Heat-sensitive record material

This invention provides a heat-sensitive record material comprising a base sheet and a heat-sensitive record layer formed over the base sheet and containing a colorless or pale-colored basic dye and a color developing material capable of forming a color when contacted with the dye, the record material being characterized in that the heat-sensitive record layer contains as the color developing material at least one compound represented by the formula ##STR1## wherein R.sub.1 and R.sub.2 are each alkyl having 1 to 8 carbon atoms, a group ##STR2## or a group ##STR3## wherein R.sub.3 and R.sub.4 are each a hydrogen atom, chlorine atom, hydroxyl or alkoxy having 1 to 8 carbon atoms, the heat-sensitive record layer further containing at least one compound selected from the group consisting of 1,1-bis(4-hydroxyphenyl)cyclohexane and hindered phenol compounds.

This invention relates to heat-sensitive record materials, and more 
particularly to a heat-sensitive record material suited to high-speed 
recording and capable of giving colorfast record images. 
Heat-sensitive record materials are well known which are adapted to produce 
record images by thermally contacting a colorless or pale-colored electron 
donative chromogenic material (hereinafter referred to as a "basic dye") 
with an organic or inorganic color developing material. 
On the other hand, heat-sensitive recording systems for producing records 
on such heat-sensitive record materials employ a thermal recording head 
which comprises, for example, an arrangement of a multiplicity of minute 
heat-generating resistance members. For recording, pulsating voltage is 
applied to required resistance members in response to image signals while 
feeding the heat-sensitive record material by a stepping motor for every 
line. 
With remarkable progress in heat-sensitive recording systems in recent 
years, high-speed recording systems become available. For example, 
heat-sensitive facsimile systems produce a copy of A4 size within 20 
seconds, and heat-sensitive printers achieve a recording speed of at least 
120 characters/sec. Research is under way to attain still higher recording 
speeds. 
For use with such high-speed recording systems, heat-sensitive record 
materials must meet various requirements such as those given below. (a) 
Record materials must have high recording sensitivity. Especially with the 
increase of recording speed, there is a tendency to apply to 
heat-generating resistance members of the thermal head pulses having a 
smaller width and lower electric energy. Although it is possible to use a 
high voltage to compensate for the reduction in pulse width, the life of 
the thermal head will then be affected adversely. In the case of 
heat-sensitive record materials for high-speed recording, it is required 
that the record layer produce a color with a high density even when low 
electric power is supplied to the thermal head. (b) Additionally it is 
required that the record material is less likely to inadvertently undergo 
undesired color forming reaction at low temperatures (about 60.degree. to 
about 70.degree. C.). Otherwise, when the record material is used for 
high-speed recording, a resistance member heated, before fully cooling off 
after pulse application, will produce a tailing color dot. Further when 
heat accumulates in the thermal head in its entirety, the record layer 
will form a pale color (so-called "static image") over the surface 
thereof. When the record material is stored in summer for a long period of 
time before use, the record material must be free of undesired color 
formation. (c) It is important that the record image obtained be 
colorfast. Generally, record images formed with use of basic dyes are 
likely to fade or disappear owing to the influence of temperature and/or 
humidity. Apparently such reduction of the record density is undesirable 
and should be avoided to the greatest possible extent. (d) It is further 
required that the record layer of the heat-sensitive record material as 
produced have a high degree of whiteness in order to produce sharp vivid 
record images and to give the product a high commercial value. 
Heat-sensitive record materials heretofore used for recording at a 
relatively high speed include those having a record layer wherein stearic 
acid amide or like sensitizer is used in combination with a basic dye and 
with a phenolic compound such as 2,2-bis(4-hydroxyphenol)propane (i.e. 
bisphenol A). However, such heat-sensitive record materials have 
drawbacks; the recording sensitivity is still low, while the record images 
obtained are affected by temperature and/or humidity to exhibit a 
seriously reduced density. Moreover, stearic acid amide or like 
sensitizer, which is incorporated in a large amount, adheres to the 
thermal head as a residue and tends to produce discontinuous record 
images. 
