Spin-melt composition and a method for spin-melting filaments

Abstract: A blended spin-melt composition for high-speed spinn­ ing of polyolefins to form air-quenched filaments while mini­ mizing air-quench dependency by incorporating a branched polyolefin additive having a Branching Index within the range of about 0.20-0.90, a method for making such a spin-melt composition, and a method for spin-melting filaments with the composition.

Description: This invention relates to a method for spin melting polymeric fiber-forming compositions, such as polyesters and linear polypropylene, to make multi-filament feed yarns that are cooled by air-quenching. In this specification, the term "spin melt composition" means a polymeric fiber-forming composition that contains at least one linear base polymer of extrudable polypropylene, polyethylene or polyester. Methods for making multi-filament feed yarns by spin melting have been improved in the post-spinning operations to permit increased production rates. However, the spinning speed itself is less amenable to improvements because it is limited by the efficiency of the filament cooling facilities. The soft fast-moving extruded filaments must be given sufficient strength and flexibility to withstand the take-up stress caused by modern high speed spinning techniques. In general, air-quenching is preferred for such high speed production because of the fragile nature of most spun filaments, but it is very difficult to assure sufficient cooling for all the filaments within large, multi-filament bundles. For example, a large spinnerette using a jet of quenching air at room temperature and flowing at a speed of over 25 m/s perpendicularly across the extruded filament bundle normally causes the rows of extruded filaments closest to the air jet to be more quickly cooled than more distant rows. The result is over-quenching of some filaments, with increased risk of filament breakage from cohesive or brittle fracture, and under-quenching of other filaments, with increased risk of ductile failure during take-up. Inadvertent changes in air temperature, spinning speed, post-spinning draw-down velocity, or melt temperature are likely to result in failure of a substantial number of filaments within the fiber bundle. A method for increasing the capacity for increased post-spinning processing rates of high denier spun polyester filaments by using a polyester copolymer comprising a polyester polymer and a chain branching agent is disclosed in U.S. Patent 4,113,704. However, the problem caused by inefficiency of the air-quenching step is not addressed by that prior art teaching, which specifically accepts the conventional limiting effect of current air-quenching procedures on the speed at which the undrawn spun filaments may be taken up. EP-A-0 192 897 discloses a blend consisting essentially of 65-95% by weight of low density polyethylene and 5-35% by weight of polypropylene which can be melt-spun into fibers. The blend is formed from crystalline polypropylene and particular low-density branched polyethylene. EP-A-0 124 722 discloses an ethylene polymer composition being a blend of two ethylene polymers one of which being characterized by molecules having long chain Y-branches. Spin-melting is not considered in this document. It would be desirable to make it possible to increase the speed at which the undrawn spun filaments may be taken up within the inherent limitations of current air-quenching procedures. According to the invention, a spin-melt composition for forming air-quenched filaments by spin-melting comprising at least one linear base polymer of extrudable polypropylene, polyethylene or polyester is characterized in that it contains 1 % to 20 % by weight, based on the total spin melt of a branched polypropylene additive having a Branching Index within the range of 0.20-0.90 blended into the spin melt composition. Also according to the invention, a method for making a spin-melt composition to form air-quenched filaments is characterized in that 1 % to 20 % by weight, based on the total spin-melt of a branched polypropylene aditive having a Branching Index within the range of 0.20-0.90 is blended into the spin melt composition comprising at least one linear base polymer of extrudable polypropylene, polyethylene or polyester before spin-melting it. The resulting spun product not only permits a substantial increase in the speed at which the undrawn spun filaments may be taken up, but also exhibits improvements in fiber quality and thermal bonding characteristics of the filaments produced, particularly for producing good quality nonwoven material. Preferably the branched polypropylene additive is present at a concentration of 1 % to 10 % by weight based on the total blend of the spin melt composition containing the branched polypropylene additive. Within that range, the most preferred amount of branched polypropylene additive is logically determined by (1) the degree of additive branching as measured by the Branching Index, (2) the molecular weight of the additive, (3) the molecular weight of the linear polymer base, (4) the spinning speed desired, and (5) the temperature of the