JPH09291296A - Production of lubricant and magnetic recording medium using the lubricant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-purity lubricant suitable for producing a magnetic recording medium excellent in traveling properties, wear resistance and durability, by esterifying a terminal carboxyl perfluoropolyether synthetic substance, extracting the esterified compound with a solvent and hydrolyzing the extracted substance. SOLUTION: A terminal carboxyl-containing perfluoropolyether synthetic substance is esterified with an alcohol containing a relatively long hydrocarbon chain (e.g. 1-octadecanol), etc., and the prepared reaction product is extracted with a solvent such as hexane or an ether to separate and remove impurities and the extracted esterified compound is hydrolyzed with a solution of sodium hydroxide or potassium hydroxide to give the objective lubricant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lubricant and a magnetic recording medium using the same, and more particularly to improvement of a lubricant using perfluoropolyethers having a carboxyl group at the terminal.

[0002]

2. Description of the Related Art In a so-called metal 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 used as a magnetic layer, the magnetic layer is bonded to a ferromagnetic powder. Compared to the coating type magnetic recording media composed of
From the point that the packing density of the magnetic material in the magnetic layer is high,
It has excellent magnetic properties and has recently been used in various magnetic recording medium systems.

[0003] Here, since the metal thin film type magnetic recording medium has extremely good smoothness on the surface of the magnetic layer, a substantial contact area with a sliding member such as a magnetic head or a guide roller is large. The coefficient becomes large, and the adhesion phenomenon (so-called sticking) is likely to occur, and there are many problems such as lack of running property and durability.

For example, when applied to an 8 mm video deck or a hard disk drive, the following problems occur.

[0005] First, a tape inserted into an 8 mm video deck is wound around a drum through ten or more guide pins. At this time, the tape tension and the tape running speed are kept constant by a pinch roller and a capstan. Usually, the tension is about 20 g, and the running speed is 0.1 mm.
5 cm / sec.

In such a running system, the magnetic layer side of the tape has a structure in contact with a fixed guide pin made of stainless steel. For this reason, when the friction on the tape surface increases, the tape causes a stick-slip, so-called tape squealing occurs, and the reproduction screen becomes tight.

Further, the relative speed between the tape and the head is very high, and particularly in a pause state, high-speed contact is made at the same place, which causes a problem of abrasion of the magnetic layer, leading to a decrease in reproduction output.

The problem of the wear of the magnetic layer is very serious in the magnetic recording medium of the metal magnetic thin film type since the magnetic layer is very thin.

On the other hand, in a hard disk drive, CSS
(Contact start / stop) method is adopted. In this CSS method, before rotation (when the disk is stopped)
The magnetic head is in contact with the disk, and when the disk starts to rotate at a high speed at the time of startup, the magnetic head flies above the disk surface by the air flow generated thereby, and recording / reproduction is performed in this state. When the operation is stopped, the rotation of the disk is decelerated, whereby the magnetic head comes into contact with the disk again.

Therefore, in this CSS system, when the operation of the disk is stopped (from the contact of the magnetic head with the disk until the rotation of the disk is stopped) or at the start of the start (after the rotation of the disk is started. Since the magnetic head runs while rubbing the surface of the medium before the magnetic head floats up, an increase in friction at that time is a serious problem.

In order to maintain product-level reliability, it is desirable that the coefficient of friction after performing the CSS operation 20,000 times is 0.5 or less. It is difficult for a medium (magnetic disk) to satisfy this condition. Further, since the head rotates at a high speed, a problem such as a head crash due to a collision between the head and the medium is one of the problems to be solved in the thin film medium.

Therefore, in order to improve these problems,
The use of various lubricants has been studied, and attempts have been made to suppress the coefficient of friction by applying a lubricant such as a higher fatty acid or its ester onto the magnetic layer of the magnetic recording medium. I have.

By the way, the lubricant used for the magnetic recording medium is required to have the following extremely strict characteristics due to its properties, and it is difficult for the lubricant used conventionally to cope with the problem. is there.

