GB2138362A

GB2138362A - Printing machines

Info

Publication number: GB2138362A
Application number: GB08310897A
Authority: GB
Inventors: Michael Hedley Richardson
Original assignee: LANSDOWNE Ltd
Current assignee: LANSDOWNE Ltd
Priority date: 1983-04-21
Filing date: 1983-04-21
Publication date: 1984-10-24
Also published as: GB8310897D0

Abstract

A conventional flat bed letterpress printing machine is converted to use dry litho plates by replacing the existing base of the machine by a specially designed base (16). The base (16) is flat on both surfaces to very fine tolerances and the dry litho plate (20) is brought into close face-to-face contact with the base (16), eg by suction or by tensioning the dry litho plate across the base (16). <IMAGE>

Description

SPECIFICATION Printing machines Field of the invention This invention relates to printing machines and in particular to flat bed letterpress printing machines.

Background to the invention Flat bed letterpress printing machines have a rotatable cylinder positioned above a bed which reciprocates below the cylinder. A rubber blanket is wrapped around the cylinder and a base is rigidly mounted on the bed. Print is set on the base so that an impression is printed onto paper fed between the cylinder and the reciprocating base.

Such flat bed letterpress printing machines are generally robust and simple in construction but are less efficient that offset litho machines for which dry litho plates have recently become available, avoiding the need for the application of water in the offest litho printing process. The invention stems from the realisation that if a conventional flat bed letterpress printing machine could be converted to use dry litho plates, the resulting machine would have most of the advantages of offset litho machines without the need to scrap the flat bed letterpress machine and incur the cost of replacing it with an offset litho machine.It is envisaged that the ability to convert a conventional flat bed letterpress printing machine to operate with dry litho plates will be commercially very attractive because there are in existance a large number of flat bed letterpress printing machines which are capable of many years of future service but which are less efficient than the more modern offset litho machines. However, this conversion is not a straightforward process because inks usually used on flat bed letterpress printing machines are not compatible with dry litho plates and because the existing base of a conventional flat bed letterpress printing machine is not suitable forthe mounting and securement of a dry litho plate.

Summary ofthe invention According to one aspect of the invention a flat bed letterpress printing machine has a dry litho plate mounted on a base of the machine. In most cases the base will be especially designed and made to support the dry litho plate and will replace the existing base on the flat bed letter press printing machine.

Preferably, the dry litho plate is detachably mounted on the base of the machine by releasable clamping means which enable the plate to be clamped in position on the base and subsequently released for replacement by another dry litho plate.

Clamping means are conveniently provided at each end of the machine to enable both ends of the dry litho plate to be clamped into position. In the preferred embodiment to be described the clamping means at each end of the machine include manually rotatable clamping screws acting on a clamping plate or a strip which extends across the width of the machine and which is capable of clamping the corresponding end of the dry litho plate.

The base must be flat on both surfaces within very fine tolerances so that the lower surface of the base makes accurate face-to-face engagement with the upper surface of the bed and so that the upper surface of the base is flat to support the dry litho plate. This degree of accuracy is preferably achieved by making the base from steel which is annealed and then precision ground to be flat on both sides.

The dry litho plate must be brought into close face-to-face contact with the base to avoid any air pockets between the base and the dry litho plate.

The base may be formed with a series of perforations to which a vacuum source is applied in order to suck the dry litho plate into intimate surface contact with the base, but a simpler and preferred alternative is to tension the dry litho plate across the base. In the preferred embodiment to be described this is achieved by providing tensioning means which operate in such a way that the clamping means at one end of the machine can be urged away from the adjacent end of the base so as to apply tension to the dry litho plate which is thereby drawn into intimate surface contact with the upper surface of the base.

The tensioning means may comprise a tensioning plate which extends along one end of the machine and against which the corresponding clamping plate can be tightened, the tensioning plate being capable of being moved with respect to the base so that the clam ping plate moves away from the adjacent end of the base to apply the required tension to the dry litho plate.

According to another aspect of the invention a method of converting a conventional flat bed letterpress machine to operate with a dry litho plate comprises replacing a base of the conventional machine with a new base and fitting a dry litho plate to the replacement base.

According to yet another aspect of the invention a kit of parts for converting a conventional flat bed letterpress printing machine to operate with a dry litho plate comprises a replacement base for fitting on the machine in place of the existing base, a dry litho plate and clamping means for clamping the plate on the replacement base. The base is preferably annealed and ground to be flat on both sides, as previously described, and the clamping means are preferably associated with tensioning means for tensioning the dry litho plate across the base.

Aflat bed letterpress printing machine converted by means of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 7 is a diagrammatic side view of the machine, Figures 2 and 3 show, at successively increased scales, sectional views of the clamping means for clamping respective ends of a dry litho plate in the machine, and Figures 4 and 5 are sectional views showing detail on planes parallel to those of Figures 2 and 3 respectively.

Detailed description of the drawings Referring to Figure 1,the converted machine has its original bed 10 which reciprocates in the directions of the two arrows A beneath a cylinder 12 carrying a rubber blanket 14. On the bed 10 is rigidly mounted a specially prepared base 16 which is fitted as a replacement for the existing base of the flat bed letterpress printing machine. The base 16 has a peripheral ledge 18 and is annealed and precision ground so as to be flat on both surfaces.

A dry litho plate 20 is illustrated in broken lines in Figure 1. The dry litho plate 20 is known as a Toray plate and is previously exposed to ultra violet light in order to fix the required imagethereon.Thedrylitho plate is clamped in the machine by clamping means 22 and 24 at respective ends of the machine. Ink is applied by means of rollers shown diagrammatically at 26 in Figure 1.

