Patent Publication Number: US-2011064928-A1

Title: Nonwoven material

Description:
FIELD OF THE INVENTION 
     This invention relates to a non-woven material. 
     BACKGROUND OF THE INVENTION 
     Non-woven materials or textiles are a type of fabric-like material which is typically manufactured by mechanically or thermally binding fibers, either from natural fibers or manmade materials. 
     One example of a non-woven material is a multi-layer material comprising several layers, each of which may be manufactured using either a spunbond or meltblown process. In the spunbond process, raw material is extruded into a thin fiber (on the order of several microns), and the extruded fiber is randomly deposited on a conveyor belt. In the meltblown process, fibers are extruded and then blown onto another layer or directly onto a conveyor belt. The layers are then mechanically or thermally bonded, i.e., via heat bonding or hydro-entanglement. In addition, additives, either to the materials themselves or in the form of topical treatments, such as surfactants, antistatic, impregnations, fluorocarbons, fire-resistant additives, etc., may be provided. It is well known that the parameters used in each step of the manufacture affect properties of the final material. 
     In addition, it is known to form non-woven materials from nanofibers produced by electro-spinning (electrostatic spinning) For example, US 2006/0290031 discloses a method of nanofibers production from a polymer solution using electrostatic spinning in an electric field created by a potential difference between a charged electrode and a counter electrode. The polymer solution is for spinning supplied into the electric field using the surface of the rotating charged electrode, while on a part of the circumference of the charged electrode near to the counter electrode is a spinning surface created, by which a high spinning capacity is reached. Further the invention relates to a device for carrying out the method, where the charged electrode is pivoted and by its (bottom) part of its circumference it is immersed in the polymer solution, while against the free part of the circumference of the charged electrode is positioned the counter electrode. 
     WO 2008/011840 discloses a collecting electrode of a device for production of nanofibers through electrostatic spinning of polymer solutions, which contains a conductive thin-walled body of electrode, in which there is performed at least one opening, on whose circumference there is arranged the border, while in the inner space of the body of electrode there is mounted at least one holder of electrode connected with at least one brace fastened in the spinning chamber, while the holder of electrode is arranged behind border of the opening. 
     WO 2008/028428 discloses a rotary spinning electrode of an elongated shape into the device for production of nanofibers through electrostatic spinning of polymer solutions comprising a pair of end faces, between them there are positioned spinning members formed by wire, which are distributed equally along the circumference and parallel with axis of rotation of the rotary spinning electrode, while the end faces are made of electrically non-conducting material and all the spinning members are mutually connected in a electrically conductive manner. 
     WO 2007/137530 discloses a device for production of nanofibers through electrostatic spinning of polymer solutions comprising a spinning chamber, in which the reservoir of polymer solution is positioned, into which by a section of its circumference extends the rotating spinning electrode of elongated shape connected to one pole of high voltage source of direct current, to whose opposite pole there is connected the collecting electrode arranged in the spinning chamber against the spinning electrode, while a section of circumference of the spinning electrode extends into a polymer solution in the reservoir while the reservoir of polymer solution is divided into the inlet section, into which leads at least one inlet opening, and into which the spinning electrode extends by a section of its circumference, and the outlet section, which is provided with outlet opening. 
     WO 2006/108364 discloses a textile containing at least one layer of polymeric nanofibers having diameter to 600 nanometers produced through electrostatic spinning of the polymer solution. The polymeric nanofibers contain particles of low-molecular substance dissolved or dispersed in solution of polymer which is subject to electrostatic spinning, possibly particles of low molecular substance which was created through a consequent chemical reaction of the original low molecular substance dissolved or dispersed in solution subjected to electrostatic spinning. The invention also relates to the production method of the layer of nanofibers from the polymer solution through electrostatic spinning in electric field created by difference of potentials between the charged electrode and the counter-electrode, at which the solution of polymer is brought into the electric field for spinning through the surface of the rotating charged electrode, at the same time the nanofibers created in this electric field are carried to the counter-electrode and they deposit on the surface designated to it. Polymer solution for spinning contains the particles of low-molecular substance, which are at spinning seized together with polymer into the nanofibers being created. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a nonwoven material comprising:
         a spunbond layer comprising fibers having an average diameter between 12 and 25 microns;   a meltblown layer adjacent to the spunbond layer and comprising fibers having an average diameter between 2 and 5 microns; and   an electrospun layer adjacent to the meltblown layer and comprising nanofibers having an average diameter between 100 and 400 nanometers;
 
wherein the electrospun layer has a basis weight of at least 0.2 gsm, the total basis weight of the meltblown layer being at least twice that of the electrospun layer, and the total basis weight of all of the meltblown layers in the material constituting at least 3% of the basis weight of the material. These features, inter alia, provide the material with the necessary operating parameters, e.g., in connection with filtration ability, breathability, basis weight, etc.
       

     The spunbond layer may comprise fibers having an average diameter between 12 and 20 microns. 
     In addition, the nonwoven material may be provided such that:
         the spunbond layer has an average pore size between 70 and 120 microns;   the meltblown layer has an average pore size between 15 and 25 microns; and   the electrospun layer has an average pore size between 500 nanometers and 2 microns.       

