EP0423428B1 - Method and apparatus for adjusting the position of a printing squeegee and a flood squeegee in screen printing - Google Patents

Abstract

In a method for adjusting the position of a printing squeegee and a flood squeegee in screen printing, the position-adjusting force, with which the printing squeegee is pressed against the fixed base of the printing carrier, and the position-adjusting force, with which the flood squeegee is pressed against the printing medium applied to the screen stencil during the flooding operation, are generated in each case by a pneumatic or hydraulic control circuit which is independent of the control circuit of the flood squeegee or the printing squeegee, the respective position-adjusting force being optimised by setting the pressure of the pressure medium initially in one or more trial prints or from empirical values and then being kept constant at this determined value in the following prints. A device for carrying out this method employs at least one cylinder unit for generating the respective position-adjusting force and a pressure controller for keeping the pressure of the pressure medium constant, the control circuit of the cylinder unit for the flood squeegee being independent of the control circuit of the cylinder unit for the printing squeegee. To compensate for the weight, the flood squeegee is prestressed in the direction facing away from the screen stencil.

Description

The invention relates to a method for delivering a doctor blade of defined and temporally constant elasticity and a flood doctor in screen printing, the feed movement of the doctor blade taking place in the direction of a solid base for a print carrier to be printed, over which there is a screen stencil and in which the feed movement of the Flood knife in the direction of the stencil.

The invention further relates to a device for performing the method.

The screen printing machines to be considered here have, in addition to a printing squeegee, a flood squeegee, which is alternately lowered with the printing squeegee and has the task of transporting the printing medium applied to the screen stencil back after feeding through the printing squeegee during the printing process and thereby distributing it over the screen stencil.

As is well known, the quality of screen printing depends on many factors, some of which have not yet been mastered in conventional screen printing machines. This includes not only a precisely defined contact pressure of the squeegee to seal between the screen stencil and a solid base during the printing process, but also an exactly defined contact pressure of the flood doctor against the pressure medium applied to the screen template during the flooding process. The Infeed force with which the flood knife is pressed against the printing medium applied to the screen stencil during the flooding process, and the distance between the bottom edge of the flood knife and the screen stencil, have a decisive influence on the type of application of the printing medium on the screen stencil and thus the result of the subsequent printing process.

Up to now, little importance has been attached to delivering the flood knife. It was overlooked that the uniform placement of the printing medium on the screen stencil decisively influences the quality of the screen printing. Irregularities in flooding are reflected in the pressure.

The setting and maintenance of the contact pressure of the pressure or flood squeegee are particularly difficult in that the squeegees have to be lifted off the screen stencil before they are returned and lowered again with the same pressure on the screen stencil after their return. The feed force must remain constant over a large number of printing processes. However, this goal can only be achieved if a pressure squeegee of defined and constant elasticity is assumed. Older squeegees that do not have these properties do not allow stable and controllable conditions and therefore no clean and even screen printing.

A method of the type mentioned is described in the subsequently published German patent application DE-A-38 42 419.3. The infeed force with which the printing squeegee is pressed against the solid base, for example a flat table or a drum, is first optimized in one or more test prints and then kept constant at this value in the subsequent prints. A pneumatic or hydraulic cylinder unit can be used to generate the feed force serve, the delivery force is initially optimized by adjusting the pressure of the printing medium in the test prints and the pressure is then kept constant in the subsequent prints at this determined value.

A method for delivering the flood doctor blade, in which the feed force with which the flood doctor blade is pressed against the printing medium applied to the screen stencil during the flooding process, is precisely defined and kept constant, is not described in the previously published German patent mentioned. The flood knife is also assigned a cylinder unit. However, this serves to move the flood doctor blade up and down during screen printing. This post-published patent application does not show that it can also be used to adjust the delivery force. Only the feed path of the flood knife to the screen template is limited by a stop that e.g. can be located on a locking ring which is arranged on a piston rod extending upward from the cylinder unit for the flood doctor blade. Since the cylinder unit assigned to the flood doctor serves only for the alternating movement of the flood doctor, it is obvious that the control circuit for the cylinder unit is connected to the control circuit for the cylinder unit of the printing doctor. With such a method, however, an optimally defined delivery of the flood doctor blade is not guaranteed.

