EP0730954A1 - Screen printing machine with changeable squeegee - Google Patents

Abstract

The printer consists of an horizontal printing table and a support for a scraper (10) and a counter-scraper on a carriage which travels lengthwise above the table and a screen (2) between the two. The carriage (3) has a master beam (31) with guides which move to-and-fro along rails (7) fixed to an upper frame, while the support consists of one arm (12) for the scraper and another for the counter-scraper. Each of the support arms is extended by end-plates (17,27) to which it is connected by regulators (16) allowing its angle of inclination to the horizontal to be adjusted. In addition, the positions of the scraper and counter-scraper are alternated by power cylinders which act on the supports.

Description

The present invention relates to a screen printing machine designed to improve the quality of printing on supports varied in nature and dimensions.

Printing by machines of this type consists in spreading ink on a screen printing screen, which is then plated on the receiving support by means of a squeegee with flexible blade by which one exerts a pressure capable of penetrating the ink to the support through the screen meshes in the areas where they have been left open depending on the patterns to be printed. The receiving support, brought for example by sheet feed, is arranged on a printing table with respect to which the squeegee is automatically driven from one end to the other of the screen, or at least from one end to the other of the area thereof which carries the pattern to be printed.

The regularity of the pressure exerted throughout this displacement is of great importance for the print quality, as well as the uniformity of this pressure at all points of the squeegee from one edge to the other of the 'table-support-screen assembly.

Now in industrial installations, where the machines are designed to print in series flat articles, such as sheets of more or less thick paper or plastic material brought successively to the printing table automatically, there is currently a need for 'use the same machine, built to print large posters for example, also to print articles of smaller dimensions. Indeed, the number of copies being always relatively small (of the order of 10 to 50), it is economically not possible to have machines with printing tables having dimensions as varied as it would be desirable. We are therefore led to use a large table, with its associated equipment, even for print smaller media on smaller print widths. And then there are difficulties in meeting the pressure requirements specific to each particular case with a long life of the squeegees.

We thought we would deal with the question using interchangeable squeegees, of widths adapted to those of the articles to be printed, which are fixed inclinable at the end of pressing members mounted on a squeegee drive carriage in its outward and return movement parallel to screen and print table. There is then a major drawback in that the squeegee models currently widely available commercially are no longer usable.

The invention aims to solve the difficulty better than the solutions that have been proposed to date. It also aims to facilitate the implementation of the machines and their maintenance, to increase the life of the squeegees, to provide greater flexibility of use, in particular in adjusting both the pressure and the inclination of the squeegee. compared to the printing table.

In addition, certain known partial solutions have appeared to be unsuitable when they do not take sufficient account of the operating characteristics of the counter-scraper which serves to collect the excess ink entrained by the scraper at each printing pass, in order to bring it back into opposite direction, by spreading it on the screen, without pressure this time, or when they are not interested in adapting the displacement stroke of the squeegee and / or the counter-squeegee to the useful length of the screen , on substrates shorter than the printing table.

It is also useful to be able to adjust the pressure force of the squeegee on the table, for example to adapt to different inks or supports or to different mesh dimensions of the screen. It should be particular that, even for high pressures and large printing widths, the squeegee does not take an arrow detrimental to a print quality that is both good and regular, while in addition such an arrow would cause rapid wear and non-uniform flexible blade.

Furthermore, providing a special squeegee holder to support the forces exerted on the flexible blade of a large squeegee without deformation or deflection considerably complicates the system, with all the drawbacks that this entails, particularly in terms of construction complexity and price. of the machine, as well as in operating cost.

For all these reasons, users cannot be satisfied with known machines when they intend to use interchangeable squeegees and be able to adjust them in height and in inclination relative to the printing table.

We have therefore arrived, according to the present invention, to prefer to act under pressure on the squeegee by means of a carrying arm permanently mounted movably on the carriage.

