EP2139683B1 - Doctor blade system for a printing unit, intended for an intaglio printing machine - Google Patents

Abstract

A doctor blade system intended for a print unit includes a doctor blade support provided with a blade, an edge of the blade is able to come into contact with a peripheral surface of an engraved printing cylinder, a supporting hub, on which the doctor blade support is mounted, a structure fixing the supporting hub to a frame of the print unit. Apparatus provides a reciprocating motion of the blade along the peripheral surface of the engraved cylinder roughly parallel to the axis of revolution of the engraved cylinder. Thrust elements drive movement of the blade along the direction of the peripheral surface of the engraved cylinder. The reciprocating apparatus directly drives the doctor blade support. The thrust element or elements move the supporting hub and the doctor blade support and the blade to maintain a constant contact over the entire length of the edge of the blade with the peripheral surface of the engraved cylinder.

Description

The present invention relates to a squeegee system, provided with a squeegee. The invention also relates to a printing unit equipped with a doctor blade system. The invention finally relates to a gravure printing machine, incorporating at least one printing unit.

Photogravure, also called rotogravure, is a rotary printing process that can be used for many substrates, including paper or cardboard, using engraved cylinders. Gravure printing is used especially for high-quality editions and large prints where graphics must play an important role in promoting a product, such as a carton pack. This printing process makes it possible in one pass to print up to ten colors, with solvent, water or other inks; to print matt, glossy or structured varnishes; print on front and / or back and emboss.

Thus, in a gravure printing machine, a medium to be printed in the form of a continuous strip passes through a succession of gravure printing units. The printing units are assembled and arranged one after the other from the input of the print medium upstream to its output downstream. Each printing group proceeds to print a pattern with a single specific color or a particular varnish, or even embossing.

The principle in gravure is to engrave, on the periphery of a printing cylinder, cells that reproduce the pattern that you want to print. The engraved cylinder rotated is coated with ink by an applicator and rotates inside a tank containing the ink, which allows to fill the cells. The printing medium is then strongly applied against the engraved cylinder, so that the ink contained in the cells can be extracted and transferred onto the medium to be printed.

• un chariot imprimeur, présentant lui-même :
  • un cylindre gravé,
  • un applicateur d'encre, qui déverse l'encre sur le cylindre,
  • un bac à encre, qui récupère le trop plein d'encre, et
  • un système de racle, qui élimine le surplus d'encre sur le cylindre au moyen d'une lame de raclage, arasant la surface périphérique du cylindre et ne laissant que l'encre qui a pénétré dans les alvéoles ;
• un rouleau presseur, qui appuie fortement le support à imprimer sur le cylindre ;
• une pompe, qui assure l'acheminement de l'encre du réservoir à l'applicateur d'encre ; et
• un sécheur, qui assure l'évaporation rapide des solvants ou de l'eau, ou bien la polymérisation des encres à UV.

A traditional printing group includes:

• a printer cart, presenting itself:
  • an engraved cylinder,
  • an ink applicator, which pours the ink on the cylinder,
  • an ink tray, which recovers too much ink, and
  • a squeegee system, which eliminates excess ink on the cylinder by means of a scraper blade, leveling the peripheral surface of the cylinder and leaving only the ink which has penetrated into the cells;
• a pressure roller, which strongly presses the support to be printed on the cylinder;
• a pump, which conveys the ink from the reservoir to the ink applicator; and
• a dryer, which ensures the rapid evaporation of solvents or water, or the polymerization of UV inks.

If the quality of the print depends greatly on the quality of the engraved cylinder, the squeegee system provides a constant print quality, ensuring control of the amount of ink contained in the cells. The blade is brought into contact with the surface of the cylinder at a line immediately preceding, following the direction of rotation of the cylinder, the zone in which the cylinder comes to contact the medium to be printed.

The blade is subjected to a movement back and forth on the surface of the cylinder, in the direction parallel to the axis of revolution of the cylinder. The angle formed by the plane of the blade with the surface of the cylinder, also known as the angle of attack, is important to avoid vibrations of the blade or to prevent ink streaks. The contact pressure of the blade on the cylinder must also be adjusted, to allow the contact surface of the edge of the blade against the cylinder, as well as the angle of attack, to remain constant.

