Polyurethane is a polymer made from chain extender or crosslinking agent, such as the polyisocyanate, polyether polyol or polyester polyol or small molecular polyol, polyamine or water and so on. By changing the type and composition of raw materials, the shape and properties of products can be greatly changed, and the final products from soft to hard can be obtained.
Exhaust reaction is divided into two stepsFirst, water reacts with isocyanates to form carbamates, which quickly decompose into amines and carbon dioxide. Carbon dioxide is injected into the crosslinks to foam them, while amines continue to react with other isocyanates to form ureas.
The two-component liquid reaction molding process of polyurethane is essentially two equilibrium forms of gelation reaction and foaming reaction under industrial production conditions, which requires accurate mixing and flow rate. In addition, there is a heat balance condition that affects and restricts each other in order to complete the two equilibrium formulas. If too much heat or poor heat dissipation occurs, it will cause excessive foaming and insufficient gel. On the contrary, the foaming is not enough and the gel is excessive. At this time, besides controlling and adjusting the ratio of two-component raw materials and mould temperature, attention should also be paid to the influence of ambient temperature on it. Especially in the hottest and coldest seasons, it is difficult to operate. Therefore, in the production process of polyurethane, in addition to temperature, flow rate, ratio, pressure and other equipment which can be controlled by some automatic control, people's operating experience is also an indispensable condition.
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