Abstract:
The invention relates to a method for producing packaging ( 18 ) from paper material ( 5 ), in particular paper, cardboard or paperboard, said method comprising the following steps: forming packaging ( 18 ) from a blank ( 19 ) made of paper material ( 5 ), which paper material overlaps at at least one joining site ( 21 ); positioning the at least one joining site ( 21 ) between a sonotrode ( 2 ) and an anvil ( 3 ); applying the joining site ( 21 ) with a joining force in a joining force direction ( 6 ); and making the sonotrode ( 2 ) ultrasonically vibrate in order to ultrasonically weld the paper material ( 5 ) at the joining site ( 21 ), which method is characterised in that the paper material ( 5 ) is moistened, preferably on the inner sides of the joining sites ( 21 ), before forming the packaging ( 18 ) and/or while forming the packaging ( 18 ) and/or after forming the packaging ( 18 ) and/or during the ultrasonic welding.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a method for producing packaging and a corresponding packaging machine. In the method and in the packaging machine, paper material, in particular paper, cardboard or paperboard, is joined by means of an ultrasonic joining process. 
         [0002]    In the European patent EP 0 340 334 A2, a device is described which is suited to joining two-ply or multi-ply paper products by means of ultrasound. The paper used in the process is provided with a thermoplastic coating. Longitudinal waves are produced by the sonotrode so that said sonotrode moves towards the anvil and away from the anvil while being ultrasonically vibrated. A sufficient compression of the paper layers is produced here by means of the corresponding ultrasonic frequency and the corresponding contact pressure. At the same time, heat builds up highly in the micro-region of the thermoplastic coating and the paper layers are thus adhesively bound. 
         [0003]    In a schematically simplified view, the attached  FIG. 10  shows an ultrasonic joining device  100  according to the prior art for joining thermoplastically coated paper material. The device  100  comprises a sonotrode  102  according to the prior art and an anvil  103  according to the prior art. The paper material  5  to be joined is located between the sonotrode  102  and the anvil  103 , wherein thermoplastic layers  108  are arranged toward one another. A joining force  106  is applied to the paper material  5  in the gap between sonotrode  102  and anvil  103 . The sonotrode  102  executes an ultrasonic vibration in a direction of vibration. In the device  100  according to the prior art, the direction of vibration  107  and the joining force direction  106  are oriented parallel to one another. The longitudinal direction of movement of the sonotrode  102  is thus used here for the joining process. 
       SUMMARY OF THE INVENTION 
       [0004]    In the case of the method according to the invention and the device according to the invention, ultrasonic welding takes place with the joining sites being moistened. This facilitates a firm and clean joining of the paper material without adhesives or thermoplastic coatings. These advantages are achieved by means of a method for producing packaging from paper material. The paper material particularly consists of paper, cardboard or paperboard. Corrugated board can particularly be used here. The method comprises the following steps: (i) forming packaging from a blank made of paper material, which paper material overlaps at at least one joining site ( 21 ); positioning the at least one joining site between a sonotrode and an anvil; applying a joining force to the joining site in a defined joining force direction; and making the sonotrode ultrasonically vibrate in order to ultrasonically weld the paper material at the joining site. Provision is made according to the invention for the paper material to be moistened preferably on the inner sides of the joining sites before forming the packaging and/or while forming the packaging and/or after forming the packaging and/or during the ultrasonic welding. The paper material is moistened with liquid water and/or water vapor and/or a humectant or something similar. In a particularly preferred manner, pure water without additives is used. It is assumed that the paper structure is lightly damaged at the joining sites as a result of the ultrasonic welding and thus forms a local paper pulp. Due to the effect of the ultrasound and the pressure by the joining force, this paper pulp makes it possible for the paper fibers to felt and consequently to form a type of adhesive bond analogous to the process used in paper production. A type of compression of the joining surfaces leads to the formation of hydrogen bridges. This is also often described as felting. The local formation of hydrogen bridges can be actively supported by the moistening process. Particularly in the packaging industry, numerous types of adhesive bonds of cardboard packagings with the aid of dispersion adhesives (cold glue) and melt adhesives (hot glue) are used. In order to make the packaging process more efficient, to design said process in a cleaner and more hygienic manner, the ultrasonic welding method according to the present invention, which comprises moistened joining sites, can be used. The method according to the invention is particularly suited for use in the serial production of high quantities due to the short cycles in the range of 0.1 to 1 second and hold times of 0.1 to 2 seconds. The method according to the invention has the following advantages with respect to the adhesive bonding method: According to the method, no joining material is required; thus enabling hot or respectively cold glue to be substituted. The paper material does not require any additional thermoplastic coating for the joining process using ultrasonic welding. Conventional adhesive bonding machines tend to easily get dirty. Because, in a preferred manner, no additives are used in the method according to the invention with the exception of water for moistening the paper material, a reduction in the contamination and therefore a compliance to the hygienic standards, which are of great importance for the food and pharmaceutical industries, can be achieved. This also has the effect that there is no danger of a migration of joining material (glue) into the packaged goods when using the method according to the invention. In addition, energy is saved to a great degree because a continuous heating of the hot glue is not required. The energy necessary for the method is required only in the range of the joining time, that is to say in the millisecond range. 
