Abstract:
A filtering mass in sheet form for an air filter for an enclosed space, particularly a motor vehicle cabin, comprising elements made of standard-type materials normally used to form filtering masses and carbon elements rendered active in the adsorption of gaseous substances.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a filtering mass in sheet form for an air filter for an enclosed space, particularly for a motor vehicle cabin, and to methods for obtaining such mass.  
           [0002]    Filters are known which are installed at ventilation systems of enclosed spaces in order to filter the external air that enters the enclosed spaces; this is the case, for example, of motor vehicle cabins, or of buildings used for living or for work.  
           [0003]    Very commonly, such filters comprise a filtering mass in sheet form, which is inserted in a pleated or flat arrangement in a supporting frame, and currently the filtering mass is substantially produced according to two types.  
           [0004]    A first type of filtering mass consists of a sheet formed by fibers of different materials, such as for example polyester, polyamide, polypropylene, pure or mixed together, providing what is known as “non-woven fabric”, or also by cellulose fibers, either substantially pure or mixed with fibers of materials such as the ones cited above, providing what is known as “filter paper”.  
           [0005]    The materials and fibers currently used are referenced respectively hereinafter as “standard-type materials” and “standard fibers”.  
           [0006]    The fiber mat meant to constitute the sheet of filtering mass is subjected, after forming, to impregnation in order to give it the necessary mechanical consistency and any other characteristics, such as for example fire-resistant and antibacterial properties, and is finally subjected to finishing operations.  
           [0007]    With this type of filtering mass, filters are produced which are known as “particulate filters” because they are capable of retaining exclusively particulate matter.  
           [0008]    If it is also necessary to retain unwanted gaseous substances, a second type of sheet of filtering mass is currently used which is constituted by an intermediate layer of carbon granules enclosed between two layers of standard fibers, which ensure particle retention, while the intermediate layer of carbon granules retains the gaseous substances.  
           [0009]    This second type of sheet of filtering mass, however, has drawbacks, such as a high cost and the generation of high load losses; moreover, carbon granules can break away and be dispersed into the environment.  
         SUMMARY OF THE INVENTION  
         [0010]    The aim of the present invention is to provide a filtering mass in sheet form for an air filter, which is capable of retaining both particulate matter and undesirable gaseous substances, has a low cost, generates limited load losses and cannot cause contamination.  
           [0011]    This aim is achieved by a filtering mass in sheet form for an air filter for an enclosed space, particularly a motor vehicle cabin, according to the invention, characterized in that it comprises elements made of standard-type materials normally used to form filtering masses and carbon elements rendered active for the adsorption of gaseous substances. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Further characteristics and advantages of the invention will become better apparent from the description of some preferred but not exclusive embodiments thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 is a view of a portion of a sheet of filtering mass with a single layer of elements in fiber form;  
         [0014]    FIGS.  2  to  5  are views of portions of different sheets of filtering mass with two layers of elements in fiber form;  
         [0015]    [0015]FIG. 6 is a view of a portion of a sheet of filtering mass with a single layer of fabric formed by elements in filament form;  
         [0016]    [0016]FIG. 7 is a view of a portion of a sheet of filtering mass with a layer of fabric formed by elements in filament form and a layer of elements in fiber form;  
         [0017]    [0017]FIG. 8 is a view of a portion of a sheet of filtering mass with three layers of elements in fiber form. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    With reference to FIG. 1, the reference numeral  1  designates a portion of a sheet of filtering mass which comprises a single layer of elements in the form of fibers of materials normally used in the manufacture of filters which, as mentioned, are referenced herein as standard fibers, are shown in thin lines and are designated by the reference numeral  2 ; these fibers are mixed with carbon fibers, shown in thick lines and designated by the reference numeral  3 , which are generally obtained from vegetable or synthetic polymers, activated for the adsorption of gaseous substances by means of known processes.  
         [0019]    All the fibers comprised in this embodiment of the invention, as well as the fibers comprised in the other embodiments described hereinafter, may have any length and may be obtained in any manner, for example by breaking up filaments as regards the carbon fibers, which obviously, regardless of how they are obtained, are always activated for the adsorption of gaseous substances.  
