EP0012934B1 - Apparatus for intermittently transferring liquid materials onto a surface to be coated, and method for operating such an apparatus - Google Patents

Description

The invention relates to a device for the discontinuous transfer of a liquid material onto a surface to be coated, with a storage container containing the material, from which the material can be transferred into depressions in the surface of a plate, a doctor device for cleaning the plate surface after the plate recesses have been filled, and an elastic transfer part, called a tampon, which can be placed against the cliché surface at the beginning of a removal stroke for receiving the material remaining in the recesses of the cliché and then movable and can be pressed against the surface to be coated for transferring the taken up material, and a method to operate such a device.

In the printing industry, processes for continuous indirect printing of materials are known, in which a plate roller is immersed and wetted in a supply of printing material which is contained in an open ink tray, and then the printing material located on the surface of the plate is doctored by a doctor blade, so that printing material only remains in the recesses (engraving). This material, which remains as the printed image, is taken over by an elastic pressure pad roller and transferred to the material to be printed by rolling or pressing on. Here, the pressure pad material is such that its surface just barely picks up the printing material from the cliché and releases it almost completely onto the material to be printed.

The transfer cylinder consists of silicone rubber with preferably high elasticity, and the printing materials used are, for. B. screen printing inks based on plastic or synthetic resin or stoving inks. A printing process and a corresponding device are described in DE-OS 2 126 091.

Indirectly and discontinuously operating printing devices are also known, in which liquid materials are removed from a cliché, the depressions of which have been filled with the materials, by means of an elastic transfer part, generally called a tampon, and transferred to a part to be printed.

In these latter devices for printing, the printed image is engraved in a plate made of steel or copper. The liquid printing material is spread out of an open material tray with a brush device over the plate and the excess printing material is scraped off. The tampon then takes over the printing material by pressing it onto the cliché. By applying the tampon provided with printing material to the part to be printed, the printing material is released to the part to be printed. There are several options for the mechanical process.

Devices are possible in which the tampon is designed to be stationary and the cliché filled with ink and the part to be printed are alternately pressed onto the tampon, or in which the tampon is movable and is alternately pressed onto the cliché and the parts to be printed.

Such a printing process is described in DE-OS 1 939437. Only relatively evaporation-resistant materials based on plastic or synthetic resin or stove enamels are used as printing materials.

Since the printing materials are removed from an open material tray in this process, solvents will still evaporate. To maintain the quality of the print, frequent refills and a constant dilution of the color is required. This shows that only evaporative-resistant printing materials are desirable for these processes, which, on the other hand, require a long drying time for the printed parts.

If printing materials that contain volatile constituents that are harmful to health or easily flammable are processed, these dangers are counteracted in practice by an additional suction, which further increases the undesirable evaporation of the surface of the material reservoir in the ink tray, which is very large compared to the volume (e.g. B. US-A 2126778).

In the last-mentioned patent specification, reference is also made at the beginning to a printing device with a rotating cylinder, which transfers ink directly to a material to be printed and for this purpose is accommodated with the ink supply, in which it is partially immersed, in a closed housing from which it is used protrudes an upper peripheral portion through a delivery opening provided in the housing wall, this protruding peripheral portion coming into contact with the material to be printed. To seal the gap between the discharge opening edge and the projecting cylinder section, this gap is sealed with a sealing material which prevents any volatile constituents from escaping. However, there is the disadvantage that the cylinder is scratched during rotation or the liquid printing material is stripped off before being applied to the material to be printed.

Certain materials, such as glue or hotmelts, cannot be processed from an open material supply, as this cools too quickly on the surface of the material supply len and / or decompose in the air.

Another disadvantage of the known devices is that due to the incrustation of the printing material on the container for the supply, on the cliché and on the squeegee, frequent work interruptions for cleaning are required, in particular when the device comes to a major standstill when the cliché is changed or the printing material is changed.

The invention is based on the object of finding a device and a method for operating such a device which, with a simple construction, also allow the use of printing materials which have volatile, flammable, atmospheric decomposing or extremely harmful components or else Materials that can only be processed when warm.

This object is achieved according to the invention with respect to a device of the type described in the introduction in that the supply of the liquid printing material, the cliché formed as a rotatable cylinder body which is partially immersed in the printing material supply on the circumferential side, with the depressions which are provided in the circumferential direction at intervals in the circumference of the roller body, and the squeegee device is encapsulated in a container closed to the outside, from which the roller body, as seen in the radial direction, protrudes slightly outwards on the circumferential side through a discharge opening, in such a way that this discharge opening is closed by the protruding roller body part except for narrow edge regions along the opening edge, and that an additional cover, which surrounds the dispensing opening with the projecting roller body part and can be opened against the roller surface for placing the tampon, is seated on the container.

