JPH09157674A - Production of lubricant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a lubricant effective for imparting a magnetic recording medium with excellent transport durability in high purity without using a fluorine-based solvent by esterifying a perfluoropolyether having terminal OH, extracting the produced ester with a solvent and hydrolyzing the product. SOLUTION: The objective lubricant is produced by esterifying a perfluoropolyether having terminal OH and contained in a synthetic material [e.g. a compound of the formula, HOCH2 CF2 (OC2 F4 )p (OCF2 )q OCF2 CH2 OH (p>=1; q>=1) with an esterifying agent such as a 6-12C carboxylic acid chloride, extracting the obtained ester compound with a solvent such as an ether and hydrolyzing the extract with a potassium hydroxide solution, a sodium hydroxide solution, etc.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a lubricant, and more particularly to a method for purifying perfluoropolyethers having a hydroxyl group at the terminal.

[0002]

2. Description of the Related Art In a so-called metal magnetic thin film type magnetic recording medium in which a magnetic layer is formed by depositing a ferromagnetic metal material on a nonmagnetic support by a method such as vapor deposition, the magnetic layer is made of a ferromagnetic material. Compared to a coating-type magnetic recording medium composed of powder and a binder, it has excellent magnetic properties, such as higher packing density of a magnetic material in a magnetic layer, and is used in various magnetic recording systems in recent years. It has become.

[0003] The magnetic recording medium of the metal magnetic thin film type has an extremely high smoothness on the surface of the magnetic layer, and therefore has a substantial contact area with a sliding member such as a magnetic head or a guide roller. Also becomes a large value. For this reason, there is a problem in that a sticking phenomenon (so-called sticking) easily occurs with these sliding members during running and the running property and durability are poor. For example, when applied to an 8 mm video deck or a hard disk drive, the following problems occur.

First, a tape inserted into an 8 mm video deck is guided by ten or more guide pins and wound around a head drum. 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 set to about 20 g and the running speed is set to 0.5 cm / s.

[0005] The running system has a structure in which the magnetic layer side of the tape is in contact with a guide pin made of stainless steel. In such a case, if the coefficient of friction between the surface of the magnetic layer of the tape and the guide pins is large, the tape causes stick-slip, a phenomenon called tape squealing, and the reproduced image becomes cramped.

Further, the relative speed between the tape and the head is very high, and particularly in the pause state, the head slides at the same position on the tape at a high speed. This causes a problem of abrasion of the magnetic layer and a resulting reduction in reproduction output. In the above-described metal magnetic thin film type magnetic tape, the magnetic layer is very thin, so that the wear of such a magnetic layer is very serious.

On the other hand, in a hard disk drive,
The SS (contact start / stop) method is adopted. In the CSS method, when the disk is stopped, the magnetic head is in contact with the disk. When the disk is rotated at a high speed at the time of startup, the magnetic head floats from the surface of the disk due to the airflow generated thereby, and recording is performed in this state Playback is performed. When the operation is stopped, the rotation of the disk is further reduced, whereby the magnetic head comes into contact with the disk again. CSS like this
In the method, at the time of startup, from the start of disk rotation until the magnetic head floats, and at the time of operation stop, from the time the magnetic head contacts the disk until the disk stops rotating, The magnetic head slides on the disk. At that time, friction between the magnetic head and the disk becomes a major problem. C to maintain product level reliability
It is desirable that the friction coefficient after performing the SS operation 20,000 times is 0.5 or less, but it is difficult to satisfy this condition with a metal magnetic thin film type magnetic disk having high surface smoothness. Another problem to be solved is head crash caused by collision between the head and the disk.

[0008] In order to solve such problems, attempts have been made to suppress the friction coefficient by top-coating the magnetic layer with various lubricants such as higher fatty acids and esters thereof.

Here, the lubricant used for the magnetic recording medium is required to have the following extremely strict conditions for its use. However, conventionally used lubricants cannot be said to sufficiently satisfy such conditions.

That is, the lubricant used for the magnetic recording medium has (1) excellent low-temperature characteristics so as to ensure a predetermined lubricating effect when used in a cold region; (2)
It can be applied very thinly because spacing with the magnetic head is a problem, and sufficient lubrication performance can be exhibited even in that case. (3) It can withstand long-time use and maintain the lubrication effect for a long time. , Etc. are required.

