NO761917L - - Google Patents

Description

LUBRICANT MIXTURE.

The present invention relates to the lubrication of substrates, and in particular an improved two-component lubricant mixture and method of application, also improved scratch-resistant lubricated substrates that have low friction, such as photographic film, parts for sound recording and reproduction and the like.

Lubrication of various substrates, and especially substrates where information is stored and from which information can be extracted using dynamic means, has long been considered a difficult problem. Examples of such substrates include recording disks for calculators, gramophone records, magnetic recording of sound and video production and photographic projection film such as

moving film, slide film and microfilm. Previous attempts to provide such lubrication have met with mixed success.

Lubrication of photographic film, and particularly lubrication of photographic film used either statically or dynamically, for image projection by directing a light beam through transparent photographic film, represents one of the most difficult lubrication problems. When photographic film is repeatedly placed in a port or holder, the mechanical interface tends to wear on the film and, in the case of moving film, such wear or sticking causes an irregular display on the screen as the photographic film adheres and lets go. Recently, an even more demanding application has appeared. This includes continuous roll film cartridges that use a continuous loop of photographic film

which is unwound inside the roll and rewound on the outer edge of the roll. A significant friction occurs as the photographic film is pulled out laterally, usually in spiral form, from the central part of the roll. In spite of greatly increased slltage potential, continuous loop film cartridges have gained acceptance for use such as for. projection of in-flight feature films, sales films, educational films etc.

Photographic film is, due to its properties, a difficult substrate when it comes to lubrication and wear. photography

fish film mainly consists of a relatively soft emulsion which is applied to a usually flexible carrier. The emulsion must be protected both against wear and tear. a low coefficient of friction. A low coefficient of friction alone does not provide the necessary protection in that the soft emulsion does not have the strength to withstand the forces to which it is exposed, even when the friction is low. An important consideration in the past has been to lower the friction coefficient, almost at the expense of increasing

reach a protective coating with regard to the strength of the surface coating. Since the emulsion has little inherent strength and wear resistance, must . the lubricating coating provides these properties, as well as low friction. In addition to the emulsion side, it is also important to protect and lubricate the "back" of the film, as scratches will also occur on this side. be visible by projection.

Another essential property of a lubricating coating for photographic film, and particularly photographic film for projection, is the transparency of the coating. Many of the previous coatings have completely avoided opacity only by using very thin coatings.

Although these are mainly transparent, little lubrication has been achieved to obtain adequate, if not complete, light transmission. The opacity problem is complex, when it is to be provided and

re properties than lubricity, i.e. strength, when using more than one component.

While photographic film is particularly difficult to smear, magnetic recording and parts for reproduction represent a somewhat different problem, but also demanding conditions. Coatings of lubricants must be thin so as not to impair the interaction between the recording or pickup head and the magnetic particles. It smeared

the coating must not accumulate on the head. In the case of disc and cylindrical rotor recording elements, "moving heads" used for such recording elements tend to collide with the element, developing strong local forces. The disc must thus be protected to prevent damage to it as a result of such "crashes". It is known that magnetic tape consists of highly abrasive particles dispersed in a binder. Without protection, the recording head can be quickly worn by the particles as the magnetic tape moves past the recording head.

In short, the operating environment and the characteristics of magnetic recording parts require a lot of the lubricants.

Apart from the lubrication of photographic film, another area of importance is that of sound-recording parts. Grammophon records deteriorate, for example.' its sound quality with increasing number of playbacks. This is due to a number of factors which include general wear via abrasive and adhesive wear mechanisms to an extent that is proportional to the stylus load. This load is not only the self-gravity load on the disc, but also includes dynamic inertial forces due to the mass of the stylus and the frequency of direction changes of the stylus as it follows the groove undulations. Reduction of deadweight load and stylus mass lowers groove wear, while wear and the subsequent loss of playback reproduction

cannot be completely eliminated. In any case, the previously known lubrication by using liquids or the wax lubricant on the plates has the disadvantage of such materials that the plate reproduction is reduced due to the hydrodynamic damping of the stylus movement. One often notices when using these materials

that the noise level increases, which is mainly due to dust that is captured • by the sticky film. Powdered, solid lubricants, such as graphite, molybdenum disulphide and. the like not only reduces the reproduction, but also increases the noise, which is due to particle-shaped disturbances in the grooves.

