Apparatus for printing images on generally cylindrical objects

Apparatus for printing images on generally cylindrical objects, such as cans, including: an image bearing surface having an image thereon; and an impression guide which is generally parallel to and spaced from the image bearing surface, which guide supports the cylindrical objects in rolling contact with the image bearing surface, whereby images are transferred from the image bearing surface to surfaces of the cylindrical objects in contact therewith.

FIELD OF THE INVENTION 
The present invention relates to printing of images in general and, more 
particularly, to devices and methods for printing images on a cylindrical 
surface. 
BACKGROUND OF THE INVENTION 
Multi-color printing on cylindrical objects, such as food or beverage cans, 
is well known. 
In general, each can is centered on and rotates about a mandrel during the 
printing process. Afterwards, the can is filled and sealed, usually at 
another site. 
The inability of the prior art to print on filled cans has several 
disadvantages. For example, placing the cans on a mandrel increases the 
time and cost of manufacture. In addition, customized printing is 
relatively expensive and logistically cumbersome, since printing and 
filling are generally carried out at different sites. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide improved apparatus and methods for 
centerless multi-color printing on circularly cylindrical or elliptically 
cylindrical objects. Such objects may include images and designs and may 
be printed on objects such as cans before or even after full or partial 
filling with liquid, carbonated beverages or other fillings either vacuum 
packed or with a gas filling the nonliquid filled portions of the can, or 
other tubular objects such as bottles, pens, markers, etc. Images or 
designs may, in accordance with one embodiment of the invention, be 
printed directly onto elliptically cylindrical objects. Using the present 
invention, the cylindrical objects may be customized with greater ease and 
at lower cost than the prior art. 
In simplified terms, cylindrical objects are brought into rolling contact 
with a printing device which prints on the surfaces of the objects as they 
roll about their own axis. More specifically, in accordance with a 
preferred embodiment of the present invention, the cylindrical objects are 
supported by an impression guide surface and brought into contact with a 
rotating toner image bearing surface of an imaging apparatus. Since the 
cylindrical objects contact both the impression guide surface and the 
toner image bearing surface, rotation of the image bearing surface causes 
the objects to roll about their own axis along the toner image bearing 
surface. 
The rotating image bearing surface transfers an electrostatic image or 
design to the objects as they roll. There is no need for holding the 
objects on a guiding mandrel; the objects simply roll about their own axis 
and are printed as they roll. 
The objects must be aligned with and conveyed to the rotating toner image 
bearing surface so that the images can be transferred onto the surfaces of 
the objects in a controlled manner. This is accomplished, in one 
embodiment of the invention by using a rotating dispenser which supplies 
the objects from to the impression guide surface. The dispenser 
incorporates a gating system designed to hold the objects and deliver them 
to the impression surface at the correct time so that they are aligned for 
proper transfer of images thereon from the image bearing surface. 
Where the units being printed are short compared to the width of the image 
bearing surface, a plurality of units may be delivered, end to end, for 
simultaneous printing. 
In a preferred embodiment of the invention, the gating system comprises a 
series of axial member disposed about the turning axis of the dispenser 
and may be disposed, in circumferentially disposed sets, axially along the 
dispenser. In a preferred embodiment of the invention, the dispenser 
dispenses two objects at a time to the image bearing surface for printing, 
the objects being spaced axially of each other. The rotating image bearing 
surface prints on the circumferential surfaces of the two objects during 
part of one revolution of the image bearing surface. The continuously 
turning image bearing surface then prints on the circumferential surfaces 
of a second set of axially spaced cylindrical objects during a second part 
of a revolution. There is a sufficient gap between printing on each set of 
two cylindrical objects to ensure that the objects do not touch and smear 
each other. Thus one printing cycle preferably includes one complete 
revolution of the image bearing surface and transfer of a plurality of 
images therefrom onto a plurality of objects. 
Alternatively, the cylindrical objects may be delivered to the image 
bearing surface by a conveyer belt. This is especially useful when 
printing is to be performed on elliptically cylindrical objects for which 
both the position and orientation of the objects is important at the start 
of printing. 
In a preferred embodiment of the invention two or more sets of two 
cylindrical objects are printed in one revolution of the image bearing 
surface. 
A controller receives information from the image bearing surface and from 
the dispenser regarding relative rotational speeds and position of the 
images to be transferred with respect to the position of the objects. The 
controller adjusts the speed of conveyance and transfer of the objects 
such that the images are precisely transferred from the image bearing 
surface to the objects. 
Generally, transfer from a heated image bearing surface fixes the images 
onto the cylindrical objects. In accordance with a preferred embodiment of 
the invention, heaters may be provided before and/or after transfer of the 
images to aid fixing the images. The heaters are preferably in direct, 
overhead contact with the cylindrical objects as they roll. Preheating 
must take into account whether the cans are filled or empty and whether 
the filling material is damaged by heat. 
When printing is performed on very thin empty cans, it may be necessary to 
insert solid or hollow mandrels into the cans prior to the transfer of 
images thereto. In this case, the mandrel may be pre-heated prior to 
insertion and both post and pre-heating steps are preferably omitted. 
After image transfer to the cans, the somewhat cooler mandrels are removed 
and preferably reheated prior to reuse. 
