EP0784541A1

EP0784541A1 - Ink printing apparatus with a cleaning assembly

Info

Publication number: EP0784541A1
Application number: EP95934337A
Authority: EP
Inventors: Hans Rudolf Baartmans
Original assignee: PHARMALABEL BV
Current assignee: PHARMALABEL BV
Priority date: 1994-10-03
Filing date: 1995-09-28
Publication date: 1997-07-23
Also published as: CA2200857A1; JPH10509384A; WO1996010487A1; AU3688495A; NL9401623A

Abstract

Ink printing apparatus (1) with a cleaning assembly comprising a wiper element or doctor blade (9) mounted such that it acts against an ink roller (8), with a fluid collection element (10) arranged beneath said doctor blade, in order to collect therein fluid flowing from the doctor blade. According to the invention, it is stated that for this purpose a fluid distribution element (11, 12, 13) is arranged at a position upstream from above the doctor blade as viewed in the direction of rotation of the ink roller in order to apply cleaning fluid, at a position upstream from above the doctor blade, essentially uniformly distributed over said ink roller, which fluid distribution element is connected to a cleaning fluid supply.

Description

Ink printing apparatus with a cleaning assembly

The invention relates to an ink printing apparatus with a cleaning assembly in accordance with the preamble of Claim 1. In order to clean an ink printing apparatus, for example because of a change-over to a different colour ink, it is known to position a cleaning doctor blade against the lowest, smooth ink roller of the assembly of ink rollers, a fluid collector being placed below said doctor blade. Whilst the ink rollers are rotating, cleaning fluid is applied by hand from a spray bottle to the uppermost ink roller of the assembly. Said cleaning fluid finds its way via the various ink rollers so as ultimately to be scraped off at the lowermost ink roller, together with ink residues, by the doctor blade for collection in the collector. There are various disadvantages associated with this known method of cleaning. Application of the cleaning fluid by hand takes a relatively long time and demands a relatively great deal of attention. Frequently the operator is insufficiently capable of applying the cleaning fluid with adequate uniformity. On the one hand, this can result in the ink rollers running dry, causing the doctor blade to display excess wear and become unusable. On the other hand, this can cause too thick a film of fluid to be formed between the ink rollers m contact with one another, as a result of which the freely rotating ink rollers start to slip or even come to a halt. Furthermore, there is a great risk of spillage. As a result of the vulnerability of the doctor blade because of the risk cf running dry, the shape and choice of material for said doctor blade are not optimum. In practice, the result of the disadvantages is that, because of the considerable time pressure, the ink rollers are cleaned inadequately. During re-starting of the printing process it is therefore frequently necessary to clean the ink rollers again. On the one hand, this leads to delays. On the other hand, this leads to loss of material in connection with the printing errors made (clamping deviations). In both cases, there is a question of a financial disadvantage.

Thus, there has long been a desire to π.aκe cleaning of ink printing apparatus simpler and more reliable, by means of a procedure by which cleaning can be carried out more rapidly with less personal attention, without the risk of spillage of cleaning fluid and wear of tne components. To this end, it is proposed according to the invention that the cleaning assembly of the ink printing apparatus be constructed in accordance with the characterising part of Claim 1.

Damage to the doctor blade as a consequence of the ink roller running dry, against which roller said doctor blade acts, is now prevented under all circumstances. Moreover, it is ensured under all circumstances that the cleaning fluid applied is accurately and regularly distributed over the ink rollers (as a thin fluid film). The risk of spillage of cleaning fluid is excluded. The accurate and uniform distribution of the cleaning fluid also prevents ink rollers from starting to slip or even coming to a halt, and as a result of this effective cleaning of all ink rollers is ensured. Finally, personal attention is minimum. Cleaning can now be carried out more rapidly because there is no longer any risk of damage to the doctor blade, whilst it is reliably prevented that any ink roller starts to slip or comes to a halt. A further advantage has proved to be the fact that the ink removed from the ink rollers can be readily diluted with the cleaning fluid, so that the mixture of cleaning fluid and ink can be removed easily from the collector in order, for example, to filter out the ink elsewhere, so that the cleaning fluid is ready for re-use. When cleaning was carried out in accordance with the prior art, a thick, sticky ink mass, with which no-one knew what to do, often formed in the collector. Cleaning of the collector was then also time-consuming.

The invention is based on the insight that when cleaning fluid is applied in the immediate upstream vicinity of the doctor blade, the latter is reliably protected against damage resulting from the ink rollers running dry, whilst the doctor blade, in turn, when arranged in the immediate downstream vicinity of the location at which the cleaning fluid is applied, guarantees uniform and well-controlled distribution of the cleaning fluid over the ink rollers, without special control equipment being necessary for this purpose, by which means a surprisingly simple and nevertheless effective construction can be achieved, "upstream" and "downstream" in respect of this application is with respect to the direction of rotation of the ink roller cooperating with the doctor blade. It will be understood, that fluid will first be applied on the roller, then while the roller rotates further, the fluid is evenly distributed and possible excess of fluid is wiped of by the doctor blade', and then the fluid film, evenly distributed and of accurate thickness will come in contact with the next roller for further distribution through the system of rollers.

As a result of the insight of the invention, it is now possible to choose a cleaning doctor blade made of a harder material, which can have a sharper edge, so that its distributing and wiping effect is even further improved. Occurrence of slipping of rollers is now prevented too.

It is preferable to mount the doctor blade such that it is elastically resilient, as a result of which said doctor blade is automatically able to follow inaccuracies in the shape of the ink roller. Doctor blade is each means cooperating with a roller for even distribution of fluid at a substantially accurate thickness.

It is also preferable to allow the doctor blade to interact with a driven, preferably steel, smooth ink roller. The dynamic interaction between the doctor blade and the ink roller is then ensured under all conditions, as a result of which the optimum constant distribution of the cleaning fluid over the ink roller is maintained irrespective of possible local, temporary, irregular fluid distribution over one or more other ink rollers, for example caused by the temporary accumulation of ink residues. "Smooth" in this respect means with conventional roughness, not meant for printing.

The cleaning assembly can be integrated with the ink printing apparatus. However, the cleaning assembly can also be a separate component which can be coupled to the ink printing apparatus as desired. The use of a wiper blade or doctor blade during the printing process is known per εe from the flexographic printing technique and the intaglio printing technique. The doctor blade system then ensures that the liquid printing ink is scraped off the surface of a printing roller provided with a screen, that is to say a printing roller which has a particularly irregular surface. In this case, printing ink remains behind in the pores of the screen, in order then to be transferred to the sheet to be printed. This known use does not have the objective of reliable and effective cleaning of the ink rollers. It is also addressed to the prevention of slip of the rollers or wear of the doctor blade. The invention is explained in more detail below with the aid of a non-limiting illustrative embodiment with reference to the appended drawings. In the drawings:

Figure 1 shows, diagra matically, a partially exposed side view of part of a printing apparatus of the letterpress type with the cleaning assembly according to the present invention;

Figure 2 shows a perspective view of the set-up of the cleaning assembly with respect to the ink roller for the embodiment in accordance with Figure 1.

Figure 3 shows a side view of Figure 2.

Figure 1 shows part of an ink printing apparatus 1 , of which, for the sake of clarity, only the most important components are shown. The film or paper sheet 2 to be printed is taken from a spool 3 and is fed through various printing stations 4, 5, two of which are shown here. The printing apparatus 1 usually comprises four such printing stations 4, 5, each suitable, for example, for applying a different colour print to the paper sheet 2. Each printing station 4, 5 has an assembly of ink distributing rollers 6 for transferring ink, in a uniform distribution and at constant dosage, from a feed 7 to the printing roller 8 with which the print is to be applied to the paper sheet 2.

In accordance with the present invention, and as is shown in more detail in Figure 2, a doctor blade 9 is arranged at the driven printing roller B, which doctor blade 9 has a collector 10 beneath it and a fluid application arm 11 above it. Said fluid application arm 11 is connected, in a manner which is not shown in more detail, via the stub pipe 12, to a pump for supplying a cleaning fluid under pressure. Said cleaning fluid is sprayed via the openings 13 onto the cylindrical surface of the printing roller 6 ιuεt above the doctor blade 9. During this procedure, metering of the cleaning fluid is preferably so adjusted that a good surplus of cleaning fluid is constantly sprayed onto the printing roller 8. Because the printing roller B is rotating in the direction of the arrow A, the surplus cleaning fluid applied will be removed virtually immediately by the doctor blade 9 so as, by flowing over the top surface of the doctor blade 9, ultimately to be collected in the collector 10 located beneath it. However, a thin film of cleaning fluid also continues to rotate past the doctor blade 9 and is distributed over the other rollers, entrains the mk located thereon and feeds this back to the doctor blade 9. The collector 10 is connected via the discharge stub 14 to a collection container, which is not shown m more detail. Said collection container can, for example, be emptied at regular times in order to purify the cleaning fluid, mixed with ink constituents, for re¬ use. Tne doctor blade 9 will also remove ink constituents from the printing roller 8, together with cleaning fluid. The surface of the printing roller B which has rotated beyond the doctor blade 9 will carry a uniform, th n film of cleaning fluid. Said film will seek a route through the printing station 4, 5 in the opposite direction to the direction in which the printing ink is distributed from the feed 7 over the assembly 6 of ink rollers. In this way, the cleaning fluid will entrain the ink residues present on the various rollers and feed these back to the printing roller 8, for removal therefrom by means of the doctor blade 9. Incidentally, in the embodiment shown, the doctor blade 9 consists of an approximately 1 mm thick strip of polyester, which strip 9a has a sharp cutting edge which interacts with the cylindrical surface of the printing roller 8. To provide the resilient mounting of said strip 9a, a rubber support strip 9b, which has a thickness of about 5 mm, is located behind said strip 9a. The two strips 9a and 9b are clamped at their base between two steel strips (not visible), which are connected by their ends to the doctor blade spacers 15, which are fixed to the collector 10 on either side of the doctor blade 9.

To ensure good operation, that surface of doctor blade 9 which faces towards the application arm 11 makes an acute angle of, preferably, thirty to sixty degrees with the radian of the printing roller 8, with respect to the imaginary contact point between the doctor blade 9 and the printing roller 8. Furthermore, the doctor blade 9 is arranged such that the radian, with respect to the imaginary contact point between the doctor blade 9 and the printing roller 8, deviates by at most twenty degrees and in particular by at most ten degrees from the horizontal. The controlled distribution of the cleaning fluid, as well as the removal of the ink residues, will take place most effectively within said limits for the arrangement of the doctor blade 9 with respect to the printing roller 8.

Although the present invention has been explained in more detail with reference to the so-called letterpress technique, said invention is also applicable to other printing techniques. For example, the invention may also be applied in so-called offset printing presses, with which ink is likewise supplied from above and fed uniformly and in a controlled manner to the printing roller by means of an assembly of ink rollers. In addition, the invention may also be applied in the so-called flexographic printing technique or intaglio printing technique, in which case the ink is supplied from below and transferred via a fairly limited set of ink rollers to the printing roller, which is located at a higher level. However, the greatest advantage will be achieved in the case of printing techniques with which the ink is applied to the printing roller via a large number of ink rollers and optionally via different feed paths, and with which the ink is transferred to the printing roller via five or more ink rollers.

In the embodiment shown in the drawings, there is only one doctor blade both for distribution of fresh cleaning fluid and for removing of used cleaning fluid with ink and other contaminants to be removed from the apparatus. However, separation of functions is possible as well in that a further doctor blade or fluid removing element cooperates with the ink roller for removal of used fluid.

Claims

1. Ink printing apparatus with a cleaning assembly comprising a wiper element or doctor blade mounted such that it cooperates with an ink roller, with a fluid collection element arranged beneath said doctor blade and/or said ink roller, in order to collect therein fluid flowing from the doctor blade, characterised in that a fluid apply element is arranged with respect to the doctor blade such that fluid is first applied on the roller, then evenly distributed on passage of the doctor blade with wiping off possible excess of fluid to have a substantial even layer of fluid with substantial accurate thickness on said roller and then the applied fluid comes into contact with the next roller of the system of rollers of said apparatus at rotation of the rollers, essentially uniformly distributed over said ink roller, which fluid distribution element is connected to a cleaning fluid supply.

2. Ink printing apparatus with a cleaning assembly according to Claim 1, wherein said ink roller is driven.

3. Ink printing apparatus with a cleaning assembly according to Claim 1 or 2, wherein said doctor blade is made of a hard plastic, for example PVC or polyester, and the side facing towards the ink roller has a sharp edge.

4. Ink printing apparatus with a cleaning assembly according to one of the preceding claims, wherein the doctor blade is mounted such that it is elastically resilient.

5. Ink printing apparatus with a cleaning assembly according to one of the preceding claims, wherein the fluid application element is a channel which runs essentially parallel to the doctor blade and has, on that side thereof which faces towards the ink roller, regularly spaced spray nozzles facing towards said ink roller.

6. Ink printing apparatus with a cleaning assembly according to one of the preceding claims, wherein the doctor blade interacts with the printing roller, that is to say the ink roller which comes into contact with the article to be printed.

7. Ink printing apparatus with a cleaning assembly according to one of the preceding claims, wherein the ink printing apparatus operates in accordance with the letterpress or offset principle.

8. Cleaning assembly, evidently suitable for use with an ink printing apparatus witn a cleaning assembly according to one of the preceding claims, comprising a doctor blade with a fluid collection element fixed beneath it and a fluid distribution element fixed above it.