SK84197A3 - Manufacture of extruded articles - Google Patents

Abstract

A method of manufacturing extruded articles of lyocell is described wherein a solution of cellulose in a tertiary amine N-oxide is extruded by way of a die (2) through an air-gap (3) into a coagulating bath (5), air being supplied to and discharged from the air-gap (3), characterised in that the air-gap (3) comprises a first region (9) adjacent the face (2a) of the die (2) and a second region (12) more remote from the face (2a) of the die (2), the moisture content of the air supplied to the first region (9) being maintained at a lower value than the moisture content of the air supplied to the second region (12). The method provides improved spinnability and may provide lyocell filaments with a reduced tendency to fibrillation.

Description

According to the present invention, the process for producing extruded lyocell products is carried out by extruding a solution of cellulose in a tertiary amine N-oxide through an air gap into a coagulation bath, whereby air is drawn into and out of the air gap. The method is characterized in that the air gap comprises a first area adjacent to the spinning plate and a second area adjacent to the bath, while the humidity of the air that is supplied to the first area is kept lower than the humidity of the air supplied to the second area.

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The extruded lyocell product may also form foils or preferably fibers (including not only spinning fibers, which may subsequently be chopped to produce staple fibers, but also yarns with continuous fibers). If the product is fibers, the extruder is generally called a spinneret and the extrusion process can generally be called a spinneret.

The length of the air gap between the nozzle and the coagulation bath is preferably in the range of 10 to 60 mm, even more preferably 15 to 100 mm or 20 to 60 mm. It is clear that the gas in the blower nozzle is preferably air, other inert gases or gas mixtures, for example nitrogen may be used.

Each of the two nozzle regions may have the same or different lengths. In one possible embodiment, which may often seem advantageous, the length of the first region is less than the length of the second region. The first region is preferably 3 to 10 mm so that the second region occupies the remaining length of the air gap. The cellulose solution (which may also be referred to as a spinning solution) is usually extruded downwards and passes through the region of the blower nozzles. The air is preferably supplied and withdrawn by means of air tanks or air nozzles in a direction substantially transverse to the direction of the passing fibers, so that it is substantially horizontal when conventional extrusion techniques are used. With such a transverse arrangement, the passage of air through the air reservoir can usually be referred to as cross-draft. The velocity of the supply air to the receiver in both regions is preferably in the range of 1 to 20 m / s, more preferably 2 to 10 m / s. It is clear that the air velocity should be high enough to maintain different atmospheric conditions around the spinneret extrudate within the two air-blowing regions, but not so high as to interfere with the passage of the extrudate, i.e. the formed fibers. In general, higher speeds can cause such disturbance in longer air gaps. The air velocity of the first and second air blow regions may be the same or different. Suitable air velocities can be determined in each particular case by a simple test.

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Methods of removing air from one or both of the regions may be performed by suction. The air can be supplied and exhausted from the air gap by a suitable blower and suction nozzles. It is clear that separate blower nozzles are required for each of the first and second regions. One or more suction nozzles may also be used. In a preferred embodiment, each blower nozzle faces a suction nozzle that is similarly sized. This arrangement has the advantage of allowing better control of the atmospheric conditions around the extrudate along the entire gap region in which the extrudate is blown through the air. In particular, _w better control of the first region is allowed if the length of the first region is less than the length of the second region.

The air supply temperature in the air gap is generally about ambient temperature, for example 0 to 40 ° C, and very often it is 20 to 30 ° C. The temperature of the dope supplied to the nozzle is generally in the range of about 80 ° C to 125 ° C, and the gas flow thus serves to cool the extrudate in the air gap. It is common practice to increase the speed of the extruded product in the coagulation bath so that it is higher than the extrusion rate at which the spinning solution passes through the nozzle. Usually the factor of this increase is 2.5 to 25, so that the extrudate is stretched to improve the mechanical properties. The humidity of the air supplied to the first region is preferably in the range of 0 to 20, more preferably 0 to 10 grams of water per kilogram of air, the humidity of the air supplied to the second region is preferably in the range of 5 to 30 grams per kilogram of air.

Lyocell fibers generally tend to fibrillate, especially when subjected to mechanical stress during a hot part of a process, such as a process in which they are further processed, such as spinning, grinding or dyeing. In fibrillation, the fibers partially break away from the surface, individual fibers (as well as yarn and products containing it) are formed, and their hairy appearance may be aesthetically undesirable. Surprisingly, it has been found that the fiber produced by the process according to the invention shows a lower tendency to fibrillation than the fiber produced by the conventional spinning technique.

