Heat-sensitive recording material

A novel heat-sensitive recording material comprising a support having coated thereon a heat-sensitive coloring layer containing a colorless or light-colored electron donor dye precursor and an electron acceptor compound which colors upon reaction with said electron donor dye precursor and a protective alyer coated on the heat-sensitive coloring layer comprising a saponified product of a vinyl acetate-acrylamide copolymer or vinyl acetate-methacrylamide copolymer having an acrylamide or methacrylamide content of about 0.5 to about 80% by weight.

FIELD OF THE INVENTION 
The present invention relates to a heat-sensitive recording material. More 
particularly, the present invention relates to a heat-sensitive recording 
material which utilizes the color reaction of a colorless or light-colored 
electron donor dye precursor and an electron acceptor compound. 
BACKGROUND OF THE INVENTION 
So-called two component system heat-sensitive recording materials which 
utilize the color reaction of a colorless or light-colored electron donor 
dye precursor and an electron acceptor compound are disclosed in Japanese 
Patent Publication Nos. 14039/70 and 4160/68. Two component coloring 
system heat-sensitive recording materials are prepared by applying to a 
support a mixture of a fine dispersion of a colorless or light-colored 
electron donor dye precursor, an electron acceptor compound, a binder and 
the like in such a manner that the two heat-reactive compounds are kept 
separated by the binder and the like. When heated, one or both of the two 
compounds are melted and brought into contact with each other whereupon 
they undergo a color reaction which is used for recording. These two 
component coloring system heat-sensitive recording materials are 
advantageous and practical in that their primary coloring mechanism 
eliminates the need for development, that their paper quality resembles 
that of normal papers, that they are convenient to handle, that the color 
density is high, and that heat-sensitive recording materials having 
various color hues can be easily prepared. Therefore, these heat-sensitive 
recording materials are most widely used as heat-sensitive recording 
materials. In recent years, these heat-sensitive recording materials have 
shown a remarkable increase in use with facsimile, recorders and printers. 
As facsimiles have been used more and more, the recording speed has been 
improved. This has required the heat-sensitive recording material to color 
with shorter pulses, i.e. lower energy, that is, to have an improved 
heat-response. 
On the other hand, these heat-sensitive recording materials are 
disadvantageous in that the primary coloring mechanism is such that a 
reaction of the electron donor dye precursor and the electron acceptor 
compound also occurs due to solvents or the like even without applying 
heat. 
This is because all heat-sensitive recording materials of this type are 
made of organic materials which are highly soluble in solvents and thus 
cause a reaction therein. Accordingly, when solvents such as water ink 
pen, oil ink pen, fluorescent pen, diazo developer, adhesives, or paste 
are brought in contact with stationery, the background having white color 
of the heat-sensitive recording material may color or printed portions 
thereof may discolor, thereby impairing commercial value. 
Attempts have been made to provide a solvent-resistant protective layer on 
the heat-sensitive coloring layer as disclosed in Japanese Patent 
Publication No. 27880/69, and Japanese Patent Application (OPI) Nos. 
30437/73 and 31958/73 (the term "OPI" as used herein means an "unexamined 
published application"). However, such a protective layer lowers the 
coloring sensitivity. Such a protective layer also makes the recording 
material insufficiently compatible with the heat-sensitive head of the 
heat-sensitive recording apparatus, causing sticking or noises upon 
recording. Moreover, the protective layer makes the recording material 
poor in writing quality as stationery, causing ink run or the like. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a 
heat-sensitive recording material excellent in chemical resistance, 
solvent resistance, compatibility with the heat-sensitive head, and 
writing quality as stationery. 
The above and other objects of the present invention will become more 
apparent from the following detailed description and examples. 
