EP0315818A2 - Screen-printing machine - Google Patents

Abstract

Known screen printing machines in which the screen frame is subjected to a lifting movement behind the traversing squeegee cannot be used for a screen printing activity in which the squeegee runs in the reverse direction without disadvantages arising. <??>It is therefore proposed to arrange the swivel axis for the screen frame through the central plane of the screen frame running vertically to the squeegee movement and in each case to provide devices which are able to lift the screen frame on both sides of the swivel axis. This configuration permits use of the screen printing machine for movements of the squeegee in both directions while retaining the advantages of a compensation for print faults. <??>The new screen printing machine is particularly suitable for the printing of circuit boards. <IMAGE>

Description

The invention relates to a screen printing machine with a printing table and with a squeegee guided back and forth in a frame above the printing table and with a screen frame which is arranged between the squeegee and the printing table so as to be pivotable about an axis running perpendicular to the squeegee movement.

In all known screen printing machines, the screen frame behind the squeegee moved over the screen must be raised so that the screen detaches from the ink applied to the sheet to be printed. The disadvantage is that this lifting movement can only be carried out on one side of the screen frame. With some printing processes, especially when printing on electrical circuit boards, it is often not possible, e.g. to introduce the so-called solder resist with a squeegee movement in only one direction into the very narrow spaces between adjacent conductor tracks, which sit on the circuit board in a plastic raised manner by etching off a copper layer. The spaces between the conductor tracks are sometimes so narrow that they are not filled sufficiently in only one direction when the doctor blade is moved. A squeegee movement in both directions, which is also possible in principle in known screen printing machines, can, however, only be connected in one direction with a perfect lifting of the screen from the printed surface.

It should be noted in this regard that in screen printing, because of the distance by which the screen lies above the printing table and by which it is pressed down onto the surface to be printed by squeegee printing, a so-called geometric printing error always occurs, which is caused by the lifting the screen frame on one side mens can be at least partially compensated for behind the squeegee. It has also already been proposed (DE-PS 27 43 234) not to pivot the screen frame up during the squeegee movement about a pivot axis located at the end of the squeegee movement and arranged directly on the screen frame, but rather about a level above the screen frame level and at a distance from the end of the screen frame Swivel axis. With this measure it is indeed possible to partially compensate for the geometrically caused printing error and possibly also for the printing error caused by the network expansion. However, as with all other known screen printing machines, this is only possible if the squeegee is moved in one direction over the screen.

The invention is therefore based on the object of designing a screen printing machine of the type mentioned at the outset in such a way that the screen frame can be raised for both directions of squeegee movement, so that in both directions of movement it is possible at least in part to compensate for the printing error occurring during screen printing.

To achieve this object, it is proposed in a screen printing machine of the type mentioned at the outset to place the pivot axis through the central plane of the screen frame running perpendicular to the squeegee movement and to provide devices for lifting the screen frame on both sides of the pivot axis. Through these measures, the screen frame can always be raised depending on the squeegee movement so that it is lifted up behind the continuous squeegee. This makes it possible to compensate for a printing error even if e.g. in the manufacture of printed circuit boards, pressure must be applied in both directions by a double squeegee movement.

This new design also offers the advantage that, due to the pivoting movement of the screen frame around its center, the - seen in the doctor blade movement - in front of or behind the pivot axis lying part of the screen frame relative to the printing table performs different relative movements that are opposite to each other. These different movements, which result in an opposite displacement of parts of the screen relative to the printing table, allow the geometric printing error, which likewise has different signs over the length of the screen frame, to be compensated in a particularly simple manner. At the same time, however, due to the screen printing process, a certain compensation of the longitudinal expansion of the screen can be achieved in that the pivoting movement of the screen frame only begins at the beginning of the squeegee movement and therefore only larger swivel angles can be achieved when the squeegee has already covered a larger distance on the screen has traveled. With the new design, an opposite compensation can therefore also be made analogous to the increasing strain on the screen during the squeegee movement.

The new device can be realized in a particularly simple manner in that the pivot axis is formed by two shaft journals projecting outwards from the screen frame, each of which is mounted in a link that can be displaced perpendicularly relative to the printing table. The backdrop can be guided laterally on a vertical guide rail which is fixed to the frame. In order to achieve a low-friction guide, it is advantageous to equip the link with two rollers on each side of the guide rail. This configuration makes it possible to keep the distance between the screen frame and the printing table in the end region of the squeegee movement constant despite the pivoting movement about the central axis. The displacement of the screen frame to the printing table according to the invention nevertheless takes place.

