Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates generally to printing
apparatus and more particularly is concerned with
electrostatic printing apparatus for color printing.
conventionally, color printing is effected
by mixing the colors on a final receptor through the use
of multiple registered impressions. For example, a color
object or image is photographed through several filters to
make color separations in the printed colors comprising
cyan, magenta, yellow and black, each of which are made into
plates, mounted in a printing press and the receptor
passed through the press and impressed with each oE the
plates in turn.
Present available electxostatic techniques for
multicolor printiny are comple~, expensive and unreliable.
Formation of the color separated plates of dieferent basic
colors is still normally requ:ired. The use of xerography
or electrofax techniques for multiple printing is
; conternplated.
The prior applicakion of eleckrostatic techniques
require a direct transfer or ima~ing ~or each example
printed. It wowld be advantageous electrostatically to
form images to be printed semipermanently on sleeves that
remain so imaged throughout the entire printing run.
With use of such technique, it also would be desirable to
2~ achieve the different parameters which may ~e required for
each color without interference with the imprinting oE other
colors, say at other stations.
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Accordingly, the invention provides a printing
apparatus and method in which an elongate substrate is
imprinked with a plurality of images o~ different color
pigments in registration to achieve a pattern composed
oE multiple colors.
The method involves trans~erring a toned
image from a sleeve to the substrate at each of a
plurality of transfer stations, the tone~ or pi~ment
used at each station being of a different color.
; 10 The apparatus provides each station with a
master sleeve upon which there is provided a semi-
permanent pattern of the single color component of
the eventual composite print which is to be applied
at that station. The master sleeve can also comprise
the transfer sleeve or the master may apply an image
to an intermediate transEer sleeve as in o~fset
printiny. The semipermanent toner in either case is
; re~uired to be dielectric in character. The transfer
or secondary toner need not be dielectric in character.
Once the master sleeve is in place at its
station, its image as transferred to the moving
substrate is re~uired to be imprinted in registration
with the images from all other stations. The stations
are preferably arranged in alignment and are independent
so that different conditions for optimum transfer can
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obtain at each. Each applied image is fixed after
development and before the substrate has moved that
image to its following station. The toner, voltages,
temperatures and the like at any one station may be
different from those same parameters at all others.
Density measurements can be made at any station
and the information fed back to the same or previous
stations to change the parameters of the printing
conditions thereat.
The preferred embodiments of this invention
: now will be described, by way oE example, with
reference to the drawings accompanying this
specification in which:
Figure 1 .is a diagrammatic view o e
apparatus for ca.rryiny out the method of the invention
and printiny composite color images on a moving
substrate;
Figure 2 is a diagrammatic view showing
a method of making a master sleeve for use with the
invention; and
Figure 3 is another cliagrammatic view
showing a seconcl method o.E making a master sleeve Eor use
with the invention.
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The printing method provided herein involves
the making of a master sleeve upon which an image is
carried. The master sleeve rotates preferably in
cylindrical form~and either contacts the substrate
directly in which case it rotates in the same direction
~as the substra~e or has a peripheral direction of
movement contra that of the substrate. In the latter,
the master sleeve serves as a medium through which the
secondary tone~ image on the master sleeve is
transferred onto a second sleeve or blanket which in
turn is transferred directly to a moving substrate
from the second sleeve and indirectly from the master
sleeve. It is impor-tant to note that the descrlbed
apparatus includes a plurality of stations each o
which is independently controlled as to the various
parameters required to produce the necessary irnpression
or image on the substrate.~
Re~erring to the drawings, in Figure 1 there
is illustrated a printing apparatus 70 having four
stations 72, 74, 76 and 78, it being assumed that said
apparatus 70 is to be used for color imprinting on
paper.
The substrate 80 passes through apparatus 70
and moves through various rollers, tensioning devices,
etc., none of which nee~ be shown hereinO At the first
station there is a maste,r sleeve 82 which is mounted on
a roller ~, the master sleeve 82 in this case being
cylindrical although it could be in the form of a belt.
The sleeve 82 need not be transparent. Preferably, the
sleeve 82 comprises a coating of photoconductive material
applied to a thin, metal cylinder maintained in its
cylindrical condition upon the roller 84 by suitable
means.
The sleeve 82 is formed of an electrophotographic
material or member comprising a substrate which, if formed
of resin such as transparent polyester, carries an ohmic
layer and a coating of photoconductive material on the
outside thereof. If the substrate is fo.rmed of metal,
the photoconductive material comprises a wholly inorganic
compound, preferabl~ cadmium sulfide, which has been
sputtered onto the substrate as a microcrystalline,
transparent, high ~uantwm ~ield deposit.
The sleeve 82 carries an image preferably in the
form of a aigital coded color separation which has been
; applied to the sleeve in a manner to be described in
connection with Figures 2 or 3, i.e., the image having
~een toned with a dielectric or primary toner and fused
so that it is semipermanently affixed to the exterior of
the master sleeve 82.
The station also includes a pressure roller 86
which can assist in driving the su~strate 80 from left
to right and/or can assist in the transfer of the toned
2~
image from the exteriOr surface of the master sleeve 82
to the bottom sur~ace of the substrate 80.
In use the imaged master sleeve 82 is charged
by any suitable means at 88 and after charying or even
at the same time is exposed to light.
As a result of the exposure to light after the
sleeve 82 has been charged, the charge remains on the
dielectric toned parts and leaks off those parts which
have not been toned thereby providing a secondary
charged image which then is passed to a secondary tonîng
bath 90 where the secondary image is now developed (toned).
