Patent ID: 7820757

Claim:
A process for producing a polyamide with titanium dioxide pigments, comprising: dispersing the titanium dioxide pigments in a mixture containing water and caprolactam with an apparatus, said apparatus comprising a dispersing chamber, a disk-shaped rotor disposed in said dispersing chamber, a stator which has radial openings and is disposed in conjunction with said rotor in a dispersing zone of said dispersing chamber, a product inlet on each side of said rotor, such that a confluence of two product streams from each of the product inlets is disposed in an outer peripheral region of the disk-shaped rotor, and a product outlet at the outer periphery of said dispersing zone of said dispersing chamber, by feeding the titanium dioxide pigments through one of said product inlets and the mixture, containing water and caprolactam, through the other said product inlet to said dispersing chamber, and obtaining a product mixture, containing water, caprolactam and the titanium dioxide pigment from said product outlet, and polymerizing said product mixture to form the polyamide containing titanium dioxide pigments and wherein water is removed from the product mixture before or during the polymerization, blending said product mixture with additional caprolactam followed by polymerizing the additional caprolactam to form a masterbatch and filtering the masterbatch in a melt through a filter, wherein an average mean pressure build-up of the polymerized masterbatch, determined as a difference between a final pressure and an initial pressure upstream of the filter, divided by an amount put through, is about 7 bar/kg.