NOVEL CLAY MINERAL COLOR DEVELOPER FOR PRESSURE SENSITIVE RECORDING PAPER AND PROCESS FOR PRODUCING SAME

摘要

A color developer for pressure-sensitive recording paper which is derived from a clay mineral having a layer-structure composed of regular tetrahedrons of silica and which shows (A) the diffraction pattern attributable to the crystals of layer-structure composed of regular tetrahedrons of silica when subjected to an electron diffraction analysis, but (B) substantially no diffraction pattern attributable to the crystals of said layer-structure when subjected to an X-ray diffraction analysis, and which (C) contains as the constituting elements besides oxygen, at least silicon, magnesium and/or aluminum. This color developer is produced by acid-treating a clay mineral having a layer-structure composed of regular tetrahedrons of silica until its SiO2 content reaches 82-96.5% by weight on dry basis (drying at 105 DEG C. for 3 hours), contacting the resulting clay mineral, in an aqueous medium, with a magnesium and/or an aluminum compound or compounds which are at least partially soluble in said aqueous medium, neutralizing the system with an alkali or an acid to form hydroxide when the soluble compound or compounds employed are other than hydroxides, whereby introducing into the acid-treated clay mineral a magnesium and/or an aluminum component, and drying the product if desired. The color developer of this invention exhibits an improved color-developing ability particularly to the primary color development dye and an improved color-developing ability to the secondary color development dye, and shows excellent light resistance after the color development, little reduction in the color-developing ability after storage in an atmosphere of a high humidity and high temperature.