LU81737A1 - THIN-WALLED DIALYSIS FILM MEMBRANE - Google Patents

Description

- 4 - A3GW31860 / 64/74 j% Thin-walled dialysis hollow fiber membrane A k z o nv

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The invention relates to a dialysis membrane in the form of a hollow thread made of regenerated cellulose. Regenerated cellulose which is suitable for the invention is a cellulose which has been coagulated from cellulose solutions by means of a precipitant, with the cuoxam process being in the foreground because it leads to hollow fibers with the best membrane properties.

Dialysis membranes according to the invention are mainly used for hemodialysis. But they can also be used for reverse osmosis.

So far, only dialysis membranes in the form of hollow fibers with relatively thick walls are known, because it was feared that the hollow fibers would collapse if the walls were thin and the blood flow would no longer exist. With support h

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π π I - 5 - A3GW31860 / 64/74 .. layers have already been made thin-walled dialysis membranes in hollow thread form. Complicated spinnerets are required to manufacture them and the process must be carried out with extreme precision.

In the case of dialysis membranes in the form of hollow fibers made of regenerated cellulose, a minimum wall thickness of more than 10y * m has previously been observed, the lumen diameter then generally being up to - 300yum.

The object of the present invention was to use hollow fibers made from regenerated cellulose as a dialysis membrane with extremely small wall thicknesses and the largest possible lumen diameter.

This object was achieved in that a hollow thread made of regenerated cellulose is used for dialysis, which is characterized in that the wall thickness is 0.5 to β ^ Am.

The hollow fiber wall is preferably formed in one layer. Such hollow threads can be produced by the known "Cuoxam process" using known hollow thread nozzles. Sulfuric acid, dilute sodium hydroxide solution or warm water can be used as coagulant. In particular, the process described in DE-PS 736 321 in Example 10 is excellently suited for the production of thin-walled hollow fibers from regenerated cellulose. By coordinating the delivery rate of cellulose-cuoxam solution and of void-forming liquid with the withdrawal speed, practically any dimension within the scope of the invention can be produced without difficulty.

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It was also an object of the present invention to provide a process for spinning thin-walled hollow fibers made of regenerated cellulose for semipermeable membranes, which allows hollow fibers to be produced with an exact cross-sectional shape predetermined by the spinneret shape, which at the same time also has excellent properties as Characterize semipermeable membranes and where the mechanical strengths are not impaired.

* This object is achieved according to the invention in that, in such a process, the hollow thread spinneret is immersed in the aqueous sodium hydroxide solution and the ratio of the withdrawal speed of the hollow thread on the first take-off roller to the discharge speed of the cellulose-cuoxam solution from the ring slot of the hollow thread spindle nozzle 1.00 to 1 , 05 and the direction of the thread run from the hollow thread spinneret to the first take-off roller forms an acute angle with the axis of the hollow thread spinneret openings.

When using hollow thread spinning nozzles with a circular cross section, hollow threads with an exactly circular I cross section are obtained with such small deviations from the ideal one

Circular shape that was previously not thought possible. If the standard deviations are determined for the deviations in the wall thickness of a hollow thread according to the invention with a concentric circular cross section, values of less than 5% are obtained.

If hollow thread spinning nozzles are used for hollow threads with a profiled or eccentric cross section, in contrast to methods according to the prior art, there is no leveling of the profile or reduction of the eccentricity. Regarding the eccentricity it has to be said that this

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* * - - - - 7 - A3GW31860 / 64/74 The honing process according to the invention can even be strengthened / even there if the thread is drawn off in such a way that the pointed winch with the axis of the hollow thread spinning nozzle openings. on t1t »r side of greater wall thickness. Here it should have been expected that the eccentricity would then weaken.

In principle, it is also possible in the method according to the invention to arrange the hollow thread spinneret in the bottom of the coagulation trough and to spin the thread upwards. Because of the greatest technical difficulties that arise with such an arrangement when changing nozzles, when sealing and piecing t't, this embodiment is used for the implementation d ^ ;; Process have less importance than the arrangement of the hollow thread spinneret on the surface of the coagulation: n.bades.

Preferably, in the process according to the invention, the hollow filament spinneret is dipped 5 to 10 mm deep into the aqueous sodium hydroxide solution. This immersion depth is already sufficient to coagulate the thread sufficiently quickly, the hollow thread spinning nozzle opening still being readily observable in the caustic soda solution, which is deep blue in color due to the Cuoxam solution.

The first drawdown is arranged in the method according to the invention in such a way that the spun hollow filament, when it emerges from the hollow filament nozzle, is not guided vertically downwards, but is changed so that the direction is offset of the thread run from the hollow thread spinning nozzle to the first take-off roller forms an acute angle with the hole of the hollow thread spinning nozzle openings. . This acute angle is preferably between 15 ° and 70 °.

