US 3592132 A
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United States Patent  Inventor Erich Weber Elchgrabenweg 2. Feldlliug, Germany [2|] Appl N01 779.542  Filed Nov. 27, I968  Patented July 13, I971  Priority Nov., 1967  Germuy [3|] P l6 l0 34!).7
 ROTARY FORAMINOUS PRINTING MACHINE WITH MAGNETICALLY ATTRACTED INTERNAL INKER 9Chl-:,5 Dnwllgflp.
[S2] U.S.Cl. [01/119  lnLCl .1 54" 13/04  FleldolScarch 14 [OI/119. I20. I23. I24. I26, I29. H4, I16
 References Cited UNITED STATES PATENTS 1,624,538 4/1927 Crain lOI/l26 'A'II'II 2.109.955 11/1959 Terrierelai 11 101/119 2.419.095 4/1941 Shuttlewortheial 101/119 2.445.140 7/1948 Hanington 101/114 2.091.543 10/1954 111101501101 101/110 3,089.!75 5/1905 11111001 1 1 H 15/250110 3,190,184 1/1905 1mm 1 1 1 1. 101/123 5.210.549 11/1905 m0 101/125 FOREIGN PATENTS 1.201.251 9/1905 Germany 1. 101/119 Primary Examiner Robert E. Puifrey A.r:i:rar1!Examiner--E1 M. Coven Attorney- Watson, Cole, Grindle and Watson ABSTRACT: The specification describes a foraminous printing apparatus in which a squeegee inside a screen or stencil cylinder is flexible in the direction of its length and is adapted to be attracted by a magnet placed under the screen cylinder IIA PATENTED JULISISYI 3593132 saw 1 BF 3 n Vfg [5 EFLICA M/cibr ROTARY FORAMINOUS PRINTING MACHINE WITH MAGNETICALLY ATTRACTED INTERNAL INKER The present invention relates to foraminous printing such as screen printing, stencil printing and film printing making use of rotating screen or stencil cylinders. The invention is more particularly concerned with squeegee arrangements which are provided in the interior of the screen or stencil cylinders. Such squeegees have a V-shape or wedge-shape in radial section and engage the interior of the screen or stencil cylinder along an edge so that during rotation of the screen or stencil cylinder ink, that is to say the material which is to be applied by the printing apparatus, is held in a mass on the upstream side of the squeegee and is pressed into the fine openings of the screen or stencil through it passes, in accordance with the image to be printed, onto paper, textile material, or other sheets to be printed. ln printing machinery with which the present invention is concerned the sheets to be printed are supported on a carrier which can for example be in the form of a rotating rubber belt which moves under the rotating screen or stencil cylinder while being itself supported by a rotary roller.
In the context of such printing machinery arrangements have already been proposed which include the use of a compression spring, a loading weight, or a pneumatic device in order to press the squeegee against the stencil or screen. Also the use of magnetic force has been previously proposed for holding rotary distributor or pressure rollers aainst screens or stencils. Such pressure rollers are, just as is the case with known squeegee mounts, rigid in the longitudinal direction and therefore cannot adapt themselves to the unavoidable unevenesses in the material to be printed and the carrier. In such cases monks and friars result, that is to say the ink density varies and the work cannot be used. In the case of the use of screens or stencils woven from synthetic or natural fibers instead of smooth metal stencils there is the further difficulty that the intersecting warp and weft threads leave recesses between them which make it difficult for a squeegee made ofa hard material to perform its proper function of pressing the ink through the screen or stencil so that a sufficient quantity of it is applied to the sheet to be printed. This difficulty with screens or stencils of woven natural or synthetic fibers cannot be overcome by the use ofa higher pressure on the squeegee and the only result of increasing pressure is to increase the rate of wear of the thin screen or stencil material.
One object of the present invention is to provide a screen printing machine which overcomes these disadvantages without an excessively high force being applied to the squeegee so that unevenesses in the carrier, in the sheet to be printed, or in the screen or stencil itself cannot prevent the printing machine from applying an even ink density.
The present invention consists in a foraminous printing machine comprising a horizontal rotary foraminous cylinder, a horizontal rotary roller whose axis is parallel to that of the cylinder, and which is adjacent to the cylinder for holding a sheet to be printed against the cylinder for printing, a carrier for guiding sheets to be printed between the cylinder and the roller, a squeegee inside the cylinder, the squeegee being flexible along its whole length and comprising material which can be magnetically attracted, and magnet means in the roller for attracting the squeegee.