         [0005]    The ultrasonic vibration generated by the sonotrode has a certain direction of vibration. At the same time that the ultrasonic vibration is generated by means of the sonotrode, a joining force is applied to the paper material in the gap between the sonotrode and the oppositely positioned anvil. This joining force is directed in a joining force direction. In a preferred manner, provision is made in a first variant for the direction of vibration and the joining force direction not to be oriented parallel to one another. In the prior art, the direction of vibration is always configured parallel to the joining force direction. As a result, primarily the longitudinal direction of movement of the vibrating particles is used in the prior art for generating energy in the joining seam. In the process, the heat energy is generated from inner molecular friction and interfacial friction of the joining partners. The heat energy from the interfacial friction is thereby obtained from the deformation energy of the deformation of the joining material via the anvil geometry. In contrast, it is recognized within the scope of the invention that a far better joining of paper material is possible if a friction welding method is used, in which the interfacial friction is primarily used. The preferably used ultrasonic friction welding has various advantages with respect to the ultrasonic longitudinal welding, in which the joining force direction is oriented parallel to the direction of vibration of the sonotrode. In the case of ultrasonic friction welding, materials having less sound attenuation can be used, which is particularly the case with paper material. As a result of the frictional movement of the paper materials being joined, there are not any sound emissions as can be recognized by the hammering movements of the sonotrode in the longitudinal ultrasonic welding method. The shear and peel strength of the joint is significantly higher for ultrasonic friction welding than for joints which have been produced using typical ultrasonic joining methods. A further decisive advantage for ultrasonic friction welding is that the entire vibration, and not only the amplitude, which acts in the direction of the joining site is used for the energy input into the paper material. As a result of eliminating a hammering movement onto the paper material to be joined, said paper material is protected when carrying out the ultrasonic friction welding process. 
         [0006]    Provision is particularly made for the joining force direction to be perpendicular or respectively at a right angle to the direction of vibration during ultrasonic friction welding. Deviations of ±10° are still considered here to be perpendicular. This orientation ensures that the amplitudes of the vibrating sonotrode act in both directions to the greatest possible extent on the paper material. At the same time, the perpendicular orientation of the joining force direction to the direction of vibration provides for an almost exclusive utilization of the interfacial friction at the joining sites. 
         [0007]    As a result of the moistening of the paper material, a good result can, however, also be achieved using ultrasonic longitudinal welding. In a second variant, provision is therefore made in a preferable manner for the joining force direction to be parallel to the direction of vibration. 
         [0008]    The ultrasonic vibration frequency of the sonotrode lies preferably between 30 and 35 kHz. In addition, provision is preferably made for the ultrasonic vibration amplitude of the sonotrode to be preferably between 10 and 50 μm, especially in particular between 20 and 40 μm. An interfacial friction at the joint sites which is favorable for the joining of the paper material occurs using these parameters for the ultrasonic vibration. 
         [0009]    The inventive use of ultrasonic welding of moistened paper material leads to very stable joining sites; thus enabling the use of adhesives or thermoplastic coatings to be eliminated. In addition, it is also not necessary for printing dye to be present at the joining sites, which would promote a bonding of the paper materials similarly to a thermoplastic coating. 
