EP0167906A2 - Printing head for a screen-printing machine - Google Patents

Abstract

In the printing head for a screen-printing machine, the printing doctor blade comprises a doctor blade carrier and an elongated support rail, which is inserted detachably into said doctor blade carrier and is made of a hard elastic material, and a profile strip made of soft elastic material. Said profile strip is attached to the edge of the support rail which is at the bottom in operation. A support profile which is made of a hard elastic material and is attached to the doctor blade carrier is provided for supporting the support rail. If the printing head bears an initial doctor blade which is provided for the purpose of improved ink distribution and is lowered alternately with the printing doctor blade, said initial doctor blade is of curved and swivellable construction.

Description

The invention relates to a print head for a screen printing machine, which is guided so that it can be pushed back and forth in the longitudinal direction of the screen and comprises a printing squeegee running transversely to the longitudinal direction of the screen.

These pressure doctor blades have so far been made entirely of flexible material and have an elongated rectangular cross section. At the upper end of this cross-section, the printing squeegees are clamped over their entire length in a holder which, during operation, guides them over the screen at a certain angle, so that the ink applied to them is pressed through by the printing squeegee.

In order to obtain clean prints, the ink must be evenly distributed and the squeegee should rest on the screen over its entire length with the most uniform possible pressure. The squeegee should have a sharp edge on its lower end resting on the screen, but on the other hand it should be soft and elastic so that the screen is not damaged or prematurely worn out.

On the other hand, a pressure squeegee made of soft elastic material bends more or less under the pressure of the holding device, so that the angle at which the squeegee rests on the screen changes.

In addition, the previous squeegees are unstable.

If the pressure doctor blades are made of a hard elastic material in order to keep their deflection as low as possible, then the screens made of textile are quickly damaged or worn out. You are then forced to use metallic sieves, but they have other disadvantages, especially that of a very high price.

The invention has for its object to provide a squeegee for screen printing, which does not have the aforementioned disadvantages, but is relatively soft directly at the support point, but above it is again relatively hard, so that it does not bend too much under pressure from its holding device .

This object is achieved in that the squeegee comprises a squeegee holder with an elongate support rail, which is removably inserted in it, made of a hard elastic material and a profile strip made of a soft elastic material, which is located on the edge of this support rail, which is at the bottom during operation, and is connected to the support rail.

The two-dimensional connection can be made in various ways, for example by gluing or welding, depending on the materials used in each case.

The carrier rail is preferably a plate which is thin in relation to its width or consists of two plates arranged at a distance from one another.

The shape of the support rail can vary within relatively wide limits. For example, the support rail can have a U-shaped cross section, the profile strip being inserted between the ends of its two legs.

Such a relatively thin support rail can hardly be bent transversely to its longitudinal direction, since it consists of a hard elastic material, for example of glass fiber reinforced polyester or also of steel.

The support rail can also be made of plastic, with the edge of the support rail lying below during operation being relatively soft and the remaining part of the support rail set to be relatively soft in a special production process, and these two sections produced in one and the same production process being integrally connected to one another.

For the rest, however, different materials can be used for the profile strip, provided that they are only flexible on the one hand and on the other hand are resistant to the screen printing inks used. In particular, natural or synthetic rubber can be used for the profile strips.

The connection between the support rail and the profile strip is made by gluing or welding or, as stated above, by integrally connecting the two together during manufacture.

If the carrier rail is made of glass fiber reinforced polyester and the profile strip is made of synthetic rubber, it is advisable to press the profile strip on before the polyester has finally hardened. There is then an intimate connection between the mounting rail and profile strip during curing. The method of connection is not the subject of the invention.

According to the invention, the profile strip has a rectangular or L-shaped or U-shaped cross section. The profile strip can also have a T-shaped or E-shaped cross-section, provided that it is inserted between two plates or legs of a support rail.

Finally, it is proposed to arrange two profile strips on both sides of the mounting rail and to connect them to the mounting rail. You can then turn over the squeegee after using one profile bar and use the profile bar on the other side.

Although the pressure doctor blades proposed above are very resistant to deflection because of the hard elastic design of the support rail, they can be bent somewhat over their length. This is desirable if a holding device for the printing squeegee is used, which is provided with a plurality of adjusting screws distributed over the length, so that one can then realize any desired distribution of the pressing forces over the length.

In such screen printing devices, however, in which such an adjustment option is not provided, printing squeegees are expediently used, in which the support rail comprises two plates arranged at a distance from one another.

But you can also use a support rail U-shaped cross section, in which a certain stiffening against deflection is also achieved.

In addition, it is proposed to achieve a further stiffening by one or more beads extending over the length of the support rail or its two plates. These beads can have different cross sections, for example triangular, trapezoidal, square, rectangular or also round.

The profile strip used in the squeegee holder is fastened either by screws or by a tensioning lever or by a pneumatic or hydraulic tensioning device.

