Coating film for structure, set of coating materials for forming coating film, coating material for undercoat layer, and coating method

A coating film on an underwater structure, comprising:

• an undercoat layer bonded to the underwater structure;
• and
• an antifouling layer bonded to the undercoat layer,
• wherein:
• a 100-gram underwater constant load peeling degree of the coating film is less than 5 (mm/20 mm);
• a ratio of a tensile breaking strength of the coating film to an adhesive force of the coating film with respect to the underwater structure, as measured after immersing the coating film in pure water at 60° C. for 5 weeks, is 1.5 or more, wherein the unit of measurement for each of the tensile breaking strength and the adhesive force is N/20 mm;
• a 1-mm square cross-cut stretching-caused peeling degree of the antifouling layer with respect to the undercoat layer is 0.05 or less;
• the undercoat layer comprises a styrene-based thermoplastic elastomer with a styrene content of 20 to 40 weight %;
• the styrene-based thermoplastic elastomer is modified by a compound containing a polar group having a content of 0.1 to 20 weight % in the styrene-based thermoplastic elastomer;
• the 100-gram underwater constant load peeling degree is measured as follows:
• the coating film is formed on a poly (methyl methacrylate) (PMMA) plate;
• subsequently, the coating film is trimmed to have a size of 20 mm×100 mm;
• then, with respect to the PMMA plate, the trimmed coating film is peeled from the side of one short side having a length of 20 mm thereof by a length of 20 mm, and folded back by 180°;
• and the short side is attached to an end of a polyethylene terephthalate (PET) film, such that a contact area therebetween becomes 20 mm×20 mm;
• a weight member having a weight adjusted to become 100 g under water is attached to the PET film to prepare a test sample;
• a tank filled with pure water at 23° C. is prepared;
• then, the sample is immersed in the pure water such that a peel angle of the sample becomes 180 degrees;
• and a distance over which the coating film is peeled from the PMMA plate in one hour is measured as the 100-gram underwater constant load peeling degree;
• the ratio of the tensile breaking strength of the coating film to the adhesive force of the coating film with respect to the underwater structure, as measured after immersing the coating film in pure water at 60° C. for 5 weeks, is measured as follows:
• after immersing the coating film in pure water at 60° C. for 5 weeks, the coating film is trimmed to have a size of 20 mm×100 mm;
• a force measured when peeling the coating film from the PMMA plate at a peel angle of 180 degrees and at a peel rate of 300 mm/min, using a tensile tester is defined as the adhesive force;
• after immersing the coating film in pure water at 60° C. for 5 weeks, the coating film is trimmed to have a size of 20 mm×60 mm, and the tensile breaking strength of the trimmed coating film is evaluated, using a tensile tester;
• the ratio of the tensile breaking strength and the adhesive force measured is the ratio of the tensile breaking strength to the adhesive force to the underwater structure, as measured after immersing the coating film in pure water at 60° C. for 5 weeks;
• and
• the cross-cut stretching-caused peeling degree is measured as follows:
• the coating film is cut into 20 mm×60 mm;
• and only the antifouling layer is slit by a cutter, using a cross-cut test cutter guide, to form 100 cross-cut cells that are each 1 cm2 at intervals of 1 mm;
• then, the coating film having the cross-cut cells is stretched along a diagonal line of the cross-cut cells at a stretching ratio of 2;
• and the cross-cut stretching peeling degree is based on a counted quantity of individual cross-cut cells peeled from the undercoat layer by the coating film having the cross-cut cells being stretched along the diagonal line of the cross-cut cells at the stretching ratio of 2.