EP1177101B1 - Inking device for a flexographic printing machine anilox roll - Google Patents

Abstract

The invention concerns an inking device, called doctor blade chamber, for a flexographic printing machine anilox roll (2). Said doctor blade chamber, which comprises a closed box (4, 6) borne mobile (10) by a frame (8) for being sealingly pressed against anilox roll (2), box (4, 6) defining a main chamber equipped with a couple of positive (16) and negative (18) blades. The invention is characterized in that the main chamber, equipped with means (32, 34) for being the seat of ink circulations at atomsphere pressure, is divided into two superposed chambers (20, 22) communication with each other through channels (24) circulating ink by simple gravity, from an upper supply chamber (20) to a lower delivery chamber (22), the two chambers (20, 22) being separated from each other by retaining blade (26) which provides an ink reserve (28) between two chambers (20, 22) and upstream of the negative blade (18).

Description

The invention is in the field of printing machines flexographic, and it relates to a device, called doctor blade chamber, for inking a anilox.

Printing units for printing machines flexographic include a roller, called anilox, for inking a supported plate by another roller, said plate holder. The printing of the plate is carried out by an ink transfer from the anilox on the plate holder.

A problem to be solved lies in the inking of anilox. Commonly, the anilox has an alveolar outer surface for the ink take.

We know a first mode of inking the anilox, relatively old, consisting of bubbling it through an ink bath. At least one intermediate roller is interposed between the anilox and the plate holder, to obtain a proper distribution of ink over the entire surface of the plate. A major drawback of this mode of inking lies in its complexity and in the ink splashes which result from bubbling and which require protection of the space surrounding the anilox by a fairing.

To remedy this drawback, it has been proposed devices, known as doctor blade chambers, for inking aniloxes. These devices include a waterproof case permanently filled with ink and disposed laterally with the anilox of so as to wrap a portion of its surface of revolution. Ink circulation at the interior of the case maintains its homogeneity. According to various variants, the ink is evacuated from the housing, either by directly exploiting the rotary movement of the anilox, either by adding various means of reflux. The seal between the housing and the anilox is obtained, on the one hand at the ends of the anilox by a pair of flanges fitted with members sealing, and on the other hand along the anilox by a couple of doctor blades arranged respectively upstream (positive doctor blade) and downstream (negative doctor blade) of the inking area of the anilox, the negative doctor blade being moreover intended to smooth the ink on the surface of anilox.

A first drawback of this type of device is in a random inking of the external surface of the anilox and an irregular distribution ink on it, due to the prevailing pressure in the housing which does not favor a suitable filling of the alveoli.

A second drawback stems from the circulation of the pressurized ink inside the case, which imposes significant constraints on the seal between the housing and the anilox, in particular at the ends of the latter, and a frequent replacement of the sealing members, necessitating a detrimental stop of the machine operation.

The object of the invention is to propose a device, kind known as doctor blade chamber, for inking an anilox of a printing machine flexographic, which guarantees a uniform inking of the anilox and whose structure makes its quick and easy maintenance.

The inventive step consisted, starting from the observation above and contrary to the habits adopted in the field, to offer a room to doctor blades inside which the ink flows naturally by gravity, from a chamber in which the ink is brought to an evacuation chamber out of which the ink flows. A doctor blade, called a retaining blade, is interposed between the two said chambers and overhanging the evacuation chamber, to obstruct the natural circulation of the ink and provide an ink reservoir, which is preferably driven naturally from the reservoir to upstream of the negative doctor blade under the effect of rotation of the anilox. Ink circulation channels allow ink to escape out of the reservoir to the evacuation chamber to maintain the natural circulation of the ink between the two chambers, notwithstanding the presence of the retaining doctor blade.

These provisions are such that, in the first place, the ink circulation inside the doctor blade chamber is not forced and takes place at the atmospheric pressure, and secondly that the ink bead formed upstream of the negative doctor blade does not induce untimely thrust thereon as in the devices of the prior art in which the ink circulates under pressure inside the housing. It results in a uniform inking, and a regular and constant smoothing of the anilox, and finally a suitable distribution of the ink over its entire periphery.

Note that the choice of a doctor blade as an organ obstacle to the natural flow of ink inside the housing is preferred due to the fact that the said doctor blade is not only capable of sparing ink retention, but also and so-called distributor, is capable of providing a distribution of suitable ink on the anilox, and an equivalent organ which would only provide the sole function of obstacle to the flow natural ink could be substituted for it without derogating from the general rule of the invention, but in this case, a member for distributing the ink on the anilox should be associated.

In other words, it will be understood that the doctor blade retainer is not only intended to provide an ink retainer upstream of the doctor blade negative, but also, also called distributor, to distribute and smooth the ink on the anilox.

Pursuing their inventive approach, the Applicants offer to close the end faces of the doctor chamber housing by means of flanges, particularly of nylon, held in simple contact against the end faces of the anilox, the said flanges forming not only the end walls of the case, but also constituting by themselves sealing members between the housing and the anilox; we note that the seal thus obtained is sufficient thanks to the circulation by simple gravity of the ink inside the case.

