Heat-sensitive recording material

Disclosed is a heat-sensitive recording material comprising (A) a support and (B) a heat-sensitive recording layer formed on the support and containing a colorless or pale-colored basic dye and a color developing material which develops a color on contact with the dye, the recording material being characterized in that the color developing material comprises at least one member selected from the group consisting of o-naphthoic acid and polyvalent metal salts thereof.

The present invention relates to a heat-sensitive recording material and 
more particularly to a heat-sensitive recording material which is 
excellent particularly in color-forming ability, storage stability and 
stability of record image. 
Heat-sensitive recording materials are well known which make use of the 
color forming reaction of a colorless or pale-colored basic dye with a 
color developing material such that the two materials are brought into 
contact with each other by heating to produce a color image. 
With the recent remarkable development of heat-sensitive recording systems, 
the heat-sensitive recording materials find various uses in various forms. 
They are not only used as recording media for facsimile or thermal printer 
but also increasingly introduced into new uses such as POS (point of 
sales) labels. 
However, heat-sensitive recording materials generally have drawbacks of 
being poor in storage stability and in resistance to various chemicals. 
Thus, when the heat-sensitive recording materials are stored under a high 
temperature or high humidity condition or are brought into contact with 
solvent, plasticizers or other chemicals, fogging (i.e., undesired color 
formation in the background white portion of the recording material) would 
be caused or the record images would be discolored or reduced in color 
density. For example, undesired color formation takes place in the white 
portion of the heat-sensitive recording layer or the record image becomes 
discolored or reduced in color density when the heat-sensitive recording 
materials are contacted with an ink such as one used for water-based ink 
pens, oil-based ink pens or fluorescent ink pens, cinnabar seal-ink, 
adhesives, pastes, diazo developers and other writing materials or office 
instruments; with cosmetics such as hand cream, hair tonics or milky 
lotions; or with polyvinyl chloride film or like wrapping materials 
containing a plasticizer. 
For this reason, it is strongly desired to develop a heat-sensitive 
recording material which is excellent in storage stability and resistance 
to chemicals, especially in the stability of the record image and in the 
effect of preventing fogging. 
Under the circumstances, in an attempt to alleviate the above problems of 
the heat-sensitive recording materials which make use of the color forming 
reaction of a basic dye and a color developing material, we have conducted 
extensive research especially on the color developing materials. As a 
result, we have found that a heat-sensitive recording material which is 
excellent not only in the color forming ability and storage stability but 
also in the stability of the record image can be obtained when at least 
one member selected from the group consisting of .alpha.-naphthoic acid 
and polyvalent metal salts thereof is(are) used as the color developing 
material. We have also found that when a specific class of basic dye is 
used in combination with .alpha.-naphthoic acid and/or a polyvalent metal 
salt thereof, the resulting heat-sensitive recording material is more 
excellent in the above properties. The present invention has been 
accomplished based on these findings. 
The present invention provides a heat-sensitive recording material 
comprising (a) a support and (b) a heat-sensitive recording layer formed 
on the support and containing a colorless or pale-colored basic dye and a 
color developing material which develops a color on contact with the dye, 
the recording material being characterized in that the color developing 
material comprises at least one member selected from the group consisting 
of .alpha.-naphthoic acid and polyvalent metal salts thereof. 
The heat-sensitive recording material of the invention is very advantageous 
from the view point of long-term preservation of records because, due to 
the use of .alpha.-naphthoic acid and/or a polyvalent metal salt thereof, 
the color density of the record image is sufficiently high and the record 
image formed is extremely stable such that the record image would not 
become substantially discolored or reduced in color density even when the 
recording material is stored in an atmosphere of high temperature or high 
humidity and that the record image is highly resistant to plasticizers and 
various solvents. 
Examples of metals constituting the polyvalent metal salts of 
.alpha.-naphthoic acid are di-valent, tri-valent and tetra-valent metals 
such as zinc, calcium, magnesium, aluminum, tin, iron and the like, among 
which zinc is particularly preferred. 
