Ionomer resin

An ionomer resin, comprising:

• a carboxylic acid ester unit (A);
• a carboxylic acid unit (B);
• a neutralized carboxylic acid unit (C);
• and
• an ethylene unit (D),
• wherein,
• the ionomer resin is derived from at least one ethylene-carboxylic acid ester copolymer (X) selected from the group consisting of an ethylene-methyl acrylate copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-ethyl methacrylate copolymer, an ethylene-n-propyl acrylate copolymer, an ethylene-n-propyl methacrylate copolymer, an ethylene-isopropyl acrylate copolymer, an ethylene-isopropyl methacrylate copolymer, an ethylene-n-butyl acrylate copolymer, an ethylene-n-butyl methacrylate copolymer, an ethylene-sec-butyl acrylate copolymer, and an ethylene-sec-butyl methacrylate copolymer;
• based on a total of monomer units constituting the ionomer resin, a content of the carboxylic acid ester unit (A) is 0.01 to 1.8 mol %, and a total content of the carboxylic acid ester unit (A), the carboxylic acid unit (B), and the neutralized carboxylic acid unit (C) is 6 to 10 mol %;
• and
• based on measurement of a molecular weight in terms of polyethylene by gel permeation chromatography with the carboxylic acid unit (B) and the neutralized carboxylic acid unit (C) being converted into a methyl carboxylate unit, the ionomer resin has a ratio of a low-molecular-weight component having a molecular weight of 2,500 g/mol or less obtained from an integral molecular weight distribution curve of 2.6 to 4.0 mass %, and a number average molecular weight of 8,000 to 14,000 g/mol.