It has been found with such an arrangement that the part of the squeegee engaging the foraminous cylinder, that is to say the screen or stencil cylinder, can adapt itself to differences in level, that is to say recesses and depressions, in the inside face of the foraminous (that is to say screen or stencil) cylinder due to unevenesses in the carrier, and possibly in the screen or stencil material. Since the screen is extremely thin it is readily deformed to adapt itself to unevenesses in the material to be printed under the action of the edge of the squeegee. In this manner good printed images are obtained and damage to the comparatively delicate screen or stencil material is avoided. It is also possible to print material which has a greater thickness more satisfactorily than hitherto since although the magnetic force may be somewhat weakened by the thickness of the material to be printed, it is still sufficient to draw a flexible squeegee effectively against the screen or stencil along the whole of the length of the squeegee.
In accordance with a preferred form of the invention which is more particularly suitable for metal screens or stencils, the squeegee is made of sheet metal which is angled in radial section so as to define an apical ridge which engages the inside of the foraminous cylinder. The sheet metal can for example be soft iron or another ferrous material which is capable of being magnetically attracted.
In accordance with a further preferred feature of the invention, which is more particularly suitable for screens or stencils of woven natural or synthetic fibers, the squeegee comprises elastically soft, abrasion-resistant material which has a V- shaped radial section so as to define an apical ridge engaging the cylinder, and magnetic material. The soft material can for example be rubber or synthetic resin and the magnetic material can be soft iron. In order to increase the flexibility of the squeegee, the magnetic material can be divided up lengthways into segments.
In accordance with a further preferred feature of the invention use is made of resilient means carrying the squeegee in the cylinder so as to allow it to move bodily in a radial direction while preventing movement about the axis of the cylinder. Mounting means for the squeegee can include holding arm means in the cylinder extending away from the axis of the cylinder, and strip spring means which extends against the direction of rotation of the cylinder from the holding means to the squeegee and is fixed to the arm means and to the squeegee. If required, spring means can be applied for loading the arm means. An especially advantageous arrangement in accordance with the invention is, however, one in which the strip spring consists of a single piece of resilient strip metal which extends from one or more holding arms in a direction opposite to the direction of rotation of the foraminous cylinder in a curved plane as far as the squeegee which is attached to it. With this arrangement the flexibility of the squeegee to adapt itself to the unevenesses is still further increased.
In accordance with a still further preferred feature of the invention the apparatus comprises a hollow shaft extending coaxially through the cylinder and carrying the holding means, the shaft being arranged to act as a supply duct for printing ink. With such an arrangement in which the ink extends under the front part of the squeegee as far as the edge of the squeegee which contacts the cylinder and therefore tends to produce a wedging action on the squeegee owing to the rotation of the cylinder, there is no net upward thrust on the squeegee since the dragging of the squeegee against the cylinder and the tangential component of the thrust exerted by the ink are converted into a downward thrust owing to the particular arrangement of the strip spring extending from the arm means in a direction opposite to the direction of rotation of the cylinder. Therefore, if there is an increase in the resistance offered by the ink in front of the squeegee, it is not necessary to apply any additional force urging the squeegee against the cylinder since the downward thrust on the squeegee is increased so as to overcome the additional upward thrust due to the wedging action of the ink under the front part of the squeegee upstream from its edge which contacts the cylinder. It is thus possible to consider the arrangement as amplifying the force provided by the magnetic means since the downward thrust on the squeegee initially depends upon the magnetic force, and this downward thrust is increased by ink resistance in the cylinder so that the thrust is amplified proportionally. In this manner setting of the squeegee so that it only applies a light pressure in the stationary condition of the cylinder is sufficient for applying sufficient ink through the cylinder for the production of a high quality image.
Further features of the invention will be gathered from the following particular description.
Embodiments of the invention are now described with reference to the accompanying drawings.
FIG. 1 shows a screen printing machine with a screen or stencil cylinder and a squeegee arrangement embodying the invention in accordance with the section line H of FIGS. 2 and 3.
FIG. 2 is a transverse section on a larger scale of the screen printing machine, following the line Il-Il of FIG. I.
FIG. 3 is a diagrammatic side view of a screen printing installation with three screen cylinders in a tandem arrangement.
FIG. 4 is a partial section through a modified form of squeegee arrangement.
FIG. 5 is a partial perspective view and section of a squeegee forming part of an embodiment generally similar to that of FIG. 4 but in which the magnetic armature is segmerited.