There is no specific restriction on the amount of at least one member 
selected from the group consisting of .alpha.-naphthoic acid and 
polyvalent metal salts thereof. However, it is usually preferred that said 
amount be adjusted to about 50 to about 700 parts by weight, preferably 
about 100 to about 500 parts by weight, per 100 parts by weight of the 
basic dye. 
While color forming ability and storage stability of the heat-sensitive 
recording material and the stability of the record image are improved by 
using the above .alpha.-naphthoic acid and/or polyvalent metal salts 
thereof as a color developing material, these properties can be further 
improved by further incorporating a polyvalent metal compound into the 
heat-sensitive recording layer. Examples of such polyvalent metal 
compounds are oxides, hydroxides, aluminates, sulfides, halides, 
carbonates, phosphates, silicates, sulfates or nitrates of di-valent, 
tri-valent and tetra-valent metals such as zinc, magnesium, barium, 
calcium, aluminum, tin, titanium, nickel, cobalt, manganese or iron, or a 
mixture of these compounds. Among these, zinc compound is preferred. 
Typical of such polyvalent metal compounds are zinc oxide, zinc hydroxide, 
zinc aluminate, zinc sulfide, zinc carbonate, zinc phosphate, zinc 
silicate, aluminum oxide, magnesium oxide, titanium oxide, aluminum 
hydroxide, aluminum silicate, aluminum phosphate, magnesium aluminate, 
magnesium hydroxide, magnesium carbonate, magnesium phosphate, and the 
like. 
The polyvalent metal compounds can be used singly or in admixture. 
Among the above polyvalent metal compounds, zinc oxide is particularly 
preferred. 
There is no specific restriction on the amount of the polyvalent metal 
compound to be used. However, it is usually preferable to use the 
polyvalent metal compound in an amount of about 1 to about 500 parts by 
weight, preferably about 5 to about 300 parts by weight, per 100 parts by 
weight of at least one member selected from the group consisting of 
.alpha.-naphthoic acid and polyvalent metal salts thereof. 
While the heat-sensitive recording material of the invention is essentially 
characterized by using .alpha.-naphthoic acid and/or a polyvalent metal 
salt thereof, a variety of known color developing materials can be used in 
combination with .alpha.-naphthoic acid and/or a polyvalent metal salt 
thereof so far as they do not impair the contemplated effect of the 
invention. Examples of such additional color developing materials are as 
follows: 
aromatic carboxylic acids such as benzoic acid, 4-tert-butylbenzoic acid, 
4-chlorobenzoic acid, 4-nitrobenzoic acid, phthalic acid, gallic acid, 
salicylic acid, 3-isopropylsalicylic acid, 3-phenylsalicylic acid, 
3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 
3-methyl-5-benzylsalicylic acid, 
3-phenyl-5-(.alpha.,.alpha.-dimethylbenzyl)-salicylic acid, 
3,5-di(.alpha.-methylbenzyl)salicylic acid or 
2-hydroxy-1-benzyl-3-naphthoic acid; 
phenolic compounds such as 4,4'-isopropylidenediphenol (Bisphenol A), 
4,4'-isopropylidenebis(2-chlorophenol), 
4,4'-isopropylidenebis(2,6-dichlorophenol), 
4,4'-isopropylidenebis(2,6-dibromophenol), 
4,4'-isopropylidenebis(2-methylphenol), 
4,4'-isopropylidenebis(2,6-dimethylphenol), 
4,4'-isopropylidenebis(2-tert-butylphenol), 4,4'-sec-butylidenediphenol, 
2,2'-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-cyclohexylidenebisphenol, 
4,4'-cyclohexylidenebis(2-methylphenol), 4-tert-butylphenol, 4-'1 
phenylphenol, 4-hydroxydiphenoxide, .alpha.-naphthol, .beta.-naphthol, 
methyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, 
2,2'-thiobis(4,6-dichlorophenol), 4-tert-octylcatechol, 
2,2'-methylenebis(4-chlorophenol), 2,2' -methylenebis(4-chlorophenol), 
2,2' -methylenebis(4-methyl-6-tert-butylphenol), 2,2'-dihydroxydiphenyl, 
methyl bis(4-hydroxyphenyl)acetate, ethyl bis(4-hydroxyphenyl)acetate, 
butyl bis(4-hydroxyphenyl)acetate, benzyl bis(4-hydroxyphenyl) acetate, 
4,4'-(p-phenylenediisopropylidene)diphenol, 
4,4'-(m-phenylenediisopropylidene)diphenol, 4-hydroxydiphenylsulfone, 
4,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, 
2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-methyl-diphenylsulfone, 
4-4-hydroxy-4'-isopropoxydiphenylsulfone, 
4-hydroxy-3',4'-tetramethylenediphenylsulfone, 
3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, bis(4-hydroxyphenyl)acetic 
acid 2-phenoxyethyl ester, 
p-hydroxy-N-(2-phenoxyethyl)-benzenesulfonamide, 4-hydroxyphthalic acid 
dimethyl ester, 1,5-bis(4-hydroxyphenylthio)-3-oxa-pentane, 
1,7-bis(4-hydroxyphenylthio)-3,5-dioxa-heptane, 
1,8-bis(4-hydroxyphenylthio)-3,6-dioxa-octane, 
(4-hydroxyphenylthio)-acetic acid 2-(4-hydroxyphenylthio)ethyl ester and 
the like; 
phenolic resins such as p-phenylphenol-formalin resin, 
p-butylphenol-acetylene resin, and the like; 
salts of the above-exemplified aromatic carboxylic acids, phenolic 
compounds or phenolic resins with polyvalent metals such as zinc, 
magnesium, aluminum, calcium, titanium, manganese, tin, nickel and the 
like; and 
metal complexes such as antipyrine complex of zinc thiocyanate, etc. 
When used, the above additional color developing material is used in amount 
of 200 parts by weight or less, per 100 parts by weight of at least one 
member selected from the group consisting of .alpha.-naphthoic acid and 
polyvalent metal salts thereof. 
Colorless or pale-colored basic dyes to be used in combination with the 
specific color developing material in the heat-sensitive recording 
materials of the present invention include those conventionally known in 
the art. Examples of such basic dyes are triarylmethane-based dyes such as 
3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 
3,3-bis(p-dimethylaminophenyl)phthalide, 
3-(4-dimethylaminophenyl)-3-(4-diethylamino-2-methylphenyl)-6-(dimethylami 
no)phthalide, 
3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide, 3-(p-dimeth 
ylaminophenyl)-3-(2-methylindol-3-yl)phthalide, 
3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 
3,3-bis(1,2-dimethylindol-3-yl)-6-dimethylaminophthalide, 
3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide, 
3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 
3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide 
and the like; diphenylmethane-based dyes such as 
4,4'-bis-dimethylaminobenzhydrylbenzylether, N-halophenyl-leucoauramine, 
N-2,4,5-trichlorophenyl-leucoauramine and the like; divinylphthalide-based 
dyes such as 
3,3-bis[1,1-bis(4-pyrrolidinophenyl)ethylen-2-yl]-4,5,6,7-tetrabromophthal 
ide, 
3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylen-2-yl]-4,5,6,7 
-tetrachlorophthalide, 
3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylen-2-yl]-4,5,6,7-t 
etrachlorophthalide and the like; thiazine-based dyes such as 
benzoyl-leucomethylene blue, p-nitrobenzoyl-leucomethylene blue and the 
like; spiro-based dyes such as 3-methyl-spiro-dinaphthopyrane, 
3-ethyl-spiro-dinaphthopyrane, 3-phenyl-spiro-dinaphthopyrane, 
3-benzyl-spiro-dinaphthopyrane, 
3-methyl-naphtho-(6'-methoxy-benzo)spiropyrane, 
3-propyl-spiro-dibenzopyrane and the like; lactam-based dyes such as 
