GB1565776A - Heat-sensitive recording composition - Google Patents

Description

(54) HEAT-SENSITIVE RECORDING COMPOSITION (71) I, WILLIAM RICHARD LAWTON, of, 6651 Jewett-Holmwood Road, Orchard Park, New York 14127, United States of America, a Citizen of the United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to recording members containing heat reactive components and, more particularly, to recording members capable of use in thermographic copying, thermal printing, event recording, and as transparencies for overhead projection.

Heat sensitive sheets containing cyclic polyketo compounds, useful for copying and recording and characterized by the ability to form a mark of contrasting color when heated to an activation temperature of 50"C are known in the art. They are used in thermographic processes wherein a recording member is positioned on a graphic original and exposed to infrared radiation to cause selective heating of the dark areas of the original sufficient to form a copy thereof on the heat sensitive member. The thermally responsive members have also been used to record the heated portions of a thermal print-head and also to record a colored trace when contacted by the hot stylus of a thermal recorder.The ninhydrinamine reaction wherein ninhydrin reacts with amino acids, primary amines, and certain derivatives of morpholine, piperidine, and pyrrolidine to give the dye commonly referred to as Ruhrman's purple, is well known. Isatin reacts with these same amines to give isatin blue.

Alloxan reacts with the amines to give a red dye. These reactions have been used in numerous inventions for thermally responsive copy and recording papers and films.

Lawton, US 3,736,166 used ninhydrin with various morpholine and piperidine derivatives to prepare transparencies for overhead projection. Lawton, US 3.293,061 combined ninhydrin or hydrindantin with isatin-amine condensates to provide thermographic copy sheets. Bauman and Lawton reacted ninhydrin or hydrindantin with complexes of amines and flavans or phenolic compounds to make thermographic copy sheets, see US 3,149,991 and US 3,149,992. Huffman, US 3,664,858 combined ninhydrin with the adducts of morpholine or piperidine and organic acids in thermal recording members. Sus, US 3,024,362 combined hydrindantin with amino acids or salts of primary amines with organic carboxylic and sulfonic acids to make a thermocopy paper. Allen, US 2,967,785 used the adducts of morpholine or piperidine with isatin or ninhydrin as the color forming material in thermocopy papers.Small, US 3,573,958 combined an amine with a halide or organometallic halide of germanium, silicone, lead, and tin with hydrindantin to provide a heat sensitive recording sheet. In each case the normal dye formations of Ruhrman's purple with ninhydrin, red dye with alloxan and isatin blue were obtained.

It is often desirable and an objective of this invention to obtain colored records which have colors differing from those normally obtained with the above cyclic polyketo compounds.

Undesirable odors and fumes are obtained by the heat dissociation or decomposition of the complexes, salts, or adducts during the imaging process. There is a problem of image bleaching during excessive heating, or aging. or prolonged exposure to ultraviolet containing light.

Attempts to use heterocyclic diimino compounds such as the piperazine derivatives result in colorless or very pale images. general deterioration of coatings, and a coating layer unacceptable due to the very hygroscopic nature of the piperazines and their unpleasant odor.

I have found that the above objectionable problems can be minimized or eliminated the combination of an N-substituted piperazine obtained by condensing the piperazine with an aromatic aldehyde, and a cyclic polyketo color precursor. The N-substituted piperazine aldehyde condensate and the color precursor react at temperatures between 50"C and 200"C to form a number of different highly colored dyes. The volatiIity, odor, hygroscopic characteristics of the original piperazine derivatives are eliminated. The materials for preparing the piperazine condensates are generally less expensive than those used for the adducts and complexes described in the prior art and the product yield is high which leads to a less costly record member.

Preparation of the piperazine condensate One gram mole of piperazine or substituted piperazine or homopiperazine is condensed with one gram mole of an aromatic aldehyde by refluxing in methanol or ethanol for 4 to 8 hours. Upon cooling, the condensate precipitates, the precipitate is filtered off, washed with alcohol and dried. If a precipitate does not readily form, precipitation may be induced by adding water to the reaction mixture.

Preparation of transparencies The cyclic polyketo compound and the piperazine condensate are dissolved in a binder contained in an organic solvent. The binder acts only as a vehicle to carry the color reacting products. Any transparent binder such as acrylic and methacrylic copolymers, cellulose esters, nitrocellulose, polyvinyl acetates, butyrals and styrene polymers and copolymers, can be used. The solvents convenient for use with this system include ketones such as methylethylketone, alcohols such as methanol, esters such as ethyl acetate, and aromatics such as toluene. It is normal to include stabilizers in the transparency formulations.

