DD149089A5 - METHOD FOR THE PRODUCTION OF HOLLOWS, OPEN CELL, MICROPOROESE POLYPROPYLENE FIBERS - Google Patents

Abstract

The present invention relates to a process for the preparation of hollow, microporous polypropylene fibers having an oxygen gas permeability of at least 35 cm & exp3! / Cm & exp3! The high gas permeability is achieved by hot spotting isotactic polypropylene at a temperature of at least 230 degrees C into a precursor hollow fiber having a mean inside diameter of at least 140 microns and a ratio of the mean inside diameter to the mean wall thickness from about 8: 1 to about 40: 1, the precursor fibers are annealed at a temperature of about 50 degrees C, but not greater than 165 degrees C, and then cold stretched, hot stretched, and finally the microporous fibers are heated. The resulting hollow, microporous fibers have a mean inner diameter of at least 100 microns. Thanks to the invention, hollow polypropylene fibers with high oxygen permeability can be produced.

Description

Berlin, 20.8.1980 57 036/17

Manufacturing process and hollow, open-cell, microporous polypropylene fibers produced thereafter

Field of application of the invention

The present invention relates to a process for producing hollow, microporous, open-celled propylene fibers and to fibers produced by this process.

Hollow, porous fibers are well known in the art. The advantages of transmissive hollow fibers in permeable films or films are also well known. For example, porous hollow fibers have a larger surface area per unit volume than a sheet of similar porous construction. As a result, the tendency has been to use hollow microporous fibers as much as possible in applications where typically permeable films have been used.

Characteristic of the known technical solutions

Although technically, in many respects, it seems technically the same in many respects to render hollow fibers and films permeable, there are particular manufacturing differences in both cases, which lead to significant unpredictable results in terms of permeability properties, so that it is precluded Sheets her known technique to transfer hollow fibers.

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For example, US Pat. No. 3,801,404 describes a cold stretch hot stretching process for producing microporous polypropylene films in which a precursor or precursor film is formed by a tubular filming method at a temperature of about 180 to 270 ^° C. by spraying and the film or film It is withdrawn at withdrawal or take-off rates of about 9 to 213 meters per minute and at a draw ratio of 20: 1 to 200: 1. The precursor film is then annealed optionally, at a temperature of less than about 120 ⁰ C, for example 25 C, cold-stretched at a temperature of above 120 ⁰ C and below the Polymerschmelztemperatiu ^5, for example, hot-stretched _"0 between 130 and 150 ⁰ C. and finally thermoset at a temperature in the range of about 125 ⁰ C bi3 below the polymer melt temperature, for example between 130 to 16O ⁰ C,

If injection molding or melt spinning temperatures less than 230 ⁰ C are used in the preparation of hollow microporous polypropylene fibers according to the invention in vfachsender manner, the uniformity of the inner and outer diameter reduced in the construction of hollow parsers are relative as well as the thickness appreciably. Therefore, the melt spinning temperature of the hollow fibers is a process parameter that can not be easily transferred in the transition from film to fiber because of the differences in the veins between fiber and film formation. The concept of the uniformity of the inner and outer fiber dimensions does not exist at all in the film or foil technique. The melt value of the polypropylene used for

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Therefore, production of the hollow fibers must be monitored to obtain uniformity in construction and dimensions of the hollow fibers.

While the production of oil by the tubular process is similar to the production of a hollow film by an air injection process, there is a significant difference between the two. The peel rate in the production of tube precursor sheets is limited by the fact that with increasingly higher peel rates (other process variables being kept constant), the uniformity of the microporous film buildup subsequently imposed on the precursor sheet decreases. Consequently, the process variability of the print history can not be sufficiently monitored (increased) in order to impose increasingly higher levels of orientation on the structure of the precursor film. Higher degrees of orientation up to a certain threshold have a beneficial effect on the final permeability of the film or film, but because of problems of uniformity of the pore structure, there is a limit to the degree of orientation which can be imposed on the precursor film by a take-off speed control.

When hollow fibers are made by the method of the present invention, the problems of uniformity of microporous structure are markedly reduced, and higher withdrawal rates can be used to obtain a higher orientation or orientation degree in the precursor hollow fibers, such as through the wide angles At this point, the fibers are given a higher permeability potential, but the enlargement of the permeability

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Potentials can not be achieved well without monitoring the inner diameter (I.D.) of the hollow precursor fiber which, in turn, determines the inner diameter of the subsequently formed hollow microporous Paser. The monitoring or determination of the dimensions of the hollow microporous. Paser represents another procedural variable that can not be adopted by the PiIm or film technology.

U.S. Patent No. 3,558,764 discloses a cold drawing process for the production of microporous films in which a polymer is injection molded at a specific predetermined temperature to form a precursor film, the precursor film is cooled, then at a specified specific temperature. is i'emperatur (5 to 100 ⁰ C below the melting point of the polymer, the polypropylene is at about 165 ⁰ C) annealed, the films thus produced with a specific, predetermined draw ratio and is cold-drawn at a predetermined temperature, and in which the cold drawn film at a temperature of about 100 to 150 C under tension is warrnverformt. The essential difference between this method and the prior cold-stretch hot stretching method is the lack of a 3-step hot-drawing process. The cold stretch hot stretching process described above represents an improvement over the cold drawing process of this patent in terms of nitrogen flow.

On the contrary, the hollow microporous fibers thus formed have varying degrees of shrinkage and tend to form a loop, which may be detrimental to the later use of the hollow fibers when the hollow ones

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Precursor fibers are annealed and thermoset, generally according to the above cold stretching techniques, especially when the thermoset temperature is at or below the original temperature.

The US patent lir. 4,055,696 describes a similar cold drawing process which is more for the production of hollow, microporous polypropylene fibers than for the production of films. This method requires that the size of the pores within a certain range be limited to 30 to 200 % of the original pore length by limiting the degree and temperature of cold stretching. ger than 1υΟ ⁰ C is held. The formed cold stretched fibers which have previously been annealed are heat set at a temperature of or above the original annealing temperature, which was used as described previously before stretching. A separate hot stretching process as in the present invention is not performed in the production of these hollow fibers. According to this patent annealed cold stretched, heat set hollow fibers tend to have different degrees of shrinkage depending on the ratio of the former A _US giühtemperatur and duration to the Warmhärtungstemperatür and duration. In addition, there is no control or monitoring of the inside diameter of the hollow fibers of this patent to improve their Sästoffstoffgasdurchlässigkeit instead.

The Japanese Kokai patent Ur. Sho 53 (1978) -38715, published April 10, 1978, relates to an improvement of the process described in U.S. Patent No. 4,055,696 for producing porous polypropylene hollow fibers. The improvement involves monitoring the annealing temperature to a value below

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155 ° C and control the Warmhärtungsteraperatur after the cold-stretching at a ^w ert 155-175 ⁰ C for a period of 3 seconds to 30 minutes. This method does not include a vacuum stretching step in addition to the cold drawing step as in the present invention or a control of the inside diameter of the hollow microporous fibers to improve the oxygen permeability.

