CA1213140A - Thermoresponsive recording paper sheet - Google Patents

Abstract

THERMORESPONSIVE RECORDING PAPER SHEET

ABSTRACT

There is disclosed the use in a thermoresponsive recording paper sheet of compounds of the formula:

Description

1213~

This invention relates ~o a thermoresponsive recording paper sheet.
More particularly, the invention relates to a thermoresponsive recording paper sheet with improved responsiveness in color production, weather-proofness and preservability.
It has long been known that colorless or pale-colored chromogenic substances, such as crystal violet lactone, and phenolic compounds can react to produce a color, and the use of such reaction in thermoresponsive paper sheet recording is disclosed in U. S. Patent No. 3,539,375, for instance.
~owever, to meet the demands for higher thermal sensitivity and high-speed responsiveness, for instance, arising from recent advances in recording devices and diversified use of thermoresponsive recording sheets, it is still necessary to solve various problems. For instance, for use on thermal printers or thermal facsimile telegraphs, thermoresponsive paper sheets should have improved thermal responsiveness in color production, since an insufficient degree of responsiveness would result in increased electric power consumption and/or decreased printing velocity. For increasing color-producing responsive-ness of thermoresponsive sheets, there has already been proposed the use of such additives as waxes (Japanese Patent Application laid open (Kokai) under No. 19,231/1973) and nitrogen-containing compounds (Japanese Kokai 34,842/
1974).
In thermoresponsive recording sheets, presumably a chromogenic substance and a phenolic compound are present each in the stable and finely divided state dispersedly in the same layer or in different layers and, when heated, at least one of the two components melts or sublimates or both give an eutectic mixture, whereby they come into intimate contact with each other to produce a color. Therefore, it is necessary that each reactive color-developing component sould be colorless or pale-colored crystals or ~Z13140 solid at normal temperature, and further it is preferable that said component should melt at 70C or over and completely liquefy and/or vaporize at 150 to 200C.
U. S. Pa~ent No. 3,539,375 descri~es as a phenolic compound adequate for such purpose 4,4'-isopropylidenediphenol, which is used today in many cases.
As a result of intensive research for a thermoresponsi~e recording paper sheet with improved responsiveness in color production, weather-proofness and preservability, the present inventors have accomplished this invention. Thus, the invention relates to a thermoresponsive recording paper sheet comprising a compound of the formula Rl_o ~ S2 ~ o R2 (I) wherein Rl is hydrogen, alkyl of 1 to 5 carbon atoms, benzyl or phenethyl, and R2 is alkyl of 1 to 5 carbon atoms, benzyl or phenethyl, b~t R2 does not represent methyl when Rl is hydrogen.
In an aspect, this invention provides a thermoresponsive recording paper sheet compricing a normally colorless or pale-colored chromogenic ~ substance and a phenolic compound of the formula:

H0 ~ S02 ~ o_R3 (I-a) wherein R is alkyl of 2 to 5 carbon atoms, benzyl or phenethyl.
The compound of formula (I-a) wherein R is methyl is hardly crystal-lizable, and so it is unsuited for use in practicing the invention.

lZ1~140 t In another aspect, the invention provides a thermoresponsive recordin~
paper sheet comprising a normally colorless or pale-colored chromogenic substance in combination with a phenolic compound, which comprises a compound of the formula:

R4-o ~ S02 ~ o-R4 (I-b) wherein R4 is alkyl of 1 to 5 carbon atoms, benzyl or phenethyl.
The compound of formula (~-a) includes, for instance, 4-ethoxy-4'-hydroxydiphenyl sulfone, 4-propoxy-4'-hydroxydiphenyl sulfone, 4-isopropoxy-4'-hydroxydiphenyl sulfone, 4-butoxy-4'-hydroxydiphenyl sulfone, 4-isobutoxy-4'-hydroxydiphenyl sulfone, 4-tert-butoxy-4'-hydroxydiphenyl sulfone, 4-amyloxy-4'-hydroxydiphenyl sulfone, 4-isoamyloxy-4'-hydroxydiphenyl sulfone, 4-tert-a~yloxy-4'-hydroxydiphenyl sulfone, 4-benzyloxy-4'-hydroxydiphenyl sulfone and 4-phenethyloxy-4'-hydroxydiphenyl sulfone.
The compound of formula (I-b) includes, for examplP, 4,4'-dimethoxy-diphenyl sulfone, 4,4'-diethoxydiphenyl sulfone, 4,4'-dipropoxydiphenyl sulfone, 4,4'-dibutoxydiphenyl sulfone, 4,4'-diisobutoxydiphenyl sulfone, 4,4'-di-tert-butyldiphenyl sulfone, 4,4'-diamyloxydipheny] sulfone, 4,4'-diisoamyloxydiphenyl sulfone, 4,4'-di-tert-amyloxydiphenyl sulfone, 4,4'-dibenzyloxydiphenyl sulfone and 4,4'-diphenethyloxydiphenyl sulfone.
The 'chromogenic substance~ as used herein means a compound capable of producing a color upon reaction with a phenolic compound and includes, among others, crystal violet lactone, malachite green lactone, 3,3-bis-~p-dimethylaminophenyl)-4,5,6,7-tetrachIorophthalide, benzo-~ -naphtho-spiropyran, 3-methyl-di-~ -naphthospiropyran, 1,3,3-trimethyl-6'-chloro-8'-methoxyindolinobenzospiropyran, N-phenylrhodamine lactam, 3-ethylamino-6-chlorofluoran, 3-morpholino-5,6-benzofluoran, 3-die~hylamino-6-methyl-:~Zl~

7-anilinofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-6,7-dimethylfluoran, 3-dimethylamino-7,8-benzofluoran, 3-diethylamino-6-methoxyfluoran, 3-die~hylamino-7-dibenzylamino~luoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-5,6-benzo-7-benzylaminofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methy-7-anilinofluoran, 3-~-ethyl-tolylamino-6-methyl-7-anilinofluoran and 3-diethylamino-7~ 3-trifluoromethylphenyl)aminofluoran, but is not limited to these.
The compounds of formula (I-a) can be used in combination with another phenolic compound which melts generally at 70C or above and thereby reacts with the above~mentioned chromogenic substance to produce a color and includes, but is not limited to, 4-phenylphenol, 4-methyl-2,6-di-ter~-butyl-phenol, 4,4'-dihydroxydiphenyl, 4,4'-isopropylidenediphenol, 4,4'-isopropylidene-bis(2-chlorophenol), 4,4'-isopropylidenebis(2-methylphenol), 4,4'-isopropylidene-bis(2-tert-butylphenol), 4,4'-isopropylidenebis(2,6-dimethylphenol~, 4,4'-~5 sec-butylidenediphenol, 4,4'-cyclohexylidenediphenol, 4,4'-cyclohex~lidene-bis(2-methylphenol), 4,4'-cyclohexylidenebis(2-isopropylphenol), 2,2'-methylenebis(4-chlorophenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol),

2,2-bis(4-hydroxyphenyl)hexane, 2,2-bis(4-hydroxyphenyl)heptane, 2,2-bis-(4-hydroxyphenyl)octane, 4,4'-thiodiphenol, 4,4'-thiobis(3-methyl-6-tert-butylphenol), methyl p-hydroxybenæoate, ethyl p~hydroxybenzoate, benzyl p-hydroxybenzoate, tolylmethyl p-hydroxybenzoate; phenethyl p-hydroxybenzoate,

