Abstract:
A filter bag for a vacuum cleaner includes a tubular bag made of a casing which has at least one nonwoven layer. The casing has a first end region which is sealed at least partially and a second sealed end region situated opposite the first end region. The first end region is folded and forms a base.

Description:
FIELD OF INVENTION 
     The invention relates to a filter bag for a vacuum cleaner, comprising a tubular bag made of a casing which has at least one nonwoven layer, said casing having a first end region which is sealed at least partially and a second sealed end region situated opposite said first end region, the first end region being folded and forming a base. The invention relates furthermore to a method for the production of a filter bag of this type. 
     BACKGROUND INFORMATION 
     Filter bags for vacuum cleaners which have a tubular bag and which, in addition to a closed end region, have a folded base, a so called block base, are known in the state of the art. Normally, filter bags of this type are manufactured from a paper material which can be processed in normal tubular bag plants. In the case of filter bags of this type, a corresponding retaining plate is generally fitted on the block base and has an opening through which the air to be cleaned is guided. The object of the block base resides in stabilising the filter bag and in forming a three-dimensional bag. Furthermore, the block base facilitates fitting of the bag in the vacuum cleaner. 
     In recent times, new developments have become known with respect to vacuum cleaner bag materials, such as are described for example in WO 01/03802 A1. A special nonwoven material comprising a plurality of layers of filter material, which are independent of each other, is disclosed therein. These independent layers are combined to form a filter material with specific properties. In practice, it has now been shown that vacuum cleaner bags which are produced with a nonwoven material of this type are significantly superior relative to those previously known with respect to the performance of the vacuum cleaner, in particular with respect to the dust storage capacity. 
     It is problematic with filter bags which are produced from a previously described material however that it is difficult to form a block base because of the floppiness of the bag material during bending. 
     There has been no lack of attempts to produce a remedy by means of specific solutions. One possibility for forming a block base in the case of a vacuum cleaner bag which is produced from a nonwoven material as described previously is described in DE 103 48 375 A1. In the case of production method disclosed there, the process thereby takes place such that, after formation of the tube, the latter is sealed on one side with formation of an at least partially sealed region. As a result, as described previously, of the fact that the tube is welded together after being cut, the result is a connection of both internally situated layers of the tubular bag in the edge region. In a subsequent method step, in the case of the previously described method, stabilisation of the base is then achieved by introducing a die and folding over the narrow sides on the base and gluing thereof. 
     The production method and also the dust filter bags formed with the production method therefore always have a central weld seam which is formed in the edge region and in the case of which the two inner sides respectively are welded to each other. 
     It is however disadvantageous with the previously described filter bags that these do not always provide a satisfactory result with respect to the stability of the base for the high requirements in the vacuum cleaner and the required different shapes of filter bag. Furthermore, the method for the production of filter bags according to DE 103 48 375 A1 is very complex and cost-intensive. Furthermore, the seam which is vertical can make gluing or welding of the retaining plate on the base very difficult. Leaks can only be avoided with difficulty. 
     SUMMARY OF INVENTION 
     The present invention relates to a filter bag comprising a casing made of at least one nonwoven layer and which has a block base which has sufficient stability even for the most varied of requirements in the field of vacuum cleaners. Furthermore, it is the object of the present invention to indicate a corresponding method for the production of a filter bag of this type which is intended in particular to be as simple as possible in the production process. 
     According to an exemplary embodiment of the present invention, the end region which forms the base is effected by overlapping the inner side and outer side of the casing, the overlapping region being connected at least partially by at least one weld seam. The filter bag according to the present invention thus differs from the filter bag as described in DE 103 48 375 A1 in that the base here is now stabilised by overlapping the inner and outer side of the casing. It emerged surprisingly that it is adequate, in order to form a stable base, if the inner and outer sides of the casing overlap and are connected at least partially by at least one weld seam. Overlapping of the inner and outer sides of the nonwoven layer is hence essential for the filter bag according to the present invention. It is thereby favourable if the overlapping of the inner and outer sides extends over a region of at least 3 mm. The overlap can thereby reach at most up to the entire width of the base, i.e. the inner and outer sides are overlapped so far that the base is completely covered by the overlap. However, it is preferred that an overlapping region is chosen which is between half of the width of the base and 3 mm. A retaining plate can be glued or welded on this horizontal weld seam without difficulty. 
