GB2045825A - Fluid jet entangled, bonded nonwoven fabric - Google Patents

Abstract

A strong, durable nonwoven fabric comprising polyester and/or polyolefin fibers arranged in a pattern of high density, lightly entangled fiber regions is produced by fluid jet entanglement followed by application of binder to discrete areas of the fabric or to the whole fabric.

Description

SPECIFICATION Nonwoven fabric and method for producing the same Specification This application is a Continuation-in-part of application Serial No. 12,417, filed February 15,1979.

This invention relates to new and improved nonwoven fabrics and methods for manufacturing the same.

Background of the Invention A. PriorArt Nonwoven fabrics have been known for some time. Nonwoven fabrics have been made from synthetic fibers such as the polyester and polypropylene fibers. Generally, these fabrics are produced by forming a web of fibers and applying an adhesive binder to the web to hold the fibers together and provide strength. In some instances (i.e., the spunbonding technique), synethetic polymers are extruded into filaments and directly formed into webs which selfbond to produce the final fabric. In other instances, the fibrous web is fluid rearranged and then resin binder is added to form a useful, coherent nonwoven fabric. See, for instance, Kalwaites, U.S. Patent Nos. 2,862,251,3,033,721, 3,193,436, and 3,769,659, and Griswold, U.S.

Patent Nos. 3,081,515 and 3,025,585. Still other nonwoven fabrics are made by forming a web of synethetic fibers and treating it with high-pressure jets to entangle the fibers and produce a strong fabric that does not require the addition of binder to be self-supporting and useful for many purposes. Such a technique is described by Evans in U.S. Patent No.3,485,706 and Canadian Patent No.791,925.

The prior art polyester fiber nonwoven fabrics suffer from one or more of the following problems: Adhesively bonded webs of textile polyester fibers require relatively large amounts of adhesive binder for most end uses to provide the fabric with adequate strength. The large amount of binder increases cost and can detract from the desirable textile-like properties of the fiber itself. The spunbonded type of product is expensive, and being of continuous extruded filaments, also has some limitations on its functional properties and its textile-like nature. For instance, spun bonded fabrics can be stiff and boardy in the higher weight range of products. The highly entangled fabrics of Evans have excellent fabric properties, but the Evans process requires a substantial capital investment and it uses large amounts of power.This invention provides a process and fabric product that eliminate many of the above-mentioned problems.

B. Objects of The Invention It is an object of the invention to provide a relatively economical process for producing strong, durable nonwoven fabrics having reduced binder content.

It is another object of the invention to provide a process for producing strong, durable nonwoven fabrics from polyester and/or polyolefin fibers.

it is a further object of the invention to provide strong, durable polyester and/or polyolefin nonwoven fabrics.

Still another object of the invention is to provide an economical process for producing strong, durable polyester and/or polyolefin nonwoven fabrics having reduced binder content.

These and other objects of the invention will be apparent from the following description of the invention.

Summary of The Invention The invention provides a strong, durable nonwoven fabric comprising a layer of polyester and/or polyolefin fibers disposed in a regular repeating pattern of lightly entangled fiber regions of higher area density than the average area density of the layer, and interconnecting fibers extending between said regions and being randomly lightly entangled with each other in said regions, and an adhesive binder material distributed in said layer. These fabrics are produced by a process which includes the steps of lightly entangling a layer of polyester and/or polyolefin fibers, followed by applying adhesive bonding material to the lightly entangled layer.

Description of The Invention The nonwoven fabric of the invention comprises a layer of polyester and/or polyolefin fibers, with the fibers being disposed in a regular repeating pattern of lightly entangled fiber regions of higher area density than the average area density of the layer. The fiber layer has interconnecting fibers which extend between the said lightly entangled fiber regions. The interconnecting fibers are randomly entangled with each other in the regions. The fabric also contains an effective amount, for instance, from about 2-1/2 per cent to about 30 per cent by weight of the fabric, plus binder, of an adhesive binder material. The adhesive binder material can be distributed in the fabric in a spaced, intermittent pattern of binder sites, or it can be uniformly distributed throughout the fabric.

