Note: Descriptions are shown in the official language in which they were submitted.
CA 02064816 2000-06-14
-1-
IMAGE TRANSFER APPARATUS AND METHOD
FIELD OF THE INVENTION
The present invention relates to image transfer techniques and apparatus or
use in
liquid toner electrostatic imaging using an intermediate transfer member.
BACKGROUND OF THE INVENTION
The use of an intermediate transfer member in electrostatic imaging is well
known in the art.
Various types of intermediate transfer members are known and are described,
for
example in U.S. Patents 3,862,848 issued January 28, 1975, 4,684,238 issued
August 4,
1987, 4,690,539 issued September 1, 1987 and 4,531,825 issued July 30, 1985.
Belt-type intermediate transfer members for use in electrophotography are
known
in the art and are described, inter alia, in U.S. Patents 3,893,761 issued
July 8, 1975,
4,684,238 and 4,690,539.
In both liquid and powder toner imaging systems employing intermediate
transfer
members it is known to heat the toner images on the intermediate transfer
member before
transfer to the final substrate. In U. S. Patent 4,708,460 a liquid toner
image is heated by
radiant heat from a heater external to the transfer member in order to
evaporate the liquid
carrier and to melt the solid toner before transfer. In U. S. Patent 4,518,976
there is
described a belt image transfer system, wherein the belt is heated by a
heating roller,
provided at the back of the belt, during transfer from the belt to the final
substrate. In
U. S. Patent 4,585,319 a radiant heater in the center of a drum ITM is used to
heat the
ITM.
The use of intermediate transfer members is well known in the printing art. In
offset printing an image formed of a viscous ink is transferred from a first
drum to a
second drum prior to transfer to the final substrate. It has been recognized
that the
pressures between the various drums and against the final substrate are
important to the
quality of the final print.
Two types of offset blankets are generally available, consistent with the ink
characteristics. Conventional printing blankets are relatively stiff and have
provide
CA 02064816 2000-12-05
-2-
little leeway for packing error. Compressible blankets are made with varying
compressibilities,
with typical curves shown for example on page 33 of "Web Offset-Press
Operating", published
by Graphic Arts Technical Foundation, Pittsburgh, PA, 1984.
The Pressures used in offset printing are generally not specified. However,
pressures
are indicated to be in the general vicinity of .03-.045 Kg/m2 (100-150 lb./sq.
in.) in the above
reference and in U.S. Patent 3,983,287.
European Patent Publication 0 176 143 A1 published April 2, 1986 describes a
powder
toner copying machine utilizing an intermediate transfer member in which the
pressure and
deformation at first transfer is less than at second transfer.
Japanesepatentpublication62-134673pub1ishedJune 17,1987 describesapowdertoner
imaging system utilizing an intermediate transfer member in which the pressure
is greater at
second transfer than at first transfer.
U.S. Patent 4, 912, 514 describes a powder toner imaging system having a
heated
intermediate transfer belt where, in one embodiment the heater is formed of
enlongate elements
and the belt includes a silicone rubber layer.
U.S. Patent 4, 708, 460 describes a liquid toner imaging system in which an
intermediate
transfer member is used.
SUMMARY OF THE INVENTION
The present invention seeks to provide apparatus and techniques for improved
electrostatic image transfer using an intermediate transfer member.
There is therefore provided an imaging system including an image bearing
surface, an
intermediate transfer member operative for transfer of liquid toner images
from the image
bearing surface to a substrate, apparatus for providing first transfer
engagement between the
intermediate transfer member and the image bearing surface for transfer of an
image from an
image bearing surface to the intermediate transfer member at a first pressure,
producing
deformation of the intermediate transfer member to a first deformation degree,
and apparatus for
providing second transfer engagement between the intermediate transfer member
and the
t ~ ~~ ~~ ~ ~.
~~ so4 - 2,1 -
1 substrate for transfer of the image from the intermediate
2 transfer member to the substrate at a second pressure,
3 producing deformation of the intermediate transfer member to
4 a second deformation degree.
In a preferred embodiment of the invention the second
6 pressure exceeds the first pressure by a first multiple and
7 the second deformation degree exceeds the first deformation
8 degree by a second multiple, substantially less than said
9 first multiple.
In a preferred embodiment of the invention the
11 intermediate transfer member comprises a blanket heater
12 operative to heat the image thereon prior to the second
13 transfer engagement.
