Transmission belt core wire production method, transmission belt production method, processing agent and processing kit

A method of producing a cord for a power transmission belt, the method comprising:

• a first treatment step of treating an untreated yarn of a cord for a power transmission belt with a first treatment agent comprising a resin component (A) to obtain a first treated yarn, wherein the untreated yarn comprises raw material fibers comprising aramid fibers, and a rubber layer of the power transmission belt with which the cord is to come into contact comprises an ethylene-α-olefin elastomer;
• and
• a second treatment step of treating the first treated yarn with a second treatment agent comprising a condensate (B1) of resorcin and formaldehyde, an unmodified styrene-butadiene-vinylpyridine latex (B2), and a maleic acid-modified polybutadiene (B3) to obtain a second treated yarn,
• wherein the resin component (A) comprises an NBR modified epoxy resin (A1-1) modified with an elastic polymer, a total concentration (in terms of solid content) of the condensate (B1) and the unmodified styrene-butadiene-vinylpyridine latex (B2) is 8 mass % to 18.2 mass % in the second treatment agent, and a concentration (in terms of solid content) of the maleic acid-modified polybutadiene (B3) is 2.7 mass % to 13.2 mass % in the second treatment agent, or
• wherein the resin component (A) comprises a condensate (A2-1) of resorcin and formaldehyde, a carboxyl-modified NBR latex (A2-2), and a curing agent (A2-3) comprising a polycarbodiimide resin having a plurality of carbodiimide groups, a total concentration (in terms of solid content) of the condensate (B1) and the unmodified styrene-butadiene-vinylpyridine latex (B2) is 5.2 mass % to 15 mass % in the second treatment agent, and a concentration (in terms of solid content) of the maleic acid-modified polybutadiene (B3) is 1.2 mass % to 9.7 mass % in the second treatment agent.