The profile strip can also be attached in a simple manner by means of a plurality of balls which are distributed over the length of the blade holder and are under spring pressure.

• Die Menge der von der Druckrakel durch das Siebgewebe hindurchgedrückten Farbe und damit der Farbauftrag auf den Druckträger wird durch die vorgenannte, auf die Druckrakel ausgeübte Kraft, die Form des Rakelprofils und den Anstellwinkel der Druckrakel gegenüber der' Ebene des Siebgewebes beeinflußt und je nach Wunsch gesteuert. Um gleichmäßige Farbaufträge zu erhalten, müssen die vorgenannten Einflußfaktoren also zeitlich so konstant wie möglich gehalten werden.

When designing a printhead with a squeegee, note the following:

• The amount of ink pressed through the screen by the printing squeegee and thus the ink application to the printing medium is influenced by the aforementioned force exerted on the printing squeegee, the shape of the squeegee profile and the angle of attack of the printing squeegee relative to the plane of the screen fabric and controlled as desired . In order to obtain uniform paint applications, the above-mentioned influencing factors must be kept as constant as possible over time.

Unfortunately, however, the soft, elastic materials from which the doctor blade profiles are made are not sufficiently stable chemically and therefore mechanically. Rather, the doctor blade profile absorbs components of the printing inks and thereby changes its density and shape, if only slightly. These changes in the shape and also in the elasticity of the squeegee profile then change the initially set angle of attack and thus also the force exerted by it on the screen fabric.

The aforementioned instability of the doctor blade profiles available today or of the materials from which they are made has the consequence that the ink application changes from print to print, even if only very gradually and imperceptibly with the naked eye. However, as soon as a larger number of prints have been made and the last print carrier is compared with the first one, you can see a clear difference with the naked eye, especially with very thin ink applications and glazed colors.

This difference may be acceptable in certain cases, for example when the individual prints are hung in different places.

However, if you want to put together a large-scale poster from several parts that are individually screen-printed, with the color applications then extending from one section to the other, the case may arise that one section has a stronger print and the next one receives weaker print only at the end of the print series. These differences are immediately noticeable when the large poster is put together, and the entire print job can be spoiled as a result.

On the other hand, the instabilities of the doctor blade profiles mentioned at the outset also affect the length of the profiles in different ways. An originally exactly linear doctor blade profile may then take on a wave form after a certain number of printing processes or at least generate different pressing forces over its length. Under certain circumstances, this means that larger color areas no longer appear uniform, but look cloudy, so that the print job can be spoiled here too.

Of course, worn doctor blade profiles are replaced with new ones. However, since the changes mentioned above already take place after the first printing processes and in a manner that cannot be calculated in advance, a replacement of the doctor blade profile is generally too late. Added to this is the fact that the doctor profiles have to be manufactured very precisely, that is to say they have a constant cross-sectional shape and size over their entire length and a sharply ground pressure edge. The price of such doctor blades is therefore quite high. In addition, the need to replace a doctor blade profile causes a break in printing, which additionally increases the cost.

In order to improve the printing doctor blade in this respect, it is proposed to assign the printing doctor blade a one-part or multi-part support profile made of a hard-elastic material, which extends over and supports the entire length of the doctor blade profile.

It is preferably provided that the support profile has an angular cross section and is arranged such that the end face of the free end his one leg against the doctor profile.

Furthermore, it is proposed that the support profile is attached with its other leg by means of several holders to a holding rail which extends parallel to and at a distance from the doctor holder.

It is preferably proposed that each holder is pivotable about an axis that runs parallel and at a distance from the doctor profile, and that adjusting means are provided for adjusting the inclination of each holder relative to the doctor holder. The adjusting means expediently each comprise an adjusting screw which support the holder and the doctor holder against one another and are screwed into a threaded bore in the holder.

If it turns out during printing that the doctor profile is not quite evenly aligned over its length or for other reasons the ink application across the doctor profile is different, these irregularities can be eliminated by the fact that the support profile over its length in several with each other not connected sections is divided, which support the doctor blade profile together and which are assigned adjusting screws.

Depending on your wishes, the support profile on the squeegee, namely on its support rail, can either engage somewhat closer to the clamping point or closer to the profile bar. Preferably, the support profile is adjustable parallel to itself, so that you can change the spring constant of the squeegee and thus its pressure properties as desired.

Furthermore, it is proposed that the support profile 1 can be pivoted about an axis which runs parallel and at a distance from the working edge of the profile strip, and that an adjusting screw is provided for adjustment, which is supported on the doctor holder. With this design, the angle which the profile strip forms with the screen fabric or the like can still be adjusted within certain limits when the doctor holder is firmly clamped.

Another, simpler design of the support profile consists of an angle assigned to the printing squeegee, which is supported with its one leg against the part of the printing squeegee adjacent to the clamping point of the support rail and is attached to the squeegee holder with the other leg. By choosing an angle with a fixed length of the support leg, you can also give the squeegee a certain spring characteristic.