Commonly used stabilizers are those described in US Patent No, 3,736,166 and include substituted ureas and thioureas such as ethylurea, n-propyl urea, allylurea, N-methyl thiourea, and allyl thiourea; gallic acid; o-, m- and p-toluic acids; 2-mercaptobenzothiazole; and 2,2'-dithiobis (benzothiazole).

Activators can be used to increase the sensitivity or thermal response of the transparencies as well as the recording papers of this invention. A simple procedure for selecting useful activators is as follows: A grind of a selected heterocyclic condensate and a cyclic polyketo compound is obtained by ball-milling these materials as a dispersion in an aqueous solution of polyvinyl alcohol.

The dispersion is coated onto a base paper and heated on a hot plate. If the color develops more rapidly in the area where the additive activator power has been applied, the activator will increase the sensitivity of the system when compounded with the heterocyclic condensate and cyclic polyketo compound of this invention.Some of the more suitable activators include the following: TABLE I 2-mercaptobenzoxazole 2-mercaptobenzothiazole 2,2'-dithiobis(benzothiazole) 2-benzoxazolethiol 2-benzothiazolol 2-morpholinothiobenzothiazole 2,4-dichloro-1-naphthol 2-chloroacetamide o-,m-, and p-toluic acids thioacetanilide thiobenzanilide phenoxazine phenyl-3-thiocarbazide N-cyclohexyl-2-benzothiazolesulfenamide N-tert-butyl-2-benthiazolesulfenamide sulfanilamide 4,4'-dithiodimorpholine 1, 1, 3, 3-tetramethyl-2-thiourea 2,4-thiazolidenedione thiazolidenethione N-methylbenzothiazole-2-thiourea p-hydroxyacetophenone 1,3-indanedione butyl ziram 2,2-dithiobis(benzothiazole) chloroacetophenone 3,5-dibromosalicylaldehyde 3,4-dihydroxybenzoic acid biphenyl acetone oxime Suitable tranparent films which may be used as the substrate for the transparencies include terephthalate polyester film, polycarbonates, polyamides, polystyrene and cellulose acetate-butyrate copolymers.

The coatings may be applied by any of the normal coating procedures such as Meyer rod, reverse roll or kiss-coat. The coating weights of the thermosensitive layers can be varied from 2 to over 10 lb/3000 sq ft.

Example A, which follows, shows typical combinations useful as transparencies for overhead projection.

Example A: Preparation of transparencies for overhead projection.

A resin solution of the following composition was prepared: Parts methanol 134 methylethylketone 386 nitrocellulose 39 polymethylmethacrylate 90 The following mixes were then prepared: "A" Mix Parts resin solution 100 stabilizer 1.0 lactic acid 0.7 piperazine-aIdehyde condensate 4.0 "B" Mix Parts resin solution 142 cyclic polyketone 4 The coating composition obtained from 13 parts "B" and 10 parts "A" was coated onto 3 mil terephthalate polyester film with a No. 24 wire wound Meyer rod and dried to give a transparent film. The dried coated transparency was placed in contact with an infrared absorbing original and passed through a thermal copier in the normal manner. Imaged transparencies suitable for overhead projection were obtained with images projected in a variety of colors. The following are examples of combinations used to prepare the transparencies.