A simple solution to being able to lift the sieve frame either at both ends can be achieved by providing sliding slides parallel to the longitudinal edge of the sieve frame, each of which is assigned a lifting slope on which in turn lateral guide pins of the sieve frame run. Due to a relative displacement of the slides relative to the sieve frame, the guide pins run up on the lifting slopes, and the sieve frame is thereby raised.

In order to simultaneously achieve, as previously indicated, that the distance of the sieve frame does not change with respect to the table surface during the lifting movement, it is advantageous if the lifting slopes are part of a slot guide in the slide, which consists of two slot parts enclosing an obtuse angle, the Length - measured parallel to the printing table - is the same size. The one slit part can run parallel to the printing table, so that when the carriage is relatively displaced, an end region, namely that which has the lateral guide pins, remains the same with its distance from the printing table and only the remaining screen frame is lifted off. The design is expediently carried out in such a way that the guide pins which engage in the slot part which runs parallel to the printing table are also arranged in the region of the ends of the printing table. Correspondingly, both ends of the screen frame are assigned slides with the slot guides on both sides, and these slot guides in the slides assigned to the opposite ends of the screen frame are mirror-symmetrical to the central plane of the screen frame. When lifting one end of the screen frame, the other end is guided parallel to the printing table and vice versa.

For the relative displacement of the carriages relative to the printing table and the screen frame, it is advantageous and simple to provide a displacement drive for both carriages, which consists of tie rods that connect the two carriages to a pivoted lever on the frame of the screen printing machine, which in turn has a drive to its rear - And movement controlled, can be initiated.

• Fig. 1 eine schematische Seitenansicht einer erfindungs­gemäß ausgestatteten Siebdruckmaschine, in der Stellung mit ungeschwenktem Siebrahmen,
• Fig. 2 die vergrößerte Teilschnittdarstellung nach der Linie II-II in Fig. 1,
• Fig. 3 eine vergrößerte Detaildarstellung eines der bei­den verschiebbar gegenüber dem Maschinengestell geführten Schlitten und
• Fig. 4 eine schematische Darstellung der beim Schwenken des Siebrahmens auftretenden Verhältnisse.

The invention is illustrated in the drawing using an exemplary embodiment and is explained below. Show it:

• 1 is a schematic side view of a screen printing machine equipped according to the invention, in the position with the screen frame not pivoted,
• 2 shows the enlarged partial sectional view along the line II-II in FIG. 1,
• Fig. 3 is an enlarged detail view of one of the two slidably guided with respect to the machine frame and
• Fig. 4 is a schematic representation of the conditions occurring when pivoting the screen frame.

In Fig. 1, a screen printing machine is shown, the printing table (1) is arranged in a manner not shown within a machine frame (2). The machine frame (2) consists essentially of a base frame with supports (20) which can be set up on the floor and in which guide columns (23) are held, to which two doctor guide bars (21) running parallel to one another are connected. A squeegee, not shown, can be guided back and forth between these squeegee guide bars (21) in the direction of the arrows (5) parallel to the printing table (1). A guide (26) is also fixedly arranged on the frame (2) and excavation rails (22) guided on this guide (26) are provided, between which a screen frame (3) is held with a pressure screen, not shown.

The screen frame (3), as can be seen in particular from FIG. 2, is provided with a pivot axis (4) which runs through the central plane (6) of the screen frame (3) which is perpendicular to the squeegee movement (5). This pivot axis (4) is formed by two in the area of the opposite longitudinal sides (3a) of the swivel frame (3), on the excavation rails (22) with a flange (8a) and outwardly projecting shaft journals (8), only one of which is shown in Fig. 2. These shaft journals (8) are pivotally held in a link (9), which in turn is displaceable in the direction of the central plane (6), ie perpendicular to the printing table (1) on a guide rail (10) which is fixed to the frame (2) Screen printing machine, in the exemplary embodiment fixedly arranged on each of the doctor guide bars (21).

The link (9) is provided with four outwardly projecting rollers (11), two of which lie on the left and right on the outer edges of the guide rail (10) and thus the vertical guidance of the link (9) and thus the swivel axis (4) secure the sieve frame (3). In the excavation rail (22), in which the sieve frame (3) lies, a slot-like recess (22a) is provided in the area of the shaft journals (8), which runs perpendicular to the sieve frame (3) and adjusts the shaft journals (8) and Backdrop (9) allowed in height. This allows the height of the swivel axis (4) to be changed compared to the sieve frame (3).