That is, as a lubricant for a magnetic recording medium,
As well as having good lubrication performance against sliding with the head, it can be uniformly and firmly adhered to the surface of the magnetic layer, and the lubrication performance can be maintained for a long period of 10 years or more. Ideally, a film that can be applied as a thin film on the order of several nanometers on the order of a single molecule is ideal.

It is known that the lubricating performance of a lubricant depends on its molecular structure. However, as a lubricant for a magnetic recording medium, a large number of compounds have been developed so far. System, hydrocarbon system and fluorinated carbon system.

First, silicon-based lubricants are one of the lubricants widely used in coating type magnetic recording media because of their good thermal stability and low vapor pressure. However, when used for a magnetic recording medium of a metal magnetic thin film type with very good surface properties, not very good lubrication performance is obtained, and the durability specification in the pin-on-disk wear acceleration test or CSS test is Not satisfied. That is, it is difficult for a silicon-based lubricant to form a lubricating film oriented on the surface of a thin-film magnetic recording medium, which is currently the mainstream, and to satisfy required lubrication characteristics.

Hydrocarbon lubricants are still the mainstream lubricants in coating type magnetic recording media. However, this hydrocarbon-based lubricant is generally inferior in thermal or chemical stability as compared with a silicon-based or fluorinated carbon-based lubricant. Also, the friction reacts with the lubricant molecules to produce a frictional polymer. This frictional polymer is very troublesome, degrading lubricating properties and sometimes causing catastrophic failure. In addition, hydrocarbon lubricants have a high vapor pressure, which is one of the drawbacks.
That is, the hydrocarbon-based lubricant exhibits excellent friction characteristics, but gradually evaporates due to its high vapor pressure. For this reason, in a 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 is not replenished, and it is difficult to maintain the lubrication performance. is there.

Fluorine-based lubricants are currently the most widely used lubricants in metal magnetic thin film type magnetic recording media. Among the fluorine-based lubricants, particularly, perfluoropolyether is widely used because of its better lubricating performance and surface protection effect as compared with other fluorine-based lubricants.
The perfluoropolyether has such good properties because of the flexibility of the CF ₂ —O—CF ₂ ether bond, the viscosity is lower than that of perfluoroalkane of the same molecular weight, and over a wide temperature range. This is because the viscosity does not change. In addition, it must be chemically inert, have low vapor pressure, have high thermal or chemical stability, have low surface energy,
The features include good boundary lubrication characteristics and high water repellency.

Regarding the thermal and chemical stability required of a lubricant, for example, in a magnetic recording system, there are some magnetic recording systems in which the relative speed between the medium and the magnetic head exceeds several meters, and the friction generated at the contact portion thereof. The temperature of the medium surface may increase instantaneously but rapidly due to heat. The temperature at the contact portion is estimated to exceed several hundred degrees Celsius by the calculated value, though an accurate measuring method has not been established yet. In particular, under boundary lubrication conditions such as in a magnetic recording system, a reactive surface is exposed at the sliding portion, which together with the temperature rise at the contact point accelerates the decomposition reaction of lubricant molecules. For this reason, thermal and chemical stability are very important as the lubricant used in the magnetic recording medium, and perfluoropolyether excellent in such a point is often used.

The properties of the above-mentioned perfluoropolyether depend very strongly 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 Fomb manufactured by Montedison Co.
lin-Y is a random copolymer of CF (CF ₃ ) CF ₂ O and CF ₂ O, and the main chain repeating unit has a branched structure. On the other hand, the company's product name “Fombli”
n-Z is a homopolymer of CF ₂ CF ₂ O and CF ₂ O and has a linear structure. Due to this linear structure, the viscosity becomes low and the lubricating properties are superior to those of other types. Made by Daikin Industries, trade name demnum and made by Dupont, trade name K
rytox is a homopolymer of hexafluoropropylene oxide and hexafluoroisopropylene oxide, respectively. This type has a higher viscosity in comparison with Fomblin-Z, but has better chemical stability.

