US3829401A - Heat sensitive recording paper - Google Patents

Abstract

IN THE HEAT SENSITIVE RECORDING SYSTEM COMPRISING COMBINATION OF A COLOR FORMING COMPOUND AND A PHENOL COMPOUND, THE FADING OF THE HEAT RECORDING COMPOSITION IN THE DARK CAN BE PREVENTED BY ALLOWING A PHENOL RESIN TO BE PRESENT IN THE HEAT SENSITIVE LAYER OR IN CONTACT WITH THE LAYER. SAID PHENOL RESIN IS THE ONE OBTAINED BY CONDENSATION OF AT LEAST ONE LOWER ALPIPHATIC ALDEHYDES, LOWER ALIPHARIC ALDEHYDE PRODUCING AGENT AND LOWER ALKYLVINYL ESTERS AND A PHENYL COMPOUND HAVING 3 OR MORE ORTHO-AND/OR PARA-POSITIONS (TO PHENOLIC HYDROXYL GROUP) HAVING NO MORE SUBSTITUENTS.

Description

United States Patent "ice 3,829,401 HEAT SENSITIVE RECORDING PAPER Kiyoshi Futaki, Kozo Haino, and Isao Kohmura, Kyoto, gapan, assignors to Mitsubishi Paper Mills, Ltd., Tokyo,

apan No Drawing. Filed Oct. 25, 1972, Ser. No. 300,873 Claims priority, application Japan, Oct. 30, 1971, 46/ 86,341 Int. Cl. B41n 5/22 U.S. Cl. 260-38 8 Claims ABSTRACT OF THE DISCLOSURE In the heat sensitive recording system comprising combination of a color forming compound and a phenol compound, the fading of the heat recording composition in the dark can be prevented by allowing a phenol resin to be present in the heat sensitive layer or in contact with the layer. Said phenol resin is the one obtained by condensation of at least one of lower aliphatic aldehydes, lower aliphatic aldehyde producing agent and lower alkylvinyl ethers and a phenol compound having 3 or more ortho-and/or para-positions (to phenolic hydroxyl group) having no substituents.

The present invention relates to a heat sensitive recording composition and a heat sensitive recording paper and more particularly it concerns prevention of fading of heat recording composition of the heat sensitive recording paper comprising combination of a usually colorless or light-colored color forming compound and a phenol compound.

It was known that a coating liquid obtained by dispersing in a binder a leuco lactone or spiropyran compound which is a usually colorless or light-colored color forming compound and a phenol compound which is solid at normal temperature and which is molten or gasified at a temperature of about 60-220 C. in fine particle state is coated on a substrate to obtain a heat sensitive recording paper. However, such conventional heat sensitive recording paper is apt to gradually fade with the lapse of time during storage even in the dark after heat recording and often causes practically serious defects.

As the results of extensive researches on production of a heat sensitive recording paper having no defects as mentioned above, the inventors have succeeded in producing a heat sensitive recording composition which is prevented from fading by the following method. That is, the heat sensitive recording composition of the present invention comprises (1) usually colorless or light-colored color forming compound, (2) a phenol compound which causes color formation of said compound (1) and (3) a three-dimensionally cross-linked phenol resin, said three components being dispersed in a binder. That is, the present invention is based on the discovery that in the heat sensitive system comprising the combination of a color forming compound and a phenol compound, the fading of the heat recording material in the dark can be markedly prevented by allowing said phenol resin to be present in a heat sensitive layer or in contact with the layer.

One of the causes of the fading is considered as follows: Lactone or spiropyran compound is stably present as developed color in dissolved state or in solid solution state in the molten phenol compound immediately after writing with heat. However, with the lapse of time, crystallizations of the phenol compound and the dye constituting the developed color images are gradually accelerated especially by humidity and a suitable temperature to form respectively independent phases, whereby 3,829,401 Patented Aug. 13, 1974 dye molecules are instabilized to return to the original colorless color forming compound.

