A method for forming a multilayer coating film, comprising the following steps (1) to (5): (1) producing a first aqueous base coating composition comprising combining an acrylic resin dispersion (A) having a core/shell structure and a melamine resin (B), (2) applying the first aqueous base coating composition onto a surface of an object to form an uncured first aqueous base coating film, (3) applying a second aqueous base coating composition onto the uncured first aqueous base coating film to form an uncured second aqueous base coating film, (4) applying a clear coating composition onto the uncured second aqueous base coating film to form an uncured clear coating film, and (5) heat-curing the uncured first aqueous base coating film, the uncured second aqueous base coating film, and the uncured clear coating film obtained in steps (2) to (4) at a time to form the multilayer coating film.

In a polyurethane dispersion obtained by water-dispersing a polyurethane resin, the polyurethane resin is a reaction product obtained by reacting at least a polyisocyanate component with an active hydrogen group-containing component containing an active hydrogen compound having an anionic group, a ratio of the total moles of a urethane group and a urea group is 1.5 mol or more with respect to 1 kg of the polyurethane dispersion, and the carbonate ion concentration is 700 ppm or less with respect to the polyurethane dispersion.

The present invention relates to a multi-aziridine compound having: a) from 2 to 6 of the following structural units (A): whereby R.sub.1 is H, R.sub.2 and R.sub.4 are independently chosen from H or an aliphatic hydrocarbon group containing from 1-4 carbon atoms, R.sub.3 is an aliphatic hydrocarbon group containing from 1-4 carbon atoms, RH or an aliphatic hydrocarbon group containing from 1 to 4 carbon atoms; R and R are independently chosen from an aliphatic hydrocarbon group containing from 1 to 4 carbon atoms, a cycloaliphatic hydrocarbon group containing from 4 to 12 carbon atoms or an aromatic hydrocarbon group containing from 6 to 12 carbon atoms, b) one or more linking chains wherein each one of these linking chains links two of the structural units A; and c) a molecular weight in the range from 600 Daltons to 5000 Daltons. ##STR00001##

The present invention relates to a multi-aziridine compound having: a) from 2 to 6 of the following structural units (A): whereby R.sub.1 is H, R.sub.2 and R.sub.4 are independently chosen from H or an aliphatic hydrocarbon group containing from 1-4 carbon atoms, R.sub.3 is an aliphatic hydrocarbon group containing from 1-4 carbon atoms, RH or an aliphatic hydrocarbon group containing from 1 to 4 carbon atoms; R and R are independently chosen from an aliphatic hydrocarbon group containing from 1 to 4 carbon atoms, a cycloaliphatic hydrocarbon group containing from 4 to 12 carbon atoms or an aromatic hydrocarbon group containing from 6 to 12 carbon atoms, b) one or more linking chains wherein each one of these linking chains links two of the structural units A; and c) a molecular weight in the range from 600 Daltons to 5000 Daltons. ##STR00001##

The present invention relates to a multi-aziridine compound having: a) at least 2 of the following structural units (A): (A) whereby R.sub.1 is H; R.sub.2 and R.sub.4 are independently chosen from H, a linear group containing from 1 to 8 carbon atoms and optionally containing one or more heteroatoms, a branched or cyclic group containing from 3 to 8 carbon atoms and optionally containing one or more heteroatoms, phenyl, benzyl, or pyridinyl; R.sub.3 is chosen from a linear group containing from 1 to 8 carbon atoms and optionally containing one or more heteroatoms, a branched or cyclic group containing from 3 to 8 carbon atoms and optionally containing one or more heteroatoms, phenyl, benzyl, or pyridinyl; or R.sub.2 and R.sub.3 (in case R.sub.2 is different than H) may be part of the same cyclic group containing from 3 to 8 carbon atoms; R and R are independently H or an aliphatic hydrocarbon group containing from 1 to 12 carbon atoms; and b) a molecular weight from 600 to 20000 Daltons, wherein the molecular weight is determined using MALDI-TOF mass spectrometry according to the description. ##STR00001##

The present invention relates to a multi-aziridine compound having: a) at least 2 of the following structural units (A): (A) whereby R.sub.1 is H; R.sub.2 and R.sub.4 are independently chosen from H, a linear group containing from 1 to 8 carbon atoms and optionally containing one or more heteroatoms, a branched or cyclic group containing from 3 to 8 carbon atoms and optionally containing one or more heteroatoms, phenyl, benzyl, or pyridinyl; R.sub.3 is chosen from a linear group containing from 1 to 8 carbon atoms and optionally containing one or more heteroatoms, a branched or cyclic group containing from 3 to 8 carbon atoms and optionally containing one or more heteroatoms, phenyl, benzyl, or pyridinyl; or R.sub.2 and R.sub.3 (in case R.sub.2 is different than H) may be part of the same cyclic group containing from 3 to 8 carbon atoms; R and R are independently H or an aliphatic hydrocarbon group containing from 1 to 12 carbon atoms; and b) a molecular weight from 600 to 20000 Daltons, wherein the molecular weight is determined using MALDI-TOF mass spectrometry according to the description. ##STR00001##

The present invention relates to a multi-aziridine compound having: a) from 2 to 6 of the following structural units (A): whereby R, R are as defined herein m is an integer from 1 to 6; b) one or more linking chains wherein each one of these linking chains links two of the structural units A; and c) a molecular weight in the range from 840 Daltons to 5000 Daltons. The multi-aziridine compound can be used for example for crosslinking of for example carboxylic acid functional polymers dissolved and/or dispersed in an aqueous medium. ##STR00001##

The present invention relates to a multi-aziridine crosslinker composition, including an aqueous dispersion having a pH ranging from 9 to 14 and including a multi-aziridine compound in dispersed form. The multi-aziridine compound has: a. from 2 to 6 of the following structural units A: (A) whereby R1, R2, R3 and R4 are H; m is 1, R and R are according to (1) or (2): (2) R=H or an aliphatic hydrocarbon group containing from 1 to 14 carbon atoms, and R=an alkyl group containing from 1 to 4 carbon atoms, CH2-O(CO)R or CH2-OR, whereby R is an alkyl group containing from 4 to 12 carbon atoms and R is an alkyl group containing from 1 to 14 carbon atoms, (2) R and R form together a saturated cycloaliphatic hydrocarbon group containing from 5 to 8 carbon atoms. ##STR00001##

The present invention relates to a multi-aziridine crosslinker composition, including an aqueous dispersion having a pH ranging from 9 to 14 and including a multi-aziridine compound in dispersed form. The multi-aziridine compound has: a. from 2 to 6 of the following structural units A: (A) whereby R1, R2, R3 and R4 are H; m is 1, R and R are according to (1) or (2): (2) R=H or an aliphatic hydrocarbon group containing from 1 to 14 carbon atoms, and R=an alkyl group containing from 1 to 4 carbon atoms, CH2-O(CO)R or CH2-OR, whereby R is an alkyl group containing from 4 to 12 carbon atoms and R is an alkyl group containing from 1 to 14 carbon atoms, (2) R and R form together a saturated cycloaliphatic hydrocarbon group containing from 5 to 8 carbon atoms. ##STR00001##

The present invention relates to a multi-aziridine compound having: a) from 2 to 6 of the following structural units (A): whereby R, R are as defined herein m is an integer from 1 to 6; b) one or more linking chains wherein each one of these linking chains links two of the structural units A; and c) a molecular weight in the range from 840 Daltons to 5000 Daltons. The multi-aziridine compound can be used for example for crosslinking of for example carboxylic acid functional polymers dissolved and/or dispersed in an aqueous medium. ##STR00001##