In practice, the preferred embodiments of the invention use conventional techniques in themselves insofar as a screen printing machine according to the invention advantageously comprises a lower frame on which a printing table is mounted , preferably movable vertically, and an upper frame, movable in inclination or in vertical displacement relative to the lower frame, which receives on the one hand the screen printing screen, preferably so as to be able to tilt about an axis pivot located at the front of the machine, and a carriage movable along the upper frame carrying squeegee and counter-squeegee and associated with drive means in the forward direction for the printing pass with the squeegee in operating position , from rear to front of the machine, and backwards with the counter-squeegee in the operating position, from front to back of the machine. On the other hand, the invention proposes a screen printing machine having different new characteristics as defined by the claims and illustrated below, which it will most often be advantageous to apply in one or other of their technically operating combinations. .

The subject of the invention is therefore a screen printing machine of the type comprising a horizontal printing table and support means for a squeegee and a counter squeegee on a movable carriage above said table in the forward and reverse directions. return in association with reversing means for alternately raising and lowering said squeegee and said counter squeegee with respect to a screen printing screen interposed between them and said printing table. According to the invention, said carriage comprises a master beam secured to means for guiding the outward and return movements of said carriage in rails fixed to an upper frame of the machine, and said support means comprise a support arm for said squeegee and a support arm of said counter-squeegee, each of said arms being extended by end plates to which it is linked by means for adjusting its inclination around a horizontal axis which is parallel to it. For the counter-squeegee, said reversing means are preferably constituted by jacks carried by said master beam and acting on said end plates that the counter-squeegee support arm comprises. For the squeegee, said reversing means alternating with the counter-squeegee are constituted by jacks acting on the squeegee support arm itself and mounted to slide on said master beam. In addition, said squeegee arm, and therefore preferably also said counter-squeegee arm, are each individually linked by their end plates to said master beam by devices guiding their vertical movements.

According to the preferred embodiments of the invention, only the squeegee is interchangeable to use squeegees of different lengths in correspondence with sheets to be printed constituting the printing medium which are of different widths. More exactly it is the area to be printed which often varies while the nature and the dimensions of the sheets of paper remain the same, when it is for example a question of adding a color on a support already partially printed.

The squeegee is constituted in a conventional manner by a blade of flexible material secured to a metal plate which envelops its upper edge. It is advantageous that the counter-squeegee is not interchangeable. It is indeed commonly a metal blade bent at an obtuse angle, which does not have to undergo the same phenomena of wear as the flexible blade of the squeegee. It also does not have to be pressed against the screen, since its purpose is to simply collect the excess ink remaining on the screen during the return movement to bring it towards the rear of the machine.

The squeegee and the counter squeegee are both mounted under the same carriage movable longitudinally relative to the upper frame of the machine. They are linked to it separately by means of support means constituted by two carrying arms which are permanently installed on the carriage and which can themselves, independently of one another, be raised or lowered relative to a main beam of the mobile carriage which is common to them. On the other hand, it is within these non-removable carrying arms that the inclination adjustment means are provided, intermediate between the main part of each of the arms on which the corresponding squeegee is fixed and its end plates. linked with the main beam, the only one truly secured to the carriage guided in the rails of the upper frame.

Given the interchangeability sought, it is advantageous that the pressure of the squeegee on the screen is adjustable by its sliding reversing jacks, generally pneumatically controlled, acting on the squeegee arm itself, in part main, when it is in its lowered position. It is also advantageous that the squeegee is mounted on said master beam of the carriage by stirrups sliding freely horizontally along this master beam as a function of the width of interchangeable squeegees, while, for its part, the counter-squeegee is preferably mounted fixed on its carrying arm.

Preferably, the squeegee arm is subjected, at its end plates, to the action of elastic means for compensating for its weight, which may in particular consist of helical springs in compression in the carriage between a fixed fixed surface therein and a bearing secured to the arm, or more precisely, preferably, associated end plates. This achieves that the latter has sufficient mechanical strength given its length, preventing it from appearing an imbalance requiring differential pressure settings on the reversing cylinders. The pressure adjustment is also facilitated when passing from one squeegee dimension to another.

In general, thanks to the way in which the machine is thus constructed, the various adjustments and movements are ensured in a completely independent manner.

We will now describe in more detail a particular embodiment of the invention which will make it better understand the object with its essential characteristics and their advantages, it being understood however that in its details, this embodiment is chosen by way of example and that it is in no way limiting.

