Background of the Invention
Field of the Invention - This invention relates to liquid transfer
rolls or the like. More particularly, it relates to an improved sleeve adapted to
be mounted on a mandrel to form a liquid transfer roll for use in transferring an
accurately metered quantity of a liquid to another surface, for example such as
a roll for use in gravure or anilox printing processes. The present invention also
relates to an improved method for producing such a sleeve.
Description of the Prior Art - A liquid transfer roll is used
in the printing industry to transfer a specified amount of a liquid, such as ink
or other substances, from the liquid transfer roll to another surface. The liquid
transfer roll generally comprises a surface with a pattern of depressions or wells
adapted for receiving a liquid, wherein said pattern is transferred to another surface
when contacted by the liquid transfer roll. When the liquid is ink and the ink is
applied to the roll, the wells are filled with the ink while the remaining surface
of the roll is wiped off. Since the ink is contained only in the pattern defined
by the wells, it is this pattern that is transferred to another surface.
In commercial practice, a wiper or doctor blade is used to remove
any excess liquid from the surface of the liquid transfer roll. If the surface of
the roll is too coarse, excessive liquid, such as ink, will not be removed from
the land area surface of the coarse roll thereby resulting in the transfer of too
much ink onto the receiving surface and/or on the wrong place. Therefore, the surface
of the liquid transfer roll should be finished and the wells or depressions clearly
defined so that they can accept the liquid.
A gravure-type roll is commonly used as a liquid transfer roll. A
gravure-type roll is also referred to as an applicator or pattern roll. A gravure
roll is produced by cutting or engraving various sizes of wells into portions of
the roll surface. These wells are filled with liquid and then the liquid is transferred
to the receiving surface. The diameter and depth of the wells may be varied to control
the volume of liquid transfer. It is the location of the wells that provides a pattern
of the liquid to be transferred to the receiving surface while the land area defining
the wells does not contain any liquid and therefore cannot transfer any liquid.
The land area is at a common surface level, such that when liquid is applied to
the surface and the liquid fills or floods the wells, excess liquid can be removed
from the land area by wiping across the roll surface with a doctor blade.
The depth and size of each well determines the amount of liquid which
is transferred to the receiving surface. By controlling the depth and size of the
wells, and the location of the wells (pattern) on the surface, a precise control
of the volume of liquid to be transferred and the location of the liquid to be transferred
to a receiving surface can be achieved. In addition, the liquid may be transferred
to a receiving surface in a predetermined pattern to a high degree of precision
having different print densities by having various depth and/or size of wells.
Typically, a gravure roll is a metal with an outer layer of copper.
Generally, the engraving techniques employed to engrave the copper are mechanical
processes, e.g., using a diamond stylus to dig the well pattern, or photochemical
processes that chemically etch the well pattern.
After completion of the engraving, the copper surface is usually plated
with chrome. This last step is required to improve the wear life of the engraved
copper surface of the roll. Without the chrome plating, the roll wears quickly,
and is more easily corroded by the inks used in the printing. For this reason, without
the chrome plating, the copper roll has an unacceptably low life.
However, even with chrome plating, the life of the roll is often unacceptably
short. This is due to the abrasive nature of the fluids and the scrapping action
caused by the doctor blade. In many applications, the rapid wear of the roll is
compensated by providing an oversized roll with wells having oversized depths. However,
this roll has the disadvantage of higher liquid transfer when the roll is new. In
addition, as the roll wears, the volume of liquid transferred to a receiving surface
rapidly decreases thereby causing quality control problems. The rapid wear of the
chrome plated copper roll also results in considerable downtime and maintenance
Ceramic coatings have been used for many years for anilox rolls to
give extremely long life. Anilox rolls are liquid transfer rolls which transfer
a uniform liquid volume over the entire working surface of the rolls. Engraving
of ceramic coated rolls cannot be done with conventional engraving methods used
for engraving copper rolls; so these rolls must be engraved with a high energy beam,
such as a laser or an electron beam. The major difference between a gravure roll
and an anilox roll is that the entire anilox roll surface is engraved whereas with
a gravure roll only portions of the roll are engraved to form a predetermined pattern.