         [0010]    In a preferred manner, a common anvil and/or a common sonotrode are used for a plurality of joining sites that are spaced apart from one another. In so doing, it is possible to simultaneously join a plurality of joining sites using only one anvil and/or only one sonotrode. Parallel joining sites are particularly processed at the same time by one anvil and/or one sonotrode. 
         [0011]    The invention further comprises a packaging apparatus for producing a packaging from paper material. The packaging apparatus comprises a forming unit. This is preferably designed as a deep drawing unit. The forming unit is used to form the packaging from a blank made of paper material. The paper material is formed in such a way that said paper material overlaps at at least one joining site. At least one sonotrode that can be set into ultrasonic vibration is furthermore provided for the ultrasonic welding of the paper material. In addition, at least one anvil is provided as a counter tool for the sonotrode. The joining force is generated by applying a corresponding force to the sonotrode and/or the anvil. The joining force thereby acts in a joining force direction. Provision is made according to invention for the paper material to be moistened by a moistening device, preferably on the inner sides of the joining sites, before forming the packaging and/or while forming the packaging and/or after forming the packaging and/or during the ultrasonic welding. The paper material is preferably moistened with liquid water and/or water vapor and/or a humectant or something similar. In an especially preferred manner, pure water is used without additives. 
         [0012]    The advantageous embodiments presented within the scope of the method according to the invention can correspondingly be advantageously applied to the packaging apparatus according to the invention. 
         [0013]    Provision is particularly made for the forming unit to comprise a movable die plate for forming the packaging. At least one anvil or at least one sonotrode is disposed on this die plate. In a particularly preferred embodiment, provision is made for at least one anvil to be provided on the die plate. The at least one sonotrode is then located outside of the forming unit. Hence, the at least one anvil is moved up and down together with the die plate. When joining the joining sites, the anvil is situated within the formed packaging. The sonotrode is applied externally to the packaging. 
         [0014]    In a preferred manner, provision is furthermore made for a supply unit. The supply unit is used to supply the blank to the forming unit. As described earlier, the joining sites are preferably moistened. In a particularly preferred manner, this moistening process takes place in the supply unit. The supply unit therefore comprises the device for moistening the joining sites during the feeding process. 
         [0015]    The packaging apparatus furthermore preferably comprises a folding tool. Portions of the blank can be folded with this folding tool, so that, for example, lugs of the blank overlap. These overlapping lugs then form the joining sites. The sonotrode is preferably integrated into the folding tool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    An exemplary embodiment of the invention is described below in detail with reference to the accompanying drawings. In the drawings: 
           [0017]      FIG. 1  shows a schematically simplified detailed drawing of a packaging apparatus according to the invention for carrying out the method according to the invention pursuant to one exemplary embodiment; 
           [0018]      FIG. 2  shows a detailed view with regard to  FIG. 1 ; 
           [0019]      FIG. 3  juxtaposes ultrasonic longitudinal welding with ultrasonic friction welding; 
           [0020]      FIG. 4  shows a diagram regarding the tensile strength of the joining site produced; 
           [0021]      FIG. 5  shows the packaging apparatus according to the invention for carrying out the method according to the invention pursuant to the exemplary embodiment; 
           [0022]      FIG. 6  shows a finished packaging as said packaging can be produced with the packaging apparatus according to the invention pursuant to the exemplary embodiment; 
           [0023]      FIG. 7  shows a blank which is folded to form a packaging in the packaging apparatus according to the invention; 
           [0024]      FIG. 8  shows a plurality of depictions of the folding process as said process is carried out by the packaging machine according to the invention pursuant to the exemplary embodiment; 
           [0025]      FIG. 9  shows a detailed view with regard to  FIG. 5 ; and 
           [0026]      FIG. 10  shows an ultrasonic joining device according to the prior art. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 1  shows a detail of a packaging apparatus  1  according to the exemplary embodiment in a highly schematically simplified view. The method according to the invention can be carried out with this packaging apparatus  1 . 
