Antistatic treatment of polyolefin fibers

Abstract: Disclosed is a method for treating polyolefin-containing spun fibers or filaments to increase their processability, in which the fibers or filaments are treated treated with a first modifier composition comprising from about 70% to 100% by weight of of a neutralized phosphoric acid ester having the formula (Alk-O) n --O-R m (1) in which Alk is an lower alkyl group having 1-8 carbon atoms; R is an amino group or an alkali metal, n and m are each a positive number of not less than about 1, the sum of which is about 3; and from 0 to about 30% by weight of a polysiloxane having the formula wherein X and Y are individually defined as a hydrophobic chemical end group such as a lower alkyl group; R′ is a lower alkyl group, and o is a positive number within the range of about 10-50 or higher; and the fibers or filaments are sub­ sequently treated with a second modifier composition compris­ ing about 70%-100% by weight of the said polysiloxane and from 0 to about 30% by weight of the said neutralized phos­ phoric acid ester.

Description: The present invention relates to polyolefin-containing hydrophobic spun fibers or filaments which are obtainable by a treatment during the processing of the fibers or filaments with an anti-static agent. The invention also relates to a method for imparting anti-static properties and lubricity to the polyolefin-containing hydrophobic fibers or filaments so as to facilitate their processability. Products used for personal hygiene, such as catamenial devices, disposable diapers, incontinence pads and the like, have a fluid-absorbent core, usually comprising one or more layers of absorbent material, a layer of hydrophobic material facing and contacting the body that prevents skin contact with the core and tends to isolate any fluids already absorbed in such a core, and a fluid impervious barrier sheet to protect the wearer's clothing from stain or wetting by any absorbed fluids. The hydrophobic material may be a nonwoven material produced from conventionally bonded webs of hydrophobic fiber such as polyolefin-containing staple- or spun-bonded webs. During conventional spinning, cutting and carding operations, such hydrophobic fiber, if not specially treated, quickly accumulates a static charge generated by friction, and becomes so difficult to process that carding, for instance, is impossible. It is known, for instance from US-A-3,341,451, that topically applied antistatic agents containing salts of phosphoric acid esters change fiber surface properties sufficiently to facilitate conventional fiber processing, but such known antistatic treatments also make the fiber, web or nonwoven material substantially more hydrophilic than the untreated spun fiber and are difficult to control. It is also taught by the prior art, for instance by US-A-3,423,314, that dimethylpolysiloxane fluids, which are effective lubricants for synthetic fibers, do not provide static protection even when modified with known antistatic agents. FR-A-2,259,938 discloses a method for imparting anti-static properties to organic fibers by applying to the fibers poly-diorganosiloxanes having a specified viscosity and having dissolved therein from 0.1 to 30 parts of anti-static phosphorus compounds for every 50 to 100 parts of the poly-diorganosiloxane. The preferred anti-static phosphorus compounds are those which have the general formula (O)P (OH) x Y 3-x where Y represents hydrocarbon or oxyhydrocarbon groups and X = 0 if Y is a hydrocarbon group whereas X = 0, 1 or 2 if Y is an oxyhydrocarbon group. There is a need for a method for imparting anti-static properties and lubricity to polyolefin-containing hydrophobic fibers or filaments to facilitate carding and other processing without excessively interfering with their hydrophobicity or bonding properties. According to the invention there are provided polyolefin-containing hydrophobic spun fibers or filaments which are obtainable by a treatment during the processing of the fibers or filaments with an anti-static agent comprising a neutralized phosphoric acid ester, being characterized in that the fibers or filaments are initially treated with about 0.09%-0.6% (for example 0.09%-0.5%), based on the weight of the fiber, of a first modifier composition comprising from about 70% to 100% by weight of a neutralized phosphoric acid ester having the formula in which Alk is an alkyl group having 1-8 carbon atoms; R is an amine salt group or an alkali metal group, n and m are each a positive number of not less than 1, the sum of which is 3; and from 0 to about 30% by weight of a polysiloxane represented by formula wherein X and Y are individually defined as a hydrophobic chemical end group; each R' is an alkyl group having 1-8 carbon atoms, and 0 is a positive number within the range of about 10-50 or higher; and the fibers or filaments are subsequently treated with about 0.05%-0.30% (for example 0.05%-0.20%), based on the weight of the fiber, of a second modifier composition comprising about 70%-100% by weight of a polysiloxane having the formula (2) and from 0 to about 30% by weight of a neutralized phosphoric acid ester having the formula (1), and after drying, the