EP1663647A1

EP1663647A1 - Device and method for screen printing

Info

Publication number: EP1663647A1
Application number: EP04764504A
Authority: EP
Inventors: Ewald König; Elmar Winterhalter; Klaus Messmer
Original assignee: Thieme GmbH and Co KG
Current assignee: Thieme GmbH and Co KG
Priority date: 2003-09-16
Filing date: 2004-09-16
Publication date: 2006-06-07
Also published as: DE10344022B4; WO2005035251A8; WO2005035251A1; US20080229944A1; DE10344022A1; CA2537836A1; DE10362093B4

Abstract

The invention relates to a device for screen printing, comprising a bearing surface (11) for an object which is to be printed (64) and a printing mechanism (12) comprising at least one printing mechanism frame (14) and a doctor blade holder (16) for securing a doctor blade (44) which can be displacably guided in a longitudinal direction in the printing mechanism frame (14) and which extends in a transversal manner inside the printing mechanism frame (14). According to the invention, the printing mechanism (12) is arranged is a displaceable manner on a plane extending parallel to the longitudinal direction and at least in a perpendicular manner on the bearing surface (11) and means (22, 24, 26, 72, 74, 76, 78) are provided for co-ordinated displacement of the printing mechanism and doctor blade holder. The inventive device can also be used, for example, for printing curved vehicle discs.

Description

Description Device for screen printing and screen printing process

The invention relates to a device for screen printing with a support surface for an object to be printed and a printing unit, at least consisting of a printing unit frame and a squeegee holder which extends in a transverse direction within the printing unit frame and is displaceably guided in the longitudinal direction in order to fasten a squeegee.

Generic devices for screen printing are suitable for printing on flat surfaces. Among other things, glass panes can be printed, for example to apply the conductor tracks of a rear window heater for a vehicle. After the conductor tracks have been printed on, the rear window can then be bent into its final shape. The printed colors are burned in simultaneously with the bending process of the pane.

A device for printing on rotating bodies by means of screen printing is known from German laid-open specification 2143137. Here, the rotary body to be printed is rolled off along a fixed screen and at the same time a doctor blade is moved along the screen on the opposite side of the screen. This screen printing device is, however, only suitable for rotary bodies whose circumferential surface to be printed can be unrolled on a screen.

The invention is intended to provide a device for screen printing and a screen printing method for printing on curved surfaces. According to the invention, a device for screen printing with a support surface for an object to be printed and a printing unit, at least consisting of a printing unit frame and a squeegee holder which extends in a transverse direction within the printing unit frame and is displaceably guided in the longitudinal direction in a longitudinal direction, is provided for attaching a squeegee which the printing unit is arranged to be movable at least in a plane running perpendicular to the support surface and parallel to the longitudinal direction and in which means are provided for coordinated movement of the printing unit and the doctor blade.

Because the printing unit is arranged to be movable at least in a plane perpendicular to the support surface and parallel to the longitudinal direction and to ensure a coordinated movement of the printing unit and doctor blade, curved surfaces, especially convex surfaces, can be printed in the longitudinal direction, that is to say seen in the direction of movement of the doctor blade become. By moving the printing unit itself relative to the support surface, it is possible to always set an optimal angular position of the screen and the doctor blade to the surface section just printed.

In a further development of the invention, the means for coordinated movement of the printing unit and the doctor blade are designed in such a way that the printing unit frame is tangential to one during a printing movement of the doctor blade, based on an imaginary line of contact between the doctor blade and an object to be printed and viewed in the transverse direction To hold the surface of the object to be printed, which is curved at least in the longitudinal direction.

In this way, the printing unit frame and a printing screen arranged in the printing unit frame are always optimally aligned with the surface section just printed. In a further development of the invention, the doctor blade holder is guided on both sides in a slide track at the base.

The slide track is adapted to the curvature of the object to be printed, so that the squeegee holder and a squeegee attached to it are guided approximately parallel to the surface of the object to be printed. The guidance of the squeegee holder in a slide track allows simple adaptation to differently curved objects to be printed by exchanging the slide track.

In a further development of the invention, the squeegee holder is guided in terms of its angular position and its distance from the support surface by means of the slide track, the guiding of the squeegee holder on the printing unit frame being designed in such a way that an angular position of the squeegee holder and printing unit frame is constant at least during a pressure movement of the squeegee holder.

In this way, the printing unit frame is aligned by the squeegee holder, so that the squeegee and printing unit frame or screen are always at an optimal angle to one another. The automatic alignment of the printing unit frame to the squeegee holder allows a structurally simple construction of the device for screen printing and in particular the device for screen printing can be adapted to different curved objects by changing only the slide tracks.

