prov:value
| - For the hardening agent, various types of hardening agents can be used, including aldehyde-based ones, aziridine-based ones (e.g., those described in PB Report 19,921, U.S. Pat. Nos. 2,950,197, 2,964,404, 2,983,611, and 3,271,175, Japanese Patent Examined Publication No. 40898/1971, and Japanese Patent O.P.I. Publication No. 91315/1975), isooxazolium-based ones (e.g., those described in U.S. Pat.
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