On the other hand, since perfluoropolyether is relatively chemically inactive, it has a drawback that it lacks the adsorption ability on the surface of the magnetic medium. Therefore, in order to improve the adsorptive power, as a perfluoropolyether in which polar groups are introduced into both ends, a product called Fomblin manufactured by Montesison Co., Ltd.
Z-DOL (introducing a hydroxyl group as a polar group) and Fomblin AM2001 (trade name, a piperonyl group as a polar group) manufactured by the company have been developed. Of these, Fom
Blin AM2001 has a very strong immobilizing action, especially on metal and carbon surfaces. For this reason, when used as a lubricant, a large friction coefficient reduction effect is obtained compared to unmodified perfluoropolyether,
The service life of the media is improved.

[0020]

However, in the reaction in which a polar group is introduced into perfluoropolyethers, the reaction yield cannot be said to be necessarily good, and unreacted impurities, that is, the polar group in the synthesized product are contained in a predetermined amount. In many cases, perfluoropolyethers that were not introduced in 1. are mixed. Since such unreacted impurities cause the durability of the lubricant to be impaired, it is desirable to remove them from the composition. However, in reality, it is difficult to separate and purify perfluoropolyethers containing a polar group from such unreacted impurities.

That is, as a method for purifying an organic compound, a physical method such as distillation, a method of selectively extracting a target organic compound with a solvent, and a column chromatography using silica gel or alumina as a column packing material are employed. Conceivable.

However, among them, physical methods such as distillation cannot be said to be suitable methods for purifying compounds having a relatively large molecular weight such as perfluoropolyethers.

On the other hand, extraction with a solvent and column chromatography require a solvent capable of dissolving perfluoropolyethers. 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.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and an object thereof is to provide a method for producing a lubricant by which a perfluoropolyether having a polar group can be obtained in high purity. To do.

[0025]

In order to achieve the above-mentioned object, the method for producing a lubricant of the present invention comprises esterifying a perfluoropolyether having a hydroxyl group at the terminal contained in a synthetic compound, and esterifying the ester. The compound is characterized in that the ester bond is hydrolyzed after the compound is extracted with a solvent.

The lubricant produced through such steps has high purity and exhibits very good lubricating performance.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described.

In the reaction for introducing a hydroxyl group into perfluoropolyethers, in addition to the perfluoropolyethers in which the desired hydroxyl group is introduced, perfluoropolyethers in which a hydroxyl group is insufficiently introduced are obtained in the obtained synthetic product. Ethers may be mixed in.

In the present invention, in order to purify only perfluoropolyethers having a desired hydroxyl group introduced from such a synthetic product in which unreacted impurities are mixed, the perfluoropolyethers are esterified, The ester compound is selectively extracted with a solvent by utilizing the difference in solubility with impurities, and the ester bond is hydrolyzed to obtain O.
It will be returned to H group. This process is performed by introducing a perfluoropolyether having hydroxyl groups introduced into both ends (Fomblin Z-DOL: HOH ₂ CCF ₂ manufactured by Montedison Co., Ltd. under the trade name.
A case of purifying (OC ₂ F ₄ ) _p (OCF ₂ ) _q OCF ₂ CH ₂ OH (where p and q are integers of 1 or more) will be described as an example.

Perfluoropolyethers having hydroxyl groups introduced at both ends include perfluoropolyethers having hydroxyl groups introduced at only one end and perfluoropolyethers having no hydroxyl group introduced. Mixed as unreacted impurities.

To purify perfluoropolyethers having hydroxyl groups introduced at both ends from such a compound,
An esterifying agent such as carboxylic acid chloride is added to the solution of this synthetic compound to esterify the hydroxyl groups of the perfluoropolyether. This reaction formula is shown in Chemical formula 1.

[0032]

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After removing the solvent from the reaction solution, the remaining reaction product is extracted with a solvent such as ether.

At this time, ester compounds derived from perfluoropolyethers having hydroxyl groups introduced at both ends,
That is, perfluoropolyethers having both ends esterified are extracted with ether. On the other hand, ester compounds derived from perfluoropolyethers having hydroxyl groups introduced only at one end that were mixed in as unreacted impurities and perfluoropolyethers having no hydroxyl groups introduced do not dissolve in ether and are insoluble. It remains as an ingredient.

