Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F15/00—Screen printers
  • B41F15/14—Details
  • B41F15/34—Screens, Frames; Holders therefor
  • B41F15/38—Screens, Frames; Holders therefor curved
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F15/00—Screen printers
  • B41F15/08—Machines
  • B41F15/0804—Machines for printing sheets
  • B41F15/0809—Machines for printing sheets with cylindrical or belt-like screens

Definitions

• the invention relates to a printing unit according to the preamble of claim 1.
• a printing unit for a rotary printing press which has a screen printing cylinder which, together with an impression cylinder, forms a printing nip in which a printing material is printed.
• This known printing unit is only suitable for single-sided printing.
• DE 26 38 344 A1 discloses a printing unit for perfecting with two interacting screen printing cylinders.
• DE 41 13 362 C2 shows a transfer printing machine in which a sheet of paper is removed from a screen printing cylinder by means of a scraper.
• the invention has for its object to provide a printing unit with a screen printing cylinder.
• the second cylinder is also a screen printing cylinder, so that each screen printing cylinder serves in each case for printing on one side of a printing material passed through the printing nip.
• At least one of the two is preferably in order to enable an exact print, also with reference to the edge of a sheet-like printing material Screen printing cylinder equipped with a holding device for the sheet-like substrates.
• a doctor device arranged in the interior of the screen printing cylinder is preferably radially displaceable so that it can avoid the indentation.
• the squeegee devices of both screen printing cylinders each have a working squeegee which touches the latter when ink is pressed through the screen, the working squeegees of both squeegee devices being exactly aligned with one another, so that the working squeegees of one squeegee device each one of the working squeegees on the other Screen pressure compensated.
• This arrangement ensures in a simple manner that there is sufficient pressure in the printing nip to push the ink required for printing through the screens and to transfer it to the printing material, on the other hand, this causes undesirable deformation of each screen due to the pressure of the doctor device arranged in it avoided that the other squeegee device exerts a corresponding counter pressure.
• each doctor device can also have a counter-pressure device spaced apart from the working doctor in the circumferential direction, which is in each case aligned with the working doctor of the other doctor device and whose pressure compensates.
• the doctoring devices In addition to their previously usual task of applying ink to the screen printing cylinder, the doctoring devices also take on the task of the conventionally used impression cylinder.
• Figure 1 is a schematic representation of a printing press with a printing unit.
• FIG. 2 shows the printing unit of the machine from FIG. 1 in a schematic section
• 3a and 3b each show the printing nip and subregions of the screen printing cylinders forming the printing nip according to a first embodiment of the printing unit, in two phases of their rotary movement;
• FIG. 6 shows the printing nip and partial areas of the screen printing cylinder forming the printing nip according to a second embodiment of the printing unit.
• Fig. 1 shows a schematic view z. B. a sheet-fed rotary printing press in which the printing unit 4 according to the invention is used.
• the printing press comprises a sheet feeder 1 with a sheet stack 2, from the top of which sheets, which are automatically kept at a constant level, are fed individually or in scales from a belt conveyor 3 to the printing unit 4, which accepts the sheets individually, prints them and outputs them to a second chain conveyor 6, which in the case of multicolor printing, this feeds further printing units in the manner of printing unit 4 or, as shown here, directly to a delivery stack 5.
• the sheets pass through the printing unit 4 from top to bottom; its structure is shown in Fig. 2 on a larger scale.
• Two transport cylinders 7, of which the upper one is only partially shown in the figure, are each provided on a section 8 of their circumference with holding devices in order to take over sheets to be printed with a register to the edge of the first belt conveyor 3.
• the lower of the two transport cylinders 7 rolls in contact with a first screen printing cylinder 12, which is also equipped on a portion 11 of its circumference with a holding device 29, in particular a gripper bridge 29 (see FIG. 3a) for taking over the sheets from the lower transport cylinder 7 ,