• la figure 1 montre une vue schématique en élévation longitudinale de la machine de sérigraphie dans son ensemble ;
• la figure 2 représente en perspective l'essentiel du chariot en position au-dessus de la table d'impression ;
• la figure 3 montre en vue transversale en coupe partielle les éléments fonctionnellement associés à la contre-raclette ;
• la figure 4 constitue l'homologue de la figure 3, cette fois pour la raclette ;
• la figure 5 illustre en vue perspective de dessus le mode de montage de l'écran au-dessus de la table d'impression ;
• la figure 6 montre plus particulièrement la raclette et la contre-raclette avec leurs bras porteurs dans leur disposition relative.;
• la figure 7 est une vue en coupe partielle illustrant la raclette dans son montage sur le bras porteur associé ;
• la figure 8 est une vue similaire au niveau des vérins de pression.

Its description is illustrated by the appended drawings, in which:

• FIG. 1 shows a schematic view in longitudinal elevation of the screen printing machine as a whole;
• Figure 2 shows in perspective most of the carriage in position above the printing table;
• Figure 3 shows in partial sectional view the elements functionally associated with the squeegee;
• Figure 4 is the counterpart of Figure 3, this time for the squeegee;
• FIG. 5 illustrates in perspective view from above the method of mounting the screen above the printing table;
• FIG. 6 shows more particularly the squeegee and the counter squeegee with their carrying arms in their relative arrangement .;
• Figure 7 is a partial sectional view illustrating the squeegee in its mounting on the associated support arm;
• Figure 8 is a similar view at the level of the pressure cylinders.

For reasons of clarity, the same elements have been designated in these figures by the same references and the representation of the drawings is schematic.

As shown in the figures, the screen printing machine according to the invention comprises, in supporting structures, an upper frame 4 and a lower frame 5 enclosed in a casing 6.

The lower frame, resting on the ground, carries the printing table 1, which is mounted normally horizontal and movable vertically in a conventional manner. The upper frame is also movable vertically with respect to the lower frame, by four columns 8 in rectangular arrangement, which make it possible to raise or lower the whole of the upper frame, by sliding these columns in fixed guides 72 under the action motorized control and drive mechanisms 71 enclosed in the casing 6. It will be noted here, however, that in certain variant embodiments, this kind of movement of the upper frame, useful in particular for providing access to the screen, is no longer ensured. vertically, but at an angle to the lower frame.

The screen printing screen 2 being mounted in the lower part of the upper frame, the above displacements allow inter alia to move the screen away from the printing table each time a sheet to be printed is brought in from the rear of the machine in the printing position, in synchronism with the evacuation of a previous sheet printed towards the front of the machine. The supply means for printing identical copies in series are also conventional in themselves.

In accordance with the invention, the squeegee (or squeegee) 10 and the counter squeegee (or squeegee) 20 are mounted separately, each under a support bar, respectively the squeegee support bar 12 and the squeegee support bar 22, these two bars being mounted on a master beam 31 of the carriage 3, on either side of this beam which is common to them. The two bars like the beam extend over the entire width of the machine, even beyond the lateral edges of the printing table 1 and whatever the width of the screen 2 used for a series of special impressions.

By cons, only the master beam 31 is truly integral with the carriage 3, being directly welded at its two ends on two symmetrical elements 32 and 33 which carry rollers on horizontal guide rails 7 forming an integral part of the upper frame 4. These rolling elements 32 and 33 are towed in one direction or the other by chains meshing in the conventional manner on an active pinion, when the latter is rotated from an electrically controlled motor 9 (FIGS. 1 and 5), in synchronism with the supply of the successive sheets to be printed.

The bars are themselves movable relative to these same elements 32, 33 both vertically in height and in inclination on the horizontal by rotation on themselves. They thus partly constitute intermediate support means between the scrapers and the mobile carriage. By them will be transmitted the inversion commands between low functional position and high rest position, alternately for the squeegee and the counter squeegee (fig. 6), these commands also being synchronized with the feeding of the sheets.

