Apparatus and method for thermographic printing

A thermographic printing apparatus, and method for thermographic printing, including a header assembly having at least two rollers for transporting a substrate having first and second sides, two edges, and powder adhering liquid on the first side thereof through the apparatus, wherein the rollers contact the substrate on the second side thereof, at least two disks each having an edge for transferring the substrate between each roller and the disks, wherein the disks position the substrate adjacent the edge thereof to provide at least one substantially contained area within the disks and substrate, and a powder supply for providing powder particles into the at least one contained area for application to the first side of the substrate, whereby an amount of the particles provided into the contained areas adheres to the powder adhering liquid on the substrate.

FIELD OF THE INVENTION 
The invention relates to an apparatus and method for high speed 
thermographic printing on a substrate, where the apparatus has a plurality 
of cylindrical disks having holes therein which emit jets of gas to float 
a web of printing substrate thereon to facilitate the scattering and 
deposition of thermographic powder on the substrate prior to heating and 
setting of the powder. 
BACKGROUND OF THE INVENTION 
Many printers have discovered that thermography can add another dimension 
to their business. Thermography today is no longer just for stationery, 
business cards and announcements, but has emerged as an art form in its 
own right. Used on its own, or as an adjunct to lithography, foil 
stamping, embossing and silk screening, it has become an extremely useful 
tool for graphic designers and artists. Other applications include 
greeting cards, labels, tags, annual reports, report covers, packaging and 
posters. 
Thermography is an established procedure whereby raised printing that 
imitates copper plate engraving or stamping from any type of printing 
process is more easily accomplished using an offset or other conventional 
printing process. Printed sheets from a conventional printing press drop 
onto a conveyer where a resin or powder, having the characteristic of 
melting under the effect of heat, is vibrated onto them. Excess powder may 
be continuously removed by vacuum suction or by hand and recycled, except 
where the powder has adhered to the wet ink. The printed and powdered 
sheet then typically passes through a tunnel-type oven, where it is heated 
to melt and fuse the powder grains into a raised film. At the exit, cold 
air is blown onto the sheet to cool and set the viscous raised film so as 
to prevent sheets from sticking together or smearing. Two examples of such 
thermographic printing procedures are U.S. Pat. Nos. 5,699,743 and 
5,098,739. 
It is known in the art that the granule size of the powder used in part 
determines the thickness of the relief film, or raised print, up to a 
certain maximum height. Larger powder granules are used to obtain greater 
heights of raised print. Thermographic raised print on the order of 0.01 
inches in height may be obtained according to the methods taught by U.S. 
Pat. No. 5,699,743 by printing an ink line about 1/16 to 1/8 inch in 
width, depositing 20 to 50 mesh powder thereon, and heating at the 
appropriate time and temperature to fuse the powder without completely 
melting it. Generally, smaller particle sizes of powder are used when 
lesser heights of the raised print are desired. 
There are two distinct types of thermographic powder generally used: 
transparent and opaque. Transparent powders generally include high gloss, 
semi-gloss, and semi-dull. Opaque powders typically include metallics, 
such as gold, silver, and bronze; white; and the relatively new pearlized 
powder. High gloss is the most commonly used powder for all thermographic 
applications. 
There are five conventional granulations for use on lines ranging in 
thickness from "fine line" to "heavy solids." Fine lines require the 
finest granulation typically described as fine as flour, while heavy 
solids require a coarser granulation typically described as loose as 
sugar. Semi-gloss, dull and semi-dull powders are primarily selected by 
designers looking for special effects. They generally provide less shine 
than the high gloss powders, but retain a similar "feel" and raise. The 
metallic and white opaque powders, on the other hand, are typically 
difficult to work with. Thus, thermography shops generally run only high 
gloss powders. 
Thermographic printing has typically been achieved by printing wet ink on a 
substrate using flat conveying devices to move the printing substrates 
(e.g., sheets of paper) under a hopper that drops powder thereon. 
Conventional thermographic printing over the last 100 years or so has 
typically only been able to achieve printing speeds of 60-70 ft/min. and 
occasionally as high as 100 ft/min., although it is unclear if this speed 
can be maintained on a continuous basis. Moreover, the thermographically 
printable area has been limited to approximately 12 inches in width. 
Reports have been made of printable widths on the order of up to 20 
inches. Offset and other types of conventional printing often have used a 
cylindrical printing apparatus that may permit higher printing speeds. The 
apparatuses used in several conventional flat printing and flat color 
printing on paper and fabrics are described as follows. 