A particularly important application for hollow, microporous fibers is in their use as oxygenation for blood, as shown in U.S. Patent No. 4,020,230, which describes hollow, microporous fibers made from polyethylene. It is known that the properties which a blood oxygenator membrane must possess, good gas permeability to gaseous oxygen and carbon dioxide, chemical resistance, blood compatibility or substantially non-thrombogenic Vernal t-gn in% ut containing environment of a sufficiently water-repellent character to be able to serve as a water vapor barrier, easy manufacturability, non-toxicity, relative neutrality to body fluids, and mechanical strength and properties which facilitate assembly and suitability as devices for oxygenation in blood. "

Microporous polypropylene fibers have heretofore been used as a membrane for raising acid scavenging in blood, and such films have been used as the previously listed requirements.

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speaking speaking. However, because of the relatively small surface area of such films, relatively large volumes of blood had to be removed from the body to allow for the desired oxygen and carbon dioxide gas transfer. In contrast, hollow, microporous polypropylene fibers offer the advantage of being able to effect this gas transfer at significantly lower blood volumes.

Object of the invention

The aim of the invention is to provide hollow, microporous polypropylene fibers which ensure high oxygen permeability.

Explanation of the invention of the invention

The present invention has a process for the preparation of hollow, microporous propylene fibers with good Säuerst off gas permeability s the subject.

Another object of the present invention is therefore to provide microporous hollow polypropylene fibers,

which have good oxygen gas permeabilities.

To achieve this object, the invention proposes a method for the production of hollow, open-cell, microporous polypropylene fibers with an oxygen flow of at least

3 2 2

35 cm / cm · min at a pressure of 0.703 kg / cm, which in a first variant comprises the following process steps:

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(A) melt spinning at a temperature of at least

230 ⁰ C of an isotactic polypropylene having a melt index of at least 1 in a Y / ice, which makes it possible to obtain hollow, non-porous propylene precursor fibers, withdrawal of these precursor fibers at a draw ratio of at least about 40, wherein said melt spinning is performed so that said Precursor fibers after withdrawal have an average inner diameter of at least about 140 microns, an average inner diameter to average wall thickness of from about 8: 1 to about 40: 1 and a degree of orientation not greater than 25 ° determined by half the width of the ( possess 110) wide-angle X-Strahldiffraktionsbogens and an elastic return to the initial state of a 50 percent Äusdehung at 25 ⁰ C, 65% relative humidity and a Kull-return time of at least 50%;

(B) annealing the precursor fibers at a temperature between 50 ^° C and less than 165 ^° C for a period of about 0.5 seconds to about 24 hours;

(C) Cold stretching of the non-porous precursor hollow fibers in the direction of its length is not at a temperature greater than the glass state transition temperature of the precursor fibers and no greater than about 100 ⁰ C to obtain porous Plächenbereiche in the direction perpendicular to the KaItetreckrichtung walls of Paser;

(D) hot stretching the annealed cold stretched hollow fibers from (C) in the cold stretch direction at a temperature above

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half the cold stretch temperature and below the polypropylene melt point to obtain an open-celled, microporous structure in the hollow fiber walls, wherein the said heat flow is performed in a manner sufficient to reduce the mean inner diameter of the resulting warmed hollow, microporous fibers to a value of at least 100 microns, and a total degree of combined stretch of from about 80 "to about 200 %, a stretch ratio of about 1:" to about 1:20, and a stress range of about 10 to about 200 % / Min, to reach;

(E) thermoforming the formed warm stretched fibers of (D) under tension to form dimensionally stable open-cell, hollow, microporous fibers having a mean inner diameter of at least 100 microns »

In a second variant, the method has the following method steps:

A ^ melt spinning at a temperature of at least 230 C of an isotactic polypropylene having a Schimmelz index of at least 1 in a manner permitting obtaining hollow nonporous polypropylene precursor fibers (5), stripping these precursor fibers (5) at a draw ratio of at least about 40 to about 100, this being

Melt spinning is performed so that said forerunners (5) after withdrawal have a mean inside diameter in the range of about 200 to about 300 microns, a mean inner diameter to mean wall thickness ratio of about 1.0: 1 to about 30: 1, a mean -

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degree of orientation, determined by the half-length of a (110) X-ray X-ray diffraction arc of not greater than 25% and an elastic recovery capability of a 50 percent elongation at 25 ° C, 65 % relative humidity and a zero return time of at least 50 %. have;

B. annealing the hollow precursor fibers (5) at a temperature in the range of about 130 to about 145 ^° C for about 30 minutes;

C, cold drawing (at 2) of the non-porous hollow precursor fibers (5) in its longitudinal direction at a temperature of about 15 to about 70 ⁰ C, a ^ executing degree of about _20%%, based on the original precursor fiber length and a Beiastungs- or strain rate in the range of about 10 to about 100 % per minute to porous surface areas in the walls of the Paser . form perpendicular to the cold stretch direction f

The tubing stretch (at 3) of the cold stretched hollow fibers (15) of (o) in the cold stretch direction at a temperature of about 130 to about 145 ° C., a ^draw ratio of about 60 to about 100% and a strain rate of about 10 to about 100 % per minute, to the hollow fiber walls an open-cell,

(Λ

microporous structure.

E. heat curing of the hollow fibers formed (20 till 61 rolls) 'form under tension at a temperature of about 130 to about 160 ⁰ C to abmaßemäßig stable, open-cell, hollow, microporous parsers are having an average inside diameter of at least 100 microns to "

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According to another feature of the present invention are hollow, open-celled, microporous polypropylene fibers having a ^ü auerstofffluß of at least 35 cc / cm. Min. Formed at 0.703 kg / cm according to the previously described method.

The said hollow, microporous fibers have a wall thickness in the range of about 10 to about 30 microns and a mean inner diameter in the range of about 200 to. 400 microns and can be used advantageously in a device for acidification of the blood.

This Sauerstoffanreichervorrichtung for blood, with bundles of fibers, which are preferably employed in an elongated, fluid-tight, tubular ^ü eliäuse, characterized in that the bundle of parsers are said to be formed of hollow, open-celled, microporous polypropylene fibers.

Execution; 3 game

In the following the invention is explained in more detail with reference to the figure:

The figure is a schematic representation of the means for carrying out the hot stretching in several stages.

The hollow, microporous fibers of the present invention are derived from isotactic polypropylene

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having an average molecular weight of about 100,000 to about 750,000 and a melt index of not less than 1 (e.g., not less than about 5), typically from about 1 to about 30 or greater, preferably from about 3 to about 15, and on best produced from about 5 to about 10.

The term melt index as used herein is defined as the value obtained by forming ASTM D-1238 under temperature conditions, applied load, time and other work variables as defined herein for the particular polymer being tested, namely polypropylene ,

When a polypropylene pore having a melt index is increasingly less than about 1, e.g. 0.5, this pasage tends to break or split more and more in increasing mass, and there is a greater variation in the evenness of the internal diameter and cross-section of the paser.

The density of the polypropylene should be about 0.90 g / cm.

