Classifications

• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
  • D04H1/56—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving in association with fibre formation, e.g. immediately following extrusion of staple fibres
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
  • D01D5/00—Formation of filaments, threads, or the like
  • D01D5/08—Melt spinning methods
  • D01D5/098—Melt spinning methods with simultaneous stretching
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
  • D01D5/00—Formation of filaments, threads, or the like
  • D01D5/12—Stretch-spinning methods
  • D01D5/14—Stretch-spinning methods with flowing liquid or gaseous stretching media, e.g. solution-blowing
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
  • D01D5/00—Formation of filaments, threads, or the like
  • D01D5/18—Formation of filaments, threads, or the like by means of rotating spinnerets
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
  • D04H1/425—Cellulose series
  • D04H1/4258—Regenerated cellulose series
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
  • D04H1/4282—Addition polymers
  • D04H1/4291—Olefin series
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
  • D04H3/013—Regenerated cellulose series
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
  • D04H3/018—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the shape
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
  • D04H3/02—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of forming fleeces or layers, e.g. reorientation of yarns or filaments
  • D04H3/03—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of forming fleeces or layers, e.g. reorientation of yarns or filaments at random
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
  • D04H3/08—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating
  • D04H3/16—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating with bonds between thermoplastic filaments produced in association with filament formation, e.g. immediately following extrusion

Definitions

• the present invention is directed to lyocell fibers having novel characteristics and to the method for their preparation. It is also directed to yarns produced from the fibers, and to woven and nonwoven fabrics containing the fibers.
• the method involves first dissolving cellulose in an amine oxide to form a dope. Latent fi- bers are then produced either by extrusion of the dope through small apertures into an air stream which draws the latent filaments of cellulose solution or by centrifugally expelling the dope through small apertures. The fibers are then formed by regenerating the spun latent fibers in a liquid nonsolvent. Either process is amenable to the production of self bonded nonwoven fabrics.
• Cellulose is also soluble in a solution of ammoniacal copper oxide. This property formed the basis for production of cuprammonium rayon.
• the cellulose solution is forced through submerged spinnerets into a solution of 5% caustic soda or dilute sulfuric acid to form the fibers. After decoppering and washing the resulting fibers have great wet strength.
• Cuprammonium rayon is available in fibers of very low deniers and is used almost exclusively in textiles.
• N- methylmorpholine-N-oxide with about 12% water present proved to be a particularly useful solvent.
• the cellulose was dissolved in the solvent under heated conditions, usually in the range of 90°C to 130°C, and extruded from a multiplicity of fine apertured spinnerets into air.
• the filaments of cellulose dope are continuously mechanically drawn in air by a factor in the range of about three to ten times to cause molecular orientation. They are then led into a nonsolvent, usually water, to regenerate the cellulose.
• Other regeneration solvents such as lower aliphatic alcohols, have also been suggested.
• Lyocell is an accepted generic term for a fiber composed of cellulose precipitated from an organic solution in which no substitution of hydroxyl groups takes place and no chemical intermediates are formed.
• One lyocell product produced by Courtaulds, Ltd. is presently commercially available as Tencel* fiber. These fibers are available in 0.9-2.7 denier weights and heavier. Denier is the weight in grams of 9000 meters of a fiber. Because of their fineness, yarns made from them produce fabrics having extremely pleasing hands.
• One limitation of the lyocell fibers made presently is a function of their geometry.
• Kaneko et al. in U.S. Patent 3,833,438 teach preparation of self bonded cellulose nonwoven materials made by the cuprammonium rayon process. Self bonded lyocell nonwoven webs have not been described to the best of the present inventors' knowledge.
• Low denier fibers from synthetic polymers have been produced by a number of extrusion processes. Three of these are relevant to the present invention. One is generally termed “melt blowing". The molten polymers are extruded through a series of small diameter orifices into an air stream flowing generally parallel to the extruded fibers. This draws or stretches the fibers as they cool. The stretching serves two purposes. It causes some degree of longitudinal molecular orientation and reduces the ultimate fiber diameter. A somewhat similar process is called “spunbonding" where the fiber is extruded into a tube and stretched by an air flow through the tube caused by a vacuum at the distal end. In general, spunbonded fibers are continuous while melt blown fibers are more usually in discrete shorter lengths.