The present inventors have found that precoating cylindrical objects, 
especially metallic objects, with polyvinylpiridine homopolymer or with 
its copolymer with styrene provides for excellent transfer of ink with 
substantially no aging effects. Other useful adhesion 
There is therefore provided, in accordance with a preferred embodiment of 
the invention, apparatus for printing images, preferably toner or liquid 
toner images, on generally cylindrical objects, comprising: 
an image bearing surface having an image thereon; and 
an impression guide which is generally parallel to and spaced from the 
image bearing surface, which guide supports said cylindrical objects in 
rolling contact with said image bearing surface, whereby images are 
transferred from said image bearing surface to surfaces of said 
cylindrical objects in contact therewith. 
In a preferred embodiment of the invention, the apparatus comprises an 
object dispenser which conveys said cylindrical objects to said impression 
guide surface in timed relation with said image on said image bearing 
surface. Preferably, the object dispenser comprises a plurality of axially 
directed gates spaced circumferentially about an axis of said dispenser, 
wherein rotation of said dispenser about said dispenser axis conveys said 
cylindrical objects onto said impression guide surface. Preferably the 
apparatus comprises a plurality of object dispensers spaced axially along 
said dispenser axis. 
In preferred embodiments of the invention the apparatus comprises a heater 
which heats heating said cylindrical objects before printing and/or a 
fixing heater which heats the objects after printing. Preferably, the 
heater comprises: 
a hot plate; and 
a moving surface situated beneath and spaced from the hot plate by at a 
distance such that an object situated between the hot plate and the moving 
surface contacts both the hot plate and the moving surface. 
In one preferred embodiment of the invention the cylindrical object is a 
generally circularly cylindrical object. In another it is a generally 
elliptically cylindrical object. As used herein elliptically cylindrical 
is used to include non-circularly cylindrical objects which may not be 
mathematical ellipses but which generally correspond to flattened circular 
cylinders. 
In one preferred embodiment of the invention the impression guide comprises 
a substantially fixed, preferably elastomer coated, surface along which 
the cylindrical object is guided. In another it comprises a tensioned 
flexible surface along which the cylindrical surface is guided. 
There is further provided fixing apparatus for fixing toner images, 
preferably, liquid toner images, on cylindrical objects such as cans 
partially filled with a liquid, the fixing apparatus comprising: 
a hot plate; and 
a moving surface situated beneath and spaced from the hot plate by at a 
distance such that an object situated between the hot plate and the moving 
surface contacts both the hot plate and the moving surface. 
There is further provided a method for printing images, preferably toner 
images or liquid toner images, on generally cylindrical objects, 
comprising: 
conveying said cylindrical objects to an image bearing surface in timed 
relation with images on the image bearing surface; 
supporting said cylindrical objects in rolling contact with said image 
bearing surface; and 
transferring said images from said image bearing surface to surfaces of 
said cylindrical objects when in contact therewith. 
In a preferred embodiment of the invention the support includes supporting 
the cylindrical object with a support which is generally parallel to the 
image bearing surface along which the cylindrical object rolls along said 
support. 
In a second preferred embodiment of the invention the support is a 
generally flexible support. In another it is a generally fixed support. 
In a preferred embodiment of the invention the cylindrical objects are 
heated before and/or after printing. 
Preferably the cylindrical objects are precoated with a polyvinylpyridine 
homopolymer or a polyvinylpyridine copolymer with styrene prior to 
printing thereon. 
There is further provided, in accordance with a preferred embodiment of the 
invention, a method or printing toner images, preferably, liquid toner 
images on a metal surface including: 
coating the metal surface with a polyvinylpyridine homopolymer or with a 
polyvinylpyridine copolymer with styrene; and 
printing the toner image on the coating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference is now made to FIGS. 1 and 2 which illustrate a multicolor 
printing or electrostatic imaging system, constructed and operative in 
accordance with a preferred embodiment of the present invention. As seen 
in FIGS. 1 and 2, an imaging sheet, preferably an organic photoreceptor 
12, is mounted on a rotating drum 10. Drum 10 is rotated about its axis by 
a motor or the like (not shown), in the direction of arrow 18, past 
charging apparatus 14, preferably a corotron, scorotron or roller charger 
or other suitable charging apparatus as are known in the art which is 
adapted to charge the surface of sheet photoreceptor 12. An image to be 
reproduced is focused by an imager 16 upon the charged surface 12 at least 
partially discharging the photoconductor in the areas struck by light, 
thereby forming an electrostatic latent image. Thus, the latent image 
normally includes image areas at a first electrical potential and 
background areas at a second electrical potential. 
Photoreceptor sheet 12 may use any suitable arrangement of layers of 
materials as is known in the art, however, in the preferred embodiment of 
the photoreceptor sheet, certain of the layers are removed from the ends 
of the sheet to facilitate its mounting on drum 10. 
This preferred photoreceptor sheet and preferred methods of mounting it on 
drum 10 are described in a copending application of Belinkov et al., 
IMAGING APATUS AND PHOTORECEPTOR THEREFOR, filed Sep. 7, 1994, assigned 
serial number 08/301,775 now U.S. Pat. No. 5,508,790 and corresponding 
patent applications filed in other countries, the disclosure of which is 
incorporated herein by reference. Alternatively, photoreceptor 12 may be 
deposited on drum 10 and may form a continuous surface. Furthermore, 
photoreceptor 12 may be a non-organic type photoconductor based, for 
example, on a compound of selenium. 
