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

1. A method for reducing flocculation and/or precipitation in a polyisocyanate mixture, the method comprising mixing the polyisocyanate mixture with an additive, wherein said mixing is carried out in the presence of water and a solvent, thereby reducing flocculation, precipitation, or both, of the polyisocyanate mixture, and

wherein the 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-C 1 to C 12 alkyl phosphate,

a4c) a mono-C 1 to C 12 alkyl phosphinate, and

a4d) an alkyl derivative of a phosphorus-containing diacid, and

wherein:

a polyisocyanate of the polyisocyanate mixture comprises an isocyanurate, biuret, allophanate, or allophanate with urethane group,

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.

2. The method according to claim 1 , wherein a polyisocyanate of the polyisocyanate mixture is (cyclo)aliphatic.

3. The method according to claim 1 , wherein a polyisocyanate of the polyisocyanate mixture is based on hexamethylene diisocyanate, isophorone diisocyanate, or both, as a monomer.

4. The method according to claim 1 , wherein a polyisocyanate of the polyisocyanate mixture comprises an isocyanurate, biuret, or an allophanate group.

5. The method according to claim 1 , wherein a polyisocyanate of the polyisocyanate mixture comprises an isocyanurate group, a urethane group, an allophanate group, or a mixture thereof, obtained in the presence of an ammonium carboxylate or an ammonium a-hydroxycarboxylate catalyst.

6. The method according to claim 1 , wherein a polyisocyanate of the polyisocyanate mixture comprises an isocyanurate group obtained by thermal deactivation of a catalyst.

7. The method according to claim 1 , wherein a polyisocyanate of the polyisocyanate mixture comprises an isocyanurate group obtained by thermal deactivation of a catalyst through addition of a deactivator.

8. The method according to claim 1 , wherein a substoichiometric amount of the additive is added in relation to an amount of the water present in the polyisocyanate mixture.

9. The method according to claim 1 , wherein the additive is selected from the group consisting of di(2-ethylhexyl) phosphate, dibutyl phosphate, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, a dioctylphosphonic ester, a di(2-ethylhexyl)phosphonic ester, a di-n-butylphosphonic ester, a diethylphosphonic ester, a dimethylphosphonic ester, a 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide, and dodecylbenzenesulfonic acid.

10. The method according to claim 1 , wherein a total amount of the water ranges from 100 to 800 ppm relative to an amount of the solvent.

11. The method according to claim 1 , wherein a total amount of the water ranges from 400 to 800 ppm relative to an amount of the solvent.

12. The method according to claim 1 , wherein the solvent is at least one selected from the group consisting of an aromatic hydrocarbon, a (cyclo)aliphatic hydrocarbon, a chlorinated hydrocarbon, a ketone, an ester, an alkoxylated alkyl alkanoate, and an ether.

13. The method according to claim 1 , wherein the solvent is at least one selected from the group consisting of n-butyl acetate, ethyl acetate, 1-methoxyprop-2-yl acetate, 2-methoxyethyl acetate, and an aromatic hydrocarbon.

14. The method according to claim 1 , wherein the polyisocyanate mixture further comprises at least one phenyl or bridged bisphenol which has one phenolic hydroxyl group on an aromatic ring of the at least one phenyl or bridged bisphenol and has alkyl groups in positions ortho to the phenolic hydroxyl group.

15. The method according to claim 14 , wherein the polyisocyanate mixture further comprises a dialkyl phosphate, a dialkyl phosphonate, an aromatic sulfonic acid, or a mixture thereof.

16. The method according to claim 14 , wherein the polyisocyanate mixture further comprises a Lewis acid.

17. 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-C 1 to C 12 alkyl phosphate,

a4c) a mono-C 1 to C 12 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.

18. The method according to claim 17 , wherein the polyisocyanate mixture comprises at least one selected from the group consisting of a Lewis acid as a catalyst and an antioxidant.

19. 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-C 1 to C 12 alkyl phosphate,

a4c) a mono-C 1 to C 12 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.

20. The method according to claim 19 , wherein the binder-comprising component comprises a compound selected from the group consisting of a polyacrylate polyol, a polyester polyol, a polyurethane polyol, a polycarbonate polyol, and a polyether polyol.

21. The method according to claim 19 , wherein the substrate is a compound in a primer, a filler, a pigmented topcoat, a basecoat and a clearcoat in an automotive refinishing or large-vehicle finishing sector and for a utility vehicle in an agricultural or construction sector.