Note: Descriptions are shown in the official language in which they were submitted.
11350S,~
1 TRANSFER LAYER FOR RESISTIVE RIBBON PRINTING
The present invention relates to ribbons for use in
electrothermic printing. More particularly, the inven-
tion is concerned with a transfer layer for such a
ribbon.
U.S. patents 2,713,822 and 3 r 744,611 are illustra-
tive of the prior art of non-impact, electrothermic
printing employing ribbons containing transfer coatings
and substrates. Electrothermic printing ribbons are,
per se, well known in the art and are shown, for example
in U.S. patents 3,744,611 and 3,989,131. In particular,
U.S. patent 3,989,131 mentions transfer layers formed
from styrene resins and/or terpene resins and epoxy
resins. It also mentions ketonic resins, ethers of
colophony and non-drying alkyd resins. (It is noted that
colophony is another name for rosin.) Polyamides,
phenol-formaldehyde resins, and ethylene-vinyl acetate
copolymers have also been found useful in transfer
layers. However, the prior art appears to contain no
suggestion of the use of glycerol ester of hydrogenated
rosin for this purpose.
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1 It has now been found that superior electrothermic
printing may be obtained using a ribbon comprising an
electrically conductive substrate and a transfer layer
which comprises coloring material and glycerol ester of
hydrogenated rosin. For reasons which are not understood,
the presence of glycerol ester of hydrogenated rosin makes
the resulting printing capable of finer resolution than
previously obtained, and also has the additional advantage
of being more readily correctable. Furthermore, the
glycerol ester of hydrogenated rosin has less tendency
to adhere to the electrically conductive substrate and,
therefore, transfers more easily than previously known
transfer layers.
When glycerol ester of hydrogenated rosin is used in
the transfer layer, the resulting printing sticks to
the paper so that it does not smear. The printing,
however, may be removed by lift-off or abrasive methods
more readily than previously obtained printing. This
totally unexpected advantage makes correction of the
printed product much easier than was previously the case.
As is well known in the art, a ribbon for thermo-
electric transfer printing comprises an electrically con-
ductive substrate. This, conveniently, may be a layer
of polycarbonate which has been made electrically con-
ductive by the inclusion of small particles of carbon.
This polycarbonate-carbon may, when desired, be coated
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1 with a layer of aluminum which is from about 1,000 to about
1,500 A units thick. The transfer layer is placed on top
of this conductive substrate. The transfer layer comprises
one or more colored materials. The coloring materials
most often employed are carbon black and various dyes
which may be used alone or in combination with each other.
In general, in the transfer layer of the present
invention, it is desirable that the ratio by weight of
colored material to glycerol ester of hydrogenated rosin
be from approximately 2~ to approximately 50~, preferably
about 10%.
The transfer layer of the present invention is most
conveniently applied to the conductive substrate from
solution, for example, by means of a meniscus coater. It
has been found that the coating properties of glycerol
ester of hydrogenated rosin are improved when there is added
to the coating mixture some ethyl cellulose. Ethyl
cellulose is usually added in an amount from about 5% to
about 10% by weight of glycerol ester of hydrogenated rosin.
EXAMPLE 1
A substrate was prepared of 70% by weight of poly-
carbonate resin and 30% conductive carbon dispersed therein.
This layer was metallized with approximately 1200 A units
of aluminum. A solution was prepared of 20 grams of
STAYBELITE ester 5, 1. 8 grams carbon black and 0.1 grams
of methyl violet in 80 grams of isopropyl alcohol.
(STAYBELITE is the trademark of Hercules, Inc. for their
brand of glycerol ester of
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partially hydrogenated wood rosin. It is a pale,
medium-hard, thermoplastic resin with resistance to
oxidation and discoloration. It has a low odor and a
low acid number.) The above solution, with the carbon
in suspension, was applied to the aluminized layer by
means of a meniscus coater. The ink layer, after drying,
was determined to be 12 microns thick. The resistive
ribbon was used in writing in an electrothermic print-
ing apparatus. At a current level of 55-60 milliamps,
excellent quality images were obtained; density and image
sharpness were a very high order. Furthermore, even
though the resulting printing was smear free, it was
possible to remove it by lift-off and by abrasion
methods.
EXAMPLE 2
Another resistive ribbon film was prepared by
coating an ink transfèr layer of the following formu-
lation on a metallized polycarbonate-carbon resistive
layer:
1.60 grams Regal~330 carbon (Cabot Corp)
1.15 grams ethyl cellulose (20Cps)
0.09 grams methyl violet
40.0 grams isopropyl alcohol.
The above was placed in an 8 oz. bottle with 200 grams
of steel balls and was mixed on a paint shaker for 45
minutes.
The mixture was allowed to cool and 17.25 grams
of Staybelite~ester 5 with 40 grams of isopropyl alcohol
was added. The mixture was again placed on a paint
shaker for an additional 45 minutes.
After cooling, the mixture was applied on a metal-
lized resistive layer by means of a meniscus coater so
that the final dry thickness was approximately 2-4
microns thick.
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The resultant resistive ribbon was used to print
high quality images with good release properties, i.e.,
the ribbon did not stick to the paper upon transfer of
the ink.
The ink must be easily released from the ribbon to
the paper during the printing step or the ink will act
as a "glue" between the paper and ribbon, preventing
separa.ion of the ribbon from the paper. The ink layer
with Staybelite ester 5 as a thermoplastic resin is
easily released from the metalli~ed resistive layer.
The images were of good resolution.
EXAMPLE 3
In another example, a ribbon was made as in
Example 2, except 0.86 grams ethyl cellulose was used
instead of 1.15 grams. The print was formed at 480 x 480
PEL (Picture Elements). In both cases the images were
non-smear with print densities of about l.0 optical
density when printed with a voltage of about 12 volts
and a current of about 50 milliamps.
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