GB2102733A - Printing presses - Google Patents

Abstract

A printing press 1 comprises four printing units 4 arranged around a common impression cylinder 3, around which a web of material is arranged to pass. Each of the printing units 4 is for printing a different colour, and comprises a flexible belt 5 arranged to bear against the impression cylinder 3, to print upon the web of material 2. Each printing unit 4 is individually movable towards and away from the common impression cylinder 3, and has a respective inking roller 6 which in turn is movable towards and away from the flexible belt 5. <IMAGE>

Description

SPECIFICATION Printing presses This invention relates to printing presses, and is particularly although not exclusively concerned with flexographic printing presses.

Conventionally, printing presses employ printing cylinders to apply print to a material, either directly or by means of off-set rollers.

Although this arrangement can permit of a relatively high degree of accuracy, it can be disadvantageous in certain respects, especially where it is necessary to change the print pattern at relatively frequent intervals. This can happen in the printing of carton or case blanks, for example, where patterns of relatively great repeat length may have to be changed frequently. This typically involves the changing of heavy printing cylinders, resulting in considerable down time of a printing press, particularly where multi-colour printing is taking place.

In an attempt to improve things, there have been proposed printing presses which comprise a series of printing stations, between which material to be printed is transferred. At each station, the print is carried on a flexible belt, which bears against a respective impression cylinder. Although this may provide the advantage that the flexible belt may be changed more readily than a corresponding printing cylinder, difficulties can arise in achieving a desirably high degree of accuracy in registration, between successive colours of a multi-colour printing press.

Preferred embodiments of the present invention aim to provide printing presses which may be improved in the foregoing respects.

More generally, according to a first aspect of the present invention, there is provided a printing press comprising means for feeding a web of material around a loop, and a plurality of printing elements disposed around said loop, each printing element comprising a flexible belt arranged to bear against an impression cylinder, to print upon said material passing therebetween.

Preferably, said impression cylinder is common to all of said printing elements, said material passing around the cylinder, in use.

Each said flexible belt is preferably mounted on a pair of spaced rollers, in such a manner that it may readily be removed therefrom and replaced by another belt. Thus, type patterns and/or type repeat lengths may readily be Changed as desired. The spacing of the pair of rollers is preferably adjustable, to accommodate belts of different lengths, and to adjust the tension of a belt mounted thereon.

Preferably, each flexible belt is of polyester material. Advantageously, each flexible belt may be formed with a plurality of sprocket holes, which engage with a sprocket wheel or the like.

According to another aspect of the present invention, there is provided a printing press comprising an impression cylinder, a printing unit, and means for moving the printing unit towards and away from the impression cylinder, the printing unit comprising a flexible belt arranged to bear against the impression cylinder to print upon material passing therebetween.

Preferably, the printing unit also includes an ink transfer mechanism, and means for moving the ink transfer mechanism towards and away from said flexible belt.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing, the single figure of which shows schematically part of a flexographic printing press embodying the invention.

The illustrated press 1 comprises means for feeding a web of material to be printed (e.g.

paper, cardboard, etc) around a common impression cylinder 3. The web 2 of material is fed to the cylinder 3 from an unwinding unit (not shown), and passes from the cylinder 3 to subsequent processing units (not shown).

Mounted on the frame of the printing press 1, around the cylinder 3, are four printing units 4.

Each printing unit 4 is arranged to print a different colour onto the web 2 of material passing around the common impression cylinder 3, and comprises a printing element in the form of a flexible belt 5, an inking roller 6, and a reverse angle doctor blade 7. The flexible belt 5 is mounted on a pair of spaced rollers 8, 9, by which it is driven principally by friction engagement between the rollers 8, 9 and the belt 5. The flexible belt 5 is advantageously made of polyester material, and carries one repeat or more of type pattern, thereon. It is formed with sprocket holes along the edges thereof, which holes engage with sprocket wheels or the like, carried on the rollers 8, 9, which are thus synchronised with the flexible belt 5.Ink is supplied from a reservoir (not shown) to the flexible belt 5 via the respective inking roller 6, with which the reverse angle doctor blade 7 co-operates.

The printing press 1 has the advantage that it may readily be changed between jobs, simply by changing the flexible belts 5. It will be appreciated that the flexible belts 5 are of relatively light weight, and are easy to handle.

This contrasts favourably with conventional printing presses, where the changing of heavy printing cylinders (particularly on large width machines), can be a very delicate and time consuming operation. The flexible belts 5 may be produced relatively economically, and may have any desired number of pattern repeats thereon. Preferably, the spacing between each pair of rollers 8, 9 is adjustable, to accommodate flexible belts 5 of differing lengths, and/ or to adjust the tension in each belt 5.