From DE 29 43 893 A1, a method and a device for printing flat goods with at least one screen printing station has become known, in which a driven stencil running back and forth above the printing area is provided, to which a double squeegee device is assigned. This double squeegee device consists of a lifting and lowering squeegee and a drag squeegee, which work alternately in the movement cycle of the stencil and rest on the stencil in the working position. A counter-pressure roller is located under the template in the area of the double doctor device. For the movement of the pressure squeegee and drag squeegee in the vertical direction, i.e. in the direction of Template, cylinders are provided, to which the doctor blade are attached and which are controlled via pressure lines via a common control unit.

This solution is intended to keep the color gaps between the print reports small in the case of discontinuous printing. The problem of a precise and, above all, constant and therefore reproducible pressing force of the printing doctor or drag doctor cannot be solved with this. This means that successive prints do not have the same print quality.

Other known methods for delivering a pressure doctor and a flood doctor use mechanical adjustment devices, e.g. Spindles, or combinations between spindles and hydraulic cylinders to define the feed movement and the feed force in advance. However, these measures are by no means optimal for screen printing that is clean and even, even with large print runs.

Such a device and a method for feeding the doctor blade of a screen printing machine have become known from DE 36 29 188 A1. Here, the doctor blade is arranged in a doctor blade holder, which is held in the region of its ends by a supporting rod. This support rod is connected to a piston and an associated cylinder via a load cell. Above the cylinder is a nut / spindle arrangement, which then move the cylinder in the vertical direction by means of an electric motor. The doctor blade is delivered in two steps in the direction of a screen frame located below it. First of all, the cylinder is pressurized for rough delivery, so that the piston and thus the doctor blade move downwards until the piston has reached its lower end position. In this position the squeegee is a short distance above the screen frame. The squeegee is then slowly moved further downwards by the spindle / nut arrangement until the load cell indicates the required force.

This solution has the particular disadvantage that the infeed movement in the decisive phase is controlled by a mechanical actuator, the spindle drive that can be moved by an electric motor. The mechanical adjustment of the feed force does not allow a sufficiently sensitive and finely controllable feed movement. It has been shown that an optimally clean and uniform screen printing cannot be achieved with this even with large runs.

The invention is therefore based on the object of providing a method for delivering a printing squeegee and a flood squeegee which ensures a previously precisely defined delivery of the printing squeegee and the flood squeegee which delivers an optimal screen print which can also be reproduced over a large print run.

The object is achieved in that the feed force with which the squeegee is pressed against the fixed base of the printing medium, and the feed force with which the squeegee is pressed during the flooding process against the pressure medium applied to the stencil, by one each from the control circuit of the Flood doctor or the pressure doctor independent pneumatic or hydraulic control circuit is generated, the respective feed force is optimized by adjusting the pressure of a pressure medium of the control circuit in one or more test prints or from empirical values and then kept constant at this value in the subsequent prints.

Due to the independent control circuits for the pressure and flood squeegees, the feed force of the pressure squeegee and the flood squeegee can be optimally adjusted in test runs. In the subsequent prints, the squeegees are then lowered in the same respective delivery force that was used for the last test prints. The delivery movement of the printing squeegee is finally limited by the fixed base of the printing medium after the printing squeegee has reached the constant delivery force Has lowered the screen template and printed it on the print carrier. The infeed movement of the flood doctor blade is limited by the pressure means applied to the screen template after the flood doctor blade has lowered onto it with the determined constant infeed force. By keeping the respective delivery force constant, it is then guaranteed that the same print quality is achieved even with repeated repetitions.

In such designs of screen printing machines, in which the screen template is held in a pivotable frame, care must be taken that the squeegee is only lowered when the screen template is first pivoted back down onto the print carrier and thus onto the solid base. Such a sequence of movements can be achieved by incorporating a time delay. In order to prevent destruction of the screen stencil by the printing squeegee in the event of a failure of such a delay circuit, the delivery path of the printing squeegee measured in the last test prints of the printing squeegee to the solid base is preferably used in the aforementioned method, as already described in DE-A-38 42 419.3 kept constant in subsequent prints. Fixing the infeed path of the flood doctor towards the screen template is also expedient and possibly necessary during flooding and in particular at higher speeds, the flood doctor can penetrate deeper into the printing medium with a constant feed force, which leads to an uneven placement of the printing medium on the screen template. For this reason, the feed path of the flood knife to the screen stencil measured during optimization of the feed force is preferably fixed before flooding and kept constant during flooding.