In another common feature, each bar 12 or 22 sees its vertical displacements relative to the beam 31 guided by rods 13, 23 to which they are linked by extension plates 17, 27 and which slide freely in sleeves 14, 24 formed in the fixed part of the carriage 3, at the level of the rolling elements 32 and 33. However, the rods 13, 23 are also provided in the upper part with knurled and lock nut assemblies 15, 25 which serve to adjust the stop positions for the squeegee arm 12 and the counter squeegee arm 22 respectively, at the end of the vertical stroke. Such a stop determining a low limit position of the counter-squeegee arm is particularly useful to prevent it from coming too close to the screen to the point of damaging it. That of the squeegee is more optional, but it constitutes a safety stop when the squeegee is out of operation and that it therefore does not have to press on the screen, by determining a low limit position of the squeegee arm avoiding that the raclette come in contact on the screen only when it does not have to be active. adjustment of a stop position at the vertical end of the squeegee arm (12), safely determining a low limit position of the squeegee arm avoiding pressure on the screen only when the squeegee does not have to be active. Finally, it is often used to also have thereby an adjustable stop determining a high limit position of the displacements of one and / or the other arm under the action of the associated reversing jacks.

In addition, the connection between each of the arms 12 and 22 and the extension plates 17, 27 takes place at each end by means of a system 16 for adjusting the inclination which determines the orientation of the corresponding arm on its horizontal axis. As is clear from FIGS. 2 and 6, this system involves a threaded stud 36 which is engaged in a slot 37 centered on a horizontal axis of fixed rotation and a cooperating nut which is tightened manually when the position of the stud in the slot corresponds to the desired inclination. Plot 36 and light 37 are respectively provided on complementary flanges facing each other which are integral first with the arm in question and the other with its extension plate. Incidentally, a second locking by nut is provided at the level of the axis of rotation of the flanges one on the other. Such a system, easily accessible from each side of the machine, is particularly simple to use, especially when it is observed that the inclination adjustment can often remain constant from one series of prints to another, insofar as the inclination of the squeegee (or counter-squeegee) is directly determined by that of its carrying arm.

The realization of the carriage is otherwise different depending on whether one considers the support means of the squeegee or those of the counter-squeegee.

It can thus be seen from FIG. 3, as regards the counter-squeegee, that the main beam 31, on the lateral edges of the machine, at the level of the rolling elements 32, 33, is equipped with two pneumatically actuated cylinders 41 and 42, the pistons of which are integral with the end plates 27 extending the arm 22 parallel to the guide rods 23 next to it of these. It is easily understood that by the pressure which is sent to them, these jacks determine the inversion between the two high and low positions of the counter-squeegee 20. The latter is fixed to the arm 22, in its central main part 40, by two removable stirrups 43 and 44, which are locked in the closed position on the arm 22 by lateral screws appearing in FIG. 3. The arm 22, meanwhile, is made in its central main part 40 by a running profile of tubular section rectangular or square.

The homologous reversing means which act on the squeegee to raise or lower it alternately with the counter-squeegee (Figure 6) appear in Figures 2 and 4. They are also cylinders 56 and 57 with pneumatic control , but here they are not fixed and they are arranged in the central part of the machine, on the main beam 31 itself. As they are supplied to exert the pressure necessary to apply the squeegee on the screen in the low functional position, they are slidably mounted both on the beam 31 and on the squeegee support arm 12.

If necessary, three cylinders can be used, for example, rather than two, to better distribute the pressure over a very long squeegee. Furthermore, they can be positioned at will vis-à-vis the middle part of the squeegee used occasionally. Although it may be preferable to limit their number to two, by placing them near the ends of the squeegee grip, as shown in Figure 4.

As it is planned to be able to use on the same machine interchangeable squeegees of lengths variable, the squeegee 10 is removable on the arm 12 and linked to the latter by sliding stirrups. There are shown in the figures two such stirrups 46 and 47, each provided with a locking screw 48 ensuring firm clamping on the arm 12, in positions close to the ends of the squeegee; but here too, one or more could be added at intermediate positions in the case of large squeegees.