These objects of the present invention are accomplished by a heat-sensitive 
recording material comprising a support having coated thereon a 
heat-sensitive coloring layer containing a colorless or light-colored 
electron donor dye precursor and an electron acceptor compound which 
colors upon reaction with the electron donor dye precursor, characterized 
in that a saponified product of a vinyl acetate-acrylamide copolymer or 
vinyl acetate-methacrylamide copolymer having an acrylamide or 
methacrylamide content of about 0.5 to about 80% by weight is incorporated 
in a protective layer provided on the heat-sensitive coloring layer. (The 
saponified product of the copolymer obtained in accordance with the 
present invention will be hereinafter referred to as "modified polyvinyl 
alcohol.") 
DETAILED DESCRIPTION OF THE INVENTION 
The effective range of the acrylamide or methacrylamide content of the 
above modified polyvinyl alcohol is about 0.5 to about 80% by weight. If 
this value is outside the above range, the objects of the present 
invention cannot be realized. The preferred range is 1 to 70% by weight. 
Acrylamides substituted with C.sub.2-8 alkyl groups such as methyl, 
ethyl, propyl, iso-propyl, butyl, amyl, octyl, etc., show similar effects 
and are advantageously used with a water-soluble polymer not related to 
the copolymers of the present invention. 
The degree of saponification is preferably about 60 to about 100 mol.%, 
most preferably 80 to 100 mol.%. The average degree of polymerization is 
preferably about 100 to about 3,000, most preferably 300 to 2,000. The 
content of carboxyl groups produced by the saponification reaction of 
acrylamide is not specifically limited but is most preferably 0.05 to 10 
mol.%. 
The preparation of the above modified polyvinyl alcohol may be accomplished 
by any conventional method such as described in Japanese Patent 
Publication No. 42724/72 corresponding to U.S. Pat. No. 3,672,941 (which 
is hereby incorporated by reference). 
It is desired that a starch is incorporated in a protective layer on the 
heat-sensitive coloring layer together with the above modified polyvinyl 
alcohol. Examples of such a starch include modified starch such as 
oxidized starch, crosslinked starch, graft starch, esterified starch and 
etherified starch. 
In the present invention, the mixing proportion of the above modified 
polyvinyl alcohol based on the weight of the starch is preferably about 5 
to about 70% by weight, most preferably 20 to 60% by weight. 
In the present invention, when the above modified polyvinyl alcohol or a 
mixture of the above modified polyvinyl alcohol and a starch is used as a 
protective layer, a pigment, a metal soap, a wax, or the like may be 
incorporated in the protective layer in order to further improve 
compatibility with the heat-sensitive head. 
The amount of the pigment to be added is preferably 0.5 to 4 times, most 
preferably 0.8 to 3.5 times the total weight of the above starch and 
modified polyvinyl alcohol. If this value is less than the above lower 
limit, the compatibility of the protective layer with the heat-sensitive 
head cannot be improved. If this value exceeds the upper limit, the 
sensitivity is remarkably reduced, impairing commercial value. Suitable 
pigments are zinc oxide, calcium carbonate, barium sulfate, titanium 
oxide, lithopone, talc, agalmatolite, kaolin, aluminum hydroxide, silica, 
amorphous silica and colloidal silica. 
As such a metal soap there may be used higher fatty acid metal soap. An 
emulsion of zinc stearate, calcium stearate or aluminum stearate may be 
used. In particular, an emulsion of zinc stearate is suitable. The amount 
of the metal soap is preferably 0.5 to 20% by weight, most preferably 1 to 
10% by weight based on the total weight of the protective layer. A 
thickness of the protective layer is 0.1 to 10 .mu.m, preferably 0.5 to 5 
.mu.m. 
As suitable wax there may be used an emulsion of paraffin wax, 
microcrystalline wax, carnauba wax, methylol aeroamide, stearylamide, 
polyethylene wax or polystyrene wax. The amount of the wax to be added is 
preferably about 1 to about 20%, most preferably 1 to 10% by weight, based 
on the total weight of the protective layer. 
