Abstract:
Disclosed is a stamp head ( 1 ) for printing uneven surfaces, especially agricultural products such as poultry eggs, by means of screen printing. The stamp ink is stored in a tampon ( 5 ) within a stamp chamber ( 2 ) and is transferred to the egg surface with the aid of structures of a small coated screen printing plate ( 4 ). The stamp head ( 2 ) can be fastened to a stamp guiding assembly ( 7 ) via a stamp pressing element ( 10 ) such that an egg stamp ( 50 ) is created which can be vertically moved up and down on a stamp bar ( 18 ), the stamping process being carried out by means of the vertical movement. Several egg stamps ( 50 ) can be mounted on the stamp bar ( 18 ) such that a stamping apparatus is created which allows several eggs to be printed simultaneously.

Description:
TECHNICAL FIELD 
       [0001]    The present invention describes an apparatus for printing uneven surfaces, especially agricultural products such as poultry eggs, by screen printing by means of a stamp head in which a tampon with a stamp ink is housed and which is closed off by a small screen printing plate. 
       PRIOR ART 
       [0002]    Printing apparatus for the printing of uneven surfaces and of poultry eggs have already been known for a long time. 
         [0003]    The egg stamper described in DE 70607 is constructed from a hollow cylinder which is closed off at one end by a stamp surface made of deformable material. This stamp surface is formed in a concave shape, projects into the volume of the hollow cylinder and has raised marks. A plunger is situated inside the hollow cylinder, the diameter of said plunger being selected so that it is movable in the hollow cylinder in a form-fitting manner. When the plunger is inserted into the hollow cylinder up to the stop, the plunger then presses onto the rear side of the stamp surface, so that the stamp surface forms a flat surface. The stamp ink can then be received by pressing the egg stamper onto a stamp pad. The hollow cylinder is held during the stamping process and the stamp surface is pressed onto the surface of the egg, in so doing, the marks of the stamp surface are printed onto the egg. The stamp surface fits itself to the surface of the egg, whereby a good printed image is produced. This stamping process corresponds to a high pressure method. 
         [0004]    This apparatus can only be operated manually, which results in a variable and non-reproducible pressure force. In order to obtain good stamper results, the fact that the diameter of the hollow cylinder and the concave curvature of the stamp surface are coordinated with the surface of the egg appears to play a part. 
         [0005]    A further arrangement for printing uneven surfaces is pursued in GB 191121471, in which a template printing device is described for marking animals, which is combined with a printing ink container. The cylindrically shaped printing ink container with a round cross-section is provided on one side with a template which is mounted on or screwed on. The opposite side of the container is closed by a cover through which a plunger is inserted concentrically and movably, which in the interior of the container presses the stamp ink through a piston ring in the direction of the template. 
         [0006]    Before the stamping process, the plunger together with the cover is moved away from the printing ink container, so that the stamp ink can be fed in. Then the plunger and the cover are put in place again and the ink container is positioned on the surface which is to be printed. The plunger is then pressed in the direction of the template, whereby the stamp ink is pressed through the template and forms the desired marks on the surface. 
         [0007]    This prior art also describes a manual printing of uneven surfaces and therefore a non-reproducible pressure force of the template onto the printing surface. Thereby, differing amounts of printing ink are applied onto the printing surface during the printing processes. 
         [0008]    EP 1457108 describes a stamp of a hollowed-out and rotationally symmetrical container made of a soft plastic or rubber, on the underside of which a coated, convex and flexible membrane is fastened which closes off the stamp so that the interior of the stamp can be filled with a stamp ink. The membrane is coated with a film into which a structure is etched photochemically, which structure forms the stamp motif. During stamping, the stamp ink travels through the structure and arrives onto the surface of the egg. 
         [0009]    In addition to two holes on the upper side of the stamp for filling the stamp with the stamp ink, a bore is provided for fastening the stamp on a bar in a stamp apparatus. In such an apparatus, several stamps can be arranged in series and by lowering the bar, several poultry eggs can be printed simultaneously. The solution shows an egg stamp which operates by the tampon printing process and is designed as a single-serving system. An exchanging of the stamp motif is not provided. 