The isotactic polypropylene is converted to a hollow precursor fiber by melt spinning. The molten polymer is made to flow through one or more orifices (d, h, jets) of a spinnerette suitable to give the paser the desired continuous hollow shape, Z. B, the melt in the preferred embodiment is melted.

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form by one or more annular injection molds or nozzles with a projecting into each central region of these forms Haßel required. A gaseous stream ^w i ^rd then passed through the needle as soon as the melt is pumped through the annular nozzle, whereby the Paser receive a hollow shape. Alternatively, the cavity of the paser can be achieved by passing the molten polymeric material through an annular opening or core which is capable of producing the desired hollow structure.

The temperature at which the polypropylene is injection molded, d, h. melt spinning (it is anticipated that spinners other than those described herein will be used) could be on the order of less than 230 ° C, preferably between about 240 and about 280 ° C, and most preferably in the range of about 240 to about 250 ^° C lie.

If "a ^ pritzteinperatur in growing else is used below about 230 ⁰ C V /, the uniformity of the ^ iber with respect to the inner and outer diameter increasingly deteriorated. On the other hand, precursor films obtained by the cold stretch hot stretching process according to the US patent ITr. 3,801,404, are prepared at spray temperatures as low as below 180 ^° C. At spray temperatures in increasing manner above 280 ⁰ C, the spinning tension or stress with which the polymer must - being splashed, is subjected can be increased significantly, whereby the

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Danger of degradation of a polymer arises.

When a hollow fiber spinnerette is used with Lufteinspritzimg, the beam diameter, the air flow rate, the withdrawal speed that ^ö injection rate and the draw ratio are controlled in sufficient V / else, so that a high precursor fiber made of polypropylene is formed which has an average Innendurchmefser and an average wall thickness with dimensions as described herein and having a degree of orientation no greater than about 25 ° C as determined by the halfway of a (110) v / eit-angle X-ray diffraction arc.

The degree of isomer-molecular orientation is determined by imposing a thickness of 50 rag / cm on the aligned grains. X-rays are then directed onto the fibers transverse to the axial direction of the fibers, and the half-width of a (110) wide-angle diffraction arc is stored on a film. The acorn area swept by this (11O) -draction is then determined. He should not be greater than 25 ⁰ C

The dimensions (d, h, the inner and outer diameters) and the wall thickness of the hollow fibers produced can be monitored or determined in different ways. Initially, the diameter of the spray nozzle and the selected pressure of the inert gas determine the inner diameter and the outer diameter, respectively the fibers produced by the widening

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Degree of fiber dimensions has been changed due to the exemption from the given injection pressure through the spinneret. The diameter and wall thickness can therefore be varied by changing the injection pressure through the spinneret and the withdrawal speed with which the fibers are pulled away from the spinneret. Changes of these values can be compensated by changes in others W _ho tes to obtain the desired results.

The previously related process parameters are controlled or monitored to ensure an inside diameter within a certain limited range. However, they are also monitored to give the precursor fibers the proper morphology to ensure that the subsequent treatment results in a microporous structure with suitable gas permeability.

As a result, the melt-spinning step or the Schimmelzepritzschritt the process is carried out at a relatively high "deduction" or "spin train" ratio, so that the hollow fibers are spin-oriented after their preparation. The draw ratio is defined as the ratio of the speed of the original withdrawal rate of the hollow fibers to the linear rate of spray of the polymer through the nip opening. The draw ratio used in the process of the present invention is at least 30, preferably at least 40 (eg, from about 40 to about 100) and could be high by about 700. The decrease rates used to obtain the required withdrawal ratios are generally at least about 200 meters / minute, typically from

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about 200 to about 1000 meters / minute, and preferably about 200 to 500 meters / minute. Typically, large shear forces are formed in the polymeric material that are not degraded prior to fiber consolidation.

The air flow velocity, d. H. The velocity of the air through the needle in the distal portion of the jet varies with the number of jet holes in the spinneret and is typically monitored or controlled to be in the range of about 5 to about 70 cm / min / jet hole, and preferably in a range of about 10 to about 50 cm / min / jet hole.

The temperature of the air at the exit of the spinnerette air injection is typically the same as the melt spinning temperature of the polymer *

The hollow spin-oriented precursor fibers may optionally be quenched by passing them through a gas stream such as normal air at room temperature or through an inert liquid such as water so as to achieve rapid cooling of the just-spun hollow fiber. The temperature of the quenching agent may be C (e.g., B. 0 to 40 ⁰ C) are of the order of 80 ⁰ C and as low as 0 ^0, depending on the other spinning parameters. However, the preferred Abschreckteinperatur located at 25 ⁰ C, and the guide of the just-spun fibers by surrounding air resulting in a angemessenen'Abschreckung when the pick roller is disposed at a distance of about 152.5 to about 305 cm from the ^s pinndüse.

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The resulting hollow polypropylene precursor fiber is non-porous and has a crystallinity of at least 30% _t preferably of at least 40% and most preferably of at least 50% (eg., About 50 to about 60% or more). The crystallinity in percent is defined by the following relationship:

% Of crystallinity = Va-V χ 100,

Va-Vc

Va therein mean specific da3 ^v olume of the 100> £ Lg amorphous polymer, Vc is the specific volume of the lOOfiig krißtalliBn polymer and V is the specific volume of the sample. The specific volume of a polymer is. 3 / D, where D is the density of the polymer. The density of the polymer is measured by means of a density gradient column as described in ASTM D-1505-68. The hollow polypropylene precursor fibers should have an elastic return property at an O-return time and in a standard stress (elongation) of 50 % at 25 ^° C. and 65 % relative humidity of at least 50/5, preferably at least about 60 % and most preferably at least about 65%.

The elastic return to initial condition, as understood herein, provides a measure of the ability of the formed articles, such as the hollow fibers, to recover their original size after stretching.

The elastic return value is determined using an Instron tensile tester fitted with a

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dizziness of 100 % / minute works, certainly. After the belt has been stretched to the desired load, the jaws of the machine are moved in the opposite direction at the same speed until the distance between them is equal to the original distance, ie. h, the original sample length. The jaws are then immediately moved in the opposite direction and stopped as soon as the stress begins to increase from zero. The elastic return is then calculated as follows:

(Total Length End Distance) Elastic Return = ^(ln stretched state - the jaw)

' Added Lange in stretched condition

The measurements on the Instron tensile Zerreißfestigkeitsv or be carried out at room temperature, ie 25 ⁰ C and in air at 65% relative humidity strength tester.

Although a standard load of 50 % is used,

-Q

To determine the elastic properties of the precursor fibers, this stress is to be considered as an example only. In general, such precursor fibers have an elastic return which is higher at stresses of less than 50 % and slightly lower at stresses appreciably higher than 50% compared to their elastic return at 50% strain.

The above-noted process conditions are monitored or controlled to provide hollow propylene precursor fibers having an average I.D. of at least 140 microns, preferably from about 140 to about 40 microns.