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In the process according to the invention, the freshly spun hollow fiber is transported in the coagulation bath only using very low tensions. The circumferential speed of the second draw-off roller arranged behind the first draw-off roller is preferably only 90 to 98% of the circumferential speed of the first draw-off roller. This causes a small shrinkage of the freshly spun hollow thread, while in the prior art methods the hollow thread is stretched immediately after leaving the spinneret.

So far it was believed that for the production of hollow fibers, especially those that are semi-permeable! Membranes are intended to serve, and the diameters from approx. 50 S to 1000 μm with wall thicknesses from 10 to approx. 200 can only be produced with hollow thread spinning nozzles, the dimensions of which are a multiple, for example 10 to 150 times the hollow thread dimensions. In the context of the invention, hollow thread spinning nozzles are preferably used in which the ratio of the dimensions of the ring slot of the hollow thread spinning nozzle is 2.5 to 6 times the dimension of the finished hollow thread.

The cellulose content of the cellulose-cuoxam solution generally does not deviate from the cellulose content which the ICellulose-Cuoxam spinning solutions have, which are usually used for the regeneration of the cellulose. However, the cellulose content is preferably 6 to 10% by weight, based on the weight of the solution. The NaOH

The sodium hydroxide content can fluctuate within further limits.

* | However, it is preferably between 10 and 20% by weight, 4 in order to ensure a sufficiently rapid formation of the Normann cellulose, which initiates the solidification of the hollow thread.

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If the hollow thread produced by the method according to the invention is to be stretched or has to be stretched, this stretching is expediently carried out when passing through the aftertreatment baths.

Thin-walled hollow fibers made from regenerated cellulose often lay flat when dry and can be wound up in the flat form and processed into flat structures. When swelling, the flat »laid hollow fibers straighten up again and a smooth, round lumen cross-section is formed, which enables the blood to flow undisturbed.

In an embodiment of the invention, the lumen thus has a round cross-section, the diameter of the lumen being 50 to 500 ^ “· m.

Round should be understood to mean any cross-sectional shape that has no corners or projections and that is curved outwards from the thread axis. Preferred cross-sectional shapes of the lumen are circular and elliptical.

The wall thickness of the hollow thread is preferably 1 to 5yuun. In one embodiment of the invention, the wall thickness remains constant over the circumference and over the length.

In another embodiment of the invention, the wall thickness can regularly change uniformly over the circumference and / or the length. Such changes in the wall thickness over the length and / or over the circumference serve to avoid the so-called glass plate effect, which consists in the fact that hollow threads stick together and the dialysis fluid cannot come into contact with the entire membrane surface.

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Wall thicknesses of 1.0 / nn, 20 ^ m, • 3.5 / tm, 5ytm and 7yftm were preferably realized, and a wall thickness of 8.5yum also did not pose any difficulties in the production. Hollow fibers whose wall thickness changes regularly and uniformly over the circumference in a ratio of up to 1: 3 also have good properties as a dialysis membrane.

The wall thicknesses mentioned in the prefix then represent the dimensions of the smallest wall thickness. In the following table, dimensions of hollow fibers made from regenerated Cuoxam cellulose are combined, where D / a is the ratio of lumen diameter to wall thickness.

Table 1

Current Lumen through wall thickness ratio D / a

No. knife 1. 30 / um 0.5. Um 60 2. 50 / um 2.0 Alm 25 3. 90 jum 3.0 / um 30 4. 150 / um 3.0 / rni 50 5. 160 / um 4.0 / around 40 6.210 / around 3.5 / around 60 7.285 / around 2.5 / around 114 8.290 / around 5.0 / around 58 9. 380 / around 7.0 / around 54 10. 390 / um 3.0 / um 130 11. 420 / um 6.0 / um 70 12. 430 / um 2.0 / um 215

The hollow fibers, the dimensions of which are listed in Table 1, were installed in a test dialyzer and tested under test conditions in vitro.

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The remaining method is described in "Evaluation of Hemodialysers and Dialysis Membranes" Report of a study group for the artificial kidney - chronic uremia program 1977;

Elias Klein et al. U.S. Department of Health Education and Welfare. Bethesda, Maryland 20014. Publication No. NIH 77-1294.

2nd

With a solution flow of 200 ml / min * m and with a second

Dialysate flow of 500 ml / min * m, a urea * clearance of up to 195 ml / min was achieved. This shows the excellent suitability of the thin-walled hollow dialysis membrane threads for use in artificial kidneys.

Such a hollow thread is shown in the attached FIGS. 1 to 3, while the method according to the invention is shown schematically in FIG.

Figure 1 shows the cut thread in perspective, while

Figure 2 shows a cross section perpendicular to the thread axis, which, however, had to be greatly distorted in the proportions. 1 is the hollow thread as such with the wall 2 consisting of regenerated cellulose.

The lumen diameter is denoted by D and the wall thickness by a.

