Note: Descriptions are shown in the official language in which they were submitted.
DESCRIPTION ~ 3 2
HEAT-SENSITIVE MELT-TRANSFER
RECORDING MEDIUM
~ECHNICAL FIELD
The present invention relates to a heat-
sensitive melt-transfer recording medium. More particu-
larly, it relates to a heat-sensitive melt-transfer re-
cording medium for use in a heat-sensitive melt-transfer
recording method using a thermal head which is adopted in
a prlnter of a computer, a typewriter or the like. The
invention also provides a method for making such a medium.
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. ~0-97888.
In the case of the conventional medium having
such two-layered construction, a coating amount of not less
than 3 g/m2, preferably from 5 to 8 gim2, for the wax layer
is required to prevent the smudge.
~owever, when such a thick wax layer ls 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
"~.
- 2 ~ J rJ '~
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 pro-
vide 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 IN~ENTION
The present invention provides a heat-sensitive
melt-transfer recording medium comprising a support and a
heat-sensitlve 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 microcrys-
tals as a main component. A novel method oE making such a
medium is also dlsclosed.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a partial cross-section showing an
- embodiment of the heat-sensitive melt-transfer recording
medium of the present invention.
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/m2. Accord-
ingly, a clear print with a high density can be obtained
with such a small guantity 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 heat-
sensitive melt-transfer ink layer (2), as shown in Fig. 1.
As the above-mentioned support (1), there can
~3
-- 3
be suitably employed resin films with a thickness of 2 to
10 Um, including polyester Eilm, polycarbonate film,
polyamide film, polyimide film and polyphenylene sulfide
film, high density papers with a thickness of 5 to 25 ~m,
including condenser paper, glassine paper and india paper
and cellophane with a thickness of 5 to 25 um. 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 oE 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 . 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/m2, especially
from 0.2 to 1 g/m2. 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.
-- 4
~he thus obtained suspension containing micro-
crystals of the wax may be used for coating as such. How-
ever, the use of a dispersion obtained by treating the
suspension containing the wax crystals by means of a dis-
persing or crushing apparatus such as attritor, ball mill
and homogenizer to divide the wax crystals more finely and
uniEormly 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 ~m, more preferably
from 0.1 to 4 ~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 crystals 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 sus-
pension 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 (or melted) 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 in-
vention include vegetable waxes such as candelilla wax,
carnauba wax, rice wax and Japan waxi anima] 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
-- 5
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 heat-
meltable resin having a softening point of about 40 to
120C 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 resinsO 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 bariurn 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
- 6
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 dloxane. These non-solvents are suitably
selected depending upon the kind of the wax used.
There is a possibility that some of the above-
mentioned solvents become a non-solvent or some of the
above-mentloned non-solvents become a solvent, depending
upon the kind of the wax used. Therefore, the above-
mentioned 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.
Exam~le 1
The colored ink with the formulation mentioned
i below was applied in a coating amount of 3.5 g/m2 onto a
polyethylene terephthalate film ~1) having a thickness of
6 ~m by means of a hot-melt coater to form a colored ink
layer (3).
Formulation of colored ink layerParts
Paraffin wax 155 F 12
Carnauba wax 3
Ethylene-vinyl acetate copolymer 2
Carbon black 3
.
.'3L 7-)~
-- 7
Into 2 parts of toluene heated to 80C was
dissolved 1 part of an oxidized wax (zommercial name "Po
WAX H-10", made by NIPPON OIL COMPANY, LTD. ) . To the
resultant was added 7 parts of isopropyl alcohol at a
temperature hisher than 50C to give a suspension
wherein microcrystals (size: 1.5 ~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 ~m2 and
then treated for 20 seconds in a ho~ air drier kept at
60C 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
~easured by a Macbeth densitometer R~ 514 and a clear
print with no blurring was obtai~ed.
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.
Comparative Example l
Onto the surface of a coloxed ink layer (3)
formed in the same manner as in Example ~ was applied PO
30 WAX H-10 in a coating amount of 1.0 g/m2 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.
, , ~ ~
~ . * Trade-mark
- 8 -
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/m2 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 80C were
dissolved 1 part of candelilla wax and 1 part of carnauba
wax. While the resultant was still hot at a temperature
higher than 50C, 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 ~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/m2 and then treated for 20 seconds in a hot air
drier kept at 60C 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.
- 35
Example 3
Onto the surface o~ a colored ink layer ~3)
formed in the same manner as in Example 1 was formed a
- 9
crystalline wax layer (4) in the manner as described
below.
Into 7 parts of toluene heated to 70C was
dissolved 4 parts of candelilla wax. While the resultant
was still hot at a temperature higher than 50C, 25 parts
o~ methanol was added thereto to obtain a suspension
wherein microcxystals (size: 2.5 ~m) o~ 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-lOL", 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 a~ter being dried
was 0.3 g/m and then treated for 20 seconds in a hot air
drier kept at 60C 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 Filmi', made by FUJI XERO~ CO.,
LTD.) in a printer for OHP ~ilm (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.
Comparative Exa~ple_3
Employing the recording medium obtained in
Comparative Example 2, printing was conducted on the O~P
film in the same manner as in Example ~. As a result,
~ ~ ~d r~ ~ V
-- 10
though no smudge occurred, the obtained print was
unclear, particularly in parts of thin lines and
`therefore it was not fit for practical use.
Comparative 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 lin~s.
