Heat-sensitive transfer material

A heat-sensitive transfer material is obtained by forming on a support a layer of heat-transferable ink comprising a heat-fusible binder, a colorant and a gas generating component capable of generating gas on heating. The gas generating component may be either a heat-decomposable foaming agent or a micro-particulate filler containing a readily volatile organic liquid. The heat-sensitive transfer material is adapted for printing on a paper having poor surface smoothness.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a heat-sensitive transfer material, more 
particularly to a heat-sensitive transfer material which can give a 
transferred recorded image of good printed letter quality even on a 
recording medium with bad surface smoothness by incorporating a component 
capable of generating a gas on heating in the heat transferable ink layer. 
2. Description of the Prior Art 
With rapid progress of information industries, various information 
processing systems have been developed, and various recording methods and 
devices suited for the respective information processing systems have been 
developed and adopted. As one of such recording methods, the 
heat-sensitive recording method has recently been widely used because of 
various advantages such that the apparatus therefor is light in weight and 
compact, does not generate noise and also is excellent in operability and 
maintenance. 
However, of the recording papers used for the heat-sensitive recording 
method, ordinary heat-sensitive recording papers are expensive since they 
are converted papers containing a color forming agent and a developing 
agent, and also involve the problems that alteration of the recording is 
possible, that the recording paper is susceptible to color formation by 
heat or organic solvents and that the storability of recording is poor, 
with the recorded image fading within a relatively short time. 
As the method which maintains the advantages of the heat-sensitive 
recording method as described above and also compensates for the 
disadvantages with the use of heat-sensitive recording papers, the 
heat-sensitive transfer recording method is particularly attracting 
attention in these days. 
In the heat-sensitive recording method a heat-sensitive transfer material 
is used, which comprises a layer of a heat-transferable ink containing a 
colorant dispersed in a heat-fusible binder coated by melting on a support 
generally in the form of a sheet, and the recording is generally conducted 
by superposing the heat-sensitive material on a recording medium such as 
paper so that the heat-transferable ink layer will contact the recording 
medium, supplying heat from the support side of the heat-sensitive 
transfer material by means of a thermal head to transfer the molten ink 
layer to the recording medium, thereby forming a transferred ink image 
corresponding to the heat supplying pattern on the recording medium. 
According to this method, the advantages of the heat-sensitive recording 
method as mentioned above can be maintained, and also the disadvantages 
with the use of the heat-sensitive recording paper can be eliminated. 
However, the heat-sensitive transfer recording method of the prior art is 
not free from drawbacks. That is, according to the heat-sensitive transfer 
recording method of the prior art, the transfer recording performance, 
namely the printed letter quality is remarkably influenced by the surface 
smoothness of the recording medium, and therefore while good printing can 
be effected on a recording medium having high smoothness, the printed 
letter quality will be markedly lowered in the case of a paper with low 
smoothness. However, even when paper which is the most typical recording 
medium may be used, a paper with high smoothness is rather special and 
ordinary papers have surface unevenness to various extents because they 
are formed through entanglements of fibers. Accordingly, in the case of a 
paper with large surface unevenness, the molten ink cannot be made to 
penetrate into fibers during printing but attaches only on the convexties 
or in the vicinity thereof on the surface, whereby the resulting printed 
image may not be sharp at the edge portion, or a part of the image may be 
missing, reducing the printed letter quality. Also, for improvement of the 
printed letter quality, it may be considered to use a heat-fusible binder 
with a low melting point. In this case, however, the heat transferable ink 
layer becomes tacky also at a relatively low temperature, whereby 
inconveniences such as a reduction in storability and staining at the 
non-printed portion may occur. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a heat-sensitive transfer 
materiaI which can give printed letters of good quality not only on a 
recording medium having high surface smoothness but also on a recording 
medium having low surface smoothness. 
Another object of the present invention is to provide a heat-sensitive 
transfer material excellent in storability. 
Still another object of the present invention is to provide a 
heat-sensitive transfer material which does not cause staining at the 
non-printed portion on a recording medium. 
