US3666525A

US3666525A - Heat sensitive copying sheet

Info

Publication number: US3666525A
Application number: US40732A
Authority: US
Inventors: Shiro Kimura; Sadao Ishige; Teruo Kobayashi
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1969-05-26
Filing date: 1970-05-26
Publication date: 1972-05-30
Anticipated expiration: 1989-05-30
Also published as: DE2025816A1; JPS4833712B1; CH560112A5; GB1260593A; NL7007577A; FR2092172A5; DE2025816B2

Abstract

HEAT SENSITIVE COPYING PAPERS USING A SPIRO COMPOUND HAVING THE FORMULA A

2-R1,2''-R2-3,3''-SPIROBI(3H-NAPHTHO(2,1-B)PYRAN

WHEREIN R1 AND R2 EACH IS SELECTED FROM THE GROUP CONSISTING OF A HYDROGEN ATOM, AN ALKYL GROUP HAVING FROM 1 TO 8 CARBON ATOMS, A CARBOXYLIC ACID ESTER, AN ARALKYL GROUP AND A PHENYL GROUP, A SOLID ORGANIC SULFONIC ACID HAVING THE FORMULA

R-SO3H (B)

WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF AN AMINO GROUP, AN N-SUBSTITUTED AMINO ALKYL GROUP HAVING FROM 2 TO 18 CARBON ATOMS, AN UNSUBSTITUTED AMINO ALKYL GROUP HAVING FROM 2 TO 18 CARBON ATOMS, AN ALKYL GROUP HAVING FROM 10 TO 20 CARBON ATOMS, AN ALKOXY GROUP HAVING FROM 10 TO 20 CARBON ATOMS, A CARBOXYLIC ACID SUBSTITUTED ALKYL GROUP, SAID ALKYL GROUP HAVING FROM 6 TO 18 CARBON ATOMS, AND AN AROMATIC RING, AND A THERMOFUSIBLE MATERIAL HAVING A MELTING POINT RANGING FROM 50 TO 180*C. ARE DISCLOSED.

Description

United States Patent 01 7 3,666,525 Patented May 30, 1972 lice- 3,666,525 HEAT SENSITIVE COPYING SHEET Shiro Kimura, Teruo Kobayashi, and Sadao Ishige, Kanagawa, Japan, assignors to Fuji Photo Film Co., Ltd., Minami-ashigara-machi, Kanagawa, Japan No Drawing. Filed May 26, 1970, Ser. No. 40,732 Claims priority, application Japan, May 26, 1969, 44/ 40,719 Int. Cl. B41m /18 US. Cl. 117-363 17 Claims ABSTRACT OF THE DISCLOSURE Heat sensitive copying papers using a spiro compound having the Formula A wherein R and R each is selected from the group consisting of a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, a carboxylic acid ester, an aralkyl group and a phenyl group, a solid organic sulfonic acid having the Formula B BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a heat sensitive copying sheet.

(2) Description of the prior art Many heat sensitive copying sheets are well known. However, above all, one having a layer comprising two colorless solid compounds contacting with each other to cause the reaction of color development and a thermofusible material on a support is general. The coloration mechanism of this heat sensitive copying sheet is as follows:

When this sheet is superposed on an original drawing and heated or irradiated with an infra-red ray, the image of the character on the original drawing is preferentially raised in temperature and the thermofusible material of the part fuses the two colorless compounds. Then the two fused compounds react to develop color. One of the two colorless compounds includes crystal violet lactones and benzo indolino spiropyrans, and another includes, for example, clays, such as acid clay, zeolite, kaolin, attapulgite, and the like; mineral acids, such as hydrochloric acid, sulfuric acid, perchloric acid, phosphoric acid, and the like; organic acids, such as benzoic acid, p-chlorobenzoic acid, gallic acid, phthalic acid, salicylic acid, oxalic acid, maleic acid, citric acid, stearic acid, and the like; and phenols, such as p-butylphenol, p-phenylphenol, a-naphthol, catechol, resorcinol, and the like.

