Honda Motor Co., Ltd.

Kansai Paint Company, Ltd.

Basf Coatings Gmbh

Yusuke Kurata

Takeshi Ogawa

Hiroshi Kitagawa

Naoto Matsushima

Hisayuki Nakashima

Takeshi Matsuda

Satoru Ihara

Kyohei Homma

Ryusuke Muramoto

Yusuke Yagi

Disclosed is a method for forming a multilayer coating film, including applying a first and second aqueous base coat, and a clear coat to an object, and thereafter simultaneously heating and curing the three-layer coating film. The first aqueous base coat includes a water-soluble or water-dispersible polyurethane resin having a glass transition temperature of &#x2212;20&#xb0; C. or below and a weight average molecular weight of 30,000 to 500,000, and a crosslinkable resin having a weight average molecular weight of 600 or more. The first aqueous base coat-coated film has a breaking strength of 2050 N/cm2 or more and a loss tangent (tan &#x3b4;) at &#x2212;20&#xb0; C. of 0.075 or more. The migration amount of a melamine resin from the second aqueous base coat-coated film layer to the first aqueous base coat-coated film layer is within 3% by mass of a total resin solid content of the first aqueous base coat.

Method for forming multilayer coating film

A method for forming a multilayer coating film includes applying an aqueous first base coating composition (A) onto a cured electrodeposition coating film, applying an aqueous second base coating composition (B) without preheating, performing preheating, further applying a clear coating composition (C), and simultaneously heat-curing the first base coating film, the second base coating film, and the clear coating film. The aqueous first base coating composition contains a specific aqueous polyester resin, a specific aqueous acrylic resin, a specific aqueous urethane resin and a melamine resin. A breaking energy of a coating film formed of the aqueous first base coating composition and a peel strength between the coating film and the cured electrodeposition coating film are controlled to specific values.

This invention provides a method for forming multilayer coating film, which comprises successively carrying out a step of applying an intermediate paint onto a coating object to form an intermediate coating film; a step of forming a base coating film by applying onto the intermediate coating film a water-based base coating paint; a step of forming a clear coating film by applying onto the base coating film a clear coating paint, and a step of heating the uncured intermediate coating film, base coating film and clear coating film to simultaneously cure these three coating films; wherein the intermediate paint has a complex viscosity at 40&#xb0; C. (&#x3b7;*) of not higher than 100 Pa&#xb7;sec under the conditions of shear stress, 1.0 Pa and frequency, 0.1 Hz, and a complex viscosity at 80&#xb0; C. (&#x3b7;*) of at least 800 Pa&#xb7;sec under the conditions of shear stress, 1.0 Pa and frequency, 0.1 Hz.

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Tokyo, Japan

Yusuke Kurata