Polytek's PT Flex is a range of fast-curing urethane rubbers available in different softnesses. They are for use in prototyping and model making and can be pigmented, rotocast (swilled) or cast solid to make a variety of objects with a fast turnover.
PT Flex is made in various softnesses depending on requirements - 20, 50, 60, 70 and 85 Shore A. Both parts are very fluid even though they get progressively less viscous as the firmness increases - for example PT Flex 20 has a viscosity of 520cP (similar to olive oil) up to the PT Flex 85 which has a viscosity of 1600 cP (similar to motor oil - still pretty fluid). All have an approximate working time/pot life of 5 minutes, although this will reduce in warmer temperatures. It can be demoulded after approximately one hour, although full strength will take several days.
Part A is a translucent yellow colour, and Part B is a much darker amber. The mixture will be a semi translucent dark amber colour which remains once cured. It can be intrinsically coloured using urethane pigments during mixing. To maximise working time, it is a good idea to measure out the required amount of part A and add & mix in your pigment to that, before then adding the same amount of part B.
It is measured in equal amounts by weight for accuracy, and it is advised that you always shake containers before dispensing to ensure a good mix. Urethanes are sensitive to moisture, so it is advisable to squeeze excess air out of containers before closing the lid or using PolyPurge, a heavier-than-air-gas in an aerosol spray can which will push out any air/moisture in an opened container and extend the life of partially used components.
Because of this fast-acting material, it is advised you have everything ready before you begin, to maximise your working time. If it is warm where you are working, it may be a good idea to keep the components chilled for a few hours before needed to buy some extra working time.
Once mixed, it will begin to thicken before setting, so pay attention to the viscosity. Ensure you attend to any detailed areas first to get the maximum quality of reproduction. For larger items, it may be advisable to use more than one mixture, as subsequent layers will bond to the previous if applied within a short time.
Once cured, the material boasts a high tear strength.
When using any products, materials or equipment, you should familiarise yourself with them and take appropriate health and safety measures to protect yourself and others around you from harm. Obtain and consult the relevant MSDS (Material Safety Data Sheet) from your supplier.
It is advisable to wear disposable protective gloves, appropriate respirator and clothing when working with this material. Take care to work in a ventilated or extracted workspace to avoid breathing in fumes.