A polishing pad has a polishing layer that is formed of a polyurethane foam having fine cells. The polyurethane foam is a reaction cured body of a chain extender and an isocyanate-terminated prepolymer which is obtained by reacting a prepolymer starting material composition that contains an isocyanate component, a high molecular weight polyol and an aliphatic diol. The high molecular weight polyol contains a polyalkylene glycol A that has a peak of the molecular weight distribution within the range of 200 to 300 and a polyalkylene glycol B that has a peak of the molecular weight distribution within the range of 800 to 1200.
1. A method for producing a polishing pad, comprising the steps of:
(C) synthesizing an isocyanate-terminated prepolymer and
(D) mixing a first component containing the isocyanate-terminated prepolymer with a second component containing a chain extender and curing the mixture to prepare a polyurethane foam, wherein:
the step (C) comprises reacting an isocyanate component with an aliphatic diol and a polyalkylene glycol A that has number average molecular weight within the range of 200 to 300 to synthesize a prepolymer precursor and then reacting the prepolymer precursor with a polyalkylene glycol B that has a number average molecular weight within the range of 800 to 1200 to synthesize the isocyanate-terminated prepolymer, and
the step (D) comprises adding 3 to 10 parts by weight of a silicone-based surfactant based on 100 parts by weight of the isocyanate-terminated prepolymer, to the first component containing the isocyanate-terminated prepolymer, further stirring the first component together with a non-reactive gas to form a cell dispersion liquid in which the non-reactive gas is dispersed in the form of fine cells, then mixing the second component containing the chain extender into the cell dispersion liquid, and curing the mixture to prepare a polyurethane foam.
2. The method according to claim 1 , wherein the aliphatic diol is 1,4-butanediol.
3. The method according to claim 1 , wherein the blending amount of the aliphatic diol is 1 to 7% by weight in the prepolymer starting material composition.
4. The method according to claim 1 , wherein the isocyanate component contains an aromatic diisocyanate and an aliphatic diisocyanate and/or an alicyclic diisocyanate.
5. The method according to claim 1 , wherein the polyurethane foam has an average cell diameter of 20 to 70 μm and a cut rate of 2 μm/min or less.
6. The method according to claim 1 , wherein the polyurethane foam has a hardness reduction rate of 20% or less at water absorption and a breaking strength reduction rate of 20% or less at water absorption.