• the first screen printing cylinder 12 forms one together with a second screen printing cylinder 17 Printing nip 14 through which the sheets gripped by the gripper bridge 29 of the first screen printing cylinder 12 are passed.
• the two screen printing cylinders 12; 17 can be rotated together in such a way that the gripper bridge 29 of the first screen printing cylinder 12 meets a channel-like indented section 18 of the second screen printing cylinder 17 with each passage through the printing gap 14.
• 3a, 3b each show a partial area of the two screen printing cylinders 12; 17 in the vicinity of the pressure gap 14.
• Each screen printing cylinder 12; 17 has at its axial ends a support ring 22, on the outer circumference of a sieve 23, z. B. made of silk or polyamide gauze or bronze wire mesh.
• a doctor device 24 is arranged, the position of which in the radial direction by a curved body, here one on the end faces of the screen printing cylinder 12; 17 formed guide slot 26 is controlled, through which a cylindrical guide extension 27 of the doctor device 24 extends.
• the guide extension 27 is mounted on both sides in the direction of the line 28 connecting the axes of rotation of the screen printing cylinder 12 and the screen printing cylinder 17.
• FIG. 3a shows the doctor device 24 in a position in which the gripper bridge 29 of the screen printing cylinder 12 passes through the printing nip 14 between the two cylinders.
• the screens 23 In the area of the gripper bridge 29 or opposite it, the screens 23 have a section 31 indented radially inwards.
• the guide slot 26 has a circular arc-shaped section 33, which is not completely shown in the figure, concentric with the cylindrical outer surface of the screen 23, and a section 32 indented inward, the course of which corresponds to the section 31.
• the course of the section 32 is selected such that when the section 32 moves past the guide extension 27 during the rotation of the screen printing cylinder 12, the doctor device 24 is retracted radially inwards to such an extent that it only exerts a minimal pressure on the screen 23 which does not cause any significant deformation of the screen 23 in the Section 31 leads, or it completely loses contact with the screen 23 and thus does not exert any pressure on its section 31, which could deform it and damage it during operation.
• 3b shows the position of the doctor devices 24 after the section 32 has passed the guide extension 27.
• the circular section 33 of the guide slot 26 holds the squeegee devices 24 pressed against the inside of the screen 23, so that an ink 34 located on a working squeegee 19 of the squeegee device 24 is pressed through the open areas of the screen 23 and in this way against the pressure gap 14 guided sheet of a substrate is transferred.
• the parallelism of the lips 16 is of great importance for a satisfactory printing result; if the lips 16 are not parallel, but intersect, there is the possibility that the screen 23 moves away from the point of intersection before the internal pressure of the squeegee device 24, with the result that little or no ink 34 passes through the screen 23 is passed through and this color is incomplete or not transferred to a sheet guided through the printing nip 14 due to the lack of an effective pressure force.
• the requirements for the parallelism of the lips 16 are higher, the narrower the zone in which the lips 16 and the screen 23 touch. It is therefore expedient to choose the elasticity of the material of the working doctor blades 19 and the contact pressure of the doctor blade device 24 against the screen 23 large enough that there is a sufficient width of the contact zone.
• an axial expansion of the screen printing cylinder 12; 17 of approximately 800 to 900 mm is an extension of the contact zone of at least 0.05 to 1 mm, preferably approximately 0.3 to 0.4 mm in the circumferential direction of the screen printing cylinders 12; 17 desirable. With deviating ones axial extensions, a proportionally larger or smaller width can be selected.
• the doctor device 24 of the screen printing cylinder 17 remains in contact with the screen 23 even during its passage through the indented section 31.
• a deformation of the screen 23 in the section 31 by the doctor device 24 is supported on its outside by a support element 36.
• the support element 36 here has the shape of a bowl or channel, for example, which is evenly curved in cross section. B. made of sheet metal or a rigid plastic, and is anchored at its two axial ends on the end faces of the screen printing cylinder 17.
• the leading and trailing end of the screen 23 are also located in the section 31 where they are covered by the support element 36.
• the support element 36 can be adjustable in the radial direction (arrow 37) in order to adjust the tension of the sieve 23.
