Abstract: A binder of this invention is a powder which comprises an intimate mixture of a copolymer of maleic anhydride with an olefinically unsaturated compound selected from the group consisting of an aliphatic .alpha.-olefin having 2 to 8 carbon atoms, styrene and methyl vinyl ether, 0.2 to 2.0 equivalents of a caustic alkali per carboxyl equivalent of said copolymer, and if desired, 30 to 500 parts by weight of an alkaline earth metal hydroxide per 100 parts of the total weight of said copolymer and said caustic alkali, and if desired, up to 300 parts by weight of additive per 100 parts of the total weight of said copolymer and said caustic alkali. A process for preparing a mold according to this invention comprises mixing said powdered binder with refractory particles and a small amount of water under agitation, and forming the resulting mixture into a shaped product, whereafter the shaped product is hardened by blowing CO.sub.2 gas therethrough.

Abstract: In a mold to be hardened by a CO.sub.2 gas, a mold binder material comprising a combination of polymers containing carboxyl groups, at least one of multi-valent metal oxides and multi-valent metal hydroxides, and resins of polyvinyl alcohol group, and at least one of sodium salt of gluconic acid and polyhydric alcohols or a mold binder material comprising a combination of polymers having carboxyl groups, at least one of multi-valent metal oxides and multi-valent metal hydroxides, and at least one of sodium salt of gluconic acid and polyhydric alcohols is provided.