Thermosensitive recording material

A thermosensitive recording material composed of a support, and a thermosensitive recording layer formed on the support, containing a leuco dye, a color developer capable of inducing color formation in the leuco dye upon application of heat thereto, and a thermofusible material including p'-methylphenyl p-chlorobenzoate serving as a thermosensitivity-improving agent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a thermosensitive recording material 
comprising as the main components a leuco dye serving as a coloring agent 
and a color developer capable of inducing color formation in the leuco dye 
upon application of heat thereto, and a particular thermosensitivity 
improving agent. 
2. Discussion of Background 
There are conventionally proposed various recording materials which utilize 
the coloring reaction between a colorless or light-colored leuco dye and a 
color developer capable of inducing color formation in the leuco dye upon 
application of heat or pressure thereto when brought into contact with the 
leuco dye. 
A thermosensitive recording material, one of the above-mentioned recording 
materials, is usable as a recording material for an electronic computer, 
facsimile apparatus, ticket vending apparatus, label printer, and recorder 
because it has the advantages that complicated processes such as 
development and image-fixing are not required, recording can be achieved 
for a short period of time using a relatively simple apparatus, there is 
no noise development, and the manufacturing cost is low. 
In such a thermosensitive recording material, colorless or light-colored 
leuco dyes having a lactone, lactam, or a spiropyran ring are used as 
coloring dyes, and organic acids or phenols are conventionally employed as 
color developers. The thermosensitive recording material using the 
above-mentioned leuco dye and color developer is widely used for practical 
use because the produced images have high density, with the whiteness of 
the background maintained high. 
In line with the increase of demands for the thermo-sensitive recording 
system, the requirements for high speed recording are increasing. 
Therefore, not only the development of a high-speed recording apparatus, 
but also the development of a recording material capable of coping with 
the above-mentioned high-speed recording apparatus is intensively desired. 
To cope with the high-speed recording system, it is proposed to use 
p-hydroxybenzoate and hydroxynaphthoate as the color developers with high 
sensitivity, as respectively disclosed in Japanese Laid-Open Patent 
Applications 56-144193 and 59-22793. However, the recording materials 
comprising the above color developers have a shortcoming in the 
preservability of the obtained images therein. 
In addition, the use of a thioester compound as a color developer is 
proposed, as disclosed in Japanese Laid-Open Patent Application 59-165680; 
and phenolsulfonic acid and derivatives thereof are used as the color 
developers, as in Japanese Laid-Open Patent Applications 58-82788 and 
60-13852. When the aforementioned compounds are used as the color 
developers, however, the sensitivity of the obtained thermosensitive 
recording materials is insufficient although image areas obtained in the 
recording materials are fast to fats and oils. 
Furthermore, the addition of various thermofusible materials is proposed to 
increase the thermal sensitivity, for example, benzoate compounds in 
Japanese Laid-Open Patent Application 57-128592; phenylether derivatives 
in Japanese Laid-Open Patent Applications 58-57989, 58-87088 and 61-31287; 
naphthol derivatives in Japanese Laid-Open Patent Application 58-87064; 
and benzylbiphenyl in Japanese Laid-Open Patent Application 60-82382. 
The thermosensitive recording materials comprising the above-mentioned 
color developers or thermofusible materials are not satisfactory from the 
viewpoints of the thermal coloring sensitivity, the whiteness degree of 
the background, and the preservability of the obtained images such as 
fading of the images and deposition of white dust on the recording 
material. 
The use of a phenyl benzoate as a thermosensitivity-improving agent is 
proposed, as disclosed in Japanese Laid-Open Patent Applications 57-128592 
and 58-59894. However, the thermosensitive recording materials comprising 
the phenyl benzoate as disclosed in the above applications are still 
insufficient in the thermal coloring sensitivity, and the preservability 
of the recording materials in terms of the image fading, deposition of 
white dust and coloring of the background. 
The formation of an intermediate layer is proposed to increase the 
recording sensitivity without decreasing the whiteness degree of the 
background. For instance, there are proposed an intermediate layer mainly 
comprising minute void particles, as in Japanese Laid-Open Patent 
Applications 59-5093 and 59-225987; and an intermediate layer comprising 
non-expandable void particles, as in Japanese Laid-Open Patent Application 
62-5886. However, these recording materials have the shortcomings that the 
thermal coloring sensitivity is insufficient and the recording properties 
are poor. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a 
thermosensitive recording material with high thermal coloring sensitivity 
and good recording properties, capable of coping with high-speed thermal 
recording, with the recorded images having high reliability and excellent 
preservability, and the whiteness degree of the background thereof 
maintained high. 