processing of the fibers or filaments is completed. The invention also provides a method for producing such fibers or filaments which comprises treating the fibers or filaments to increase their anti-static properties and lubricity while maintaining their hydrophobic properties, which treatment is as defined above. The invention also provides the use of such fibers or filaments for personal hygiene products. Examples of such products are, as mentioned above, catamenial devices, disposable diapers and incontinence pads. The invention also provides personal hygiene products having a fluid absorbent core comprising one or more layers of absorbent material, a facing layer of hydrophobic material for contacting the body, and a fluid impervious barrier sheet, characterized in that the hydrophobic material is a web of fibers or filaments in accordance with the invention. The alkyl groups may preferably have 1-4 carbon atoms. A methyl group is suitable. After the application of the second modifier composition according to the invention, the spun fibers or filaments have the desired level of hydrophobicity, and readily undergo carding and other processing steps required for web formation, including bonding steps. In addition, the nonwoven material made from the treated spun fibers or filaments can be conventionally embossed and calender-printed with various designs and colors, as desired, to increase loft, augment wet strength, and provide easy market identification. In the method according to the invention, the modifier compositions can be applied by various conventional procedures to the polyolefin-containing spun fibers or filaments, which include melt-spun staple fiber, filament or fibrillated film of bicomponent or monofilament types. For instance, the fibers or filaments can be drawn over feed wheels partially immersed in baths of the modifier composition, or they can be dipped in the baths, or the compositions can be sprayed on the fibers or filaments. The specific proportions of the ingredient of the modifier compositions can easily be varied to achieve the balance of properties desired, including resistance to static formation during crimping of continuous spun fibers or filaments or other processing steps and the final degree of hydrophobicity. Preferably, the application of the first modifier composition should precede and the application of the second modifier composition should follow any conventional crimping step in such processing. The method according to the invention is particularly applicable to high speed production of nonwoven materials that use webs obtained from spun bonded or carded staple. The term "processing" in the method according to the invention includes conventional techniques for forming webs from continuous or staple fibers. The polyolefin-containing spun fibers or filaments include those made from conventionally blended isotactic polypropylene as well as conventional hydrophobic copolymers of polypropylene with ethylene, 1-butene, 4-methylpentene-1, and the like. The resulting blended and extruded spun melt preferably has a weight average molecular weight varying from about 3 X 10⁵ to about 5 X 10⁵, a molecular weight distribution (Mw/Mn) of about 5.0-8.0, a melt flow rate of about 2.5 to about 4.0 g/10 minutes, and a spin temperature within a range of about 220°C-300°C. The invention is further illustrated by the following Examples and Tables: EXAMPLE 1 A. Polypropylene in flake form and characterized as follows: (crystallinity 60%, M W 3.5 x 10⁵, molecular weight distribution 6.4, and melt flow 3.2 g/10 minutes) is mixed in an impact blender. After thorough blending, the mixture is fed into a 38mm (1.5 inch) extruder and spun through a 210 hole spinnerette at 280°C., air quenched, and stretched at 115°C (4 X) to obtain a 2.22 dtex (2 dpf) circular filament that is then passed over a feed or kiss wheel partly immersed in a tank of first modifier composition consisting of a 50% aqueous solution of Lurol™ AS-Y, a neutralized phosphoric acid/alcohol ester available from George A. Goulston Company of Situate, Mass., contact being of sufficient duration and speed to topically apply about 0.6 wt. % of the dried composition. The resulting continuous filament is crimped at about 100°C. and again passed over a kiss roll and coated (.10 wt %) with a second modifier composition consisting of a 20:1 mixture by weight of a 60% polydimethyl siloxane emulsion commercially available from Union Carbide Corporation, as LE-458HS and a 50% aqueous solution of Lurol AS-Y. After air drying, the coated 2.22 dtex (2.0 dpf) fiber is chopped to 38mm (1.5 inch) length staple and set aside for conventional ASTM Sink Time tests in which a given weight of fiber is loosely packed into a mesh basket and the sink time measured in seconds. The remainder is carded into webs weighing about 23.9g/m² (20 g/yd²), two webs being calendar bonded at 162°C. to obtain test nonwoven material. The test nonwoven is cut into strips of convenient dimensions for carrying out conventional strength and run off tests using syn-urine, available from Jayco Pharmaceuticals of Camp Hill, Pa., as the wetting fluid. Test results, are summarized and reported in Tables I and II.