The effects of the present heat sensitive recording composition will be detailedly explained in the Examples.

The normally colorless or light-colored color forming compounds used in the present invention are known as so-called leuco lactone and spiropyran compounds th representatives of which are as follows:

Crystal violet lactone Malachite Green lactone 3,3-Bis (p-dimethylaminophenyl)-6-amino phthalide 3,3-Bis(p-dimethylaminophenyl)-6-p-toluene sulfonamide phthalide 3-Diethylamino-7-dibenzylamino fluoran 3 -Diethylamino-7- (N-methylanilino -fluoran 3-Dimethylamino-6-methoxy-fluoran 3-Diethylamino-6-methyl-7-chlorofluoran 3-Dibutylamino-6-methyl-7-chlorofluoran 3-Diethylamino-7-phenylfluoran 3-Morpholino-5,6-benzofiuoran Spiro 1-benzopyran-2,2'-naphthopyran) 6-Chloro-8-methoxy-1',3',3-trimethyl-spiro( l-benzopyran-2,2-indoline) The phenol compounds used in the present invention are those which are solid at normal temperature and are molten and/or gasified at a temperature of about -220 C. to react with said color forming compound to cause color formation of this compound. Especially, the phenol compounds which are difficultly soluble in water or petroleum and have a melting point of C. are practically preferred. The examples of the compounds are as follows:

4,4'-Isopropylidene diphenol 4,4'-Isopropylidene-bis (Z-methylphenol) 4,4-Isopropylidene-bis (Z-phenylphenol) 4,4'-Isopropylidene-bis(2-tertiary butyl phenol) 4,4-Secondary butylidene-diphenol 4,4-Secondary butylidene-bis(2-methylphenol) 4,4'-Cyclohexylidene-diphenol 4,4'-Cyclohexylidene-bis(2-isopropylphenol) 4,4'-Ethylidenediphenol 2,2-Methylenebis(S-methylphenol) 4,4'-Ethylidene-bis(Z-methylphenol) 4,4-( l-Methylpentylidene -diphenol 4,4'-( l-Methyl-isopentylidene -diphenol 4,4'-( l-Methyl-Hexylidene -diphenol 4,4'- l-Ethyl-butylidene) -diphenol 4,4'-( l-Ethyl-propylidene -bis (Z-methyl phenol) 4,4'-Isopropylidene-dicatechol 4,4'-Benzyliclenediphenol 4,4-Isopropylidene-bis (2-chlorophenol) 2,2-Dihydroxydiphenyl 2,2'-Methylene-bis(4-chlorophenol) 2,2-Methylene-bis(4-methyl-6-tertiary butylphenol) 4,4'-Isopropylidene-bis(2,6-dimethylphenol) 2,2-thiobis(4,6-dimethylphenol) 4,4-Ethylenediphenol 4,4'-( l-Methylbenzylidene)-diphenol is one which has totally 3 or more ortho-positions and/ or para-positions (to phenolic hydroxyl group) having no substituents in one molecule. The representatives thereof may be represented by the following general formulas,

(wherein R is hydrogen, a hydroxyl group, an alkyl group, an alkoxy group or a halogen) or R2 a a (11) [wherein R is hydrogen or hydroxyl group, R is hydrogen, hydroxyl group, a halogen, an alkyl group or an alkoxy group and X is S, 0, S phenylene or Phenol,