• centrifugal spinning differs in that the molten polymer is expelled from apertures in the sidewalls of a rapidly spinning drum.
• the fibers are drawn somewhat by air resistance as the drum rotates.
• meltblowing there is not usually a strong air stream present as in meltblowing. All three processes may be used to make nonwoven fabric materials.
• Exemplary patents to meltblowing are Weber et al., U.S. Patent No. 3,959,421, and Milligan et al., U.S. Patent No. 5,075,068.
• the Weber et al. patent uses a water spray in the gas stream to rapidly cool the fibers.
• Centrifugal spinning is exemplified in U.S. Patents Nos. 5,242,633 and 5,326,241 to Rook et al. Okada et al., in U.S. Patent No. 4,440,700 describe a centrifugal spinning process for thermoplastic materials. As the material is ejected the fibers are caught on an annular form surrounding the spinning head and moved downward by a curtain of flowing cooling liquid. Included among the list of polymers suited to the process are polyvinyl alcohol and polyacrylonitrile. In the case of these two materials they are spun "wet"; i.e., in solution, and a "coagulation bath" is substituted for the curtain of cooling liquid.
• Microdenier fibers generally are regarded as those having a denier of 1.0 or less.
• Meltblown fibers produced from various synthetic polymers, such as polypropylene, nylons, or polyesters are available with diame- ters as low as 0.4 ⁇ m (approximately 0.001 denier).
• the strength or "tenacity" of most of these fibers tends to be low and their generally poor water absorb- ency is a negative factor when they are used in fabrics for clothing.
• Microdenier cellulose fibers, as low as 0.5 denier, have been produced before the present only by the viscose process.
• the present process produces a new lyocell fiber that overcomes many of the limitations of the fibers produced from synthetic polymers, rayons, and the presently available lyocell fibers. It allows formation of fibers of low denier and with a distribution of deniers. At the same time each fiber has a pebbled surface, a cross section of varying shape and diameter along its length, and significant natural crimp. All of these are desirable characteristics that are found in most natural fibers but are missing in lyocell fibers produced commercially to the present.
• the present invention is directed to a process for production of regenerated cellulose fibers and webs and to the fibers and webs so produced.
• cellulose and "regenerated cellulose” as used here should be construed sufficiently broadly to encompass blends of cellulose with other natural and synthetic polymers, mutually soluble in a spinning solvent, in which cellulose is the principal component by weight.
• cellulose is directed to low denier fibers produced from cellulose solutions in amine N-oxides by processes analogous to melt blowing or centrifugal spinning.
• melt blowing spun blowing
• spunbonding spunbonding
• centrifugal spinning processes that are similar or analogous to the processes used for production of thermoplastic fibers, even though the cellulose is in solution and the spinning temperature is only moderately elevated.
• continuous drawn refers to the present commercial process for manufacture of lyocell fibers where they are mechanically pulled, first through an air gap to cause elongation and molecular orientation then through the regeneration bath.
• the processes involve dissolving a cellulosic raw material in an amine oxide, preferably N-methylmorpholine-N-oxide (NMMO) with some water present.
• NMMO N-methylmorpholine-N-oxide
• This dope, or cellulose solution in NMMO can be made by known technology; e.g., as is discussed in any of the McCorsley or Franks et al. patents aforenoted.
• the dope is then transferred at somewhat elevated temperature to the spinning apparatus by a pump or extruder at about 90°C to 130°C.
• the dope is directed through a multiplicity of small orifices into air.
• the extruded threads of cellulose dope are picked up by a turbulent gas stream flowing in a generally parallel direction to the path of the filaments.
• the liquid strands or latent filaments are drawn (or significantly decreased in diameter and increased in length) during their continued trajectory after leaving the orifices.
• the turbulence induces a natural crimp and some variability in ultimate fiber diameter both between fibers and along the length of individual fibers. This is in marked contrast to continuously drawn fibers where diameters are uniform and crimp is lacking or must be introduced as a post spinning process.
• the crimp is irregular and will have a peak to peak amplitude greater than about one fiber diameter and a period greater than about five fiber diameters.
