Anhydrously curing polyisocyanate-based adhesives
The present invention relates to adhesives which are characterized in that they cure in the absence of water and at room temperature with the formation of isocyanurate groups.
1. A process for producing an adhesive joint comprising:
a) applying a coating composition to a surface to form a coated surface, the coating composition comprising:
a polyisocyanate composition A having an average isocyanate functionality of at least 1.5, and
at least one catalyst B, which at 23° C. catalyzes a reaction of NCO groups to form isocyanurate groups and/or uretdione groups,
wherein an isocyanate content of the coating composition is 5% by weight to 60% by weight and a molar ratio of isocyanate groups to isocyanate-reactive groups optionally present in the coating composition is at least 5:1;
b) contacting the coated surface with a further surface; and
c) curing the coating composition at a temperature of at least 10° C. and at most 60° C.,
wherein in process step c) initially a temperature between 10° C. and 40° C. is maintained until the adhesive joint reaches a tensile shear strength according to DIN EN 1465 for adhesives of at least 0.5 N/mm 2 and then a temperature of at least 50° C. is maintained until the adhesive joint reaches a strength of at least 2 N/mm 2 .
2. The process as claimed in claim 1 , additionally comprising providing the coating composition by mixing the polyisocyanate composition A and the at least one catalyst B prior to applying the coating composition, wherein a period of time of at least 30 minutes elapses between providing the coating composition and the end of process step b).
3. The process as claimed in claim 1 , wherein in process step b) at least 20% of the isocyanate groups present in the coating composition at the start of process step b) are converted to isocyanurate groups and at most 30% of the isocyanate groups present in the coating composition at the start of process step b) are converted to urea groups.
4. The process as claimed in claim 1 , wherein the coating composition additionally comprises at least one compound C comprising on average at least 1.0 group reactive with isocyanate groups per molecule.
5. The process as claimed in claim 4 , wherein the compound C is selected from the group consisting of ethanol, 1-propanol, 1-butanol, ethanediol, glycol, 1,2,10-decanetriol, 1,2,8-octanetriol, 1,2,3-trihydroxybenzene, glycerol, 1,1,1-trimethylolpropane, 1,1,1-trimethylolethane, pentaerythritol, sugar alcohols, polyethylene glycol (PEG) 200, PEG 300, PEG 400, PEG 600, diethanolamine, triethanolamine, and combinations thereof.
6. The process as claimed in claim 1 , wherein the polyisocyanate composition A comprises isocyanate-terminated prepolymers.
7. The process as claimed in claim 1 , wherein the coating composition comprises at least 5% by weight isocyanate groups, based on an organic phase of the coating composition.
8. The process as claimed in claim 1 , wherein the coating composition comprises less than 0.1% by weight transition metals, based on a total weight of the coating composition.
9. The process as claimed in claim 1 , wherein the coating composition additionally comprises at least one filler D.
10. The process as claimed in claim 1 , wherein the polyisocyanate composition A comprises at least 80% by weight polyisocyanates having aliphatically bonded isocyanate groups.
11. The process as claimed in claim 1 , wherein the surface is selected from the group consisting of glass, ceramic, glass ceramic, concrete, mortar, brick, tiles, gypsum, natural stone, metal, metal coated with cathode electrodeposition material, plastic, leather, paper, wood, resin-bonded wood-based materials, textiles, resin-textile composites, polymer composites, and combinations thereof.
12. The process as claimed in claim 1 , wherein the adhesive joint has a thickness of at least 1 mm.
13. The process as claimed in claim 1 , wherein the curing is completed in no more than 24 hours.