EP0805024A2 - Rotary screen printing machine for printing large images - Google Patents

Abstract

According to the invention, the rotary screen printing machine for printing large-repeat images (32) has round templates (4), each with an individually assigned individual drive (5), preferably implemented by stepping motors (5), and the lifting and lowering of the round templates (4), each assigned to a partial repeat, is individual, also controllable by using stepper motors (21). Compared to known devices for the continuous printing of large repeat patterns (32), the individual control of the stencil drive (5, 21) enables a considerably faster pattern change without mechanical conversion of the machine and the adjustment of the individual printing station is considerably easier. <IMAGE>

Description

The invention relates to a rotary screen printing machine for printing large images by means of a plurality of circular templates synchronized with respect to their relative rotational speed, which, according to a partial repeat, can optionally be lifted out of their printing position and lowered onto the goods to be printed.

For the sequential and continuous printing of large images composed by adding a plurality of partial repeats, the partial repeats being printed onto the goods to be printed (for example textile materials) by means of a circular stencil or group of stencils, several methods are known which are similar to one another. The individual printing stencils are driven via a vertical shaft and individually assigned angular gears, so that individual control of a single stencil drive is not possible. It is known, for example from DE-GM 72 30 388, to control the lifting of individual circular templates synchronized to the printing blanket speed by crank drives, eccentrics, cams and the like, the speed adjustment for circular templates of different diameters being achieved by a suitable choice of the transmission stages. Similar rotary printing machines for large repeat patterns are described in the documents AT-311 289, DE-A-2 224 480 and DE-GM 73 32 801.

Difficulties with all currently known printing processes for large reports result from the fact that - due to the rigid connection of the stencil drives - a pattern change is only possible through a complicated mechanical change, which is time-consuming during the changeover, in particular the adjustment of the successive partial reports requires experience and great expenditure of time , not to mention considerable wear on the goods and printing paste. Nevertheless, due to mechanical inaccuracies, large repetitions with high accuracy of fit are difficult to achieve.

Document EP 0 396 924 B1, which forms the preamble of claim 1, describes a rotary screen printing machine for printing large images by means of a plurality of circular stencils which are synchronized with respect to their relative speed and which, according to a partial repeat, can optionally be lifted out of their printing position and lowered onto the goods to be printed and each with a single drive for template turning are provided. This machine also has the problem of complex adjustment.

The invention is therefore an object of the invention to provide a rotary screen printing machine for printing large repeat images, in which a pattern change can be carried out comparatively very quickly and with which a very precisely fitting print quality can be achieved without the need for larger quantities when upgrading or converting the machine Rejects, loss of printing paste and the like must be accepted.

The achievement of the object is characterized in that the circular templates each have a single lifting drive for lifting and lowering the individual circular templates, the individual lifting drives being individually and incrementally actuatable by a programmable controller.

Each rotary individual drive and the acceleration of the circular templates can preferably be set individually and incrementally relative to the other rotary individual drives to a speed that is synchronous with the printing blanket by means of a programmable control. The individual drives are preferably - as is known in principle from EP 0 396 924 B1 - realized by stepper motors which can be operated in continuous operation.

All drive and setting parameters for a single circular template can be specified and changed via the program control, either from a central master computer unit or via individually assigned, parameterizable control units.

• Fig. 1 in schematischer Darstellung den prinzipiellen Aufbau mit zugeordneter programmierbarer Steuereinheit einer erfindungsgemäßen Rotationssiebdruckmaschine für Großrapportdruck mit zeitsynchron und digital steuerbaren Hubzylindern für die einzelnen Druckschablonen;
• Fig. 2 eine abgewandelte Ausführungsvariante der Großrapportdruck-Siebdruckmaschine gemäß Fig. 1 mit Spindelhubgetrieben für das zeitsynchrone Abheben bzw. Absenken der Druckschablonen;
• Fig. 3 eine Detaildarstellung für die Ausführungsvariante einer Rotationssiebdruckmaschine nach Fig. 3 zur besseren Verdeutlichung einzelner Funktionsgruppen; und
• Fig. 4 ein großrapportiges Druckbild mit zugeordnetem Zeitablaufdiagramm für das Absenken und Anheben, Beschleunigen und Verzögern der einzelnen Druckschablonen im Verlauf des aufeinanderfolgenden, kontinuierlichen Druckens der einem jeweiligen Teilrapport zugeordneten Bilder.

An advantageous embodiment of the invention and an example of large-scale printing by means of a rotary screen printing machine according to the invention are explained in more detail below with reference to the drawing. Show it:

• 1 shows a schematic representation of the basic structure with an assigned programmable control unit of a rotary screen printing machine according to the invention for large repeat printing with time-synchronously and digitally controllable lifting cylinders for the individual printing templates;
• FIG. 2 shows a modified embodiment variant of the large repeat screen printing machine according to FIG. 1 with screw jacks for the time-synchronous lifting or lowering of the printing templates;
• 3 shows a detailed representation of the embodiment variant of a rotary screen printing machine according to FIG. 3 for better clarification of individual functional groups; and
• Fig. 4 is a large-repeat print image with an associated timing diagram for lowering and raising, accelerating and decelerating the individual printing templates in the course of the successive, continuous printing of the images assigned to a respective sub-repeat.

