EP3569416A1 - Squeegee for screen printing - Google Patents

Abstract

The invention relates to a screen printing machine with a cylindrical screen and a squeegee arranged in the cylinder. According to the invention, the squeegee is divided into several individual short squeegees or single squeegees, the individual short squeegees each covering only one area to be printed of a certain squeegee or printing width and whose distance from the inside of the cylinder mold is individually adjustable transversely to the direction of rotation of the cylinder mold. This means that the distance between each individual short squeegee from the cylinder mold can be set differently depending on the respective arrangement in the cylinder mold, so that the same doctor blade pressure can be built up in the middle of the cylinder mold as at the outer ends, without the areas at the outer ends of the To load the cylinder mold with too high a squeegee pressure.

Description

The invention relates to a screen printing machine with a cylindrical round screen and a squeegee arranged in the round screen.

Out DE 10 2006 012 735 A1 There is known a screen printing machine with a rotary screen printing cylinder and a corresponding method for printing a substrate in the rotary screen printing method and a squeegee for use in the rotary screen printing cylinder and in the method. In this case, the doctor blade is arranged in the rotary screen printing cylinder so that it sweeps over the inner peripheral surface of the cylindrical hollow body substantially only in the areas of the printing screen areas. In this case, the squeegee preferably comprises a plurality of squeegee blades, which are arranged at a distance from each other in such a way that they substantially only cover the printing screen areas. However, an adjustability of the individual doctor blade areas is not provided.

For a good print quality, however, the correct setting of the squeegee pressure is essential in screen printing, ie the mechanical pressure with which the squeegee presses against the inside of the round screen. In known from the prior art Rundsiebmaschinen the squeegee pressure is set only with two screws on the left and right of the press. This has the consequence that the squeegee pressure on the outer sides of the round screen is rather high, because there are also the frames of the sieve guide, in the middle of the round screen, however, the squeegee pressure remains rather low because screen tension and squeegee pressure drop there. However, if more squeegee pressure is needed in the middle of the round screen for a neat expression, the squeegee must be forwarded from the outside, so that the squeegee pressure continues to increase even at the edge of the round screen and thus unnecessarily burdened the round screen. This Effect is among other things a reason for premature wear or defect of the round screen.

The invention is therefore the object of developing a generic screen printing machine such that the disadvantages of the prior art are eliminated and the squeegee pressure can be adjusted to the round screen over the entire width of the round screen.

This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, the doctor blade is subdivided into a plurality of individual short doctor blades or single doctor blades, the individual short doctor blades each covering only one area of specific doctor blade or printing width to be printed, and the distance thereof from the inside of the round screen being individually adjustable transversely to the direction of rotation of the round screen. Thus, the distance of each individual short doctor from the round screen can be set differently depending on the particular arrangement in the round screen, so that in particular in the middle of the round screen, the same squeegee pressure as at the outer ends can be constructed without the areas at the outer ends of the Strainers with excessive squeegee pressure to burden. The adjustability of individual doctor blades according to the invention particularly preferably enables an improvement in the service life or service life of a round screen due to a more uniform mechanical load of the round screen.

The squeegee or printing width is preferably up to 5 cm, wherein the squeegee width or printing width can also have different or different sizes depending on the printing area, for example even more than 5 cm, and wherein the distribution of the squeegee in also different or different Quantities of single squeegees are possible. The squeegee can thus be divided into single squeegee, each individual squeegee is of different widths and adapted to the particular conditions in the sieve.

According to a preferred embodiment it is provided that the adjustment of the position of the respective individual short doctor blade takes place from outside the screen or from the outside and can thus take place during operation of the screen printing machine. Thus, particularly preferably, the squeegee pressure can be varied as a function of the printing image produced during the printing process and adapted accordingly. For adjustment, the basic adjustment is first made via the left and right feed of the entire doctor blade until the outer tracks produce a good print image, and then the squeegee pressure of the further inward tracks is optimized by means of individual delivery. In some screen printing machines, the ratios between the middle and outer tracks are exactly the opposite, which in this case also reverses the procedure.

The adjustment of the individual short doctor blade or single doctor blade can be carried out manually by means of gears deflected by toothed wheels, which are guided for adjustment on the left and right to the sieve opening, or via flexible shafts led outwards by each single doctor blade.

The adjustment can also be made via a wedge system, in which the distance of an obliquely or conically shaped at its rear edge single blade is adjusted to the round screen by means of a sliding wedge. In this case, preferably, each single doctor receives its own wedge. Particularly preferably, the displacement of the respective wedge by means of piezoelectric or pneumatic actuators or by means of a spindle or threaded rod, which is driven mechanically or by electric motor or rotated.