When the protective layer is applied to the heat-sensitive coloring layer, 
a surface active agent may be added thereto in order to provide a uniform 
protective layer. Suitable surface active agents are sulfosuccinic acid 
alkali salts or fluorine-containing surface active agents. Specific 
examples of such surface active agents include sodium salts or ammonium 
salts of di-(2-ethylhexyl)sulfosuccinic acid and di-(n-hexyl)sulfosuccinic 
acid. Most anionic surface active agents are effective. 
In the present invention, compounds which are normally used as agents for 
rendering PVA water-resistant may be used for the purpose of rendering the 
heat-sensitive material water-resistant. Specific examples of such a 
compound include water-soluble precondensation resins such as N-methylol 
urea, N-methylol melamine, urea-formalin, melamine-formalin, 
benzoguanamine-formalin, and acetoguanamine-formalin, dialdehyde compounds 
such as glyoxazol and glutaraldehyde, inorganic crosslinking agents, and 
blend heat-treating agents such as polyacrylic acid, methylvinyl, 
ether-maleic acid copolymer and isobutylene-maleic anhydride. The amount 
of the agent for rendering the heat-sensitive material water-resistant to 
be used is preferably about 0.5 to about 30% by weight based on the weight 
of the modified polyvinyl alcohol. 
As the colorless or light-colored electron donor dye precursor of the 
present invention there may be used triaryl methane compounds, diphenyl 
methane compounds, xanthene compounds, thiazine compounds, or spiropyran 
compounds. Specific examples of such electron donor dye precursors include 
those described in Japanese Patent Application (OPI) No. 27253/80. 
Examples of these electron donor dye precursors are triaryl methane 
compounds such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide 
(i.e. crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)phthalide, 
3-(p-dimethylaminophenyl)-3-(1,3-dimethylindol-3-il)phthalide, and 
3-(p-dimethylaminophenyl)-3-(2-methylindol-3-il)phthalide, diphenyl 
methane compounds such as 4,4'-bis-dimethylaminobenzhydrinebenzylether, 
N-halophenyl-leuco Auramine, and N-2,4,5-trichlorophenyl leuco Auramine, 
xanthene compounds such as rhodamine-B-anilinolactam, rhodamine(p-nitrino) 
lactam, 2-(dibenzylamino)fluorane, 2-phenylamino-6-diethylamino fluorane, 
2-(o-chloroanilino)-6-diethylamino fluorane, 
2-(3,4-dichloroanilino)-6-diethylamino fluorane, 
2-anilino-3-methyl-6-piperidino fluorane, and 2-phenyl-6-diethylamino 
fluorane, thiazine compounds such as zenzoyl leucomethylene blue, 
p-nitrobenzyl leucomethylene blue, and spiro compounds such as 
3-methyl-spiro-dinaphthopyran, 3-ethyl-spirodinaphthopyran, 
3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspiro-dinaphthaopyran, 
3-methyl-naphtho-(3-methoxybenzo)-spiropyran and 
3-propyl-spiro-dibenzopyran. These compounds may be used singly or in 
combination. Triaryl methane compounds such as crystal violet lactone and 
xanthene compounds provide less fog and, hence, higher color density and, 
thus, are preferable electron donor dye precursors. More preferred 
electron donor dye precursors include xanthene compounds of the general 
formula (II): 
##STR1## 
wherein R.sub.1 and R.sub.2, which may be the same or different, each 
represent a C.sub.1-10 alkyl group or cycloalkyl group which may be 
substituted; R.sub.3 represents an aryl group which may be substituted; 
and X represents a C.sub.1-10 alkyl group which may be substituted or a 
halogen atom. 
In the general formula (II), the alkyl group represented by R.sub.1 and 
R.sub.2 may be either straight-chain or branched, and may optionally have 
substituent groups. The aryl group represented by R.sub.3 preferably has 6 
to 20 carbon atoms and is preferably a phenyl group or phenyl group having 
substituent groups. Such substituent groups are preferably C.sub.1-10 
alkyl groups. 