FIG. 1 shows in a schematic functional representation, which corresponds to that of FIG. 1 in EP-0 366 924 B1, a rotary screen printing machine set up for printing large-scale images, in which program-controllable individual drives are provided for the individual printing stations with the simultaneous possibility of the round stencils / printing stencils of the printing stations can be lifted and lowered individually and also under program control.

In a known manner, a drive roller 14 and a tension roller 11 are provided for a rotating printing blanket 3 in the rotary screen printing machine. Furthermore, three printing units are shown as an example, which in a manner known per se only have printing stencils 4 indicated only schematically and each have a stencil drive pinion 12 mounted laterally and below the printing blanket 3 (the printing blanket). The printing blanket 3 is driven via the drive roller 14 by means of a direct current motor 1, which is regulated by a converter 2, which is controlled analogously via a master computer 8. A pulse generator 7, which is assigned to the tensioning roller 11 and which generates a digital signal f _m corresponding to the speed of movement of the printing blanket 3, is provided as all the individual drives of the printing templates. A frequency divider 9 connected downstream of the pulse generator 7 reduces the digital signal f _m with a ratio that can be determined by the master computer 8 and feeds the corresponding digital signals to the master computer 8. These digital signals are processed in the master computer 8 in a known manner to digital control signals which are supplied to a plurality of sub-computers (CPU) 6 corresponding to the number of printing templates 4 with a downstream power driver for a respective stepper motor 5. In this way, the printing stencils 4 are driven with an angular position (phase position) that is exactly constant relative to one another. In Fig. 1 only three printing stencils 4 are shown with associated drive units; however, it is obvious that any number of stencils 4 can be driven in the same way.

For the time-synchronous lifting from and lowering into the printing position as well as for accelerating and decelerating in the correct manner, each printing unit (each printing stencil) is assigned a lifting cylinder 16, which can be pressurized with pressure fluid via a valve that can be controlled digitally from the host computer 8, with the lifted upper end position by an upper limit switch 13 and the lowered lower pressure position are determined by a further limit switch 17. The positioning of the individual printing templates takes place - as explained in more detail below - in a time-controlled manner and depending on the setting of the limit switches 13, 17. The position of the printing unit raising / lowering can be inductively, capacitively, opto-electronically, by ultrasonic sensors and by potentiometers or electronic sensors the like.

In the embodiment variant of the invention according to FIG. 2, if the same modules are present, the same reference notes as in FIG. 1 are used; a renewed description can be omitted. In this exemplary embodiment, screw jacks 20 are provided for the correct raising and lowering of the printing stencil, which can be driven via direct current motors 21 or stepper motors.

In the case of DC motors, a linear potentiometer 22 is provided for the exact position determination of the position of a respective printing template, the readout value of which is given as a read-in value to the host computer 8 via a respective analog / digital converter 23. Instead of the linear potentiometers 22, inductive proximity sensors could also be used in each case.

The partial view of FIG. 3 clearly shows the module assignment for a specific and implemented exemplary embodiment of the invention, the stepping motor 5 for the template drive including the associated stepper motor 21 with an associated reference sensor for determining an end position via the screw jack 20 assigned gear box 25, the printing template 4 can be incrementally raised and lowered again.

The sequence of a printing process for large repeat image printing by means of a rotary screen printing machine explained with reference to FIGS. 1 to 3 is described in more detail with reference to FIG. 4.

All the round templates 4 required for a pattern have been upgraded and are at a standstill and raised. The stencils 4 are now positioned manually or with an automatic pattern finding in such a way that a non-engraved area is located at the bottom, ie in alignment with the printing blanket 3. The stencils 4 are then filled with printing paste in a known manner. Since the non-engraved area is located on the underside of the individual stencils 4 facing the printing blanket 3, printing paste cannot run out. The printing processes possible with the invention are therefore also suitable for printing pastes of different viscosities.

As an example, the pattern 32 shown in FIG. 4 should be printed, for example as a multicolored print, and a cut line 30 or 31 in the direction of passage or printing in front of and behind the pattern 32. The pattern 32 has a maximum pattern length of, for example, 500 mm . The repeat length of the cutting lines 30, 31 can be variable.

First, the printing blanket 3 is set in motion. To print the first cutting line 30 to be printed, the assigned cutting line template, that is to say the first circular template 4 in area a - see time diagram under the pattern of FIG. 4 - is accelerated to the synchronous speed with the printing blanket 3 and, at the same time, not position-dependent, and simultaneously lowered. At time b, a working magnet (not shown) arranged under the printing blanket is switched on, which attracts a roller or doctor blade inside the circular stencil 4 in a known manner with a predetermined magnetic force. At time c, section line 30 or 31 is printed. The printing process is ended at the latest at time d, whereupon the printing stencil 4 is lifted off again in the period e and, depending on the diameter and repeat length, is possibly delayed or stopped to a lower rotational speed.

