The catalyst is a chemical substance that can change the chemical reaction rate. The catalysts used in the polyurethane synthesis process can be roughly divided into tertiary amine catalysts, organotin compounds, non-tin organometallic compounds, and other novel catalysts.
2. Characteristics of various types of catalysts
Amine catalysts are good catalysts for the reaction of NCO and water; organic tin and organic mercury have high selectivity for the reaction of NCO and OH, and are insensitive to water and NCO reactions; some new catalysts such as temperature-sensitive catalysts have different temperatures. Catalytic efficiency is widely used in some two-component polyurethane products.
3. Use of catalyst purpose
Usually we use the purpose of the catalyst has two main purposes: 1, let the reaction proceed in the direction we expected; 2, adjust the reaction rate, shorten the reaction time, increase production efficiency.
4. Selection principles of catalysts for different polyurethane products
Polyurethane products can be roughly classified into foams, elastomers, and polyurethane resins. Below we analyze the selection of catalysts for these three types of products.
4.1 Polyurethane Foam Catalyst Selection
Polyurethane foam products are mainly synthesized from polyethers, isocyanates, foaming agents, catalysts and the like. The main process of foam formation is generally considered as follows: 1. Physical and chemical methods are used to generate foam in the polyurethane reaction system, and the foam is evenly dispersed in the reaction system. The main foaming method is to use water and isocyanate to produce carbon dioxide. bubble. 2. The foam production process requires that the viscosity of the reaction system increase as the foam is stabilized from being escaped. 3. When the foam formation reaches the required number and size, the viscosity of the reaction system needs to be continuously increased or a crosslinking system is formed to stabilize the foam and shape the product.
In this case, we need at least two kinds of catalysts to regulate the progress of the reaction. One kind of catalyst is to promote the reaction of isocyanate and water, that is, to promote the foaming reaction. Normally, the amine catalyst is selected; the other is needed. To promote the reaction of isocyanates with polyethers or alcohols, that is, the growth of polyurethane chains and cross-linking reactions, metal catalysts are generally used. Therefore, in the polyurethane foam synthesis process, we generally use amine catalysts and organometallic catalysts in combination to produce synergistic effects to achieve the best results. The types and proportions of specific amine catalysts and organometallic catalysts need to be experimentally or empirically adjusted according to different products, and no more statements will be made here.