In a further development of the invention, at least one first rolling surface running parallel to the slide track is provided, on which a second rolling surface of the printing unit frame rolls during a printing movement of the squeegee. These measures allow the printing frame to be supported on the first rolling surface in addition to being guided by the doctor holder. A stable structure of the device is thereby achieved.

In a development of the invention, the first and the second rolling surface are provided with teeth.

In this way, a displacement of the printing unit frame parallel to the longitudinal direction during the printing process can be avoided, so that a high printing quality is ensured. Due to the toothing of the rolling surfaces, the printing unit frame is thus fixed parallel to the longitudinal direction and can nevertheless perform a rocking movement in order to always be oriented tangentially to the surface section to be printed.

In a further development of the invention, the printing unit frame can be adjusted in its angular position to the base by means of several actuators.

By guiding the printing unit frame by means of several actuators, an extremely flexible device for screen printing is created, in which different curvatures of an object to be printed can be taken into account by controlling the actuators differently.

In a further development of the invention, a control unit is provided for controlling the actuators, the actuators being actuated as a function of a surface geometry of an object to be printed and a position of the doctor blade relative to the object to be printed. For example, a surface geometry of an object to be printed can be scanned in a learning process by means of the doctor blade or geometric data of an object to be printed can be entered directly. The control unit then determines the appropriate angular position of the printing unit frame for the respective squeegee position and controls the actuators accordingly.

In a further development of the invention, the actuators are designed as lifting columns driven by actuators.

Such a design allows, for example, the connection of the printing unit frame to a base via four lifting columns arranged at the corners of the printing unit frame. This ensures a stable and flexible arrangement.

The problem on which the invention is based is also solved by a screen printing method for printing curved surfaces, in which the steps of reading in a surface contour of an object to be printed and aligning a printing unit during a printing process are provided in such a way that a screen frame during a Pressure movement of a doctor blade in an imaginary line of contact between the doctor blade and the object to be printed is always held tangential to the object to be printed.

Further features and advantages of the invention result from the claims and the following description of preferred embodiments of the invention in connection with the drawings. The drawings show: 1 is a perspective view of a device for screen printing according to the invention according to a first embodiment of the invention,

2 is a perspective view of a device for screen printing according to a second preferred embodiment of the invention,

3 shows a doctor blade for use with the devices for screen printing of FIGS. 1 and 2 and

4 shows a squeegee attached to a squeegee holder for use in a device for screen printing according to FIGS. 1 and 2.

1 shows a device 10 for screen printing with a support surface 11, which forms the top of a base 12. An object to be printed is placed on the support surface 11, for example a curved vehicle window to be printed. The support surface 11 can be loaded by means of an automatic transport device or can itself be part of a transport device. The device 10 for screen printing further has a printing unit 12 which has a printing unit frame 14 and a doctor blade holder 16. The squeegee holder 16 extends transversely to a longitudinal direction 13, which is indicated by an arrow on the support surface 11, over the printing unit frame 14 and is guided on two longitudinal beams of the printing unit frame 14 running parallel to one another, each in a longitudinal guide rail 18, in the illustration in FIG 1 only a guide rail 18 can be seen. The guide rail 18 and the matching counterparts on the doctor blade holder 16 are designed in such a way that the doctor blade holder 16 and the printing unit frame 14 always assume a constant angular position relative to one another during a movement of the doctor blade holder 16 along the guide rails 18. at In the illustrated device 10 for screen printing, the squeegee holder 16 and printing unit frame 14 always remain perpendicular to one another.

The squeegee holder 16 is moreover provided at its right and left end with a respective support plate 20 with a triangular shape, a tapered end of the support plates 20 being fastened to the squeegee holder 16. Two guide rollers 22, which are spaced apart in the longitudinal direction 13, are each attached to a wider end of the support plates 20. The guide rollers 22 of each support plate 20 are arranged in a slide track 24 or 26. The left-hand slide track 24 seen in the longitudinal direction 13 is provided in a left-hand slide support 28 and the right-hand slide track 26 seen in the longitudinal direction 13 is provided in a right-hand slide support 30.

The link supports 28 and 30 are connected to the base 12 via an intermediate support 32 and 34, respectively. The course of the slide tracks 24 and 26 follows the course of a surface of an object to be printed in the longitudinal direction 13, which means in or against a direction of movement of the squeegee 16 relative to the printing unit frame 14, so that the squeegee 16 is essentially parallel by means of the slide tracks 24 and 26 is guided to a surface of an object to be printed when the doctor blade holder 16 is moved along the guide tracks 24 and 26.

The device 10 for screen printing can be set up in a simple manner on objects with different curvatures, by exchanging the intermediate supports 32, 34 with the link supports 28 and 30 and exchanging them for link supports with link tracks adapted to the object to be printed.