m-Cresol,

m-Ethoxy phenol,

m-Chlorophenol, 2,4'-Methylene-diphenol, 4,4-Isopropylidene di-resorcinol, 2,2-Methylene bis 5-bromophenol 4,4-Isopropylidene bis(3-chlorophenol), 2,2-Methylene bis(5-isopropylphenol), 4,4-Ethylene bis 3-methoxyphenyl) 4,4'Isopropylidene-diphenol 4,4'-Secondary butylidene-diphenol 4,4Cyclohexylidene-diphenol 4,4'-Ethylidene-diphenol 4,4-( l-Methylpentylidene) diphenol 4,4-( l-Methyl-isopentylidene diphenol 4,4'-( l-Methyl-hexylidene diphenol 4,4'-( 1-Ethylbutylidene) diphenol 4,4'-Isopropylidene-dicatechol 4,4'-Benzylidene-diphenol 4,4,4-Methy1-triphenol 4,4'-( l-Methylbenzylidene) diphenol 4,4'-Ethylene diphenol 4,4-Tetramethylene diphenol 4,4'-Hexamethylene diphenol 4,4-Thio diphenol 2,4-Sulphenyl diphenol 2,2'-Oxy diphenol.

The phenol resins may be used in combination of two or more in the present invention.

The phenol resins used in the present invention can be easily prepared by reacting said starting phenol com pounds and said lower aliphatic aldehydes or similar cross linking agents in the presence of an acid catalyst, usually in a solvent, grinding the resultant condensate and, if necessary, washing the ground condensate. Especially, a gelled condensate of 4,4'-isopropylidene diphenol and formalin is suitable for economical reasons. Practically, those which are not softened at lower than 130 C. are preferred. Among phenol resins, some of the known novolak phenol resins prepared by the reaction of formalin and phenol compounds having two unsubstituted orthoand/or para-positions to phenolic hydroxyl group in one molecule such as cresol, tert-butylphenol,

octylphenol, phenylphenol, etc. are similarly effective for prevention of fading of heat recording composition. However, being diiferent from the phenol resins of the present invention, these known phenol resins damage the heat stability of heat sensitive composition when jointly used in the heat sensitive composition and apt to cause gradual deep color formation in the ground of heat sensitive recording layer because these known phenol resins have low melting point and cause reduction of color formation temperature due to mixed melting effect with the phenol compound used as a color forming agent. Thus, these known phenol resins are not suitable. On the other hand, the phenol resins used in the present invention have the property that they are insoluble in solvents such as methanol, but swollen therein. Fading of a heat sensitive layer in the dark which contains said phenol resins can be prevented by the melting of the phenol compound which is a color forming agent by heating to cause the phenol resins to swell and the phenol resins have no property of decreasing the melting point of the phenol compound to cause reduction of color forming temperature. Therefore, these phenol resins have no such defect as lowering heat stability as seen when other phenol resins are used.

The weight ratio of the phenol compound and phenol resin in the heat sensitive compositions of the present invention is 1:20-20:1 and preferably 1:5-5 :1. When the amount of thephenol compound is too small, the density of the recorded matter is low and when the amount of the phenol resin is too small, the elfect of prevention of fading is not satisfactory.

According to the present invention, generally the above mentioned three components are dispersed in water or petroleum and coated on a support such as paper or film. Therefore, a binder for binding said components is nec essary. As the binder, generally known water soluble resins are suitable and examples thereof are polyvinyl alcohol, hydroxyethyl cellulose, gum arabic, styrenemaleic acid copolymer, gelatin, etc. As the petroleum binder, terpene resins, petroleum resins, cyclized rubber, etc. may be used. In the present invention, as mentioned before, the normally colorless or light-colored color forming compound, the phenol compound and the pheol resin are dispersed in a binder and in this case, the dispersed particles are preferably ground to those of as small as possible, specifically of less than several ,u in diameter. In this case, when particle size is large, the surface of coating on a heat sensitive recording paper is naturally roughened and the commercial value thereof is reduced. Furthermore, as a grinding assistant, the activators such as dispersant, defoaming agent, etc. may be used, if necessary. Moreover, waxes can be added to a heat sensitive layer to bring about the effect of preventing color formation due to pressure. Additionally, talc, zinc oxide, titanium oxide, calcium carbonate, etc. may also be added to result in white appearance of heat sensitive recording layer.

