GB2068775A

GB2068775A - Lubricated magnetic member

Info

Publication number: GB2068775A
Application number: GB8002756A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-01-17
Filing date: 1980-01-28
Publication date: 1981-08-19
Also published as: GB2068775B

Abstract

A magnetic member, such as a magnetic disc, has a smooth continuous layer formed by a solid lubricant and a liquid lubricant. The layer is formed by spraying the magnetic record with a carrier in which the solid and liquid lubricants are dissolved. In a preferred embodiment, tetrafluoroethylene telomer, a solid lubricant, is applied to a magnetic disc and then buffed. Perfluoroalkylpolyether, a liquid lubricant, is then applied and buffed. The lubricants are dissolved in a carrier of trichlorotrifluoroethane.

Description

SPECIFICATION Lubricated magnetic member This invention relates to the lubrication of magnetic members and, more particularly to the use of solid and liquid lubricants and a method of applying them to a magnetic member.

Magnetic members, such as magnetic discs and magnetic tapes, are operated at extremely high speeds in data processing systems. A lubricant is either included in a magnetic recording medium of such members or it is applied as a very thin layer over the recording medium to reduce friction and protect the surface against contact by heads of the system.

In magnetic disc systems, the heads normally "fly" on an air film immediately above the magnetic surface. When the disc starts to rotate or when it is stopped, the lubricating layer provides smooth head takeoffs and landings. Also, the lubricating layer protects the recording medium against crashes caused by particles or debris on the disc which may upset the flying characteristics of the heads. Where the heads contact the magnetic surface before stability occurs, this contact should take place on a low friction layer which will restore stability faster and which will protect the fragile heads and magnetic surface.

According to a first aspect of the invention, there is provided a magnetic member having at least one surface for recording and reproducing signals, a smooth continuous layer of a solid lubricant on the surface, and a smooth continuous layer of a liquid lubricant on the layer of solid lubricant, each of said layers having a thickness of between 0.25 x 10-8 metres and 50 x 1 o-8 metres.

According to a second aspect of the invention, there is provided a magnetic member having at least one surface for recording and reproducing signals and a smooth continuous layer of a solid lubricant and a liquid lubricant which have been dispersed in a carrier and sprayed on the surface to form a layer having a thickness between 0.25 x 10-8 metres and 50 x 10-8 metres.

According to a third aspect of the invention, there is provided a method of lubricating a magnetic member having at least one surface for recording and reproducing signals, the method comprising dispersing a solid lubricant in a carrier and a liquid lubricant in a carrier, spraying the solid lubricant and the carrier therefor onto the surface to form a smooth continuous layer of solid lubricant on the surface and then spraying the liquid lubricant and the carrier therefor on top of the layer of solid lubricant to form a smooth continuous layer of liquid lubricant on top of the layer of solid lubricant, the thickness of each of the layers being between 0.25 x 10-8 metres and 50 x 10-8 metres.

According to a fourth aspect of the invention, there is provided a method of lubricating a magnetic member having at least one surface for recording and reproducing signals, the method comprising mixing a solid lubricant and a liquid lubricant in a carrier, and then spraying said solid lubricant and said liquid lubricant dispersed in said carrier onto said surface to form a layerthereon of solid and liquid lubricants, said layer having a thickness of between 0.25 x 108 metres and 50 x 108 metres.

The following is a more detailed description of one embodiment of the invention, by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of a magnetic disc subsystem; and Figure 2 is a cross-section of a magnetic record of the subsystem having a lubricating layer thereon.

Referring first to Figure 1, the magnetic disc subsystem includes a plurality of magnetic records which, in this case, are discs 11 having separate top and bottom record surfaces. These are moved past flying heads 12 for recording and reproducing data.

Figure 2 shows a cross-section of one magnetic disc which includes the surface 13 which may typically be aluminum alloy. The magnetizable layer 14 includes magnetic particles in a binder. Typically, this layer is approximately 125 x 10-8 metres thick.

A thin, uniform, continuous layer of a solid lubricant 15 and a liquid lubricant 16 covers the magnetizable layer 14. As used herein, the term "solid lubricant" shall mean an organic material that is solid at ambient temperatures and soluble in the carrier used.

The layer may be formed by applying a first layer of solid lubricant 15 into the surface 13 and then buffing the first layer. Then, a second layer of liquid lubricant 16 is applied to the first layer and buffed.

Other means of solution coating techniques including flow coating, brushing, dipping, doctoring and other well known methods can also be used.

The layers 15 and 16 are preferably each 2.5 x 1 o-8 metres thick, but good results may be obtained with a layer which is between 0.25 x 10-8 metres and 100 x 10-8 metres thick.

Alternatively, a single layer may be formed by mixing the solid and liquid lubricants in a carrier and then applying the mixture to the surface of the magnetic record member. The lubricants may be dissolved in a carrier of trichlorotrifl uoroethane.

