1. Introduction
A catalyst is a chemical substance that can change the rate of a chemical reaction. The catalysts used in the synthesis of polyurethane can be roughly divided into tertiary amine catalysts, organotin compounds, Non-tin organometallic compounds and other new catalysts.
2. Characteristics of various 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 have no reaction for water and NCO Sensitive; Some new catalysts, such as temperature-sensitive catalysts, have different catalytic efficiencies at different temperatures, and are widely used in some two-component polyurethane products.
3. Use catalyst purpose
Usually we use catalysts for two main purposes: 1. Let the reaction proceed in the direction we expected; 2. Adjust the reaction rate, shorten the reaction time, and improve Productivity.
4. Principles of Catalyst Selection for Different Polyurethane Products
Polyurethane products can be roughly divided into foam, elastomer and polyurethane resin. Below we analyze the selection of catalysts used in these three types of products respectively.
4.1 Polyurethane foam catalyst selection
Polyurethane foam products are mainly synthesized from polyether, isocyanate, blowing agent, catalyst, etc. The main process of foam formation is generally considered as follows: 1. Foam is generated in the polyurethane reaction system by physical and chemical methods, 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 generation process requires the viscosity of the reaction system to increase in order to stabilize the foam 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-linking system to stabilize the foam and shape it into a product.
In this case, we need at least two catalysts to regulate the reaction, one catalyst is to promote the reaction of isocyanate and water, that is, to promote the Foam reaction, usually choose amine catalyst; the other is to promote the reaction of isocyanate and polyether or alcohol, that is, the reaction of polyurethane molecular chain growth and crosslinking, generally choose metal catalyst. Therefore, in the synthesis of polyurethane foam, we generally use amine catalysts and organometallic catalysts in combination to produce synergistic effects to achieve the best results. The types and ratios of the specific amine catalysts and organometallic catalysts need to be adjusted and selected according to different products through experiments or experience, so I will not make too many statements here.
4.2 Polyurethane elastomer catalyst selection
The reaction of polyurethane elastomers to NCO and water should be strictly avoided, so metal catalysts are generally used at this time, such as organic tin, organic bismuth, or even eliminated organic mercury, etc.
4.3 Polyurethane resin catalyst selection
During the synthesis of polyurethane resin, the reaction between NCO and water should be avoided as much as possible, so organic bismuth and organic tin are generally used.
| Chinese name | Polyurethane catalyst | foreign name | PU Catalyst |
| include | DY-DMAEE/DY-12/DY-8/DY-5 etc | mainly divided into | Organic amines, organic metal salts, etc. |
| Common use | Only more than twenty kinds |
5.Classification
The catalysts commonly used in the synthesis of polyurethane and its raw materials mainly include tertiary amine catalysts and organometallic compounds. There are many kinds of tertiary amines and organometallic compounds. Considering various factors, there are only more than 20 kinds commonly used in polyurethane production.
Amine Catalyst
Amine catalysts are generally used in the production of polyurethane foam, mainly divided into the following categories:
Aliphatic amine catalysts include N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl)ether, N,N,N ‘,N’-tetramethylalkylenediamine, triethylamine, N,N-dimethylbenzylamine, etc.
Alicyclic amine catalysts include solid amine, N-ethylmorpholine, N-methylmorpholine, N,N’-diethylpiperazine wait.
Alcohol compound catalysts include triethanolamine, DMEA, etc.
Aromatic amines include pyridine, N,N’-lutidine, etc.
Organometallic Catalyst
Dibutyltin dilaurate (DY-12 ) and other organometallic catalysts are commonly used. It is very effective in promoting the reaction between isocyanate groups and hydroxyl groups, but it also has a certain acceleration effect on the reaction between water and isocyanate in formulas with moisture; in formulas such as plastic track, organic lead can be used. catalyst.
Organometallic compounds include carboxylates, metal alkyl compounds, etc., and the metal elements contained mainly include tin, potassium, lead, mercury, zinc, etc., commonly used It is an organotin compound.
