Patent Application
20050056956
(Not applicable)
(Not Applicable)
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1. Field of the Invention
This invention relates to a process of melt blowing a cellulose solution through a concentric melt blown die with a plurality of spinning nozzles to form cellulosic microfiber webs with different web structures.
2. Description of the Prior Art
Cellulosic fibers are man-made fibers regenerated from a proper cellulose solution (dope) with different techniques. As an example, Lyocell fiber is one of the regenerated, man-made cellulose fibers. It is traditionally made by a dry-jet-wet-spinning process, where the cellulose solution of a solvent, such as N-methyl morpholine N-oxide, is extruded through a spinneret to form filaments. These filaments travel a short distance in air (the dry-jet), then get into a coagulation bath for regeneration. A proper mechanical pulling force is applied onto the regenerated fibers to attenuate the fiber in the “dry-jet” section. Regenerated fibers then go through a series of washing/finishing baths and drying units to form final products in the form of continuous filaments or short fibers. U.S. Pat. Nos. 4,142,913; 4,144,080; 4,211,574; 4,246,221, and 4,416,698 and others described the details of this process.
Jurkovic et al., in U.S. Pat. No 5,252,284 and Michels et al., in U.S. Pat. No. 5,417,909 deal especially with the geometry of extrusion nozzles for spinning cellulose dissolved in NMMO. Brandner et al., in U.S. Pat. No. 4,426,228, is exemplary of a considerable number of patents that disclose the use of various compounds to act as stabilizers in order to prevent cellulose and/or solvent degradation.
Zikeli et al., in U.S. Pat. Nos. 5,589,125 and 5,607,639, direct a stream of air transversely across strands of extruded lyocell dope as they leave the spinnerets. This air stream serves only to cool and does not act to stretch the filaments. French laid open application 2,735,794 describes formation of lyocell fibers by a process of melt blowing. However, these are highly fragmented microfibers useful principally for production of self bonded non-woven webs.
U.S. Pat. No. 6,306,334 teaches a process using much larger sectioned spinning orifices compared with the above referenced technologies enabling a higher dope throughput per orifice to minimize tendency for orifice plugging problem. Although Example of this patent described a single orifice melt blown die with air delivered from both sides of the die through parallel slots at an angle of 30 degree, it failed to teach more details of a die with multiple orifices, such as that how the orifices are arranged, and how the air applied to extruded filaments. Due to the unique characteristic of cellulose-NMMO solution and complexity of MB technology, it is uncertain that if the same results from a single orifice MB die could be obtained from a multiple orifice MB die.
The present invention is directed to a process of melt blowing a cellulose solution through a concentric melt blown die with multiple rows of spinning nozzles to form cellulosic microfiber webs with different web structures. The term of “cellulose” as used here should be understood as either cellulose from natural resources or a synthetic polymer blend with cellulose. The term of “die” is often used as the term of “spinneret” in this invention. The term of “concentric melt blown die” refers to an apparatus described in U.S. Pat. No 5,476,616 with the hot air nozzles concentric with the polymer spinning nozzles and the air flows parallel with the polymer filaments near the exits of the nozzles.
The cellulose solution is extruded out through each spinning nozzle at a proper temperature (ranging from 80 to 140° C.) and a proper throughput. The extrudates are attenuated quickly by high velocity hot air jets from a few hundred micrometers in diameter to a few micrometers in diameter within a few centimeters from the nozzle exits. These microfibers are collected on the surface of a moving collecting device, which can be either a drum collector or a flat screen collector. A set of jets of solvent/non-solvent mixture shoots from a series of fine orifices/nozzles on the flying fibers and the collected web. The term of solvent used in the present invention refers to NMMO, dilute caustic soda, phosphoric acid, mixture of liquid ammonia/ammonia thiocynate and others. The term of “non-solvent” used here refers to water, alcohol (CnH2n+1OH, n≦10), and/or water/alcohol/solvent solutions. The term “water” is often used as the term of “non solvent” in this invention. Depending on the position and angle of the non-solvent jet, the amount of non-solvent applied, and other factors, the resultant cellulose microfiber nonwoven web exhibits different characteristics. The jets of solvent/non-solvent solution serves two functions in this process, coagulating (fully or partially) the filaments and hydro-entangling the filaments to form webs.