     The weld seam which is provided according to the present invention in order to join the overlapping region is thereby guided preferably over the entire width of the base. A weld seam of this type is preferably linear. The invention thereby comprises of course also embodiments in which two or more parallel weld seams are provided according to the width of the overlapping region. 
     In the case of the filter bag according to the invention, it should be emphasised in particular that, as a result of the previously described configuration of the base, i.e. by overlapping the inner and outer sides and forming an overlapping region, self-stabilisation of the base is achieved which has actually such high stability that the base is sufficiently stable even without additional fixing of a retaining plate. 
     The base preferably has an oblong shape, particularly preferred a rectangular shape. 
     Further stabilisation of the base can be achieved in addition with filter bags of the invention in that stacked layers are formed by folding the narrow sides of the rectangular base which in turn are connected to each other at least partially. These stacked layers of the narrow sides can be folded back thereby on the base and be connected to the latter. On the other hand, folding of these stacked layers of the narrow side is also possible on the side faces of the tubular bag. Finally, the invention also comprises embodiments in which the stacked layers of the narrow sides are removed, however the prerequisite here then being that the consequently laterally resulting open region is sealed again by welding. 
     For the stacked layers of the narrow sides which are formed in regions by folding, the connection can be effected by gluing and/or by welding. 
     In the case of the vacuum cleaner bag according to the invention, it is favourable in addition if, over the longitudinal sides, i.e. over those surfaces of the vacuum cleaner bag which are between the closed ends and the at least partially closed end with the base configured according to the invention, pre-folds are introduced into the consequently extending side face so that a fold is possible. The pre-folds can thereby be configured such that they extend for example from the respective corners of the base, if the latter is formed with corners or quadrilaterally, and are guided up to the opposite end. It is advantageous in addition if, starting in addition from the central weld seam, one further pre-fold respectively is introduced into the casing. The introduction of side folds is consequently facilitated and the surface of the vacuum cleaner bag is enlarged. At the same time, the pre-folds which are introduced in the longitudinal sides of the vacuum cleaner bag can serve for further stabilisation of the bag material. There should be understood by pre-fold in the sense of the invention, material compressions which are preferably configured linearly. The pre-folds can be introduced by suitable shaping tools and/or by welding. Advantageously, the filter bag according to the invention likewise has a pre-fold which is guided parallel to the central weld seam. This pre-fold serves to fold over the base in the direction of the longitudinal sides of the filter bag. It is therefore adequate if one pre-fold of this type is present. The spacing of the pre-fold is chosen such that it corresponds to half the width of the base starting from the central weld seam. 
     With respect to the retaining plate, it is possible according to the present invention to join the latter either to the block base or to fit the retaining plate on the free side faces of the vacuum cleaner bag. However, the embodiment is hereby preferred in which the retaining plate is connected securely to the base. The retaining plate can thereby cover the entire base or also only partially. If the retaining plate is attached to the base, it is of course necessary that a corresponding through-opening is introduced into the base, said through-opening corresponding to the through-opening of the retaining plate. If, as previously described, the retaining plate and the through-openings are fitted on the base, the initially described continuous weld seam is of course interrupted. 
     The retaining plate is thereby constructed as known per se from the state of the art and has at least one through-opening which serves for the supply of air to be cleaned. The retaining plate can have in addition an element, e.g. a slide or a flap for closing the opening. The retaining plate can thereby be connected to the base of the bag with all current techniques of the state of the art. There are possible for this purpose gluing or welding. 