The above-mentioned object of the present invention can be achieved by a 
thermosensitive recording material comprising a support and a 
thermosensitive recording layer formed on the support, comprising a leuco 
dye, a color developer capable of inducing color formation in the leuco 
dye upon application of heat thereto, and a thermofusible material 
comprising p'-methylphenyl p-chlorobenzoate serving as a 
thermosensitivity-improving agent. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The thermosensitive recording material of the present invention comprises a 
thermosensitive recording layer which comprises p'-methylphenyl 
p-chlorobenzoate serving as a thermosensitivity-improving agent, so that 
the recording sensitivity is improved, the whiteness degree of the 
background is sufficiently high, the matching properties with a thermal 
head are good in the course of thermal recording, and the preservability 
of the recording material is satisfactory, free from the deposition of 
white dust and the sublimation property of p'-methylphenyl 
p-chlorobenzoate. Therefore, the thermosensitive recording material of the 
present invention is suitable for high speed thermal recording. 
The thermosensitive recording material of the present invention may further 
comprise an intermediate layer comprising as the main component plastic 
void particles in the form of sphere, which is provided between the 
support and the thermosensitive recording layer. This intermediate layer 
serves as a heat-insulating layer. Owing to the intermediate layer, 
therefore, thermal energy supplied by a thermal head can efficiently be 
utilized, thereby improving the thermosensitivity of the recording 
material. 
The void particles for use in the intermediate layer comprise a 
thermoplastic resin for forming a shell of each void particle. A copolymer 
resin mainly comprising vinylidene chloride and acrylonitrile is 
preferably used a the above-mentioned thermoplastic resin. Air or other 
gasses are contained in the void particles in the expanded state. 
It is preferable that the particle diameter of the void particles be 2 to 
10 .mu.m in the present invention. When the particle size of the void 
particles is within the above range, there is no problem in the production 
of the intermediate layer because the voidage of the void particles can 
freely be determined. In addition, the surface smoothness of the 
intermediate layer prepared by coating a coating liquid comprising the 
void particles and drying the same is not decreased, so that the adhesion 
of the recording layer to the thermal head does not lower, and 
consequently, the thermosensitivity of the recording material can be 
prevented from deteriorating. When the above-mentioned advantages are 
further taken into consideration, it is preferable that the void particles 
classified in a narrow distribution be employed for use in the 
intermediate layer. 
It is preferable that the voidage of the void particles for use in the 
present invention be 50% or more, and more preferably 90% or more, from 
the viewpoint of the heat insulating effect. In the present invention, the 
voidage of the void particles for use in the intermediate layer is 
expressed by the following formula: 
##EQU1## 
When the voidage of the void particles is within the above range, 
sufficient heat insulating effect of the intermediate layer can be 
obtained, so that the thermal energy supplied by the thermal head is 
prevented from escaping through the support of the thermosensitive 
recording material. As a result, the thermosensitivity-improving effect 
can be increased. In the present invention, when the intermediate layer 
comprises void particles with an average particle diameter of 2 to 10 
.mu.m and a voidage of 90% or more, the flexibility of the obtained 
recording material is so much increased that the adhesion to the thermal 
had is further increased, thereby improving the dot reproduction 
performance. 
The intermediate layer for use in the present invention may further 
comprise an inorganic or/and organic pigment. In this case, the oil 
absorption of the pigment is preferably 30 ml/100 g or more, and more 
preferably 80 ml/100 g or more. 
The above-mentioned inorganic and/or organic pigment used in the 
intermediate layer, which may be employed alone or in combination, can be 
selected from any pigments for use in the conventional thermosensitive 
recording materials. Specific examples of the inorganic pigment are 
calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, 
zinc hydroxide, barium sulfate, clay, talc, and surface-treated calcium 
and silica. Specific examples of the organic pigment are urea-formaldehyde 
resin, styrene-methacrylic acid copolymer and polystyrene resin. 
The thermosensitive recording layer of the recording material according to 
the present invention comprises a leuco dye serving as a coloring agent 
and a color developer. 
