Antifouling coating composition and antifouling coating film

An antifouling coating composition comprising a silicon atom-containing resin,

• wherein
• the silicon atom-containing resin includes:
• a constituent unit (A) derived from a monomer (a) having at least one kind of silicon atom-containing group selected from the group consisting of a group represented by a formula (I) below, a group represented by a formula (II) below, a group represented by a formula (III) below, and a group represented by a formula (IV) below;
• and
• a constituent unit (B) derived from a monomer (b) which is a polyfunctional (meth)acrylic acid ester having two or more (meth)acryloyloxy groups:
• [Chemical formula 1]
• in the formula (I), a and b each independently represent an integer of 2 to 5, m represents an integer of 0 to 50, and n represents an integer of 3 to 270;
• and R1 to R5 each independently represent an alkyl group, an alkoxy group, a phenyl group, a substituted phenyl group, a phenoxy group, or a substituted phenoxy group;
• [Chemical formula 2]
• in the formula (II), c and d each independently represent an integer of 2 to 5, and p represents an integer of 0 to 50;
• R6, R7 and R8 each independently represent an alkyl group, Ra, or Rb;
• Ra is
• [Chemical formula 3]
• in the formula, x represents an integer of 0 to 200, and R23 to R27 are the same or different and each represent an alkyl group;
• and
• Rb is
• [Chemical formula 4]
• in the formula, y represents an integer of 1 to 200, and R28 and R29 are the same or different and each represent an alkyl group;
• [Chemical formula 5]
• in the formula (III), e, f, g, and h each independently represent an integer of 2 to 5, q and s each independently represent an integer of 0 to 50, and r represents an integer of 3 to 270;
• and R9 to R12 each independently represent an alkyl group, an alkoxy group, a phenyl group, a substituted phenyl group, a phenoxy group, or a substituted phenoxy group;
• [Chemical formula 6]
• in the formula (IV), i, j, k, and l each independently represent an integer of 2 to 5, t and u each independently represent an integer of 0 to 50, and v and w each independently represent an integer of 0 to 70;
• and R13 to R22 are the same or different and each represent an alkyl group, and
• wherein a content of the constituent unit (B) is less than or equal to 30 mass % in all constituent units contained in the silicon atom-containing resin, and the monomer (b) is a compound (b-1) represented by a formula (b-1) below
• in the formula (b-1), RA each independently represents a hydrogen atom or a methyl group, RB represents a divalent hydrocarbon group that may have a substituent, and at least one-CH2-of the hydrocarbon group may be replaced by—O—or —C (═0)—1.