Cardable hydrophobic polyolefin fiber, material and method for preparation thereof

Abstract: An improved method for producing hydrophobic polyolefin-containing staple fiber for processing, with reduced waste and improved crimp by sequential treatment with two finish compositions comprising at least one neutralized phosphoric acid ester and at least one polysiloxane of defined classes and amounts.

Description: This invention relates to a process using topically applied fiber finishes to obtain polyolefin-containing hydrophobic fiber or filament capable of accepting a high crimp without undue end waste in subsequent processing operations and without substantial loss of hydrophobicity in the resulting fiber or nonwoven product. US-A-4 938 832 discloses a method for preparing essentially hydrophobic polyolefin-containing spun fibers comprising A. initially treating corresponding continuous spun fiber or filament with an effective amount of a first modifier composition comprising (a) about 70%-100% by weight of modifier composition of at least one neutralized phosphoric acid ester represented by the formula wherein Alk is individually defined as a lower alkyl group, R is defined as an amino group or an alkali metal, n and m are individually defined as positive numbers of not less than about 1, the sum of which is about 3; and (b) up to about 30% by weight of modifier composition of at least one polysiloxane represented by the formula wherein X and Y are defined as hydrophobic chemical end groups, R' is individually defined as a lower alkyl group, and o is defined as a positive number within the range of about 10-50 or higher; B. crimping the resulting continuous fiber or filament in a crimper; C. applying to said fiber or filament an effective amount of a second modifier composition comprising (a) about 70%-100% by weight of second modifier composition, of at least one polysiloxane represented by formula (2), and (b) up to about 30% by weight of second modifier composition, of at least one neutralized phosphoric acid ester represented by formula (1); D. processing the resulting modifier-treated fiber or filament to obtain one or more webs for bonding; and E. bonding the resulting web to obtain a desired hydrophobic nonwoven material. FR-A-2 259 938 discloses a process for increasing the lubricity of organic fibers and for rendering them anti-static by the application of poly-diorganosiloxanes mixed with anti-static compounds and optionally paraffin waxes, the polydiorganosiloxanes having a specified viscosity range and having dissolved therein 0.1 to 30 parts of anti-static phosphorus compounds for every 50 to 100 parts of polydiorganosiloxane. A particularly troublesome technical problem arises when a high degree of hydrophobicity is desired on cuffs or borders in a diaper or similar product produced from conventionally-bonded webs of hydrophobic fiber such as polyolefin-containing staple. This problem arises because the untreated hydrophobic fiber quickly becomes unworkable due to friction and accumulated static charges generated during conventional processing such as spinning, crimping, cutting and carding. For this reason, the prior art recognizes the use of various topically-applied fiber lubricants and finishes which generally change fiber surface properties sufficiently to permit processing. Unfortunately, however, such conventional treatment often results in fibers and nonwoven end products which are substantially more hydrophilic than desired and difficult to control quality-wise. In particular, because of the nature of commercial high speed fiber-processing operations, and the unpredictable affinity of known finishing agents to individual batches or bales of hydrophobic fiber, it becomes very difficult to obtain a full crimp in the fiber component and to maintain a uniform hydrophobicity in the final nonwoven product. The above-indicated dual properties now can be obtained in accordance with the present invention by a two step processing of polyolefin-containing spun fiber or filament in accordance with the steps of A. initially treating the corresponding continuous spun fiber or filament with 0.09%-0.6% based on fiber weight of a first modifier composition comprising (a) O% to 40% (preferably about 20% to 40%), by weight of first modifier (spin finish) composition of at least one neutralized phosphoric acid ester represented by the formula wherein Alk is individually defined as an alkyl group having 1-8 carbon atoms and preferably a 1-4 carbon alkyl group; R is defined as an amine salt group or an alkali metal group, n and m are individually defined as positive numbers of not less than 1, the sum of which is 3; and (b) 100%-60% by weight of first modifier composition of at least one polysiloxane