     The retaining plate, as known per se from the state of the art, can be made of plastic material or cardboard. 
     The filter bag according to the present invention is preferably formed from a nonwoven material, as is described in WO 01/03802 A1. It is preferred in the case of the filter bag according to the invention if the latter comprises a plurality of nonwoven layers, these being able to have different filter properties. Reference is made expressly to the disclosure content of WO 01/03802 A1. 
     The invention relates in addition to a method for the production of a filter bag as previously described. 
     The method is thereby implemented such that, in a first step, folding of a casing web of the filter bag material is undertaken in order to form a tube. 
     In the second step, the tube is then placed on a corresponding anvil which defines the shapes of the filter bag. 
     In a subsequent step (method step c)), separation of the corresponding tube section is then undertaken and subsequently (method step d)) the folding over of the longitudinal sides is then effected onto the anvil whilst forming an overlap of the inner and outer sides of the casing. 
     Subsequently, welding of the overlapping region is then implemented and the filter bag is then removed from the anvil. Finally, welding of the second end region is also implemented as last method measure. 
     It is therefore essential in the method according to the invention that overlapping of the inner and outer sides of the casing is undertaken and consequently stabilisation of the base can be achieved. As a result of the fact that the method according to the invention can be implemented in a cycle by means of one device, the method can be implemented simply and economically with respect to processing technology. It has been shown furthermore that the method proceeds with high precision and with a very low reject rate. 
     The method according to the invention as described previously can be modified such that another folding-over of the narrow sides is integrated jointly at the same time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention is described subsequently in more detail with reference to  FIGS. 1 to 18 . 
         FIGS. 1 to 6  show the sequence for the production of a first embodiment of a filter bag according to the invention. 
         FIGS. 7 to 12  show the corresponding Figure sequence for the production of a filter bag according to the invention in a second embodiment. 
         FIGS. 13 to 18  show the Figure sequence for the production of a third embodiment of the filter bag according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The Figure sequence  1  to  6  shows the individual steps for the production of a filter bag according to the invention according to a first embodiment. 
       FIG. 1  thereby shows the first method step for formation of the tube in which a casing web  8  is folded over a template  9  which defines the shape of the filter bag and a weld seam  7  then being applied in order to form a tube. In the case of the example according to  FIG. 1 , the template  9  is configured in the form of a rectangular box so that, as is shown with reference to the further Figure sequence, the base of the filter bag to be produced subsequently has a rectangular shape which corresponds to that prescribed approximately by the template  9 . One advantage of the method according to the invention and hence also that of the filter bag which is produced resides in the fact that, by prescribing the template  9 , any shapes of filter bags can be produced with respect to the base. The casing web  8 , which is used according to the embodiment according to  FIG. 1 , concerns a multilayer nonwoven layer with different filter properties. Corresponding composite materials are mentioned in WO 01/03802 A1. 
     As emerges in addition from  FIG. 1 , it is favourable if, after this method step, i.e. after formation of the tube by folding over the template  9  and welding on the longitudinal seam  7 , subsequent lateral folds  10  are introduced into the tube. The introduction of the lateral folds  10  can be effected by measures which are known per se from the state of the art, i.e. for example by shaping tools or by weld seams. 
     In  FIG. 2 , the next method step of the method according to the invention is represented. After formation of the tube, the thus produced tube is drawn onto an anvil  11 , as here in the case of the example with the introduced lateral folds  10 . The pre-folds produced during formation of the lateral folds are thereby maintained. The shape of the anvil  11  is thereby preferably chosen like that of the template  9  in the present method step. After drawing the tube onto the anvil  11 , a corresponding tube section is separated (method step c)), as then shown in  FIG. 2 . Subsequently, folding of the longitudinal sides  12  and  13  onto the anvil is effected whilst forming an overlapping region  3  (see  FIG. 3 ). 
