Thermosensitive recording material

1. A heat-sensitive recording material comprising

a substrate;

a heat-sensitive recording layer containing color formers and color acceptors; and

a protective layer containing a binder and covering said heat-sensitive recording layer; and wherein

said heat-sensitive recording layer has, as the only color acceptor, at least 66⅔ percent by weight of 4,4′-dihydroxydiphenyl sulfone in said heat-sensitive recording layer, and

said protective layer has, as the only binder, at least 60 percent by weight of diacetone-modified polyvinyl alcohol in said protective layer.

2. The heat-sensitive recording material according to claim 1 , wherein said color formers of said heat-sensitive recording layer are one or more selected from the list comprising 3-diethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tolyl)amino-6-methyl-7-anilinofluoran, and 3-(N-ethyl-N-tetrahydrofuryl)amino-6-methyl-7-anilinofluoran.

3. The heat-sensitive recording material according to claim 1 , wherein said heat-sensitive recording layer includes at least one sensitizer selected from the list comprising methylolstearamide, stearic acid amide, and dimethyl terephtalate.

4. The heat-sensitive recording material according to claim 3 , wherein the ratio of 4,4′-dihydroxydiphenyl sulfone to sensitizer, selected from the list comprising methylolstearamide, stearic acid amide, and dimethyl terephtalate, is in the range of 1:0.5 to 1:2 based on percent by weight in said recording layer.

5. The heat-sensitive recording material according to claim 1 , wherein said the binder in The heat-sensitive recording layer is polyvinyl alcohol, ethylene vinyl alcohol copolymers, or a combination of polyvinyl alcohol and ethylene vinyl alcohol copolymers.

6. The heat-sensitive recording material according to claim 1 , wherein said protective layer contains at least one inorganic pigment selected from the group comprising silicon dioxide, aluminum hydroxide, bentonite, calcium carbonate, kaolin.

7. The heat-sensitive recording material according to claim 6 , wherein the ratio of inorganic pigment to diacetone-modified polyvinyl alcohol ranges from 1:1.5 to 1:4.5 based on the respective percent by weight of pigment and polyvinyl alcohol in said protective layer.

8. The heat-sensitive recording material according to claim 1 , additionally comprising a pigmented intermediate layer formed between said substrate and said heat-sensitive recording layer.

9. The heat-sensitive recording material according to claim 8 , wherein said pigmented intermediate layer comprises organic pigments and inorganic pigments, said inorganic pigments being selected from the list comprising calcined kaolin, silicon oxide, bentonite, calcium carbonate, aluminum oxide and boehmite.

10. The heat-sensitive recording material according to claim 1 , wherein said substrate is a paper web containing at least 70 percent by weight of recycled fibers based on the total fiber content in said paper web.

11. The heat-sensitive recording material according to claim 10 , wherein said paper web has at least 98 percent by weight of recycled fibers based on the total fiber content in said paper web.

12. The heat-sensitive recording material according to claim 10 , additionally comprising recycled fibers of higher grade recovered papers and wherein said recycled fibers of said paper web have a proportion of said recycled fibers of higher-grade recovered papers of at least 70 percent by weight.

13. The heat-sensitive recording material according to claim 10 , wherein said recycled fibers of said paper web have a proportion of said recycled fibers of higher-grade recovered papers of 100 percent by weight.