The nonwoven fabric of the invention is made by forming a layer of overlapping, intersecting polyester and/or polyolefin fibers. The fibrous layer is supported on an apertured patterned member having apertures arranged in a pattern. Liquid streams are jetted at the layer to randomly and lightly entangle the layer in a pattern of high-density regions interconnected by fibers extending between regions. An adhesive binder material is then applied to the layer of lightly entangled fibers.

The fibrous web can be formed in any convenient known manner, as by air-laying or carding. The web is then lightly entangled by passing the fibrous web under essentially columnar liquid streams while the web is supported on a foraminous forming or patterning member. Apparatus such as the general type disclosed by Evans in U.S. Patent No. 3,485,706 can be employed to carry out the entangling. It is an important feature of the invention that the fiber layer is lightly entangled.For instance, it is preferred that the lightly entangled fibrous layer have a structural measure of fiber entanglement of less than 0.1. (The test procedure for measuring the structural measure of fiber entanglement is set forth below.) A typical apparatus for carrying out the process of the invention employs rows of orifices through which liquid (usually water) is jetted under pressure in the form of essentially columnar jets. A suitable apparatus has up to 20-25 rows of orifices, with the orifices being spaced such that there are about 30 to 50 orifices per linear inch. The orifices are preferably circular, with diameters of from 0.005 to 0.007 inch. The travelling fibrous web can be positioned about 1 to 2 inches below the orifices.

Using the above-described typical apparatus, representative conditions include a liquid pressure of about 200 to 700 psi and a web speed of up to 100 yards per minute, for a fibrous web weighing about 1/2 to 2-1/2 ounces per square yard. Routine experimentation that is well within the ordinary skill in the art will suffice to determine the desired conditions for particular cases.

After the fibrous web has been lightly entangled, it is bonded employing known procedures. For instance, the lightly entangled web may be passed through a print-bonding station which employs a set of counterrotating rolls. The upper (back-up) roll is adjustable, and the lower (applicator) roll is engraved with a predetermined pattern to be printed. The lower roll is partially immersed in a bath of binder solution or suspension. As the roll rotates, it picks up binder, and a doctor blade wipes the roll clean except for the binder contained in the engraved pattern. As the web passes through the nip between the rolls, the binder is printed on the web from the engraved pattern. This procedure is well known in the art. U.S. patents which disclose such print bonding of nonwoven fibrous webs include Nos. 2,705,498, 2,705,687, 2,705,688, 2,880,111, and 3,009,822.If desired the web may also be overall saturation bonded.

The adhesive binder employed can be any of the aqueous latex binders that are conventionally employed as binders for nonwoven fabrics. Such binders include acrylics, ethylene-vinyl acetate copolymers, SBR latex rubbers, and the like.

After the binder has been applied, the printed web is dried in the usual fashion, as by passing the web over a series of drying cans.

The binder is employed in an effective amount, that is, that amount which will result in a fabric having sufficient strength and cohesiveness for the intended end-use application. The exact amount of binder employed depends, in part, upon factors such as nature of fiber, weight of fibrous layer, nature of binder, and the like. Usually, an effective amount will be found within the range of from about 5 to about 30 weight percent, based upon weight of fibers plus binder.

The fibers used to produce the products of the invention are polyester or polyolefin, such as polypropylene or high density polyethylene, fibers. The fibers may have a denier of from 1 or less up to 15 or more and they may be in the form of short fibers such as 1/4 inch in length up to as long as continuous filament fibers.

Preferably, fibers in the range of 3/4 to 2 inches in length are used. The weight of the fiber layer used to produce the fabrics of the present invention may vary from 100 grains per square yard to a few thousand grains per square yard.

The invention will be further illustrated in greater detail by the following specific examples.