3-phenylpropyl p-hydroxybenzoate, phenyl p-hydroxybenzoate, 4--nydroxyaceto-phenone, 4-hydroxybenzophenone, salicylanilide, novolak type phenolic resin, halogenated novolak type phenolic resin, d-naphthol and ~-naphthol.
-25 In a thermoresponsive recording paper sheet comp~ising the compound of formula (I-b) as an agent for increasing responsiveness in color production, weather-proofness and preservability, the 'phenolic compound' as used herein lZ13~40 means the compound of formula (I-a) and/or ~he above-mentioned another phenolic compound. The compound of formula (I-b) is used, for example, in an amount of 0.01 to 1 part by weight per part by weight of such phenolic compound.
The thermoresponsive recording paper sheet in accordance with the present invention can be prepared by a conventional method, for instance, (1) by c = inuting the chromogenic substance and the phenolic compound separately, if necessary tDgether with a surfactant, binder and/or dispersing agent, in water or in an organic solvent, or (2) by comminuting the chromogenic substance, the phenolic compound and the compound of formula (I-b) each separately, or the chromogenic substance and the phenolic compound separately with the compound of formula (I-b) combined with the chromogenic substance and/or the phenolic compound~ if necessary together with a surfactant,binder and/or dispersing agent, in water or in an organic solvent, in a crusher such as ball mill or sand grinder and coating a paper sheet with the resulting dispersions, followed by heat drying.
Some of compounds of formula (I) are described in Beilsteins ~andbuch, and the compounds ~f formula (I) can be produced by alkylation of 4,4'-bisphenol sulfone.
Typical examples of the compound of formula (I~ are:
(1) 4-Ethoxy-4'-hydroxydiphenyl sulfone, m.p. 163-164C
(2) 4-Propoxy-4'-hydroxydiphenyl sulone, m.p. 138-140.5C
(3) 4-Butoxy-4'-hydroxydiphenyl sulfone, m.p. 118-119C
~4) 4-Benzyloxy-4'-hydroxydiphenyl sulfone, m.p. 162-164C
(5~ 4-Phenethyloxy-4'-hydroxydiphenyl sulfone, m.p. 143-144C
(6) 4,4'-Dimethoxydiphenyl sulfone, m.p. 129-130C
(7) 4,4'-Diethoxydiphenyl sulfone, m.p. 164C

1~13~4~

~8) 4,4'-Dipropoxydiphenyl sulfone, m.p. 142-143C
(9~ 4,4'-Diisopropoxydiphenyl sulfone, m.p. 157C
(10) 4,4'-Dibutoxydiphenyl sulfone, m.p. 92.5C
(11) 4,4'-Diamyloxydiphenyl sulfone, m.p. 86.5C
(12) 4,4'-Diisoamyloxydiphenyl sulfone, m.p. 98C
(13) 4,4'-Dibenzyloxydiphenyl sulfone, m.p. 188-189C and (14) 4,4'-Diphenethyloxydiphenyl sulfone, m.p. 136-138C

Preparative Example 1 A mixture of 5 g of 4,4'-bisphenol sulfone, 40 ml of dimethyl sulfoxide, 1 g of sodium hydroxide and 2.7 g of propyl bromide is stirred at room temperature for 5 hours. The reaction mixture is then made acidic with hydrochloric acid and extracted with ethyl acetate. The extract is washed with aqueous hydrochloric acid and adjusted to pH 10 with aqueous sodium hydroxide to remove the unreacted starting materials which pass over into the aqueous layer. The organic layer i5 washed with aqueous hydrochloric acid and concentrated. The residue is crystallized from toluene to give

4-propoxy-4'-hydroxydiphenyl sulfone, melting at 138-140.5C.
Preparative Example 2 A mixture of 5 g of 4,4'-bisphenol sulfone, 40 ml of methyl cellosolve, 1 g of sodium hydroxide and 4.1 g of phenethyl bromide is stirred at 90C
for 5 hours. The reaction mixture is concentrated, and to the residue is ad~ed aqueous sodium hydroxide until the pH of the aqueous layer reachs p~ 10. The aqueous layer is extracted with ethyl acetate, and the extract is washed with aqueous hydrochloric acid and concentrated. The residue is crystallized from toluene to give 4-phenethyloxy-4'~hydroxydiphenyl sulfone, melting at 143-144C.