Finally, it is proposed to provide a joint in the squeegee holder of the squeegee between the part to be clamped in the screen printing machine and the other part which removably carries the squeegee, to which a spring means for pressing the clamped support rail against the screen printing surface is assigned. With such a design, the pressure force can be adjusted very precisely.

The printhead according to the invention in the manner described above can also carry in a manner known per se, in addition to the printing squeegee, a preliminary squeegee guided together with it, which is offset in the longitudinal direction of the screen relative to the printing squeegee and can be lowered or lowered alternately with the printing squeegee can be raised.

Such a known doctor blade serves for the uniform distribution of the printing ink applied to the screen. In the known print heads, the pre-squeegee and the print squeegee have a straight working edge. However, since the sieve sags in the transverse direction in the middle, the known pre-squeegee must be pressed down so far that the sieve finally lies more or less well against the straight working edge. Only then can the ink be distributed by moving the doctor blade forward. However, since the known squeegee must be shorter than the width of the screen, the printing ink cannot be evenly distributed up to the edge of the screen.

In order to improve such a pre-doctor blade and thus to make the print head according to the invention more effective, it is further proposed that the pre-doctor blade has an arcuate working edge and is arranged in the print head so as to be rotatable about an axis running through its ends. This axis runs transverse to the direction of movement of the print head and parallel to the print doctor.

This squeegee can be lowered by pivoting about said axis with its arcuate working edge onto the surface of the screen sagging in the transverse direction in the center, the working edge lying against the surface of the screen over its entire length, so that the printing ink moves as the print head moves forward is evenly distributed over the entire width of the sieve. The arch shape of the working edge of the pre-doctor blade can be adapted to the most frequently occurring curvature of the sag of the screen. As the doctor blade moves forward with its arcuate curved working edge, the printing ink applied in the middle of the screen on both sides of the curved working edge decreases slide so that the distribution of the printing ink is effected very evenly up to the lateral edges of the screen.

The pre-doctor blade is preferably formed by an arcuately curved band-shaped element. The band-shaped element is preferably provided at its ends with bearing journals which are aligned with one another and are inserted into corresponding bearings in the print head. As a result, a smaller or greater curvature of the band-shaped element can be achieved by displacing the two bearing journals or at least one of them in the axial direction. This makes it possible to optimally adapt the pre-doctor blade to different screens. Depending on the material of the screen and its mesh size, this will have a larger or smaller sag in the transverse direction, to which the curvature of the pre-doctor can then be adjusted.

• Fig. 1 einen Schnitt durch eine bekannte Druckrakel, aufgesetzt auf ein Siebgewebe mit Druckträger auf einer Druckauflage, in schematisch vereinfachter Darstellung;
• Fig. 2 bis
• Fig. 11 erfindungsgemäße Druckrakeln verschiedener Ausführung, mit einfacher und doppelter Trageschiene und verschiedenen Profilleisten;
• Fig. 12 einen erfindungsgemäßen Rakelhalter mit herausnehmbarer Druckrakel und Spannhebel;
• Fig. 13 einen Schnitt durch eine andere Ausführung eines Rakelhalters mit einer pneumatischen Spannvorrichtung;
• Fig. 14 einen Schnitt durch Teile eines erfindungsgemäßen Druckkopfes mit StUtzprofil;
• Fig. 15 einen Schnitt durch Teile eines abgewandelten erfindungsgemäßen Druckkopfes mit Stützprofil, wobei das Stützprofil schwenkbar und federnd angedrückt ist;
• Fig. 16 eine Teilansicht auf den Druckkopf, gesehen in Richtung des Pfeiles XVI in Fig. 15;
• Fig. 17 einen Schnitt längs der Linie A-A in Fig. 15;
• Fig. 18 einen Schnitt ähnlich Fig. 17, jedoch mit einem mehrteiligen Stützprofil;
• Fig. 19 einen Schnitt durch einen Rakelhalter mit verschiebbarem StUtzprofil;
• Fig. 20 einen Schnitt durch einen Rakelhalter mit verschwenkbarem Stützprofil;
• Fig. 21 einen Schnitt durch einen Rakelhalter mit festem Stützwinkel;
• Fig. 22 einen Schnitt durch einen Rakelhalter mit Spannhebel und Gelenk;
• Fig. 23 einen Schnitt durch einen Rakelhalter mit Gelenk;
• Fig. 24 eine Draufsicht auf einen Druckkopf mit Druckrakel und Vorrakel und auf einen Teil 1 des unterhalb des Druckkopfes liegenden Bereiches der Siebdruckmaschine;
• Fig. 25 eine Ansicht in Richtung des Pfeiles XXV in Fig. 24;
• Fig. 26 einen Schnitt längs der Linie XXVI in Fig. 24 und
• Fig. 27 einen Schnitt durch einen Rakelhalter mit herausnehmbarer Druckrakel und einfacher Kugelbefestigung.

