This printing apparatus and technique incorporates a color transfer station to impart a desired color to a fusible ink layer on a ribbon. The color transfer station is located between a supply reel providing the ribbon for printing, and the location where actual printing occurs. This color transfer technique is particularly suitable for use in resistive ribbon thermal transfer printing, where economical use of the ribbon is mandatory. The structure for transferring color to the ink layer of the ribbon utilizes wicks, felt-coated rollers, nozzles, etc., to bring a selected colorant solution into contact with the ink layer of the ribbon, in accordance with the color desired for printing.

DESCRIPTION 
1. Field of the Invention 
This invention relates to ribbon printing in which colors are printed, and 
more particularly to a ribbon printing system and technique wherein a 
selected color is applied to a ribbon ink layer prior to transfer of the 
ink to a receiving medium, in order to provide the selected color in a 
manner which makes economical use of the ribbon. The invention is 
particularly suited for that type of thermal transfer printing known as 
resistive ribbon thermal transfer printing. 
2. Background Art 
Thermal transfer printing is one type of non-impact printing which is 
becoming increasingly popular as a technique for producing high quality 
printed materials. Applications for this type of printing exist in 
providing low volume printing such as that used in computer terminals and 
typewriters. In this type of printing, ink is printed on the face of a 
receiving material (such as paper) whenever a fusible ink layer is brought 
into contact with the receiving surface, and is softened by a source of 
thermal energy. The thermal energy causes the ink to locally melt and 
transfer to the receiving surface. Depending upon the pattern of heat 
applied to the ink layer, a character, such as a letter or a number, is 
transferred to the receiving material. 
The thermal energy used for thermal transfer printing is supplied from 
either an electrical source or an optical source, such as a laser. When 
electrical sources are used, a thermal head can provide the heat to melt 
the ink layer. An example of a thermal head is one which consists of 
tantalum nitride thin film resistor elements, such as that described by 
Tokunaga et al, IEEE Trans. on Electron Devices, Vol. ED-27, No., page 
218, January 1980. Laser printing is known in which light from laser 
arrays is used to provide the heat for melting and transferring the ink to 
the receiving medium. However, this type of printing is not very popular 
because lasers providing sufficient power are quite expensive. 
Another type of thermal transfer printing, called resistive ribbon thermal 
transfer printing, also uses a ribbon containing a layer of fusible ink 
that is brought into contact with the receiving surface. The ribbon 
includes a layer of resistive material which is brought into contact with 
an electical power supply and selectively contacted by a thin printing 
stylus at those points opposite the receiving surface that are desired to 
be printed. When current is applied, it travels through the resistive 
layer and provides local heating in order to melt a small volume of the 
fusible ink layer. This type of printing is exemplified by U.S. Pat. No. 
3,744,611. An electrothermal printhead for use in combination with a 
resistive ribbon is shown in IBM Technical Disclosure Bulletin, Vol. 23, 
No. 9, February 1981, at page 4305. A technique for reinking a resistive 
ribbon after it has been used for printing is described by A. Aviram et 
al, in U.S. Pat. No. 4,268,368. 
Several types of resistive ribbons are known in the art, including those 
which are comprised of a support layer, or substrate, a resistive layer, a 
thin highly conductive layer serving as a current return layer, and a 
fusible ink layer. Typically, the fusible ink layer is located at one side 
of the substrate, while the resistive layer and current return layer are 
located on the other side of the substrate. In another known type of 
resistive ribbon, the resistive layer is the support substrate for the 
fusible ink layer. 
Whether it is comprised of an electrically nonconductive or conductive 
material, the support layer is flexible enough to allow the formation of 
spools or other "wrapped" packages for storing and shipping. If it is of 
the nonconductive type, it is usually comprised of a material which does 
not significantly impede the transfer of thermal energy from the resistive 
layer on one side of the support layer to the fusible ink layer on the 
other side. Polymer films are generally used for the support layer. The 
resistive layer can be comprised of many materials, but is usually 
comprised of graphite dispersed in a binder. The thin conductive layer is 
generally comprised of a metal, such as aluminum. The ink layer is 
comprised of a low melting point polymer binder and a colorant, such as a 
carbon black. Many ink compositions are described in aforementioned U.S. 
