USE OF A POLYMER-TREATED MINERAL PIGMENT IN PAPER COATINGS

Mineral particles intended for the coating of paper and board were sur face-treated with a copolymer based on styrene and acrylic acid. The m ineral pigment used was ground CaCO3. The polymer was grafted to the m ineral by first adsorbing the acrylic acid to the surface and then all owing this monomer to take part in the polymerization with the styrene . The grafting was performed in the aqueous phase, which was considere d to be a prerequisite. The surface treatment of the mineral particles markedly improved the surface strength of papers coated with these pi gments. This was interpreted as being a result of improved compatibili ty between the surface-treated pigment and the synthetic binder used i n the coating layer. The surface treatment caused some decrease in the gloss of the coated papers but appeared otherwise not to impair impor tant properties of the coated product. To some extent the surface trea tment was also applied to kaolin particles. An improvement in the surf ace strength of papers coated with the modified particles was also obs erved with this pigment.