It should be noted that in other, alternative, preferred embodiments of the 
invention, non-electrophotographic methods may be used for generating the 
electrostatic latent image. For example, the latent image may be a 
changeable or a permanent latent image generated by ionographic or other 
electrostatic image forming means. 
In a preferred embodiment of the present invention, imager 16 is a 
modulated laser beam scanning apparatus, or other laser imaging apparatus, 
such as is known in the art. 
Also associated with drum 10 and photoreceptor sheet 12, in the preferred 
embodiment of the invention, are a multicolor liquid developer spray 
assembly 20, a developing assembly 22, color specific cleaning blade 
assemblies 34, a background cleaning station 24, an electrified squeegee 
26, a background discharge device 28, an intermediate transfer member 30, 
cleaning apparatus 32, and, optionally, a neutralizing lamp assembly 36. 
Developing assembly 22 preferably includes a development roller 38. 
Development roller 38 is preferably spaced from photoreceptor 12 thereby 
forming a gap therebetween of typically 40 to 150 micrometers and is 
charged to an electrical potential intermediate that of the image and 
background areas of the image. Development roller 38 is thus operative, 
when maintained at a suitable voltage, to apply an electric field to aid 
development of the electrostatic latent image. 
Development roller 38 typically rotates in the same sense as drum 10 as 
indicated by arrow 40. This rotation provides for the surface of sheet 12 
and development roller 38 to have opposite velocities at the gap between 
them. 
Multicolor liquid developer spray assembly 20, whose operation and 
structure is described in detail in U.S. Pat. No. 5,117,263, the 
disclosure of which is incorporated herein by reference, may be mounted on 
axis 42 to allow assembly 20 to be pivoted in such a manner that a spray 
of liquid toner containing electrically charged pigmented toner particles 
can be directed either onto a portion of the development roller 38, a 
portion of the photoreceptor 12 or directly into a development region 44 
between photoreceptor 12 and development roller 38. Alternatively, 
assembly 20 may be fixed. Preferably, the spray is directed onto a portion 
of the development roller 38. 
Color specific cleaning blade assemblies 34 are operatively associated with 
development roller 38 for separate removal of residual amounts of each 
colored toner remaining thereon after development. Each of blade 
assemblies 34 is selectably brought into operative association with 
development roller 38 only when toner of a color corresponding thereto is 
supplied to development region 44 by spray assembly 20. The construction 
and operation of cleaning blade assemblies is described in PCT Publication 
WO 90/14619 and in U.S. Pat. No. 5,289,238, the disclosures of which are 
incorporated herein by reference. 
Each cleaning blade assembly 34 includes a toner directing member 52 which 
serves to direct the toner removed by the cleaning blade assemblies 34 
from the development roller 38 to separate collection containers 54, 56, 
58, and 60 for each color to prevent contamination of the various 
developers by mixing of the colors. The different color toners collected 
by collection containers 54, 56, 58 and 60 are recycled to corresponding 
toner reservoirs 55, 57, 59 and 61. A final toner directing member 62 
always engages the development roller 38 and the toner collected thereat 
is supplied into collection container 64 and thereafter to a 
carrier-liquid reservoir 65 via a separator 66 which is operative to 
separate relatively clean carrier liquid from the various colored toner 
particles. The separator 66 may be typically of the type described in U.S. 
Pat. No. 4,985,732, the disclosure of which is incorporated herein by 
reference. 
In a preferred embodiment of the invention, as described in PCT Publication 
WO 92/13297, the disclosure of which is incorporated herein by reference, 
where the imaging speed is very high, a background cleaning station 24 
typically including a reverse roller 46 and a wetting roller 48 is 
provided. Reverse roller 46 which rotates in a direction indicated by 
arrow 50 is preferably electrically biased to a potential intermediate 
that of the image and background areas of photoconductive drum 10, but 
different from that of the development roller 38. Reverse roller 46 is 
preferably spaced apart from photoreceptor sheet 12 thereby forming a gap 
therebetween which is typically 40 to 150 micrometers. 
Wetting roller 48 is preferably partly immersed in a fluid bath 47, which 
preferably contains carrier liquid received from carrier liquid reservoir 
65 via a conduit 88. Wetting roller 48, which preferably rotates in the 
same sense as that of drum 10 and reverse roller 46, operates to wet 
photoreceptor sheet 12 with non-pigmented carrier liquid upstream of 
reverse roller 46. The liquid supplied by wetting roller 48 replaces the 
liquid removed from drum 10 by development assembly 22, thus allowing the 
reverse roller 46 to remove charged pigmented toner particles by 
electrophoresis from the background areas of the latent image. Excess 
fluid is removed from reverse roller 46 by a liquid directing member 70 
which continuously engages reverse roller 46 to collect excess liquid 
containing toner particles of various colors which is in turn supplied to 
reservoir 65 via collection container 64 and separator 66. 
Wetting roller 48 is preferably electrically biased to a potential 
intermediate that of the image and background areas of photoconductive 
drum 10, but lower than that of the development roller. This biasing of 
wetting roller 48 assists in removing toner particles from the background 
areas of photoreceptor sheet 12. Wetting roller 48 is preferably spaced 
apart from photoreceptor sheet 12 thereby forming a gap therebetween which 
is typically 40 to 200 micrometers. 