However, these heat sensitive copying sheets sufier from the disadvantages that a color development fog is formed before heating, the preservation of the developed color image, such as the light resistance, resistance to water, and the like, is poor, and the sheets are not developed in color the instant they are heated, and the like, because the two compounds are coated on the support in contact with each other. As a result, an excellent heat sensitive copying sheet has been desired.

Therefore, an object of the present invention is to provide a heat sensitive copying sheet in which such color development fog is not formed before heating and develops color instantly on heating. The developed color image is excellent in light resistance and resistance to water.

SUMMARY OF THE dNVEN'I ION The present inventors have found that the above object is attained by combining a spiro compound and an organic sulfonic acid.

More specifically, the heat sensitive copying sheet of this invention is one having a spiro compound, represented by Formula A wherein R and R each is a hydrogen atom, an alkyl group having from .1 to 8 carbon atoms, a carboxylic acid ester, an aralkyl group, or a phenyl group, a solid organic sulfonic acid, represented by the Formula B DETAILED DESCRIPTION OF THE INVENTION The general process for preparing the heat sensitive copying sheet of the present invention is as described below.

A nearly colorless spiro compound, an organic sulfonic acid and a thermofusible material, as described above, are sufliciently mixed in a solution or suspension of a binder in an organic solvent or water, and coated on a support such as paper, natural or synthetic resin films, and the like, and dried. The above liquid mixture can be combed into the support. Also, on mixing, an opacifying agent can be added and mixed therein. The heat sensitive copying sheet of the present invention is not limited to this technique. For example, the abovementioned spiro compound and the thermofusible material can be mixed in the binder solution, and alternatively the organic sulfonic acid and the thermofusible material can be mixed in the binder solution, and then both solutions can be mixed and coated on a support, or the former solution may be coated on the support and then the latter solution may be coated thereon.

The amount of each component to be used for producing the heat sensitive copying sheet of the present invention is from 1 to 2. parts by weight of the spiro compound (the Formula A); from 1 to 6 parts by weight of the organic sulfonic acid (the Formula -B); from 3 to 30 parts by weight of the thermofusible material; from 3 to 15 parts by weight of the binder; and from 20 to 300 parts by weight of solvent.

Examples of the spiro compounds represented by the 19. CH COGHC s l above Formula A are shown in the following table: 3 2 O Color developing Melting agent R" R point, 0. Name I H H 258 2,igpirogflbenzo[f]chromene) J. Chem. 500.,

27,1 II CH3 H 203 3-Inethy1-2,2-spirobi(benzolflchromene) J.

Pract. Chem.,[2] 114, 190 Ben, 59, 1381. III CH(CH1); H 204 3-iso-propyl-2,2'-spirobi(benz0[f]ch1omene) J.

Chem. 300., 1929, 942. IV 05H 11 182 3-zgin3gg,2'-spirobi(benzolflchromene) Ben, V CsHu H 157 3-ocyl-2;2-spir0bi(benzo[f]ehromene) J. Chem.

500., 1929, 937. VI CH; CH; 238 3,3-dimethyl-2,2-spirobi(benzoIflchromene) J.

Chem. 800., 1927, 1703 Ber., 61, 967. VII CO 0 01H; CO QCzHs 205207 3, 3-dica.rboethoxy-2, 2-spirobi(b nzolflchronxene) J Chem. 300., 1927, 1703. VIII H 207 3-benzyl-2,2'-splrobi(benzo[i]chromene) Ben,

CHz- .59. 1382.

IX CH2-CHz- H 210-220 3-phenylethyl-2,2spirobl(benzomchromene) J.

Chem. $00., 1931, 1336.

X H 240 3-phenyl-2, 2'-sip10bl(benzolflchromene) Ben,

These compounds are almost colorless crystals.

These spiro compounds can be prepared by condensing Q-NH-Q-SO H 2-hydroxyl-l-napthoaldehyde with the respective corresponding ketones as described in the literature references.