As the leuco dye for use in the present invention, which may be employed 
alone or in combination, any conventional dyes for use in the conventional 
leuco-dye-containing recording materials can be employed. For example, 
triphenylmethanephthalide leuco compounds, triallylmethane leuco 
compounds, fluoran leuco compounds, phenothiazine leuco compounds, 
thiofluoran leuco compounds, xanthene leuco compounds, indophthalyl leuco 
compounds, spiropyran leuco compounds, azaphthalide leuco compounds, 
couromeno-pyrazole leuco compounds, methine leuco compounds, 
rhodamineanilinolactam leuco compounds, rhodaminelactam leuco compounds, 
quinazoline leuco compounds, diazaxanthene leuco compounds and bislactone 
leuco compounds are preferably employed. Specific examples of those leuco 
dyes are as follows: 
3,3-bis(p-dimethylaminophenyl)phthalide, 
3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (or Crystal Violet 
Lactone), 
3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide, 
3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 
3,3-bis(p-dibutylaminophenyl)phthalide, 
3-cyclohexylamino-6-chlorofluoran, 
3-dimethylamino-5,7-dimethylfluoran, 
3--diethylamino-7-chlorofluoran, 
3-diethylamino-7-methylfluoran, 
3-diethylamino-7,8-benzfluoran, 
3-diethylamino-6-methyl-7-chlorofluoran, 
3-(N-p-tolyl-N-ethylamino)-6-methyl-7-anilinofluoran, 
3-pyrrolidino-6-methyl-7-anilinofluoran, 
2-[N-(3'-trifluoromethylphenyl)amino]-6-diethylaminofluoran, 
2-[3,6-bis(diethylamino)-9-(o-chloroanilino)xanthylbenzoic acid lactam], 
3-diethylamino-6-methyl-7-(m-trichloromethylanilino)-fluoran, 
3-diethylamino-7-(o-chloroanilino)fluoran, 
3-dibutylamino-7-(o-chloroanilino)fluoran, 
3-N,N-di-N-amylamino-6-methyl-7-anilinofluoran, 
3-N-methyl-N-amylamino-6-methyl-7-anilinofluoran, 
3-N-methyl-N-iso-propylamino-6-methyl-7-anilinofluoran, 
3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluoran, 
3-(N-methyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 
3-(N-methyl-N-isobutylamino)-6-methyl-7-anilinofluoran, 
3-diethylamino-6-chloro-anilinofluoran, 
3-(N-ethyl-N-2-ethoxypropylamino)-6-methyl-7-anilinofluoran, 
3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 
3-diethylamino-6-methyl-7-anilinofluoran, 
3-dibutylamino-6-methyl-7-anilinofluoran, 
3dibutylamino-6-methyl-7-anilinofluoran, 
3-(N,N-diethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran, 
benzoyl leuco methylene blue, 
6'-chloro-8'-methoxy-benzoindolino-spiropyran, 
6'-bromo-8'-methoxy-benzoindolino-spiropyran, 
3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthali 
de, 
3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-nitrophenyl)phthalid 
e, 
3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl)phthalid 
e, 
3-diethylamino-6-methyl-7-(2',4'-dimethylanilino)fluoran, 
3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-methylphen 
yl)phthalide, 
3-morphorino-7-(N-propyl-trifluoromethylanilino)fluoran, 
3-pyrrolidino-7-trifluoromethylanilinofluoran, 
3-diethylamino-5-chloro-7-(N-benzyl-trifluoromethylanilino)fluoran 
3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluoran, 
3-diethylamino-5-chloro-7-(.alpha.-phenylethylamino)fluoran, 
3-(N-ethyl-p-toluidino)-7-(.alpha.-phenylethylamino)fluoran, 
3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, 
3-diethylamino-5-methyl-7-(.alpha.-phenylethylamino)fluoran, 
3-diethylamino-7-piperidinofluoran, 
2-chloro-3-(N-methyltoluidino)-7-(p-n-butylanilino)fluoran, 
3-(N-ethyl-N-cyclohexylamino)-5,6-benzo-7-.alpha.-naphtylamino-4'-bromofluo 
ran, 
3-(N-benzyl-N-cyclohexylamino)-5,6-benzo-7-.alpha.-naphthylamino-4'-bromofl 
uoran, 
3-diethylamino-6-methyl-7-mesidino-4',5'-benzofluoran, 
3-(p-dimethylaminophenyl)-3-[1,1-bis(p-dimethylaminophenyl)ethylene-2-yl]ph 
thalide, 
3-(p-dimethylaminophenyl)-3-[1,1-bis(p-dimethylaminophenyl)ethylene-2-yl]-6 
-dimethylaminophthalide, 
3-(p-dimethylaminophenyl)-3-(1-p-dimethylaminophenyl-1-phenylethylene-2-yl) 
phthalide, 
3-(p-dimethylaminophenyl)-3-(1-p-dimethylaminophenyl-1-p-chlorophenylethyle 
ne-2-yl)-6-dimethylaminophthalide, 
3-(4'-dimethylamino-2'-methoxy)-3-(1"-p-dimethylaminophenyl-1"-p-chlorophen 
yl-1",3"-butadiene-4"-yl)-benzophthalide, 
3-(4'-dimethylamino-2'-benzyloxy)-3-(1"-p-dimethylaminophenyl-1"-phenyl-1", 
3"-butadiene-4"-yl)benzophthalide, 
3,6-bis(dimethylamino)fluorenespiro(9,3')-6'-dimethylaminophthalide, 
3-dimethylamino-6-dimethylamino-fluorene-9-spiro-3'-(6'-dimethylamino)phtha 
lide, 
3,3-bis-[2-[p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetr 
achlorophthalide, 
3-bis[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl]-5,6-dichloro-4,7-dibromoph 
thalide, 
bis(p-dimethylaminostyryl)-1-naphthalenesulfonylmethane, and 
bis[p-dimethylaminostyryl)-1-p-tolylsulfonylmethane. 
