Patent ID: 7253228

Claim:
A process for producing a polyurethane emulsion by emulsifying a urethane prepolymer, which contains substantially no organic solvent and also has at least two isocyanate groups per one molecule, with water and then completing chain extension, the process comprising: a preliminary step of assembling an emulsifying apparatus comprising one pair of a stator section (A) having a surface (a) and a rotor section (B) having a surface (b), in which the surfaces (a) and (b) face and are parallel to each other, the stator section (A) being fixed inside a cylindrical casing and the rotor section (B) being fixed to a rotational shaft provided in the casing, wherein the stator section (A) has the surface (a) wherein multiple stator teeth are arranged on the surface along with two or more concentric circles, and the rotor section (B) has the surface (b) wherein multiple rotor teeth are arranged on the surface along with two or more concentric circles, in which a ring axis of the circles is the same as the ring axis of the circles of the stator section (A), but diameters of the concentric circles of the rotor section (B) are different from those of the stator section (A), side surfaces of said rotor teeth being parallel to an axis of rotation for said rotational shaft for said rotor section, a distance between the surface (a) and a top of the multiple stator teeth of the stator section (A) is longer than a distance between the surface (a) and a top of the multiple rotor teeth of the rotor section (B), and the stator section (B) has a supply inlet which is positioned in the smallest circle of the stator section (A), and an outlet, which is positioned at a side portion of the stator section (A), a first step of supplying a stream containing the urethane prepolymer into the emulsifying apparatus and separately supplying a stream containing water into the emulsifying apparatus so as to form an emulsion of the urethane prepolymer in water, from the inlet and continuously emulsifying them by having a peripheral velocity of a rotor tooth located at the outermost periphery among multiple rotor teeth of the emulsifying apparatus be within a range from 30 to 70 m/second so as to obtain an emulsion of the urethane prepolymer having an average particle size of 0.1 to 2.5 μm, and discharging the emulsion from the outlet, and a second step of reacting the emulsion of the urethane prepolymer obtained in the first step with a chain extender, thereby completing chain extension of the urethane prepolymer.