         [0028]    The packaging apparatus  1  comprises a sonotrode  2  and an anvil  3 . A gap  4  is formed between the sonotrode  2  and the anvil  3 . The paper material  5  to be joined is situated in this gap  4 . Two lugs  20  of a packaging  18  (see  FIGS. 6 and 7 ) which overlap within the gap  4  are shown. These two lugs  20  are connected to one another by means of the packaging apparatus  1 . 
         [0029]    A joining force acts on the paper material  5  in the gap  4  via the anvil  3 . This joining force is directed in a joining force direction  6 . 
         [0030]    The sonotrode  2  is excited to carry out an ultrasonic vibration in the direction of vibration  7 . This direction of vibration  7  corresponds to the direction of extension of the amplitudes of the ultrasonic vibration. 
         [0031]    As can be easily recognized in  FIG. 1 , The joining force direction  6  is perpendicular to (also: at a right angle to) the direction of vibration  7 . Thus, the process here relates to an ultrasonic friction welding method. As previously described, an ultrasonic longitudinal welding method can also be carried out. The joining force direction  6  and the direction of vibration  7  are then parallel to one another. 
         [0032]      FIG. 2  shows a detailed view with regard to  FIG. 1 , likewise schematically simplified. According to  FIG. 2 , force is applied to the anvil  3  via a cylinder rod  8 ; thus enabling the anvil  3  to exert the joining force onto the paper material  5  in the gap  4 . Accordingly, the cylinder rod  8  is also disposed parallel to the joining force direction  6 . 
         [0033]    In addition,  FIG. 2  shows in a schematically highly simplified manner the option of moistening the paper material  5  with water  9 . As previously described, this moistening promotes the joining process. 
         [0034]      FIG. 3  shows the principle of ultrasonic longitudinal welding on the left side. The amplitude of the ultrasonic vibration is not depicted true to scale in order to clarify the functional principle. The amplitude is, for example, between 20 and 40 μm. In  FIG. 3 , the principle of ultrasonic friction welding is depicted on the right side. It can be seen in this depiction that only the lower positive amplitude can have an effect in the direction of the paper material  5  during ultrasonic longitudinal welding. On the other hand, as shown in  FIGS. 1 and 2 , a lateral contact pressure on the paper material  5  towards the sonotrode results during ultrasonic friction welding. As a result, both amplitude directions, i.e. the expansion in the positive amplitude direction and the contraction or pulling back in the negative amplitude direction, can be effectively used for the joining process. By moistening the joining sites, a good result can be achieved using ultrasonic friction welding as well as ultrasonic longitudinal welding. 
         [0035]      FIG. 4  shows the test results in a diagram by means of which cardboard having a surface density 300 g/m 2  was tested with an apparatus  100  according to the prior art and with a packaging apparatus  1  according to the invention. The applied joining force in [N] is plotted on the horizontal axis. The vertical axis shows the tensile strength in [N/ 15 ] of the joining site that was created. An upper curve  10  shows the result of the inventive method comprising moistened joining sites and ultrasonic friction welding. A lower curve  101  shows the result when using the apparatus  100  according to the prior art. 
         [0036]    Within the scope of the invention, it has been shown in experimental trials that paper, cardboard and paperboard can be better connected to one another if ultrasonic friction welding is used as the joining method. In contrast to ultrasonic longitudinal welding, the direction of vibration  7  is not parallel to the joining force direction  6  but preferably perpendicular (also: at a right angle) thereto. In comparison to the longitudinal ultrasonic welding method, the strength values of the joint are significantly increased with respect to the shear and peel strength. In addition, as shown in  FIG. 4 , relatively high tensile strengths are to be achieved in the range of low joining forces. 
         [0037]    It is assumed on the basis of tests that have been performed that not only micro-splicing of the fibers and new hydrogen bridges are crucial for the joint. The results speak for a plasticizing and solidifying of fiber-containing polymers, natural or synthetic bonding agents as well as polymer-like additives. It can be assumed that plasticized regions are situated on the contacting surfaces during the joining process. The longitudinal ultrasonic joining process stresses the joining partners with an increased penetration. In order to improve the joint quality, it is more expedient to allow the mechanical stress to act parallel to the joining plane, as this has been shown within the scope of the present invention. A further significant advantage which speaks for pressing the sonotrode  2  laterally towards the paper material  5  is the complete utilization of the sonotrode vibrations in both amplitude directions. During ultrasonic friction welding, the expansion as well as the contraction movement from the standing wave generated in the vibration structure is used. If the sonotrode is pressed against the joining partner during longitudinal ultrasonic welding, only the expansion has an effect on the welding process. During contraction, the sonotrode loses contact with the paper material. A doubling of the effective amplitude can thus be achieved during ultrasonic friction welding, from, for example, 24 μm to 48 μm at 30 kHz. 
