NO784312L - PREPARATION OF HYDROPHOBE SUBSTRATES WITH MODIFIED GRAPHITE - Google Patents

Description

The present invention relates to objects with a hydrophobic surface coated with hydrophobized graphite, and a method for producing such.

Graphite powders, both natural and synthetic, are by their nature hydrophilic and are easily dispersible in water without the presence of emulsifiers or wetting agents. As a result, such powders will not easily stick to hydrophobic surfaces, and especially not if they are tried to be applied to such surfaces in the presence of water, such as e.g. from an aqueous suspension. Graphite has for many years been the subject of extensive study and has been treated in numerous ways in attempts to change or improve its physical, chemical and electrical properties in order to adapt it to special purposes and also as part of scientific research.

In studies the applicant has carried out of both natural and synthetic graphite powder, it was observed that the graphite particles or flakes have a double property. Each particle behaves as if part of its surface is hydrophobic and part of the surface is hydrophilic, and it is the combined net effect of these individual particles when combined in a powder that results in the observed hydrophilic property that can be observed in conventional graphite powders. A summary review of the extensive literature on graphite suggests that the above-mentioned net hydrophilic effect of graphite can be converted into a fully hydrophobic effect, e.g. by grinding graphite under n-heptane for 8 hours. Such a treatment has been reported to make graphite powder oleophilic (Proe. Roy. Soc. Lond. A 314, 473-498

(476), (1970) A.J. GROSZEK).

Graphite is also treated with many other polar and non-polar solvents. Such additional treatments are discussed in THE JOURNAL OF PHYSICAL CHEMISTRY 71 No. 11, 3408-3413 (1967), PIERCE and EMING, as well as in the above-mentioned publication by A.J. GROSZEK. However, the publication by PIERCE and EMING mentions no observations regarding the hydrophilic or hydrophobic properties of graphite.

There are probably other publications that refer to the treatment of graphite with both polar and non-polar materials, and some of these may possibly also refer to results relating to graphite's hydrophilic or hydrophobic properties, but the applicant is not aware of any other such publications than those mentioned above. As mentioned, the applicant's literature research was cursory, since the enormous amount of literature on graphite made a detailed literature research economically unfeasible. The present application concerns an object with a hydrophobic surface,

characterized by a surface coating of modified graphite without the presence of a binder, whereby the graphite has at least two hydrophobic surfaces, one of which faces and is attached to the hydrophobic substrate, while the other is free.

The present application also concerns modified graphite (agent) for the preparation of the above-mentioned object as well as the method for producing the object.

The application also relates to three different embodiments of the present invention.

According to the present invention, conventional processing is carried out

natural and synthetic graphite with non-polar or hydrophobic materials in liquid or gaseous form to produce a graphite powder with strong attraction to hydrophobic surfaces when applied to such in a dry or wet state, and also from an aqueous or polar dispersion. The graphite film applied to the hydrophobic surface is even more hydrophobic than the graphite powder used to deposit the film. The invention includes a solid hydrophobic surface with such a graphite film applied. Embodiments of the present invention include hydrophobic ski soles with the treated graphite applied to them, audio tapes and video tapes with the treated graphite attached to the recording surface and/or to the opposite surface, as well as to the hydrophobic, insulating surface of telephone cables.

Such an applied graphite film can be used due to its lubricating ■ properties, its electrical properties (dissipation of electrostatic charges) or a combination of these properties.

The treated graphite will, when applied as a film or

when used in other forms, could also exhibit unexpected properties in certain areas of use that are not yet fully understood, and which will be discussed in the following.

For several areas of use within the industry, it is important

to be able to apply graphite to a surface from an aqueous graphite dispersion without the presence of emulsifiers or wetting agents. The use of emulsifiers will not only inhibit or disrupt the hydrophobic properties of the graphite film, but also affect their adhesion to hydrophobic surfaces, especially if the films are used in the presence of moisture, such as e.g. on ski soles. The use of emulsifiers or wetting agents can also affect the hydrophobic surface of the substrate during application, e.g. by application and rubbing in on a surface consisting of a hydrophobic ski wall. The treated graphite powder can be applied to a surface as a dry powder. However, this method affects the film's performance

homogeneity, in many industrial areas requires special equipment, is impractical and naturally polluting. Selection of graphite dispersants should be made taking into account the particular end purpose so that the dispersant does not have a harmful effect on the hydrophobic surface on which the graphite is to be applied. E.g. should a non-aqueous dispersant not be able to dissolve the hydrophobic substrate surface on which the graphite is to be placed. Thus, the present invention does not exclude the use of non-aqueous dispersants nor the use of non-aqueous compounds in connection with water as long as they do not adversely affect the intended use of the graphite. E.g. an antifreeze such as isopropanol or ethanol can be used alone or in a mixture with an aqueous dispersion.