Pat. No. 4,268,368. 
Various techniques for color printing are known in the prior art. These 
techniques use a ribbon which has multiple colors thereon, a plurality of 
different colored ink rollers. An example of multi-color printing using a 
resistive layer is described by A. D. Edgar et al, IBM Technical 
Disclosure Bulletin, Vol. 23, No. 7A, page 2633, December 1980. The 
fusible ink layer 5 of this reference uses one or more 
temperature-sensitive inks and a printing temperature control in order to 
select the temperature to which the ink layer is heated. Depending upon 
the temperature, one or two colors are printed. This is a type of 
color-on-demand system which is somewhat restricted and which requires 
more extensive electrical circuitry and a more complex thermal head. 
Another type of ribbon color printing system is that represented by IBM 
Product 3287, sold by the International Business Machines Corporation. 
This is a color accent matrix printer which uses a multi-strike ribbon 
that has four regions of different colors. When the color of the printing 
has to be changed, the position of the ribbon is changed to bring the 
appropriate color portion of the ribbon beneath the printing head. This 
technique is economical when the ribbon used is of the multi-strike type, 
but the colored portions of the ribbon can be under-utilized due to the 
fact that when the black portion is used up, the entire ribbon has to be 
discarded. An alternative technique that would index each color separtely 
is not economically feasible because of the need and cost of four separate 
ribbon drives. 
Another type of thermal print system using a thermal transfer ribbon having 
a repeating series of segments of the three basic colors, yellow, magenta, 
and cyan, as well as black, is disclosed in U.S. Pat. No. 4,250,511. In 
that ribbon, the stripes are disposed perpendicular to the ribbon's 
direction of transport, and they span the whole length of print line, 
i.e., the whole print media width. The heat-applying printhead is formed 
by a series of elements arranged in a row transverse to the print media 
and ribbon transport direction. Each element is connected to a ground lead 
and to a selection lead. A control means selectively energizes the 
selected leads. The print media, usually ordinary paper, is pressed 
against the colored surface of the thermal ribbon by a page-wide roller 
whose axis is parallel to the print line. The thermal ribbon itself is 
kept against and supported by the stationary arranged printhead so that 
the print line is formed by the nip between the printhead and the vacuum 
roller. Upon printing, any one of the thermal elements may be energized to 
transfer a spot of a particular color of that color stripe being carried 
over the head. To permit the deposit of any color at a given location on 
the print media, the ribbon is advanced at a faster rate than the print 
media. 
References generally describing multicolor recording using ink rollers are 
Japanese patents 57-72873 and 57-140176, both of which are in the name of 
M. Sekido. The first of these patents uses an arrangment comprising a 
plurality of ink rollers, directing rollers, and ink supply containers on 
a concentric circumference in order to record the three primary colors at 
the same position. The second of these patents uses a plurality of ink 
supply rollers 16-18 and a cylindrical ink character body 14 having a 
plurality of ridges around its periphery. Ink of different colors can be 
fed into reservoirs located between the ink supply rollers 16-18, and then 
transferred to the ridges along the periphery of the cylindrical ink 
carrier body. 
Two techniques for reinking a thermal ribbon are descirbed by A. E. Graham 
et al, IBM Technical Disclosure Bulletin, Vol. 25, No. 11A, page 5814, 
April 1983, and W. Crooks et al, U.S. Pat. No. 4,253,775. In this patent, 
a doctor blade 9 is used for supplying ink into the depleted regions 5 of 
a used ribbon containing an ink layer 3. The resupplying ink can be a 
liquid ink having a pigment therein, as described in column 4, lines 1-3 
of this patent. 
In the prior art using ribbons for thermal transfer printing, most colored 
printing is provided by a prearranged ribbon having the ink colorants 
already in the ribbon. The use of this ribbon is often uneconomical, 
espcially when only a single color is utilized for extensive periods of 
time. While the cost of the ribbon is not a difficult problem in thermal 
transfer printing of the type using a thermal head (in contrast with 
resistive ribbon thermal transfer printing), no good technique exists for 
providing, in an economical way, any desired color at a time just prior to 
the actual printing operation. The only operation for doing this is the 
aforementioned IBM Technical Disclosure Bulletin article to A. D. Adgar et 
al using temperature sensitive inks of different colors. 