NOH Next, the orgamc sulfomc aclds represented by the Formula B can be exemplified as follows: 0= 5 S 0 1. NHzSOaH 21 2. Nmcmoms 03H (0211.5)2NQ 3. CHr-CH:

o N CHCHOHCHSOH 03H 2 2 2 a a i 23. 02155 our-0H, 3o

4. H N -s0 11 Q-NHCHrGH S 03H 2 3 6 H 5. (CHahNCHzCHzC H25 03H 2 2 B 6. 016111150111 40 CH Q-SOzl-I 7. GMHnS B 8. C11H2OSO5H NH! 9. CrsHgzOSOaH 25. 10. C1aHaafi rH HZN SOSH l C OOH 00211. 11. omuofisoan m o 0011 OH2CONHQ-SO3E 12. I

CHaCH2SO H CH3 27. Q HO ooQ-Mm HO-U-OILS 03H 28 H0 0 c l 14. H1o-c=o @4031;

\N l N02 Q 803E HO S03H 16. NH;- 30. OH

11o-so.11

SOQH 18. 1

H088 SOaH These compounds are almost colorless solids.

Suitable thermofusible materials are acetanilide, urea, diphenylamine, diphenyl, naphthalene, benzoin, anaphthol, fi-naphthol, para-t-butyl phenol, para-phenylphenol, 4,4'-cyclohexyiidene diphene diphenol, 4,4-isopropylidene diphenol, phthalic anhydride, maleic anhydride, stearic acid, benzoic acid, a-naphthyl acetic acid, methyl para-hydroxybenzoate, diphenyl phthalate, triphenyl phosphate, para-hydroxydiphenyl ether, and the like.

These compounds are colorless or lightly colored solids at ordinary temperatures of lower than 50 C. and have sharp melting points near the temperature suitable as the heating temperature for copying, that is, from 50 to 180 0., and dissolve the above spiro compounds (the Formula A) and the organic sulfonic acids (the Formula B) in the fused state. The above three components are not necessarily used on or in the same support, and one or two of said components can be used on two separate supports.

The binders to be used in the present invention are ex emplified by styrene-butadiene copolymers, alkyd resins, polybutylmethacrylates, vinyl chloride-vinyl acetate copolymers, styrene maleic anhyride copolymers, synthetic rubbers, gum arabic, polyvinyl alcohol, hydroxyethylcellulose, and the like.

These materials bind the above spiro compounds (the Formula A) and the thermofusible materials and not easily discolored on heating. They can be used alone or in combination.

The solvents to be used in the present invention are examplified by organic solvents such as benzene, toluene, hexane, xylene, ligroin, acetone, ethyl acetate, and the like; and water.

These solvents are used to dissolve the above binders or as dispersion emulsions, and are finally distilled off.

In general, with organic sulfonic acids having an amino group in the Formula B, an organic solvent or water may be optionally used. With organic sulfonic acids not having an amino group or ones easily soluble in an organic solvent, water is preferable. With organic sulfonic acids easily soluble in water, use of water is allowed. This appears to result from the lack of solubility of the coupler represented by the Formula A in water.

Pacifying agents which can be used in the present invention are exemplified by titanium oxide, zinc oxide, barium sulfate, calcium sulfate, starch and the like.

The heat sensitive copying sheet of this invention has the advantages that a color development fog is not formed during the preparation and during the period after drying and before heating even though the compounds of the Formulas A and B are in contact with each other, that, even if the sheet is exposed before copying color develop ment, it is good in stability during the lapse of time without any lowering of the color developing ability, and that, when copying using a heatsensitive copying machine, the copied part develops color instantly and the developed color is good in light resistance and resistance to Water.