• Spunbonding can be regarded as a species of meltblowing in that the fibers are picked up and drawn in an airstream without being mechanically pulled.
• meltblowing and spunbonding should be regarded as functional equivalents.
• the dope strands are expelled through small orifices into air and are drawn by the inertia imparted by the spinning head
• the filaments are then directed into a regenerating solution or a regenerating solution is sprayed onto the filaments.
• Regenerating solutions are nonsolvents such as water, lower aliphatic alcohols, or mixtures of these.
• the NMMO used as the solvent can then be recovered from the regenerating bath for reuse. Turbulence and oscillation in the air around the latent fiber strands is believed to be responsible for their unique geometry when made either by the melt blowing or centrifugal spinning process.
• Denier can be controlled by a number of factors including but not lim- ited to orifice diameter, gas stream speed, spinning head speed, and dope viscosity. Dope viscosity is, in turn, largely a factor of cellulose D P. and concentration Fiber length can be similarly controlled by design and velocity of the air stream surrounding the extrusion orifices Continuous fibers or relatively short staple fibers can be produced depending on spinning conditions. Equipment can be readily modified to form individual fibers or to lay them into a mat of nonwoven cellulosic fabric. In the latter case the mat may be formed and become self bonded prior to regeneration of the cellulose. The fibers are then recovered from the regenerating medium, further washed, bleached if necessary, dried, and handled conventionally from that point in the process.
• Gloss or luster of the fibers is considerably lower than continuously drawn lyocell fiber lacking a delusterant so they do not have a "plastic" appearance. This is believed to be due to their unique "pebbled" surface apparent in high magnification micrographs
• the fibers can be formed with variable cross sectional shape and a relatively narrow distribution of fiber diameters Some variation in diameter and cross sectional configuration will typically occur along the length of individual fibers and between fibers.
• the fibers are unique for regenerated cellulose and similar in morphology to many natural fibers.
• the fibers, while having many of the attributes of natural fibers, can be produced in microdenier diameters unavailable in nature. It is possible to directly produce self bonded webs or tightly wound multi-ply yarns.
• a particular advantage of the present invention is the ability to form blends of cellulose with what might otherwise be considered as incompatible polymeric materi- als.
• the amine oxides are extremely powerful solvents and can dissolve many other polymers beside cellulose. It is thus possible to form blends of cellulose with materials such as lignin, nylons, polyethylene oxides, polypropylene oxides, poly(acrylonitrile), poly(vinylpyrrolidone), poly(acrylic acid), starches, poly(vinyl alcohol), polyesters, polyketones, casein, cellulose acetate, amylose, amylopectins, cationic starches, and many others. Each of these materials in homogeneous blends with cellulose can produce fibers having new and unique properties.
• FIG. 1 is a block diagram of the steps used in practice of the present process.
• FIG. 2 is a partially cut away perspective representation of typical centrifugal spinning equipment used with the invention.
• FIGS. 3 is a partially cut away perspective representation of melt blowing equipment adapted for use with the present invention.
• FIG. 4 is a cross sectional view of a typical extrusion head that might be used with the above melt blowing apparatus.
• FIGS. 5 and 6 are scanning electron micrographs of a commercially available lyocell fiber at 100X and 10,000x magnification respectively.
• FIGS. 7 and 8 are scanning electron micrographs of a lyocell fiber produced by centrifugal spinning at 200X and 10,000x magnification respectively.
• FIGS. 9 and 10 are scanning electron micrographs at 2,000X showing cross sections along a single centrifiigally spun fiber .
• FIGS. 11 and 12 are scanning electron micrographs of a melt blown lyocell fiber at 100X and 10,000x magnification respectively.
• FIG. 13 is a drawing illustrating production of a self bonded nonwoven lyocell fabric using a melt blowing process.
• FIG. 14 is a similar drawing illustrating production of a self bonded non- woven lyocell fabric using a centrifugal spinning process.
• cellulosic raw material used with the present invention is not critical. It may be bleached or unbleached wood pulp which can be made by various processes of which kraft, prehydrolyzed kraft, or sulfite would be exemplary. Many other cellulosic raw materials, such as purified cotton linters, are equally suitable. Prior to dissolving in the amine oxide solvent the cellulose, if sheeted, is normally shredded into a fine fluff to promote ready solution.