That is, the lubricant used for the magnetic recording medium includes (1) excellent low-temperature characteristics so as to ensure a predetermined lubrication effect when used in a cold region, and (2) a lubricant with a magnetic head. Since pacing poses a problem, it is required that the coating be able to be applied extremely thinly, that sufficient lubrication properties be exhibited even in such a case, and that (3) long-term use or long-term use, and that the lubrication effect be maintained. Is done.

The most important solution to these problems of increasing coefficient of friction or durability is to study the lubricant applied to the surface. That is, as a lubricant for a magnetic recording medium, good lubrication performance with a head, uniform and strong adhesion to a tape or disk surface, long-term retention of these performances (for example, 10 years), and such requirements n
In order to achieve a film thickness on the order of a monomolecular level of about m, it is necessary to study a lubricant.

It is known that the lubrication characteristics depend on the molecular structure of the lubricant, but the ones developed especially for the magnetic recording medium are roughly classified into three types: silicon type, hydrocarbon type and fluorinated carbon type. are categorized.

Of these, silicon-based lubricants are one of the lubricants that are often used in coating-type media because of their good thermal stability and low vapor pressure. However, there is no good lubrication performance on thin-film magnetic recording media with very good surface properties like the current one, and lubrication characteristics in pin-on-disk wear acceleration tests or CSS tests satisfy durability specifications. do not do. That is, silicon-based lubricants are extremely limited in forming an oriented lubricating film on the surface of a thin-film magnetic recording medium, which is currently mainstream, and satisfying required lubricating characteristics.

Further, hydrocarbon-based lubricants are still the mainstream lubricants in coating type magnetic recording media. However, in terms of thermal or chemical stability, hydrocarbon-based lubricants are generally inferior to silicon-based or fluorine-based lubricants, and frictional polymers formed by the reaction of molecules by friction, It is easy to produce in systems using hydrocarbon-based lubricants. This polymer degrades the lubricating properties, sometimes resulting in catastrophic failure. Further, the high vapor pressure of this hydrocarbon-based lubricant is also a drawback. That is, although this hydrocarbon-based lubricant exhibits excellent lubricating performance, it gradually volatilizes due to its high vapor pressure.
For this reason, in the magnetic recording medium of the metal magnetic thin film type in which the lubricant is held only by top-coating the lubricant, if the lubricant volatilizes from the surface, it cannot be replenished.
It is difficult to maintain the lubrication performance, and it is difficult to use it for an actual thin film magnetic medium.

The fluorine-based lubricant is a lubricant most frequently used at present in a magnetic recording medium of a metal magnetic thin film type. Among the fluorine-based lubricants, the above-mentioned perfluoropolyether is widely used because of its better lubricating performance and surface protection effect as compared with other fluorine-based lubricants. The reason for this is that the CF ₂ —O—CF ₂ ether bond is flexible, so that the viscosity is lower than that of a perfluoroalkane having the same molecular weight, and the viscosity does not change in a wide temperature range. In addition, they must be chemically inert, have low vapor pressure, have high thermal or chemical stability, have low surface energy, have good boundary lubrication properties, and have good water repellency. Is a feature.

For example, with respect to the thermal and chemical stability required for a lubricant, in some magnetic recording systems, the relative speed between the medium and the magnetic head exceeds several meters, and the friction generated at the contact portion is large. The temperature of the medium surface may increase instantaneously but rapidly due to heat. The temperature at the contact point has been estimated to exceed several hundred degrees Celsius, although a precise method of measurement has not yet been established, but has been evaluated by calculation. In particular, under such boundary lubrication conditions, a reactive surface is exposed on the sliding portion, and this is combined with the above-mentioned temperature rise at the contact point, thereby promoting the decomposition reaction of the lubricant molecules. Therefore, lubricants used in magnetic recording media include:
Thermal and chemical stability are very important, and perfluoropolyether which is superior in such a point will be used frequently.

Here, the characteristics of the perfluoropolyether very strongly depend on its molecular structure. Currently, several types of perfluoropolyethers are commercially available, but they differ in molecular weight, main chain repeating units, and terminal groups.

