Transfer apparatus

An apparatus which transfers a liquid image from an image support surface to a sheet. A deformable cylindrical member made from a flexible, dielectric material presses the sheet against the image support surface. As the cylindrical member presses the sheet against the image support surface, it deforms to define a transfer area. A conductive roll, disposed interiorly of the cylindrical member in the transfer area, tacks the liquid image to the image support surface. A corona generating device, positioned adjacent the conductive roll interiorly of the cylindrical member, transfers the liquid image from the image support surface to the sheet.

This invention relates generally to a color printing machine, and more 
particularly concerns an apparatus which transfers successive liquid 
images from a photoconductive surface to a sheet. 
There are different printing processes employed to make color proof copies. 
One such technique produces multiple color proof copies from halftone film 
separations. Initially, an electrostatic master is exposed to a halftone 
film separation. This forms an electrostatic latent image on the master 
corresponding to the halftone film separation. Four masters are made. One 
of the masters corresponds to black with the other masters corresponding 
typically to the subtractive primary colors of the desired proof copy. The 
masters are then placed in the printing machine and secured to rotating 
cylinders. One master is mounted releasably on each cylinder. Each master 
is charged to a substantially uniform potential. The charge bleeds away 
except in the image areas to form an electrostatic latent image thereon 
corresponding to the image areas of the halftone film separation The 
latent image is developed by bringing a liquid developer material into 
contact therewith. The liquid developer material comprises a liquid 
carrier having pigmented particles dispersed therein. The pigmented 
particles are deposited, in image configuration, on the master. These 
latent images are developed with developer material having a color 
corresponding to the substrative primary color of the corresponding 
halftone film separation. Thereafter, the differently colored developed 
images are transferred from the masters to the sheet in superimposed 
registration with one another. Heat is then applied to permanently fuse 
the image to the sheet so as to form a color proof copy. A linear printing 
machine of this type is rather large and requires four linear printing 
stations, i.e. one printing station for each master. Alternatively, a 
recirculating type of printing may be used in which one printing station 
is used a plurality of cycles. In this type of printing machine, the copy 
sheet is recirculated for four cycles with a different color image being 
transferred thereto during each cycle. This necessitates the placement of 
the four masters on a common drum, or alternatively, recording four 
electrostatic latent images on the drum. This may be achieved by using an 
electrophotographic printing process. 
In an electrophotographic printing machine, a photoconductive member is 
charged to a substantially uniform potential to sensitize the surface 
thereof. The charged portion of the photoconductive member is exposed. 
Exposure of the charged photoconductive member selectively dissipates the 
charge thereon in the irradiated areas. This records an electrostatic 
latent image on the photoconductive member corresponding to the 
informational areas contained within the original document being 
reproduced. After the electrostatic latent image is recorded on the 
photoconductive member, the latent image is developed by bringing 
developer material into contact therewith. This forms a developed image on 
the photoconductive member which is subsequently transferred to a copy 
sheet. The copy sheet is heated to permanently affix the image thereto. 
Multi-color electrophotographic printing is substantially identical to the 
foregoing process of black and white printing. However, rather than 
forming a single latent image on the photoconductive surface, successive 
latent images corresponding to different colors are recorded thereon. Each 
single color electrostatic latent image is developed with developer 
material of a color complementary thereto. This process is repeated a 
plurality of cycles for differently colored images and their respective 
complementarily colored developer material. Each single color developed 
image is transferred to the copy sheet in superimposed registration with 
the prior image. This creates a multi-colored image on the copy sheet. 
which is permanently affixed thereto creating a color copy. A printing 
machine designed to produce high quality color proofs uses a liquid 
developer material. It is thus necessary to employ a transfer apparatus 
which is capable of transferring a plurality of different color liquid 
images in superimposed registration with one another without smear or 
degradation of image quality. 
Various approaches have been devised for for transferring powder images 
from a photoconductive member to a copy sheet. The following disclosures 
appear to be relevant: 
U.S. Pat. No. 3,924,943; Patentee: Fletcher; Issued: Dec. 9, 1975. 