U.S. Pat. No. 537,923 discloses an apparatus for producing designs on paper 
having a stencil sheet cut with the pattern of the desired design, 
vessel(s) for holding and delivering the inks or colors, and a blast 
apparatus for delivering the inks or colors through the stencil sheet to 
come into contact with the paper or other surface upon which the design is 
desired. 
U.S. Pat. No. 2,049,495 discloses a printing apparatus for continuously 
replenishing a supply of ink to a material which is to be imprinted. The 
ink supply is provided from within a cellular cylinder to fill the pattern 
running along the sealing surface of the cylinder. 
U.S. Pat. No. 2,334,909 discloses a press roller to print on fabric at 
relatively high speeds by supplying ink of different colors to the 
interior side of a stencil, which has openings through which the ink 
passes to print on the fabric. Also disclosed is an ink or color holder in 
contact with the stencil that permits the loader to be filled externally 
from the press and swung into the color holder without the need to stop 
the press. 
U.S. Pat. No. 3,613,635 discloses a spot printing apparatus for printing a 
powder onto a substrate including a perforated hollow roller, means for 
rotating the roller, and a hopper means within the roller for holding the 
powder. The perforated hollow roller has a discontinuous pattern of holes 
for depositing the dry powder. 
U.S. Pat. No. 5,713,275 discloses a stencil printing machine having a 
holding device for holding the perforated stencil sheet, an ink supply 
device, a printing sheet conveying device, and an air ejection means for 
ejecting air to the stencil sheet from within and causing the ink to pass 
through the image on the stencil sheet and transfer to the printing sheet. 
These conventional printing devices are generally directed to printing flat 
patterns or text on fabrics or paper. It was believed that cylindrical 
rollers were not suitable for the powdering stage of thermographic 
printing for various reasons, e.g., loose powder on the substrate would be 
more likely to smear. As thermographic printing has gained commercial 
success in various printing endeavors, however, it has become desired to 
improve the efficiency and quality of thermographic printed products. 
Thus, it is desired to have an apparatus capable of providing a 
thermographic printed product that is capable of high speed use and has 
multiple colors on different parts of the product while still maintaining 
the high quality achieved by conventional thermographic printing. 
SUMMARY OF THE INVENTION 
The present invention relates to a thermographic printing apparatus having 
a header assembly having at least two rollers for transporting through the 
apparatus a substrate having first and second sides, two edges, and a 
powder adhering liquid located on the first side thereof, wherein the 
rollers contact the substrate on the second side thereof, at least two 
disks each having an edge for transferring the substrate between the 
rollers, wherein the disks position the substrate adjacent the edge 
thereof to provide at least one substantially contained area between the 
disks and substrate, and a powder supply for providing powder particles 
into at least one contained area for application to the first side of the 
substrate, whereby an amount of the particles provided into the contained 
areas adheres to the liquid on the substrate. 
In one embodiment, the apparatus further includes a gas supply in the 
header assembly directed at the first side of the substrate for removing 
excess powder particles from the substrate to avoid smearing of the liquid 
or powder particles on the substrate. In a preferred embodiment, the 
header assembly is configured to permit the substrate to move continuously 
through the apparatus. 
In another embodiment, each edge of the substrate is positioned adjacent a 
corresponding edge of a disk. In another embodiment, the apparatus further 
includes at least one additional disk located between the two disks to 
separate the contained area into at least two separate substantially 
contained areas to facilitate application of different powder types onto 
different portions of the substrate. 
In yet another embodiment, each disk has an edge that includes holes 
therein to emit a gas at a sufficient velocity to prevent direct contact 
of the substrate with the disk edge. In a preferred embodiment, the disk 
edge holes have a diameter from about 0.001 to 0.5 inches and are spaced 
apart by about 0.25 to 3 inches. In a more preferred embodiment, the holes 
have a diameter from about 0.01 to 0.05 inches and are spaced apart by 
about 0.75 to 1.5 inches. In another preferred embodiment, the disks are 
substantially circular. In one embodiment, each disk has a diameter from 
about 12 to 60 inches and a thickness from about 0.25 to 6 inches. In a 
preferred embodiment, disk has a diameter from about 24 to 36 inches and a 
thickness from about 1 to 3 inches. 
