However, there is publicly available as of now. JIS standards are typically revised every 5–10 years, and the current version is JIS K 6258:2016 (identical to ISO 1817:2015).
I notice you're asking about — this is a Japanese Industrial Standard for Rubber, vulcanized or thermoplastic — Determination of the effect of liquids . -New release- Jis K 6258 Pdf