Thick moulding compound

Carefully selected x-diketones allow an excellent efficiency in the near U V-visible region for the photopolymerization of clear thick moulded objects [160], Excited-state properties of various compounds have been described in Ref. [161],... 

In recent years rotational casting methods have made the slush moulding process virtually obsolete. In these processes an amount of material equal to the weight of the finished product is poured into a mould. The mould is then closed and rotated slowly about two axes so that the paste flows easily over the cavity walls in an oven at about 200-250°C. When the compound has gelled, the moulds are cooled and the moulding removed. Compared with the slush moulding process there is no wastage of material, little flash, and more even wall thickness. Completely enclosed hollow articles such as playballs are most conveniently made. 

The initial use was as a blow moulded vessel for vegetable oil candles. However, because of its biodegradability it is of interest for applications where paper and plastics materials are used together and which can, after use, be sent into a standard paper recycling process. Instances include blister packaging (the compound is transparent up to 3 mm in thickness), envelopes with transparent windows and clothes point-of-sale packaging. 

Additionally, plastisol ( paste ) type PVC compounds are in the form of a thick paste that can be applied by techniques such as coating, dipping, or rotational moulding. 

Tread-type rubber compound extruded in a variety of thicknesses and widths for use in tyre retreading. The standard section is in the shape of a regular trapezium, but variations are made to suit particular types of tyre and different makes of moulding equipment. 

A former having roughly the shape of the article to be moulded is immersed in a suitable liquid compound that forms a deposit onto the former, which is possibly heated to ease the increase in thickness of the deposit. The former can be first sheathed with a knitted fabric to reinforce the dipped polymer. This process is used in special cases ... 

The cure time will vary according to the compound in use, the rubber sectional thickness, and the moulding conditions. The optimum value should be determined by the trials planned in step 6.3.4. For guidance see Table 6.2. The overall cure time will depend on the temperature of the injected rubber. The hotter that this can be sustained without incurring scorch penalties, the more even will be the crosslink density across the rubber section. The optimum value that is often quoted for crosslink density is 90%. This value was determined from a 2 mm thick sheet tested for tensile and related properties. 

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