Abstract:
A process for producing a multi-layered non-woven fabric includes: (a) forming a plurality of non-woven fabric layers from a plurality of filament materials which are produced respectively from a plurality of spinning devices disposed along an advancing forming screen; (b) forming at least one of the filament materials as a composite filament material which includes at least two filament components having high and low melting points by means of one of the spinning devices; and (c) depositing the filament materials on the advancing forming screen one over the other to form a plurality of non-woven fabric layers. An apparatus to carry out the process, and a multi-layered non-woven fabric produced thereby are also disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a multi-layered non-woven fabric which provides high air permeance, high water-pressure resistance, relatively small pores, and low pressure difference characteristics, and to a process and an apparatus for producing the multi-layered nonwoven fabric.  
           [0003]    2. Description of the Related Art  
           [0004]    Referring to FIG. 1, a conventional process for producing a spun-bonded non-woven fabric generally includes forcing a polymeric composition through a spinning nozzle  11  to form long filaments, depositing the long filaments onto a depositing device  12  to form a web, and passing the web between a pair of heat embossing rollers  13  to form a non-woven fabric. However, the non-woven fabric produced from the conventional process includes only one layer and only one filament component with a single melting point. In addition, when the single-melting point filaments are heat-treated by the heat embossing rollers  13 , they cannot provide a non-woven fabric with satisfactory surface softness and comfortable feel.  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the present invention is to provide a multi-layered non-woven fabric with high air permeance, high water-pressure resistance, relatively small pores, and low pressure difference characteristics.  
           [0006]    Another object of the present invention is to provide a process for producing the multi-layered non-woven fabric.  
           [0007]    Yet another object of the present invention is to provide an apparatus for producing the multi-layered non-woven fabric.  
           [0008]    According to one aspect of the present invention, a process for producing a multi-layered non-woven fabric includes: (a) forming a plurality of non-woven fabric layers from a plurality of filament materials which are produced respectively from a plurality of spinning devices disposed along an advancing forming screen; (b) forming at least one of the filament materials as a composite filament material which includes at least two filament components having high and low melting points by means of one of the spinning devices; and (c) depositing the filament materials on the advancing forming screen one over the other to form a plurality of non-woven fabric layers.  
           [0009]    According to another aspect of the present invention, a multi-layered non-woven fabric includes a plurality of non-woven fabric layers bonded together to form a laminate. The non-woven fabric layers are obtained from a plurality of filament materials which are produced respectively by a plurality of spinning devices disposed along an advancing forming screen. At least one of the non-woven fabric layers contains a composite filament material which includes at least two filament components of high and low melting points.  
           [0010]    According to yet another aspect of the present invention, an apparatus for producing a multi-layered non-woven fabric includes an advancing forming screen, and a plurality of spinning devices disposed successively adjacent to and along the direction of the forming screen so as to extrude a plurality of filament materials, respectively, and depositing means for depositing the filament materials one over the other on the forming screen to form a plurality of non-woven fabric layers. At least one of the spinning devices produces a composite filament material from at least two polymeric compositions. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a schematic view illustrating a conventional process and apparatus for producing a nonwoven fabric;  
         [0013]    [0013]FIG. 2 is a schematic view illustrating a process and apparatus embodying the present invention;  
         [0014]    [0014]FIG. 3 is a schematic view illustrating another process and apparatus embodying the present invention; and  
         [0015]    [0015]FIG. 4 illustrates cross-sections of bicomponent filaments that can be formed by the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Referring to FIG. 2, the preferred embodiment of an apparatus according to the present invention is shown to include an advancing forming screen  22  which is configured as a moving belt of a belt conveyor  21 , a first spun-bonding spinning device  30 , a first melt-blowing spinning device  40 , a second melt-blowing spinning device  50 , a second spun-bonding spinning device  60 , and a depositing unit which includes a suction device  23  disposed below the forming screen  22 . The spinning devices  30 ,  40 ,  50 ,  60  are disposed successively adjacent to and along the advancing direction of the forming screen  22  so as to extrude a plurality of filament materials of different types on the forming screen  22 . In practice, the spinning devices  30 ,  40 ,  50 ,  60  can be selectively activated to form a non-woven fabric with a desired number and desired types of fabric layers.  