In another embodiment, the gas is maintained at a pressure from about 15 
psi to 120 psi for release from the holes. In yet another embodiment, the 
apparatus further includes a heating device located at a distance from the 
substrate having particles of powder and wet ink thereon, wherein the 
heating device is capable of adjustment to increase the distance from the 
substrate as the substrate speed is slowed, which inhibits burning of the 
substrate and imparts a substantially constant amount of heat to the 
substrate to melt and fuse the powder particles thereon. In a preferred 
embodiment, the heater contains a heat source disposed at a distance from 
about 0.1 to 2 inches from the substrate and the substrate is disposed 
between the powder and the heater. In another embodiment, the powder 
adhering liquid is an ink which is capable of drying as the substrate 
passes through the heating device. In yet another embodiment, the 
apparatus further includes at least one of a feed roller capable of 
providing substrate to the header assembly in a continuous fashion or a 
rewind spool capable of continuously receiving and rolling the substrate. 
In one embodiment, the header assembly has an intake roller and an output 
roller and the intake roller is disposed at an angle from about 1 to 80 
degrees above the horizontal relative to the output roller to inhibit the 
loss of powder supply. 
The invention also relates to a thermographic printing apparatus having 
means for transporting a substrate having first and second sides and wet 
ink on the first side thereof, wherein the means for transporting contacts 
the substrate on the second side of the substrate, means for positioning 
the substrate in the apparatus to provide at least one substantially 
contained area inside the means for positioning and the substrate, wherein 
the means for positioning does not contact the substrate, and means for 
providing powder particles for application to the first side of the 
substrate capable of adhering an amount of the particles to the wet ink on 
the substrate. 
In one embodiment, the means for positioning includes at least two 
substantially circular disks having holes for emitting gas spaced around 
the circumferential edge thereof. In another embodiment, the apparatus 
further includes means for removing excess powder particles from the 
substrate sufficient to inhibit smearing of the wet ink or powder 
particles on the substrate. 
The invention further relates to a method of thermographic printing by 
transporting a continuous substrate having first and second sides, two 
edges, and a powder adhering liquid on the first side thereof along a 
path, providing powder particles onto a portion of the first side of the 
substrate, whereby at least some of the powder particles adhere to the 
liquid on the substrate, and circulating the powder particles that do not 
adhere to the first portion of the substrate for application to further 
portions of the substrate. 
In one embodiment, the substrate is directed along a substantially circular 
path and the non-adhering powder particles are positioned along the path 
adjacent the substrate for deposition onto further portions thereof. In 
another embodiment, the powder adhering liquid is an ink and which further 
includes removing excess powder particles from the substrate before the 
powder coated substrate is heated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A suitable web apparatus for high speed thermographic printing has now been 
discovered. A preferred use for this apparatus is for depositing particles 
of thermographic powder on a continuous printing substrate, such as a roll 
of paper, that has a powder adhering liquid, such as an ink, placed 
thereon in the form of a pattern or printed image. The apparatus 
advantageously permits a wet ink substrate to have powder placed thereon 
in a continuous fashion. Moreover, the present invention provides a 
powdering device that permits different color and size powders to be 
rapidly placed onto various portions of the substrate, also in a 
continuous fashion. This is accomplished by a powdering device that 
contains a plurality of disks which are hollow and which have holes in the 
circumferential edges thereof to permit the substrate to float around the 
disks on a wave of air, thereby inhibiting the smearing of any wet ink or 
powders during the powdering of the substrate. These disks, in connection 
with the substrate, form contained areas in which powder particles are 
placed for application to the wet ink on the substrate, which is 
continuously fed through the powdering device. The powder is more readily 
distributed onto the wet ink areas on the substrate due to the constant 
substrate movement around the disks. Excess powder is removed by a 
combination of an air knife, or blast of gas, and gravity in the powdering 
device to prevent smearing of the powder to provide a consistent quality 
final thermographic product. The powdering device contains the powder 
particles to prevent their escape, which also advantageously inhibits 
contamination of the surrounding air and permits powder to be readily 
recycled for application to the substrate. 
FIG. 1 shows an overview of the web apparatus of the present invention. A 
substrate 1 having two sides to be provided with thermographic print on 
one side is provided in continuous form, e.g., as a roll or web of paper, 
from a press that places wet ink onto one side of the substrate (not 
shown). The substrate may be of any size desired, but preferably has a 
width from about 8 to 60 inches, preferably about 12 to 48 inches, more 
preferably about 24 to 36 inches. The substrate may have any thickness up 
to about 1/4 inch, although thicker substrate stock is less likely to be 
flexible enough to flow smoothly around the disks in the powdering device. 
The substrate may be sheets of substrate having sufficient length to 
completely enclose the circumference of the disks. Preferably, however, a 
long substrate material having the width described above is used to permit 
the high speed application of thermographic powder to the substrate. 