The graphite according to the present invention is produced by treating conventional natural or synthetic graphite with a non-polar material in liquid or gaseous form, under such conditions that the graphite is made substantially hydrophobic or achieves a net hydrophobic effect while simultaneously maintaining a sufficiently hydrophilic effect to be dispersed in water or alcohol without the use of emulsifiers or wetting agents and is applied to a surface from the dispersion of water or alcohol. The most important condition for achieving the desired properties of the graphite is the amount of non-polar material used for treating the graphite. Obviously, an amount that is too small will not be sufficient to give the graphite a net effect of hydrophobicity, and an amount that is too large will be able to make the graphite substantially hydrophobic, so that it cannot be dispersed in water without the use of an emulsifier or a wetting agent. In general, the quantity will be between oa. 1% by weight and 3% by weight of the non-polar substance based on the weight of the graphite. These quantities will of course be able to vary somewhat, mainly depending on the particular non-polar compound used, since some compounds are known to be more polar or less polar than others. To achieve the desired results, the optimal amount of any given lipolar compound can be easily determined by one skilled in the art by routine examination.

The treatment temperature or time is not particularly important. Room temperature is preferred for non-polar materials which exist in a liquid or gaseous state at such temperatures. In terms of processing time, the non-polar compound should simply be thoroughly mixed with the graphite, stirred for a few minutes, and then allowed to stand for a few hours or overnight. The treated graphite can then be directly applied to a hydrophobic surface or dispersed in water or alcohol for later use.

Practically any non-polar solvent or non-polar substance can be used to treat graphite according to present invention. Nonpolar compounds are well known to those skilled in the art. Some non-polar compounds work better than others, not only because of the compound's degree of polarity, but also for other, not yet fully understood reasons. E.g. The alkyl silicates or alkoxy silanes, especially ethyl silicate (tetraethyl orthosilicate) and tetra-n-propyl silane, seem to give

the best results that have been achieved so far, although their non-polar properties need not be as great as with other substances that are more non-polar. Other examples of non-polar compounds that can be used include hexane, mineral oil and silicone oil. However, hexane does not appear, despite the fact that it greatly increases the graphite's affinity to hydrophobic surfaces, e.g. of poly-

ethylene, to give some lasting effect/and the new properties disappear after a certain time, at least under the treatment conditions which only include stirring the graphite with hexane and standing for a few hours at room temperature.

As previously mentioned, the graphite must be treated with the non-polar material in a liquid or gaseous state.

This does not preclude the use of materials that are normally available

in solid form, if they can be transferred to liquid form, e.g. during heating. Thus, nonpolar organic polymers such as polyvinylidene fluoride ("Kynar") can be used, and the graphite can be treated as described in U.S. Pat. Patent No. 4,051,075 or U.S. Pat. patent No. 3,992,558.

Before it is processed, the graphite should be dry, i.e. substantially free of extraneous polar compounds. This is especially the case when using alkyl silicates, since these, e.g. tetraethylorthosilicate, tends to hydrolyse, which can cause these monomers to acquire polar properties. Thus, it is particularly important when using alkyl silicates that the graphite is practically water-free and acid-free, and that the ethyl silicate is not allowed to hydrolyse to any noticeable extent before it is used to treat the graphite.

The substrates on which the treated graphite can be applied are hydrophobic or non-polar. As will be known to those skilled in the art, there are some substrates which are considered to be hydrophobic, which actually have polar features and take up water. When it comes to hydrophobic or non-polar substrates, the applicant is interested in the net effect of the substrate, which must be non-polar.

