Abstract:
A filter element has a fold arrangement and a shaped seal extending about at least one section of a circumference of the fold arrangement. The shaped seal consists of a thixotropic sealing material or at least contains such a thixotropic sealing material. The thixotropic sealing material is thixotropic PUR or thixotropic silicone or a mixture of both.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a filter element that is provided with a seal extending about its circumference as well as a method for producing such a filter element. 
         [0002]    A filter element serves in general for filtration of, for example, fluid flows or gaseous media such as air flows that, for example, are supplied to the passenger compartment (interior) of a motor vehicle. Aside from their use in motor vehicles, such filters can also be used in other fields, for example, in air-conditioning devices and venting systems of buildings or for filtering liquid media. 
         [0003]    The efficiency of a filter depends in particular on the size of the surface area of the filter through which the air passes. In the case of interior air filters of motor vehicles, zigzag-folded (or accordion-folded) filters are therefore primarily used. By means of such a fold arrangement, as a function of the fold height and the fold spacing of the various fold sections of the filter, an effective enlargement of the filter surface area through which the air flow passes can be achieved. 
         [0004]    A filter element that is used e.g. as an interior air filter of a motor vehicle, serves for filtering by means of a suitable filter the ambient air that is supplied to the interior of the motor vehicle after having been conditioned. For this purpose, for example, particle filters or odor-removing filters or combinations of such filters are employed that remove by filtration the contained particles and inherent odors from the ambient air. In interior air filters of motor vehicles there is the problem that the filter element must be installed in a corresponding receiving space in such a way that it rests seal-tightly therein and that no gap between filter element and receiving space is formed that would cause leakage. 
         [0005]    Filter elements, for example, interior filters, are known in the prior art wherein the filter element is sealed off by a hard or flexible textile lateral strip. Such a lateral strip serves at the same time as a seal relative to the receiving space. 
         [0006]    Such filter elements however have the disadvantage that the lateral strips are only insufficiently effective as a seal and frequently hit their limitations. Moreover, the sealing contour of such a textile lateral strip cannot be varied easily. 
         [0007]    DE 101 63 026 discloses a filter element comprising a seal that projects past a face of a flat filter. The seal is configured as an unshaped sealing bead made form a thixotropic reaction mixture. 
         [0008]    There is therefore a need to provide a filter element with a seal that rests with satisfactory seal tightness against a receptacle in such a way that no leaks can occur. 
         [0009]    In addition there is a need that such a filter element with a seal can be produced in a simple and inexpensive way. 
         [0010]    Advantageously, the seal should be attachable to a side of the filter element. 
         [0011]    The seal should be advantageously configured such that it can be shaped, i.e., non-round shapes should be possible, e.g. one or several projecting sealing strips or lateral beads. 
         [0012]    In view of these demands, the present invention has the object to provide a filter element with an improved seal which filter element moreover should be predicable inexpensively. 
       SUMMARY OF THE INVENTION 
       [0013]    According to the present invention, this object is solved by a filter element that is provided on at least one section of its circumference with a seal wherein the seal consists of a thixotropic sealing material or at least comprises a thixotropic material. 
         [0014]    The object is furthermore solved in connection with the method for producing such a filter element with a seal by the following steps: metering a thixotropic sealing material into a mold cavity of a molding tool; pressing the mold cavity with the thixotropic sealing material contained therein against at least one section of the circumference of the fold arrangement of the filter element; and removing the molding tool with the mold cavity after the sealing material has formed a seal with the desired shape on the filter element. 
         [0015]    The object is furthermore solved in connection with the method for producing such a filter element with a seal by the following steps: applying a thixotropic sealing material onto at least one section of the circumference of the fold arrangement of the filter element; placing a molding tool with a mold cavity onto the thixotropic sealing material; shaping the sealing material by means of the mold cavity so that a seal with the desired shape is formed on the filter element; and subsequently removing the molding tool with the mold cavity. 
