Coatings from polyisocyanurate coatings (rim) and their use in injection molding processes
The present invention relates to the use of polyisocyanate compositions and trimerization catalysts for production of coatings by reaction injection molding. The present disclosure also describes the coatings obtained by the use. The correspondingly coated workpieces are also described in this disclosure. A method for coating workpieces by reaction injection molding is also described herein.
1 . Method for coating workpieces by reaction injection molding by providing a reaction mixture having a molar ratio of isocyanate groups to isocyanate-reactive groups of at least 3:1, wherein the reaction mixture contains
a) at least one polyisocyanate composition A and
b) at least one trimerization catalyst B
wherein at least 30 mol % of free isocyanate groups present in the reaction mixture are converted into isocyanurate groups during the reaction injection molding process.
2 . The method as claimed in claim 1 , wherein the reaction mixture additionally contains at least one isocyanate-reactive compound selected from the group consisting of mono- or polyhydric alcohols, amines, amino alcohols and thiols.
3 . The method as claimed in claim 1 , wherein the polyisocyanate composition A consists to an extent of at least 70% by weight, based on its total weight, of polyisocyanates which comprise exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.
4 . The method as claimed in claim 1 , wherein the polyisocyanate composition A contains at least one blocked polyisocyanate whose blocking agent is selected from the group consisting of lactams, oximes, cyclopentanone 2-alkyl esters and phenols.
5 . The method as claimed in claim 1 , wherein the workpieces consists of at least one material selected from the group consisting of thermoplastic polymers, thermosetting polymers, wood and metal.
6 . The method of claim 1 , wherein a coating formed on the workpiece by the reaction injection molding process is a polyisocyanurate plastic.
7 . A process for coating a workpiece, comprising the steps of
a) introducing a workpiece into a mold which surrounds at least a portion of the workpiece and has dimensions such that a distance between a surface of the workpiece and an inside of the mold corresponds to a thickness of a coating;
b) injecting at least one reaction mixture as defined in claim 1 ; and
c) curing the reaction mixture injected in process step b) at a temperature between 60° C. and 300° C., wherein at least 30 mol % of the free isocyanate groups present at commencement of process step c) are converted into isocyanurate groups.
8 . The process as claimed in claim 7 , wherein process step c) is performed at a temperature between 80° C. and 130° C.
9 . The process as claimed in claim 7 , wherein process step c) is performed for 10 seconds to 900 seconds and the coated workpiece is demoldable.
10 . The process as claimed in claim 7 , wherein the workpiece to be coated consists to an extent of at least 90% by weight of a thermoplastic and said workpiece was produced by injection molding not more than 5 minutes before commencement of process step a).
11 . The process as claimed in claim 7 , wherein the distance between the surface of the workpiece and the inside of the mold is 50 μm to 5 mm.
12 . The process as claimed in claim 7 , wherein the polyisocyanate composition A contains at least one silane-functional polyisocyanate.
13 . A coating obtained or obtainable by the process according to claim 7 .
14 . The coating as claimed in claim 13 , wherein a ratio of an absolute peak heights of a CH 2 band and an NH-δ band is at least 0.85:1 and a ratio of an absolute peak heights of an isocyanurate band and the NH-δ band is at least 5.5:1 and the coating has a Tg of 40° C. to 300° C.
15 . The coating as claimed in claim 13 , having a density of at least 0.95 g/cm 3 .
16 . A workpiece coated with the coating as claimed in claim 13 .