[0001] This invention relates to printing rolls, and is especially applicable to rolls suitable
for accepting photo-originating designs, such as used in the gravure or lithographic
printing processes.
[0002] Conventionally, a gravure printing surface is provided by etching the surface of
a metal printing roll. The production of the roll and the need to replace or discard
it after use makes the process very expensive, and only suitable for relatively long
printing runs.
[0003] Our.British Patent Applications Nos. 609/76, 700/76 and 14060/77 describe improved
methods of producing printing rolls, particularly for flexographic printing. A sleeve
made of plastics material, preferably reinforced plastics material, is fitted onto
a roll core which can be of metal construction. Thus, for different printing jobs
different sleeves can be used with a common roll core. -In order to assist in getting
the sleeve on and off the core, the internal diameter of the sleeve is slightly larger
at one end than the other, and the external diameter of the core is similarly slightly
larger at one end than the other so that the sleeve can be slid partly onto the core
before it wedges. The core is provided with apertures in that region which is initially
covered by the sleeve and through which compressed air can be forced to slightly expand
the sleeve so that it can be slid fully onto the core.
[0004] The present invention, however, provides a sleeve substantially as described in the
foregoing paragraph, but made substantially entirely of metal so as to provide a conductive
path from the inside to the outside of the sleeve to assist in electro-plating the
outer surface of the sleeve.
[0005] More particularly, the invention provides a method of making such a sleeve, comprising
taking a generally cylindrical mandrel the external diameter of which is slightly
larger at one end than the other, and optionally having fluid outlet apertures in
a region intermediate its ends, coating the outside surface of the mandrel with a
release agent, applying a first layer of metal over the outside surface of the mandrel,
grinding the outside surface of the first metal layer to provide it with a uniform
external diameter, and electro-plating a second metal layer onto the first metal layer.
Suitably at least one, and preferably both, of the metal layers are copper. It is
particularly preferred that said second layer is copper. The outer surface of the
second metal layer can be finished in conventional manner to provide a surface suitable
for gravure printing. Such finishing may for example take the form of grinding, polishing
and eventually etching to provide the imaged surface, and possibly flash chrome-plating
to provide a more durable finish.
[0006] The first layer may be provided by spraying molten metal onto the outside surface
of the mandrel, the fluid outlet holes having been masked beforehand. Alternatively,
the first layer may be applied by straining a preformed metal sheet around the mandrel,
with either a helical or a longitudinal butt seam, and welding the seam to secure
the layer. In the case of a sprayed metal layer, the fluid outlet holes may be masked
before or after application of the release agent, but preferably they are masked after,
using metal shim, such as copper shim, which is thereby incorporated in the sprayed
metal layer.
[0007] The metal sleeve is at some suitable point in the process removed from the mandrel.
This may be done by applying fluid, for example air, under pressure to the apertures
in the mandrel so as to slightly expand the sleeve and allow it to be withdrawn axially
from the smaller diameter end. Removal from the mandrel may take place when the electro-plated
layer has been fully finished. However, it may be desirable to mount the sleeve on
different mandrels at different stages during the process; for example for applying
the first metal layer, for the electro-plating, and for the etching. In such a case,
the sleeve can be removed, in the manner described, from the one mandrel and fitted
onto the next mandrel by a process which involves sliding the sleeve over the mandrel
until the fluid outlet holes are covered and then applying fluid under pressure to
the fluid outlet. holes to slightly expand the sleeve so that it can be slid fully
onto the mandrel. This is more completely described in our British Patent Applications
referred to earlier. However, if the sleeve is transferred from one mandrel to another
between applying the first layer and the electro-plating application of the second
layer, the first layer may not be sufficiently strong or resilient to withstand the
fluid pressure without distortion, and other means may be needed for removing it from
the first mandrel and fitting it to the second mandrel. This may be achieved by heating
and cooling so as to take advantage of thermal expansion and contraction.