It may be appreciated that the feed path of the web 2 of material between the successive printing units 4, around the impression cylin der 3, is relatively small. This is especiallly advantageous, in that registration to a high degree of accuracy may be obtained between the various colours of the printing units 4.

Moreover, the sprocket wheel connection between each pair of rollers 8, 9 and its respective flexible belt 5 enables the various flexible belts 5 to be driven with a high degree of synchronism, both with respect to one another, and with respect to the impression cylinder 3, which drives the roller 8 via gear ing.

Thus, the illustrated printing press 1 provides a machine which can provide relatively high quality work at relatively low cost, both as regards machine costs and machine operating costs.

Although the illustrated printing press 1 is especially advantageous, it may be appreciated that various modifications may be made thereto. For example, the common impression cylinder 3 may be replaced by four individual impression cylinders each for a respective printing unit 4. The important thing is that the printing units 4 are disposed around a common loop of the web 2 of material, such that distance between successive units is relatively small. More or less than four printing units 4 may be provided, and an alternative ink transfer mechanism to the illustrated inking roller 6/ doctor blade 7 may be employed.

In an important modification to the illustrated arrangement, each of the printing units 4 comprises an independent unit which is individually movable towards and away from the common impression cylinder 3. This may be particularly important in allowing for individual settings of the respective nips between each of the flexible belts 5 and the impression cylinder 3.

In such a preferred arrangement, in each printing unit 4, the roller 8 is mounted on a first support which is movable towards and away from the common impression cylinder 3.

The inking roller 6 with its doctor blade 7 (or alternative ink transfer mechanism) is mounted on a second support, which in turn is mounted on the first support for movement towards and away from the roller 8. The first support may be mounted on the main frame of the machine, and the second roller 9 on which the flexible belt 5 is mounted may also be mounted on the frame of the machine. In use, the first support is moved towards or away from the common impression cylinder 3 (for example by means of a fine adjustment lead screw and a double acting hydraulic cylinder), to achieve the desired nip between the flexible belt 5 and the impression cylinder 3, such that the flexible belt 5 bears against the web 2 with the desired pressure.The second support is moved towards or away from the roller 8, so that the inking roller 6 bears against the flexible belt 5 with the desired pressure (again, a fine adjustment lead screw and double acting hydraulic cylinder may be used, for example). When the.

printing press is stopped, the aforementioned double acting cylinders are actuated to move the inking roller 6 away from the belt 5, and to move the belt 5 in turn away from the web 2.

By adopting such an arrangement, the printing units 4 may be individually adjusted in a ready manner. In an especially advantageous arrangement, the flexible belt 5 and roller 8 may be dispensed with as desired, and replaced by a conventional printing cylinder in place of the roller 8. Thus, such a printing press may readily be adaptable to print patterns having either relatively small or relatively large repeats.

The adjustable mounting arrangement for the printing units 4 is not confined to the case wherein the printing units are disposed around a common loop of a web of material to be printed.

Claims (10)

1. A printing press comprising means for feeding a web of material around a loop, and a plurality of printing elements disposed around said loop, each printing element comprising a flexible belt arranged to bear against an impression cylinder, to print upon said material passing therebetween.

2. A printing press according to Claim 1, wherein said impression cylinder is common to all of said printing elements, said material passing around the cylinder, in use.

3. A printing press according to Claim 1 or 2, wherein each said flexible belt is mounted on a pair of spaced rollers, in such a manner that it may readily be removed therefrom and replaced by another belt.

4. A printing roller according to Claim 3, wherein the spacing of the pair of rollers is adjustable, to accommodate belts of different lengths and/or to adjust the tension of a belt mounted thereon.

5. A printing roller according to any preceding claim, wherein each flexible belt is of polyester.

6. A printing press according to any preceding claim, wherein each flexible belt is formed with a plurality of sprocket holes, which engage with a sprocket wheel or the like.

7. A printing press comprising an impression cylinder, a printing unit, and means for moving the printing unit towards and away from the impression cylinder, the printing unit comprising a flexible belt arranged to bear against the impression cylinder to print upon material passing therebetween.

8. A printing press according to Claim 7, wherein the printing unit also includes an ink transfer mechanism, and means for moving the ink transfer mechanism towards and away from said flexible belt.

9. A printing press according to Claim 7 or 8, wherein the or each said means comprises an hydraulic cylinder.

10. A printing press according to Claim 7, 8 or 9 including fine adjustment means for adjusting the position of the printing unit with respect to the impression cylinder, and/or the position of the ink transfer mechanism with respect to the flexible belt.

.11. A printing press according to any one of Claims 7 to 10, and also according to any one of Claims 1 to 6.

1 2. A printing press according to any preceding claim, wherein the or at least one of the flexible belt(s) is removable and the printing press is adapted to receive a printing cylinder in its place.

1 3. A printing press substantially as hereinbefore described with reference to the accompanying drawing.