14 The blanket heater is operative in a further embodiment
1s
17
18
19
21
22
23
24
26
27
28
2s
31
32
33
34
36
37
38
W'O 91 /U3006 p~'i'/'~ L9U/OUUA9
- 3 _
Of °.'hss i n~ro"t; r.,. o..~ L~_.. ~L _
2 su: °ient to enhance transfer of liquid toner images fror.,
3 the :~termediate transfer member to the substrate.
4 In a preferred embodiment of the invention the
intermediate transfer member comprises a conductive layer
'6 operative to apply an electric field to the image to enhance
7 transfer of liquid toner images from the image bearing
8 surface to the intermediate transfer member.
9 In a preferred embodiment of the invention the
intermediate transfer member comprises a outward facing
11 transfer surface, a compressible layer, a backing layer and
12 a heating layer, the heating layer being ~ disposed
Z3 intermediate the backing layer and the transfer surface. In
14 a preferred embodiment of the invention the heating layer is
disposed intermediate the backing layer and the compressible
16 layer. In a preferred embodiment of the invention the
17 heating layer is disposed intermediate the transfer surface
18 and the compressible layer.
19 In a preferred embodiment of the invention the
intermediate transfer member also includes ~a second
21 compressible layer and the heating layer is disposed
22 inter7:ediate the compressible layer and the second
23 compressible layer.
24 In a further preferred embodiment of the invention the
intermediate transfer member .comprises at least one
26 compressible layer including a heating layer and a backing
27 layer disposed away from the image bearing surface. In a
28 preferred embodiment the heating layer is internal to the at
29 least one compressible layer.
In a preferred embodiment the pressure is substantially
31 constant along particular lines upon the first and second
32 transfer engagements on the intermediate transfer member,
33y and the heating layer is formed of elongate elements,
34 preferably thin wires, along the lines.
3~ There is further provided an imaging system including
36 an image bearing surface, an intermediate transfer member
37 operative far transfer of toner images from the image
38 bearing surface to a transfer surface of the intermediate
Wa 91/03006 PCf/'~'L90/00~49
transfer member and for subsequent transfer to a sub~~Y~tP~.
2 the transfer member including a compressible layer, a
3 backing layer disposed away from the transfer surface, and a
4 heating layer disposed intermediate the backing layer and
the transfer surface.
I6 In a preferred embodiment of the invention the heating
7 layer is disposed intermediate the compressible layer and
8 the transfer surface.
In a preferred embodiment of the invention the heating
layer is disposed intermediate the compressible layer and
11 the backing layer.
12 The transfer member further comprises, in a preferred
13 embodiment of the invention, a second compressible layer,
14 and the heating layer is disposed intermediate the
compressible layer and the second compressible layer.
16 There is further provided in a preferred embodiment of
17 the invention an imaging system including an image bearing
18 surface, an intermediate transfer member operative for
19 transfer of liquid toner images from the image bearing
surface to a substrate, the transfer member including at
21 least one compressible layer including a heating layer and a
22 backing layer disposed away from the image bearing surface.
23 In a preferred embodiment of the invention the heating
24 layer is internal to the at least one compressible layer.
In a preferred embodiment of the invention the
26 intermediate transfer member includes a conductive layer
27 operative to apply an electric field to the image to enhance
28 transfer of toner images from the image bearing surface to
29 the intermediate transfer member.
The heating layer is operative in a preferred
31 embodiment of the invention to heat the image to a
32 temperature sufficient to enhance transfer of toner images
33.. from the intermediate transfer member to the substrate.
34 According to a preferred embodiment of the invention
the apparatus also includes apparatus for providing first
36 transfer engagement between the intermediate transfer
37 member and the image bearing surface for transfer of an
38 Image from the image bearing surface to the intermediate
~'O 91/03006 PCT/'~L90/000.~9
1 transfer member at a first pressure and apparatus for
2 providing second transfer engagement between the
3 intermediate transfer member and the substrate for transfer
4 of the image from the intermediate transfer member to the
substrate at a second pressure, the pressure being
~6 substantially constant along particular lines upon the
7 first and second transfer engagements on the intermediate
8 transfer member, the heating layer is formed of thin wires
9 along the lines.
There is provided in a further embodiment of the
11 invention an intermediate transfer blanket for the transfer
12 of toner images from a first surface to a second surface and
13 including a transfer surface for operative engagement with
14 the first and second surfaces, a relatively compliant sponge
layer, and an area heater placed between the relatively
16 compliant sponge layer and the transfer surface.
17 In a preferred embodiment of the invention the blanket
18 also includes a relatively less.compliant resilient layer
19 placed between the heater and the transfer surface.