When substituting phenols, such as, for example, parabutyl phenol, para-phenylphenol, a-naphthol, catechol, resorcinol, 2,2'-methylene-bis (4-chlorophenol), 4,4-iso propylidine diphenol, and the like for the compounds represented by the Formula B, the sheet does not develop color even on; heating, and thus is not practical. Substituting benzoic acid, parachlorobenzoic acid, gallic acid, phthalic acid, salicylic acid, oxalic acid, maleic acid, citric acid, stearic acid, and the like, for the compounds represented by the Formula B, the sheet is hardly developed color even on heating, has no contrast, and is poor in light resisting property, and this is not practical. When active clays such as, for example, acid clay, zeolite, kaolin, attapulgite, and the like, or mineral acids such as, for example, hydrochloric acid, sulfuric acid, perchloric acid, phosphoric acid, and the like, are used, the sheet has the disadvantage of forming a color development fog during mixing in the solvent and immediately after coat ing and drying.

When crystal violet lactone and benzo indolino spiropyrans are substituted for the compounds represented by the Formula A, the sheet develops a fog color all over the surface at the time of copying printing, and is poor in light resistance. The combinations of couplers and acids, which are used in the present invention, have overcome these disadvantages.

The present invention will be illustrated further by reference to the following examples:

Example 1.35 g. of coupler No. I, 31 g. of organic sulfonic acid No. 17, 39 g. of acetanilide, 120 g. of styrenebutadiene copolymer, and 1200 g. of toluene were mixed and ground in a ball mill for 2 days. The solution mixture was coated on a paper and dried at 40 C. to obtain a heat sensitive copying sheet. This sheet was superposed on an original drawing and heated by means of a heat sensitive copying machine (manufactured by Thermofax Secretary 3M Co.) to obtain a blue-violet image. The copied image was exposed to sunlight for 20 hours. As the result, the developed color image was not lowered in concentration at all and undeveloped portion, i.e. non-image part, remained white as it was initially and was not changed. That is the light resistance was excellent. Even on allowing the sheet to stand at a temperature of 50 C. and a relative humidity of for 20 hours, or even on wettingit with water immediately after it was obtained, the concern tration of the color developed image was not lowered. That is, resistance to water was excellent.

0n the other hand, a heat sensitive copying sheet was prepared using crystal violet lactone (a known coupler), gallic acid an organic acid), acetanilide (a thermofusible material), a styrene-butadiene copolymer (a binder) and toluene (a solvent) in the same manner as described above. The heat sensitive copying sheet was heated in the same manner as described above to obtain a blue-violet image. The image faded and disappeared in the test for light resistance and resistance to water under the same condition as described above.

On substituting 3-chloro-sulfanilic acid (organic sulfonic acid No. 17) for gallic acid, the light resistance and resistance to water were similarly poor.

Also, on using 1,3,3-trimethyl8'-methoxy-indoline-benzospiropyran (a known coupler) and 4,4'-isopropylidiue diphenol (both as an organic acid and a thermofusible material), the light resistance was poor, and even on using organic sulfonic acid No. 17 together therewith, the light resistance was poor.

Example 2.35 g. of coupler No. II, 70 g. of organic sulfonic acid No. 57,500 g. of ,S-naphthol and 800 g. of ligroin were mixed and ground in a ball mill for 1 day. Subsequently, g. of a styrene-butadiene copolymer and 800 g. of toluene were added thereto and mixed and ground for 2 hours. The solution was coated on a film and dried at 40 C. to obtain a heat sensitive copying sheet. The sheet was superposed on an original drawing and heated by means of a heat sensitive copying machine (trademark: *Risofax; manufactured by Riso Kagaku Co., Ltd.) to obtain a blue image which was similarly excellent as in Example 1 in light resistance and resistance to water.

Example 3.50 g. of coupler No. IH, 300 g. of urea and 600 g. of acetone were mixed and ground in a ball mill for 2 days. On the other hand, 30 g. of organic sulfonic acid No. 8, 300 g. of urea, 200 g. of polybutyl-methacrylate, and 600 g. of ethyl acetate were mixed and ground in a ball mill. The ground materials were mixed and further treated in a ball mill for 5 hours. The resulting mixture, thus treated, was coated on a support and dried to obtain a heat sensitive copying sheet. The sheet was heated in the same manner as in Example 1 to obtain a blue image. The light resistance and resistance to water of the image were similarly excellent as in Example 1.

