FR2656831A1 - Printing unit for flexography machine - Google Patents

Abstract

The printing unit according to the invention comprises at least one block holder roll (1) intended to receive, on its cylindrical surface, a block (2), a press roll (3) arranged so as to apply a printing support (medium) (4) on the block (2) and a distributor roll (5) coming into contact with the block (2). The block holder roll (1) and the press roll (3) are rotationally mounted about two respective axles which can be moved in a plane P2, P'2 passing through these two axles. The invention makes it possible to make adjustments, taking into account both the thickness of the block and that of the printing support.

Description

 PRINTING GROUP FOR FLEXOGRAPHIC MACHINE.

The present invention relates to a printing unit for a flexographic machine.

In general, it is known that the printing units used in flexography usually involve at least three rollers oriented parallel to each other, namely - a plate roller for receiving, on its surface
this cylindrical, a cliché generally made of photopolymer,
on which the pattern to be printed is engraved in relief - a pressure roller around which passes the support
printing roll (such as a strip of paper)
being arranged so as to apply tangentially the
print media on the plate; and - a distributor roller, usually of the "anilox" type,
(trademark registered by KOENIG & BAUER AKTIENGESEL
LSCHAFT) whose cylindrical surface has a structu
re alveolar forming a frame, this "anilox" roller
coming in tangential contact with the stereotype.

Of course, these flexographic printing units further comprise an inking system (with or without doctor blade) of the distributor cylinder, this system can for example comprise a rubber inking roller dipping in an inkwell and coming to bear on its upper part, on the distributor roller.

Thanks to this set of provisions, the "anilox" roller inked in a homogeneous manner by the ink roller, distributes the ink uniformly on the raised parts of the plate which can then carry out the printing of the support.

 It is important to note that, in principle, tangential contact with the printing medium / plate must be made without pressure so as to avoid any crushing of the plate which would inevitably cause deterioration in the quality of the printing.

 It turns out that in the current state of the art, printing units are usually used in which the pressure roller and the "anilox" roller are rotatably mounted around two parallel fixed axes, while the plate holder is rotatably mounted around a movable axis which can move, in translation, remaining parallel to itself and to the axes of the other two rollers, in a median plane perpendicular to the plane passing through the lines of tangency of the pressure and "anilox" rollers with the plate roller. This mobility of the plate roller makes it possible, in particular, to take account of the thickness of the plates and to ensure the necessary adjustments as a function of this thickness.

However, it can be seen that this structure does not allow adjustments to be made which take account of the thickness of the printing medium as well as variations in mechanical alignment, and this, without generating constraints for overwriting the plate.

 This is a particularly important drawback which penalizes flexography in terms of its flexibility of use and, consequently, of its diffusion.

The invention therefore more specifically aims to eliminate these drawbacks.

It proposes, for this purpose, a printing unit in which only the distributor roller is rotatably mounted around a fixed axis, while the plate roller and the pressure roller are rotatably mounted around two respective axes movable in a plane passing through these two axes.

 It appears clearly that, thanks to this arrangement, it becomes possible to carry out adjustments taking into account both the thickness of the plate and that of the print medium.

Taking into account that the displacements of each movable roller are ensured by means of two lateral adjustment devices acting respectively at the end of the shaft of the rollers, it also becomes possible to compensate for variations in mechanical alignment of the whole of the 'apparatus.

Of course, a flexography apparatus can involve several printing groups, in particular to allow printing in color, each printing group then being assigned to a fundamental color.

The invention will appear more clearly on reading the description below, which refers to the accompanying drawings in which
Figure 1 is a schematic cross section
illustrating the principle of a printing unit
flexographic of known type; and
Figure 2 is a schematic cross section
of a printing unit according to the invention.

In the example shown in Figure 1, the printing unit conventionally comprises four rollers rotatably mounted around parallel axes, namely - a plate roller 1 on which a plate is mounted
2, for example in photopolymer - a pressure roller 3 around which the support passes
impression 4, which comes tangentially to the contact
from picture 2 - an "anilox" roller 5 coming into tangential contact with the
plate 2; and - an ink roller 6 partially immersed in ink
7 contained in an inkwell 8 and coming tangentially in
contact with the anilox roller "5.

According to this known embodiment, only the screened roller 1 is movable and can be moved in translation by means of a mechanical assembly involving, on each side of the rollers - a lateral bearing 9 in which a barrel engages
lon 10 of the roller 1 - a slide 12 centered (axis X, X ') perpendicular to the
plane P1, P'1 passing through the straight lines materializing the
contact between the pressure roller 3, the "anilox" roller 5
and the plate roller 1; and - a threaded rod 13 integral with the bearings 9 and on which
there is mounted a knurled nut 14 axially retained in the
two directions, so that it can cause displacement
from bearing 9 in slide 12.

 I1 clearly appears that only an adjustment intended to adapt the printing unit to the thickness of the plate 2 can be validly executed by acting on the knurled nut 14. On the other hand, an adaptation of the printing unit to the thickness of the printing medium 4 cannot be carried out without causing compression of the plate 2, compression which is incompatible with the principle of flexography.

In addition, given the fact that the pressure roller 3 is fixed, it is hardly possible to make an adjustment aimed at mechanically realigning the elements of the printing units.

These drawbacks do not exist in the printing unit according to the invention in which, as shown in Figure 2, the plate roller 1 and the pressure roller 3 are both movable in the same plane P2, P'2 passing through their axes and can each be moved in translation by means of two respective mechanical assemblies of the type of that previously described with reference to FIG. 1 and each involving two lateral bearings 9 ′, 9 ″ movable in two slides 12 ′, 12 ″ and being able to be moved along these thanks to two threaded screws 13 ', 13 "carrying two knurled nuts 14', 14" axially retained in both directions.

 Thanks to this arrangement, the adjustment of the printing unit, as a function of the thickness of the printing medium 4, is obtained by adjusting the position of the pressure roller 3 by means of the knurled nut 14 ".

 The adjustment of this group, depending on the thickness of the plate, is then obtained by adjusting, firstly, the position of the plate roller 1 by means of the knurled nut 14 'then, secondly , by adjusting the position of the pressure roller 3 by means of the knurled nut 14 ". It is clear that the two types of adjustment previously mentioned can be carried out by ensuring tangential contact between the" anilox "roller 5 and the pressure roller 3 with Plate 2, without doing the compression of this plate.

This result makes it possible both to ensure greater flexibility in the use of the machines and a better quality of the result obtained because the application of the plate 2 on the printing medium 4 is carried out in an optimal manner.

Claims (3)

Resell icat ions  1. Printing unit for flexographic machine of the type comprising at least - a plate-carrying roller (1) intended to receive on its  cylindrical surface a plate (2) - a pressure roller (3) arranged so as to apply  tangentially a print medium (4) on the plate  (2); and - a distributor roller (5) whose cylindrical surface  has a honeycomb structure forming a frame, this  distributor roller (5) coming into tangential contact with  the plate (2), characterized in that only the distributor roller (5) is rotatably mounted around a fixed axis, while the plate roller (1) and the pressure roller (3) are rotatably mounted around two respective axes, movable in a plane P2, P'2 passing through these two axes.  2. Printing unit according to claim 1, characterized in that the above dispensing roller (5) is an "anilox" roller.  3. Printing unit according to one of claims 1 and 2, characterized in that the movements of each movable roller (1, 3) are ensured by means of two lateral adjustment devices (12 ', 13', 14 ' - 12 ", 13", 14 ") acting respectively at the end of the shaft of the rollers (1, 3).