Finally and according to an advantageous embodiment, the negative doctor blade is secured to the housing by means of a removable support, so provide easy access to the inside of the doctor blade chamber for cleaning in particular, and in order to allow a quick and easy replacement of the negative doctor blade, by replacement of the support by another previously fitted with a doctor blade, without having to interrupt the operation of the machine for a long time and without having to modify the position of the doctor blade chamber relative to the anilox, and therefore to empty the latter.

la fig. 1 est une vue schématique en coupe transversale d'un dispositif d'encrage selon une forme préférée de réalisation de l'invention,

la fig.2 est une vue schématique de dessus en coupe de l'intérieur d'une chambre à racles d'un dispositif d'encrage illustré sur la figure précédente.

The present invention will be better understood, and details will be apparent from the description which will be made of a preferred embodiment, in relation to the figures in the appended plate, in which:

fig. 1 is a schematic cross-sectional view of an inking device according to a preferred embodiment of the invention,

Fig.2 is a schematic top view in section of the interior of a doctor blade chamber of an inking device illustrated in the previous figure.

In the figures, an inking device, called a chamber doctor blades, of a rotary drum 2, called anilox, of a flexographic printing machine, includes a closed case 4.6 with longitudinal extension. This box is supported by a chassis 8 by means of mobility means 10 for its application against the anilox 2 so as to tightly wrap a portion of its surface of revolution, called inking area. The box 4,6 delimits an interior space, called main bedroom, intended to be the seat of an ink circulation and is equipped for this purpose with a supply conduit 12 and a conduit 14 for discharging the ink. The case 4,6 is further equipped with a couple of longitudinal squeegees 16 and 18, respectively said positive for that 16 intended to be located upstream of the inking zone, and negative for that 18 intended to be placed in downstream of the inking area.

The master bedroom, equipped with 32.34 means for to be the seat of a circulation of ink at atmospheric pressure, is divided in two superimposed chambers 20 and 22 communicating with one another by circulation channels 24 ink by simple gravity, from the upper chamber 20, called supply towards the lower chamber 22, called the evacuation chamber, the two said chambers 20 and 22 being separated from each other by a doctor blade 26, called a retaining blade, to provide an ink retention in the upper chamber 20 and upstream of the negative doctor blade 18. These provisions are such that the ink can circulate by simple gravity inside the casing 4,6 and that the ink retention 28 is provided for the inking of anilox 2.

According to the preferred embodiment illustrated on the Figures, the so-called ink circulation channels 24 are formed by a passage formed beyond of the ends of the retaining doctor 26, between the latter 26 and the walls end 6 of the housing.

Preferably, and thanks to the circulation of the ink at the atmospheric pressure, the end walls of the housing 4,6 are formed by flanges 6 intended to be applied in sliding contact against the corresponding end faces of the anilox 2, the so-called flanges 6 constituting in themselves sealing members between the box 4,6 and the anilox 2.

According to a preferred embodiment, the doctor blade negative 18 is attached to the housing 4.6 by means of a removable support 30, such that the negative doctor blade 18 can be removed from the housing 4,6 by removing the support 30, without requiring an overall displacement of the doctor blade chamber by setting mobility means 10.

Preferably, the retaining doctor 26 forms with the tangent of the anilox 2 taken at the point of contact between the retaining blade 26 and the anilox 2, a closed angle between 5 ° and 15 ° opening towards the negative doctor blade 18.

It will be understood that in the usual way, one at least any of the positive 16, negative 18 and retaining 26 doctor blades is provided with means for adjusting the contact pressure which they are intended to exert on the anilox 2 (not shown in the figures).

According to a preferred embodiment, the mobility means 10 of the housing include a member 11 exerting on the housing an elastic thrust towards the anilox, the housing bearing under the effect of said elastic thrust, against the chassis by means of adjustable stops 13, the housing of which is team.

However, it should be noted in this connection that thanks to the circulation of the ink inside the casing 4,6 by natural flow under pressure atmospheric and unlike the doctor blade chambers of the prior art, the positive doctor blade 16 may not be in contact with the anilox 2 without allowing an escape plenty of ink out of the case 4.6 in this area.

In the example shown in fig. 1, the pressure prevailing inside the case 4,6 is obtained by supplying the ink, by means of a pump 32, from a reserve 34 to the interior of the chamber supply 20 through the supply conduit 12. The ink flows to the retaining squeegee 26, and then forms the ink retainer 28. The anilox is inked and the ink flows through the passages 24 to the discharge chamber 22, then flows through the discharge pipe 14 to reserve 34. It will be understood that this example supply of the doctor blade chamber of the invention is not limiting, and that other solutions can be envisaged without derogating from the general rule of the invention set out above.