The invention is explained in more detail below in exemplary embodiments with reference to the drawing. Show:

• Figure 1 shows a section through a known squeegee, placed on a screen fabric with printing medium on a print run, in a schematic simplified representation.
• Fig. 2 to
• 11 pressure squeegees according to the invention of various designs, with single and double support rails and various profile strips;
• Fig. 12 a squeegee according to the invention with a removable squeegee and Tension lever;
• 13 shows a section through another embodiment of a doctor blade holder with a pneumatic clamping device;
• 14 shows a section through parts of a printhead according to the invention with a support profile;
• 15 shows a section through parts of a modified printhead according to the invention with a support profile, the support profile being pivotally and resiliently pressed on;
• Fig. 16 is a partial view of the print head, seen in the direction of arrow XVI in Fig. 15;
• 17 shows a section along the line AA in FIG. 15;
• 18 shows a section similar to FIG. 17, but with a multi-part support profile;
• 19 shows a section through a doctor blade holder with a displaceable support profile;
• 20 shows a section through a doctor blade holder with a pivotable support profile;
• 21 shows a section through a doctor blade holder with a fixed support angle;
• 22 shows a section through a doctor blade holder with a tensioning lever and a joint;
• 23 shows a section through a doctor blade holder with a joint;
• 24 is a plan view of a print head with a doctor blade and a doctor blade and of a part 1 of the area of the screen printing machine lying below the print head;
• FIG. 25 is a view in the direction of arrow XXV in FIG. 24;
• Fig. 26 is a section along the line XXVI in Fig. 24 and
• 27 shows a section through a squeegee holder with a removable squeegee and simple ball attachment.

The known squeegee 1 shown in FIG. 1 consists of a squeegee holder 2 and a squeegee profile 3 inserted into a slot in a narrow side thereof. The squeegee holder generally consists of metal or another hard and stable material, while the squeegee profile consists of a more or less soft elastic material, for example made of rubber or a thermoplastic material.

Fig. 1 shows this squeegee 1 in the working position, wherein an edge on the end face of the free end of the squeegee profile 3 touches the top of the screen fabric 5 and the squeegee profile 3 here at an acute angle with respect to the plane of the screen fabric is posed. In the acute angle there is an amount of ink 4 applied to the screen cloth, which is spread over the screen cloth 5 by moving the squeegee 1 (in the drawing) to the right.

A certain, constant pressure is exerted on the squeegee 1 from above, with the result that the squeegee profile 3 bends. Depending on the strength of this force and the shape and size as well as the material properties of the doctor blade profile, the deflection will be more or less strong, so that at the same time the angle of attack to the screen fabric is reduced. Such a bent position 3 'of the doctor blade profile is shown in dash-dot lines in FIG. 1.

During the movement of the printing squeegee 1 over the screen fabric, the printing ink 4 is pressed through the permeable points of the screen fabric and there represents the print job 7 on the print carrier 6 lying under the screen fabric, which rests on a print bed 8. Paper, cardboard, textile, plastic film or the like are used as print media.

As already stated, the contact of the doctor blade profile with the printing ink causes a chemical and physical change in the dimension of this profile and its mechanical properties, so that the deflection changes more or less strongly over time.

In addition, a different deflection over the length of the doctor profile can result from the aforementioned changes.

As described above, according to the invention, not a doctor blade profile can be used made of a soft elastic material in the _R akelhalter, but a support rail of a hard elastic material, which carries a profiled strip made of flexible material at its lower end.

In the figures 2 to 11 different versions of such pressure doctor blades are shown, wherein either a simple support rail 9 or a double support rail 11, 12 and at the lower end of a profile strip 10 are connected to each other. The same reference numerals are used in FIGS. 2 to 11 for the various exemplary embodiments, but with different indices a ... k.

6, 7, 10 and 11, each with a double support rail, have the advantage of an even greater stability against bending thereof. The designs according to FIGS. 4 to 7 of the profile strip allow the one lower working edge of the profile strip to also be used by the opposite lower edge by simply turning the support rail in its holder.

The doctor blade holders shown in FIGS. 12 to 14 and 27, which are inserted into a print head on the upper side, each comprise an elongated block with an approximately rectangular profile, which on the underside carries the support rail or, in the case of FIG. 14, also directly a short pressure profile.

The doctor blade holder 13a shown in FIG. 12 removably carries a support rail 19a made of a hard elastic plastic in a slot 14a on its underside. The determination is made with the interposition of a steel strip 15a by means of several over the length the pressure squeegee distributed tensioning levers 18a, which are pivotably mounted in the opening 16a receiving the steel strip 15a and are provided with eccentrics 17a.