For example, the product name Fom manufactured by Montedison Co.
Blin-Y type is CF (CF ₃ ) CF ₂ O and CF ₂
While the repeating unit of the main chain has a branched structure in a random polymer of O, the Fomblim-Z type has a C structure.
It is a polymer of F ₂ CF ₂ O and CF ₂ O and has a linear structure. Due to this linear structure, the viscosity becomes low and shows excellent lubricating properties as compared with other types. In addition, the product name “Demnum type” manufactured by Daikin Industries and the product name “Kry” manufactured by Dupont
The tox type is a homopolymer of hexafluoropropylene oxide and hexafluoroisopropylene oxide, respectively. This type has a higher viscosity in comparison with the Fomblim-Z type, but has better chemical stability.

In addition, perfluoropolyether lacks the ability to adsorb on the surface of a magnetic medium because it is relatively inert chemically. Therefore, in order to improve the adsorptive power, as a perfluoropolyether having polar groups at both ends, a product name Fomblin Z-DOL (a hydroxyl group is introduced as a polar group) manufactured by Montedison Co. or a product name Fomblin manufactured by the same company is used.
AM2001 (introducing a piperonyl group as a polar group) has been developed. Of these, Fomblin AM20
01 has a very strong fixing effect particularly on the surface of metal or carbon, and the introduction of a polar group at the end reduces the coefficient of friction and improves the useful life of the magnetic disk.

[0024]

However, when a polar group is introduced into the perfluoropolyethers, the reaction yield is not always good, and unreacted impurities, that is, polar groups are introduced in a predetermined amount into the product. Missing perfluoropolyethers are often mixed.

Since such unreacted impurities cause deterioration of the durability of the lubricant, it is desirable to remove them from the composite. However, it is actually difficult to separate and purify polar group-containing perfluoropolyethers from such unreacted impurities.

That is, as a method of purifying an organic compound, a physical method such as distillation, a method of extracting a target organic compound with a solvent, a column chromatography using silica gel or alumina as a column packing material, and the like can be considered. .

However, physical methods such as distillation are not suitable methods for purifying compounds having a relatively high molecular weight such as perfluoropolyethers.

Further, in the case of extraction with a solvent or column chromatography, a solvent in which perfluoropolyethers are dissolved is required. However, perfluoropolyethers show sufficient solubility only in fluorocarbon solvents such as CFCs or perfluorocarbons, that is, solvents that are limited in terms of global environmental protection, and they must be used. So, there is a problem to do at the industrial level.

As described above, in the field of magnetic recording media, when it comes to perfluoropolyether, which is a lubricant used, its performance is insufficient from the viewpoint of its purity, and practical properties such as running durability are impaired. I am dissatisfied.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and provides a method for producing a lubricant capable of obtaining a perfluoropolyether having a polar group with high purity, and various methods. An object of the present invention is to provide a magnetic recording medium which has excellent lubricity under use conditions, has a long-lasting lubrication effect, and is excellent in running property, abrasion resistance, durability, etc. .

[0031]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies as a means to achieve the above-mentioned object, and as a result, regarding a perfluoropolyether having a carboxyl group at the terminal, a relatively long hydrocarbon chain Is esterified with an alcohol having a carboxylic acid, and impurities are separated by utilizing the solubility difference in solvents such as hexane or ether, and further hydrolyzed to have a highly purified terminal carboxyl group. It was found that a perfluoropolyether can be obtained, and that the purified perfluoropolyether or a magnetic recording medium coated with a lubricant obtained by modifying the perfluoropolyether exhibits good results, and the present invention has been completed.

That is, the method for producing the lubricant of the present invention is
It is characterized in that perfluoropolyether having a carboxyl group at the terminal contained in the synthetic product is esterified, the ester compound is extracted with a solvent, and then the ester compound is hydrolyzed.

The magnetic recording medium of the present invention is a magnetic recording medium having at least a magnetic layer on a non-magnetic support, and is a perfluoropolyether having a carboxyl group at the terminal purified by the above method or the magnetic recording medium. The modified compound is coated or internally added on the magnetic layer.

