Rewettable polyolefin fiber nonwoven

Abstract: A method for imparting hydrophillc properties to non­ woven material containing hydrophobic fiber or fibrillated film, in which a wettability modifying composition comprising a polyalkoxylated secondary or tertiary fatty acid amine is compounded into the molten polyolefin-containing composition prior to spinning or casting, optionally in combination with from 1% to 60% by weight of primary fatty acid amide, and such nonwoven material to which the hydrophilic properties have been so imparted, are disclosed.

Description: This invention relates to a method for imparting hydrophilic properties to nonwoven material containing hydrophobic fiber, and to such nonwoven material to which hydrophilic properties have been imparted 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 facing or cover stock layer of essentially nonabsorbent material that encloses the absorbent core and prevents skin contact with the core, thus tending to isolate any fluids already absorbed in the core, and a fluid impervious barrier sheet to protect the wearer's clothing from stain or wetting by any absorbed fluids. On the side that is placed against the body, the facing or cover stock material should be pervious to fluids with minimal surface fluid retention, so as to promote the immediate transfer of the fluid into the absorbent core material and inhibit lateral migration of fluid along its surface. It should also feel smooth and soft to the touch, and may have additional characteristics that are sometimes desired, such as visual opacity, particular coloring, and a lustrous outer surface. To obtain such desirable characteristics, the cover stock comprises essentially hydrophobic polymeric material, such as polyolefin fiber or film, that is made sufficiently hydrophilic to receive and transmit aqueous fluids even after several wettings (sometimes colloquially referred to in the art as "insults"). Agents used to promote such hydrophilicity must have the ability to resist the tendency of such wettings to reduce their effectiveness by washing or leaching. This is particularly important in the case of cover stock for diapers, so as to avoid lateral migration of liquid and leakage at the edges. Also, treatment with such agents obviously should not interfere with fabric-bonding steps in manufacture or the wet strength of the final product U.S.Patent 4,578,414 discloses a method for imparting surface wettability to hydrophobic polyolefin fibers, including polypropylene, that includes compounding with the bulk molten polymer a surface-active agent that comprises an alkoxylated alkylphenol and/or a polyoxyalkylene fatty acid ester, or either of them together with a triglyceride. However, there is still a need for wettability modifying additives that have greater resistance to wash-out and leaching, that possess better fluid control, and reduce interference with bonding properties under high speed commerical operation. According to the invention, a method for imparting hydrophilic properties to nonwoven material containing hydrophobic fiber, in which a wettability modifying composition is compounded into a molten polyolefin-containing composition prior to spinning, is characterized in that the modifying composition comprises a polyalkoxylated secondary or tertiary fatty acid amine having a molecular weight within the range of 258 to 2000 and having the general formula or in which the group is a fatty acid amine moiety containing 10-22 carbon atoms and R is a linear straight chain; "Alk" is an alkylene chain having 2-4 carbon atoms; "n" and "m" are each independently a number ranging from 0-26; and "Y" is a polar anionic radical, the amount of the modifying composition based on the weight of the polyolefin-containing composition being 0.1%-4.0%. The stated amount of the modifying composition is determined as being the amount that is effective for the purpose of the invention, and is preferably 0.5-2.0%, based on the weight of the polyolefin-containing composition. Preferably the fatty acid amine moiety is derived from capric, lauric, palmitic, myristic, stearic, arachidic, or oleic acid or a tallow fatty acid, and more preferably from stearic acid. Preferably the polar anionic radical is -OH, or -SO 4 , and more preferably -OH. Preferably 1% to 60%, and more preferably 1-45% by weight of the modifying composition is a primary or secondary fatty acid amide having the general formula or in which the group is a fatty acid acyl moiety containing 10-22 carbon atoms. Preferably the fatty acid acyl moiety is derived from capric, palmitic, behenic, stearic, or oleic acid, or its corresponding N,N'-ethylene bis counterpart having formula (4). Most preferably the weight ratio of amine-to-amide is from 8-4 to 2-6. After the conventional steps of spinning or casting the resulting