FIG. 13 shows a doctor blade holder 13b with a receiving slot 14b into which a support rail 19b made of sheet steel with a profile strip 20b made of soft rubber which is glued on at the bottom is inserted. Here, too, a steel bar 15b for distributing the clamping forces over the entire length of the support rail is placed on it, which was introduced into the opening 16b. A plurality of cam levers 17b distributed over the length of the doctor holder are also pivotably mounted in this opening. The piston rod of a pneumatic clamping device 22b is articulated to the other ends of these cam levers at 21b. This tensioning device is fastened to the doctor holder 13b by means of an angle 23b. Optionally, all cam levers 17b arranged distributed over the length of the doctor holder 13b can be actuated by a single pneumatic clamping device 22b.

The printing doctor blade 24 shown in FIG. 14 comprises a doctor blade holder 25 made of metal, which can be inserted into a print head (not shown), and a doctor blade profile 26 made of a predetermined softness inserted into a slot of the doctor blade holder. In this case, the squeegee 25 takes over the task of the support rail. This is possible in that the squeegee profile 26, which is made of soft rubber, is supported over its entire length on its side opposite the printing ink 4 by an angled support profile 27 made of sheet steel. The support profile has a lower leg 29, which lies just above the lower free end of the doctor profile 26 against it and thereby supports it. The upper leg 28 the support professional 27 is attached to a holder 30, which is also attached to the printhead.

A simplified form of fastening the support rail in the doctor blade holder is shown in FIG. 27. The squeegee holder 13m with screwed-on cover plate 82 has a slot 80 on the underside for receiving the upper edge of a support rail 19m, and has a plurality of bores distributed over its length, in which there are compression springs 81 and balls 15m acted upon by them. The bores are somewhat narrowed at their openings in the slot 80, which is done in a simple manner by deforming the edges of the bores with a chisel. The balls cannot fall into the slot, but are partially pressed into this slot 80 by the compression springs 15m. The dimensions are such that the balls hold a pressed-in support rail 19m under pressure.

15 and 16, the doctor blade holder 35 carries a solid support rail 25c, into which a profile strip 26c made of soft rubber is inserted on the underside. The support rail 25c is plugged onto the doctor holder 35 and is held thereon by fastening means, not shown.

The squeegee holder 35 also carries a plurality of supports 33 distributed over its length, each of which is fastened to the squeegee holder 35 by means of two fastening screws 34. Each of these carriers 33 has at its lower free end a transverse bore (without reference number) which runs parallel to the longitudinal direction of the doctor holder 35. This bore receives the bearing part 38 of a bearing pin 36, which has a threaded part 37 at its other end. The bearing pin 36 is with this threaded part 37 in a threaded hole in a holder 30c screwed tight. Each of these holders 30c, which is distributed over the length of the doctor holder, is screwed to an angled support profile 27c by means of two screws 31, to be precise with the upper leg 28c thereof, while the lower leg 29c is supported against the profile strip 26c. The support profile 27c is thus supported at several points along its length by such holders 30c, which are each pivotally connected to the doctor holder 35 via the bearing bolts 36 and the supports 33.

The free pivotability of the supporting section 27c opposite the doctor blade holder 35 is, however, at each individual holder 30c by means of a screwed-in this adjusting screw 32 to one side limited currency _- rend a free pivotability in the other direction is limited by that of the legs 29c of the Support profile 27c against the pressure profile 26c.

One can thus cause the individual holders 30c and thus the support profile 27c to pivot counterclockwise (in FIG. 3) by turning the adjusting screws 32 deeper, and thereby the bending which occurs in operation, i.e. after the profile strip 26c has been placed on the screen fabric change this squeegee profile by the supporting force. In particular, if the profile strip 26c should not be aligned quite uniformly over its length, or if the paint application across the profile strip 26c should be different for any other reason, these differences can be eliminated by adjusting the individual adjusting screws 32 in FIG Adjust holder 30c in different ways.

Since the support profile 27c consists of relatively thin sheet steel, one can use the adjusting screws 32 make a slight bend of the support profile 27c along its length in the desired manner, provided that it is only a slight bend.

17 shows the support profile 27c with its lower leg 29c, which rests on the profile strip 26c and supports it.

A stronger deformation of the support profile is no longer possible due to its angled shape. If you want to make major bends, use the multi-part design of the support profile shown in FIG. 18, which here consists of several short parts 27d. The lower legs 29d of these individual parts lie side by side on the profile strip 26d. The upper legs of the individual support profiles 27 d are then each attached to individual holders which can be adjusted independently of one another by means of their adjusting screws (not shown).

It has been shown that with the aid of such a design of the support, it is even possible to make certain desired differences in the color application over the length of the profile strip, which are desired for certain printing tasks.

The service life of such a squeegee is considerably increased compared to the known squeegees, and there are practically no uncontrolled changes even after many printing processes. As tests have shown, the printing capacities of a screen printing machine can be increased by approximately 30% and more.

The squeegee holder 25e shown in FIG. 19 in turn has a slot 14e on its underside, into which a support rail 9e made of sheet steel with a profiled strip 10e made of soft rubber is inserted, a steel strip 15e again being placed underneath and fastened by screws 40.