Claims: Polyolefin-containing hydrophobic spun fibers or filaments which are obtainable by a treatment during the processing of the fibers or filaments with an anti-static agent comprising a neutralized phosphoric acid ester, being characterized in that the fibers or filaments are initially treated with about 0.09%-0.6%, based on the weight of the fiber, of a first modifier composition comprising from about 70% to 100% by weight of a neutralized phosphoric acid ester having the formula in which Alk is an alkyl group having 1-8 carbon atoms; R is an amine salt group or an alkali metal group, n and m are each a positive number of not less than 1, the sum of which is 3; and from 0 to about 30% by weight of a polysiloxane represented by formula wherein X and Y are individually defined as a hydrophobic chemical end group; each R' is an alkyl group having 1-8 carbon atoms, and 0 is a positive number within the range of about 10-50 or higher; and the fibers or filaments are subsequently treated with about 0.05%-0.30%, based on the weight of the fiber, of a second modifier composition comprising about 70%-100% by weight of a polysiloxane having the formula (2) and from 0 to about 30% by weight of a neutralized phosphoric acid ester having the formula (1), and after drying, the processing of the fibers or filaments is completed. Fibers or filaments as claimed in claim 1, further characterized in that X and Y are alkyl groups having 1-8 carbon atoms. Fibers or filaments as claimed in claim 1 or 2, further characterized in that the first modifier composition comprises about 100% of a neutralized phosphoric acid ester having the Formula (1). Fibers or filaments as claimed in any of claims 1-3, further characterized in that the alkyl groups in formula (1) have 1-4 carbon atoms. Fibers or filaments as claimed in claim 4, further characterized in that the alkyl group in formula (1) is a methyl group, n is 2, and m is 1. Fibers or filaments as claimed in any of claims 1-5, further characterized in that the processing of the fibers or filaments includes a crimping step. Fibers or filaments as claimed in claim 6, further characterized in that the application of the first modifier composition precedes and the application of the second modifier composition follows the crimping step. Fibers or filaments as claimed in any of claims 1-6, further characterized in that the amount of the first modifier composition is 0.09%-0.5% and the amount of the second modifier composition is 0.05%-0.20%, based on the weight of the fiber. A method for treating polyolefin-containing spun fibers or filaments to increase their anti-static properties and lubricity while maintaining their hydrophobic properties, in which the fibers or filaments are treated during the processing of the fibers or filaments with an anti-static agent comprising a neutralized phosphoric acid ester, being characterized in that the fibers or filaments are initially treated with about 0.09%-0.6%, based on the weight of the fiber, of a first modifier composition comprising from about 70% to 100% by weight of a neutralized phosphoric acid ester having the formula in which Alk is an alkyl group having 1-8 carbon atoms; R is an amine salt group or an alkali metal group, n and m are each a positive number of not less than 1, the sum of which is 3; and from 0 to about 30% by weight of a polysiloxane represented by formula wherein X and Y are individually defined as a hydrophobic chemical end group; each R' is an alkyl group having 1-8 carbon atoms, and 0 is a positive number within the range of about 10-50 or higher; and the fibers or filaments are subsequently treated with about 0.05%-0.30%, based on the weight of the fiber, of a second modifier composition comprising about 70%-100% by weight of a polysiloxane having the formula (2) and from 0 to about 30% by weight of a neutralized phosphoric acid ester having the formula (1), and after drying, the processing of the fibers or filaments is completed. A method as claimed in claim 9, further characterised in that X and Y are alkyl groups having 1-8 carbon atoms. A method as claimed in claim 9 or 10, further characterised in that the first modifier composition comprises about 100% of a neutralised phosphoric acid ester having the formula (1). A method as claimed in any of claims 9-11, further characterised in that the alkyl groups in formula (1) have 1-4 carbon atoms. A method as claimed in claim 12, further characterised in that the alkyl group in formula (1) is a methyl group, n is 2, and m is 1. A method as claimed in any of claims 9-13, further characterised in that the processing of the fibers or filaments includes a crimping step. A method as claimed in claim 14, further characterised in that the application of the first modifier composition precedes and the application of the second modifier composition follows the crimping step. A method as claimed in any of claims 9-15, further characterised in that the amount of the first modifier composition is 0.09%-0.5% and the amount of the second modifier composition is 0.05%-0.20%, based on the weight of the fiber. The use for personal hygiene products of fibers and filaments as claimed in any of claims 1-8 or produced by the method of any of claims 9-16. The use according to claim 17 wherein the personal hygiene products are catamenial devices, disposable diapers or incontinence pads. Personal hygiene products having a fluid absorbent core comprising one or more layers of absorbent material, a facing layer of hydrophobic material for contacting the body, and a fluid impervious barrier sheet, characterized in that the hydrophobic material is a web of fibers or filaments as claimed in any of claims 1-8 or produced by the method of any of claims 9-16.

Inventors: SCHMALZ ALFRED CHANDLER, SCHMALZ, ALFRED CHANDLER
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1990
Main classification: D06M15
IPC codes: D01F11, D06M23, D06M101, D06M13, D02G1, D06M15