One mixture particularly suitable for use is a perfluoroalkylpolyether liquid lubricant and a tetrafluoroethylene telomer solid lubricant in the proportions of one to one. However, good results can be obtained with ratios ranging from one/tenth to one to a ratio of one to one/tenth by weight.

One perfluoroalkylpolyether suitable for use is commercially available from E. l. duPont de Nemours & Co. undertheirtrade name "KRYTOX".

These fluorinated lubricants are described in that company'sTechnical Bulletin "KRYTOX 143, Fluorinated Oils, No. L6". A solid lubricant suitable for use is commercially available under the trade name "VYDAX AR". The solid lubricant should be decanted or otherwise purified so that no particles are in the solution, U.S. Patent Specification No.

3,862,860 describes a suitable purification technique.

Other liquid lubricants which are suitable for use include chlorofluorocarbons such as described in Halocarbon Products Bulletin, refined hydrocarbons such as Biddles' Apezon C, synthetic hydrocarbons, ethers and esters, described in William F. Nye Bulletins. Other solid lubricants which are suitable for use include waxes, including synthetic and natural waxes such as Petroiite Corp. Bulletins 200,300 and 400. U.S. Patent Specification No.3,466,156 describes a solid wax lubricant which is suitable for use.

Afatty acid solid lubricant, such as described in U.S. Patent Specification No.3,704,152 is also suitable for use.

U.S. Patent Specification No.3,319,012 describes a polytetrafluoroethylene which is suitable for use as the solid lubricant.

The carrier should be a solvent for both the liquid and solid lubricants. Trichlorotrifluoroethane (Freon Registered Trade Mark) is a particularly suitable carrier when the liquid lubricant is perfluoroalkylpolyether and the solid lubricant is tetrafluoroethylene telomer. It has been found that a mixture of approximately 99.5% carrier and .5% or less lubricant is particularly suitable for spray coating magnetic discs, although mixtures containing as much as 10% and as little as 0.1%, or less, have been found to be useful for some purposes. When the carrier evaporates, a smooth continuous layer of lubricant remains.

Anti-static agents may be added to the lubricants.

Examples of anti-static agents suitable for use are amine types, such as that sold under the trade name "Armostat 310" manufactured by Armak Chemical Division and ester type, such as that sold under the trade name "Drewplast 017", manufactured by PVO International, Inc.

While the surface described above with reference to the drawings is the surface of a magnetic disc, the surface may be a surface of a magnetic tape, owt of other magnetic members which are subject to wear, such as magnetic heads.

EXAMPLES Five 14" magnetic discs made by Minnesota Mining and Manufacturing Co. were coated. The lubricants were in a solution with Freon TF as a carrier.

The spraying was carried out so that approximately 7 milligrams of lubricant were laid down in 10 seconds of spraying with a 0.25% solution. This resulted in a final coating thickness of approximately 7.5 x 10-8 metres. Approximately 3.5 milligrams of lubricant were laid down in 10 seconds of spraying with a .125% solution. Hand buffing was carried out on each sample by the same person for twenty seconds with the disc spinning at 1200 rpms, using Texwipes (trade name)TX 309 cloth. The discs were tested for lubricant life by applying a 0.9525 x 10-2 metre diameter aluminum oxide ball mounted on an aluminum arm with a pre-load weight of 80 gm. The discs were rotated at 100 rpm. When the ball breaks through the lubricant layer, there is an audible vibration. The time to this failure was measured for each disc.

TIME TO FAILURE ON DESCRIPTION OFLUBRICATION PIN WEAR TESTER DISC NO. PROCESS 75 (min) T1 Spray 0.25% solution Krytox (trade name) AD for 10 seconds Hand buff.

69 T2 Spray 0.125% solution Krytox (trade name) AD for 10 seconds. Spray 0.125% solution Vydax (trade name) for 10 seconds. Hand buff.

94 T3 Spray 0.25% solution Vydax (trade name) for 10 seconds. Hand buff.

760 T4 Spray 0 125% solution Vydax (trade name) for 10 seconds. Hand buff.

Spray 0.125% solution Krytox (trade namel for 10 seconds. Hand buff.

117 T5 Spray 0.25% solution of 50-50 Vydax (trade name) and Krytox AD (trade name) for 10 seconds. Hand buff.

Tests designated T1 and T 3 are for a liquid lubricant by itself and a solid lubricant by itself respectively. Test T 4, wherein the disc was first coated with solid lubricant and then coated with liquid lubricant, demonstrates an exceptionally large increase in wear life, in a disc of the kind described above with reference to the drawings. The wear life is ten times longer than that obtained with the corresponding liquid lubricant by itself (Test T 1) and eight times as long as the wear life of the corresponding solid lubricant by itself (Test T 3). Test 5 demonstrates that a mixture of solid and liquid lubricants gives a better wear life than either the solid lubricant by itself or the liquid lubricant by itself. Test T 2 shows that where the liquid layer was applied first and then the solid lubricant layer was applied, the wear life is actually decreased. This is unacceptable for magnetic discs for which increase in wear life is more important than lowering the coefficient of the friction. Coefficient of friction tests were performed on the above five discs by measuring the slide angle of a piece of steel with three magnetic heads. The total load was 30 grames with approximately 10 grams for each head. Coefficients of friction were: UNLUBRICATED DISC .18 T1 .16 T1 .11 T3 .12 T4 .18 T5 .19 Discs T 4 and T 5 show practically no change in coefficient of friction over the unlubricated disc.