The cylinder for gravure printing has dimensions and a very large weight which cause, on the one hand, transport difficulties, and on the other hand, positioning difficulties. During a change of work, the cylinder-tank group is removed by the removable printer carriage, which facilitates its handling and its permutation, as described for example in the document FR-2.539.325 .

Thus, because of the many cylinder changes, it is positioned with deviations from the frame of the printing unit. These differences, constituting a lack of parallelism between the blade and the cylinder, cause a spacing between the long line edge of the blade and the axis of rotation of the cylinder. This phenomenon implies the need to have a catch for the scraper blade.

It happens that the cylinder is possibly etched off-axis, or that the support to be printed is skewed inside the printing unit. To correct such defects, resulting in printing defects, a technique of adjustment by offsetting the engraved cylinder, known under the name of "skewing", is used. This voluntary bias causes a defect of parallelism between the cylinder and the blade, which must be corrected to avoid scraping of poor quality.

State of the art

We know from the document DE 38.41.116 a device for use in gravure printing which comprises a doctor blade holder. Means for balancing the pressure of the blade are provided and incorporate two lateral support rods on each of which is embedded a spring, coming to rest against the doctor blade support, and adjusting elements of the hardness of the springs. The squeegee support, and thus the squeegee, are also provided for pivoting, with respect to a central axis, passing through the squeegee support and perpendicular to the plane formed by the blade. A shaving of the printing surface is achieved with minimal wear of the blade, the squeegee pressure remaining guaranteed at all points along the squeegee.

However, such a device has the disadvantage of having a pivot point, which results in the existence of a stop point for the blade when moving towards the surface to be scraped. The blade will not be able to optimally follow the surface to be scraped.

The document EP-0.765.745 discloses a cleaning device, used in gravure printing, which comprises a doctor blade that can follow the movement of a cleaning roller by means of a cam link mechanism. A carrier is secured with pins passing through elongated holes. A hydraulic cylinder is attached to the carrier, and an actuating portion of the hydraulic cylinder is connected to the doctor support. By actuation of the hydraulic cylinder, the squeegee carrier moves relative to the carrier, with elongated lumens, allowing the doctor blade holder to move forward and backward with respect to the roller independently.

However, with such a device, the connecting mechanism to follow the movement of the cleaning roller is essential to ensure that the blade comes touching the surface to be wiped. Since this linking mechanism is linked together Laterally with respect to the cylinder and the hydraulic cylinder is attached laterally to the carrier, the contact between the doctor blade and the surface will be very localized at a single point. In addition, the elongated lights limit the movements of the doctor blade support.

The document EP-0.422.344 discloses a doctor blade device for use with a platen roller for gravure printing. The scraper device comprises a blade, a scraper holder mounted on journals, which are pivotable relative to corresponding lower parts. The lower parts, the squeegee holder and thus the squeegee move back and forth along the cylinder. The lower parts slide in guides towards the cylinder. Air pistons are mechanically connected and press directly on the doctor blade support, so as to slide the lower parts, the doctor blade holder and thus the blade, against the cylinder.

However, the pistons provide a constant pressure, but only when a portion of the blade comes into contact with the peripheral surface of the cylinder. In addition, the presence of the trunnions for pivoting causes the thrust of the pistons against the squeegee carrier causes rotational movements of rotation. Finally, the back and forth movement also drives each of the pistons.

The document GB-2,085,363 discloses a scraper holder attached to a rotatable carrier member in a printing press. The doctor blade is able to move back and forth parallel to the axis of the impression cylinder. The squeegee support is guided in a slide disposed on the carrier element. The support assembly and carrier element is mounted to a sliding guide bar, the latter being able to pivot.

The document EP-0.072.554 discloses a drive for reciprocating a doctor blade in a printing press. A doctor blade holder is provided with a slide, which allows it to swing relative to a base frame. The doctor blade is held against the impression cylinder by a pivot connection, which includes a piston unit so as to selectively move the blade away from the cylinder.