         [0016]    The principle upon which the present invention is based resides in that a filter element is provided with a seal that enables an improved sealing action of the filter element in a filter receiving space (receptacle). For this purpose, a seal made from a thixotropic sealing material is applied to at least one section of the circumference of the fold arrangement (folded filter material) of the filter element. 
         [0017]    In this way it is possible to provide a filter element that has improved lateral sealing action in a filter receiving space in comparison to textile lateral strips as they are employed currently. Moreover, such a filter element with such a seal can be produced easily and comparatively inexpensively. This is so because the thixotropic sealing material can be processed in a particularly simple and easy way. A further advantage is that such a seal can be produced or foamed with any desired contour. 
         [0018]    Advantageous embodiments and further developments of the invention can be taken from the dependent claims as well as the description in connection with attached drawings. 
         [0019]    In an advantageous embodiment, the thixotropic sealing material of the seal of the filter element is, for example, thixotropic PUR and/or thixotropic silicone. The thixotropic PUR has the advantage that it forms a substantially closed surface into which bacteria cannot easily penetrate in comparison to the known textile lateral strips. In principle, it also conceivable to employ a sealing material that behaves similar to the thixotropic sealing materials. This means that these sealing materials when applied to the filter element do not run down and, moreover, can be easily formed to the desired shape. 
         [0020]    Advantageously, the seal is shaped, i.e., it deviates from a round sealing bead. In this way, the adaptation to different receptacles and sealing geometries within a housing can be realized. The seal can be designed, for example, as a profiled section provided with one for several rectangular or semi-circular projections. In different embodiments, the seal can act in the inserted state alternatively in a radial or axial direction or can act both radially as well as axially. 
         [0021]    In one embodiment, in addition to its function of providing a sealing action fir the filter element within the housing, the seal can close off simultaneously the folds at the end faces, or parts of the end faces of the fold arrangement, where the folds are open. 
         [0022]    In a further embodiment the seal is provided with at least one additional sealing element, for example, a sealing lip. This has the advantage that the sealing action of the filter element is further improved. Moreover, in contrast to known textile strips, a thixotropic seal can be very easily provided with additional sealing elements or foamed so as to have additional sealing elements. The sealing elements or the contour of the seal can be varied as desired without any problems. 
         [0023]    In another advantageous embodiment the filter element has a zigzag-folded (or accordion-folded) and/or undulated fold arrangement. This has the advantage that filter elements with any fold arrangement can be utilized without any limitation and can be provided with a seal made from a thixotropic sealing material. 
         [0024]    In a further advantageous embodiment, the filter element has a partially circumferentially extending or completely circumferentially extending seal. This has the advantage that a filter element, depending on function and purpose, can be provided with a circumferential seal or can be provided only partially with a seal. 
         [0025]    In another advantageous embodiment, the folds of the filter element are at least partially or completely closed off by the seal. By complete closure of the folds, an optimal sealing action can be achieved by means of the filter element because there are no gaps through which a medium to be filtered could pass without having been filtered. 
         [0026]    In another advantageous embodiment the seal is attached by means of an adhesive to the filter element. For this purpose, for example a hot melt adhesive or any other suitable adhesive can be used. This has the advantage that the seal, for example, in the form of an endless strip, can be produced beforehand and subsequently can be glued to the circumferential sides or faces of the filter element in question. 
         [0027]    According to another advantageous embodiment the thixotropic sealing material is applied onto the filter element by means of a molding tool provided with a corresponding mold cavity. This has the advantage that the seal is formed directly on the filter element. 
         [0028]    In another advantageous embodiment, the filter element is an odor-removing filter and/or a particle filter or a liquid filter. This has the advantage that the filter element provided with a seal of a thixotropic sealing material can be used for a variety of applications and is not limited to air filters but can be in principle used for all other types of filters. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a schematic perspective view of a filter element whose seal is shaped by means of a molding tool with a mold cavity. 
