CA1175624A - Printing cylinder with an outside covering (coating) and a method and apparatus for applying a covering on a cylinder surface - Google Patents

Abstract

Abstract PRINTING CYLINDER

Printing cylinder with an outside covering of a thermo-plastic elastomeric composition which can be hardened by exposure to light said covering being snugly applied to the circumference of the cylinder by suction in the annular clearance between cylinder and covering; the cylinder consists of several coaxial parts during the covering process, only the central portion with its covering forming the printing cylinder.

Description

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-2-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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4- b 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, ~ 6~

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 'P,i ~%~ :

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 f ~756~4 , 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 s ~L7S62gl 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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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for forming a printing cylinder compris-ing the steps of completely covering the outer surface of a cylin-der with a closely fitting layer of a thermoplastic elastomeric composition adapted to be hardened by exposure to light, maintain-ing a space between said cylinder and said layer by the provision of a pattern of interconnected cavities or channels on said outer surface of said cylinder, enveloping the outer side of the layer with a flexible film of gas-tight material after application of the layer, applying a vacuum to said space for removing any accumulated gases, and thereafter heating said cylinder and said covered layer for 10 to 120 min. at a temperature of 100° to 150°C., while maintaining the vacuum, thereafter removing the application of vacuum and the film, and further heating said cylinder and said covered layer for 10 to 60 min. at a temperature of 100° to 150°C.

2. Method according to claim 1, wherein the vacuum is applied at a maximum absolute pressure of 50 mm of mercury in the space between said cylinder and said layer, the temperature during the heating step being maintained at 140°C. for a period of one hour and subsequently for a second period of half an hour.

3. Method according to claim 1, wherein the covering step includes joining free ends of the layer together, and the enveloping step includes overlapping free ends of the film and locating the overlapped ends a circumferential distance from the joined ends.

4. Method according to claim 1, wherein the flexible film comprises a plasticized polyvinylchloride foil having a thickness of 10 to 20 microns.

5. Method according to claim 4, wherein the thickness of the foil is 15 microns.

6. A printing cylinder comprising a metal cylinder and a layer of thermoplastic elastomeric composition adapted to be hardened by exposure to light completely covering the outer surface of the metal cylinder and which is secured thereto by the application of heat and pressure, the outer surface of the metal cylinder having a pattern of interconnected channels or cavities provided thereon and which enhance securement of the layer of thermoplastic elastomeric composition to the metal cylinder and permit removal by vacuum of accumuated gases during secure-ment.

7. A printing cylinder according to claim 6, wherein the interconnected channels or cavities extend throughout the length of the metal cylinder.