Particularly preferred among the dye precursors of the general formula (II) 
are those represented by the general formula (III): 
##STR2## 
wherein R.sub.1 and R.sub.2, which may be the same or different, each 
represents a C.sub.1-10 alkyl group which may be substituted; R.sub.4 
represents a hydrogen atom or C.sub.1-8 alkyl group, preferably hydrogen 
atom or lower alkyl group, particularly CH.sub.3 ; and X represents a 
C.sub.1-8 alkyl group or a chlorine atom. 
In the general formula (III), the alkyl group represented by R.sub.1 and 
R.sub.2 may form a ring and may have substituent groups. 
In the general formula (III), X is most preferably a methyl group or 
chlorine atom. 
As these colorless or light-colored electron donor dye precursors there may 
be used the following compounds. However, the present invention is not 
limited thereto. 
Specifically, these electron donor dye precursors include 
2-anilino-3-methyl-6-dimethylamyl fluoran, 
2-anilino-3-methyl-6-N-methyl-N-ethylamino fluoran, 
2-anilino-3-methyl-6-N-methyl-N-(iso-propyl)amino fluoran, 
2-anilino-3-methyl-6-N-methyl-N-pentyl amino fluoran, 
2-anilino-3-methyl-6-N-methyl-N-cyclohexylamino fluoran, 
2-anilino-3-methyl-6-diethylamino fluoran, 
2-anilino-3-chloro-6-dimethylamino fluoran, 
2-anilino-3-methyl-6-N-ethyl-N-isoamylamino fluoran, 
2-anilino-3-methyl-6-N-methyl-N-isoamylamino fluoran, 
2-anilino-3-chloro-6-diethylamino fluoran, 
2-anilino-3-chloro-6-N-methyl-N-ethylamino fluoran, 
2-anilino-3-chloro-6-N-methyl-N-(iso-propyl)amino fluoran, 
2-anilino-3-chloro-6-N-methyl-N-pentylamino fluoran, 
2-anilino-3-chloro-6-N-methyl-N-cyclohexylamino fluoran, 
2-anilino-3-methyl-6-N-ethyl-N-pentylamino fluoran, 
2-anilino-3-chloro-6-N-ethyl-N-pentylamino fluoran, 
2-(p-methylanilino)-3-methyl-6-dimethylamino fluoran, 
2-(p-methylanilino)-3-methyl-6-diethylamino fluoran, 
2-(p-methylanilino)-3-methyl-6-N-methyl-N-ethylamino fluoran, 
2-(p-methylanilino)-3-methyl-6-N-methyl-N-(iso-propyl)amino fluoran, 
2-(p-methylanilino)-3-methyl-6-N-methyl-N-pentylamino fluoran, 
2-(p-methylanilino)-3-methyl-6-N-methyl-N-cyclohexylamino fluoran, 
2-(p-methylanilino)-3-methyl-6-N-ethyl-pentylamino fluoran, 
2-(p-methylanilino)-3-chloro-6-dimethylamino fluoran, 
2-(p-methylanilino)-3-chloro-6-diethylamino fluoran, 
2-(p-methylanilino)-3-chloro-6-N-methyl-N-ethylamino fluoran, 
2-(p-methylanilino)-3-chloro-6-N-methyl-N-(iso-propyl)amino fluoran, 
2-(p-methylanilino)-3-chloro-6-N-methyl-N-cyclohexylamino fluoran, 
2-(p-methylanilino)-3-chloro-6-N-methyl-N-pentylamino fluoran, 
2-(p-methylanilino-3-chloro-6-N-ethyl-N-pentylamino fluoran, 
2-anilino-3-methyl-6-N-methyl-N-furylmethylamino fluoran and 
2-anilino-3-ethyl-6-N-methyl-N-furylmethylamino fluoran. These electron 
donor dye precursors can be used singly. These electron donor dye 
precursors can also be used in combination to adjust color tone and 
inhibit discoloration of color images. 
