KR100563788B1 - Methods of manufacture of nonwoven fabric - Google Patents

Abstract

A nonwoven cellulose fabric is manufactured by extruding a solution of cellulose through at least one spinning jet to form fibres, subjecting the fibres to a high velocity gas flow, and passing the fibres through a vapour mist which at least partially coagulates the fibres prior to collection as a fabric web. The vapour mist may be a low alkyl alcohol or water, and is preferably formed by an atomiser nozzle located below the spinning jet(s). The gas flow is preferably compressed air which is directed onto the fibres at an angle of 30‹ to the axis of the extrudate fibres. The cellulose solution preferably contains 4-22%, and most preferably 10-15%, by weight cellulose, using an amine oxide as solvent. The fibre web may be collected on a dry surface with the subsequent treatment of the web with a coagulant, or it may alternatively be collected onto a surface wetted with coagulant. The fibre web is preferably collected on a compliant surface, which may be provided by a 2mm thick foam layer.

Description

Nonwoven Fabric Manufacturing Method {METHODS OF MANUFACTURE OF NONWOVEN FABRIC}

The present invention relates to a process for producing a nonwoven from cellulose, in particular a cellulose solution.

Cellulose fibers and filaments produce cellulose filaments that can be cut into staple fibers through a coagulation process by spinning a cellulose solution in an amine oxide solvent and washing with a water or dilute amine oxide solution. The extrusion and coagulation process is called solvent spinning, and the solvent spun cellulose fibers produced in this way are generally termed lyocell fibers.

Staple fibers can be entangled with each other to produce fiber products of small decitex up to 1.0 decitex. However, this method is expensive and requires high energy consumption.

Applicant's PCT / GB97 / 03391 discloses a nonwoven cellulose fabric by spinning the cellulose solution from at least one spinneret, exposing the spinning extrudate to a high velocity gas stream and collecting the fibers on the surface where the fibers are solidified. A process for preparing the same has been disclosed. The fibers thus produced tend to bond together before solidification to form a relatively dense, relatively dense nonwoven fabric.

Some applications, such as filter media or materials that require high absorption capacities, do not require highly bound high density filter media.

The present invention provides a method of making a cellulose nonwoven fabric having high lift characteristics and relatively low density.

The present invention consists of a method for manufacturing a cellulose nonwoven fabric that exposes extruded fibers spun in a spinning jet to a high velocity gas stream and passes the fibers into a vapor mist to solidify before the fibers are collected as a fibrous web.

The extruded fibers can be cut into incorrect lengths by being crushed by the gas flow.

Vapor mists may be formed from suitable coagulants. The steam mist is good at steam, but vapor of lower alcohols may be used, for example. Most preferred is to atomize the atomized water from a nozzle located below the spinning jet.

The cellulose solution is preferably an amine oxide solvent such as tersary amine oxide, in particular a cellulose solution in N-methylmorpholine-N-oxide (NMMO). The cellulose solution comprises 4-22% by weight of cellulose, in particular 10-15% by weight, and it is preferred that the cellulose has a degree of polymerization of 200-5,000, in particular 400-1,000.

In a preferred form of the invention it is preferred that the cellulose solution comprises 14% by weight cellulose, 12% by weight water and 74% by weight NMMO and the cellulose has a degree of polymerization of about 600.

The crushed fiber-forming microfibers or fibrils are collected and then solidified (commonly referred to as regeneration) by a dilute aqueous solution of amine oxides comprising 20% water or amine oxides. Fibrils may be collected directly into the coagulation bath or may be collected and solidified on the fiber collection surface.

Gases, especially air or dry steam, are sprayed onto the extruded fiber at a rate of 200 ms ⁻¹ (meters per minute) to 500 ms ⁻¹ , and the temperature of the gas is 100-155 ° C. for a cellulose concentration of 14-15%. Range, but the preferred temperature is about 145 ° C. The lower the cellulose concentration in the dope, the lower the air temperature. The gas velocity may be at least 50 times the rate of extrudate exiting the extrusion jet, but the preferred gas velocity is preferably 1,000-2000 times the extrusion rate. Air is preferably sprayed into the fiber extrudate at an oblique angle, with the preferred angle being sprayed at an angle of 15-45 °, in particular 30 °, with respect to the longitudinal axis of the fiber being extruded. The air injectors are preferably deflected at a second skew angle with respect to the spinning jet so that the axes of the air injectors and the fiber axes do not cross each other. According to this configuration, the air injection is tangential to the fiber extrudate.

