Method for producing polymers with a neutral color tone

摘要

A method is disclosed for producing polymers with a neutral color tone, wherein a blue and red dye are added before entry into the last polyreaction stage, wherein adjustment of a neutral color tone of the polymer, using a total dye concentration in the polymer of no more than 3 ppm and a proportion of the blue dye in the resulting dye mixture of at least 50% by weight, occurs through independent adjustment of a and b color values in the Lab color space by determination of a and b color values of the polymer without addition of dyes, establishment of the total dye concentration depending on the b-value shift to be achieved, establishment of the required mixture ratio of the colors red and blue depending on the a-value shift to be achieved, and metering of the established content of dye mixture into the reaction mixture.

主权项

1. A method for producing a polymer with a neutral color tone in which cobalt is omitted, suitable for making food packaging or beverage containers, in one or more reaction stages through independent adjustment of a and b color values in the Hunter l,a,b color space of the polymer, which comprises the steps of:
(a) producing sample chips of the polymer and determining the a and b color values of the Hunter l,a,b color space of the sample polymer chips by measuring in a tristimulus colorimeter, the color tone of the sample polymer chips with three photocells, ahead of which respectively one red, green and blue filter was placed prior to any addition of a dye; (b) establishing a total dye concentration not exceeding 3 ppm and in which cobalt is omitted for the polymer depending on the b color value to be achieved following a b value shift, whereby the b value decreases with increasing total dye concentration; (c) mixing red and blue dyes in which cobalt is omitted to establish a required dye mixture ratio of the red and blue dyes for the polymer depending on the a color value to be achieved following an a value shift, where the proportion of the blue dye in the dye mixture is at least 50% by weight, whereby with a mixture ratio of 80 to 85% by weight blue to 20 to 15% by weight red, the a value in the polymer remains unchanged, and all other mixture ratios of blue to red can be used for adjustment of the a value; and (d) following steps (b) and (c) metering into a reaction mixture for forming the polymer at a point before entry into the last polyreaction stage, the dye mixture having the total dye concentration as defined in step (b) and the required dye mixture ratio of the red and blue dyes as defined in step (c), to independently adjust the a color value, if necessary, and the b color value in the Hunter l,a,b color space of the polymer, thereby obtaining the polymer with a neutral color tone.