US Patent 7635661 Heat-sensitive recording material

A heat-sensitive recording material has a support, and a heat-sensitive recording layer including at least a leuco dye, a developer and a binder. The heat-sensitive recording layer contains secondary particles with an average particle diameter of 30 to 900 nm formed by aggregation of primary particles of amorphous silica with a particle diameter of at least 3 nm and less than 30 nm, and optionally a basic pigment. A protective layer may be formed on the heat-sensitive recording layer.