Abstract:
A press fabric includes a substantially flat inner sleeve having first and second ends; and an outer sleeve around the inner sleeve and comprising at least one machine direction yarn wound around the inner sleeve and defining first and second seam loops at the first and second ends of the inner sleeve. A method for making the fabric is also disclosed.

Description:
CROSS REFERENCE TO PROVISIONAL APPLICATION 
     This application claims the benefit of the filing date of provisional patent application 60/759,649 filed Jan. 17, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to fabric for paper making machines and, more particularly, to a seam press fabric. 
     Paper is conventionally manufactured by conveying a paper furnish, usually consisting of an initial slurry of cellulosic fibers, on a forming fabric or between two forming fabrics in a forming section, the nascent sheet then being passed through a pressing section and ultimately through a drying section of a papermaking machine. In the case of standard tissue paper machines, the paper web is transferred from the press fabric to a Yankee dryer cylinder then creped. 
     Paper machine fabric or clothing is essentially employed to carry the paper web through these various stages of the papermaking machine. In the forming section, the fibrous furnish is wet-laid onto a moving forming wire and water is encouraged to drain from it by means of suction boxes and foils. The paper web is then transferred to a press fabric that conveys it through the pressing section, where it usually passes through a series of pressure nips formed by rotating cylindrical press rolls. Water is squeezed from the paper web and into the press fabric as the web and fabric pass through the nip together. Press fabrics generally comprise a batt of fibers needled to a base fabric. In the final stage, the paper web is transferred either to a Yankee dryer, in the case of tissue paper manufacture, or to a set of dryer cylinders upon which, aided by the clamping action of the dryer fabric, the majority of the remaining water is evaporated. 
     The base fabrics of press felts are woven endless, whether they are seamed or not, such that the yarns of the weft in the loom lie in the machine direction of the fabric on the paper machine. The weft yarns weave back and forth continuously between the laterally extending edges of the fabric and form a seam loop at the reversals on one side. The two ends formed are then joined together on the machine by means of a pintle wire. 
     Press felts consist of multiple layers which are secured together by needling. This works by mechanically locking the constituent batt fibers into various layers and in so doing holds them together. In addition, the batt fiber gives a homogenous paper support surface. 
     Thus, in the paper making industry, paper making felts or fabrics are used to carry the cellulosic material as it is formed into paper, and one such fabric is an endless woven base with a pin seam for securing the ends of the fabric together once the fabric is in place on the machine. 
     Numerous disclosures have been made in connection with manufacture of pin seam fabrics, including U.S. Pat. Nos. 6,283,165, 6,000,441, 3,283,388 and 4,495,680 as non-exhaustive examples. These teachings and others tend to be costly and slow, and the need remains in the industry for reduced cost and faster delivery time. 
     It is the primary object of the invention to provide a press fabric which meets these needs. 
     Other objects and advantages will appear below. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the foregoing objects and advantages have been attained. 
     According to the invention, a press fabric is provided which comprises a substantially flat inner sleeve having first and second ends; and an outer sleeve around the inner sleeve and comprising at least one machine direction yarn wound around the inner sleeve and defining first and second seam loops at the first and second ends of the inner sleeve. 
     Still further according to the invention, a method for making a press fabric is provided, which method comprises the steps of winding at least one machine direction yarn around an inner sleeve having first and second opposite ends so as to define first and second seam loops at the first and second opposite ends; flattening the inner sleeve; and joining the first and second seam loops. 
     According to the invention, the inner sleeve can be a woven or non woven base which is preferably formed into an endless loop upon which the machine direction yarns are wound to form an outer sleeve with seam loops. This is particularly advantageous since the seam loops are formed form yarns which are not woven with cross direction yarns, and there are therefore no cross direction yarn knuckles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of preferred embodiments of the present invention follows, with reference to the attached drawings, wherein: 
         FIG. 1  shows a press fabric according to the invention; 
         FIG. 2  is a schematic sectional view of the outer sleeve seam portion of the fabric of  FIG. 1 ; and 
         FIG. 3  shows starting material for an inner sleeve according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention relates to press fabrics and more particularly to a seam press fabric and a method for making same. 
       FIG. 1  shows a press fabric  10  according to the invention. Fabric  10  is useful in paper making machines and is mounted in such machines to carry cellulosic material through the various stages of the machine as the material is being formed into paper. One such section is the press section of the machine, and the fabric of the present invention is particularly well suited for use as a press fabric. 
     As shown in  FIG. 1 , fabric  10  has an inner sleeve  12  and an outer sleeve  14 . 
     Inner sleeve  12  can be any suitable substrate upon which outer sleeve  14  can be applied, and which will have the appropriate properties for use in a paper making machine fabric. Thus, inner sleeve  12  should be an open structure having void volume for accepting and holding water. One example of suitable material for inner sleeve  12  is an open scrim having machine direction components  16  and cross direction components  18 . 