According to a particular embodiment, a pawl which is actuated by the tampon during the removal stroke and which engages in a ratchet wheel on the roller body is provided to interrupt the rotation of the roller body in the delivery position.

The tampon also controls the closing and opening of the additional cover of the take-off opening by means of a mechanical, pneumatic or electromechanical control so that it opens when the tampon is lifted down for material removal and closes on the upward lift after removal. According to a special embodiment, the cover can also be closed by a timer during longer standstills, while the cover remains in the open position at high cycle rates.

The additional closure formed by the cover can be designed both as a sliding closure or as a folding mechanism.

An embodiment suitable for high quality requirements has an inlet and outlet connection for the container, through which the level in the container and the viscosity can be regulated by circulation from the outside.

For processing toxic or very volatile substances, a special embodiment is provided with an extraction nozzle for generating and maintaining a negative pressure in the container.

In order to achieve high cycle numbers, a device is used that transports and transports the materials to be coated or printed in cycles.

According to a special embodiment, the container and the tampon are heated for processing hot glue, hot melt and similar materials to be processed warm.

Due to the surprisingly simple construction, namely only the use of a container whose opening is closed with a roller that rotates through a material supply and the use of the surface of this roller as a cliché, one of the recesses of the opening of the Container is assigned in a defined position, this method results in a considerable extension to areas of application which were previously closed. In addition to the previously used screen printing inks and stoving sheets, it is now also possible to use materials that are harmful to health, volatile and possibly flammable and that decompose if air is exposed. Even the use of viscous to pasty materials is possible with the method and with the device.

With the encapsulation, a metering and circulating device can also advantageously be connected, which ensures a constant adjustment of the viscosity of the material to be transferred and thus ensures a uniform output.

In the largely dense design of the device, when processing extremely dangerous substances, it is only necessary to maintain a slight negative pressure inside the container instead of a suction with high air output, but this does not result in any significant evaporation.

• daß die zusätzliche Abdeckung kurz vor dem Aufsetzen des Tampons auf die Klischeeoberfläche, durch die Tamponbewegung gesteuert, geöffnet wird,
• dann die Materialentnahme durch den Tampon erfolgt,
• beim Aufwärtshub des Tampons zur zu beschichtenden Oberfläche hin die Abdeckung verschlossen und die Rotation des Walzenkörpers wieder in Gang gesetzt werden, und daß schließlich der Tampon zur Materialübergabe auf das zu beschichtende Teil gebracht wird, welches mit anderen zu beschichtenden Teilen im Rhythmus eines Arbeitstaktes mit einer Fördereinrichtung an- und abgeführt wird.

The method for operating a device according to the invention which solves the object is that when the tampon is moved during its removal stroke in the direction of the cliché surface, the rotation of the roller body is interrupted such that a depression of the cliché surface always remains in the dispensing opening of the container,

• that the additional cover is opened shortly before the tampon is placed on the cliché surface, controlled by the tampon movement,
• then the material is removed through the tampon,
• during the upward stroke of the tampon towards the surface to be coated, the cover was closed and the rotation of the roller body again be set in motion, and that the tampon for material transfer is finally brought onto the part to be coated, which is fed in and out with other parts to be coated in rhythm with a work cycle with a conveyor.

Since the processability and quality of the material to be transferred is constantly maintained by the present invention, in particular in conjunction with a level control and a viscosity control device, it is possible to run the machine without supervision during continuous operation with automatic feeding and removal of the parts to be printed to let.

The machine is immediately ready for use even in single-cycle operation, even after long pauses between two printing processes. It has also been found that at the end of the work the removal of the material to be transferred and the careful cleaning of the device are no longer necessary. The time required for this and the associated loss of material are eliminated. In addition, it is surprisingly found that the structurally complex solution for the reciprocating movement of the material application brush and the doctor blade is simplified by a rotary movement of the cliché with constantly interlocking doctoring on its circumference.

A particular advantage of the invention is that the complete container can be exchanged when the plate or the liquid material has to be changed, so that the device is immediately ready for use again after a short standstill.

There is no limit to the number of cycles due to the liquid material, as it is in a closed system and splashing is not possible as with brush application.

• Figur 1 einen Teilschnitt einer erfindungsgemäßen Vorrichtung mit schematischer Darstellung der Arbeitstakte des Tampons,
• Figur 2 einen Teilschnitt einer erfindungsgemäßen Vorrichtung mit einer Abdeckung, die als Schiebeverschluß ausgeführt ist, in geöffnetem Zustand während des Entnahmehubs des Tampons,
• Figur 3 einen Teilschnitt der erfindungsgemäßen Vorrichtung gemäß Figur 2 mit geschlossenem Schiebeverschluß,
• Figur 4 einen Teilschnitt der erfindungsgemäßen Vorrichtung mit einer in Form eines Klappmechanismus ausgebildeten Abdeckung in geöffnetem Zustand,
• Figur 5 einen Teilschnitt der erfindungsgemäßen Vorrichtung gemäß Figur 4 mit geschlossenem Klappmechanismus.