The part ofa screen printing machine shown in FIGS. 1 and 2 is more especially adapted for use with metal screens or stencils which are preferably in the form of screen cylinders I made of thin metal sheet perforated in accordance with the image to be printed. Each screen cylinder 1 is carried at both ends by the flanges of two end plates 2 and 3 which are journaled by means of ball of needle bearings 4 on a stationary hollow shaft 5 which passes through the cylinder lengthways. The hollow shaft 5 is carried at positions to the side of the end plates 2 and 3 by stands 6. The cavity or bore 7 in the hollow shaft 5 is closed at both ends by means of plates 8 and is connected by means of a hose connection 9 with a container 10 filled with printing ink 11. The hollow shaft 5 is provided with openings [2 through which the printing ink 11 flows into the interior space 13 ofthe stencil cylinder I.
The bearing bush 14 of end plate 3 of the screen or stencil cylinder I passes through an outer or support bearing 15 in the adjacent stand 6 serving for supporting the hollow shaft 5. To the end of this bearing sleeve 14 a gearwheel I6 is attached which cooperates with a pinion 17 on the output shaft 18 of a stepdown gearing 19 whose input shaft 20 is connected by means of a V-belt pulley 2], a V-belt 22 and a further V-belt pulley 23 on the output shaft 24 of an electric motor 25. With this drive means the screen or stencil cylinder I on the fixed shaft 5 can be caused to rotate in the direction of the arrow S (see FIG. 2).
In the interior space I3 of the screen or stencil cylinder 1 two or more holding rings 27 are fixed on the hollow shaft 5. These rings, which form parts of holding arms 29, can be swung about the axis of the shaft on releasing setting screws 28, the setting screws serving to set the angular position of the arms 29 as may be desired. The holding arms 29 extend radially from the shaft in a downwardly sloping direction in the interior space I3 of the screen or stencil cylinder 1. At the free ends of the holding arms 29 a thin strip spring 20 is attached which is in the form of a thin metal sheet extending along practically the entire length of the screen cylinder I and at the two ends of the cylinder ends slightly short of the flanges of the end plates 2 and 3. This sheet metal plate constituting the strip spring 30 is made of a flexible material such as steel sheet, brass sheet or synthetic resin. If required, the strip spring 30 can be made up of several strip spring elements with axial spacing between them. The strip spring 30 extends from its end attached to the holding arms 29 in a direction opposite to the direction S of rotation of the screen or stencil cylinder I in a curved plane as far as a position near the periphery of the cylinder 1 approximately vertically under the shaft 5. At this position, that is to say at the lower edge of the strip spring 30 there is squeegee 31 extending along the whole length of the strip spring. This squeegee consists of an armature sheet which is of V-shaped cross section. The material is soft iron or other material, such as a steel alloy which is capable of being attracted by a magnet. The angle of the squeegee 31 as seen in a radial section has such a shape that it serves to press the mass of ink II into the screen or stencil cylinder for passage of the material through the whole of the cylinder in accordance with the image to be printed. The strip spring 30 serves to press the squeegee consisting of the angled piece of sheet metal against the interior of the screen or stencil cylinder, the squeegee making actual contact with the interior of the cylinder with its apical ridge or edge 32. The squeegee 31 is not rigid in the direction of its length so that it can be easily bent and thus adapt itself to differences in level along the length of the screen which it overlies, whether these differences be due to differences in the thickness of the screen or stencil material itself or due to the material to be printed or to unevenesses in the sheet carrier 34 about to be described.
The sheet 33 to be printed by means of ink which is pressed through the screen cylinder I by means of the squeegee, is carried on the carrier 34 and held on it temporarily by tacking with glue. In accordance with the embodiment shown the sheet carrier consists of an endless band of rubber sheet which, as shown in FIG. 3, runs over end guide rollers 35 which are journaled in a machine frame 36. The sheet 33 to be printed, for example in the form of a band or strip of paper, textile material or synthetic resin, is, in the embodiment shown in FIG. 3, unwound from a supply roll 37 and passes onto the carrier 34 moving in the direction of arrow G. The material is then printed with three colors in the three printing stations arranged along the carrier 34.
At each printing position, that is to say under the hollow shaft 5 of each stencil or screen cylinder I, the carrier 34 is supported by a hollow cylindrical roller 38 which is journaled on a nonrotary elongated magnet assembly by means of needle bearings 39. The magnet assembly, which is carried at its ends in the stands 6 of the machine, could comprise a series of permanent magnets, but in the embodiment described is made up of electromagnets in order to provide for a variable field strength. The electromagnets 40 are arranged inside the rotary hollow roller 38 and their windings 41 are connected by means of leads 42 with a DC power pack 43 which includes a transformer. The electromagnets 40 can all have U-shaped cores so that their magnetic axes are directed towards the screen or stencil cylinder 1 above for attracting the sheet metal of the squeegee 31 so that it is pressed magnetically along its whole length against the interior face of the screen or stencil cylinder 1. The rotary hollow roller 38 preferably consists of a nonmagnetic material in order not to hinder the attraction of the squeegee by the electromagnets.