         [0017]    The first spun-bonding spinning device  30  includes two separate feed tanks  31 ,  31 ′ for respectively receiving two different polymeric compositions having high and low melting points, two extruders  32 ,  32 ′ connected respectively to the feed tanks  31 ,  31 ′ for extruding the polymeric compositions, respectively, two filters  33 ,  33 ′ for filtering the extruded polymeric compositions, respectively, a spinning box  35  connected to the filters  33 ,  33 ′, and a pump  34  for pumping the filtered polymeric compositions into the spinning box  35 . The spinning box  35  has a spinning nozzle for forming the polymeric compositions into a bicomponent composite filament material that includes two different filament components having high and low melting points. A cooling chamber  351  is provided below the spinning nozzle of the spinning box  35  for cooling and setting the composite filament material. A high-speed air flow  36  at the ambient temperature is directed to a bottom outlet  352  of the cooling chamber  351  for suctioning and drawing the spun-bonded composite filament material out of the cooling chamber  351  via the bottom outlet  352 . The suction device  23  disposed below the forming screen  22  produces a downward suction force to deposit the spun-bonded composite filament material on the forming screen  22  to form a first spun-bonded composite fabric layer.  
         [0018]    The spun-bonded fabric layer includes long continuous filaments, and is prepared from a bicomponent combination selected from the group consisting of a combination of polypropylene and polyethylene, a combination of polyethylene terephthalate and polyethylene, a combination of polyethylene terephthalate and polypropylene, a combination of polypropylene and compound polypropylene (COPP) with a low melting point, a combination of polyethylene terephthalate and compound polyethylene terephthalate, a combination of nylon with a high melting point and nylon with a low melting point, and the like. The bicomponent composite filament material produced from the spinning nozzle of the first spun-bonding spinning device  30  includes a bicomponent filament with one of the structures shown in FIG. 4, such as a core-sheath structure or a side-by-side structure, depending on the design of the spinning nozzle.  
         [0019]    The first melt-blowing spinning device  40  is disposed downstream of the first spun-bonding spinning device  30 , and includes two separate feed tanks  41 ,  41 ′ for respectively receiving two different polymeric compositions of different melting points, two extruders  42 ,  42 ′ connected respectively to the feed tanks  41 ,  41 ′ for extruding the polymeric compositions, respectively, two filters  43 ,  43 ′ for filtering the extruded polymeric compositions, respectively, a spinning box  45  connected to the filters  43 ,  43 ′, and a pump  44  for pumping the filtered polymeric compositions into the spinning box  45 . The spinning box  45  has a spinning nozzle for forming the polymeric compositions into a bicomponent composite filament material that includes two different filament components. A cooling chamber  451  is provided below the spinning nozzle of the spinning box  45  for cooling and setting the composite filament material. A high-speed air flow  46  at the ambient temperature is guided to a bottom outlet  452  of the cooling chamber  451  for drawing the meltblown composite filament material out of the cooling chamber  451  via the outlet  452 . With the suction device  23  disposed below the forming screen  22 , the melt-blown composite filament material is deposited on top of the first spun-bonded composite fabric layer to form a first melt-blown composite fabric layer on the first spun-bonded composite fabric layer.  
         [0020]    The second melt-blown spinning device  50  has a structure similar to that of the first melt-blown spinning device  40 , and operates in a manner similar to that of the first melt-blown spinning device  40 . The second melt-blown spinning device  50  is disposed downstream of the first melt-blown spinning device  40  so as to produce a second melt-blown composite fabric layer on the first melt-blown composite fabric layer.  