Apparatus embodied in reference numerals 46, 47, 48 and 70 is generally not 
required for low speed systems, but is preferably included in high speed 
systems. 
Preferably, an electrically biased squeegee roller 26 is urged against the 
surface of sheet 12 and is operative to remove liquid carrier from the 
background regions and to compact the image and remove liquid carrier 
therefrom in the image regions. Squeegee roller 26 is preferably formed of 
resilient slightly conductive polymeric material as is well known in the 
art, and is preferably charged to a potential of several hundred to a few 
thousand volts with the same polarity as the polarity of the charge on the 
toner particles. 
Discharge device 28 is operative to flood sheet 12 with light which 
discharges the voltage remaining on sheet 12, mainly to reduce electrical 
breakdown and improve transfer of the image to intermediate transfer 
member 30. Operation of such a device in a "write black" system is 
described in U.S. Pat. No. 5,280,326, the disclosure of which is 
incorporated herein by reference. 
FIGS. 1 and 2 further show that multicolor toner spray assembly 20 receives 
separate supplies of colored toner typically from four different 
reservoirs 55, 57, 59 and 61. FIG. 1 shows four different colored toner 
reservoirs 55, 57, 59 and 61 typically containing the colors Yellow, 
Magenta, Cyan and, optionally Black, respectively. Pumps 90, 92, 94 and 96 
may be provided along respective supply conduits 98, 101, 103 and 105 for 
providing a desired amount of pressure to feed the colored toner to 
multicolor spray assembly 20. Alternatively, multicolor toner spray 
assembly 20, which is preferably a three level spray assembly, receives 
supplies of colored toner from up to six different reservoirs (not shown) 
which allows for custom colored tones in addition to the standard process 
colors. 
A preferred type of toner for use with the present invention is that 
described in Example 1 of U.S. Pat. No. 4,794,651, the disclosure of which 
is incorporated herein by reference or variants thereof as are well known 
in the art. For colored liquid developers, carbon black is replaced by 
color pigments as is well known in the art. Other toners may alternatively 
be employed, including liquid toners and, as indicated above. Preferred 
liquid toners are also described in the various patents and patent 
applications referred to herein and/or incorporated herein by reference. 
Toners that can be used with the present invention are described in Example 
1 of U.S. Pat. No. 4,794,651, the disclosure of which is incorporated 
herein by reference or variants thereof as are well known in the art. For 
colored liquid developers, carbon black is replaced by color pigments as 
is well known in the art. Other toners may alternatively be employed, 
including liquid toners and, as indicated above, including powder toners. 
Other toners for use in the invention can be prepared using the following 
method: 
1) Solubilizing 1400 grams of Nucrel 925 (ethylene copolymer by Dupont) and 
1400 g of Isopar L (Exxon) are thoroughly mixed in an oil heated Ross 
Double Planetary Mixer at least 24 RPM for 1.5 hours, with the oil 
temperature at 130.degree. C. 1200 g of preheated Isopar L is added and 
mixing is continued for an additional hour. The mixture is cooled to 
45.degree. C., while stirring is continued over a period of several hours, 
to form a viscous material. 
2) Milling and Grinding 762 grams of the result of the Solubilizing step 
are ground in a 1S attritor (Union Process Inc. Akron Ohio), charged with 
3/16" carbon steel balls at 250 RPM, together with 66.7 grams of Mogul L 
carbon black (Cabot), 6.7 grams of BT 583D (blue pigment produced by 
Cookson), 5 grams of aluminum stearate (Riedel Dehaen) and an additional 
1459.6 grams of Isopar L for eight hours at 30.degree. C. 
3) Continuation of Grinding In one embodiment of the invention an 
additional grinding step is performed. In this step 34.5 grams of ACumist 
A-12 (a micronised polyethylene wax produced by Allied Signal) is added 
after step 2 and grinding is continued for an additional 4 hours. The 
resulting particles are fibrous particles have a measured diameter in the 
range of 1-3 micrometers. 
The resulting material is diluted with additional Isopar L and Marcol 82 to 
give a working developer in which the dry solids portion is about 1.7% and 
in which the overall ratio of Isopar L to Marcol is between about 50:1 and 
500:1, more preferably between about 100:1 and 200:1. Charge director as 
described in U.S. patent application Ser. No. 07/915,291 (utilizing 
lecithin, BBP and ICIG3300B) and in WO 94/02887, in an amount 
approximately equal to 40 mg/gm of solids in the final dispersion, is 
added to charge the toner particles. Other charge directors and additional 
additives as are known in the art may also be used. 
The above described process produces a black toner. Cyan, magenta and 
yellow toners can be produced by using a different mix of materials for 
step 2). For Cyan toner, 822 g of the solubilized material, 21.33 grams 
each of BT 583D and BT 788D pigments (Cookson), 1.73 grams of D1355DD 
pigment (BASF), 7.59 grams of aluminum stearate and 1426 grams of Isopar L 
are used in step 2. For Magenta toner, 810 grams of solubilized material, 
48.3 grams of Finess Red F2B, 6.81 grams of aluminum stearate and 1434.2 
grams of Isopar L are used in step 2. For yellow toner 810 grams of 
solubilized material, 49.1 grams of D1355DD pigment, 6.9 grams of aluminum 
stearate and 1423 grams of Isopar L are used in step 2. 
