GB2274430A

GB2274430A - Air-cooled U.V.dryers in printing machine

Info

Publication number: GB2274430A
Application number: GB9300300A
Authority: GB
Inventors: Malcolm Charles Rae
Original assignee: Gew EC Ltd
Current assignee: Gew EC Ltd
Priority date: 1993-01-08
Filing date: 1993-01-08
Publication date: 1994-07-27
Anticipated expiration: 2013-01-08
Also published as: GB2274430B; GB9300300D0

Abstract

A multi-colour printing machine is disclosed in which U.V. cured inks are applied sequentially to a web at a plurality of ink application stations as the web travels around an impression cylinder (21), wherein at each station a U.V. dryer (31, 31 etc) is positioned to irradiate the web with U.V. light, the U.V. dryers each comprising a lamp within a housing and having shutters arranged to control the duration of irradiation of the web. The web may carry spaced labels for printing, and each dryer is cooled by air circulation. <IMAGE>

Description

AIR-COOLED U.V DRYERS This invention relates to air-cooled ,V. dryers.

In our copending Patent Application No. 92 1986.3, there is described a U.V. dryer which is wholly air-coolec and includes a tubular heat barrier disposed between the lamp and the path of the coated or printed sheets or webs to be dried.

Although dryers of the kind described in our copending patent application are advantageous, there are some instances in which dryers of this type are too bulky to be totally effective.

A particular problem arises in drying printed webs in multi-colour lithographic and flexographic offset printing processes in which heat-activated inks or coatings are applied sequentially to a web as it travels around a single impression cylinder. In such cases, the dryer needs to be very thin in order to fit between successive ink application stations. At the same time, the dryer must be capable of being rapidly brought up to full power, but must not irradiate the impression cylinder when the web is not running through the machine because the impression cylinder often has a plastics surface which is damaged by excessive U.V. irradiation.

Another requirement is that the U.V. lamps are adequately cooled and conventional cooling systems have been unsatisfactory in that dirt and other contaminants have been drawn into the dryer housing, coating the lamp and leading to reduction in performance after about 50-80 hours running time. As a consequence, effective lamp life is short. The present invention seeks to overcome these problems by providing a U.V. dryer fitted with a shutter which is capable of rapidly opening and shutting so as to irradiate the web only when required and including a cooling system in which air is caused to flow over the back of the lamp reflector and generally axially thereof, the lamp itself being cooled by a separately directed stream of air.

In a preferred arrangement, an axial air flow is generated over the back of the reflector (which is generally finned to increase heat transfer) by application of suction to one end of the lamp housing. Air guide paths are also provided between the shutter blades and the housing so that a secondary flow of air cools the shutters. Because of the relative size of such air guide paths and of the axial opening into the housing, the primary air flow in the housing is axially of the reflector and constitutes the major proportion of the cooling air, e.g. 80 to 90%, which is sucked into the housing. The balance is sucked into the housing through gaps between the shutter blades and housing and through small holes in the face of the housing which direct air over the ceramic ends of the lamp.

The reflector is set back from the longitudinal opening facing the web to provide space for the shutters and is sealed in the sense, that there is no path for air to flow through the reflector surface. Consequently, there is no current of cooling air carrying contaminants passing over the lamp and the effective lamp life is significantly extended. Preferably, a separate supply of cooling air, e.g. from a compressed air source, is provided to cool the lamp itself.

The shutters may be constructed as described in our above copending patent application. By using the shutter mechanism to control the duration of the irradiation of the web instead of continually switching the lamps on and off, the impression cylinder is protected and the operating life of the lamp is further extended.

Other features of the air cooled dryer in accordance with the invention will become clear from the following description and accompanying drawings in which: Figure 1 is a longitudinal section through a dryer; Figure 2 is an end elevation, partly in section of the dryer shown in Figure 1, and Figure 3 is a schematic view of a commercial multicolour label printing press fitted with U.V. dryers in accordance with this invention.

Referring to the drawings, the dryer comprises a housing 1 having a U.V. lamp 2 mounted thereon. A slot like opening 3 in the base of the housing can be closed by a pair of shutter blades 4, operated by a mechanism 5 which is driven by an electric motor 6. The shutter mechanism is constructed as described in our above copending application, see particularly Figures 3A, 3B and 3C.

A reflector 7 of generally parabolic shape partially surrounds the lamp and is formed with extended cooling fins 9 on its back surface.

At one end of the housing an outlet duct 10 is connected to means for sucking air through the housing.

Air is drawn into the housing mainly through an air inlet 11 at the opposite end of the housing. This inlet is protected with baffles 12 to allow air to pass freely but to prevent escape of any reflected light. Although not shown in the drawing, the inlet is preferably protected with a filter in order to limit dirt or other contaminants being carried into the housing. A minor amount of air is also drawn into the housing transversely over the shutter blades which exerts a cooling effect on the blades. This is shown by arrows in Figure 2.Although not very clearly seen in the drawing because of the small scale, there is a narrow passage between the shutter blades and the housing and between the outer surface of the reflector and the housing, so that some air can flow under the influence of the suction applied to outlet duct (10), and into the plenum chamber (15). The reflector surface (7) is sealed in the sense that there is no passage for air from the opening (33 through the reflector and into the plenum chamber. However, there is no tendency for air from atmosphere to be drawn over the lamp envelope. Small orifices (14) in the housing may be provided to permit a stream of air to flow over the ceramic ends of the lamp.

Direct cooling is applied to the lamp by feeding air from a compressed air source through a fitting (13) and into tubular passages such as (16) in the reflector body, from which orifices bathe the lamp envelope with air. The compressed air feed is clean or filtered air and the construction of the cooling passages in the reflector body may be similar to that described in our above copending patent application, see particularly Figure 1 of that application.

Typical dimensions of the dryer housing are as follows. The housing width may be about 40 mms, and the lamp aperture in the base about 270 mms long. The overall length of the housing may be about 575 mms and its overall height about 210 mms. The air outlet duct may be about 75 mms in diameter.

The U.V. dryers manufactured in accordance with the invention are particularly useful in drying inks at intermediate stages in a multi-stage lithographic or flexographic printing process. For such use, the lamp is conveniently controlled so that it is switched to a standby power of say 0.5 KW from a fully operational power output of say 2.5 KW. Control means are arranged so that the lamp is switched to stand by power in synchronism with the closing of the shutter blades. Timing of the shutter operation is typically about 0.1 second from closed to fully open condition.

Figure 3 shows a typical commercial multi-stage printing press. The particular press shown is a Ko-Pack Type 250-9 colour label printing press. An example of another press to which dryers in accordance with the invention can be fitted is a Sanjo Printmaster 6 colour press.

Referring to Figure 3, the unprinted web is drawn from a reel (20) and passes through various preliminary stages including a stage for delaminating the backing sheet and printing on the adhesive side. The web (22) bearing the labels is fed to a single impression cylinder (21). As can be seen, the web passes almost totally around the cylinder and is then led away for final drying with a conventional dryer (23) and reeling downstream from (24). The machine illustrated is a 6-colour machine in which individual colours are printed sequentially at stations (25, 26, 27, 28, 29 & 30). Immediately after stations (25, 26, 28 and 29) a 'thin' U.V. dryer (30, 31, 32 & 33) is fitted so as to irradiate the web immediately after the preceding printing step. Conventional dryers can be used after printing stations (27 & 30) because there is more space on this particular machine in these locations. The position of the thin U.V. dryers (30 etc.) is shown diagrammatically. They are, in fact, located with the opening (3) close to the surface of the impression cylinder. Because of the compact nature of the dryers in accordance with the invention, there is reasonable space for replacing the cylinders at the printing stations Although the U,V. dryers of this invention are particularly useful in the above-mentioned type of lithographic apparatus, other possible uses are those where U.V. irradiation is required for short periods, especially where there is a shortage of space.

Claims

1. A multi-colour printing machine in which U.V.

cured inks are applied sequentially to a web at a plurality of ink application stations as the web travels around an impression cylinder, wherein at each station a U.V. dryer is positioned to irradiate the web with U.V.

light, the U.V. dryers each comprising a lamp within a housing and having shutters arranged to control the duration of irradiation of the web.

2. A printing machine as claimed in claim 1 wherein a U.V. dryer is located immediately after each ink application station spaced around a single impression cylinder.

3. A printing machine as claimed in claim I or 2 in which the shutters are controlled to open immediately after the application of ink at an adjacent station and to close after the ink carrying area of the web passes the dryer.

4. A printing machine as claimed in any one of the preceding claims in which the web is arranged to support labels to be printed at said stations.

5. A printing machine as claimed in any one of the preceding claims in which the UK dryers include a cooling system in which air is caused to flow generally axially of a reflector for the lamp and over the back of the reflector.

6. A printing machine according to claim 5 wherein the lamp housing and reflector are cooled by application of suction to one end of the lamp housing.

7. A printing machine according to claim 6, wherein a minor part of the cooling air is sucked into the housing through gaps between the shutter blades and housing and through holes in the face of the housing which direct air over the ceramic ends of the lamp.