Also proposed are heat-sensitive record materials which have a record layer 
incorporating a hindered phenol in combination with a basic dye and 
2,2-bis(4-hydroxyphenyl)propane or like phenolic compound, or 
4-hydroxybenzoic acid, an ester thereof or like aromatic carboxylic acid 
derivative (Unexamined Japanese Patent Publications No. 57990/1983 and No. 
87089/1983). These record materials are less susceptible to the reduction 
of record image density, but still remain to be improved in recording 
sensitivity and in initial whiteness, and are not always suited to 
high-speed recording. 
An object of the present invention is to provide a heat-sensitive record 
material which is outstanding in recording sensitivity, especially in 
sensitivity when a low electric power is being supplied to the thermal 
head of the record system. 
Another object of the invention is to provide a heat-sensitive record 
material for producing record images which are less susceptible to the 
density reduction due to the influence of temperature and/or humidity. 
Another object of the invention is to provide a heat-sensitive record 
material which is free of undesired color formation at low temperatures of 
about 60.degree. to about 70.degree. C. 
Still another object of the invention is to provide a heat-sensitive record 
material having a high degree of whiteness. 
These objects and other features of the invention will become apparent from 
the following description. 
The present invention provides a heat-sensitive record material comprising 
a base sheet and a heat-sensitive record layer formed over the base sheet 
and containing a colorless or pale-colored basic dye and a color 
developing material capable of forming a color when contacted with the 
dye, the record material being characterized in that the heat-sensitive 
record layer contains as the color developing material at least one 
compound represented by the formula 
##STR4## 
wherein R.sub.1 and R.sub.2 are each alkyl having 1 to 8 carbon atoms, a 
group 
##STR5## 
or a group 
##STR6## 
wherein R.sub.3 and R.sub.4 are each a hydrogen atom, chlorine atom, 
hydroxyl or alkoxy having 1 to 8 carbon atoms, the heat-sensitive record 
layer further containing at least one compound selected from the group 
consisting of 1,1-bis(4-hydroxy)cyclohexane and hindered phenol compounds. 
I conducted extensive research on color developing materials in order to 
obtain heat-sensitive record materials suited to high-speed heat-sensitive 
recording systems and found that when the compound of the formula (I) was 
used as a color developing material for preparing a heat-sensitive record 
material, the record material had high recording sensitivity and high 
amenability to high-speed recording. However, when only the compound of 
the formula (I) was used which have so-called thermochromic properties, 
the density of the record image obtained was greatly reduced when the 
record image was affected by temperature and/or humidity. Thus, this 
problem remained to be overcome before using the compound of the formula 
(I) as a color developing material for heat-sensitive record materials. 
Accordingly I have further conducted continued research to develop a 
heat-sensitive record material incorporating the compound of the formula 
(I) and a colorless or pale-colored basic dye, having high recording 
sensitivity and giving record images without the likelihood of the density 
decreasing. Consequently I have found that the above object can be 
fulfilled when the compound of the formula (I) is used conjointly with at 
least one 1,1-bis(4-hydroxyphenyl)cyclohexane and hindered phenol 
compounds. The present invention has been accomplished based on this novel 
finding. 
The heat-sensitive record material of the present invention has high 
recording sensitivity, giving record images of high density even when low 
power is applied to heat-generating resistance members of the thermal 
head. Moreover, the record images obtained are almost unlikely to have 
their identity reduced by temperature and/or humidity. The present record 
material further has the advantage of being high in the degree of 
whiteness and less susceptible to undesirable color formation at low 
temperatures. Additionally, the present record material, unlike 
conventional heat-sensitive record materials, does not require use of any 
sensitizer and is therefore usable without entailing adhesion of residue 
to the thermal head and the resulting problem of discontinuous record 
images. 
Although the reason why the heat-sensitive record material of the invention 
has such outstanding characteristics, especially high recording 
sensitivity, has yet to be clarified, the remarkable characteristics 
appear attributable to the fact that the compound of the formula (I) has 
good crystallinity and a low melting point and exhibits sharp melting 
characteristics within the heat-sensitive record layer which contains the 
compound, a basic dye and a hindered phenol compound or like component. 