The assembly of the inversion and pressure jacks 56, 57 is carried out as it appears in FIGS. 2 or 7. The jack body is integral with a jack carrier block 49 which slides in three grooves 51 formed on the side the along the beam 31. The arrangement of the grooves on a lateral face of the beam 31 has the advantage of avoiding their fouling by splashes of ink. The cylinder block 49 is clamped against the beam 31 in the fixed position chosen by means of a locking handle 52, which acts relative to the single central groove.

The piston rod of the cylinder is linked to the arm 12 by means of a stirrup 53 which has been designed so that it is permanently freely sliding on the arm 12. Therefore, it can be positioned automatically just below the cylinder exerting the overpressure in the low position of the squeegee. Furthermore, the connection between the piston of the pressure cylinder and the squeegee is articulated on the yoke so as to follow the angular orientation given to the arm 12 by means of the tilt adjustment by the system 16.

As is best seen by observing FIGS. 7 and 8, but also in FIG. 2, the arm 12, in its main central part 70, is constituted by a main carrying profile, more precisely a steel tube 72 of square section (analogous to that which constitutes the arm 22 of the actual squeegee), supplemented by a section 73 welded to it and bearing on its upper face. The additional profile 73 laterally has a groove 74 of guiding the sliding of the stirrups 53. This not only makes it possible for the groove 74 to be practically insensitive to fouling by splashes of ink, but also for each stirrup 53 to be freely supported on the upper face of the complementary profile 73.

For this purpose, it is beneficial for the security of the transmission of the pressure forces, although these are generally relatively low, that this support takes place by a flat surface of the stirrup 53. To allow permanent free sliding , it is interposed between the profile and the stirrup of the intermediate parts, called "lardons" in current terms of the trade, which prevent the stirrup from locking on the profile 73, even after the usual screws 76 have been tightened.

The connection between the piston rod 80 of each of the reversing and pressure cylinders 56 acting on the squeegee arm and the stirrup 53 in its vertical position, is articulated as it should be around a material axis lying in line with the axis around which the tilt adjustment is made at the level of the systems 16 connecting the central part 70 of the arm 22 to its end plates 17. A yoke 79 has been shown in FIGS. 2 and 7 which is integral with the caliper 53 and cooperates for this purpose with such a hinge pin provided at the end of the piston rod 80. However, it is preferable that with respect to what is shown here, the two cheeks of the yoke be offset in 90 degree orientation, for convenience of construction and mechanical strength.

The squeegee arm 12 is calculated as a whole to remain rigid under all the operating conditions envisaged. It was therefore planned, in accordance with the invention, to complete the machine with a system for compensating the weight of the squeegee arm 12, which can be seen illustrated in FIGS. 2 and 4, by helical springs 77, maintained in compression in a chamber 78 formed in the rolling elements of the carriage, between a fixed bearing formed by the lower wall thereof and a disc terminating a vertical rod 54 welded at its other end to the upper face of the corresponding end plate extending the squeegee arm 12, so as to constitute a bearing integral with this plate.

Finally, FIG. 5 illustrates the means for receiving the screen 2 on the upper frame of the machine in that they are designed suitable for the use of screens of various dimensions. The clean frame of the screen used 59 rests on side panels arranged transversely 81 and 83, which can be moved manually on the side members 82 of a support frame 60 permanently mounted on the upper frame 4. The screen frame is then fixed in the position chosen by clamping levers 62, operated remotely by means of small pneumatic cylinders 82 mounted on these drop sides.

A motorized lever control system 61 makes it possible to lift the frame 60 from the rear, to rotate it around an axis 63, located at the front of the machine, in order to take off the screen from the sheet in progress. behind the squeegee as it passes. Limit switches 64, 65 for the carriage 3 are arranged on the fixed members of the upper frame 4, in positions which are adjustable longitudinally, by sliding in suitable slots, in correspondence with the length and the position of the screen in its support frame 60, so as to cause the reversal of the direction of drive of the carriage and thus limit its movements in the forward direction as in the return direction relative to the guide rails 7.

Although this has not been shown in all its details in the figures, it is advantageous that the support frame 60 is actually made up of two frames, one in the other, involving an external frame, effectively tilting on the upper frame 4 around the axis 63, and an intermediate internal frame, deformable relative to this main external frame (60).