U.S. Pat. No. 4,063,808; Patentee: Simpson; Issued: Dec. 20, 1977. 
U.S. Pat. No. 4,382,673; Patentee: Nakajima et al.; Issued: May 10, 1983. 
U.S. Pat. No. 4,601,963; Patentee: Takahashi et al.; Issued: July 22, 1986. 
U.S. Pat. No. 4,607,935; Patentee: Kindt et al.; Issued: Aug. 26, 1986. 
The relevant portions of the foregoing patents may be briefly summarized as 
follows: 
U.S. Pat. No. 3,924,943 discloses a transfer roller made from a thin outer 
layer, an electrically relaxable inner layer and a central cylindrical 
conductive core. A constant current electrical bias is electrically 
connected to the conductive core. The relaxable layer is made from a thick 
layer of a low durometer elastomeric material. The transfer roll is 
pressed into contact with the photoconductive drum and deflects to form an 
extended transfer zone. 
U.S. Pat. No. 4,063,808 describes a transfer roller made from a conductive 
metal hub surrounded by a resilient rubber layer having a thin flexible 
dielectric layer on the exterior circumferential surface thereof. The 
transfer roller is pressed into engagement with the photoconductive drum 
and deflects to form an extended transfer zone. 
U.S. Pat. No. 4,382,673 describes a transfer roller in the form of a brush 
roll. The transfer roller is made from an aluminum cylindrical core or bar 
having an elastic layer of foaming polyurethane formed on the outer 
circumferential surface thereof. An electrically conductive adhesive is 
coated on the circumference and ends of the elastic layer. Surface furs 
are planted in the adhesive layer and extend outwardly therefrom. 
U.S. Pat. No. 4,601,963 discloses a photoreceptor made from a shaft having 
an elastic cylindrical core mounted thereon and an outer layer comprising 
a supporting layer and a photosensitive layer. The photoreceptor is 
constructed in the shape of a drum being adapted to deform locally while 
maintaining the remainder of the drum nondeformed. 
U.S. Pat. No. 4,607,935 discloses a film sheet interposed between a 
compliant back-up roller and a transfer roller. A receiver sheet is 
releasably secured to the transfer roller. As the film passes through the 
nip defined by the back-up roller and transfer roller, the image on the 
film is transferred to the sheet. The back-up roller rather than the 
transfer roller is complaint. 
Pursuant to the features of the present invention, there is provided an 
apparatus for transferring a liquid image from an image support surface to 
a sheet. A deformable cylindrical member presses the sheet against the 
image support surface and deforms to define a transfer area. The 
cylindrical member is made of a dielectric material. Means, disposed 
interiorly of the cylindrical member in the region of the transfer area, 
tack the liquid image to the image support surface. Means, disposed 
interiorly of the cylindrical member in the region of the transfer area 
adjacent the tacking means, transfers the liquid image from the image 
support surface to the sheet. 
In another aspect of the present invention, there is provided a printing 
machine of the type in which a liquid image is transferred from a 
photoconductive drum to a sheet. The improved printing machine includes a 
deformable cylindrical member comprised of a dielectric material. The 
cylindrical member deforms to define a transfer area when pressing the 
sheet against the photoconductive drum. Means, disposed interiorly of the 
cylindrical member in the region of the transfer area, tack the liquid 
image to the photoconductive drum. Means, disposed interiorly of the 
cylindrical member in the region of the transfer area adjacent the tacking 
means, transfer the liquid image from the photoconductive drum to the 
sheet.

While the present invention will hereinafter be described in connection 
with a preferred embodiment thereof, it will be understood that it is not 
intended to limit the invention to that embodiment. On the contrary, it is 
intended to cover all alternatives, modifications and equivalents as may 
be included within the spirit and scope of the invention as defined by the 
appended claims. 
For a general understanding of the features of the present invention, 
reference is made to the drawings. In the drawings, like reference 
numerals have been used throughout to designate identical elements. It 
will become evident from the following discussion that the present 
invention is equally well suited for use in a wide variety of printing 
machines, and is not necessarily limited in its application to the 
particular machine shown herein. 
