Pleatable nonwoven material and method and apparatus for production thereof

Abstract

A pleatable nonwoven material is provided, including thicker form-giving fibers and thinner fibers determining the filter effect, wherein the thinner fibers are incorporated largely homogeneously in the thicker fibers running in the direction along the surface of the nonwoven material and a distribution density gradient of the thinner fibers is established perpendicular to the surface of the nonwoven material such that the highest concentration of thinner fibers is in the region of the center or on one of the two outsides, wherein the thicker and thinner fibers are bonded together by solidification from the melted condition and are made from the same material.

1 . A pleatable nonwoven material comprising supporting, form-stabilizing thicker fibers and thinner fibers determining the filter effect, wherein the thinner fibers are incorporated largely homogeneously in the thicker fibers in a direction along the surface of the nonwoven material and wherein there is a distribution-density gradient of the thinner fibers in a direction perpendicular to the surface of the nonwoven material such that the highest concentration of thinner fibers is in the region of one of the group comprising the center and one of the two outsides, with the thicker and the thinner fibers being bonded together by solidification from the melted condition while being made of the same material, the thicker fibers being larger-diameter polymer threads and the thinner fibers being smaller-diameter polymer threads which are tangled and intertwined with each other. 
   
   
       2 . A pleatable nonwoven material according to  claim 1 , wherein the thicker fibers have a diameter >2 μm and the thinner diameters have a diameter <1000 nm. 
   
   
       3 . A pleatable nonwoven material according to  claim 2 , wherein the thicker fibers have a diameter of between 2 and 200 μm. 
   
   
       4 . A pleatable nonwoven material according to  claim 2 , wherein the thinner fibers have a diameter of between 50 nm and 1000 nm. 
   
   
       5 . A pleatable nonwoven material according to  claim 1 , wherein the fibers consist of polyamide, polypropylene, polyester or a mixture thereof. 
   
   
       6 . A method of producing a pleatable nonwoven fabric, in which a polymer is melted and pressed through the spinnerets of a spinning beam, and in which the polymer threads thus produced are laid down on a conveyor belt such as to form a nonwoven layer, wherein spinnerets ( 2 ) of different diameters are used and higher- and lower-thickness polymer threads ( 8 ,  9 ) are simultaneously produced and laid down in a single process step, the diameter of the spinnerets ( 2 ) for the thin fibers being <0.2 mm, and >0.2 mm, for the larger-thickness fibers, with high-viscosity polymer melts being used with a melt flow index “mfi” of well below 500. 
   
   
       7 . A method according to  claim 6 , wherein at least two spinning beams ( 1 ) are used which are arranged at an angle to each other, wherein the polymer threads ( 9 ) leaving the spinnerets ( 2 ) of each spinning beam ( 1 ) tangle and intertwine with each other before contact with the base. 
   
   
       8 . A method according to  claim 6 , wherein two spinning beams ( 1 ) are used, wherein a first spinning beam ( 1 ) comprises comprising larger-diameter spinnerets and a second spinning beam ( 1 ) comprising smaller-diameter spinnerets. 
   
   
       9 . A method according to  claim 6 , wherein high-viscosity polymer melts are used. 
   
   
       10 . A method according to  claim 9 , wherein the melt flow index “mfi” is well below 500. 
   
   
       11 . A method according to  claim 6 , wherein the spinning beams are supplied with air having a pressure in the order of magnitude of 500 mbar. 
   
   
       12 . An apparatus for implementation of the method according to the invention, comprising spinning beams including a plurality of spinnerets arranged next to each other and a conveyor for laying down the polymer threads leaving the spinnerets, wherein at least two spinning beams ( 1 ) are provided which are arranged relative to each other such that the leaving polymer threads tangle with each other before contact with the conveyor belt ( 7 ), a first spinning beam ( 1 ) comprising larger-diameter spinnerets ( 2 ) and a second spinning beam ( 1 ) comprising smaller-diameter spinnerets ( 2 ), with the diameter of the smaller-diameter spinnerets ( 2 ) being <0.2 mm, and that of the larger-diameter spinnerets ( 2 ) being >0.2 mm. 
   
   
       13 . An apparatus according to  claim 12 , wherein at least two spinning beams ( 1 ) are arranged at an angle (β) to each other. 
   
   
       14 . An apparatus according to  claim 12 , wherein fans are provided in the outlet region of the spinnerets ( 2 ) for generation of an air stream with a pressure in the order of magnitude of 500 mbar. 
   
   
       15 . An apparatus, according to  claim 12 , wherein the spinnerets ( 2 ) are produced by laser drilling. 
   
   
       16 . A method of producing a pleatable nonwoven fabric according to  claim 6 , wherein the diameter of the spinnerets ( 2 ) is 0.15 mm for the thin fibers, and 0.3-0.4 mm for the larger thickness fibers. 
   
   
       17 . An apparatus according to  claim 13  for implementation of the method, wherein the diameter of the smaller-diameter spinnerets ( 2 ) is approximately 0.15 mm, and that of the larger-diameter spinnerets is 0.3-0.4 mm.