This invention relates to moulding of materials such as plastics and metals.

In my patent application no. 8911557.0, there is disclosed a self-lubricating material capable of use in a wide range of products from bearings and gears to artificial ski slopes.

In the manufacture of articles from plastics by, for example, injection or compression moulding or in the diecasting of metals, it has hitherto been the practice to spray the mould with a release agent prior to moulding, to prevent the plastic or metal material from sticking to the mould. Applying the release agent requires an extra m -.ufacturing stage which increases the moulding cycle time and also rec ires spray equipment, adding to basic capital costs. The use of certain sprays may also be environmentally hazardous.

It is an object of the present invention to provide a method of p ^r oducing materials capable of use in moulding without such spraying steps .

According to the invention there is provided a me-hod cf producing a self-releasing material for use in moulding, the method comprising absorbing a mould-release agent into a

microporous carrier and incorporating the carrier into a base material, preferably when the latter is in a molten state.

The base material may be a plastics material to be injection or compression moulded or may be a metal intended to be diecast.

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

Desirably, the 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 base material can be a plastics, such as polypropylene, polyethylene or a polyamide (e.g. nylon) , or a metal such as aluminium or aluminium alloy.

Desirably, the carrier incorporating the release agent is mixed with the base material and the resulting mixture is then subjected to a melting operation. The mixture may then be moulded or cast without preliminary spraying of the mould or dies with a release agent.

The release agent may be a lubricant or a non-oil based mould release agent.

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

In order to produce a self-releasing moulding material, a microporous carrier is caused to absorb a non-oil based mould release agent of conventional' type or any form of lubricant which will have a mould releasing action. Particles of the treated carrier are then mixed either with a molten plastics or metal or, particularly in the case of a plastics material, are mixed with granules of a base plastics material in a finely divided state.

Since the release agent is only required to act at the surfaces of the moulded article to release it from the mould, and since only one release operation is necessary, a very small quantity of mould release agent is required. Since a highly absorbent carrier material is available, capable of absorbing approximately two-thirds of its own weight of release agent, only a very small quantity of carrier material needs to be added to provide adequate release of the finished moulded article. The proportion of carrier to base material may be of the order of 1%.

Because of the microporous nature of the carrier, the release agent is dispersed in minute pockets throughout the finished component. Because the concentration is very low, this should have little effect on the properties of the product

except at the surface where the pockets of release agent make intimate contact with the mould and provide a self-releasing function.

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 tradename ACCUREL. This substance is capable of absorbing approximately two-thirds of its own weight of the release agent.

According to the nature of the base material, different forms of microporous carrier may be used, where the base material is a polyamide plastics, polyethylene or polypropylene for example.

The above-described method has the advantages that no modifications are needed to the mould, and the correct percentage of lubricant can readily be obtained by adding the oil-bearing microporous carrier in appropriate quantities as a masterbatch to the base material.