Substrate is typically provided in rolls, such as rolls of paper, although 
the substrate supply is not a critical aspect of the invention. Although 
paper is the preferred substrate, any other sheet materials which can 
withstand the heat of the thermographic process can be used, including 
cardboard, fabric, and certain plastics. 
The substrate 1, having passed through a press or other source of powder 
adhering liquid (not depicted), has already received a supply of the 
liquid, which may be of any color including clear, that has not yet fully 
dried. The substrate 1 enters the powdering device 4 of the present 
invention through the header assembly 5 and passes around two or more 
powder-retaining disks 6 that are disposed below the header assembly. It 
should be noted that the powdering device 4 depicted in FIG. 1 has a frame 
8 that supports the powdering device 4. The frame is not a crucial feature 
of the invention, and in another embodiment (not shown) the powdering 
device 4 may be mounted on two oppositely facing walls, for example. Only 
the area of one disk is depicted in FIG. 1, as further discussion is set 
forth below. The powdering device 4 contains a powder hopper 7 that 
releases powder in measured quantities that are intended to stick to the 
wet ink on the substrate 1 as it moves around the disks and through the 
powdering device 4. The direction of the substrate along a circular path 
imparts a circular motion to the powder in the powdering device. Thus, any 
powder that does not deposit on the web ink is circulated through the 
device so that it can deposit on further portion of the substrate. As 
noted above, the amount of powder is metered into the device so that an 
excess of that necessary to coat the substrate is provided, as is 
generally understood by one of ordinary skill in the art. 
The substrate 1 then exits the powdering device 4 and passes through a 
heater 10 that fuses the powder on the substrate 1 to form raised 
thermographic print. The substrate 1 then passes through a cooler 15 that 
chills the powder of the print to solidify and inhibit smearing thereof. 
Suitable heating and cooling processes and apparatuses are well known to 
those of ordinary skill in the art, and the substrate 1 may be 
subsequently passed to further conventional post-processing operations 
such as folding, cutting, or rolling up of the substrate, and the like. 
FIG. 2 shows a perspective view of the web apparatus that more clearly 
depicts a plurality of powder-retaining disks 6 in the powdering device 4. 
In this view, the substrate 1 is not depicted so as to provide a clear 
view of the disks 6. When the substrate is present, the disks 6 and 
substrate 1 form substantially contained areas 12 between each pair of 
disks 6. The only substantial opening in the contained areas 12 is at the 
top of the powdering device where the powder hopper 7 releases powder into 
the contained areas 12. 
The powder hopper 7 is designed to be easily removed and replaced on the 
device so as to facilitate continuous operation. In certain situations, 
the size of the powder hopper can be selected to provide the appropriate 
amount of powder for the substrate. Generally, however, the hopper is 
sized so as to be easily manipulated by the operator for replacement as 
necessary as the powder is used. Instead of this hopper, it is possible to 
provide powder from a continuous supply, for example by introducing a 
fluidized stream of powder from a suitable air fluidizing device. 
FIG. 3 shows the header assembly 20 of the powdering device 4, which guides 
the substrate 1 around intake roller 21 and adjacent the disks 6 (not 
shown) of the powdering device. After passing around these disks 6 with 
the wet ink facing inward, the substrate 1 returns to the header assembly 
and passes around output roller 22. The rollers 21, 22 are preferably 
substantially cylindrical and may be powered to facilitate movement of the 
substrate 1 through the powdering device 4, although if other means to 
move the substrate are present at other points in the web apparatus then 
the rollers 21, 22 may be unpowered and act only to guide the substrate 
around the disks 6. For example, in one embodiment, the web is pulled 
through the entire printing apparatus from the output of the substrate, 
which advantageously keeps tension relatively smooth over portions of the 
web. Once the substrate 1 leaves the powdering device 4 through the header 
assembly 5, the substrate is then typically heated to fuse the 
thermographic powder retained on the wet ink during passage through the 
powdering device 4. The header assembly 5 also contains a powder passage 
25 between the rollers 21, 22, which permits powder from the powder hopper 
7 to be released into the contained areas 12. 