The heat-sensitive transfer material according to the present invention 
comprises a support and a heat-transferable ink layer formed on the 
support, said heat-transferable ink layer containing a colorant and a gas 
generating component capable of generating gas on heating in a 
heat-fusible binder. 
Thus, in order to accomplish the above objects of the present invention, it 
has been found very effective to have a gas generating component capable 
of generating a gas on heating dispersed in the heat-transferable ink 
layer. In the thus formed heat-transferable ink layer, it is rendered 
possible that the ink can penetrate into the interior of a recording 
medium. For this reason, even for a recording medium having poor 
smoothness, generation of defects in printed image can be prevented to 
enable improvement of printed letter quality. Also, the dispersion of the 
gas-generating component does not cause a lowering in the melting point of 
the heat-transferable ink layer as a whole or a decrease in storability 
before use. 
The present invention will described in further detail below by referring 
to the drawings according to necessity. In the following description, "%" 
and "parts" representing proportions of amount are by weight unless 
specifically otherwise noted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a schematic sectional view in the thickness direction of the most 
basic embodiment of the heat-sensitive transfer material in the present 
invention. More specifically, the heat-sensitive transfer material 1 
generally comprises a heat-transferable ink layer 3 formed on the support 
2 in the form of a sheet (""sheet" being used to include films). 
As the support 2, it is possible to use films or papers known in the art as 
such. For example, films of plastics having relatively good heat 
resistance such as polyester, polycarbonate, triacetylcellulose, nylon, 
polyimide, etc., Cellophane or parchment paper can be preferably used. The 
support should have a thickness desirably of about 2 to 15 microns when 
considering the thermal head as the heat source during heat transfer, but 
it is not particularly limited when using a heating source capable of 
heating selectively the heat-transferable ink layer such as laser beam. 
Also, in the case of using a thermal head, the surface of the support to 
contact the thermal head can be provided with a heat-resistant protective 
layer comprising a silicone resin, a fluorine resin, a polyimide resin, an 
epoxy resin, a phenol resin, a melamine resin or nitrocellulose to improve 
the heat resistance of the support. Alternatively, a support material 
which could not be used in the prior art can also be used by provision of 
such a protective layer. 
The heat-transferable ink layer 3 comprises a coated layer of a 
heat-fusible ink comprising a heat-fusible binder 4 containing a colorant 
dispersed or mixed compatibly therein, and a gas generating component 5 
further dispersed in the heat-fusible binder. 
The heat-fusible ink comprising a colorant and a heat-fusible binder may be 
one conventionally used in the heat-sensitive transfer material, which can 
be used as such. More specifically, as the colorant, various dyes, 
pigments or carbon black widely used in the field of printing or recording 
can be used. Useful heat-fusible binders may include waxes such as 
carnauba wax, paraffin wax, sazol wax, microcrystalline wax, castor wax 
and the like; higher fatty acids or derivatives thereof, for example, 
metal salts or esters thereof such as stearic acid, palmitic acid, lauric 
acid, aluminum stearate, lead stearate, barium stearate, zinc stearate, 
zinc palmitate, methylhydroxy stearate, glycerol monohydroxystearate and 
the like; thermoplastic resins comprising homopolymers or copolymers of 
olefins or their derivatives such as polyethylene, polypropylene, 
polyisobutylene, polyethylene wax, polyethylene oxide, 
polytetrafluoroethylene, ethylene-acrylic acid copolymer, ethylene-ethyl 
acrylate copolymer, ethylene-vinyl acetate copolymer and the like. These 
heat-fusible binders may be used either singly or as a mixture of two or 
more compounds. 
The heat-fusible ink constituting the heat-transferable ink layer 3 
comprises a gas generating component 5 dispersed in an ordinary 
heat-fusible ink as described above. The gas generating component to be 
used in the present invention is a component capable of generating a gas 
by the heat applied during heat transfer of ink, and, because the pressing 
force of the gas generated is utilized, it is more preferable to use a gas 
generating component of the kind which can generate larger amount of gas 
within a short time than the one with smaller amount of gas generation. 
