A color developer for a thermal recording layer includes: a compound of formula (I):

##STR00001##

; and an N-substituted amino acid derivative of formula (II): (R.sup.0X)Y(Z). The color developer is excellent in plasticizer resistance.

A thermosensitive recording body has at least a thermosensitive recording layer and a topcoat layer formed on a substrate. The substrate consists of a transparent film. At least the thermosensitive recording layer and the topcoat layer includes a diffuse reflection suppressor component that suppresses diffuse reflection of light from particles constituting the thermosensitive recording layer and the topcoat layer.

The present invention provides a heat-sensitive recording material having a high recording density, excellent plasticizer resistance in recorded portions, and excellent resistance to thermal background fogging in high-temperature environments. The heat-sensitive recording material includes a heat-sensitive recording layer containing a specific sulfonamide compound.

A thermosensitive recording medium is provided that is excellent in heat discoloration resistance in the blank portions and in bar code readability. It also has excellent water resistance and printing (recording) run-ability. The thermosensitive recording medium includes a support, a thermosensitive recording layer installed on the support, and a protective layer on the thermosensitive recording layer. The thermosensitive recording layer contains two kinds of electron accepting color developing agents, a sulfonic acid compound and a diphenyl sulfone compound. Both the thermosensitive recording layer and the protective layer contain crosslinking agents, and at least one, and preferably both, of the thermosensitive recording layer and the protective layer contain an ammonium zirconium carbonate as the crosslinking agent.

A thermosensitive recording medium, comprising: a thermosensitive recording layer containing colorless or pale colored electron donating leuco dye and an electron accepting color developing agent on a substrate, wherein the thermosensitive recording layer contains at least one of a urea compound represented by the following general formula (Formula 1) as the electron accepting color developing agent

##STR00001##

(where, X represents O or NH, R.sup.1 represents a hydrogen atom or SO.sub.2R.sup.3, R.sup.3 represents a substituted or unsubstituted alkyl group, an aralkyl group or aryl group, R.sup.2 represents a hydrogen atom or alkyl group, and m represents 0 or 1), and wherein the substrate consists of a paper base material having water dispersibility.

Disclosed is a heat-sensitive recording material comprising at least an undercoat layer and a heat-sensitive recording layer in this order on a support, the undercoat layer containing an inorganic pigment, hollow particles, and a binder, the heat-sensitive recording layer containing a leuco dye, developers, and a binder, the heat-sensitive recording layer containing a first developer and a second developer as the developers, the heat-sensitive recording layer containing an N,N-diarylurea-based compound represented by formula (1) as the second developer:

##STR00001## wherein R.sub.2 represents a C.sub.1-12 alkyl group, a C.sub.7-12 aralkyl group, or a C.sub.6-12 aryl group, the aralkyl group and aryl group may be substituted with a C.sub.1-12 alkyl group, a C.sub.1-12 alkoxy group, a C.sub.6-12 aryl group, or a halogen atom, and a plurality of R.sub.2s may be the same or different; and A.sub.1 represents a hydrogen atom or a C.sub.1-4 alkyl group, and a plurality of A.sub.1s may be the same or different.

There is disclosed a heat-sensitive recording material including an undercoat layer formed on one surface of a support and a heat-sensitive recording layer formed on the undercoat layer. The heat-sensitive recording layer contains a leuco dye and a coloring agent. The undercoat layer contains hollow particles and a binding resin. A maximum particle diameter (D100) of the hollow particles is 10 to 30 m. A particle diameter (D50) of the hollow particles at cumulative 50 volume % is 4.0 to 15 m. A ratio D100/D50 of the maximum particle diameter (D100) of the hollow particles to the particle diameter (D50) of the hollow particles at cumulative 50 volume % is 1.8 to 3.0. A volume percentage of the hollow particles having particle diameters of 2.0 m or less is 1% or less.