Polyester films, such as "Mylar", are examples of hydrophobic substrates that are usually weakly polar. Regarding such substrate types, it is preferred to treat dry graphite with an unhydrolysed alkyl silicate for application on these substrates.

A graphite treated in this way will adhere to the "Mylar" to a greater extent than it will adhere to itself, and the occurrence of debris or loose particles after application is minimal.

The amount of treated graphite is not important: with dry treatment, you simply rub the dry powder on the surface and wipe away any excess.

When applying from an aqueous or alcoholic solution, you only mix approx. 15 g in approximately 100 ml of water or alcohol and apply the dispersion to the surface with a little rubbing with a paper towel.

When such films are applied to a hydrophobic surface, they adhere very strongly to this, and the graphite will not come off and be transferred to the skin when touched. The films are resistant to alcohol and water and exhibit a homogeneous electrical conductivity. The films are also very thin, and when applied to a transparent surface, e.g. a polyester or polyethylene film, the treated product is still transparent with a greyish haze.

The electrical resistance of the films is very constant when they are applied to the same hydrophobic substrate. For example, the resistance when applied to polyethylene is approximately 1000 ohms per square and on polyester ("Mylar") approximately 6000 ohms per square. The resistance can be increased by thinning the graphite with a non-conductor, e.g. mica flakes. If electrical conductivity is desired, care must be taken not to use too much mica, so that the film's conductivity is broken. A mixture of graphite and mica in the weight ratio 1:1 will generally increase the resistance of film on polyethylene to approximately 4000 - 5000 ohms per square. The treated graphite, which is net hydrophobic but dispersible in water, can also be used in water-based boron oils as a coolant and lubricant for cutting tools.

In the following, some embodiments of the present invention will be reviewed and discussed.

A very important embodiment is coating the sliding surface of skis with modified graphite according to the present invention.

The sliding mechanism for skis on dry snow includes development

of a lubricating layer of water on the crystal surface of the snow, which is due to a combination of pressure and frictional heat. Therefore, the friction on dry snow (which also applies to wet snow) is a function of adhesion of water to the contact surfaces. For this reason, the Skiover surface is generally composed of strongly hydrophobic materials, such as e.g. polyethylene or paraffin wax compounds, e.g. wax on wood.

Another important factor on dry snow is the friction-electric effect between the snow and the sliding surface. Thus, it is precisely the materials that are most desirable to use due to

its water-repellent ability, also highly dielectric and seeks to accumulate electrical charges on its surfaces. These charges induce an opposite charge on the snow crystals,

which in turn causes an attraction and friction.

A combination of high hydrophobicity and high conductivity would consequently be desirable properties for a ski surface or a preparation for coating a ski surface. However, the two above-mentioned characteristics cannot be easily combined without making use of significant compromise solutions. For example, it has been proposed to embed graphite both in the ski's sliding surface and in the ski wall, e.g. in ski wax, to make the ski surfaces highly dielectric. In such experiments, however, the applied amount of graphite or other conductive material used must be of such a high order of magnitude to make the surface conductive, that the entire surface itself becomes substantially hydrophilic.

The treated graphite produced in h.h.t. the present invention can be applied alone without the use of a binder such as e.g. resin or wax, in order to make the ski surface not only conductive, but at the same time without affecting the hydrophobic nature of the ski sole, and

in most cases make the surface even more hydrophobic

than the materials in the ski surface are in themselves. These graphite coatings, even though they are very thin, are nevertheless strongly adherent and resistant to grinding and can be used both as a base coating to strengthen the bond between skid masonry and poly-alkene bases or also to modify the waxed surfaces. The graphite coating on the ski rafts in terms of the present invention provides excellent gliding without hampering downhill skiing to any noticeable extent.

When preparing a hydrophobic ski surface with the modified graphite according to the present invention, it is advantageous that the graphite is applied from a suspension in water containing smaller amounts of an antifreeze agent, e.g. isopropanol. A few drops of this suspension are placed on the surface

of the ski sole and simply rub over this with e.g. a paper towel until the surface assumes a faint metallic sheen. •The use of the antifreeze is very useful for this purpose because if you use water alone when applying graphite to a cold ski outdoors, the water can easily freeze to ice on the surface. The prepared graphite can also be applied in a dry state, but this method is very difficult and unclean to carry out, especially in the wind outdoors. The modified graphite can also be advantageously applied from an alcoholic solution.