SYNTHESIZING EXAMPLE 1 OF THE PHENOL RESIN 4,4'Isopropylidene-diphenol g 45.6 Ethyl alcohol -ml 60 Water ml 40 37% Aqueous solution of formaldehyde g 30 Concentrated hydrochloric acid and I water (1:1) ml 10 The above components were introduced into a flask and mixed. Then, the mixture was refluxed with heat on a water bath for 3 hours. After allowing it to stand for cooling, the supernatant liquid was removed by decantation and the residue was kneaded with water and washed by the decantation method. Furthermore, 200 ml. of methanol was added thereto and after allowing to stand overnight, the supernatant was removed by decantation. The residual gel-like material was ground with a household mixer in the presence of water and then was filtered, washed with water and dried to obtain slightly browncolored substantially white powders, which were not molten at a temperature of lower than 200 C. Yield was 46 g.

SYNTHESIZING EXAMPLE 2 OF THE PHENOL RESIN The procedure of Synthesizing Example 1 was repeated except that 4,4'-(l-methylhexylidene)diphenol was used in place of 4,4'-isopropylidene-diphenol to obtain substantially white powdery bisphenol resin.

SYNTHESIZING EXAMPLE 3 OF THE PHENOL RESIN The procedure of Synthesizing Example 1 was repeated except that 4,4-cyclohexylidene diphenol was used in place of 4,4'-isopropylidene-diphenol to obtain substantially white powdery bisphenol resin.

Example 1 Liquid A: G. Crystal violet lactone 1 5% aqueous solution of hydroxyethyl cellulose" 5 Water 5 Liquid B:

4,4 (l Methylhexylidene)-diphenol 4 Resin obtained by condensation of 4,4'-isopropylidene diphenol and formalin (Synthesis Example 1) 1 5% Aqueous solution of hydroxyethyl cellulose 25 Water 22 Said liquids A and B were separately ground and dispersed in a ball mill for 2 days and they were mixed. The mixture was coated on an ordinary paper having a weight of 50 g./m. in such a manner that the coating amount when dried was about 4 g./m. and was dried at lower than 40 C. to obtain a heat sensitive recording paper. The ground color of the coating layer was white and was stable even when it was stored at room temperature for a long period and rapidly formed clear deep blue color by hot pen or hot writing. Substantially no fading of this paper was caused even when it was filed and stored for a long period. On the other hand, a recording paper which contained no phenol resin of the present invention in the heat sensitive layer gradually faded after heat recording. Moreover, a recording paper which contained a phenol resin from p-octylphenol, p-butylphenol, p-phenylphenol, etc. in place of the phenol resin of the present invention did not fade after heat recording, but the gradually formed ground color and this was not preferred in practical use.

Table 1 shows the results of heat resistant test on these heat sensitive recording paper.

cording paper was obtained in accordance with the same method as in Example 1. The ground color was white and deep red color was formed by heat recording. Substantially no fading of the heat recording material in the dark was recognized. On the other hand, fading of portions of letter written with heat was gradually caused when the bisphenol resin of the present invention was omitted from said heat sensitive composition.

Example 3 Liquid A: G. Crystal violet lactone 1 5% Aqueous solution of polyvinyl alcohol 5 Water 4 Liquid B:

4,4-Isopropylidene-diphenol 4 Resin obtained by condensation of 4,4-isopropylidenediphenol and formalin (Synthesizing Example 1) 5% Aqueous solution of polyvinyl alcohol 25 Water 20 Using the above liquids A and B, a heat sensitive recording paper was obtained in the same manner as in Example 1. The ground color of this paper was white and deep blue color was formed by writing with heat. Substantially no fading of the written letters in the dark was recognized. On the other hand, when the bisphenol resin of the present invention was omitted, fading of the written letters gradually occurred.

