Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFIC~TION
.
This invention relates to a printing roller and ~ ;
particularly to such a roller for current assisted printing
systems, or for use in conventional gra wre systems.~
The invention relates further to an improved printing ~ -
roller for electrically assisted printing systems.
The invention also concerns an improved gravure im-
pression cylinder capable of utilizing an elastomer material
of optimum thermal conductivity and resilience.
A significant contribution o the present invention
10` resides in the provision of a printing roller capable of hav-
ing a new covering applied thereto at the user's plant, and
, to a novel method and apparatus for effecting such result.
A feature of the present invention resides in the `
provision of a covering for an electrical printing roller com- ;
prising an extruded sleeve capable of being manufactured with
; great uniformity particularly with respect to its electrical ;
properties.
A further feature of the invention resides in the pro-
vision of a sleeve capable of forming a protective covering
for a conventional grawre impression roller, and thus enabling
the use of an optimum substrate material without regard to
its solvent resistance, for example.
The invention further concerns a system for assisting ~`
the transfer o ink7 carried on a metal printing cylinder
connected to ground potential, to a web of substantially non-
conductive material as the web passes along a web path through
a nip between the grounded printing cylinder and the outer
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perimeter of a resiliently covered metal impression cylinder,
including the combination of an electrically conductive inner
layer of resilient material on said impression cylinder, means
mounting said impression cylinder for rotation on its central
axis and insulating said electrically conductive layer of
resilient material on said impression cylinder from ground
potential, an outer sleeve of dielectric material of homo-
geneous continuous annular cross section having a width sub-
stantially equal to the width of the outer perimeter of the
~ lO impression cylinder, and having a resistivity sybstantially
` greater than that of said conductive layer, and means com-
prising an electric circuit connected with said electrically
conductive layer for applying an electric potential between
. said electrically conductive layer and said grounded printing
cylinder, the entire operative width of the outer perimeter
of tl~e impression cylinder being for~led entirely by said di-
`; electric material of said outer sleeve, said dielectric mate-~-. rial having a thickness less than one-eighth of an inch and :
`` having a dielectric constant between twenty and one hundred,
: 20 and said electric circuit comprising an alternating potential :~
source for applying an alternating current electric potential
~ between said electrically conductive inner layer of resilient
: material and said grounded printing cylinder to produce an
alternating reactive current from said electrically conductive
inner layer through said dielectric material of said outer
sleeve over the entire operative width of said impression
cylinder.
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Other objects, features and advantages of the inven-
tion will be readîly apparent from the following description ~ ;
of certain preferred embodiments thereof, taken in conjunction
with the accompanying drawings, although variations and modi-
fications may be effected without departing from the spirit
and scope of the novel concepts of the disclosure.
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ON THE DRAWINGS:
Fig. I is a somewhat diagrammatic side elevational view of
an impression roller for an electrically assisted printing system,
with a portion of the impression roller broken away to show the
novel construction thereof;
Fig. 2 is a somewhat diagrammatic end elevational view of
an electrically assisted printing system utilizing the impression
roller of Fig. I and showing the impression roller in cross
` section; and
Fig. 3 is a somewhat diagrammatic end elevational view of
a further form of electrically assisted printing system utilizing
an impression roller in accordance with the present invention.
The electrical printing roller, for example in an elec.trically
assisted gravure printing system, is considered to be the most
critical component because of the stringent and relatively narrow I ;
electrical requirements for such rolLer.
Conventional gravure impression rollers used in presses
without the application of electric potential are limited in their
advantageous characteristics because of the need for solvent
resistance in the printing environment. Accordingly, optimum
thermal conduction and resilience, for example, have not been
achieved in the conventional gravure impression roller. Tt is
conceived that the provision of a sleeve cover, for example
formed of heat shrinkable material, will enable the use of a
covering with excellent chemical and abrasion resistance, while
the underlying substrate of the roller can have optimum thermal
conduction and resilience. For example, the outer covering
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sleeve may be of neoprene, while the material of the substrate
may be of natural rubber or other material with thermal
conductivity and resilience substantially equivalent to that of
natural rubber. This permits not only longer life, but higher
press speeds. When excessive wear or catastrophic failure
takes place, the covering sleeve is simply replaced. Such
replacement can take place at the user's plant, thus avoiding the
delay due to shipping and the like which is generally the case
at present
In an electric printing roller, in addition to conventional
parameters, one needs an electrical parameter critically related
to the printing system. Such printing systems include those
utilizing direct current potential and alternating current potential,
for example, as will hereinafter be explained.