As the color developer for use in the present invention, a variety of 
electron-acceptors, for instance, phenolic compounds, thiophenolic 
compounds, thiourea derivatives, organic acids and metallic salts thereof 
can be employed. Specific examples of the color developer are as follows: 
4,4'-isopropylidenebisphenol, 
3,4'-isopropylidenebisphenol, 
4,4'-isopropylidenebis(o-methylphenol), 
4,4'-sec-butylidenebisphenol, 
4,4'-isopropylidenebis(o-tert-butylphenol), 
4,4'-cyclohexylidenediphenol, 
4,4'-isopropylidenebis(2-chlorophenol), 
2,2'-methylenebis(4-methyl-6-tert-butylphenol), 
2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 
4,4'-butylidenebis(6-tert-butyl-2-methyl)phenol, 
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 
1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 
4,4'-thiobis(6-tert-butyl-2-methyl)phenol, 
4,4'-diphenolsulfone, 
4,2-diphenolsulfone, 
4-isopropoxy-4'-hydroxydiphenylsulfone, 
4-benzyloxy-4'-hydroxydiphenylsulfone, 
4,4'-diphenolsulfoxide, 
isopropyl p-hydroxybenzoate, 
benzyl p-hydroxybenzoate, 
benzyl protocatechuate, 
stearyl gallate, 
lauryl gallate, 
octyl gallate, 
1,7-bis(4-hydroxyphenylthio)-3,5-dioxaheptane, 
1,5-bis(4-hydroxyphenylthio)-3-oxapentane, 
1,3-bis(4-hydroxyphenylthio)-propane, 
2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 
1,3-bis[4-hydroxyphenylthio)-2-hydroxypropane, 
N,N'-diphenylthiourea, 
N,N'-di(m-chlorophenyl)thiourea, 
salicylanilide, 
5-chloro-salicylanilide, 
salicyl-o-chloroanilide, 
2-hydroxy-3-naphthoic acid, 
antipyrine complex of zinc thiocyanate, 
zinc salt of 1-acetyloxy-2-naphthoic acid, 
zinc salt of 2-acetyloxy-3-naphthoic acid, 
zinc salt of 2-acetyloxy-1-naphthoic acid, 
2-hydroxy-1-naphthoic acid, 
1-hydroxy-2-naphthoic acid, 
zinc hydroxynaphthoate, 
aluminum hydroxynaphthoate, 
calcium hydroxynaphthoate, 
bis(4-hydroxyphenyl)methyl acetate, 
bis(4-hydroxyphenyl)benzyl acetate, 
4-[.beta.-(p-methoxyphenoxy)ethoxy]salicyl acid, 
1,3-bis(4-hydroxycumyl)benzene, 
1,4-bis(4-hydroxycumyl)benzene, 
2,4'-diphenolsulfone, 
3,3'-diallyl-4,4'-diphenolsulfone, 
.alpha.,.alpha.-bis(4-hydroxyphenyl)-.alpha.-methyltoluene, 
tetrabromobisphenol A, 
tetrabromobisphenol S, 
4,4'-thiobis(2-methylphenol), 
4,4'-thiobis(2-chlorophenol), 
zinc p-nitrobenzoate, 
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid, 
2,2-bis(3,4'-dihydroxyphenyl)propane, and 
bis(4-hydroxy-3-methylphenyl)sulfide. 