Intermediate transfer member (ITM) 30 may be any suitable intermediate 
transfer member, for example, as described in U.S. Pat. Nos. 4,684,238 and 
4,974,027 or in PCT Publication WO 90/04216, the disclosures of which are 
incorporated herein by reference. Alternatively, in a preferred embodiment 
of the invention, ITM 30 has a multilayered transfer portion such as those 
described below or in U.S. Pat. Nos. 5,089,856 and 5,047,808, or in U.S. 
patent application Ser. No. 08/371,117 now U.S. Pat. No. 5,745,829, filed 
Jan. 11, 1995 and entitled IMAGING APATUS AND INTERMEDIATE TRANSFER 
BLANKET THEREFOR, the disclosures of all of which are incorporated herein 
by reference. In a preferred embodiment of the invention a softer than 
normal intermediate transfer member is used and is produced according to 
the following method. 
FIG. 7 shows a transfer portion 204 comprises a release layer 209 which is 
outermost on the blanket when it is mounted on drum 30. Underlying layer 
209 is a conforming layer 211 preferably of a soft elastomer, preferably 
of polyurethane and preferably having a Shore A hardness of about 40, 
although other hardnesses between about 30 and 60 are also sometimes 
suitable. Underlying layer 211 is a conductive layer 214 which overlays a 
thin barrier layer 215. Barrier layer 215 overlays a blanket body 216 
comprising a top layer 218, a compressible layer 220 and a fabric layer 
222. Underlying the fabric layer is preferably an adhesive layer 226 which 
is in contact with the core of drum 30. 
1--The starting structure for blanket construction is a blanket body 216 
generally similar to that generally used for printing blankets. One 
suitable body is MCC-1129-02 manufactured and sold by Reeves SpA, Lodi 
Vecchio (Milano), Italy. Other preferred blanket bases have been described 
previously in the parents of parents of U.S. patent application Ser. No. 
08/371,117 now U.S. Pat. No. 5,745,829, which are incorporated herein by 
reference. In a preferred embodiment of the invention, body 216 comprises 
a fabric layer 222, preferably of woven NOMEX material and having a 
thickness of about 200 micrometers, a compressible layer 220, preferably 
comprising about 400 micrometers of saturated nitrile rubber loaded with 
carbon black to increase its thermal conductivity. Layer 220 preferably 
contains small voids (about 40-60% by volume) and a top layer 218 
preferably comprised of the same material as the compressible layer, but 
without voids. Layer 209 is preferably about 100 micrometers thick. The 
blanket body is produced by manufacturing methods as are generally used 
for the production of offset printing blankets for ink offset printing. 
Blanket body 216 is preferably sized to a relatively exact thickness by 
abrading portions of the surface of top layer 218. A preferred thickness 
for the finished body 216 is about 700 micrometers, although other 
thicknesses are useful, depending on the geometry of the printing system 
in which it is used and the exact materials used in the blanket body. 
2--The fabric side of blanket body 216 is preferably coated with a 30 
micrometer thick coating of silicone based adhesive (preferably, Type D 66 
manufactured by Dow Corning) for mounting onto the core. 
3--Top layer 218 is preferably coated with a sub-micron layer of primer 
before being coated with additional layers. A preferred primer is Dow 
Corning 1205 Prime Coat. The type of primer depends on the properties of 
the top layer and of the conductive layer. Preferably, 0.3 micron of 
primer is coated onto a clean top layer with a No. 0 bar in a wire-rod 
coating apparatus and is allowed to dry before applying the conductive 
layer. 
4--Since blanket body 216 may contain materials such as anti-oxidants, 
anti-ozonants or other additives which may migrate through the upper 
layers of the blanket, for example as a gas when the blanket is heated 
during the imaging process and/or in the presence of carrier liquid such 
as Isopar L, barrier layer 215 is preferably coated onto top layer 218 (or 
more exactly onto the primer). This barrier layer should be substantially 
impervious to such materials in the blanket body which may migrate and/or 
to the carrier liquid which is used. 
If this layer is omitted, under certain circumstances the additive 
materials can cause deterioration of the photoreceptor. In particular, it 
was found that the imaging process may become humidity dependent. 
In a preferred embodiment of the invention, a 4-11 micrometer layer of 
polyvinyl alcohol (88% hydrolyzed) is coated onto the primer layer 
covering top layer 218. 
Polyvinyl alcohol, 88% hydrolyzed, having an average molecular weight 
preferably between 85,000 and 145,000 (Aldrich Chemical Co. Inc., 
Milwaukee, Wis.) is dissolved in water at 90.degree. C. by continuously 
stirring the mixture in a reflux system for 30 minutes. After 30 minutes, 
a quantity of ethanol equal to twice the quantity of water is added to the 
solution, the resulting polyvinyl alcohol concentration being preferably 
less than 10%. Higher concentration solutions can be used; however, they 
give a more viscous solution which is hard to spread evenly. 
The solution is deposited on layer 218 of body 216 using a fine wire rod or 
knife inclined at 30.degree.-45.degree. to the direction of movement of 
the knife or body. The solvent is evaporated either by drying at room 
temperature or by blowing hot air on the layer. 
One or more coating passes are employed to give the required thickness. 