Accordingly, it is an object of this invention to provide color-on-demand 
ribbon printing which is economical and does not require the need and cost 
of multiple ribbon drives or complex thermal heads. 
It is another object of this invention to provide color-on-demand printing 
in resistive ribbon thermal transfer printing. 
It is another object of this invention to provide an improved technique for 
color printing in resistive ribbon thermal transfer printing, where the 
color printing technique is economical. 
It is another object of this invention to provide resistive ribbon thermal 
printing which allows one to select the desired color prior to the actual 
printing operation, in order to have economical use of the resistive 
ribbon. 
It is another object of this invention to provide resistive ribbon thermal 
transfer printing wherein the ribbon can be colored with a selected color 
over any desired length of the ribbon. 
It is another object of the present invention to provide a technique for 
color-on-demand printing in resistive ribbon thermal transfer printing, 
where a portion of the ribbon or the entire width of the ribbon can be 
colored with a selected color. 
It is another object of this invention to provide the ability to color any 
type of ribbon with a selected color and in a selected portion thereof, 
prior to printing. 
It is a further object of this invention to provide ribbon printing 
techniques having color-on-demand where the ribbon can be toned with a 
desired color just prior to printing in accordance with desired operator 
control. 
It is another object of this invention to provide a technqiue for 
color-on-demand resistive ribbon printing using only a single ribbon to 
provide any desired color. 
DISCLOSURE OF INVENTION 
This invention relates to a color printing method and apparatus that is 
particularly suitable for resistive ribbon thermal transfer printing, but 
which also can be used with thermal head printers. A single ribbon is used 
in which color is imparted to the ribbon just prior to printing in order 
to permit economical utilization of the ribbon without increasing the 
number of ribbon carriers. 
In this technique, a ribbon having an ink layer thereon is brought into 
contact with a color means including a transfer means containing a 
colorant that is to be added to the ink layer on the ribbon. Means are 
provided for contacting the ink layer on the ribbon with the transfer 
medium in order to transfer the colorant to the ribbon just prior to 
actual printing. In this manner, the color to be imparted is applied to 
the ribbon over an area of the ribbon correlated to the amount of color 
printing using that selected color. If printing with another color is 
subsequently desired, this other color can be imparted to the ribbon in a 
second color transfer operation. 
In selected embodiments, the transfer medium is a wick or felt-type member 
which receives the proper color solution from an adjacent reservoir of 
other source of the color. Generally, the ink layer of the ribbon includes 
all of the ink components with the exception of a colorant (for example, a 
dye or pigment). By contacting the moving ribbon and the absorbing wick or 
felt-type material, the colorant in the wick or felt is transferred to the 
ribbon ink layer. After transfer of the desired colorant to the ink layer, 
the ink layer is generally heated to remove any residual solvents from the 
colorant solution. Of course, the ink layer could initially be black, or 
another color, and then have its color altered by this technique. 
These and other objects, features, and advantages will be apparent from the 
following more particular description of the preferred embodiments.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows a conventional type of printing apparatus using a ribbon 10 
for printing onto a receiving medium, such as paper 12 which is supported 
by platen 14. Ribbon 10 starts at a supply reel 16 and wraps around a 
printhead 18 which is mounted on a carrier 20 that is exaggerated in size. 
Movement of carrier 20 to provide relative printing motion is guided by a 
rail 22 and controlled by a lead screw 24, as is known in the art. 
Ribbon 10 is threaded past a current collection means 26 and is wrapped 
around a guide roller 28. From the guide roller 28, the ribbon 10 is 
directed to the takeup reel 30. In this embodiment, current contacting 
means 26 is a pair of metal roller brushes 32 that are cylindrical in 
form, such as the type of brushes known for cleaning rifles. Pressure to 
assure good contact is applied by an opposing pressure pad 34. It should 
be noted that guide means such as guide roller 28 serves to wrap the 
ribbon 10 around the printhead 18 to permit convenient access to the 
surface of ribbon 10 defined by the ink layer of the ribbon which is in 
contact with the paper 12. This type of apparatus is described more 
particularly in aforementioned U.S. Pat. No. 4,329,071. 