Example 1 A web of 1.75 denier 1.5 inch polyester fibers weighing 537 grains per square yard is formed using an air-laying machine sold by the Rando Machine Corporation of Rochester, New York under the tradename Rando Webber. The web is placed on a woven belt. The belt is woven with 22 warp filaments per inch and 24 filling filaments. The belt has 528 openings per square inch. The web and belt are passed under 16 manifolds. Each manifold contains 2 rows of 12 orifices per inch running in the transverse direction of the web. Each orifice is rectangular, with an opening of about 0.012 inch by 0.014 inch. Water is jetted through the orifices onto the web at a pressure of about 250 pounds per square inch to lightly entangle the fibers into a pattern of high density regions. The lightly entangled web is passed through a pair of print rolls.The top roll is a flannel-covered, rubber back-up roll, and the bottom roll is an engraved roll. The engraved roll is engraved with 6 wavy lines per inch running parallel to the axis of the roll. (See. Figure 1 of U.S. Patent No.

3,009,822.) Each line has a width of about 0.024 inch. The roll rotates in a pan of binder material and picks up the binder material and places it on the web. The binder material has the following composition: a self-cross-linking vinyl acrylic terpolymer sold by the National Starch Company as NS2853; water; and water soluble hydrophylic surfactant sold by Atlas Chemicals as Tween 20. Approximately 125 grains per square yard of binder is applied. The fabric is dried at a temperature of 270"F. for 1 minute to remove excess water and cure the binder. The fabric contains lightly entangled fiber areas of higher density. The higher density areas are interconnected by fibers extending between the areas. The binder material runs transverse of the fabric and bonds the fibers together. The strength of the resultant fabric is tested using an Instron Tensile Tester in accordance with ASTM Method No. D-1 117. The fabric has a strip tenacity in the machine direction of 1.19 pounds per inch per 100 grains and a strip tenacity in the cross direction of 0.89 pound per inch per 100 grains.

Control Example 1 For comparison purposes, a part of the air-layed polyester fiber web used in Example 1 is not lightly entangled, but binder is applied to the air-layed web and then cured using conditions analogous of those described in Example 1. Also, another portion of the air-layed polyester fiber web is lightly entangled as described in Example 1, and is then dried to remove water. No adhesive binder is applied. Both of these comparative samples are tested for tenacity by the same method described in Example 1. The fabric which is only adhesively bonded and not lightly entangled has a strip tenacity in the machine direction of 0.505 pound per inch per 100 grains, and a strip tenacity in the cross direction of 0.209 pound per inch per 100 grains.The fabric which was lightly entangled but not adhesively bonded had a strip tenacity in the machine direction of 0.476 pound per inch per 100 grains, and a strip tenacity in the cross direction of 0.358 pound per inch per 100 grains.

Example 2 By procedures analogous to those described above in Example 1 and Control Example 1, polypropylene fibers were formed into a web using the "Rando Webber" air-laying machine, and were then subjected to light entanglement plus print bonding with NS2853 (Run 1), light entanglement only (Run 2), and print bonding only with NS2853 (Run 3). The resulting nonwoven fabrics were tested for grab tensile strength (ASTM D-1117) and specific grab tensile (ASTM D-1 117) in the machine and cross directions.The results are displayed in Table I: TABLE I Specific Grab Weight, Grab Tensile, Tensile Run No. Grainslyd2 poundslinch Ibslinigrlyd2 MID CID MID CID 1 597 11.1 8.7 1.86 1.46 2 432 0.6 0.5 0.15 0.12 3 588 2.6 1.6 0.44 0.27 Control Example 2 By a procedure analogous to that described in Example 1 and Control Example 1, rayon fibers were formed into a web using the "Rando Webber' air-laying machine, and then subjecting to light entanglement plus print bonding with NS2853 (Run 1), light entanglement only (Run 2), and print bonding only (Run 3). The resulting nonwoven fabrics were tested for strip tenacity (ASTM D-1117) in the machine and cross direction.

The results are displayed in Table il: TABLE II Weight, Strip Tenacity, Run No. Grainslyd2 lbslinl 700 grainslyd2 MID CID 1 697 0.94 0.53 2 514 0.84 0.51 3 676 1.03 0.67 Unlike the case with polyester and polypropylene fibers, when rayon fibers are lightly entangled plus print bonded, the strengths are not greater than the sum of the strengths obtained by entangling and printing along. In fact, printing without entangling actually gave higher strength than printing plus light entangling.