During a printing process, a printing screen, not shown, is inserted into the device 10 and likewise not into the doctor holder 16 squeegee shown clamped. The printing screen is provided with ink in a known manner, which presses the doctor blade 16 through openings in the printing screen when the doctor holder 16 moves along the printing unit frame 14, so that the ink is applied to the object to be printed at the locations provided for this purpose. During such a printing movement, the squeegee holder 16 is always held perpendicular by the guide rollers 22 in the link tracks 24 and 26 to the surface section of the object to be printed that has just been scanned. As a result, the printing unit frame, and thus the printing screen, is always held tangentially to a surface section of the object to be printed, which is being swept over, by the guide rails 18 by guiding the squeegee holder 16 in the printing unit frame 14 by means of the guide rails 18. In this way, an optimal printing process can be achieved.

The link supports 28 and 30 are each provided with teeth 36 and 38 on their upper edge facing the printing unit frame 14. The toothings 36, 38 are each realized by means of a toothed belt stretched over the upper edge of the link carrier 28, 30. An underside of the longitudinal beams of the printing unit frame 14 opposite the toothings 36 and 38 is provided with a toothed strip 40 and 42, the toothing of which engages in the toothing 36 and 38 of the link carrier 28 and 30, respectively. The intermeshing toothings are designed in such a way that displacement of the printing unit frame 14 parallel to the longitudinal direction 13 relative to the link carriers 28, 30 is prevented. The printing unit frame 14 thus executes a rocking movement during a printing process and a movement of the squeegee holder 16 along the slide track 24, 26 and rolls on the upper edges of the slide carriers 28, 30. Since a displacement parallel to the longitudinal direction 13 through the teeth 36, 38 on the link supports 28, 30 and the toothed strips 40, 42 on Printing unit frame 14 is avoided, an exact print image is guaranteed on the object to be printed.

FIG. 3 shows a front view of a doctor blade 44 which can be inserted into the doctor blade holder 16 of the device of FIG. 1. The doctor blade 44 has an elastic application element 46, which extends over the entire width of an object to be printed and whose printing edge 48 facing the object to be printed is curved. The curved printing edge 48 is adapted to a curvature of the object to be printed in the transverse direction. The doctor blade 44 is provided with a total of three holding sections 50, 52, 54 which are connected to the elastic application element 46 at a distance from one another. It should be noted that more than three holding sections can be provided. As a result, the holding sections 50, 52 and 54 can be moved relative to one another since they are only connected to one another via the elastic application element 46. From each holding section 50, 52, 54 a guide plate 56, 58 or 60 extends, which bears at least during a printing process on the elastic application element 46 and ensures a uniform contact pressure of the printing edge 48 on the printing screen or the object to be printed. A lower edge of the guide plates 56, 58 and 60 facing the pressure edge 48 runs parallel to the pressure edge 48.

If an object to be printed has a curvature that is constant in the transverse direction, the curvature of the printing edge 48 is selected to match this curvature. If the curvature of the object to be printed changes in the transverse direction over the longitudinal direction of the object to be printed, ie seen in the direction of movement of the doctor blade, the printing edge 48 is selected in accordance with an average curvature of the object to be printed in the transverse direction. 4 shows a particularly advantageous arrangement of the squeegee 44 on the squeegee holder 16. Each of the holding sections 50, 52 and 54 is connected to the squeegee holder 16 by two adjusting cylinders 62 in each case. The adjusting cylinders 62 can be controlled individually, so that a contact pressure of the doctor blade 44 on an object 64 to be printed can be changed. In addition, a position of the holding sections 50, 52, 54 relative to the doctor holder 16 can also be changed. By changing the contact pressure or the relative position, an adaptation to a changing curvature of the object 64 to be printed can take place. This is because the holding sections 50, 52 and 54 are movable relative to one another, so that the doctor blade 44 can be deformed in itself by suitable actuation of the adjusting cylinders 62.

The illustration in FIG. 2 shows a further embodiment of the invention in a schematic perspective view. 1, functionally identical parts are designated with the same reference numerals. As in the device of FIG. 1, the object 64 to be printed, for example an already bent vehicle window, rests on a support surface on the top of the base 12. The squeegee holder 16 is guided in guide rails 18 on the printing unit frame 14. In contrast to the device 10 of FIG. 1, the printing unit frame 14 in the device 70 for screen printing according to FIG. 2 is connected to the base 12 by means of four lifting columns 72, 74, 76 and 78 and can be moved through these lifting columns 72, 74, 76 and 78 can be adjusted in its angular position relative to the contact surface of the base 12. The lifting columns 72, 74, 76, 78 are designed, for example, as threaded spindles which are adjusted via geared motors. The lifting columns 72, 74, 76, 78 are connected to the legs of a U-shaped frame 80. The lifting columns 72 and 74 are connected to a first leg of the frame 80 and the lifting columns 76, 78 are connected to a second leg of the frame 80. On the legs of the U-shaped frame 80, the guide rails are ken of the printing unit frame 14 slidably arranged. The printing unit frame 14 is displaceably arranged on the frame 80 parallel to the direction of movement of the doctor blade holder 16, that is to say parallel to the longitudinal direction. The displaceability of the printing unit frame 14 on the frame 80 is indicated by means of the double arrows 82. The U-shaped frame 80 is rotatably connected to the lifting columns 72, 78 by means of a fixed bearing. The U-shaped frame 80 is each connected to the lifting columns 75, 76 by means of a floating bearing. This floating bearing is realized in each case by means of an elongated hole running parallel to the longitudinal direction in the lifting columns 74 and 76 and a bearing pin on the frame 80 guided in the elongated hole. This fixed mounting of the U-shaped frame 80 on the lifting columns 72, 74, 76, 78 makes it possible to compensate for the length difference between the bearing points on the lifting columns 72 and 74 or 78 and 76 that necessarily occurs when the frame 80 is tilted.