Presentation of the invention

A main problem to be solved by the invention is to develop a squeegee system for optimal scraping of a peripheral surface of the cylinder. A second problem is to achieve a squeegee system allowing both a back and forth movement of the blade and an optimal scraping efficiency of the blade. cylinder with this same blade. A third problem is that of providing a squeegee system remaining permanently in a printing unit, while ensuring its perfect adaptation to each new cylinder. A fourth problem is to use a squeegee system that is independent of the printer carriage and therefore the cylinder, with several possibilities of adjustment of the squeegee system relative to the cylinder. A fifth problem is to obtain a squeegee system for a printing group, which is both simple and inexpensive to produce. Still another problem is to mount a squeegee system in a gravure printing machine printing unit to provide high print quality.

The invention relates to a doctor blade system according to claim 1.

In other words, with the means of the invention, the blade of the squeegee system will touch and remain constantly in contact with the cylinder, regardless of the angular positioning of the latter relative to the blade. By a free and unhindered movement of the blade towards the cylinder, its straight edge can land on the peripheral surface and remain in abutment along its length, during the complete rotation of the cylinder. If the cylinder has surface defects, wear or mounting inaccuracies, the means present on the squeegee system compensate for the differences, regular or variable, existing or occurring when the cylinder performs a revolution.

The fine adjustments of the pressure exerted by the edge of the blade on the peripheral surface of the cylinder are not ensured by the pushing elements. The goal is to maintain a linear contact of the edge of the blade on the surface rotating cylinder device. Such contact will be obtained with each change of cylinder, when new work is requested.

The back and forth means are used to prevent localized wear too fast blade, detrimental to the quality of printing. The doctor blade system thus combines for the blade an ability to move freely, until it enters and remains in constant contact with the surface of the cylinder, and an ability to go back and forth at that surface. of this cylinder. In addition, the means to ensure a movement back and forth of the blade only move the doctor blade holder and blade, without the thrust elements, which results in a lightening of fast moving parts.

The thrust elements generate thrust forces acting on the hub carrier. These forces can be oriented in the plane defined by the blade. The doctor blade system may comprise two thrust elements, which may advantageously be in the form of two springs. These means of applying the thrust to maintain the contact are elastic. These two springs can be arranged laterally, on both sides of the carrier hub, so as to push each side of the carrier hub, towards the peripheral surface of the engraved cylinder.

Favorably, the system may comprise means for compensating a torque induced by the movement of the back and forth of the blade. The torque is induced by the additional degree of freedom imparted to the hub carrier, squeegee support and blade, associated with the reciprocating movement of the doctor carrier and the blade. The means for compensating the torque may comprise a washer, mounted at one end of an axis of rotation of the carrier hub. This axis of rotation allows the adjustment of an angle between the blade and the peripheral surface of the engraved cylinder and constitutes a point of attachment of the carrier hub with the structure.

The means for reciprocating the blade may include a pulse finger projecting from the doctor support. This finger can come into contact with pulse means for the back and forth, which are motorized and independent of the doctor blade system. The means for reciprocating the blade may comprise a return spring, positioned between the doctor support and the carrier hub, and providing a free return of the blade. squeegee support, after impulse.

According to a second aspect of the present invention, a printing unit is characterized in that it is equipped with a doctor blade system having one or more of the technical features described above.

According to a third aspect of the present invention, a gravure printing machine is characterized in that it comprises at least one printing unit provided with a doctor blade system having one or more of the technical characteristics described above.

Brief description of the drawings

• la Figure 1 représente une vue simplifiée, latérale, en élévation, de deux groupes imprimeurs successifs, faisant partie d'une machine d'impression en héliogravure ;
• la Figure 2 représente une vue simplifiée, latérale, en élévation d'un chariot imprimeur ;
• la Figure 3 représente une vue en perspective du système de racle selon l'invention ; et
• la Figure 4 représente une vue du dessus du système de racle selon l'invention.

The invention will be better understood and its various advantages and different characteristics will become more apparent in the following description, of the nonlimiting exemplary embodiment, with reference to the appended diagrammatic drawings, in which:

• the Figure 1 is a simplified, side elevational view of two successive printing units forming part of a gravure printing machine;
• the Figure 2 represents a simplified, side elevational view of a printer carriage;
• the Figure 3 represents a perspective view of the doctor blade system according to the invention; and
• the Figure 4 represents a view from above of the doctor blade system according to the invention.