In view of the fact that liquid transfer rolls frequently are used
under severe temperature, pressure and/or speed conditions and are often subject
to corrosive attacks, the engraved roll surface wears relatively quickly even when
using ceramic coatings. Therefore the liquid transfer roll must be frequently restored.
With the above described rolls, the restoration operation is complicated and costly,
and must be carried out by the roll manufacturer. In this respect, the operation
requires the use of special tools both to remove the worn coating and to restore
the cylinder surface. Thus, it is necessary for the user to send the roll to the
manufacturer for restoration, and this involves transportation problems and the
need to keep stand-by rolls for use while awaiting the return of the restored rolls.
The restoration operation can also alter the dimensions of the metal cylinder as
its diameter may be reduced by surface machining if this is necessary to remove
every residue of the worn material.
In an effort to avoid the afore-mentioned drawbacks liquid transfer
rolls comprising a mandrel and a sleeve adapted to be mounted on and to be demounted
from the mandrel have been developed. Typical examples of such sleeves are described
in DE-A-4 426 485, EP-A-0 196 443, EP-A-0 278 017, EP-A-0 295 319, EP-B-0 384 104
and GB-A-2 051 681. These prior sleeves are composed of one or more layers of plastic
material, with at least one of these plastic layers being fiber-reinforced and with
the radially outermost plastic layer being coated with a metal layer to be etched
or engraved, usually a layer of copper, sometimes with an intermediate layer of
nickel or silver. The outer metal layer usually is applied by electroplating. In
the case of another known printing sleeve consisting of an inner tube of fiber-reinforced
polyester or epoxy resin and a layer of rubber applied thereon (DE-A-2 700 118)
the rubber layer itself, upon being cured, is engraved.
The known sleeves with engravable outer copper or rubber layer are
subject to rapid wear and require very careful handling to avoid damaging of the
outer surface thereof during the production and the assembly of the sleeve and of
the printing roll provided with such a sleeve. Particularly, the outer layer of
copper is thin and relatively soft, and will not resist impact damage. This, of
course, also applies if the rubber layer itself defines the outer engravable surface
of the sleeve. In addition, the corrosion properties of both copper and engravable
plastic materials, such as rubber, are unsatisfactory.
It has also been proposed in DE-U-85 32 300 to provide a sleeve which
is intended for use in printing machines and which is made of fiber-reinforced plastic
material, said sleeve being provided by flame spraying or plasma spraying with an
engravable coating of nickel, chromium or tungsten carbide. However, in view of
the temperature limitations of the resins used in the manufacture of such sleeves
it is very difficult to thermally coat the sleeve with a wear-resistant material.
This also affects the ability to form an adequate bond between the coating and the
It is an object of the invention, therefore, to provide an improved
sleeve for forming a liquid transfer roll.
It is a further object of the invention to provide a sleeve having
improved mechanical robustness.
It is another object of the invention to provide a sleeve adapted
for being thermally coated with a wear-resistant coating, particularly a coating
of ceramic material or metal carbide, said coating having a high bonding strength.
It is a further object of the invention to provide a sleeve adapted
to resist degradation by the heat of a thermal coating process used to apply a wear-resistant
It is also an object of the invention to provide improved processes
for producing such a sleeve.
With these and other objects in mind, the subject invention is hereinafter
described in detail, the novel features thereof being particularly pointed out in
the appended claims.
Summary of the Invention
One aspect of the subject invention is a sleeve aapted to be mounted
on a mandrel to form a liquid transfer roll or the like, said sleeve having radially
inner and outer surfaces and a pair of opposite axial ends, said sleeve comprising:
- a radially expandable inner skin defining said radially inner surface of said
sleeve and adapted to withstand wear and abrasion during mounting of the sleeve
on said mandrel and demounting of the sleeve from said mandrel;
- at least one radially compressible intermediate layer of resilient plastic material;
- a rigid, self-supporting metal outer tube.
The rigid, self-supporting metal outer tube not only is mechanically
strong and protects the sleeve from being damaged by impact or the like during handling
and assembling of the liquid transfer roll, but also forms an excellent base for
applying a wear-resistant coating.