By way of example, in an electrically assisted gravure
printing system, printing conditions are encountered whereby
portions of the impress ion roller contact the des ign cylinder
to print a partial web. Using an applied direct current potential,
for example, such contact interferes with the electrical function
and the amount of assist becomes a compromise. With the use
of the extruded sleeve configuration contemplated herein, it is
entirely practical to use a partial sleeve covering of the
impression roller, thus permitting an adjustment of the width of
the conducting surface to correspond to that of the web without
any change of the basic impression roller.
In the case of electrically assisted printing, when an
electrical property is required of the sleeve, the present
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3~
invention provides an optimized geometry enabling precise control
of the parameter in manufacture and in auditingO Conventional
rollers must be refaced frequently to extend the life of the
rollers with a consequent progressive reduction in diameter.
;` 5 This change adversely affects the electrical properties. When
the covering sleeve configuration of the present disclosure is
replaced, satisfactory control for the electrical parameters is
maintained simply by the proper selection of the thickness of
the replacement covering sleeve. Although the sleeve cover
may be refaced, one has a satisfactory control for the electrical
parameters by maintaining a defined thickness.
Replacement of ~he sleeve for any roller may be done
locally and in a few tlours. Where rollers must be returned to
the vendor and revulcanized as with prior art impression rollers ,
a time loss of several weeks commonly results. ~ollers are
heavy and conseqwently shipping costs are hi~h.
A preferred apparatus for applying a heat-shrinkable sleeve
to a roll is shown in MacCallum, Howard and Coberley U.S.
Patent No. 3,677,8S6 issued July 18, 1972, and assigned to the
present assignee, and may comprise an impression roller support
which is rotatable on a vertical axis and which is so shaped as ;
to receive the lower journal of the roller and to support the
roller during insertion into a sleeve. A means to rotate the
roller at a variable speed is provided fixed to the rate of rise
of a circumferential heater. The heater is so constructed as to
permit convection to preheat the s leeve and to provide a
maximum average radiant watt density of 80 watts per square
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inch (variable). A belt is wrapped for at least 360 about the
lower part o~ the sleeve and is tensioned to exert uniform
pressure about the entire perimeter of the sleeve. Energy is
then applied, for example heat energy by means- of the aforesaid
heater, tending to cause the sleeve to constrict onto the roller.
The rotation of the roller serves to drive the belt and also to
cause the belt to move progressively along the axis of the roller
to smoothly apply the sleeve to the roller and to progressively
remove entrapped gases. In one embodiment, a reservoir of
adhesive is formed between the roller and sleeve at the lower
portion thereof, the belt serving to progressively move the
reservoir upwardly to distribute the adhesive over the interface
between the roller and the s leeve.
Referring specifically to the embodiment of Figs. I and 2,
an electrically assisted printing systlem is shown including a
design cylinder 10 rotatable about a horizontal axis and supported
by means of a grounded metal shaft 11 so that the surface of the
design cylinder contacting the under sur~ace of web 12 is
essentially at ground potentiaL. In the system as illus~rated in
Fig. 2 it is contemplated that the web 12 moves in the direction
of arrow 13 through a nip region between design cylinder 10 and
an impression roller 14 in accordance with the present invention.
In the system illustrated, a high voltage supply 15 supplies a
direct current potential through an idler roller 16 rotating in
the direction of arrow 17 and of conductive m~terial so as to
transmit the applied potential to an electrically conduccive
covering 18 of the impression roller 14. The impression roller
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is provided with a metal core 19 mounted for rotation on a
shaft 20, which may be grounded in the illustrated embodiment,
a resilient insulating layer 21 being interposed between the metal
core 19 a nd the cond uct ive outer cover ing or s leeve 18 . A s seen
in Fig. 1, the insulating layer 21 tapers at its opposite axial
ends, as indicated at 21a and 21b.