The lubricant produced by applying the present invention has good durability even when used under severe conditions such as high temperature and high humidity or low temperature and low humidity, and its characteristics are not deteriorated. In addition, the perfluoropolyether purified by this esterification method, or a magnetic recording medium in which a lubricant obtained by modifying the perfluoropolyether is applied to the surface of the magnetic layer not only exerts a good lubricating action but reduces the friction coefficient. Improves still durability and shuttle durability.

The film thickness of the lubricant is preferably 0.1 to 20 nm. When the film thickness of the lubricant is thicker than 20 nm, the electromagnetic conversion characteristics are significantly deteriorated, and conversely 0.1 n
If it is thinner than m, the durability is insufficient.

In the magnetic recording medium to which the present invention is applied, a ferromagnetic metal material is directly deposited on the surface of a non-magnetic support by a vacuum thin film forming technique such as vapor deposition to form a metal magnetic thin film as a magnetic layer. A magnetic recording medium of a so-called metal magnetic thin film type may be used, or a magnetic coating prepared by mixing a ferromagnetic powder and a binder with an organic solvent is applied to a non-magnetic support to form a magnetic layer. A so-called coating type magnetic recording medium may be used.

The metal magnetic thin film type magnetic recording medium may have a structure in which an underlayer is interposed between the non-magnetic support and the magnetic layer.

In this metal magnetic thin film type magnetic recording medium, the non-magnetic support and the metal magnetic thin film are not particularly limited, and any conventionally known one can be used.

For example, the non-magnetic support may be the same as the above-mentioned coating type magnetic recording medium. Polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, and cellulose triacetate. , Cellulose diacetate, cellulose derivatives such as cellulose acetate butyrate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, polycarbonate, polyimide, polyamide,
Examples thereof include plastics such as polyamide-imide, paper, metals such as aluminum and copper, light metals such as aluminum alloys and titanium alloys, ceramics, single crystal silicon and glass. Of these, when a rigid substrate such as an Al alloy plate or a glass plate is used as the non-magnetic support, an oxide film such as an alumite treatment or a Ni-P film is formed on the surface of the substrate to harden the surface. You may do it.

The metal magnetic thin film is formed as a continuous film by a PVD method such as plating, sputtering or vacuum deposition, and is made of a metal such as Fe, Co or Ni or Co-N.
i-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
Examples include in-plane magnetization recording metal magnetic films and Co—Cr based alloy thin films made of system alloys, Fe—Co—Ni—B based alloys and the like.

In particular, in the case of an in-plane magnetization recording metal magnetic thin film,
Bi, Sb, Pb, Sn, Ga, on the non-magnetic support in advance
An underlayer of a low-melting point non-magnetic material such as In, Ge, Si, or Ti is formed, and a metal magnetic material is vapor-deposited or sputtered from the vertical direction to diffuse the low-melting point non-magnetic material in the metal magnetic thin film. The orientation may be eliminated to secure the in-plane isotropic property, and the coercive force may be improved.

The most general method for retaining the above-mentioned lubricant on the metal magnetic thin film is to similarly dip-coat a lubricant layer on the surface of the metal magnetic thin film or the surface of the protective film.

In this case, the film thickness of the lubricant is 5 to 50 n.
m, the coating amount is 0.5 to 100 mg / m ² , and more preferably 1 to 20 mg / m ² . When the film thickness of the lubricant is less than 5 nm, a sufficient lubricating effect cannot be obtained, and conversely, when it is more than 50 nm, the electromagnetic conversion characteristics may deteriorate.

When the present invention is applied to the coating type magnetic recording medium, the lubricant can be applied to the surface of the magnetic layer as in the case of the metal magnetic thin film type magnetic recording medium. It is also possible to add internally in the layer.

Here, as the molecular structure of the above-mentioned perfluoropolyether, examples of monofunctional perfluoropolyethers include F (CF ₂ CF ₂ CF ₂ O) _n having a perfluoropropyloxy group and perfluoropolyether. Examples thereof include those represented by the following chemical formula 1 which are copolymers of a propyloxy group and a perfluorooctylene group, and those represented by the following chemical formula 2 having a perfluoroisopropyloxy group.