In operation, electrical printing currents are selectively supplied by 
printing electrode driver 36 via the signal channels 38 to the printhead 
18. These currents enter the resistive layer of the ribbon 10 and tend to 
pass directly to the conducting layer of the ribbon. From the conducting 
layer of the ribbon, these currents are collected at least in part by the 
contacting means 26. To assure a current path for startup when no bare 
areas of the conducting layer of the ribbon may be present, some 
conducting material, such as carbon, may be provided in the ink layer of 
the ribbon or an alternate path may be provided using the pressure means 
34 with a separate connection 40 to ground. With the connection 40, the 
current divides between the contacting means 26 and pressure means 34, 
providing an even lower impedance return path. It is also possible to 
provide a section at the bginning of the ribbon 10 that does not have the 
ink layer on it, so that access may be had to the conducting layer for 
startup. 
While the ribbon 10 has been described in the preceding paragraphs as being 
a resistive ribbon used for resistive ribbon thermal transfer printing, it 
will be understood that the ribbon can be the type used for printing 
wherein heat to melt the fusible ink layer is provided by a thermal head, 
rather than by current flow through the ribbon. However, the primary 
application of the present invention is in resistive ribbon thermal 
transfer printing, where no good technique exists for providing 
color-on-demand printing. 
In the printing apparatus of FIG. 1, a color-on-demand apparatus means 42 
is provided. This apparatus is the means by which a desired color is 
imparted to ribbon 10, just prior to the printing (ink transfer) 
operation. Thus, coloring means 42 is located between the supply reel 16 
and the printhead 18. 
FIG. 2 is an expanded view of a portion of the apparatus of FIG. 1, and in 
particular illustrates the printing operation. In FIG. 2, the current 
return path utilizes a contacting means 44 which is different than the 
contacting means 26 of FIG. 1. Contacting means 44 is comprised of a 
conductive roller 46 and a pressure roller 48. Contacting roller 46 can be 
comprised of an electrically conducting rubber that deforms under pressure 
from the opposing roller 48 in order to enter voids in the ink layer of 
the ribbon. 
The ribbon 10 in this embodiment is comprised of three layers: an outer ink 
transfer layer 49, a resistive layer 50 having a moderate resistance 
(e.g., 200-1000 ohms/sq., and an intermediate contacting layer 52. This 
type of ribbon is well known in the art, and is used in cooperation with a 
printhead 18, comprising a set of electrodes 54, where the printhead 18 
includes clamping blocks 56 between which an insulating pad 58 and the set 
of electrodes 54 are pressed. The printing current flow is indicated by 
the arrows 60. During printing the electrodes 54 swipe across the ribbon 
10 which is pressed against the paper surface 12 supported by platen 14. 
Current enters the ribbon through resistive layer 52 and tends to flow 
directly to the conducting layer 50 which is greatly exaggerated in 
thickness in this figure. At least a portion of the current is collected 
for return by direct contact with the conductive layer 50 through the ink 
layer side of the ribbon 10. This direct contact enables the conducting 
roller 46 to enter voids 62 in the printing ribbon in order to establish 
electrical contact with the conductive layer 50. While it is not shown in 
FIG. 2, a return path connection from roller 46 to the current source (not 
shown) is also provided. 
FIG. 3 represents one embodiment for the coloring means 42 which was 
schematically illustrated in FIG. 1. In order to relate FIG. 3 to the more 
complete apparatus of FIG. 1, the same reference numerals are used for the 
ribbon 10, paper 12, and printing head 18. 
In more detail, color means 42 is comprised of a carousel-like device 64 
which includes a plurality of colorant reservoirs B, R, M, and C 
containing solutions of the colors black, red, magenta and cyan, 
respectively. Wicks 66 are located in each of the reservoirs to absorb the 
colorant solution therein for later transfer to the ink layer of ribbon 
10. Carousel device 64 is rotatable in the direction of the arrow 67 to 
bring a wick 66 associated with a selected color to a location which is 
opposite the pressure roller 68 which is connected to the actuator 70. 