2Q In a preferred embodiment of the invention the toner
21 image is a liquid toner image.
22 Tn a preferred embodiment of the invention the heater
23 is energized by alternating current and the thin wires are
24 arranged in adjoining pairs, the voltage on each wire of the
pair being equal and of opposite sign to that of the other
26 with respect to a reference voltage. In a preferred
27 embodiment of the invention the reference voltage is ground.
28 An imaging system is further provided in a preferred
29 embodiment of the invention including an image bearing
surface and an intermediate transfer member operative for
31 transfer of toner images from the image bearing surface to a
32 transfer surfaee of the intermediate transfer member and
33. for subsequent transfer to a substrate, the transfer member
34 including at least one layer disposed toward the image
bearing surface and a backing layer disposed away from the
36 image bearing surface, the at least one layer including a
37 heating layer.
WO 91/03006 PCT/~3~,90/00049
!a .7 ,. '
~~~'~.~~~
1 13RTEF DES CRTJ?T'I0N l7F ~'HE DRAWIN_G_S
2 The present invention will be understood and
3 appreciated more fully from the following detailed
4 description, taken in conjunction with the drawings in
,5 which:
6 Fig. 1 is a simplified sectional illustration of
7 electrostatic imaging apparatus constructed and operative in
8 accordance with a preferred embodiment of the present
9 invention;
Fig. 2 is a simplified sectional illustration of
11 electrostatic imaging apparatus constructed and operative in
12 accordance with another preferred embodiment of the present
13 invention;
14 Fig. 3A is a simplified, Conceptual, sectional
illustration of an intermediate transfer member constructed
16 and operative in accordance with a preferred embodiment of
17 the present invention;
18 Fig. 3B is a simplified, conceptual, sectional
19 illustration of a portion of a preferred embodiment of the
intermediate transfer member of Fig. 3A;
21 Fig. 3C is a simplified, conceptual, sectional
22 illustration of a portion of a second preferred embodiment _
23 of the intermediate transfer member of Fig. 3A;
24 Fig. '3D is an illustration of a preferred heater for
the intermediate transfer member;
26 Fig. 3E is a detailed illustration of a portion of the
2~ heater of Fig. 3D;
28 Fig. 3F is an illustration of another preferred heater
29 for the intermediate transfer member;
Fig. 3G is a detailed illustration of a portion of the
31 heater of Fig. 3F;
32 Fig. 3H is a detailed illustration of a portion of an
33'. alternative to that of Fig. 3F;
34 Fig. 3T is an illustration of another preferred heater
for the intermediate transfer member;
36 Fig. 4 is a simplified sectional illustration of the
37 manufacture of part of the apparatus of Figs. 3A and 3H;
38 Fig. 5 is a graphical illustration of the relationship
CA 02064816 2000-06-14
_7_
between pressure and deformation of the apparatus of Fig. 3B; and
Fig. 6 is a schematic illustration of a preferred circuit for energizing the
heaters
of Figs. 3F - 3I.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is now made to Fig. 1, which illustrates electrostatic imaging
apparatus
constructed and operative in accordance with a preferred embodiment of the
present
invention. This and other embodiments of the invention are described by way of
example
for apparatus utilizing liquid toner with negatively charged toner particles,
and for a
write-white system. Forpositively charged tonerparticles and/or for a write-
black system
the magnitudes and or the polarities of the voltages may be adjusted as is
well known in
the art. In a preferred embodiment of the invention the toner of Example 1 of
U. S. Patent
4,794,651 is employed, but a variety of liquid toner types may be used in the
practice of
the invention.
As in conventional electrophotographic systems, the apparatus of Fig. 1
comprises
a drum 10 arranged for rotation about an axle 12 in a direction generally
indicated by
arrow 14. The drum 10 is formed with a cylindrical photoconductor surface 16.
A corona discharge device 18 is operative to generally uniformly charge the
photoconductor surface 16 with a positive charge. Continued rotation of the
drum 10
brings the charged photoconductor surface 16 into image receiving relationship
with an
exposure unit including a lens 20, which focuses a desired image onto the
charged
photoconductor surface 16, there by selectively discharging the photoconductor
surface
and producing an electrostatic latent image thereon. Lens 20 may be the lens
of a
photocopier, as illustrated. Alternatively the latent image may be formed by a
laser
scanner.