It is known that during the spinning of lyocell fibers, the spinning solution extrudate, for example in the form of fibers, can occasionally remain in the air gap. This defect can be referred to as a loss of spinning stability or poor spinability. Poor spinning can be detected by observing damaged or chopped fibers in the overall product or, in some cases, by recording complete yarn breakage in the air gap or in the spin bath. Surprisingly, it has been found that the process according to the invention solves better spinning stability than conventional techniques, especially with longer air gaps. This effect can be difficult to quantify, but can be easily detected by observation.

The average polymerization degree (D.P. of cellulose in the dope can generally be in the range of from 250 to 2000 and is preferably in the range of from 500 to 2000, even more preferably from

750-1000. It has been found that good spinnability is achieved in a wide range of conditions if D.P. cellulose ranges from 750 to 1000. The degree of polymerization of D.P. The cellulose is usually controllable by viscosimetry of a dilute solution of cellulose in an aqueous solution of a metal amine complex, for example an ammoniacal copper complex. A useful method is the TAPPI Standard T206-based method and is further described herein as Test Method no. 3. D.P. cellulose is measured in anhydroglucose units per molecule. It is clear that the D.P. in this case the mean viscosity D.P.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying drawings which schematically represent an apparatus for carrying out the method according to the invention.

As can be seen in the figure, the solution of cellulose in aqueous amine oxide is supplied to the spinneret 2 by means of a pump 1. The spinning solution can, for example, contain 5 to 25 wt. % cellulose, 70 to 85 wt. % NMMO and 5 to 15 wt. water, its temperature can range from 80 to 125 ´C. The spinning solution is extruded down through the orifices of the spinnerets 2 into an air gap 2 maintained at a temperature below the spinning solution temperature, thereby obtaining a solid form of fiber bundle 4. The fibers 4 then proceed to the aqueous coagulation bath 5 while partially passing through the roller 6 and discharged for rinsing, drying and other usual operations. The peripheral speed of the roller 6 is higher than the speed of the spinning solution at the entrance to the openings of each spinneret 2 so that the fibers 4 are drawn. Stretching of the fibers takes place mainly in the air gap 2 ·

The first part of the air is supplied by a blower nozzle 7 to the air gap 2 in the first region 9, which is adjacent to the spinnerette 2 and discharged from the air gap 2 through the suction nozzle 8 so that air passes through the air gap 2 transversely to the fiber passage direction. 8 are arranged such that the process makes it possible to maintain the temperature and humidity of the atmosphere of the first region 9 adjacent the face 2a of the spinneret 2 ^{at the} desired value. The second part of the air is supplied in a similar manner to the air gap 3 in the second region 12 farther from the spinneret 2 and uses a blower nozzle 10 and a discharge suction nozzle 11. The nozzles 10, 11 are arranged in such a way as to maintain the temperature and moisture of the second region 12 located between the first region 9 and the coagulation bath 5 at the desired values. Nozzles 2 ^and 10 increase the amount of air supplied to the passing bundle of fibers 4. The humidity of the air supplied by the blower nozzle 7 is lower than the humidity of the air supplied by the blower nozzle 10. The temperatures of the two supplied air portions may be the same or different.

Although the figures show the delivery of two different portions of air of different characteristics to the air gap, it is understood that three or more mutually different such portions may also be used, each of which is delivered to a separate air gap region without departing from the basic idea of the invention. The tendency to lyocell fiber fibrillation can be monitored by the following test methods.

DETAILED DESCRIPTION OF THE INVENTION.

Test method 1 (sand test).

A small piece of fiber containing 100 to 200 monofilaments is chopped to a length of 5 mm. The short fibers are placed in a 20 ml flask containing 4 g glass microscopic particles and 8 ml water is added. The vessel is reliably sealed and shaken on a Stewart shaker at 2800 rpm for 20 minutes.

A portion of the fibers are removed and placed on a microscope slide. The fibrillation index (CI) is calculated from optical microspheres on fibrillating fibers. The overall lengths of the fibrils attached to the base fiber of length L are measured by measuring under the microscope. The fibrillation index is given by the equation c _f = f / L

This operation can be performed manually or by image analysis. Alternatively, a set of standard microts can be used for comparison. An experienced fiber worker can easily master this method. In practice, it is not possible to measure fibrillation indices having a value greater than about 30, because of the difficulty in the visibility of a large number of fibrils. Data are measured at the center of the 5 mm fiber and at the end. Experience has shown that the result correlates well with machine execution and therefore only these numbers are referred to herein as (TMI).

