Method for producing rigid polyurethane foam, and rigid polyurethane foam

A method for producing a rigid closed-cell polyurethane foam, which comprises a step of reacting a polyol having a hydroxyl value of from 200 to 800 mgKOH/g and an average number of functional groups of from 3 to 6 with a polyisocyanate compound in the presence of an amino-modified silicone compound, a catalyst, a blowing agent and a surfactant, wherein the blowing agent is water and is present in an amount of from 4 to 12 parts by mass per 100 parts by mass of the polyol, wherein the amino-modified silicone compound is in an amount from 0.001 to 0.1 parts by mass per 100 parts by mass of the polyol and is at least one member selected from the group consisting of a compound represented by the following formula (1) and a compound represented by the following formula (2):

• wherein in the formula (1), R1 is a C1-10 alkylene group, R2 is a C1-10 alkyl group, and k is an integer of from 1 to 2,000, and in the formula (2), m is an integer of from 0 to 100, n is an integer of from 1 to 2,000, each of R3, R4 and R5 which may be the same or different from one another, is a group selected from the group consisting of a C1-10 alkyl group, a C1-10 alkoxy group and a C1-10 alkyl group having a nitrogen atom;
• provided that when m is 0, at least one of R3 and R5 is a C1-10 alkyl group having a nitrogen atom, and when m is an integer of from 1 to 100, at least one selected from R3, R5 and R4, is a C1-10 alkyl group having a nitrogen atom;
• wherein the rigid closed-cell polyurethane foam has a core density of from 20 to 40 kg/m3;
• wherein the polyurethane foam has a high temperature dimensional change as measured in accordance with ASTM D 2126-75, wherein the maximum value of dimensional change among absolute values of respective changes in length, width and thickness directions of a sample is less than 5%;
• and
• wherein the polyurethane foam has a thermal conductivity as measured at 24° C. in accordance with JIS A1412 of 0.0257 W/m·K or less.