In the device according to the invention for practicing the method described above, it is proposed that at least one cylinder unit, consisting of a cylinder and a double-acting piston with a piston rod, be provided for generating the respective feed force, that a pressure regulator is provided to keep the pressure of the pressure medium constant , the control circuit of the cylinder unit for the flood doctor blade is independent of the control circuit of the cylinder unit for the printing squeegee and that the cylinder unit is carried by a guide block which has a guide for a holding device of the squeegee holder connected to the piston rod of the cylinder unit.

Keeping the pressure constant has proven to be particularly advantageous in practice, although basically other options for keeping the feed force defined by adjusting the pressure constant are being considered.

The fact that the feed forces are generated by double-acting pistons and pressure regulators are used in control circuits which are formed independently of one another to keep the pressure constant, in connection with the guide block ensuring stable guidance, a print quality which is constant even during long runs can be achieved. The double-acting pistons on the one hand enable the delivery of the pressure and flood doctor blades with a precisely defined pressure force and, on the other hand, a rapid return movement in one step.

Since the flood knife during the flooding process may only bear a relatively low pressure on the pressure medium applied to the screen template, the flood knife is preferably biased in the direction facing away from the screen template.

It is expedient that the feed force of the flood doctor blade is generated exclusively by the cylinder pressure. Therefore, the amount of prestress is preferably at least equal to the weight of the flood doctor blade and its doctor blade holder. The bias can e.g. be generated by a tension spring or a counter cylinder.

The described prestressing of the flood doctor blade in the direction facing away from the screen template also has the advantage that the change between the downward and upward movement of the flood doctor blade can be carried out very quickly.

In a preferred embodiment, the holding device has a cylindrical part which is displaceably guided in a bearing sleeve arranged in the guide block and has a central bore in which a ball is arranged without play and through which the piston rod runs with a lateral play, the lower end the piston rod is firmly connected to the ball.

With the help of this construction, a rigid parallel guidance of the piston rod, in which the piston rod could possibly tilt in the guide block, is avoided.

To arrange the ball without play, the bore of the cylindrical part expediently has a cylindrical extension at one end with an internal thread and a hemispherical base region, the radius of which corresponds to the radius of the ball. A counterpart with a dome-shaped recess directed towards the ball is then screwed into the cylindrical extension, to which the doctor holder is attached.

Since canting can occur in the vertical plane in the case of longer doctor blades, the compensating element on or in the doctor blade holder can be rotated with limited play about an axis pointing in the horizontal guide direction of the flood doctor blade or the pressure doctor blade and displaceable in the horizontal transverse direction to the axis.

The compensating element is expediently arranged between two side walls of the squeegee holder which extend in the horizontal transverse direction of the pressure or flood squeegee and has an elongated hole which extends in the same direction and in which a block is displaceably arranged in the direction of expansion of the elongated hole, the block also being provided Is rotatably attached to both side walls by means of a bolt extending perpendicularly to both side walls.

A particularly stable guidance can be achieved in that the pressure doctor blade and the flood doctor blade or their doctor blade holder are carried by one and the same guide block, which has parallel guides for the holding devices of the two doctor blade holders.

The common guide block for the two doctor blades also has the advantage that they can be easily pivoted with the guide block. The doctor blades can be easily replaced or cleaned by swiveling the guide block.

For this purpose, the guide block can be pivotably supported by a shaft which extends in the horizontal transverse direction of the pressure and flood doctor blade and which is rotatably mounted in a guide block for the pivoting movement.

A pneumatic or hydraulic cylinder unit, which consists of a cylinder and a double-acting piston with a piston rod and is carried by the guide block for the pivoting movement, is preferably used to generate the pivoting movement. A gear wheel which is fixedly connected to the shaft can be mounted in the guide block and can be actuated and locked by a toothed rack connected to the piston rod of the cylinder unit.

In order to enable the doctor blade to be easily replaced or cleaned, the guide block can preferably be pivoted by approximately 90 ° with respect to the vertical position.

