Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PRINTING CYLINDER WITH AN OUTSIDE COVERING AND METl10D
AND APPARATUS FOR APPLYING A COVERING ON A~YLINDER
SURFACE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing cylinder
which is covered at the outside with a layer of a thermo-
plastic elastomeric composition, which can be hardened by
light which covering is formed by attaching a covering
material in sheet form to the cylin~er surface under
influence of heat and pressure.
2. Description of the Prior Art
A printing cylinder of this type is known in the art.
To manufacture such a known cylinder a sheet of covering
material isaLtached to the cylinder surface prior to
exposure to light in such a way that the edges of the sheet
which are to be joined are very close fitting to each
other, which is accomplished by forming a certain shape to
both edaes. When the thermoplastic sheet has been wrapped 5
around the cylincler, said sheet is attached to the cylinder r
surface by application of heot and pressure to the sheet,
during which operation also the two edges are attached to
each other.
This known printing cylinder has the drawback that
due to the application oF mechanical pressure at relatively
high temperatures,very easy an unevenness in the covering
is introduced which has to be removed by subsequent grinding
operations.
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Additionally very frequently ~nclusion of air between
the covering layer and the cylincler surface is observed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide
a printing cylinder which has none of said drawbacks.
Accordiny to the invention this object is obtained by pro-
viding a plurali~y of channels or cavities in the cylinder
surface apposite to the covering layer which are arranged in
a regular pattexn and which are interconnected.
Preferably a regular pattern of cavities, channels
or indentations is formed in the cylinder surface which P
cavities, channels or indentations are connected with each
other and with both ends of the cylinder. Upon use of such a
cylinder surface prior to the heating of the cylinder and the
covering which is wrapped around the cylinder, a vacuum may
be formed in the space between the covering and the cooper~ting
cylinder surface, by which action the covering is pressed
firmly onto the cylinder surface and adhered to the surfacz
whithout the danger of air inclusions between the covering and
the cylinder surface. By maintaining a vacuum in the space
between the cylinder surface and -the covering, gases or vapors
which would otherwise accumulate in said space are removed,
resulting in an optimal adhesion.
A further advantage of such a printing cylinder consists
in that the covering is applied without tension and that
accordingly an eventual plastic memory effect of the covering
is not observed.
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Due to this, less ~ear problems and less problems
relating -to the seam formed by joining the edges of the
sheet of elastomeric composition, are observed.
It is another object of the present invention to
provide a method for covering a printing cylinder surface
with a thermoplastic elastomeric composition which can be
hardened by exposure to actinic radiation in which method
a sheet of said elastomeric composition is wrapped around
the cylinder thereby covering the surface completely and
fitting closely; subsequently said sheet is attached by
application of heat artd pressure to the cylinder surface,
in which me~c~hod said sheet of elastomeric material is wrapped
around a cylinder surface ~hich cylinder has a pattern of
cavities or channels in said surface; consequently a vacuum
is generated in said cavities or channels between the cylinder
surface and the covering, in order to remove q~cumulated
gases, after which the cylinder with said sheet of material
on its surface is heated while maintaining the vacuum.
~ith preference heating is carried out at a tempera-
ture which lies between the glass transition temperature
and the melting temperqture of the elastomeric composition
and more preferably to a temperature between 100 and 150C,
which temperature is maintained from 10 to 120 min.
In a very suitable form of the present method, prior to the
heating operation after having wrapped the sheet nround the
cylinder, the sheet is enveloped at its outside with a very t
thin flexible material preferably in an overlapping way, I
which overlap is situated at a suitable distance from the
edges of the sheet of covering material which are to be joined,
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after which the heating operation is carried out. A very
suita~le Form of the method is further distinguished in
that after the period of heating the vacuum is shut off,
said thin flexible material is removed, after which a second
heating operatlon is carried out at a temperature of
100-150C duri.ng 10-60 min. The usecl vacuum has preferably k,
an absolute pressure of a maximum of 50 mm of mercury
column, the temperature is preFerably 140C, the first
heuting period is preferably one hour and the second period
half an hour~ The flexible material consists preferably of
a very thin foil such as a plasticized polyvinylchloride
foil with a thickness of 2~ to 25 microns, preferably 15
microns.
It is another object of the present invention to
provide an apparatus w'ith which a covering can be applied
on a printing cylinder sur~ace which covering consists
of a thermoplastic elastomeric composition which can be
hardened hy exposure to actinic radiation and where a
sheet of said elastomeric composition is wrapped round
the printing cylinder surface in a closely fitting way after
which said sheet by application of heat and outside pressure,
is attached to the cylinder surface, comprising a printing
cylinder surface and means for application of pre~sure to
the sheet of covering material which apparatus according to
the invention comprises means to aenerate a vacuum between
the printing cylinder surface and a covering sheet.
The features of the present invention which are
belleved to be novel are set forth with particularity in
the appended claims.
OtheI claims and many of the attendant advantages
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will be more readily appreciated as the same becomes better
understood by reference to the Followiny de-tailed des
cription and considered in connection with the accompanying
drawing 5 .