Example 3 A web of 1-1/2 denier 1-3/4 inch polyester fibers weighing about 375 grains per square yard is formed by a "Rando Webber". The web is placed on a 1 6X1 4 woven belt. The web and belt are passed under four strips, each containing 50 orifices per inch running in the cross direction. Each orifice is circular with a diameter of 0.005 inch. Water at a temprature of 140"F. is jetted through the orifices at a pressure of 500 psi to lightly entangle the fibers into a pattern of high density regions. The speed of the belt and web under the orifices is 45 feet per minute. The lightly entangled web is dried by passing it over a series of steam cans.

Portions of the lightly entangled web are saturation bonded by padding with varying proportions of a self-cross-linking vinyl acrylic terpolymer latex sold by National Starch Company as NS2853. The samples with binder are dried at 300 F. The unbonded and bonded webs are tested for specific grab tenacity and strip tenacity. The results are set forth below in Table Ill.

Control Example 3 Using the same polyester fiber described in Example 3, a "Rosebud" web is Rando Webber-laid web using the process of Kalwaites, U.S. Patent Nos. 2,862,251, and 3,033,721. The water pressure employed is 200 psi.

The web product weighs about 400 grains per square yard. The web is dried, and then portions of it are saturation bonded with varying proportions'of the binder described in Example 3, and then dried at 300"F.

The unbonded and bonded webs are tested for specific grab tenacity and strip tenacity. The results are displayed in Table Ill.

TABLE Ill Binder Specific Grab Content, Tenacity, Per Cent Ibslinigrlyd2 Example 3 Control Example 3 MID C/D MID CID 0 1.62 1.11 0.12 0.11 2-1/2 2.73 2.36 1.96 1.26 5 3.23 2.55 2.05 1.75 10 3.61 3.06 2.97 2.99 20 3.01 2.41 3.48 3.30 40 3.37 2.31 2.91 2.84 Strip Tenacity lbslin/100 grainslyd2 Example 3 Control Example 3 MID CID MID CID 0 0.38 0.17 0.03 0.02 2-1/2 1.03 0.55 0.33 0.22 5 1.13 0.78 0.57 0.51 10 1.57 0.96 1.10 1.00 20 2.31 0.91 1.48 1.56 40 2.00 0.84 1.54 1.51 On visual examination of the above-described samples, the sample of Example 3, containing 2-1/2 per cent binder is strong enough to be handled, and could be used as an interlining in clothing manufacture.The Control Example 3 containing 2-1/2 per bent binder is just barely strong enough to be handled, has very poor abrasion resistance and surface fiber tie-down, and appears to lack sufficient integrity to have any significant commercial use. It is probably that the Control Example lacks sufficient integrity to have significant commercial use until the 10 per cent binder level is attained; but at 10 percent binder, stiffness imparted by the binder begins to be a factor which limits potentiai commercial uses.

Structural Measure of Fiber Entanglement The unbonded sampls of Example 3 and Control Example 3 are evaluated for "S", the Structural Measure of Fiber Entanglement. The results are as follows: Example 3 - 0.0564 Control Example 3 - 0.0190 The procedure for determining this value is the following: Structurally, the extent of fiber interentanglement is related to the concentration of fibers in the intertangled area (C) and the density of the interentangled mass (d). The product of these two factors provides a measure of the frictional engagement and interaction of the fibers in the interentangled area serving to lock the fibers in the interentangled area serving to lock the fibers in place in the fabric to thereby permit maximum utilization of fiber strength when the fabric is subjected to stress. Also influencing maximum utilization of fiber strength is the cooperation-under-stress exhibited by the group of fibers which extends between any two entangled areas, which cooperation is inversely related to the average-free-length factor of the individual fibers in the group (F). The structural measure of entanglement and cooperation (S) is defined by the following equation: C S=T S is, in turn, related to the per cent of fiber strength converted to fabric strength.The relationship is approximated by the following empirical equation: S = 0.0593 + 0.00362 (% conversion) + 0.000543 (% conversion)2 The fiber concentration factor (C) is the ratio of the length of fiber actually in the entangled area to the length which would be there if there were no patterning and/or entanglement of the fibers, i.e., if the fibers of the fabric were uniformly distributed in the plane of the fabric. Since there is a direct relation between fibre length and fiber weight, the fiber concentration factor (C) may also be described as the ratio of the weight per unit area of the entangled portion (W1) to the weight per unit area of the entire fabric (W1), i.e.: Wa C =W2 W1 and W2 are determined from the fabric sample by direct measurement.For W1, an average of ten values is used and each value is determined by cutting the entangled mass or representative portion thereof from the fabric with a suitable die. The area of the mass then corresponds to the area of the die. All ten specimens are weighed at one time on a suitable microbalance.