• Fig. 1 einen Schnitt in der Vertikalebene der Flutrakel durch die Siebschablone sowie darüber eine schematisch vereinfachte Ansicht der Flutrakel mit den darüber angeordneten Zustellvorrichtungen,
• Fig. 2 einen quer zu dem Schnitt der Figur 1 geführten Schnitt durch die Siebschablone, die darüber angeordnete Druck- und Flutrakel und die darüber befindlichen Zustellvorrichtungen mit teilweise aufgebrochener Ansicht,
• Fig. 3 eine Teilansicht des Schnittes längs der Linie III-III in Fig. 2, aus der insbesondere die Verbindung zwischen Kolbenstange und Rakelhalter und das zwischengeschaltete Ausgleichselement ersichtlich sind, und
• Fig. 4 eine teilweise aufgebrochene Ansicht der Lagerung der die Zustellvorrichtungen tragenden Welle sowie der Schwenkvorrichtung für die Welle.

An embodiment of the invention is described below with reference to the drawing. The drawing shows:

• 1 shows a section in the vertical plane of the flood doctor blade through the screen template and, above it, a schematically simplified view of the flood doctor blade with the delivery devices arranged above it,
• 2 shows a cross section of the FIG. 1 section through the screen stencil, the printing and flood squeegee arranged above it and the delivery devices above it, with a partially broken view,
• Fig. 3 is a partial view of the section along the line III-III in Fig. 2, from which in particular the connection between the piston rod and doctor holder and the intermediate compensating element can be seen, and
• Fig. 4 is a partially broken view of the storage of the shaft carrying the feed devices and the pivoting device for the shaft.

The device shown in the figures works according to a method to be described below. The device shown in FIG. 1 corresponds to the device shown in FIG. 2 except for the locking device contained in FIG. 2 and discussed below. 1 shows a section along the line I-I in FIG. 2.

The device shown in FIG. 4 connects to the shaft shown in FIG. 1 on the left. A corresponding symmetrical device is connected to the shaft on the right.

In the screen printing unit shown in FIGS. 1 and 2, the flood knife 1 is lowered into the flood position. The screen template 2 is lifted during the flooding process from the print carrier, not shown in the drawing, and the solid base. The printing medium 3 is applied to the screen stencil 2 and is transported back from the flood knife 1 in the direction of arrow 4 after the printing process and is distributed over the screen stencil 2. The pressure doctor blade 5, which is arranged approximately parallel to the flood doctor blade 1, is raised during the flooding process, so that it cannot impair the flooding of the printing medium 3.

After the flooding process, the screen stencil 2 is moved downward again to a small distance from the print carrier arranged on the fixed base. The up and down movement of the screen template 2 is effected in the screen printing machine on which this is based, by a pivotable frame in which the screen template 2 is clamped. The squeegee 5 is then lowered against the screen template 2, which is pressed against the solid base for sealing between the screen template 2 and the fixed base.

It is assumed here that a doctor blade 5 comprises a doctor blade 6 made of thin sheet steel and at the lower end thereof a doctor blade profile 7 made of a flexible plastic.

The flood squeegee 1 and the pressure squeegee 5 are each clamped in a squeegee holder 8 which is carried by a guide block 9 via a holding device to be described, which is in turn pivotally supported by a shaft 10. As shown in FIG. 4, the shaft 10 is rotatably mounted in a guide block 12, which is arranged towards a side wall 11 of the screen printing machine, for the pivoting movement.

Above the guide block 9 for the upward and downward movement of the flood doctor blade 1 and the pressure doctor blade 5 are two cylinder units 13 and 14, each of which consists of a cylinder 15 or 16 and a double-acting piston 17 which is supported by a continuous piston rod 19 or 20 is worn. The piston rod 19 or 20 protrudes from the top of the cylinder unit 13 or 14. The lower end of the piston rod 19 or 20 is connected to the holding device to be described for the respective doctor holder 8.

The cylinders 15 and 16 are supplied with compressed air via compressed air connections 21 and 22 by control circuits which are independent of one another, corresponding to the respective changing position of flood knife 1 and pressure knife 5, above or below the piston 17.

Since a single guide block 9 is not sufficient in the case of a longer flood knife 1 and pressure knife 5, two guide blocks 9, which are identical to one another, are shown in FIG. 1.

The delivery devices for the flood doctor blade 1 and the pressure doctor blade 5 carried by the two guide blocks 9 are also identical.

As can be seen from FIG. 2, the flood knife 1 is prestressed in the direction facing away from the screen template 2. The pretension is generated by a tension spring 25 which is arranged between an arm 26 fastened to the doctor holder 8 and an arm 27 fastened to the guide block 9. The preload compensates for the weight of the flood doctor blade 1, the doctor blade holder 8 and the holding device of the doctor blade holder 8 guided through the guide block 9.