To obtain a thermosensitive recording material according to the present 
invention, a variety of conventional binder agents can be employed in the 
thermo-sensitive recording layer of binding the above-mentioned leuco 
dyes, color developers, thermosensitivity-improving agent and auxiliary 
components to be described later to the support of the thermosensitive 
recording material. As the binder agent for use in the present invention, 
any conventional binder agents used in the conventional thermo-sensitive 
recording materials can appropriately be employed. Examples of the binder 
agent are water-soluble polymers such as polyvinyl alcohol, starch and 
starch derivatives, cellulose derivatives such as methoxycellulose, 
hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and 
ethylcellulose, sodium polyacrylate, polyvinyl pyrrolidone, 
acrylamide-acrylic ester copolymer, acrylamide-acrylic ester-methacrylic 
acid terpolymer, alkali salts of styrene-maleic anhydride copolymer, 
alkali salts of isobutylene-maleic anhydride copolymer, polyacrylamide, 
sodium alginate, gelatin, and casein; emulsions such as polyvinyl acetate, 
polyurethane, polyacrylic ester, polymethacrylic ester, vinyl 
chloride-vinyl acetate copolymer, and ethylene-vinyl acetate copolymer; 
and latexes such as styrene-butadiene copolymer and 
styrene-butadiene-acrylic copolymer. 
According to the present invention, the thermosensitive recording layer 
comprises a thermofusible material as the thermosensitivity-improving 
agent, which comprises p'-methylphenyl p-chlorobenzoate. When necessary, a 
variety of thermofusible compounds may be used in combination with 
p'-methylphenyl p-chlorobenzoate. 
The specific examples of the above-mentioned thermofusible compounds are as 
follows: fatty acids such as stearic acid, and behenic acid; fatty amides 
such as stearic acid amide, and palmitic acid amide; fatty acid metallic 
salts such as zinc stearate, aluminum stearate, calcium stearate, zinc 
palmitate, and zinc behenate; and p-benzylbiphenyl, terphenyl, 
triphenylmethane, benzyl p-benzyloxybenzoate, .beta.-benzyloxy 
naphthalene, phenyl .beta.-naphthoate, phenyl 1-hydroxy-2-naphthoate, 
methyl 1-hydroxy-2-naphthoate, diphenyl carbonate, guaiacol carbonate, 
dibenzyl terephthalate, dimethyl terephthalate, 1,4-dimethoxynaphthalene, 
1,4-ethoxy-naphthalene, 1,4-dibenzyloxynaphthalene, 
1,2-bis(phenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, 
1,2-bis(4-methyl-phenoxy)ethane, 1,4-bis(phenoxy)butane, 
1,4-bis(phenoxy)-2-butene, 1,2-bis(4-methoxyphenylthio)ethane, 
dibenzoylmethane, 1,4-bis(phenylthio)butane, 1,4-bis(phenylthio)-2-butene, 
1,2-bis(4-methoxyphenylthio)ethane, 1,3-bis(2-vinyloxyethoxy)benzene, 
1,4-bis(2-vinyloxyethoxy)benzene, p-(2-vinyloxyethoxy)biphenyl, 
p-aryloxybiphenyl, p-propargylxybiphenyl, dibenzoyloxymethane, 
1,3-dibenzoyloxypropane, dibenzyl disulfide, 1,1-diphenyl-ethanol, 
1,1-diphenylpropanol, p-(benzyloxy)benzylalcohol, 
1,3-diphenoxy-2-propanol, N-octadecylcarbamoyl-p-methoxycarbonylbenzene, 
N-octadecylcarbamoylbenzene, dibenzyl oxalate, bis(4-methylbenzyl)oxalate, 
bis(4-chlorobenzyl)oxalate, 1,5-bis{p-methoxyphenyloxy)-3-oxapentane, and 
1,2-bis(4-methoxyphenoxy)propane. 
When necessary, the thermosensitive recording layer for use in the present 
invention may further comprise auxiliary additive components such as a 
filler, a surface active agent, a lubricant and an agent for preventing 
color formation by pressure application, which are used in the 
conventional thermosensitive recording materials. Example of the filler 
for use in the present invention are finely-divided particles of inorganic 
fillers such as calcium carbonate, silica, zinc oxide, titanium oxide, 
aluminum hydroxide, zinc hydroxide, barium sulfate, clay, kaolin, talc, 
surface-treated calcium and surface-treated silica; and finely-divided 
particles of organic fillers such as urea-formaldehyde resin, 
styrene-methacrylic acid copolymer, polystyrene resin and vinylidene 
chloride resin. 
Examples of the lubricant for use in the present invention include higher 
fatty acids and amides, esters and metallic salts thereof; and a variety 
of waxes such as an animal wax, a vegetable wax, a mineral wax, and a 
petroleum wax. 