In order to minimize the loss of color in the sieve and during cleaning, a single doctor blade according to another preferred embodiment is closed as far as possible around the single doctor blade so that hardly any ink can leave the system, except via screen contact with the printed product. The single doctor blade is here preferably closed at its outer edges with strips of felt or elastomer, these strips form a kind of counter-shape to the round screen, and closed at the top by a lid made of felt or elastomer. A complete separation of the single blade by glued in the sieve elastomer or foam rubber rings is possible. This procedure is similar to a chambered doctor blade system and is therefore also referred to as a quasi-chamber doctor blade, in which, however, the squeegee lifts off easily at the passages of the printing cylinder twice per revolution. In a doctor blade according to the invention in the horizontal or slightly above, however, the unwanted leakage of ink in the channel region can be largely avoided because the color of gravity tends to flow backwards by a slight inclination of the blade down or not much color to the outside occurs. Out WO 2004/096545 A2 It is known that a plane parallel to the cylinder axis web is arranged at the, before the squeegee conveyed color facing side surface of the doctor blade, wherein the squeegee, touched by her section of the round screen and the squeegee outgoing web one against the direction of rotation of the Screen printing cylinder open channel sole form, and that at least in the two longitudinal end portions of the web guide means for deflecting by the doctor of the round screen stripped color in the longitudinal direction of the doctor towards the center are arranged.

Additionally or alternatively, the squeegee may be provided with a shutter which prevents the discharge of paint when the squeegee is lifted off the wire. This shutter, preferably a thin metal or plastic leaflets, closes only during the short lifting of the doctor blade, the residual gap of the quasi-chamber doctor blade, preferably by being moved from above the blade edge. This movement can be carried out either mechanically via a pressure curve (similar to the control of a gripper) or electromechanically by means of a motor or lifting magnet and a release synchronously with the corresponding circumferential position of the cylinder.

According to a preferred embodiment, it is provided that in addition the angle of each individual short doctor blade, ie the angle of attack of the doctor to the round screen, and / or the height of each short doctor blade, ie a displacement parallel to the inside of the round screen but transverse to the longitudinal axis (which also changed the angle of the squeegee blade to the round screen), is adjustable. As a result, the print quality, screen life and color guide is further improved. In the screen printing, the angle of attack of the squeegee is usually 45 ° to 135 °, preferably 90 ° ± 15 °, the angle of attack being known to determine the edge sharpness and to influence the ink application. A squeegee angle of 90 ° means that the squeegee is aligned perpendicular to the screen surface. The adjustment of the height of each short doctor blade is preferably carried out by ± 10 mm.

In the above example "quasi chamber doctor blade" can be avoided by the appropriate adjustment of the angle of attack of the doctor (as preferred above between 45 ° and 135 °) that too much color flows into the sieve or when lifting the doctor on the gripper channels of the squeegee is running. The remaining, emerging into the sieve small amount of ink can be returned by appropriate, attached to the doctor, obliquely employed Gummischieber lips in the printing area and thus in the squeegee.

The single doctor blade according to the invention are preferably mounted on a doctor blade holder in such a way that they can be laterally displaced and adjusted prior to installation of the overall doctor blade in the printing press, so that the respective desired printing position is made transverse to the printing direction.

The device according to the invention and the method for adjusting the squeegee pressure can in principle also be used for other printing methods which have a squeegee, and of course is also suitable for any printing applications outside the banknote printing. Possible further areas of application include, for example, the NotaProtector® coating machine from KBA NotaSys, flexographic printing units with chambered doctor blade and inking units for offset printing or indirect high-pressure printing.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations, without departing from the scope of the present invention, insofar as this is covered by the scope of the claims.

Reference to the following embodiments and the additional figures, the advantages of the invention will be explained. The embodiments represent preferred embodiments, to which, however, the invention should not be limited in any way. Furthermore, the representations in the figures of better understanding are highly schematized and do not reflect the realities. In particular, the proportions shown in the figures do not correspond to the conditions present in reality and serve exclusively to improve the clarity. Furthermore, the embodiments described in the following exemplary embodiments are reduced to the essential core information for the sake of clarity. In the practical implementation much more complex designs can be used.

Fig. 1

in Seitenansicht einen Ausschnitt einer Rundsieb-Druckmaschine mit einer Rakel,

Fig. 2

in schräger Draufsicht eine Rundsieb-Druckmaschine, bei der eine Rakel in sechs in Richtung der Drehachse des Rundsiebs verschiebbare Einzelrakel aufgeteilt ist,

Fig. 3

den Ausschnitt aus Fig. 1 mit einer Rakel, deren Rakelwinkel und Rakelhöhe justierbar ist,

Fig. 4

in Draufsicht von oben eine Zustellung eines Einzelrakels zur Innenseite des Rundsiebs über ein Keilsystem.

In detail, show schematically:

Fig. 1

in side view a section of a rotary screen printing machine with a squeegee,

Fig. 2

in an oblique top view, a rotary screen printing press, in which a doctor blade is divided into six displaceable in the direction of the axis of rotation of the round screen single doctor blade,

Fig. 3

the cutout Fig. 1 with a squeegee whose squeegee angle and squeegee height are adjustable,

Fig. 4

in plan view from above a delivery of a single blade to the inside of the round screen via a wedge system.

