Printing – Printing members – Plate mountings
Reexamination Certificate
2001-10-11
2004-09-28
Nguyen, Anthony H. (Department: 2854)
Printing
Printing members
Plate mountings
C101S382100
Reexamination Certificate
active
06796234
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a holding device for a flexographic printing sleeve.
A nongeneric holding device for a printing cylinder is already known from FR 1275904. This device has two conical receiving members for the printing cylinder provided with the printing image.
The fundamentally narrow contact surface between cone and cylinder providing the purely frictional transmission of force from the rotationally driven conical receiving members to the printing cylinder is disadvantageous in that comparatively heavy, thick-walled printing cylinders must be used which provide a sufficiently large contact surface for transmission of force through beveling at the two end faces of the cylinder. This large wall thickness also ensures that the compressive forces needed to hold the printing cylinder in place between the two receiving members do not deform the printing cylinder.
CH 377854 also discloses a likewise non-generic clamping device for the bearing support of rollers with paper, foil, and the like, in which device each end of the roller attaches to a conical receiving member in the form of a clamping cone. A form-fitting element acting as a rotational locking element is provided between the sleeve-shaped roller core and the clamping cone.
For this purpose, either a plurality of ribs and matching grooves must be formed on these two components, or the clamping cone must be molded in the material of the roller core such that this roller core is permanently deformed.
The device presented in CH 377854 is designed for holding only single-use rollers.
When the design disclosed in CH 377854 is transferred to printing equipment, the addition of grooves or ribs in sleeves of small wall thickness would not be possible. Permanent deformation of the printing sleeves by the receiving members would inhibit or preclude the multiple use of the printing sleeves, and would also carry the additional risk that the surface with the printing image would exhibit undesirable eccentricities.
In contrast to the teaching of FR 1275904, in one type of printing technology called “flexographic printing” instead of a complete one-piece printing cylinder, each with its own printing image, replaceable sleeves are used which may be slipped onto a cylindrical metal receiving member.
DE 2700118C2 or DE 3633155A1 disclose generic holding devices in which the cylindrical metal receiving member in each case extends through the entire length of the sleeve. The cylindrical receiving member is in other words a “permanent printing cylinder” since it may be used with multiple sleeves and thus for multiple printing images. Here each sleeve can display the printing image directly, for example etched or burned in by laser, or it can have a separate external plate layer with the printing image.
To mount the sleeves in flexographic equipment, compressed air exits the inner cylindrical receiving member and expands the partially mounted sleeve so that this may be slipped completely onto the receiving member. When the compressed air is switched off, the sleeve constricts and lies firmly in place on the cylindrical receiving member such that the sleeve may rotate together with the latter. The cylindrical receiving member is made of metal, and its resulting high cost of production and high weight impeding handling are thus disadvantageous.
In addition to utilization in the printing facilities themselves, i.e. in the printing presses, many of these devices are employed in the processing stations which are needed to create a printing sleeve and which also have a rotatable holder for the printing sleeves or their associated preliminary production stages, for example coating machines which coat the surface of the unfinished sleeve with light-sensitive or acid-sensitive materials by which the printing images are later applied to the sleeve surface by laser-based or etching processes. These etching or laser machines also require this type of rotatable holder for the printing sleeves.
Both during printing as well as during the preparatory production processes for the printing sleeves, a fundamental problem consists in the fact that printing sleeves of widely varying outside diameters are required. In one comparatively old technology, noticeably thin-walled metal printing sleeves were slipped onto cylindrical receiving members. The wall thickness of these sleeves had to be small to ensure the flexibility needed to allow the sleeves to be expanded by compressed air. As result, the cylindrical receiving members had almost the same diameters as the printing sleeves. Given a variety of outside sleeve diameters for the varying sizes of the printing images, a matching number of receiving members of varying diameters had to be kept on hand.
One simplification of the above for the user lies in the fact that sleeves of varying wall thickness may be used with receiving members of the same diameter so that a greater number of sleeves of varying outside diameters may be used where a reduced number of different receiving members are employed. Based in part on the use of plastics, these sleeves exhibit the flexibility needed to be expanded by compressed air despite these wall thicknesses.
Nevertheless, it is common to have a gradation in 10 mm steps of the outside diameters of the cylindrical receiving members. Given a size range of around 250 mm to 2000 mm for the sleeve circumferences matching the size of the printing images, even in the flexographic process a comparatively large number of receiving members need be kept on hand. This requires a very high total investment for the printing facilities, especially for the above-mentioned shops involved in the preparatory production: whereas a printing facility may specialize in processing printing images within a limited size range, laser-gravure and similar facilities are usually oriented around creating sleeves for the entire range of the above sleeve circumferences.
As a result, to reduce in practice the inventory of receiving members with differing outside diameters, sleeves are employed having sometimes very large wall thicknesses so that a sleeve of large outside diameter with a correspondingly large printing image may be used on a “small” receiving member.
The result is considerable expense and effort, especially when sleeves of such large wall thickness or diameter are used due to the considerable weight of such sleeves and especially of their associated cylindrical receiving members. Not all facilities have suitable in-plant handling equipment such as cranes, lifts, or the like which require a very high investment. For this reason, only sleeves of comparably small diameter can be processed. In addition, set-up times for changing receiving members are considerably shorter and thus more inexpensive if this change can be effected by hand, i.e. without such handling equipment.
SUMMARY OF THE INVENTION
The object of the invention is to improve a generic holding device such that the most inexpensive possible holding device simplifies the following: handling of the receiving member when the receiving member is changed, sleeve changeovers, and the changeovers of sleeves with different diameters.
This object of the invention is achieved by a holding device for a flexographic printing sleeve according to the teachings of the present invention.
The invention proposes, in other words, using two receiving members instead of one, which receiving members receive the sleeve between them, the receiving members each having two or more shoulders with varying diameters.
In contrast to a single cylindrical receiving member which extends the entire length of the printing sleeve, as is well known in flexography, the invention provides for considerable savings in weight, thereby simplifying handling when the receiving member or holding device is changed. Specifically, such changes are required less often since the receiving members allow various sleeves of differing inside diameters to be handled.
In contrast to the utilization of two conical receiving members familiar from other technical are
Lahive & Cockfield LLP
Nguyen Anthony H.
Rotec-Hulsensysteme GmbH & Co. KG
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