[0046]

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[0047]

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The polyfunctional perfluoropolyether is, for example, a copolymer of a perfluorooxyethylene group and a perfluorooxymethylene group (OC
₂ F ₄ ) p (OCF ₂ ) q and the like.

Here, l, m, n, k, p and q in the chemical structural formula of the perfluoropolyether represent integers of 1 or more (hereinafter the same). The molecular weight is not particularly limited, but is preferably about 600 to 5,000.
If the molecular weight is too large, the effect of the polar group will be small, and if it is small, the vapor pressure will be high and the thermal stability will be poor.

A specific example of the structure of the perfluoropolyether having a carboxyl group at the terminal is Fomblin Z-DIAC under the trade name of Fomblin Z-DIAC manufactured by Montedison.
HOOCH ₂ CCF ₂ (OC ₂ F ₄ ) p (OCF ₂ ) q
OCF ₂ CH ₂ COOH, trade name Demnum SA manufactured by Daikin Industries, Ltd. shown in Chemical formula 3 below, and product name Krytox manufactured by DuPont shown in Chemical formula 4 below are available.

[0051]

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[0052]

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When Rf is used, the perfluoropolyethers having different molecular structures may be used. That is, the molecular structure and the repeating unit are not particularly limited.

The purified lubricant may be applied alone on the magnetic recording medium, or may be used after being modified. For example, an ester compound with a long-chain alcoholic acid may be used again, or a compound having an amino group and a carboxylic acid amine salt compound may be formed. Increasing the hydrocarbon content in the molecule allows the use of solvents other than freon. Further, the introduction of the hydrocarbon component increases the intermolecular interaction, increases the oil film strength of the lubricating film, and exerts an effect on durability.

This lubricant is a conventionally known lubricant,
For example, long-chain carboxylic acids or their esters generally used in magnetic recording media, long-chain alcohols,
It may be used in combination with long-chain amines.

Further, an extreme pressure agent may be used in combination in order to cope with more severe conditions and maintain the lubricating effect.

This extreme pressure agent reacts with the metal surface by frictional heat generated when a metal contact is partially generated in the boundary lubrication region, and forms a reaction product film to prevent friction and wear. Any of phosphorus-based extreme pressure agents, sulfur-based extreme pressure agents, halogen-based extreme pressure agents, organic metal-based extreme pressure agents, complex-based extreme pressure agents and the like can be used.

This extreme pressure agent is used in a weight ratio to the above lubricant.
It is suitable to use the compounding ratio of about 30:70 to 70:30.

In addition to the extreme pressure agent, the lubricant may be used in combination with a rust preventive or the like, if necessary.

As the rust preventive, any rust preventive commonly used as a rust preventive for magnetic recording media of this type can be used. For example, phenols, naphthols, quinones, and heterocycles containing a nitrogen atom can be used. Examples thereof include compounds, heterocyclic compounds containing an oxygen atom, and heterocyclic compounds containing a sulfur atom.

Further, in the above-mentioned metal magnetic thin film type magnetic recording medium, in addition to the metal magnetic thin film which is the magnetic layer, an undercoat layer or the like is formed below the back coat layer or the magnetic layer as needed. Good. In this case, it is possible to apply or internally add the lubricant to the back coat layer as described above.

[0062]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described, but it goes without saying that the present invention is not limited to these embodiments.

<Purification Method of Lubricant> In the reaction of introducing a carboxyl group into perfluoropolyethers, in addition to the perfluoropolyethers into which the desired carboxyl group is introduced, a carboxyl group is introduced into the obtained synthetic product. In some cases, perfluoropolyethers or the like having insufficient introduction of groups may be mixed.

In the present invention, the perfluoropolyethers are esterified in order to purify only the perfluoropolyethers into which the desired carboxyl group has been introduced, from the compound in which such unreacted impurities are mixed. ,
After removing the solvent from the reaction solution, the remaining reaction product (ester compound) is selectively extracted with an extraction solvent by utilizing the difference in solubility with impurities, and further extracted into the extraction solvent. When an alkaline solution is added to the dissolving portion, the ester bond of the perfluoropolyethers dissolved in the extraction solvent is hydrolyzed to return to the carboxyl group.

