Coating method and hardener for polyurethane paint

Patent metadata

Field	Value
Publication number	US-9802223-B2
Application number	US-201314410183-A
Country	US
Kind code	B2
Filing date	Jul 3, 2013
Priority date	Jul 9, 2012
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

[Problem] In a coating method of a two-coat one-bake system where a clear coat paint is coated after a base coat paint is coated, then these two coated layers are simultaneously hardened, adhesive strength between the two coated layers is to increase in comparison with the conventional method.
[Solution] Provided is a coating method; A specific hardener is used in the clear coat paint. The hardener is one containing a polyisocyanate derived from 1,6-hexamethylene diisocyanate, satisfying all the following conditions:
1) Hardener does not virtually include diisocyanate monomer, 2) Viscosity of hardener is not more than 1000 mPa·s/23° C., 3) Content of HDI trimer in hardener is not less than 60 weight %, and 4) Content of HDI dimer in hardener is less than 10 weight %.

First claim

The invention claimed is:

1. A coating method comprising applying a base coat paint comprising an active hydrogen-containing resin and a blocked isocyanate, without hardening the base coat paint by cross-linking, subsequently coating a clear coat paint comprising a hardener and an active hydrogen-containing resin on the base coat paint, hardening the base coat paint and the clear coat paint simultaneously by cross-linking, wherein the clear coat paint is a two-pack polyurethane paint with a mole ratio of 0.9 to 2.0 in NCO/H (active hydrogen), wherein the hardener comprises a polyisocyanate derived from 1,6-hexamethylene diisocyanate, satisfying all the following conditions:
1) the hardener includes an amount of diisocyanate monomers included in polyisocyanate of 0.25 weight % or less
2) viscosity of hardener when it is not diluted with any organic solvent is not more than 1000 mPa·s/23° C.,
3) content of 1,6-hexamethylene diisocyanate trimer in hardener is not less than 60 weight %, wherein the 1,6-hexamethylene diisocyanate trimer comprises an isocyanurate structure of HDI, an iminooxadiazinedione structure of HDI, or mixtures thereof, and
4) content of 1,6-hexamethylene diisocyanate dimer in hardener is less than 10 weight %.

2. The method of claim 1 , wherein the hardener for the clear coat paint comprises not less than 13 mole % of iminooxadiazinedione ring of 1,6-hexamethylene diisocyanate relative to the total of isocyanurate ring and iminooxadiazinedione ring.

3. The method of claim 1 , wherein the amount of active hydrogen is from 0.01 to 2 weight % of active hydrogen atom to the weight of resin.

4. The method of claim 1 , wherein the polyisocyanate derived from 1,6-hexamethylene diisocyanate is 60 weight % or more relative to the hardener.

5. The method of claim 2 , wherein the amount of iminooxadiazinedione ring of 1,6-hexamethylene diisocyanate is 25 mole % or more.

6. The method of claim 2 , wherein the amount of iminooxadiazinedione ring of 1,6-hexamethylene diisocyanate is 30 to 80 mole % or more.

7. The method of claim 1 , wherein the polyisocyanate derived from 1,6-hexamethylene diisocyanate is 95 weight % or more relative to the hardener.

Assignees

• Bayer Materialscience Ag
• Covestro Deutschland Ag

Inventors

• Shigemori Tomokazu
• Morita Hiroshi

Classifications

• C08G18/7837

  containing allophanate groups · CPC title

• C08G18/7818

  containing ureum or ureum derivative groups · CPC title

• C08G18/79

  characterised by the polyisocyanates used, these having groups formed by oligomerisation of isocyanates or isothiocyanates · CPC title

• B05D7/532 Primary

  the two layers being cured or baked together, i.e. wet on wet · CPC title

• Y10T428/31554

  Next to second layer of polyamidoester · CPC title