Then, when an alkaline solution such as a potassium hydroxide solution is added to the ether-soluble component containing perfluoropolyethers whose both ends are esterified, it is dissolved in ether as shown in Chemical formula 2. The ester bonds at both ends of the present perfluoropolyethers are hydrolyzed back to hydroxyl groups, and perfluoropolyethers having hydroxyl groups at both ends are obtained.

[0036]

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The perfluoropolyethers having hydroxyl groups at both ends thus obtained are of high purity,
Exhibits good lubrication performance.

Here, the case of purifying perfluoropolyethers having hydroxyl groups introduced at both ends has been described as an example, but the perfluoropolyethers purified by the present invention have hydroxyl groups introduced at one end. Perfluoropolyethers may also be used. Any of the perfluoropolyethers can be purified to high purity by the same principle by selecting an appropriate esterifying agent and extraction solvent. In addition, a typical example of perfluoropolyethers having a hydroxyl group introduced at one end is represented by 3
The trade name is Demnum SA) and the chemical formula 4 is a trade name (Krytox manufactured by DuPont).

[0039]

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[0040]

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(However, n and k are integers of 1 or more.)
As the esterifying agent for esterifying the perfluoropolyether having a hydroxyl group introduced at the terminal, a relatively long-chain carboxylic acid chloride or the like is used as exemplified here.

The carbon number of the esterifying agent is set in order to enhance the extraction selectivity depending on the degree of esterification. For example, HOH ₂ CCF ₂ (OC
_{When 2} F ₄ ) _p (OCF ₂ ) _q OCF ₂ CH ₂ OH is esterified and extracted with ether, the number of carbon atoms is 6 to 6
It is better to use the one of 12. When the esterifying agent has a long chain, the ester compound derived from unreacted impurities in which the amount of introduced hydroxyl groups is insufficient is also dissolved in the ether, resulting in a low degree of purification. Further, when the chain is short, the target ester compound is not dissolved in ether and the recovery rate is low.

As a solvent for extraction, 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.

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

The purified perfluoropolyethers may be modified for the purpose of further improving the properties. For example, when an ester compound with a long-chain carboxylic acid is used as described in JP-A-5-194970, the hydrocarbon component increases, so that it becomes possible to dissolve it in a solvent other than chlorofluorocarbon, 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 hydroxyl groups purified as described above are retained as a lubricant in, for example, the magnetic layer of the magnetic recording medium. When the perfluoropolyethers are held in the magnetic layer, good lubrication performance is maintained for a long time in the magnetic layer even under severe environments such as high temperature, high humidity and low temperature, as well as under normal temperature and normal humidity environment, The coefficient is reduced, and the running durability is improved.

In a magnetic recording medium to which such a lubricant is applied, a magnetic layer is formed by depositing a ferromagnetic metal material on a non-magnetic support by a vacuum thin film forming technique such as vapor deposition. Even in a thin film type magnetic recording medium, a magnetic layer is formed by applying a magnetic paint prepared by mixing a ferromagnetic powder and a binder with an organic solvent onto a non-magnetic support. Magnetic recording medium may be used.

Of these, the following materials are used as the constituent material of the metal magnetic thin film type magnetic recording medium.

First, as the non-magnetic support, polyesters such as polyethylene terephthalate, polyethylene,
Polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide, polyamide, and polyamideimide; paper; and aluminum. , Metal such as copper, aluminum alloy, light metal such as titanium alloy, ceramic,
Single crystal silicon, glass, or the like is used. When a rigid substrate such as an aluminum alloy plate or a glass plate is used, an oxide film such as alumite treatment or a Ni-P film may be formed on the substrate surface to make the surface hard. .

As the metal magnetic thin film, Fe, Co, Ni
Such as metals, Co-Ni alloys, Co-Pt alloys, Co
-Pt-Ni alloy, Fe-Co alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe-Ni-B alloy, Fe-Co-B alloy, Fe-Co-Ni-B An in-plane magnetization recording metal magnetic film made of a system alloy or the like and a perpendicular magnetization recording metal magnetic thin film made of a Co—Cr alloy or the like are exemplified.