In the thermosensitive recording layer, it is preferable that the amount of 
the color developer be 0.5 to 10.0 parts by weight to one part by weight 
of the leuco dye. In addition, the sensitizer is preferably contained in 
the thermosensitive recording layer in a amount of 0.5 to 10.0 parts by 
weight, more preferably 1 to 5 parts by weight, to one part by weight of 
the leuco dye. 
The thermosensitive recording material of the present invention may further 
comprise an additional layer comprising a pigment, a binder agent and a 
thermofusible material when necessary, which is provided between the 
previously mentioned intermediate layer and the thermo-sensitive recording 
layer. 
Furthermore, the thermosensitive recording material may further comprise a 
protective layer which is provided on the thermosensitive recording layer 
in order to improve the preservation stability of the recorded images and 
the writing quality of the recording material. The protective layer 
comprises the previously mentioned pigment, binder agent, and 
thermofusible material.

Other features of this invention will become apparent in the course of the 
following description of exemplary embodiments, which are given for 
illustration of the invention and are not intended to be limiting thereof. 
EXAMPLE 1Formation of intermediate layer 
A mixture of the following components was stirred and dispersed, so that a 
coating liquid A for an intermediate layer was prepared: 
______________________________________ 
[Liquid A] Parts by Weight 
______________________________________ 
Dispersion of finely-divided void 
30 
particles (copolymer resin comprising 
styrene and acryl as the main 
components) 
(solid content: 38 wt. %, average 
particle diameter: 0.7 .mu.m, and 
voidage: 80%) 
Styrene - butadiene copolymer latex 
10 
(solid content: 47.5 wt. %) 
Water 60 
______________________________________ 
The thus obtained intermediate layer coating liquid A was coated on a sheet 
of commercially available high quality paper with a basis weight of 52 
g/m.sup.2, serving as a support, and then dried so as to have a coating 
amount of 5 g/m.sup.2 on a dry basis, whereby an intermediate layer was 
formed on the support. 
Formation of Thermosensitive Recording Layer 
A mixture of the following components was separately pulverized in a 
porcelain ball mill for 2 days, so that a Liquid B, a Liquid C, a Liquid D 
and a Liquid E were prepared: 
______________________________________ 
Parts by Weight 
______________________________________ 
[Liquid B] 
3-(N-methyl-N-cyclohexyl)amino-6- 
20 
methyl-7-anilinofluoran 
10% aqueous solution of polyvinyl 
20 
alcohol 
Water 60 
[Liquid C] 
4,4'-isopropylidenediphenol 
20 
10% aqueous solution of polyvinyl 
20 
alcohol 
Water 60 
[Liquid D] 
p'-methylphenyl p-chlorobenzoate 
20 
(m.p.: 99.degree. C.) 
10% aqueous solution of polyvinyl 
20 
alcohol 
Water 60 
[Liquid E] 
Calcium carbonate 20 
Methyl cellulose 20 
Water 60 
______________________________________ 
10 parts by weight of the Liquid B, 30 parts by weight of the Liquid C, 20 
parts by weight of the Liquid D, 40 parts by weight of the Liquid E and 10 
parts by weight of a commercially available dispersion of zinc stearate 
(Trademark: Hidorin Z-730", made by Chukyo Yushi Co., Ltd.) with a 
concentration of 30% were mixed to prepare a thermosensitive recording 
layer coating liquid. The thus prepared thermosensitive recording layer 
coating liquid was coated on the above prepared intermediate layer and 
dried in such a fashion that the deposition amount of the dye was 0.5 
g/m.sup.2 on a dry basis, whereby a thermosensitive recording layer was 
formed on the intermediate layer. Furthermore, the surface of the thus 
prepared thermosensitive recording layer was subjected to calendering so 
as to have a surface smoothness of 500 to 600 sec, whereby a 
thermosensitive recording material according to the present invention was 
obtained. 
EXAMPLE 2 
The procedure for preparation of the thermosensitive recording material in 
Example 1 was repeated except that the Liquid A used in formation of the 
intermediate layer in Example 1 was replaced by a Liquid F with the 
following formulation: 
______________________________________ 
[Liquid F] Parts by Weight 
______________________________________ 
Dispersion of finely-divided 
30 
void particles (copolymer comprising 
vinylidene chloride and acrylo- 
nitrile as the main components) 
(solid content: 32 wt. %, average 
particle diameter: 5 .mu.m, and 
voidage: 92%) 
Styrene - butadiene copolymer latex 
20 
(solid content: 47 wt. %) 
Water 60 
______________________________________ 
Thus, a thermosensitive recording material according to the present 
invention was obtained. 