Of the compounds represented by the formula (I), preferable are those 
wherein R.sub.1 and R.sub.2 are each alkyl having 1 to 4 carbon atoms, 
phenyl or benzyl. Typical examples of compounds represented by the formula 
(I) are as follows. 
______________________________________ 
Dimethyl 4-hydroxyphthalate 
m.p. 110.degree. C. 
Diethyl 4-hydroxyphthalate 
m.p. 65.degree. C. 
Di-isopropyl 4-hydroxyphthalate 
m.p. 103-105.degree. C. 
Dibenzyl 4-hydroxyphthalate 
m.p. 87-90.degree. C. 
Dimethyl 4-hydroxyisophthalate 
m.p. 98.degree. C. 
Dimethyl 2-hydroxyisophthalate 
m.p. 72.degree. C. 
Diethyl 2-hydroxyisophthalate 
m.p. 112.degree. C. 
Diphenyl 2-hydroxyisophthalate 
m.p. 99.degree. C. 
Diethyl 5-hydroxyisophthalate 
m.p. 103.degree. C. 
Dimethyl hydroxyterephthalate 
m.p. 94.degree. C. 
______________________________________ 
At least two of these compounds are of course usable in combination. 
Of the hindered phenol compounds useful for the present invention, 
preferable are phenols having an alkyl substituent at least at one of the 
2- and 6-positions (i.e., two ortho-positions relative to the hydroxyl) 
and derivatives thereof. Of these, more preferable are phenols substituted 
with tert-butyl at least at one of the 2-position and 6-position, and 
derivatives thereof. Also preferable are hindered phenol compounds having 
a plurality of phenol groups, especially two or three phenol groups, in 
the molecule. Examples of such compounds are given below. 
1,1,3-Tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane 
4,4'-Thiobis(3-methyl-6-tert-butylphenol) 
4,4'-Thiobis(2-methyl-6-tert-butylphenol) 
2,2'-Thiobis(4-methyl-6-tert-butylphenol) 
2,2'-Methylenebis(4-methyl-6-tert-butylphenol) 
2,2'-Methylenebis(4-ethyl-6-tert-butylphenol) 
4,4'-Butylidenebis(3-methyl-6-tert-butylphenol) 
4,4'-Methylenebis(2,6-di-tert-butylphenol) 
The thermochromic properties of the compound of the formula (I) are 
eliminated when the compound of the formula (I) is used conjointly with 
1,1-bis(4-hydroxyphenol)cyclohexane or the hindered phenol compound. 
Although the reason therefore has not been clarified, the compound of the 
formula (I), melted and reacted for color formation by heating, will be 
prevented from recrystallization by the conjoint use of such compounds 
despite a reduction of temperature to produce the above effect. 
Of the foregoing 1,1'-bis(4-hydroxyphenol)cyclohexane and the hindered 
phenol compounds, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenol)butane 
is most preferable, since the use of this compound gives a heat-sensitive 
record material which is even less susceptible to the reduction of record 
image density, and which is even more excellent due to its whiteness and 
absence of undesired color formation at low temperatures. 
Examples of colorless or pale-colored basic dyes which can be used to form 
the record layer for the present heat-sensitive record materials include 
those heretofore known as given below: 
Triarylmethane-based dyes, e.g., 
3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 
3,3-bis(p-dimethylaminophenyl)phthalide, 
3-(p-dimethylaminophenyl)-3-(1,2-dimethylindole-3-yl)phthalide, 
3-(p-dimethylaminophenyl)-3-(2-methylindole-3-yl)phthalide, 
3,3-bis(1,2-dimethylindole-3-yl)-5-dimethylaminophthalide, 
3,3-bis(1,2-dimethylindole-3-yl)-6-dimethylaminophthalide, 
3,3-bis(9-ethylcarbazole-3-yl)-6-dimethylaminophthalide, 
3,3-bis(2-phenylindole-3-yl)-6-dimethylaminophthalide, 
3-p-dimethylaminophenyl-3-(1-methylpyrrole-3-yl)-6-dimethylaminophthalide, 
etc. 