Various waxes and other compounds have been used to lubricate the substrates. Fluorinated compounds have also been used as lubricants in various applications, and include the use of fluorinated polymers in connection with the lubrication of magnetic tape.

The closest prior use in photographic film appears to be the use of "Vydax AR", a trade name for tetrafluoroethylene telomer, as a lubricant for photographic film. This lubricant is used as a reference compound when it comes to examining the method and the mixtures according to the present invention.

The present invention, which provides a wear-resistant, lubricating coating for substrates, comprises a two-component mixture, one of which mainly provides lubricity and the other mainly provides strength to the coating. In combination, the two components possess the synergistic property that they provide a coefficient of friction that is lower than that obtained with each of the components alone. Optionally, the mixture can be easily modified so that a transparent coating for photographic film is obtained which retains the desired

lubrication properties.

According to the present invention, a mixture is used

which consists of a relatively short-chain copolymer or mixture of copolymers which provides a hard, abrasion-resistant surface and a relatively short-chain telomer of tetrafluoroethylene which provides lubricity,

for producing an excellent, wear-resistant coating on a substrate that has low friction, and if desired transparent to light. The copolymers are copolymers of trifluorochloroethylene and vinylidene fluoride. Copolymers of trifluorochloroethylene and vinylidene fluoride work

not as lubricants. When such copolymers are used alone, e.g. on photographic films, you get a coefficient of friction that is greater than 0.3. The telomer of tetrafluoroethylene is not a lubricant

and gives,, when used alone., e.g. photographic films with friction coefficients of approx. 0.11. However, when the two compounds are used together on photographic film, i.e. a combination of the telomer and the copolymer, friction coefficients of 0.08 are obtained. As far as the application on standard vinyl records is concerned, the telomer alone has a coefficient of friction of the order of approx. 0.14 and the copolymer approx. 0.23, while the combination gives friction coefficients that are mainly reduced to approx. 0.07. This substantial reduction in the coefficient of friction in relation to the coefficient of the individual lubricant in the mixture is in addition to the primary function of the copolymers, i.e. providing a tough, friction-resistant surface. It was not obvious that this latter effect could be achieved with an acceptable coefficient of friction, and certainly not that the overall coefficient of friction could be improved that much.

The clarity of the mixtures containing copolymers of trifluorochloroethylene and vinylidene fluoride, telomeres and solvent has generally been found to be excellent. If, however, there is some ambiguity, a separation can be carried out using conventional filtration, decantation or centrifugation.

While certain solvents are usable provided that there is no adverse effect on the substrate, trichlorofluoroethane is particularly preferred as it has a suitable organic solubility, high volatility and little physical and chemical effect on the substrate. Trichlorotrifluoroethane can either be an isomer, i.e. it can be 1,1,1-trichlorotrifluoroethane or 1,1,2-trichlorotrifluoroethane. Other solvents include benzotrifluoride and perfluorodimethylcyclobutane. Other halogenated aliphatic hydrocarbons that can be used together with the previously mentioned solvents are 1,1,1-trichloroethane, chloroform, tetrachloroethylene, • trichloroethylene, methylene chloride, carbon tetrachloride, dichloroethylene, dichloroethane, and mixed

gives hence.

In the copolymer, the ratio between trifluorochloroethylene and vinylidene fluoride is preferably approx. 80 to 20, and the copolymerization is stopped when the average molecular weight is low enough to

be soluble in trichlorotrifluoroethane at a concentration of at least up to approx. 10% by weight. This copolymer has a specific weight of approx. 2.02 and supplied by 3M Company, St. Paul, Minnesota, under the trade name "Kei F 800".