Example 4.l g. of coupler No. IV, 20 g. of organic sulfonic acid No. 36, 200 g. of stearic acid, 70 g. of styrenemaleic anhydride copolymer and 2000 g. of xylene were treated in the same manner as in Example 1 to obtain a heat sensitive copying sheet. The sheet was heated in the same manner as in Example 1 to obtain a blue image. In case of the omission of the organic sulfonic acid, the color was not developed.

Example 5.-10 g. of coupler No. V, 30 g. of organic sulfonic acid No. 49, 100 g. of p-phenylphenol, 40 g. of chlorinated rubber, and 3000 g. of benzene were treated in the same manner as in Example 1 to obtain a heat sensitive copying sheet which Was then heated to obtain a blue image. In case of the omission of the organic sulfonic acid, the color was not developed at all.

Example 6.-10 g. of ground coupler No. VI, and 100 g. of acetanilide were dispersed in a solution of 30 g. of polyvinyl alcohol and 500 g. of water. On the other hand, 10 g. of ground organic sulfonic acid No. 29 and 50 g. of acetanilide were dispersed in a solution of 15 g. of polyvinyl alcohol and 300 g. of water. Both dispersions were mixed and were treated in a ball mill for hours, and then were coated on a paper and dried to obtain a heat sensitive copying sheet which was then heated to obtain a blue image. In case of substituting salicyclic acid for organic sulfonic acid No. 29 (solfosalicyclic acid), the color was not developed.

Example 7.Example 1 was repeated using coupler Nos. VII, VHI, IX and X, respectively, to obtain a blue image.

Example 8. g. of coupler No. X, g. of organic sulfonic acid No. 18, 140 g. of benzoic acid, 50 g. of a vinyl chloride-vinyl acetate copolymer and 1500 g. of toluene were mixed and ground in a ball mill for 2 days, and were coated on a paper and dried to obtain a heat sensitive copying sheet. The sheet was superposed on an original drawing and heated by means of a heat sensitive copying machine to obtain a blue image coresponding to the characters on the original drawing. Also, the sheet was treated in the same manner as described above, in the exception of substituting 50 g. of hydroxyethylcellulose and 1500 g. of water for vinylchloride-vinyl acetate copolymer and toluene to obtain the same result.

In every case, when an organic sulfonic acid was not used, a colored image could not be obtained.

Example 9.-The color development of the respective combination of couplers Nos. I to X and organic sulfonic acids Nos. 1 to 60 in the same manner as in Examples 1 to 8 was blue. However, in using the coupler No. l, the color developed was blue violet, and in using the coupler No. VII, the color obtained first was blue by increasing the amount of an organic sulfonic acid to be used by about 30% by weight.

What is claimed is:

1. A heat sensitive copying sheet comprising a support having coated thereon a layer comprising (a) a spiro compound having the Formula A I -O O wherein R and R each is selected from the group consisting of a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, a carboxylic acid ester, an aralkyl group and a phenyl group, (b) a solid organic sulfonic acid having the Formula B,

wherein R is selected from the group consisting of an amino group, an N-substituted amino alkyl group having from 2 to 18 carbon atoms, an unsubstituted amino alkyl group having from 2 to 18 carbon atoms, an alkyl group having from 10 to 20 carbon atoms, an alkoxy group having from 10 to 20 carbon atoms, an alkyl group substituted with a carboxylic acid group, said alkyl group having from 6 to 18 carbon atoms, an alkyl group, and an aromatic ring, and (c) a thermofusible material having a melting point ranging from 50 to C., from 1 to 2 parts by weight of the spiro compound being present for every 1 to 6 parts by weight of the solid organic sulfonic acid.

