Method of using a heat-sensitive melt-transfer recording medium

A heat-sensitive melt-transfer recording medium comprising a support (1) and a heat-sensitive melt-transfer ink layer (2) provided on one side thereof is disclosed. The above-mentioned heat-sensitive melt-transfer ink layer (2) comprises a colored ink layer (3) and a layer (4) which is formed on the surface of the colored ink layer (3) and which comprises a wax in the form of microcrystals as a main component, for preventing a smudge of a receiving medium is transfer recording and for obtaining a good print with a small printing energy. This recording medium is used for a heat-sensitive melt-transfer recording system using a thermal head.

TECHNICAL FIELD 
The present invention relates to a heat-sensitive melt-transfer recording 
medium. More particularly, it relates to a heat-sensitive melt-transfer 
recording medium for use in a heat-sensitive melt-transfer recording 
method using a thermal head which is adopted in a printer of a computer, a 
typewriter or the like. 
BACKGROUND ART 
Heretofore there was proposed a heat-sensitive melt-transfer recording 
medium wherein a layer of a wax in the form of film was provided on the 
surface of a heat-meltable colored ink layer to prevent the so-called 
smudge of a receiving medium, which means the phenomenon that the colored 
ink layer is transferred to areas of the receiving medium on which no 
print is to be formed, as disclosed, for instance, in Japanese Unexamined 
Patent Publication No. 59-114098 and No. 60-97888. 
In the case of the conventional medium having such two-layered 
construction, a coating amount of not less than 3 g/m.sup.2, preferably 
from 5 to 8 g/m.sup.2, for the wax layer is required to prevent the 
smudge. 
However, when such a thick wax layer is provided on the colored ink layer, 
a large quantity of printing energy is required to melt the wax layer for 
transferring. 
When the ink layer is melted with such a small quantity of energy as 
required for transferring an ink layer of a recording medium wherein no 
such surface layer is provided, there arises the problem that the ink 
layer is not transferred satisfactorily, which results in a lowering of 
the density of a print. When the printing energy is increased in order to 
solve the problem, there arises another problem that the use of a 
recording medium having a thick wax layer gives rise to blurring of a 
print, which results in an impossibility of obtaining a clear print. 
It is an object of the present invention to provide a heat-sensitive 
melt-transfer recording medium which is capable of preventing a receiving 
medium from smudging and of providing a good print with a small quantity 
of printing energy. 
DISCLOSURE OF THE INVENTION 
The present invention provides a heat-sensitive melt-transfer recording 
medium comprising a support and a heat-sensitive melt-transfer ink layer 
provided on one side thereof, said ink layer comprising a colored ink 
layer and a layer which is formed on the surface of said colored ink layer 
and which comprises a wax in the form of microcrystals as a main component 
.

In accordance with the present invention, the layer composed of a wax in 
the form of microcrystals can prevent sufficiently a smudge of a receiving 
medium, when the thickness is in the order of 0.2 to 1 g/m.sup.2. 
Accordingly, a clear print with a high density can be obtained with such a 
small quantity of printing energy as required for printing using a 
recording medium wherein no wax layer is provided. 
The heat-sensitive melt-transfer recording medium (hereinafter referred to 
as "recording medium") of the present invention comprises a support (1) 
and a heatsensitive melt-transfer ink layer (2), as shown in FIG. 1. 
As the above-mentioned support (1), there can be suitably employed resin 
films with a thickness of 2 to 10 .mu.m, including polyester film, 
polycarbonate film, polyamide film, polyimide film and polyphenylene 
sulfide film, high density papers with a thickness of 5 to 25 .mu.m, 
including condenser paper, glassine paper and india paper and cellophane 
with a thickness of 5 to 25 .mu.m. These materials are well known 
conventionally as a support for recording medium. 
The above-mentioned heat-sensitive melt-transfer ink layer (2) comprises a 
colored ink layer (3) and a layer which is provided on the surface thereof 
and which is composed of a wax in the form of microcrystals as a main 
component (hereinafter referred to as "crystalline wax layer (4)"). 
