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US-12624245-B2 - Clear coating composition and method for producing coated article

US12624245B2US 12624245 B2US12624245 B2US 12624245B2US-12624245-B2

Abstract

Provided is a clear coating composition from which a coating film superior in color shift and appearance can be obtained. A clear coating composition comprising: a hydroxy group-containing acrylic resin (A); a polyisocyanate compound (B); and an organic solvent (C), wherein the hydroxy group-containing acrylic resin (A) includes a primary hydroxy group-containing acrylic resin (A1) and a secondary hydroxy group-containing acrylic resin (A2); the primary hydroxy group-containing acrylic resin (A1) has a weight average molecular weight of 6,000 or less; the secondary hydroxy group-containing acrylic resin (A2) has a weight average molecular weight of 6,000 or more; the organic solvent (C) includes a ketone compound having 7 or more carbon atoms (C1); and the clear coating composition has a solid concentration at a time of application of 55% by mass or more.

Inventors

  • Tomoyuki Ishikawa
  • Azusa JIZODO
  • Kaito FUKUI
  • Kohei Yamaguchi
  • Yoshito ARAKI

Assignees

  • NIPPON PAINT AUTOMOTIVE COATINGS CO., LTD.

Dates

Publication Date
20260512
Application Date
20230710
Priority Date
20221223

Claims (7)

  1. 1 . A clear coating composition comprising: a hydroxy group-containing acrylic resin (A); a polyisocyanate compound (B); and an organic solvent (C), wherein the hydroxy group-containing acrylic resin (A) includes a primary hydroxy group-containing acrylic resin (A1) and a secondary hydroxy group-containing acrylic resin (A2), the primary hydroxy group-containing acrylic resin (A1) does not contain a secondary hydroxy group, the primary hydroxy group-containing acrylic resin (A1) has an acid value of 0 mg KOH/g or more and 40 mg KOH/g or less, the primary hydroxy group-containing acrylic resin (A1) has a weight average molecular weight of 6,000 or less, the secondary hydroxy group-containing acrylic resin (A2) has a weight average molecular weight of 6,000 or more, the organic solvent (C) includes a ketone compound having 7 or 8 carbon atoms (C1), and the clear coating composition has a solid concentration at a time of application of 55% by mass or more.
  2. 2 . The clear coating composition according to claim 1 , wherein the secondary hydroxy group-containing acrylic resin (A2) has an acid value of 0 mg KOH/g or more and 40 mg KOH/g or less.
  3. 3 . The clear coating composition according to claim 1 , wherein the weight average molecular weight of the primary hydroxy group-containing acrylic resin (A1) is 3,000 or more and 6,000 or less.
  4. 4 . The clear coating composition according to claim 1 , wherein a mass ratio (A1)/(A2) of a content of the primary hydroxy group-containing acrylic resin (A1) to a content of the secondary hydroxy group-containing acrylic resin (A2) is 1/99 to 80/20.
  5. 5 . The clear coating composition according to claim 1 , wherein a solid concentration of the clear coating composition at 60 seconds after application during spray application is 60 mass % or more and 80 mass % or less, wherein the spray application was conducted under the following conditions: discharge amount: 220 cc/min, air motor: 30,000 rpm, voltage: −90 kV, linear velocity: 400 mm/sec, path pitch: 125 mm, gun distance: 250 mm, and booth conditions: 24° C., humidity: 68%.
  6. 6 . The clear coating composition according to claim 1 , wherein the organic solvent (C) further includes at least one member having a boiling point of 200° C. or higher selected from the group consisting of monocarboxylic acid esters, dibasic ester compounds, cellosolves, and carbitols.
  7. 7 . A method for producing a coated article, comprising: applying a base coating composition onto an article to be coated to form an uncured base coating film; applying a clear coating composition to the uncured base coating film to form an uncured clear coating film; and simultaneously curing the uncured base coating film and the uncured clear coating film, wherein the clear coating composition includes: a hydroxy group-containing acrylic resin (A); a polyisocyanate compound (B); and an organic solvent (C), wherein the hydroxy group-containing acrylic resin (A) includes a primary hydroxy group-containing acrylic resin (A1) and a secondary hydroxy group-containing acrylic resin (A2), the primary hydroxy group-containing acrylic resin (A1) does not contain a secondary hydroxy group, the primary hydroxy group-containing acrylic resin (A1) has an acid value of 0 mg KOH/g or more and 40 mg KOH/g or less, the primary hydroxy group-containing acrylic resin (A1) has a weight average molecular weight (Mw) of 6,000 or less, the secondary hydroxy group-containing acrylic resin (A2) has a weight average molecular weight (Mw) of 6,000 or more, the organic solvent (C) includes a ketone compound having 7 or 8 carbon atoms (C1), and the clear coating composition has a solid concentration at a time of application of 55% by mass or more.