According to recent methods of execution, the chamber doctor blade consists of a profiled aluminum body, material side seals plastic and adjustable doctor blade supports. It benefits from the advantage of a plastic material which creates a "wedge" of ink allowing good force-feeding of the alveoli the anilox before the surpluses are recovered by the negative doctor blade. This surplus is evacuated, by passages at the ends of the distributor and a digging of the chamber at same level, towards the second chamber which is sealed by the positive doctor blade. Finally, a recovery chute allows the ink to be brought back to the pump.

The distributor is flush with the anilox to allow the ink to come "to hit" by a hydrodynamic phenomenon the anilox. The lower doctor blade is now moved back 5/10 ° mm compared to the anilox. Indeed, this doctor blade is not used for ensure a good distribution of the ink in the cells, and the sealing of the chamber remains maintained since the ink does not descend on this area of the doctor blade. The withdrawal of this doctor blade reduces wear on the anilox, which is only scraped once, and allows also to use only one doctor blade. In addition, there is no more fouling of the doctor blade by ink that is not transferred to the plate. Indeed, the surface tension of the ink by compared to the ceramic coating, we get a "domed" on the top of the cell. The cells, which do not transfer ink on the plate, were therefore scraped unnecessarily by the lower doctor blade.

Ink arrives at the distributor contrary to the rotation of the anilox. Thus, it really "knocks" the alveoli; what allows a complete renewal of the ink. It is the speed of rotation of the anilox which creates suppression in the alveoli.

The ink that does not remain in the cells is entrained towards the top of doctor blade 18, and a vortex (arrows 31) is thus formed which is evacuated on the sides through the passages 24. Obtaining this vortex allows a good distribution of the ink over the entire width of the anilox, and a perfect renewal of the ink in the alveoli. This vortex is a helix whose pitch decreases when the viscosity of the ink increases and also when the speed decreases.

Thanks to all the old and news the doctor blade chamber works at atmospheric pressure, which avoids constraints on the anilox and thus to preserve it from premature wear, with perfect ink distribution even at high peripheral running speeds (higher at 300 meters / minute), even with fatty inks.

Claims (7)

1. Inking device for a rotary drum (2), known as an anilox roller, of a flexographic printing machine, of the type of device known as a scraper chamber, comprising a closed case (4,6) with longitudinal extension which is supported by a frame (8) by mobility means (10), for application of the device against the anilox roller (2) such as to envelope in a sealed manner a portion of the surface of revolution of the latter, known as the inking area, the said case (4,6) delimiting an inner space, known as the main chamber, which is designed to be the seat of circulation of ink and being equipped for this purpose with a duct (12) for intake and a duct (14) for discharge of the ink, as well as with a pair of longitudinal scrapers, known respectively as positive (16) for the one which is designed to be situated upstream from the inking area, and negative (18) for the one which is designed to be placed downstream from the inking area, characterised in that the main chamber, which is equipped with means (32,34) for being the seat of circulation of ink at atmospheric pressure, is divided into two superimposed chambers (20,22) which communicate with one another by channels (24) for circulation of the ink by simple gravity, from the upper chamber (20), known as the supply chamber, to the lower chamber (22), known as the discharge chamber, the said two chambers (20,22) being separated from one another by a scraper (26), known as a reserve scraper, in order to provide a reserve of ink (28) in the upper chamber (20) and upstream from the negative scraper (18), such that the ink can circulate by simple gravity inside the case (4,6) and the ink reserve (28) is provided for the purpose of inking the anilox roller.
2. Device according to claim 1, characterised in that the said circulation channels (24) are formed by a passage provided beyond the ends of the reserve scraper (26), between the latter (26) and the end walls (6) of the case.
3. Device according to either of the preceding claims, characterised in that the end walls of the case (4,6) are formed by flanges (6) which are designed to be applied in sliding contact against the corresponding end surfaces of the anilox roller (2), the said flanges (6) constituting in themselves sealing units between the case (4,6) and the anilox roller (2).
4. Device according to any one of the preceding claims, characterised in that the negative scraper (18) is attached to the case (4,6) by means of a detachable support (30), such that the negative scraper (18) can be extracted from the case (4,6) by removal of the support without requiring global displacement of the scraper chamber.
5. Device according to any one of the preceding claims, characterised in that the reserve scraper (26) forms together with the tangent of the anilox roller (2) taken at the point of contact between the reserve scraper (26) and the anilox roller (2), a closed angle of between 5° and 15° which opens towards the negative scraper (18).
6. Device according to any one of the preceding claims, characterised in that at least any one of the positive (16), negative (18) and reserve (26) scrapers is provided with means for regulation of the contact pressure which the scrapers are designed to exert on the anilox roller (2).
7. Device according to any one of the preceding claims, characterised in that the means (10) for mobility of the case (4,6) comprise a unit (11) which exerts on the case resilient thrust towards the anilox roller (2), the case (4,6) being supported under the effect of the said resilient thrust against the frame (8), by means of adjustable stops (13) with which the case (4,6) is provided.

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