| 摘要 |
PURPOSE:To obtain using MDI, which is inexpensive, an elastomer comparable in strength and durability to that obtained using NDI, which is expensive, by mixing a prepolymer obtained under special conditions with a foaming ingredient to. foam and cure the prepolymer. CONSTITUTION:A polyester polyol having a number-average mol.wt. of 1,000-3,000 is reacted with diphenylmethane 4,4-diisocyanate (MDI) in a weight ratio of 1:(0.2-0.6). 100 pts.wt. this reaction product is reacted with 0.1-2.0 pts.wt. low-mol. polyol having two to three active-hydrogen groups at molecular ends to obtain a partially crosslinked isocyanate-terminated prepolymer. This prepolymer is mixed with a foaming ingredient comprising at least 50% water as the main foaming agent, a catalyst, a foam stabilizer, etc., in such a proportion that the amount of the isocyanate groups of the prepolymer is 0.9-1.2 equivalents to the hydroxyl groups of the foaming ingredient. The obtained elastomer has a durability in an endurance test of 500,000 passes or more, a yielding of 10% or lower, and a service life of 4 hr or longer. |
