With the rapid development of industry, the demand for high performance, light weight, leakproof performance of new industrial sealing ring materials is increasing. Sealants, from the shape of the distinction, basically can be divided into two categories of elastic sealants and non-elastic sealants. The former can bear large relative displacement and deformation without tearing. With good adhesion, it has the double function of waterproof and sealing. The inelastomeric sealant can not adapt to some displacement and deformation well. Therefore, in the modern fluid machinery industry, the traditional non-elastomeric sealant has been gradually replaced by the elastomeric sealant
The main types of elastomeric sealant are polysiloxane, polysulfide rubber and elastic polyurethane.
Polyurethane elastomeric sealants can be divided into two types: one component and two components. The main material of the former is a polyurethane prepolymer with a high reactivity - NCO group at the end base band. But the content of one NCO group is low, generally less than 2%. The curing process is mainly dependent on its reaction with the moisture of external moisture. Generally, the curing time is long and the modulus of the product is low. In order to meet the need of sealing, in the main agent of polyurethane prepolymer, a variety of additives such as catalyst, plasticizer and filler must be added. The formula is as follows (mass fraction): prepolymer 35~65;Catalyst 0~0.5;Filler and pigment 20~40;Stabilizer 0~0.5;Plasticizer 5~25;Solvent 0 ~ 10;Thixotropic agent 0~5.
In the development of single-component polyurethane elastomeric sealants, the imidazole catalysts and potential catalysts have been developed, such as diketone imide, dialdehyde imide and other compounds. These substances are stable in the absence of water, and when they encounter water, they decompose, reacting with an NCO group and water, producing carbon dioxide bubbles in the sealant.