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to obtain about 400 microns or greater, most preferably from about 200 to about 300 microns, The above mean internal diameters have been found to be necessary to obtain precursor hollow fibers having a high gas permeability potential where high gas permeability does not provide a control factor in the The desired end use case of the hollow fibers, the inner diameters can be reduced to below 140 microns.

The dimensions of the hollow fibers are given as mean values, since these dimensions change to a certain extent, depending on where the dimensions along the length are determined. As a result, the average inner diameter and the average outer diameter are determined by cutting the fiber at intervals of about 15.24 cm at a number of 5 pitches along the fiber length in the cross-sectional direction and then measuring the dimensions of the paser at each of these pitches. The cross sections are then immersed in conventional optical dip oil and the dimensions determined at each interval using an optical microscope and an optical scale. Averages are then determined from the results to indicate the mean inner diameter and the mean outer diameter.

The minimum wall thickness of the orläuferhohlfasern ^v should be as eein that the wall does not rupture or suffers in other ^w else physical damage at a speed which asern the application of this ^ 'can appear unattractive, after they have been rendered microporous according to the methods described herein. The maximum W _to ßstärke of the hollow fibers is limited by the degree of permeability of the final

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product should be given.

Measurement of the mean wall thickness is carried out by determining the average outer diameter and the average inner diameter of the Paser, wherein the wall thickness is taken as half the difference of these average diameters.

Me average wall thickness or wall thickness can also be expressed as a function of the mean inner diameter of the hollow fiber. The ratio of the mean inner diameter of the hollow fiber to its mean thickness may vary from about 8: 1 to about 40: 1, preferably from about 10: 1 to about 30: 1, and most preferably about 10: 1. 1 to about 20: 1. In more specific, an average wall thickness ^of the precursor fiber ^we ~ nigstens 10 microns, and typically from about 10 to about 25 microns preferred.

While it is believed that the inside diameter and the associated wall thickness of the final microporous hollow product are the major determinants of gas permeability, it is the inside diameter and wall thickness of the precursor hollow fiber which determine the maximum achievable inside diameter and wall thickness of the final product. This follows from the fact that the inner diameter of the precursor fiber shrinks by about 25 % when subjected to the two-stage draw process previously described. % e average wall thickness of the hollow, microporous parsers are remains substantially unchanged during the treatment compared to the precursor fiber, although it could be to a low ^A usmaß reduced.

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The hollow precursor fibers are then subjected to a heat treatment or a usglühschritt ^A, wherein the degree of crystallinity and / or crystal structure can be improved. This process step increases the crystallite size and removes imperfections in the molecular orientation. The annealing is performed at a balanced rate and temperature to obtain the desired improvements described above, which are now sufficient to prevent destruction or degradation of the precursor polymer structure (eg, orientation and / or or crystallinity).

Hie preferred ^ Hisglühtemperaturen can range from about 130 to about 145 ⁰ C vary during a period of about 30 minutes, '' hen the Ausglühtemperatür a * 'ert of rises above about 145 ⁰ C, the time during which it is annealed precursor fiber , reduced accordingly. However, if the anneal einperatur a "ert below 130 ⁰ C decreases, longer usglühzeiten be used in increasing manner.

If the annealing temperature exceeds in increasing manner 145 C at a ^A usglühzeit of 30 minutes, the flow is influenced erpolymerfaserstruktur disadvantageous and the gas permeability potential of the precursor fiber is reduced to an increasing extent, when the annealing temperature is less than 130 ⁰ C for 30 minutes in a growing way, In addition, the gas permeability potential of the precursor fiber is also increasingly reduced.

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Due to the foregoing, the annealing at intervals of about 0.5 seconds to about 24 hours at a temperature of about 50 ⁰ C to below the melting point of polypropylene (z. B. 165 ⁰ C is based on a ^ ifferenzia la BTA STKA calorimetry ) carried out.

The annealing step may be in a stretched or de-energized state by introducing the precursor fiber in .One static location in a Verwärmungszone, which is maintained at a required high temperature, or by continuously perform the Paser v / ground performed by the heating or heating zone Z _e as can the high temperature can be achieved by using a conventional airflow furnace, by infrared heating, dielectric heating or by direct contact of the running Paser with a heating surface, which is preferably curved to ensure a contact. The precursor fiber may be passed continuously through a sheathed tube or sheath which radiates heat at the desired temperature, but the precursor fiber may also be wound in a state without significant mechanical stress or stress on a coil during annealing easier ^ else in the heating zone in bulk, as a bundle or in loops ^ state be inserted continuous parsers are. If you want to get the best possible results, it is recommended to keep the hollow fibers at a constant length during the annealing process, ie _Annun under a Sp g _f sufficient to avoid expansion or shrinkage in the longitudinal direction greater than 5 % , this can be accomplished by placing the seals in their length

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above and via a voltage insulation device through a heating zone maintained at a suitable temperature and thereafter passing above and above a second voltage isolation device. Each stress isolation device may be in the form of a pair of skew rolls. The monitoring or control of the ratio of the surface speeds of the zv / ei roller sets permits the isolation and the control or determination of the stress on the fibers between the rollers during the ^A usglühens.

The formed nonporous precursor hollow fiber is then subjected to a two-stage drawing process and then to a thermoset.

In the first ^ü executing stage, which is referred to herein as' Kaltstreckeri ", the hollow precursor fibers are stretched at a temperature above the glass transition temperature (Tg), and the ^v orläuferfa3er not greater than about 100 ⁰ C. Typical cold-stretching temperatures can be between about vary from 0 to about 100 ⁰ C, preferably between about 15 to about 70 ⁰ C and most conveniently be room temperature, for example 25 ⁰ C ^ ie temperature of the Paser itself is referred to as ^ stretching temperature _έ..;

It is known to those skilled in the polymer art that the glass transition temperature (Tg) is the temperature at which the structure of a wholly or partially amorphous polymeric material changes from the glassy state to a visco-elastic state. The glass transition temperature of polypropylene is reached by recording its specific heat versus temperature and detection

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the temperature at which a change occurs in the course of the characteristic curve. This measurement is generally referred to as thermomechanical analysis and can with commercially available instruments, such as a thermomechnischen ^A nalysiermodell manufactured by DU Pólit # 990,., Are performed. The glass transition temperature is also referred to as the second order transition temperature.

Cold drawing confers porous surface areas or areas perpendicular to the stretching direction to the wall.

The second stretching phase, referred to herein as hot stretching or stretching, is carried out at a temperature which is above the cold stretching temperature but below the melting point of the precursor fiber before or after the initial stretching, i.e., at least two times. H. below the transition temperature of the first order, which is determined by calorimetric analysis by means of differential scanning.

typical V'armstrecktemperaturen lie above about 100 ⁰ C and can vary between about ⁰ C to 1υ5 etv / a 145, preferably to about 145 ⁰ C and most suitably from about UO from about 135 to about 145 ⁰ C.% e temperature of the Fiber itself, which has been stretched, is referred to as the hot-draw or hot-stretch temperature.

When the hot-stretching temperature, which is in increasing manner less than 130 ⁰ C, it is found higher levels of shrinkage in the Endfiberprodukt increasingly.