melt to be used. Most preferably, the method according to the invention is operated at a production rate up to and exceeding about 400 m/s by incorporating into the melt an amount of branched polypropylene additive sufficient to produce a concentration of 1 % to 10 % by weight. Preferably the spin melt composition according to the invention has sufficient plasticity to permit high speed extrusion through standard production spinnerettes of the type having up to about 2,600 holes or more, to form large filament bundles. The spin melt composition according to the invention normally contains the conventional extrudable linear fiber former, particularly polyolefin fiber formers, that face substantial risk of filament failure when operating at high speed spinning rates, particularly within the range of about 250 m/s - 500 m/s in large melt spinning devices containing up to and in excess of about 2600 holes per spinnerette. Preferably these polyolefin fiber formers include linear polyolefins such as polyethylene and polypropylene resins having weight average molecular weights within a range of about 5 X 10 4 to 5 X 10 5 , and melt indices within the range of about 0.1 to 50.0. They are commercially available, for instance, from Himont Incorporated under the trademarks Profax R 6301, 6501, 6801 and from E I du Pont de Nemours & Company Inc. under the trademark Alathon 7840. The branched polypropylene additives for use in the method according to the invention preferably have a weight average molecular weight of from about 150,000 to 1,000,000, The most preferred molecular weight value is from about 150,000 to 400,000. Such additives can be used singly or in admixture, and can include low density cross-linked polypropylenes or obtained by irradiation and crosslinkage of available linear polypropylenes, using conventional beam irradiation techniques. Such techniques usually employ about 1-10 Mrad to obtain a Branching Index within the range of about 0.2-0.9. The preparation of suitable polypropylene fiber formers is exemplified by treatment of the linear base polypropylene resin obtained commercially from Himont Incorporated under the trademark Profax 6501 by irradiation within a range of 1 to 10 Mrad. The general relation of the amount of radiation dosage-to-Branching Index, and the correlation between Branching Index and required concentration of branched polypropylene additive in the melt is further demonstrated in Table I. Branched Polypropylene Additive (*2) 0.5% - 10% 10% - 20% 20% - 90% (% by wt. Melt) Branching Index (an) 0.20 - 0.40 0.40 - 0.60 0.60 - 0.90 Branching Category H (*3) M (*4) L (*5) The term "Branching Index", (supra) is further defined by the formula: B.I. = IV 1 IV 2 in which "IV 1 " represents the intrinsic viscosity of the branched additive and "IV 2 " represents the intrinsic viscosity of a corresponding linear base of the same molecular weight, and H, M, and L indicate a high, medium, and low degree of branching respectively. Preferably the temperature of the spin melt composition according to the invention, as well as the corresponding extruder zone, should vary from about 185°C to 310°C and most preferably from about 245°C to 290°C, when operating at high speed spinning rates, particularly within the range of about 250 m/s - 500 m/s in large melt spinning devices containing up to and in excess of about 2600 holes per spinnerette depending upon the particular base polymer, the amount of branched additive, and its Branching Index. Preferably the spin melt composition is visbroken and pelletized before blending with an active amount of desired branched additive (optionally in similar form) by tumble mixing, re-extrusion or similar conventional combining techniques. Various other additives known to the art can also be incorporated into spin melt compositions as desired. These include for instance, antioxidants, such as commercially obtained Cyanox R 1790; degrading agents such as that commercialy obtained from the Penwalt Corporation as Lupersol R 101; pigments, whiteners and colorants such as TiO 2 ; and pH-stabilizing agents known to the art such as calcium stearate. The present invention is further illustrated, but not limited by the following examples: Example I polypropylene spin melt compositions identified as samples S-1 through S-15 are prepared by tumble mixing pellets of linear polypropylene (Profax 6301) respectively with 1%, 10% and 20% by weight of corresponding branched polypropylene additives obtained by irradiating a corresponding linear base. The resulting polypropylene branched additives are 5%, conveniently classified as high "(H)", medium "(M)" or low "(L)" in general accordance with the Branching Indices as set out in Table I (supra). Each branched additive plus Cyanox 1790 antioxidant (0.06% by weight), calcium stearate stabilizer (0.1%) and a polymer degradant (2%), are then tumble mixed with a pelletized commercially obtained linear base polymer, double extruded and spun at 245°C, using a standard monofilament spinnerette at a take up rate of 250 m/s. Test results are reported in Table II below. Sample # Additive Branch Evaluation* Concentration (% by weight) Spin