TABLE II -- TRANSPARENCY EXAMPLES Condensate cyclic Diimino polyketo image Compound aldehyde compound color 1, piperazine benzaldehyde ninhydrin brown 2. " salicylaldehyde " brown 3. n 5-nitrosalicyl- " brown aldehyde 4. D o-chlorobenzalde- I, brown hyde TABLE 2 Con't 5. " p-chlorobenzalde- " brown hyde 6. " bromosalicylalde- D brown hyde 7. " 3,5-dibromosalicyl- " brown aldehyde 8. " 2,4-dimethoxyben- I, brown zaldehyde 9. " 2-hydroxy-3-methoxy- " brown benzaldehyde 10. " o-vanillin N brown black 11. " 3,4,5-trimethoxy- " brown benzaldehyde black 12. " cinnamaldehyde " brown 13. n a-methoxy cinna- " brown maldehyde 14. " p-hydroxybenzalde- " brown hyde black 15. " 5-hydroxy-2-nitro- " brown benzaldehyde black 16. " m-nitrobenzaldehyde " brown black 17. " o-nitrobenzaldehrde " blue black 18. " 9-anthraldehyde " brown black 19. " 2-hydroxy-1-naph- " brown thaldehyde 20. " p-isopropyl- " brown benzaldehyde 21. " p-cyanobenzal- " brown dehyde 22. " 1-naphthaldehyde " brown 23. " o-methoxybenza:ldehyde " brown 24. " o-ethoxybenza Idehyde " brown black 25. " 6-nitroveratra l- " brown dehyde 26. " 3-ethoxy-4-hydroxy- " brown benzaldehyde black TABLE 2 Con't 27. " 2,4-dinitrobenzal- " brown dehyde black 28. " o-phthalic " dark dicarboxaldehyde blue 29. " terphthal- " brown dicarboxaldehyde 30. " p-N,N-dimethylamino " brown cinnamaldehyde black 31. homopipera- p-chlorobenzaldehyde " dark zine brown 32. " m-nitrobenzaldehyde " dark brown 33. 1I cinnamaldehyde I, brown 34. 2,5-dimethyl 1-naphthaldehyde " brown piperazine 35. " m-nitrobenzaldehyde Ir brown 36. " o-phthalic " dark dicarboxaldehyde brown 37. 2-methyl- 2-naphthaldehyde " dark piperazine brown 38. D o-phthalic ninhydrin dark dicarboxaldehde brown 39. homopiper- p-chlorobenzal. isatin brown azine dehyde 40. " " 5-bromoisatin brown 41. " " 5,7-di chloro-isatin brown 42. I, 5-nitroisatin brown 43. " 1I alloxan red 44. " " alloxazine red brown 45. 2-methyl- o-phthalic 5-nitroisatin piperazine dicarboxaldehyde 46. 2-methyl- I, alloxan piperazine 47. 2,5-dimethyl- " alloxan I, piperazine In Examples 37, 38, 45 and 46 above the peferred heterocyclic diimino compound is 2-methylpiperazine. Persons skilled in the at will understand that equivalent alkylsubstituted piperazines such as 2-ethylpiperaine give substantially the same results.

Similarly, other 2,5-dialkyl substituted piperazires such as 2,5-dipropyl piperazine may be used in Examples 34, 35, 36 and 47 above.

Example B: Preparation of coated papers for thermocopy, thermal printer, and thermal stylus chart recording applications.

Separate grinds were made of the piperazine condensates, the cyclic polyketone derivatives, and any additives used as accelerators or stabilizers. The following examples list the combinations, ratios, coating weights and image colors obtained when used on a thermal copier, a matrix thermal printer and a thermal chart recorder. The mixes were prepared by ball-winding the components in a 5 percent aqueous polyvinyl alcohol solution at a 15 percent concentration of the dry components. The mixes were combined in the indicated ratios and coated with a No. 16 wire wound Meyer rod onto a 25 lb/3000 sq ft sulfite paper base stock.