The final cellulose microfibers have an average fiber diameter ranging from 1 micrometer to 20 micrometer with a relatively broad fiber diameter distribution
Spinning nozzles have an inside diameter in the range of 0.005-0.050 inch with a length/diameter (L/D) ratio in the range of 40-300. Under proper operation conditions, the resultant melt blown web is free of “shot”, a defect in the form of glob of polymer which is significantly large than the fiber. Fibers produced by the method of this invention possess desirable crimps.
There is an object of the present invention to provide a method of forming cellulose microfiber nonwoven fabrics from a solution of a cellulose solvent, such as NMMO, by utilizing melt blown technology with concentric multiple-row spinning nozzles
It is an additional object to provide a method for making the said nonwoven web without additional processes, i.e. carding, web forming, and bonding.
It is a further object to provide a method for making cellulose nonwovens with different web structures.
It is another object to provide a method for forming a biodegradable nonwoven web.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
The process of the present invention is suitable to various cellulose solutions. The solvent includes NMMO, dilute caustic soda, phosphoric acid, mixture of liquid ammonia/ammonia thiocynate and others. The ways making a solution of the cellulose are known to the art, as reported by Petrovan, Collier, and Negulescu in “Rheology of Cellulosic N-Methymorpholine Oxide Monohydrate Solutions of Different Degrees of Polymerization” (Journal of Applied Polymer Science, Vol 79, 396-405 (2001)), by Albrecht in “Lyocell Fibers” (Chemical Fiber International, Vol 47, 298-304 (1997)), by Luo in U.S. Pat. No 6,306,334 B1, and by Liu, Cuculo, Smith in “Diffusion competition between solvent and nonsolvent during the coagulation process of cellulose/ammonia/ammonium thiocynate fiber spinning system” (Journal of Polymer Science Part B: Polymer Physics Vol 28, Issue 4, Pages 449-465 (1990))
Reference to
The present process produces significantly more filaments per inch spinneret compared to the process disclosed in U.S. Pat. No. 6,306,334 B1 and U.S. Pat. No. 6,358,461 B1, where a melt blowing die of single row of spinning holes employed.
The optical micrographs shown in
A ¾ inch extruder is fed with a NMMO solution comprising 10.5% by weight cellulose, 77.5% by weight of NMMO and the rest is mainly water. The solid solution are in the form of pellet of 0.05″˜0.08″ in size. The feeding hoper is filled with Argon gas to prevent moisture takeup. The cellulose has an average degree of polymerization from 330˜360.
The extruder has three heating zones and the temperatures were set as 165° F. (Zone 1, near the feeding hoper), 210° F., 230° F., respectively. The molten solution was forced into the body of a 5-inch-2-row spinneret, with 126 spinning nozzles (I.D.=0.009″) and protruding length of 0.1915″. The solution temperature and pressure at the spinneret were kept in 230° F. and 600 PSI, respectively. The air temperature and pressure in the spinneret were held at 250° F. and 15 PSI respectively. The solution throughput was about 0.16 gram/nozzle/min.
The attenuated microfibers are deposited on a perforated rotating drum right after contacted with the hydro needling jets. These strong needling jets serve as a pre-coagulation means and a fiber entangling means. The web goes through another set of hydro needling jets for better mechanical bonding and regenerating. The well bonded web is regenerated, washed, post-treated, and air dried.
A 1 inch extruder is fed with a NMMO solution comprising 14% by weight cellulose, 76% by weight of NMMO and the rest is mainly water. The solid solution are in the form of pellet of 0.05″˜0.08″ in size. The feeding hoper is filled with Argon gas to prevent moisture takeup. The cellulose has an average degree of polymerization of 670.
The extruder has three heating zones and the temperatures were set as 185° F. (Zone 1, near the feeding hoper), 230° F., 250° F., respectively. The molten solution was forced into the body of a 5-inch-2-row spinneret, with 63 spinning nozzles (I.D.=0.020″) and protruding length of 0.180″. The solution temperature and pressure at the spinneret were kept in 250° F. and 860 PSI, respectively. The air temperature and pressure in the spinneret were held at 270° F. and 10 PSI respectively. The solution throughput was about 0.8 gram/nozzle/min.
The inventors have herein described the best present mode of practicing their invention. It will be evident to others skilled in the art that many variations that have not been exemplified should be included within the broad
