HOT MELT INKS FOR COLORED INK JET IMAGES

ENCRES THERMOFUSIBLES POUR LA REALISATION D'IMAGES AU JET D'ENCRE COLOREE

English Abstract

Black Ink for Ink Jet Systems
Abstract
In the particular embodiments described in the
specification, a black ink for an ink jet system con-
tains a vehicle which is sol d at room temperature and
may be liquefied at elevated temperature together with
1% to 10% black pigment and 0.1% to 3.0% of a dye
which, together with the color of the ink vehicle,
produces a black appearance.

Claims

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Claims
1. A black ink for an ink jet system comprising a
vehicle which is solid at room temperature and
may be liquefied at elevated temperature, from
about 1% to about 10% by weight of a black pig-
ment dispersed in the vehicle, and from about
0.1% to about 3.0% of a dye which is soluble in
the vehicle and which, together with any color in
the vehicle, produces a black appearance.
2. A black ink in accordance with Claim 1 containing
from about 3% to about 5% black pigment.
3. A black ink in accordance with Claim 1 containing
from about 1% to about 2% soluble dye.

Description

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Description
Black Ink for Ink Jet Systems
Technical Field
This invention relates to black inks for use in
ink jet systems and, more particularly, to a new and
improved black ink for ink jet systems.
Backqround Art
Many ink jet systems utilize black inks contain-
ing a dye which is soluble in the ink vehicle. Such
dyes, however, which are usually based on organic
compounds, tend to lack long-term stability and may be
degraded by extensive exposure to heat and light.
Moreover, such dyes, when used in hot melt ink sys-
tems, tend to produce perceptible offset from a
printed page onto the hand of a user, for example.
To overcome such problems, black inks for ink jet
systems have been formulated with a finely dispersed
pigment such as carbon black which does not degrade in
response to environmental conditions or tend to pro-
duce offset. It has recently been found, however,that, when hot melt ink drops are caused to spread
after application by maintaining them above the melt-
ing point to reduce the contact angle, as described,
for example, in the Fulton et al. Patent No.
4,873,134, the concentration of black pigment in the
periphery of the drop is decreased so that a projected
image of the drop takes on the color of the ink ve-
hicle which may be brown, rather than appearing black.
Disclosure of Invention
Accordingly, it is an object of the present in-
vention to provide a new and improved black ink for
ink jet systems which overcomes the above-mentioned
disadvantages of the prior art.
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Another object of the invention is to provide a
black ink for ink jet systems in which the thin edges
of a drop which has been spread upon a substrate are
projected as substantially black.
These and other objects of the invention are
attained by providing a hot melt ink comprising a
vehicle which is solid at room temperature and may be
liquefied by heating for projection in drop form onto
a substrate, a black pigment uniformly dispersed in
the vehicle, and a dye which is soluble in the vehicle
and causes the thin layers of the vehicle to be pro-
jected as black.
Further objects and advantages of the invention
will be apparent from a reading of the following de-
scription of preferred embodiments.
Best Mode for Carryinq Out the Invention
During the application of hot melt ink to atransparent substrate, as described in the Fulton et
al. Patent No. 4,873,134, the ink drops tend to solid-
ify with a hemispherical shape which refracts lightfrom a projection system, preventing good color rendi-
tion in the projected image. As described in the
Fulton et al. patent, this problem can be overcome by
maintaining the ink at a temperature above its melting
point until the drops have spread to provide a reduced
contact angle with the surface of the transparent sub-
strate. Surprisingly, however, the ink vehicle
spreads during such spreading at a rate which is more
rapid than the rate of diffusion of a pigment such as
carbon black into the periphery of the drop. As a
result, when the enlarged drop is solidified, the
peripheral region is significantly depleted of black
pigment, whereas the central portion retains black
pigment to appear opaque in transmission. As a re-
sult, the projected enlarged drops have an opaquecentral region with a peripheral region which projects
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essentially the inherent color of the ink vehicle
rather than that of the black pigment.
In ord~r to overcome this problem in accordance
with the invention, a pigmented black ink is provided
which includes from about 0.1% to about 3.0%, and
preferably from about 1~ to about 2~ by weight, of a
dye which is soluble in the ink vehicle. Preferably,
the dye is a conventional black dye such as Calco
nigrosine, but it may also be a colored dye which, in
combination with the inherent color of the ink ve-
hicle, absorbs all colors uniformly so as to appear
substantially black.
The hot melt ink includes a transparent carrier
of any conventional type, such as a wax or wax-based
system, and 1~ to 10%, and preferably 3~ to 5~, of
finely divided black pigment such as carbon black
dispersed therein, along with 0.1% to 3.0%, and pref-
erably 1~ to 2~, of a black dye, such as Calco nigro--
sine black, which is soluble in the ink vehicle.
In a preferred embodiment, the ink vehicle con-
tains about 4% carbon black and about 1~ Calco nigro-
sine black.
If the ink vehicle is yellow or brown in tone, a
blue dye, such as Neozapon blue-807, Orient oil blue-
603 or Shimado oil blue SB, may be used. If the ink
vehicle is gray or blue in tone, a red or magenta dye
such as oil scarlet may be used.
With a black ink prepared in accordance with the
invention, ink drops can be caused to spread on a
substrate by maintaining them above the melting point
of the ink for a selected time to reduce the contact
angle of the drop without resulting in a loss of
opacity or color change in the peripheral regions of
the drop.
Although the invention has been described herein
with reference to specific embodiments, many modifica-
tions and variations therein will readily occur to
those skilled in the art. Accordingly, all such vari-

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ations and modifications are included within the in-
tended scope of the invention.
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