Abstract:
The invention concerns a pad-printing ink cup fitted with at least one magnet ( 10 ). The minimum of one magnet ( 10 ) may be positioned at different heights relative to the plane of the doctor edge ( 22 ), the magnetic force effective in the said plane depending on said heights.

Description:
TECHNICAL FIELD 
     The invention relates to a pad-printing ink cup fitted with at least one magnet. 
     BACKGROUND OF THE INVENTION 
     A pad-printing ink cup is known from the European patent document EP 0 347 762 B 1. In a pad printing machine, the ink cup sits on a printing plate containing recesses in the form of a print picture to be transferred. The ink from the ink cup penetrates the recesses. The printing plate is displaceable underneath the ink cup and as a result the recesses constituting the picture to be transferred a first time shall be situated underneath the ink cup and another time underneath a printing pad (tampon). The pad is lowered onto the ink-filled recesses from which it removes the ink and hence the print image which it transfers—once the printing plate has been moved out of the pad&#39;s vicinity—onto an object to be printed. A pad printing machine is known for instance from the European patent document EP 0 315 769 B 1, (U.S. Pat. No. 4,905,594). 
     The following documents contain further state of the art: DE 196 44 366 A1; DE 195 02 802 A1; DE 42 10 521 A1; DE 40 15 684 A1; EP 0 945 266 A1; WO 99 07 556 A1 and WO 93 04 862 A1. 
     Printing plates illustratively are made of metal or plastic. 
     Depending on the printing-plate surface material, a hard or soft ink cup doctor edge, shall be advantageous. The doctor edge may be constituted by the very wall of the ink cup or by means of a doctor ring affixed to the ink cup wall. The doctor edge may consist of a metal, a plastic or ceramic or another material. 
     Depending on the material of the printing-plate surface and of the doctor&#39;s edge, this edge may be pressed more or less hard against said surface to prevent ink from leaking between the doctor edge and the printing-plate surface. The higher the printing rate (image transfer from printing plate to an object being printed), the more rapidly the ink cup must be moved above the printing plate. However speeds entail dynamic pressures inside the doctor and there will be a commensurate danger of the ink leaking between the printing-plate surface and the doctor edge, or that it will float on the printing-plate ink (aquaplaning). As a result, and depending on the materials of the doctor edge and printing-plate surface and on the printing rate, the doctor edge may have to be pressed harder against the printing-plate surface in order to avoid unduly high friction on one hand and on the other hand to assure cleanly wiping the ink from the printing-plate surface. 
     SUMMARY OF THE INVENTION 
     This problem is solved by a pad-printing ink cup fitted with a cup structure open at its bottom and at the lower end of its wall with a doctor edge to wipe the ink off a printing plate, and further fitted with a magnet situated in the lower zone of the ink cup to attract this ink cup against the printing plate, the ink cup being characterized in that the minimum of one magnet is displaceable relative to the plane of the doctor edge to assume different heights from the plane, the magnetic force effective in the doctor edge plane varying with height. 
     In particular the invention offers the following advantages: 
     The invention allows adjusting in simple manner the magnetic force by which the doctor edge is attracted against the printing-plate surface. In this manner the compression of the doctor edge against the printing-plate surface can be matched to various materials which in practice are used for the doctor edge and/or the printing-plate surface. Moreover the compression against the printing-plate surface can be matched to the various viscosities of the inks in the ink cup and deposited by said ink cup on said plate. Thus the same ink cup can be used for different kinds of printing plates. Henceforth it will no longer be necessary to use different ink cups for different printing plates. Advantageously the doctor edge shall be an exchangeable element allowing affixing different doctor edges to the ink cup wall to match different kinds of printing plates and different kinds of inks or ink viscosities. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is elucidated below by means of an illustrative embodiment and in relation to the drawings. 