EXAMPLE 3 
The procedure for preparation of the thermosensitive recording material in 
Example 1 was repeated except that the Liquid C used in formation of the 
thermosensitive recording layer in Example 1 was replaced by a Liquid G 
with the following formulation: 
______________________________________ 
[Liquid G] Parts by Weight 
______________________________________ 
4,4'-isopropylidenediphenol 
20 
10% aqueous solution of polyvinyl 
20 
alcohol 
1,1,3-tris(2-methyl-4-hydroxy-5- 
20 
cyclohexylphenylbutane) 
Water 60 
______________________________________ 
Thus, a thermosensitive recording material according to the present 
invention was obtained. 
COMATIVE EXAMPLE 1 
The procedure for preparation of the thermo-sensitive recording material in 
Example 1 was repeated except that the Liquid D used in formation of the 
thermosensitive recording layer in Example 1 was replaced by a Liquid H 
with the following formulation: 
______________________________________ 
[Liquid H] Parts by Weight 
______________________________________ 
p-methylphenyl benzoate 
20 
(m.p.: 72.degree. C.) 
10% aqueous solution of polyvinyl 
20 
alcohol 
Water 60 
______________________________________ 
Thus, a comparative thermosensitive recording material was obtained. 
COMATIVE EXAMPLE 2 
The procedure for preparation of the thermosensitive recording material in 
Example 1 was repeated except that the Liquid D used in formation of the 
thermosensitive recording layer in Example 1 was replaced by a Liquid I 
with the following formulation: 
______________________________________ 
[Liquid I] Parts by Weight 
______________________________________ 
p-chlorophenyl benzoate 
20 
(m.p.: 88.degree. C.) 
10% aqueous solution of polyvinyl 
20 
alcohol 
Water 60 
______________________________________ 
This, a comparative thermosensitive recording material was obtained. 
COMATIVE EXAMPLE 3 
The procedure for preparation of the thermosensitive recording material in 
Example 1 was repeated except that the Liquid D used in formation of the 
thermosensitive recording layer in Example 1 was replaced by a Liquid J 
with the following formulation: 
______________________________________ 
[Liquid J] Parts by Weight 
______________________________________ 
Phenyl p-chlorobenzoate (m.p.: 103.degree. C.) 
20 
10% aqueous solution of polyvinyl 
20 
alcohol 
Water 60 
______________________________________ 
Thus, a comparative thermosensitive recording material was obtained. 
COMATIVE EXAMPLE 4 
The procedure for preparation of the thermosensitive recording material in 
Example 1 was repeated except that the Liquid D used in formation of the 
thermosensitive recording layer in Example 1 was replaced by a Liquid K 
with the following formulation: 
______________________________________ 
[Liquid K] Parts by Weight 
______________________________________ 
2,4-dichlorophenyl benzoate 
20 
(m.p.: 92.degree. C.) 
10% aqueous solution of 
20 
polyvinyl alcohol 
Water 60 
______________________________________ 
Thus, a comparative thermosensitive recording material was obtained. 
COMATIVE EXAMPLE 5 
The procedure for preparation of the thermosensitive recording material in 
Example 1 was repeated except that the Liquid D used in formation of the 
thermosensitive recording layer in Example 1 was replaced by a Liquid L 
with the following formulation: 
______________________________________ 
[Liquid L] Parts by Weight 
______________________________________ 
p-methylbenzyl oxalate 
20 
(m.p.: 106.degree. C.) 
10% aqueous solution of 
20 
polyvinyl alcohol 
Water 60 
______________________________________ 
Thus, a comparative thermosensitive recording material was obtained. 
Using a commercial available test apparatus for evaluating the thermal 
coloring performance of thermo-sensitive sheets, images were recorded on 
each of the thermosensitive recording material obtained in Example 1 to 3 
and Comparative Examples 1 to 5 under the conditions that the applied 
electric power was 0.45 W/dot and the period for one lien was 8 ms/line, 
with the pulse width changes to 0.2 msec, 0.3 msce and 0.4 msce. The 
coloring density of the recorded image was measured by Mcbeth densitometer 
RD-914. The results are given in Table 1. 