Detailed description of the preferred embodiments

As illustrated by Figure 1 , a gravure printing machine (1) is composed of several printer groups (2 and 3) successively mounted one after the other (only two groups being shown here). The support to be printed (4) returns upstream (Arrow S in Figure 1 ) in the first printing unit (2), to be printed with a first color, spring (S) downstream, then enter (S) upstream in the second printing unit (3), to be printed with a second color, and leaves (S) downstream. The print medium (4) can enter and exit in as many printer groups as necessary to make the different color prints.

Each printer unit (2 and 3) comprises a frame (6), a printer carriage (7) inserted in the center of the frame (6), a dryer (8), a pressure roller (9) and a pump (not shown in FIGS. Figures) which provides the ink supply. Due to the routing mechanism of the medium to be printed (4), the first printing unit (2) performs a single-sided printing and the second printing unit (3) performs a back printing of the same medium to be printed (4).

The printing carriage (7) comprises (see Figures 1 and 2 ) an engraved cylinder (11) with rotating cells (12) (P-arrow) with respect to its axis of revolution (O) in an ink tank (13), which recovers the overflow of ink (I), and an ink applicator (14), only shown in Figure 2 , powered by the pump. The cells (12) are represented very greatly enlarged in Figure 2 .

The medium to be printed (4) is strongly pressed ( Figure 2 ) against the engraved cylinder (11) by the pressure roller (9), so as to carry out a transfer of the ink (I) contained in the cells (12) of the engraved cylinder (11) on the surface of this support (4). ). A squeegee system (16), which in this embodiment is not part of the printer carriage (7), has the function of wiping off the excess ink (I) on the engraved cylinder (11), by means of of a blade (17), visible in Figures 2 and 4 (with dots).

The squeegee system (16) is secured to the frame (6) of each printing unit (2 and 3). It should be noted that (see Figure 1 ), in the case of single-sided printing, the squeegee system (16) is provided on the downstream side of the frame (6) of the printing unit (2), and in the case of back printing, the squeegee system (16) ) is provided upstream side of the frame (6) of the printing unit (3).

The squeegee system (16) comprises (see Figures 3 and 4 ) a doctor blade support (18), a carrier hub (19) and a structure (21). The blade (17) is inserted into the doctor holder (18), so that its edge (22) protrudes and comes into contact with the engraved cylinder (11). The carrier hub (19) is made with two lateral cheeks (23) connected by a central piece (24). The structure (21) of the squeegee system (16) is formed by two side plates (26) which are fixed on corresponding uprights of the frame (6).

The squeegee system (16) comprises adjustment means according to the format, that is to say according to the diameter of the engraved cylinder (11). These format adjustment means comprise a crank (27) meshing a series of pinions (28), to advance (Arrow F in Figure 3 ) or back (Arrow R in Figure 3 ) the carrier hub (19) along two rails in the structure (21).

The squeegee system (16) comprises means for adjusting the angle of attack of the blade (17) with respect to the peripheral surface of the engraved cylinder (11), so as to optimize its scraping. These means for adjusting the angle rotate (Arrows A in Figure 3 ) the central piece (24) of the carrier hub (19), upwardly and downwardly relative to the two side flanges (23), with respect to an axis (X).

The squeegee system (16) comprises means for causing the blade (17) to move back and forth (arrows B in Figures 3 and 4 ) on the peripheral surface of the engraved cylinder (11). These means comprise a finger (29) extending laterally from the doctor support (18). The finger (29) is actuated by motorized means (not shown in the Figures) outside the doctor blade system (16). The doctor blade holder (18) is mounted in a slide (not visible) formed in the upper surface of the central piece (24) of the carrier hub (19). The doctor blade support (18) has a lower portion passing through the central piece (24) of the carrier hub (19) and bearing against a return coil spring (31).

The back-and-forth movement (B) is in a direction substantially parallel to the axis of revolution (O) of the engraved cylinder (11). The doctor blade support (18) slides laterally in one direction in the slide, being pushed by the finger (29), then slides laterally in another direction in the slide, being pushed by the coil spring (31).

