The production process of sponges and the introduction of raw materials

The production process of sponges and the introduction of raw materials
Sponge is a kind of polyurethane foam, belongs to the soft polyurethane foam. Because of the porous honeycomb structure, so has excellent softness, elasticity, water absorption, water resistance characteristics, is widely used in sofas, mattresses, clothing, soft packaging and other industries.

I. Main raw materials

1.1 Polyether polyol sponge mostly uses polyether propylene glycol, polyether propylene glycol, which has less functional degree (2-3), low hydroxyl value and large molecular weight. Molecular formula is

1.2 Organic isocyanate The most commonly used is methyl dumb diisocyanate, referred to as TDI, there are two isomers, namely 2,4-TDI, 2,6-TDI. in the production of sponges 2,4 -TDI accounted for 80%, 2,6-TDI accounted for 20% 1.3 Water in the production of sponges, water is indispensable, water and TDI reaction to release CO2 gas, while playing a chain growth role.

1.4 Catalysts The catalysts that promote the reaction between polyether polyol and isocyanic acid to make chain growth are stannous octanoate and dibutyltin. Catalysts that promote the cross-linking reaction and can facilitate the reaction between isocyanate and water to release CO2 gas include triethanolamine, triethylenediamine, triethylamine, etc.

1.5 Topical foaming agents are commonly low boiling point fluorocarbon compounds, such as monofluorotrichloromethane (F-11). As it is not environmentally friendly, cyclopentane is generally used instead of F-11, or methylene chloride, with good results. If the sponge is not produced in a very light density, the ratio of the main raw materials can be adjusted appropriately without the use of external blowing agents.

1.6 Foam stabiliser (levelling agent) commonly used silicone foam stabiliser, currently mainly with silicon – carbon bond Si-C copolymer, the amount of 0.5% – 5%.

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Second, the synthesis principle of sponge

The sponge synthesis process, mainly chain growth reaction, foaming and cross-linking processes, these reactions and the raw material molecular structure, functional degree, molecular weight and other related.

2.1 Chain expansion reaction isocyanate and difunctional polyether polyol chain expansion reaction, due to the reaction of isocyanic acid excess of about 5%, so the final product of chain expansion is isocyanate group, so repeatedly promote the rapid growth of the chain.

In the process of producing sponges, the foaming gas mainly comes from the reaction between TDI and water, generating a large amount of CO2 gas, while the newly generated amine reacts with the isocyanate to produce a urea-bonded compound. 

2.3 Cross-linking reactions Cross-linking reactions are very important for the preparation of sponges and can lead to a reduction in quality or even scrap of the sponge if they occur too early or too late.

2.3.1 Cross-linking of polyfunctional compounds The reaction between polyether polyol and isocyanate directly affects the density of the sponge, the molecular weight of the cross-linking point is 2000-20000, the smaller the molecular weight, the higher the cross-linking density, the higher the hardness of the foam, the softness and elasticity are relatively lower.

2.3.2 Diurea crosslinking Water reacts with isocyanate to form a urea-bonded compound, which further reacts with isocyanate to form a three-way structured diurea crosslinking compound.

2.3.3 Ureidoformate crosslinking Hydrogen on the nitrogen atom of the carbamate group reacts with the isocyanate to form a three-way crosslinked structure of ureidoformate.

III. Production process and flow

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

3.1 The process is divided into two components: A component, polyether polyol, water, amine catalyst, silicone oil, stirring and mixing 20S. B component, TDI, flame retardant, organic tin, stirring 10S. A, B two components mixed high-speed stirring 10S, quickly pour into the forming box, the mould white time 6-8S, foaming time of about 1min. Maturing 2H, 24H can be cut into the required size. Sponge production technology