The above esterification can be carried out, for example, by using anhydrous toluene,
In a solvent such as hexane (including hydrogen nitride) and ketone solvents,
It can be obtained by removing the produced water by using sulfuric acid or p-toluenesulfonic acid as a catalyst. It is also possible to convert perfluoropolyether into carboxylic acid chloride and react it with a long-chain alcohol. The reaction formula in the purification process of the perfluoropolyether having a carboxyl group at its terminal is shown in Chemical Formula 5 below.

[0066]

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However, the perfluoropolyethers having a carboxyl group at the terminal thus obtained are of high purity and exhibit good lubricating performance.

Here, the case of purifying perfluoropolyethers having a carboxyl group introduced only at one end has been described as an example, but the perfluoropolyethers to be purified in the present invention have carboxyl groups at both ends. A perfluoropolyether having a group introduced may be used. In the perfluoropolyethers having carboxyl groups introduced at both ends, when the carboxyl groups are introduced into the perfluoropolyethers, the perfluoropolyethers having a carboxyl group introduced at only one end are obtained. Fluoropolyethers and perfluoropolyethers with insufficient introduction of carboxyl groups are mixed as unreacted impurities.

Purification of these perfluoropolyethers having a carboxyl group introduced at only one end or at both ends can be highly purified by the same principle by selecting an appropriate esterifying agent and extraction solvent. You can

As the above extraction solvent, ether is practical because it can deal with many perfluoropolyethers. However, it is basically selected from the viewpoint that the target ester compound is selectively dissolved and unreacted impurities are not dissolved.

A strong alkaline solution in which a potassium hydroxide solution, a sodium hydroxide solution or the like is dissolved is used as the alkaline solution for hydrolyzing the extracted ester compound.

The purified perfluoropolyethers may be modified for the purpose of further improving the properties. For example, as described in JP-A-5-194970, when an ester compound with a long-chain carboxylic acid is used, the hydrocarbon component increases, so that it becomes possible to dissolve it in a solvent other than CFC, thus protecting the environment. In terms of Further, the introduction of the hydrocarbon component increases the intermolecular interaction, thereby increasing the oil film strength of the lubricating film and improving the durability.

The perfluoropolyethers having a carboxyl group at the terminal purified as described above are retained as a lubricant in, for example, the magnetic layer of the magnetic recording medium. In the magnetic recording medium in which the perfluoropolyethers are held in the magnetic layer, good lubrication performance is obtained in the magnetic layer not only under normal temperature and normal humidity environment but also under severe environment such as high temperature and high humidity and low temperature. Maintained for a long time,
Paper with reduced friction coefficient and improved running durability.

Here, as a perfluoropolyether having a carboxyl group introduced at the terminal, a Krytox (trade name, manufactured by DuPont) having a molecular weight of 1800 and having one terminal is manufactured by DuPont.
q is an integer of 1 or more. ), And the case where it is purified by the present invention will be described as an example.

150 g of Krytox and stearyl alcohol are added to toluene (or hydrogen nitride-containing hexane, a ketone solvent, or the like can be used), and water produced is removed while heating under reflux.

The reaction is completed by refluxing for 5 hours.

After the reaction is completed, the toluene-dissolved portion and the undissolved portion are separated, so the undissolved portion is removed. Toluene in the toluene-dissolved portion was removed, and the residue was purified by silica gel chromatography using hexane as a developing solvent, 130 g.
To obtain the ester of.

1 and 2 show the IR spectra of the toluene undissolved part and the dissolved part of this compound, respectively.

From FIGS. 1 and 2, CH stretching vibration (300
Around 0 cm ^-1 , belonging to hydrocarbon component) and CF
Existence of stretching vibration, CO stretching vibration (around 1600 cm ^-1 )
This compound is determined from the high wavenumber shift of. In this case, the small intensity of these absorption peaks means that the degree of esterification is small.