• the solution of the cellulose can be made in a known manner; e.g., as taught in McCorsley U.S. Patent No. 4,246,221.
• the cellulose is wet in a non- solvent mixture of about 40% NMMO and 60% water.
• the ratio of cellulose to wet NMMO is about 1:5.1 by weight.
• the mixture is mixed in a double arm sig a blade mixer for about 1.3 hours under vacuum at about 120°C until sufficient water has been distilled off to leave about 12-14% based on NMMO so that a cellulose solution is formed.
• the resulting dope contains approximately 30% cellulose.
• NMMO of appropriate water content may be used initially to obviate the need for the vacuum distillation.
• cellulose dopes in aqueous NMMO preparation of the cellulose dopes in aqueous NMMO is conventional. What is not conventional is the way these dopes are spun. The cellulose solution is forced from extrusion orifices into a turbulent air stream rather than directly into a regeneration bath as is the case with viscose or cuprammonium rayon. Only later are the latent filaments regenerated.
• the present process also differs from the conventional processes for forming lyocell fibers since the dope is not continuously drawn linearly 5 downward as unbroken threads through an air gap and into the regenerating bath.
• FIG. 2 is illustrative of a centrifugal spinning process.
• the heated cellulose dope 1 is directed into a heated generally hollow cylinder or drum 2 with a closed base and a multiplicity of small apertures 4 in the sidewalls 6.
• dope is forced out horizontally through the apertures as thin strands 8.
• these strands are illustrative of a centrifugal spinning process.
• the dope strands either fall by gravity or are gently forced downward by an air flow into a non-solvent 10 held in a basin 12 where they are coagulated into individual oriented fibers having lengths from about 1 to
• the dope strands 8 can be either partially or completely regenerated by a water spray from a ring of spray nozzles 16 fed by a source of regenerating solution 18. Also, as will be described later, they can be formed into a nonwoven fabric prior to or during regeneration. Water is the preferred coagulating non-solvent although ethanol or water-ethanol mixtures are also useful. From this point the fibers are col- 0 lected and may be washed to remove any residual NMMO, bleached as might be necessary, and dried.
• Example 2 that will follow gives specific details of laboratory centrifugally spun fiber preparation.
• FIGS. 3 and 4 show details of a typical melt blowing process.
• a supply of dope is directed to an extruder 32 which forces the cel- 5 lulose solution to an orifice head 34 having a multiplicity of orifices 36.
• Air or another gas is supplied through lines 38 and surrounds and transports extruded solution strands 40.
• a bath or tank 42 contains a regenerating solution 44 in which the strands are regenerated from solution in the solvent to cellulose fibers.
• the latent fibers can be showered with a water spray to regenerate or partially regenerate them.
• the 0 amount of draw or stretch will depend on readily controllable factors such as orifice size, dope viscosity, cellulose concentration in the dope, and air speed and nozzle configuration.
• FIG. 4 shows a typical extrusion orifice.
• the orifice plate 20 is bored with a multiplicity of orifices 36. It is held to the body of the extrusion head 22 by a series of 5 cap screws 18.
• An internal member 24 forms the extrusion ports 26 for the cellulose solution. It is embraced by air passages 28 that surround the extruded solution filaments 40 causing them to be drawn and to assist in their transport to the regenerating medium.