Referring now to FIGS. 1 and 2, there is shown a printing machine employing 
a photoconductive drum 10. Preferably, the photoconductive drum 10 is made 
from a selenium alloy coated on an aluminum grounding layer. Other 
suitable photoconductive materials and grounding layers may also be 
employed. Drum 10 rotates in the direction of arrow 12 to advance 
successive portions of the photoconductive surface sequentially through 
the various processing stations disposed about the path of movement 
thereof. 
Initially, a portion of photoconductive drum 10 passes through the charging 
station. At the charging station, two corona generating devices, indicated 
generally by the reference numerals 14 and 16, charge photoconductive drum 
10 to a relatively high, substantially uniform potential. 
Next, the charged photoconductive surface is rotated to the exposure 
station. At the exposure station, a raster output scanner (ROS) 18 
illuminates the charged portion of photoconductive drum 10 to selectively 
discharge photoconductive drum 10 so as to record an electrostatic latent 
image thereon. The regions of the charged photoconductive drum illuminated 
by ROS 18 correspond to the image regions. Thus, the image regions are 
discharged and the non-image regions remain charged. For example, if the 
image is to contain red, the charged, non-image regions will be developed 
with a cyan colored liquid developer material. Similarly, if the image is 
to contain green, the non-image regions will be developed with magenta 
colored liquid developer material, while an image containing blue will be 
developed with yellow liquid developer material. ROS 18 includes a laser 
with a a rotating polygon mirror. Preferably, the laser is a helium neon 
laser. 
After the electrostatic latent image has been recorded on photoconductive 
drum 10, drum 10 advances the electrostatic latent image to the 
development station. The development station includes four individual 
developer units generally indicated by the reference numerals 20, 22, 24 
and 26. Each of the developer units is substantially identical to one 
another. The only distinction between the developer units is the color of 
the liquid developer material contained therein. Each developer unit 
includes developer rolls which advance the liquid developer material into 
contact with photoconductive drum 10. The liquid developer includes a 
clear carrier and colored toner. In this way, liquid developer material is 
brought into contact with the latent image formed on drum 10. Developer 
material is attracted electrostatically to the image areas forming a 
liquid image on drum 10. Preferably, the developer material includes a 
clear liquid insulating carrier having pigmented particles, i.e. toner 
particles, dispersed therien A suitable clear insulating liquid carrier 
may be made from an aliphatic hydrocarbon, such as an Isopar, which is a 
trademark of the Exxon Corporation, having a low boiling point. The toner 
particles include a pigment associated with a polymer. A suitable liquid 
developer material is described in U.S. Pat. No. 4,582,774, issued to 
Landa in 1986, the relevant portions thereof being incorporated into the 
present application. The color of the toner particles contained within 
each developer unit is adapted to absorb light within a preselected 
spectral region of the electromagnetic wave spectrum. For example, 
developer unit 20 includes a liquid developer material containing a clear 
liquid carrier and green absorbing magenta toner particles. Similarly, 
developer unit 22 includes a liquid developer material containing a clear 
liquid carrier and blue absorbing yellow toner particles. Developer unit 
24 includes a clear liquid carrier and red absorbing cyan toner particles. 
Developer unit 26 contains a clear liquid carrier and black toner 
particles. Each of the developer units is moved into and out of the 
operative position. In the operative position, the developer roll is 
closely adjacent the photoconductive belt. In the non-operative position, 
the developer roll is spaced from the photoconductive drum. During 
development of each electrostatic latent image only one developer unit is 
in the operative position, the remaining developer units are in the 
non-operative position. This insures that each electrostatic latent image 
is developed with appropriate colored liquid developer material without 
co-mingling. In FIGS. 1 and 2, developer unit 20 is shown in the operative 
position with developer units 22, 24 and 26 being in the non-operative 
position. All of the developer units are mounted on a trolley 28 which 
translates. Trolley 28 moves one of the developer units to the operative 
position opposed from photoconductive drum 10. The developer unit 
translated to the operative position is then elevated to a position 
adjacent drum 10. Metering roll 30 controls the quantity of developer 
material deposited on drum 10 and removes the excess therefrom. 