     In the production method which is represented in the Figure sequence  1  to  6 , an embodiment is achieved in which the narrow sides  14 ,  15  of the base are folded back in addition onto the base  2  itself. The layers of the narrow sides which are folded one over the other can now be fixed on the base  2  by methods known per se from the state of the art, i.e. for example by means of gluing or likewise by means of ultrasonic welding. In  FIG. 3 , the imaginary central line of the base  2  through the line  20  is represented. 
       FIG. 4  now shows the next method step for the production of the filter bag, as is represented by way of example in  FIGS. 1 to 6 . As emerges from  FIG. 4 , the overlapping region  3  is welded by applying a base seam  6  after folding over the narrow sides  14 ,  15 . As emerges from  FIG. 4 , another hole punch is undertaken here into the base  2  so that a through-opening  16  is formed in the base  2 . 
     In  FIG. 5 , the state of the filter bag  1  is now represented, which is produced when, according to the method step represented in  FIG. 4 , another retaining plate  4  is applied subsequently on the base  2 . The retaining plate  4  can thereby be connected to the base  2  either by gluing or by welding. The retaining plate  4  thereby has a corresponding opening to the opening  16  in the base  2  of the filter bag. The invention thereby comprises all the embodiments in which the retaining plate not only has the rectangular shape represented in  FIG. 5  but also other shapes which can cover for example also the entire base  2 . The retaining plate  4  is thereby preferably configured in one piece and can also have elements for sealing the through-opening  16 . 
     Finally, in  FIG. 6  of the Figure sequence  1  to  6  for the production of a first embodiment of the filter bag according to the invention, the final state is shown which is produced after conclusion of the method. Subsequent to the method state represented in  FIG. 5 , the filter bag  1  is removed for this purpose from the anvil  11  and the second end region  5  situated opposite the base  2  is sealed by a weld seam  17 . 
     In the Figure sequence  7  to  12 , the production method for a second embodiment of a filter bag according to the invention is represented. The first two method steps which are represented in  FIGS. 7 and 8  are thereby identical to those described in detail in  FIGS. 1 and 2 . Deviating from the first embodiment however, the stacked layers  14 ,  15  which are formed by folding over the narrow sides are not folded back on the base  2  but on two lateral anvils  18  and  19  (see  FIG. 9  in this respect). As now shown in  FIG. 10 , the base seam  6  is formed in a subsequent method step by welding, a continuous weld seam which extends from the outer end of the folded-over narrow sides  14  to the other end of the folded-over narrow side  15  now being produced by applying the lateral anvils  18  and  19 . Advantageously, again a through-opening  16  is introduced during this method step in addition also by punching, over which through-opening a retaining plate with a corresponding opening is fitted subsequently. 
     Subsequently, the anvils  18  and  19  are then removed and the narrow sides  14  and  15  are folded over completely onto the side faces of the filter bag  1  ( FIG. 11 ). 
     Subsequently, the filter bag  1  is then removed from the anvil  11  and the second sealed end region  5  is formed by introducing a weld seam  17 . The then resulting filter bag  1  is in the end state, represented in  FIG. 12 . 
     In the Figure sequence  13  to  18 , the production method for a further preferred embodiment of a filter bag according to the invention is represented. The first method steps which are represented in  FIGS. 13 ,  14  and  15  correspond to those previously discussed according to  FIGS. 7 ,  8  and  9 . In contrast to the previous embodiment, however now the folded-over narrow sides  14  and  15 , as represented in  FIG. 16 , are not folded back onto the longitudinal sides but are removed by cutting after welding the overlapping region  3  by means of the central weld seam  6 . In order to seal the filter bag  1 , it is then provided in this embodiment that the narrow sides in the region of the base  2  are then sealed by an additional weld seam  23  and  24 . After sealing by means of welding, the protruding region can then be separated. The state which is then produced is represented in  FIG. 17 . The ultimate form of the filter bag  1  which is produced in this embodiment is then reproduced in  FIG. 18 .