In this construction, the conductive sleeve 18 should have
a thickness of not greater than about 1/8 inch. It is considered
that the operable range where the sleeve 18 is applied by a heat
shrinking technique extends from a maximum thickness of about
.140 inch down to a minimum thickness of about .020 inch.
The resistivity of the material is in the range from about 104
ohm-centimeters to 108 ohm-centirneters. Such resistivity may
be measured in accordance with A.S.T. M. standards Durometer
is an important parameter for impression rollers. One finds
that with a sleeve covering thickness of 1/8 ~nch or less, a , ;
sleeve material durometer of 80-85 Shore A, a substrate thick-
ness of 1/2 inch or more and a substrate durometer of 65-95
Shore A, the composite roller as indicated at 14 in Fig. 2 will -
have a durometer of 65-95 Shore A7 that is a durometer
corresponding to that of the substrate.
In the illustrated embodiment, it is contemplated that the
resilient layer 21 is bonded to the core 19 or vulcanized by
conventional methods. The outer covering sleeve 18 is preferably
adhes ively bonded to the layer 21 by the method and apparatus
referred to herein. An example of a suitable conductive
elastomer material for the outer conductive sleeve 18 is a heat
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shrinkable irradiated neoprene. An example of material for the
substrate resilient layer 21 would be natural rubber or a synthetic
material having substantially e(luivalent characteristics, particular-
ly equivalent thermal conductivity and resilience.
An impression roller such as shown at 14 in Figs. I and 2
and having the characteristics herein described is of substantial
value in a conventional gravure printing system where no electric
potential is applied thereto. Thus, the covering sleeve 18 may
be of a materiaL having optimum solvent resistance so as to be
relatively irnmune to the printing environment, while the substrate
layer 21 can be selected for optimum properties other than
solvent resistance such as optimum thermal conductivity and
resilience. ~s an e~ample, natural rubber would not have the
required solvent resistance to provide optimum life, but would
have substantially better thermal corlductivity and resilience than
the neoprene mater ia I of the s leeve 18 .
In each o~ the embodiments, the sleeve 18 is preferably
formed by extruding so as tO be- of homog@neous continuous
annular cross section and preferably with a thickness of not more
than about 1/8 inch.
Referring to Fig. 3, there is illustrated an alternating
current printing system including a design cylinder 30 having a
grounded shaft 31 and cooperating with an impression roller 32
which receives an alternating current potential from an alter-
nating potential source 33. A web 34 is indicated as moving in
the direction of arrow 35 through a printing zone or nip region
between the design cylinder 30 and impression roller 32.
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In this embodiment an insulated bearing 34' journals a metal
shaft 35' which serves to supply the alternating current potential
tobrush means such as indicated at 36and 37 in sliding contact
with the metal core 38 of the roller. The roller 32 further
includes a resilient substrate layer 39 and an outer covering
sleeve 40 of dielectric material. By way of example, the
dielectric material of sleeve 40 may have a dielectric constant
between 20 and 40. By way of example where the sleeve 40 is
of a heat shrinkable elastomer dielectric material, the thickness
thereof is not more than about 1/8 inch Preferably the sleeve
40 is bonded to the substrate 39 by means of an adhesive as
previously described, the substrate 39 being bonded or vulcanized
to the core 38. As an example, the sleeve 40 may be made of .
a heat shrinkable irradiated elastomer material such as neoprene.
Neoprene has the advantage of being ozone resistant, to a
substantially greater degree than natural rubber, for example.
As another example, the sleeve 40 may comprise a sletove
of homogeneous continuous annular cross section and of dielectric
elastomer material having a thickness between about 1/16 inch
and about 1~8 inch, and a dielectric constant between about
twenty (20) and about 100, for example substantially forty (40). ;
The sleeve may be of vulcanized rubber or the like rather than
being formed of heat shrinkable material. Further the sleeve
preferably has a resistivity substantially greater than the
resistivity of the conductive layer 39 and preferably in the range
from about 108 ohm-centimeters to about 1012 ohm-centimeters,
or greater.
