Press felt

Abstract

The present invention relates to a press felt having a first surface provided by a nonwoven structure and a second surface opposite the first surface, as well as a load absorbing base structure which is bonded with the nonwoven structure and is arranged between the first and the second surface. The press felt according to the present invention further includes particulate polymer material which is penetrated into the nonwoven structure from the first surface in sections in the direction of the second surface and which is adhered to the fibers of the nonwoven structure in a manner that the press felt has a permeability of at least 5 cfm, for example, at least 10 cfm. The present invention is characterized in that at least one filter layer is arranged in the nonwoven structure or at the barrier surface between the nonwoven structure and the base structure which is permeable for fluid and is substantially impermeable for polymer material from, for example, a predetermined particle size on.

1 . A press felt, comprising:
 a nonwoven structure having a first surface and a second surface opposite said first surface;   a load absorbing base structure bonded with said nonwoven structure, said base structure arranged between said first surface and said second surface;   particulate polymer material penetrated into said nonwoven structure from said first surface in sections of said nonwoven structure in a direction of said second surface, said particulate polymer material being adhered to fibers of said nonwoven structure in a manner such that the press felt has a permeability of at least approximately 5 cfm; and   at least one filter layer arranged in one of said nonwoven structure and at a barrier surface between said nonwoven structure and said base structure, said at least one filter layer being permeable for fluid and substantially impermeable for particulate polymer material of at least a predetermined particle size.   
   
   
       2 . The press felt according to  claim 1 , wherein the press felt has a permeability of at least 10 cfm. 
   
   
       3 . The press felt according to  claim 2 , wherein said at least one filter layer has a thickness of approximately 0.5 mm or less. 
   
   
       4 . The press felt according to  claim 3 , wherein said at least one filter layer is a nonwoven layer formed by fibers with approximately 3.3 dtex or less. 
   
   
       5 . The press felt according to  claim 4 , wherein said at least one filter layer is formed by fibers with approximately 1.7 dtex or less. 
   
   
       6 . The press felt according to  claim 5 , wherein said fibers of said at least one filter layer are configured to be fused with each other at common contact points. 
   
   
       7 . The press felt according to  claim 6 , wherein said fibers of said at least one filter layer are configured to be fused by heat effect. 
   
   
       8 . The press felt according to  claim 6 , wherein said at least one filter layer has a basis weight in a range of between approximately 20 g/m 2  and 180 g/m 2 . 
   
   
       9 . The press felt according to  claim 8 , wherein said at least one filter layer includes at least one of polyurethane fibers, polypropylene fibers and polyamide fibers. 
   
   
       10 . The press felt according to  claim 9 , wherein said at least one filter layer is one of hydrophobic and hydrophilic. 
   
   
       11 . The press felt according to  claim 10 , wherein said at least one filter layer is formed by a sacrificial material configured to dissolve from the press felt at a time subsequent to fixation of said particles said nonwoven structure. 
   
   
       12 . The press felt according to  claim 11 , wherein said sacrificial material is thermoplastic polyurethane configured to melt at the time of fixation of said polymer particles in said nonwoven structure. 
   
   
       13 . The press felt according to  claim 12 , wherein said at least one filter layer is configured to be formed in one of a layer in said nonwoven structure and at said barrier surface between said nonwoven structure and said base structure, said at least one filter layer being at least one of physically and chemically treated and is fluid permeable and substantially impermeable to said particles of polymer material having a predetermined size. 
   
   
       14 . The press felt according to  claim 13 , wherein said at least one filter layer is a perforated foil. 
   
   
       15 . The press felt according to  claim 14 , wherein said at least one filter layer has a thickness of approximately 0.2 mm or less. 
   
   
       16 . The press felt according to  claim 15 , wherein said at least one filter layer has a thickness of approximately 0.1 mm or less. 
   
   
       17 . The press felt according to  claim 16 , wherein said at least one filter layer is two filter layers, said two filter layers including a first filter layer and a second filter layer, said first filter layer being impermeable to said particles of said polymer material having a predetermined size and a second of said two filter layers being substantially impermeable to said particles of said particulate polymer material having a smaller size. 
   
   
       18 . The press felt according to  claim 17 , wherein in a direction from said first surface to said second surface, said first filter layer is arranged before said second filter layer. 
   
   
       19 . The press felt according to  claim 18 , wherein said particulate polymer material includes particles of different sizes, a first portion of said particulate material having one of a predetermined size and a predetermined range of sizes in said nonwoven structure and a second portion of said particulate polymer material having one of a size and a range of sizes larger than said first portion, said larger particles emanating from said first surface. 
   
   
       20 . The press felt according to  claim 19 , wherein said particulate polymer material is configured to be added into said nonwoven structure of the form of at least one suspension. 
   
   
       21 . The press felt according to  claim 20 , wherein said particles of particulate polymer material are configured to be fused together and with fibers of said nonwoven structure subsequent to addition of said particulate polymer material. 
   
   
       22 . The press felt according to  claim 21 , wherein said fibers of said nonwoven structure are at least approximately 6.7 dtex. 
   
   
       23 . The press felt according to  claim 22 , wherein said nonwoven structure includes a plurality of nonwoven layers stacked one on top of another between said first and said second surface. 
   
   
       24 . The press felt according to  claim 23 , wherein at least one of said nonwoven layers includes fibers having a greater thickness than fibers of another of said nonwoven layers. 
   
   
       25 . The press felt according to  claim 24 , wherein said first surface including said polymer particles forms a paper-side surface of the press felt. 
   
   
       26 . The press felt according to  claim 25 , wherein said first surface including said polymer particles forms a machine-side surface of the press felt. 
   
   
       27 . The press felt according to  claim 26 , wherein said polymer particles and said fibers of said nonwoven structure are configured to form a porous layer in said nonwoven structure, said porous layer being located below said paper-side surface, said porous layer being applied to said filter layer. 
   
   
       28 . The press felt according to  claim 27 , wherein said porous layer has a thickness of 1.0 mm or less. 
   
   
       29 . The press felt according to  claim 28 , wherein said porous layer has a thickness of 0.7 mm or less. 
   
   
       30 . The press felt according to  claim 29 , wherein said polymer particles include a plurality of particles having a predetermined size penetrated into said nonwoven structure from said first surface to said filter layer, a concentration of said polymer particles one of decreasing over a penetration depth, increasing over said penetration depth and remaining constant over said penetration depth.