[0008] The invention can be further understood by reference to the accompanying drawings
wherein:
Figs. 1, 2 and 3 show diagrammatically in cross- section the stages in fitting a printing
sleeve to a roll core in a manner more particularly described in the above- mentioned
British Patent Applications;
Fig. 4 shows a diagrammatically enlarged cross-sectional view of part of one embodiment
of sleeve being produced according to the present invention;
Fig. 5 shows a diagrammatically enlarged cross-sectional view of part of a second
embodiment of sleeve being produced according to the present invention; and
Fig. 6 shows diagrammatically a cross-sectional side view through one end portion
of a mandrel and sleeve at the electro-plating stage in an alternative procedure of
the present invention.
[0009] Referring to Figs. 1 to 3, the sleeve 10 is made from a thermosetting resin, such
as polyester or epoxy resin, reinforced with glass fibre, which is preferably spirally
wound so as to provide hoop strength for the sleeve. The outside surface 12 of the
sleeve is of uniform diameter, but the inside surface 14 has a very small taper from
one end to the other. (This taper is greatly exaggerated in the drawing for the sake
of clarity in explanation). The sleeve is removably mounted to a roll core 16, shown
separately in Fig. 1, suitably made of steel, having an axle 18 for rotatably mounting
the core. The outside surface of the core is similarly slightly tapered, and is dimensioned
so as to allow the sleeve to be manually slid onto the core to rather more than half
its length before the sleeve wedges on the core as shown in Fig. 2. An air supply
passage 20 extends axially along the core and emerges at outlets 22 on the surface
of the core about half way along its length. These outlets are thus covered by the
sleeve at the point where the sleeve wedges onto the core. Compressed air is then
applied through the passage 20 so as slightly to expand the sleeve and allow it to
be completely slid onto the core, as shown in Fig. 3. The supply of air is then discontinued
and the sleeve is then firmly fitted to the core.
[0010] Referring to Fig.-4; a steel mandrel 38 on which the sleeve is to be formed has the
same general shape and construction as the roll core 16, but its outside diameter,
point for point along its length, is very slightly less than that of the roll core
to which the sleeve is eventually fitted. In this way, the sleeve thus produced will
be slightly undersized with respect to the roll core, and will therefore be a tight
fit on it. The mandrel has air outlets 22.about halfway along its length. In the first
stage of construction, the outside surface of the mandrel is covered with a layer
39 of a silicone release agent. Then a strip or hoop of copper shim 40 is fitted around
the mandrel so as to cover the outlets 22. Then a particulate copper composition is
sprayed on to form a copper layer 41. This can be done by known techniques, for example
by feeding copper rod or powder into a spraying head where a plasma electric arc melts
it and forms minute droplets of molten copper which are protected from oxidation by
an inert gas while they are sprayed onto the surface of the mandrel. The outside surface
of this first layer is then ground so as to produce a uniform outside diameter (as
compared with the slightly tapering outside diameter of the mandrel). Then the first
copper layer is electro-plated to provide a second copper layer 42 of desired thickness,
the outside surface of which is ground, polished, etched to produce the gravure printing
surface, and finally flash chrome-plated.
[0011] The sleeve is removed from the mandrel by applying air under pressure to the outlets
22 which slightly expands the sleeve so that it can be withdrawn lengthwise from the
narrower end of the mandrel.
[0012] Referring to Fig. 5; in this method, a similar mandrel 38 just is used, and a silicone
release agent applied to it. Then a thin sheet of copper 43 is strained around the
mandrel so as to provide a butt joint 45 which is secured by plasma welding; that
is using a very narrow well-defined electric plasma arc flame produced from a tungsten
tip with inert gas protection, to locally melt the copper along the seam and weld
the two butting edges together. Thereafter this first copper layer is ground to produce
a uniform external diameter, before electro-plating the second layer as previously
described.
[0013] The all copper sleeves of this invention will generally have a somewhat smaller taper
than the corresponding reinforced plastics sleeves described in our British Patent
Applications referred to above. For example a taper of about 1:5000 might be appropriate
for the sleeves one metre long.
[0014] In another procedure of the present invention, the mandrel coated with a silicone
release agent is heated to about 100°C above ambient temperature. An electrically
conductive metal, preferably zinc, is sprayed onto the release coated mandrel to form
a metal base sleeve. A typical wall thickness is of the order of 0.5 to 0.8 mm. The
mandrel is heated in order to accept more easily the sprayed metal and also to assist
in removing the metal base sleeve from the forming mandrel by contraction of the mandrel
on cooling.