Continued rotation of the drum 10 brings the charged photoconductor surface 16
bearing the electrostatic latent image into operative association with a
development unit
CA 02064816 2000-12-05
_g_
22, including development electrodes 24, which is operative to apply a liquid
developer
comprising carrier liquid and toner particles to the photoconductor surface to
develop the
electrostatic latent image thereon.
In accordance with a preferred embodiment of the invention, following
application of toner to photoconductor surface 16, photoconductor surface 16
passes a
typically positively charged, rotating roller 26, preferably rotating in a
direction indicated
by an arrow 28. Typically the spatial separation of the roller 26 from the
photoconductor
surfacel6 is about 50 microns.
Preferably, the voltage on roller 26 is intermediate the voltages of the
latent image
areas and of the background areas on the photoconductor surface 16. Typical
voltages
are: roller 26: + 300 to + 500 V, background area: +SOV and latent image
areas: up to
+1000 V.
It is appreciated that roller 26, rotating in the direction indicated by arrow
28,
functions as a metering roller and reduces the thickness of liquid carrier on
the
photoconductor surface 16, as is known in the art.
In any event, the photoconductor surface 16, after passing the roller 26,
should
be relatively free of pigmented toner particles except in the region of the
latent image.
Downstream of roller 26 there is preferably provided a rigidizing roller 30.
Rigidizing roller 30 is preferably formed of a resilient polymeric material,
such as the
conductive resilient polymeric materials described in either or both of U.S.
Patents
3,959,574 and 3,863,603. Roller 30 is preferably maintained in contacting and
preferably
pressured relationship with the photoconductor surface 16.
In a preferred embodiment of the invention, the biased described in U.S.
Patent
4,286,039, is used as the roller 30. A negative voltage of about 1000 to 2000
Volts,
preferably about 1500 Volts (for a write-white system), is
wV0 9l/03006 pL'!'/'wL90/OOd~9
-- 9 A
1 maintained on the squeegee. A corona discharge takes place
2 and a current of approximately 50 - 100 microamperes for a
3 drum width of 30 cm, flows from the squeegee. ~toller 30
4 repels negatively charged pigmented toner particles and
. 5 causes them to more closely approach the image areas of the
6 photoconductor surface 16, thus compressing and rigidizing
7 the toner image thereon.
8 Downstream of rigidizing roller 30 there is provided an
9 intermediate transfer m--fiber 40, which rotates, as shown by
arrow 41, in a sense opposite to that of drum l0, and is
11 operative for receiving the toner image from surface 16 and
12 for transferring the toner image to a receiving substrate
13 42, such as paper, which is supported by a roller 43.
14 In accordance with a preferred embodiment, a particular
feature of the invention is that intermediate transfer
16 member 40 is configured and mounted with respect to drum l0
17 so as to provide first transfer engagement between
18 intermediate transfer member 40 and image bearing
19 photoconductor surface 16 for transfer of an image from
surface 16 to the intermediate transfer member 40 at a first
21 pressure, thereby producing radial deformation of the
22 intermediate transfer member to a first deformation degree.
23 The configurations and arrangements of intermediate
24 transfer member 40, substrate 42 and roller 43 are
preferably such as to provide second transfer engagement
26 between intermediate transfer member 40 and substrate 42 for
27 transfer of the image from intermediate transfer member 40
28 to substrate 42 at a second pressure, which exceeds the
29 first pressure by a first multiple, producing radial
deformation of the intermediate transfer member to a second
31 deformation degree which exceeds the first deformation
32 degree by a second multiple substantially less than the
3'~ first multiple.
34 Additionally in accordance with a preferred embodiment
of the present invention there is provided an intermediate
36 transfer member characterized in that deformation thereof
37 increases less than linearly with the application of
38 increased pressure thereto. The structure of intermediate
CA 02064816 2000-06-14
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transfer members in accordance with preferred embodiments of the invention is
described hereinbelow in detail.
Transfer of the image to intermediate transfer member 40 is preferably
facilitated
by providing electrification of the intermediate transfer member 40 to a
voltage opposite
that of the charged particles, although other methods known in the art may be
employed.
Subsequent transfer of the image to substrate 42 is preferably facilitated by
heat and
pressure, although other methods known in the art may be employed.
It has been noted that when the negatively biased squeegee roller of U.S.
Patent
4,286,039, with high negative voltage, is utilized as the roller 30, the
positive voltage on
the intermediate transfer member required to transfer the image thereto is
sharply
reduced, typically from about 1000 volts or more to about 500 to 600 volts or
less. It is
believed that this reduction is possibly due to a discharge of the charges in
the image area
of the photoconductor surface 16 by current from the squeegee roller.