Plate-like slide guides (16), which are arranged in the region of the ends of the printing table (1) on both sides in the direction of the squeegee movement (5), are fixed to the opposite squeegee guide bars (21). These slide guides (16) are each equipped with slot-like longitudinal guides (25) which each run parallel to the printing table (1). In both of these slot-like longitudinal guides (25) engage sliding blocks (24) which are firmly connected to plate-like slides (12, 12 '). The carriage (12, 12 ') can be moved parallel to the printing table (1) in this way. They are both connected to each other via a connecting rod (18 ') and are connected to a further pull rod (18) with a swivel lever (19) which is attached to the frame (2) or in each case on the doctor guide bar (21) is arranged pivotably and is connected in a manner not shown to a pivot drive, which optionally allows the lever to be pivoted in the direction of the arrows (27).

In the carriage (12, 12 '), as can be seen from Fig. 3, a slot guide (15) is provided, which consists of two at an obtuse angle sloping parts 15a and 15b). The slot part (15a) is designed to run parallel to the surface of the printing table (1). The slot part (15b) rises relative to the printing table (1) at an angle to the outside and forms a lifting slope (13), which will be discussed later. Measured parallel to the printing table (1), the two slot parts (15a and 15b) have the same length.

As shown in Fig. 1, the slot guides (15 and 15 ') of the two carriages (12 and 12'), which are each assigned to the areas of the ends of the printing table (1), have an identical, but mirror image of the central plane ( 6) arranged training on. In both slot guides (15 and 15 ') engage guide pins (14) which are arranged in the region of the ends of the printing table (1) on the excavation rails (22) on which the screen frame (3) is held. By a relative displacement of the carriage (12 and 12 ') relative to the frame (2), a pivoting movement of the screen frame (3) about the pivot axis (4) is therefore effected, with a movement of the carriage (12, 12') in Fig. 1 from the position shown to the left the right side of the screen frame (3) is raised and the area of the screen frame (3) which is held at the left end of the printing table (1) by the guide pins (14), its distance from the printing table (1) does not change, but its position relative to the printing table (1) does.

This is clear from the schematic Fig. 4, where the ratios of the relative position of the screen frame (3) to the pressure table (1) are shown with a pivoting movement of the screen frame (3) counterclockwise and how it is carried out with a squeegee movement in the direction of arrow (28). When the frame (3) is pivoted about the pivot axis (4), which is arranged in the center plane (6) of the sieve frame (3), the frame parts lying to the right of the pivot axis (4) are in the position (3 ′) are pivoted in the direction of arrow (28) by the amount (+ d) in their relative position to the printing table (1) when the screen, as is known, is pressed by the doctor blade against the surface of the printing table (1) during the printing process. The parts of the screen frame (3) to the left of the swivel axis, on the other hand, are shifted by the amount (- d) against the direction of the arrow (28) relative to the printing table (1). Since it is known that the geometrical error in screen printing, due to the, albeit small, distance of the screen frame (3) from the printing table surface and due to the squeegee being pressed down, is also corresponding with respect to the center plane (6), however 4, then it becomes clear that a very simple but effective method is created by the design according to the invention in order to be able to compensate for the geometrical error in screen printing. No complicated sieve frame movement is necessary for this. Swiveling around the swivel axis (4) is sufficient.

It is also known that, due to the squeegee pressure on the sieve and the resulting strain on the sieve, an additional printing error also occurs, which depends on the elastic properties of the sieve and the squeegee pressure and which increases with the squeegee movement, in the case of FIG 4 therefore increases with increasing movement of the squeegee in the direction of the arrow (28). The pivoting movement of the screen frame (3) according to the invention also counteracts this error if the pivoting angle is chosen to be correspondingly large. A certain compensation for the fact that this screen elongation error is smaller at the beginning of the squeegee movement is in the invention Device achieved in that the pivoting movement of the screen frame (3) is initiated only at the beginning of the squeegee movement, so that the pivoting angle which the screen frame (3) travels becomes larger as the squeegee moves in the direction of the arrow (28). The displacement of the sieve parts in the direction of arrow (28) will therefore initially be very small at the beginning of the squeegee movement and will only increase with increasing squeegee travel. This allows qualitative compensation of the strain on the screen.

It should be noted that, due to the parallel guidance of the guide pins (14) of the screen frame (3), no other conditions occur in the position of the screen frame (3) relative to the printing table (1) than are shown in FIG. 4. By guiding the vertical center plane (6), when the sieve frame (3) swivels, there is always a longitudinal displacement of the guide pins relative to the printing table (1), which is made possible by the slot parts (15a) of the slot guides (15) in the two slides (12 and 12 ′).