A suitable tetrafluoroethyl hettelomer has a specific gravity of approx. 2.16 and a melting point of 300°C, and is supplied as a 20% solids suspension in trichlorotrifluoroethane from E. I. dupont de Nemours&Company, Wilmington, Delaware, under the trade name "Vydax AR". Another commercial tetrafluoroethylene telomer is supplied by Pennwalt Chemical Corporation, 3 Penn Center, Philadelphia, Pennsylvania, under the trade name "MP-51". This telomere is usually a fully halogenated telomere, i.e. the hydrogen content is equal to zero, and has a molecular weight in the range from approx. 700 to approx. 1800.

It will be understood that the given copolymers can be easily mixed with a number of other suitable copolymers which include copolymers of trifluorochloroethylene and vinyl chloride. Average molecular weights below approx. 100,000 for trifluorochloroethylene and vinyl chloride copolymer appears to be the desired range for such copolymers for use as an added component in compositions according to the invention. however, the molecular weights are not critical, in that the less desirable fractions with a high molecular weight are easily removed in a separation step according to a preferred embodiment according to the invention.

The concentrations of poly(trifluorochloroethylene-covinylidene fluoride) copolymers and tetrafluoroethylene telomers in the solvent can vary over a wide range. A preferred mixture, however, is a mixture where poly (trifluorochloroethylene-covinylidene fluoride) has been added to the solvent in a concentration of at least approx. 0.005% by weight and tetrafluoroethylene telomere in a concentration of at least approx. 0.01% by weight. The previously mentioned separation step can, if necessary, be easily carried out even when the copolymer and the telomer are present in a very dilute state, indicated by low concentrations.

Additives adapted to a given application can be added to the mixture. A conventional antistatic agent can e.g. added to coatings for photographic film, gramophone records, etc. to prevent an electrical charge from occurring on the substrate when this is used. Such components should of course be miscible with the lubricants in terms of solubility, reactivity etc., but the person skilled in the art will have no difficulty in determining usable additives.

Lubrication of the substrates can be achieved by applying the above diluted solutions of the lubricant mixtures to such substrates, evaporating the solvent and, if desired, lightly rubbing the coated substrate to obtain a clear coating.

<p>the application of the mixtures can take place in a number of ways,

spraying, dipping, brushing, streaming and wiping are all usable. For most purposes, it is preferred to use spray-on and immersion, since these methods provide good coverage. Alternatively, poly(trifluorochloroethylene-covinylidene fluoride) can be applied first and then a coating of the telomere; this gives results

which are comparable to the results obtained when the components are applied together.

The following examples illustrate the invention.

EXAMPLE I

Lubricant composition according to the present invention was prepared by adding the indicated amounts of copolymer to solutions of telomer, as indicated in Table I. As for those that were decanted, the solution was prepared by allowing the mixture of solvent plus ingredients to come to equilibrium, and decant the dissolved parts of the constituents and the solvent from undissolved solids. An acetate-based color film was then machine-treated by immersion in the solutions of lubricant mixtures, excess solution being used. The film was then dried and lightly rubbed. Next, the resulting lubricated film was analyzed on the "Pin and Disk Wear Test", a laboratory test that shows a significant correlation with wear resistance of film in real use.

The "Pin and Disk Test" was performed by attaching a short length of film to the surface of a disk and rotating it at a speed of 30 rpm. minute with a load of 410 g applied against a stationary 12.2 mm steel ball slider bearing against the film. The films were tested for breakage, which becomes apparent by a visible break in the emulsion and/or an increase in the friction between the slider and the film.