According to the invention, the squeegee system (16) comprises means for maintaining a constant contact of the entire length of the edge (22) of the blade (17) with the peripheral surface of the engraved cylinder (11). These means are two pushing elements, in the form of two springs (32). These two springs (32) are arranged laterally and act by moving and pushing (Arrows C) each side cheek (23) of the carrier hub (19). With this displacement of the carrier hub (19), the doctor blade holder (18) and the blade (17) move in the direction of the peripheral surface of the engraved cylinder (11).

The two springs (32) placed laterally make it possible to exert a differential thrust on one side and / or on the other side of the carrier hub (19). The edge (22) of the blade (17) thus adapts to the irregularities of the peripheral surface and the mounting defects of the engraved cylinder (11) and remains pressed against the peripheral surface of the engraved cylinder (11).

Each of the springs (32) is a flat spring fixed and respectively bearing on each of the two side plates (26) of the structure (21) of the doctor blade system (16). The carrier hub (19) moves linearly with respect to the structure (21) of the doctor system (16).

The lateral cheeks (23) of the carrier hub (19) and the two side plates (26) of the structure (21) are arranged to allow movement of the carrier hub (19), the doctor blade support (18) and the blade (17) in the same plane as that formed by the blade (17).

When the reciprocating movement (B) of the blade (17) is performed at the same time as a movement to maintain a constant contact along the entire length of the edge (22) of the blade (17) with the peripheral surface of the engraved cylinder (11), an induced parasitic torque is created at the level of the carrier hub (19). To do this, a washer (33) is mounted at one end of an axis of rotation (X) of the carrier hub (19) allowing adjustment (A) of an angle between the blade (17) and the peripheral surface of the engraved cylinder (11).

Claims (7)

1. Doctor blade system, intended for a print unit (2, 3) provided with an engraved cylinder (11), comprising:

   - a doctor blade support (18) provided with a blade (17), an edge (22) of the blade (17) being able to come into contact with a peripheral surface of the engraved cylinder (11),

   - a supporting hub (19), on which the doctor blade support (18) is mounted,

   - a structure (21), fixing the supporting hub (19) to a frame (6) of the print unit (2, 3),

   - means for providing a reciprocating motion (B) of the blade (17) on the peripheral surface of the engraved cylinder (11), along a direction substantially parallel to the axis of revolution (O) of said engraved cylinder (11), and directly driving the doctor blade support (18) provided with the blade (17),

   characterized in that it comprises thrust elements, bearing on the structure (21), generating forces exerted on the supporting hub (19), moving the supporting hub (19) and the doctor blade support (18) provided with the blade (17), and driving a movement of the blade (17) in the direction of said peripheral surface of said engraved cylinder (11), so as to maintain a constant contact over the entire length of the edge (22) of the blade (17) with the peripheral surface of the engraved cylinder (11).
2. System according to claim 1, characterized in that it comprises two thrust elements, in the form of two springs (32), arranged laterally on both sides of the supporting hub (19), so as to thrust each side of said supporting hub (19) in the direction of the peripheral surface of the engraved cylinder (11).
3. System according to claim 1 or 2, characterized in that it comprises means for compensating a torque created by the reciprocating motion (B) of the blade (17).
4. System according to claim 3, characterized in that the means for compensating the torque comprise a washer (33) mounted at one end of an axis of rotation (X) of the supporting hub (19) enabling the adjustment (A) of an angle between the blade (17) and the peripheral surface of the engraved cylinder (11).
5. System according to any one of the preceding claims, characterized in that the means for providing a reciprocating motion (B) of the blade (17) comprise a push arm (29) projecting from the doctor blade support (18), coming into contact with motorized reciprocating means, and a return spring (31) positioned between the doctor blade support (18) and the supporting hub (19).
6. Print unit, characterized in that it is equipped with a doctor blade system (16) according to any one of the preceding claims.
7. Photogravure printing machine, characterized in that it comprise at least one print unit (2, 3) provided with a doctor blade system (16) according to any one of claims 1 to 5.

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