2C-PUR adhesives

In isocyanates, the hazard potential depends to a cmisiderable extent on air moisture. Because of the high level of reactivity, with water amcmg other substances, the primary products show rapid chemical changes in moist air and lose their toxicity. It is therefore always better to work under cmiditions of high humidity and to wipe off the adhesive joints with a wet rag after fixation if possible. Outgassing in 1C and 2C PUR adhesives are reduced to practically zero within 10% of the total curing time. 

Figure 61 Curing mechanism of 2C-PUR adhesives. R and R are polymer chains.

C-PUR systems can cross-link within minutes and thereby their workability ends (No. 7 in Fig. 64). This high speed cross-linking can reduce the time to build up adhesion. When the speed of cross-linking is reduced and the open time is prolonged, and better adhesion is achieved. 

After 1 week, Sikaflex -650 AI cures with moisture to a final strength of 2.5 MPa, shore A hardness of 60,450% elongation with excellent adhesion to the substrates. For optimised adhesion on PVC, a pretreatment with SikaPrimer -215 AI with a minimum open time of 10 min is applied. Further, Sikaflex -650 AI must also adhere to 2C-PUR systems when present and they must also be pretreated with SikaPrimer -215 AI. 

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