FIG. 3 also depicts optional roller adjusters 23, 24 in connection with the 
rollers 21, 22, respectively, to alter the circumference or placement of 
the rollers as needed to modify the speed, tension, or location of the 
substrate 1 as it passes through the powdering device. The substrate may 
be passed through the machine at speeds from about 10 to 2000 ft/min., 
preferably from about 400 to 1500 ft/min., and more preferably 600 to 1000 
ft/min. The housing 29, 30, used to partly surround rollers 21, 22, 
defines the size of the powder passage 25. As shown here, the housing 30 
adjacent roller 22 includes a source of gas 33, typically pressurized air, 
that is directed through a gap 35 in the housing 30. Generally, excess 
powder particles 37 are not substantially in contact with the wet ink and 
are thus easier to dislodge from the substrate than powder particles that 
contact and adhere to the wet ink. This gap 35 directs the high pressure 
gas 33 onto the surface of the substrate 1 in a manner like an "air knife" 
that helps dislodge the excess thermographic powder particles 37 from the 
wet ink. The pressure of the air knife is generally from about 0 psi to 
100 psi, preferably from about 1 psi to 80 psi, and more preferably from 
about 5 to 50 psi. The air knife pressure will depend upon the speed of 
the substrate 1, as higher speeds may be require less pressure to remove 
excess powder particles. The precise pressure may be readily determined by 
one of ordinary skill in the art. At this location of the powdering 
device, the powdered and inked side of the substrate is facing downward 
toward the disks. Thus, the pull of gravity also assists the high pressure 
gas 33 in removing excess powder particles from the substrate. Since the 
excess powder particles 37 are removed from the substrate 1 before the 
substrate 1 enters the header assembly 5, the particles 37 remain in the 
contained areas of the powdering device for continued application to 
substrate 1 containing wet ink but having insufficient powder particles. 
This air knife advantageously avoids the need for a cyclone, dust bag, 
vacuum or other mechanism to remove excess powder particles from the 
substrate, as is typically required in conventional thermographic 
processes. Advantageously, the path of the substrate changes direction 
when passing by the air knife to assist in the removal of excess powder 
therefrom. The excess powder returns to the contained area for application 
to further portions of the substrate. 
In the embodiment depicted in FIG. 3, an imaginary plane passes through the 
center of each roller in a horizontal fashion. In one preferred 
embodiment, intake roller 21 is disposed at a larger distance from the 
disks below than output roller 22 (see FIG. 3a). Thus, the substrate 1 
enters the intake roller 21 at a height greater than when it leaves the 
output roller 22, so that the imaginary plane through the roller centers 
is inclined at an angle from between about 1 to 80 degrees, preferably 
from about 20 to 70 degrees, and more preferably from about 30 to 60 
degrees from the horizontal plane in the embodiment depicted in FIG. 3. An 
exemplary placement of the rollers 21, 22 is to have the intake roller 
disposed to form about a 45.degree. angle of the imaginary plane through 
the roller centers. By positioning the intake roller 21 above the output 
roller 22, the excess powder removed by the air knife is advantageously 
maintained in the powdering device and is less likely to exit the device 
through the header assembly 5. This increases the dwell time of the powder 
in the powdering device, which tends to improve the quality of the final 
thermographic product. It has also been found that the dwell time is 
longest when the disk diameters have a particular ratio to the substrate 
speed. It should be understood that the invention successfully operates 
with any ratio of disk diameter to substrate speed. The longest dwell 
times, however, were obtained by using disks having a diameter of about 6 
inches for every about 100 feet/min. of linear substrate speed. Thus, a 
disk diameter of about 3 feet should be used for the highest quality 
thermographic printing of a substrate being printed upon at 600 feet/min. 
FIG. 4 shows a side view, more specifically, a section view on a disk's 
vertical plane along a disk axis as viewed from the web feed, of a 
plurality of powder-retaining disks 6 that are used to contain the loose 
powder in a plurality of contained areas 12 of the powdering device 4. The 
disks may be any shape having no sharp corners, although they are 
preferably substantially ellipsoidal, oval or circular. The disks are more 
preferably circular to promote smooth movement of the substrate over the 
disk edges and circulation of the excess powder therebetween. A diameter 
of about 12 to 60 inches, preferably from about 18 to 48 inches, more 
preferably from about 24 to 36 inches and a width from about 0.15 to 6 
inches, preferably about 0.25 to 4 inches, and more preferably about 0.5 
to 2 inches is used when circular disks are used. The width should be 
large enough to contain a passage within each disk for the gas that 
escapes from the holes 40 along the circumferential edge of each disk 6. 
It is also desired to use as narrow a disk as possible to keep the 
powdering areas as large as possible. 
The contained areas inside the disk assemblies are preferably maintained at 
pressures from about 15 psi to 120 psi, more preferably from about 50 psi 
to 100 psi. This source of pressured air may be provided merely from the 
source of high pressure gas 33, gas flowing from the holes in the 
circumferential edges of the disks, the fluidized powder stream (when 
used), another independent high pressure gas source, or a combination 
thereof. 
