Process for preparing polyisocyanates which are flocculation-stable in solvents from (cyclo)aliphatic diisocyanates

A method for stabilizing a polyisocyanate or a polyisocyanate mixture in a solvent against flocculation during storage, the method comprising mixing, in the presence of water and a solvent, the polyisocyanate or the polyisocyanate mixture with at least one additive selected from the group consisting of

• a1) an organic acid having a pKa of below 4.2, selected from the group consisting of
• a1a) an aromatic sulfonic acid, and
• a1b) a singularly or doubly alkoxy-, mercapto- or alkylmercapto-substituted alkanecarboxylic acid having two carbon atoms, a singularly or doubly halogen-, alkoxy-, mercapto- or alkylmercapto-substituted alkanecarboxylic acid, an alkenedicarboxylic acid or an alkanedicarboxylic acid having at least three carbon atoms;
• a2) a phosphite:
• and
• a4) an acidic phosphorus derivative selected from the group consisting of
• a4a) a mono- and di-C1 to C12 alkyl phosphate,
• a4c) a mono-C1 to C12 alkyl phosphinate, and
• a4d) an alkyl derivative of a phosphorus-containing diacid,
• wherein:
• the polyisocyanate mixture comprises at least one selected from the group consisting of a Lewis acid as a catalyst, an antioxidant, and a coating additive;
• the additive does not include a 2-chloroalkanecarboxylic acid or a 3-chloro alkanecarboxylic acid;
• and
• R is optionally an aryl group which is substituted in positions 2, 4 and 6 as follows:
• position 2:
• tert-butyl, or tert-amyl,
• position 4:
• hydrogen, alkyl, tert-butyl, or tert-amyl, and
• position 6:
• hydrogen, alkyl, tert-butyl, or tert-amyl,
• with the proviso that at least one of substituents in positions 4 and 6 is not hydrogen.

A method for coating a substrate with a polyisocyanate or a polyisocyanate mixture stabilized against flocculation during storage in a solvent in the presence of water, the method comprising:

• mixing the polyisocyanate or the polyisocyanate mixture with at least one additive, thereby forming a first mixture,
• mixing the first mixture with a solvent and optionally with at least one other additive, thereby forming a second mixture,
• optionally storing the second mixture in the presence of the water,
• mixing the second mixture with at least one binder-comprising component, thereby forming a third mixture, and
• applying the third mixture to a substrate,
• wherein the at least one additive is selected from the group consisting of
• a1) an organic acid having a pKa of below 4.2, selected from the group consisting of
• a1a) an aromatic sulfonic acid, and
• a1b) a singularly or doubly alkoxy-, mercapto- or alkylmercapto-substituted alkanecarboxylic acid having two carbon atoms, a singularly or doubly halogen-, alkoxy-, mercapto- or alkylmercapto-substituted alkanecarboxylic acid, an alkenedicarboxylic acid or an alkanedicarboxylic acid having at least three carbon atoms;
• a2) a phosphite:
• and
• a4) an acidic phosphorus derivative selected from the group consisting of
• a4a) a mono- and di-C1 to C12 alkyl phosphate,
• a4c) a mono-C1 to C12 alkyl phosphinate, and
• a4d) an alkyl derivative of a phosphorus-containing diacid,
• wherein:
• the additive does not include a 2-chloroalkanecarboxylic acid or a 3-chloro alkanecarboxylic acid;
• and
• R is optionally an aryl group which is substituted in positions 2, 4 and 6 as follows:
• position 2:
• tert-butyl, or tert-amyl,
• position 4:
• hydrogen, alkyl, tert-butyl, or tert-amyl, and
• position 6:
• hydrogen, alkyl, tert-butyl, or tert-amyl,
• with the proviso that at least one of substituents in positions 4 and 6 is not hydrogen.