These ferromagnetic metal materials are formed as a continuous film by PVD techniques such as plating, sputtering and vacuum deposition.

In the case of the in-plane magnetization recording type metal magnetic thin film among the metal magnetic thin films formed in this way, Bi, Sb, Pb, Sn, and the like are previously formed on the non-magnetic support.
An underlayer of a low-melting nonmagnetic material such as Ga, In, Ge, Si, or Ti may be formed. When a ferromagnetic metal material is vapor-deposited or sputtered from above on the underlayer, the low-melting non-magnetic material diffuses into the metal magnetic thin film, the orientation is eliminated, and the in-plane isotropy is secured. And the coercivity is improved.

In order to retain the above lubricant on such a metal magnetic thin film, a dip coating method of applying a lubricant on the surface of the metal magnetic thin film may be used. In this case, the thickness of the lubricant film is 5 to 50 nm, and the coating amount is 0.5 to 100 mg.
/ M ² , more preferably 1 to 20 mg / m ² . If the thickness of the lubricant film is less than 5 nm, the effect of the lubricant cannot be sufficiently obtained. On the contrary, the film thickness of the lubricant is
If it is thicker than 50 nm, the electromagnetic conversion characteristics deteriorate.

Although the above is the basic configuration of the magnetic recording medium, the magnetic recording medium may be further provided with a protective film made of carbon or the like on the metal magnetic thin film. In this case, the lubricant is retained on the protective film. The method and conditions for retaining the lubricant in the protective film may be the same as those for retaining the lubricant in the metal magnetic thin film.

Further, the above lubricant may be used in combination with a lubricant generally used in magnetic recording media. Examples of such lubricants include long-chain carboxylic acids or esters thereof, long-chain alcohols, long-chain amines, and the like.

Besides, it is also possible to use it together with an extreme pressure agent or a rust preventive agent.

The 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, thereby performing a friction and wear preventing action. It is a thing. Examples of such extreme pressure agents include phosphorus extreme pressure agents, sulfur extreme pressure agents, halogen extreme pressure agents, organometallic extreme pressure agents, and complex extreme pressure agents. These extreme pressure agents are used in an amount of 30:70 to 7 with respect to the lubricant.
It is appropriate to use a weight ratio of 0:30.

As the rust preventive agent, those usually used as a rust preventive agent for magnetic recording media of this kind, for example, phenols, naphthols, quinones, heterocyclic compounds containing nitrogen atoms, heterocycles containing oxygen atoms. There are compounds and heterocyclic compounds containing a sulfur atom.

Further, in the magnetic recording medium, as another additional structure, an undercoat layer is formed between the non-magnetic support and the magnetic layer, or a metal magnetic thin film of the non-magnetic support is formed. A back coat layer may be formed on the surface opposite to the open side. In this case, a purified lubricant may be applied to the back coat layer or may be internally added.

On the other hand, in the coating type magnetic recording medium, a magnetic coating is prepared by mixing a magnetic powder prepared by mixing a ferromagnetic powder and a binder with an organic solvent to form a magnetic layer.

As the non-magnetic support, any of those exemplified as the magnetic recording medium of metal magnetic thin film type can be used.

The following are used as the ferromagnetic powder and the binder which constitute the magnetic layer.

First, as the ferromagnetic powder, γ-Fe is used.
_{In addition to 2} O ₃ , Fe ₃ O ₄ , Co-modified iron oxide, synthetic fine powder containing iron as a main component, modified barium ferrite, modified strontium ferrite and the like are used.

As the binder, a modified or non-modified vinyl chloride resin, polyurethane resin or polyester resin may be used alone or in combination. Further, a fibrous resin, a phenoxy resin, or a thermoplastic resin having a specific usage, a thermosetting resin, a reactive resin, or an electron beam curing resin may be used in combination.

The group introduced for the modification of the resin is --SO ₃ M,-, for the purpose of improving the dispersibility of the magnetic powder.
_{OSO 3 M, -COOM, -PO (} OM') 2 ( However, M
Represents an alkali metal atom such as Na, and M ′ represents an alkali metal atom such as Na or an alkyl group).

