METHOD FOR PRODUCING PLASTICS CYLINDERS FOR PRINTING IN GENERAL, IN PARTICULAR FOR ROTOGRAVURE AND FLEXOGRAPHY, AND THE CYLINDER OBTAINED

METHODE GENERALE DE FABRICATION DE CYLINDRES D'IMPRESSION EN PLASTIQUE APPLIQUEE EN PARTICULIER A LA ROTOGRAVURE ET A LA FLEXOGRAPHIE ET CYLINDRES OBTENUS AVEC CETTE METHODE

English Abstract

METHOD FOR PRODUCING PLASTICS CYLINDERS FOR PRINTING IN GENERAL,
IN PARTICULAR FOR ROTOGRAVURE AND FLEXOGRAPHY, AND THE CYLINDER
OBTAINED.
ABSTRACT
The method according to the invention consists essentially of (a)
preparing an inner cylindrical tube of self-supporting rigid
material, advantageously epoxy resin reinforced with glass or
carbon filament or fabric, (b) coating said cylindrical tube with
an expanded plastics material, advantageously rigid polyurethane,
(c) making the outer surface of said coating perfectly smooth, (d)
making said outer smooth surface expanded material
by applying metallic materials in any manner,
and (e) making said electro-conductive surface engravable,
advantageously by applying electroplated copper or applying
engravable materials of photopolymer type.

Claims

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THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for producing a plastic cylinder for printing
which process comprises:
preparing an inner cylindrical tube [of given diameter]
from self-supporting rigid material;
coating said cylindrical tube with an expanded plastic
material;
smoothing the outer surface of the expanded plastic
material coating;
rendering said outer smooth surface electro-conductive;
rendering said electro-conductive surface engravable.
2. A method according to claim 1 wherein said inner
cylindrical tube comprises a material to which said expanded
plastic material bonds.
3. A method according to claim 2 wherein said inner cylin-
drical tube comprises epoxy resin reinforced with glass or carbon
fibre or fabric
4. A method according to claim 2 wherein the inner cylin-
drical tube comprises a base material to which the expanded
plastic material does not bond, treated to effect said bond.
5. A method according to claim 1 wherein said expanded
plastic material is rigid polyurethane.
6. A method according to claim 5 wherein the polyurethane
has a density of between 0.400 and 0.500 kg/dm3.

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7. A method according to claim 5 wherein the polyurethane
has a density of about 0.480 kg/dm3.
8. A method according to claim 1 wherein the outer surface
of the expanded plastic material is smoothed by moulding.
9. A method according to claim 1 wherein the outer surface
layer is sufficiently thick to allow the cylinder to be ground
to a required diameter.
10. A method according to claim 1 wherein said outer smooth
surface is rendered electro-conductive by applying a metallic
material.
11. A method according to claim 1 wherein the electro-
conductive surface is rendered engravable by electroplating copper
thereon.
12. A method according to claim 1 wherein the electro-
conductive surface is rendered engravable by applying an engravable
photopolymer material.
. 13. A plastic cylinder for printing comprising:
an inner cylindrical tube of a self-supporting rigid
material of given diameter; and
an expanded plastic material coated upon and bonded to
said inner cylindrical tube, said expanded plastic material having
a smoothed, electro-conductive, engravable outer surface.
14. A cylinder according to claim 13 wherein said inner

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cylindrical tube comprises epoxy resin reinforced with glass or
carbon fibre or fabric.
15. A cylinder according to claim 13 wherein said expanded
plastic material comprises rigid polyurethane.
16. A cylinder according to claim 15 wherein said poly-
urethane has a density of between 0.400 and 0.500 kg/dm3.
17. A cylinder according to claim 15 wherein said poly-
urethane has a density of about 0.480 kg/dm3.
18. A cylinder according to claim 15 wherein the outer
surface comprises copper.
19. A cylinder according to claim 15 wherein the outer
surface comprises an engravable photopolymer material.