[0015] The metal base sleeve on the forming mandrel is then machined to a uniform external
diameter and is ready for removal from the forming mandrel. The temperature of the
mandrel in the meantime has cooled down and in order to remove the metal base sleeve
its temperature is raised quickly and it is slid lengthwise off the forming mandrel.
Air is used at this stage for the removal of the metal base sleeve from the mandrel,particularly
if the metal base sleeve is made of zinc, since zinc is too soft and the sleeve would
be distorted.
[0016] The metal base sleeve 48 is expanded by heat and slid onto a plating mandrel 50 (Fig.
6). The ends of the sleeve extend beyond the body of the mandrel and are closed by
end plugs 52, e.g. of acetal resin, with 0-ring seals 54 to prevent the migration
of the plating bath solution between the sleee and the mandrel but allowing the end
faces of the sleeve to be plated. For this purpose a gap 55 is left between the end
faces and the plugs. The metal base sleeve is then plated with copper to a required
thickness and is then ground to a finish diameter. The copper layer strengthens the
sleeve to such an extent that the sleeve can be removed from the plating mandrel and
mounted and demounted from a printing roll core by compressed air as described above.
1. A printing sleeve for fitting to a printing roll one end of which is of slightly
larger diameter than the other end, the sleeve being similarly dimensioned so that
it can be mounted on the roll by sliding it on lengthwise until it covers fluid outlet
openings in the roll intermediate the ends of the roll, applying fluid under pressure
to the outlets to slightly expand the sleeve, and then sliding the sleeve the rest
of the way onto the roll; characterised in that the sleeve (10) is made entirely of
metal and has an inner metal layer (41,43,48) which contacts the roll and an electro-plated
outer metal layer (42).
2. A printing sleeve according to claim 1 characterised in that both the inner layer
and said electro-plated layer are of copper.
3. A printing sleeve according to claim 1 characterised in that the inner layer is
of zinc and said electro-plated layer is copper.
4. A method of making a printing sleeve for fitting to a printing roll one end of
which is of slightly larger diameter than the other end, the sle'eve being similarly
dimensioned so that it can be mounted on the roll by sliding it on lengthwise until
it covers fluid outlet openings in the roll intermediate the ends of the roll, . applying
fluid under pressure to the outlets to slightly expand the sleeve, and then sliding
the sleeve the rest of the way onto the roll; characterised in that the method comprises
taking a generally cylindrical mandrel (38) the external diameter of which is slightly
larger at one end than the other, coating the outside surface of the mandrel with
a release agent (39), applying a first layer (41,43,48) of metal over the outside
surface of the mandrel, grinding the outside surface of the first metal layer to provide
it with a uniform external diameter, and electro-plating a second metal layer (42)
onto the first metal layer.
5. A method according to claim 4 characterised in that said first layer is provided
by spraying molten metal onto the outside surface of the mandrel.
6. A method according to claim 4 or claim 5 characterised in that the sleeve is removed
from the mandrel by applying fluid under pressure to said fluid outlet apertures to
slightly expand the sleeve and allow it to be withdrawn axially from the smaller diameter
end of the mandrel.
7. A method according to claim 5 characterised in that after applying the first metal
layer (48) the sleeve is transferred from the first mandrel to a plating mandrel (50)
at which the second layer is electro-plated.
8. A method according to claim 7 characterised in that the sleeve (48) is removed
from the first mandrel by heating it to a higher temperature than the mandrel so that
it expands relative to the mandrel and can be withdrawn axially therefrom.
9. A method according to claim 8 characterised in that the sleeve (48) is slid axially
onto the plating mandrel (50) while at a relatively higher temperature so that it
contracts to fit the plating mandrel (50) tightly on cooling.
10. A method according to any one of claims 7, 8 and 9 characterised in that the end
portions of the sleeve (48) extend beyond the body of the plating mandrel (50), the
ends of the sleeve being closed by members (52,54) which seal against the inside surface
of the sleeve, whereby the end faces of the sleeve (48) are exposed for plating.