In the period f, the template 4 assigned to the pattern 32 is lowered and at the same time accelerated to the synchronous speed with the printing blanket 3. At time b ', the working magnet assigned to this template is switched on. The pattern 32 is printed within the time slot g, it being emphasized that the pattern 32 can also be composed of the printing of a number of templates, that is to say it can be designed in multiple colors. If a multicolored print is desired for the pattern 32 and / or the cutting lines 30, 31, a correspondingly higher number of groups of printing stations must be provided. At time d ', the working magnet is switched off and the corresponding template is lifted off and, according to its diameter and the partial repeat to be printed, decelerated in the period h to a lower speed or to a standstill.

By programming individual drive parameters, the acceleration of the individual printing stencils 4 and their lowering or lifting off are controlled in such a way that the individual stencil 4 is in synchronism with the printing blanket 3 when it first comes into contact with the printing blanket and is precisely positioned in the repeat.

It should also be noted that a repeat, i.e. a large repeat each consists of a first cutting line 30 and the pattern 32. The second cutting line belongs to the second repeat that follows. Repeat length, pattern length and template offset are variable. Of course, a repeat does not necessarily have to include a cutting line; it can also - as is usually the case - be assembled from several equivalent templates.

Preferably, the individual printing stencils 4, as can be seen from the time diagram of FIG. 4, are already lowered in the non-engraved area, so that the magnetic force for lowering the roller or coating squeegee can be switched on, and a color wedge forms in good time, as a result of which stable conditions for good print quality before the actual printing process begins.

The system arrangement of a rotary screen printing machine according to the invention can also be used for other coating and metering systems, especially also when using non-magnetic roller and doctor blade variants; i.e. the variant described here with a magnetic roller or doctor blade is not the only variant to be adopted in connection with the invention.

If a partial repeat is printed by a template 4, i.e. if the relative position of the template 4 to the printing blanket 3 is again in an area that is not engraved, the working magnet is switched off again (see times d, d ', d''... in Fig 4). The relevant template 4 is raised and decelerated so that it is again in the starting position, for example, when it comes to a standstill. As already mentioned, it is not absolutely necessary that the templates 4 are brought to a complete standstill; they can (preferably very slowly) turn around until the next mission. that is, until it is lowered again and accelerated to the synchronized blanket speed.

It should be emphasized that there are applications, especially in multi-color printing, that several stencils 4 are used simultaneously or with little time difference.

In the embodiment variant of the invention according to FIG. 2, it is advantageous to actuate the screw jack 20 via a lifting drive with a stepper motor instead of the DC motor mentioned. For exact positioning of the lifting, it is advantageous for all design variants that the drive motor 5 with pinion 12 is lifted together with the template 4, so that a corresponding rappor wheel on the template and the pinion 12 are always in mutual engagement.

Instead of the screw jack 20, an eccentric or a swash plate with a stepping motor or with a DC motor drive can also be used; in the latter case again equipped with a potentiometer and position sensors.

Due to the exact, precise angular position determination when lifting out the stencils, a non-engraved area of the stencil can be kept very small. This means that the relative size of the templates usually also becomes smaller, so that manufacturing costs can be saved.

Systems of rotary screen printing machines according to the invention are only limited with regard to the number of printing stations and the maximum possible repeat diameter of the templates that can be used.

A rotary screen printing machine of the type according to the invention is suitable for all goods to be printed or coated, but preferably for fabrics, woven goods, floor coverings, carpets, foils and the like.

It is particularly advantageous that a rotary screen printing machine of the type described here can also be used as a normal rotary screen printing machine (continuous repeat) and, because of the possibility of printing images without mechanical changes, can also be used as a replacement for a planographic printing machine, that is to say not only for large-repeat images. The setting and conversion of such a machine to different patterns is very easy thanks to digitally inputable default values, correction and change parameters, so that no specially trained specialist personnel are required. Stencils that do not run in the image printing process can be operated in normal rotary printing (continuous repeat) during the image printing process. The stencil pressure meters are freely selectable.

Claims (2)

Rotary screen printing machine for printing large images by means of a plurality of circular templates (4) which are synchronized with regard to their relative speed, which can be lifted from their printing position and lowered onto the goods to be printed according to a partial repeat, and are each provided with an individual drive (5) for rotating the template; characterized in that the circular templates (4) each have an individual lifting drive (16; 20, 21) for lifting and lowering the individual circular templates (4), the individual lifting drives being individually and incrementally actuatable by a programmable control. Rotary screen printing machine according to claim 1, characterized in that each rotary single drive (5) and the acceleration of the round stencils (4) can be set individually and incrementally by a programmable control to a speed which is synchronous with the printing blanket (3).

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