• Example 3 that follows will give specific details of laboratory scale fiber preparation by melt blowing
• FIGS 5-6 are of lyocell fibers made by the conventional continuously drawn process It is noteworthy that these are of quite uniform diameter and are essentially straight The surface seen at 10,000X magnification in FIG 6 is remarkably smooth
• FIGS 7-10 are of fibers made by a centrifugal spinning process of the present invention
• the fibers seen in FIG 7 have a range of diameters and tend to be somewhat curly giving them a natural crimp This natural crimp is quite unlike the regular sinuous configuration obtained in a stuffer box Both amplitude and period are irregular and are at least several fiber diameters in height and length Most of the fibers are somewhat flattened and some show a significant amount of twist Fiber diameter varies between extremes of about 1 5 ⁇ m and 20 ⁇ m ( ⁇ 0 1 - 3 1 denier), with most of the fibers closely grouped around a 12 ⁇ m diameter average (c 1 denier)
• FIG 8 shows the fibers of FIG 7 at 10,000x magnification The surface is uniformly pebbly in appearance, quite unlike the commercially available fibers This results in lower gloss and improved spinning characteristics
• FIGS 9 and 10 are scanning micrographs of fiber cross sections taken about 5 mm apart on a single centrifugally spun fiber The variation in cross section and diameter along the fiber is dramatically shown This variation is characteristic of both the centrifugally spun and melt blown fiber
• FIGS 1 1 and 12 are low and high magnification scanning micrographs of melt blown fiber Fiber diameter, while still variable, is less so than the centrifugally spun fiber However, crimp of these samples is significantly greater
• the micrograph at 10,000X of FIG 12 shows a pebbly surface remarkably like that of the centrifugally spun fiber
• FIG 13 shows one method for making a self bonded lyocell nonwoven material using a modified melt blowing process
• a cellulose dope 50 is fed to extruder 52 and from there to the extrusion head 54
• An air supply 56 acts at the extrusion orifices to draw the dope strands 58 as they descend from the extrusion head
• Process parameters are preferably chosen so that the resulting fibers will be continuous rather than random shorter lengths
• the fibers fall onto an endless moving foraminous belt 60 supported and driven by rollers 62, 64 Here they form a latent nonwoven fabric mat 66
• a top roller, not shown, may be used to press the fibers into tight contact and ensure bonding at the crossover points
• a spray of regenerating solution 68 is directed downward by sprayers 70
• FIG 14 is an alternative process for forming a self bonded nonwoven web using centrifugal spinning.
• a cellulose dope 80 is fed into a rapidly rotating drum 82 having a multiplicity of orifices 84 in the sidewalls.
• Latent fibers 86 are expelled through orifices 84 and drawn, or lenghtened, by air resistance and the inertia imparted by the rotating drum. They impinge on the inner sidewalls of a receiver surface 88 concentrically located around the drum.
• the receiver may optionally have a frustroconical lower portion 90.
• a curtain or spray of regenerating solution 92 flows downward from ring 94 around the walls of receiver 88 to partially coagulate the cellulose mat impinged on the sidewalls of the receiver.
• Ring 94 may be located as shown or moved to a lower position if more time is needed for the latent fibers to self bond into a nonwoven web.
• the partially coagulated nonwoven web 96 is continuously mechanically pulled from the lower part 90 of the receiver into a coagulating bath 98 in container 100. As the web moves along its path it is collapsed from a cylindrical configuration into a planar two ply nonwoven structure. The web is held within the bath as it moves under rollers 102, 104. A takeout roller 106 removes the now fully coagulated two ply web 108 from the bath. Any or all of rollers 100, 102, or 104 may be driven. The web 108 is then continuously directed into a wash and/or bleaching operation, not shown, following which it is dried for storage. It may be split and opened into a single ply nonwoven or maintained as a two ply material as desired.
• Example 1 Cellulose Dope Preparation
• the cellulose pulp used in this and the following examples was a standard bleached kraft southern softwood market pulp, Grade NB 416, available from Weyerhaeuser Company, New Bern, North Carolina. It has an alpha cellulose content of about 88-89% and a D P. of about 1200. Prior to use, the sheeted wood pulp was run through a fluffer to break it down into essentially individual fibers and small fiber clumps. Into a 250 mL three necked glass flask was charged 5.3 g of fluffed cellulose, 66.2 g of 97% NMMO, 24.5 g of 50% NMMO, and 0.05 g propyl gallate.
• Example 2 Fiber Preparation by Centrifugal Spinning
• the spinning device used was a modified "cotton candy" type, similar to that shown in U.S. Patent No. 5,447,423 to Fuisz et al.
• the rotor, preheated to 120°C was 89 mm in diameter and revolved at 2800 rpm.
• the number of orifices could be varied between 1 and 84 by blocking off orifices. Eight orifices 700 ⁇ m in diameter were used for the following trial.
