Barrier layers for use in substantially light-insensitive thermographic recording materials

1. A substantially light-insensitive black and white monosheet thermographic recording material comprising a support and further comprising on one side of said support a thermosensitive element and at least two layers comprising a barrier layer and an outermost protective layer, said thermosensitive element being exclusive of a high contrast agent and comprising at least one substantially light-insensitive silver salt of a carboxylic acid, at least one reducing agent therefor in thermal working relationship therewith, at least one toning agent and at least one binder, wherein said at least one reducing agent is an ortho-dihydroxy-benzene derivative and said barrier layer comprises a copolymer comprising vinyl chloride units and vinyl acetate and/or vinyl alcohol units, a copolymer comprising styrene units and acrylonitrile units, a copolymer comprising cationic units and/or a copolymer comprising styrene units and maleic acid units.

2. A substantially light-insensitive black and white monosheet thermographic recording material comprising a support and further comprising on one side of said support a thermosensitive element, a barrier layer, and an outermost protective layer, said thermosensitive element being exclusive of a high contrast agent and comprising at least one substantially light-insensitive silver salt of a carboxylic acid, at least one reducing agent therefor in thermal working relationship therewith, at least one toning agent and at least one binder, wherein said at least one reducing agent is an ortho-dihydroxy-benzene derivative, said barrier layer comprises a copolymer comprising vinyl chloride units and vinyl acetate and/or vinyl alcohol units, a copolymer comprising styrene units and acrylonitrile units, a copolymer comprising cationic units and/or a copolymer comprising styrene units and maleic acid units, and said barrier layer is interposed between said thermosensitive element and said outermost protective layer.

3. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 1 , wherein said copolymer comprising vinyl chloride units and vinyl acetate units contains up to 95% by weight of vinyl chloride.

4. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 1 , wherein said copolymer comprising styrene units and acrylonitrile units contains between 20 and 60% by weight of acrylonitrile.

5. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 1 , wherein said copolymer containing cationic units contains quaternary ammonium, quaternary phosphonium or ternary sulphonium units.

6. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 5 , wherein said quaternary ammonium units are methacrylamidopropyl-trimethylammonium chloride or dimethyl-diallylammonium chloride units.

7. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 1 , wherein said toning agent is selected from the group consisting of naphthoxazine dione, naphthoxazine derivatives, 7-methyl-benzo[e][1,3]oxazine-2,4-dione, 7-methoxy-benzo[e][1,3]oxazine-2,4-dione and 7-(ethylcarbonato)-benzo[e][1,3]oxazine-2,4-dione.

8. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 1 , wherein said ortho-dihydroxy-benzene derivative is selected from the group consisting of catechol, 3-(3,4-dihydroxyphenyl) propionic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid esters, gallic acid, gallic acid esters, 3,4-dihydroxy-benzaldehyde, 3,4-dihydroxy-acetophenone, 3,4-butyrophenone, 3,4-dihydroxy-benzophenone, 3,4-dihydroxybenzophenone derivatives, 3,4-dihydroxy-benzonitrile, and tannic acid.

9. A substantially light-insensitive black and white monosheet thermographic recording material comprising a support and further comprising on one side of said support a thermosensitive element, a baffler layer, and an outermost protective layer, said thermosensitive element being exclusive of a high contrast agent and comprising at least one substantially light-insensitive silver salt of a carboxylic acid, at least one reducing agent therefor in thermal working relationship therewith, at least one toning agent and at least one binder, wherein said at least one reducing agent is an ortho-dihydroxy-benzene derivative; said barrier layer comprises a copolymer comprising vinyl chloride units and vinyl acetate and/or vinyl alcohol units, a copolymer comprising styrene units and acrylonitrile units, a copolymer comprising cationic units and/or a copolymer comprising styrene units and maleic acid units, and said outermost protective layer comprises the reaction product of at least one hydrolyzed polyalkoxysilane and a hydroxy-group containing polymer.

10. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 1 , wherein said outermost protective layer comprises the reaction product of a hydrolyzed tetra-alkoxysilane, e.g. tetramethoxysilane or tetra-ethoxysilane, and polyvinyl alcohol.

11. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 2 , wherein said copolymer containing cationic units contains quaternary ammonium, quaternary phosphonium or ternary sulphonium units.

12. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 2 , wherein said copolymer comprising vinyl chloride units and vinyl acetate units contains up to 95% by weight of vinyl chloride.

13. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 2 , wherein said copolymer comprising styrene units and acrylonitrile units contains between 20 and 60% by weight of acrylonitrile.

14. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 11 , wherein said quaternary ammonium units are methacrylamidopropyl-trimethylammonium chloride or dimethyl-diallylammonium chloride units.

15. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 2 , wherein said toning agent is selected from the group consisting of naphthoxazine dione, naphthoxazine derivatives, 7-methyl-benzo[e][1,3]oxazine-2,4-dione, 7-methoxy-benzo[e][1,3]oxazine-2,4-dione and 7-(ethylcarbonato)-benzo[e][1,3]oxazine-2,4-dione.

16. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 2 , wherein said ortho-dihydroxy-benzene derivative is selected from the group consisting of catechol, 3-(3,4-dihydroxyphenyl)propionic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid esters, gallic acid, gallic acid esters, 3,4-dihydroxy-benzaldehyde, 3,4-dihydroxy-acetophenone, 3,4-butyrophenone, 3,4-dihydroxy-benzophenone, 3,4-dihydroxybenzophenone derivatives, 3,4-dihydroxy-benzonitrile, and tannic acid.

17. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 2 , wherein said outermost protective layer comprises the reaction product of at least one hydrolyzed polyalkoxysilane and a hydroxy-group containing polymer.

18. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 2 , wherein said outermost protective layer comprises the reaction product of a hydrolyzed tetra-alkoxysilane, e.g. tetramethoxysilane or tetra-ethoxysilane, and polyvinyl alcohol.

19. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 9 , wherein said copolymer comprising vinyl chloride units and vinyl acetate units contains up to 95% by weight of vinyl chloride.

20. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 9 , wherein said copolymer comprising styrene units and acrylonitrile units contains between 20 aid 60% by weight of acrylonitrile.

21. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 9 , wherein said copolymer containing cationic units contains quaternary ammonium, quaternary phosphonium or ternary sulphonium units.

22. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 21 , wherein said quaternary ammonium units are methacrylamidopropyl-trimethylammonium chloride or dimethyl-diallylammonium chloride units.

23. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 9 , wherein said toning agent is selected from the group consisting of naphthoxazine dione, naphthoxazine derivatives, 7-methyl-benzo[e][1,3]oxazine-2,4-dione, 7-methoxy-benzo[e][1,3 ]oxazine-2,4-dione and 7-(ethylcarbonato)-benzo[e][1,3]oxazine-2,4-dione.

24. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 9 , wherein said ortho-dihydroxy-benzene derivative is selected from the group consisting of catechol, 3-(3,4-dihydroxyphenyl) propionic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid esters, gallic acid, gallic acid esters, 3,4-dihydroxy-benzaldehyde, 3,4-dihydroxy-acetophenone, 3,4-butyrophenone, 3,4-dihydroxy-benzophenone, 3,4-dihydroxybenzophenone derivatives, 3,4-dihydroxy-benzonitrile, and tannic acid.

25. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 23 , wherein said copolymer containing cationic units contains quaternary ammonium, quaternary phosphonium or ternary sulphonium units.

26. The substantially light-insensitive black and white monosheet thermographic recording material according to claim 25 , wherein said quaternary ammonium units are methacrylamidopropyl-trimethylammonium chloride or dimethyl-diallylammonium chloride units.