Further advantages, features and possible applications can be seen from the following description in conjunction with the accompanying drawings. It shows

• FIG. 1 shows a partial section of a device according to the invention with a schematic representation of the working cycles of the tampon,
• FIG. 2 shows a partial section of a device according to the invention with a cover, which is designed as a slide closure, in the open state during the removal stroke of the tampon,
• FIG. 3 shows a partial section of the device according to the invention as shown in FIG. 2 with the slide closure closed,
• FIG. 4 shows a partial section of the device according to the invention with a cover in the form of a folding mechanism in the open state,
• 5 shows a partial section of the device according to the invention according to FIG. 4 with the folding mechanism closed.

Figure 1 shows the device according to the invention for the discontinuous, indirect transfer of liquid materials in a schematic representation. The print material supply 1 is located in an encapsulated system, which in this preferred embodiment is designed as a closed container 2, which has a delivery opening 3, at which the material to be transferred from the tampon 12 through the removal stroke 14-13 is used as a cliché Roll surface 5 is taken from the wells 6.

Only during this removal stroke 14-13 of the tampon 12 is the constant rotation of the roller body and the cleaning of the cliché surface 5 taking place thereby interrupted by the squeegee device 7 and by latching a latching pawl 8 into a ratchet wheel 9 for assigning a recess 6 provided with material to the dispensing opening 3 worried.

After the removal stroke 14-13 of the tampon 12 during the lifting into the upper stroke position 14, the cover 10, 11 shown in FIGS. 2, 3, 4 and 5 and designed as an additional closure hermetically closes the opening 3. At the same time, the locking pawl 8 is brought out of engagement with the ratchet wheel 9 and thus the rotation of the roller body is started again.

After reaching the upper stroke position 14, the tampon 12 is moved laterally up to the level of the surface 16 to be coated and lowered onto this surface 16 for material transfer (14-15).

Thereafter, the tampon 12 is raised again into the upper stroke position 14 and laterally moved back into the plane of the removal stroke 13. The tampon 12 is thus ready for material removal again. During the working strokes of the tampon 12, the emptied depression 6 is filled again with printing material by the rotation of the roller body 4 through the material supply 1.

Since a certain gap is required between the discharge opening 3 of the container 2 and the roller 4 in order not to scratch the cliché surface 5, a complete seal cannot be achieved at this point.

The squeegee 7 arranged over the entire width inside the container 2 contributes to the sealing. For complete sealing, however, an additional cover 10, 11 is arranged according to the invention, which ensures complete encapsulation during longer downtimes. The cover 10, 11 can be opened during the removal stroke 14-13 of the tampon 12. In the case of a printing sequence with a single cycle, the cover 10, 11 is opened in each case at the removal stroke 14-13 and is closed again immediately after the material has been taken over by the tampon 12. With a continuous print sequence with a high number of cycles and a small time difference between the working cycles, the cover can remain in the open position at all times. The closure of the additional closure in the form of the cover 10, 11 after the end of continuous operation can be done by a timer take place, which, when a certain downtime of the machine is exceeded, ensures that the discharge opening is closed again by the covers 10, 11.

Figures 2 and 3 show the preferred embodiment of the device according to the invention with a cover designed as a sliding closure 10. This sliding closure 10 is only opened during the removal stroke 14-13, as shown in FIG. 2, and is in the closed state after the material removal, as shown in FIG.

FIGS. 4 and 5 show a further advantageous embodiment of the device according to the invention with a cover designed as a folding mechanism 11, which according to FIG. 4 is open during the removal stroke 14-13 of the tampon 12 and, according to FIG. 5, is in the closed state after the material has been removed .

The printing device can be driven purely mechanically, with a motor driving the roller body 4 via friction and the tampon 12, the latching pawl 8 and the cover 10, 11 being actuated via a mechanical transmission. A speed-controllable motor is advantageously used, so that different cycle numbers of the printing process can be selected depending on the task.

It is also possible to frictionally drive the roller body with a motor and to carry out all other movements pneumatically or hydraulically with pistons and cylinders. Here, the tampon 12 to control the pawl 8 and the cover 10, 11 initiate the control on its downward stroke 14-13.

