Abstract:
A device for the application of adhesive and machine and method for manufacturing paper cups. The device applies adhesive, particularly for the manufacture of a paper cup from at least one paper segment, and includes a stamp for the application of the adhesive. The stamp is made of a compression-resistant porous sintered material.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for the application of adhesive, more particularly for the manufacture of a paper cup from at least one paper segment, which device comprises a stamp for applying the adhesive. The invention also relates to a machine and to a method for the manufacture of paper cups. 
     BACKGROUND OF THE INVENTION 
     In the production of paper cups from segments of paper material, it is known to produce these cups from paper that is coated on one or both sides with polyethylene (PE). Such coated paper segments can be joined to each other by sealing, that is to say, by heating the plastic layer. A primer or an adhesion promoter is used at critical sites for increasing the sealability. Such a primer is a type of adhesive and substantially consists of a low-viscosity aqueous polymer solution. Such a primer is applied to the paper segment, for example, with the aid of felt saturated with the primer. The low viscosity of the primer causes the machine to be soiled relatively severely, and the felt used for applying the primer is also subjected to considerable wear and has consequently to be replaced at regular intervals. It is further known to pre-break paper segments, whether coated or uncoated, at a segment edge before they are wound up on a folding mandrel, in order to facilitate the winding process and particularly the production of an overlap on the breaking mandrel. Uncoated paper segments are coated with adhesive in the region of the overlap and then glued to form a sleeve. 
     SUMMARY OF THE INVENTION 
     The invention relates to the provision of an improved device for the application of adhesive and to an improved machine and an improved method for the production of paper cups. 
     For this purpose, a device is provided, according to the invention, for the application of adhesive, more particularly for the production of a paper cup from at least one paper segment, which device comprises a stamp for applying the adhesive, which stamp is made of compression-resistant porous sintered material. 
     It has been found, surprisingly, that adhesive and particularly a low-viscosity primer or adhesion promoter can be readily applied with the aid of a stamp made of compression-resistant porous sintered material. By virtue of the fact that the stamp is made of rigid, non-resilient sintered material, there is practically no wear on the stamp. Furthermore, it is possible to simultaneously apply adhesive and shape the paper segment by pressing the stamp against the paper. It has also been observed, surprisingly, that the adhesive does not create blots or continue to drip at sites other than the intended points of application even in the case of very low-viscosity adhesive such as a primer. Also in the case of very low-viscosity aqueous adhesives, it is possible to achieve a very economical consumption of adhesive. Moreover, it is extremely easy to clean the sintered material, since the stamp can simply be fully immersed in solvent or rinsed with the same. 
     In a development of the invention, the adhesive is supplied from an adhesive supply line to an adhesive applying surface of the stamp, at least partially through the porous sintered material of the stamp. 
     Such an embodiment of the device of the invention is suitable for high cycle rates in the production of paper cups. A continuous supply of adhesive is readily achieved by means of a pressure line. In the case of very low-viscosity adhesive, the application of pressure can, for example, be left until the stamp is resting on the paper segment. With the exception of the adhesive applying surface of the stamp, the other outer surfaces of the stamp are sealed, for example, by simply closing the sintered material by grinding. By virtue of the fact that the adhesive is supplied through the porous sintered material of the stamp, a uniform distribution of adhesive can be achieved over the entire adhesive applying surface of the stamp. 
     In a development of the invention, the sintered material is sintered metal. 
     Sintered metal is compression-resistant and wear-resistant. The flow resistance of sintered metal is suitable for supplying adhesive. 
     In a development of the invention, the porosity of the sintered material is adapted to match the viscosity of the adhesive to be used, the supply pressure in the adhesive supply line and the intended rate of application of the adhesive. 
     In this way, it can be ensured that the exact amount of adhesive required is applied accurately to the paper segment at all times. A low consumption of adhesive can thus be achieved particularly for the series production of paper cups at high cycle rates. 
     In a development of the invention, the adhesive applying surface is provided with a curved shape. 
     In this way, the paper segment can be partly shaped at the same time as the application of adhesive and, for example, a segment edge can be pre-broken concurrently with the application of adhesive in order to facilitate the subsequent winding process of the paper to form a cup sleeve. 
     In a development of the invention, the adhesive applying surface is shaped in the form of a section of a sleeve of a circular cylinder. In this way, the segment edge can be pre-broken reliably in a manner that facilitates the subsequent winding process. 
     The problem underlying the invention is also solved with the aid of a machine for the production of paper cups, which machine comprises a device of the invention for the application of adhesive. In such a machine, the device for the application of adhesive can be provided in a pre-breaking station for at least partial formation of a paper segment. In this way, the formation of the paper segment and the pre-breaking process can be effected concurrently with the application of adhesive and it is possible to economize on an additional processing station, if necessary. 