DESCRIPTION OF THE GRA~INGS
F
Fig. 1 is a printing cylinder according to the
present invention of which the covering is partially ~,
removed; r
Fig. 2 is a longitudinal side view of the apparatus
for carrying out the method accordina to the invention
in the situation in which the covering sheet is not yet
presse~ to the surface of the printing cylinder;
Fig. 3 is a printing cylinder with a thin flexible
material wrapped in an overlapping way around the elastomeric
composition; ~!
Fig. 4 is a cross section along line IV-IV in Fig.
3;
Fig. 5 is a cross section through a printing cylinder
according to Fig. 1.
DESCRIPTION OF A PREFE~RED EMBODIMENT
Referring now to Fig. 1 on the surface 2 of a metal r~
cylinder 1 a sheet 3 is situated of a thermoplastic elasto-
meric composition which can be hardened with light and on
~hich by exposure a certain pattern may be formed which may s
serve for the purpose of printing. In order to ensure proper
adhesion of said sheet 3 on the outside surface 4 of the r
metal cylinder, bulges 5 are applied which together form
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channels 6 which enable the removal of gases present t
between sheet 3 and the outside surface 4 thus ensuring
optimal adhesian without air inclusions between the inside
surface of sheet 3 and the outside surface 4 of the rnet'dl
cylinder 1.
Instead of bulges 5 also longitudinal channels can
be provided in the outside surface 4 of the metal printing
cylinder 1.
Referring now to Fig. 2 an apparatus servdng for the
application of said sheet 3 on the surface 4 of a metal
printing cylinder 1, comprises two cylindrical flanges 7
with a cylindrical raised border 8. In the flanges concen-
tric channels 9 are formed which are sealed with an 0-ring
10.These channels of ringform 9 are connected to a vacuum
source 12 via tube 11. At the outside surface of the cylinder
1, a sheet 3 of a thermoplastic elastomeric composition
which can be hardened by light is applied, which may be r
given a printing pattern by exposure to light for printing
purposes. After application of sheet 3 adhesive tape 14 is
applied covering the outside of the end-part of sheet 3 and
the roised border 8 of ~langes 7. Channel 9 is formed in
such a way that the available clearance in the form of
channels 6 is conn0cted with the said channel 9. After
application of adhesive tape 14, gas present between the
outside surface 4 of cylinder 1 and the inside surface
of sheet 3 is removed by suction; subsequently cylinder
surfacc 4 of cylinder 1 is heated. Heating is carried out
during 10 to 120 min; preferably during 10-60 min. at a
temperature of 100-150C. In order to ensure an optimal
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attachment of said sheet of light hardenable thermoplastic
elastomeric composition on the outer surface 4 of printing
cylinder 1, after application of sheet 3, a thin foil 15
is wrapped around the total of cylinder 1 and sheet 3,
which foil suitably consists of polyvinylchloride with a
thickness of ~,5 25 microns, preferably of 15 microns.
Overlap 16 is situated q good distance from the area where
edges 13 of sheet 3 contact each other.
By maintaining the exhaust of gases via tube 11 and
vacuum source 12 during the heating operation also gases
which are developed during said heating are removed, so .
ensuring an optimal adhesion between sheet 3 and surface 4
of cylinder 1.
The invention will now be explained more in detail
in the following example.
Example
A metal cylinder 1 ~ith a surface 4 comprising
longitudinally applied channels 6 which are formed by notches
5 on the outside of the cylinder, is covered with a sheet 3
of a thermoplastic elastomeric composition which may be
hardened by exposure to light (Cyrel of DuPont). Edges 13
of sheet 3 are contacted in a close fitting way. The whole
is subsequently introduced in an apparatus as outlined above.
By creation of a vacuum of an absolute prQssure of a maximum
of 50 mm of mercury, preferably 20 mm, gases present between
sheet 3 and surface 4 are removed. Subsequently the whole
is wrapped with a polyvinylchloride foil with a thickness of
15 mi~rometer. After this the cylinder is heated to a tempera-
ture of 140C; said h0ating lasting for one hour.
Subsequently exhaust via vacuum source 1~ is ended, the
wrappina foil 15 is removed after which another heating
at 140C during half an hour is carried out.Upon
application of wrapping foil 15 of polyvinylchloride,
care is taken to situate overlapping parts 16 at a good
distance from the seam which is formed ~y edges 13 of
sheet 3. The whole is subsequently cooled and a printing
cylinder is obtained which is optimally united with sheet
3; after this sheet 3 can be processed to obtain the
desired printing pattern The used foil has a thickness
of 2,5-25 micrometer, preFerably a thickness of lO to 20 ~;
microns ,more preferably of 15 microns. The used foil is
preferably a plasticized polyvinylchloride foil.
The cylinder l of the apparatus may be provided
at both ends with a separate ring being located close to
the cylinder l and having an outer diameter which corres- -~
ponds to that of the said cylinder. The coating or sheet 3
must have a width such, that both additional rings are f
covered. L'
After -the completion of the manu-facturing process, L
both rings with their annular covering are discarded,
thus eliminating the side edges of the printing cylinder.
These side edges have appeared to possess a slightly
increased thickness, which should be avoided in ~ printing
cylinder.
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