The doctor blade holder 25e has a further slot at a distance from the aforementioned slot 14e, which continuously runs through it from top to bottom. At certain distances distributed over the length of the doctor holder 25e, however, webs (not shown) are provided which pass through the aforementioned slot and hold the part of the doctor holder 25e located to the left of the slot. In said slot, the upper leg 27e of an angled support profile is slidably arranged, the lower leg of which lies against the support rail 9e. The upper leg of the support profile 27e, which is displaceable in the slot, is provided with a toothing 41 into which a pinion 42 rotatably mounted in the doctor holder 25e engages. This pinion can be rotated by a lever 44, so that the support profile 27e then inevitably moves in the direction of the arrow 43 downwards or upwards. As a result, the free length "1" of the support rail 9e can be changed within certain limits, as a result of which the spring characteristic can then be changed as desired.

It goes without saying that the adjustment of the support profile to change the spring characteristic of the support rail 9e must be carried out uniformly over the entire length. It will therefore be provided at least at the two ends of the doctor holder 25e pinion 42 and ensure a uniform movement of the same. This can be done for example by a continuous common shaft for the two pinions.

In the embodiment according to FIG. 20, the squeegee holder 25f again has a slot 14f on the underside for receiving a support rail 9f made of sheet steel with a profiled strip 10f made of soft rubber placed at the bottom. A steel strip 15f is in turn inserted into the slot, which can be tightened by screws 40f.

At the lower left end in FIG. 20, the squeegee holder 25f has a rounded projection 45, which serves as a pivot bearing for an n support profile 1 27f. This support profile is angled on the underside and presses with the lower leg 29f against the support rail 9f.

A screw 46 is screwed into said projection 45, which extends through a slightly further held hole in the upper leg of the support profile 27f. This support profile can be pivoted to a limited extent.

On the upper part of the support profile, also held by the screw 46, there is a support plate 47 which reinforces the end of the support profile 27f. An adjusting screw 32f is screwed through the upper end of the support professional 1s and the support plate, and its end lies against the adjacent surface of the doctor profile 25f. By screwing in this adjusting screw, the support profile 27f is pivoted counterclockwise and thereby also bends the support rail 9f counterclockwise.

21 shows a doctor holder 25g with a receiving slot 14g and fastening screw or fastening screws 40g. Here too, with the interposition of a steel strip 15g, a support rail 9g made of hard plastic with a profile strip 10g made of soft-elastic plastic glued on at the bottom is used.

A continuous support bracket 48 is screwed onto the underside of the squeegee holder 25g by means of screws 49, which, with its free, downwardly projecting leg, fits snugly against one side of the support rail 9g and thereby supports it. The squeegee holder shown in FIG. 22 consists of an upper part 25h to be clamped in the printhead and a lower part 50 connected to the latter via a joint 51, which again has a slot 14h on the underside for receiving a support rail 9h made of a rigid plastic. Here, too, a steel bar 15h is inserted into the opening 16h and the fastening is carried out by a tensioning lever 18h, which is designed as an eccentric 17h in its part adjacent to the joint. In the upper part 25h of the squeegee holder, a leaf spring 53 is fastened by means of screws 54, which presses with its lower free end against the other part 50 of the squeegee holder and, when the upper part 25h is clamped in, the lower part 50 and thus the support rail 9h is pivoted to the right.

23 shows another embodiment of a two-part doctor blade holder, the two parts 25i and 50i of which are pivotally connected to one another by a joint 51i. The upper part 25i is intended for clamping in the print head of a screen printing machine and has a blind hole 55, into which a helical compression spring 56 is inserted. With a longer length of the doctor holder, two or more such bores with helical compression springs are expediently provided.

The lower part 50i of the squeegee holder is angular in profile and carries, by means of screws 40i, a support rail 9i made of a hard plastic, which carries a profile strip 10i made of flexible plastic on the underside.

The helical compression spring 56 presses with its lower end onto the upper side of the lower part 50i of the squeegee holder and thereby pivots this and with it the support rail 9i counterclockwise.

As already stated at the outset, the print head shown in FIGS. 24 to 26 contains not only the actual print doctor, but also a preliminary doctor connected upstream of it. The printhead is designed so that either the pre-squeegee or the printing squeegee is alternately lowered onto the screen while the other squeegee is raised. This technique is known and the pre-squeegee is used to distribute ink applied to the screen as evenly as possible over the screen before printing.

In order to be able to explain the process better, not only the printhead further developed according to the invention is shown in FIGS. 24 to 26, but also the screen underneath.

This screen 61 of a screen printing machine, which is only indicated by two rails 64, 65 running alongside the screen in the longitudinal direction thereof, can consist of silk, nylon or V2A steel wire or for textile printing of polyester or bronze wire with a different number of meshes. The screen has reinforcements 62 on its longitudinal edges, which are also tensioned when the screen is tensioned in the longitudinal direction. The central area in the transverse direction of the screen, however, depends more or less depending on the different material properties.