As the electron acceptor compound of the present invention there may be 
preferably used compounds of the general formulae (IV) to (VIII): 
##STR3## 
wherein X represents S, O, SO.sub.2, S.sub.2 or 
##STR4## 
l represents an integer of 0 to 3; R.sub.1 and R.sub.2, which may be the 
same or different, each represents a hydrogen atom, C.sub.1-8 alkyl group 
or a cycloalkyl group formed by connection of R.sub.1 and R.sub.2 ; and R, 
each of which may be the same or different, each represents a C.sub.1-8 
straight-chain or branched alkyl group or halogen atom. 
##STR5## 
wherein Y represents a hydrogen atom, --CH.sub.3 or --OH; and R.sub.3 
represents 
##STR6## 
in which m represents an integer of 0 to 3; n represents an integer of 1 
to 3; and Z represents a hydrogen atom, a halogen atom or --CH.sub.3. 
##STR7## 
wherein R.sub.4 represents a benzyl group, a halogen atom or a benzyl 
group substituted by a C.sub.1-8 straight-chain or branched alkyl group. 
##STR8## 
wherein R.sub.6 and R.sub.7, which may be the same or different, each 
represents a C.sub.1-8 alkyl group. 
##STR9## 
wherein R.sub.8 represents an alkylene group having 1 to 5 ether bonds. 
Specific examples of the compounds represented by the general formulas (IV) 
to (VIII) include 2,2-bis(4'-hydroxyphenyl)propane, 
2,2-bis(4'-hydroxyphenyl)pentane, 
2,2-bis(4'-hydroxy-3',5'-dichlorophenyl)propane, 
1-1-bis(4'-hydroxyphenyl)cyclohexane, 2,2-bis(4'-hydroxyphenyl)hexane, 
1,1-bis(4'hydroxyphenyl)propane, 1,1-bis(4'-hydroxyphenyl)butane, 
1,1-bis(4'-hydroxyphenyl)pentane, 1,1-bis(4'-hydroxyphenyl)hexane, 
1,1-bis(4'-hydroxyphenyl)heptane, 
1,1-bis(4'-hydroxyphenyl)-2-methylpentane, 
1,1-bis(4'-hydroxyphenyl)-2-ethyl-hexane, 
1,1-bis(4'-hydroxyphenyl)dodecane, 3,3-bis(4-hydroxyphenyl)pentane, 
1,2-bis(4'-hydroxyphenyl)ethane, 1,1-bis(4'-hydroxyphenyl)sulfide, 
1,1-bis(4'-hydroxyphenyl)sulfone, 1,1-bis(4'-hydroxyphenyl)ether, 
2,2-bis(4'-hydroxy-3',5'-dichlorophenyl)butane, 2,4-dihydroxyphenyl 
benzoate, 2,4-dihydroxy-4'-methylphenyl benzoate, 
2,4-dihydroxy-4'-chlorophenyl benzoate, 2,4-dihydroxy-6-methylphenyl 
benzoate, 2,4,6-trihydroxyphenyl benzoate, 
2,4-dihydroxy-6,4'-dimethylphenyl benzoate, 
2,4-dihydroxy-6-methyl-4'-chlorophenyl benzoate, 2,4-dihydroxy-benzyl 
benzoate, 2,4-dihydroxy-4'-methyl benzyl benzoate, 
2,4-dihydroxy-4'-chlorobenzyl benzoate, 2,4-dihydroxy-6-methyl benzyl 
benzoate, 2,4,6-trihydroxy benzyl benzoate, 2,4-dihydroxy-6,4'-dimethyl 
benzyl benzoate, 2,4-dihydroxy-6-methyl-4'-chloro benzyl benzoate, 
4-hydroxy-ethyl ester benzoate, 4-hydroxy propyl ester benzoate, 4-hydroxy 
isopropyl ester benzoate, 4-hydroxy benzyl ester benzoate, 
4-hydroxy-2-ethylhexyl ester benzoate, 4-hydroxy-4'-chloro benzyl ester 
benzoate, 4-hydroxy-4'-methyl benzyl ester benzoate, 4-hydroxy-4'-ethyl 
benzyl ester benzoate, 3-hydroxy-m-dimethyl phthalate, 3-hydroxy-m-diethyl 
phthalate, 3-hydroxy-m-methylethyl phthalate, 3-hydroxy-m-dibutyl 
phthalate, 3-hydroxy-o-dimethyl phthalate and 3-hydroxy-o-diethyl 
phthalate. 