Diphenylmethane-based dyes, e.g., 4,4'-bis-di-methylaminobenzhydryl benzyl 
ether, N-halophenyl-leucoauramine, N-2,4,5-trichlorophenyl-leucoauramine, 
etc. 
Thiazine-based dyes, e.g., benzoyl-leucomethyleneblue, 
p-nitrobenzoyl-leucomethyleneblue, etc. 
Spiro-based dyes, e.g., 3-methyl-spiro-dinaphthopyran, 
3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 
3-benzyl-spiro-dinaphthopyran, 
3-methyl-naphtho-(6'-methoxybenzo)spiropyran, 3-propyl-spiro-dibenzopyran, 
etc. 
Lactam-based dyes, e.g., rhodamine-B-anilinolactam, 
rhodamine-(p-nitroanilino)lactam, rhodamine(o-chloroanilino)lactam, etc. 
Fluoran-based dyes, e.g., 3-dimethylamino-7-methoxyfluoran, 
3-diethylamino-6-methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 
3-diethylamino-7-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 
3-diethylamino-6,7-dimethylfluoran, 
3-(N-ethyl-p-toluidino)-7-methylfluoran, 
3-diethylamino-7-N-acetyl-N-methylaminofluoran, 
3-diethylamino-7-N-methylaminofluoran, 
3-diethylamino-7-dibenzylaminofluoran, 
3-diethylamino-7-N-methyl-N-benzylaminofluoran, 
3-diethylamino-7-N-chloroethyl-N-methylaminofluoran, 
3-diethylamino-7-N-diethylaminofluoran, 
3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluoran, 
3-diethylamino-6-methyl-7-phenylaminofluoran, 
3-dibutylamino-6-methyl-7-phenylaminofluoran, 
3-diethylamino-7-(2-carbomethoxyphenylamino)fluoran, 
3-(N-methyl-N-n-amyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-n-amyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-methyl-N-n-hexyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-n-hexyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-cyclohexy-N-methylamino)-6-methyl-7-phenylaminofluoran, 
3-pyrrolidino-6-methyl-7-phenylaminofluoran, 
3-piperidino-6-methyl-7-phenylaminofluoran, 
3-diethylamino-6-methyl-7-xylidinofluoran, 
3-diethylamino-7-(o-chlorophenylamino)fluoran, 
3-dibutylamino-7-(o-chlorophenylamino)fluoran, 
3-pyrrolidino-6-methyl-7-p-butylphenylaminofluoran, etc. 
The basic dyes in the present invention are not limited to those 
exemplified above, and at least two of these dyes can be used in 
admixture. 
Of these dyes, fluoran-based dyes represented by the formula 
##STR7## 
wherein R.sub.5 is alkyl having 1 to 4 carbon atoms and R.sub.6 is alkyl 
having 1 to 6 carbon atoms or cyclohexyl are very useful in the production 
of record materials markedly suitable for high-speed recording because 
these dyes are outstanding in compatibility with the compounds of the 
formula (I) used in the present invention. Of the fluoran-based dyes of 
the formula (II), those disclosed in Examined Japanese Patent Publication 
No. 52759/1981, e.g., 
3-(N-methyl-N-n-amyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-n-amyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-methyl-N-n-hexyl)amino-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-n-hexyl)amino-6-methyl-7-phenylaminofluoran, etc. are 
excellent in giving both whiteness and recording sensitivity and can 
exhibit even more improved characteristics when used conjointly with the 
compound of the formula (I). Accordingly it is particularly preferred to 
use the dyes in the present invention. 
The compound of the formula (I) to be incorporated into the record layer in 
the present invention is used in an amount of about 1 to about 50 parts by 
weight, preferably about 2 to about 10 parts by weight, per part by weight 
of the basic dye. 
At least one of the 1,1-bis(4-hydroxyphenyl)cyclohexane and hindered phenol 
compounds is used in an amount of usually about 1 to about 1000 parts by 
weight, preferably about 10 to about 300 parts by weight, per 100 parts by 
weight of the compound of the formula (I). 
