Patent ID: 7942187

Claim:
A method for manufacturing a mold, comprising steps of: (a) expanding a powder mixture containing a water-soluble first inorganic salt powder, a second inorganic salt powder consisting of magnesium sulfate, and at least one water-soluble organic polymer powder selected from polgvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, methyl cellulose, ethyl cellulose, ethylhydroxymethyl cellulose, carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC) and hydroxypropylmethyl cellulose (HPMC) in a plane on a table and then selectively spraying a spray liquid containing at least one selected from a water-miscible organic solvent and water through a nozzle on this powder mixture layer to make a bonding strength among particles of the powder mixture in a sprayed region higher than that among particles of the powder mixture in an unsprayed region; (b) further expanding the powder mixture on the powder mixture layer after spraying and then selectively spraying the spray liquid through the nozzle on this powder mixture layer; (c) repeatedly conducting the step (b) over several times to form a mold shaped by the sprayed regions; (d) taking out the mold; and (e) heating the mold at a temperature between the temperature at which the water-soluble organic polymer is burned out and the temperature at which the first and second inorganic salts are not fused, wherein a surface of the mold after the step (e) is further sprayed with a treatment composition containing a third inorganic salt having a melting point lower than those of the first and second inorganic salts and at least one liquid selected from water and a water-miscible organic solvent, or the mold is dipped in the treatment composition, and the mold after either treatment is heated at a temperature at which the first and second inorganic salts are not fused but the third inorganic salt is fused.