In this case, a deformation at four points is particularly advantageous. It results, for example, and according to the invention, in the fact that the internal frame consists of four sides which are not integral with each other; which can be moved in translation at the angles of the quadrilateral they form, relative to the external frame. In this case, the deformation is ensured by means of knurling systems, stops and connection plates, without it being necessary for a deformation thus determined during a prior manual adjustment, to extend over more than a few millimeters or centimeters. In practice, however, it is useful to be able to thus have an autonomous and convenient adjustment mode in adaptation to the specific angular deformations of the screen frame 59, while in addition, the screen frame 59 can be without disadvantage. of all lengths and all widths, since it is fixed only on movable drop sides 81,83.

However, and as it already clearly follows from the above, the invention is in no way limited to the details of the embodiment described above, of which it encompasses all the variants remaining within the scope of the invention in accordance with the appended claims.

Claims (11)

Screen printing machine of the type comprising a horizontal printing table and support means for a squeegee and a counter-squeegee on a carriage movable longitudinally above said table in the forward direction and in the return direction, in association with means of inversion to raise and lower alternately said squeegee and said counter squeegee with respect to a screen printing screen interposed between them and said printing table, characterized in that said carriage (3) comprises a master beam (31) integral with means of guiding the back and forth movements of said carriage in rails (7) fixed on an upper frame of the machine, in that said support means comprise an arm (12) carrying said squeegee (10) and an arm (22) carrying said counter-squeegee (20), each of said arms being extended by end plates (17, 27) to which it is linked by means (16) for adjusting its inclination around a horizontal axis ntal which is parallel to it, in that for the squeegee (10) said reversing means alternating with the counter-squeegee are constituted by jacks (56, 57) acting on the squeegee support arm (12) itself , in its central main part, and mounted to slide on said master beam (31), and in that said squeegee arm and said counter-squeegee arm are each individually linked by their end plates to said master beam (31 ) by devices guiding their vertical movements (13-14,23-24). Screen printing machine according to claim 1, characterized in that for the counter-squeegee (20), said reversing means are constituted by jacks (43,44) carried by said master beam (31) and acting on said plates d end which the counter-squeegee support arm (22) has. Screen printing machine according to claim 1 or 2, characterized in that said squeegee is mounted on its support arm (12) by stirrups adjustable in horizontally sliding position on said arm as a function of the width of interchangeable squeegees. Screen printing machine according to claim 1, 2 or 3, characterized in that the pressure of the squeegee on the screen is adjustable by said jacks (56, 57) acting on the squeegee arm itself, in its main part central, in its lowered position. Machine according to any one of Claims 1 to 4, characterized in that the piston rod of each of said jacks (56, 57) acting on the squeegee support arm is in articulated connection with a stirrup for mounting the squeegee on its carrying arm sliding freely along the lateral faces of the latter. Machine according to claim 5, characterized in that said articulated connection is ensured around an axis in line with the axis around which said tilt adjustment is carried out, cooperating with a yoke (79) of said stirrup (53), this the latter having a flat bearing surface on an upper face of the squeegee arm. Machine according to any one of claims 1 to 6, characterized in that said stirrups (53) for mounting the squeegee (10) on its support arm (12) are in permanent sliding connection with said arm (12) through grooves (74) formed in the lateral face of a profile (73) attached to a main carrier profile (72) of said central main part (70) of the squeegee arm (12). Screen printing machine according to any one of the preceding claims, characterized in that said squeegee arm (12) is subjected, at its end plates, to the action of elastic means for compensating for its weight. Screen printing machine according to claim 8, characterized in that said compensating means comprise helical springs (77) compressed between a bearing secured to the end plates of the squeegee bar (12) and a fixed bearing of a chamber ( 78) formed in said carriage. Screen printing machine according to any one of the preceding claims, characterized in that the said squeegee (20) is mounted on its support arm (22) in a fixed position by removable stirrups (43,44). Screen printing machine according to any one of the preceding claims, characterized in that the said screen printing screen is mounted by a frame of its own (59) on side walls (81,83) movable longitudinally on an intermediate internal frame, deformable from preferably at four points, relative to an external main frame (60) fixed on the upper frame (4), tiltable around a tilting axis (63) located at the front of the machine.

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