Method of producing polishing pad-use polyurethane foam and polyurethane foam

1. A method of producing polishing pad-use polyurethane foam comprising the steps of:

charging a first component, a foaming agent and a second component that reacts with the first component to form polyurethane in specified amounts into a tank and foaming/mixing them for a specified time by a mixer,

wherein the mixer comprises a first mixer blade and a second mixer blade having shaft centers in a vertical direction, and the first and second mixer blades are allowed to rotate in reversed directions in a manner so as to engage each other, and are also designed so that the two blades do not interfere with each other so as to allow a gas to be involved in the solution through rotations of the mixer,

wherein the number of revolutions in each of the mixer blades is set in a range from 500 to 3000 rpm, and

after the above-mentioned step, pouring the mixed solution into a mold so as to react with one another to be cured,

wherein the mixed solution is poured into the mold through a valve attached to a bottom of the tank said mold being disposed underneath the tank,

wherein said polyurethane foam has an average cell diameter in a range from 10 to 70 μm with the number of cells in a range from 100 to 700/mm 2 .

2. The method of producing a polishing pad-use polyurethane foam according to claim 1 , further comprising a step of raising the first and second mixer blades from the solution face after the step of foaming/mixing,

wherein at this raising process, the solution that has adhered to the first and second mixer blades is allowed to flow downward along the blade portions.

3. A method of producing a polyurethane foam comprising:

loading a first component, a foaming agent, and a second component that reacts with the first component to form polyurethane into a tank;

mixing and foaming the first and second components and the foaming agent in the tank,

wherein the mixing is conducted using a first mixer blade and a second mixer blade having shaft centers in a vertical direction and rotating in reverse directions, wherein the first mixer blade and the second mixer blade have smoothly curved shapes to facilitate a portion of the mixture adhering to the blade to flow down along the blades and drip into the mixture without splashes when the blades are separated from the mixture so as to inhibit the occurrence of air voids;

wherein the number of revolutions in each of the mixer blades is set in a range from 500 to 3000 rpm, and

pouring the resultant mixture into a mold from a bottom of the tank through a valve attached to said bottom said mold being disposed underneath the tank;

wherein said polyurethane foam has an average cell diameter in a range from 10 to 70 μm with the number of cells in a range from 100 to 700/mm 2 .

4. The method according to claim 3 , wherein the first component contains an isocyanate-group-containing compound, the second component contains an active hydrogen-containing compound, and the foaming agent is a silicon-containing nonionic surfactant having no hydroxide group.

5. The method according to claim 3 , wherein the mold is allowed to slide in a longitudinal direction of a supporting base.