melt to obtain fiber or film and processing the fiber have been carried out, the corresponding webs can be formed, oriented, and bonded by conventional means to obtain the desired nonwoven material. Preferably, the modifying composition is applied as a dry powdered material. The polyalkoxylated fatty acid amine is commercially obtainable, for instance, as Kemamine® AS-990, 974, 971, and 650. The fatty acid amide is commercially obtainable, for instance, as as Kemamide® S, or B. All are products of the Humko Chemical Division of Witco Chemical Company of Memphis, Tenn. The modifying composition is blended with a suitable polyolefin-containing resin, in conventional flake or pellet form. For instance, a melt of an isotactic polypropylene or conventional hydrophobic polypropylene copolymer preferably has a weight average molecular weight from about 3 X 10 5 to about 5 X 10 5 , 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 minute, and a spin temperature of about 220°C.-300°C. The parameters obviously will be modified according to conventional principles to achieve varying objectives, for instance, to accommodate melt-blown nonwoven materials or to obtain particularly desired characteristics. When using webs containing fiber of a conventional sheath/core configuration, it is preferred to incorporate the modifying composition primarily in the sheath component in order to facilitate availability at the surface and surface-directed migration, and to reduce the total amount of modifier composition required. The bonding techniques used to form nonwoven materials from the hydrophobic fiber containing the wettability modifying composition according to the invention are well known, for instance using adhesive binders, thermal bonding, and and powder bonding. Conventional additives, including pH stabilizers such as calcium stearate, antioxidants, degrading agents, and pigments including whiteners and colorants such as TiO 2 may be used in the polyolefin-containing resin. The following examples further illustrate, but do not limit the present invention. The following tests were performed and the results reported in the tables. "Sink time" (liquid absorbency time): Five (5) gram samples of each filament are loosely packed into identical 3 gram mesh baskets (in accordance with ASTM Method D-1117-79) increases in sink time or submergence time after repeated treatments being correlated to the loss of hydrophilicity. "Strike-through time" is the time in seconds required for 5 ml of syn-urine to pass through a single sheet of nonwoven fabric then into absorbent paper (filter paper) pads. "Strike-through time/rewet" or "Strike Time Rewets" is a combination test performed by first carrying out the Strike-through time test with 5 ml of liquid and fresh absorbent paper and then measuring the times for successive additions of 10 ml of the same liquid to pass through the fabric; the time in seconds is recorded in the indicated column. After each addition, the value in the "Rewets" column is determined by placing an absorbent pad on top of the fabric and under a 3.63 kg (8 lb) weight, and measuring the weight of liquid in grams that is passed back during 5 minutes from the wet pad through the fabric into the top pad. As already indicated, each wetting is referred to as an "Insult". EXAMPLE 1 A. Polypropylene in flake form and characterized as follows: (crystallinity 60%, M w 3.5 x 10 5 , molecular weight distribution 6.4, and melt flow 3.2 g/10 minutes) is mixed in an impact blender at high speed for 2 hours with .5% by weight of powdered Kemamine® AS 990 (an ethoxylated stearyl amine obtained commercially from Humko Chemical Division of Witco Chemical Corporation) as the modifying composition. After blending, the mixture is fed into a 1 1/2" extruder and spun through a 210 hole spinnerette at 285°C., air quenched, and processed to obtain 2.2 dpf 1.5" staple filament. The filament is then carded into webs weighing about 20 g/yd 2 and conventionally calendar bonded at 164°C. to obtain sample nonwoven material, which is then cut into test strips identified as A-1 for strike through, rewet and tensile-strength tests using Syn-Urine™ (an aqueous commercial product obtained from Jayco Pharmaceutical Company of Camp Hill, PA). Test results are reported in Table 1 below as sample A-1, the control sample (C-1) being identically prepared and tested except for the absence of Kemamine 990 in the fiber. B. Filaments, webs and nonwoven materials are obtained in accordance with Example 1A, by incorporating 1.0% by weight of Kemamine AS 990 in the spun melt as modifier composition. The resulting 2.3 dpf fiber is cut to 1 1/2 inch staple, carded into webs and thermally bonded as before to obtain a 20 g/yd 2 test nonwoven. Strips of this nonwoven, identified as B-1, are tested for strike through, rewet, and