These materials are formulated into a coating composition for 
heat-sensitive record layer generally with use of water as a dispersion 
medium and a stirring or pulverizing device, such as a ball mill, attritor 
or sand mill, by dispersing these materials at the same time or 
separately. Usually the coating composition has incorporated therein a 
binder, such as starches, hydroxyethyl cellulose, methyl cellulose, 
carboxymethyl cellulose, gelation, casein, gum arabic, polyvinyl alcohol, 
styrene-maleic anhydride copolymer salt, styrene-acrylic acid copolymer 
salt, styrene-butadiene copolymer emulsion or the like. The binder is used 
in an amount of about 5 to about 40% by weight, preferably about 10 to 
about 30% by weight, based on the total solids content of the composition. 
Various auxiliary agents can be further admixed with the coating 
composition. Examples of useful auxiliary agents are dispersants such as 
sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium 
lauryl sulfate and fatty acid metallic salts; ultraviolet absorbers of the 
benzophenone, triazole or like type; defoaming agents, fluorescent dyes; 
coloring dyes, etc. A dispersion or emulsion of stearic acid, 
polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, 
ester wax or the like can be incorporated into the coating composition in 
order to prevent the heat-sensitive record material from sticking to the 
recording machine or thermal recording head on its contact therewith. An 
inorganic pigment such as kaolin, clay, talc, calcium carbonate, calcined 
clay, titanium oxide, diatomaceous earth, fine granular anhydrous silica, 
activated clay or the like can be added to the coating composition in 
order to eliminate or reduce the tendency of the residue to be piled on 
the thermal recording head. When required, an agent for improving the 
recording sensitivity can be admixed with the coating composition, 
although usually such agent is not incorporated therein. Examples of such 
agent useful in the present invention are stearic acid amide, stearic acid 
methylenebisamide, oleic acid amide, palmitic acid amide, sperm oleic acid 
amide, coconut fatty acid amide, etc. 
A phenol compound or like color developing material which is conventionally 
used in the art can also be used in the invention so far as its use does 
not adversely affect the advantages of the invention. 
According to the present invention, useful base sheets include paper, 
plastic film, synthetic fiber sheet and the like among which paper is most 
preferred in terms of the costs, ease for coating, etc. The amount of the 
coating composition which is applied to the base sheet to form a record 
layer thereon is not particularly limited, but is generally about 2 to 
about 12 g/m.sup.2, preferably about 3 to about 10 g/m.sup.2, based on the 
dry weight. An overcoat can be applied over the record layer to protect 
the record layer. Further an undercoat can be formed, of course, between 
the base sheet and the record layer. In practicing the present invention, 
it is possible to use various techniques heretofore known in the field of 
manufacture of heat-sensitive record materials. 
The heat-sensitive record materials thus obtained according to the present 
invention are suitable for high-speed recording, have high whiteness and 
have improved properties including those of preventing the image from 
fading away and involving a less amount of residue piled on the thermal 
recording head.

The present invention will be described below in more detail with reference 
to the following Examples to which the present invention, of course, is 
not limited. In the Examples, the parts and the percentages are all by 
weight unless otherwise specified. 
EXAMPLE 1 
(1) Preparation of mixture A 
3-(N-Cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran: 10 parts 
Methyl cellulose, 5% aqueous solution: 5 parts 
Water: 40 parts 
The above mixture was pulverized by a sand mill to a mean particle size of 
3 .mu.m. 
(2) Preparation of mixture B 
Dimethyl 4-hydroxyphthalate: 20 parts 
Methyl cellulose, 5% aqueous solution: 5 parts 
Water: 55 parts 
The above mixture was pulverized by a sand mill to a mean particle size of 
3 .mu.m. 
(3) Preparation of mixture C 
1,1,3-Tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane: 20 parts 
Methyl cellulose, 5% aqueous solution: 5 parts 
Water: 55 parts 
The above mixture was pulverized by a sand mill to a mean particle size of 
3 .mu.m. 