2. The heat sensitive copying sheet as claimed in claim 1 wherein said spiro compound is selected from the group consisting of 2,2-spirobi-(benzolflchromene), 3-methyl- 2,2'-spirobi( benzo [f 1 chromene) 3-isopropyl-2,2'-spirobi- (benzo [f] chromene 3-amyl-2,2'-spirobi (benzo [f] chromene), 3-octyl-2,2'-spirobi(benzo[f]chromene), 3,3'-dimethyl-2,2-spirobi (benzo [f 1 chromene) 3,3 '-dicarboethoxy-2,2-spirobi (benzo [f chromene 3-benzyl-2,2'-spirobi (benzo [f] chromene) 3-phenylethyl-2,2'-spirobi (benzo- [f]chromene), or 3-phenyl-2,2-spirobi(benzo[f]chromene).

3. The heat sensitive copying sheet as claimed in claim 1 wherein said thermofusible material is selected from the group consisting of acetoanilide, urea, diphenylamine, diphenyl, naphthalene, benzoin, a-naphthol, fi-naphthol, p-t-butylphenol, p-phenylphenol, 4,4'-cyclohexylidine-diphenol, phthalic anhydride, maleic anhydride, stearic acid, benzoic acid, u-naphthyl acetic acid, methyl p-hydroxybenzoate, diphenyl phthalate, triphenyl phosphate or p-hy droxydiphenyl ester.

4. A heat sensitive copying sheet comprising a support having coated thereon a layer comprising (a) a spiro compound having the Formula A Ill; R1

wherein R is selected from the group consisting of an amino group, an N-substituted amino alkyl group having from 2 to 18 carbon atoms, an unsubstituted amino alkyl group having from 2 to 18 carbon atoms, an alkyl group having from 19 to 20 carbon atoms, an alkoxy group having from 10 to 20 carbon atoms, an alkyl group substituted with a carboxyl group, said alkyl group having from 6 to 18 carbon atoms, an aralkyl group, and an aromatic ring, (c) a thermofusible material having a melting point ranging from 50 to 180 C. and which is substantially colorless at a temperature lower than 50 C., and (d) a binder, from 1 to 2 parts by weight of the spiro compound being present for every 1 to 6 parts by weight of the solid organic sulfonic acid.

5. The heat sensitive copying paper as claimed in claim 4 wherein said binder is selected from the group consisting of styrene-butadiene copolymers, alkyd resins, polybutyl methacrylates, vinyl chloride-vinyl acetate copolymers, styrene-maleic anhydride copolymers, synthetic rubbers, gum arabic, polyvinyl alcohol and hydroxyethyl cellulose.

6. A heat sensitive copying sheet comprising a support having coated thereon (a) a spiro compound having the Formula A wherein R and R each is selected from the group consisting of a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, a carboxylic acid ester, an aralkyl group and a phenyl group, (b) a solid organic sulfonic acid having the Formula B wherein R is selected from the group consisting of an amino group, an N-substituted amino alkyl group having from 2 to 18 carbon atoms, an unsubstituted amino alkyl group having from 2 to 18 carbon atoms, an alkyl group having from 1-0 to 20 carbon atoms, an alkoxy group having from to carbon atoms, a carboxylic acid substituted alkyl group, said alkyl group having from 6 to 18 carbon atoms, an aralkyl group, or an aromatic ring, and (c) a thermofusible material having a melting point ranging from 50 to 180 C., from 1 to 2 parts by Weight of the spiro compound being present for every 1 to 6 parts by weight of the solid organic sulfonic acid.

7. Heat sensitive copying sheets comprising a combination of two supports, one support having coated thereon a layer comprising (a) a spiro compound having the Formula A Y CCCXXQ wherein R and R each is selected from the group consisting of a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, a carboxylic acid ester, an aralkyl group and a phenyl group, and (b) as a coupler, a solid organic sulfonic acid having the Formula B R SO3H (B) wherein R is selected from the group consisting of an amino group, an N-substituted amino-alkyl group having from 2 to 18 carbon atoms, an unsubstituted amino alkyl group having from 2 to 18 carbon atoms, an alkoxy group having from 10 to 20 carbon atoms, a carboxylic acid substituted alkyl group, said alkyl group having from 6 to 18 carbon atoms, an aralkyl group, and an aromatic ring, and the other support having coated thereon a layer containing a thermofusible material having a melting point ranging from 50 to 180 C., from 1 to 2 parts by weight of the spiro compound being present for every 1 to 6 parts by weight of the solid organic sulfonic acid.