The figures in Table I show that the combination of copolymer

pure and the telomeres provide a mixture that gives longer wear times, compared to the tetrafluoroethylene telomer itself. It thus appears that the addition of 0.02% poly(trifluorochloroethylene-covinylidene fluoride) to 0.25% tetrafluoroethylene telomer increases the average wear time from 390 to 802 cycles (Example A and Example B); and the addition of 0.05% poly(trifluorochloroethylene-covinylidene fluoride) increases the significantly to 1882 cycles (Example A and Example C). It is also noted that the addition of 0.5% poly(trifluorochloroethylene-covinyl chloride) to 0.25% tetrafluoroethylene telomer (Example A and Example D) gives a marginal average wear time which increases from 390 to 454 cycles, but when 0.5% poly(trifluorochloroethylene-covinyl chloride) was added to 1% tetrafluoroethylene-telomer (Example

E and Example F), the average wear time increases from 997' to 1652 cycles.

EXAMPLE II

The effect of the copolymer component on the frictional properties of the lubricant was determined both on film for the motion picture industry and as a substrate for gramophone records. The results appear in Table II.

The figures in Table II show that combinations of the indicated copolymers and the tetrafluoroethylene telomeres result in mixtures which provide substrates with lower friction coefficients than with the tetrafluoroethylene telomeres themselves. Thus, when 0.5% poly(trifluorochloroethylene-covinyl chloride) was added to 0.1% tetrafluoroethylene telomer (Examples A and B, Table II) and decanted as indicated, the film-to-film friction of the films treated with these solutions, from 0.11 - 0.13 for the tetrafluoroethylene-telomer solution to 0.08 - 0.11 for the mixture.

In the film-to-film friction test, a length of the film is attached to the outer cylinder surface of a disc with a horizontal axis. A second length of film is placed over the first attached film length with the emulsion side of the attached film in contact with the back of the second length. A calibrated weight was attached to one end of the second length of film and a force was applied to the other end until a movement between the two lengths of film took place. Using common calculations, the coefficient of friction between the film lengths can be calculated for different films.

Using a paperclip friction method as set forth in "Processed Film Lubrication: Measurement by Paper Clip Friction Test and Improvement of projectionLife", T.Anvelt, J.F. Carroll and L.J. Snyder, Journal of the Society of Motion Picture and Television Engineers, Vol. 80, pp. 734-739 (1971) found, as shown in Table II, that there was a reduction in the coefficient of friction from 0.11 to 0.08 (Example C and Example D) when 0.04% poly(trifluorochloroethylene-covinylidene fluoride) was added to 1 % tetrafluoroethylene-telomer, with any insoluble tetrafluoroethylene-telomer residue having been decanted from each solution in advance. A mixture of 1% tetrafluoroethylene telomer, "Vydax AR',' in trichlorotrifluoroethane gives, after sedimentation and decantation, a solution containing about 0.04% dissolved tetrafluoroethylene telomer). It is noted that poly(trifluorochloroethylene-covinylidene fluoride) is not per se a lubricant as evidenced by the high value of the coefficient of friction (greater than 0.3) obtained on the film treated with a solution of 0.28% poly(trifluorochloroethylene-covinylidene fluoride) in trichlorotrifluoroethane (Example E, Table II).

Table II also shows friction values obtained on standard vinyl gramophone records that were treated with trichlorotrifluoroethane solutions of poly(trifluorochloroethylene-covinylidene fluoride), tetrafluoroethylene telomeres and mixtures thereof. It is noted that 0.2% tetrafluoroethylene-telomer solution alerte gave a friction value of 0.14 (Example F), but a mixture of 0.125% tetrafluoroethylene telomer and 0.075% poly(trifluorochloroethylene-covinylidene fluoride) gave 0.07 (Example G). A solution of the latter (0.28%) alone gave 0.23 (Example H).

EXAMPLE III

Lubricant mixtures were prepared to show the effect on disc friction by mixing mixtures of tetrafluoroethylene-telomer plus poly(trifluorochloroethylene-covinyl chloride) on one side with mixtures of the same telomer plus poly(trifluorochloroethylene-covinylidene fluoride) on the other side, as shown of Table III.