In addition to the screen 61, rails 64, 65 run in the longitudinal direction thereof, on which the print head is slidably arranged. The printhead includes two slides 66, 67 guided on the rails, one extending between the slides and for printing on the Sieve 61 lowerable printing squeegee 70 and a preliminary squeegee 71 and 71 ″ offset with respect to the printing squeegee in the longitudinal direction of the sieve. Both the printing squeegee 70 and the preliminary squeegee 71 are carried at their ends by holders 68, 69 which are arranged on the slides 66, 67 The brackets 68, 69 comprise mechanisms by means of which the squeegee 70 can be lowered for printing on the screen 61 and then raised again, and the same mechanism comprises the brackets 68, 69 for the squeegee 71. Both mechanisms cooperate in such a way that when the squeegee is lowered, the squeegee is raised, and when the squeegee 71 is lowered, the mechanisms automatically raise the squeegee 70.

In the embodiment shown in the drawing, the doctor blade 71 is formed by a band-shaped element which is curved in an arc. The curvature is shown in solid lines in Fig. 24. (However, the band-shaped element can also be curved in the opposite direction in the form of an arc, as is illustrated in dash-dot lines at 71 "in FIG. 24.)

The two ends of the band-shaped element carry journals 72, 73. These journals are rotatably supported in the brackets 68, 69. The bearing pin 73 carries a stop disc 77 so that it cannot move further than shown in the drawing into the holder.

The bearing journal 72, on the other hand, is provided with an external thread in the area between the end of the band-shaped element and the holder, onto which nuts 75, 76 are screwed. When the nuts on the threaded portion of the trunnion 72 are screwed away from the end of the band-shaped element, the trunnion 72 becomes out of the holder 69 moved to the other journal 73. A predetermined curvature of the band-shaped element can be set by the displacement of the bearing pin. The set curvature is fixed by tightening the two nuts 75, 76. The free end of the journal 72 is provided with a handle 74 in a rotationally fixed manner. As a result, the entire preliminary doctor blade can be pivoted about the axis of the two bearing journals 72, 73. The curved area of the pre-squeegee can thus be lowered onto the screen, as is illustrated by dash-dotted lines in FIG. 26 at 71 '. As a result, the working edge of the pre-doctor adapts to the sagging surface of the screen.

If printing ink is applied to the center of the sieve and the pre-squeegee is lowered into the desired position after pivoting, as indicated by arrow 78 in FIG. 26, the applied printing ink becomes in front of the arrow head as it moves forward in the direction of arrow X. reach the inclined surface of the doctor blade 71 '. When the print head is moved further in the direction of arrow X, the printing ink, which is initially only in the middle, moves outward along the working edge of the squeegee, that is to say toward the two edges of the ribbon. In this way, the printing ink is distributed over the entire width of the band 61 as the print head moves forward. After this process, the squeegee 71 'is raised by the corresponding mechanism in the direction of the arrow 78, while the squeegee 70 is lowered in the direction of the arrow 79. The pad to be printed is then moved up against the screen as the print head is moved in the direction of arrow X ', the lowered squeegee 70 pressing the ink through the screen onto the pad.

When the printing process has ended, the printing squeegee 70 is raised again in the direction of the arrow 79, as a result of which the preliminary squeegee 71 'lowers onto the screen 61, which is now sagging again in its central region. When the print head is returned in the direction of the arrow X, the printing ink is again distributed evenly over the entire width of the screen 61, so that after the mechanisms have been changed, i. by lowering the squeegee 70 and raising the squeegee 71 ', a new printing process can begin.

If the pre-doctor blade is curved as indicated by the dot-dash line 71 "in FIG. 24, the movements are reversed accordingly.

Claims (32)