       REPRESENTATION OF THE INVENTION 
       [0010]    The object of the present invention is to provide a stamp head which is distinguished by simple and rapid re-filling of the stamp ink and exchanging of the small screen printing plate without dismantling the stamp. Furthermore, the level status of the stamp ink in the stamp head described here has no influence on the quantity of stamp ink which is delivered. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    The invention is described below in connection with the drawings. 
           [0012]      FIG. 1  shows a section through a single stamp head with a spacer element. 
           [0013]    In  FIG. 2  a sectional drawing is shown of a stamp head with a tampon pressing element. 
           [0014]      FIG. 3  shows a stamp device with two egg stamps which are fastened to a horizontal stamp bar. 
       
    
    
       [0015]    In the attached drawing, a preferred example embodiment of the subject matter of the invention is illustrated and is explained by means of the following description. 
       DESCRIPTION 
       [0016]    The multi-part stamp head  1  is constructed from a stamp head  2 , in the simplest case cylindrical in shape, with a circular base surface, in the interior of which a tampon  5  is placed which receives the stamp ink. The stamp chamber  2  is formed by a cylindrical wall  21  which is closed off at the upper end by a covering surface  22 . The cylindrical wall  21  and the covering surface  22  can be formed from one piece, as is shown in the figure, or from two parts which are securely connected with each other or are able to be joined together. 
         [0017]    The thickness of the tampon  5  can be at a maximum equal to the depth of the stamp chamber  2  and hence completely fill the volume of the stamp chamber  2 . The tampon  5  is produced from an open-pored microporous material, such as polyurethane foam for example, which can absorb and store the stamp ink. The surface of the tampon  5  which faces away from the stamp chamber  2  can be flat here, or can be concave (e.g. in the manner of an ellipsoid) in shape. 
         [0018]    In the circular covering surface  22  of the stamp chamber  2  there is situated a ventilation- and re-filling opening  9  in the form of a through-bore which can serve for pressure equalization during the stamping process and for re-filling the stamp ink. The filling of the stamp chamber  2  with the stamp ink can therefore be carried out simply and quickly without dismantling the stamp head  1 . To prevent the stamp-ink from escaping through the ventilation- and re-filling opening  9 , it is advantageous to select the thickness of the tampon  5  to be somewhat smaller than the depth of the stamp chamber  2  and to use a spacer element  20  which is loose or is fastened to the chamber. An inserted spiral spring can serve as a loose spacer element, for example. 
         [0019]    Underneath the tampon  5  there is situated a small screen printing plate  4 , the chamber side  41  of which lies against the tampon  5 . The small screen printing plate  4  consists of a flexible plastic which is elastic, stretchable and hard-wearing. 
         [0020]    The small screen printing plate  4  is coated with a barrier layer of a light-sensitive photo-emulsion or of a light-sensitive film on the delivery side  42 . By exposure with UV light, parts of the barrier layer which are covered in a light-tight manner form transmission channels which are able to be washed out, which form a template for the subsequent printing. 
         [0021]    The barrier layer can be pressed by the stamp ink through the transmission channels from the chamber side  41  up to the pressure side  42  and arrive onto the print object. Different stamp inks with various characteristics are available on the market. Stamp inks are also available for the foodstuffs field which, in addition to the desired characteristics with regard to flow and printing are also licensed by the Health Departments for printing on foodstuffs. To prevent drying out, oil-based stamp inks are used here. 
         [0022]    The small screen printing plates  4  are to be circular in shape and to have a raised form, by the pressure side  42  being curved in a convex manner away from the tampon  5 . During the printing process, the pressure side  42  of the small screen printing plate  4  is lowered until it comes into contact with the surface of the hen&#39;s egg which is to be printed and surrounds the latter, whereby a plane printing of the convex surface of the egg is ensured with the most varied of sizes and shapes of egg. 
         [0023]    The diameter of the small screen printing plates  4  is to be greater than or equal to the diameter of the covering surface  22  of the stamp chamber  2 , so that the small screen printing plate  4  is able to be fixed on the stamp chamber  2  and can span this, without the stamp ink being able to escape onto the print object past the edge of the small screen printing plate  4 . A small screen printing plate mounting  3  with an internal thread  31  which is able to be screwed onto an external thread  32  of the stamp chamber  2  serves for fastening the small screen printing plate  4 , whereby the small screen printing plate  4  is stretched over the tampon  4  and the stamp chamber  2 . The small screen printing plate  4  must be stretched so that an optimum print result is produced and the stamp ink is pressed in a defined manner through the transmission channels lying taut on the curved surface of the hen&#39;s egg. 
