Di-isocyanides are chemicals which are normally fluid at room temperature and which forms polyurethanes at reactions with hydroxyl chemicals as for instance polyols. The most common types are TDI and MDI.
Polyols are fluid, oil-like substances which chemically seen can be polyester- or polyether-based, which influence on the properties of the end product. Polyols can be added a number of small quantity aids like catalysts, blowing agents and substances, which influence on the cytogenesis.
The chemical structure of the polyols do have a high influence on the properties of the end product that is stiffness, elasticity, density and the skin formation just like the additives have.
ADDITIVES, HARDENERS AND OTHER AIDS
Under the production, you can add additives in order to control the reaction speed, foam stability, cell structure, and density, and to give the end product specific use- and function properties. As an example, you can mention hardeners like diols, diamines, alkanolamines that can be added both common PU-systems as PU-prepolymers to control the hardening process.
For the production of cellular polyurethanes a combination of chemically- and physically blowing agents are used.
Hydrocarbons, especially pentane-isomers, are used by the production of stiff polyurethane foam, while fluid carbon dioxide is used at the production of flexible polyurethane foam.
Rules and handling
Only the chemicals approved from the authorities can be used at the production of polyurethane products. Like this, it is for instance not allowed to use CFC's or HCFC's as blowing agents. The production, transport, and other handling of chemicals are regulated in the persisting laws and regulations.
Production - konventional methods
The principle of the production is that the liquid components are mixed and react under the formation of the polyurethane material. The mixture and dosing takes place industrially using mechanically mixing- and dosing equipment, at so-called low- or high-pressure methods.
At the productions of elastomers, glues and sealants, prepolymers are often used, which means that isocyanide and polyol pre-react. After that, the other chemicals are added and the end of the hardening takes place.
Thermoplastic polyurethane is produced by the same processes as at the production of thermoplastic, which is using injection moulding, extrusion or blow moulding.
COMMON PRODUCTION METHODS
The most common production methods:
- Block moulding
- RIM reaction moulding (Reaction Injection Moulding)
- RRIM reaction moulding with fiber interference
(Reinforced Reaction Injection Moulding)
- Low- and high pressure moulding in open forms
- Injection Moulding, extrusion and blow moulding (for TPE-PU)