Following transfer of the toner image to the intermediate transfer member, the
photoconductor surface 16 is engaged by a cleaning roller assembly 50,
including a pair
of rollers 52, which typically rotate in opposite directions, and a nozzle 54.
Cleaning
roller assembly 50 is operative to scrub and clean surface 16. A cleaning
material, such
as liquid developer, may be supplied to the assembly 50 via nozzle 54. A
suitable
cleaning assembly is shown and described in U.S. Patent 4,439,035. Any
residual charge
left on the photoconductor surface 16 may be removed by flooding the
photoconductor
surface 16 with light from a lamp 58.
Reference is now made to Fig. 2 which illustrates electrophotographic imaging
apparatus constructed and operative in accordance with another preferred
embodiment
of the present invention. The apparatus of Fig. 2 shares many common elements
with that
of Fig. 1. These elements are indicated by identical reference numerals, and
for the sake
of conciseness are not described herein a second time.
CA 02064816 2000-06-14
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The embodiment of Fig. 2 differs from that of Fig. 1 in that a belt-type
intermediate transfer member 70 is employed instead of the roller type member
40 in the
embodiment of Fig. l . Belt-type intermediate transfer members are well known
in the art
and are described, inter alia, in U.S. Patents 3,893,761, 4,684,238 and
4,690,539.
Intermediate transfer member 70 preferably charged so as to provide
electrophoretic transfer thereto of the image from the photoconductor surface
16. The
efficiency of electrophoretic transfer of the image is generally enhanced by
increasing the
potential difference between photoconductor surface 16 and intermediate
transfer
member 70. Increase in the potential difference between the photoconductor
surface 16
and the intermediate transfer member 70 is limited, however, by the danger of
severe
electrical breakdown, which increases with an increase in potential
difference.
Reference is now made to Fig. 3A which conceptually illustrates an
intermediate
transfer member 40 comprising a drum 80 having a generally cylindrical surface
over
which is tensioned a mufti-layer intermediate transfer blanket 82, which is
supported and
tensioned by a blanket lockup mechanism 84. The electrical connections to the
various
voltage bearing portions of intermediate transfer blanket 82 are not shown, it
being
understood that they are achieved in a conventional manner using rotating
contacts.
A preferred embodiment of mufti-layer intermediate transfer blanket 82 is
illustrated in Fig. 3B and comprises a substrate (backing layer) 90 with high
temperature
capabilities, preferably formed of Kapton' (Dupont) polyimide film of
thickness about
100 microns. Over the substrate 90 there is provided a blanket heater 92
preferably
comprising a meandering ribbon conductor of Nichrome in a sandwich of Kapton'.
Blanket heater 92 has a total thickness of about 250 microns.
Normally one surface of blanket heater 92 has a slightly raised pattern due to
the
presence of the ribbon. Accordingly, it is preferable to arrange the blanket
heater 92 such
that the surface having the slightly raised pattern lies facing substrate 90.
Blanket heater 92, in conjunction with the rest of the intermediate transfer
blanket 82, operates to improve transfer of the image to the final substrate
by heating the
toner image. When a liquid toner for which the particles solvate the carrier
at a
temperature below the melting point of the toner particles is utilized in the
practice of the
invention, the surface of the blanket should be heated to a temperature above
the
solvation temperature of the toner image, i.e. above the temperature at which
the toner
* Trade Mark
CA 02064816 2000-06-14
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particles become tacky to the final substrate. For the preferred toner of
Example
1 of U.S. Patent 4,794,651, the blanket heater is preferably operative to heat
the image
on the intermediate transfer member to about 100-100° C.
To ensure even heating, the top of the blanket heater 92 is preferably
attached
to an approximately 100 micron thick aluminum foil 93. This foil also provides
electromagnetic shielding of the image transfer regions of the imaging
apparatus from
interference produced by AC currents used to heat the blanket 92. The width of
the
Nichrome ribbon is chosen such that the ribbon covers a major portion,
preferably over
80%, of the blanket, to ensure even heating thereof.
Disposed over foil 93 is a three part sponge assembly layer 94, including a
layer
96 typically formed of Kapton*, typically of thickness 100 microns, a sponge
layer 98,
typically of thickness 300 microns and a fabric layer 100, typically formed of
NOMEX*
(DuPont) and being typically of thickness 350 microns. The total sponge
assembly layer
thickness is typically 800 microns. Nomex* is basically an aromatic polyamide
and chars
at 420 ° C.