However, this coefficient of friction is suitable for operation of magnetic discs.

Example2~Magnetic Tapes.

3M Type 177 1/4" Low Noise Magnetic Tape was coated with 10-20 x 10-8 metres (total thickness) of lubricants. The coefficient of friction was tested by the inclined plane tests described in SMPTE Journal, Vol.80, September 1971, pp. 734-739.

CONDITION COEFFICIENT OF FRICTION Sample 1 Untreated above 0.3 Vydax (solid) (trade name) 0.2 Krytox (liquid) (trade name) 0.15 Vydax + Krytox (trade names) 0.15 Sample 2 Untreated above 0.3 Ester (solid) 0.17 Krytox (liquid) (trade name) 0.20 Ester + Krytox (trade name) 0.08 The lowering of the coefficient of friction is extremely important in coating magnetic tape. There is a large area of wear between magnetic tape and a magnetic head. Reduction of friction at this interface is important. The above tests show that a mixture of solid and liquid lubricant is effective in reducing the coefficient of friction.

While particular embodiments of the invention have been shown and described above with reference to the drawings, various modifications are within the scope of the invention as defined by the appended claims.

Claims

1. A magnetic member having at least one surface for recording and reproducing signals, a smooth continuous layer of a solid lubricant on the surface, and a smooth continuous layer of a liquid lubricant on the layer of solid lubricant, each of said layers having a thickness of between 0.25 x 10-8 metres and 50 x 10-8 metres.

2. A magnetic member having at least one surface for recording and reproducing signals, and a smooth continuous layer of a solid lubricant and a liquid lubricant which have been dispersed in a carrier and sprayed on the surface to form a layer having a thickness between 0.25 x 10-8 metres and 50 x 10-8 metres.

3. A magnetic member according to claim 2 wherein said solid and liquid lubricants are mixed in a ratio ranging from 0.1:1 to 1:0.1 by weight.

4. A magnetic member according to claim 2 orto claim 3 wherein solid and liquid lubricants are mixed in the ration of 1:1 by weight.

5. A magnetic member according to any one of claims 1 to 4 wherein said liquid lubricant is perf luoroalkylpolyether.

6. A magnetic member according to any one of claims 1 to 5 wherein said solid lubricant is tetrafluoroethylene telomer.

7. A magnetic member according to any one of claims 1 to 4 wherein said liquid lubricant is selected from the group comprising fluoroalkylpolyethers, chlo rofl uorocarbons, refined and synthetic hydrocarbons and ethers.

8. A magnetic member according to any one of claims 1 to 4 orto claim 7 wherein said solid lubricant is selected from the group including waxes, tetrafluoroethylene telomer, and tetrafluoroethylene.

9. A method of lubricating a magnetic member having at least one surface for recording and reproducing signals, the method comprising dispersing a solid lubricant in a carrier and a liquid lubricant in a carrier, spraying the solid lubricant and the carrier therefor onto the surface to form a smooth continuous layer of solid lubricant on the surface and then spraying the liquid lubricant and the carriertherefor on top of the layerofsolid Iubricanttoform a smooth continuous layer of liquid lubricant on top of the layer of solid lubricant, the thickness of each of the layers being between 0.25 x 10-8 metres and 50 x 10-8 metres.

10. A method according to claim 9 wherein the liquid lubricant is perfluoroalkylpolyether and the solid lubricant is tetrafluoroethylene telomer and wherein the carrier istrichlorotrifluoroethane, the liquid and solid lubricants behind dissolved in said carrier before spraying.

11. A method according to claim 9 or claim 10 and comprising including anti-static agents in said layerofsolid and liquid lubricants.

12. A method according to any one of claims 9 to 11 and further comprising buffing each layer after the application thereof.

13. A method of lubricating a magnetic member having at least one surface for recording and reproducing signals, the method comprising mixing a solid lubricant and a liquid lubricant in a carrier, and then spraying said solid lubricant and said liquid lubricant dispersed in said carrier onto said surface to form a layer thereon of solid and liquid lubricants, said layer having a thickness of between 0.25 x 10-8 metres and 50 x 10-8 metres.

14. A method according to claim 13 and further comprising adding anti-static agents to the lubricants before spraying said lubricants onto said surface.

15. A method according to any one of claims 9 to 14 wherein said member is a magnetic recording disc.

16. A magnetic member having at least one surface for recording and reproducing signals, and substantially as hereinbefore described with reference to the accompanying drawings.

17. A method of lubricating a magnetic member having at least one surface for recording and reproducing signals, and substantially as hereinbefore described with reference to the accompanying drawings.