The fiber collection surface can be flexible or elastic. Preferred fiber collection surfaces are preferably foams impregnated with water or aqueous NMMO solutions.

The present invention also relates to a nonwoven fabric in which fibers are bonded or entangled together without a tack, which has a density of up to 175 g.dm ⁻³ and / or a tensile strength to rupture of at least 7%.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Brief description of the drawings

1 is a schematic view showing a nonwoven fabric production apparatus according to the present invention,

2 is a plan view of the spinning nozzle used in the apparatus of FIG.

3 is a side view of the nozzle shown in FIG. 2 showing an internal air passage,

4 is a longitudinal sectional view of the nozzle shown in FIGS. 2 and 3;

Detailed Description by Drawing

1 shows an extruder 10 with a nozzle 11. The extruder 10 is supplied with a solution comprising 14% by weight of cellulose, 12% by weight of water and 74% by weight of N-methylmorpholine N-oxide (NMMO). Cellulose has an average degree of polymerization of about 600.

The cellulose solution can be prepared by the method described in WO 94/28217. The cellulose solution is maintained at a temperature of 95-110 ° C., in particular 105 ° C. and spun through the nozzle to extrude into a continuous filament of cellulose dope.

The nozzle 11 is shown in FIGS. 2 and 3, which may be fixed directly to the extruder 10 or installed in an adapter (not shown) fixed to the extruder 10. The tubular threaded portion 13 is integrally formed on the rear surface 12 of the nozzle 11, and the central passage 14 of the threaded portion 13 is connected to the spinneret 15. The spinneret 15 has a diameter of 0.2 to 0.3 mm, in particular about 0.27 mm.

The cellulose dope is pressed into the central passage 14 and radiated through the spinneret 15. The nozzle 11 has a plurality of gas discharge holes 16, in particular three, arranged at regular intervals around the central passage 14. These respective gas discharge holes 16 are formed to be inclined with respect to the axis of the spinning fiber and are arranged to maintain a constant distance in a circular shape around the spinneret for the filament from which the gas flow injected from the respective gas discharge holes 16 is extruded. The same effect was achieved.

The gas outlet hole 16 has an eccentricity or convergence angle of 15 to 45 ° with respect to the radiation axis, but preferably has an eccentricity or convergence angle of 30 °. The gas outlet holes 16 should be formed at an angle to be asymmetrical so that their axes do not converge in one place. These gas discharge holes 16 have a diameter of about 2.0 mm.

The rear surface 12 of the nozzle 11 has a circular groove 17 connected to the gas discharge holes 16.

When the nozzle 11 is coupled to the extruder 10, the central passage 14 of the nozzle is connected to a cellulose dope supply and the annular groove 17 is connected to a gas supply, in particular a compressed air supply.

According to FIG. 1, compressed air (not shown) is a groove 17 of the nozzle 11 through a flow control valve 21, a flow meter 22, an air heater 23, and a temperature sensor 24 from a source. ) Is supplied into. The temperature sensor 24 is connected to an air heater 23 for regulating the air temperature.

The extruded filaments exiting the nozzle 11 are blown into contact with the high velocity air exiting the gas outlet 16 and ruptured into the coagulation bath 27 located about 30 cm away from the nozzle 11 or collecting the fibers. Supplied to the surface 26. The flow rate of the cellulose dope is about 0.2 g.min. ^-1 is preferred. In FIG. 1 the collecting surface 26 is formed of the cylindrical outer circumferential surface of the rotating drum 28 rotating at 10 rpm. The filaments are collected in a layer of nonwoven on the outer circumferential surface of the drum 28 described above.

The extruded filaments are vapor mist 30 produced by fine water particles sprayed from an air jet nozzle 32 located about 10 cm below the nozzle 11 before being fed into the collecting surface 26 or the coagulation bath 27. Pass).

The surface of the drum 28 may be covered with a resilient material, such as a foam layer, in particular a polyurethane foam having an average bubble size of 50 μm. The foam may be impregnated with water or a solution of NMMO.

After the nonwoven layer is formed on the surface of the drum 28, the drum is inserted into a coagulation bath containing a suitable coagulant such as water or a dilute amine oxide solution to solidify the nonwoven fabric surrounding the drum. The nonwoven fabric layer is washed with water to remove the solvent and then dried in a drum.

