This invention relates to self-lubricating materials.

If it is desired to produce, for example, a bearing from oil-filled plastics, then it is presently necessary to machine the bearing to the desired dimensions from a block of pre-cast material. Heretofore, it has not been practicable to produce the component in its finished form by direct moulding, casting or extrusion of the material. This greatly increases the cost of producing such items.

It is an object of the present invention to obviate or mitigate this problem.

According to one aspect of the present invention, there is provided a method of producing a self-lubricating material, comprising absorbing a lubricant (such as oil or wax) into a microporous carrier, and incorporating the lubricant-bearing carrier into a base material. Advantageously, the resultant mixture is used to mould, cast or extrude a desired component directly in its finished form.

According to a second aspect of the present invention, there is provided a method of producing a self-lubricating article such as a bearing or gear, comprising absorbing a lubricant (such as oil or wax) into a microporous carrier, mixing the carrier with a base material such as metal or plastics, and moulding, casting or extruding the bearing or gear in its finished form directly from the resultant mixture.

Preferably, the microporous carrier has a structure comprising a plurality of substantially spherical microcells distributed substantially uniformly through the structure, adjacent cells being interconnected by pores smaller in diameter than the microcells. The microcells conveniently have an average diameter of between 0.5 and 100 microns.

Desirably, the microporous carrier is a substance as defined in the claims of UK Patent No. 1576228.

The microporous carrier can be made of plastics material, and is preferably a polymer or copolymer of an ethylenically unsaturated monomer, a condensation polymer, a polyphenylene oxide or a blend thereof. More particularly, the plastics material can be polypropylene, polyethylene or a polyamide (e.g. nylon). Alternatively, the microporous carrier can be made of a metal or metal

alloy, such as aluminium or aluminium alloy.

Advantageously, the microporous carrier is made of the same material as the base material .

Desirably, the microporous carrier has a density within the approximate range of 0.9 to 0.945 gm/cc ³ , a void volume of substantially 75%, a cell size within the approximate range of 0.5 to 6.0 microns, and/or a pore size within the approximate range of 0.05 to 5.0 microns.

The carrier incorporating the lubricant can be mixed with the base material in solid form, with the resultant mixture then being subjected to a melting operation. Alternatively, the carrier incorporating the lubricant can be incorporated into the base material when the latter is in a molten state.

The invention will now be further described, by way of example only.

In order to produce a self-lubricating material, a lubricant such as oil or wax is absorbed into a microporous carrier. Particles of the lubricant-bearing carrier are then mixed with granules of a base material (such as plastics), for example using one part of carrier to ten parts of base material, and the resultant mixture is

employed as a raw material for e.g. a moulding, casting or extrusion process. In this way, a high percentage of lubricant is held within the material during moulding, casting or extrusion, and minimal loss of lubricant occurs: this enables an article or component to be produced directly in its final shape and with the desired dimensions. Such direct forming of components is extremely difficult with existing forms of self-lubricating materials, particularly self-lubricating plastics, which must usually be cast and then machined to the desired dimensions. Accordingly, components can be produced quickly and relatively cheaply, with no need for a final machining operation.

Because of the microporous nature of the carrier, the lubricant is dispersed in minute pockets throughout the finished component. Accordingly, as the surface of the component wears, fresh pockets are exposed thereby maintaining the lubricating function in an effective manner.

The above-described process can be utilised in any field where self-lubrication is required, a prime example being moulded plastics bearings or gears. It is also feasible that, for example, a wax could be incorporated into the carrier with the resultant material being used to form a surface-contacting part of a ski to provide "lifetime"

waxing and/or to form the surface of an artificial ski slope.

A suitable form of carrier for use in the above-described process is that described and claimed in UK patent no. 1576228 and sold by Azko Chemicals under the trade name ACCUREL. This substance is capable of absorbing approximately two-thirds of its own weight of the lubricant.

Different forms of microporous carriers can be used according to the nature of the base material, and carriers having the following properties are preferred, respectively, where the base material is a polyamide plastics (e.g. nylon), polyethylene or polypropylene:

75 3 mm 1.0-6.0 0.1-0.5

75 400- 0.5-3.0 0.05-0.3 1000 microns

Polyethylene

Density Void Particle Cell Pore (gm/cc ³ ) Volume Size Size Size (Microns) (Microns)

0.915 75 < 200 1.0-5.0 0.1-0.5 microns 200- 400 microns

0.915 75 3 mm 1.0-5.0 0.1-0.5

0.945 75 3 mm 1.0-5.0 0.1-0.5

Polypropylene - 8 -

0.902 75 200 0.5-5.0 1.0-5.0 microns 200- 400 microns 400- 1000 microns >1000 microns

0.906 75 3 mm 1.0-5.0 0.1-1.0