Patent Publication Number: US-7721769-B2

Title: Paper machine fabric with trapezoidal shaped filaments

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to fabrics for use in paper machines, and, more particularly, to fabrics used for moulding fiber webs. 
   2. Description of the Related Art 
   A paper machine typically includes a number of discrete sections along the running length of the machine, such as the fordrinier section, forming section, press section, and drying section. Each section of the paper machine typically includes a plurality of rolls and possibly other components which carry a corresponding fabric. A fabric typically has opposite ends which are joined together to define an endless fabric carried by the rolls, with the particular configuration of the fabric corresponding to the particular use in the paper machine. 
   One type of fabric is a through air dryer (TAD) fabric used to produce a tissue web. During production of such a tissue web using the TAD drying process, the tissue web is moulded inside the fabric structure, creating pillows that provide desired bulk and water absorption properties to the tissue web. At the end of the TAD process, the tissue web is removed from the fabric topography to be transported downstream in the machine direction (MD) of the paper machine. It is therefore desirable for the fabric to have good sheet release properties so that the tissue web can be successfully removed from the TAD fabric. The release properties of the fabric can be affected by the shape of the individual filaments in the fabric and chemical release agents applied to the fabric. The use of chemical release agents is minimized so as not to adversely affect the runability and production cost issues. 
   What is needed in the art is a fabric for TAD applications having better release properties than conventional fabrics. 
   SUMMARY OF THE INVENTION 
   The present invention provides a fabric for use on a paper machine, including at least some filaments having a trapezoidal shaped cross section. 
   The invention in one form is directed to a fabric for use on a paper machine, including a plurality of filaments woven together. At least a portion of the filaments have a machine side base, a web side face, and a pair of side walls extending between the base and the face. The portion of the filaments having a generally trapezoidal shaped cross section is defined by the face and the pair of side walls. 
   The invention in another form is directed to a fabric for use on a paper machine, including a plurality of filaments woven together. At least a portion of the filaments have a generally flat machine side base, a generally flat web side face, and a pair of generally flat side walls extending between the base and the face. The portion of the filaments having a generally trapezoidal shaped cross section is defined by the base, the face and the pair of side walls. 
   The invention in yet another form is directed to a paper machine, including a roll and a fabric carried by the roll. The fabric includes a plurality of filaments woven together. At least a portion of the filaments have a generally flat machine side base, a generally flat web side face, and a pair of generally flat side walls extending between the base and the face. The portion of the filaments having a generally trapezoidal shaped cross section is defined by the base, the face and the pair of side walls. 
   An advantage of the present invention is that the fabric has better release properties. 
   Another advantage is that less release chemicals are needed on the fabric, thereby reducing runnability issues and production costs. 
   Yet another advantage is that the flat base of the filaments increases the life potential for the fabric. 
   A further advantage is that the fabric can be used as a TAD fabric. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a schematic illustration of a portion of a paper machine, including an embodiment of a fabric of the present invention; 
       FIG. 2  is a schematic, perspective view of the fabric shown in  FIG. 1 ; 
       FIG. 3  is an enlarged, perspective view taken at detail A in  FIG. 2 , showing the cross section of a single filament; 
       FIG. 4  is an end view showing an exemplary weave pattern of MD filaments and CD filaments; and 
       FIG. 5  is an end view of another embodiment of a filament of the present invention. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a schematic representation of a portion of a paper machine  10 , which may generally include a variety of configurations depending upon the application. Paper machine  10  may include a forming section, press section, drying section, etc. each of which typically includes a plurality of rolls  12  (one of which is shown in  FIG. 1 ) carrying a fabric  14 . A configuration of roll  12  may vary, depending upon the particular area of use along the running length in machine direction (MD) of paper machine  10 . Similarly, fabric  14  of the present invention may also vary in specific filament types, weave patterns, etc., depending upon the particular area of use along the running length in machine direction MD of paper machine  10 . In the embodiment shown, fabric  14  of the present invention is assumed to be a TAD fabric. 
   Referring now to  FIG. 2 , TAD fabric  14  will be described in greater detail. In general, a TAD fabric has two primary characteristics. First, the fabric is constructed to allow a relatively high volumetric flow rate of air through the fabric for drying the fiber web. Further, the TAD fabric is constructed in such a way that the fiber web is drawn into the spaces between the MD filaments and the cross machine direction (CD) filaments, thereby forming pillows in the fiber web upon release with a great degree of bulk and absorbency. 
   According to an aspect of the present invention, some or all of the MD filaments and/or some or all of the CD filaments are formed with a trapezoidal shaped cross section allowing better release of the fiber web from TAD fabric  14  at the end of the TAD drying process. More particularly, the cross sectional shape of a single filament  16  is shown in  FIG. 3 , derived from detail A in  FIG. 2 . Filament  16  has a machine side base  18 , a web side face  20 , and a pair of side walls  22  extending between base  18  and face  20 . Base  18  is positioned adjacent roll  12  of paper machine  10 , and face  20  is positioned adjacent to and carries the fiber web. Each of base  18 , face  20  and side walls  22  are generally flat to thereby define the generally trapezoidal shaped cross section of filament  16  shown in  FIG. 3 . Base  18  and face  20  are positioned generally parallel to each other, with face  20  having a width X 1  which is shorter than a width X 2  of base  18 . Side walls  22  are positioned to define a draft angle α with base  18  and face  20  providing better release properties to the fiber web carried thereby. Draft angle α is between approximately 0 to 20°, more preferably is between approximately 1 to 20°, and even more preferably is approximately 10°. Additionally, side walls  22  have a height Z extending between and perpendicular to base  18  and face  20 . Height Z of side walls  22  is between approximately 0.75 to 1.05 times the width X 2  of base  18 , and preferably is approximately 0.90 times the width X 2  of base  18 . 
   As indicated above, it is possible to configure fabric  14  such that some or all of MD filaments  16  and/or CD filaments  24  have a trapezoidal shaped cross section as described above. For example, the following combinations of filaments are possible:
         Fabric containing 100% of the yarn filaments trapezoidal. Use of trapezoidal filaments on both directions, machine direction (MD) and on cross machine direction (CD).   Use all the MD filaments with standard circumferential shape and apply trapezoidal yarns on the CD filaments.   Use trapezoidal yarns on the MD filaments and use standard circumferential shape on the CD filaments.   CD filaments having more than one type of trapezoidal yarn dimensions.   MD filaments having more than one type of trapezoidal yarn dimensions.       