Test Method 2 (Color Washing)

The following method was used to determine the fibrillation index (F.I.). Fiber samples were stacked according to increasing degrees of fibrillation. The standard fiber length of each sample was then measured and the number of fibrils (fine hairs extending from the fiber base body) along the full standard length were then added. The length of each fibril was then measured, and a number showing the number of fibrils multiplied by the mean length of the fibril was calculated for each fiber. The fiber having the highest value of this critical number was then labeled as the most fibrillated fiber and given a fibrillation index of 10. The complete non-fibrillated fiber received a fibrillation index of 0 and the other fibers were labeled between 0 and 10 based on microscopically determined critical numbers.

The measured fibers were then used to form a standard ascending scale. To determine the fibrillation index of any other fiber sample, five or ten fibers were visually compared under standard microscope fibers. Visual determination of the critical numbers for each fiber was then the basis for determining the fibrillation index of the test samples. It is clear that the visual test and the average calculation are in many cases faster than the measurement. It has been found that an experienced fiber technician can easily learn this fiber assessment.

The fibrillation index of the articles can be determined on fibers pulled from the surface of the article. Woven and knitted articles having F.I. greater than about 2.0 to 2.5 are not good in appearance.

Lyocell fiber-based 1.7 dtex yarns were crimped and cut into 30 mm fiber samples that were combined in a 20 tex yarn. The yarn was cut into 80 mm long pieces, which were washed and dyed to a light blue shade. The chopped products were rinsed at 40 ° C in a household washing machine and dried in a domestic hot air dryer. The fibrillation index was then determined on the fibers pulled from the surface of the treated dry product after rinsing and dyeing. This index was also determined after

one or more (W / T = wash / tumble). cycles wash and drying Test method (measurement viscosity and D.P. ammonia copper solution). This test is founded on the norm TAPPI Standard T206

os-63rd Cellulose is dissolved in an ammoniacal copper solution containing 15 ± 0.1 g / l of copper and 200 ± 5 g / l of ammonia with a nitric acid concentration of less than 0.5 (Shirley Institute Standard) in such a quantity as to form a pre-solution at the chosen concentration (about 1%). The flow rate of the solution by the Shirley viscometer at 20 ° C is determined after measurement and the viscosity is calculated in a standard manner. Viscosity value D.P. is determined using an empirical equation

D.P. = 412,4285 ln [100 (tk / t) / nC] - 348 where t is the flow time in seconds, k is the gravitational constant, C is the pipe constant and n is the water density in g / ml at test temperature (0.9982 at 20 ° C) ).

The invention is illustrated by the following examples in which parts and ratios are by weight except where expressly stated otherwise.

Example 1

A spinning solution containing wood pulp slurry (different concentrations, different polymerization steps (D.P)) as described below, 74-80% NMMO and 7.5-12.6% water was prepared. This solution was extruded through a spinneret (115 ° C inlet temperature) with 95 orifices each of 80 microns in diameter, through an air gap of the length below, into a coagulation bath containing 25% NMMO and 75% water at 25 ° C, thereby forming a lyocell fiber. The air was blown transversely and passed through the extruded fibers through the upper and lower inlets. The depth of the first, upper region of these cross-feeds was approximately 4 mm. The second, lower transverse inlets were formed such that the air flow from the manually adjusted electric fan into the appropriate space was blown through a suitably directed shaped funnel. The humidity of the lower transverse blowing air was increased, if necessary, by admitting a small amount of low pressure steam to the blowing air at the inlet of the funnel, thereby increasing the relative humidity (R.H.). The fiber was rinsed in water to remove NMMO residues and dried. The fibrillation tendency was then tested by Test Method 1. The fiber samples were then chopped to form pieces of fiber which were then twisted into a yarn. The yarn quality was assessed visually and attributed a value of 1 (very poor) to 5 (very good). The details of the experiments and the results are shown in Table 1 below.

Table 1

Cellulose

D.P.