Too thin a layer will result in some transfer of material from body 216, 
which has been correlated with reduced transfer efficiency from the 
photoreceptor to the intermediate transfer blanket, which is believed to 
be caused by photoreceptor deterioration. While four micrometers of 
material appears to be sufficient to avoid leaching, a somewhat larger 
thickness such as 6 micrometers is preferably used. 
Other barrier materials and other thicknesses may be used depending on the 
carrier liquid used for the toner or the gasses omitted by body 216. Other 
barrier materials may require lesser or greater thickness depending on 
their resistance to the carrier liquid or the gasses released by body 216. 
Alternatively, if body 216 resists leaching by the carrier liquid or does 
not contain materials which are released (especially when body 216 is 
heated) or any anti-oxidants and/or anti-ozonants, layer 215 may be 
omitted. 
Polyvinyl alcohol is a thermoplastic crystalline material having a melting 
point which is higher than the temperature of the blanket during 
operation. Polyvinyl alcohol is also believed to form a layer which is 
impervious to gasses and to the hydrocarbon carrier liquid used in the 
liquid toner. 
5--Conductive layer 214 is preferably formed of acrylic rubber loaded with 
conductive carbon black. In a preferred embodiment of the invention, only 
2-3 micrometers of conductive coating are required. The conductive layer 
is formed by first compounding 300 grams of Hytemp 4051EP (Zeon Chemicals) 
with 6 grams of Hytemp NPC 50 and 9 grams of sodium stearate in a two-roll 
mill for 20 minutes; and then dissolving 150 grams of the compounded 
material in 2000 grams of methyl ethyl ketone (MEK) by stirring for 12 
hours at room temperature. 
40 grams of conductive carbon black, such as, for example, Printex XE2 
(Degussa) are added to the solution and the mixture is ground in a 01 
attritor (Union Process) loaded with 3/16" steel balls. Grinding proceeds 
at 10.degree. C. for 4 hours after which time the material is diluted by 
the addition of MEK to a concentration of 7.5-8% solids and discharged 
from the grinder in the form of a conductive lacquer. 
The blanket (after step 3 or step 4) is overcoated with about 3 micrometers 
of the conductive lacquer (three passes using a No. 0 rod) and allowed to 
dry for 5 minutes at room temperature. 
An additional coating of primer is added over the conductive lacquer 
(except for the portion which is to be inserted into bar 108, as described 
hereinbelow) before the soft elastomeric conforming layer is applied. 
The resistance of the conductive layer should preferably be more than about 
20 kohms/square and preferably less than about 50 kohm/square. This value 
will depend on the resistivity of the layers above the conducting layer 
and on the aspect ratio of the blanket. In general, the resistance should 
be low enough so that the current flowing on the conducting layer (to 
supply leakage current through the overlying layers) should not cause a 
substantial variation of voltage along the surface of the blanket. The 
resistance of the conducting layer and, more importantly, the resistance 
of the overlying layers control the current flowing through the overlying 
layers. Generally speaking, the conductive layer has a relatively low 
resistance and resistivity, the conforming layer (layer 211) has a higher 
resistivity and the overlying release layer (layer 209) has a still higher 
resistivity. 
6--One kilogram of pre-filtered Fomrez-50 polyester resin (Hagalil Company, 
Ashdod, Israel) is dehydrated and degassed under vacuum at 60.degree. C. 
660 grams of the degassed material is mixed with 1.4 grams of 
di-butyl-tin-diluarate (Aldrich) and degassed at room temperature for 2 
hours. 33 grams of the resulting material, 3.5 grams of RTV Silicone 118 
(General Electric) and 4.0 grams of Polyurethane cross-linker, DESMODUR 
44V20 (Bayer) are stirred together. A 100 micrometer layer of the material 
is coated over the primed conductive layer using a No. 3 wire rod with 
several passes under clean conditions, preferably, class 100 conditions. 
The coating is cured for two hours at room temperature under a clean hood 
to form a polyurethane layer. 
Other methods of forming suitable conforming layers are shown and described 
in the parents of U.S. patent application Ser. No. 08/371,117 now U.S. 
Pat. No. 5,745,829. Alternatively, the conductive layer may be omitted and 
layer 218 made conductive. 
Layer 211 which is thus formed should have a resisivity of the order of 
about 10.sup.9 ohm-cm, good thermal stability at the working temperature 
of the blanket surface, which is preferably about 100.degree. C. or less. 
The function of the conforming layer is to provide good conformation of the 
blanket to the image forming surface (and the image on the image forming 
surface) at the low pressures used in transfer of the image from the image 
forming surface to the blanket. While a thickness of 100 micrometers is 
preferred, other thicknesses, between 50 micrometers and 300 micrometers 
can be used, with 75 to 125 micrometers being preferred. 
7-9 grams of RTV silicone 236 (Dow Corning) release material and 3 grams 
RTV 118 (General Electric) and 0.72 grams of Syl-off 297 (Dow Corning) are 
mixed together. A wire rod (bar No. 1) coating system is used, with five 
or six passes, under clean conditions to achieve an 8 micrometer release 
layer thickness. The material is cured at 140.degree. C. for two hours. 
The cured release material has a resistivity of approximately 10.sup.14 to 
10.sup.15 ohm-cm. 
Member 30 is maintained at a suitable voltage and temperature for 
electrostatic transfer of the image thereto from the toner image bearing 
surface of photoreceptor 12. 