As can easily be seen, the screen printing machine according to the invention can also achieve a pivoting movement of the screen frame (3) in a clockwise direction if, for example, printing is to be carried out by a doctor blade movement opposite to the arrow (28) in FIG. 4. The conditions are then the same, but with the opposite sign. The new screen printing machine can therefore be used for screen printing in two different doctor blade directions without having to give up the advantages of lifting the screen frame behind the doctor blade and the advantages of a certain error compensation.

Claims (15)

1. Screen printing machine with a printing table and with a squeegee guided back and forth in a frame above the printing table, and with a screen frame which is arranged between the squeegee and the printing table so as to be pivotable about an axis running perpendicular to the squeegee movement, characterized in that the pivot axis (4 ) runs through the central plane (6) of the screen frame (3) perpendicular to the squeegee movement (5), and that devices (7) for lifting the screen frame (3) are provided on both sides of the pivot axis (4). 2. Screen printing machine according to claim 1, characterized in that the pivot axis (4) is formed by two from the screen frame (3) outwardly projecting shaft journals and that the shaft journals are each mounted in a vertically displaceable link (9). 3. Screen printing machine according to claims 1 and 2, characterized in that the link (9) is laterally guided on a vertical guide rail (10) which is fixedly arranged on the frame (2). 4. Screen printing machine according to claims 1 to 3, characterized in that the link (9) with two laterally on the guide rail (10) adjacent rollers (11) is provided. 5. Screen printing machine according to claim 1, characterized in that the means (7) for lifting from parallel to the longitudinal edge (3a) of the screen frame (3) displaceable carriage 12), which are provided with lifting bevels (13) on which lateral guide pins ( 14) the sieve frame (3) is running. 6. Screen printing machine according to claim 5, characterized in that the lifting bevels (13) are part of a slot guide (15) in the carriage (12), which form an obtuse angle from two enclosing slot parts (15a, 15b), the length (a) parallel to the printing table is the same size. 7. Screen printing machine according to claim 5, characterized in that both ends of the screen frame (3) are laterally assigned carriages (12) and that the slot guides (15, 15 ') in the opposite ends of the screen frame (3) assigned carriage (12 , 12 ') are mirror-symmetrical to the central plane (6) of the screen frame (3). 8. Screen printing machine according to claim 7, characterized in that the slot guides (15) and the guide pin (14) of the screen frame (3) are each arranged in the region of the end edges of the printing table (1). 9. Screen printing machine according to claim 5, characterized in that the carriage (12) on guides (16) of the frame (2) are guided and connected to a displacement drive (17) acting in the same direction. 10. Screen printing machine according to claim 9, characterized in that the displacement drive (17) consists of tie rods (18) connecting the two carriages (12, 12 ') with a reciprocating drive (19). 11. Screen printing machine according to claim 10, characterized in that the drive is a on the frame (2) mounted with a drive mechanism connected pivot lever (19). 12. Screen printing machine with a printing table and with a squeegee guided back and forth in a frame above the printing table, and with a screen frame (3) which is arranged between the squeegee and the printing table about a central plane (6) running perpendicular to the squeegee movement (5) Swivel axis (4) is arranged pivotably and with devices (7) for lifting on both sides of of the pivot axis (4), characterized in that the pivot axis (4) is formed by two shaft journals projecting outwards from the screen frame (3), each of which is mounted in a vertically displaceable link (9) such that the link ( 9) is laterally guided on a vertical guide rail (10) which is fixedly arranged on the frame (2) and that the devices (7) for lifting consist of slides 812 which can be displaced parallel to the longitudinal edge (3a) of the sieve frame (3) are provided with lifting bevels (13) on which lateral guide pins (14) of the sieve frame (3) run. 13. Screen printing machine according to claim 12, characterized in that the lifting bevels (13) are part of a slot guide (15) in the carriage (12) which consists of two slot parts (15a, 15b) enclosing an obtuse angle, the length (a) of which parallel to the printing table is the same size. 14. Screen printing machine according to claim 12, characterized in that both ends of the screen frame (3) are laterally assigned to carriages (12) and that the slot guides (15, 15 ') in the opposite ends of the screen frame (3) assigned to carriage (12 , 12 ') are mirror-symmetrical to the central plane (6) of the screen frame (3). 15. Screen printing machine according to claim 12, characterized in that the slot guides (15) and the guide pin (14) of the screen frame (3) are each arranged in the region of the end edges of the printing table (1).

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