Yarn quality C _f (TMI)

Fiber bonding

speed spinning 60 m / min, air gap 20 mm, upper air cooling (first area) 20 ° C / 0% R.H., bottom air cooling (second region) 20 ° C / 40 % RH 15 850 4 5.5 not 15 630 5 6.5 not 15 472 5 9.4 not 12.5 630 4 5.9 not 10 850 4 5.3 not

Spinning speed m / min, air gap 75 mm, top blowing (first area) 20 'C / 0% RH . lower air cooling (second Area) 20 ° C % RH 15 850 4 6.6 not 15 630 5 4.9 not 15 472 4 3.3 some 12.5 630 3 4.1 some 10 850 4 4.2 not Spinning speed m / min, air gap 150 mm, top blowing (first area) 20 ° C RH . lower air cooling (second Area) 30 ° C % RH 15 850 3 3.2 some 15 630 3 0.0 a little 15 472 2 0.1 Yes 12.5 630 1 0.0 Yes 10 850 4 2.5 Yes

Spinning speed 30 m / min, air gap 150 mm, top blow (first zone) 20 ° C / 40% R.H., bottom blow (second zone) 30 ° C / 60% R.H.

15 850 4 3.8 a little 15 630 2 1.3 each 15 472 2 0.0 some 12.5 630 1 0.7 Yes 10 850 1 3.5 Yes speed spinning 30 m / min air gap mm, top blowing (first area) 20 ° C / 40% R.H., bottom air cooling

(second region) 30 ° C / 60% R.H.

15 850 4 0.0 not 15 630 3 1.5 minimum 15 472 2 0.0 Yes 12.5 630 1 2.1 Yes 10 850 1 4.8 Yes Example 2 Example 1 was repeated with that 'that difference spinning solution

contained 12.2% wood pulp slurry (D.P. 600), 75% NMMO and 9.8% water. The fiber thus prepared was tested for fibrillation tendency using Test Methods 1 and 2. Details of the experiments and results are given in Table 2 below.

Table 2

Air ° C / RH% Quality C _f (TMl) FI Improvement (TM2)

Upper Bottom Yarn Rinse / Dyeing 1W / T

Spinning speed 60 m / min, air gap 20 mm: 5.5 6.0 20/40 30/60 5 5 11.0 9.0 not not 4.7 4.7 Spinning speed m / min, air 150 mm gap: 30/60 3.0 0.1 Yes 1.7 4.1 20/40 30/60 2.7 1.7 Yes 1.9 1.9

Speed, spinning 10 m / min, air gap 75 mm: 30/60 60/40 30/60 3.3 4.0 3.6 0.7 some 2,5 no 1,0 3.5 2.0 Spinning speed m / min, air gap 150 mm: 20/40 1.3 1.2 each - 20/40 2.0 3.1 yes 2,7 5.2

Experiments with a 20 mm air gap were performed with a rotating head at a temperature of 110 C. Experiments with longer air gaps were conducted with a rotating head and at temperatures of 90, 100, 110 ’C. There were small differences between the results and therefore averages were used.

Example 3

Example 1 was repeated except that the temperatures and relative humidity of the upper part of the supply air were 20 ° C and 40% and the lower part of the supply air were 30 ° C and 60%.

Table 3

Cel. D.P. Cel. % Spinning speed m / min Air gap mm Air speed m / s Yarn tension Spinning stability ^c f 630 15 10 20 2 44 good 3.8 630 15 10 20 8 53 good 1.9 630 15 10 40 2 25 bad 0.0 630 10 40 8 52 good 0.0 630 15 10 80 2 45 good 0.0 630 15 20 20 2 100 good 7.1 630 15 20 20 8 165 good 6.4 630 15 20 40 2 80 bad 5.8 630 15 20 40 8 148 good 3.0 630 15 20 80 2 69 good 2.1 630 15 40 20 2 120 Very good 10.6 630 15 40 20 8 150 Very good 9.5 630 15 40 40 2 150 Very good 6.2 630 15 40 40 8 225 Very good 6.0 630 15 40 80 2 126 good 5.4

Cel. D.P. Cel. % Spinning speed m / min Air gap mm Air speed m / s Yarn tension Spinning stability ^c f 850 15 10 20 2 240 Very good 2.7 850 15 10 20 8 650 good 1.4 850 15 10 40 2 250 Very good 0.0 850 15 10 40 8 920 bad 1.3 850 15 10 80 2 220 good 0.6 850 15 10 160 2 310 good 0.0 850 15 20 20 2 300 Very good 5.8 850 15 20 20 8 900 bad 6.0 850 15 20 40 2 220 Very good 2.4 850 15 20 40 8 900 bad 2.0 850 15 20 80 2 220 Very good 0.2 850 15 20 80 8 280 good 0.2 850 15 40 20 2 460 Very good 4.6 850 15 40 20 8 1000 bad 5.8 850 15 40 40 2 290 Very good 5.4 850 15 40 40 8 800 good 5.0 850 15 40 80 2 210 Very good 0.0