The assembly layer 94 is preferably formed by blending the following
materials,
which form the sponge layer 98, in the following proportions, in a two roll
mill:
a. Fluorosilicone (FSE-2080 General Electric)* 78.39%
b. Silicone (Silastic* 4-2735 Dow Corning) 11.71%
c. Blowing Agent (#9038 Rhone Poulenc) 9.00%
d. Cross-Linker (Di Cumyl Peroxide) 0.90%
The blended material is formed into the assembly layer 94 by calendering
between the fabric layer 100 and the Kapton* layer 96 as illustrated in Fig.
4.
The total thickness of assembly layer 94 is typically about 670 microns after
calendering. The assembly layer 94 is then preferably cured for 10 minutes
under
nitrogen at 170° C and preferably in a jig to control the total
swelling thereof to a final
total thickness of about 800 microns. After the curing, the assembly layer 94
preferably
undergoes a post-cure at 200° C for four hours.
It is a particular feature of the present invention that the sponge assembly
layer
94 allows conformity between surface 16 and intermediate transfer member 40 at
the first
* Trade Mark
CA 02064816 2000-06-14
-13-
transfer at a relatively low pressure, such as 100 - 500 gm/cm2 at a
temperature
of about 100-110° C, with relatively low deformation, such as 30 - 200
microns,
overcoming any surface unevenness of the mating surfaces.
According to a preferred embodiment of the present invention, sponge assembly
layer 94 is further characterized in that it undergoes relatively high
pressure, such as 2000
to 4000 gm/cm2 at the second transfer with proportionately low deformation,
greater than
that at first transfer, preferably about 250 microns.
It is believed that when the voltage on the rigidizing roller 30 is high
enough to
cause substantial compression of the image, generally at a value which also
causes
corona, the pressure at the first transfer surface can be increased up to
about 500 gm/cm2,
without substantial image degradation.
Returning now to the structure of the intermediate transfer blanket 82, it is
seen
that over sponge assembly layer 94, there is provided a blanket 102, typically
of about
1200 microns thickness.
Blanket 102 typically includes a layer 104 of relatively stiff sponge, over
which
is formed a layer 106 of nitrilic rubber. Blanket 102 may be produced by
removing the
fabric layer from the three-ply Vulcan 714' offset printing blanket
commercially
available from Reeves Brothers, Inc.
Over printing blanket 102 there is provided a 2-3 micron thick layer 108 of
nitrocellulose loaded with carbon black to provide a conductive layer for the
high voltage
applied to the intermediate transfer member. This layer has an end to end
resistance of
about 20 - 30 kohm, but since the current drawn to the drum is only 50 - 100
microamperes, the voltage drop on the layer is less than 3 volts out of the
applied voltage
of 500 - 600 volts.
An outer layer 110 typically comprises a 2 - 3 micron thick layer of silicone
rubber, such as Syl-Off 294*, which acts as a release layer.
A blanket 114 in accordance with an alternative preferred embodiment of the
invention is shown conceptually in cross section in Fig. 3C. In this
embodiment the
lowest level of the blanket is a Kapton* layer 116, typically 100 microns
thick, which is
similar to layer 96 of Fig. 3B. The next layer is a sponge layer 118,
functionally similar
to sponge layer 98 shown in Fig. 3B and typically 300 microns thick.
Situated above layer 118 is a heater 120, with typical thickness 650 microns,
°Trade Mark
CA 02064816 2000-06-14
-14-
whose structure and manufacture are described hereinbelow. An acrylic rubber
layer 122 is formed onto the heater 120 and preferably penetrates thereinto. A
conducting
layer 124 and a release layer 126 complete the blanket. Additional spacer
material 128,
typically of Kapton*, may be added below the blanket, if additional blanket
thickness is
required. Alternatively the Kapton* layer 116 may be thicker than the
indicated thickness.
As is shown in Figs. 3D and 3E, heater 120 may be formed by weaving heater
wire 130 forming the woof and twisted thread 132 as the warp. In a typical
application
for forming a blanket with a 30 cm axial dimension (when wrapped on drum 80)
and a
41 cm circumferential dimension, wire 130 is formed of a 300 micron diameter
copper
core with a 10 micron lacquer coating, for a total diameter of 320 microns.
Thread 132
is preferably of twisted Nomex* thread with a nominal diameter of 320 microns.
When
wire 130 and thread 132 are formed into heater 120, the overall heater
thickness and the
center to center spacing of the wires are each approximately 650 microns.