strength as before; and results reported in Table 1. C. Monofilament of 6 dpf are prepared, using the polypropylene flake of Example 1A admixed respectively with .5%, 1% and 2% by weight of Kemamine AS 990. Five (5) gram samples of each filament are loosely packed into identical 3 gram mesh baskets for sink-time tests in accordance with ASTM Method D-1117-79, increases in sink time or submergence time after repeated insults being correlated to the degree of wash out and loss of hydrophilicity. Test results are reported in Table 2 as Samples D-1 through D-3 and the control (no modifier) is reported as C-2. D. A bicomponent sheath/core polypropylene fiber of 6 dpf is prepared having a 30 wt % sheath, is prepared from isotactic polypropylene flake of Example 1A which is blended with 1% by polymer weight of Kemamine AS 990 and spun at 250°C. as a sheath or cover. The corresponding 70 wt. % or core is obtained from the corresponding unmodified isotactic polypropylene of Example 1A using a conventional spin pack arrangement (well known for instance from U.S Patent 3,700,544). The resulting bicomponent fiber and an unmodified homogeneous polypropylene fiber as a control are tested in the manner of Example 1 C with respect to sink time, strike through, and rewet, and test results reported in Tables 3 and 4 as E-1 and C-3 (control). E. Two batches of continuous spun isotactic polypropylene fiber containing, respectively 0.5% and 1.0% Kemamine modifier composition are prepared and spun (2.2 dpf) in accordance with Example 1 A, some of the fiber being crimped and false twisted to obtain a test yarn and some crimped, cut, to 1.5" staple, carded, and the resulting web thermally bonded as before to obtain test nonwoven material. The fiber, yarn and strips of nonwoven (40 gm/yd2) are then tested for sink time as before, using identical weight samples lightly packed into 3 gram mesh basket. Test results are reported in Table 5 below. F. Filaments, webs and corresponding nonwoven materials are produced in the manner of Ex 1 C., supra, using respectively 10%, 25%, 40%, 50%, 60% and 100% by weight of 0.75% Kemamine-treated 2.2 dpf 1.5 inch staple blended with 90%, 75%, 60%, 50%, 40% and 0% by weight, respectively, of untreated but otherwise identical 2.2 dpf 1.5 inch staple in a continuous blender, the blended staple is then carded, combined to form webs, thermally bonded and tested as before, the test results being reported in Table 6. Sample # % Kemamine® 990 Type Insults Sink Time (Sec) C-2 0 Monofil. 1 Did not sink D-1 0.5 #4 " 1 1.0 " 2 1.5 " 3 3.2 " 4 5.4 " 5 4.8 D-2 0.5 " 1 31.0 " 2 20.0 " 3 6.4 " 4 14.7 " 5 20.0 D-3 1.0 " 1 6.0 " 2 7.8 " 3 7.7 " 4 6.5 " 5 4.9 D-4 2.0 " 1 11.0 " 2 4.0 " 3 12.0 " 4 5.0 " 5 5.0 Sample # % Kemamine® Type Insults Sink Time (sec) E-1 1% By Melt Wt. Bicomp. 1 1 2 1.6 3 3.5 4 16.0 5 25.0 C-3 1% By Melt Wt. Monofil. 1 3.7 2 2.5 3 6.9 4 10.5 5 20.6 Samples Sample Type % Kemamine AS 990 Modifier Sink Time (Sec) No. Insults F-1 (2.2 dpf) Spin Yarn 0.5 3.8 1 3.8 2 4.9 3 6.9 4 10.6 5 F-1 Staple 0.5 8 1 42 2 48.7 3 36 4 29 5 F-1 Fabric 0.5 6 1 7 2 28 3 20 4 30 5 F-2 (2.1 dpf) Spun Yarn 1.0 3.1 1 3.2 2 3.9 3 4.4 4 4.5 5 F-2 Staple 1.0 45.2 1 105 2 48.7 3 67.0 4 37.0 5 F-2 Fabric 1.0 5.4 1 7.7 2 14.7 3 28 4 39 5 C-4 Control (2.2 dpf) Spin Yarn 0.0 1.12 1 4.0 2 60.0 3 600.0 4 |3600.0 5 C-4 " Staple 0.0 1.0 1 72.0 2 |300 3 -- 4 -- 5 C-4 " Fabric 0.0 2.96 1 600 2 | 4 hrs. 3 -- 4 -- 5 WETTABLE POLYPROPYLENE FABRICS REWETTABLE / NON-REWETTABLE FIBER BLENDS Samples Rewettable Fiber (%) Insults Strike/Rewet Time (sec.) Rewets (G.) G-1 10 1 1.95 0.1 2 186.7 0.11 3 169.6 0.11 4 274.9 0.11 5 254.5 0.11 G-2 25 1 1.75 0.11 2 57.4 0.11 3 62 0.11 4 239.5 0.11 5 264.6 0.11 G-3 40 1 1.7 0.11 2 24.6 0.11 3 26.6 0.11 4 139 0.11 5 160 0.11 G-4 50 1 1.6 0.12 2 15.5 0.13 3 10.6 0.12 4 95 0.13 5 185.1 0.13 G-5 60 1 1.3 0.11 2 8.5 0.13 3 7.5 0.13 4 59 0.13 5 180.2 0.13 G-6 100 1 1.2 0.11 2 3.6 0.11 3 4.5 0.11 4 11.3 0.11 5 54.5 0.12 C-5 (Control) 0 1 1.6 0.11 2 300 3 300 4 300 5 300

Claims: A method for imparting hydrophilic properties to nonwoven material containing hydrophobic fiber , in which a wettability modifying composition is compounded into a molten polyolefin-containing composition prior to spinning, characterized in that the modifying composition comprises a polyalkoxylated secondary or tertiary fatty acid amine having a molecular weight within the range of 258 to 2000 and having the general formula or in which the group is a fatty acid amine moiety containing 10-22 carbon atoms and R is a linear straight chain; "Alk" is an alkylene chain having 2-4 carbon atoms; "n" and "m" are each independently a number ranging from 0-26; and "Y" is a polar anionic radical, the amount of the modifying composition based on the weight of the polyolefin-containing composition being 0.1%-4.0%. A