FIG. 3 shows a cross section perpendicular to the thread axis, which, however, had to be greatly distorted in terms of dimensions, in which the wall thickness changes regularly and uniformly over the circumference. 1 is * the hollow thread as such with that from regenerated

Cellulose existing wall 2. The lumen diameter 7 is denoted by D and the wall thickness by a. * h .... i I - 12 - A3GW31860 / 64/74

Figure 4 shows a process diagram.

The cellulose-Cuoxam spinning solution 1 and the cavity-forming liquid 2, for example isopropyl myristate or paraffin oil, are fed to the hollow fiber spinneret 3. This hollow fiber spinning nozzle 3 is immersed in the aqueous sodium hydroxide solution passed through the coagulation trough 4. The hollow thread 5 coming from the hollow thread spinning nozzle 3 is deflected on the first draw-off roller 6 and via the second draw-off roller 7. fed to the after-treatment baths. The thread running direction between the first take-off roller 6 and the hollow thread spinning nozzle 3 forms an acute angle with the axis of the hollow thread spinning can openings. The post-treatment baths are expediently designed as tubs, two of which are shown in the sketch, for example (8; 14). Deflection rollers 9 are arranged in the aftertreatment baths. The driven rollers 10; 11; 12 and 13 are driven with increasing peripheral speed, whereby the hollow thread 5 is stretched to the desired extent. The washed hollow thread 5 is passed into the dryer 15 via a last deflecting roller, dried there and wound up into bobbins in the winding 16.

For the aftertreatment baths, dilute sodium hydroxide solution, water, dilute sulfuric acid, "acid water" and pure water are generally used in succession. Before the ! Drying the hollow threads are expediently treated with glycerin.

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Claims (14)

1. Dialysis membrane in the form of a hollow thread made of regenerated cellulose, characterized in that the wall thickness is 0.5 to 8 ^ m. 2. Dialysis membrane according to claim 1, characterized in that the hollow fiber wall is formed in one layer. 3. Dialysis membrane according to claims 1 to 2, characterized in that the lumen has a round cross section perpendicular to the thread axis and the lumen diameter is 50 to 500y * <m. 4. dialysis membrane according to claims 1 to 3, characterized in that the wall thickness of the hollow thread 1 to 5 ^ fcm bëtrâgt. 5 cellulose for Dialysemexnbranen according to claims 1 1 to 7 by squeezing a cellulose-Cuoxam solution through the ring slot of a hollow thread spinning nozzle in aqueous sodium hydroxide solution and a cavity-forming liquid through the inner bore of the hollow thread spinning nozzle and customary aftertreatment, characterized in that the hollow thread spinning nozzle in the aqueous sodium hydroxide solution immersed and the ratio of the pull-off speed of the hollow thread on the first take-off roller to the discharge speed of the cellulose-cuoxam solution from the ring slot of the hollow-thread spinneret is 1.00 to 1.05 and the direction of the thread run from the hollow-thread spinneret to the first take-off roller is sharp! Forms an angle with the axis of the hollow thread spinning nozzle openings. 5. dialysis membrane according to claims 1 and 4, characterized in that the wall thickness over the circumference and the length of the hollow thread remains the same. 6. Dialysis membrane according to claims 1 and 4, characterized in that the wall thickness changes regularly and uniformly over the circumference and / or the length. 7. dialysis membrane according to claims 1 to 6, characterized in that the ratio of lumen diameter to wall thickness is 20 to 280. l * ^ I -2 ~ I; · Γ Π 1 - 2 - A3GW31860 / 64/74 ι 8. Process for spinning hollow fibers from regenerated 9. The method according to claim 8, characterized in that the hollow thread spinneret is immersed 5 to 10 mm deep in the aqueous sodium hydroxide solution. [ 10. The method according to claims 8 to 9, characterized thereby! records that the angle that the direction of the thread runs from the hollow thread spinning nozzle to the first draw-off roller with the axis of the hollow thread spinning nozzle opening is 15 ° to 70 °. 11. The method according to claims 8 to 10, characterized in that the peripheral speed of the second take-off arranged behind the first take-off roller roller is 90 to 98% of the peripheral speed of the first take-off roller. 'f ~ "J I - 3 - A3GW31860 / 64/74 I- 12. The method according to claims 8 to 11, characterized in that the ratio of the dimensions of the annular slot of the hollow fiber spinning nozzle is 2.5 to 6 times the dimensions of the finished hollow thread. 13. The method according to claims 8 to 12, characterized in that the cellulose content of the Cuoxam solution 6 to 10 wt .-% and the NaOH content of the aqueous sodium hydroxide solution 10 to 20 wt .-%, each based on the 'weight of Solutions is. 14. The method according to claims 8 to 13, characterized in that the hollow thread is stretched as it passes through the aftertreatment baths. ΚΧλΧΧλΙλ - 4 -