface of the metal magnetic thin film, and a lubricant comprising a fluorine-based lubricant and a compound having two or more hydroxyl groups shown in Table 1 as a lubricant on the carbon protective film. It can be seen that the friction coefficient after CSS under the high-temperature and low-humidity conditions is significantly improved in each of the sample discs using, as compared with the lubricant composed of only the fluorine-based lubricant.

〔The invention's effect〕

As is clear from the above description, the magnetic recording medium of the present invention comprises a perfluorocarboxylate having a very excellent lubricating property and an organic compound having a hydroxyl group or a perfluorosulfonic acid salt and an organic compound having a hydroxyl group. Since it is retained as a lubricant, it can maintain lubricity under any use conditions, especially under high temperature and low humidity, and can maintain its lubricity over a long period of time.

Therefore, the magnetic recording medium of the present invention has excellent running properties, wear resistance, and durability.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part showing one configuration example of a magnetic recording medium to which the present invention is applied. FIG. 2 is an enlarged sectional view of a main part showing another example of the configuration of the magnetic recording medium to which the present invention is applied. DESCRIPTION OF SYMBOLS 1 ... Non-magnetic support 2 ... Magnetic layer 3 ... Lubricant layer 4 ... Rust inhibitor layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C10M 129: 08 129: 14) (C10M 169/04 105: 72 129: 08 129: 14) C10N 40 : 18

Claims (2)

(57) [Claims] A metal magnetic thin film is formed on a nonmagnetic support, and a lubricant mainly composed of a perfluorocarboxylate and an organic compound having two or more hydroxyl groups is formed on the metal magnetic thin film. Magnetic recording medium. 2. A metal magnetic thin film is formed on a nonmagnetic support, and a lubricant mainly composed of a perfluorosulfonic acid salt and an organic compound having two or more hydroxyl groups is formed on the metal magnetic thin film. Magnetic recording medium.