Method of injection molding ultra-high molecular weight polyethylene sliding members

A method for producing a sliding member comprising a polyethylene having a viscosity-average molecular weight of 500,000 to 6,000,000 inclusive, having a low coefficient of friction and excelling in both its own wear resistance and its property of preventing the abrasion of an associated member by injection molding, which comprises the steps of:

• preparing a composite material by dry-blending:
• (i) an ultra-high molecular weight polyethylene resin powder having a viscosity-average molecular weight of 1,000,000 to 6,000,000 inclusive,
• (ii) a high molecular weight polyethylene resin powder having a viscosity-average molecular weight of 300,000 to 1,000,000 inclusive, and
• (iii) an additive comprising an organic or inorganic material at a temperature up to the melting point of said resin powders (i) and (ii), in the presence of stirring acceleration, thereby depositing said additive onto only the surface of said polyethylene resin powder particles to obtain the composite material;
• introducing said composite material into an injection cylinder in a non-oxidizing atmosphere in which said composite material is melted within a short time by fixing the compression ratio of a screw of said injection cylinder at 1.3 to 2.0 and regulating the length to diameter ratio of the screw to from 15 to 20;
• vacuumizing a mold cavity portion;
• injecting the melted composite material into said mold cavity prior to the initiation of thermal crosslinking;
• and
• compressing the injected melted composite material by reducing a space of said cavity prior to solidifying said composite material, thereby obtaining said sliding member.