Intermediate transfer member 30 preferably transfers the image onto the 
surfaces of generally cylindrical objects 72, such as full or empty tin 
coated steel or aluminum cans, which roll between member 30 and an 
impression guide surface 71, preferably by heat and pressure. Impression 
guide surface 71 is preferably made of a compliant, non-slip material such 
as neoprene or synthetic rubber. Member 30 is preferably rotated by a 
motor 73, such as a servomotor or the like, as shown in FIG. 3. 
A conveyor device 100 for transporting cylindrical objects 72 is described 
hereinbelow in greater detail with reference to FIGS. 3, 4 and 5. 
Cleaning apparatus 32 is operative to scrub clean the surface of 
photoreceptor 12 and preferably includes a cleaning roller 74, a sprayer 
76 for spraying a non polar cleaning liquid, preferably cool and fresh 
carrier liquid from reservoir 65, and a wiper blade 78 to complete the 
cleaning of the photoconductive surface. The sprayed carrier liquid 
assists in the scrubbing process and cools the photoreceptor surface. 
Cleaning roller 74 which may be formed of any synthetic resin known in the 
art for this purpose is driven in the same sense as drum 10 as indicated 
by arrow 80, such that the surface of the roller scrubs the surface of the 
photoreceptor. Any residual charge left on the surface of photoreceptor 
sheet 12 may be removed by flooding the photoconductive surface with light 
from optional neutralizing lamp assembly 36, which may not be required in 
practice. 
In accordance with a preferred embodiment of the invention, after 
developing each image in a given color, the single color image is 
transferred to intermediate transfer member 30. Subsequent images in 
different colors are sequentially formed on sheet 12 and electrostatically 
transferred, in alignment with the previous images, onto intermediate 
transfer member 30. When all of the desired images have been transferred 
thereto, the complete multi-color image is transferred from transfer 
member 30 to the surfaces of the cylindrical objects 72, preferably by 
heat and pressure. Impression guide surface 71 produces resilient 
operative engagement between intermediate transfer member 30 and 
cylindrical objects 72 when transfer of the composite images to 
cylindrical objects 72 takes place. 
It should be understood that the invention is not limited to the specific 
type of image forming system used and the present invention is also useful 
with any suitable imaging system. The specific details given above for the 
image forming system are included as part of a best mode of carrying out 
the invention, however, many aspects of the invention are applicable to a 
wide range of systems as known in the art for electrostatic and offset ink 
printing and copying. Furthermore, other specific details of the present 
image forming system, some of which may be part of the best mode of 
carrying out the invention, are included in the publications incorporated 
herein by reference. 
Reference is now made to FIGS. 3 and 4 which illustrate conveyor device 
100. Device 100 conveys circularly cylindrical objects 72 in timed 
relation with the toner image bearing surface of the intermediate transfer 
member 30, in accordance with a preferred embodiment of the present 
invention. Conveyor device 100 preferably includes an object dispenser 
102, which is rotated about an axis 104 by a motor 105, such as a 
servomotor or the like, the operation of which is controlled by a 
controller 122, as described in detail hereinbelow. 
A plurality of gate arms 106 are axially directed and circumferentially 
spaced on dispenser 102, each gate being adapted to pass one of 
cylindrical objects 72 when it is rotated in a counterclockwise direction. 
Alternatively, or additionally, groups of gates 106 may be axially spaced 
along the dispenser 102. As an example, FIGS. 3 and 4 illustrate two 
axially spaced groups of gates 106, each group comprising four gates 106 
spaced circumferentially about the axis 104. The groups are preferably 
separated from each other by a partition 108. Partition 108 is optional 
and may be removed especially where the cans or other objects nest into 
each other as is often the case with one piece aluminum can bodies. 
In a preferred embodiment of the present invention, a conveyor belt 110, 
located upstream of the object dispenser 102, conveys cylindrical objects 
72 to dispenser 102. Conveyor belt 110 includes partitions 112 which are 
sized and arranged for transferring the cylindrical objects 72 into gates 
106 of dispenser 102. As seen best in FIGS. 4, dispenser 102 is located 
somewhat below conveyor belt 110 and in juxtaposition therewith, such that 
cylindrical objects 72 exit conveyor belt 110 and generally smoothly enter 
gates 106. 
Impression guide surface 71 is located somewhat below dispenser 102 and is 
substantially parallel to a portion of the intermediate transfer member 30 
where transfer of images takes place, as seen in FIGS. 3 and 4A. As seen 
best in FIG. 4A, each cylindrical object 72 exits its corresponding gate 
106, drops onto impression guide surface 71 and comes into contact with 
intermediate transfer member 30. Since cylindrical objects 72 contact both 
impression guide surface 71 and intermediate transfer member 30, rotation 
of intermediate transfer member 30 causes each cylindrical object 72 to 
roll about its own axis in a direction indicated by arrow 116. 
An overhead guide 118, fully shown in FIGS. 4 and partially shown in FIG. 
3, is preferably located generally above the area where the cylindrical 
objects 72 start to enter and exit gates 106, to guide cylindrical objects 
72 into the gates and in their drop onto impression guide surface 71. 
Overhead guide 118 preferably comprises one or more idler rollers 120. 
In accordance with a preferred embodiment of the present invention, a 
controller 122 is provided which coordinates conveyance of cylindrical 
objects 72 from conveyor device 100 to intermediate transfer member 30, 
such that images are transferred from intermediate transfer member 30 to 
the surfaces of the cylindrical objects 72 in a predetermined manner. 
