The chemical principles of core foams can be divided in […]
The chemical principles of core foams can be divided into two categories:
Chemical blowing agents are used which liberate gases when heated. Commonly used chemical blowing agents, such as azodicarbonamide, azobisisobutyronitrile, N,N'-dinitrosopentamethylenetetramine, sodium hydrogencarbonate and the like. Many thermoplastics can be made into foams by this method. For example, PVC foam shoes are made of resin, plasticizer, foaming agent and other additives into the injection molding machine. The foaming agent is decomposed in the barrel and the material is foamed in the mold. . The foamed artificial leather is mixed with a foaming agent into a polyvinyl chloride paste, which is scraped or calendered on the fabric, continuously passed through a tunnel heating furnace, and the material is plasticized and melted, the foaming agent is decomposed and foamed, cooled and surface-finished, that is, Made of foam artificial leather. The rigid polyvinyl chloride low foaming sheet, pipe or profile is formed by extrusion. The foaming agent is decomposed in the barrel. When the material leaves the machine head, the pressure drops to normal pressure, and the dissolved gas expands and foams. The foaming process is properly matched with the cooling and setting process to obtain a structural foam article.
A typical example is a by-product gas in a polymerization process, which is a polyurethane foam. When an isocyanate and a polyester or a polyether are subjected to a polycondensation reaction, a part of the isocyanate reacts with water, a hydroxyl group or a carboxyl group to form carbon dioxide. As long as the gas evolution rate and the polycondensation reaction rate are properly adjusted, it is possible to produce a highly foamed product in which the cells are very uniform. There are two types of polyurethane foam, soft opening type sponge, widely used as a seat cushion, sofa cushion and sound absorption, filter materials, etc.; hard closed hole type is ideal for insulation, insulation, shock absorption And floating materials.