8. Heat sensitive copying sheets comprising a combination of two supports, one support having coated thereon a layer comprising (a) a spiro compound having the Formula A,

12 wherein R and R each is selected from the group consisting of a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, a carboxylic acid ester, an aralkyl group and a phenyl group, and (b) a thermofusible material having a melting point ranging from 50 to C., the other support having coated thereon a layer comprising a solid organic sulfonic acid having the Formula B,

wherein R is selected from the group consisting of an amino group, an N-substituted amino alkyl group having from 2 to 18 carbon atoms, an unsubstituted amino alkyl group having from 2 to 18 carbon atoms, an alkyl group having from 10 to 20 carbon atoms, an alkoxy group having from 10 to 20 carbon atoms, a carhoxylic acid substituted alkyl group, said alkyl group having from 6 to 18 carbon atoms, an aralkyl group, and an aromatic ring, from 1 to 2 parts by weight of the spiro compound being present for every 1' to 6 parts by weight of the solid organic sulfonic acid.

9. Heat sensitive copying sheets comprising a combination of two surfaces, one surface having coated thereon a layer comprising a spiro compound having the Formula A,

wherein R and R each is selected from the group consisting of a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, a carboxylic acid ester, an aralkyl group and a phenyl group, the other surface having coated thereon a layer comprising (a) a solid organic sulfonic acid having the Formula B wherein R is selected from the group consisting of an amino group, an N-substituted amino alkyl group having from 2 to 18 carbon atoms, an unsubstituted amino alkyl group having from 2 to 18 carbon atoms, an alkyl group having from 10 to 20 carbon atoms, an alkoxy group having from 10 to 20 carbon atoms, a carboxylic acid substituted alkyl group, said alkyl group having from 6 to 18 carbon atoms, an aralkyl group, and an aromatic ring, and (b) a thermofusible material having a melting point ranging from 50 to 180 C., from 1 to 2 parts by weight of the spiro compound being present for every 1 to 6 parts by weight of the solid organic sulfonic acid.

10. The heat sensitive copying sheet of claim 1 wherein the thermofusible material is substantially colorless at a temperature lower than 50 C., and is present in an amount of from 3 to 30 weight parts.

11. The heat sensitive copying sheet of claim 4 wherein said thermofusible material is present in an amount from 3 to 30 weight parts and said binder is present in an amount of from 3 to 15 weight parts. 12. The heat sensitive copying sheet of claim 6 wherein said thermofusible material is substantially colorless at a temperature lower than 50 C., and is present in an amount of from 3 to 30 weight parts.

13. Heat sensitive copying sheets as claimed in claim 7 wherein the thermofusible material is substantially colorless at temperatures lower than 50 C., and is present in an amount of from 3 to 30 weight parts.

14. Heat sensitive copying sheets as claimed in claim 8 wherein the thermofusible material is substantially colorless at temperatures lower than 50 C., and is present in an amount from 3 to 30 weight parts.

15. Heat sensitive copying sheets as claimed in claim 9 wherein the thermofusible material is substantially colorless at temperatures lower than 50 C., and is present in an amount from 3 to 30 weight parts.

16. The heat sensitive copying sheet as claimed in claim 1 wherein the layer further comprises from 3 to 15 weight parts of a binder.

13 14 17. The heat sensitive copying sheet as claimed in claim OTHER REFERENCES 6 wherein the material coated thereon further contains Day: chemical Review VOL 63 1963 65 80 from 3 to 15 weight parts of a binder. (only 65 and 66 Pertinent).

References Cited 5 MURRAY KATZ, Primary Examiner UNITED STATES PATENTS 3,293,060 12/1966 Harbort 117-36.9

3,445,261 5/1969 Talvalkar 11736.9' l17l55 UA; 260-3452