The clamping means 22 are shown in greater detail in Figure 2. The clamping means 22 include a clamping plate 28 which extends across the width of the base 16 and which can be clamped against a sloping edge surface 30 of the base 16 by means of a plurality of clamping screws one of which is shown at 32 in Figure 2. The clamping means 24 at the opposite end of the machine are shown in a greater detail in Figure 3. An edge plate 34 is secured to the end of the bed by two screws 36 the heads of which project with clearance into respective holes 38 in a tensioning plate 40. A clamping plate 42 can be tightened against a sloping upper surface 44 of the tensioning plate 40 by means of a plurality of clamping screws one of which is shown at 46.To the lower edge of the tensioning plate 40 is attached an elongate heal plate 48 which locates with clearance in a slot 50 formed in the edge plate 34.

Each end of the dry litho plate 20 is slotted for the reception of the shanks of the clamping screws 32 and 46, when the ends of the dry litho plate 20 are inserted under the clamping plates 28 and 42.

Atthree locations along the length ofthetensioning plate 40 are disposed means for moving the tensioning plate with a rocking movement with respect to the edge plate 34. Figure 4 shows the construction at each of these three locations. A threaded stud 52 projects from the end of the bed 10 and co-operates with a hollow, internallythrnaded sleeve 54 having a shoulder 56 at its inner end and a rod or hand wheel 58 at its outer end for ease of turning. It will be appreciated that rotation of the sleeve 54 causes the tensioning plate 40 and heal plate 48 to rock or pivot about the slot 50 as fulcrum.

At two locations along its length, the tensioning plate 40 is urged towards the edge plate 34 by springs. One of these locations is illustrated in Figure 5, the spring 60 acting between the outer surface of the tensioning plate 40 and the flange of a nut 62 threaded onto a stud 64 projecting from the bed 10.

Afterthe image has been formed in the dry litho plate 20, one end of the plate 20 is clamped in the clamping means 22 and the other end clamped in the clamping means 24. The rods or hand wheels 58 are then turned to rotate the sleeves 54 so as to move the upper edge of the tensioning plate 40 away from the adjacent end of the base 16. This tensions the dry litho plate 20 across the base 16. The ink used is specially formulated to suit the dry litho plate and the image is printed onto the paper by feeding the latter between the dry litho plate and the blanket 14 as the cylinder 12 rotates and as the bed 10 reciprocates. It will be appreciated that the dry litho plate can be unclamped and replaced by another dry litho plate, the base 16 remaining in position.

To convert an existing flat bed letterpress printing machine it is envisaged that a conversion kit consisting of the specially prepared base 16 together with the clamping and tensioning means would be provided. This would up date the flat bed letterpress printing machine to enavble the latter to accept dry litho plates with the advantages of film setting.

Claims

1. A flat bed letterpress printing machine having a dry litho plate mounted on a base of the machine.

2. A machine according to claim 1, wherein the base is especially designed and made to support the dry litho plate and replaces a conventional base of the flat bed letterpress printing machine.

3. A machine according to claim 1 or 2, wherein the dry iitho plate is detachably mounted on the base of the machine by releasable clamping means which enable the plate to be clamped into position on the base and subsequently released for replacement by another dry litho plate.

4. A machine according to claim 3, wherein clamping means are provided at each end of the machine to enable both ends of the dry litho plate to be clamped into position.

5. A machine according to claim 4, wherein the clamping means at each end of the machine include manually rotatable clamping screws acting on a clamping plate or strip which extends across the width of the machine and which is capable of clamping the corresponding end of the dry litho plate.

6. A machine according to any of the preceding claims, wherein the base is made from steel which is annealed and then precision ground to be flat on both sides, so that the lower surface of the base makes accurate face-to-face contact with the upper surface of the bed.

7. A machine according to claim 6, wherein the base is formed with a series of perforations to which a vacuum source is applied in order to suck the dry litho plate into intimate surfce contact with the base.

8. A machine according to claim 6, wherein the dry litho plate is tensioned across the base.

9. A machine according to claim 8, wherein tensioning means are provided and operate in such a way that the clamping means at one end of the machine can be urged away from the adjacent end of the base so as to apply tension to the dry litho plate which is thereby drawn into intimate surface contact with the upper surface of the base.

10. A machine according to claim 9, wherein the tensioning means comprise a tensioning plate which extends along one end of the machine and against which the corresponding clamping plate can be tightened, the tensioning plate being capable of being moved with respect to the base so that the clamping plate moves away from the adjacent end of the base to apply the required tension to the dry litho plate.

11. A method of converting a conventional flat bed letterpress machine to operate with a dry litho plate, comprising replacing a base of the conventional machine with a new base and fitting a dry litho plate to the replacement base.

12. A kit of parts for converting a conventional flat bed letterpress printing machine to operate with a dry litho plate, comprising a replacement base for fitting on the machine in place of the existing base, a dry litho plate and clamping means for clamping the plate on the replacement base.

13. A kit of parts according to claim 12, wherein the base is annealed and ground to be flat on both sides, and the clamping means are associated with tensioning means for tensioning the dry litho plate across the base.

14. Aflat bed letterpress printing machine our a method of converting a conventional flat bed letterpress machine, or a kit of parts for converting a conventional fiat bed letterpress printing machine, substantially as herein particularly described with reference to the accompanying drawings.