Powder released from the powder hopper 7 of FIGS. 1 and 2 or otherwise 
introduced into the device falls through the powder passage 25 of the 
header assembly 5 of FIG. 3 and into the contained areas 12 around which 
the substrate 1 is passed. The substrate 1 is passed over the edge of each 
disk 6. The substrate 1, although it could actually rest on the edge of 
the disks 6, preferably passes around the disks 6 while being kept 
slightly out of contact by gas being released from the edge of each disk 
6. Maintaining the substrate away from the edge of each disk 6 
advantageously inhibits smearing of the wet ink on the substrate that 
would tend to occur if the wet ink of the substrate were in contact with 
the disks 6. 
Each disk 6 has a plurality of holes 40 in the circumferential edge thereof 
to permit the flow of gas from the disk 6 to facilitate maintenance of the 
substrate away from the edge of the disk 6. The gas flow may be supplied 
to each disk in a variety of ways. In one embodiment, tubing containing a 
continuously flowing pressurized gas feed is furnished into a hollow area 
within each disk 6 that contains the gas therein until the gas escapes 
from the holes 40. The tubing may be arranged to enter from the top of 
each disk, for example, through the header assembly of FIG. 3 and downward 
to hang in a hollow area inside each disk. The hollow area is thus 
pressurized and the gas flow escapes through the holes 40. In another 
embodiment depicted in FIG. 5, the tubing 42 supplying the pressurized gas 
enters each disk in the same fashion, but the tubing 42 is disposed about 
the inside of the circumferential edge 45 of the disk and is attached to 
the inside edge 45 of the disk. The tubing 42 has holes 40' spaced 
corresponding to the holes 40 in the edge of each disk 6, as discussed 
below, to permit the gas to flow into each disk 6 through the tubing 42 
and directly out the holes 40' and 40 in the tubing 42 and each disk 6. 
This advantageously avoids the need to pressurize the entire hollow area 
47 inside the disk 6, which reduces or eliminates air leakage problems 
that can undesirably reduce the gas pressure. If brittle materials are 
used to form the disk 6, a high pressure hollow area 47 therein can force 
the disk to explode. Avoiding pressurization of the hollow area thus also 
eliminates this potential problem of warping or shattering the disk 6. 
Regardless of how the gas supply is fed into the disks, each disk 6 may 
also have one or more supports 50, such as a pins, in the hollow area 47 
to increase the structural integrity of the disk 6 from the inside. 
The disks 6 may be formed by any method known to those in the art, for 
example, by molding. The disks 6 may also be formed of one or more pieces 
of one or more types of materials. In the embodiment depicted in FIG. 5, 
the disk is formed of two plates 52, 53 having the same shape as each 
other and as described above for the disks. The plates 52, 53 may have a 
hollow area 47 therebetween to permit pressurized gas input to the disk 6 
and output through the holes 40, although in the embodiment where the 
tubing 42 is disposed circumferentially around the edge the hollow area 47 
may be negligible in size or even avoided altogether if the tubing 47 can 
be properly positioned otherwise. The plates may be made of any suitable 
material having sufficient strength to maintain a substantially constant 
shape, preferably one or more thermoplastic or elastic materials. It is 
also preferred that the plates 52, 53 be made of a clear material so that 
the operator of the device can more easily monitor the powdering device 
operation and intervene if any problems should arise during operation 
thereof. Thus, a more preferred material for the plates 52, 53 of each 
disk includes acrylic, LEXAN, PLEXIGLASS, or the like. LEXAN is 
commercially available plastic from General Electric Company of Fairfield, 
Conn. Although the plates 52, 53 may be positioned at an angle to each 
other, this may hinder powder deposition. Thus, the plates are preferably 
maintained in a position substantially parallel to each other. This is 
accomplished by "capping" the plates 52, 53 with an edge 55 having 
sufficient flexibility to be disposed around the rims 57, 58 of the plates 
52, 53. The edge 55 should preferably provide a substantially gas-tight 
contact with the plates 52, 53 to prevent gas from escaping the hollow 
area 47, particularly if the hollow area is pressurized. In the embodiment 
depicted in FIG. 5, the edge 55 has grooves therein that correspond to the 
plate rims 57, 58 so that the edge forms a "cap" on the rims to maintain 
the plates 52, 53 in a substantially fixed position. The edge 55 may be 
made of any suitable material that permits holes to be provided in the 
edges thereof, preferably one or more thermoplastic or elastic materials, 
and more preferably including polypropylene. The substrate (not depicted 
in FIG. 5) will pass adjacent and above the edge 55 as the edge is 
depicted in FIG. 5. It should be understood, of course, that the disks 6 
may be constructed in any manner described herein or known to those of 
ordinary skill in the art that permits the disks 6 to act as a guide for 
the substrate as it passes through the powdering device. For example, in 
another embodiment (not shown) where the tubing 42 of FIG. 5 is passed 
circumferentially around the edge 55, only one plate 52 (or 53) is 
required since the tubing 42 avoids the need to have a hollow area within 
the disk 6. In another embodiment (also not shown), the tubing 42 may be 
integrally formed as a hollow chamber disposed circumferentially within 
the edge 55 itself, such as by extrusion or molding. 