1. Print head for a screen printing machine, which is guided in the longitudinal direction of the screen back and forth and includes a transverse to the longitudinal direction of the screen, lowerable on this squeegee, characterized in that the squeegee has a squeegee holder (13, 25) with a in this removably inserted elongated support rail (9, 12) made of a hard elastic material and a profile bar (10, 20, 26) located on the edge of this support rail lying at the bottom during operation and comprising the support rail made of a soft elastic material. 2. Printhead according to claim 1, characterized in that the support rail is a thin plate with respect to its width. 3. Printhead according to claim 1, characterized in that the support rail comprises two spaced plates (11, 12). 4. Printhead according to claim 1, characterized in that the support rail has a U-shaped cross section, the profile strip (10e) between the ends of its two legs (lle, 12e) is inserted. 5. Printhead according to claim 1 to 4, characterized in that the support rail or its two plates or legs has or have one or more beads running along its length. (Figs. 8 to 11) 6. Printhead according to claim 1 to 5, characterized in that the profile strip (10a, g, h, i) has a rectangular cross section. 7. Printhead according to claim 1 to 5, characterized in that the profile strip (10b) has an L-shaped cross section. 8. Printhead according to claim 1 to 5, characterized in that the profile strip (lOd) has a U-shaped cross section. 9. Printhead according to claim 1 to 5, characterized in that the profile strip (10e, lOk) has a T-shaped cross section. 10. Printhead according to claim 1 to 5, characterized in that the profile strip (10f) has an E-shaped cross section. 11. Printhead according to claim 1 to 5, characterized in that two profiles strips (10c, 10c ') arranged on both sides of the support rail (9c) and connected to it. 12. Printhead according to claim 1 to 11, characterized in that the support rail consists of glass fiber reinforced polyester. 13. Printhead according to claim 1 to 11, characterized in that the support rail consists of sheet steel. 14. Printhead according to claim 1 to 13, characterized in that the profile strip consists of natural or synthetic rubber. 15. Printhead according to claim 1 to 5, characterized in that the support rail and profile strip consist of polyvinyl chloride, the lower edge of the support rail forming the profile strip having a higher plasticizer content than the supporting part thereof. 16. Printhead according to claim 1 to 15, characterized in that the fastening of the inserted profile strip (9, 19) in the squeegee holder (25, 50) is carried out by screws (40). 17. Printhead according to claim 1 to 15, characterized in that the fastening of the inserted profile strip (19a, 9h) is carried out by a clamping lever (17a, 18a; 17h, 18h). 18. Printhead according to claim 1 to 15, characterized in that the attachment of the profile strip (19m) by several, over the length of the doctor holder (13m, 82) distributed balls (15m), which are in bores in one side wall of the the profile strip (19m) receiving slot (80) are under the influence of a compression spring (81) and partially protrude into the slot (80), the holes at their mouths in the slot being narrowed and preventing the balls from falling out. 19. Printhead according to claim 1 to 15, characterized in that the fastening of the profile strip (19b) used is carried out by a pneumatic or hydraulic clamping device (17b, 19b, 22b). 20. Printhead according to claim 1 to 19, marked-drawn by a printing squeegee (24) associated, supporting laterally against the squeegee profile (26) and extending over its entire length, one-part or multi-part support profile (27) made of a hard elastic material . 21. Printhead according to claim 20, characterized in that the support profile (27) is angular in cross section and is arranged such that the end face of the free end of one leg (29) lies against the doctor profile (26). 22. Printhead according to claim 21, characterized in that the support pro fil (27) is attached with its other leg (28) by means of several holders (30c) to a holding rail (35) which extends parallel to and at a distance from the doctor holder (25c). 23. Printhead according to claim 22, characterized in that each holder (30c) is pivotable about an axis which runs parallel and at a distance from the doctor profile (26c), and that adjusting means for adjusting the inclination of each holder (30c) relative to the Doctor blade holders are provided. 24. Printhead according to claim 23, characterized in that the adjusting means each comprise an adjusting screw (32) which support the holder (30c) and the doctor holder (25c) against one another and are screwed into a threaded bore in the holder. 25. Printhead according to claim 20 to 24, characterized in that the support profile (27d) is divided over its length into a plurality of sections which are not connected to one another and which jointly support the doctor profile (26d) and to which adjusting screws are assigned. 26. Printhead according to claim 20 to 25, characterized in that the support profile (27 e) is adjustable parallel to itself. 27. Printhead according to claim 26, characterized in that the support profile (27f) is pivotable about an axis which runs parallel and at a distance from the working edge of the profile strip (9f, 10f), and that an adjusting screw (32f) is provided for adjustment, which is supported on the doctor holder (25f). 28. Printhead according to claim 20 to 24, characterized by an angle associated with the printing squeegee (48) which, with its one leg, supports the part adjacent to the clamping point of the support rail of the printing squeegee and with the other leg on the squeegee holder (25g ) is attached. 29. Printhead according to claim 20 to 28, characterized in that the doctor holder consists of two parts (25h, 50h; 25i, 50i) pivotally connected to one another by a joint (51, 51i), to which a spring means (53; 56) is assigned to press the clamped support rail (9h; 9i) against the screen printing surface. 30. A printhead according to claims 1 to 29, which, in addition to the printing squeegee, carries a preliminary squeegee guided together with it, which is offset in the longitudinal direction of the screen relative to the printing squeegee and can be lowered or raised alternately with the printing squeegee on the screen, thereby gekennzeich-net that the squeegee (71, 71 '') has an arcuate working edge and is rotatably arranged in the print head (66, 67) about an axis extending through its ends, which is transverse to the direction of movement of the print head (66, 67) and parallel to the squeegee (70). 31. Printhead according to claim 30, characterized in that the pre-doctor blade (71, 71 ") is formed by an arcuately curved band-shaped element. 32. Printhead according to claim 31, characterized in that the band-shaped element carries at its ends aligned bearing journals (72, 73) which are displaceably displaceable relative to one another in order to set a predetermined curvature in the axial direction.

Images