Ethylene-vinyl alcohol copolymer and resin composition, and molded product obtained using the same

A method of producing a resin composition, comprising:

• copolymerizing ethylene with vinyl acetate having a content of acetaldehyde of from 1 ppm to 100 ppm to obtain an ethylene-vinyl acetate copolymer;
• saponifying the ethylene-vinyl acetate copolymer to obtain an ethylene-vinyl alcohol copolymer (A) having a degree of saponification of at least 85 mol %;
• neutralizing a catalyst for the saponification;
• washing the ethylene-vinyl alcohol copolymer (A) with water;
• pelletizing the washed ethylene-vinyl alcohol copolymer (A) to obtain pellets of the washed ethylene-vinyl alcohol copolymer (A),
• immersing the pellets in an aqueous solution of an alkali metal salt (B1), wherein the alkali metal salt is one or more selected from the group consisting of sodium acetate, potassium acetate, sodium stearate, potassium stearate, and a sodium salt of ethylenediaminetetraacetic acid,
• separating the pellets containing the alkali metal salt (B1) from the aqueous solution, and
• drying the pellets containing the alkali metal salt (B1) to obtain the resin composition;
• and
• adding an ethylene-vinyl alcohol copolymer (F) having an ethylene content of 30 mol % to 60 mol % and a degree of saponification of at least 85 mol % to the resin composition,
• wherein:
• an ethylene content of the ethylene-vinyl alcohol copolymer (A) is from 20 mol % to 60 mol % as measured by H1-NMR,
• a value obtained by subtracting the ethylene content of the ethylene-vinyl alcohol copolymer (A) from the ethylene content of the ethylene-vinyl alcohol copolymer (F) is 8 mol % or greater,
• a mass ratio of (A/F) of the ethylene-vinyl alcohol copolymer (A) to the ethylene-vinyl alcohol copolymer (F) is from 60/40 to 95/5,
• after subjecting the ethylene-vinyl alcohol copolymer (A) to heat treatment in a nitrogen atmosphere at 220° C. for 50 hrs, molecular weights of the ethylene-vinyl alcohol copolymer (A) determined by gel permeation chromatography with a differential refractive index detector and an ultraviolet and visible absorbance detector satisfy (I′) and (i):
• (Ma−Mb)/Ma≤0.019 (I′),
• Mb≥50,000 (i);
• Ma represents a peak top molecular weight of the ethylene-vinyl alcohol copolymer (A) after the heat treatment measured by the differential refractive index detector calibrated with polymethyl methacrylate, and
• Mb represents an absorption peak molecular weight of the ethylene-vinyl alcohol copolymer (A) at a wavelength of 220 nm after the heat treatment measured by the ultraviolet and visible absorbance detector calibrated with polymethyl methacrylate;
• and
• a content of the alkali metal salt (B1) in terms of metal equivalent is from 10 ppm to 150 ppm of the resin composition.