Referring again to FIG. 4, the holes 40 in the edge of each disk 6 are 
generally spaced apart at about 0.25 to 3 inches, preferably about 0.5 to 
2 inches, and more preferably about 0.75 to 1.5 inches apart to ensure 
that the appropriate amount of gas is released to force and maintain the 
substrate away from the disks 6. The escaping gas provides an air film 
that maintains the substrate at a distance from about 0.001 to 0.3 inches, 
preferably from about 0.01 to 0.25 inches, and more preferably from about 
0.05 to 0.2 inches away from the disks 6. The holes should have a diameter 
from about 0.001 to 0.5 inches, preferably 0.005 to 0.1 inches, and more 
preferably about 0.01 to 0.09 inches. The gas, which is preferably air, is 
provided from a gas source that escapes from the holes 40 at a sufficient 
velocity to push the substrate 1 off the edge of each disk 6. The gas 
pressure for release from the holes 40 is generally from about 0.001 psi 
to 150 psi, preferably from about 1 psi to 120 psi, and more preferably 
from about 15 psi to 100 psi. Suitable gas pressure will depend upon the 
tension on the web of substrate 1, and may be readily determined by one of 
ordinary skill in the art. The gas then advantageously escapes into the 
adjacent contained area(s) 12, thereby inhibiting loose powder particles 
in the contained area(s) 12 from escaping that particular contained area 
12 and from contacting the substrate anywhere outside that particular area 
12. The maximum velocity for the gas is limited by the need to avoid: (a) 
tearing of the substrate; and (b) forcing powder particles too far away 
from each disk 6, which tends to leave blank areas on the substrate near 
the disks where the powder particles were unable to contact the ink on the 
substrate. Suitable gas velocities may be readily determined by those of 
ordinary skill in the art. Although the disks may rotate, they are 
preferably stationary since the substrate advantageously floats over the 
disks on the gas forced from the edges of each disk 6. 
The number of disks 6, and distance between each, may be adjusted over the 
length of the rollers as necessary to provide one or more contained areas 
12 that will permit powder to be retained by the wet ink on the substrate, 
thus forming a powdered area that may be subsequently heated to form the 
thermographic print on the substrate. For example, the disk 6 closest to 
each end of the rollers may be adjusted depending upon the substrate width 
so that the outermost edge of each disk is positioned correspondingly 
under each edge of the substrate 1. Thus, at least two disks 6 are used 
for the edges of the substrate 1, although more disks may be added in any 
location along the rollers if it is desired to deposit different powders 
on different areas of the substrate. This flexibility in adjusting the 
disks 6 advantageously permits different color or quality powder particles 
to be used in each contained area 12. The powder hopper 7 of FIGS. 1 and 2 
may release such different color and/or quality powders into the different 
contained areas 6, and the disks 6 will completely prevent any of the 
powder from migrating to a different contained area 12. It should be 
understood, of course, that suitable thermographic powders may be of any 
size or quality used in thermographic printing, from small particles up to 
the size of those described in U.S. Pat. No. 5,699,743, which is 
incorporated herein by express reference thereto. The powder may also 
include any of a variety of suitable conventional fillers used in 
thermographic printing, such as glitter, pearlescent pigment, sand, 
metallic pigment, and the like. 
After leaving the powdering device 4, the substrate 1 passes through a 
heater 10 as depicted in FIG. 1. The heater may be any conventional 
heater, although preferably the heater is height adjustable. When the 
substrate is in motion at the full speed described above, the height of 
the heater is reduced to move it closer to the substrate for greater heat 
transfer. The temperature of the substrate is typically raised to a 
maximum of about 200.degree. F. to no greater than 450.degree. F., 
preferably from about 250.degree. F. to 375.degree. F., and more 
preferably from about 300.degree. F. to 350.degree. F., to avoid igniting 
the substrate, although the actual temperature will depend upon the type 
and size of powder particle, the type of substrate and speed thereof, and 
the desired height of the finished thermographic product. Suitable 
temperatures may be readily determined by those of ordinary skill in the 
art when considered in combination with the disclosure herein. When the 
substrate is moving at slower speeds, the heater height is increased 
proportionally relative to the substrate speed to provide the same heat 
transfer as at higher speeds. This height adjustment also permits the 
heater to be raised far enough away from the substrate to avoid any 
burning thereof when the substrate is stopped. 