         [0024]    The small screen printing plate mounting  3  has an annular wall  35  with the above-mentioned internal thread  31 . A radially inwardly directed collar-shaped pressure surface  33  is formed on the end. This pressure surface  33  can run perpendicularly to the annular wall  35  or, preferably, in an inclined manner. The inclination of the pressure surface corresponds approximately to the curvature of the small screen printing plate  4  along its edge. Likewise, the edge of the cylindrical wall  21  is shaped so as to be adapted to this inclination or is constructed with a rounded pressure edge  34 , so that a defined linear bearing occurs on pressing, without causing a distortion of the small screen printing plate  4 . 
         [0025]    The small screen printing plate  4  is consequently fixed in a taut manner ( . . . ) pressure surface  33  of the small screen printing plate mounting  3  and the cylindrical wall  21  of the stamp chamber  2 , underneath the tampon  5 . In order to tighten the small screen printing plate  4 , the diameter of the small screen printing plate  4  must be slightly greater than the diameter of the stamp chamber  2 , so that a slight pre-stressing occurs, which assists the convex curvature of the small screen printing plate  4 . In addition to the above-mentioned screw connection  31 ,  32 , the small screen printing plate mounting  3  can also be fixed in a clamping manner on the stamp chamber  2 . Thereby, a form-fitting and also a force-fitting connection of stamp chamber  2  and small screen printing plate mounting  3  is possible. 
         [0026]    The components of the stamp head  1 , stamp chamber  2  and the small screen printing plate mounting  3  can be optionally milled from metal, light metal, produced from plastic by injection moulding or manufactured from flexible plastic. 
         [0027]    In order to ensure that the tampon  5  lies against the chamber side  41  of the small screen printing plate  4  and so that the stamp ink reaches the print object during the printing process through the transmission channels, a tampon pressing element  6  can be integrated into the stamp head. Here, the tampon pressing element  6  presses the tampon  5  in the direction of the longitudinal axis of the stamp head  1  against the curved small screen printing plate  4 . The tampon pressing element  6  can be realized for example in the form a helical spring which is placed between the covering surface  22  of the stamp chamber  2  and the tampon  5  and is fixed by milling in the covering surface  22  of the stamp chamber  2 . 
         [0028]    The structure of an egg stamp  50  using the stamp head  1  described above can consist of the stamp head  1 , a stamp pressing element  10  and a stamp guiding assembly  7 . In order to move the stamp head  1  vertically upwards and downwards, it is fastened to the stamp guiding assembly  7 . The fastening takes place via the stamp pressing element  10 , which constitutes an articulated connection, and can be realized by a helical spring, a simple rubber elastic element or a cardan shaft. In a further embodiment, the stamp pressing element  10  can be constructed as a ball joint, on the ball of which the stamp head  1  is mounted. 
         [0029]    The stamp pressing element  10  allows the stamp head to incline as desired in order to ensure a correct stamping of an inclined surface of the material which is to be stamped or respectively the egg shell. 
         [0030]    When a helical spring is used as a stamp pressing element  10 , it is useful to provide a fastening bead  8  on the stamp chamber  2 , so that the stamp pressing element  10  does not slip off from the stamp chamber  2  unintentionally. On the side lying opposite the stamp head  2 , the stamp pressing element  10  is fastened to a stamp pressing weight  11  which presses the stamp pressing element  10  together with the stamp head  1  onto the hen&#39;s egg. The contact pressure of the stamp head  1  onto the egg is defined by the weight of the stamp pressing weight  11  and is therefore always identical. The stamp pressing weight  11  is fastened to a guide rod  13  which runs through a stamp fastening element  12 . In order to achieve a quiet and error-free linear movement, it is expedient to provide a bearing bore  17  in the stamp fastening element  12  with a plastic bearing bush  16 . The linear movement, guided by the guide rod  13 , has play perpendicularly to the longitudinal axis of the guide rod  13 , because a non-rigid stamp pressing element  10  is used. By these means, a linearly guided upward and downward movement of the stamp head  1  is to be achieved with controlled contact pressure, which carries out the screen printing process on the surface of the hen&#39;s egg in a reproducible manner. 