Two connection wires 134 for energizing the heater are extensions of the
heater
wires 130. A Nomex cloth extension 136 is provided beyond each end of the
heater
portion of the heater 120.
The unconventional structure ofthe blanket heater 120 of Figs. 3D and 3E
enables
its placement over sponge layer 118. It is noted that heater 92 of the
embodiment
illustrated in Fig. 3B is placed below the sponge layer 98. Since heater 92 is
relatively
stiff in both the circumferential and the axial directions, placement of the
heater 92 above
the sponge layer would substantially shield the blanket-photoconductor and
blanket-final
substrate image transfer interfaces from the compression properties of the
sponge
assembly 94.
Heater 120, on the other hand, is stiff in the axial direction, but is pliable
in the
circumferential direction and thus transmits the pressure at the respective
interfaces to the
sponge layer. Placing the heater closer to the transfer surface allows for a
lower heater
temperature for the same surface temperature, and allows the sponge layer to
be much
cooler. The pressure along lines in the axial direction is substantially
constant compared
to the variations in the circumferential direction; it would be perfectly
constant were the
transfer surfaces perfect and the mechanical tolerances equal to zero. The
imperfections
and tolerances cause some small minor variations in deformation and hence in
pressure
along the axial lines.
CA 02064816 2000-06-14
-15-
An alternative preferred heater 150 is shown in Figs. 3F and 3G. In this
embodiment two inputs 151 and 152 are at the same end of the heater wires and
the wires
are threaded in a paired spaced relationship as shown in Figs. 3F and 3G.
Additional
input 153 is electrically connected to the other end of the heater such that
the current path
between inputs
b~0 91/03006 PCi'/~L90/~049
~- 16 ~.
w
1 151 and 153 is of substantially the same length as that of
2 the current path between inputs 152 and 153.
3 The heater 150 is preferably energized with the circuit
4 of Fig. 6, wherein the input to a transformer 157 is an AC
.5 voltage and a pair of output terminals 154 and 156 of
6 transformer 157 are at the same voltage and at opposite
7 phases with respect to a third terminal 155. Terminals 154,
8 155 and 156 are electrically insulated from the AC input.
In operation, heater 150 is incorporated in a blanket,
and installed in the apparatus of Fig. 1. Terminals 154 and
11 156 are electrically cannected to inputs 151 and 152, and
12 additional input 153 is connected to terminal 155.
13 Alternatively the wires can be "crossed" at each reversal of
14 the wire direction (at the edges of the heater). One such
crossing is shown in Fig. 3Fi.
16 Alternatively, wire 153 and terminal 155 may be
17 externally electrically connected to the bias layer 124.
18 Alternatively wire 153 and terminal 153 may be connected to
19 a source of high voltage in order to provide a field at the
transfer regions and layer 124 may be omitted. For this
21 last alternative, a substantially higher voltage would be
22 required to provide the field due to the greater distance of
23 the heater from the transfer surface.
24 ' An alternative preferred heater 160 is shown in Fig.
3I. In this embodiment the wire and thread are woven in a
26 similar manner to that of the embbdiment shown in Fig. 3D.
27 Two connection wires 162 and 164 for energizing the heater
28 are extensions of the heater wire and an additional wire 168
29 is electrically connected to the center of the length of
wire used to form the heater. In operation the heater is
31 energized by connecting wires 162 and 164 to terminals 154
32 and 156 respectively, and connecting wire 168 to terminal
33~ 155.
34 Alternatively, wire 168 and terminal 155 could be
externally electrically connected to the bias Layer 124.
36 Layer 122 preferably has the following properties:
37 a) high electrical resistivity at the operating
38 temperature;
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b) high resilience, especially at second transfer (to receiving substrate 42),
under the high pressures and deformation at that transfer;
c) suitable hardness- approximately 40 Shore A;
d) castablity and bondablity to adjacent layers;
e) high strength, especially in tension and tear; and
f) stability under temperature and pressure, that is to say, its pressure-
deformation curve remains relatively stable after repeated compression and
release at the
temperature of operation.
Blanket 114 is preferably manufactured using the following process, although
any
other suitable manufacturing method may be used:
STEP I - Forming of layer 122 onto heater 120.
100 parts by weight of HYTEMP Acrylic rubber compound manufactured
by B.F. Goodrich is mixed in a two roll mill with 15 parts of very fine
silica, 4
parts sodium stearate and 2 parts NPC-50' crosslinker, until the mixture is
smooth. The silica is added to increase the electrical resistivity, mechanical
cohesiveness and strength of the final polymer. A heater 120 is placed in a
mold
coated with silicone oil, and is covered with the rubber/silica mixture. The
mixture is cured in the mold to a final thickness of 1500 microns at a
temperature
of 180 ° C for 15 minutes. The mold is cooled and the resulting sheet
is removed.
