Process to obtain a radial filler, especially for use in the paper industry, a filler product formed by anhydrous and hemihydrate calcium sulfates and composition useful to prepare said filler

摘要

The invention refers to a process to obtain a radial filler for use in the paper industry, and to a calcium sulfate dihydrate product obtained by cocrystallization of hemihydrate calcium sulfates and anhydrite II as well as to a composition that comprises said sulfates. The process comprises the preparation of a composition from a ponderal mixture of hemihydrate calcium sulfate and anhydrite II and inclusion thereof under agitation in an aqueous medium in proportions higher than the supersaturation point of the solution, wherein calcium sulfate dihydrate molecules formed from the hemihydrate crystallize linearly and divergently, upon nuclei comprised of anhydrite II. Crystallization is produced without the need of crystallization regulators chemically different from calcium sulfate since anhydrite II acts as such a regulator. The filler product is comprised at least partially of crystalline star-shaped aggregates that show exceptional electrostatic adhesion to cellulose fibers and due to the multiple ramifications thereof, it offers excellent physical interaction with the framework formed by the cellulose fibers. The crystallized filler can be used directly in solution, or can be previously dried to be used in aqueous redispersion.