• the screen printing cylinder 12 has a corresponding support element 36 in its indented section 31.
• the support element 36 expediently forms a closed plate through which no ink 34 can pass and onto the exterior of the screen printing cylinder 12; 17 can reach.
• FIG 5 shows an alternative construction of the screen printing cylinder 17 on the basis of a detail.
• the support element 36 is here mounted radially inside the sieve 23, and the leading end 42 and trailing end 43 of the sieve 23 overlap one another in that of the Supporting element 36 supported section 31. In this way, the sensitive connection between the two ends 42; 43 of the sieve 23, the z. B. can be welded, protected from contact with the lip 16 of the doctor device 24 and thus against premature wear.
• an actuator for adjusting the doctor device 24 in the radial direction such as the guide slot 26 shown in FIGS. 3a, 3b, could be provided.
• the inner radius of the surface swept by the doctor device 24 fluctuates only minimally, it is considered sufficient to compensate for these fluctuations solely by a radially resilient mounting of the doctor device 24 (not shown).
• edges 46; 47 do not run exactly parallel to a generatrix of the outer surface of the screen printing cylinder 17 or to the lip 16 of the squeegee device 24, but at a small angle to it. It is conceivable, for. B. a sawtooth, rafter or sinusoidal course of the edges 46; 47; preferably the edges 46; 47 each have a helix with a pitch that is a multiple of the axial length of the screen printing cylinder 17.
• FIG. 6 shows in an axial section the surroundings of the pressure gap 14 of a further variant of the printing unit 4 according to the invention, in the same phase of its rotary movement as in FIG. 3b.
• Elements already with reference to FIGS. 3a and 3b described correspond to the same reference numerals and are not described again here.
• the printing unit 4 from FIG. 6 has two different doctor devices 24a; 24b. Each of them comprises a working squeegee 19a or 19b made of an elastically deformable material, with a lip 16 which strokes over the inside of the screen 23 in the course of the rotary movement of the screen printing cylinder 17 in order to press ink 34 through it.
• each doctor device 24a; 24b a counter pressure device 21a; 21 b in the form of a web which extends in the axial direction of the screen printing cylinder 17 over the same length as the working squeegee 19a; 19b extends and has an end face 13 which sweeps over the inside of the screen 23.
• the counter pressure device 21a; 21b is oriented such that the end face 13 of the lip 16 of the working doctor blade 19b or 19a is opposite the other doctor blade device 24b or 24a.
• Abandonment of these counter pressure devices 21a; 21b is an abutment for the working squeegee 19b; 19a to exert pressure which ensures that sufficient quantity of ink passes through the screen 23 and is imprinted on the printing material passed through the printing nip 14 in good quality.
• the end face 13 of the counter pressure devices 21a; 21b can have a width in the circumferential direction of several millimeters. As a result, even if the two doctor blades 24a; 24b ensures that the pressure of each lip 16 is compensated for over its entire length and thus a uniform print quality is achieved over the entire width of the printing substrate.
• the working squeegee 19a lies in front of the counterpressure device 21a in relation to the direction of rotation of the screens 23, and the reverse is the case in the squeegee device 24b.
• the doctor blade device 24b can therefore be designed in a simple manner as a chamber doctor blade, the counterpressure device 21b forming a closing doctor blade.
• the chamber delimited by working squeegee 19b and counterpressure device 21b can be pressurized in order to control the ink throughput.
• the screen printing cylinder 12; 17, the indented sections 31 can be equipped with support elements 36 as shown in FIGS. 4 and 5.
• Section section (26) section (26) color - support element arrow - - - - end, leading end, trailing - - leading edge trailing edge

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Screen Printers (AREA)
• Inking, Control Or Cleaning Of Printing Machines (AREA)

Applications Claiming Priority (5)

Publications (2)

Family

ID=26003973

Family Applications (1)

Country Status (3)

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Family Cites Families (3)

• 2000
  • 2000-12-16 EP EP00991085A patent/EP1250229B1/fr not_active Expired - Lifetime
  • 2000-12-16 WO PCT/DE2000/004502 patent/WO2001054906A1/fr active IP Right Grant
  • 2000-12-16 AT AT00991085T patent/ATE264194T1/de not_active IP Right Cessation

Non-Patent Citations (1)

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