Warming opens the porous surface areas that

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have been formed by the cold stretching, so that an open-cell, microporous structure is formed.

The stretching in the two stretching stages or phases must be carried out successively in the same direction and in this order, that is to say first the cold stretching and then the warming are carried out, but in a continuous, semi-continuous or batch process, as long as the cold stretched fiber is not allowed to shrink a substantial amount (eg, not greater than about 10 % _t, based on the original length of the forerunner).

The total draw ratio of the above-described cold and deep draw steps may be from about 80 to about 200 % (eg, about 80 to about 155 %), and preferably from about 85 to about 120 % (eg, about 90 °), based on the original length of the precursor fibers, vary. When the total degree of stretching is increasingly less than about 80 % , the resulting permanent material permeability is 0.703 kg / cm in

3 2

growing less than 35 cm / cm. ilin. The ratio of ^D grades executing the first (cold) ° executing phase to the second (hot) stretching phase is referred to herein as an expansion ratio. The stretch ratio may vary from about 1: 3 to about 1:20, preferably from about 1: 3 to about 1:10 (eg, 1: 3 to about 1: 5).

It is assumed that the particular degree of stretching and the stretch ratio from the above ranges

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be chosen so that the final average inner diameter of the heat drawn microporous fibers within the limits described herein can be monitored or controlled.

The stress or strain rate, d. the degree of stretching per unit time at which the precursor fibers are stretched during the two stretching phases or stages is preferably the same for both phases and may be from about 10 to about 200% / minute, preferably from about 10 to about 100 ^ / minute and on most suitably from about 15 to about 30% / minute (e.g., about $ 20 / minute).

At the preferred overall stretch level of from about 80 to about 120 % , the preferred aspect ratio is 1: to about 1: 5, e.g. B, 20 % cold runs and from about 60 to about 100 % hot runs.

The cold and hot stretching of the precursor fibers may be accomplished in any suitable manner using known techniques. For example, the hollow fibers may be stretched in a conventional draw frame located in a preheat zone that monitors the temperature of the fibers during stretching. Alternatively, the fibers may be stretched or warmed in a continuous manner by means of two sets of stress or strain isolation devices (one set for each step or phase) similar to those used in conjunction with the annealing step.

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As a result, the precursor fibers can be wound a number of times around a first pair of tapered rolls, through a heating zone in which they may e.g. B. maintained with a suitable heating device or a heating medium, are guided and "maintained at a suitable cold drawing temperature and wound several times around a second pair of oblique rollers.This arrangement allows the isolation or separation and control of the longitudinal loads of the The fibers are then passed through a similar set of pairwise tapered rolls while being heated to the appropriate "half stretch temperature." The differential ratio of the surface speed of each second roll pair to the surface speed of each first pair of rolls determines the draw ratio and Deformation or tension speed, which are adjusted in accordance with ^.

It is noted that in a continuous process, the cold-stretching fibers in the transition from the cold-stretching stage to the ^w armstreckstufe can shrink. This is caused by the heating of the necked fibers as they enter the hot draw zone, such as a hot air oven, but before they are warmed up. As a result, it is desirable to install a tension device between the cold and hot draw stages to prevent shrinkage greater than 5 / »in terms of the cold stretch fiber length. This tension device may be formed by a single pair of skew rolls."

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The heating zones that heat the precursor fibers to the appropriate cold or hot stretch temperature are the same as those described in the pre-cold annealing step, and may be conveniently formed from a gas such as air, a heated plate, a heated liquid or the like , The preferred heating device is formed by a hot air oven containing the diluents.

Following the cold and heat stretching operations just described, the stretched fibers are heat cured or annealed in the stretched state at a temperature of from about 125 ° C to a temperature about below the polymer crumb temperature. As one skilled in the art will appreciate, the melting temperature may be determined by a conventional differential laser or by other means which detect the heat transfer of a polymer. The preferred hot curing temperatures may vary from about 130 to about 145 ° C. The most preferred thermosetting temperature is the temperature used during warming. The Wannhärten does not change the fiber dimensions, as they are after Warrastrecken not.

The thermosetting step can be carried out in a batch process, such as in an oven or autoclave, or in a continuous manner. For example, the hollow, microporous fibers may be wound on a bobbin after hot stretching and subjected to annealing in this form. Alternatively, the hollow fibers may be stretched and heat-set in a continuous manner by means of two pairs of rotating rollers. the downstream of

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the stretch rollers are mounted, moving at the same speed as the material between the rollers, which runs continuously at a constant length after warming through the heating zone. As a result, the stretching and thermosetting steps of the process may be performed sequentially or combined in a single row step.

Hot tempering may be performed while the fibers are held under tension, such that the fibers can not shrink or shrink to a certain extent, which does not exceed \ 5% of their stretched length, but the tension is not may be large that the fibers undergo an additional elongation of more than 15 % . Preferably, the tension is chosen so that no noticeable shrinkage or stretching was applied. The change in stretch length should be less than 5 % .

The period of hardness treatment which is preferably carried out after the thermosetting step should not be longer than 0.1 seconds at the highest heat setting temperature, and generally within the range of about 5 seconds to one hour, and preferably in the range of about 1 to 30 Minutes.

Because the most preferred hot curing temperature is the same

In this Pall, the total standing time in the furnace during the hot drawing and heat setting steps can be within a range of .mu.m.

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about 10 to about 45 minutes and preferably in a range of about 25 to about 35 minutes (e.g., B. 35 minutes) at V / armstrecktemperaturen of about 130 to about 145 ⁰ C vary.

The thermosetting step is performed to improve the thermal stability of the microporous structure and to reduce the shrinkage of the fibers.

In another embodiment, the vacuum stretching and heat setting steps may be combined into a single step.

this embodiment of the invention, the Warmstreckei using a ^ ielzahl of independent consecutive ^v "'a.rmstreckvorgängen performed at the appropriate hot stretch temperature. For example be introduced parsers are after its cold-drawing in means, which are capable of the ^ asera in incremental ^ while maintaining them at the proper thermal stretching temperature so that the total degree of stretching of each increment adds to the desired degree of total thermal stretching.

The multi-stage heat drawers may be suitably formed from a plurality of bumps arranged in an oven. Preferably, the rollers are arranged garland-like, similar to that described in U.S. Patent No. 3,843,761. The text of this patent will be hereby incorporated by reference. The use of a garland arrangement is therefore to be preferred

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because it allows an extended delivery time in the furnace containing the multi-stage heat recovery means and therefore eliminates the need for a thermosetting step after the hot stretching step.

For a description of a preferred way of carrying out the multi-stage hot drawing and the heat curing combined therewith, refer to the attached figure.