represented by the formula wherein X and Y are individually defined as a hydrophobic chemical end group such as a lower alkyl group, R' is individually defined as an alkyl group having 1-8 carbon atoms, for example as a methyl group, and o is defined as a positive number which is 10 or higher, for example within the range of 10-50; B. crimping the resulting treated continuous fiber or filament; C. applying to said treated and treated crimped continuous fiber or filament, preferably at a point downstream of the crimping step, an effective amount, varying from 0.05%-.80% by fiber weight, of a second modifier composition (an overfinish) comprising (a) 100%-50%, by weight of second modifier composition, of at least one neutralized phosphoric acid ester represented by formula (1) supra; and (b) 0% to 50%, by weight of second modifier composition comprising at least one polysiloxane represented by formula (2) supra, in sufficient amount to obtain a final cumulative concentration within a range of 0.01% to 1.0% and preferably 0.03%-.8%, based on fiber weight; D. processing the resulting treated fiber or filament, As desired, the above-obtained fiber is formed into webs, compiled and bonded in a conventional manner to obtain a desired hydrophobic nonwoven material. For present purposes the term "polyolefin-containing spun fiber or filament" is defined as including continuous as well as staple melt spun fibers obtainable from conventionally blended isotactic polypropylene as well as hydrophobic copolymers thereof with ethylene, 1-butene, 4-methylpentene-1 and the like. The resulting blended and extruded spun melt conveniently has a weight average varying from 3 X 10 5 to 5 X 10 5 , a molecular weight distribution of 2.0-12.0, a melt flow rate of about 5-70 g/10 minutes, and a spin temperature conveniently within a range of 220°C-325°C. Also includible within spun melt of the present process are art-recognized fiber additives, including pH stabilizers such as calcium stearate, antioxidants, pigments, including whiteners and colorants such as TiO 2 and the like. Generally such additives vary from 0.05%-3% by weight of spun melt. The present invention is found particularly applicable to high speed production of a variety of nonwoven materials utilizing webs obtained, for instance, from carded staple and may also comprise additional web components such as fibrillated film and the like. The term "processing" as used herein in process step "D", includes art-recognized web formation techniques applied to continuous as well as crimped, cut and carded staple fiber, the crimping step, being optional with respect to webs formed solely of fiber or filament. Continuous spun fiber or filaments used to form webs within the present invention preferably comprise topically treated spun melt staple fiber, filament, or fibrillated film of bicomponent or monofilament types, the modifier compositions or finishes being conventionally applied, for instance, by drawing over a feed wheel partially immersed in a bath of modifier composition, dipped therein, or by spraying, in effective amounts to permit fiber processing, and then dried. For present purposes, webs used to form nonwovens within the scope of the present invention can be formed by spun bonded, melt blown or conventional "Dry" carded Process using staple fiber and then bonded together using techniques employing adhesive binders (US-A-4,535,013), calender rolls, hot air, sonic, laser, pressure bonding, needle punching and the like, known to the art. Webs used to fabricate nonwoven material can also usefully comprise conventional sheath/core (concentric or otherwise) or side-by-side bicomponent fiber or filament, alone or combined with treated or untreated homogenous-type fiber or filament and/or fibrillated film. The present invention also relates to the use of polyolefin-containing fibers or filaments, prepared by the method of the invention, in the production of a nonwoven material. Such nonwovens may for example comprise one or more bonded webs of modifier-treated polyolefin fiber- and/or fiber-like (fibrillated film) components having a mixed fiber denier of homogeneous and/or bicomponent types not exceeding 44.4 dtex (40 dpf). Such webs preferably utilize fiber or filaments within a range of 0.11-44.4 dtex (0.1-40 dpf). Webs used in forming nonwovens within the scope of the present invention are produced from one or more types of conventionally spun fibers or filaments having, for instance, round, delta, trilobal, or diamond cross sectional configurations, or mixtures thereof. Nonwoven cover stock of the above-defined types can usefully vary in weight from 12-54 gm m 2 (10-45 gm yd 2 ) or higher. The invention is further illustrated but not limited by the following Example and Tables: EXAMPLE 1 A. Polypropylene fiber samples S-1 and S-2 are separately spun from separate resin batches in flake form generally characterized as follows: a crystallinity 60%, a molecular weight distribution 6.4 a melt flow 3.2 g/10 minutes which are individually processed in an impact blender. After 30 minutes the individual mixes having MFR values within a range of 24-27, are separately spun through a 210 circular hole spinnerette at 280°C. The resulting spun filaments, are air quenched at room temperature, and stretched at 115°C. (4 X) to obtain 2.22-2.82 dtex (2.0-2.54 dpf) circular filaments, to which spin and over finishes are applied upstream and downstream of a conventional steam crimper by passing the filaments over a feed or kiss wheel partly immersed in a first modifier finish composition consisting of Lurol R AS-Y/LE458HS polysiloxane emulsion (5%/95% by weight), respectively a neutralized phosphoric acid/alcohol ester product of George A. Goulston Company of Monroe, NC. and a product of Union Carbide Corporation, contact being of sufficient duration to apply about 0.40% and 0.59% dried spin composition (based on tow weight). The coated continuous filaments are then individually batch crimped at 100°C. and then passed over a second kiss roll at sufficient speed and concentration to coat the fiber with an over-finish consisting of 100% Lurol AS-Y to impart 0.1% overfinish to the dry fiber. After air drying, the coated and processed test fiber is chopped to 3.81 cm (1.5") length staple and set aside for conventional tests. Test results are summarized and reported in Table I below, in which the relative retained hydrophobicity as determined by fiber contact angle (% of fiber having a contact angle greater than 90°) of the processed fiber is indicated in column 3 and the relative amounts of spin finish (first modifier) an over finish (second modifier) are set out in columns 5 and 6 and by footnote.

Claims: A method for preparing polyolefin-containing high crimp spun fiber or filament suitable for production of nonwoven material of high hydrophobicity, comprising A. initially treating corresponding continuous spun fiber or filament with 0.09 to 0.6% based on fiber weight of a first modifier finish composition comprising (a) 0% to 40% by weight of modifier composition of at least one neutralized phosphoric acid ester represented by the formula wherein Alk is individually defined as an alkyl group having 1-8 carbon atoms, R is defined as an amine salt group or an alkali metal group, n and m are individually defined as positive numbers of not less than 1, the sum of which is 3; and (b) 100%-60% by weight of first modifier composition of at least one polysiloxane represented by the formula wherein X and Y are individually defined as a hydrophobic chemical end group, R' is individually defined as an alkyl group having 1-8 carbon atoms; and o is defined as a positive number which is 10 or higher; B. crimping the resulting treated continuous fiber or filament. C. applying to the continuous fiber or filament, at a point downstream of the crimping step, an effective amount of a second modifier composition comprising (a) 100%-50%, by weight of second modifier composition, of at least one neutralized phosphoric acid ester represented by formula (1); and (b) 0% to 50% by weight of second modifier composition, comprising at least one polysiloxane represented by formula (2) in sufficient amount to obtain a final cumulative concentration on the fiber within a range of 0.01%-1.0% based on fiber weight; D. processing the resulting modifier-treated fiber or filament. The method of claim 1 wherein the Alk-0 group of the neutralized phosphoric acid ester is defined as a straight 1-4 carbon alkoxy group; n is 2; and m is 1. The method of claim 1 or 2 wherein at least some of the second modifier composition is topically applied to fiber or filament upstream of the crimping step. The method of any of claims 1-3 wherein the second modifier composition is topically applied to an at least partially crimped continuous spun fiber or filament. The method of any of claims 1-4 wherein the "D" processing step comprises a fiber cutting and carding operation. The method of any of claims 1-5 wherein the second modifier composition comprises 0-15% by weight of a polysiloxane represented by formula (2). The method of any of Claims 1-6 wherein o is a positive number within the range of 10-50. Use of polyolefin-containing fibers or filaments prepared by the method of any of claims 1-7 in the production of a nonwoven material.

Inventors: SCHMALZ A CHANDLER, SCHMALZ, A CHANDLER
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1991
Main classification: D06M13
IPC codes: D04H1, D02G3, D02G1, D06M101, D06M15, D06M13, D01F11, D02J3, D04H3, D01D5