Depending upon the presence of an electrical control signal on conductor 
72, actuator 70 is used to move the pressure roller 68 into contact with 
the back of ribbon 10. This deflects the ribbon into contact with the wick 
66 that has been brought to a position on the ink side of ribbon 10 
directly opposite the pressure roller 68. The color from the associated 
colorant reservoir will be transferred to the ink layer of ribbon 10 by 
the contact of the wick 66 and the ink layer. Any length of ribbon 10 can 
be colored with the selected color, depending upon the signal provided by 
the control circuit 74 to the motor 84 (FIG. 4) attached to the carousel 
device 64. The signal for movement of carousel device 64 is provided along 
conductor 76. 
After the ribbon 10 is toned by the addition of a colorant thereto, it 
passes a heater fan 78 which has a duct 80 attached thereto. Fan 78 
provides a flow of heated air through duct 80 onto the color-toned ink 
layer of ribbon 10, in order to remove any residual solvents resulting 
from the color-adding operation. 
FIG. 4 presents more detail of a portion of the apparatus of FIG. 3, and 
particularly shows the carousel device 64 and the wicks 66. Carousel 64 is 
attached to a shaft 82 which in turn is connected to a motor 84, only a 
portion of which is shown. This motor could be, for example, a stepping 
motor of any type well known in the art which advances a set amount in 
response to a control signal. 
FIGS. 5-8 
These figures illustrate another embodiment for the color means 42, and in 
particular another type of device for transferring a colorant solution to 
the ribbon 10. 
In more detail, FIGS. 5 and 6 are top and side views, respectively, of a 
carousel-type of device 88 that is used to house containers 90 having the 
colorant solution therein. Each container 90 has a bottom portion 92 and a 
top lid 94 which is used to prevent evaporation of the colorant solution 
at those times when that particular color is not being transferred to the 
ribbon. Each of the containers 90 is located in a recessed portion 96 of 
the carousel 88 and includes a roller 98 having a felt-like coating 
thereon which absorbs the colorant solution. The rollers 98 are attached 
to carousel 88 in such a manner in that they can rotate easily when 
contacted by the ribbon 10. For example, roller 98 can be bearing-mounted 
in the carousel 88. During transfer of color from the felt layer on roller 
98 to the ribbon 10, there will be substantially zero relative velocity 
between the roller 98 and the ribbon 10. 
As will be more apparent from FIG. 8, each of the lids 94 of the containers 
is attached to a shaft 100, which causes the lid 94 to be raised or 
lowered into contact with the bottom portion 92 of the containers. This 
prevents evaporation of the coloring solution in the containers. Carousel 
88 is connected to a motor (FIG. 8) via a shaft 102. This allows the 
carousel to be stepped in the direction of arrow 104, in accordance with 
the color which is desired to be imparted to the ribbon. 
As mentioned previously, container lid 94 keeps the container closed at 
those times when the colorant solution in the associated reservoir is not 
needed. In order to accomplish this, means is provided for raising and 
lowering the container lids 94, This is shown more clearly in FIG. 8, 
while FIG. 7 illustrates the timing sequence that is followed as the 
carousel 88 rotates. Referring to FIG. 8, the same reference numerals are 
used whenever possible to coordinate FIGS. 5-8. Accordingly, container 
lids 94 are raised and lowered by the attached shafts 100, which are 
connected to rollers 106 that follow a cam track 108 defined by the upper 
and lower can surfaces 100 and 112, respectively. Movement of carousel 88 
is by the stepping motor 114, which is attached to carousel 88 by shaft 
102. 
In FIG. 8, only two colorant solution containers are shown for ease of 
illustration. For the left-most container of this figure, lid 94 is raised 
to be out of contact with the lower half 92 of the container. This exposes 
the felt layer on roller 98 so that it can be contacted by the ribbon 10 
in order to tranfer colorant solution from container portion 92 to the 
ribbon 10. Since the other container in this figure is not being used for 
the color transfer operation, lid 94 is in contact with the bottom portion 
92 of the container. This occurs when the attached wheel 106 is in a lower 
portion of the cam track 108. 
