Here we mainly talk about how to reduce bubbles in products by selecting the appropriate polyurethane catalyst.
Catalysts have played an important role in the rapid development of the polyurethane industry. Currently, there are more than two hundred types of catalysts used in the synthesis of polyurethane materials. Basically divided into two categories: tertiary amine and its salt catalysts; metal alkyl compounds. The former mainly includes triethylenediamine, dimethylethanolamine, DMDEE, etc.; the latter mainly includes dibutyltin dilaurate, bismuth carboxylate, stannous octoate, etc. The principle of its use should not only be based on the catalytic activity of the catalyst, but also consider the catalytic selectivity, chemical toxicity, compatibility with other raw materials, price, stability, etc.
Tertiary amines are the most widely used category of polyurethane catalysts. They are highly alkaline and highly active, and can quickly catalyze the isocyanate-hydroxyl reaction. At the same time, it also catalyzes the reaction between isocyanate and water to produce carbon dioxide, which is widely used in the production of various types of polyurethane foams and the preparation of many microcellular elastomers. The most representative one is triethylenediamine. Because it is a solid and inconvenient to use, domestic manufacturers usually dilute it with glycol (EG/DEG/DPG) into a 33% concentration solution, commonly known as A-33. (Our brand number is DY-33). As a very versatile tertiary amine catalyst, in addition to the foam field, it also plays an important role in polyurethane adhesives/coatings/microcellular elastomers.
But what cannot be ignored is that if the polyurethane reaction is simply and crudely divided into foaming and gel, the reaction between triethylenediamine and isocyanate and water The catalytic reaction efficiency accounts for about 60% of the total efficiency, which means that it has a strong catalytic foaming effect. When we cannot remove the moisture in the system and have strict requirements on the bubbles of the product, the use of amine catalysts should be avoided.
In terms of organic metals, alkyl compounds such as lead, tin, mercury, bismuth, manganese, zinc, copper, and titanium all have certain catalytic properties in polyurethane systems. effect. However, since the discovery in 1956 that organotin catalysts have a strong catalytic effect on hydroxyl groups and isocyanates, and can effectively promote the growth of molecular chains, their status as the most important organometallic catalyst in the polyurethane industry has hardly been shaken. Organotin catalysts have high selectivity for hydroxyl groups and isocyanates and few side reactions. Therefore, they have important applications in foams, adhesives, elastomers, coatings, sealants and other fields.
But in the production of foam-free products, the best polyurethane catalyst choice is still organic mercury (phenylmercuric acetate). This extremely toxic catalyst [LD50: 39.5mg/kg (orally for mice); 35mg/kg (orally for rats)] has almost no catalytic activity for isocyanate-water, but can catalyze the isocyanate-hydroxyl reaction. Using this Catalyst polyurethane will not produce bubbles due to trace amounts of moisture. However, its toxicity is very high and its practical application is widely limited.
