PURPOSE: To form a master pattern for casting so as to have adequate workability and compressive strength and to provide a smooth surface having low water absorptivity thereto by putting the prefoamed particles of a crosslinked PP resin having a specific gel fraction into a mold and heating the same to expand to the specific density and average cell size.
CONSTITUTION: Adequate amts. of water, antisticking agent talc, org. peroxide crosslinking agent such as 1,1-bis(t-butyl peroxy)3,3,5-trimethyl cyclohexane and crosslinking assistant divinyl benzene are added to the PP resin such as ethylene/propylene random copolymer having ≤40% residue of n-heptane extraction and the mixture is heated in an autoclave to form the crosslinked resin particles. Suitable amts. of water and volatile org. foaming agent such as dichlorofluoromethane are added thereto and the particles are released after the pressurizing and heating up to form the prefoamed and crosslinked particles having 0.01W50% gel fraction. Such particles are put into a metallic mold and are heated to expand, then the foamed molding having 0.2W0.02g/cm3 density and 70W1,000μm average cell size is obtd. The good master pattern for casting having the adequate cutting workability, compressive strength, smooth surface and low water absorptivity is thus obtd.
NAITO MASATO
HAMADA TADATSUGU
WATANABE TEISHIRO
MITSUBISHI HEAVY IND LTD
| JPS4743404A |
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