         [0031]    The downward movement of the egg stamp  50  is limited by a movement limiter  14  at the upper end of the guide rod  13 , which can be constructed almost arbitrarily. Damping rings  15  on the surfaces of the stamp pressing weight  11  allocated to the guide rod  13  and of the movement limiter  14  provide for a damped stopping of the upward and downward movement. 
         [0032]    In order to print several hen&#39;s eggs simultaneously, several egg stamps  50  can be arranged in series on a stamp bar  18 . For this, the respective stamp fastening elements  12  of the egg stamps  50  must be mounted on the stamp bar  18 . This can take place in one line for egg tray cartons or even in several lines, so that all the hen&#39;s eggs can be printed simultaneously directly in a 6-, 10- or 12-box. Likewise, poultry eggs can be printed in holding devices on egg transportation installations. 
         [0033]    The stamp bar  18  must be moved in a controlled manner vertically up and down in order to carry out the printing process. In so doing, the stamp heads  1  of the various egg stamps  50  rise and fall. 
         [0034]    The length of the guide rod  13  is designed so that in the absence of an egg in the egg tray carton, the stamp head  1  can not arrive down onto the carton. In addition, however, it is also to be ensured that in the case of the largest conceivable egg, the stamp pressing weight  11  does not come to lie on the stamp fastening element when, in a stamp movement, the stamp bar  18  is disengaged in its lowest position. 
         [0035]    The contact pressure of an egg stamp  50  or respectively of the stamp head  1  is determined by the associated stamp pressing weight  11 . The shape of the small screen printing plate  4  adapts itself to the surface of the egg on contact and curves in a concave shape towards the stamp chamber  2  and dips partially into the latter. Here, the surface of the small screen printing plate lies with its full surface on the egg and the print motif is transferred. 
         [0036]    The printing process is controlled by the articulated stamp pressing element  11 , without damaging the egg surface. 
         [0037]    To re-fill stamp ink, the printing process only has to be briefly interrupted, so that the stamp ink can be re-filled through the ventilation- and re-filling opening  9 . As the small screen printing plate  4  can be easily removed from the stamp head  1 , to change the print motif and, in the case of wear of the small screen printing plate  4  by intensive use, a quick exchange is possible. The egg stamp  50  can therefore be operated again after a very short period of standstill. 
         [0038]    In addition to the printing process by the movement of the egg stamp  50  onto the surface of the egg, the printing process can be carried out by the movement of the egg which is to be printed, by the pressing of the egg towards the stamp head  1  of the egg stamp  50 . 
         [0039]    The stamp head  1  which is very robust and complex here in its construction is a high-grade element with a long lifespan, in which the favourably priced small screen printing plates  4  are easily and quickly exchangeable. As mentioned, the stamp ink is also able to be re-filled without difficulty and quickly. The more expensive stamp head  1  is very easy to operate and all the expendable materials are favourably priced and able to be exchanged without the stamp machine being interrupted for a long time. 
         [0040]    The stamp head  1  can be produced in a conventional manner as a turned piece from metal, which applies both to the stamp chamber  2  and also to the small screen printing plate mounting  3 . However, both parts can also be produced from a flexible plastic, and by injection moulding from plastic or by die casting from certain metal alloys. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           1  stamp head 
           2  stamp chamber 
           3  small screen printing plate mounting 
           4  small screen printing plate 
           5  tampon 
           6  tampon pressing element (optional) 
           7  stamp guiding assembly 
           8  fastening bead for stamp pressing element 
           9  ventilation- and re-filling opening 
           10  stamp pressing element 
           11  stamp pressing weight 
           12  stamp fastening element 
           13  guide rod 
           14  movement limiter 
           15  damping ring 
           16  plastic bearing bush 
           17  bearing bore (in  12 ) 
           18  stamp bar 
           20  spacer element 
           41  chamber side 
           42  pressure side 
           50  egg stamp 
           21  cylindrical wall of the stamp chamber 
           22  covering surface of the stamp chamber 
           31  internal thread of the small screen printing plate mounting 
           32  external thread on the cylindrical wall  21  of the stamp chamber 
           33  pressure surface on the small screen printing plate 
         mounting 
           34  pressure edge on the cylindrical wall  21   
           35  annular wall of the small screen printing plate mounting