(4) Formation of record layer 
Fifty-five parts of the mixture A, 80 parts of the mixture B, 80 parts of 
the mixture C, 15 parts of fine granular anhydrous silica (oil absorption 
180 ml/100 g), 50 parts of a 20% aqueous solution of oxidized starch and 
10 parts of water were mixed together and agitated to obtain a coating 
composition for heat-sensitive record layer. The composition was applied 
to non-coated paper weighing 50 g/m.sup.2 in an amount of 7 g/m.sup.2 
based on dry weight, and dried to obtain a heat-sensitive record material. 
EXAMPLES 2 TO 8 
Seven kinds of heat-sensitive record materials were prepared in the same 
manner as in Example 1 with the exception of using the following color 
developing materials in place of the dimethyl 4-hydroxyphthalate employed 
in preparing the mixture B. 
______________________________________ 
Example Color Developing Material 
______________________________________ 
2 Di-isopropyl 4-hydroxyphthalate 
3 Dibenzyl 4-hydroxyphthalate 
4 Diethyl 2-hydroxyisophthalate 
5 Diphenyl 2-hydroxyisophthalate 
6 Dimethyl 4-hydroxyisophthalate 
7 Diethyl 5-hydroxyisophthalate 
8 Dimethyl hydroxyterephthalate 
______________________________________ 
EXAMPLES 9 TO 11 
Three kinds of heat-sensitive record materials were prepared in the same 
manner as in Example 1 with the exception of using the following hindered 
phenol compounds in place of the 
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane employed in 
preparing the mixture C. 
______________________________________ 
Example Hindered Phenol Compound 
______________________________________ 
9 4,4'-Butylidenebis(3-methyl-6-tert-butylphenol) 
10 2,2'-Methylenebis(4-methyl-6-tert-butylphenol) 
11 4,4'-Thiobis(3-methyl-6-tert-butylphenol) 
______________________________________ 
EXAMPLE 12 
A heat-sensitive record material was prepared in the same manner as in 
Example 1 with the exception of using 
3-(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluoran in place of the 
3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran in preparing 
the mixture A. 
EXAMPLE 13 
A heat-sensitive record material was prepared in the same manner as in 
Example 1 with the exception of using 
3-(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluoran in place of the 
3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran in preparing 
the mixture A, and 1,1-bis(4-hydroxyphenyl)cyclohexane in place of the 
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane employed in 
preparing the mixture C. 
EXAMPLE 14 
A heat-sensitive record material was prepared in the same manner as in 
Example 1 with the exception of using 10 parts of each of 
3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran and 
3-(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluoran in place of 20 
parts of the 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran 
employed in preparing the mixture A. 
COMISON EXAMPLE 1 
(1) Preparation of mixture A 
3-(N-Cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran: 10 parts 
Methyl cellulose, 5% aqueous solution: 5 parts 
Water: 40 parts 
The above mixture was pulverized by a sand mill to a mean particle size of 
3 .mu.m. 
(2) Preparation of mixture B 
Dimethyl 4-hydroxyphthalate: 20 parts 
Methyl cellulose, 5% aqueous solution: 5 parts 
Water: 55 parts 
The above mixture was pulverized by a sand mill to a mean particle size of 
3 .mu.m. 
(3) Formation of record layer 
Fifty-five parts of the mixture A, 80 parts of the mixture B, 15 parts of 
fine granular anhydrous silica (oil absorption 180 ml/100 g), 50 parts of 
a 20% aqueous solution of oxidized starch and 20 parts of water were mixed 
together and agitated to obtain a coating composition. The composition was 
applied to non-coated paper weighing 50 g/m.sup.2 in an amount of 7 
g/m.sup.2 based on dry weight, and dried to obtain a heat-sensitive record 
material. 
COMISON EXAMPLE 2 
A heat-sensitive record material was prepared in the same manner as in 
Comparison Example 1 with the exception of using dimethyl 
4-hydroxyisophthalate in place of the dimethyl 4-hydroxyphthalate employed 
in preparing the mixture B. 
COMISON EXAMPLE 3 
A heat-sensitive record material was prepared in the same manner as in 
Example 1 with the exception of using benzyl 4-hydroxybenzoate in place of 
the dimethyl 4-hydroxyphthalate employed in the preparing the mixture B. 