• Cellulose dope also at 120°C, was poured onto the center of the spinning rotor.
• the thin strands of dope that emerged were allowed to fall by gravity into room temperature water contained in the basin surrounding the rotor. Here they were regenerated. While occasional fibers would bond to each other most remained individualized and were several centimeters in length.
• microdenier fibers were also successfully made from bleached and unbleached kraft pulps, sulfite pulp, mi- crocrystalline cellulose, and blends of cellulose with up to 30% corn starch or po!y( acrylic acid).
• Diameter (or denier) of the fibers could be reliably controlled by several means. Higher dope viscosities tended to form heavier fibers. Dope viscosity could, in turn, be controlled by means including cellulose solids content or degree of polymerization of the cellulose. Smaller spinning orifice size or higher drum rotational speed pro- Jerusalems smaller diameter fibers. Fibers having diameters from about 5-20 ⁇ m (0.2-3.1 denier) were reproducibly made. Heavier fibers in the 20-50 ⁇ m diameter range (3.1-19.5 denier) could also be easily formed. Fiber length varies between about 0.5-25 cm and depended considerably on the geometry and operational parameters of the system.
• Example 1 Fiber Preparation by Melt Blowing
• the dope as prepared in Example 1 was maintained at 120°C and fed to an apparatus originally developed for forming melt blown synthetic polymers.
• Overall orifice length was about 50 mm with a diameter of 635 ⁇ m which tapered to 400 ⁇ m at the discharge end.
• This feature is expected to be especially advantageous in spinning tight yarns using the microdenier material of the invention since the fibers more closely resemble natural fibers in overall morphology.
• the fibers were allowed to impinge on a traveling stainless steel mesh belt before they were directed into the regeneration bath. A well bonded nonwoven mat was formed.
• the lyocell nonwoven fabrics need not be self bonded. They may be only partially self bonded or not self bonded at all. In these cases they may be bonded by any of the well known methods including but not limited to hy- droentangling, the use of adhesive binders such as starch or various polymer emulsions or some combination of these methods.
• Example 1 The process of Example 1 was repeated using a microcrystalline furnish rather than wood pulp in order to increase solids content of the dope.
• the product used was Avicel ® Type PH-101 microcrystalline cellulose available from FMC Corp., Newark, Delaware Dopes were made using 15 g and 28.5 g of the microcrystalline cellulose (dry weight) with 66.2 g of 97% NMMO, 24.5 g of 50% NMMO and 0.05g propyl gal- late. The procedure was otherwise as described in Example 1.
• the resulting dopes contained respectively about 14% and 24% cellulose. These were meltblown as described in Example 3.
• the resulting fiber was morphologically essentially identical to that of Examples 2 and 3.
• fiber denier is dependent on many controllable factors. Among these are solution solids content, solution pressure and temperature at the extruder head, orifice diameter, air pressure, and other variables well known to those skilled in meltblowing and centrifugal spinning technology. Lyocell fibers having an average 0.5 denier or even lower may be consistently produced by either the melt blowing or centrifugal spinning processes. A 0.5 denier fiber corresponds to an average diameter (estimated on the basis of equivalent circular cross sectional area) of about 7-8 ⁇ m.
• the fibers of the present invention were studied by x-ray analysis to determine degree of crystallinity and crystallite type. Comparisons were also made with some other cellulosic fibers as shown in the following table. Data for the microdenier fibers are taken from the centrifugally spun material of Example 2. Table 1 Crystalline Properties of Different Cellulose Fibers
• Fibers of Present Invention Lvocell Tencel* Cotton Crystallinity Index 67% 65% 70% 85%
• microdenier fibers of the present invention are compared with a number of other fibers.
• the pebbled surface of the fibers of the present invention result in a desirable lower gloss without the need for any internal delustering agents. While gloss or luster is a difficult property to measure the following test will be exemplary of the differences between a fiber sample made by the method of Example 2 and a commercial lyocell fiber, Small wet formed handsheets were made from the respective fibers and light reflectance was determined. Reflectance of the Example 2 material was 5.4% while that of the commercial fiber was 16.9%.

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• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Artificial Filaments (AREA)
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