GB1069089A - Solid self-lubricating articles and a process for manufacturing them - Google Patents

Abstract

A P.T.F.E. wax having a molecular weight in the range 700 to 100,000 is made by heating tetrafluoroethylene with a telogen in the presence or absence of a radical initiator. The telogen may be carbon tetrachloride, chloroform, ethylenetetrachloride, trichlorotrifluoroethane, dichlorodifluoromethane, trichlorofluoromethane, tetrachlorodichloroethane used singly or as a mixture of two or more thereof. Alternatively, the telogen may be a mixture of any of said substances and one or more aliphatic hydrocarbons and their derivatives having a carbon-hydrogen bond, e.g. isobutane, methylcyclohexane, dimethyl ether, tetrahydrofuran, ethylene dioxide, dioxane, trimethylamine, triethylamine, methanol, isopropanol, cyclohexanol, ethyl mercaptane, dimethyl disulphide, acetaldehyde, propionaldehyde, acetone, methyl ethyl ketone, cyclohexanone, ethyl acetate, ethyl aceto-acetate, isolactic acid, dimethyl sulphonamide, diethylsulphide, dimethyl formamide, dimethyl dichlorosilane and polysiloxane. The radical initiator may be benzoyl peroxide, diteriary butyl peroxide, azobisisobutylonitrile, diisopropyl peroxydicarbonate, tertiary butyl perbenzonate, in the range of 0.5 to 30% by weight. The P.T.F.E. wax may also be made by pyrolyzing high molecular weight P.T.F.E. resin at a temperature of about 350 DEG C. or more in the presence or absence of an alkaline metal salt, e.g. potassium nitrate. Alternatively, the P.T.F.E wax may be made by subjecting liquid tetrafluoroethylene to ionizing radiation in the presence of at least one of the fluoroalkanes referred to above for use as a telogen. Telomerization is thus effected at normal atmospheric temperature and e.g. normal atmospheric pressure. The said fluoroalkane may be in the proportion of 1 to 20 mols. per mol. of tetrafluoroethylene. The ionizing radiation may be a -rays, b -rays, g -rays, X-rays, electrons or neutrons at a rate of 102 to 108 r./hr. within a range of total radiation of 103 r. to 109 r. Additionally, the P.T.F.E. wax may be made by supplying to a reaction tower a solution comprising a radical initiator dissolved in a telogen in conjunction with excess tetrafluoroethylene gas at a pressure of 1 to 15 kg./cm2. A mixture comprising telomers, formed, excess and unreacted tetrafluoroethylene and excess telogen is removed from the top of the tower to isolate by condensation the formed telomers dispersed in excess telogen from unreacted tetrafluoroethylene. The telogen and radical initiator are as specified above. In a first example of preparing a P.T.F.E. wax, a mixture of P.T.F.E. resin having a molecular weight 2 x 106 and potassium nitrate is pyrolized at 450 DEG C. for 20 minutes to form P.T.F.E. wax having a molecular weight of 1800 and melting point of 270 DEG C. In a second example, P.T.F.E. wax having a molecular weight of 20,000 and a melting point of 320 DEG C. is prepared by telomerizing tetrafluoroethylene with carbon tetrachloride.