TABLE 1 
______________________________________ 
Deposition 
Head- 
Coloring Density 
Density of White matching 
0.2 0.3 0.4 of Back- 
Dust on Properties 
ms ms ms ground Images (*) 
______________________________________ 
Ex. 1 0.35 0.70 1.22 0.07 Nil o 
Ex. 2 0.40 0.85 1.30 0.07 Nil o 
Ex. 3 0.35 0.82 1.25 0.07 Nil o 
Comp. 0.40 0.80 1.24 0.07 Nil o 
Ex. 1 
Comp. 0.35 0.69 1.20 0.07 Nil o 
Ex. 2 
Comp. 0.36 0.73 1.22 0.07 Nil o 
Ex. 3 
Comp. 0.33 0.68 1.20 0.07 Observed 
o 
Ex. 4 
Comp. 0.33 0.60 1.17 0.07 Nil x 
Ex. 5 
______________________________________ 
[Note 
(*): Headmatching properties 
o: Dust formed from the thermosensitive recording material did not adhere 
to the thermal head. 
x: Dust formed from the thermosensitive recording material adhered to the 
thermal head. 
In particular, with respect to the thermosensitive recording materials 
obtained in Examples 2 and 3, the dot reproduction performance of the 
recorded images was excellent. 
Furthermore, thermal recording was carried out on each thermosensitive 
recording material using a heated block of 130.degree. C. under the 
application of a pressure of 2 kg/cm.sup.2 thereto. Each image sample 
obtained by the above-mentioned thermal recording was subjected to the 
following tests: (1) Heat-resistance test (a): After the image sample was 
allowed to stand at 60.degree. C. in a dry condition for 16 hours, the 
coloring density of the image was measured. (2) Heat-resistance test (b): 
After the image sample was allowed to stand at 70.degree. C. in a dry 
condition for one hour, the coloring density of the image was measured. 
(3) Water-resistance test: After the image sample was immersed in tap 
water at room temperature for 16 hours, the coloring density of the image 
was measured. (4) Sublimation property test: After the image sample was 
allowed to stand at 60.degree. C. in a dry condition for 16 hours, the 
coloring thermosensitivity of the recording material was again examined, 
which was affected by the sublimation property of p'-methylphenyl 
p-chlorobenzoate. 
The results are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
After Heat- 
After Heat- 
Density Before 
resistance Test 
resistance Test 
After Water- 
Tests (a) (b) resistance Test 
Density Density Density Density 
of of of of Sublima- 
Coloring Back- 
Coloring 
Back- 
Coloring 
Back- 
Coloring 
Back- 
tion 
Density ground 
Density 
ground 
Density 
ground 
Density 
ground 
Property 
__________________________________________________________________________ 
Ex. 1 
1.36 0.07 1.38 0.10 1.37 0.13 1.02 0.07 Nil 
Ex. 2 
1.35 0.07 1.38 0.10 1.37 0.13 1.00 0.07 Nil 
Ex. 3 
1.36 0.07 1.37 0.10 1.37 0.13 1.10 0.07 Nil 
Comp. 
1.35 0.07 1.35 0.18 1.35 0.32 0.79 0.07 Observed 
Ex. 1 
Comp. 
1.35 0.07 1.36 0.14 1.35 0.29 0.82 0.07 Observed 
Ex. 2 
Comp. 
1.34 0.07 1.37 0.12 1.36 0.15 0.69 0.07 Observed 
Ex. 3 
Comp. 
1.35 0.07 1.38 0.12 1.35 0.18 0.52 0.07 Nil 
Ex. 4 
Comp. 
1.35 0.07 1.38 0.10 1.34 0.13 0.93 0.07 Nil 
Ex. 5 
__________________________________________________________________________ 
As can be seen from the results shown in Table 1 and 2, the thermal 
coloring sensitivity and the coloring density of the obtained images are 
excellent in the thermosensitive recording materials according to the 
present invention. In addition, the head-matching properties are improved 
and the images recorded on the thermosensitive recording materials of the 
present invention are resistant to heat and water, so that the 
preservation stability of recorded images is excellent. Therefore, the 
thermosensitive recording materials of the present invention are regarded 
as very useful in the practical use. 
As previously explained, since the thermosensitive recording layer of the 
thermosensitive recording material of the present invention comprises 
p'-methylphenyl p-chlorobenzoate as a thermosensitivity-improving agent, 
the coloring sensitivity is remarkably improved, with the whiteness degree 
of the background maintained high. In addition, the heat-resistance and 
water-resistance of the recorded images are excellent, and neither the 
deposition of white dust on the recorded images is observed, nor the 
sublimation property of p'-methylphenyl p-chlorobenzoate is detected. 
Furthermore, the head-matching properties of the recording material are 
excellent. 
When the intermediate layer comprising the plastic void particles is 
interposed between the support and the thermosensitive recording layer in 
the present invention, the thermal energy supplied by the thermal head can 
efficiently be utilized, so that the thermosensitivity is further 
improved, and at the same time, the head-matching properties are further 
improved.