Abstract: A heat-sensitive recording material which has a high recording density, ensures recorded images of high quality and allows printing on the reverse side. A base paper for the recording material is subjected to multilayer paper making by means of a paper machine having a multilayer head box. The surface layer of the base paper has a bulk density of below 0.85 g/cu. cm and a printing smoothness of above 15% (pressure: 20 kg/sq. cm) as measured by means of a printing smoothness tester.

Abstract: The heat-sensitive record materials have, between the base sheet and the recording layer, a middle layer which mainly comprises a binder and at least one pigment having an oil absorption of at leasat 80 cc/100 g measured by JIS K 5101. The middle layer comprises an acrylic thickener in an amount of 0.05 to 5 parts by weight per 100 parts by weight of the pigment on dry basis.The middle layer is formed by blade-coating on a base sheet a coating composition comprising at least one pigment having an oil absorption of at least 80 cc/100 g measured by JIS K 5101 and a binder, in which an acrylic thickener is comprised in such amount as described above.

Abstract: Disclosed is a two-color heat-sensitive recording material which comprises a base sheet and a recording layer of single-layer or multi-layer structure formed on the base sheet, the recording layer comrising:(a) a diazonium salt,(b) a basic leuco dye,(c) a 2-hydroxy-3-naphthoic acid derivative which acts as a coupler compound for causing the diazonium salt to develop color when heated and which also acts as a color developing material for causing the basic leuco dye to develop color when heated, and(d) a basic substance, wherein the diazonium salt and the basic leuco dye each form a color upon application of heat, thereby giving the first image of a mixed color, and, then, after irradiation of an active ray to decompose the diazonium salt, the basic leuco dye alone forms its own color upon application of heat, thereby giving the second image whose color is different from the mixed color of the first image.

Abstract: A new phthalide derivative useful as a colorless chromogenic material has the following formula: ##STR1## wherein A and n have the same meaning as defined hereinbefore.

Abstract: Cycloalkyl aminophenol derivatives are produced by reacting o-, m- or p-aminophenol with a cycloalkanone having 5 to 12 carbon atoms in the presence of a reducing agent and preferably with the addition of an acid.

Abstract: Fluoran compounds of the structural formula: ##STR1## wherein R.sub.1 is propyl or butyl, R.sub.2 is an alkyl of from one to four carbon atoms, R.sub.3 is methyl or ethyl, and R.sub.4 is hydrogen or methyl are particularly suitable for use in providing high quality pressure, heat or electrothermal sensitive recording sheets containing a color former in operative association with an electron-accepting substance.