     FIG. 1 is a vertical section of a pad-printing ink cup along the plane II—II of FIG. 2, and 
     FIG. 2 is a bottom view of the pad-printing ink cup of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The pad-printing ink cup of the invention shown in the Figures comprises, as seen in horizontal cross-section, a preferably substantially cylindrical wall  2  fitted at its inside and in the lower zone with an annular salient  4  (offset) projecting radially inward and supporting an annular external circumferential rib  6  of a an annular magnet holder  8 . A plurality of permanent magnets  10  is integrated into the annular magnet holder and preferably these are bonded in place by a curing adhesive  12 . Instead of an annular salient  4  running over 360° and/or an annular external circumferential rib  6 , salients or ribs running over only a small part of the circumference may also be used. 
     The external circumferential rib  6  is situated approximately at the half-height of the annular magnet holder  8 . The height differential  14  between the permanent magnets  10  and the top side  16  of the annular magnet holder  8  is larger than their distance  18  to the bottom side  20  of the annular magnet holder  8 . Therefore the height differential between the permanent magnets  10  and the plane containing a doctor edge  22  is a lesser height differential  24  in the embodiment of FIG. 1 when the top side  16  of the annular magnet holder  8  points upward than in a reversed position of the annular magnet holder  8  wherein its top side  16  points down, and its bottom side  20  points up, resulting in a larger height differential  26  between the permanent magnets  10  and the plane of the doctor edge  22 . 
     Accordingly the force exerted by the permanent magnets  10  in their upright positions shown in the plane of the doctor edge  22  in FIG. 1 shall be larger than in the omitted, that is the upside down position of the annular magnet holder  8 . In one case the doctor edge  22  (FIG. 1) is attracted more strongly and in the other case more weakly toward the surface of a printing plate  27  against the surface of a printing plate by a magnetizable body, in particular iron, which may be the printing plate per se or another part added to it, preferably underneath. 
     The height differentials and the height of the external circumferential rib  6  relating to the top side  16  and bottom side  20  of the annular magnet holder  8  determine the magnetic force in the upright position shown in FIG.  1  and in the omitted, upside down position of the annular magnet holder  8 . 
     The distance between the permanent magnets  10  and the doctor edge  22  also can be adjusted using annular spacers between the annular inner salient  6  of the cup wall  2  and the external circumferential rib  4  and thereby also the magnetic force in the plane of the doctor edge. 
     The ink cup is wide open at the bottom and the ink it contains can freely flow down through the annular magnet holder  8  onto a permitting plate  27 . The ink cup also comprises an open upper end  28  which can be sealed by a lid  30  attached to the cup wall  2  and be reopened to refill ink into the cup. 
     The doctor edge  22  may consist of the lower end of the cup wall  2 . In the shown, preferred embodiment, the doctor edge  22  assumes the form of an annular doctor  32  inserted in exchangeable manner into an annular channel  34  in the lower end face  36  of the cup wall  32  and illustratively being sealed by a seal  38 . 
     Magnetizable metal, preferably iron pins  42  are inserted into boreholes  40  in the lower end face  36  and are magnetically attracted by the permanent magnets  10 . As a result the annular magnet holder  8 , that is its external circumferential rib  6 , is magnetically pulled down against the magnetic salient  4  of the cup wall  2  and thereby it is also retained at said annular salient  4  both in the cup&#39;s axial and circumferential direction, when the ink cup is turned upside down. The permanent magnets  10  might be replaced by electromagnetic ones, though this feature so far remains unconventional. 
     A plurality of circumferentially distributed overflow ducts  44  are present between the cup wall  2  and the annular magnet holder  8  and run from the bottom side  20  to the top side  16  of said holder  8 , allowing ink subjected to dynamic pressure during doctoring to flow from the inside of the doctor edge  22  through these ducts from the bottom side  20  to the top side  16 . In the embodiment shown in the Figures, the overflow ducts  44  are in the form of channels running axially in the inside of the cup wall  2  and opposite the annular magnet holder  8 . In another embodiment mode, such ducts also may instead or additionally be present in the annular magnet holder  8 . 
     When seen in horizontal cross section, the cup wall  2  preferably exhibits a cylindrical cross-section, though this cross-sectional contour may vary in other embodiment modes. Preferably the cup wall  2  is made of a non-magnetic material such as aluminum or plastic.