Polyurethane products can be roughly divided into foam, elastomer, and polyurethane resin. The following editor will briefly analyze the selection of polyurethane catalyst for these three types of products.
1. Selection of polyurethane foam catalyst
Polyurethane foam products are mainly composed of polyether, Synthesis of isocyanates, blowing agents, catalysts, etc. The main process of foam formation is generally considered as follows:
1. Foam is generated in the polyurethane reaction system through physical and chemical methods, and the foam is evenly dispersed in the polyurethane reaction system. In the reaction system, the main foaming method is to use water and isocyanate to produce carbon dioxide for foaming.
2. The foam generation process requires the viscosity of the reaction system to increase in order to stabilize the foam and prevent it from escaping.
3. When the foam formation reaches the required number and size, the viscosity of the reaction system needs to continue to increase or even form a cross-linked system to stabilize the foam and shape it into a product.
In this case, we need at least two catalysts to regulate the progress of the reaction. One catalyst is to promote the reaction of isocyanate and water, that is, to promote the foaming reaction. Usually Choose an amine catalyst; the other is to promote the reaction between isocyanate and polyether or alcohol, which is the reaction of polyurethane molecular chain growth and cross-linking. Generally, metal catalysts are used.
Therefore, in the polyurethane foam synthesis process, we generally use amine catalysts and organometallic catalysts to produce synergistic effects to achieve the best results. The specific types and proportions of amine catalysts and organometallic catalysts require experiments or experience to adjust and select based on different products, and will not be elaborated here.
II. Catalyst selection for polyurethane elastomer
Polyurethane elastomer’s effect on NCO and water The reaction must be strictly avoided, so metal catalysts are generally used at this time, such as organotin, organobismuth, and even eliminated organic mercury.
3. Selection of polyurethane resin catalyst
In the process of polyurethane resin synthesis, we should also try our best to To avoid the reaction between NCO and water, organic bismuth and organic tin are generally used.