         [0020]    The mat that leads to the formation of the described sheet can be obtained in a conventional apparatus supplied with the cited materials in the required proportions.  
         [0021]    A sheet of filtering mass has thus been obtained which is capable of retaining both the particulate fraction, by virtue of the presence of the standard fibers, and, by virtue of the presence of the carbon fibers, the undesirable gaseous substances contained in the air that crosses it in a direction that can be the one indicated by the arrows in the figure but can also be the opposite direction.  
         [0022]    Further embodiments of the invention are now described, always adopting the graphical representation in which the standard fibers  2  are shown in thin lines and the carbon fibers  3  are shown in thick lines.  
         [0023]    The sheet  4  of FIG. 2 comprises two layers, i.e., a layer  4   a  comprising pure standard fibers  2  and a layer  4   b  comprising pure carbon fibers  3 .  
         [0024]    The sheet  5  of FIG. 3 also comprises two layers  5   a ,  5   b,  both comprising standard fibers  2  and carbon fibers  3 .  
         [0025]    The sheet  6  of FIG. 4 comprises two layers: a layer  6   a,  which comprises pure standard fibers  2 , and a layer  6   b,  which comprises standard fibers  2  and carbon fibers  3 .  
         [0026]    Finally, the sheet  7  of FIG. 5 comprises two layers  7   a  and  7   b : the first one comprises pure carbon fibers  3  and the second one comprises standard fibers  2  and carbon fibers  3 .  
         [0027]    All these sheets are arranged in the filter so that the first layer crossed by the air is the one that comprises standard fibers, as shown by the arrows in the figures.  
         [0028]    A method for obtaining a sheet of filtering mass of the type described with reference to FIGS.  2  to  5  comprises a first step, for obtaining in output from an appropriately supplied apparatus a mat suitable to form the first layer of the sheet, and a second step, for depositing on said mat, in the presence of adhesive or not, loose fibers suitable to form the second layer; this is followed by the impregnation and finishing steps.  
         [0029]    Another method for obtaining a sheet of the type shown in FIGS.  2  to  5  comprises a first step, in which two mats are formed in a superimposed configuration by two different appropriately supplied apparatuses, such mats being meant to form respectively the first and second layers of the sheet, and subsequent impregnation and finishing steps.  
         [0030]    Another method for obtaining a sheet of filtering mass with two layers provides for the formation of two perfectly finished separate mats, suitable to form respectively the first and second layers of the sheet, and the gluing thereof in a superimposed configuration.  
         [0031]    [0031]FIG. 6 illustrates another variation  8  of the invention, which comprises a single layer formed bv elements in filament form made of standard-tvpe materials such as  9  and of carbon filaments such as  10 , woven so as to form an actual fabric.  
         [0032]    Obviously, the carbon filaments such as  10  are activated, and so are the carbon fibers considered earlier, for the adsorption of gaseous substances.  
         [0033]    In the variation  11  of FIG. 7 there is a first layer  11   a  of fabric, exactly of the type shown in FIG. 6, and a second layer  11   b  comprising pure standard fibers.  
         [0034]    Further variations can be provided by combining a layer of actual fabric, such as  8  of FIG. 6 or  11   a  of FIG. 7, with a layer that comprises pure carbon fibers, or with a layer comprising mixed standard fibers and carbon fibers.  
         [0035]    All the above described embodiments can be provided with an additional supporting layer, normally arranged on the air exit side, as in the case for example of the sheet  12  of FIG. 8, which is obtained by adding to a sheet with two layers  12   a  and  12   b , such as the one shown in FIG. 2, a third layer  12   c  made of standard fibers  2 .  
         [0036]    A sheet such as the one described above can be obtained with a method that provides for a first step for forming three superimposed mats produced by different apparatuses suitable to form respectively the three layers, and final steps for impregnation and finishing, or also with a method that provides for a step for gluing two finished mats made of standard fibers, after inserting carbon fibers between them in any manner.  
         [0037]    In a different embodiment, the supporting layer can be provided by means of a net.  
         [0038]    The invention is susceptible of numerous other modifications and variations, all of which are within the scope of the inventive concept.