Examples of such preferable gas generating components include heat 
decomposable foaming agents and microparticulate fillers containing or 
enclosing a readily volatile organic liquid therein. 
As a heat decomposable foaming agent to be used in the present invention, 
there may be preferably employed a substance which can be chemically 
decomposed on heating to generate gas and also satisfy the following 
conditions: 
(1) it can be stably dispersed or dissolved in the ink material (thus, in 
the present specification, the "dispersed" state of the heat decomposable 
foaming agent in the heat-fusible binder is also inclusive of the 
dissolved state); 
(2) it should be stable at room temperature and can be decomposed at a 
temperature of 200.degree. C or lower; 
(3) the decomposed gas should not be corrosive or toxic; 
(4) the decomposed gas should be free from objectionable odor or 
contaminating property; and 
(5) the agent itself or its decomposed residue should not react with the 
ink material to cause decoloration or denaturation. 
For example, as inorganic foaming agents, there are bicarbonates such as 
sodium bicarbonate, ammonium bicarbonate and the like; carbonates such as 
ammonium carbonate, magnesium carbonate and the like; an equimolar mixture 
of sodium nitrite and ammcnium chloride; azide compounds such as CaN.sub.6 
or BaN.sub.6; ferrous oxalate; ammonium persulfate; sodium borohydride; 
and so on. Examples of organic foaming agents are azo type foaming agents 
such as azodicarbonamide (ADCA), azobisisobutyronitrile (AIBN), 
diazoaminobenzene (DAB) and the like; nitroso type foaming agents such as 
N,N'-dinitrosopentaethylenetetramine (DPT or DNTD), 
N,N'-dimethyl-N,N-'-dinitroterephthalamide (DMDNTA) and the like; sulfonyl 
hydrazide type foaming agents such as p-toluenesulfonyl hydrazide (TSH), 
benzenesulfonyl hydrazide (BSH), p,p'-oxybisbenzenesulfonyl hydrazide and 
the like. 
These inorganic foaming agents or organic foaming agents may be used either 
singly or as a mixture of two or more kinds in the same system or two or 
more kinds selected from both of the systems. If desired, a foaming aid 
may be also formulated in the foaming agent for the purpose of controlling 
the decomposition temperature of the foaming agent. 
The foaming aid may be any compound having an action which can lower the 
decomposition temperature of the foaming agent employed when combined with 
the foaming agent, and depending on the foaming agent used, those 
enumerated below may be available. For example, there may be included 
oxalic acid, lactic acid, citric acid, succinic acid, malic acid, benzoic 
acid, salicylic acid, fumaric acid, malonic acid, adipic acid, gallic 
acid, toluenesulfonic acid, phosphoric acid, guanidine carbonate, 
ethanolamine, potassium carbonate, borax, boric acid, silicic acid, 
cadmium oxide, zinc oxide, zinc acetate, zinc chloride, zinc nitrate, zinc 
laurate, zinc powder, mercury acetate, mercury oxide, barium stearate, 
calcium stearate, magnesium oxide, calcium carbonate, lead carbonate, lead 
acetate, lead oxide, lead sulfate, dibasic phosphite, stannous oxide, 
Dexy-clay, dimethylformamide, aluminum stearate, titanium oxide, boron 
trifluoride, urea and so on. When there is a possibility of generation of 
a small amount of formaldehyde during heat decomposition as in the case of 
using an organic weak acid as the foaming aid, it is preferred to employ a 
compound having an action to capture formaldehyde such as urea in 
combination. 
In the heat-transferable ink layer, it is preferred to disperse 30 parts or 
less of a heat decomposable foaming agent alone or in combination with a 
second foaming agent per 100 parts of the heat-fusible binder. 