The density (d) of the entangled mass can be measured by calculating the volumes of the cut-out specimens mentioned above. To do this, the specimens are mounted axially on broaches and are photographed at 20X to provide a cross-sectional view. The cross-section thus photographed may be irregular in shape. If so, the shape is approximated with rectangles and/or triangles. The shapes are then measured and, using the appropriate geometric formulas, the corresponding volumes are calculated. The total weight of the ten specimens is then divided by the sum of the ten volumes to give the average density (d) in grams/cu.centimeter of the entangled area. The average-free-length-factor (F) of the fibers in the group extending between any two entangled areas is estimated by direct observation (under a microscope) of the fibers in the group and comparison to a set of standards.

In practice, it is observed that structures made from straight (i.e., non-crimped or -curled) fibers do not have ratings of one (corresponding to no curvature). Instead, there is always some free length and an appropriate class rating which may be used for structures made from straight fibers is F = 1.4. Similarly, it is observed that the rating for samples made from conventional staple fibers or low crimp continuous filaments ranges from 1.8 to 2.5. For such fibers, an average class rating of F = 2.1 may be used. For highly crimped fibers, the actual measured values of F should be used. The formula for S recognizes that the free-length-factor is inversely related to strength conversion, i.e., the greater the free-length-factor, the more chance for poor fiber cooperation and the greater the reduction in weight per unit area of the sample when stressed until a break occurs.

Claims (12)

1. A strong, durable nonwoven fabric comprising a layer of polyester or polyolefin or both fibers, said fibers being disposed in a regular repeating pattern of lightly entangled fiber regions of higher area density than the average area density of the layer, and interconnecting fibers extending between the lightly entangled fiber regions and being randomly entangled with each other in said regions, and an effective amount of an adhesive binder.

2. The fabric of claim 1 wherein the fibers are polyester.

3. The fabric of claim 1 wherein the fibers are polypropylene.

4. The nonwoven fabric of claims 1, 2, or 3, wherein the adhesive binder material is uniformly distributed throughout the layer.

5. The nonwoven fabric of claims 1, 2, or 3, wherein the adhesive binder material is distributed in an intermittent pattern of spaced binder areas.

6. A method of producing a strong, durable nonwoven fabric comprising: a) forming a layer of overlapping intersecting polyester or polyolefin or both fibers; b) supporting said layer on an apertured support member; c) directing essentially columnar jets of fluid against the supported layer to rearrange the fibers into a regular repeating pattern of lightly entangled fiber regions, and; d) applying an effective amount of an adhesive bonding material to said rearranged layer.

7. A method of producing a nonwoven fabric according to claim 6 wherein the apertured support member has a predetermined topography.

8. A method of producing a nonwoven fabric according to claim 6 wherein the jets of fluid are streams of water.

9. A method of producing a nonwoven fabric according to claim 6 including drying the fabric at an elevated temperature to cure the adhesive bonding material.

10. A method of producing a nonwoven fabric according to claim 6 wherein the apertured support member has a predetermined topography, the jets of fluid are streams of water, and the fabric is dried at an elevated temperature to cure the adhesive bonding material.

11. A method according to claim 6, substantially as described in Example 1, 2 or 3.

12. A nonwoven fabric produced bv a method according to any of claims 6 to 11.