     The problem underlying the invention is also solved by a method for the production of paper cups, which method comprises the following steps: placing the adhesive applying surface of a stamp made of compression-resistant porous sintered material on a portion of a paper segment to be subjected to gluing, supplying adhesive from an adhesive supply line through the sintered material of the stamp to the adhesive applying surface and joining the paper segment by adhesion to form a cup sleeve by producing an overlap over at least that portion of the paper segment to which adhesive has been applied. 
     In a development of the invention, the paper segment is deformed at the same time as the stamp is placed thereon. Advantageously, one edge of the paper segment is pre-broken concurrently with impression by the stamp. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features and advantages of the invention will become apparent from the claims and the following description of preferred embodiments of the invention, with reference to the drawings. Individual features of the different embodiments illustrated can be combined with each other in any desired way without going beyond the scope of the invention. In the drawings: 
         FIG. 1  is a sectional view of a device of the invention for the application of adhesive, 
         FIG. 2  is a lateral view of the device shown in  FIG. 1 , 
         FIG. 3  is a view, taken obliquely from above, of a paper segment used for producing a paper cup, 
         FIG. 4  is a side view of the paper segment shown in  FIG. 3 , 
         FIG. 5  is a view of a cup sleeve produced from the paper segment shown in  FIG. 3 , 
         FIG. 6  is a diagrammatic sectional view of another device of the invention for applying adhesive, 
         FIG. 7  is a diagrammatic top view of the device shown in  FIG. 6 , and 
         FIG. 8  is a diagrammatic sectional view of another device of the invention for the application of adhesive, 
         FIG. 9  is a part of another device of the invention for the application of adhesive, and 
         FIG. 10  is a section of another device of the invention for the application of adhesive. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A pre-breaking station  10  of a machine for producing paper cups is shown in  FIG. 1 . Paper segments  12  that are coated by a plastics material on one side are processed to form paper cups with the aid of such a machine. At the pre-breaking station  10 , the paper segment  12  is deformed in the region of one edge and, at the same time, adhesive is applied in the region of this deformed edge with the aid of a device  14  for the application of primer. The term “primer” denotes a special adhesive that forms an aqueous solution containing plastics material. This primer is applied to the plastic-coated side of the paper segment  12  and serves as an adhesion promoter in the process of thermally sealing the paper segment  12 . 
     Downstream of the pre-breaking station  10 , the pre-broken paper segments  12  provided with primer are wound on a folding mandrel and joined to each other in the region of a resulting overlap by means of a thermal sealing process. The finished cup sleeve is then provided with a bottom and optionally with a mouth roll. For example, it is possible to push on an additional, insulating sleeve made from another paper segment, in order to produce a double-walled insulating cup. 
     The device  14  for the application of adhesive comprises a stamp  16  made of a porous but compression-resistant sintered metal. This stamp  16  is attached to a stamp carrier  18  that can be moved up and down in the directions of the double arrow  20 . The stamp  16  is also referred to as the “lower pre-breaking bar” and is moved toward an upper pre-breaking bar  22  when moved upwardly. The paper segment  12  present between the stamp  16  and the upper pre-breaking bar  22  is consequently deformed since it is bent up in the region of its edge (not visible in  FIG. 1 ). The stamp carrier  18  is attached to a mainframe  24  for vertical displacement with the aid of screw bolts  26  which can slide up and down in elongated holes (not visible) in the mainframe  24 . A balcony-like projection  28  of the stamp carrier  18  is biased with the aid of a pressure spring  30  in a downward direction away from the upper pre-breaking bar  22 . 
     In the stamp carrier  18 , a liquid duct is provided which can be connected by means of a union  32  to an adhesive supply line. Starting from the union  32 , adhesive—in the present case, the so-called primer—can flow into the liquid duct and up to the stamp  16  by way of a number of branch ducts. The primer is pressurized and can therefore spread out inside the stamp  16  consisting of porous sintered metal. The primer is thus discharged at an adhesive applying surface  36  of the stamp  16 , which surface has a curved shape and, in particular, the shape of a section of the sleeve of a circular cylinder. When the stamp  16  is moved in the direction of the upper pre-breaking bar  22 , a paper segment  12  present between the stamp  16  and the upper pre-breaking bar is thus deformed in the region of its edge and provided with primer on one side thereof. 
     A collecting trough  38  is provided below the stamp carrier  18  to collect any primer that may emerge. The exposed lateral surfaces of the stamp  16  are sealed with the exception of the adhesive applying surface  36  so that the primer can be discharged exclusively at the adhesive applying surface  36 . Such sealing of the stamp  16  can be effected by simply closing the lateral surfaces to be sealed by grinding. 