~his secondary toned image is passed around by rotation
of the roll 84 into engagement with the passing
substrate 80 at the point where the roller 86 is juxtaposed.
Transfer can be effected either by pressure or b~ an
electric ~ield ~urnished by the power supply 92 connected
to the roller 86 and to the toner bath 90 or to the
roller 84. In any event, there is a bias voltage field
across the space between which the substrate 80 is moving
2n and this assists in the transEer of secondary toner to the
lower surface of the substrate. An intermediate blanket
or transfer roll can be provided.
A~ter the said secondary toned image is applied
to the substrate, it passes over a heating device 94 at
which point the image is fixed.
All of the remaining stations operate in the
same way and are constructed in the same wa~, the
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difference between them being the parameters o~ heat,
temperature and so on. It has been -found that ~ifferent
toners require different voltages, temperatures, etc.
so that the use of a sequence of stations operating
independently is more likely to give best results.
It has even been found that certain cases of transfer
require biases of opposite polarity for optimum results.
Information on density can be sensed after
each image is applied, for example at 64 which comprises
an optical transducer, to a control signal converter 66
from which the bias voltage generated in 92 will be
varied for optimum densit~ condition.
When the substrate 80 emerges from the station 78,
all four images are compositely applied to the hottom
surface thereof, it being assumed that registratiOn is
mainta.ined by suitable means which are not shown. From
here the substrate 80 moves to slitters, cutters, folders,
supply rolls, etc., none of which are shown but presumed
to comprise structure using the oncoming substrate.
In Figure 2 there is shown a roll 96 of the
transparent electrophotographic material from which a
sleeve is made. This material may be welded together to
form a flexible belt which is indicated at 20 either
; before or after the image has been applied. The belt 20
is capable of being formed into sleeve 82 and mounted
cylindrically. The image can be projected onto the belt 20
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optically, this being done by charging followed by
imaging, toning with dielectric toner and fixing. It
is preEerred however, that the image be applied in a
digital fashion so that there is no need for a screen
and no problem deriving Erom optical projection means.
~ A suitable multi-colored pattern is scanned and
its colors separated and digitized into bits which are
stored in an electronic store 98. The store 98 then is
used to modulate a low power laser, such as for example
a helium-neon laser 100. The laser 100 projects its
modulated beam by way of reflecting means 102 and 10~
onto the surface of the electrophotographic material of
the roll 96 at 106 as this material is being unrolled.
By suitable drives, the reflectors 102 and 104 are capable
of correcting and compensating for khe conversion ~rom
the continuous flow o~ bits to applicakion to a sur~ace
as khe beam swinys back and forth. The material first
is charged at 108, imaged at 106, toned at 110 and fixed
at 112. The resulting image is now semipermanently fixed
and the length of material can be cut from the roll 96
and formed into the sleeve 20 in the form of a belt by
welding the ends together. The belt also is capable of
being in sheet form and clamped to a mandrel~
In Figure 3 there ~s illustrated apparatus which
can be used to make a sleeve dLrectly as a cylinder such
as shown at 82 in Figure 1. The sleeve 82 is in the Eorm
of a thin cylinder of metal or the like having a coatiny of
the photoconductive material described mounted on a mandrel
114 which is driven. The same type of laser 116 as
shown in Figure 3 at 100 fed from an electric store 117
directs a modulated beam of light 118 composed of
digitized bits to a travelling mirror 120 mounted on a
suitable driven guide rod 122 so that the digitized bits
are properly laid dGwn upon the sur~ace of the sleeve 82
to produce the desired image representing a single color of
a composite. A corona device 124 is arranged to charge the
surface and a toning device 126 is provided to tone it
after the image has been laid downv At 128 one can see
a representation of a toner Eixing device which is on the
opposite side of the view in Figure 3 semipermanently to
lS affix the dielectric toned image to the master cy:Linder 82.
After the rnaster cylinder has been toned and
the image fixed it is removed from the mandrel 114 and
installed in an apparatus such as 72.
- In the operation of the apparatus 72 after the
secondary toner has been trans~erred to the substrate 80,
any toner which remains on the sur~ace of the sleeve 82
can be rernoved by suitable cleaning apparatus such as
shown at 87~
It is feasible to have the sleeve 82 imaged on
line, that is, permarlent]y secured in place in the
apparatus 72 but provided with means ~or applying the .ima~e
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from the store and Eixing the same for wse. Thus, on
station 76 there i5 illustrated a block 130 at which
location the same functions are performed as performed
by the laser 116 and the moving mirror 120 of Figure 3.
The charging means 88' charges the sleeve 82', and the
toning apparatus 90' accomplishes the toning, all of
this being done in a series of revolutions be~ore the
substrate 80 is brought against the surface of the
sleeve 82'. The cleaning apparatus 87' is not used
in this preliminary operation but a fixing device is
required at 132 after toning.
Once the image has been semipermanently applied
to the sleeve 82' the apparatus 130 and 132 are rendered
inoperative and the toning device 90' then ~or~s in
conjunction with the charging device 88' and the cleaniny
device 87'.
In re~erring to the images as semipermanent, it
is meant that khe images can be removed by suitable
chemicals which will not affect the photoconductive
surface. For example, even fused images of dielectric
toner can be removed by acetone or in some instances warm
ethyl or methyl alcohol.
The dielec-tric toned images need not be pigmented.
The secondary toned images are required to be pigmented.
~ielectric toner is de~ined herein as toner which,
when fixed, is highly insulating so that charge will not
leak off.