The forms of squeegee shown in FIG. 4 and 5 have been devised for use, more especially with screens or stencils woven from natural or synthetic fibers. In this arrangement I make the squeegee of a resilient material, for instance rubber or synthetic resin for the purpose of enabling the edge of the squeegee to adapt itself to the small recesses in the fabric due to the crossing of the weft and warp threads of the screen or stencil fabric. I have found that printing is more satisfactory with a squeegee made of such a resiliently soft material and this I attribute to the material of the squeegee being able to adapt itself to the recesses between the threads of the screen or stencil and thus being able to act more effectively on the ink between the threads. In the embodiment shown in FIG. 4 the lower end of the strip spring 30 is fitted into the squeegee which, as just mentioned, is made of an elastically soft material which is, however, resistant to abrasion against the interior face of the screen or stencil cylinder. The material can be readily selected from available rubbers and synthetic resin on the basis of the property to be obtained. On the squeegee 44 there is an armature sheet 45 which overlies the edge 46 of the squeegee which contacts the interior face of the screen or stencil cylinder.
The armature sheet 45 can, if it is sufficiently flexible extend over the whole length of the squeegee 44 which is V- shaped in radial cross section. Electromagnets as in FIG. I are provided inside roller 38. In order to increase the flexibility of the squeegee and of the shee 45 and in particular to allow for the use of a comparatively thick sheet 45 it is possible to divide the sheet 45 up into parts 45' shown in FIG. 5. These parts 45' have small clearances between them. FIG. 5 also shows that the strip spring 30, instead of consisting of a single metal or other resilient sheet extending along substantially the whole length of the screen cylinder 1, can be made up of separate strips 30 with gaps between them which are considerably greater than the axial width of the strip themselves. These individual strips 30 are attached to the holding arms 29 as was the case with single resilient metal sheet while their lower or free ends are connected with the elastic squeegee 44.
I, A foraminous printing machine comprising a horizontal rotary foraminous cylinder, a horizontal rotary roller whose axis is parallel to that of the cylinder, and which is adjacent to the cylinder for holding a sheet to be printed against the cylinder for printing, a carrier for guiding sheets to be printed between the cylinder and the roller, the roller serving to support the carrier in contiguous relation with the cylinder, a squeegee blade which is held inside the cylinder in a position adjacent to the roller and in pressure contact with the inside of the cylinder, the squeegee blade being flexible along its whole length for flexure in a radial plane in relation to the cylinder and comprising material which can be magnetically attracted, magnet means in the roller for attracting the squeegee, at least one movable lever arm carrying at one free end the squeegee blade, means carrying the other end of the lever arm in a stationary fashion inside the cylinder behind the squeegee blade with reference to the direction of rotation of the cylinder, the squeegee blade having a V-shaped ridge that makes substantially linear contact with the inner surface of the cylinder, a leading side of the blade with reference to the direction of rotation of the cylinder making an acute angle with the carrier.
2. A printing machine in accordance with claim 1 in which the squeegee blade is made of sheet material which is angled in radial section so as to define an apical ridge which engages the inside of the foraminous cylinder.
3. A printing machine in accordance with claim 1 in which the squeegee blade comprises elastomeric abrasion-resistant material which has a V-shaped radial section so as to define an apical ridge engaging the cylinder, and magnetic material forming part of the squeegee blade and extending with the squeegee blade along the interior of the cylinder.
4. A printing machine in accordance with claim 3 in which the magnetic material is divided up transversely into segments.
5. An apparatus in accordance with claim 1 comprising a shaft in the cylinder, holding arm means in the cylinder extending away from the axis of the cylinder and carried by the shaft, and strip means which extends against the direction of rotation of the cylinder from the holding means to the squeegee blade and is fixed to the arm means and to the squeegee blade.
6. An apparatus in accordance with claim 5 in which the strip spring means is in the form of a single resilient sheet extending in an axial direction along substantially the whole length of the squeegee blade.
7. An apparatus in accordance with claim 5 in which the strip means includes several metal strips.
8. An apparatus in accordance with claim I in which the magnetic means is in the form of an elongated assembly which carries the roller.
9. An apparatus in accordance with claim 8 in which the magnetic means comprises a row of electromagnets with their magnetic axes directed towards the cylinder.