       FIG. 2  illustrates a side view of the pre-breaking station  10  shown of  FIG. 1 . An end plug  40  is clearly seen in the stamp carrier  18 . The diameter of the end plug  40  is equal to that of a liquid duct running transversely through the stamp carrier  18  into the drawing plane of  FIG. 2 , that is to say, parallel to the stamp  16 , and the union  32  for the adhesive supply line is provided on the rear side (not visible in  FIG. 2 ) of the liquid duct. Starting from the liquid duct closed with the aid of the end plug  40 , branch ducts  42  extend inside the stamp carrier  18  upwardly and toward the stamp  16 . These branch ducts  42  are actually not visible in  FIG. 2  and are therefore indicated by dashed lines. The stamp  16  is provided with blind bores  44  in continuation of the branch ducts  42 , which blind bores likewise cannot in fact be seen and are therefore indicated by dashed lines. The low-viscosity primer flows through the branch ducts  42  and the blind holes  44  into the interior of the stamp  16  and, since the exposed lateral surfaces of the stamp  16  are sealed with the exception of the adhesive applying surface  36 , this low-viscosity primer is discharged exclusively in the region of the adhesive applying surface  36 . It can be clearly seen that the curvature of the adhesive applying surface  36  is adapted to match that of the upper pre-breaking bar  22  so that the paper segment  12  is accommodated between the convexly curved edge of the upper pre-breaking bar  22  and the concavely curved adhesive applying surface  36  and, as a result, is curved upwardly when the stamp carrier  18  is moved upwardly against the force of the pressure spring  30 . The stamp carrier  18  can be pushed upwardly by pneumatic means, for example. While the adhesive applying surface is resting against the paper segment  12 , the primer is discharged and that portion of the paper segment  12  which is adjacent to the adhesive applying surface  36  is wetted by the primer. 
     The porosity of the stamp  16  is adapted to match the viscosity of the adhesive used and the intended rate of application of the adhesive to the paper segment  12 . Advantageously, the primer is supplied to the union  32  under pressure in the adhesive supply line, and it may be advantageous to switch on the pressure means only when the stamp carrier  18  has been moved upwardly and the paper segment  12  has been clamped between the stamp  16  and the upper pre-breaking bar  22 . As soon as the stamp carrier  18  has moved down again, the pressure is removed from the adhesive supply line so that no further primer can be discharged from the adhesive applying surface  36 . 
       FIG. 3  diagrammatically shows the paper segment  12  in a pre-broken state in which a region  46  adjoining a left segment edge in  FIG. 3  is curved upwardly. It is also apparent from  FIG. 3  that primer has already been applied to this upwardly curved region  46 , which is indicated by light gray shading. 
       FIG. 4  shows a side view of the paper segment  12 . The primer is applied to the convex side of the region  46 . 
       FIG. 5  now shows a finished cup sleeve  48  as created by winding the paper segment  12  on a folding mandrel and sealing it in the region of an overlap. The overlap is produced in the region in which the pre-broken region  46  had been supplied with primer. This considerably stabilizes and improves a bond produced by a thermal sealing process in the region of the overlap. Thus there is no difficulty in forming a mouth roll at the top edge of the cup sleeve  48  of larger diameter due to the conical shape of the cup sleeve  48 , without breaking the seal in the region of the overlap as a result of the rolling process. 
     Since the stamp  16  is made of compression-resistant porous sintered material, it is subject to virtually no wear and also has a very long service life at high cycle rates in the production of paper cups. If, for example, any primer remaining in the stamp becomes touch-dry after long production downtimes, the stamp  16  can be easily cleaned by removing the entire stamp  16  and immersing it in solvent or rinsing it with the same. The device  14  of the invention for the application of adhesive thus provides a much more reliable bond in the region of the overlap during production of a cup sleeve  48  and can furthermore almost completely avoid downtimes caused by cleaning or maintenance. 
     The diagrammatic illustration in  FIG. 6  shows another device  50  of the invention for the application of adhesive. The device  50  is shown diagrammatically as a side view. The device  50  serves to provide a truncated conical paperboard sleeve with adhesive on the inner side in the region of its lower edge. Such an adhesive or primer application at the lower end of the sleeve can assist in improving the leak-tightness of the skirt joining the bottom edge to the lower edge of the sleeve after the insertion of the bottom and thus seals the paper cup to make it leak-proof for liquids. For this purpose, the device  50  comprises three stamps  54   a ,  54   b , and  54   c , which are each made of a sintered material such as a sintered metal and are pervious to the primer to be applied. The means used for supplying the stamps  54   a ,  54   b ,  54   c  with adhesive and for forcing the adhesive therethrough are not shown for the sake of clarity. 