In a special embodiment, which is particularly suitable for fully automatic operation, the liquid material 1 is continuously circulated by feeding it in and out via the nozzle 18. By means of a level control and a viscosity control of a known type, there is always liquid material 1 in the same quantity and quality within the container 2.

In order to completely prevent the escape of evaporated constituents of the liquid material 1 to the outside, a small negative pressure can be maintained in the container via a suction connection 17.

The construction of the device is advantageously designed such that the container 2 with roller body 4 and doctor device 7 and the covers 10, 11 can be replaced as a complete component, so that when changing over to another liquid material 1 or a different printing plate 5 only a short one Interruption arises.

For an automatic operation of the device at a high number of cycles, the parts 16 to be printed are fed and removed in a known manner on transport devices 19 such as belts, chains or switching wheels. The device according to the invention also allows hot glue or hot melt to be applied to parts or tapes to be bonded if the container 2 and the tampon 12 are equipped with heating.

The method and the device with its embodiments can be used both for the plastic or synthetic resin paints previously used in practice and for stoving enamels, the short changeover times including the saving on cleaning times being particularly advantageous and large numbers of printed parts of very uniform quality possible are.

The method and the device can be used particularly advantageously for volatile, toxic or decomposing substances, since high numbers of items are possible here due to the short drying times of the printed parts. For the first time, however, it is also economically possible to apply hot glue and hot melts to parts and strip-shaped materials in a discontinuous printing process.

Claims (10)

1. Device for discontinuously transferring a liquid material on to a surface to be coated, which device has a storage container holding the material, from which container the material is able to be transferred to indentations in the surface of a cliche, a doctor device for cleaning the surface of the cliche after the indentations of the latter have been filled, and an elastic transfer element, called a pad, which can be applied to the surface of the cliché at the beginning of a take-up stroke to receive the material resting in the indentations of the cliche and which pad can then be moved towards and pressed against the surface to be coated for the purpose of transferring the received material, characterised in that the store of liquid printing material (1), the cliché (5) which is in the form of a rotatable roller element (4), the circumference of which is partly immersed in the printing material store and which has indentations (6) which are distributed at intervals in a circumferential direction around the circumference of the roller element, and the doctor device (7) are encapsulated in a container (2) which is closed to the exterior, from which container the circumference of the roller element (4) projects slightly in a radial direction through a supply opening (3), in such a way that this supply opening (3) is closed by means of the projecting section of the roller element except for narrow peripheral areas along the edge of the opening, and in that an additional covering element (10, 11), which encloses the supply opening (3) and the projecting section of the roller element and which can be opened for the application of the pad (12) to the roller surface, is mounted on the container (2).

2. Device according to Claim 1, characterised in that a latch (8) is provided for interrupting the rotation of the roller element (4) and is actuated by the pad (12) during the take-up stroke (14-13), which latch engages in a notched wheel (9) on the roller element (4).

3. Device according to Claim 1 or 2, characterised in that for opening and closing the additional cover (10, 11) for the supply opening (3) of the container (2) a mechanical, pneumatic or electromechanical control means is present which is influenced by the downward stroke (14-13) and the upward stroke (13-14) of the pad (12).

4. Device according to Claim 1, characterised in that a timer switch clock is provided for opening and closing the additional covering element (10, 11).

5. Device according to Claim 1, characterised in that the additional covering element (10, 11) is in the form of a sliding cover (10) or a hinged cover (11).

6. Device according to Claim 1, characterised in that an inlet and an outlet tube (18) are arranged on the container (2) by means of which the level of the printing material (1) in the container (2) and its viscosity can be controlled by circulation from the exterior.

7. Device according to Claim 1, characterised in that a suction tube (17) is provided for maintaining a reduced pressure in the container (2).

8. Device according to Claim 1, characterised in that a device (19) is provided for the time-controlled automatic conveyance of the parts to be coated (16) to and from the device.

9. Device according to Claim 1, characterised in that the container (2) and the pad (12) are heatable.

10. Method of operating a device according to Claim 1, characterised in that

when the pad (12) moves in the direction of the cliche surface (5) on its take-up stroke (14-13) the rotation of the roller element (4) is interrupted in such a way that in each case always one indentation (6) of the cliche surface (5) rests in the supply opening (3) of the container (2),

in that the additional covering element (10, 11) is opened, governed by the movement of the pad, shortly before the pad (12) touches down on the cliche surface (5),

then the pad (12) takes up the material (1),

during the upward stroke (13-14) of the pad (12) towards the surface to be coated (16) the covering element (10, 11) is closed and the rotation of the roller element (4) is reactuated,

an in that finally the pad (12) is brought to the part (16) to be coated for the purpose of transferring the material, which part, together with other parts to be coated, is conveyed towards and away from the device by means of a conveying device (19) in synchronisation with a working cycle.

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