Fig. 1 shows a schematic section of a rotary screen printing machine, which consists of a round screen 1 and a squeegee 2 made of a resilient plastic material or elastomer, wherein the squeegee 2 is clamped between a base 3 and a cover plate 4, which consist for example of aluminum. Above the squeegee 2 is formed upon rotation of the round screen 1 in the direction of arrow by accumulation of color a Farbwulst. 5

The doctor blade 2 can also be designed as a system squeegee, which consists of two components. The one component consists of a hard-elastic carrier, for example glass-fiber-reinforced plastic profile, which ensures a constant doctor blade angle and squeegee pressure as well as constant flexibility. The carrier is with a soft elastic strip or a Elastomer profile, for example made of polyurethane with a Shore hardness of 55 ° to 85 ° permanently connected as a pressure edge, which is in contact with the sieve. Such system doctor blades are produced, for example, by RK Siebdrucktechnik GmbH (RKS®). For example, the RKS system squeegee type 32 HQ has a GRP plastic profile with a height of 50 mm to 115 mm and a thickness of 2.5 mm and an elastomer profile with a thickness of 6 mm to 8 mm and a Shore hardness of 55 °, 65 ° or 75 °. The length of this RKS squeegee can be up to 2600 mm.

Fig. 2 shows a rotary screen printing machine in which a doctor blade is divided into six single doctor blade 2.1 to 2.6, which are arranged parallel to the longitudinal axis of the round screen 1. Each single squeegee 2.1 to 2.6 can each be directed in the direction of Fig. 2 shown double arrows are moved perpendicular to the round screen to or away from him. This means that each individual doctor blade 2.1 to 2.6 can be adjusted independently of the other individual doctor blades in such a way that it rests against the inside of the round screen 1 on the surface of the round screen 1. Different or changing diameter of the round screen in the longitudinal axis can thus be compensated.

Fig. 3 shows the squeegee Fig. 1 , in which in addition its angle in the direction of the double arrow 7, ie the angle of attack of the doctor blade 2 to the round screen, and / or its height in the direction of the double arrow 8, ie a displacement parallel to the inside of the round screen but transverse to the longitudinal axis (which also the angle of attack the squeegee blade 2 to the round screen changed), is adjustable. As a result, the print quality, screen life and color guide is further improved. If the squeegee is designed as a "quasi-chamber squeegee" can be avoided by the many adjustment options of the squeegee angle that too much color flows into the sieve or runs when lifting the squeegee on the gripper channels of the squeegee.

Fig. 4 shows a delivery of a doctor blade 2 of a single doctor according to Fig. 2 to the inside of the round screen via a wedge system. The squeegee 2 is chamfered at the trailing edge, which is opposite to the leading edge, which abuts against the round screen. A wedge 9 is disposed on the chamfered trailing edge of the squeegee 2. If the wedge 9 in the direction of arrow 10 by means of a rotatable spindle or threaded rod 11 before (in the figure up) and back (in the figure down) moves, the doctor blade 2 in the direction of arrow 12 to the round screen to or from moved him away. The rotatable spindle or threaded rod 11 is guided in a frame 13 and, for example, by a (not shown) electric motor with a torque of 0.35 Nm rotated.

The squeegee 2 has in this embodiment at its front edge, a thickness of 14 mm and an average width (middle between the top edge and bottom edge) of 45 mm. The wedge 9 is 15 mm wide at its narrow upper edge and 25 mm wide at its broad lower edge.

Claims (5)

Screen printing machine with a cylindrical cylinder mold and arranged in the cylinder mold blade, characterized in that the doctor blade is divided into a plurality of individual short doctor blade, wherein the individual short blade in each case only one area to be printed with specific squeegee or printing width, preferably up to 5 cm, and wherein the distance of the individual short doctor blade from the inside of the round screen transverse to the direction of rotation of the round screen is individually adjustable, so that the distance of each short doctor blade from the round screen can be set differently depending on the particular arrangement in the round screen. Screen printing machine according to claim 1, characterized in that the adjustment of the position of the respective individual short doctor blade takes place from outside the screen or from the outside. Screen printing machine according to claim 2, characterized in that the setting of the individual short doctor blade manually by means of gears deflected axes, which are guided for adjustment left and right to the screen opening, or over each of each short doctor blade outwardly guided flexible waves. Screen printing machine according to one of the preceding claims, characterized in that the setting of the individual short doctor blade via a wedge system, in which the distance of an obliquely or conically shaped at its trailing edge single blade is adjusted to the round screen by means of a sliding wedge. Screen printing machine according to one of the preceding claims, characterized in that the angle of each individual short squeegee, ie the angle of attack of the squeegee to the round screen, and / or the height of each short squeegee, ie a displacement parallel to the inside of the round screen but transverse to the longitudinal axis, is adjustable.

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