Table 1 describes various conditions used for the formation of the extruded filaments.

2.4 An air flow rate of 1.s ^{-1 corresponds to} an air velocity of 250 ms ^-1 .

Samples 3 and 4 were prepared by the present invention.

Table 2 summarizes the web Loftineness by the measurement method measured using a Mitotoyo dial Dickness gauge fixed to a film / web plate. Since the basis weights were different, the thickness was based on a basis weight of 25 gm ⁻² .

According to the above table it can be seen that the samples according to the invention produce a less dense fabric having a density of 170 g.dm ⁻³ or less.

According to the sample, the foam is believed to serve two purposes. That is, (a) a tendency to mitigate the impact of the initial fibers striking the hard collector surface—the elastic surface tends to remove some of the impact energy and thereby reduce the bond, and (b) the pore of the foam due to compression of the foam upon impact. It is thought that the coagulant contained in it comes out to the surface to help rapid regeneration.

To evaluate the mechanical properties, the web was cut to form a 5 mm wide strip, and then tested using a test metric tensile tester at a gauge length of 20 mm and a cross head speed of 20 mm / sec. Tensile strength was leveled against a web basis weight of 25 gm ⁻² depending on the absolute tensile strength. This tensile strength accurately represents the comparative mechanical properties when the basis weight parameters are removed.

Table 3 shows the characteristics of the fabric web produced in the drum 26.

In samples 2, 3, and 4, the surface of the drum was immersed in the coagulation bath such that the surface of the drum was wet. As a result, the coagulation occurred when the fiber was in contact with the wet drum or the fibers already laid.

In Sample 1, the surface of the drum was dry and the fabric was regenerated after it had accumulated on the drum.

Samples 3 and 4 collected in the drum after passing the water vapor particulates retained lower tensile strength and exhibited elongation to greater rupture, while retaining some integrity after the burst point. These high loft materials are suitable for use as filters and high absorbent materials.

Although the above-described example of the present invention has described the use of cellulose dope containing 14% by weight of cellulose, the present invention can also be used for other types of dope described in PCT / GB97 / 03391.

Claims (17)

Spinning a cellulose solution in an amine oxide solvent through one or more spinning jets and contacting the extruded filaments in a high velocity gas stream to produce the fibers, and through a vapor mist that at least partially aggregates the fibers before collecting the fibers into the web. To produce a nonwoven fabric. The method of claim 1 wherein the cellulose solution is a solution of cellulose dissolved in an amine oxide solution and the vapor mist consists of aqueous particulates. The method of claim 1 or 2, wherein the gas flow rate is at least 200 m / sec. 4. The method of claim 3 wherein the flow of gas is at least 50 times faster than the flow rate of the extrudate. 3. The method of claim 1, wherein the gas in the gas stream has a temperature of at least 100 ° C. 4. 3. Method according to claim 1 or 2, characterized in that the vapor mist is formed by spray nozzles installed at a distance below the spinning jet. Method according to claim 1 or 2, characterized in that the cellulose solution comprises 4-22% by weight of cellulose, in particular 15% by weight. 3. The method of claim 1, wherein the cellulose has an average degree of polymerization of about 600. 4. 3. The method of claim 1, wherein the gas stream described above is compressed air injected into the fiber at an angle of inclination of 30 ° with respect to the axis of the extruded fiber. 4. The method of claim 1 or 2, wherein the fibrous web is collected on a dry surface and subsequently treated with a coagulant. The method of claim 1 or 2, wherein the fibrous web is collected by the coagulant on the wet collection surface. The method of claim 1 wherein the fibrous web is collected on the resilient surface. 13. The method of claim 12, wherein the resilient surface is formed by a foam layer about 2 mm thick. A lyocell nonwoven fabric prepared by the method of claim 1. Passing a vapor mist which agglomeration into contact the filaments extruded through the spinning jet to be emitted and a high-speed gas flow, and then the fiber prior to collection as a web fibers have been manufactured to be coupled together without binder, the fabric web is about 175 g.dm ^-3 A lyocell nonwoven fabric having the following density. 15. The lyocell nonwoven fabric of claim 14, wherein the fabric has an elongation to rupture at least 7%. 15. The lyocell nonwoven fabric of claim 14, wherein the fibers are bonded without the use of a binder and the fabric web has an elongation to rupture at least 7%.

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