When a microparticulate filler containing a readily volatile organic liquid 
therein is used as a gas generating component, the readily volatile 
organic liquid is generally enclosed within the microparticulate material 
comprising a resin by impregnation or microencapsulation. As the readily 
volatile organic liquid, any of the compounds used in the field of resin 
treatment as the evaporation type foaming agent or the readily volatile 
foaming agent can be used as such also in the present invention. The 
readily volatile organic liquid may be chosen depending on the form 
enclosed within the microparticulate filler, but generally a compound 
which is liquid around normal temperature and normal pressure and has a 
boiling point of 130.degree. C or lower, particularly 100.degree. C. or 
lower, may preferably be used. Typical examples of the readily volatile 
organic liquid are set forth below: 
(a) Aliphatic hydrocarbons: 
For example, hydrocarbons having 4 to 7 carbon atoms such as n-propane, 
n-pentane, n-hexane, neopentane, isohexane, n-heptane, isoheptane and the 
like. These are low in toxicity and cheap. 
(b) Chlorinated aliphatic hydrocarbons: 
For example, methyl chloride, methylene dichloride, trichloroethylene, 
dichloroethane (sym), and the like. 
(c) Fluorinated aliphatic hydrocarbons: 
For example, chlorine-fluorine derivatives of methane or ethane such as 
Freon-11 (CC1.sub.3 F), Freon-12 (CC1.sub.2 F.sub.2), Freon-21 (CHC1.sub.2 
F), Freon-22 (CHClF.sub.2), Freon-113 (CC1.sub.2 F-CClF.sub.2), Freon-114 
(CClF.sub.2 -CClF.sub.2) are frequently used. 
(d) Aromatic hydrocarbons: 
Benzene, toluene and the like. 
These microparticulate fillers containing readily volatile organic liquid 
therein can be prepared according to the resin impregnation method or the 
microencapsulation method known in the art. In the case of the resin 
impregnation method, it is possible to employ, for example, the method in 
which a readily volatile organic liquid is added during the process of 
suspension polymerization of an appropriate monomer (Japanese Patent 
Publication No. 3190/1958) or the method in which the beads obtained by 
suspension polymerization are swelled with a solvent and a readily 
volatile organic liquid is added thereto (Japanese Patent Publication No. 
10628/1961). If desired, the resin may be micropulverized before 
impregnation with a readily volatile organic liquid. 
The microencapsulation method is also inclusive of various methods such as 
the complex coacervation method, the interfacial polymerization method and 
the phase separation method known in the art. Various commercial products 
are available as microcapsules enclosing readily volatile organic liquid, 
such as Matsumoto Microsphere F30, F50, F60 produced by Matsumoto Yushi 
Seiyaku K.K. or Expancell produced by Nippon Philite K.K. (enclosing a 
foaming agent of isobutane within a wall material of vinylidene 
chloride/acrylonitrile copolymer). 
Including those as described above, as the microparticulate filler material 
containing a readily volatile organic liquid, it is preferred to use one 
having particle sizes of 0.1 to 30 micron, particularly 0.1 to 10 micron, 
above all one with smaller particle sizes. 
In the heat-transferable ink layer 3, it is preferred to disperse 50 parts 
or less of a microparticulate filler per 100 parts of the heat-fusible 
binder as described above. 
The heat-sensitive transfer material 1 according to the present invention 
can be prepared by applying a coating solution composed mainly of the 
heat-fusible ink containing the heat-fusible binder, colorant and the 
gas-generating component as described above and drying the coating to form 
the heat-trans-ferable ink layer 3. The thickness of the heat-transferable 
ink layer 3 is generally 1 to 30 microns, preferably 2 to 20 microns. 
The shape of the heat-sensitive transfer material of the present invention 
is not particularly limited as far as it is basically planar, but it is 
generally shaped in the form of a tape or ribbon as in a typewriter ribbon 
or a tape with wide width as used in line printers, etc. Also, for the 
purpose of color recording, the heat-sensitive transfer material of the 
inventions can be formed by applying several kinds or color tones of 
heat-fusible inks in stripes or blocks on a support. 