TABLE III - COATED PAPER EXAMPLES weight Piperazine lb/3000 Condensate additive polyketone ratio sq ft color 1. terephthaldehyde - hydrindantin 1/2 1.5 black " - " 2/1 2.3 black 2. " - Isatin 1/2 2.7 brownblack 3. " - alloxan 1/2 3.9 red-brown 4. " - hydrindantin 1/4 3.8 black 5. " p-toluic acid ninhydrin 1/1/2 2.5 brown-black " " " 2/1/2 1.5 dark-brown " " " 4/1/2 1.4 brown " " " 8/1/2 1.9 yellow-brown 6. " " hydrindantin 1/1/2 1.5 dark brown " " " 1/1/1 2.3 brown-black 7. " 2-mercaptobenzothi- " 1/5/2 3.2 dark-brown zole 8. " 2-mercaptobenzoxa- " 1/5/2 2.9 dark brown zole 9. " 2,2'-dithiobis " 1/5/2 3.3 brown (benzothiazole) 10. " 2-benzoxazolethiol " 1/5/2 3.5 dard brown TABLE 3 Con't 11. " 2-benzothiazolol " 1/5/2 2.8 dark brown 12. " 2-morpholino " 1/5/2 4.0 dark brown thiobenzothiazole 13. terephthaldehyde 2,4-dichloro-1- hydrindantin 1/1/2 3.5 brown-black naphthol 14. " 2-chloroacetamide " 1/2/2 4.4 purple-black 15. o-phthalic p-toluic acid ninhydrin 8/1/2 3.1 brown dicarboxaldehyde " " " 4/1/2 1.5 brown " " " 2/1/2 2.7 brown " " " 1/1/2 3.5 brown 16. m-phthalic dicarboxaldehyde o-toluic acid hydrindantin 2/1/1 3.2 brown-black 17. 9-anthraldehyde p-toluic acid ninhydrin 8/1/2 1.5 brown " " " 2/1/4 1.8 brown " " " 2/1/2 1.1 brown-black " " " 1/1/2 0.5 dark brown 18. o-vanillin p-toluic acid " 1/1/2 2.2 brown-black " " " 2/1/2 2.6 dark brown " " " 4/1/2 2.5 yellow-brown " " " 8/1/2 2.5 yellow-brown TABLE 3 Con't 19. m-nitrobenzaldehyde m-toluic acid ninhydrin 1/1/2 2.5 dark brown " " " 2/1/2 2.6 dark brown " " " 4/1/2 2.3 brown " " " 8/1/2 1.6 brown 20. 2-naphthaldehyde p-toluic acid " 8/1/2 2.5 yellow-brown " " " 4/1/2 1.2 dark brown " " " 2/1/2 1.9 brown-black " " " 1/1/2 1.6 brown-black 21. 1-naphthaldehyde p-toluic acid ninhydrin 8/1/2 2.5 dark brown " " " 2/1/2 2.6 brown-black " " " 1/1/2 2.8 black 22. o-nitrobenzaldehyde p-toluic acid " 1/1/2 1.8 black " " " 2/1/2 2.2 black " " " 4/1/2 2.0 black " " " 8/1/2 2.1 black 23. 1,3,5-trimethoxy- p-toluic acid " 1/1/2 2.0 purple-black benzaldehyde " " " 2/1/2 1.8 purple-black " " " 4/1/2 1.8 purple-black " " " 8/1/2 1.6 dark brown TABLE 3 Con't 24. 2,4-dinitrobenzaldehyde p-toluic acid ninhydrin 1/1/2 1.8 black " " " 2/1/2 2.0 black " " " 4/1/2 1.9 dark brown " " " 8/1/2 1.7 @brown 25. p-piperazino- p-toluic acid ninhydrin 1/12 3.2 black acetophenone 26. p-piperazino p-toluic acid hydrindantin 1/1/2 3.0 brown-black acetophenone

Claims (9)

WHAT I CLAIM IS:

1. A colourless non-volatile, non-hygroscopic, heat-sensitive recording composition acquiring a colour in a selected region thereof upon heating said selected region to an elevated temperature, comprising an N-substituted condensation product of a heterocyclic diimino compound and an aromatic aldehyde, said heterocyclic diimino compound being selected from the group consisting of piperazine, homopiperazine, 2-alkylpiperazine, and 2,5-dialkylpiperazine; and a cyclic polyketo compound reactive with amines and amides at elevated temperatures to form a coloured compound.

2. The composition of claim 1, wherein said 2-alkylpiperazine comprises 2-methyl piperazine.

3. The composition of claim 1. wherein said 2,5-dialkylpiperazine comprises 2,5dimethyl piperazine.

4. The composition of claim 1, wherein said cyclic polyketo compound is selected from the group consisting of ninbydrin isatin, 5-bromoisatin, 5,7-dichloroisatin, alloxan, alloxazine and hydrindantin.

5. The composition of claim 1, wherein said aromatic aldehyde is an aldehyde selected from Table II of the specification.

6. The composition of claim 1, and further comprising a stabilizer selected.from the group consisting of substituted ureas and thioureas, gallic acid; o-toluic acid; m-toluic acid; p-toluic acid; 2-mercaptobenzothiazole; and 2,21-dithiobis (benzothiazole).

7. The composition of claim 1 and further comprising an activator selected from Table I of the specification.

8. The composition of claim 1, and further comprising binder means for binding said composition to a substrate.

9. A heat-sensitive, non-volatile, non-hygroscopic. and odor-free recording composition, substantially as hereinbefore described with reference to the Examples.