CO was added to the undissolved portion of toluene (FIG. 1).
It is considered to be an impurity that does not have stretching vibration and does not contain a carboxyl group at the end contained in the raw material. Therefore, it became possible to remove the impurities in the raw material by this esterification method.

Furthermore, caustic potash was added to a mixed solvent of ether, ethyl alcohol and water to the purified ester (toluene-dissolved portion), and the mixture was heated to reflux for 5 hours and extracted with perfluorooctane (ester is difficult to dissolve). A purified perfluoropolyether having a carboxyl group at the terminal can be easily obtained.

The alcohol used for purification is not particularly limited, but specifically, the number of carbon atoms is preferably 10 or more, more preferably 10 to 30. If it is too short, the ester compound will not dissolve in toluene, so caution must be taken regarding the solvent in this case as well.

With respect to the modification of the purified perfluoropolyether having a carboxyl group at the terminal, for example, long-chain ester can be synthesized by the same method as in JP-A-5-194970.

[0084]

Embodiments of the present invention will be described below based on experimental results.

First, an example of a metal magnetic thin film type magnetic recording medium (vapor-deposited tape) using as a lubricant perfluoropolyether having a carboxyl group at the terminal purified by the above method will be described.

Example 1 Co was deposited on a 14 μm-thick polyethylene terephthalate film by the oblique evaporation method to give a film thickness of 200 nm.
Was formed.

Next, a solution of perfluoropolyether having a carboxyl group at the terminal (see Table 1 below) purified by the above method on this metal magnetic thin film was dissolved in perfluorooctane to give a coating amount of 5 mg / m 2. ^A lubricant layer was formed by coating so as to be ² .

Then, the obtained magnetic film was cut into a width of 8 mm to prepare a sample tape.

Example 2 In Example 1, the purified perfluoropolyether having a carboxyl group at the end as a lubricant is shown in Table 1 and the product name is Fomblin Z-DIA manufactured by Montedison Co. under the trade name.
It changed to C and refined. Then, a sample tape was produced by the same method as in Example 1 except that this lubricant was used.

Example 3 In Example 1, the molecular structure of perfluoropolyether having a carboxyl group at the terminal as a lubricant was changed to Demnum SA (molecular weight 2000) manufactured by Daikin Industries, Ltd. shown in Table 1 for purification. . Then, a sample tape was produced by the same method as in Example 1 except that this lubricant was used.

[0091]

[Table 1]

Each of the sample tapes manufactured as described above had a temperature of −5 at a temperature of 25 ° C. and a humidity of 60%.
When the temperature was 40 ° C., aging was performed under the conditions of a temperature of 40 ° C. and a humidity of 80%, and the friction coefficient before and after aging, the still durability and the shuttle durability were measured.

For the still durability, the decay time until the output decreased by 3 dB in the paused state was evaluated. Shuttle durability is 3 minutes each time the shuttle runs for 2 minutes
It was evaluated by the number of shuttles until it decreased by dB.

The results are shown in Table 2.

As a comparative example, as shown in Table 1 above, a blank tape containing no lubricant (Comparative Example 1
And ), When using unpurified perfluoropolyether and unpurified perfluoropolyether (referred to as Comparative Example 2 and Comparative Example 3, respectively), friction measurement, still durability and shuttle durability were performed in the same manner as described above. Was measured and the results are also shown in Table 2 below.

[0096]

[Table 2]

As is clear from Table 2, as compared with the unpurified perfluoropolyethers (Comparative Examples 2 and 3), the purified perfluoropolyethers having the carboxyl groups at the terminals as in Examples 1 to 3 were used. It was found that the sample tape using ether as a lubricant shows very good results in terms of friction coefficient, still durability and shuttle durability under various conditions. It was also found that in Examples 1 to 3, excellent lubricating performance was maintained with almost no deterioration in characteristics due to aging.

Next, an example of a metal magnetic thin film type magnetic recording medium (evaporated tape) using as a lubricant a perfluoropolyether having a carboxyl group at the terminal, which has been purified by the above-mentioned method, converted to a stearyl ester is used. explain.