The colored ink layer (3) is formed by dispersing and mixing a coloring 
agent including pigment and/or dye, and if necessary, a softening agent 
such as oil, into a wax and/or a heat-meltable resin and applying the 
resulting mixture onto one side of the support (1) preferably in a coating 
amount (the value calculated in terms of solid content) of about 2 to 7 
g/m.sup.2. These components are known conventionally. 
The crystalline wax layer (4) is a layer formed by applying a wax in the 
form of microcrystals onto the surface of the above-mentioned colored ink 
layer (3). The preferred coating amount (the value calculated in terms of 
solid content) is from 0.1 to 2 g/m.sup.2, especially from 0.2 to 1 
g/m.sup.2. When the coating amount is too small, a smudge is apt to take 
place. When the coating amount is too large, there is a possibility to 
invite reduction of a transfer sensitivity. Accordingly both cases are 
unfavorable. 
As a method for preparing the wax in the form of microcrystals, there is 
adopted preferably a method wherein a wax is dissolved into an appropriate 
solvent by heating, and, thereafter, the resulting solution is cooled 
rapidly or a non-solvent is added to the solution to precipitate 
microcrystals. 
The thus obtained solution containing microcrystals of the wax may be used 
for coating as such. However, the use of a dispersion obtained by treating 
the solution containing the wax crystals by means of a dispersing or 
crushing apparatus such as attritor, ball mill and homogenizer to divide 
the wax crystals more finely and uniformly is more effective for 
preventing smudge to obtain a clear print. 
The size (the average particle size measured by Coulter counter method, 
hereinafter the same) of the wax crystals is preferably from 0.01 to 5 
.mu.m, more preferably from 0.1 to 4 .mu.m. When the size of the wax 
crystals is larger than the above range, the crystalline wax layer (4) is 
apt to become thick, which leads to an insufficient transfer so that a 
clear print is hardly obtained. When the size of the wax crytals is 
smaller than the above range, the crystalline wax layer (4) is apt to 
become a film-like layer and, as a result, a smudge takes place if the 
coating amount is not large. 
The thus prepared wax crystals-containing solution is applied to the 
surface of the colored ink layer (3) previously formed on the support (1) 
by an appropriate coating method, and then heated at such a temperature 
that the wax is not dissolved to remove the solvent, thereby forming a 
crystalline wax layer (4) on the colored ink layer (3). 
Any conventional coating method such as Meyer bar coating, gravure coating 
or a method using reverse coater may be used as the above-mentioned 
coating method. 
Examples of the wax used in the present invention include vegetable waxes 
such as candelilla wax, carnauba wax, rice wax and Japan wax; animal waxes 
such as bees wax, lanolin and whale wax; mineral waxes such as montan wax; 
petroleum waxes such as paraffin wax and microcrystalline wax; higher 
fatty acids such as palmitic acid, stearic acid and behenic acid; higher 
alcohols such as palmityl alcohol, stearyl alcohol and behenyl alcohol; 
higher fatty acid esters such as methyl stearate, cetyl stearate and 
myricyl palmitate; amide waxes such as stearoyl amide and palmitic acid 
amide; and synthetic waxes such as polyethylene wax, coal wax and 
Fischer-Tropsch wax. These waxes may be used singly or as admixtures 
thereof. 
Thus, the term "wax' intended in the present invention is a concept 
encompassing wax-like substances as well as normal waxes. 
For the purpose of improving an adhesiveness to the colored ink layer (3), 
etc, if necessary, a heatmeltable resin having a softening point of about 
40.degree. to 120.degree. C. may be added to the wax in an amount of 1 to 
20 parts (parts by weight, hereinafter the same) per 100 parts of the wax. 
An excessively high proportion of the heat-meltable resin is undesirable, 
because it is apt to invite the problem that microcrystals of the wax are 
not formed or the problem that the transfer sensitivity is reduced. 
Examples of the heat-meltable resin include rosins and derivatives thereof, 
polyamide resins, acrylic resins, phenolic resins, xylene resins, 
cellulosic resins, vinyl acetate resins and butyral resins. These resins 
may be used singly or as admixtures thereof. 