     The stamps  54   a ,  54   b ,  54   c  together form the shape of a ring comprising a truncated cone-shaped outer surface and a cylindrical inner surface and circular ring-shaped top and bottom surfaces. Each of the stamps  54   a ,  54   b ,  54   c  forms a circular ring segment and extends over an angular range of only about 120°. The stamps  54   a ,  54   b ,  54   c  can be moved outwardly in the radial direction as indicated by the arrows  56 . For moving or expanding the stamps  54   a ,  54   b ,  54   c  in the radial direction, a mandrel is used, for example, which is inserted into the inner space of the circular ring formed by the three stamps  54   a ,  54   b  and  54   c . As a result of the radial movement of the stamps  54   a ,  54   b ,  54   c , the latter come to rest against the inner side of the paperboard sleeve  52 . A limit is set for the radial movement of the stamps  54   a ,  54   b ,  54   c  in that they move toward the truncated cone-shaped inner surface of a counter tool  58 . The lower edge of the sleeve  52  is then clamped between the truncated cone-shaped inner surface of the counter tool  58  and the outer surface of the stamps  54   a ,  54   b ,  54   c  and adhesive is applied at the same time to the region against which the stamps  54   a ,  54   b ,  54   c  bear. 
       FIG. 7  shows the device  50  illustrated in  FIG. 6  in a diagrammatic top view. The arrows  56  denote the expanding movement of the ring formed by the stamps  54   a ,  54   b  and  54   c . The counter tool  58  can likewise be open below the free inner space of the ring formed by the stamps  54   a ,  54   b ,  54   c , in order to be able to insert or slide in an expanding mandrel. As indicated by the double arrow  60  in  FIG. 6 , the counter tool  58  can be advanced in the longitudinal direction of the paperboard sleeve  52  toward the stamps  54   a ,  54   b ,  54   c.    
       FIG. 8  shows a section of another device  62  of the invention for the application of adhesive. The design of the device  62  is basically similar to that of the device  50  shown in  FIG. 6 . Altogether three circular ring segment-shaped stamps  64 , of which only one segment is shown partially in  FIG. 8 , are made at least partly of sintered material and can be moved outwardly in the radial direction to bear against the lower edge of a paperboard sleeve. The paperboard sleeve is not shown in  FIG. 8 , but is present in the annular gap between the stamp  64  and a counter tool  66 . The stamp  64  has various chamfers in the region of its outer surface. From the base of a depression in the counter tool  66 , that is, starting from the bottom edge of a paperboard sleeve provided with an adhesive in the device  62 , the outer surface of the stamp  64  forms an angle of about 30°. The angle of the outer surface of the stamp then changes as its movement is continued to finally assume, for example, an angle of about 10° to a central longitudinal axis of the ring formed by the stamp segments  64 . When viewed from the bottom edge of the stamps  64 , the angle to a central axis  68  is thus initially acute and then becomes more obtuse and is substantially equal, in the more obtuse region, to the inclination angle of the sleeve. 
     The inner surface of the counter tool  66  is also designed accordingly so that a paperboard sleeve supplied with adhesive in the device  62  is simultaneously pre-broken in that the lowermost edge section of the paperboard sleeve is bent inwardly. The sleeve can thus be subjected to a pre-breaking action during the application of primer, which facilitates the process of turning over the lower edge when forming the skirt in a subsequent process step, that is to say, when the lower edge of the sleeve is joined to the edge of a bottom element in order to seal the cup, making it leak-proof for liquids. 
     During operation, the sleeve  72 , shown partially and diagrammatically, is inserted in the gap formed between the stamp segments  64  and the counter tool  66  and the stamps  64  are then moved outwardly in the radial direction and then retracted, as indicated by the double arrow  70 . In doing so, the sleeve  72  is pre-broken in the region of its lower edge concurrently with application of the primer. 
       FIG. 9  shows a part of another device  74  of the invention for the application of adhesive. Unlike the device  72 , a stamp  76  and a counter tool  78  are curved outwardly in a lower corner region, as viewed from the central axis  68 . At the same time as the application of adhesive to a sleeve, this sleeve is pre-broken at its lower edge in that the lower edge is bent downwardly in accordance with the curvatures provided on the stamp  76  and in the counter tool  78 . 
       FIG. 10  shows a section of another device  80  of the invention for the application of adhesive. A stamp  82  and a counter tool  84  are provided with matching steps  86 ,  88 , at which the cross-sections of both the stamp  82  and the counter tool  84  decrease from top to bottom, as viewed from a direction extending parallel to the central longitudinal axis  68  as depicted in  FIG. 10 . The step is formed with rounded transitions. A sleeve inserted in the gap formed between the stamp  82  and the counter tool  84  is thus provided with adhesive and at the same time with a shoulder-like step in its lower region. As a result, the sleeve is pre-broken in the region of this step so that the sleeve can then be easily turned over in a defined manner in the region of this step when forming the skirt which joins the bottom element to the sleeve in order to create a cup that is leak-proof for liquids.