The nonporous fibers (5) which have been annealed are unwound from a supply roll 4 and fed via guide rolls 6 and 7 into a cold draw zone, generally designated 2. The cold stretcher comprises two pairs of tapered rolls 8th to 9th and 11th to 12th, each driven at peripheral speeds S, B, and S by suitable drive means 10 and 13 to achieve the desired degree of cold, as in Figs previously described. For reasons of representation is \, the cold stretch temperature, the rears ENIP era door, and hot or coolant are not required for this stage. However, if desired, suitable temperature monitoring or control means as described herein may be provided. The cold stretched fibers, now designated 15, are routed in a general manner 3 designated hot stretch agents over one or more Pührungsrollen 14. Tension rollers are not used because they would tend to deform the hollow fibers, which is unfavorable to the final product. The hot stretchers 3 comprise a single section of tapered rollers 16 and 17 and a plurality of additional multiple heat stretching rollers arranged in a garland-shaped oven

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unsupported fiber length between adjacent hot stretch rolls, which is relatively long in the preferred garland arrangement, to be as small as possible, at least one guide roll is provided between adjacent hot stretch rolls.

The single set of tapered rollers 16 and 17 helps to control the cold stretched fibers by controlling the peripheral speeds S ₁ . The tensioning prevents shrinkage, sagging and the like caused by preheating the fibers as they enter the oven before being hot stretched. Such tensioning helps to prevent deterioration of the properties of the cold stretched fibers caused by preheating. Although this voltage step for preventing fiber relaxation leads to some extent of stretching, the initial effect of this step is stretching, and the peripheral speeds S ₁ and S, are respectively controlled by drive means 18 to control the length between the cold-drawn and hot-stretch zones to keep constant. Therefore, this step represents only a preferred embodiment of means for ^ ufrechterhaltung fiber tension before the hot stretch. Other measures to prevent fiber relaxation during warm-up of the parsers are before ^w can be used Arm extension.

The tensioned cold stretched fibers 15 are then fed downstream via guide rollers 19 and 20 onto a first hot stretch roller 21. The fibers are between the hell 21 and the second 16 ^s pannungsrolle hot-stretched for the first time. This is caused by the fact that the downstream

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The first time stretch roller 21 is driven at a peripheral speed S "exceeding the peripheral speed S ₁ - given to the fibers by the bale 16. It should be noted that a guide roller 19 is disposed between the rollers 16 and 20 to reduce the unsupported excess during the hot stretching step.

This will be continued for as many steps as desired. For example, parsers are to be stretched a second time between the first hot stretch roll 21 and a second "armstreckrolle 23 by means of hell 22nd In this second hot stretch step S _ft is the peripheral speed of the second ^ armstreckrolle 23. The peripheral speed Sg is greater than the peripheral speed of ^ the first hot stretch roll 21 * Therefore, in the second heat drawing step, the fibers warp in a hot stretch ratio of Sg / S _7. Again, at least one guide roll 24 is provided between the second and third hot stretch rolls 23 and 25 so as to minimize the unsupported fiber length In a preferred embodiment, shown in the figure, the guide rollers are located approximately midway between two adjacent roller stretching rollers.

In the illustrated on the figure, ^A usführungsform 20 Streckscnritte which take place successively, is provided. As the figure shows, 21 ^ Armstreckrollen are required to perform the 20 stretching steps can. It should be noted that the second tension roller 16 of the first hot stretch roller

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is equivalent. In general, in the hot stretching apparatus of the preferred embodiment (η + 1) hot stretch rolls are necessary to perform η consecutive hot stretching steps. Preferably, 2 to 40 stretching steps are preferred in the multi or multi-stage stretching procedure.

Two preferred methods can be used to obtain the continuously increasing peripheral speed for each additional downstream hot stretch roll. In a preferred embodiment, all rollers are driven by a common drive device. Each hot stretch roller is therefore driven at the same rotational speed. "However, each roller has a different diameter. In other words, each additional, further downstream Viarmstreckrolle has a larger diameter than the previous upstream role. As a result, the roller 23 has a larger diameter than the roller 21, and the roller has the most downstream hot-stretching roller, has an diameter larger than the diameter of the penultimate, downstream roller 55. The skilled person knows that the circumferential or Surface speed of a larger diameter roller rotating in its center at the same speed as a smaller diameter roller, larger than that of the smaller roller. Therefore, by using rollers of increasing diameter, differential circumferential speeds are obtained between adjacent heat stretching rollers.

A second preferred method of obtaining differential rising circumferential speeds between adjacent sprockets is to separate sprockets for each spool.

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leavening provide, In this preferred A _us ftüirungsform all rollers have the same diameter. The increasing speed of adjacent downstream hot stretch rolls is then a function of the power applied to each roll.

It is clear that the process variables described in the preceding in connection with the individual increment hot-stretching procedure lstufen bath stretching procedure can be applied to the ^ i _e, with the exception, however, that obvious changes are necessary in the transition from the former to the latter operation. For example, as described above, the total degree of hot stretching is the same for both stretching modes, except that in the multi-stage rolling process, the overall stretch is formed in a plurality of preferably equal increments. The strain rate for each y-rate increment is preferably controlled or controlled to achieve a total stall time in the multiple-wake drag zone that is approximately equal to the combined stall time for i-arm-hardening used in conjunction with single-increment warm-up This is obtained when the strain or strain rate is within the limits for arming distances described herein in a single phase or stage.

The hollow microporous fibers thus formed have an average diameter as defined above of from about 100 to about 300 microns or more, and preferably from about 200 to about 300 microns (e.g., 250 microns).

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The average wall thickness of the hollow microporous fibers is not significantly different from that of the corresponding precursor fiber, and the change in the ratio of the mean inner diameter to the mean wall thickness of the microporous fibers relative to the precursor fibers is due to the reduction in the mean diameter of the fibers Precursor fiber which has been effected by stretching.

The ratio of the mean inner diameter to the mean wall thickness of the hollow microporous fibers varies from about 7: 1 to about 35: 1 ». and preferably from about 10: 1 to about 30: 1. The particular wall thickness is determined by the precursor fiber thickness which, as described above, is determined by the end use to which the fibers are intended and by the pressure these are to be acted upon depends. Preferably, the particular wall thickness selected is the smallest possible that will withstand the normal working conditions for a particular end use without physical degradation at an unacceptable speed.

When the hollow, microporous, acid affluxing fibers are used for blood, the wall thickness can vary from about 10 to about 30 microns, and the mean inner diameter can vary in the range of about 200 to about 400 microns, yet high gas permeability and structural integrity Possess uniformity.

When the average inside diameter of the hollow microporous fibers falls below 100 microns at a given y / and thickness, the gas permeation decreases.

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Laxity noticeably decreases at 0.703 kg / cm ² .

When the mean inner diameter of the microporous hollow fibers of the present invention is at least 100 microns and the ratio of inner diameter to wall thickness is less than about 7: 1, such have

hollow fibers have an acid content of 0.703 kg / cm of

3 2 at least 35 cm / cm · Mn., Typically about 35

«3 ρ

"to 85 cm / cm · min and preferably from about 40 to

3 2

about 60 cm / cm. Minute

Oxygen flow J is determined by the passage of acid gas through a hollow fiber module, which will be discussed in detail in the Examples. The hollow

Fibermodul allows gas under pressure (eg, 0.703 kg / cc) to be passed through the interior of the hollow fibers, through the microporous hollow fiber wall, and the collection of this gas. The volume of gas collected during a period

3 2 is then used to measure the gas flow in cm "/ cm

To calculate hollow fibers according to the following equation:

j ^g (A)

where ν is the volume of collected gas; A is the inner surface of the hollow fibers, determined by the equation A = η dl, where η is the number of hollow fibers, d the inner diameter of the hollow fibers in centimeters and 1 the fiber length in centimeters; T is the time in minutes during which the gas is collected.