           [0030]      FIG. 2  is a side view of the filter element according to  FIG. 1  wherein the sealing material is filled into the mold cavity of the molding tool. 
           [0031]      FIG. 3  is a side view of the filter element according to  FIG. 1  wherein the sealing material is applied to the fold arrangement of the filter element and subsequently a mold cavity of a molding tool is placed onto the sealing material. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    In the drawings, components, elements and features that are the same, or functionally identical, are identified by same reference numerals, if not noted otherwise. 
         [0033]      FIG. 1  shows a schematic perspective illustration of a filter element  10  according to the invention comprised of a fold arrangement of filter material with a seal  12 . The seal  12  is comprised of a thixotropic sealing material  24 , for example, thixotropic PUR (thixotropic polyurethane) or thixotropic silicone. This list is to be understood to be exemplary only and is non-limiting. Basically, for the seal  12  of the filter element  10  any type of suitable thixotropic sealing material  24  can be used or a sealing material that behaves similar to or substantially in the same way as a thixotropic sealing material. 
         [0034]    In order to shape the seal  12  form the thixotropic sealing material  24 , a molding tool (not illustrated) with a mold cavity  14  is used, for example. The mold cavity  14  forms the desired contour of the seal  12  and is removed after the shaping process is completed. The finished filter element  10  with seal  12  can subsequently be used, for example, in the form of an air filter or odor-removing filter and/or particle filter. Basically, any other type of filter element can be provided with the afore described seal. For example, a liquid filter is conceivable also as a filter element  10 . 
         [0035]    The thixotropic sealing material, for example, thixotropic PUR has the advantage that, as soon as it has been applied to the filter element  10 , it solidifies to such an extent that it can be shaped by the molding tool with the mold cavity  14  without the sealing material running down the filter element  10 . In contrast, a non-thixotropic PUR is relatively liquid so that after having been applied to the filter element  10  it will run down. Moreover, polymerization of the thixotropic PUR occurs relatively quickly so that the shaping process by means of the molding tool can be completed rather quickly and the molding tool can then be subsequently removed. Non-thixotropic PUR requires in contrast thereto in a shaping process several minutes in order to solidify to a satisfactory degree. A further advantage of thixotropic PUR is that it forms a substantially closed surface in which bubbles are connected with one another. In this way, bacteria cannot penetrate and settle in the PUR. In case of textile lateral strips, bacteria can however easily penetrate into the fabric. 
         [0036]    The term thixotropy refers to the property of a non-Newton fluid in which the viscosity decreases at constant shear strain across a time axis X. After cancelling the shear strain, the initial viscosity will return. Modern strong and enduring sealing materials are examples of thixotropically reacting products. They can be easily spread and exhibit in this connection also the required flow behavior, but they essentially solidify immediately when they are no longer mechanically loaded. 
         [0037]    The sealing strip or the seal  12 , as illustrated in the  FIGS. 1 to 3 , is provided with a sealing lip  16  as an additional sealing element  18 . This has the advantage that a lateral sealing action can be improved even more. Basically, the sealing strip  12  can have any suitable contour or, as needed, can be provided with at least one additional sealing element  18  such as a sealing lip  16  or can be foamed so as to have such a sealing element  18 . 
         [0038]    Basically, the filter element  10 , respectively, the fold arrangement of filter material, can be provided circumferentially or at least across one or several sections with the afore described seal  12 , depending on which area of the filter element  10  is to be configured to provide a sealing action. 
         [0039]    The seal  12  can be premanufactured as an endless strip wherein, as needed, additional sealing elements  18 , for example, one or several sealing lips  16 , can be provided. The endless strip can be, for example, attached by means of an adhesive to a corresponding filter element  10  (not illustrated). This has the advantage that a continuous manufacture that does not required a casting mold is possible wherein the filter elements  10  can be cut to the required length and then be provided with the sealing strip  12 . This corresponds to the manufacture used in regard to textile lateral strips. However, the use of seals  12  made form a thixotropic sealing material  24  has the advantage that the lateral sealing action of the filter elements  10  can be significantly improved relative to the use of textile lateral strips. As needed, additional sealing elements  18  can be foamed; this further improves the sealing action. 
