GB2190364A - An assembly for preventing the detachment of a substrate from a revolving cylinder - Google Patents

Abstract

A substrate is prevented from detaching from a revolving cylinder (4) (e.g. of a printing press) by maintaining or intermittently providing a zone of pressurised gas over the path of the substrate around the cylinder, forcing the substrate against the cylinder and preventing its detachment. As shown, pressurised air is pumped into a canopy (16) around an arcuate perforated plate (12) and escapes through perforations (14) which direct it against the surface of the cylinder. <IMAGE>

Description

GB2190364A 1 SPECIFICATION tachment of the substrata from the surface of

the cylinder.

An assembly for preventing the detachment Preferably the assembly includes a LIV lamp of a substrate from a revolving cylinder mounted above an aperture in the plate for 70 drying the substrate as it passes under the The present invention relates to an assembly plate. The UV lamp may be backed by a for preventing the detachment of a substrate reflector for focusing the lamp. A quartz win from a revolving cylinder. dow may be mounted across the aperture to At the present time there is a steady inprevent cold air from being blown onto the crease in the use of ultra-violet radiation for 75 lamp, and to help retain the air pressure built drying coatings such as inks and varnish up between the plate and the cylinder.

which have been printed on substrates by In another aspect, the present invention pro way of e.g. a printing press. A typical printing vides a printing press comprising a plurality of press comprises a series of colour units each colour units for printing a variety of colours on of which in turn comprises a blanket cylinder 80 a substrate, at least one of said colour units for applying the coating to the substrate including a cylindrical printing cylinder having mounted in contact with an impression cylin- adjacent its surface the assembly described der. During printing, the substrata is fed from above.

one colour unit to the next as it passes In the drawings:

through the press. 85 Figure 1 is a schematic sectional view of Typically, ultra-violet drying is provided at part of a printing press according to one as- each stage of the printing process by mount- pect of the present invention.

ing between each of the colour units, or occa- Figure 2 is a close-up schematic sectional sionally after the last unit, a UV lamp and view of the drying assembly shown in Figure reflector assembly adjacent the face of the im- 90 1.

pression cylinder to dry the coating on the Figure 3 is a close-up schematic sectional substrate as it is transported away from the view of a lamp and reflector assembly for use nip between the cylinders. Unfortunately, al- in the present invention.

though such assemblies prove effective in dry- The present invention will now be more par- ing the coating, their presence introduces 95 ticularly described with reference to the ac fresh problems. For example, they can cause companying drawings. Turning firstly to Figure the cylinder at which they are directed to 1, this shows part of a printing press gener overheat leading to an increase in the risk of ally indicated at 1 which apart from the inclu press damage, substrate distortion and even sion of the invention is of conventional design, fire. Also they may cause smudging or smear- 100 so that only those parts needed for an under ing of the wet coating when tail-end flick-up standing of the invention will be described.

occurs, which is the tail-end of the substrate The press comprises a series of colour units flicking-up as it leaves the nip between a pair 2 each of which in turn comprises a blanket of cylinders e.g. in this case the blanket and cylinder 3 for applying the coating to the sub impression cylinders. When this occurs, the 105 strate mounted in contact with an impression tail-end of the substrate drags along the bot- cylinder 4. The coating is generally one which tom surface of the UV lamp and reflector as- may be dried by means of a UV lamp such as sembly causing the undried coating to a UV ink or a specially formulated varnish.

smudge. Transfer cylinders 5 are provided between To overcome the problem of the cylinder 110 each of the units 2. A sheet of substrate e.g.

overheating, one proposal has been to extract paper is fed from one colour unit to the next the air from between the UV lamp and cylin- and hence through the printing press by the der. Unfortunately this increases the problem relative rotation of the cylinders i.e. from cyl of tail-end flick-up because the substrate is inder B to cylinder C to cylinder D etc.

drawn away from the surface of the impres- 115 An assembly for drying the substrate as it sion cylinder by the partial vacuum produced. passes from cylinder B to cylinder C is indi In one aspect, the present invention aims to cated generally at 10 in Figure 1 and is more overcome these problems by providing an as- particularly shown in Figures 2 and 3.

sembly which both prevents tail-end flick-up, As will be appreciated from Figure 1, ac- and cools the cylinder as it passes under the 120 cess to the part of cylinder indicated at Z UV lamp. which carries the substrate bearing the coating In accordance with one aspect of the pre- is limited, and therefore the drying assembly sent invention, there is provided an assembly needs to be of compact design particularly for preventing the detachment of a substrate where it faces the cylinder. The assembly 10 from a revolving cylinder comprising a part 125 consists of a part cylindrical plate 12 having cylindrical perforated plate, a canopy formed perforations formed through its surface which over said plate, and means for delivering air are in the form of a plurality of orifices 14.

into the space between the canopy and the An air-tight canopy 16 is formed over the plate, whereby the air is forced through the plate and has air pumped into it by means of perforations toward the cylinder preventing de-130 a compressed air source 18 e.g. a compres- 2 GB2190364A 2 sor. The air from the orifices also helps to cool The assembly 10 is mounted above cylinder the surface of the revolving cylinder preventing 4 in a manner which permits it to be radially it from overheating. This function is further adjusted with respect to the cylinder. This al- aided if the air is pre- cooied or refrigerated lows different thicknesses of substrate to be 70 prior to it being delivered from the orifices. If passed between the plate 12 and the cylinder required, additional cooling means such as a without the substrate coming into contact refrigerated plate 6 (see Fig. 1) may be pro with the plate and smudging the undried coat- vided around the cylinder 4 to help to cool it.

ing. It should be noted that even in printing An elongate UV lamp 22 is located within 75 presses without provision for ultra-violet dry- the canopy, and is backed by an elongate alu- ing, these still tend to have tail-end flick prob minium reflector 24 which focuses the radia- lems, so that the plate and canopy assembly tion from the lamp towards the surface of of the present invention would still be of use cylinder 4 through an elongate aperture 26 in connection with these.

formed in the plate 12. Each of these compo- 80 Turning now to Figure 3, this shows an en nents extends parallel to the axis of the cylin- larged cross-sectional view of the UV lamp der. The assembly 10 extends along the and its backing reflector mounted adjacent the whole length of cylinder 4 so that the as- nip 8 between the drums 3 and 4. Thus an sembly is able to dry substrates having a elongate ultra-violet lamp 22 has behind it a width of up to the length of the cylinder. 85 reflector 24 which is conveniently made from A quartz window may be mounted across aluminium. The reflector causes the radiation the aperture 26. This both prevents the air from the UV lamp to be focused towards the which is released from orifices 14 from cool- surface of the cylinder 4 through the aperture ing the UV lamp and also air escaping from 26 in the plate 12. For the reasons described between the plate and the cylinder. 90 above, a quartz window may be mounted When the press is in use, the substrate 20 across the aperture.

emerges from the nip between cylinders 3 The arrows A in this figure indicate the flow and 4 in contact with roller 4. The substrate of air within the canopy and through the ori then passes under the UV lamp 22 and the fices 14 in the plate. The air is introduced at coating which has been deposited on its sur- 95 one end of the elongate canopy by means of face by the blanket cylinder 3 is dried by the a manifold and that remaining in the canopy at action of the UV lamp. the other end is extracted by any suitable As the tail-end of the substrate emerges means.

from the nip, it is prevented from detaching Because of the heat generated by the UV from the surface of the cylinder by the force 100 lamp, the aluminium reflector requires cooling.

of the air from the orifices 14. This prevents This may conveniently be done by circulating tail-end flick-up, which in previous printing water by means of inlet and outlet pipes 32 presses has caused smudging of the wet through hollows 30 formed within the reflec coating by the substrate coming into contact tor.

with the surface of the lamp and reflector as- 105 As is well known, UV lamps produce sembly. ozone. This has to be extracted and safely In one embodiment of the invention, air is disposed of from the assembly of the present continuously supplied from air source 18 so invention due to its toxicity. This is done by that the substrate is forced towards the cylinproviding an additional vent 34 formed inte der at all times and in particular as soon as it 110 grally with the canopy which is open to the emerges from the nip. However, in some atmosphere at one end of the canopy and has cases this may lead to excessive turbulence at a negative pressure applied to its other end the nip resulting in the leading edge of the resulting in the ozone being extracted from substrate being stripped away from the cylin- the canopy and into the vent, through slot 32 der 4 and then over the canopy. Such an 115 as indicated by arrows 0. When the ozone event would quickly lead to machine break- reaches the end of the vent having negative down. To prevent this from happening, a sen- pressure it is then circulated to disposal sor is provided to detect the location of the means.

substrate as it passes through the press, and It will be appreciated from the foregoing as the leading edge of the substrate emerges 120 that in broad terms the invention provides from the nip the sensor switches the air means for maintaining or intermittently provid source 18 in to reverse to extract air from ing a zone of pressurised gas over a region of between the cylinder and the plate through a revolving cylinder (for example of a printing the canopy. This results in a partial vacuum press) adjacent to the downstream side of the being provided between the plate and the cyl125 nip between two cylinders to maintain a sub inder thus overcoming the problem of turbu- strate against said region of the cylinder as it lence. When the leading edge has passed leaves the nip to prevent tail- end flick-up. Pre safely under the plate, the air source is ferably the means for maintaining the pressur switched back to deliver air to the canopy to ised gas zone has incorporated with it a dry push the substrate against the cylinder. 130 ing lamp, such that the gas flow serves also 3 GB2190364A 3 to remove heat from the cylinder delivered there by the lamp.

Claims (10)

1. An assembly for preventing the detachment of a substrate from a revolving cylinder comprising means for maintaining or intermittently providing a zone of pressurised gas over at least a part of the path of the sub- strate on the cylinder.

2. An assembly according to claim 1 wherein the means comprises an elongate plate having an axis parallel to that of the cylinder, the plate being positioned around the surface of the cylinder and spaced therefrom and having perforations formed through its thickness for directing the gas towards the cylinder.

3. An assembly according to claim 2 wherein the plate is of substantially arcuate cross section.

4. An assembly according to claim 2 or claim 3 wherein the means further comprises a canopy formed over the plate to define a substantially enclosed space therebetween and means for supplying pressurised gas to said space.

5. An assembly according to claim 4 wherein said gas supply means is a compres- sor.

6. An assembly according to claim 5 wherein the gas is pre-cooled or refrigerated by the compressor prior to its supply to the space.

7. An assembly according to claim 5 or claim 6 wherein the gas is supplied continuously by the compressor to said space, said gas being air.

8. An assembly according to any preceding claim further comprising an elongate U-V lamp mounted above an elongate slit in the plate for drying the substrate as it passes under the plate.

9. An assembly according to claim 8 further comprising a quartz window mounted across the slit.

10. A printing press comprising a plurality of colour units, at least one of said units having a blanket cylinder and an impression cylin- der including a nip therebetween, and an assembly according to any preceding claim mounted adjacent to the surface of the impression cylinder downstream of the nip for preventing the detachment of a substrate as it emerges from the nip.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.