rhodamine-B-anilinolactam, rhodamine(p-nitroanilino)lactam, 
rhodamine(o-chloroanilino)lactam and the like; fluorene-based dyes such as 
3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, 
3-diethylamino-6-(N-allyl-N-methylamino)fluorene-9-spiro-3'-(6'-dimethylam 
ino)phthalide, 
3,6-bis(dimethylamino)-spiro[fluorene-9,6'-6'H-chromeno(4,3-b)indole], 
3,6-bis(dimethylamino)-3'-methyl-spiro[fluorene-9,6'-6'H-chromeno(4,3-b)in 
dole], 
3,6-bis(diethylamino)-3'-methyl-spiro[fluorene-9,6'-6'H-chromeno(4,3-b)ind 
ole]and the like; fluoran-based dyes such as 
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-methylamino)fluoran, 
3-diethylamino-7-N-methylaminofluoran, 3-diethylamino-7 
-dibenzylaminofluoran, 3-diethylamino-7-(N-methyl-N-benzylamino)fluoran, 
3-diethylamino-7-(N-chloroethyl-N-methylamino)fluoran, 
3-diethylamino-7-diethylaminofluoran, 
4-benzylamino-8-diethylamino-benzo[a] fluoran, 
3-[4-(4-dimethylaminoanilino)anilino]-7-chloro-6-methylfluoran, 
8-4-(4-dimethylaminoanilino)anilino]-benzo[a]fluoran, 
3-diethylamino-7-(2-carbomethoxyphenylamino)fluoran, 
2,2-bis{4-[6'-(N-cyclohexyl-N-methylamino)-3'-methylspiro[phthalido-3,9'-x 
anthen]-2'-yl-amino]phenyl}propane, and fluoran dyes represented by the 
following formulas [I], [II] and [III]: 
(1) a dye represented by the following formula 
##STR1## 
wherein R.sub.1 represents C.sub.1 -C.sub.6 alkyl group, R represents 
C.sub.1 -C.sub.6 alkyl group, C.sub.3 -C.sub.6 alkoxyalkyl group, a 
cyclopentyl group, a cyclohexyl group, a tetrahydrofurfuryl group or 
p-tolyl group, or R.sub.1 and R.sub.2 taken together with the nitrogen 
atom to which they are attached may form a pyrrolidine ring or a 
piperidine ring, X is a methyl group and n is 0 or an integer of 1 or 2; 
(2) a dye represented by the formula 
##STR2## 
wherein R.sub.3 and R.sub.4 each represent C.sub.1 -C.sub.6 alkyl group; 
and 
(3) a dye represented by the formula 
##STR3## 
wherein R.sub.5 and R.sub.6 each represent C.sub.1 -C.sub.6 alkyl group 
and Y represents a chlorine atom, a fluorine atom or a trifluoromethyl 
group. 
Preferably examples of the fluoran-based dyes represented by the formula 
[I] are as follows: 
3-diethylamino-6-methyl-7-phenylaminofluoran, 
3-di-n-butylamino-6-methyl-7-phenylaminfluoran, 
3-di-n-pentylamino-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-p-toluidino)-6-methyl-7-p-toluidinofluoran, 
3-(N-ethyl-N-isobutylamino)-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-isoamylamino)-6-methyl-7-phenylaminofluoran, 
3-(N-cyclohexyl-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-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-phenylaminofluoran, 
3-(N-methyl-N-n-propylamino)-6-methyl-7-phenylaminoflruoan, 
3-(N-methyl-N-n-hexylamino)-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-n-hexylamino)-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-cyclopentylamino)-6-methyl-7-phenylaminofluoran, 
3-(N-methyl-N-ethoxypropylamino)-6-methyl-7-phenylaminofluoran, 
3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-phenylaminofluoran, etc. 
Preferable examples of the fluoran-based dyes represented by the formula 
[II] are as follows: 
3-diethylamino-6-chloro-7-phenylaminofluoran, 
3-di-n-butylamino-6-chloro-7-phenylaminofluoran, 
3-di-n-pentylamino-6-chloro-7-phenylaminofluoran, 
3-(N-ethyl-N-isoamylamino)-6-chloro-7-phenlaminofluoran, 
3-(N-methyl-N-n-propylamino)-6-chloro-7-phenylaminofluoran, 
3-(N-ethyl-N-isobutylamino)-6-chloro-7-phenylaminofluoran, 
3-(N-methyl-N-n-hexylamino)-6-chloro-7-phenylaminofluoran, 
3-(N-ethyl-N-n-hexylamino)-6-chloro-7-phenylaminofluoran, etc. 
