Provided is a heat-sensitive recording material that can provide clear and high print image quality with less printing omission, and that has high sensitivity and is excellent in recording density in halftone printing. The heat-sensitive recording material includes an undercoat layer and a heat-sensitive recording layer on a support in this order, in which: the undercoat layer contains hollow particles; the heat-sensitive recording layer contains a leuco dye and a color developer; and the heat-sensitive recording material has one characteristic selected from a group consisting of following (A) to (C): (A) the undercoat layer further contains an adhesive and a water retention agent and a maximum particle size (D100) of the hollow particles is 10 ?m to 30 ?m; (B) an average particle size (D50) of the hollow particles is 3 ?m to 20 ?m and the heat-sensitive recording layer further contains an inorganic layered compound; and (C) the undercoat layer further contains an adhesive, the hollow particles include at least two kinds of hollow particles including large particle size hollow particles and small particle size hollow particles, a maximum particle size (D100) of the large particle size hollow particles is 10 ?m to 80 ?m, an average particle size (D50) of the large particle size hollow particles is 7.5 ?m to 25 ?m, and an average particle size (D50) of the small particle size hollow particles is 0.7 ?m to 6 ?m.

A reversible recording medium of an embodiment of the present disclosure includes a support base and a recording layer. The recording layer is provided on the support base and reversibly changes between a recorded state and a deleted state. A chroma difference C* between the support base and the recording layer satisfies the relational expression (1) where an absorption spectrum in a visible region of the recording layer in the deleted state and an absorption spectrum in a visible region of the support base are each denoted by L*a*b*.

A reversible recording medium of an embodiment of the disclosure includes a support base, and a recording layer provided on the support base and reversibly changing between a recorded state and a deleted state. The recording layer includes a photothermal conversion material including one or more of a compound having a phthalocyanine skeleton, a compound having a squarylium skeleton, a compound having a cyanine skeleton including, in a molecule, one or both of a counter ion of SbF.sub.6, PF.sub.6, BF.sub.4, ClO.sub.4, CF.sub.3SO.sub.3 and (CF.sub.3SO.sub.3).sub.2N and a methine chain containing a five-membered ring or a six-membered ring, and an inorganic compound; a coloring compound having an electron-donating property; and a color developing/quenching agent having an electron-accepting property and including at least one salicylic acid compound represented by the general formula (1) and including a linear hydrocarbon group having 25 to 34 carbon atoms via a linking group containing an amide moiety.

A mess-free coloring system comprising a coloring medium and optionally one or more coloring utensils is disclosed. The coloring medium can include a substrate with or without decorative effects and one or more coating layers on a surface of the substrate. In various examples, the one or more coating layers include a color-triggering developer, e.g., in the form of a substantially clear resin, and an opaque pigment. Decorative effects integrated with or disposed on the substrate, while initially obscured by the one or more coating layers, can be revealed when the coating layers are mixed with at least one color precursor stored and dispensed from a coloring utensil. The opaque pigment is selected and configured such that, upon receipt of at least one color precursor by the one or more coating layers, a change in the pigment's reflective index occurs as the pigment dissolves into the clear resin developer.

A mess-free coloring system comprising a coloring medium and optionally one or more coloring utensils is disclosed. The coloring medium can include a substrate with or without decorative effects and one or more coating layers on a surface of the substrate. In various examples, the one or more coating layers include a color-triggering developer, e.g., in the form of a substantially clear resin, and an opaque pigment. Decorative effects integrated with or disposed on the substrate, while initially obscured by the one or more coating layers, can be revealed when the coating layers are mixed with at least one color precursor stored and dispensed from a coloring utensil. The opaque pigment is selected and configured such that, upon receipt of at least one color precursor by the one or more coating layers, a change in the pigment's reflective index occurs as the pigment dissolves into the clear resin developer.

A reversible recording medium according to an embodiment of the present disclosure includes: a recording layer including a leuco pigment as a coloring compound; and a first barrier film that is provided on one surface and a side surface of the recording layer and suppresses mixing of at least one of water or oxygen.

The invention relates to a color developer of the formula (I), wherein m and n independently of one another are ?1, Ar.sup.1 is an unsubstituted or substituted (hetero) aromatic radical, Ar.sup.2 is an unsubstituted or substituted phenyl radical, and Y is at least one (m+n)-times substituted benzene or naphthalene group, and to a heat-sensitive recording material, comprising a supporting substrate and a heat-sensitive color-forming layer containing at least one color former and at least one phenol-free color developer, wherein the at least one color developer is the compound of the formula (I). The invention further relates to a method for producing said heat-sensitive recording material. ##STR00001##

The invention relates to a color developer of the formula (I), wherein m and n independently of one another are ?1, Ar.sup.1 is an unsubstituted or substituted (hetero) aromatic radical, Ar.sup.2 is an unsubstituted or substituted phenyl radical, and Y is at least one (m+n)-times substituted benzene or naphthalene group, and to a heat-sensitive recording material, comprising a supporting substrate and a heat-sensitive color-forming layer containing at least one color former and at least one phenol-free color developer, wherein the at least one color developer is the compound of the formula (I). The invention further relates to a method for producing said heat-sensitive recording material. ##STR00001##

Disclosed is a heat-sensitive recording material comprising an undercoat layer and a heat-sensitive recording layer formed in this order on a support, the undercoat layer containing hollow plastic particles and a binder, the heat-sensitive recording layer containing a leuco dye and a developer, and the heat-sensitive recording material having an elastic modulus of 200 N/mm.sup.2 or less as measured by a nanoindentation method.

Disclosed is a heat-sensitive recording material comprising an undercoat layer and a heat-sensitive recording layer formed in this order on a support, the undercoat layer containing hollow plastic particles and a binder, the heat-sensitive recording layer containing a leuco dye and a developer, and the heat-sensitive recording material having an elastic modulus of 200 N/mm.sup.2 or less as measured by a nanoindentation method.