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The pores of the hone, microporous fibers are substantially interconnected by tortuous paths which may extend from one outer surface or surface regions to the other, i. they are open-celled. The term "open cell structure" means that most of the void or pore space within the geometric boundaries of the walls of the hollow fiber is in communication with the surfaces of the fiber walls.

Further, the porous hollow fibers according to the present invention are microscopic, i. that is, that the details of their pore construction can only be determined by microscopic examination. In fact, the open cells or pores in the fibers are smaller than those that can be measured with a conventional light microscope because the length of visible light, which is on the order of 5,000 angstroms (one angstrom is one ten-billionth of a meter), is longer is the longest plane or surface dimension of the open cell or pore, however, the microporous hollow fibers according to the present invention can be identified by the electron microscope technique capable of resolving details of pore structure below 5,000 angstroms.

The open-celled, microporous hollow fibers, which have been prepared according to the invention have an average pore size from 100 to 5000 g _n A ₃ tröm and usually 150 to 3,000 angstroms. These values are determined by mercury porosimetry as described in an article by R, G, QTJJNN on pages 21 to 34 of the Textile Research Journal of January 1963. Alternatively, an electron micrograph of the fibers may be taken

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The measurements of pore length and width can be made using an oil analyzer or brush rule, which allows direct measurement of the length and width of the pores, usually at 5,000 to 12,000 times magnification, and scaled down to the appropriate size. In general, the pore length values obtainable by electron microscopy are approximately equal to the pore size values obtainable by means of mercury porosimetry.

However, the hollow microporous fibers according to the present invention are characterized by a reduced bulk density, sometimes referred to simply as "low" density hereinafter. The volume density is therefore a measure of the increase in the porosity of the fibers. That is, these microporous hollow fibers have a volume or bulk density that is less than the bulk density of corresponding precursor hollow fibers that are comprised of the same polymeric material but are not open celled nor have any other hollow structure. The term "bulk density", as used herein, means the weight per unit of gross or geometric volume of ^ ^he ^ ^aser i wherein said gross volume is determined by immersing a known ^ asergewichtes in a vessel partially filled with mercury at 25 ⁰ C and atmospheric pressure is filled. The volumetric increase in mercury levels is a direct measure of gross volume. This method is known as the mercury volumeometer method and is described in the "Encyclopedia of Chemical Technology", Vol. 4, page 892 (Interscience, 1949).

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The hollow, microporous fibers have a bulk density of no greater than 95 % and preferably in the range of from about 40 to about 85 % of the precursor fibers. Stated another way, the volume density has been reduced by at least 5 %, and preferably by about 15 to about 60 % . The bulk density is also a measure of the porosity, inasmuch as the bulk density of a ^w ert of about 40 to 85% of the precursor fiber has the porosity has been increased by 60 to 15% as Polge of the pores or holes.

The finite crystallinity of milcroporösen hollow parsers are is preferably at least 35% _t more preferably at least 45% and most preferably, as determined about 50 to 100 # according to the above-mentioned density method.

The hollow microporous fibers also have an elongation (ASTM D123-70) of not less than about 50 %, and preferably not less than 100%,

The surface area of the hollow, micro-

2 has a porous parsers are ^rt ert of at least 15 m / g and

preferably from about 20 to about 60 m / g.

The surface area can be determined using nitrogen or cryptone gas absorption isotherms using a method and apparatus as described in US Pat. No. 3,262,319. The surface area that is thus determined is usually Expressed in square meters per gram.

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To simplify the comparison of different substances, this value can be multiplied by the volume density of the substance in grams per cubic centimeter resulting in a surface area size in square meters per cubic centimeter

become.

The microporous hollow polypropylene fibers according to the invention have good liquid flow in addition to the good gas permeability and are suitable for a number of applications such as oxygenation of the blood, ultrafiltration, dialysis, separation of gamma globulin from the blood, for an ascites treatment as well as for a variety of other applications where hollow, microporous fibers are used. For some applications, it may be desirable to render the normally water-repellent, hollow, microporous fibers of the present invention hydrophilic, which can be accomplished in any manner known to those skilled in the art, such as by impregnating the pores of the fibers with a suitable surfactant Example of a high molecular weight, nonionic surfactant sold under the tradename Pluronics ™ by Wyandotte Chemicals' Corporation and prepared by condensing ethylene oxide with a hydrophobic base formed by condensation of propylene oxide with propylene glycol. Other surfactants) include a series of nonionic surfactants available under the tradename Tween ™, which are polyoxyalkylene derivatives of hexitol anhydride, partial long chain fatty acid esters. However, the fibers can

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also be treated with sulfuric acid, chlorosulfonic acid or other suitable means to make the fibers hydrophilic.

To use the hollow fibers to oxygenate blood, a desired number of fiber-containing hollow fiber bundles are formed by applying an adhesive to each end of a group of previously parallel aligned hollow fibers. The bundled fibers are then preferably inserted into an elongate, fluid-tight, tubular housing which is made of a suitable material such as steel. Each end of the bundled fibers communicates with the exterior of the housing, while at each end of the housing a means is provided for sealing each end of the fiber bundle from the ends of the housing. Thus, the blood can be pumped through the hollow fibers. ,

The tubular housing is further equipped with valves which open to the interior of the housing and to the outside surface of each paser in the bundle and serve as a means for the flow of acid gas around the hollow fibers. Although the puffer bundle should be made in as close as possible a packed porm, it should nevertheless be loose enough to permit gas to pass between the individual fibers and to flow around each hollow fiber.

The oxygen gas can then pass through the outer walls of the hollow fibers and oxygenate the Bx _u t, which flows inside the fibers, while the carbon dioxide from the

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Blood escapes through the hollow fibers.

j. )

However, it is also possible to introduce the oxygen gas into the center of the hollow fibers and the blood flowing through the housing while contacting the outer surface of the hollow fibers.

However, instead of using a double-ended, tubular housing in which both ends are open to allow blood to pass, it is possible to have a permeator. in which the hollow fiber bundles are arranged in a loop so that both sides of each paser exit through the same opening in the tubular housing.

To further illustrate devices using hollow fibers for oxygenation in the blood, reference is made to U.S. Patent Nos. 2,972,349, 3,373,876, and 4,031,012, the specification of which has thus been incorporated herein by reference.

The invention will be further explained in connection with the following examples, which should be considered as illustration of the present invention. It is to be understood, however, that the invention is not limited to the specific details of these examples. All components, amounts, and specifications in the claims and in the remainder of the application are by weight unless otherwise specified.

