| 摘要 |
PURPOSE:To prevent ground fogging and enhance matching property and color forming sensitivity, by incorporating silicon dioxide or a silicon dioxide-calcium carbonate composite having a specific surface area of not more than 150m<2>/g and an oil absorption of not less than 100ml/100g into a protective layer for a thermal color forming layer. CONSTITUTION:Ground fogging is attributable to the acidic property of silicon dioxide or a silicon dioxide-calcium carbonate composite and the high activity of the surface of particles of silicon oxide or the composite. There is close relationship between the activity of the surface of the particles and the specific surface area of the particles, namely, the activity is high and ground fogging occurs when the specific surface area is in excess of 150m<2>/g, particularly, not less than 200m<2>/g. In addition, particles having an oil absorption of less than 100ml/100g, particularly, not more than 50ml/100g have a low effect of enhancing the matching property because of the low oil absorptivity for color forming components. The specific surface area mentioned herein is based on the BET method, and the oil absorption is based on JIS K-5101. Silicon oxide or the silicon oxide-calcium carbonate composite may be used in mixture with an ordinary filler, and a binder for forming the protective layer may be an aqueous emulsion of a known water-soluble high molecular weight substance. |