FIG. 7 illustrates the movement of wheels 106 along the cam track 108 as 
the carousel 88 rotates. During most of the rotation of carousel 88, a 
wheel 106 attached to any container lid 94 will be in a position of low 
dwell in the cam track and will maintain the associated container closed. 
Just prior to the movement of this container to a position where color 
transfer will occur, the container lid 94 will begin to rise to a position 
of high dwell. This position can be adjusted for any length of time in 
accordance with the control provided to the stepping motor 114. When the 
container lid 94 is moved away from lower container portion 92, the roller 
98 will be exposed and can be contacted by the ribbon 10. After the color 
transfer is complete, carousel 88 will rotate and wheel 106 will begin to 
move downwardly along track 108 to provide the "fall" portion of the 
cycle. 
As an example, color toning in accordance with the present invention has 
been achieved in an ink layer of 5 microns thick of Macromelt 6203 (a 
trademark of Henkel Co.). This ink layer was subsequently toned with color 
marker ink made by Rowe Company and used in printing experiments on a 
resistive ribbon thermal transfer printer. To improve the color spreading, 
micron size particles of TiO.sub.2 were incorporated in the clear ink 
layer on the ribbon. The color of the film became white with the addition 
of these particles and was sandy. The rough surface of the ink layer was 
receptive to coloration and provided even coatings. The original white 
appearance of the ink layer did nothing to alter the good color printing 
results that were obtained. Another suitable roughening particle that can 
be added to the ink layer is silica. 
The need for a roughening (matting) agent to insure uniform coloration of 
the ink layer in the ribbon is more necessary with the type of color means 
42 shown in FIGS. 3 and 4. This is because of the "smearing" action that 
exists in the moving ribbon and the relatively stationary wick 66 which 
contacts it in order to transfer color to the ribbon. However, in the 
embodiment of FIGS. 5-8, wherein a cylindrical, rotatable roller 98 is 
used, it is not necessary to add a matting additive to the uncolored ink 
layer on the ribbon. Uniform coloration results when the cylindrical 
roller is free to rotate when contacted with the moving ribbon wherein 
essentially zero velocity exists between the ribbon and the roller 98. 
Coloration of the ink may be applied a line at a time or in short sections 
as required during printing. For example, when a printer is to operate in 
a typewriter mode, there is considerable start-stop operation. Color 
toning of the ribbon can occur when the carriage is returning. In this 
way, the ribbon will be toned with the proper color for printing of the 
next line on the paper. On the other hand, when the printer is operating 
in a conventional printing mode, the ribbon moves at generally constant 
velocity. It is easier to uniformly color the ribbon when it moves at a 
constant velocity. 
Multicolors within a line can also be achieved with this tyep of color 
transfer. For example, when a printer is operating in a typewriter mode, 
different colors can be applied to the ribbon during the carriage return. 
Also, several passes over a line may be made to superimpose colors in 
order to obtain a wider range of colors than those supplied by the inking 
station (comprised of the ink reservoirs and transfer media). For example, 
a new color can be added to the same portion of the ribbon during separate 
carriage returns, there being no printing until all of the colors have 
been added to the same portion of the ribbon. In this operation, the 
ribbon would be moved to the same starting point each time. As an 
alternative, multiple transfer media can contact the ribbon at the same 
time. 
In the practice of this invention, the good erasure properties inherent in 
resistive ribbon thermal transfer printing are not altered, and all other 
features of this type of printing can be maintained. 
While the invention has been described with respect to specific embodiments 
thereof, it will be apparent to those of skill in the art that variations 
can be made therein without departing from the spirit and scope of the 
present invention. For example, other techniques for applying the colorant 
solution to the ribbon can be undertaken, and the color applying means can 
use multiple wicks, etc. which contact the ribbon at the same time. 
Further, it is also within the scope of this invention to provide a 
nozzle-type of apparatus for uniformly applying the colorant solution to 
the ribbon, just prior to actual printing.