The printing unit frame 14 can be displaced relative to the U-shaped frame 80 by means of an actuator 84. A shift in the longitudinal direction or printing direction of the printing unit frame 14 relative to the U-shaped frame 80 during the printing process contributes to an improvement in the print quality since, for example, smearing of the printed image is prevented.

The lifting columns 72, 74, 76 and 78 and the actuator 84 are controlled by means of a control device 86, which is only shown schematically. The control device 86 has the geometric data of the surface of the object 64 to be printed and, depending on a position of the doctor blade holder 16 relative to the surface of the object 64 to be printed, controls the lifting columns 72, 74, 76 and 78 so that the printing unit frame 40 is always tangential is aligned with a just printed surface portion of the article 64. The geometry data of the surface of the object 64 is obtained by the control advises 86, for example, about a teach-in process in which the object 64 is scanned with a squeegee or by directly entering this geometry data into a memory of the control unit 86. The device 70 of FIG. 2 can be adjusted in a particularly simple manner to objects of different curvature to be printed , since only the geometry data in the memory of the control unit 86 need to be changed for this.

Claims

claims

1. Device for screen printing with a support surface (11) for an object to be printed (64) and a printing unit (12), at least consisting of a printing unit frame (14) and one extending in a transverse direction within the printing unit frame (14) and in the printing unit frame (14) in a longitudinal direction (13) slidably guided squeegee holder (16) for attaching a squeegee (44), characterized in that the printing unit (12) at least in a plane perpendicular to the support surface (11) and parallel to the longitudinal direction (13) is movably arranged and that means (22, 24, 26; 72, 74, 76, 78) are provided for coordinated movement of the printing unit (12) and the doctor blade holder (16).

2. Device according to claim 1, characterized in that the means (22, 24, 26; 72, 74, 76, 78) are designed in a manner related to the printing unit frame (14) during a printing movement of the doctor blade (44) viewed at an imaginary line of contact between the doctor blade (44) and an object (64) to be printed and viewed in the transverse direction, tangential to a surface of the object (64) which is curved at least in the longitudinal direction (13).

3. Device according to one of the preceding claims, characterized in that the doctor holder (16) is guided on both sides in a slide track (24, 26) relative to the bearing surface (11).

4. The device according to claim 3, characterized in that the doctor holder (16) is guided with respect to its angular position and its distance from the support surface (11) by means of the slide track (24, 26), the guide (18) of the doctor holder (16) on Druckwerksrah- men (14) is designed in such a way that an angular position of the doctor holder (16) and printing unit frame (14) is constant at least during a pressure movement of the doctor holder (16).

5. Device according to one of claims 3 or 4, characterized in that at least one first rolling surface (36, 38) running parallel to the sliding track (24, 26) is provided, on which a second rolling surface (40, 42) of the printing unit frame ( 14) rolls off during a pressure movement of the squeegee (44).

6. The device according to claim 5, characterized in that the first and the second rolling surface (36, 38, 40, 42) are provided with a toothing.

7. The device according to claim 1 or 2, characterized in that the printing unit frame (14) by means of several actuators (72, 74, 76, 78) in its angular position to the support surface (11) is adjustable.

8. The device according to claim 7, characterized in that a control unit (80) for controlling the actuators (72, 74, 76, 78) is provided, the actuators (72, 74, 76, 78) depending on a surface geometry printing object (64) and a position of the squeegee (44) relative to the object to be printed (64).

9. The device according to claim 7 or 8, characterized in that the actuators are designed as lifting columns driven by servomotors (72, 74, 76, 78).

10. Screen printing method for printing curved surfaces, with the steps of reading in a surface contour of an object to be printed (64) and aligning a printing Plant (12) during a printing process in such a way that a screen frame is always held tangent to the object (64) to be printed during a printing movement of a squeegee (44) in an imaginary line of contact between the squeegee (44) and the object (64) to be printed ,