Although the modified graphite can be used directly on hydrophobic ski soles, the best results have so far been achieved by applying the graphite to a hydrophobic polyethylene ski sole and then applying a conventional ski coating on top of the graphite coating. This treatment alone will improve the glide of the skis, but it is further advantageous to apply another coating of graphite on the outside of the ski wall.

With regard to the use of the graphite coating on a polyethylene surface, it is most desirable to treat dry graphite powder by exposing it to vapors of tetraethyl orthosilicate (1-2% by weight) before application as a dry powder or from a liquid dispersion. This product provides excellent adhesion and water-repellent properties even when applied to polyethylene from an alcoholic suspension.

Another important embodiment of the present invention is the preparation of recording/playback tapes (e.g. audio and video tapes) with modified graphite according to the invention.

Recording tape generally consists of a hydrophobic plastic base, e.g. a polyester ("Mylar") which is coated on one side with a recordable and playable surface or composition which is generally an iron oxide type coating. When recording or playing back such tapes, they must be fed mechanically, sometimes at high speeds, and the lubrication of such tapes has presented a problem. For lubrication purposes, many ribbons today are coated with a graphite-containing resin on the opposite side of the playing side. Such a coating seems to be able to lubricate, but it is opaque, and it is time-consuming and difficult to apply, and it obviously cannot be applied to the recording side.

The modified graphite produced in h.h.t. present invention can be easily applied to polyester film ("Mylar") by applying it in a dry state or lightly rubbing it on the film. It can of course also be applied from a polar suspension which re-

spoken in the foregoing. A graphite composition for the treatment of recording tapes in terms of present invention can be prepared as described above by treating commercial graphite with about 1-3% by weight of tetraethyl-ortho-silicate (15 drops on 15 g of graphite) or other non-polar compounds until equilibrium is achieved, and leaving it overnight. If the prepared graphite is applied to polyester ("Mylar") in a dry state (on recording/playback tape), it is advantageous

like mixing it with a mica powder in a ratio of approx. 1:1. The combination of adhesion (marking), transparency, conductivity and smoothness is very favorable for tape applications.

The hitherto known optimal treatment of "Mylar" film comprises a first application of the film with approx. 1% tetraethyl-ortho-silicate in isopropanol followed by smearing, possibly light rubbing of the prepared graphite as produced as mentioned above, on the "Mylar" surface. The surface can be cleaned of any loose particles by lightly wiping with a slightly moistened paper towel.

The present invention comprises the application of the modified graphite without the use of a binder, directly on the recording surface of the tape. By processing audio tapes in this way, improved sound quality and significantly reduced background noise have been achieved. It is of course highly surprising that such modified graphite could be applied directly to the recording surface and alone provide improved sound and essentially eliminate background noise. There is no explanation as to why applying the modified graphite to the recording surface can produce such results.

A further embodiment of the present invention involves preparing signal-carrying electrical lines or cables with modified graphite according to the invention.

Signal-carrying electrical cables or lines, e.g. conventional telephone cables are generally insulated with a hydrophobic insulating agent, e.g. polyethylene.

It is common knowledge that the industry has been faced with significant disturbances and interference between such lines. The message on a line can be transmitted in whole or in part or

move on to another line. In technical language, this phenomenon is generally referred to as crosstalk. An embodiment of the present invention comprises the application of modified graphite on the outer surface of the insulation of signal-carrying cables or lines, in the same way as described above on recording tapes. It has been found that this treatment substantially eliminates crosstalk, especially with telephone cables.

Although the present invention is described with regard to the limited treatment of graphite powder to impart to the graphite a net hydrophobic effect while retaining sufficient hydrophobicity to be dispersible in water without the use of emulsifiers, and although this represents a significant advantage in many cases , which will be understood and appreciated by those skilled in the art, the graphite may also be treated with an excess of a non-polar solvent to render it substantially hydrophobic in those cases where dispersibility in a polar material is not desirable or necessary. Such a hydrophobic graphite can, if desired, be applied to skis, recording tapes, etc.

Example.