     The average pore size of the spunbond layer may be between 2.8 and 8 times that of the adjacent meltblown layer. 
     The average pore size of the meltblown layer may be between 7.5 and 50 times that of the adjacent electrospun layer. 
     The average diameter of the fibers of the spunbond layer may be between 2.4 and 10 times that of the fibers of the meltblown layer. 
     The average diameter of the fibers of the meltblown layer may be between 5 and 50 times that of the fibers of the electrospun layer. 
     The layers may be intermittently bonded to one another. 
     The spunbond layer may be made from a material selected from the group comprising polyester, PLA, polyolefin, polypropylene, and polyethylene. 
     The meltblown layer may be made from a material selected from the group comprising polyester, polyolefin, polypropylene, polyurethane, latex, elastic adhesive, elastomeric polyethylene, and elastomeric polypropylene. 
     The electrospun layer may be made from a material selected from the group comprising PVA, PVA C, PA 6, PA 6/12, PA 12, PAA, PAN, PEOX, PESO, PS, PUR, PVP, PVP, polyolefin, polypropylene, and polyethylene. 
     According to another aspect of the present invention, there is provided a nonwoven material comprising:
         a spunbond layer having an average pore size between 70 and 120 microns;   a meltblown layer adjacent to the spunbond layer and having an average pore size between 15 and 25 microns; and   an electrospun layer adjacent to the meltblown layer and having an average pore size between 500 nanometers and 2 microns;
 
wherein the electrospun layer has a basis weight of at least 0.2 gsm, the total basis weight of the meltblown layer being at least twice that of the electrospun layer, and the total basis weight of all of the meltblown layers in the material constituting at least 3% of the basis weight of the material.
       

     In addition, the nonwoven material may be provided such that:
         the spunbond layer comprises fibers having an average diameter between 12 and 25 microns;   the meltblown layer comprises fibers having an average diameter between 2 and 5 microns; and   the electrospun layer comprises nanofibers having an average diameter between 100 and 400 nanometers.       