     Outer sleeve  14  is defined according to the invention by winding machine direction yarn or yarns around inner sleeve  12 , preferably in a spiral fashion, such that outer sleeve  14  is formed primarily if not entirely of machine direction yarns  20 . 
     The machine direction is indicated in the drawings as MD, and refers to the direction in which the fabric will move when in use in a paper making machine. 
     The cross direction (CD in the drawings) is also a direction referred to herein, and refers to the direction transverse to the machine direction when the fabric is used on a paper making machine. 
     Batt material is typically attached to fabric  10  and can be positioned between inner sleeve  12  and outer sleeve  14 . After winding of outer sleeve  14 , it should be clear that inner sleeve  12  has two ends  22 ,  24 , and batt material and any CD yarns in areas  22 ,  24  can be removed to expose seam loops  26 ,  28  formed from yarns  20  of outer sleeve  14  (See also  FIG. 2 ). At this point, fabric  10  is structurally ready for mounting on a paper making machine, which typically involves feeding the fabric through the various rolls of the machine, preferably using a leader, until the fabric is on the machine with loops  26 ,  28  substantially adjacent to each other as shown in  FIG. 2 . These loops can then be pinned, for example using a pintle  30  schematically illustrated in  FIG. 2 , to join the ends together and finish installation of fabric  10  onto a paper making machine. 
     It should be appreciated that manufacturing fabric  10  in this manner provides seam loops  26 ,  28  from machine direction material which is not woven with cross direction material. This is desirable since the machine direction yarns are typically under tension, and when they are woven with cross direction yarns, cross direction knuckles can be formed which are not desirable as they adversely impact the paper product made on the machine. 
     The absence of cross direction yarns in outer sleeve  14  is compensated by the cross direction yarns or components of inner sleeve  12 . Thus, one desirable aspect of inner sleeve  12  is a good cross machine direction strength. one way to arrive at this structural strength is to start with a length of open material such as a scrim or the like which has a length that is about twice the length of the desired eventually fabric. This material  32  is shown in  FIG. 3  as having a length 2L, that is, a length twice the desired length L of fabric  10 . Material  32  can be a woven or non-woven structure, and preferably has a greater number of cross direction threads or components than machine direction threads or components. This is schematically illustrated in both  FIGS. 1 and 3  as the spacing between the schematically illustrated yarns or components of inner sleeve  12  in those drawings. 
     In order to make material  32  into inner sleeve  12 , material  32  is preferably wound around rollers or the like and ends  34 ,  36  are pinned together. Thus, machine direction yarns or components of material  32  can also preferably be formed into inner sleeve seam loops  38  which can be joined to each other as described so as to provide inner sleeve  12  as shown in  FIG. 1 . Of course, the actual method of preparation of inner sleeve  12  can vary, and although the disclosed embodiment is a particularly preferred embodiment, other materials and manufacturing methods could of course be used for inner sleeve  12 , well within the broad scope of the invention. 
     Suitable material for inner sleeve  12  includes but is not limited to open mesh scrim or screen, thin single layer woven fabric, joined spun bonded fibers, films and the like which preferably have cross direction stability. The material should have minimal machine direction, or warp, yarns. Suitable material could be a 0.005 inch PET, which has good stretch resistance. The machine direction yarns can preferably have a spacing of about 5-25 yarns per inch, preferably 10-15 yarns per inch. Cross direction yarns can be in the typical amounts normally used for such structures. Further, as an alternative and/or enhancement to pin seaming, inner sleeve  12  can be joined using an ultrasonic cutter or the like, and the joint can be reinforced with a thin perforated film or iron-on adhesive if desired. 
     Another alternative for inner sleeve  12  would be to provide same through a preferably low cost extruded netting process for making the scrim. 
     Once inner sleeve  12  is provided and formed into an endless loop, machine direction yarns of outer sleeve  14  can be applied. 
     Machine direction yarns  20  can, as one non-limiting example, be a single mono or plied monofil yarn. Winding of yarn onto inner sleeve  12  can be done from a creel, and reeds can be used to maintain spacing. After winding of the yarns of outer sleeve  14 , a batt material is attached to fabric  10  to lock inner sleeve  12  and machine direction yarns  20  of outer sleeve  14  together. The batt can be needle punched, and a low melt adhesive can be used as well. 
     The composite tube of inner sleeve  12 , outer sleeve  14  and batt material is then collapsed to substantially flatten the structure, and batt and any scrim material present at ends defined by the 180° opposite seam loops can be removed to clear the seam loops. Preferably after feeding onto a paper making machine, these loops are joined for example using a pintle. More batt fiber can then be needled into the structure as needed, and a batt flap can be attached to cover the seam if desired. 
     The final product is a four layer fabric, with two woven inner layers and two outer machine direction only layers. The final product is about half the length of the starting inner sleeve material, and has two superimposed, laminated endless bases. This structure produces excellent pressing uniformity, compaction resistance and void volume capability as well as good fiber bonding and wear resistance, all of which help to satisfy the above identified need in the industry. 
     It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.