Method for forming multilayer coating film

Patent metadata

Field	Value
Publication number	US-11247231-B2
Application number	US-202017267968-A
Country	US
Kind code	B2
Filing date	May 18, 2020
Priority date	May 30, 2019
Publication date	Feb 15, 2022
Grant date	Feb 15, 2022

Abstract

The present invention aims to provide a method for forming a multilayer coating film having good coating film smoothness. A method for forming a multilayer coating film, comprising a first aqueous coating composition application step of applying a first aqueous coating composition (A) to form an uncured first aqueous coating film; a second aqueous coating composition application step of applying a second aqueous coating composition (B) onto the uncured first aqueous coating film to form an uncured second aqueous coating film; a clear coating step of applying a clear coating composition (C) onto the uncured second aqueous coating film to form an uncured clear coating film; and a curing step of heat-curing at once these coating films to form a multilayer coating film, wherein the first aqueous coating composition (A) contains a water-dispersible polyurethane resin (a1) and a viscosity modifier (a2), and the second aqueous coating composition (B) contains water and an organic solvent as diluent components besides solid matters in a state of dilution to a coating viscosity.

First claim

The invention claimed is:

1. A method for forming a multilayer coating film, comprising:
a first aqueous coating composition application step of applying a first aqueous coating composition (A) to a surface of an article to form an uncured first aqueous coating film;
a second aqueous coating composition application step of applying a second aqueous coating composition (B) onto the uncured first aqueous coating film to form an uncured second aqueous coating film;
a clear coating step of applying a clear coating composition (C) onto the uncured second aqueous coating film to form an uncured clear coating film; and
a curing step of heat-curing at once the uncured first aqueous coating film, the uncured second aqueous coating film, and the uncured clear coating film in the steps defined above to form a multilayer coating film,
wherein
the first aqueous coating composition (A) comprises a water-dispersible polyurethane resin (a1) and a viscosity modifier (a2),
the second aqueous coating composition (B) comprises water and an organic solvent as diluent components besides solid components in a state of dilution to a coating viscosity, and contains, as a part of the organic solvent, an organic solvent having a solubility in water of 0.1% or more and 7% or less, in an amount of 0.4% by mass or more and 5.0% by mass or less per the total amount of the coating material, and also contains an organic solvent insoluble in water in an amount of 0.05% by mass or more and 2.5% by mass or less per the total amount of the coating material, and
M B , which is a droplet mass of the second aqueous coating composition (B) at the time of applying the composition to the uncured first aqueous coating film, V B , which is a collision speed, and η A , which is a shear viscosity of the uncured first aqueous coating film measured at a shear rate of 10,000 sec −1 , satisfy the following formula:
M B V B /η A <3.0×10 −7 .

2. The method for forming a multilayer coating film according to claim 1 ,
wherein the second aqueous coating composition (B) is an aqueous coating composition comprising an acrylic resin emulsion and a melamine resin.

3. The method for forming a multilayer coating film according to claim 1 , wherein
the organic solvent having a solubility in water of 0.1% or more and 7% or less contained in the second aqueous coating composition (B) is an organic solvent having a boiling point of 160° C. or higher and 280° C. or lower, and
the organic solvent insoluble in water is a hydrocarbon-based organic solvent having a boiling point of 145° C. or higher and 200° C. or lower.

4. The method for forming a multilayer coating film according to claim 1 , wherein the shear viscosity ηA of the uncured first aqueous coating film is a viscosity η A1 measured under the conditions of a temperature of 23° C. and a shear rate of 10,000 sec −1 at the time of 3 minutes after the first aqueous coating composition (A) is applied under a coating condition such that a dry film thickness of 20 μm is achieved.

5. The method for forming a multilayer coating film according to claim 1 , wherein the first aqueous coating composition (A) comprises the water-dispersible polyurethane resin (a1), the viscosity modifier (a2), a curing agent (a3), and an acrylic resin emulsion (a4).

6. The method for forming a multilayer coating film according to claim 1 , wherein the viscosity modifier (a2) is one or more species selected from the group consisting of a polyamide-based viscosity modifier, a urethane-based viscosity modifier, a polycarboxylic acid-based viscosity modifier, a cellulose-based viscosity modifier, an inorganic layered compound-based viscosity modifier, and an aminoplast-based viscosity modifier.

7. The method for forming a multilayer coating film according to claim 1 , wherein
regarding the shear viscosity η A of the uncured first aqueous coating film,
the viscosity η A measured under conditions of a temperature of 23° C. and a shear rate of 10,000 sec −1 at a time of 3 minutes after applying the composition under a coating condition such that a dry film thickness of 20 μm is achieved,
the viscosity η A2 measured under conditions of a temperature of 23° C. and a shear rate of 10,000 sec −1 at a time of 5 minutes after applying the composition under a coating condition such that a dry film thickness of 20 μm is achieved, and
the viscosity η A3 measured under conditions of a temperature of 23° C. and a shear rate of 10,000 sec −1 at a time of 7 minutes after applying the composition under a coating condition such that a dry film thickness of 20 μm is achieved satisfy
M B V B /η A1 <3.0×10 −7

M B V B /η A2 <3.0×10 −7

M B V B /η A3 <3.0×10 −7 .

Assignees

• Nippon Paint Automotive Coatings Co Ltd

Inventors

• Senda Akiko
• Takemura Kenta
• Ishida Satoshi

Classifications

• C09D5/00

  Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced {(electrically insulating plastics, resins or waxes H01B3/30)}; Filling pastes · CPC title

• B05D7/572 Primary

  all layers being cured or baked together · CPC title

• B05D2420/01

  first layer from the substrate side · CPC title

• B05D2502/00

  Acrylic polymers · CPC title

• B05D2451/00

  Type of carrier, type of coating (Multilayers) · CPC title