Next, the heat-sensitive transfer recording method employing the above 
heat-sensitive transfer material is described by referring to the case in 
which a thermal head is employed as the most typical heat source. FIG. 2 
is a schematic sectional view in the thickness direction of the 
heat-sensitive transfer material showing its outline. More specifically, 
the heat-fusible ink 3 of the heat-sensitive transfer material 1 is caused 
to closely contact the recording medium, and while giving a heat pulse by 
means of the thermal head 8 with additional heat pulse, if desired, from 
the platen 7, the ink layer 3 is heated locally corresponding to the 
desired printing or transfer pattern. The heated portion of the ink layer 
3 is softened or melted on reaching a certain temperature and, at almost 
the same time, the gas generating component is also heated to be 
decomposed with generation of a gas. By the volume expansion of the ink 
layer and the pressure of the gas, the ink can sufficiently penetrate into 
and fill even the concavities of the recording medium surface where a 
conventional heat transfer ink could not penetrate, thus giving a recorded 
image 3a of good printed letter quality even on the recording medium of 
poor surface smoothness. 
The above description has been made by referring to an embodiment in which 
a thermal head is used as the heat source for heat transfer recording, but 
it will readily be understood that the method can be similarly practiced 
also in the case of using other heat sources such as a laser beam, etc. 
As described in detail above, the heat transfer material of the present 
invention is capable of performing recording even on a recording medium 
with poor surface smoothness and yet no lowering in storability of the 
heat transfer material is brought about. Thus, it may be considered to be 
applicable widely for information recording system which is expected to be 
diversified in the future. 
The present invention will be described more specifically by referring to 
actual example of production and use of heat-sensitive transfer materials. 
EXAMPLE 1 
One part of carbon black, one part of polyethylene wax (softening point: 
about 95.degree. C.), 2 parts of paraffin wax (softening point: about 
70.degree. C.) and one part of carnauba wax were mixed by heating at 
100.degree. C. under stirring. Then, 25 parts of toluene were added to the 
mixture, and the mixture was heated at about 100.degree. C. and thereafter 
cooled under vigorous stirring to room temperature to obtain a fine 
dispersion of carbon black/wax in toluene. 
In a ball mill, 0.5 part of ammonium carbonate and 5 parts of toluene were 
crushed together, and the resultant mixture was added to the fine 
dispersion of carbon black/wax in toluene as previously obtained, followed 
by vigorous stirring. 
The above coating mixture was applied by means of a wire bar on a polyester 
film of a thickness of 6 .mu.m and dried to obtain a heat-sensitive 
transfer material having a transfer layer of a thickness of 4 .mu.m. 
COMATIVE EXAMPLE 1 
Only the fine dispersion of carbon black/wax in toluene of Example 1 was 
applied by means of a wire bar on a polyester film with a thickness of 6 
.mu.m and dried to obtain a heat-sensitive transfer material having a 
transfer layer of a thickness of 4 .mu.m. 
EXAMPLE 2 
A heat-sensitive transfer material was prepared similarly as in Example 1 
by replacing ammonium carbonate in Example 1 with calcium azide. 
EAMPLE 3 
To the fine dispersion of carbon black/wax in toluene produced in Example 1 
was further added 0.5 part of azodicarbonamide and the mixture was further 
stirred in a ball mill. The resultant coating mixture was applied on a 
polyester film of a thickness of 6 .mu.m and dried to obtain a 
heat-sensitive transfer material having a transfer layer of a thickness of 
4 .mu.m. 
EXAMPLE 4 
Example 3 was repeated except for replacing 0.5 part of azodicarbonamide 
with 0.8 part of azobisisobutyronitrile to prepare a heat-sensitive 
transfer material. 
EXAMPLE 5 
To the fine dispersion of carbon black/wax in toluene produced in Example 1 
were further added 0.5 part of azodicarbonamide and 0.03 part of 
ethanolamine, and following otherwise the same procedure of Example 3, a 
heat-sensitive transfer material was prepared. 