The self-supporting metal outer tube has a wall thickness which is
considerably larger than that of the thin outer copper layer of prior sleeves and
which usually is in the range of about 1 mm to about 10 mm. This leads to a correspondingly
increased specific heat capacity of the metal outer tube. Therefore, the self-supporting
metal outer tube also will effectively protect the compressible intermediate layer
or layers of resilient plastic material against the heat of a thermal coating process.
The metal used for the outer tube preferably is selected from aluminum, aluminum
alloys and steel, most preferably stainless steel. These metals are particularly
suited to withstand chemical and mechanical attacks; they also have a substantially
lower heat conductivity than copper whereby the protective action of the outer tube
during thermal coating processes is further improved.
The sleeve including the radially expandable inner skin, the at least
one radially compressible intermediate layer of resilient plastic material and the
rigid, self-supporting metal outer tube preferably is mounted on a mandrel, and
then the outer circumferential surface of the metal tube is machined to the required
size and concentricity.
Preferably, the sleeve comprises a coating selected from ceramic materials
and metal carbides, which coating defines the radial outer surface of the sleeve.
Any suitable ceramic coating, such as a refractory oxide or metal
carbide coating, may be applied to the surface of the metal outer tube of the sleeve.
For example, tungsten carbide-cobalt, tungsten carbide-nickel, tungsten carbide
cobalt chromium, tungsten carbide-nickel chromium, chromium nickel, aluminum oxide,
chromium carbide-nickel chromium, chromium carbide-cobalt chromium, tungsten-titanium
carbide nickel, cobalt alloys, oxide dispersions in cobalt alloys, aluminum-titania,
copper based alloys, chromium based alloys, chromium oxide, chromium oxide plus
aluminum oxide, titanium oxide, titanium plus aluminum oxide, iron based alloys,
oxide dispersed in iron based alloys, nickel and nickel based alloys, and the like
may be used. Preferably chromium oxide (Cr2O3), aluminum oxide
(Al2O3), silicon oxide or mixtures thereof could be used as
the coating material, with chromium oxide being the most preferred.
The ceramic or metallic carbide coatings preferably are applied to
the machined metal outer tube of the sleeve by a thermal coating process, particularly
the flame spray coating process, the detonation gun process or the plasma coating
process. The detonation gun process is well known and fully described in US-A-2,714,563;
US-A-4,173,685; and US-A-4,519,840, the disclosures of which are hereby incorporated
by reference. Conventional plasma techniques for coating a substrate are described
in US-A-3,016,447; US-A-3,914,573; US-A-3,958,097; US-A-4,173,685; and US-A-4,519,840,
the disclosures of which are incorporated herein by reference. The thickness of
the coating applied by either of the afore-mentioned processes can range from 10
microns to 2.5 mm, and the roughness ranges from about 1 to about 25 microns Ra
depending on the process, the type of coating material, and the thickness of the
The ceramic or metallic carbide coating on the sleeve can be preferably
treated with a suitable material or a suitable underlayer may be provided to prevent
moisture or other corrosive materials from penetrating through the ceramic or metallic
carbide coating to attack and degrade the underlying metal structure of the sleeve.
After application of the coating, it may be finished by conventional
grinding techniques to the desired dimensions and tolerances of the sleeve surface
and for a smoothness of e.g. between about 0.50 microns Ra and about
0.25 microns Ra, in order to provide an even surface for a subsequent
The coated sleeve preferably is engraved with a high energy beam,
such as a laser or an electron beam.
A wide variety of laser machines are available for forming wells in
the ceramic or metallic carbide coatings. In general, lasers capable of producing
a beam or pulse of radiation of from 0.0001 to 0.4 joule per laser pulse for a duration
of 10 to 300 microseconds can be used. The laser pulses can be separated by 30 to
2000 microseconds depending on the specific pattern of well desired. Higher or lower
values of the energy and time periods can be employed and other laser-engraving
techniques readily available in the art can be used for this invention. After laser
engraving, the roughness should typically range from 0.5 to 25 microns Ra,
and the wells can range e.g. from 10 microns to 300 microns in diameter and from
2 microns to 250 microns in height.