Moreover, for the purpose of adjusting the strength of the crystalline wax 
layer (4), if necessary, a white pigment or body pigment including silica, 
alumina, titanium oxide, zinc oxide, calcium carbonate and barium 
carbonate may be added as an additive in an amount of about 5 to 100 
parts, preferably about 5 to 20 parts, per 100 parts of the wax. An 
excessively high proportion of the additive is undesirable, because the 
problem that microcrystals of the wax are not formed or the problem that 
the crystalline wax layer (4) is too brittle is apt to occur. 
Examples of the solvent used to dissolve the wax include toluene, benzene, 
xylene, ethyl acetate, methyl ethyl ketone, tetrahydrofuran and acetone. 
These solvents are suitably selected depending upon the kind of the wax 
used. 
Examples of the non-solvent of the wax include water, alcohols (methanol, 
ethanol, isopropyl alcohol, butanol and others), ethyl acetate, n-heptane, 
n-octane, cyclohexane and dioxane. These non-solvents are suitably 
selected depending upon the kind of the wax used. 
There is a possibility that some of the abovementioned solvents become a 
non-solvent or some of the above-mentioned non-solvents become a solvent, 
depending upon the kind of the wax used. Therefore, the abovementioned 
solvents and non-solvents are merely examples. 
Generally papers are used as a receiving medium used in printing by using 
the recording medium of the present invention. Especially it has been 
found that when the recording medium of the present invention was used, a 
clear print was obtained with no smudge on a resin film for use in an 
overhead projector (hereinafter referred to as "OHP"). 
BEST MODE FOR CARRYING OUT THE INVENTION 
The present invention will be explained by referring to the following 
Examples and Comparative Examples. 
EXAMPLE 1 
The colored ink with the formulation mentioned below was applied in a 
coating amount of 3.5 g/m.sup.2 onto a polyethylene terephthalate film (1) 
having a thickness of 6 .mu.m by means of a hot-melt coater to form a 
colored ink layer (3). 
______________________________________ 
Formulation of colored ink layer 
Parts 
______________________________________ 
Paraffin wax 155 F 12 
Carnauba wax 3 
Ethylene-vinyl acetate copolymer 
2 
Carbon black 3 
______________________________________ 
Into 2 parts of toluene heated to 80.degree. C. was dissolved 1 part of an 
oxidized wax (commercial name "PO WAX H-10", made by NIPPON OIL COMPANY, 
LTD.). To the resultant was added 7 parts of isopropyl alcohol at a 
temperature higher than 50.degree. C. to give a suspension wherein 
microcrystals (size: 1.5 .mu.m) of the oxidized wax were precipitated. 
The suspension was applied onto the surface of the colored ink layer (3) by 
means of Meyer bar so that the coating amount after being dried was 0.7 g 
/m.sup.2 and then treated for 20 seconds in a hot air drier kept at 
60.degree. C. to remove the solvent substantially completely, thereby 
forming a crystalline wax layer (4). 
Employing the thus obtained sample, printing was conducted using an 
electrostatic copying paper (commercial name "Xerox M", made by FUJI XEROX 
CO., LTD.) as a receiving medium in a heat transfer printing type word 
processor WD-200 made by Sharp Corporation at a room temperature. As a 
result, the print image formed on the receiving medium showed an OD value 
of about 1.1 as measured by a Macbeth densitometer RD 514 and a clear 
print with no blurring was obtained. 
Further there were no traces that the colored ink was transferred to areas 
other than the prescribed image-bearing areas, namely no so-called smudge 
occurred. 
COMATIVE EXAMPLE 1 
Onto the surface of a colored ink layer (3) formed in the same manner as in 
Example 1 was applied PO WAX H-10 in a coating amount of 1.0 g/m.sup.2 by 
a hot-melt coating method to form a film-like wax layer on the surface of 
the colored ink layer (3). 
Employing the obtained sample, a printing test was conducted in the same 
manner as in Example 1. As a result, smudges were frequent and the density 
of the print was 0.95. 