Furthermore, examples of the above general formulae include the following 
compounds: 
##STR10## 
Preferred examples of electron acceptor compounds other than those 
represented by the general formulae (IV) to (VIII) include bis-hydroxy 
cumylbenzene or bis-hydroxy-.alpha.-methylbenzylbenzene such as 
1,4-bis-p-hydroxy cumyl benzene, 1,4-bis-m-hydroxy cumyl benzene, 
1,3-bis-p-hydroxy cumyl benzene, 1,3-bis-3-m-hydroxy cumyl benzene, 
1,4-bis-o-hydroxy cumyl benzene, 1,4-bis-p-hydroxy-.alpha.-methylbenzyl 
benzene and 1,3-bis-p-hydroxy-.alpha.-methylbenzyl benzene, salicylic acid 
derivatives such as 3,5-di-.alpha.-methylbenzyl salicyclic acid, 
3,5-ditertiarybutyl salicyclic acid, 3-.alpha.,.alpha.-dimethylbenzyl 
salicylic acid, and polyvalent metal salts (most preferably zinc or 
aluminum) thereof, and phenol such as p-phenylphenol, 3,5-diphenyl phenol, 
and cumyl phenol. However, the present invention is not limited to these 
compounds. 
The amount of the above electron acceptor compounds to be used is 
preferably about 50 to about 1,000% by weight, more preferably 100 to 500% 
by weight based on the weight of the electron donor dye precursor to be 
used. These electron acceptor compounds may be used singly or in 
combination. 
In the heat-sensitive material of the present invention, a heat-fusible 
material may be incorporated in the heat-sensitive coloring layer in order 
to improve its heat response. 
As suitable heat-fusible materials there may be used compounds of the 
general formulae (IX) to XIV): 
##STR11## 
wherein R.sub.1 to R.sub.4, R.sub.1 and R.sub.2 being the same or 
different, each represents a phenyl group, benzyl group, or lower alkyl-, 
halogen-, hydroxy-, or alkoxy-substituted compounds thereof; R.sub.5 and 
R.sub.6 each represents an alkyl group having 12 to 24 carbon atoms; and 
R.sub.7 represents a hydrogen atom or phenyl group. 
If the phenyl group or benzyl group represented by R.sub.1 to R.sub.4 in 
the general formulae (IX) to (XI) is substituted by a lower alkyl group, 
the lower alkyl group has 1 to 8, preferably 1 to 3 carbon atoms. If the 
phenyl group or benzyl group is substituted by a halogen atom, the 
substituent halogen atom is preferably chlorine atom or fluorine atom. 
##STR12## 
wherein R.sub.8 represents a divalent group, preferably represents an 
alkylene group, alkylene group having ether bonds, alkylene group having 
carbonyl groups, alkylene group having halogen atoms or alkylene group 
having unsaturated bonds, more preferably represents an alkylene group or 
alkylene group having ether bonds; and X, Y, Z, X', Y', and Z', which may 
be the same or different, each represents a hydrogen atom, alkyl group, 
lower alkoxy group, lower aralkyl group, halogen atom, alkyloxycarbonyl 
group, or aralkyloxycarbonyl group. 
The compounds of the general formulae (IX) to (XIV) preferably have a 
melting point of about 70.degree. C. to about 150.degree. C. More 
preferred melting point of these compounds is 80.degree. C. to 130.degree. 
C. 