After development, the liquid image is moved to the transfer station where 
the liquid image is transferred to a sheet 32, such as plain paper amongst 
others. Sheet 32 is advanced to the transfer station. Before sheet 32 
advances to the transfer station, it passes through a pre-wetting station. 
At the pre-wetting station, a wetting roll 34 applies a solvent to a 
surface of sheet 32. At the transfer station, a transfer drum, indicated 
generally by the reference numeral 36, receives sheet 32. The sheet is 
advanced from a stack of sheets 38 disposed on a tray. The sheet is 
advanced in synchronism with the movement of a gripper rotating with drum 
36. In this way, the leading edge of the sheet arrives at a preselected 
position to be received by the open gripper. The gripper then closes 
securing the sheet thereto for movement therewith in a recirculating path. 
The leading edge of the sheet is secured releasably by the gripper. 
Internal and external corona generators 42 and 44 tack sheet 32 to drum 
36. As transfer drum 36 rotates in the direction of arrow 40, the sheet 
moves into contact with the photoconductive drum, in synchronism with the 
liquid image developed thereon. Drum 36 is pressed into contact with 
photoconductive drum 10 at transfer zone 46 and deforms thereat to define 
a wide contact area. A conductive rubber roll 48, disposed internally of 
drum 36, is electrically biased to tack the liquid image to 
photoconductive drum 10. A corona generating device, disposed internally 
of drum 36 adjacent roll 48, sprays ions onto the backside of the drum so 
as to charge the sheet to the proper magnitude and polarity for attracting 
the liquid image from photoconductive drum 10 thereto. The sheet remains 
secured to the gripper so as to move in a recirculating path for four 
cycles. In this way, the cyan, yellow, magenta and black liquid images are 
transferred to the sheet in superimposed registration with one another to 
form a multi-color image. 
After the last transfer operation, the grippers open and release the sheet. 
Internal and external corona generators detack sheet 32 from drum 36 and 
discharge transfer drum 36. A conveyor transports the sheet to the fusing 
station where fuser plate 52 heats the sheet to permanently fuse the 
transferred image to the sheet. Thereafter, the sheet is advanced by 
forwarding roll pairs 54 to a catch tray 90 for subsequent removal 
therefrom by the machine operator. 
Referring now to FIG. 3, transfer drum 36 is shown in greater detail. 
Transfer drum 36 includes opposed spaced cylindrical hubs 56 and 58. A 
flexible tubular sheet 60 is supported on opposed end regions by hubs 56 
and 58. Hubs 56 and 58 are mounted internally of tubular sheet 60 in 
opposed marginal end regions thereof. Resilient strips 62 and 64 are 
interposed between hubs 56 and 58 and cylindrical sheet 60 in the end 
regions thereof. Strips 62 and 64 are cylindrical and preferably made from 
a rubber or polyurethane foam material. Flexible sheet 60 is made from a 
dielectric material, such as Mylar or Kynar, a trademark of the DuPont 
Corporation. 
In recapitulation, the printing machine of the present invention includes a 
transfer drum which is made from a flexible, tubular dielectric sheet 
supported by a pair of spaced hubs disposed internally therof. Resilient 
strips are interposed between the hubs and the sheet to provide a 
resilient mounting for the sheet. The drum presses against the 
photoconductive member to form a wide transfer area through which the 
sheet is advanced. The sheet is secured to the drum and moves in a 
recirculating path so that successive different color liquid images may be 
transferred thereto in superimposed registration with one another. An 
electrically biased conductive roll, positioned internally of the transfer 
drum, tacks the liquid image to the photoconductive drum. A corona 
generating device, located internally of the drum adjacent the conductive 
roll, attracts the liquid image from the photoconductive drum to the 
sheet. 
It is, therefore, evident that there has been provided in accordance with 
the present invention, a transfer apparatus that fully satisfies the aims 
and advantages hereinbefore set forth. While this invention has been 
described in conjunction with a specific embodiment thereof, it is evident 
that many alternatives, modifications and variations will be apparent to 
those skilled in the art. Accordingly, it is intended to embrace all such 
alternatives, modifications and variations as fall within the spirit and 
broad scope of the appended claims.