Laser engraving processes which are particularly suited for engraving
the coated sleeve are described in detail in EP-A-0 400 621 and in EP-A-0 472 049,
the disclosures of which are incorporated herein by reference.
The inner skin of the sleeve preferably is defined by a radially expandable
inner tube made of metal, such as nickel or steel, or plastic material, such as
polyester or epoxy resin, and most preferably consisting of reinforced plastic material,
e.g. glass or carbon fiber fabric or yarn impregnated with epoxy resin which is
polymerized in a conventional manner. Other elastomers with embedded reinforcement
likewise can be used. The reinforcement also may consist e.g. of metal wires.
It is essential, that the inner tube is radially expandable by an
amount sufficient to permit mounting of the sleeve on a mandrel and demounting of
the sleeve from the mandrel, such as an amount of about 0.1 to about 1 mm across
the diameter, under the influence of a pressure as usually applied in sleeve/mandrel
systems, such as an air pressure of about 2 to about 8 bar. The wall thickness of
the inner tube depends amongst others on the material used, the dimension of the
sleeve and the pressure intended to be used for expanding the inner tube for mounting
and demounting the sleeve. When the inner tube is made of reinforced, particularly
fiber-reinforced, plastic material, the wall thickness thereof generally is from
about 0.6 to about 1 mm, whereas the inner tube normally will have a wall thickness
of from about 30 microns to about 150 microns if it is made of metal, particularly
nickel or steel.
The at least one radially compressible intermediate layer is made
of a resilient plastic material, preferably rubber or a rubber-like elastomer. The
material and the wall thickness are selected so that the radially inner surface
of the intermediate layer or layers may follow the radial expansion of the inner
skin whilst the radial outer surface of the intermediate layer or layers is prevented
from substantial radial expansion.
Particularly, the intermediate layer or layers may comprise a material
which itself is compressible, such as a foamed plastic material. The intermediate
layer or layers, however, also may comprise an non-compressible, hydraulic material
which is capable of flow in a manner permitting compression of the intermediate
layer or layers under the influence of the pressure applied for mounting and demounting
Preferably, the intermediate layer or layers is made of a heat resisting
elastomer, such as a silicone or polyurethane elastomer. The hardness of the compressible
intermediate layer suitably is in the order of about 30 to 50 shore, most preferably
about 40 shore.
A fiber-reinforced intermediate tube may be disposed between the compressible
layer and the rigid metal outer tube. This tube may have a wall thickness which
is substantially larger than that of the inner tube to provide for an effective
thermal barrier between the compressible intermediate layer of resilient plastic
material and the self-supporting outer metal tube, which barrier is particularly
desirable when the outer metal tube is to be thermally coated. The intermediate
tube may consist of the same or similar materials as the afore-mentioned inner tube,
but need not be radially expandable.
A metal ring may be disposed at each of the axial ends of the sleeve,
preferably radially within the metal outer tube, wherein the metal rings are designed
and arranged so as to permit radial expansion of the inner skin as well as radial
compression of the intermediate layer or layers. The metal rings may be composed
of the same metal as the metal outer tube, i.e. particularly stainless steel or
an aluminium alloy. Such rings improve the rigidity of the complete sleeve assembly.
Preferably the metal rings are positioned radially between the inner and outer tubes
with radial gaps permitting radial expansion of the inner tube and radial compression
of the intermediate layer being provided between the metal rings and the inner tube.
One preferred method for producing a sleeve of the afore-mentioned
type comprises the steps of providing a prefabricated sleeve assembly including
a radially expandable inner skin adapted to withstand wear and abrasion during mounting
of the sleeve on the mandrel and demounting of the sleeve from the mandrel, and
at least one compressible intermediate layer of resilient plastic material; and
fixing said prefabricated sleeve assembly within a rigid, self-supporting metal
outer tube. The prefabricated sleeve assembly may include a relatively thin-walled
inner tube and a relatively thick-walled intermediate tube between which the compressible
intermediate layer is disposed. The inner and intermediate tubes may be made of
reinforced plastic material, such as carbon or glass fiber fabric or yarn impregnated
with epoxy resin or the like. Prefabricated sleeve assemblies suitable for the production
of the sleeve of the present invention are commercially available, e.g. in the form
of the sleeves "Cyrel"® of DuPont. The prefabricated sleeve assembly and the
self-supporting metal outer tube may be firmly bonded to each other by glue applied
to the outer circumferential surface of the prefabricated sleeve assembly and/or
the inner circumferential surface of the metal outer tube.