Description

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DESCRIPTI0~
This industrial inv~ntlon patent rslatas to a method for produclng
plastlcs cylinders for prlntlng ln ~eneral, and in particul~r
roto~ravure .1nd i`lexography. Ths patsnt also relatas to ths
cylinder obtained by said msthod.
~any methods have been propos~d for producin~ plastlos prlnting
cylinders, however such known mathods are ex-tremely compllcated
and difflcult to implement, in particular wlth re~ard to coating
the baslc plastics cyllnder wlth metal, a~ i5 apparent for exa~pl~
from USA patent 4,503,769 in the name of Andersen Dennis. In
additlon, cyllnders produced by conventional methods are of poor
rsllabillty or lndeed unraliable.
As is well known, currently used c~li.nders oi good reliability are
those of steel construction, and rarely of ~luminium, and thus
variou~ problems arise including thuss o~ their weight and their
need i`or dynamic balancing. ~urther drawbac~s ar~ wall known -to
the expert of tha art
An obJeot of the presa~t invention is to pro~ide a mathod i`or
produclng cyllnders for printing in ganeral, and in partlcular
roto~ravure and ~lexo~raphy, which is very slmp].e to implement
uslng any sultable apparatus.
A further obJsct i5 to provids a method of the aforesaid type
which enahles plastlcs printin~ cylinders to ba producad which are
of maxlmum reliability and low wei~ht, so -that they can be easily
handled and stored.
A furthar o~Ject ls to provide a method which enables a pla~tlcs
prlntln~ cyllnder to he produGed, the diamster of whlch can be

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varled at wlll durlng its produ&tiont without encounterlng
pnrtlcular di~ficulty.
hese and further ohJect5 of the invention will be apparent to the
e~pert of the art from tha following descriptlon.
The method of the lnvention canslsts essentlally of ~a) praparlng
an inner cyllndrlcal tu~e of self-supporting ri~id ~aterial,
advantageously epoxy resln r~lnforced with glass or carbon
filament ar fabrlc, ~b) coating said cylindrical tube with an
expanded plastics material, advantageously rlgld polyurethane, ~c)
making the outer surface of said coating perfectly smooth, ~d~
maki.n$ said outer smooth surface of the expanded material
electro-conductive b~ applylng 3netallic 3~terials in any manner,
and (e) 33laklng sald electro-conduotive surface engravable,
advantageously by applyin~ electroplated copper or applying
en~ravable photopolymer materials.
The stages of the method acoordlng to the ln~ention will be
apparent from the followlng example.
A glass fibre fabrlc or yarn i~pregnated with epo~y resin is wound
about a perfectly cylindrioal steel mandrel having a $round,
lapped and chrol~u3~plated 6urface, untll a thiokness of between
1.5 and 2 mm is obtalned. The struoture 15 then polymeri2ed in
conventlonal manner at a temperature of between ~0C and 120~C.
The resultant tube is then mounted on the central shaft of a
casting mould consiatlng of a cylinder in which sai/i shaft is
centrally po~itloned and which has its inner surfaoe perfectly
ground and lapped. The mould is ti~htly closed and a quAntity Q~
polyurethane ls introduoed such that the final expanded produot

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will have a density of 0.4~0 k~dm~, said polyurethane being
prepared by mixin~ Laooyanate and polyol ln stoichiometric
proportion in a ~ixln$ machlne.
Both the components and the mould are temperature-controlled at
20-35 C, and preferably at 30C.
On removin~ the ~truoture con~lstin~ of the tube and expanded
coating from the mould the surface o~ this coatln~ ls per~eGtly
smooth due to the actlon of the lnner mould ~urface. The
structurc i~ checked i`or perfect cyllndriclty and if necessary can
be ground untll of correct geometry.
The structure ~btained can be made electrically conductive by
applylng~ a si.lver or nic~el~based palnt by ~pray or bru6h to a
thickness of 20~uc.~ ~opper is then applied in an electroplating
tank to a thick~le~s ~ufficient to ~nable the required en~raving of
the oylinder ~urface to be effectcd, thi~ -thic~ness belng
advantageausly 500~c.
The thlckness oi` the axpanded polyurethane layer can be varled
accordin~ to requiremints without varying the dimensiona of the
lnternal tuba, ta ell4ble cyllnd~r~ of varlable outer diameter to
be mounted on tbe same standard support shaft.