Preferable examples of the fluoran-based dyes represented by the formula 
[III] are as follows. 
3-diethylamino-7-(o-chlorophenylamino)fluoran, 
3-di-n-butylamino-7-(o-chlorophenylamino)fluoran, 
3-dimethylamino-7-(m-trifluoromethylphenylaino)fluoran, 
3-diethylamino-7-(m-trifluoromethylphenylamino)fluoran, 
3-di-n-butylamino-7-(m-trifluoromethylphenylamino)fluoran, 
3-diethylamino-7-(o-fluorophenylamino)fluoran, 
3-di-n-butylamino-7-(o-fluoromethylphenylamino)fluoran, 
3-di-n-pentylamino-7-(o-chlorophenylamino)fluoran, 
3-(N-ethyl-N-isoamylamino)-7-(o-chlorophenylamino)fluoran, 
3-(N-ethyl-N-n-hexylamino)-7-(o-chlorophenylamino)fluoran, etc. 
The basic dyes useful in the invention are not limited to the examples 
given above, and at least two of them may be conjointly used. 
Among the above basic dyes, more preferable are the above-exemplified 
fluoran-based dyes such as those represented by the formulas [I], [II] and 
[III]. 
Of the fluoran-based dyes, particularly preferred are those represented by 
the following formulas [IV], [V] and [VI]: 
(1) a dye represented by the formula 
##STR4## 
wherein R.sub.7 is a methyl or ethyl group and R.sub.8 is C.sub.3 -C.sub.5 
alkyl group, an ethoxypropyl group or a tetrahydrofurfuryl group, or 
R.sub.7 and R.sub.8 are the same and represent a n-butyl or n-pentyl 
group; 
(2) a dye represented by the formula 
##STR5## 
wherein R.sub.9 represents an ethyl or n-butyl group; and 
(3) a dye represented by the formula 
##STR6## 
wherein R.sub.10 represents an ethyl or n-butyl group, R.sub.11 represents 
an ethyl, n-butyl or isoamyl group and Y represents a chlorine atom, a 
fluorine atom or a trifluoromethyl group. 
The most preferable fluoran-based dyes are 
3-di-n-butylamino-6-methyl-7-phenylaminofluoran, 
3-di-n-pentylamino-6-methyl-7-phenylaminofluoran, 
3-diethylamino-7-(o-chlorophenylamino)fluoran, 
3-di-n-butylamino-7-(o-chlorophenylamino)fluoran and 
3-(N-ethyl-N-isoamylamino)-7-(o-chlorophenylamino)fluoran, since they not 
only afford excellent stability of the record image but also allow 
particularly low degree of fogging. 
According to the present invention, various heat-fusible materials can be 
used as a recording sensitivity improving agent in order to give a 
heat-sensitive recording material which is more suited to high-speed 
recording. Such heat-fusible materials include, for example, caproic acid 
amide, capric acid amide, palmitic acid amide, stearic acid amide, oleic 
acid amide, erucic acid amide, linoleic acid amide, linolenic acid amide, 
N-methylstearic acid amide, stearic acid anilide, N-methyloleic acid 
amide, benzanilide, linoleic acid anilide, N-ethylcapric acid amide, 
N-butyllauric acid amide, N-octadecylacetamide, N-oleylacetamide, 
N-oleylbenzamide, N-stearylcyclohexylamide, polyethylene glycol, 
1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 1-hydroxynaphthoic acid 
phenyl ester, 1,2-diphenoxyethane, 1,4-diphenoxybutane, 
1,2-bis(3-methylphenoxy)ethane, 1,2-bis(4-methoxyphenoxy)ethane, 
1-phenoxy-2-(4-chlorophenoxy)ethane, 1-phenoxy-2-(4-methoxyphenoxy)ethane, 
1-(2-methylphenoxy)-2- C(4-methoxyphenoxy)ethane, terephthalic acid 
dibenzyl ester, dibenzyl oxalate, di(4-methylbenzyl) oxalate, 
p-benzyloxybenzoic acid benzyl ester, p-benzylbiphenyl, 
1,5-bis(p-methoxyphenoxy)-3-oxa-pentane, 1,4-bis(2-vinyloxyethoxy)benzene, 
p-biphenyl p-tolyl ether, benzyl p-methylthiophenyl ether and the like. 