Example 4 A heat sensitive recording sheet was obtained in the same manner as of Example 3 except that a condensation product of 4,4'-(l-methylhexylidene)diphenol of Synthesis Example 2 and formalin was used in place of the phenol condensate of Synthesizing Example 1 used in Example 3. The ground color of thus obtained sheet was white and formed deep blue color by writing with heat. These written letters showed substantially no fading in the dark.

Example 5 A heat sensitive recording sheet was obtained in the same manner as of Example 3 except that a condensation product of 4,4-cyclohexylidene diphenol of Synthesizing Example 3 and formalin was used in place of the phenol TABLE l.STABILITY OF HEAT SENSITIVE RECORDING PAPER Portions of letter Written with heat Optical density of ground color Fading after After one After one one week at Before week at week at 40 C.

Phenol resin in heat sensitive layer heating 40 C. 50 0. (percent) None 0. 03 0. 04 O. 0 0 Phenol resin of synthesizing, Example 1 (the present in- 6 9 vention) 0. 04 0. O5 0. 08 0 #51042-0 1 (not the present invention) 0.06 0.28 0.32 0

#26799 1 (not the present invention)..- 0. 06 0.10 0.22 0

#26141 3 (not the present invention)..- 0.15 0.26 0.63 0

#51027 4 (not the present invention)... 0. 04 0.09 0. 15 50 1 #51042-0: Para-tert-octyl phenol resin (m.p. 8090 C.) manufactured by Sumitomo Durez K. K.

2 #26799: Para-tertbuty1 phenol resin (m.p. 80 O.) manufactured by Hooker Chemical Co.

condensate of Synthesizing Example 1 used in Example 3. The resultant sheet had the same properties as in Example 4.

What is claimed is:

1. A fading-prevented, heat sensitive recording composition which comprises:

(1) a normally colorless or light-colored color forming compound selected from the group consisting of leuco lactone and spiropyran compounds;

(-2) a phenol compound capable of causing color formation of said color forming compound upon heating; and

(3) a three-dimensionally cross-linked phenol resin which is a condensation reaction product of at least one lower aliphatic aldehyde, lower aliphatic aldehyde producing agent or a lower alkyl vinyl ether and a phenol compound having at least 3 ortho positions or para positions or ortho and para positions to the phenolic hydroxyl group free of substituents, and the weight ratio of said phenol compound (2) to said phenol resin (3) being from 1:20 to 20:1.

2. A heat sensitive recording composition according to claim 1 wherein the phenol resin is a condensation product of a phenol with formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acrolein, glyoxal, paraformaldehyde, paraldehyde, methyl vinyl ether, or ethyl vinyl ether.

3. A heat sensitive recording composition according to claim 2 wherein the phenol resin is a condensation product of a phenol and an aldehyde.

4. A heat sensitive recording composition according to claim 3 wherein the aldehyde is formaldehyde.

5. A heat sensitive recording composition according to claim 2 wherein the phenol of the phenol resin has the formula HO X- OH I R: a s 2 Tat.

where R, and R are hydrogen, alkyl, phenyl, hydroxyphenyl or a cyclic alkylene group to which R and R are bonded and n is an integer from 0 to 8.

6. A heat sensitive recording composition according to Claim 1, wherein said phenol compound is one which is solid at normal temperature and which is liquefied or gasified at a temperature of --220 C. and reacts with said color forming compound to cause color formation of the color forming compound.

7. A heat sensitive recording paper which comprises a support and the heat sensitive recording composition of Claim 1 which is coated on said support.

8. A heat sensitive recording composition according to Claim '1, wherein said phenol resin is a condensation reaction product of 4,4'-isopropylidene diphenol and formalin.

References Cited UNITED STATES PATENTS 3,539,375 11/1970 Baum 11736.8 X 3,663,256 5/1972 Miller et al. 117-36.2 3,322,557 5/1967 Schwab ll736.8 X

ALLA-N LIEBERMA N, Primary Examiner S. M. PERSON, Assistant Examiner US. Cl. X.R. 11736.2, 36.8