The holding device for the flood doctor blade 1 or the pressure doctor blade 5, which has already been mentioned several times, consists of a cylindrical part 28 or 29, which is displaceably guided in a bearing sleeve 30 or 31 arranged in the guide block 9 and has a central bore 32 or 33. The bore 32 or 33 has at its downward-facing end a cylindrical extension 34 or 35 with an internal thread and a hemispherical bottom region 36 or 37. In the cylindrical extension 34 or 35 a ball 38 or 39 is inserted, the Radius corresponds to the radius of the hemispherical bottom region 36 or 37.

The piston rod 19 or 20 of the cylinder unit 13 or 14 arranged on the guide block 9 runs through the bore 32 or 33 from above. The outer diameter of the piston rod 19 or 20 is smaller than the inner diameter of the bore 32 or 33, so that the piston rod 19 or 20 has a lateral play. The lower end of the piston rod 19 or 20 is screwed from above into the ball 38 or 39 along the center thereof.

A counterpart 40 or 41 with a dome-shaped recess 42 or 43 directed towards the ball 38 or 39 is screwed into the cylindrical extension 34 or 35 from below, so that the ball 38 or 39 is free of play but rotatable in the extension 34 or 35 is arranged.

The counterpart 40 or 41 projects with its external thread downward relative to the cylindrical part 28 or 29 and is secured against being unscrewed from the cylindrical part 28 or 29 by a lock nut 44 or 45.

Is on the lower end of the counterpart 40 or 41 the squeegee holder 8 for the flood squeegee 1 or the squeegee 5 attached.

This attachment is made via a compensating element 46. 3, the compensating element 46 consists of an upper plate 47 and a lower block 48, which are screwed together. The plate 47 is fastened to the lower end face of the cylindrical part 28 or 29 by means of a screw 49 countersunk therein.

The lower block 48 has an elongated hole 50 which expands in the horizontal transverse direction of the flood doctor blade 1 or the pressure doctor blade 5. In the elongated hole 50, a cuboid block 51 is also arranged to be displaceable in the direction of expansion of the elongated hole 50. The cuboid block 51 has a bore 52 extending through the elongated hole 50.

This compensating element 46 is arranged between two side walls of the doctor blade holder 8 which extend in the horizontal transverse direction of the flood doctor blade 1 or pressure doctor blade 5. With the aid of a bolt extending through the bore 52 of the cuboid block 51, the block 51 is rotatably attached to the two side walls. The compensating element 46 can therefore rotate in the doctor blade holder 8 with limited play about an axis pointing in the horizontal guide direction of the flood doctor blade 1 or pressure doctor blade 5 and move it in the horizontal transverse direction to the axis.

As can be seen from FIG. 4, the shaft 10 carrying the guide block for the flood doctor 1 and the pressure doctor 5 extends through a bore 53 of the guide block 12 for the pivoting movement and is supported therein by a bearing sleeve (not shown in the drawing). In the guide block 12 a gear 54 is fixedly connected to the shaft 10, that is driven by a pneumatic cylinder unit 55 carried by the guide block 12, consisting of a cylinder 56 and a double-acting piston with a piston rod, for rotating the shaft 10. The piston rod of the cylinder unit 55 actuates a rack 57 which interacts with the gear 54.

On the side of the guide block 12 which is remote from the shaft 10, a recirculating ball unit 58 is fixedly attached. In a screen printing machine that uses a table as a fixed base, the ball circulation unit 58 slides on a guide rail 59 arranged on a side wall 11 of the screen printing machine parallel to the table surface. If, on the other hand, a drum is used as a fixed base, the ball circulation unit 58 is fixed to the side wall 11 of the Screen printing machine arranged.

The cylinder unit 55 for the pivoting movement works in such a way that when compressed air is applied to the upper chamber of the cylinder 56, the guide block 9 is pivoted approximately into a horizontal position and fixed there. In this position, the flood doctor blade 1 and the pressure doctor blade 5 can be easily replaced or cleaned. By pressurizing the lower chamber of the cylinder 56, the guide block 9 is pivoted back into its vertical position and fixed there.