Conventional heating typically occurs by radiation heating of the 
substrate, with the heat then being conducted through the substrate to the 
substrate portions under the ink and powder. This occurs because the 
energy used for heating is typically selected to have a wavelength to 
match the absorption of the substrate, and the powder and ink typically 
have a different absorption wavelength. Thus, it is preferable to dispose 
the heating elements below the substrate so that the powder does not 
"block" the radiation. In this manner, the heat may be applied more evenly 
across the substrate, which permits less energy to be used and avoids 
overheating portions of the substrate that are not covered by powder in an 
attempt to heat and fuse the powder. 
It is also preferred to have the substrate as close as possible to the heat 
source, which also reduces the energy required for heating and permits the 
more rapid heating required when passing the substrate through the heater 
at the high speeds achieved by the present invention. Thus, in a preferred 
embodiment, the substrate passes through the heater directly in contact 
with a refractory surface that forms part of the heater to decrease the 
distance from the heating coils or energy source to the substrate. 
Suitable distance for an energy source should thus be from about 0.1 to 2 
inches, preferably 0.12 to 0.3 inches from the surface of the substrate in 
this embodiment. It should be understood, however, that these are various 
preferred embodiments and that any conventional heating mechanism may 
adapted for use with the invention. 
It should be understood that the terms "air" and "gas," as used herein, are 
interchangeable and mean any suitable gas phase component that does not 
react chemically with the powder, substrate, or powdering device. Air is 
preferred but inert gases or mixtures thereon can be used, if desired. 
Although the preferred embodiment is disclosed with the use of an ink as 
the powder adhering liquid, one of ordinary skill in the art will readily 
understand that other liquids such as adhesives or glues, shellac, paints 
and the like can be used, the only limitation being that such liquids are 
sufficiently moist or tacky so that the powder adhered thereto and that 
the liquid can be dried or cured by heating or drying operations. 
After the substrate is dried and cooled, any of a number of conventional 
post-processing operations can be conducted. FIG. 6 depicts the substrate 
being fed from a feed roller 59, passing through the powdering apparatus 
4, heater 10, and cooler 15, with the final product substrate 1 being 
returned to be taken up on a rewind spool 60, also known as a take-up 
roll, to provide a continuous web of final product immediately after 
passing through the cooler 15. Alternatively, a variety of additional 
operations not depicted may be performed after the substrate 1 leaves the 
cooler 15, such as cutting the web into discrete sheets and then 
collecting the sheets in stacks or reams rather than returning them for 
take up on a rewind spool 60. If desired, the sheets can be folded and, if 
necessary, collated prior to being collected. In short, any substrate 
handling operation conventionally used in printing or thermographic 
printing may also be combined with the present invention to achieve high 
speed thermographic printing. Persons of ordinary skill in the art of 
handling paper webs are aware of all these operations so that they need 
not be further described herein. 
While the term "continuous" is intended to mean the application of the 
powder to the entire length of a roll or web of the substrate, there are 
other known techniques for changing such rolls "on the fly" so that a 
fully continuous process can be achieved, such as by splicing and/or use 
of an accumulator. This is conventionally done with an arrangement of 
multiple rollers and rolls of substrate with a feeder roll of substrate to 
be fed into the printing apparatus and a take-up roll to receive and 
re-roll the substrate after it has been thermographically printed upon, as 
depicted in FIG. 6. In one embodiment depicted in FIG. 6, the take-up roll 
is moved by powered rollers 64, 65 to pull the substrate web 1 through the 
entire apparatus. Continuous printing is well known to those of ordinary 
skill in the printing industry. 
It is to be recognized and understood that the invention is not to be 
limited to the exact configuration as illustrated and described herein. 
For example, it should be apparent that a variety of suitable arrangements 
and materials would be suitable for use in the apparatus according to the 
Detailed Description of the Invention. For example, when the powder is 
introduced as a fluidized stream, it could be introduced into the side of 
the disk rather than the top since it is not being gravity fed. 
Accordingly, all expedient modifications readily attainable by one of 
ordinary skill in the art from the disclosure set forth herein are deemed 
to be within the spirit and scope of the present claims.