The amount of the heat-fusible material to be used is not specifically 
limited and may be in the range of about 50 to about 700 parts by weight, 
preferably about 100 to about 500 parts by weight, per 100 parts by weight 
of the basic dye. 
The coating composition for forming the heat-sensitive recording layer can 
be prepared usually by dispersing a basic dye, a color developing material 
and if desired a heat-fusible material conjointly or separately with an 
agitating and pulverizing means such as a ball mill, attritor, vertical or 
horizontal sand mill, colloid mill or the like using water as a dispersing 
medium. 
The coating composition may usually contain a binder such as starches, 
hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, 
gelatin, casein, gum arabic, poly-vinyl alcohol, salts of styrene-maleic 
anhydride copolymer, salts of styrene-acrylic acid copolymer, 
styrene-butadiene copolymer emulsion or the like. The binder is used in an 
amount of about 10 to about 40% by weight, preferably about 15 to about 
30% by weight, based on the total solids content of the coating 
composition. It is possible to use at least two of these binders in 
mixture. 
The coating composition may further contain auxiliaries such as sodium 
dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl 
sulfate, metal salts of fatty acids and like dispersants, ultraviolet 
absorbers of the triazole type and the like, defoaming agents, fluorescent 
dyes, coloring dyes, etc. 
To prevent the recording material from sticking to the recording device or 
the thermal head on contact therewith, it is possible to use a dispersion 
or an emulsion of stearic acid ester wax, polyethylene wax, carnauba wax, 
microcrystalline wax, carboxy-modified paraffin wax, zinc stearate, 
calcium stearate or the like. 
Additionally, in order to reduce the adhesion of residual substances to the 
thermal head, there may be incorporated inorganic pigments such as kaolin, 
clay, talc, calcium carbonate, magnesium carbonate, calcined clay, 
titanium oxide, diatomaceous earth, particulate anhydrous silica, 
activated clay and the like, or organic pigments such as styrene 
microball, nylon powder, polyethylene powder, urea-formalin resin filler, 
raw starch powder and the like. 
The coating composition thus prepared is applied to a suitable support such 
as paper, plastic film, synthetic paper, non-woven sheet or formed body by 
a conventional coater to produce a heat-sensitive recording material of 
the invention. 
The amount of the coating composition to be applied is not specifically 
limited and is generally about 1 to about 12 g/m.sup.2, preferably about 2 
to about 10 g/m.sup.2 on dry basis. 
Other techniques used in the art for production of heat-sensitive recording 
materials can be employed if necessary and include, for example, provision 
of an overcoat layer on a heat-sensitive recording layer for protecting 
said recording layer and for imparting better suitability for writing, 
provision of a protective layer on the rear side of the heat-sensitive 
recording material, application of undercoats on the support, application 
of an adhesive on the rear side of recording material, etc.

EXAMPLES 
The present invention will be described below in more detail with reference 
to the following examples, but the invention is not limited thereto. In 
the examples, "parts" and "percentages" are all by weight unless otherwise 
specified. 
EXAMPLE 1 
(1) Preparation of Dispersion A 
______________________________________ 
3-Di-n-butylamino-6-methyl-7- 
10 parts 
phenylaminofluoran 
1,2-Bis(3-methylphenoxy)ethane 
20 parts 
5% Aqueous solution of 
30 parts 
polyvinyl alcohol 
Water 100 parts 
______________________________________ 
The mixture of these components was pulverized by a sand mill to an average 
particle size of 1 .mu.m. 
(2) Preparation of Dispersion B 
______________________________________ 
Zinc salt of .alpha.-naphthoic acid 
20 parts 
5% Aqueous solution of 
30 parts 
polyvinyl alcohol 
Water 50 parts 
______________________________________ 
The mixture of these components was pulverized by a sand mill to an average 
particle size of 2 .mu.m. 
