Introduction of Self-skinning Products
• Self-skinning foam, also known as integral skin molding foam, English as "Selfskinning foam" or "Integral skin foam" (ISF for short), it does not use other plastics as surface material, relying on foaming components in foam molding At the same time, the surface material and the foam core material are formed at one time, that is, the polyurethane component is formed into a foam plastic product with a solid skin at one time by a special process. Since the self-skin foam has a high-strength outer layer, the overall physical and mechanical properties of its products greatly exceed those of ordinary polyurethane foams of the same density. On the contrary, under the premise of requiring the same physical properties, only lower density self-skinning products are required. In this way, under the premise of quality assurance, the purpose of saving dosage and reducing product cost is achieved. Therefore, self-skin foam plastic products are widely used in automobile steering wheels, armrests, headrests, bicycle saddles, motorcycle saddles, armrests and headrests of easy chairs, door handles, spoilers and bumpers.
• Self-skin foam (ISF) synthesized by polymer polyol (POP), because the molecular weight of the parent polyether PPG of synthetic polymer polyol POP is between 3000 and 6000, and the grafting amount is less than 40%. For self-skin foam, other properties are not significantly improved except for increasing the hardness, and the storage stability of the combination material is reduced, so POP is rarely used in self-skin foam ISF products. High grafted POP can improve the open porosity and mechanical properties of the skin of ISF products, and has good miscibility with low hydroxyl value, high molecular weight and high activity polyethers. These characteristics are useful for improving the yield of ISF products and reducing ISF product density, reducing production costs and improving market competitiveness are of great significance. Therefore, in recent years, high-grafted POP has been widely used in ISF products abroad.
• Approaches to be taken in the experiment
• Using manual foaming, basic foaming data was obtained in a small steel mold of 10 cm × 125px × 5 cm. The product mold adopts the sample aluminum material mold
• Raw materials for experiments
Polyether TEP 330N, POP 34/28, crosslinking agent, EG; isocyanate 5005,; catalyst, A33, DMEA,; 141B blowing agent; silicone oil, a stirrer; 10 cm × 5 cm × 5 cm small steel mold one piece.
Reaction Mechanism
The self-skin foam belongs to the solvent foaming system, and its chemical reaction system is relatively simple, and the following two reactions generally occur:
The skin and core layer of self-skin polyurethane foam are produced simultaneously in one molding process, that is, the skin and core layer are made of the same material. A strong outer skin is produced as a result of physical action. A reaction mixture consisting of a polyol component and an isocyanate component, as the added 141B blowing agent forms cells due to the exothermic reaction. The cells are filled with 141B steam. If it hits the low temperature mold wall, the 141B steam is dissolved in the polyurethane due to the heat being discharged, and the cells are ruptured. until the heat output is balanced.
Auxiliary impact size
• Chain extenders and crosslinkers
Chain extenders and crosslinkers react with isocyanate to form rigid segments, which play a very important role in the formability, productivity and mechanical properties of ISF products. Increasing the rigid segment content can improve rigidity, heat resistance and dimensional stability. Experiments show that the chain extender of POP system adopts dihydric alcohol, such as ethylene glycol, diethylene glycol, 1, 4-butanediol, etc.; the crosslinking agent adopts trihydric alcohol or copolymerization of trihydric alcohol and ethylene oxide thing. This is the same as the chain extender and crosslinker for a single polyether system, but at a slightly lower level.
Auxiliary influence
• Catalyst
• Catalyst is one of the most important additives in the foaming process of polyurethane self-skin foam. The catalyst must ensure that the foaming reaction and the gelling reaction in the foaming process reach a dynamic equilibrium, otherwise, collapse or shrinkage of the foam will occur. The catalyst suitable for the self-skinning system can be prepared by compounding a strong basic tertiary amine compound (such as triethylenediamine) with a strong catalytic effect on the foaming reaction and a strong catalytic effect on the gel reaction. .
Impact of POP
The viscosity of high grafted POP is larger than that of ordinary polyether. With the increase of POP content, the viscosity of the combined polyether increases, and the mold filling property gradually deteriorates. However, the content of styrene-acrylonitrile grafts, which is beneficial to the opening of the foam, increases, and the opening of the foam becomes better.
The addition of POP makes the early reaction speed of the combined polyether and isocyanate basically unaffected, but it speeds up the late reaction speed. In this way, the mold filling property of the combined polyether is not affected, the later curing time is shortened, the film release speed is accelerated, and the production efficiency is improved.