The solvent for forming the coating material may be an organic solvent selected from ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons and the like.

To retain the lubricant in such a coating type magnetic layer, the dip coating method may be used as in the case of the magnetic recording medium of the metal magnetic thin film type, and the lubricant is added to the magnetic paint in advance. It may be added internally.

If necessary, the coating type magnetic layer may further include a dispersant such as lecithin, a lubricant such as long-chain carboxylic acid, an antistatic agent such as carbon black, and an abrasive such as chromium oxide. A rust preventive agent may be added. As the dispersant, the lubricant, the antistatic agent, and the rust preventive, any conventionally known materials can be used other than those exemplified above.

Also in this coating type magnetic recording medium, the undercoat layer is formed between the non-magnetic support and the magnetic layer, or the side of the non-magnetic support on which the metal magnetic thin film is formed. A back coat layer may be formed on the opposite surface. Also in this case, a purified lubricant may be applied to the back coat layer or may be internally added.

[0070]

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

Example 1 First, HOH ₂ CCF ₂ (OC ₂ F ₄ ) _{p was} prepared as follows.
_{(OCF 2) q OCF 2 CH} 2 OH (FombliZ-DO
L: molecular weight 2000) was purified.

150 g of Fomblin Z-DOL,
16 g of triethylamine (about 2 times mol based on perfluoropolyether) was dissolved in perfluorooctane. Then, at room temperature, 16 g of octanoic acid chloride serving as an esterifying agent was added dropwise over 1 hour while stirring the solution. After completion of dropping, heating reflux was carried out for 1 hour to complete the esterification reaction.

Next, the hydrochloride of triethylamine produced by the reaction was removed by extraction with water, and the reaction solution was dried over anhydrous magnesium. Further, perfluorooctane was removed from the reaction solution, and the residue was extracted 5 times with 200 cc of diethyl ether.

As a result, ester compounds derived from perfluoropolyethers having hydroxyl groups introduced at both ends,
That is, perfluoropolyethers having both ends esterified are extracted with ether. On the other hand, ester compounds derived from perfluoropolyethers having hydroxyl groups introduced only at one end that were mixed in as unreacted impurities and perfluoropolyethers having no hydroxyl groups introduced do not dissolve in ether and are insoluble. It remains as an ingredient (69 g). Then, the ether-dissolved component was purified using silica gel chromatography. The amount of ether-soluble component after passing through the column was 90 g.

For confirmation, infrared absorption spectra of the ether-soluble component and the ether-insoluble component are shown in FIGS. 1 and 2, respectively.

Looking at the infrared absorption spectra of FIGS. 1 and 2, both have absorption peaks at 3000 cm ⁻¹ and 1600 cm ⁻¹ , but the absorption intensities of these peaks are higher in the ether-insoluble component. It is smaller than the ether soluble component. Of these, the absorption peak at 3000 cm ^-1 belongs to the hydrocarbon component and is 1600 cm ^-1.
The absorption peak of is attributed to CO stretching vibration. In this case, the small absorption intensity of these means that the degree of esterification is small.

That is, the ether-insoluble component contains a large amount of perfluoropolyethers esterified at only one end or perfluoropolyethers having no hydroxyl group introduced, and the ether-soluble component contains both ends. It can be seen that a large amount of esterified perfluoropolyethers are contained. That is, it is shown that perfluoropolyethers having both ends esterified were selectively extracted into ether.

Then, an alkaline solution prepared by adding potassium hydroxide to a mixed solvent of ether, ethyl alcohol and water was added to the ether-dissolved component and heated under reflux for 5 hours to hydrolyze the ester compound. As a result, perfluoropolyether having hydroxyl groups at both ends was obtained, and this was extracted with perfluorooctane to obtain a lubricant solution.

On the other hand, Co was adhered to a 14 μm thick polyethylene terephthalate film by the oblique evaporation method to form a metal magnetic thin film having a film thickness of 200 nm. Then, on the metal magnetic thin film, the lubricant solution was added at 5 mg /
A sample tape was prepared by applying a coating amount of m ² and cutting into a width of 8 mm.