(3) Formation of heat-sensitive recording layer 
A 160 parts quantity of Dispersion A, 100 parts of Dispersion B, 30 parts 
of silicon oxide pigment (oil absorption: 180 ml/100g), 150 parts of a 20% 
aqueous solution of oxidized starch and 210 parts of water were mixed 
together with stirring, giving a coating composition for forming a 
heat-sensitive recording layer. 
The coating composition thus obtained was applied to a base paper weighing 
50 g/m.sup.2 with use of a rod blade coater in an amount of 5.0 g/m.sup.2 
on dry basis and dried, giving a heat-sensitive recording paper. 
EXAMPLES 2-13 
Twelve kinds of heat-sensitive recording papers were prepared in the same 
manner as in Example 1 except that the following dye was used in place of 
3-di-n-butylamino-6-methyl-7-phenylaminofluoran in the preparation of 
Dispersion A. 
______________________________________ 
Example Dye 
______________________________________ 
2 3-di-n-pentylamino-6-methyl-7- 
phenylaminofluoran 
3 3-(N-ethyl-N-isoamylamino)-6-methyl-7- 
phenylaminofluoran 
4 3-di-n-butylamino-7-(o- 
chlorophenylamino)fluoran 
5 3-diethylamino-7-(o-chlorophenylamino)fluoran 
6 3-(N-ethyl-N-isoamylamino)-7-(o- 
chlorophenylamino)fluoran 
7 3-(N-methyl-N-n-propylamino)-6-methyl-7- 
phenylaminofluoran 
8 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7- 
phenylaminofluoran 
9 3-diethylamino-7-(o-fluorophenylamino)fluoran 
10 3-diethylamino-6-chloro-7-phenylaminofluoran 
11 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl- 
7-phenylaminofluoran 
12 3-(N-methyl-N-cyclohexylamino)-6-methyl-7- 
phenylaminofluoran 
13 3-pyrrolidino-6-methyl-7-phenylaminofluoran 
______________________________________ 
EXAMPLES 14 and 15 
Two kinds of heat-sensitive recording papers were prepared in the same 
manner as in Example 1 except that in the preparation of Dispersion B 
calcium salt of .alpha.-naphthoic acid (Example 14) or magnesium salt of 
.alpha.-naphthoic acid (Example 15) was used in place of zinc salt of 
.alpha.-naphthoic acid. 
EXAMPLE 16 
A heat-sensitive recording paper was prepared in the same manner as in 
Example 1 except that in the preparation of Dispersion B 20 parts of 
.alpha.-naphthoic acid, 10 parts of zinc oxide and 40 parts of water were 
used in place of 20 parts of zinc salt of c-naphthoic acid and 50 parts of 
water. 
EXAMPLES 17-20 
Four kinds of heat-sensitive recording papers were prepared in the same 
manner as in Example 16 except that the following basic dye was used. 
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Example Dye 
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17 3-di-n-pentylamino-6-methyl-7- 
phenylaminofluoran 
18 3-di-n-butylamino-7-(o- 
chlorophenylamino)fluoran 
19 3-diethylamino-7-(o-chlorophenylamino)fluoran 
20 3-(N-ethyl-N-isoamylamino)-7-(o- 
chlorophenylamino)fluoran 
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EXAMPLES 21 and 22 
Two kinds of heat-sensitive recording papers were prepared in the same 
manner as in Example 16 except that in the preparation of Dispersion B 
zinc salt of .alpha.-naphthoic acid (Example 21) or calcium salt of 
.alpha.-naphthoic acid (Example 22) was used in place of .alpha.-naphthoic 
acid. 
EXAMPLE 23 
A heat-sensitive recording paper was prepared in the same manner was in 
Example 1 except that in the preparation of Dispersion B 20 parts of 
4-hydroxy-4'-isopropoxydiphenylsulfone and 30 parts of water were used in 
place of 50 parts by weight of water. 
Comparative Examples 1-4 
Four kinds of heat-sensitive recording papers were prepared in the same 
manner as in Example 1 except that in the preparation of Dispersion B the 
following compound was used in place of zinc salt of .alpha.-naphthoic 
acid. 