~213140 Brief Explanation of the Drawing Fig. 1 shows the temperature-dependency of the optical density as measured with a photoelectric densitometer. In Fig. 1, curve (1) is for the thermoresponsive recording paper sheet of Comparative Example 1, curve (2) for that of Exa~ple 6, curve (3) for that of Example 7, and curve (4) for that of Example 8.
The present invention will be better unders~ood from the following examples, but they are not to be construed as limiting the present invention.
'Part(s)' means 'part(s) by weight'.
Comparative ~xample 1 Dispersion Al Crystal violet lactone 1 part

5% Polyvinyl alcohol solution 5 parts Water 40 parts Dispersion B:
4,4'-Isopropylidenediphenol 5 parts 5Z Polyvinyl alcohol solution 25 parts Water 20 parts Comparative Rxample 2 Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B:
4,4'-Butylidenebis(6-tert-butyl-m-cresol) 5 parts 5% Polyvinyl alcohol solution 25 parts Water 20 parts 1~13~40 g Ex~pLe 1 ~ispersion A: .
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B:
4-Propoxy-4'-hydroxydiphenyl sulfone5 parts 5% Polyvinyl alcohol solution 25 parts Water 20 parts Example Z
Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B:
4-Ethoxy-4'-hydroxydiphenyl sulfone5 parts 5% Pol~vinyl alcohol solution 25 parts Water 20 parts Example 3 Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B:
4-Butoxy-4'-hydroxydiphenyl sulfone5 parts 5% Polyvinyl alcohol solution 25 parts Water 20 parts Example 4 Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B: .
4-Benzyloxy-4'-hydroxydiphenyl sulfone5 parts 5% Polyvinyl alcohol solution 25 parts Water 20 parts 12~31~0 Exam~le 5 Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B:
4-Phenethyloxy-4'-hydroxydiphenyl sulfone5 parts 5% Polyvinyl alcohol solution 25 parts Water 20 parts Example 6 Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B:
4,4'-Isopropylidenediphenol .4 parts 4,4'-Butoxydiphenyl sulfone 1 part 5% Polyvinyl alcohol solution 25 parts Water 20 parts Example 7 Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts Dispersion B~
4-Propoxy~4' hydroxydiphenyl sulfone 4.75 parts 4,4'-Diamyloxydiphenyl sulfone 0.25 part 5% Polyvinyl alcohol solution 25 parts Water 20 parts Example 8 Dispersion A:
Same as Dispersion A in Comparative Example 1 46 parts lZ~3~40 Dispersion B:
4-Butoxy 4'-hydroxydiphenyl sulfone 4 parts 4,4'-Dibutoxydiphenyl sulfone 1 part 5% Polyvinyl alcohol solution 25 parts Water 20 parts In each of ~he above examples, Dispersions A and B were prepared separately (i.e. without mixing Dispersion A with Dispersio~ B) hy diSperS-ing the solid component by grinding in a ball mill for 2 days and then combined to give a coating composition for making a thermoresponsive recording paper sheet. A sheet of fine quality paper having the basis weight of 50 g/m2 was coated on one side with the coating composition to the coat amount Of 4 g/m2 (on the dried basis) and dried at 50C in a drier.
The thermoresponsive paper sheet thus obtained was caused to produce a color by pressing the sheet against a plate heated at 80-150C under the pressure of 1.5 kg/cm2 (gauge) for 5 seconds.
The thermores?onsive recording paper sheets o f Ex~mples 1 to 5 and Comparative Examples 1 and 2 were tested for the responsiveness and the preservability of recorded images. The results are shown in Table 1~

The thermoresponsive recording paper sheets of Examples 6 to 8 and Compara-tive Example 1 were measured for the intensity of color using a photoelectric densitometer. The results are shown in Fig, 1.

lZ13140 Table 1 _ Responsiveness Discoloration of -in Recording Recorded Images *
Example 1 ++
Example 2 + . _ Example 3 ++
Example 4 .
Example 5 ++ . ~+
Comparative . . . .
Example 1 + +

Comparative _ * After storing at normal temperature for 24 hours Responsiveness:
~+ : Excellent + : Fair - : Poor Discoloration of Recorded Images:
++ : No discoloration + : Moderate discoloration - : The image al st disappeared.