   Other configurations are also possible, with the particular configuration of trapezoidal shaped filaments being selected to provide optimum performance for fabric  14 . 
   Referring to  FIG. 4 , a weave pattern for filaments  16 ,  24  is shown. CD filaments  24  are also assumed to have a trapezoidal shaped cross section, and thus it will be appreciated that only a single side wall  22  of each CD filament  24  is seen in  FIG. 4 . By placing the wider base  18  of fabric  14  against roll  12 , the runability and service life of fabric  14  is improved. 
   Referring to  FIG. 5 , another embodiment of a filament  26  which could possibly be used in the MD or CD directions is shown. Similar to filament  16  shown in  FIG. 3 , filament  26  shown in  FIG. 5  has a face  28  which defines a draft angle α with side walls  30  providing improved release of the fiber web. However, base  32  is not a generally flat surface extending between the apex points of side walls  30  (indicated by the dashed line). Rather, base  32  is a curved surface which could be desirable for some applications against a machine side component of paper machine  10 . 
   During operation, the fiber web is drawn into the spaces between adjacent MD filaments  16  and CD filaments  24  of fabric  14 . The flow of air through fabric  14  dries the fiber web with pillows for increased bulk. Release of the fiber web from fabric  14  at the end of the TAD process is improved because of the trapezoidal shaped cross section of MD filaments  16  and/or CD filaments  24 . 
   While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.