Another preferred method for producing a sleeve of the above described
general type comprises the steps of:
- providing a radially expandable inner tube which defines an inner skin adapted
to withstand wear and abrasion during mounting of the sleeve on the mandrel and
demounting of the sleeve from the mandrel;
- providing a rigid, self-supporting metal outer tube;
- arranging the inner and outer tubes in concentric relationship to each other;
- filling the space between the inner and outer tubes with a plastic material
forming, upon curing, a compressible intermediate layer of resilient plastic material
whilst maintaining the concentric relationship.
The sleeve of the present invention may be used in combination with
any conventional mandrel. Suitable examples are mandrels using a compressed air
system for forming between mandrel and sleeve an air cushion which expands the sleeve
to allow smooth and precise positioning of the sleeve on the mandrel. Upon the supply
of compressed air being discontinued, the inner skin of the mandrel firmly grips
the circumferential surface of the mandrel such that sleeve and mandrel operate
as an integral unit. Such mandrels e.g. are described in more detail in EP-A-0 196
443, EP-A-0 278 017, WO-A-94/25284 and DE-A-27 00 118.
It is also possible to use a radially expandable mandrel, such as
the mandrel known from EP-A-0 527 293.
Brief Description of the Drawings
The invention is further described herein with reference to the accompanying
drawings in which:
- Fig. 1 is a partial longitudinal sectional view of a liquid transfer roll comprising
a mandrel and a sleeve in conformity with the present invention;
- Fig. 2 is an enlarged partial longitudinal sectional view of the sleeve illustrated
in Fig. 1;
- Fig. 3 is a cross-sectional view of a sleeve in conformity with a further embodiment
of the present invention; and
- Fig. 4 is a partial longitudinal sectional view of the sleeve of Fig. 3.
Fig: 1 shows a liquid transfer roll 10 comprising a mandrel 11 and
a sleeve 12. Mandrel 11 is of any conventional type. In the embodiment illustrated
it is provided with a cylindrical shell 13 fixed on lateral end members 14 and 15
each provided with an axially projecting axle stub 16 and 17, respectively. A plurality
of axially and radially distributed passages, such as 18, 19, 20, 21 and 22, are
provided in the mandrel 11 and communicate with a feed port 23. Feed port 23 of
the mandrel may be connected to a source of pressurized air. When the sleeve 12
is in place on the mandrel 11, the pressurized air issuing from passages 19 and
21 provides a cylindrical cushion of air 24 around the mandrel that slightly expands
and supports the sleeve 12 and allows to completely remove the sleeve from the mandrel
or to slid the sleeve onto the mandrel, respectively. As soon as the supply of air
is discontinued, the sleeve 12 is firmly fitted on the mandrel 11.
The sleeve 12, as illustrated in more detail in Fig. 2, comprises
a radially expandable inner tube 26, a radially compressible intermediate layer
27, an intermediate tube 28 and a rigid, self-supporting metal outer tube 29. Inner
tube 26 defines a radially expandable inner skin 30 at the radially inner surface
of sleeve 12. All these members are firmly interconnected to define an integral
The inner tube 26 and the intermediate tube 28 are made from a resin,
such as polyester or epoxy resin reinforced with glass, aramide or carbon fibers,
such as Kevlar®. Intermediate tube 28 is substantially thicker than inner tube
26 and, different from inner tube 26, need not be expandable under the applied air
pressure. The intermediate layer 27, in the embodiment shown, is made of a compressible
material, preferably a rubber foam material, such as polyurethane foam. The rigid
metal outer tube 29 is made of aluminum, an aluminum alloy or steel, preferably
stainless steel. Tube 29 may be coated, preferably thermally coated, with a wear
and corrosion resistant coating 31, which may be laser-engraved as schematically
indicated in Fig. 2 at 32. Intermediate tube 28 forms an effective thermal barrier
during the thermal coating process.
