Patent ID: 8163828

Claim:
A process for the production of an additive for polymers, comprising: a. phosphoric acid H 3 PO 4 or a water-soluble phosphate compound is added in an amount of 0.1 to 10% by weight, calculated as P 2 O 5 and with respect to dry BaSO 4 , to an agitated aqueous suspension containing 0.5 to 50% by weight of BaSO 4 ; b. Na 2 SiO 3 is added in an amount of 0.1 to 15% by weight, calculated as SiO 2 and with respect to dry BaSO 4 , to the agitated suspension in accordance with process step (a), wherein the pH value of the suspension is kept below 7.5; c. a water-soluble aluminium compound is added in an amount of 0.1 to 20% by weight, calculated as Al 2 O 3 and with respect to BaSO 4 , to the agitated suspension in accordance with process step (b), wherein the pH value of the suspension is not kept below 4.5; and d. the suspended solid is separated from the aqueous phase of the suspension in accordance with process step (c) and dried; wherein the process steps (a), (b), and (c) are each respectively carried out over a period of 30 to 90 minutes in a temperature range of below 65° C.