EP0854036A1 - Device for inking an engraved roll - Google Patents

Abstract

The inker consists of a pressure roller (7) which is positioned inside a sealed chamber and is formed between two scrapers (2,3) to apply the ink in layers inside the chamber. The pressure roller has a shaft (8) turning in a bearing (9) which slides in a recess (10) and is loaded by a spring (11). The pressure roller is rubber-covered and the sealed chamber forms an inlet (5) for the ink, which is fed under pressure between the cylinder and the pressure roller, with the surplus removed through a return channel (6).

Description

Flexographic printing processes are increasingly using screened cylinders called "anilox" to ensure good ink distribution.

The advantage of this system, compared to the old systems using the rolling of two smooth cylinders to dose the quantity of ink by pressure, lies in a much better regularity of the ink film distributed and this regardless of the printing speed.

This is mainly due to the constant volume formed by the alveoli of the cylinder.

A first improvement to this grid cylinder distribution system has was obtained by adding a doctor blade which removes excess ink from a rigorously whatever the speed and this much better than a cylinder ordinary wringer.

1 - de supprimer les débordements d'encre et par conséquent fait que la machine flexo est devenue propre,

2 - d'améliorer la pénétration de l'encre dans les alvéoles grâce à la pression de l'encre à l'intérieur de la chambre.

A second improvement was obtained by installing a second doctor blade in order to constitute a sealed supply chamber, with a circulation of ink under pressure, which has the effect:

1 - to remove ink overflows and therefore the flexo machine has become clean,

2 - to improve the penetration of the ink into the cells thanks to the pressure of the ink inside the chamber.

The known devices however have a defect which consists of the impression of a ghost image.

The invention is part of the observation that the above phenomenon is explained as follows :

The screened cylinder abandons the ink contained in the cells on the parts snapshot printers, creating a negative image of the printed image.

The cells which have been emptied of their ink fill with air which penetrates thus in the sealed chamber.

This air must therefore be expelled by the pressure of the ink circulating in the chamber and discharged with excess ink through the return port.

Unfortunately we realize that the faster the cylinder turns, the less the ink pressure has time to evacuate the air contained in the alveoli, which are therefore not fully inked.

The ratio between the screened system and the plate cylinder is generally different from 1/1, it results in an irregular impression showing a return of the previously printed image. This phenomenon is well known under the Anglo-Saxon term of "ghosting" that is to say ghost.

The object of the invention is, therefore, to ensure better and more rapid evacuation of air.

According to the invention, the device for inking a screened cylinder is characterized in that to ensure regular inking, there is a roller presser inside the sealed chamber formed between the doctor blades to laminating the ink inside said sealed chamber.

Various other characteristics of the invention also emerge from the detailed description which follows.

An embodiment is shown in detail by way of nonlimiting example. to the accompanying drawings.

Fig. 1 shows a schematic sectional view of a sealed chamber for inking a convex screened cylinder.

Fig. 2 is a schematic section similar to FIG. 1 but showing the ink rolling device of the invention.

In the drawing, 1 designates a screened cylinder called "anilox", 2 represents a doctor blade for remove excess ink, 3 designates an inlet doctor blade to ensure sealing, 4 the body of the sealed chamber into which opens an inlet orifice 5 pressurized ink and 6 a return port for ink also provided in the body 4.

The roller 7 is lined with rubber and has an axis 8 which rotates in a bearing 9 sliding in a housing 10. The cylinder 7 is pressed on the cylinder screened by a spring 11.

The ink arriving under pressure in the sealed chamber is introduced between the two cylinders 1 and 7 where it is laminated into a thin film, thanks to the pressure exerted by the spring 11.

The laminated film becomes thinner the lower the viscosity of the ink. It the result is that air, whose viscosity is about 1000 times lower than that of ink, is almost completely rejected.

Excess ink and rejected air are then evacuated through return port 6.

The alveoli cleared of the air they contained are finally scraped by the outlet scraper 2.

The invention is not limited to the embodiment shown and described in detail because various modifications can be made without leaving its frame.

Claims (4)

Device for inking a screened cylinder, characterized in that for ensure regular inking, there is a pressure roller (7) inside of the sealed chamber formed between the doctor blades (2, 3) to laminate the ink to the interior of said sealed chamber. Device according to claim 1, characterized in that the roller presser has an axis (8) which pivots in a bearing (9) sliding in a housing (10) and is pressed by a spring (11). Device according to claim 1 and 2, characterized in that the roller presser (7) is lined with rubber. Device according to claim 1, characterized in that the chamber sealed (4) delimits an inlet orifice (5) for ink under pressure pipe between the cylinder (1) and the pressure roller (7).

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