Description

TECHNICAL FIELD The present invention relates to a clear coating composition and a method for manufacturing a coated article. BACKGROUND ART A clear coating film is usually formed as an outermost layer of a vehicle body of an automobile or the like. Clear coating films are required to have high designability and appearance. Meanwhile, in recent years, reduction of emission of volatile organic compounds (VOC) from factories and the like has been required for environmental conservation. One of the techniques for reducing VOC emission is to increase the solid concentration of a coating composition. Patent Document 1 describes a coating composition comprising (A) a hydroxy group-containing acrylic resin having an acid value of 0 to 30 mg KOH/g, (B) a hydroxy group-containing acrylic resin having an acid value of 60 to 120 mg KOH/g, and (C) a polyisocyanate compound, and having a solid content at the time of application of 50% by mass or more. PRIOR ART DOCUMENT Patent Document Patent Document 1: WO 2022/107847 A SUMMARY OF THE INVENTION Problems to be Solved by the Invention When the clear coating composition described in Patent Document 1 is used, a coating film superior in color shift and in appearance is obtained. However, as consumers are increasingly demanding higher designability and appearance due to their higher-grade intention, these performances are still insufficient. An object of the present invention is to provide a clear coating composition from which a coating film having superior color shift and appearance can be obtained, and a method for producing a coated article using the clear coating composition. Solutions to the Problems In order to solve the above-described problems, the present invention provides the following embodiments. [1] A clear coating composition including: a hydroxy group-containing acrylic resin (A);a polyisocyanate compound (B); andan organic solvent (C),in which the hydroxy group-containing acrylic resin (A) includes a primary hydroxy group-containing acrylic resin (A1) and a secondary hydroxy group-containing acrylic resin (A2),the primary hydroxy group-containing acrylic resin (A1) has a weight average molecular weight of 6,000 or less,the secondary hydroxy group-containing acrylic resin (A2) has a weight average molecular weight of 6,000 or more,the organic solvent (C) includes a ketone compound having 7 or more carbon atoms (C1), andthe clear coating composition has a solid concentration at a time of application of 55% by mass or more. [2] The clear coating composition according to [1], in which the primary hydroxy group-containing acrylic resin (A1) has an acid value of 0 mg KOH/g or more and 40 mg KOH/g or less. [3] The clear coating composition according to [1] or [2], in which the secondary hydroxy group-containing acrylic resin (A2) has an acid value of 0 mg KOH/g or more and 40 mg KOH/g or less. [4] The clear coating composition according to any one of [1] to [3], in which the weight average molecular weight of the primary hydroxy group-containing acrylic resin (A1) is 3,000 or more and 6,000 or less. [5] The clear coating composition according to any one of [1] to [4], in which a mass ratio (A1)/(A2) of a content of the primary hydroxy group-containing acrylic resin (A1) to a content of the secondary hydroxy group-containing acrylic resin (A2) is 1/99 to 80/20. [6] The clear coating composition according to any one of [1] to [5], in which a solid concentration of the clear coating composition at 60 seconds after application during spray application is 60 mass % or more and 80 mass % or less. [7] The clear coating composition according to any one of [1] to [6], in which the organic solvent (C) further includes at least one member having a boiling point of 200° C. or higher selected from the group consisting of monocarboxylic acid esters, dibasic ester compounds, cellosolves, and carbitols. [8] A method for producing a coated article, including: applying a base coating composition onto an article to be coated to form an uncured base coating film;applying a clear coating composition to the uncured base coating film to form an uncured clear coating film; andsimultaneously curing the uncured base coating film and the uncured clear coating film,in which the clear coating composition includes:a hydroxy group-containing acrylic resin (A);a polyisocyanate compound (B); andan organic solvent (C),wherein the hydroxy group-containing acrylic resin (A) includes a primary hydroxy group-containing acrylic resin (A1) and a secondary hydroxy group-containing acrylic resin (A2),the primary hydroxy group-containing acrylic resin (A1) has a weight average molecular weight (Mw) of 6,000 or less,the secondary hydroxy group-containing acrylic resin (A2) has a weight average molecular weight (Mw) of 6,000 or more,the organic solvent (C) includes a ketone compound having 7 or more carbon atoms (C1), andthe clear coating composition has a solid concentration at a time of application of 55