FLEXIBLE POLYURETHANE SLABSTOCK FOAM  (FPSF)

FPSF is a cellular polymeric material, often referred to as foam rubber or foam plastic which is produced by the chemical reaction between a polyol and a diisocyanate, together with other ingredients, to yield an open-cell structure material which is best suited to cushioning applications.

Figure 1. One Shot System

Flexible PU foam making can be carried out on  small or large scale equipment, ranging from cup or bench scale, up to large high-throughput machines.

The most frequently used methods are :

• Bench foaming where the quantities produced per batch would be between 0.2 to 5kg.
• Commercial box foaming for quantities between  5 and 100kg.
• Continuous slabstock machine foaming using raw material throughputs of 100 to 300kg/min.
• Foam moulding.

Almost all modern slab-stock foam machines are based upon the One-Shot system (Figure 1), a process of combining components and dispensing them to a mixing head where they are mixed and dispensed.

              Bench foaming

This is the method which is used mainly in laboratory work for testing raw                                             materials and developing new formulations.

The chemicals are conditioned to the correct temperature and accurately weighed into a suitable mixing vessel according to an established procedure, after which they are mixed together  for a prescribed time before being poured into a suitable container, like a plastic lined cardboard box.

TDI is usually the last component to be added to the mix, and the foaming reaction will not start until the TDI has been added. The whole process, from mixing to full expansion and polymerisation, takes about 1 to 3 minutes.

Continuous Machine Foaming

Continuous foam production is by far the most popular and efficient method for the manufacture of FPSF and is practised in one of its many forms by all the world's major foamers.

Although the degree of sophistication built into these types of machines can vary from simple manually controlled to highly computerised and automated, the basic principles outlined below apply to all continuous machines.

The raw materials are stored in suitably sized tanks or containers and are conditioned to the required temperature to achieve optimum control over the process.

Commercial Box Foaming

This process is quite similar to the laboratory  procedure, except that the scale is much larger. Also the process can be  partly automated to minimise manual handling of the raw materials.

The moulds are much larger, up to 2 X 2  metres , and 1 metre high, and are usually on a wheeled carriage to facilitate their transfer from the mixing area to a curing room. This method is generally regarded as being a back-yard operation, and is not practised by any of  the Dunlop foaming operations.