Example 4 A sample was prepared in the same manner as in Example 1 except that the perfluoropolyether having a carboxyl group at the terminal refined as a lubricant in Example 1 was modified to the stearyl ester shown in Table 3. A tape was made.

[0100]

[Table 3]

With respect to the obtained sample tape, the friction coefficient before and after aging, the still durability and the shuttle durability were measured in the same manner as described above.

The results are shown in Table 4.

As a comparative example, a case where unpurified perfluoropolyether modified into stearyl ester as shown in Table 3 above was used (referred to as Comparative Example 4).
The friction measurement, the still durability and the shuttle durability were measured in the same manner as described above, and the results are also shown in Table 4 below.

[0104]

[Table 4]

As is clear from Table 4, in comparison with the one obtained by modifying the unpurified perfluoropolyether into stearyl ester (Comparative Example 4), a carboxyl group is present at the terminal purified as in Example 4. It was found that the sample tape using perfluoropolyether modified to stearyl ester as a lubricant shows very good results in friction coefficient, still durability and shuttle durability under various conditions. In addition, in Example 4, it was found that the characteristic deterioration due to aging hardly occurred and the excellent lubricating performance was maintained.

Further, an example of a metal magnetic thin film type magnetic recording medium (vapor-deposited tape) using the amine salt of perfluoropolyether having a carboxyl group at the terminal purified by the above-mentioned method as a lubricant will be described.

Example 5 A sample was prepared in the same manner as in Example 1 except that the perfluoropolyether having a carboxyl group at the terminal purified as a lubricant in Example 1 was modified to the amine salt shown in Table 5, and the other conditions were the same as in Example 1. A tape was made.

[0108]

[Table 5]

With respect to the obtained sample tape, the friction coefficient before and after aging, the still durability and the shuttle durability were measured in the same manner as described above.

The results are shown in Table 6.

As a comparative example, as shown in Table 5 above, when the unpurified perfluoropolyether modified into an amine salt was used (referred to as Comparative Example 5), the friction was performed in the same manner as described above. Measurement, still durability and shuttle durability were measured, and the results are also shown in Table 6 below.

[0112]

[Table 6]

As is clear from Table 6, in comparison with a product obtained by modifying an unpurified perfluoropolyether into an amine salt (Comparative Example 5), a carboxyl group is present at the terminal purified as in Example 5. It was found that the sample tape using the amine salt of perfluoropolyether as a lubricant shows very good results in terms of friction coefficient, still durability and shuttle durability under various conditions. In addition, the fifth embodiment
In, it was found that there is almost no characteristic deterioration due to aging, and excellent lubricating performance is maintained.

[0114]

As is apparent from the above description, in the present invention, perfluoropolyethers having a carboxyl group at the terminal are purified by the steps of esterification, solvent extraction and hydrolysis, so that high purity is achieved. It is possible to obtain various perfluoropolyethers.

Further, the magnetic recording medium using the perfluoropolyether purified by this method or the lubricant modified with the perfluoropolyether can maintain the lubricating performance under any conditions of use, and its lubricity can be maintained for a long period of time. Can be kept. Further, regarding its characteristics, good lubricating characteristics are exhibited without depending on the molecular structure of perfluoropolyether.

Therefore, according to the present invention, it is possible to provide a magnetic recording medium excellent in running property, wear resistance and durability.

[Brief description of drawings]

FIG. 1 is an IR spectrum of a perfluoropolyether having a carboxyl group at the terminal, which is purified by applying the present invention.

FIG. 2 is an enlarged view of a main part of an IR spectrum of a perfluoropolyether having a carboxyl group at a terminal, which is purified by applying the present invention.

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Claims (2)

[Claims] 1. A lubricant characterized by esterifying perfluoropolyether having a carboxyl group at a terminal contained in a synthetic product, extracting the ester compound with a solvent, and then hydrolyzing the ester compound. Manufacturing method. 2. A magnetic recording medium having at least a magnetic layer on a non-magnetic support, wherein the perfluoropolyether having a carboxyl group at the terminal purified by the above method or a compound obtained by modifying the perfluoropolyether is on the magnetic layer. A magnetic recording medium characterized by being coated or internally added.