         [0038]      FIG. 5  shows the exact configuration of the packaging apparatus  1  pursuant to the exemplary embodiment. According to this depiction, the packaging apparatus  1  comprises a forming unit  11 , designed as a drawing unit. This forming unit  11  comprises a die plate  12 . The die plate  12  can be moved by means of a cylinder  13  in the vertical direction. The cylinder  13  is, for example, designed as a pneumatic or hydraulic cylinder. A guiding carriage of the packaging apparatus  1  is located below the die plate  12 . A folding tool can be positioned with this guiding carriage  14 . 
         [0039]    In addition, the packaging apparatus  1  comprises a supply unit  16 . A blank  19  (see  FIG. 7 ) is fed into the forming unit  11  via this supply unit  16 . 
         [0040]    The supply unit  16  comprises a moistening device  17 . The joining sites  21  (see  FIG. 6 ) are moistened by means of this moistening device  17 . 
         [0041]      FIG. 5  furthermore shows the finished packaging  18 , designed as a box. This packaging  18  is shown in detail in  FIG. 6 . According to  FIG. 6 , the packaging  18  has joining sites  21  on the edges thereof. These joining sites  21  are joined by means of the sonotrode  2  and the anvil  3 . 
         [0042]      FIG. 7  shows the blank  19  from which the packaging  18  is formed in the forming unit  11 . The blank  19  consists of paper material, for example corrugated paper. A plurality of lugs  20  is provided on the blank  19 . These lugs  20  are made to overlap by means of the forming unit  11  and the folding tool  15  so that the joining sites  21  are created. 
         [0043]    In a plurality of depictions,  FIG. 8  shows the folding process which is carried out by the folding tool  15 . The die plate  12  of the forming unit  11  is masked out here for the sake of clarity. As shown in  FIG. 8 , a first lug  20  is initially folded at each joining site. A second lug  20  is subsequently folded so that both lugs  20  overlap and a joining site  21  is thus created. This folding or bending of the lugs  20  takes place by means of forming shoulders  22  and metal plates  23  on the folding tool  15 . 
         [0044]      FIG. 9  shows a detailed view with regard to  FIG. 5 . It can be seen in  FIG. 9  that at least one anvil  3  is disposed on the die plate  12 . This anvil  3  is move by means of a short-stroke cylinder  24 . This short-stroke cylinder  24  is likewise disposed on the die plate  12 . This short-stroke cylinder  24  is depicted only as a cylinder rod  8  in the schematically simplified depiction pursuant to  FIG. 2 . 
         [0045]    The sonotrode  2  is located outside of the packaging  18 . Provision is furthermore made for a hold-down device  26 . This hold-down device  26  is pressed against the sonotrode  2  by means of a sonotrode holder  25 . This movement of the sonotrode holder  25  is brought about by a booster  27  and a converter  28 . Sonotrode  2  and anvil  3  can be moved toward one another by means of the short-stroke cylinder  24  and the sonotrode holder  25 . The joining site  21  of the packaging  18  is located between sonotrode  2  and anvil  3 . The movements of the short-stroke cylinder  24  and the sonotrode holder  25  therefore generate the joining force in the joining force direction  6 . In this depicted example, the joining force direction  6  is oriented horizontally. In order to join the joining site  21 , the sonotrode  2  is set into vibration in the plotted direction of vibration  7 , i.e. perpendicular to the joining force direction  6 . 
         [0046]    Provision is also alternatively made for the direction of vibration  7  and the joining force direction  6  to be oriented parallel to one another in the case of an ultrasonic longitudinal welding process. 
         [0047]      FIG. 9  further shows that the folding tool  15  and the sonotrode  2  comprising the sonotrode holder  25  are integrated into one tool.