Controller 122 is preferably in electrical communication with motors 105 
and 73 which respectively control rotation of dispenser 102 and rotation 
of intermediate transfer member 30, and may be in electrical communication 
with motors which control movement of the conveyor belt 110 and other 
parts of the printing device as well, such as drum 10. Controller 122 also 
communicates with intermediate transfer member 30 and receives information 
therefrom regarding the position of images on member 30. The controller 
122 ensures proper registration of the cylindrical objects 72 as they come 
into printing contact with intermediate transfer member 30. 
FIG. 5 shows a system, similar to that of FIG. 4, in which the cylindrical 
objects are gravity fed directly into the gates. Such a system has been 
found to operate well with a feed slope of about 5%. Use of a much smaller 
slope results in poor feeding of the objects. A higher feed slope will 
result in additional pressure on the gate. This can be reduced by 
providing intermediate gates along the slope to reduce the pressure on any 
one gate. 
In the preferred embodiment illustrated in FIGS. 3, 4 and 5, each image 
transferred from member 30 includes four sub-images, one for each 
cylindrical object 72, such that each printing cycle includes printing on 
four cylindrical objects 72. Of course, where smaller objects or a larger 
drum 30 is used, more objects are printed per rotation of drum 30. 
Additionally in accordance with a preferred embodiment of the present 
invention, there is provided a heater 124 for heating cylindrical objects 
72 before printing, as shown in FIGS. 3 and 4. Heater 124 is preferably 
located above conveyor belt 110 upstream of the conveyor drum 102 and in 
contact with cylindrical objects 72. Pre-heating of cylindrical objects 
72, especially empty cans may help in fixing the image. 
It should be noted that transfer from a heated intermediate transfer member 
generally fixes the images. However, if additional fixing is required, an 
optional fixing heater 126, preferably a hot plate at a temperature of 
about 200.degree. C. is provided for heating the cylindrical objects 72 
after printing to give improved fixing of the transferred and fixed 
images, as shown in FIG. 3. Heater 126 is preferably located directly 
above and in contact with cylindrical objects 72 downstream of impression 
guide surface 71. 
Cylindrical objects which contain food or beverages are not normally 
completely filled, but rather an air or gas filled gap, or substantially 
evacuated gap, exists between the uppermost portion of the envelope of the 
cylindrical objects and their contents. Each cylindrical object is 
conveyed under heaters 124 and 126 in a horizontal orientation, so that 
this space lies between the contents and the inner top surface of the 
cylindrical object. This gap helps to thermally insulate the contents of 
the cylindrical objects from the thermal energy of heaters 124 and 126 and 
thereby help prevent thermal damage. The gap also enables a relatively 
high surface temperature to be reached to give good fixing, without the 
contents carrying away the heat. 
Temperature control apparatus may also be provided to ensure that heaters 
124 and 126 do not cause thermal damage to the contents of cylindrical 
objects 72. 
Generally, to provide suitable fixing it is necessary for cans 72 to be 
subject to heater 126 for a long time. In order to provide an efficient 
and compact fixer and fuser, cans 72 travel at a much slower speed through 
the fuser than when they are printed. Since printing on the cylindrical 
objects takes place only once every n rotations thereof, where n is the 
number of colors in the image, the speed in the fuser may be several times 
slower than the speed of the cans in the image transfer region without any 
pile-up of cans occurring. 
FIG. 6 shows a schematic representation of a system for printing on the 
surface of elliptically cylindrical objects. In this embodiment of the 
invention, an elliptical cylindrical object 72' is brought to the image 
bearing surface of 30 by a conveyer belt 148 timed to bring the object to 
a first meeting point 150 together with a corresponding image on the image 
bearing surface of drum 30. Object 72' is fed by belt 148 and drum 30 into 
contact with an impression guide surface 71' which is the surface of a 
tensioned flexible and possibly somewhat elastic belt 152 which is 
pivotably fixed at its right end. The left end of belt 152 is tensioned by 
a spring which allows the distance between the portion of belt 71' beneath 
object 72' and drum 30 to vary as the elliptically cylindrical object 72' 
rolls along the belt under the influence of the drum. During this rolling 
action the belt maintains pressure between object 72' and the drum and the 
image is transferred to the object from the drum under the influence of 
heat and pressure. At the end of the printing process, the object is 
removed from the belt either by gravity (as in the embodiment shown) or by 
some other means. 
Some cans or other metallic cylindrical objects are sometimes precoated by 
epoxy paint or other white coating, as is known in the art. 
The present inventors have found that precoating cylindrical objects with a 
polymer having basic moieties on their backbone, such as, 
polyvinylpyridine homopolymer or with its copolymer with styrene prior to 
printing provides for excellent transfer of ink with substantially no 
aging effects. Other useful adhesion promoters are EVA (ethylene vinyl 
acetate) or hot melt adhesives such as members of the Macromelt family and 
particularly Macromelt 6239. 
If additional protection of the image is desired, it may be coated with a 
protective coating of a lacquer or other protective substance. 
It will be appreciated by persons skilled in the art that the present 
invention is not limited by the description and example provided 
hereinabove. Rather, the scope of this invention is defined only by the 
claims which follow: