GB2054464A

GB2054464A - Printing press

Info

Publication number: GB2054464A
Application number: GB8023039A
Authority: GB
Original assignee: Wartsila Oy AB
Current assignee: Wartsila Oy AB
Priority date: 1979-07-05
Filing date: 1980-07-15
Publication date: 1981-02-18
Also published as: DE3025291A1; FR2461590A1; FI61147B; FI61147C; FI792121A

Abstract

An intaglio or rotogravure press comprises a form cylinder 1, and an impression roller 2 together providing a printing nip, through which a web 3 is led for picking up ink or other treatment medium from the form cylinder. The treatment medium is supplied to an elongate, rigid trough 3 having a length at least substantially corresponding to the length of the form cylinder 1 and a width smaller than the diameter of the form cylinder. The trough 3 is located diametrically opposite the impression roller 2. The trough 3 and the cylinder 1 form together a substantially closed space and there are means for producing an overpressure in the trough, thereby counteracting deflection of the form cylinder by the impression roller. The trough is provided with means for providing a flow of the treatment medium therethrough. <IMAGE>

Description

SPECIFICATION Printing press This invention relates to an intaglio or rotogravure printing press of the kind comprising a form cylin der, means for supplying a printing ink, a coating substance or the like treatment medium to the form cylinder, and an impression roller which, together with the form cylinder, forms a printing nip through which, in use of the press, a web is led for picking up said treatment medium from the form cylinder, said supplying means comprising an elongate, rigid, treatment medium-receiving trough of a length at least substantially corresponding to the length of the form cylinder and of a width smaller than the diameter of the form cylinder, said trough and said impression roller being located at the opposite sides of the form cylinder, and said trough forming, together with said form cylinder, a substantially closed space.

One problem in rotogravure printing presses is the spreading of ink on the form cylinder as evenly as possible to obtain a printing image of the best possible quality. For this purpose it is known to use separate ink transfer rollers. This, however, leads to a complicated construction and increases the manufacturing costs. It is also possible to arrange an ink holder in connection with the form cylinder so that the cylinder is partly submerged therein. In this case, however, splashes of ink and an uneven printing image cause trouble, in particular if the speed of the running web is increased.

A good printing image also requires a rather high line pressure between the form cylinder and the impression roller. As a consequence there may be too great a deflection of the form cylinder, which is harmful forthe printing quality. In order to prevent this, separate supporting rollers have been used, which results in a rather complicated construction.

The present invention aims to provide an improved inaglio or rotogravure printing press, in which the abovementioned defects are eliminated.

The invention also aims to provide a construction which is relatively uncomplicated, but which can be used art a much higher speed of the web than in conventional presses of the kind referred to.

According to the invention, an intaglio or rotogravure printing press of the kind referred to is characterised in that it comprises means for producing an overpressure in said trough, said pressure loading the form cylinder in a region opposite the impression roller and extending substantially throughout the total length of the form cylinder, thus counteracting deflection of said form cylinder by the impression roller, and in that said trough is provided with means for providing a flow of said treatment medium therethrough.

As well as preventing downward deflection of the form cylinder, the relatively high pressure in the treatment medium trough prevents air from being drawn into the trough by the rotating form cylinder.

As a consequence, there will be no air in the engraved regions of the form cylinder, which improves the printing quality. The invention makes it possible to perform rotogravure printing at speeds of up to 1000 m/min, whereas the conventional speeds are from 300 to 500 m/min.

At high speeds, dust or other undesired material, may be carried by the web into the printing nip and led therefrom by the form cylinder into the trough.

The dust will stay in the treatment medium in the form of undissolved particles, which may be harmful for the printing image. By providing the trough with means for providing flow of the treatment medium therethrough, these particles are effectively removed from the trough.

It is recommended to use a pressurep in the trough fulfilling the condition: 0.5 rv2 3 p 0.05 rv2, preferably 0.2 rv2 > p 0.15 rv2, in which risthe density of the treatment medium used, for instance, the printing ink density, and v is the speed of the web, p, v and r being SI-units (or units based on a logic similar to the SI-system).

When the speed ofthe web being printed or treated in any other way is about 1,000 m/min, the pressure in the trough may be up to about 1.4 bar (gauge). If a pressure lower than the lowest limit given in the formula is used, this may be harmful for the printing quality due to air penetrating into the form cylinder engravings, unless the speed of the web is lowered considerably.

In order to obtain an even pressure in the trough, the flow in the trough should be taken into consideration when its form is determined. If the supply aperture is at one end of the trough, the trough should be given a varying cross-section diminishing from the supply end towards the opposite end. An outlet duct can be provided atthe narrow end ofthe trough, so that a trough flow can be maintained in order to keep the treatment medium well stirred and as homogeneous as possible. The outlet duct may be provided with a throttle valve for controlling the through flow rate.

Naturally, the supply aperture could equally as well be at the central portion of the trough. The trough should then have its largest cross-section at the middle narrowing towards both ends. In this case, both ends should be provided with outlet ducts. An equivalent solution is the simultaneous supply of treatment medium from both ends of the trough and having an outlet duct in the middle portion of the trough. However, harmful turbulence is easily generated in the trough, and the best mode in most cases is to supply treatment medium at one end of the trough only.

The overpressure in the trough may be obtained by pumping or otherwise supplying the treatment medium into the trough at a suitable pressure. In order to maintain the overpressure at a desired value, and for properly controlling the amount of treatment medium being transferred to the form cylinder, the distance between the trough and the form cylinder should preferably be adjustable. Further, lips made of soft material with a low coefficient of friction, preferably of polytetrafluoroethylene, may be arranged between the form cylinder and the trough, following the longitudinal trough sides which are parallel to the form cylinder. An effective pressure seal is obtained by making the lips next tio the form cylinder very narrow, preferably sharpedged.The trough can be constructed to have a generally U-shaped cross-section, which is geometrically a suitable design with a low levei of flow turbulence. It also gives a rigid, practically deflection-free trough.

Apart from being employed as a printing press, the press according to the invention may be used to coat a web, for example with a copying layer.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a schematic perspective view of part of a printing press according to the invention, and Figure 2 is a sectional view taken on the line ll-ll of Figure 1.

In the drawings, the numeral 1 designates an intaglio or rotogravure form cylinder, above which an impression roller 2 is located. A web 3 to be printed is led through a printing nip formed between the cylinder 1 and the roller 2. Below the form cylinder 1 there is located an ink trough 4 into which printing ink, coating material or any other treatment medium is supplied at superatmospheric pressure at the wider end 5 thereof. At the opposite end of the trough an outlet duct 6, provided with a throttle valve 7, allows a flow of the treatment medium through the trough.

In principle, the impression roller 2 and the ink trough 4 do not necessarily have to be in a vertical plane. They should preferably be disposed in diametrically opposed regions of the form cylinder, but their common plane may be inclined to the vertical, theoretically even horizontal. However, ink splashes or leaks from the trough may cause difficulties the more said plane is inclined to the vertical.

There are soft lips 8 between the trough 4 and the form cylinder 1. The clearance between the lips 8 and the form cylinder, should preferably be about 0.1 to 0.2 mm. In this manner an adequate sealing is ensured between the trough and the form cylinder preventing treatment medium from splashing out of the ink trough into the surroundings. The exact position of the lips 8 relative to the trough 4 and the form cylinder 1 may be adjusted.

A rotogravure printing press also comprises a separate doctor blade unit which, since it is not significant for the invention, is not shown in the drawings.

Claims

1. An intaglio or rotogravure printing press comprising a form cylinder, means for supplying a printing ink, a coating substance orthe like treatment medium to the form cylinder, and an impression roller which, together with the form cylinder, forms a printing nip through which, in use of the press, a web is led for picking up said treatment medium from the form cylinder, said supplying means comprising an elongate, rigid, treatment medium-receiving trough of a length at least substantially corresponding to the length of the form cylinder and of a width smaller than the diameter of the form cylinder, said trough and said impression roller being located at the opposite sides of the form cylinder, and said trough forming, together with said form cylinder, a substantially closed space, characterised in that the press comprises means for producing an overpressure in said trough, said pressure loading the form cylinder in a region opposite the impression roller and extending substantially throughout the total length of the form cylinder, thus counteracting deflection of said form cylinder by the impression roller, and in that said trough is provided with means for providing a flow of said treatment medium therethrough.

2. A printing press according to claim 1, in which said pressure producing means maintains a pressurep in the trough defined by: 0.5 rv2 3 p 3 0.05 in which r is the density of said treatment medium, and v is the speed of said web.

3. A printing press according to claim 2, in which the pressure p is defined by: 0.2rv23p 30.15rev2.

4. A printing press according to any of the preceding claims, in which there is a supply aperture for the treatment medium at one end of said trough, and an outlet duct at that end of said trough which is opposite said one end.

5. A printing press according to claim 4, in which said trough has a varying cross-section decreasing from the treatment medium supply end of the trough towards its opposite end.

6. A printing press according to claim 4 or 5, in which said duct is provided with a throttle valve for adjusting the flow rate of the treatment medium through said trough.

7. A printing press according to any of the preceding claims, in which the distance between the trough and the form cylinder is adjustable.

8. A printing press according to any of the preceding claims, in which said trough is provided with lips located between the form cylinder and the trough, said lips following the longitudinal trough sides, which are parallel to the longitudinal axis of the form cylinder, and being made of a soft material having a low coefficient of friction, the portions of said lips disposed next to said form cylinder being very narrow.

9. A printing press according to claim 8, in which said lips are made of polytetrafluoroethylene.

10. A printing press according to claim 8 or 9, in which the portions of said lips disposed next to said form cylinder have a sharp edge.

11. A printing press according to any of the preceding claims, in which said trough is of Ushaped cross-section.

12. A printing press according to any of the preceding claims, in which said trough is disposed below the form cylinder.

13. An intaglio or rotogravure press constructed and arranged substantially as herein described with reference to, and as illustrated in, the accompanying drawings.