Composition for preparing rigid polyurethane foam having good demolding property

A composition for preparing a rigid polyurethane foam comprising:

• a mixed polyol 100 weight parts comprising 40–60 wt. % of polyol (a) which is obtained by polymerization with an alkylene oxide using sorbitol as an initiator, 5˜10 wt. % of polyol (b) which is obtained by polymerization with an alkylene oxide using ethylene diamine as an initiator, 20˜30 wt. % of polyol (c) which is obtained by polymerization with an alkylene oxide using toluene diamine as a single initiator or a mixture of toluene diamine and triethanol amine as a complex initiator, and 5˜20 wt. % of multivalent polyol (d) of an ester structure, on a basis of total weight of mixed polyol;
• 1.6˜3.5 weight parts of reaction catalyst component including 0.3˜0.7 weight parts of a foaming catalyst, 1.0˜1.5 weight parts of a gelling catalyst and 0.3˜0.5 weight parts of a trimerization catalyst, per polyol 100 weight parts;
• 10˜50 weight parts of a foam blowing agent;
• 1.5˜2.5 weight parts of water;
• and
• 150˜170 weight parts of an organic isocyanate.