0.40 parts by weight of tetraethyl-ortho-silicate was added thereto

15 parts by weight graphite ("Dylan GPF" - manufactured by Eylon Industries Inc.). The mixture was stirred for a few minutes to ensure homogeneity and then allowed to stand for about 3 hours.

The next day, the treated graphite was dispersed in 85 parts by weight of water and 15 parts by weight of isopropanol. The isopropanol is not necessary and in this case was added solely to prevent the water from freezing. If water freezing is not a problem, the alcohol can be omitted, or the composition can be used in a dry state as described earlier.

This composition or one very similar to it was used in the above example in the dry state, in aqueous suspension of a mixture of water or alcohol, on skis and on recording tapes.

A composition produced in terms of U.S. patent no. 3,992,558 which included 2.5% by weight of polyvinylidene fluoride ("Kynar"), as well as replacing carbon with graphite in Example 1 of the above-mentioned U.S. Pat. patent, was also used in the above examples, either in dry form or in polar dispersions, on skis, recording tapes and signal/communication cables.

Although the preferred percentage amount of non-polar material has been stated to be between about 1% and 3% by weight based on the graphite, the exact parameters for any non-polar material have not been determined. It is believed that 5% ethyl silicate may well make the graphite substantially completely hydrophobic, but certainly as much as 10% ethyl silicate will do this.

Claims (13)

1. Object with a hydrophobic surface, characterized by a surface coating of modified graphite without the presence of a binder, whereby the graphite coating has at least two hydrophobic surfaces, one of which faces and is attached to the hydrophobic substrate, and the other is free. 2. Modified graphite for the preparation of an object according to claim 1, characterized in that the majority of the flake-like graphite particles have at least two substantially hydrophobic surfaces and at least one substantially hydrophilic surface with sufficient hydrophilicity to maintain the graphite powder's dispersibility in water, while at the same time having the ability to adhere strongly to a hydrophobic surface. 3. Modified graphite according to claim 2, characterized by a hydrophilicity which is insufficient for the graphite to be dispersed in water once it has attached to the hydrophobic substrate. 4. Method for producing an object according to claim 1, characterized in that graphite powder is treated with a non-polar compound in a sufficient amount to make the graphite composition net hydrophobic, but at the same time allowing it to retain its dispersibility in polar liquids as before treatment, that one or several surfaces of the above article apply said graphite composition without the presence of a binder, whereby the graphite composition, after it is applied to the surface or surfaces of the article, becomes hydrophobic and not dispersible in polar liquids. 5. Method according to claim 4, characterized in that the amount of non-polar material is between approx. 1% and approx. 3% based on the weight of graphite. 6. Method according to claim 4 or 5, characterized in that the non-polar material is an alkyl silicate. 7. Method according to claims 4-6, characterized in that the non-polar material is ethyl silicate. 8. Item according to claim 1, consisting of a hydrophobic ski sole, characterized in that a coating of modified graphite is attached to the ski sole without the presence of a binder, whereby the graphite particles have at least two substantially hydrophobic surfaces, one of which is attached to the ski sole and the others are free. 9. Ski sole according to claim 8, characterized in that the graphite particles have at least one hydrophilic area with sufficient hydrophilicity to be able to preserve the graphite's dispersibility in water before applying the graphite coating to the ski, but not enough hydrophilicity to cause the graphite to be able to be dispersed in water after it has been applied as film on the hydrophobic surface of the ski sole. 10. Ski sole according to claim 6 or 7, characterized by the fact that it has a coating of conventional ski masonry, and that the graphite composition is applied on the outside of the ski masonry. 11. Item according to claim 1, consisting of a hydrophobic audio tape or video tape with a recording/playback surface on one side, characterized in that the graphite composition ion is placed on the tape's recording/playback side or on the opposite side or on both sides of the tape. 12. Object according to claim 1, consisting of a signal-carrying electric cable or line insulated with a hydrophobic material, characterized in that it has a coating of modified graphite without the presence of a binder, on top of the insulation, whereby the graphite particles have at least two hydrophobic surfaces, of which the one is facing and attached to the hydrophobic insulation layer, and the other graphite surface is free. 13. Item according to claim 12, characterized in that the object is a telephone cable or telephone line.