Cel. D.P. Cel. % Spinning speed m / min Air gap mm Air speed m / s Yarn tension Spinning stability ^c f 850 13 10 20 2 57 Very good 5.1 850 13 10 20 8 84 Very good 3.0 850 13 10 40 2 65 good 2.2 850 13 10 40 8 151 good 0.2 850 13 20 20 2 110 Very good 5.5 850 13 20 20 8 117 Very good 1.0 850 13 20 40 2 90 good 4.5 850 13 20 40 8 256 good 6.0 850 13 40 · 20 2 140 Very good 8.9 850 13 40 20 8 170 Very good 6.8 850 13 40 40 2 130 good 7.1 850 13 40 40 8 340 good 6.0 850 ¹³ 40 80 2 110 good 5.4

The yarn tension is a significant number, its higher values mean higher tension. Some parts of the fibers were damaged by observation when using a longer air gap, especially at higher air speeds.

Example 4

The spinning solution was prepared containing 13% cellulose (mean D.P. 800), 75% NMMO and 12% water. It was extruded down through a spinneret having 18400 holes, each 70 microns in diameter, divided into three parallel rows, each about 1 mm long (83 ° C spinning temperature), through a 30 mm air gap into a coagulation bath. containing 25% NMMO and 75% water to form a lyocell fiber yarn. Air was blown through the fibers in two regions across the gap, an upper region at a speed of 12 m / s with a 5 mm blower nozzle located immediately at the spinneret and a lower region at 9 m / s with a 25 mm blower nozzle located behind the bottom of the air gap. Air was sucked out by suction nozzles located opposite respective blower nozzles at the same speeds. The temperature of the upper (relatively dry) air was 20 ° C and its relative humidity was 40% (dew point 6 ° C). The temperature of the lower air stream (relatively humid) was 28 ° C. its relative humidity was 78% (the dew point temperature is 24 ° C). Spinning quality and stability were good. The upper air stream was then removed. Immediately thereafter, the spinning quality deteriorated significantly and the upper air nozzle had to be quickly renewed to prevent the yarn from completely breaking (loss of spinning stability) in the coagulation bath.

Claims (14)

A method for producing an extruded lyocell product, wherein a solution of cellulose in a tertiary amine N-oxide is extruded through an air gap into a coagulation bath, air is supplied to the air gap, and air is drawn from the air gap, characterized in that the air gap is formed by an area adjacent to the edge of the extruder and a second area farther from the exit edge of the extruder, maintaining the humidity of the air supplied to the first region at a lower value than that of the air supplied to the second region. Method according to claim 1, characterized in that the air gap length is in the range of 10 to 160 mm, preferably 20 to 60 mm. Method according to claim 1 or 2, characterized in that the length of the first region is less than the length of the second region. 'I Method according to claim 3, characterized in that the length of the first region is in the range of 3 to 10 mm. Method according to any one of the preceding claims, characterized in that the speed of the air supplied to each first region and the second region is in the range of 1 to 20, preferably 2 to 10 m / s. Method according to any one of the preceding claims, characterized in that air is supplied to the first region and to the second region in a direction substantially transverse to the direction of the extrudate flow through the air gap. Method according to any one of the preceding claims, characterized in that air is supplied to the air gap in both the first region and the second region by blowing nozzles that are separate for each region. Method according to claim 7, characterized in that the air is extracted from the air gap by one suction nozzle directed against the blowing nozzles. Method according to claim 7, characterized in that the air is extracted from the air gap by separate suction nozzles directed against each blower nozzle and with a similar design. Method according to any one of the preceding claims, characterized in that the humidity of the air supplied to the second region is higher than that of the air supplied to the first region. Method according to any one of the preceding claims, characterized in that the humidity of the air supplied to the first region is in the range of 0 to 20, preferably 0 to 10, grams of water per kilogram of air. Method according to any of the preceding claims, characterized in that the humidity of the air supplied to the second region is in the range of 5 to 30 grams per kilogram of air. Method according to any one of the preceding claims, characterized in that the average polymerization degree of cellulose in solution is in the range of 750 to 1000. Method according to any one of the preceding claims, characterized in that the extruded product is in the form of lyocell fibers.