By use of the various kinds of heat-sensitive transfer materials thus 
obtained, recording was effected on three kinds of recording paper with 
different Bekk smoothnesses according to a facsimile device of a 
heat-sensitive transfer type, and their resolutions were evaluated. As the 
original manuscript, an electrophotographic test chart was employed and 
the evaluation was conducted by measurement of resolution of images. The 
evaluation results are listed below. 
______________________________________ 
Recording paper (Bekk smoothness) 
Bond paper 
High quality paper 
High quality 
Example No. 
(15 sec.) (30 sec.) (100 sec.) 
______________________________________ 
Comparative 
Up to 3.6 Up to 4.5 lines/mm 
Up to 6.3 
Example 1 
lines/mm lines/mm 
Example 1 
Up to 5.6 Up to 6.3 lines/mm 
Up to 6.3 
lines/mm lines/mm 
Example 2 
Up to 5.6 " Up to 6.3 
lines/mm lines/mm 
Example 3 
Up to 5.6 " Up to 6.3 
lines/mm lines/mm 
Example 4 
Up to 5.6 " Up to 6.3 
lines/mm lines/mm 
Example 5 
Up to 5.6 " Up to 6.3 
lines/mm lines/mm 
______________________________________ 
EXAMPLE 6 
One part of carbon black, 2 parts of polyethylene wax (softening point: 
70.degree. C.) and one part of carnauba wax were dispersed by mixing in an 
attritor by heating at about 100.degree. C. Then, 30 parts of a petroleum 
solvent (trade name: Isopar H, produced by Esso) were added to the 
dispersion, and the mixture was heated at about 100.degree. C and cooled 
under vigorous stirring to room temperature to obtain a fine dispersion of 
carbon black/wax in Isopar H. Further, to the above dispersion was added 
one part of a microparticulate filler enclosing a readily volatile organic 
liquid (trade name: Microsphere F, produced by Matsumoto Yushi Seiyaku 
K.K.), followed by mixing under stirring, to obtain a coating mixture. The 
coating mixture was applied on a polyester film with a thickness of 6 
micron and dried to obtain a heat-sensitive transfer material with a 
transfer ink layer of 10 micron in thickness. 
By use of the above heat-sensitive transfer material, according to the 
heat-sensitive transfer type facsimile with an electrophotographic chart 
as the original manuscript, recording was performed on papers with 
different smoothnesses, and their resolutions were evaluated. As the 
result, a resolution of 6.3 lines/mm was obtained for a paper with Bekk 
smoothness of 100 sec., and 5.6 lines/mm for a paper with Bekk smoothness 
of 15 sec. Sharpness of the recorded image was good for each paper. 
COMATIVE EXAMPLE 2 
Only the fine dispersion of carbon black/wax in Isopar H of Example 6 was 
applied on a polyester film of a thickness of 6 micron and dried to obtain 
a heat-sensitive transfer paper of a thickness of the transfer ink layer 
of 10 microns. 
By use of this heat-sensitive paper, heat-transfer recording and evaluation 
of resolution of the recorded image was conducted similarly as in Example 
6. As the result, the resolution of 6.3 lines/mm was obtained for a paper 
with Bekk smoothness of 100 sec., but the resolution was lowered to 3.6 
lines/mm for a paper of 15 sec., with the sharpness of the recorded image 
being also inferior. 
EXAMPLE 7 
Example 6 was repeated except for using fine particles of a polystyrene 
containing butane in place of the microsphere to obtain a heat-sensitive 
transfer material. With the use of this heat-sensitive transfer material, 
high resolution recording could be done similarly as in Example 6. 
As apparently seen from the above results, when using the heat-sensitive 
transfer material of the present invention, lowering in resolution is very 
little even when the smoothness of the paper may be lowered. The recorded 
image obtained by using the heat-sensitive transfer material of Example 5 
especially had a very good sharpness of recording. This may be 
attributable to closeness of the melting temperature of the heat-fusible 
ink to the decomposition temperature of the foaming agent, whereby the 
molten ink could be very effectively transferred.