Metal rings 33 and 34 are fitted into the metal outer tube 29 at both
axial ends thereof. The rings 33 and 34 cover the end faces of intermediate tube
28 and part of the end faces of intermediate layer 27. Radial gaps 35 are left between
the inner circumferential surface of the rings 33 and 34 and the outer circumferential
surface of inner tube 26. The gaps 35 are dimensioned to permit the radial expansion
of inner tube 26 and the radial compression of intermediate layer 27 under the pressure
applied by mandrel 11. Circumferential grooves 36 in rings 33 and 34 can receive
glue for firmly bonding the rings to the outer tube 29.
A prefabricated sleeve assembly comprising the inner and intermediate
tubes 26 and 28 as well as the intermediate layer 27, such as the afore-mentioned
Cyrel® sleeve of DuPont, may be used and fitted into the rigid, self-supporting
metal outer tube 29. The prefabricated sleeve assembly and the metal outer tube
may be interconnected by glue or in any other suitable manner to define an integral
unit, and the rings 33 and 34 may be inserted at the axial ends of outer tube 29
as illustrated in Fig. 2. Subsequently the sleeve may be mounted on a mandrel and
the outer tube 29 may be finished and thermally coated with wear and corrosion resistant
coating 31. Coating 31 may be laser-engraved and finished as described above.
Whereas rings 33 and 34 shown in Fig. 2 are fitted into the outer
tube 29, Fig. 1 illustrates modified rings 33' and 34' which also cover the end
faces of tube 29. In this case, too, the rings 33' and 34' are to be designed and
arranged so as to permit radial expansion of the inner skin 30 and radial compression
of intermediate layer 27.
A single intermediate layer 27 is shown in Figs. 1 and 2. However,
two or more such layers likewise may be interposed between tubes 26 and 29.
Figs. 3 and 4 illustrate an embodiment in which a sleeve 40 comprises
three components only, namely the radially expandable inner tube 26, the rigid,
self-supporting metal outer tube 29 and a single radially compressible intermediate
layer 41. In this embodiment layer 41 differs from layer 27 in not consisting of
a compressible material, particularly plastic foam material, but rather of an essentially
incompressible material, such as a silicone elastomer, showing hydraulic behavior.
Such a hydraulic material permits radial compression of layer 41 by a certain amount
of flow in axial direction.
The sleeve 40 of Figs. 3 and 4 may be manufactured by holding the
tubes 26 and 29, in a fixture (not illustrated), in concentric relationship to each
other and by filling the annular space defined by tubes 26 and 29 with a suitable
elastomer material, e.g. silicone, to form intermediate layer 41. This filling may
be effected by pouring, injection or evacuation of the selected material. Then the
elastomer is cured, preferably by ultraviolet radiation. Subsequently the assembly
is mounted on a mandrel and the outer surface thereof is machined, and optionally
thermally coated, laser-engraved and again machined as explained in more detail
above to obtain the finished sleeve.
The sleeves of the subject invention are particularly stable and robust.
In practical use thereof no resonances will be set-up between the inner and outer
surfaces thereof. The rigid, self-supporting metal outer tube permits a particularly
high accuracy of the sleeve and of the roll obtained by mounting the sleeve on a
mandrel. No measurable expansion will occur at the outer circumferential surface
of the sleeve when the sleeve is mounted or demounted. Therefore, a coating on the
rigid metal outer tube is not subjected by the expansion of the inner skin to forces
tending to damage or loosen the coating.
The sleeves described and shown therein not only may be used as liquid
transfer rolls but also are useful in other applications. For example, the sleeves
may be provided with a dielectric coating, such as alumina, and used in corona discharge
systems. The sleeves also can be provided with ceramic or metallic coatings and
used as transporter rolls for paper, film, textiles etc.