method for imparting hydrophilic properties to nonwoven material as claimed in claim 1, further characterized in that the amount of the modifying composition is 0.5-2.0% by weight. A method for imparting hydrophilic properties to nonwoven material as claimed in claim 1 or 2, further characterized in that the fatty acid amine moiety is derived from capric, lauric, palmitic, myristic, stearic, arachidic, or oleic acid or a tallow fatty acid. A method for imparting hydrophilic properties to nonwoven material as claimed in claim 3, further characterized in that the fatty acid amine moiety is derived from stearic acid. A method for imparting hydrophilic properties to nonwoven material as claimed in any of the preceeding claims, further characterized in that the polar anionic radical is -OH, or -SO 4 . A method for imparting hydrophilic properties to nonwoven material as claimed in claim 5, further characterized in that the polar anionic radical is -OH. A method for imparting hydrophilic properties to nonwoven material as claimed in any of the preceeding claims, further characterized in that 1% to 60% by weight of the modifying composition is a primary or secondary fatty acid amide having the general formula or in which the group is a fatty acid acyl moiety containing 10-22 carbon atoms. A method for imparting hydrophilic properties to nonwoven material as claimed in claim 7, further characterized in that 1-45% by weight of the modifying composition is constituted by the primary or secondary fatty acid amide. A method for imparting hydrophilic properties to nonwoven material as claimed in claim 7 or 8, further characterized in that the fatty acid acyl moiety is derived from capric, palmitic, behenic, stearic, or oleic acid, or its corresponding N,N'-ethylene bis counterpart having formula (4) in claim 7. A method for imparting hydrophilic properties to nonwoven material as claimed in any of claims 7, 8 or 9, further characterized in that the weight ratio of amine-to-amide is from 8-4 to 2-6. A web of nonwoven material comprising polyolefin fiber obtainable from a polymeric composition containing a wettability modifying composition, characterized in that the modifying composition comprises a polyalkoxylated secondary or tertiary fatty acid amine having a molecular weight within the range of 258 to 2000 and having the general formula or in which the group is a fatty acid amine moiety containing 10-22 carbon atoms and R is a linear straight chain; "Alk" is an alkylene chain having 2-4 carbon atoms; "n" and "m" are each independantly a number ranging from 0-26; and "Y" is a polar anionic radical, the amount of the modifying composition based on the weight of the polyolefin-containing composition being 0.1%-4.0%. A web of nonwoven material as claimed in claim 11, further characterized in that the amount of the modifying composition is 0.5-2.0% by weight. A web of nonwoven material as claimed in claim 11 or 12, further characterized in that the fatty acid amine moiety is derived from capric, lauric, palmitic, myristic, stearic, arachidic, or oleic acid or a tallow fatty acid. A web of nonwoven material as claimed in claim 11 or 12, further characterized in that the the polar anionic radical is -OH. A web of nonwoven material as claimed in any of claims 11 to 14, further characterized in that 1% to 60% by weight of the modifying composition is a primary or secondary fatty acid amide having the general formula or in which the group is a fatty acid acyl moiety containing 10-22 carbon atoms. A web of nonwoven material as claimed in claim 15, further characterized in that 1-45% by weight of the modifying composition is constituted by the primary or secondary fatty acid amide. A web of nonwoven material as claimed in claim 15 or 16, further characterized in that the fatty acid acyl moiety is derived from capric, palmitic, behenic, stearic, or oleic acid, or its corresponding N,N'-ethylene bis counterpart having formula (4) in claim 15. A method for imparting hydrophilic properties to nonwoven material as claimed in any of claims 1 to 10, wherein hydrophobic fiber has a sheath/core configuration. A method for imparting hydrophilic properties to nonwoven material as claimed in claim 18, wherein the wettability modifying composition is incorporated primarily in the sheath component of the hydrophobic fiber. A web of nonwoven material as claimed in any of claims 11 to 17 containing hydrophobic fibers of sheath/core configuration. A web of nonwoven material as claimed in claim 20, wherein the wettability modifying composition is incorporated primarily in the sheath component of the hydrophobic fibers.

Inventors: HARRINGTON JAMES HENRY, HARRINGTON, JAMES HENRY
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1990
Main classification: D01F6
IPC codes: C08L23, D01F6, C08K5, C08L71, D01F1, D04H1