It will be appreciated that this sheet comprises heater 120 and rubber layer
122
formed into an integral unit due to the filling of the heater by the
rubber/silica
mixture before curing.
STEP II - Forming of the ~onge layer 118.
The procedure described above for the manufacture of the sponge
assembly 94 (described in conjunction with Fig. 3B) is followed for this step,
with the exception that the fabric layer 100 of that procedure is replaced by
the
double layer 120 and 122 produced by Step I above. The spacing of the rollers
and the thickness of the sizing jig are adjusted to account for the increased
CA 02064816 2000-06-14
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thickness of the new material. In an alternative and preferred embodiment of
the
invention, the following procedure is followed:
100 parts by weight of HYTEMP 4051* Acrylic rubber compound
* Trade Marks
manufactured by B.F. Goodrich is mixed in a two roll mill with 15 parts
of very fine silica, 4 parts of sodium stearate, 2 parts of NPC-50*
crosslinker and
11 to 33 parts by weight of Blowing Agent (#9038 Rhone Poulenc) until the
mixture is smooth. The silica is added to increase the cohesiveness of the
sponge.
1 part of the mixture is mixed with preferably 2 parts of a solvent,
preferably
acetone or MEK*, in order to reduce its viscosity.
The blended material is calendered between the double layer 120 and 122
and the Kapton* layer 116 essentially as described above and as illustrated in
Fig.
4 for the manufacture of sponge layer 98.
The total thickness of the resulting multilayer sheet 118, 122, 120 and 116
after calendering will depend on the amount of blowing agent used and can be
determined experimentally.
The triple layer is cured, preferably in a jig, to control the total swelling
thereof, at a temperature of 180°C for 15 minutes. The mold is cooled
and the
resulting sheet is removed. It will be appreciated that this sheet comprises
all
four layers formed into an integral unit. In an alternative embodiment of the
invention the Kapton* layer 116 can be replaced by a Nomex* cloth layer, since
the acrylic rubber layers together with a Nomex* cloth layer appear to give
sufficient structural strength to the blanket.
STEP III - Adding the conducting i(bias) layer 124.
15 parts of HYTEMP 4051, 100 parts of MEK* (methylmetacrilate), 6
parts of carbon black (Printex XE-2* manufactured by Degussa) and 2 parts of
NPC-50* cross-linker are mixed in a cooled ball attritor for 12 hours. This
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material is wire coated onto the surface of layer 122 and cured at
150°C for 15
minutes to form an approximately 2 micron thick conducting layer with a
resistance of between 10-100 kohm/square, preferably 30-50 kohm/square,
bonded to layer 122.
STEP IV - Post Curing
Post curing of the HYTEMP* 4051 * is not part of the process as
* Trade Marks
recommended by the manufacturer, however it has been found that the
stability of the material under compression cycling at operating temperature
was
improved by the addition of a 180°C, 12 hour post curing step.
STEP V - Adding the silicone release layer 126
100 parts of Syl-off 294P is diluted 1:1 with Isopar L*. 15 parts of Syl-off
297* ancorning agent and 5 parts of Dow Corning 176 cross-linker are added to
the mixture. This mixture is wire coated onto the surface of conducting layer
124
and air cured at 110 ° C for 10 minutes to provide a 5-6 micron thick
layer.
Fig. 5 is a graph which illustrates the approximate desired
pressure/deformation characteristics of the intermediate transfer member
structures shown in Fig. 3B-3I, under ordinary use conditions, in intermediate
transfer apparatus constructed and operative according to a preferred
embodiment
of the present invention.
The invention is illustrated herein with examples employing a single
developer station. The invention is especially useful in imaging systems with
a
multiplicity of development stations preferably with different color liquid
developers, or with a single station in which the liquid developer is changed
between colors. For either of these systems each individual color image may be
transferred to the final substrate from the ITM individually, or the colored
images
may be transferred sequentially to the ITM and then transferred to the
substrate
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together. Color imaging equipment is described in U.S. Patents 4,788,572;
4,690,539 and 3,900,003.
It will be appreciated by persons skilled in the art that the present
invention is not limited by what has been particularly shown and described
hereinabove. Rather the scope of the present invention is defined only by the
claims which follow:
