GB2109781A

GB2109781A - Graphite-fluoride coated with organic polymer and method of preparing same

Info

Publication number: GB2109781A
Application number: GB08229787A
Authority: GB
Inventors: Hitoshi Tsukuda; Akira Sakanoue; Takao Miyoshi
Original assignee: Central Glass Co Ltd
Current assignee: Central Glass Co Ltd
Priority date: 1981-10-22
Filing date: 1982-10-19
Publication date: 1983-06-08
Also published as: IT1153280B; DE3239213C2; FR2515190A1; FR2515190B1; IT8223857A0; DE3239213A1; GB2109781B

Abstract

Graphite fluoride, such as (CF)n or (C2F)n, in powder form coated with a vinylic polymer, e.g. polymethyl methacrylate, which is bonding to the surfaces of the graphite fluoride particles by graft polymerization. The polymer-coated graphite fluoride retains unique properties of graphite fluoride such as high lubricating ability, can readily be dispersed in water and organic liquids, and can readily be press-shaped with or without the addition of a synthetic resin powder. The polymer-coated graphite fluoride is prepared by mixing graphite fluoride in powder form with at least one vinylic monomer which undergoes radical polymerization in the presence of water, for example by dispersing these materials in a mixture of water and ethanol, and then adding a polymerization initiator to the resultant mixture. The polymerization reaction takes place even at room temperature and can be promoted by heating up to 70 DEG C. Preferably the pH of the polymerization reaction system is adjusted to 5-9 by adding alkali or by treating graphite fluoride with alkali in advance.

Description

SPECIFICATION Graphite fluoride coated with organic polymer and method of preparing same This invention relates to a modified graphite fluoride consisting of graphite fluoride particles coated with an organic polymer and a method of preparing the same. The polymer-coated graphite fluoride of the invention is of use either in powder form, as solid lubricant for example, or in compacted form optionally with addition of a synthetic resin as bearings or sealing elements for example.

Graphite fluoride is a solid material in the form of white or grayish powder obtained by reaction between graphite or carbon in different form and fluorine. As typical examples of graphite fluoride, (CF)n and (C2F)n are known as stable and industrially useful polymeric compounds. Generally graphite fluoride exhibits remarkably high lubricating and water- and oil-repelling properties and is excellent in resistance to various chemicals. Accordingly graphite fluoride has been used as solid lubricant in many fields and, besides, serves for relasing, water- or oil-repelling and anti-contaminating purposes. Also it is known to produce a solid body of a specific use, such as an electrolytic cell electrode, by pressshaping of a composition containing graphite fluoride as a main ingredient.

In practical applications, however, very strong water- and oil-repelling property of graphite fluoride, which is attributed to extraordinarily low surface energy of this material, offers inconvenience or difficulty in various respects. That is, this material can hardly be dispersed in water and is very low in miscibility with organic materials and poor in formability.

Regarding the use of graphite fluoride as solid lubricant, it is ideal that fine particles of pure graphite fluoride provide a continuous and closely contacting film on the applied surface, and for this reason often it is wished to dispersed graphite fluoride in water without using any auxiliary material.

Actually, however, graphite fluoride is practically devoid of wettability with water as demonstrated by the fact that the contact angle of (CF)n for water is 1 45 C, which is a very large value compared with the 100~1 contact angle of polytetrafluoroethylene (PTFE) useful as solid lubricant, and therefore it is practically impossible to disperse pure graphite fluoride in water.

In view of this problem, it has been proposed to use a dispersing agent such as colloidal silica jointly with graphite fluoride. Although the use of such a dispersing agent is effective for preparation of an aqueous dispersion, there arises another problem that the content of graphite fluoride in the dispersed solid phase cannot be made so large as desired: the graphite fluoride content must be limited to about 60% by weight at the maximum. Therefore, it becomes impossible to fully utilize the favorable properties of graphite fluoride originated in the low surface energy of this material.Also it has been proposed to coat the particles of graphite fluoride with a binding material such as wax or a mixture of a binding material and a surface-active agent In practice, however, it is very difficult to achieve uniform coating of the graphite fluoride particles by using a desirably small amount of such a coating material so as to allow the coated graphite fluoride to sufficiently exhibit its characteristic properties.

Furthermore, the coating is not always stable under various conditions in the uses of the coated graphite fluoride because the coating is established mereby by adsorption and adhesion, i.e. physical bonding, of the binding material onto the surfaces of the graphite fluoride particles.

In the case of producing an electrode of a primary cell by using graphite fluoride as a typical example of compacting of compositions containing graphite fluoride as the principal ingredient, it is known to press-shape a mixture of graphite fluoride and PTFE. The mixture is usually prepared by using an aqueous dispersion of PTFE obtained by emulsion prolymerization of tetrafluoroethylene. Since graphite fluoride is strongly water-repelling, there is the need of suspending graphite fluoride particles ir an organic solvent having strong affinity for water in advance of the addition of graphite fluoride to the aqueous dispersion of PTFE, and it is necessary to use a considerably large amount of organic solvent in order to fully wet the graphite fluoride particles.However, the use of such a large quantity of organic solvent causes coagulation of PTFE particles during mixing of the graphite fluoride suspended in the solvent with the aqueous dispersion of PTFE, so that the mixing results in formation of undesirably large aggromelates and fails to give a uniformly mixed powdery mixture. Furthermore, the large aggromelates are very tacky and, hence, are difficult to thoroughly pulverize. If the mixture containing the large aggromelates left uncrushed is subjected to press-shaping, it is very difficult to obtain a shaped body of good quality because the existence of the aggromelates becomes a significant obstacle to uniform transmission of the applied pressure and therefore is liable to produce strains in the pressshaped body.

It is an object of the present invention to provide a modified graphite fluoride, which consists of graphite fluoride particles coated with an organic polymer and is greatly improved in the capability of dispersing in water and organic media, in miscibility with organic materials and also in formability and retains the favorable properties characteristic of graphite fluoride, to thereby solve the above described problems about practical uses of graphite fluoride.

It is another object of the invention to provide a method of preparing the modified or polymercoated graphite fluoride according to the invention.

It is still another object of the invention to provide a solid body shaped by compacting the polymer-coated graphite fluoride of the invention optionally with the addition of a synthetic resin.

A modified graphite fluoride according to the invention consists essentially of fine particles of graphite fluoride coated with a vinylic polymer which is bonding to the surfaces of the graphite fluoride particles by graft polymerization.

Preferably the graphite fluoride in this invention is either (CF),, or (C2F),,, or a mixture of (CF),, and (C2F),,. Preferred examples of the vinylic polymer are polymethyl acrylate, polymethyl methacrylate, polystyrene and polyacrylonitrile. It is preferred that the content of the vinylic polymer in the modified graphite fluoride is in the range from 0.5 to 50% by weight.

A method according to the invention for the preparation of the modified graphite fluoride comprises the steps of mixing graphite fluoride in the form of fine particles with at least one vinylic monomer capable of undergoing radical polymerization or radical copolymerization, the mixing being performed in the presence of water, adding a polymerization initiator for the monomer(s) to the mixture prepared by the preceding step thereby allowing the monomer(s) to undergo polymerization and to bond to the surfaces of the graphite fluoride particles by graft polymerization.

In most cases it is suitable to perform the initial step of mixing graphite fluoride with vinylic monomer(s) by dispersing these materials in water with the addition of either an organic solvent soluble in water or a surface-active agent and to use a water-soluble polymerization initiator, though it is also possible to employ a semi-dry process in which only an almost negligibly small quantity of water is used. The graft polymerization process according to the invention can be performed at room temperature, but it is effective for enhancement of the rate of polymerization to heat the reaction system up to about 700C.

A dispersion of graphite fluoride in water becomes acidic and exhibits a pH value of about 2-3, and most of polymerization initiators for vinylic monomers are acidic. The graft polymerization process according to the invention can be performed under an acidic condition attributed to the acidity of graphite fluoride and the initiator, but it is very preferable to raise the pH of the reaction system to 5 to 9 prior to substantial proceeding of the polymerization reaction because such adjustment of the pH produces a surprisingly great increase in the efficiency of graft polymerization of the vinylic compound on the surfaces of the graphite fluoride particles. The adjustment of the pH is accomplished by adding an alkaline compound to the reaction system containing the polymerization initiator.Alternatively, graphite fluoride is treated with an alkaline solution or gas prior to mixing of graphite fluoride with vinylic monomer.

As a unique feature of the modified or polymer-coated graphite fluoride according to the invention, the vinylic polymer coating is chemically bonding to the surfaces of the graphite fluoride particles by graft polymerization. Unlike conventional coatings produced by mere adsorption or physical adhesion, the polymer coating according to the invention is so high in the bonding strength that the coating cannot easily be removed even by solvent extraction. Therefore, it is possible to realise a uniform and very firm coating on every particle of the treated graphite fluoride without the need of using an undesirably large amount of coating material. It will be permissible to describe the polymercoated graphite fluoride of the invention as "microcapsulated graphite fluoride".However, the present invention is not strictly limited to graphite fluoride particles each completely coated with vinylic polymer. Even when the polymer coating specified hereinbefore is incomplete so that the surfaces of the graphite fluoride particles are partly exposed, both the polymer-coated graphite fluoride and the above stated preparation method are within the scope of the invention.

The polymer-coated graphite fluoride according to the invention is easy to disperse in water or in various organic liquids and long remains in well dispersed state. Furthermore, this polymer-coated graphite fluoride is excellent in formability and is readily miscible with various synthetic resins, so that it is easy to produce solid bodies by press-shaping of this polymer-coated graphite fluoride or a powder mixture of this material and a synthetic resin with uniform distribution of the coated graphite fluoride particles in every shaped body.

The polymer-coated graphite fluoride of the invention retains and fully exhibits the favorable characteristics of graphite fluoride typified by high lubricating ability. Accordingly this polymer-coated graphite fluoride has very wide uses in various fields. For example, this polymer-coated graphite fluoride is very suitable for addition to lubricating oils and greases and various rubbers and plastics, and also is suitable for press-shaping into self-lubricating bearings and packings or into electrodes of certain batteries.

Furthermore, we have confirmed that the graft polymerization coating method according to the invention is applicable to various powdery materials useful as solid lubricants, such as graphite, molybdenum disulfide, boron nitride, tungsten disulfide, mica, talc and polytetrafluoroethylene, with the effects of facilitating dispersion of these materials in various media and also improving formability of these materials.

The following is a more detailed description of the present invention.

In the accompanying drawings: Fig. 1 is a micrograph of a pulverized graphite fluoride used in an example of the invention, and Fig. 2 is a micrograph of a polymer-coated graphite fluoride prepared in that example; Fig. 3 is a micrograph of a different graphite fluoride used in another example of the invention, and Fig. 4 is a micrograph of a polymer-coated graphite fluoride prepared in that example; Fig. 5 is a chart showing the infrared absorption spectrum pattern of an organic substance obtained by subjecting the polymer-coated graphite fluoride of Fig. 2 to benzene extraction, and Fig. 6 shows the infrared absorption spectrum pattern of the undissolved residue of the benzene extraction;; Fig. 7 is a micrograph showing a section of a solid body produced by press-shaping of the polymer-coated graphite fluoride of Fig. 2, and Fig. 8 is a micrograph showing a section of a solid body produced by press-shaping of the untreated graphite fluoride of Fig. 1; and Fig. 9 is a micrograph of a polymer-coated graphite fluoride prepared in still another example of the invention with adjustment of the pH of the polymerization reaction system, and Fig. 10 is a micrograph of a polymer-coated graphite fluoride prepared in the same example without adjusting the pH.

In the present invention, both graphite fluoride expressed by (CF),, and graphite fluoride expressed by (C2F),, are almost similarly useful, and also it is possible to use a mixture of these two kinds of graphite fluorides in any proportion. Furthermore, it will be possible to use graphite fluoride of a still different type generally expressed by (CF,), where x ranges from about 0.1 to about 1.5, aside from industrial availability thereof. In every case it is preferable that graphite fluoride is in the form of fine particles, such as particles smaller than 100 ,xtm in mean particle size.

As to the material for the polymer coating, an almost free selection can be made from vinylic monomers that undergo radical polymerization, and where desired it is possible to jointly use two or more kinds of vinylic monomers which undergo radical copolymerization. Examples of useful compounds having vinyl bond are acrylic acid, methacrylic acid, acrylates, methacrylates, acrylic esters, methacrylic esters, acrylonitrile, N-methylolacrylamlde, vinyl chloride, vinyl acetate, styrene, divinylbenzene and vinylidene fluoride.

In the polymer-coated graphite fluoride, the content of the vinylic polymer should be at least 0.5% by weight in order to produce a substantial improvement on the dispersing property. In theory there is no clear upper boundary of the polymer content in the coated graphite fluoride, but in practice it is important that the coated graphite fluoride sufficiently exhibits the desired characteristics of graphite fluoride and therefore it is preferred to limit the polymer content in the coated graphite fluoride at 50% by weight. Within these limitations, the polymer content in the coated graphite fluoride can freely be determined by adjusting the proportion of the vinylic monomer to graphite fluoride.

In the method according to the invention for the preparation of the above described polymercoated graphite fluoride, it is a normal way to disperse graphite fluoride and vinylic monomer in either a mixture of water and an organic solvent which is soluble in water or a mixture of water and a surfaceactive agent. The organic solvent can be selected from, for example, alcohols typified by methanol and ethanol, ketones typified by acetone, ethers and amines. The most preferable solvent is ethanol particularly because the use of ethanol is effective for enhancement of the grafting efficiency, which is herein defined as the weight ratio of the vinylic polymer bonded to the graphite fluoride by graft polymerization to the vinylic monomer subjected to the polymerization reaction.The organic solvent is used in an amount sufficient for good dispersion of the graphite fluoride in the resultant aqueous medium, but it is unfavorable to use an excessively large amount of organic solvent because it will cause lowering of the grafting efficiency. In the case of ethanol, a preferred range of the proportion of water to ethanol is from 0.1:1 to 2.3:1 by weight. The surface-active agent may be anionic, cationic or nonionic, or may be a mixture of surface-active agents of different types.

As to the polymerization initiator for the selected vinylic monomer, it is suitable to use a watersoluble initiator such as sulfur dioxide, aqueous solution of sulfurous acid, aqueous solution of a hydrogensulfite, potassium persulfate, azobiscyanovaleric acid or 2,2'-azobis-(2-amidinopropane) dihydrochloride.

It is suitable to prepare an aqueous dispersion system by adding 1 to 100 parts by weight of graphite fluoride and 0.1 to 100 parts by weight of vinylic monomer in a mixture of 100 parts by weight of water and either 1 to 100 parts by weight of organic solvent or 1 to 50 parts by weight of surface-active agent and well stirring the resultant mixture. Then a polymerization initiator is added to the aqueous dispersion and stirring is continued. It suffices that the polymerization initiator amounts to 0.01 to 20% by weight of the vinylic monomer.

After the addition of the polymerization initiator the vinylic monomer in the aqueous dispersion undergoes radical polymerization, and graft polymerization with the graphite fluoride, even at room temperature. However, it is favorable to maintain the reaction system at an adequately elevated temperature such as about 50 to 700C to thereby enhance the rate of polymerization and complete the polymerization reaction in a shortened time. By this process a high degree of polymerization can be achieved in a relatively short reaction time such as 1 to 5 hr.

After completion of the polymerization reaction, the reacted slurry is filtered to separate the solid component which is a polymer-coated graphite fluoride in powder form, and the polymer-coated graphite fluoride is thoroughly washed with water and dried. Thus, the preparation of the polymercoated graphite fluoride according to the invention is accomplished by easy operations and is convenient to desirably control the proportion of the reactants and the reaction conditions.

In this method, it is especially preferable to adjust the pH of the polymerization reaction system after the addition of the polymerization initiator to 5 to 9 because such adjustment of the pH has the effect of greatly enhancing the grafting efficiency. Numerically, the grafting efficiency becomes more than 90% and in some cases nearly 100%. When graphite fluoride is dispersed in water by the aid of an organic solvent or a surface-active agent as described above, the dispersion becomes acidic and exhibits a pH value of about 2 to 4. Presumably this is because of the existence of a small quantity of free fluorine on the surfaces of the graphite fluoride particles. Besides, the above described polymerization initiators preferred in this invention are acidic materials.Without adjustment of the pH, it is natural that the polymerization reaction takes place under an acidic condition represented by a pH value above 2 but below 5. The preparation of the polymer-coated graphite fluoride according to the invention is fully practicable even under such acidic condition, but then it is difficult to raise the grafting efficiency beyond about 70%.

Presumably the reason for such enhancement of the grafting efficiency by the adjustment of the pH of the reaction system to 5-9 by using an alkali is that the neutralization of the free fluorine as the source of acidity by the attack of the alkali on the surfaces of the graphite fluoride particles results in the appearance of numerous active points on the same surfaces. In an experiment on an aqueous dispersion of graphite fluoride (CF),, having a pH value of about 3, the addition of an alkali to raise the pH of the dispersion up to about 8 caused the initially white color of the dispersion to change to a brownish color, so that a neutralization phenomenon on the surfaces of the graphite fluoride was understandable.

The range of the adjusted pH of the reaction system is specified to be from 5 to 9 firstly because the effect of the adjustment remains insufficient if the adjusted pH is still below 5 and secondly because when the pH exceeds 9 there arises a possibility of decomposition of graphite fluoride. The adjustment of the pH can be accomplished by adding an alkaline material such as an alkali metal hydroxide, alkali metal carbonate, aqueous ammonia, ammonia gas or ammonium salt to the polymerization reaction system after the addition of the polymerization initiator. Alternatively, the same object is accomplished by treating graphite fluoride with an alkaline solution or gas in advance of the preparation of the polymerization reaction system.

In the case of performing the polymerization reaction by the aforementioned semi-dry process, only very small quantities of water and organic solvent are used so that the graphite fluoride and vinyl monomer are only wetted with the liquid medium rather than dispersed therein. When such semi-dry process is taken into consideration, suitable proportions of the materials in the method according to the invention can be expressed as follows. For 100 parts by weight of graphite fluoride, it is suitable to use 0.1 to 600 parts by weight of water, 0.1 to 300 parts by weight of an organic solvent soluble in water or 0.1 to 1 50 parts by weight of a surface-active agent, 0.1 to 100 parts by weight of vinylic monomer(s), and a polymerization initiator amounting to 0.01 to 20% by weight of the vinylic monomer(s).

In the semi-dry process, there is no need of filtering the reaction system after completion of the polymerization reaction, and a polymer-coated graphite fluoride is obtained by thoroughly washing the reaction product with water and drying the washed product. The semi-dry process has advantages such as the possibility of treating a large quantity of graphite fluoride in a reaction vessel of a relatively small capacity, great decrease in the consumption of organic solvent or elimination of a solvent recovery process, and simplification of the product recovery operations. However, the grafting efficiency in the semi-dry process remains lower than that in the the normal process using an aqueous dispersion when there is no difference in other factors of the reaction.

Also in the case of the semi-dry process, it is very preferable to adjust the pH of the reaction system to 5-9. In this case it is convenient to perform alkali treatment of graphite fluoride in advance of mixing with vinylic monomer and water. If it is desired to perform adjustment of the pH after preparation of the polymerization reaction system, it is suitable to use a gaseous alkali such as ammonia gas.

The polymer-coated graphite fluoride according to the invention exhibits good dispersing property in various liquid media and has high affinity or miscibility with various organic powdery materials such as rubbers and synthetic resins. Furthermore, in this polymer-coated graphite fluoride a very firm and almost ideal polymer coating is established even when the proportion of the polymer to graphite fluoride is very small. Therefore, this polymer-coated graphite fluoride can fully exhibit the excellent lubricating property or any other desirable property characteristic of graphite fluoride, and by using this material it is possible to provide a continuous lubricating film which can practically be regarded as consists of pure graphite fluoride powder.

Furthermore, this polymer-coated graphite fluoride has good formability so that it is possible to compact this material alone into a solid body of a desired shape by application of adequate pressure and heat. The good dispersing property of the polymer-coated graphite fluoride is exhibited also in press-shaping of the material, so that the shaped body has a dense and tight structure.

By using a mixture of the polymer-coated graphite fluoride and a suitable synthetic resin powder, it becomes more easy to produce press-shaped bodies of various shapes and the strength of the shaped bodies can be enhanced. Various resins are useful for this purpose as will be described hereinafter, and phenolic resin, polymethyl methacrylate resin, polyacetal resin and ABS resin can be named as preferred examples. In principle there is no strict limitation to the amount of the resin to be added, but from the viewpoint of fully utilizing the favorable characteristics of graphite fluoride it is preferred to limit the amount of the resin such that the total weight of the polymer coated on the graphite fluoride particles and the resin added for press-shaping does not exceed the weight of the graphite fluoride in the resultant mixture.

The press-shaping of a mixture of the polymer-coated graphite fluoride and a selected resin in powder form is accomplished by a usual method which may use a metal die set. As to the pressshaping conditions, usually it suffices to apply a pressure of 1 50-450 kg/cm2 while the mixture is kept heated to 1 00-2500C, though most suitable pressure and temperature are variable depending on the kinds of the vinylic polymer coated on the graphite fluoride and the resin mixed with the coated graphite fluoride.

Owing to good dispersing property and affinity for resins, press-shaping of the polymer-coated graphite fluoride added with a resin gives a tightly compacted solid body in which the polymer-coated graphite fluoride particles are very uniformly distributed. The press-shaped bodies are excellent in physical properties, and it is possible to produce even intricately shaped bodies. If it is desired to expose graphite fluoride on the surface of the press-shaped body so that the surface may strongly exhibit the unique properties of graphite fluoride, the desire can be met by grinding the surface of the press-shaped body to thereby remove the resin from the surface, or alternatively by treating the surface with a suitable organic solvent to dissolve out the resin existing on the surface.Where greater interest is attached to the utilization of the properties of graphite fluoride rather than the physical strength of the press-shaped body, it is suitable to add only a small amount of resin to the polymer-coated graphite fluoride, or to press-shape the polymer-coated graphite fluoride alone.

Though unessential, it is possible to add any auxiliary material selected from conventional additives used in press-shaping of synthetic resins and/or inorganic materials to a mixture of the polymer-coated graphite fluoride and a selected resin.

The polymer-coated graphite fluoride of the invention, either in powder form or in compacted form, has greatly widened uses compared with untreated graphite fluoride or graphite fluorides treated by hitherto proposed methods. Typical examples of the wide uses are listed in the following.

(1) Preparation of composite materials A variety of composite materials can be obtained by mixing the polymer-coated graphite fluoride with natural or synthetic rubber, synthetic resin, glass fiber, ceramics, graphite or other carbonaceous material, asphalt, tar and/or pitch. Shaped members of such composite materials are useful as selflubricating bearings and sealing elements such as packings and gaskets, and it is also possible to form some of these composite materials into fibers.Since the polymer coating according to the invention is firmly bonding to the graphite fluoride particles, in the uses of these composite materials very stable lubricating film can be formed on the sliding contact face, and therefore the shaped members are very low in the rate of abrasion and can endure severe frictions represented by large values of the product of the applied pressure by the velocity of relative movement of the shaped member.

Examples of synthetic rubbers for this use are styrene rubber, butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, ethylene-propylene rubber, Hypalon or chlorosulfonated polyethylene rubber, acrylic rubber, urethane rubber, fluorine rubber, silicone rubber, thiokol and ethylene-vinyl acetate rubber.

Examples of synthetic resins for this use are phenolic resin, urea resin, melamine resin, aniline resin, unsaturated polyester resin, diallyl phthalate, epoxy resin, alkyd resin, polyimido, silicone resin, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyacrylonitrile, polyvinyl butyral, polyamide, ABS resin, polycarbonate, polyacetal, polyethyleneterephthalate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyurethane, ionomer resin, fluorine resin and cellulose base plastics.

(2) Addition to lubricating oil or grease The polymer-coated graphite fluoride in powder form is added to various lubricating oils and greases for use as gear oil, spindle oil, refrigerator oil, dynamo oil, turbine oil, machine oil, cylinder oil, Iubricating oil for reciprocating engines of aircraft, marine engine oil, fiber grease, cup crease, glass fiber grease, automotive bearing grease and ball-and-roller bearing grease for example.

As for the aformentioned lubricating oils, polyolefins, glycols, carboxylic acid esters, phosphoric acid esters, silicones, perfluorocarbons and chlorinated aromatic compounds are named as useful materials. As for the aforementioned greases, calcium soap grease, sodium soap grease, aluminum soap grease, barium soap grease, mixed soap grease, calcium complex soap grease, barium complex soap grease, and non-soap greases that utilize non-soap materials such as bentonite or fine silica as viscosity modified are named as examples.

(3) Application to form dry film for lubrication The polymer-coated graphite fluoride in powder form, either singly or jointly with an organic or inorganic binder, is applied to sliding contact faces of various apparatus in the manner of coating to thereby form a dry and lubricating film which serves for the purpose of permanent lubrication, fitting at initial stage of operation or releasing.

(4) Use as releasing agent The polymer-coated graphite fluoride in powder form is useful as a lubricating and releasing agent in die-casting and press-shaping operations for the production of sintered alloy bodies, shaped plastic bodies or shaped rubber bodies for example. For this use, the polymer-coated graphite fluoride powder may be dispersed in a liquid or gas for spraying onto the desired surfaces.

(5) Use in metal machining In metal machining operations such as cutting, rolling, drawing, pressing grinding and polishing, the polymer-coated graphite fluoride in powder form is added to cutting oil, rolling oil, pressing oil, grinding oil and polishing liquid for the purpose of augmenting the lubricating effect of the oils.

It should be noted that the above listed uses are only exemplary, and that the polymer-coated graphite fluoride of the invention is useful in the entire areas of the application of graphite fluoride and in almost every case offers many advantages over the use of untreated graphite fluoride.

Hereinafter some examples are presented to illustrate the present invention without the least intention of limiting the invention in any respect.

Example 1 A three-necked one-liter flask was held immersed in a constant temperature bath maintained at 600C, and 280 ml of water, 200 ml of ethanol, 100 g of graphite fluoride (CF),, and 25 g of methyl methacrylate monomer were charged into the flask. The graphite fluoride was in the form of fine particles obtained by pulverization in a jet mill and passed through a 300-mesh sieve. Fig. 1 is a micrograph of the graphite fluoride particles used in this example. Stirring the mixture in the flask, 20 ml of 6% aqueous solution of sulfurous acid was added to initiate polymerization of methyl methacrylate. At this stage the pH of the aqueous reaction system was about 2. Stirring of the reaction system was continued for 4 hrfrom the addition of the sulfurous acid solution.Then the solid component of the reacted slurry was separated from the liquid by filtration, thoroughly washed with water and then dried at 800C in vacuum to obtain a powdery product which weighed 11 7.8 g.

Fig. 2 is a micrograph of the thus treated graphite fluoride. As will be understood from this micrograph, it was confirmed that the graphite fluoride particles were well coated with polymerized methyl methacrylate without recognizing the existence of the methacrylate polymer independent of the graphite fluoride particles. The polymer-coated graphite fluoride was subjected to benzene extraction for 48 hr, and both the extract and the solid remained undissolved in benzene were subjected to infrared absorption spectrum analysis. Fig. 5 shows the infrared absorption spectrum pattern of the extract and Fig. 6 shows that of the undissolved solid. By this analysis the extract was confirmed to be homopolymer of polymethyl methacrylate, and also it was confirmed that the absorption spectrum of the indissolved solid was in agreement with the spectrum of polymethyl methacrylate.These facts evidenced the realization of graft bonding of polymethyl methacrylate to the surfaces of the graphite fluoride particles. The polymer-coated graphite fluoride was subjected to thermogravimetric analysis (TGA), which revealed that the content of polymethyl methacrylate in the coated graphite fluoride calculated from the weight loss was 15.1% by weight.

Also in the following examples, the above described microscopic observation, infrared absorption spectrum analysis and thermogravimetric analysis were carried out to confirm graft bonding of vinylic polymer to graphite fluoride and to measure the polymer content in the coated graphite fluoride.

Example 2 In this example, 330 ml of water, 150 ml of graphite fluoride (C2F),, and 30 g of methyl methacrylate monomer were charged into a three-necked flask which had a capacity of one liter and was held immersed in a constant temperature bath maintained at 600 C. The graphite fluoride was in the form of fine particles obtained by pulverization in a jet mill and passed through a 250-mesh sieve.

Fig. 3 is a micrograph of this graphite fluoride. Stirring the mixture in the flask, 20 ml of 6% aqueous solution of sulfurous acid was added to initiate polymerization of methylmethacrylate. At this stage the pH of the aqueous reaction system was about 2. Stirring of the reaction system was continued for 3 hr from the addition of the sulfurous acid solution. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum. Fig. 4 is a micrograph of polymer-coated graphite fluoride obtained by this process.

The polymer-coated graphite fluoride in dry state was 124.7 g in total weight and contained 19.8% by weight of polymethyl methacrylate.

Example 3 In this example, 300 ml of water, 1 50 ml of ethanol, 100 g of the graphite fluoride (CF),, particles mentioned in Example 1 and 30 g of methyl acrylate monomer were charged into a three-necked oneliter flask held immersed in a constant temperature bath maintained at 600 C. Stirring the mixture in the flask, 20 ml of 6% aqueous solution of sulfurous acid was added to initiate polymerization of methyl acrylate. At this stage the pH of the aqueous reaction system was about 2. Stirring of the reaction system was continued for 3 hr from the addition of the sulfurous acid solution. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 700C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 121.2 g in dry state and contained 17.5% by weight of polymethyl acrylate.

Example 4 Using the same apparatus as in the preceding examples, 285 mi of water, 200 ml of methanol, 100 g of the graphite fluoride (C2F),, particles mentioned in Example 2 and 20 g of methyl acrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C.

Continuing the stirring, 1 5 ml of 6% aqueous solution of sulfurous acid was added to the mixture in the flask to initiate polymerization of methyl acrylate. At this stage the pH of the aqueous reaction system was about 3. Stirring of the reaction system was continued for 4 hr from the addition of the sulfurous acid solution. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 700C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 111.8 g in dry state and contained 10.8% by weight of polymethyl acrylate.

Example 5 Using the same apparatus as in the preceding examples, 470 ml of water, 10 ml of polyoxyethylene alkyl ether employed as a nonionic surface-active agent, 100 g of the graphite fluoride (CF),, particles mentioned in Example 1 and 30 g of methyl methacrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 500 C. Continuing the stirring, 20 ml of 6% aqueous solution of sulfurous acid was added to the mixture in the flask to initiate polymerization reaction. At this stage the pH of the aqueous reaction system was about 3. Stirring of the reaction system was continued for 4 hr from the addition of the sulfurous acid solution. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 700C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 120.1 g of dry state and contained 17.4% by weight of polymethyl methacrylate.

Example 6 Using the same apparatus as in the preceding examples, 280 ml of water, 200 ml of ethanol, 100 g of the graphite fluoride (CF),, mentuoned in Example 1 and 30 g of acrylonitrile monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 20 ml of 10% aqueous solution of 2,2'-azobis-(2-amidinopropane)dihydrochloride was added to the mixture in the flask to initiate polymerization reaction. At this stage the pH of the aqueous reactions system was about 3. Stirring of the reaction system was continued for 3 hr from the addition of the polymerization initiator solution. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 123.9 g in dry state and contained 1 9.3% by weight of polyacrylonitrile.

Example 7 Using the same apparatus as in the preceding examples, 280 ml of water, 200 ml of ethanol, 100 g of the graphite fluoride (CF),, mentioned in Example 1, 1 5 g of methyl methacrylate monomer and 15 g of styrene monomer were mixed by stirring, while the constant temperature bath was maintained at 600C. Continuing the stirring, 20 ml of 6% aqueous solution of sulfurous acid was added to the mixture to initiate copolymerization reaction. At this stage the pH of the aqueous reaction system was about 3.

Stirring of the reaction system was continued for 3 hr from the addition of the sulfurous acid solution.

Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 122.5 g in dry state and contained 18.8% by weight of copolymer of styrene and methyl methacrylate.

Example 8 Using the same flask as in the preceding examples, 280 ml of water, 200 ml of acetone, 100 g of the graphite fluoride (CF),, mentioned in Example 1 and 10 g of methyl methacrylate monomer were mixed by stirring at room temperature. Continuing the stirring, 10 ml of 6% aqueous solution of sulfurous acid was added to initiate polymerization reaction. At this stage the pH of the aqueous reaction system was about 3. Stirring of the reaction system was continued for 5 hr from the addition of the sulfurous acid solution. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 700C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 105 g in dry state and contained 4.8% by weight of polymethyl methacrylate.

To evaluate the dispersing property of this polymer-coated graphite fluoride in oil, 1 part by weight of the coated graphite fluoride was added to 100 parts by weight of No. 40 turbine oil at room temperature, and mixing was performed by means of a homomixer which was operated for 10 min at 10 000 rpm. Then the mixture was kept in a centrifugal separator operated at 3000 rpm for 5 min, and thereafter the mixture was left standing at room temperature. After the lapse of 60 min, still the coated graphite fluoride particles remained almost uniformly dispersed in the oil through sedimentation of a small portion of the graphite fluoride particles was recognized.

For comparison, the untreated graphite fluoride particles used as the starting material in Example 8 were dispersed in the same turbine oil by the same procedure. After the withdrawal from the centrifugal separator, the graphite fluoride particles in the oil almost entirely uhderwent sedimentation within a period of 15 min.

Example 9 The graft polymerization process of Example 8 was repeated generally similarly but by reducing the quantity of methyl methacrylate to 5 9 and by shortening the duration of the polymerization reaction to 3 hr.

Obtained as the result was a polymer-coated graphite fluoride which weighed 101.2 g in dry state and contained 1.2% by weight of polymethyl methacrylate.

Example 10 The polymer-coated graphite fluoride prepared in Example 1 was shaped into a solid cylindrical body by using a metal die. No extra material was added to the coated graphite fluoride, and the pressshaping was performed at 1 800C by applying a pressure of 250 kg/cm2 for 10 min. It was easy to achieve the press-shaping.

The press-shaped body was subjected to bending strength test, which gave an average bending strength value of 310 kg/cm2. Fig. 7 is a micrograph showing a section of the press-shaped body produced in this example. As can be seen from this micrograph, the polymer-coated graphite fluoride particles were very uniformly distributed throughout the press-shaped body.

Besides, the polymer-coated graphite fluoride prepared in Examples 2, 4, 6, 7, 8 and 9 were individually subjected to the above described press-shaping under the same press-shaping condition.

in every case it was easy to achieve the press-shaping, and the polymer-coated graphite fluoride particles were very uniformly distributed in the press-shaped body. The following Table 1 shows the bending strength values of the solid bodies produced by press-shaping of these polymer-coated graphite fluorides. In the Table, "PMMA" refers to polymethyl methacrylate and "PMA" to polymethyl acrylate.

Reference 1 For comparison, the untreated graphite fluorides (CF),, and (C2F),, used respectively as starting materials in Examples 1 and 2 were subjected to the press-shaping described in Example 10. Prior to the press-shaping, each of these untreated graphite fluorides was mixed in a dry state with the resin corresponding to the polymer coating formed in Example 1,2,4,6,7,8 or 9 such that the resin content in the resultant mixture became in agreement with the polymer content in the polymer-coated graphite fluoride of Example 1, 2, 4, 6, 7, 8 or 9.

In every case, however, it was impossible to achieve the intended press-shaping under the shaping condition described in Example 10, or the press-shaped body was too weak and fragile to measure its bending strength.

Reference 2 Also for comparison, the untreated graphite fluoride (CF),, used in Example 1 was mixed with powdered polymethyl methacrylate in the proportion of 1:1 by weight, and the resultant mixture was press-shaped into a solid cylindrical body by the same method and under the same shaping condition as in Example 1 0. In this case the press-shaping was possible, and the bending strength of the pressshaped body was measured to be 17 kg/cm2 as can be seen in Table 1. Figure 8 is a micrograph showing a section of this press-shaped body. As can be seen from this micrograph, the distribution of the graphite fluoride particles in the press-shaped body was far from uniformity.

Table 1

Content of Bending Graphite grafted Added strength fluoride polymer ('wit%) resin Formability (kg/cm2) Ex.1 15.1 - good 310 coated (CF),, (PMMA) Ex. 2 1 9.8 - good 348 coated (C2F),, (PMMA) Ex.4 10.8 - good 225 coated (C2F),, (PMA) Ex.6 19.3 - good 318 coated (CF),, (polyacrylo nitrile) Ex.7 18.8 - good 285 coated (CF),, (PMMA styrene) Ex. 8 4.8 - good 85 coated (CF),, (PMMA) Ex.9 1.2 - good 26 coated (CF),, (PMMA) Reference 2 - PMMA interior 17 Untreated (CF),, 59 Example 11 The polymer-coated graphite fluoride prepared in Example 1 was shaped into a solid cylindrical body by the press-shaping method and under the shaping condition described in Example 10, and test pieces each in the shape of a rectangular plate 10 mmx30 mm wide and 2 mm thick were cut out of the press-shaped body.The test pieces were divided into four groups, which were subjected to the following four kinds of treatments, respectively. On each of the treated test pieces, the contact angle of the polymer-coated and compacted graphite fluoride for water was measured at 250C by the usual droplet method with respect to a surface normal to the direction of pressing at the press-shaping.

Treatment A: the surface for measurement of the test piece was washed with ethanol.

Treatment B: in a closed glass vessel the test piece was submerged in about 50 ml of water, and the glass vessel was shaken for 1 hr at a rate of about 200 cycles per minute, and thereafter the surface for measurement of the test piece was washed with ethanol.

Treatment C: the surface for measurement of the test piece was lightly polished with No. 800 emery sand paper, and then the surface was washed with ethanol.

Treatment D: the test piece was subjected first to the treatment C and next to the Treatment B.

The following Table 2 shows the results of the measurement of the contact angle.

Reference 3 For comparison, test pieces of the dimensions mentioned in Example 11 were cut out of the press-shaped body of Reference 2 (mixture of untreated graphite fluoride and polymethyl methacrylate) and subjected to the treatments and measurement described in Example 11. Table 2 contains the contact angle data obtained by measurement on the test pieces of Reference 3.

Table 2

Contact angle Pretreatment Pretreatment Pretreatment Pretreatment A B C D Example 11 1150 1150 1300 1280 Reference 3 13101 1050 1100 890 *The surface of the test piece was not smooth and had considerable undulations.

With respect to the samples of Example 11, both the pretreatments C and D resulted in larger contact angle values compared with the data obtained after the pretreatment A or B. The reason is presumed to be partial or local peeling of the polymethyl methacrylate coating by the polishing to result in exposure of the graphite fluoride surfaces. In the case of the sample of Reference 3 subjected to the pretreatment D, the very small value of contact angle is presumed to be by reason of separation of some graphite fluoride particles from the treated surface of the test piece.

The following Examples 12 and 1 3 illustrate the addition of a synthetic resin powder to a polymer-coated graphite fluoride according to the invention in press-shaping the graphite fluoride into a solid body.

Example 12 Each of the polymer-coated graphite fluorides prepared in Examples 1,2,4,6,7,8 and 9 was mixed in dry state with a powdered synthetic resin selected from polymethyl methacrylate (PMMA) phenolic resin, polyacetal resin and ABS resin in the proportion as shown in the following Table 3. Each mixture of the coated graphite fluoride and resin powder was press-shaped into a cylindrical solid body having a diameter of 50 mm by using a metal die. The press-shaping was performed at 1 800C by applying a pressure of 250 kg/cm2. Every mixture exhibited good formability so that the press-shaping was easily accomplished, and there was no difficulty in releasing the shaped body from the metal die.

The press-shaped bodies were subjected to bending strength test of which the results are presented in Table 3. Besides, by microscopic observation it was confirmed that the polymer-coated graphite fluoride particles in every solid body shaped in this example were uniformly distributed in the shaped body.

Reference 4 For comparison, the untreated graphite fluoride (CF),, mentioned in Example 1 was mixed with each of the resin powders used in Example 12 in the proportion as shown in Table 3, and the untreated graphite fluoride (C2F),, mentioned in Example 2 was mixed with the polymethyl methacrylate powder also as shown in Table 3. The press-shaping operation described in Example 12 was repeated by alternately using these mixtures. However, in some cases it was impossible to achieve the intended shaping, and even the cases of success in the press-shaping it was revealed that the distribution of the graphite particles in every shaped body was significantly nonuniform. The solid bodies shaped in this experiment were subject to bending strength test of which the results are contained in Table 3.

Table 3

Resin added Content of to 10 g of Bending Graphite grafted graphite strength fluoride polymer fwto/ol fluoride Formability (kg/cm2) Example 1 15.1 PMMA good 335 coated (CF)n (PMMA) 1.0 g Example 1 ditto phenolic good 350 coated (CF)n 3.0 g Example 2 19.8 phenolic good 398 coated (C2F)n (PMMA) 7.5 g Example 4 10.8 phenolic good 340 coated (C2F),, (PMA) 3.0 g Example 6 19.3 phenolic good 385 coated (CF)n (polyacrylo- 7.5 g nitrile) Example 7 18.8 acetal good 320 coated (CF),, (PMMA- 2.1 g styrene) Example 8 4.8 ABS good 295 coated (CF),, (PMMA) 1.0 g Example 8 ditto PMMA good 310 coated (CF)n 1.0 g Example 9 1.2 PMMA good 45 coated (CF)n (PMMA) 0.1 g Example 9 ditto ABS good 360 coated (CF)n 6.0 g untreated (CF)n 1.5 g to shape - Reference 4 - PMMA ditto untreated (C2F)n 3.0 g Reference 4 - PMMA inferior 17 untreated (CF)n 5.0 g ditto - phenolic inferior 21 5.0g ditto - acetal inferior 28 7.0g ditto - ABS inferior 18 5.Og Example 13 The polymer-coated graphite fluoride prepared in Example 8 was mixed in dry state with a powdered ABS resin, phenolic resin or polyacetal resin each in the proportion as shown in the following Table 4, and every mixture was subjected to press-shaping in a metal die to produce a solid cylindrical body. The press-shaping was performed at 100--180 C (measured on the metal die surface) by applying a pressure of 150-200 kg/cm2 for about 10 min.

The shaped bodies were subjected to an abrasion test, in which every sample was forced to make a relative movement at a velocity of 1000 m/min under a pressure of 30 kg/cm2. Table 4 contains the results of this test.

Reference 5 For comparison, the untreated graphite fluoride used in Example 8 was mixed in dry state with each of the three kinds of resins -mentioned in Example 13, and each mixture was subjected to the press-shaping operation described in Example 13. The shaped bodies were subjected to the aforementioned abrasion test, of which the results are shown in Table 4.

Table 4

Added resin, and weight ratio of Graphite the resin to Abrasion fluoride graphite fluoride (mg/cm2. hr) coated (CF),, phenolic resin 2.0 (Ex.8) 6.50:100 Ex. 13 ditto polyacetal resin 17.1 6.30:100 ditto ABS resin 18.6 6.50:100 untreated (CF)n phenolic resin 19.3 50:50 polyacetal resin 70:30 ditto ABS resin 91.1 50:50 The following examples show the effects of adjusting the pH of the aqueous reaction system to 5-9 in the graft polymerization process according to the invention.

Example 14 This example was a modification of the graft polymerization process of Example 1 only in respect of the pH of the reaction system.

In the apparatus and at the temperature mentioned in Example 1, the mixing of the pulverized graphite fluoride (CF),, (100 g), water (280 ml), ethanol (200 ml) and methyl methacrylate monomer (25 g) and the addition of 6% aqueous solution of sulfurous acid (20 ml) were carried out in accordance with Example 1. At this stage the pH of the reaction system in the state of aqueous dispersion was about 2.

Soon after the addition of the sulfurous acid solution, the pH of the aqueous dispersion was raised up to 7.7 by the addition of sodium hydroxide. The stirring of the reaction system was continued for 4 hr after the adjustment of the pH, and the reaction system was filtered to separate the solid component, which was washed and dried in the same manner as in Example 1.

This process gave 122.5 g of dry product in powder form, which was confirmed by microscopic observation to be graphite fluoride particles individually well coated with a polymer. Neither graphite fluoride independent of the polymer nor the polymer independent of the graphite fluoride particles was observed in this product. The polymer-coated graphite fluoride was subjected to benzene extraction for 48 hr, and both the extract and the undissolved solid were subjected to infrared absorption spectrum analysis, which gave the same results as in example 1. Therefore, graft bonding of polymethyl methacrylate to the surfaces of the graphite fluoride particles was unquestionable. By thermogravimetric analysis of the polymer-coated graphite fluoride, the content of polymethyl methacrylate therein was confirmed to be 18.4% by weight. (In Example 1, the polymer content was 1 5.1%.) From this value of the polymer content, the grafting efficiency represented by the proportion of the polymer grafted onto the graphite fluoride to the monomer initially charged into the polymerization reaction vessel was calculated to be 90%. For comparison, in the case of Example 1 the grafting efficiency was calculated to be 71%.

Example 15 Using the. same apparatus as in the preceding examples, 250 ml of water, 200 ml of ethanol,100 g of the graphite fluoride (C2F),, mentioned in Example 2 and 30 g of methyl methacrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 50 ml of 4% aqueous solution of 2,2'-azobis-(2-amidinopropane)dihydrochloride was added to the mixture as a polymerization initiator. At this stage the pH of the aqueous reaction system was about 3. Soon after the addition of the polymerization initiator, sodium hydroxide was added in order to adjust the pH of the reaction system to 7.0. After the adjustment of the pH, stirring of the reaction system was continued for 3 hr.Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 128.5 g in dry state and contained 22.2% by weight of polymethyl methacrylate. In this process the grafting efficiency was calculated to be 95%.

For comparison, this process was repeated generally similarly except that the addition of sodium hydroxide was omitted. That is, the pH of the aqueous reaction system was left at about 3.

The polymer-coated graphite fluoride obtained in this case was 11 8.3 g in dry weight and contained 15.5% by weight of polymethyl methacrylate, so that the grafting efficiency was calculated to be 61%.

Example 16 Using the same apparatus as in the preceding examples, 250 ml of water, 250 ml of ethanol, 100 g of the graphite fluoride (CF),, mentioned in Example 1 and 30 g of methyl acrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 20 ml of 6% aqueous solution of sulfurous acid was added to the mixture in the flask. At this stage the pH of the aqueous reaction system was about 2. Soon after the addition of the sulfurous acid solution, aqueous solution of potassium hydroxide was added so as to adjust the pH of the reaction system to 6.5. After the adjustment of the pH, stirring of the reaction system was continued for 3 hr.

Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 700C in vacuum.

Fig. 9 is a micrograph of the polymer-coated graphite fluoride obtained by this process. This product weighed 129.4 g in dry state and contained 22.7% by weight of polymethyl acrylate, so that the grafting efficiency was calculated to be 98%.

For comparison, this process was repeated generally similarly except that the addition of potassium hydroxide solution was omitted. That is, the pH of the aqueous reaction system was left at about 2.

The polymer-coated graphite fluoride obtained in this case was 11 5.3 g in dry weight and contained 13.3% by weight of polymethyl acrylate, so that the grafting efficiency was calculated to be 51%. Fig. 10 is a micrograph of the polymer-coated graphite fluoride obtained in this case.

Example 17 Using the same apparatus as in the preceding examples, 250 ml of water, 200 ml of methanol, 100 g of the graphite fluoride (C2F),, used in Example 1 5 and 20 g of methyl acrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 50 ml of 4% aqueous solution of 2,2'-azobis-(2-amidinopropane)dihydrochloride was added to the mixture as polymerization initiator. At this stage the pH of the aqueous reaction system was about 3. Soon after the addition of the initiator, the pH of the reaction system was adjusted to 5.4 by adding aqueous solution of sodium hydroxide. After the adjustment of pH, stirring of the reaction system was continued for 4 hr.Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 700C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 11 8.0 g in dry state and contained 15.3% by weight of polymethyl acrylate. In this case the grafting efficiency was 90%.

For comparison, this process was repeated generally similarly except that the addition of sodium hydroxide was omitted. That is, the pH of the aqueous reaction system was left at about 3. The polymer-coated graphite fluoride obtained in this case weighed 109.4 g in dry state and contained 8.6% by weight of polymethyl acrylate, so that the grafting efficiency was 47%.

Example 18 Using the same apparatus as in the preceding examples, 250 ml of water, 200 ml of methanol, 100 g of the graphite fluoride (CF),, used in Example 14 and 20 g of methyl methacrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 50 ml of 4% aqueous solution of the polymerization initiator used in Example 1 7 was added to the mixture in the flask. At this stage the pH of the aqueous reaction system was about 3. Soon after the addition of the polymerization initiator, the pH of the reaction system was adjusted to 8.5 by adding sodium hydroxide. After that, stirring of the reaction system was continued for 4 hr. Then the reacted slurry was filtered to separate the solid component, which was washed with water and dried at 700C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 11 9.4 g in dry state and contained 16.2% by weight of polymethyl methacrylate. In this case the grafting efficiency was 97%.

For comparison, this process was repeated generally similarly except that the addition of sodium hydroxide was omitted. That is, the pH of the aqueous reaction system was left at about 3. The polymer-coated graphite fluoride obtained in this case weighed 110.8 g in dry state and contained 9.7% by weight of polymethyl methacrylate, so that the grafting efficiency was 54%.

Example 19 Using the same apparatus as in the preceding examples, 200 ml of water, 200 ml of ethanol, 100 g of the graphite fluoride (CF),, used in Example 14 and 30 g of acrylonitrile monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 50 ml of 4% aqueous solution of the polymerization initiator used in Example 1 7 was added to the mixture in the flask. At this stage the pH of the aqueous reaction system was about 3. Soon after the addition of the polymerization initiator, the pH of the reaction system was adjusted to 7.1 by adding sodium hydroxide. After that, stirring of the reaction system was continued for 3 hr. Then the reacted slurry was filtered to separate the solid component, which was washed with water and dried at 800C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 127.0 g in dry state and contained 21.3% by weight of polyacrylonitrile. In this case the grafting efficiency was 90%.

For comparison, this process was repeated generally similarly except that the addition of sodium hydroxide was omitted. That is, the pH of the reaction system was left at about 3. The polymer-coated graphite fluoride obtained in this case weighed 11 8.0 g and contained 15.3% by weight of polyacrylonitrile, so that the grafting efficiency was 60%.

Example 20 Using the same apparatus as in the preceding examples, 250 ml of water, 200 ml of ethanol, 100 g of the graphite fluoride (CF),, used in Example 14 and 20 g of styrene monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 50 ml of 4% aqueous solution of the polymerization initiator used in Example 17 was added to the mixture in the flask. At this stage the pH of the aqueous reaction system was about 3. Soon after the addition of the polymerization initiator, the pH of the reaction system was adjusted to 7.1 by adding sodium hydroxide. After that, stirring of the reaction system was continued for 3 hr. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 11 8.2 g in dry state and contained 15.4% by weight of polystyrene. In this case the grafting efficiency was 91%.

For comparison, this process was repeated generally similarly except that the adjustment of pH by the addition of sodium hydroxide was omitted. The polymer-coated graphite fluoride obtained in this case weighed 111.0 g and contained 9.9% by weight of polystyrene, so that the grafting efficiency was 55%.

Example 21 Using the same apparatus as in the preceding examples, 280 ml of water, 200 ml of ethanol, 100 g of the graphite fluoride (CF),, used in Example 14 and 6 g of methyl methacrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 600 C. Continuing the stirring, 20 ml of 4% aqueous solution of the polymerization initiator used in Example 17 was added to the mixture in the flask. At this stage the pH of the aqueous reaction system was about 3. Soon after the addition of the polymerization initiator, the pH of the reaction system was adjusted to 7.5 by adding sodium hydroxide. After that, stirring of the reaction system was continued for 5 hr. Then the reacted slurry was filtered to separate the solid component, which was thorougly washed with water and dried at 700C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 105.4 g in dry state and contained 5.1% by weight of polymethyl methacrylate. In this case the grafting efficiency was 90%.

For comparison, this process was repeated generally similarly except that the adjustment of pH by the addition of sodium hydroxide was omitted. The polymer-coated graphite fluoride obtained in this case weighed 102.7 g in dry state and contained 2.6% by weight of polymethyl methacrylate, so that the grafting efficiency was 45%.

Example 22 As a pretreatment 1 10 g of the graphite fluoride (CF),, described in Example 1 was dispersed in a mixture of 200 ml of ethanol and 300 ml of water, followed by the addition of sodium hydroxide to adjust the pH of the mixture to about 10, and the resultant mixture was stirred for 30 min. After that, the graphite fluoride was recovered, washed with water and dried at 800C in vacuum.

Using the same apparatus as in the preceding examples, 250 ml of water, 200 ml of ethanol, 100 g of the alkali-treated graphite fluoride and 20 g of methyl methacrylate monomer were mixed by stirring, while the constant temperature bath was maintained at 650 C. Continuing the stirring, 50 ml of 6% aqueous solution of SO2 was added to the mixture in the flask. At this stage the pH of the aqueous reaction system was about 5. After that, stirring of the reaction system was continued for 4 hr. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum.

The polymer-coated graphite fluoride obtained by this process weighed 11 8.2 g in dry state and contained 15.4% by weight of polymethyl methacrylate. In this case the grafting efficiency was 91%.

Example 23 The polymer-coated graphite fluorides prepared in Examples 14, 1 5,1 7, 1 9, 20 and 21 by adjusting the pH of the polymerization reaction systems were individually subjected to the pressshaping operation described in Example 10 without the addition of any extra material. In every case it was easy to achieve the press-shaping, and the polymer-coated graphite fluoride particles were uniformly distributed in the press-shaped body. The press-shaped bodies were subjected to bending the strength test, of which the results are presented in the following Table 5. For comparison, the polymer-coated graphite fluorides prepared in the same Examples without adjusting the pH of the polymerization reaction systems were individually subjected to the same press-shaping operation.

Also, in these cases the polymer-coated graphite fluoride particles were uniformly distributed in every shaped-body. Table 5 contains the results of the bending strength test on the shaped bodies of these polymer-coated graphite fluorides.

Table 5

Polymer-coated by Polymer-coated adjusting pH l without adjusting pH Content of Bending Content of Bending Graphite grafted strength grafted strength fluoride polymer (wt%) (kg/cm2) polymer (wit%) (kg/cm2) Ex. 14 18.4 378 12.1 280 coated (CF)n (PMMA) Ex.15 22.2 390 15.5 318 coated (C2F),, (PMMA) Ex.17 15.3 319 8.6 203 coated (C2F)n (PMA) Ex.19 21.3 I 351 15.3 275 coated (CF)n (polyacrylo nitrile) Ex.20 15.4 233 9.9 219 coated (CF)n (polystyrene) Vex. 21 5.1 90 2.6 47 coated (CF),, (PMMA) Example 24 The polymer-coated graphite fluoride prepared in Example 21 by adjusting the pH of the polymerization reaction system was mixed in dry state with a powdered polymethyl methacrylate resin, phenolic resin, ABS resin or polyacetal resin each in the proportion as shown in the following Table 6, and every mixture was press-shaped into a solid cylindrical body under the same shaping condition as in Examples 10 and 23. In every case the press-shaping was easily achieved, and there was no difficulty in releasing the shaped body from the metal die. By microscopic observation it was confirmed that the polymer-coated graphite fluoride particles were uniformly distributed in every shaped body.The results of bending strength test on the press-shaped bodies are presented in Table 6.

Table 6

Resin added Content of to 10 g of Bending Graphite grafted graphite strength fluoride polymer (wt%) fluoride (kg/cm2) Example 21 5.1 PMMA 300 coated (CF),, (PMMA) 1.0 g ditto ditto PMMA 375 7.5 g ditto ditto phenolic 330 3.0g ditto ditto ABS 360 6.0g ditto ditto acetal 325 3.0g The following Examples 25-27 illustrate the preparation of polymer-coated graphite fluoride according to the invention by a semi-dry process characterized by an extremely small quantity of the liquid medium in the graft polymerization process.

Example 25 As a pretreatment, 500 9 of the graphite fluoride (CF),, described in Example 1 was dispersed in a mixture of 1 500 g of water and 1000 g of ethanol contained in a 5-liter beaker, followed by the addition of 10% aqueous solution of sodium hydroxide to adjust the pH of the mixture to 9 while continuing stirring of the mixture. As the pH lowered from 9 by reason of the consumption of the added sodium hydroxide in a neutralizing reaction, the sodium hydroxide solution was further added so as to raise the pH to 9. This procedure was repeated until the pH of the mixture became almost unchanged from 9, and after that stirring was further continued for 30 min. Then the slurry-like mixture was filtered to separate the graphite fluoride particles, which were washed with water and dried.About 500 9 of alkali-treated graphite fluoride (CF),, was obtained by this treatment.

A three-necked flask having a capacity of one liter was held in a constant temperature bath maintained at 650C, and 100 g of the alkali-treated graphite fluoride was put into the flask. Then 0.6 g of water and 0.4 g of ethanol were added to the graphite fluoride in the flask with forced stirring. Next, 10 ml of 6% sulfurous acid solution and 10 g of methyl methacrylate monomer were added to the mixture in the flask. After that, stirring of the resultant reaction system was continued for 4 hr to complete polymerization reaction. The product of the polymerization reaction was dried at 800C in vacuum for 6 hr.

The product of this process weighed 105.0 g in dry state and was confirmed to be polymercoated graphite fluoride containing 4.8% by weight of polymethyl methacrylate graft-bonded to the surfaces of the graphite fluoride particles. The grafting efficiency was calculated to be 50%.

The graft polymerization process of this example was repeated generally similarly except that the quantities of the sulfurous acid solution and methyl methacrylate monomer were reduced to 5 ml and to 5 g, respectively. The polymer-coated graphite fluoride obtained in this case weighed 102.3 g in dry state and contained 2.2% by weight of polymethyl methacrylate, so that the grafting efficiency was 46%.

Example 26 The alkali treatment of graphite fluoride (CF),, described in Example 25 was performed generally similarly except that an increased quantity of sodium hydroxide was used to thereby adjust the pH of the treatment system to 11.

Using 100 g of the thus treated graphite fluoride, the graft polymerization process of Example 25 was carried out generally similarly but by using 2 g of 2,2'-azobis-(2-amidinopropane)dihydrochloride instead of the sulfurous acid solution and by increasing the quantity of methyl methacrylate monomer to 30 g.

The polymer-coated graphite fluoride obtained by this process weighed 109.7 9 in dry state and contained 8.8% by weight of polymethyl methacrylate. The grafting efficiency was 32%.

The graft polymerization process of this example was again repeated generally similarly but by using 10 ml of the sulfurous acid solution as polymerization initiator and by using 10 g of acrylonitrile monomer instead of methyl methacrylate. The polymer-coated graphite fluoride obtained in this case weighed 104.4 g in dry state and contained 4.2% by weight of polyacrylonitrile, so that the grafting efficiency was 44%.

Example 27 A three-necked 3-liter flask was held in a constant temperature bath maintained at 400 C, and 500 g of graphite fluoride (C2F),, described in Example 2 was charged into the flask. Stirring the graphite fluoride, ammonia gas was blown into the flask for 30 min at a rate of 100 ml/min. After that the temperature of the bath was raised to 1 300C, and this temperature was maintained for 1 hr thereafter. The thus treated graphite fluoride was washed with water and dried.

Using 100 g of the ammonia-treated graphite fluoride, the graft polymerization process of Example 25 (using 10 ml of the sulfurous acid solution and 10 g of methyl methacrylate monomer) was carried out identically.

The polymer-coated graphite fluoride obtained by this process weighed 105.4 g in dry state and contained 5.1% by weight of polymethyl methacrylate. In this case the grafting efficiency was 54%.

Example 28 By using 100 9 of untreated graphite fluoride (CF),, described in Example 1 in place of the alkalitreated graphite fluoride used in Example 26, the graft polymerization process of Example 26 for polymerization of methyl methacrylate was carried out with no modification in other respects.

The polymer-coated graphite fluoride obtained in this case weighed 102.1 g in dry state and contained 2.1% by weight of polymethyl methacrylate, so that the grafting efficiency was 7%.

Example 29 By using 100 g of untreated graphite fluoride (C2F),, described in Example 2 in place of the ammonia-treated graphite fluoride used in Example 27, the graft polymerization process of Example 27 was carried out with no modification in other respects.

The polymer-coated graphite fluoride obtained in this case weighed 101.2 g in dry state and contained 1.2% by weight of polymethyl methacrylate. The grafting efficiency was 12%.

As mentioned hereinbefore, the graft polymerization coating method according to the invention is applicable not only to graphite fluoride but also to many other materials that are useful as solid lubricants. The following examples illustrate the application of the invention to typical solid lubricants.

Example 30 A three-necked one-liter flask was held in a constant temperature bath maintained at 600 C, and 250 ml of water, 200 ml of ethanol, 100 9 of powdered molybdenum disulfide and 12 9 of methyl acrylate monomer were mixed in the flask by stirring. Continuing the stirring, 50 ml of 4% aqueous solution of 2,2'-azobis-(2-amidinopropane)dihydrochloride was added to the mixture. At this stage the pH of the aqueous reaction system was about 2. Then the pH of the reaction system was adjusted to 8.5 by adding aqueous solution of sodium hydroxide. After that, stirring of the reaction system was continued for 4 hr to complete polymerization reaction.Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum.

