The production process and principle of polyurethane foam

Foam is a kind of polyurethane foam, which belongs to soft polyurethane foam. Because of the porous honeycomb structure, so it has excellent softness, elasticity, water absorption, water resistance characteristics, is widely used in sofa, mattress, clothing, flexible packaging and other industries.

1. Main raw materials

1.1 Polyether polyols

Polyether propylene glycol and polyether propylene glycol are mostly used in foam, which have less functional degree (2-3), low hydroxyl value and large molecular weight. The molecular formula is:

CH3-CHO(C3H6O)m(C2H4O)nHCH2O(C3H6O)m(C2H4O)nH

1.2 Organic isocyanates

The most commonly used is alpha-diisocyanate, or TDI, which comes in two isoforms, 2, 4-TDI, and 2, 6-TDI. In the production of foam cotton, 2, 4-TDI accounted for 80% and 2, 6-TDI accounted for 20%

1.3 Water in the production of foam, water is indispensable, water and TDI reaction to release CO[sub]2[/sub] gas, at the same time plays the role of chain growth.

1.4 catalyst

The catalysts that promote the chain growth of polyether polyol and isocyanic acid are stannous octanoate and dibutyltin. Promote the cross-linking reaction and can promote the reaction between isocyanate and water to release CO[SUB]2[/sub] gas catalysts triethanolamine, triethylene diamine, triethylamine and so on.

1.5 External foaming agent

Commonly used are low-boiling fluorohydrocarbon compounds, such as fluorotrichloromethane (F-11). Because it is not environmentally friendly, cyclopentene is generally used instead of F-11, or methylene chloride, which works well. If it is not the production of super light density foam, you can also adjust the proportion of main raw materials, do not use external blowing agent.

1.6 Foam stabilizer (homogenizer) Silicone foam stabilizer is commonly used, and silicon-carbon bond Si-C copolymer is mainly used at present, with the dosage of 0.5%-5%.

2, the synthesis principle of foam

In the synthesis process of foam cotton, there are mainly chain growth reaction, foaming and cross-linking processes, which are related to the molecular structure, functional degree and molecular weight of raw materials.

2.1 Chain extension reaction

Isocyanate and difunctional polyether polyol chain expansion reaction, because the reaction isocyanate excess of about 5%, so the final product of chain expansion is isocyanate group, so repeated to promote rapid chain growth.

2.2 Foaming reaction is accompanied by chain growth

In the process of foam production, the foaming gas mainly comes from the reaction of TDI with water to generate a large amount of CO[sub]2[/sub] gas, and the newly formed amine reacts with isocyanate to generate urea bond compound, so repeated with chain growth.

2.3 Crosslinking reaction

The cross-linking reaction is very important for the preparation of sponge. If it occurs too early or too late, the quality of foam will decrease or even be scrapped.

2.3.1 The reaction of polyfunctional compound cross-linked polyether polyol and isocyanate directly affects the foam density. The molecular weight of cross-linking point is 2000-20000. The smaller the molecular weight, the higher the cross-linking density, the higher the hardness of foam, and the relative decrease of softness and elasticity.

2.3.2 Water reacts with isocyanate to form urea bond compound, and further reacts with isocyanate to form three-way structure biurea cross-linked compound.

2.3.3 Urea-formate cross-linking

The hydrogen on the nitrogen atom of the carbamate group reacts with isocyanate to form a three-way cross-linked urea-formate.

3. Production technology and process

At present, most of the foam production adopts one-step box foaming method, all kinds of raw materials in high speed stirring, quickly added to the forming box, in the forming box to complete chain growth, foaming, cross-linking, curing and other reactions, so as to complete the foam production. The advantages of the process are short process flow, low material viscosity, easy control, energy saving, small equipment investment, wide range of applicable density.