COMISON EXAMPLE 4 
A heat-sensitive record material was produced in the same manner as in 
Example 1 with the exception of using 
3-(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluoran in place of the 
3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran employed in 
preparing the mixture A, benzyl 4-hydroxybenzoate in place of the dimethyl 
4-hydroxyphthalate employed in preparing the mixture B, and 
1,1-bis(4-hydroxyphenyl)cyclohexane in place of the 
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane employed in 
preparing the mixture C. 
COMISON EXAMPLE 5 
A heat-sensitive record material was produced in the same manner as in 
Example 1 with the exception of using 2,2-bis(4-hydroxyphenyl)propane in 
place of the dimethyl 4-hydroxyphthalate employed in preparing the mixture 
B and stearic acid amide in place of the 
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane employed in 
preparing the mixture C. 
The 19 kinds of heat-sensitive record materials thus obtained were checked 
for properties as follows. 
(i) Whiteness 
The whiteness of the record layer of the heat-sensitive record materials 
was determined by a Hunter multipurpose reflectometer according to JIS 
P8123 with the results as shown in Table 1 below. 
(ii) Image density at low power 
Each of the heat-sensitive record materials was caused to form images 
thereon with use of a heat-sensitive facsimile tester equipped with a 
thermal recording head (KRT-256-8 IIIA, product of Kyocera Corporation, 
Japan) operated at a low electric power of 0.5 W/dot, and the image 
density of each record material was measured by a Macbeth reflection 
densitometer (Model RD-100R, product of Macbeth Corp., U.S.A. with use of 
amber filter). Table 1 below shows the results. 
(iii) Image density (D.sub.1) 
Each of the heat-sensitive record materials was caused to form images 
thereon with use of a heat-sensitive facsimile (model HIFAX-700, product 
of Hitachi, Ltd., Japan) and the resulting image density (D.sub.1) was 
determined by the same type of a Macbeth reflection densitometer as used 
above in (ii) with the results as shown in Table 1 below. 
(iv) Image density (D.sub.2) 
The record materials with the images formed in (iii) were left to stand in 
an atmosphere maintained at 40.degree. C. and 90% RH for 24 hours, and 
then the image density (D.sub.2) was determined again by the same type of 
Macbeth reflection densitometer. Image density retentivity (%) which is 
given by (D.sub.2 /D.sub.1).times.100 was calculated and shown in Table 1 
below. 
TABLE 1 
______________________________________ 
Image Image density (D.sub.2) 
Image 
White- density Image (after temperature 
density 
ness (low density humidity resistance 
retentiv- 
(%) power) (D.sub.1) 
test) ity (%) 
______________________________________ 
Ex. 
1 83 0.94 1.03 1.01 98 
2 83 0.95 1.05 1.01 96 
3 80 0.97 1.09 1.00 92 
4 83 0.92 1.00 0.98 98 
5 82 0.95 1.03 0.97 94 
6 81 0.96 1.06 0.98 93 
7 82 0.95 1.04 1.01 97 
8 80 0.96 1.07 1.02 95 
9 83 0.94 1.03 0.77 75 
10 82 0.96 1.04 0.75 72 
11 80 0.95 1.04 0.87 84 
12 85 0.98 1.11 1.08 97 
13 79 0.96 1.05 0.96 91 
14 83 0.99 1.09 1.06 97 
Comp. 
Ex. 
1 83 0.85 0.93 0.28 30 
2 81 0.86 0.95 0.24 25 
3 76 0.72 0.88 0.83 94 
4 74 0.75 0.91 0.85 93 
5 73 0.49 0.75 0.38 51 
______________________________________ 
In Table 1, the values of whiteness indicate that the greater the value, 
the whiter the record layer, and those of image density show that the 
greater the value, the higher the image density. 
Table 1 reveals that the heat-sensitive record materials of the present 
invention have a high whiteness and an excellent recording sensitivity 
particularly even when recorded at a low electric power and involve little 
or no reduction in the image density of the color formed thereon.