Process for the production of a pigment suspension of high solids comprising carboxymethylcellulose based dispersant

摘要

A process for preparing an aqueous suspension comprising the steps of a) providing a mineral pigment, b) providing a depolymerized carboxymethylcellulose having a degree of carboxylation in the range of 0.2 to 2.2, a molecular weight in the range from 5000 to 40,000 g / mol and a polydispersity in the range of 2 to 10, wherein the carboxymethylcellulose depolymerized is prepared by depolymerization of a carboxymethylcellulose of high molecular weight in a process comprising the following steps: i) providing a high molecular weight carboxymethylcellulose having a molecular weight above 40000 g / mol and a degree of carboxylation in the range of 0.2 to 2.0, ii) providing a peroxide selected from hydrogen peroxide and / or an alkali metal salt thereof, iii) providing a catalyst, iv) mixing at least part of the high molecular weight carboxymethylcellulose step i) and / or at least one of the peroxide step ii) and / or at least part of the catalyst of step iii) and water in any order at a reaction temperature of 50 to 85 ° C, and v) adding the remaining part of carboxymethylcellulose high weight molecular and / or the remaining portion of the peroxide and / or the remaining portion of catalyst in one or more steps to the mixture obtained in step iv) until the mixture of step v) containing 10 to 60% by weight carboxymethylcellulose depolymerized, based on the total weight of the mixture of step v), and until the mixture of step v) while having a Brookfield viscosity between 30 and 10,000 mPa.s at 20 ° C; wherein during step v), the Brookfield viscosity of the mixture is maintained between 200 and 1500 mPa · s, measured at the reaction temperature; c) mixing the carboxymethylcellulose depolymerized step b), the material of mineral pigment of step a) and water to form an aqueous suspension, wherein the material of mineral pigment is added in an amount of 10 to 80% by weight , based on the total weight of the suspension, and wherein the depolymerized carboxymethylcellulose is added in an amount of 0.05 to 5.0% by weight, based on the total weight of the material of mineral pigment in suspension and such such that the Brookfield viscosity of the aqueous suspension is between 40 and 2000 mPa-s at 20 ° C.