It can be readily seen from the figures in Table III that uniform, beneficial results are obtained by mixing the two copolymers in the telomer, regardless of the relative concentrations, as shown (Examples A - F), when compared with the telomer-

the solution alone (Example G).

Although a number of embodiments according to the present invention are illustrated using particularly demanding substrates, it will be clear to the person skilled in the field that certain changes and modifications can be made which are covered by the present invention, and which include the application of the invention to other substrates, and that such changes can take place within the scope of the present invention.

Claims (21)

1. Lubricant mixture, characterized in that it comprises a mixture of a copolymer of trifluorochloroethylene and vinylidene fluoride; en.tetrafluoroethylene telomere; and a solvent for the copolymer and the telomer. 2. Lubricant mixture as stated in claim 1, characterized in that the solvent is a halogenated aliphatic hydrocarbon and that the copolymer is present in a concentration of at least approx. 0.005% by weight and that the telomere is present in a concentration of at least approx. 0.01% by weight. 3. Lubricant mixture as stated in claim 2, characterized in that the solvent is trichlorotrifluoroethane. 4. Lubricant mixture as stated in claim 1, 2 or 3, characterized in that the tetrafluoroethylene telomer has a molecular weight between approx. 700 and approx. '4,000. 5. Lubricant mixture as stated in claim 1, characterized in that the mixture has poly(trifluorochloroethylene-covinylidene fluoride) in a concentration of at least approx. 0.005% by weight and that the telomere is present in a concentration of at least approx. 0.01% by weight. 6. Lubricant mixture as stated in claim 1, characterized in that the mixture has poly(trifluorochloroethylene-covinylidene fluoride) in a concentration of at least approx. 0.02% by weight and the telomere in a concentration of at least approx. 0.1% by weight. 7. Lubricant composition as set forth in any of the preceding claims, characterized in that it contains a copolymer of trifluorochloroethylene and vinyl chloride. 8. Method for lubricating a substrate, characterized in that a mixture is formed comprising a copolymer of trifluorochloroethylene and vinylidene fluoride, a tetrafluoroethylene telomer and a solvent, applying the mixture to a substrate and removing the solvent from the mixture, whereby a lubricating coating is deposited on the substrate. 9. Method for lubricating a substrate as stated in claim 8, characterized in that the treated substrate is rubbed after the solvent has been removed. 10. Method for lubricating a substrate as stated in claim 8 or 9, characterized in that the solvent comprises a halogenated aliphatic solvent. 11. Method for lubricating a substrate as stated in claim 8, 9 or 10, characterized in that the tetrafluoroethylene telomer has a molecular weight between approx. 700 and approx. 4,000, as the mixture contains said copolymer in a concentration of at least approx. 0.005% by weight and the telomere in a concentration of at least approx. 0.01% by weight. 12. Method for lubricating a substrate as specified in claim 11, characterized in that the tetrafluoroethylene telomer has a molecular weight of between approx. 800 and 3,700. 13. Method for lubricating a substrate as stated in any one of claims 8 to 12, characterized in that the solvent is trichlorotrifluoroethane. 14. Method for lubricating a substrate as stated in any one of claims 8 to 13, characterized in that a copolymer of trifluorochloroethylene and vinyl chloride is included in the mixture. 15. Method for lubricating a substrate as stated in any of claims 8 to 14, characterized in that the substrate is a gramophone record. 16. Method for lubricating a substrate as stated in any one of claims 8 to 14, characterized in that the substrate is a photographic film. 17. Lubricated substrate consisting of: the substrate has a coating consisting of a copolymer of trifluorochloroethylene and vinylidene fluoride and a tetrafluoroethylene telomer. 18. Lubricated substrate as specified in claim 17, characterized in that the substrate is a recording substrate. 19. Greased substrate as stated in claim 17, characterized in that the substrate is photographic film. 20. Lubricated substrate as stated in claim 17, characterized in that the substrate is a magnetic substrate. 21. Greased substrate as specified in claim 17, characterized in that the substrate is a gramophone record.