Examele 9 In dispersions B in Example 6 and Example 8, the proportion of 4,4'-dibutoxydiphenyl sulfone to the phenolic compound was varied as specified below in Table 2 while the total amount of the two components was retained, and thermoresponsive recording paper sheets were prepared in the same manner as mentioned above.

~;213~40 Table 2 ~ ... .. ~
Thermoresponsive Sheet No.
Compound 1 2 4 5 ~ 8 - _ _ Compound A 2 2 2 1 1 1 0.5 0.5 0.5 O
. _ _ Phenol I 3 _ 4 _ _ 4.5 _ _ 5 Phenol II 3 4 4.5 _~ _._ . _ Phenol III _ 3 4 4.5 Compound A: 4,4'-Dibutoxydiphenyl sulfone Phenol I : 4,4'-Isopropylidenediphenol Phenol II : Benzyl p-hydroxybenzoate Phenol III: 4-Butoxy-4'-hydroxydiphenyl sulfone When recording was carried out on a thermal printer, the thermorespon-sive recording paper sheets Nos. 1-9 produced distinct images with good preservability at high degree of dynamic responsiveness.

Example 10 Dispersion A:
3-Diethylamino-6-methyl-7-anilinofluoran 1 part 5% polyvinyl alcohol solution 5 parts Water 40 parts Dispersion B:
Same as Dispersion B in Example 3 50 parts lZ~3140 Example 11 Dispersion A:
Same as Dispersion A in Example 10 46 parts Dispersion B:
Same as Dispersion B in Example 6 50 parts Using Dispersions A and B of Example 10 or 11, thermoresponsive record-ing pap~r sheets were prepared in the same manner as mentioned above. The sheets, when recording was performed by means of a thermal printer, gave distinct images with good preservability at high degree of responsiveness in color production.

Claims (12)

What is claimed is:

1. A thermoresponsive recording paper sheet comprising a compound of the formula:

wherein R1 is hydrogen, alkyl of 1 to 5 carbon atoms, benzyl or phenethyl, and R2 is alkyl of 1 to 5 carbon atoms, benzyl or phenethyl, but R2 does not represent methyl when R1 is hydrogen.

2. A thermoresponsive recording paper sheet according to Claim 1, which comprises a normally colorless or pale-colored chromogenic substance and a phenolic compound of the formula:

wherein R3 is alkyl of 2 to 5 carbon atoms, benzyl or phenethyl.

3. A thermoresponsive recording paper sheet according to Claim 2, wherein the phenolic compound is 4-butoxy-4'-hydroxydiphenyl sulfone.

4. A thermoresponsive recording paper sheet according to Claim 1 comprising a normally colorless or pale-colored chromogenic substance in combination with a phenolic compound, which comprises a diether compound of the formula:

wherein R4 is alkyl of 1 to 5 carbon atoms, benzyl or phenethyl.

5. A thermoresponsive recording paper sheet according to Claim 4, wherein the diether compound is 4,4'-dibutoxydiphenyl sulfone.

6. A thermoresponsive recording paper sheet according to Claim 4, wherein the phenolic compound is 4,4'-isopropylidenediphenol.

7. A thermoresponsive recording paper sheet according to Claim 4, wherein the phenolic compound is benzyl p-hydroxybenzoate.

8. A thermoresponsive recording paper sheet according to Claim 4, wherein the phenolic compound is 4-butoxy-4'-hydroxydiphenyl sulfone.

9. A thermoresponsive recording paper sheet according to Claim 2, wherein the chromogenic substance is a fluoran compound.

10. A thermoresponsive recording paper sheet according to Claim 4, wherein the chromogenic substance is a fluoran compound.

11. A thermoresponsive recording paper sheet according to Claim 9 or 10, wherein the fluoran compound is 3-diethylamino-6-methyl-7-anilinofluoran.

12. A thermoresponsive recording paper sheet according to Claim 2 or 4, wherein the chromogenic substance is crystal violet lactone.