         [0021]    Each of the first and second melt-blown fabric layers includes fine filaments, and is prepared from a bicomponent combination selected from the group consisting of a combination of polypropylene and polyethylene, a combination of polyethylene terephthalate and polyethylene, a combination of polyethylene terephthalate and polypropylene, a combination of polypropylene and compound polypropylene (COPP) with a low melting point, a combination of polyethylene terephthalate and compound polyethylene terephthalate with a low melting point, a combination of nylon with a high melting point and nylon with a low melting point, and the like. The melt-blown composite filament material includes a bicomponent filament with one of the structures shown in FIG. 4, such as a core-sheath structure or a side-by-side structure, depending on the design of the spinning nozzle. The melt-blown composite filament material has an average diameter smaller than that of the spun-bonded composite filament material. The average diameter of the meltblown composite filament material is less than 5 μm. The melt-blown composite fabric layer has an orientation of filaments with a more uniform compactness to obtain low pressure difference characteristics.  
         [0022]    The second spun-bonded spinning device  60  has a structure similar to that of the first spun-bonded spinning device  30 , and is operable in a manner similar to that of the first spun-bonded spinning device  30 . The second spun-bonded spinning device  60  is disposed downstream of the second melt-blown spinning device  50  so as to produce a second spun-bonded composite fabric layer on the second melt-blown composite fabric layer.  
         [0023]    The multi-layer non-woven fabric produced from the above-described process includes a first spun-bonded composite fabric layer, a first melt-blown composite fabric layer formed on the first spun-bonded composite fabric layer, a second melt-blown composite fabric layer formed on the first melt-blown composite fabric layer, and a second spun-bonded composite fabric layer formed on the second melt-blown composite fabric layer. The composite fabric layers are bonded together to form a laminate. To obtain a good structural connection between the adjacent composite fabric layers, one of the following heat treatments may be conducted.  
         [0024]    (1) The laminate is passed between a pair of heat-embossing rollers  71  to heat-bond the filaments of the composite fabric layers.  
         [0025]    (2) The laminate is passed through a hot air box  72  at a temperature not higher than the high melting point of the filament component of the spun-bonded and meltblown composite fabric layers so as to solely heat-bond the filament component of the lower melting point.  
         [0026]    After heat treatment, the laminate is taken up via a rolling-up device  90 . Because, after the heat treatment with the hot air box  72 , the filaments having high melting point in the fabric layers are not subjected to heat-bonding, the non-woven fabric thus produced has a loose and soft structure.  
         [0027]    Referring to FIG. 3, there is shown another apparatus according to the present invention which includes an advancing forming screen  22 , a first spun-bonding spinning device  30 , a first melt-blowing spinning device  40 , a second melt-blowing spinning device  50 , a second spun-bonding spinning device  60 , and a depositing unit which includes a suction device  23  disposed below the forming screen  22 . The spinning devices  30 ,  40 ,  50 ,  60  are disposed successively adjacent to and along the advancing direction of the forming screen  22  so as to extrude a plurality of filament material of different types on the forming screen  22 . As with the previous embodiment, the spinning devices  30 ,  40 ,  50 ,  60  can be selectively activated to form a non-woven fabric with a desired number and desired types of fabric layers. The filament materials produced from the spinning devices  30 ,  40 ,  50 ,  60  have one or more composite filament structures whose cross-sections are shown in FIG. 4. These filaments can be split. A water jet device  80  is disposed at the end of the forming screen  22  to produce a jet of water onto the laminate of the non-woven fabric layers for splitting the composite filaments in the composite fabric layers into finer filaments. In this manner, the filament materials in the fabric layers can be interlaced more uniformly. Thus, the nonwoven fabric has high air permeance and high water-pressure resistance.  
         [0028]    The multi-layered non-woven fabric produced from the process of the present invention is suitable for use as a filter for filtering water and air. Moreover, since the non-woven fabric according to the present invention is relatively soft, the non-woven fabric can thus be used in making diapers, sanitary napkins, surgical garments, surgical caps, surgical mouthpieces, etc.  
         [0029]    With this invention thus explained, it is apparent that numerous modifications and variations can be made without departing from the scope and spirit of this invention. It is therefore intended that this invention be limited only as indicated in the appended claims.