Example 2 In Example 1, the purified perfluoropolyether having hydroxyl groups at both ends extracted with perfluorooctane was used as an ester compound with stearic acid C ₁₇ H ₃₅ COOH.
₂ CCF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _q OCF ₂ CH ₂ OC
OC ₁₇ H ₃₅ .

A sample tape was prepared in the same manner as in Example 1 except that this modified lubricant solution was applied onto the metal magnetic thin film.

Example 3 F (CF ₂ CF ₂ CF ₂ O) _n CF ₂ CF ₂ CH ₂ OH (De
mnumSA: molecular weight 2000) was purified according to the purification of perfluoropolyethers in Example 1 to obtain a lubricant solution.

A sample tape was prepared in the same manner as in Example 1 except that this lubricant solution was applied on the metal magnetic thin film.

Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 except that the lubricant solution was not applied on the metal magnetic thin film.

Comparative Example 2 Unpurified HOH ₂ CCF ₂ (OC ₂ F ₄ ) _p (OC
A sample tape was prepared in the same manner as in Example 1 except that a lubricant solution of F ₂ ) _q OCF ₂ CH ₂ OH was applied onto the metal magnetic thin film.

Comparative Example 3 Unpurified C ₁₇ H ₃₅ COOH ₂ CCF ₂ (OC ₂ F ₄ )
_A sample tape was prepared in the same manner as in Example 1 except that a lubricant solution of _p (OCF ₂ ) _q OCF ₂ CH ₂ OCOC ₁₇ H ₃₅ was applied onto the metal magnetic thin film.

Comparative Example 4 Unpurified F (CF ₂ CF ₂ CF ₂ O) _n CF ₂ CF ₂ C
A sample tape was produced in the same manner as in Example 1 except that a lubricant solution of H ₂ OH was applied on the metal magnetic thin film.

The lubricants used in the examples and comparative examples are summarized in Table 1.

[0089]

[Table 1]

Each of the sample tapes manufactured as described above was aged at a temperature of 60 ° C. and a relative humidity of 80% for 2 days, and the friction coefficient before and after aging, the still durability and the shuttle durability were measured. The measurement conditions are a temperature of 25 ° C. and a relative humidity of 60%, a temperature of −5 ° C. or a temperature of 40 ° C. and a relative humidity of 80%.

The still durability was evaluated by measuring the decay time until the output decreased by 3 dB in the pause state.

The shuttle durability was evaluated by carrying out shuttle travel for 2 minutes each time and measuring the number of shuttles until the output decreased by 3 dB.

The results are shown in Table 2.

[0094]

[Table 2]

As shown in Table 2, Example 1 in which perfluoropolyethers having a hydroxyl group at the terminal were purified and used
The tape of Example 3 has a smaller friction coefficient than the tapes of Comparative Examples 2 to 3 in which the perfluoropolyethers having a hydroxyl group at the end are used without purification, and good running durability is obtained. To be Moreover, this running durability is not impaired even after aging.

From this, it was found that when the perfluoropolyethers having a hydroxyl group at the end were purified and used in the steps of esterification, solvent extraction and hydrolysis, the lubricating performance thereof was significantly improved.

[0097]

As is apparent from the above description, in the present invention, since perfluoropolyethers having a hydroxyl group at the terminal are purified by the steps of esterification, solvent extraction and hydrolysis, the hydroxyl group at the terminal is The perfluoropolyethers having a can be purified to high purity without using a fluorine-based solvent.

The perfluoropolyethers thus purified with high purity exhibit good lubricating performance. For example, when used as a lubricant for magnetic recording media, the friction coefficient on the surface of the magnetic layer is significantly reduced, not only under normal temperature and normal humidity conditions, but also under severe conditions such as high temperature and high humidity, low temperature, and good running durability. You can get sex.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing an infrared absorption spectrum of an ether-dissolved component when an ether extraction is carried out after an esterification step.

FIG. 2 is a characteristic diagram showing an infrared absorption spectrum of an ether-insoluble component when an ether extraction is performed after the esterification step.

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Claims (1)

[Claims] 1. A method for producing a lubricant, which comprises esterifying perfluoropolyether having a hydroxyl group at a terminal contained in a synthetic product, extracting the ester compound with a solvent, and then hydrolyzing the ester bond. Method.