The guide block 9 is preferably attached to the shaft 10 by an expansion dowel 60. Such an expansion dowel 60 permits simple and quick adjustment of the angle setting of the guide block 9 with respect to the shaft 10, which is important for a precisely defined feed movement of the flood doctor blade 1 and the pressure doctor blade 5.

Fig. 2 shows, as already indicated, an additional locking device through which the the last test print measured delivery path of the printing squeegee 5 to the solid base and the flood squeegee 1 to the screen stencil 2 can be set and kept constant in the subsequent prints. This device is a locking ring 61 or 62, which is loosely displaceably placed on the continuous piston rod 19 or 20 and can be fixed thereon by means of a locking screw 63 or 64. Instead of a locking screw, another mechanically, pneumatically or hydraulically adjustable stop can also be used. In addition, means, such as a certain pressure acting on the lower chamber of the cylinder 15, can be provided which prevent the flood knife 1 from lifting under the piston rod 19 under certain circumstances.

The delivery of the pressure doctor blade 5 and the flood doctor blade 1 takes place in the case of a device equipped in this way as follows:

To adjust the flood doctor blade 1, it is lowered towards the screen template 2 by applying air pressure to the cylinder 15 above the piston 17, the locking screw 63 on the locking ring 61 being loosened. On the controller for the air pressure in the cylinder 15, above the piston 17, a pressure value corresponding to the previous experience is set, which has the consequence that the flood doctor 1 presses with a defined feed force onto the compression medium 3 applied to the screen template 2.

A test flooding is then carried out with this air pressure and then checked whether it meets the desired quality requirements. If it is not yet satisfied, the air pressure is adjusted and a further test flooding is carried out. This is repeated until a perfect order from the Compression means results. Then, with the flood knife 1 lowered, the locking screw 63 is tightened and thus the locking ring 61, which rests on the upper end face of the cylinder unit 13 due to its own weight, is blocked in this position. The locking ring 61 is now firmly connected to the continuous piston rod 19.

The delivery force for the pressure doctor blade 5 is optimized in a manner analogous to the method described above for the flood doctor blade 1 by adjusting the air pressure in the cylinder 16. The air pressure in the cylinders 15 and 16 can also be optimized alternately during test flooding and subsequent test printing. The air pressures are adjusted until there is a perfect screen print. In particular, with the device described above, the air pressure values can then be kept constant even with a large number of subsequent pressure and flood processes.

Reference list

1.

Flood knife

2nd

Screen template

3rd

Pressure medium

4th

arrow

5.

Squeegee

6.

Doctor blade

7.

Doctor blade profile

8th.

Doctor blade holder

9.

Guide block

10th

wave

11.

Side wall

12th

Guide block

13.

Cylinder unit

14.

Cylinder unit

15.

cylinder

16.

cylinder

17th

piston

19th

Piston rod

20th

Piston rod

21.

Compressed air connection

22.

Compressed air connection

25th

Tension spring

26.

poor

27.

poor

28

cylindrical part

29.

cylindrical part

30th

Bearing sleeve

31

Bearing sleeve

32.

drilling

33.

drilling

34.

cylindrical extension

35.

cylindrical extension

36.

hemispherical bottom area

37.

hemispherical bottom area

38.

Bullet

39.

Bullet

40.

Counterpart

41.

Counterpart

42.

dome-shaped recess

43.

dome-shaped recess

44.

Lock nut

45.

Lock nut

46.

Compensating element

47.

top plate

48.

lower block

49.

screw

50.

Long hole

51.

Log

52.

drilling

53.

drilling

54.

gear

55.

Cylinder unit

56.

cylinder

57.

Rack

58.

Recirculating ball unit

59.

Guide rail

60.

Expansion dowels

61.

Locking ring

62.

Locking ring

63.

Locking screw

64.

Locking screw

Claims (13)