Tension Grams Swell Denier % CV S- 1 (Control) 0 0.32 1.54 19.7 S- 2 L- 1% 0.24 1.54 11.5 S- 3 L- 5% 0.22 1.55 10.6 S- 4 L-10% 0.22 1.55 8.3 S- 5 L-20% 0.30 1.56 10.4 S- 6 M- 1% 0.27 1.55 15.0 S- 7 M- 2% 0.26 1.53 11.4 S- 8 M- 5% 0.25 1.55 13.2 S- 9 M-10% 0.26 1.55 10.2 S-10 M-20% 0.33 1.58 8.0 S-11 H- 1% 0.27 1.53 17.0 S-12 H- 2% 0.31 1.52 11.5 S-13 H- 5% 0.42 1.50 10.2 S-14 H-10% 0.55 1.43 17.6 S-15 H-20% (Would Not Spin) Example II Eighteen samples of the linear polypropylene base of Example I, identified as S-16 through S-33, are admixed and re-extruded with 1%, 2%, 5%, 10% and 20% by weight of high (H), medium (M) and low (L) branched polypropylene additive, and prepared in the manner reported in Example I by tumbling and re-extrusion. The resulting spin melts are spun at 245°C, using the same air-quench temperature and flow rates as used in Example 1. Spun filaments are monitored respectively at 3, 9, and 11 cm distances from the spinnerette during spinning operation using a standard laser micrometer available from Techmet Co. of Dayton, Ohio (Model 60) and the respective elongational viscosities determined and reported in Table III. Sample Branched Polypropylene Additive (% by wt) Additive Branching Evaluations Apparent Elongational Viscosity x 10 -5 Pa·s (X10-4 (Poise)) Distance From Jet (cm) (H) (M) (L) S-16 0 (Control) 9.3 3 S-17 0 (Control) 10.7 9 S-18 0 (Control) 11.2 11 S-19 1% H,M,L 10, 10.3 9.5 3 S-20 1% H,M,L 15, 12.2, 11.5 9 S-21 1% H,M,L 17, 13.0, 11.8 11 S-22 2% H,M,L 12.0, 11.0, -- 3 S-23 2% H,M,L 19.0, 15.5, -- 9 S-24 2% H,M,L 21.5, 17.0, -- 11 S-25 5% H,M,L 14.0, 12.2, 12.8 3 S-26 5% H,M,L 25.3, 17.0, 16.2 9 S-27 5% H,M,L 29.2, 18.5, 17.5 11 S-28 10% H,M,L 22.0, 11.5, 11.2 3 S-29 10% H,M,L --, 17.0, 12.9 9 S-30 10% H,M,L -- , 19.0, 13.5 11 S-31 20% H,M,L -- , 16.2, 10.0 3 S-32 20% H,M,L -- , 25.8, 15.0 9 S-33 20% H,M,L -- , 28.3, 16.5 11 *9 - Calculated from the formulae Example III Staple fiber samples S-5 and S-11 of Example I are individually spun using the same test spinnerette as Example I (1.5 denier, 38 mm cut). The fibers are carded and laid to form webs weighing about 14.4-17.9 g/cm 2 (12-15 g/yd 2 ) and lightly thermally bonded using a diamond pattern collender (140°C 275.8 kN/m 2 (40 psi)) to obtain nonwoven test material exhibiting satisfactory bulk, feel and dry tensile strength, using a conventional Instron Test Instrument, with 12.7 cm (5") gauge length and 5.08 cm (2")/mininute crosshead speed. Example IV Nonwoven material obtained from Example III is cut into 30.48 cm(12") test ribbons and fed into the garniture of a standard filter rod-making apparatus (Model UK5 manufactured by the Molins Company of London, England) and maintaining a velocity differential of about 20% between the ribbon feed rate and the rod-making apparatus feed belt, to obtain fiber rods and 90 mm fiber tips exhibiting satisfactory crush and draw characteristics as determined by a Filtrona Harkness Resilience Tester, (Mark V Series) manufactured by Abbey Mfg., Ltd., Wimbly, England.

Claims: A spin-melt composition for forming air-quenched filaments by spin-melting, comprising at least one linear base polymer of extrudable polypropylene, polyethylene or polyester characterized in that it contains 1 % to 20 % by weight, based on the total spin melt of a branched polypropylene additive having a Branching Index within the range of 0.20-0.90 blended into the spin melt composition. A spin-melt composition as claimed in claim 1 characterized in that the branched polypropylene additive is present at a concentration of 1 % to 10 % by weight based on the total spin melt. A spin-melt composition as claimed in any of the preceding claims characterized in that the branched polypropylene additive has a weight average molecular weight of from 150,000 to 1,000,000. A spin-melt composition as claimed in claim 3 characterized in that the branched polypropylene additive has a weight average molecular weight of from 150,000 to 400,000. A spin-melt composition as claimed in claim 1 characterized in that the branched polypropylene additive has a Branching Index of 0.2 to 0.4. A method for making a spin-melt composition for forming air-quenched filaments as claimed in any of claims 1-5, characterized in that 1 % to 20 % by weight, based on the total spin-melt of a branched polypropylene additive having a Branching Index within the range of 0.20-0.90 is blended into the spin melt composition comprising at least one linear base polymer of extrudable polypropylene, polyethylene or polyester before spin-melting it. A method for spin-melting filaments characterized in that the spin melt composition as claimed in any of claims 1 to 5 is spin-melted at a temperature between 185°C and 310°C and the filaments are then air-quenched. A method for spin-melting filaments as claimed in claim 7 further characterized in that the air-quenched filaments are drawn and crimped. A polyolefin filament yarn made by the method claimed in claim 8 .

Inventors: HOSTETTER BARRY JASON, HOSTETTER, BARRY JASON
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1986
Main classification: D01F1
IPC codes: C08L101, D04H1, C08L23, C08L67, D01F1, D01F6