     The spunbond layer may comprise fibers having an average diameter between 12 and 20 microns. The average pore size of the spunbond layer may be between 2.8 and 8 times that of the adjacent meltblown layer. 
     The average pore size of the meltblown layer may be between 7.5 and 50 times that of the adjacent electrospun layer. 
     The average diameter of the fibers of the spunbond layer may be between 2.4 and 10 times that of the fibers of the meltblown layer. 
     The average diameter of the fibers of the meltblown layer may be between 5 and 50 times that of the fibers of the electrospun layer. 
     The layers may be intermittently bonded to one another. 
     The spunbond layer may be made from a material selected from the group comprising polyester, PLA, polyolefin, polypropylene, and polyethylene. 
     The meltblown layer may be made from a material selected from the group comprising polyester, polyolefin, polypropylene, polyurethane, latex, elastic adhesive, elastomeric polyethylene, and elastomeric polypropylene. 
     The electrospun layer may be made from a material selected from the group comprising PVA, PVA C, PA 6, PA 6/12, PA 12, PAA, PAN, PEOX, PESO, PS, PUR, PVP, PVP, polyolefin, polypropylene, and polyethylene. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it may be carried out in practice, an embodiment will now be described, by way of a non-limiting example only, with reference to the accompanying drawings, in which: 
         FIGS. 1A through 1C  are schematic cross-sectional views of non-woven materials. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     As illustrated in  FIG. 1A through 1C , a non-woven material, which is generally indicated at  10 , is provided. The material  10  comprises at least three layers: a spunbond layer (S)  12 , a meltblown layer (M)  14 , and a solvent- or water-based electrospun, or melt electrospun (E, hereafter collectively referred to as electrospun) layer  16  of nanofibers. 
     It will be appreciated that the term “layer” when used herein refers to both distinct layers, i.e., a layer which is formed as a single stratum, as well as to multiple similar strata which are formed or disposed one atop another, e.g., multiple layers of the same type (i.e., spunbond, meltblown, or electrospun) which are formed one atop another may be considered as a single layer of that type. 
     Reverting to  FIG. 1A , there is illustrated a material  10 , comprising a spunbond layer  12 , a meltblown layer  14 , and an electrospun layer  16 . Such a material is typically indicated as SME. 
       FIG. 1B  illustrates another example of the material  10 , comprising a first spunbond layer  12 , a meltblown layer  14 , an electrospun layer  16 , and a second spunbond layer  12 . Such a material is typically indicated as SMES. 
       FIG. 1C  illustrates a further example of the material  10 , being symmetric, and comprising a first spunbond layer  12 , a first meltblown layer  14 , an electrospun layer  16 , a second meltblown layer  14 , and a second spunbond layer  12 . Such a material is typically indicated as SMEMS. 
     It will be appreciated that the examples illustrated in  FIGS. 1A through 1C  are not limiting, and a material may contain any combination of layers without departing from the spirit and scope of the invention, provided that the material contains at least three layers, one each of S, M, and E, in that order. 
     According to any one of the above examples, the layers may be intermittently bonded to one another, for example to form a pattern on faces of the material  10 . 
     The spunbond layer  12  may comprise fibers having an average diameter in a range between 12 and 25 microns, or more particularly, in a range between 12 and 20 microns. The average fiber diameter of the spunbond layer  12  may be between 2.4 and 10 times that of the meltblown layer  14 . The average pore size of the spunbond layer  12  may be between 70 and 120 microns. The average pore size of the spunbond layer  12  may be between 2.8 and 8 times that of the meltblown layer  14 . 
     The meltblown layer  14  may comprise fibers having an average diameter in a range between 2 and 5 microns. The average fiber diameter of the meltblown layer  14  may be between 5 and 50 times that of the electrospun layer  16 . The average pore size of the meltblown layer  14  may be between 15 and 25 microns. The average pore size of the meltblown layer  14  may be between 7.5 and 50 times that of the electrospun layer  16 . 
     The electrospun layer  16  may comprise nanofibers having an average diameter in a range between 100 and 400 nanometers (0.1 and 0.4 microns). The average pore size of the electrospun layer  16  may be between 15 and 25 microns. The average pore size of the electrospun layer  16  may be between 500 and 2,000 nanometer (0.5 and 2 microns). 
     The basis weight of the electrospun layer  16  is at least 0.2 g/m 2  (gsm). The basis weight of the meltblown layer  14  is at least twice that of the electrospun layer  16 . In addition, the weight of the meltblown layer  14  is at least 3% of that of the entire material. 
     The spunbond layer  12  may be formed in any known way, for example from a continuous fiber, having been forced through an extruder having spinnerets with capillary diameters that range between approximately 0.35 and 0.8 mm and a hole density ranges between approximately 2000 and 8000 holes/m. It may be made from any suitable material, including, but not limited to, polyester grades including PLA, polyolefin, polypropylene, or polyethylene. 
     The meltblown layer  14  may be formed in any known way, for example from fibers having been extruded through spinnerets with capillary diameters that range between approximately 0.2 and 0.5 mm and a hole density ranges between approximately 15 and 50 holes/in. A hot air stream may be used to draw the extruded polymer into fine fibers, thus forming the meltblown layer. The meltblown layer  14  may be made of any appropriate material, including, but not limited to, polyester, polyolefin, polypropylene, polyurethane, latex, elastic adhesive, elastomeric polyethylene, or elastomeric polypropylene. 
     The electrospun (E) layer may be made in any known way, and may be made from PVA, PVA C, PA  6 , PA 6/12, PA 12, PAA, PAN, PEOX, PESO, PS, PUR, PVP, PVP, a polyolefin, polypropylene, or polyethylene. 
     Any one or more of the layers  12 ,  14 ,  16  may be made as a bi-component fiber of two or more materials listed above, or any other appropriate material. 
     The layers may be formed directly on the adjacent layers (e.g., in the example illustrated in and described with reference to  FIG. 1A , the meltblown layer  14  may be formed directly on its adjacent spunbond layer  12 , and the electrospun layer  16  may be formed directly on the meltblown layer), after which the layers are bonded to one another. Alternatively, each layer may be formed independently, and then unwound in the appropriate sequence (e.g., in the example illustrated in and described with reference to  FIG. 1A , the layers are arranged such that the meltblown layer  14  is between the spunbond layer  12  and the electrospun layer  16 ),), after which the layers are bonded to one another. 
     The gradient of the pore sizes across the material  10  allows for a high degree of filtering with a reduced pressure drop between adjacent layers. It will be appreciated that, when the spunbond layer faces the medium to be filtered (for example, if used in an air filter whose intended function is to filter air before it reaches the user, the spunbond layer  12  would typically be facing away from the user), such an arrangement increases the breathability of the material without forgoing the high level of filtration afforded by the electrospun layer  16 . 
     The material according to any of the examples given above, as well as according to any example which is within the scope of the invention, has several advantages over a similarly formed material which lacks an electrospun layer. For example, it exhibits a high score in “hydro-head” tests (a test which aims to measure water resistance), lower pore size and narrower pore distribution, and a lower pressure drop across the material for gases traversing its thickness. 
     Such a material may be useful, inter alia, in the following applications:
         it may be used in diaper liners or other diaper components, due, e.g., to its low weight, high weight, high breathability, fluid-resistance properties, and ability to contain fine solid particles;   it may be used in medical garments and masks, due, e.g., to its low pore size, which makes it a bacterial barrier, its low weight, its breathability, and its fluid-resistance properties; and   it may be useful for manufacture of high efficiency/low pressure drop filter media. The low pressure drop experienced across its surface and small pore size make it suitable for use is manufacture of HEPA (high efficiency particulate air) and/or ULPA (ultra low penetration air) filters.       

     It will be clear that the material  10  may further be used in applications other than the above without departing from the spirit and the scope of the present invention. 
     Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations and modifications can be made without departing from the scope of the invention mutatis mutandis.