The powdery product of this process weighed 111.6 9 in dry state and was confirmed to contain 10.4% by weight of polymethyl acrylate graft-bonded to the surfaces of molybdenum disulfide particles. In this case the grafting efficiency was 97%.

The process was repeated generally similarly except that the pH was adjusted to 7.0 by decreasing the quantity of sodium hydroxide used for the adjustment purpose. The polymer-coated molybdenum disulfide obtained in this case weighed 118.4 g in dry state and contained 1 5.5% by weight of polymethyl acrylate. The grafting efficiency was 92%.

The process of this example was again repeated generally similarly except that the adjustment of the pH was omitted. That is, the pH of the aqueous reaction system was left at about 2. The polymercoated molybdenum disulfide obtained in this case weighed 106.4 g in dry state and contained 6.0% by weight of polymethyl acrylate. The grafting efficiency was 53%.

Example 31 Using the same apparatus as in Example 30, 480 ml of water, 100 g of powdered graphite of natural occurrence and 20 g of methyl acrylate monomer were mixed by stirring. Continuing the stirring, 20 ml of 6% aqueous solution of sulfurous acid was added to the mixture in the flask. At this stage the pH of the aqueous reaction system was about 2. Then the pH of the reaction system was adjusted to 7.3 by adding aqueous solution of sodium hydroxide. After that, stirring of the reaction system was continued for 4 hr to complete polymerization reaction. Then the reacted slurry was filtered to separate the solid component, which was thoroughly washed with water and dried at 800C in vacuum.

The powdery product of this process weighed 11 9.2 g in dry state and was confirmed to contain 1 6.1% by weight of polymethyl acrylate graft-bonded to the surfaces of the graphite particles. In this case the grafting efficiency was 96%.

This process was repeated generally similarly except that the addition of sodium hydroxide for adjustment of the pH was omitted. The polymer-coated graphite obtained in this case weighed 111.8 9 in dry state and contained 10.6% by weight of polymethyl acrylate, so that the grafting efficiency was 59%.

Claims

1. A modified graphite fluoride comprising fine particles of graphite fluoride coated with a vinylic polymer which is bonding to the surfaces of said graphite fluoride particles by graft polymerization.

2. A modified graphite fluoride according to Claim 1, wherein the content of said polymer in the modified graphite fluoride is at least 0.5% by weight.

3. A modified graphite fluoride according to Claim 2, wherein the content of said polymer in the modified graphite fluoride is not larger than 50% by weight.

4. A modified graphite fluoride according to Claim 1,2 or 3, wherein said polymer is selected from polyacrylic acid, polymethacrylic acid, polyacrylates, polymethacrylates, polyacrylonitrile, poly-Nmethylolacrylamide, polyvinyl chloride, polyvinyl acetate, polystyrene, polyvinyl benzene, polyvinylidene fluoride and copolymers thereof.

5. A modified graphite fluoride according to Claim 4, wherein said polymer is selected from polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene and copolymer of styrene and acrylonitrile.

6. A modified graphite fluoride according to any one of Claims 1 to 5, wherein said graphite fluoride is selected from (CF),, (C2F),, and mixtures thereof.

7. A modified graphite fluoride according to any one of the preceding claims, wherein the graphite fluoride particles coated with said polymer are compacted so as to form a solid body.

8. A modified graphite fluoride according to Claim 7, wherein said solid body further comprises a synthetic resin compacted together with the modified graphite fluoride.

9. A modified graphite fluoride according to Claim 8, wherein the total weight of said synthetic resin and said polymer is not greater than the weight of the graphite fluoride in the solid body.

10. A modified graphite fluoride according to Claim 9, wherein said synthetic resin is selected from polymethyl methacrylate, phenolic resin, polyacetal resin and ABS resin.

11. A method of preparing a modified graphite fluoride according to Claim 1 ,the method comprising the steps of mixing graphite fluoride in the form of fine particles with at least one vinylic monomer capable of undergoing radical polymerization or radical copolymerization, the mixing being performed in the presence of water, and adding a polymerization initiator for said at least one vinylic monomer to the mixture obtained by the preceding step thereby allowing said at least one vinylic monomer to undergo polymerization or copolymerization and to bond to the surfaces of the graphite fluoride particles by graft polymerization.

12. A method according to Claim 11, wherein the pH of the polymerization reaction system after the addition of said initiator is adjusted to a value in the range from 5 to 9.

13. A method according to Claim 12, wherein the pH of said reaction system is adjusted by adding an alkali to said reaction system.

14. A method according to Claim 12, wherein the pH of said reaction system is adjusted by treating said graphite fluoride with an alkali prior to the step of mixing said graphite fluoride with said at least one vinylic monomer.

15. A method according to any one of Claims 11 to 14, wherein the mixing step is performed by dispersing said graphite fluoride and said at least one vinylic monomer in a mixture of water and an organic solvent soluble in water.

16. A method according to Claim 15, wherein said organic solvent is selected from alcohols, ketones, ethers and amines.

17. A method according to Claim 1 6, wherein said organic solvent is ethyl alcohol, the weight ratio of said water to said ethyl alcohol is in the range from 0.1:1 to 2.3:1.

18. A method according to Claim 1 6, wherein 1 to 100 parts by weight of said graphite fluoride and 0.1 to 100 parts by weight of said at least one vinylic monomer are dispersed in a mixture of 100 parts by weight of water and 1 to 100 parts by weight of said organic solvent.

19. A method according to any one of Claims 11 to 14, wherein the mixing step is performed by dispersing said graphite fluoride and said at least one vinylic monomer in a mixture of water and a surface-active agent.

20. A method according to Claim 1 9, wherein 1 to 100 parts by weight of said graphite fluoride and 0.1 to 100 parts by weight of said at least one vinylic monomer are dispersed in a mixture of 100 parts by weight of water and 1 to 50 parts by weight of said surface-active agent.

21. A method according to any one of Claims 11 to 14, wherein the mixing step is performed by wetting said graphite fluoride and said at least one vinylic monomer with a relatively small amount of water.

22. A method according to Claim 21, wherein said water is mixed with an organic solvent soluble in water.

23. A method according to any one of Claims 11 to 14, wherein 100 parts by weight of said graphite fluoride is mixed with 0.1 to 100 parts by weight of said at least one vinylic monomer in the presence of a mixture of 0.1 to 600 parts by weight of water and 0.1 to 300 parts by weight of an organic solvent soluble in water.

24. A method according to any one of Claims 11 to 14, wherein 100 parts by weight of said graphite fluoride is mixed with 0.1 to 100 parts by weight of said at least one vinylic monomer in the presence of a mixture of 0.1 to 600 parts by weight of water and 0.1 to 1 50 parts by weight of a surface-active agent.

25. A method according to Claim 20, 23 or 24, wherein the amount of said polymerization initiator is in the range from 0.01 to 20% by weight of said at least one vinylic monomer.

26. A method according to any one of Claims 11 to 25, wherein said at least one vinylic monomer is selected from acrylic acid, methacrylic acid, acrylates, methacrylates, acrylic esters, methacrylic esters, acrylonitrile, N-methylolacrylamide, vinyl chloride, vinyl acetate, styrene, divinyl benzene and vinylidene fluoride.

27. A method according to Claim 26, wherein said polymerization initiator is selected from sulfur dioxide, sulfurous acid, hydrogen sulfites, potassium persulfate, azobiscyanovaleric acid and 2,2'azobis-(2-amidinopropane)dihydrochloride.

28. A method according to any one of Claims 11 to 27, wherein said graphite fluoride is selected from (CF),, (C2F),, and mixtures thereof.

29. A method according to any one of Claims 11 to 28, wherein the polymerization reaction is performed at a temperature in the range from room temperature to 700 C.

30. A method of forming a solid body which comprises a modified graphite fluoride prepared by a method according to Claim 11, the forming method comprising the steps of mixing said modified graphite fluoride in powder form with a synthetic resin in powder form, and applying a pressure to the mixture of said modified graphite fluoride and said synthetic resin at an elevated temperature.

31. A method according to Claim 30, wherein the amount of said synthetic resin is such that the total weight of said synthetic resin and said polymer in said modified graphite fluoride is not greater than the weight of graphite fluoride in said modified graphite fluoride.

32. A method according to Claim 31, wherein said synthetic resin is selected from polymethyl methacrylate, phenolic resin, polyacetal resin and ABS resin.

33. A method according to Claim 30, 31 or 32, wherein said pressure is in the range from 150 to 450 kg/cm2, said elevated temperature being in the range from 100 to 2500C.

34. A method of preparing a modified graphite fluoride according to Claim 1, substantially as herein described in any one of Examples 1 to 9, Examples 14 to 22 and Examples 25 to 29.

35. A method of forming a solid body comprising a modified graphite fluoride according to Claim 1, substantially as herein described in any one of Examples 11 to 13 and Examples 23 and 24.