Specific examples of these compounds include p-benzyloxy benzyl benzoate, 
.beta.-naphthylbenzyl ether, stearic acid amide, palmitic acid amide 
palmitate, N-phenyl stearic acid amide, N-stearyl urea, 
.beta.-phenylesternaphthoate, 1-hydroxy-2-phenylesternaphthoate, 
.beta.-naphthol(p-chlorobenzyl)ether, 
.beta.-naphthol(p-methylbenzyl)ether, .alpha.-naththyl benzyl ether, 
1,4-butanediol-p-methylphenyl ether, 1,4-propane diol-p-methylphenyl 
ether, 1,4-butane diol-p-isopropyl phenyl ether; 1,4-butane 
diol-p-t-octylphenyl ether, 2-phenoxy-1-p-tolyl-oxy-ethane, 
1-phenoxy-2-(4-ethylphenoxy)ethane, 1-phenoxy-2-(4-chlorophenoxy)ethane 
and 1,4-butane diolphenyl ether. 
The above mentioned heat-fusible materials may be used singly or in 
combination. In order to obtain a sufficient heat response, the 
heat-fusible materials are preferably used in an amount of at least about 
10 to 20% by weight based on the weight of the electron acceptor compound. 
A more preferred amount fo the heat-fusible materials to be used is 20 to 
150% by weight based upon the weight of the electron acceptor compound. 
In a two-component system heat-sensitive recording material comprising an 
electron donor dye precursor and an electron acceptor compound, the 
recorded images are generally subject to discoloration due to outer 
conditions such as moisture and heat. 
In the heat-sensitive recording material of the present invention, a 
discoloration inhibiting compound is preferably incorporated in the 
heat-sensitive coloring layer to inhibit such discoloration and render the 
image fast. 
As such a discoloration inhibitor there may be effectively used a phenol 
derivative, particularly a hindered phenol compound. Examples of suitable 
discoloration inhibitors include compounds of the general formulae (XV) to 
(XVIII): 
##STR13## 
wherein R.sub.1, each of which may be the same or diffrent, each 
represents a C.sub.3-8 branched alkyl group; R.sub.2, each of which may be 
the same or different, each represents a hydrogen atom or C.sub.3-8 
branched alkyl group; R.sub.3, each of which may be the same or different, 
each represents a hydrogen atom or C.sub.1-3 alkyl group; R.sub.4 
represents a hydrogen atom or C.sub.1-8 alkyl group; R.sub.5, R.sub.6 and 
R.sub.7, which may be the same or different, each represents a hydrogen 
atom or C.sub.1-3 alkyl group; and R.sub.8 represents a hydrogen atom or 
C.sub.1-8 alkyl group. 
##STR14## 
wherein R.sub.1 and R.sub.3, which may be the same or different, each 
represents a C.sub.3-8 branched alkyl group; R.sub.2 and R.sub.4, which 
may be the same or different, each represents a C.sub.1-8 alkyl group; X 
represents S, O, SO.sub.2, S.sub.2, 
##STR15## 
a cyclopentylene group or a cyclohexylene group; n represents an integer 
of 0 to 3; and R.sub.5 and R.sub.6, which may be the same or different, 
each represent a hydrogen atom or C.sub.1-8 alkyl group. 
##STR16## 
wherein R.sub.1 and R.sub.4, which may be the same or different, each 
represent a C.sub.3-8 branched alkyl group; R.sub.2, R.sub.3, R.sub.5 and 
R.sub.6, which may be the same or different, each represent a hydrogen 
atom or C.sub.1-8 alkyl group; Y represents S, O, SO.sub.2, S.sub.2, or 
##STR17## 
m represents an integer of 0 to 3; and R.sub.7 and R.sub.8, which may be 
the same of different, each represents a hydrogen atom or C.sub.1-8 alkyl 
group or R.sub.7 and R.sub.8 are bonded to each other to form a cyclo 
pentamethylene group. 