COMATIVE EXAMPLE 2 
Onto the surface of a colored ink layer (3) formed in the same manner as in 
Example 1 was applied PO WAX H-10 in a coating amount of 3.0 g/m.sup.2 by 
a hot-melt coating method to form a film-like wax layer on the surface of 
the colored ink layer (3). 
Employing the obtained sample, a printing test was conducted in the same 
manner as in Example 1. As a result, the obtained print was pale such that 
the density thereof was 0.5, though no smudge occurred. 
EXAMPLE 2 
Onto the surface of a colored ink layer (3) formed in the same manner as in 
Example 1 was formed a crystalline wax layer (4) in the manner as 
described below. 
Into 6 parts of toluene heated to 80.degree. C. were dissolved 1 part of 
candelilla wax and 1 part of carnauba wax. While the resultant was still 
hot at a temperature higher than 50.degree. C., 12 parts of methanol was 
added thereto to obtain a suspension wherein microcrystals of the wax were 
precipitated. The suspension was subjected to a crushing treatment in an 
attritor filled with glass beads for about 30 minutes. 
The suspension (size of wax crystals: 3.6 .mu.m) thus subjected to the 
crushing treatment was applied onto the surface of the colored ink layer 
(3) by means of Meyer bar so that the coating amount after being dried was 
1.0 g/m.sup.2 and then treated for 20 seconds in a hot air drier kept at 
60.degree. C. to remove the solvent substantially completely, thereby 
forming a crystalline wax layer (4). 
Employing the thus obtained sample, a printing test was conducted in the 
same manner as in Example 1. As a result, no smudge occurred and a clear 
print having a density of 1.0 was obtained. 
EXAMPLE 3 
Onto the surface of a colored ink layer (3) formed in the same manner as in 
Example 1 was formed a crystalline wax layer (4) in the manner as 
described below. 
Into 7 parts of toluene heated to 70.degree. C. was dissolved 4 parts of 
candelilla wax. While the resultant was still hot at a temperature higher 
than 50.degree. C., 25 parts of methanol was added thereto to obtain a 
suspension wherein microcrystals (size: 2.5 .mu.m) of the wax were 
precipitated. 
To the suspension was added 4 parts of a resinous solution prepared by 
dissolving 1 part of polyvinyl alcohol (commercial name "UMR-10L", made by 
UNITIKA CHEMICAL KABUSHIKI KAISHA) into 9 parts of methanol. The resulting 
mixture was agitated for 10 minutes by means of a homogenizer. 
The suspension mixed with the resin was applied onto the surface of the 
colored ink layer (3) by means of Meyer bar so that the coating amount 
after being dried was 0.3 g/m.sup.2 and then treated for 20 seconds in a 
hot air drier kept at 60.degree. C. to remove the solvent substantially 
completely, thereby forming a crystalline wax layer (4). 
Employing the thus obtained sample, a printing test was conducted in the 
same manner as in Example 1. As a result, no smudge occurred and a clear 
print having a density of 1.1 was obtained. 
EXAMPLE 4 
Employing each of the recording media obtained in Examples 1 to 3, printing 
was conducted on an OHP film (commercial name "Xerox Film", made by FUJI 
XEROX CO., LTD.) in a printer for OHP film (No. 842 made by KYOCERA 
CORPORATION). As a result, a clear print, particularly being clear in 
parts of thin lines, was obtained and no smudge occurred. 
COMATIVE EXAMPLE 3 
Employing the recording medium obtained in Comparative Example 2, printing 
was conducted on the OHP film in the same manner as in Example 4. As a 
result, though no smudge occurred, the obtained print was unclear, 
particularly in parts of thin lines and therefore it was not fit for 
practical use. 
COMATIVE EXAMPLE 4 
A recording medium which was the same as in Example 1 except that the 
crystalline wax layer (4) was not provided on the colored ink layer (3) 
was produced. Employing the recording medium, printing was conducted on 
the OHP film in the same manner as in Example 4. As a result, the obtained 
print was unclear, particularly in parts of thin lines.