         [0040]    A further possibility for producing a filter element  10  according to the invention with a seal  12  will be explained in relation to  FIG. 2 . In this connection, for example, a thixotropic PUR is metered into a circumferential mold cavity  14  of a molding tool. Further sealing elements  18 , for example, two rounded sealing lips  16  can be integrated in the mold cavity  14 . The still liquid thixotropic PUR is pressed against the fold arrangement  20  of the filter element  10  wherein the sealing material  24  can be used at the same time for laterally closing the folds  22  of the filter element  10 . The folds  22  are at least partially, or completely, closed off by the sealing material  24 . This holds true for all embodiments. 
         [0041]    Moreover, the inventive filter element can be produced with a seal as illustrated in  FIG. 3 . The sealing material  24  is a thixotropic PUR that is applied to the side of the filter element  10 . Subsequently, the molding tool with a correspondingly shaped mold cavity  14  is placed onto the thixotropic PUR and the thixotropic PUR is shaped by means of the contour of the mold cavity  14 . The thixotropic PUR has the advantage relative to non-thixotropic PUR that it can be applied without problems to the filter element  10  and that it solidifies quickly without running down the filter element  10 . In contrast, a non-thixotropic PUR behaves in such a way that it will run down the filter element  10  after having been applied to the filter element  10  because in the beginning it is rather liquid and requires several minutes in order to solidify to a satisfactory degree so that it can be shaped. 
         [0042]    Even though the present invention has been explained supra in detail with the aid of preferred embodiments, the invention is not limited to these embodiments and can be modified in many ways. 
         [0043]    The present invention is in particular not limited to the above explained configurations of the described embodiments and variants. In particular, the present invention is not limited to thixotropic PUR and thixotropic silicone as sealing material  24 . In principle, any other thixotropic sealing material  24  can be used or a sealing material that behaves in a similar way as a thixotropic material. 
         [0044]    Moreover, the invention is not limited to the mold cavities  14  shown in  FIGS. 1 to 3 . Instead of having one or two sealing lips  16 , the seal  12  can also be provided with several sealing lips  16  that have the same shape or different shapes. Basically, the contour of the seal  12 , as well as the shape and number of additional sealing elements  18 , such as sealing lips  16 , can be varied depending on the application and function of the seal. 
         [0045]    Moreover, the invention is not limited to filter elements  10  for filtering gaseous media but can also be used advantageously for filter elements  10  for filtering liquids. Also, the invention is not limited necessarily to filter elements  10 , for example, for air-conditioning devices and the like in the automotive field, but can also be used in an advantageous manner in any application in which filter elements  10  are employed. 
         [0046]    Moreover, the fold arrangement  22  of the filter element  10  must not be zigzag-folded or accordion-folded but can also be undulated. 
         [0047]    Furthermore, in the afore described embodiments, the sealing material  24  can be applied circumferentially or partially circumferentially or across sections on the sides or faces of the filter element  10 . The seal  12 , as shown in  FIGS. 1 to 3 , can be flush with the filter element  10  but can also slightly project past at least one side of the filter element  10  (not illustrated). 
         [0048]    Furthermore, the filter element  10  must not have a quadrangular shape and a zigzag-folded arrangement of folds as shown in  FIG. 1  but can have any type of shape or fold arrangement. The filter element  10 , in addition to a quadrangular shape, can also have any other polygonal shape or can be round or oval and can be a combination of polygonal and round contours. The outer contour of the filter element  10 , as described above, is provided with a seal  12  of a thixotropic sealing material  24 . 
         [0049]    Moreover, the invention is not limited to the afore described manufacturing processes. The methods are to be understood only as exemplary and preferred embodiments, wherein modifications are possible. 
         [0050]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.