1. Method of advancing a squeegee (5) of defined and constant elasticity and a doctor blade (1) in silk-screen printing, the squeegee (5) advancing towards a fixed support for a printing carrier to be printed, over which a silk-screen stencil (2) is disposed, and the doctor blade (1) advancing towards the silk-screen stencil, in which the advancing force with which the squeegee (5) is pressed against the fixed support of the printing carrier, and the advancing force with which the doctor blade (1) is pressed against the printing medium (3) applied to the silk-screen stencil (2) during the wiping process are brought about by means of respective pneumatic or hydraulic control circuits which are independent of the control circuits of the doctor blade (1) and of the squeegee (5), respectively, the respective advancing forces being optimized by the adjustment of the pressure of a pressure medium of the control circuit in one or a plurality of test prints or from experimental values, and then being kept constant at these values during the subsequent prints.
2. Method according to Claim 1, characterized in that the advancing travel, measured during the test prints, of the squeegee (5) towards the fixed support and of the doctor blade (1) towards the silk-screen stencil (2) are kept constant during subsequent prints and during wiping.
3. Device for implementing the method according to Claim 1, with a squeegee (5) of defined and constant elasticity which can be advanced towards a printing carrier to be printed, the printing carrier being disposed on a fixed support, and with a doctor blade (1) which can be advanced towards a silk-screen stencil (2), the advance of the squeegee (5) and of the doctor blade (1) taking place by means of a pneumatic or hydraulic advance device, in which, in order to bring about the respective advancing forces, at least one cylinder unit (13, 14) consisting of a cylinder (15, 16) and a double-acting piston (17) with a piston rod (19, 20) is provided, a pressure regulator being provided to keep the pressure of the pressure medium constant, the control circuit of the cylinder unit (13) for the doctor blade (1) being independent of the control circuit of the cylinder unit (14) for the squeegee (5), and the cylinder unit (13, 14) being carried by a guide block (9) which comprises a guide for a locating device of the blade-holder (8), connected to the piston rod (19, 20) of the cylinder unit (13, 14).
4. Device according to Claim 3, characterized in that the doctor blade (1) is biased away from the silk-screen stencil (2).
5. Device according to Claim 4, characterized in that the amount of the biasing is at least equal to the weight of the doctor blade (1) and of its blade-holder (8).
6. Device according to Claim 3, characterized in that the locating device comprises a cylindrical portion (28, 29) which is guided for sliding in a bearing sleeve (30, 31) disposed in the guide block (9) and has a central bore (32, 33) in which a ball (38, 39) is disposed without clearance, and through which the piston rod (19, 20) extends with lateral clearance, the lower end of the piston rod (19, 20) being fixed firmly to the ball (38, 39).
7. Device according to Claim 6, characterized in that the bore (32, 33) in the cylindrical portion (28, 29) comprises, at one end, a cylindrical extension (34, 35) with an internal thread and a hemispherical base region (36, 37), the radius of which corresponds to the radius of the ball (38, 39), a matching element (40, 41) with a dome-shaped recess (42, 43) facing towards the ball being screwed into the cylindrical extension (34), and the blade-holder (8) being fixed to the matching element (40, 41).
8. Device according to any one of Claims 3 to 7, characterized in that the locating device is connected firmly, at its opposite end to the piston rod (19, 20), to a compensating element (46) which is rotatable on or in the blade holder (8), with limited clearance, about an axis pointing in the horizontal direction in which the doctor blade (1) or the squeegee (5) is guided, and which is movable horizontally transverse the axis.
9. Device according to Claim 8, characterized in that the compensating element (46) is disposed between two side walls of the blade-holder (8) which extend horizontally transverse the doctor blade (1) or the squeegee (5) and comprises an elongate slot (50)which extends in the same direction and in which a block (51) is movable in the direction in which the elongate slot (50) extends, the block (51) being fixed rotatably to both side walls with the aid of a bolt extending through it, perpendicular to both side walls.
10. Device according to any one of Claims 3 to 9, characterized in that the squeegee (5) and the doctor blade (1) or the blade-holders (8) thereof are carried by one and the same guide block (9) which comprises parallel guides for the locating devices of the two blade-holders (8).
11. Device according to any one of Claims 3 to 10, characterized in that the guide block (9) is carried pivotably by a shaft 10 which extends horizontally transverse the squeegee (5) and the doctor blade (1) and which is mounted rotatably in a guide block (12).
12. Device according to Claim 11, characterized in that, in order to bring about a pivoting movement, a pneumatic or hydraulic cylinder unit (55) consisting of a cylinder (56) and a double-acting piston with a piston rod is provided and is carried by the guide block (12) for the pivoting movement, and in that a gear wheel (54) fixed firmly to a shaft (10) is mounted in the guide block (12) and can be operated and locked by means of a toothed rack (57) connected to the cylinder unit (55).
13. Device according to Claim 10 or Claim 11, characterized in that the guide block (12) is pivotable through about 90° relative to the vertical position.

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