Comparative 
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Example Compound 
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1 4,4'-isopropylidenediphenol 
2 zinc salt of 3,5-di(.alpha.- 
methylbenzyl)salicylic acid 
3 zinc salt of 4-chlorobenzoic acid 
4 zinc salt of .beta.-naphthoic acid 
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The 27 kinds of the heat-sensitive recording papers obtained above were 
subjected to recording with use of a facsimile machine (Model HIFAX-700, 
product of Hitachi, Ltd.), and the color density of the record image thus 
formed was measured by Macbeth densitometer (Model RD-914, product of 
Macbeth Corporation, U.S.A.). The results are shown in Table 1 below. 
Then the heat-sensitive recording papers with the record images formed 
thereon were allowed to stand at 40.degree. C. in a highly humid 
atmosphere of 90% RH for 48 hours. Thereafter the color density of the 
record images was measured again with use of the Macbeth densitometer in 
order to evaluate the humidity resistance of the record images. The 
results are shown in Table 1. 
Furthermore, in order to evaluate the resistance to chemicals, a sheet of 
polyvinyl chloride film was superposed on the heat-sensitive recording 
layer each of the above heat-sensitive recording papers with the record 
images formed thereon with use of the above facsimile machine (resistance 
to plasticizer). Seperately, 0.2 ml of ethanol was applied to the 
heat-sensitive recording layer each of the above heat-sensitive recording 
papers with the record images formed thereon with use of the above 
facsimile machine (resistance to alcohol). In each case, the degree of 
fogging (i.e., undesired color formation) in the white background portions 
and the degree of reduction in the color density of the record images were 
evaluated according to the following criteria. 
1: The recording paper allowing substantially no fogging or substantially 
no reduction in color density, raised no practical problem at all and was 
rated excellent. 
2.: The recording paper allowed slight degree of fogging or slight degree 
of reduction in color density, raised no practical problem and was rated 
good. 
3: The recording paper allowed fogging or reduction in color density and 
had a bit low quality but was practically usable. 
4: The recording paper suffered from marked fogging or marked reduction in 
color density, and raised practical problem. 
The results are shown in Table 1. 
As clear from Table 1, the heat-sensitive recording material of the 
invention can give record images which have high color density and 
excellent stability, and has high resistance to chemicals. 
TABLE 1 
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Resistance Resistance 
to plasticizer 
to alcohol 
Humidity Reduc- Reduc- 
resistance tion in tion in 
Color of record color color 
density image Fogging density 
Fogging 
density 
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Ex. 1 1.25 1.21 2 2 1 2 
Ex. 2 1.24 1.21 2 2 1 2 
Ex. 3 1.25 1.22 2 2 2 2 
Ex. 4 1.23 1.20 2 2 1 2 
Ex. 5 1.22 1.20 2 2 1 2 
Ex. 6 1.24 1.21 2 2 1 2 
Ex. 7 1.23 1.20 2 2 2 2 
Ex. 8 1.24 1.21 2 2 2 2 
Ex. 9 1.23 1.20 2 2 2 2 
Ex. 10 
1.24 1.21 2 2 2 2 
Ex. 11 
1.25 1.22 2 2 2 2 
Ex. 12 
1.23 1.20 3 2 2 2 
Ex. 13 
1.22 1.20 3 2 2 2 
Ex. 14 
1.21 1.13 2 3 2 3 
Ex. 15 
1.20 1.12 2 3 2 3 
Ex. 16 
1.29 1.25 2 1 1 2 
Ex. 17 
1.28 1.24 2 1 1 2 
Ex. 18 
1.27 1.24 2 1 1 2 
Ex. 19 
1.26 1.23 2 1 1 2 
Ex. 20 
1.28 1.25 2 1 1 2 
Ex. 21 
1.30 1.28 2 1 1 2 
Ex. 22 
1.29 1.27 2 1 1 2 
Ex. 23 
1.32 1.27 2 2 2 2 
Comp. 1.08 0.85 2 4 4 4 
Ex. 1 
Comp. 1.13 0.98 4 3 4 3 
Ex. 2 
Comp. 0.98 0.89 4 3 4 3 
Ex. 3 
Comp. 0.95 0.78 2 4 2 4 
Ex. 4 
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