##STR18## 
wherein R.sub.1 and R.sub.2, which may be the same or different, each 
represents a C.sub.3-8 branched alkyl group; Z represents --NH-- or 
--O(CH.sub.2).sub.n -- in which n represents an integer of 1 to 5; and i 
represents an integer of 1 to 4, wherein when i=1 W represents a 
C.sub.1-18 alkyl group, when i=2 W represents S, O, or 
##STR19## 
in which R.sub.3 and R.sub.4, which may be the same or different, each 
represent a hydrogen atom or C.sub.1-8 alkyl group and j represents O or 
an integer of 1 to 8, when i=3 W represents .tbd.C--R.sub.5 represents a 
hydrogen atom or C.sub.1-8 alkyl group and when i=4 W represents 
##STR20## 
Typical examples of the phenol derivatives of the general formulae (XV) to 
(XVIII) are described hereinafter. 
(A) Examples of the phenol derivatives of the general formula (XV) include 
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 
1,1,3-tris(2-ethyl-4-hydroxy-5-tert-butylphenyl)butane, 
1,1,4-tris(3,5-di-tert-butyl-4-hydroxyphenyl)butane and 
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenol)propane. 
(B) Examples of the phenol derivatives of the general formula (XVI) include 
2,2'-methylene-bis(6-tert-butyl-4-methylphenol) and 
2,2'-methylene-bis(6-tert-butyl-4-ethylphenol). 
(C) Examples of the phenol derivatives of the general formula (XVII) 
include 4,4'-butylidene-bis(6-tert-butyl-3-methylphenol) and 
4,4'-thio-bis(3-methyl-6-tert-butylphenol). 
(D) Examples of the phenol derivatives of the general formula (XVIII) 
include: 
##STR21## 
The phenol compounds of the general formulae (XV) to (XVIII) are preferably 
used in an amount of about 1 to about 200% by weight based on the weight 
of the electron acceptor compound. A more preferred amount of the phenol 
compounds to be used is 5 to 50% by weight. 
In addition to the modified polyvinyl alcohol of the present invention or a 
mixture of the modified polyvinyl alcohol and a starch, a water-soluble 
high polymer may be incorporated in the recording layer of the 
heat-sensitive material of the present invention. 
As these binders there may be preferably used compounds which are soluble 
in water at a temperature of 25.degree. C. in a proportion of at least 5% 
by weight thereof. Specific examples of such compounds include methyl 
cellulose, carboxy methyl cellulose, hydroxy ethyl cellulose, starch, 
gelatin, gum arabic, casein, hydrolyzate of styrene-maleic anhydrous 
copolymer, hydrolyzate of ethylene-maleic anhydrous copolymer, hydrolyzate 
of isobutylene-maleic anhydrous copolymer, polyvinyl alcohol, 
carboxy-modified polyvinyl alcohol and polyacrylamide. 
A pigment, water-insoluble binder, metal soap, wax, surface active agent or 
the like may be optionally incorporated in the recording layer of the 
heat-sensitive recording material of the present invention. 
As such a pigment there may be used zinc oxide, calcium carbonate, barium 
sulfate, titanium oxide, lithopone, talc, agalmatolite, kaolin, aluminum 
hydroxide, silica, or amorphous silica. 
As such a water-insoluble binder there may be generally used a synthetic 
rubber latex or synthetic resin emulsion. Examples of such a latex or 
emulsion include styrene-butadiene rubber latex, acrylonitrile-butadiene 
rubber latex, methyl acrylate-butadiene rubber latex and vinyl acetate 
emulsion. 
As such a metal soap there may be used higher aliphatic acid metal salts. 
Examples of such metal soaps include emulsions of zinc stearate, calcium 
stearate, aluminum stearate, etc. 
Example of waxes which may be used include emulsions of paraffin wax, 
microcrystalline wax, carnauba wax, methylol stearo amide, polyethylene 
wax and polystyrene wax, etc. 
As such surface active agents there may be used sulfosuccinic acid alkali 
metal salts and fluorine-containing surface active agents. 
The present invention will be further illustrated in the following examples 
but should not be construed as being limited thereto. In the following 
examples all percentages, ratios, etc. are by weight, unless otherwise 
specified.