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EXAMPLE 1

Isotactic polypropylene with a melt index of 5 »a mean molecular weight of 380,000 and a caliber of 0.90 g / cnr is spun-melted by means of a five-hole concentric hollow jet spinneret. Each jet hole of the spinnerette is of the conventional tube-in-orifice type, the tube being connected to a low pressure air source, the pressure of which is monitored by an air flow meter, which indicates 3.8, the instantaneous flow rate of 120 cm / min is. The outer diameter of each injection port (jet hole) of the spinneret is 1,391 mm, and the inner diameter of each injection port is 0.772 mm. The diameter of the air tube inside each spray opening is 0.332 mm. Polypropylene flocs are fed into a Barbender 3/4 "extruder and are gravity fed into the feed zone of the extruder. The extruder is equipped with a metering pump to control the melt pressure of the spinneret device to ensure passage through the spinneret of 23 g / min. The temperatures in the feeding zone, the measuring and melting zones of the extruder are monitored or controlled by separate mantle zones. The temperature of the spinneret device is controlled by a separate, electrically heated jacket, and a constant extrusion temperature, that is, the spinning temperature of 245 ° C is maintained and _f indicated by means of a thermocouple in the spinning nozzle device. An adjustable feed take-off device collects the extruded fibers at a take-up speed (TUS) of 500 meters / minute.

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te. The hollow precursor fibers are therefore drawn off at a draw or spin ratio of 100: 1. The pickup roller is located 3.05 meters from the spinneret, and the extruded parsers are quenched by passing it performs air at room temperature that is 25 ⁰ C. The degree of orientation is determined in the, in the previous described ^w else with the help of X-Strahldiffraktionsanalyse, 16 °. The precursor fibers have an elastic Rückkehrf ^ BILITY of a 50 percent extension at a Nuil-return time, 25 ⁰ C and 65 ⁰ C relative humidity of 70 fe _t has an average internal diameter of 223 microns, an average outer diameter of 257 j & ikron and an average wall thickness of 17 Micron. The formed fibers are then annealed at constant length into a wound state around the take-up roll by placing the take-off roll in an oven and heating the fibers to a temperature of 140 ° C for 30 minutes.

Samples of the annealed precursor fibers different degrees of cold-stretching at ambient temperature in accordance with the • working periods 1 to 6 of the panel are then subjected to I and then hot yield varying degrees at 140 ⁰ C as described in steps 1 to 6 of Table I. The loading rate or rate of deformation of the Vfarmstreckschrittes and the cold drawing step is also given in Table 5. The cold and hot drawing steps are carried out using a conventional Bruckner stretching frame, and the high temperatures during hot stretching are produced by inserting the stretching frame in a hot air oven, the warm stretched fibers are left in the oven for 30 minutes to give a V / cowering on the

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Hot stretch temperature, namely at 140 ⁰ C ₁ effect. The fibers are held at a constant length by the stretching frame during heat setting.

For work periods 7 to 10, the precursor fiber sample preparation is changed in terms of spinning temperature, drawdown speed, drawdown ratio, throughput rate, and airflow metering adjustment according to Table I. The degree of orientation (as determined by the X-Strahldiffraktionsanalyse, as described herein) of the precursor fibers formed according to the working periods 7 and 8 is 16 °, and 22 ° at the operating periods 9 and Hie elastic recovery (ER) of a 50 percent elongation at a Hull-- Return time at working periods 9 and 10 is 64 % · ER for working periods 7 and has not been determined. The degree of stretching and cold stretching as well as the strain or strain rate are also indicated in Table I.

The resulting thermoset microporous hollow fibers are then tested for surface areas by nitrogen uptake as described herein and also for acid flux. The oxygen flux is determined in the following manner:

Twenty hollow, microporous fibers each about 48.8 cm (16 inches) in length each are placed in parallel fibers and then looped so that the 40 open ends of the pasals are juxtaposed and aligned in one plane , The open ends of the Paserschleifen are then passed through a hard plastic tube with an inner diameter of 0.38 cm

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and a short length (3.8 cm). The paseins are then jacketed with epoxy resin 15.24 "to 18.2 cm cpn from the open ends of the looped fibers." The plastic tube is then pushed over the resin coated area so that about 6.1 cm of the unclad puffer bundle is coated project out of the tube and carry the open ends of the loop bundle out of the tube.

When the resin has hardened, "the open ends of the loop fiber bundle are cut flush with the plastic tube, but to preserve the open circularity of the open fiber ends, the fibers for separation are first dipped in liquid nitrogen immersed in isopropyl alcohol to fill the cavities with liquid, then dipped anew in liquid nitrogen for a period of 1.5 minutes to freeze the alcohol, and then placed on a narrow wooden block while still immersed in the liquid nitrogen. The open ends of the fibers can then be easily cut off with a blade against the wood block without damage The pipe-paser assembly is then sealed in a 0.76 cm or 1-inch Diameter Sweglok ™ adapter with epoxy resin. one etv / a 2.3 cm long piece of tube protruding from the adapter The epoxy-unclad fiber assembly is then inserted into a copper tube of ei a length of about 21.55 cm and a diameter of 1.14 cm introduced and sealed the Sweglok TM adapter with suitable seals. To allow access, a 3-piece EG-T seal is inserted into the distal end of the copper tube (relative to the Sweglok seal) and a T-seal outlet is sealed. An end to one

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Rubber tubing is connected to the open mouth of the T-seal and the other end is inserted into an inverted, graduated cylinder filled with water and immersed in a water bath. Oxygen gas is then passed through the fiber walls through the open fiber ends and collected in the graduated cylinder. The gas pressure is initially set to a value of

2 2

0.351 kg / cm and then to a value of 0.703 kg / cm, as indicated in Table I. The gas flow (J) in cm / cm. Min. Is then determined using the given equation.

As can be seen from the results of Table I, oxygen permeabilities or flows of greater than 80 cnr / cm · min are obtainable with hollow, microporous fibers made according to the invention. Such permeabilities, when normalized to the flow per micron fiber thickness, represent a substantial improvement over normalized gas permeabilities of microporous films, reported in flow per micron film thickness, when such films are subjected to the cold stretch hot drawing process of U.S. Patent No. 3 801404 have been produced.

Z. ß. becomes the normalized flow of the hollow, microporous i'asera with an acid gas permeability at 0.703

2 3 2

kg / cm of 82.9 cm / cm · min achieved by this

Permeability is divided by the average fiber wall thickness of 15 microns, so that a normalized flow is achieved

per micron fiber wall thickness of 5 _f 5.

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Similarly, a microporous film made by the cold stretch hot stretching method of U.S. Patent No. 3,801,404 and having a film thickness of about 25.5 microns has a gas flow of about

3 2 44 car / cm · min. When this gas flow is normalized for comparison with the normalized gas flow of the hollow microporous fibers of the present invention, a fluke per micron film thickness of 1.73 is obtained. Similar comparisons can be made in work periods 1 to 9 of Example I.

As a result, hollow microporous fibers can be made by the process of the present invention having a normalized flux three times greater than the normalized flow of microporous films formed from the patents previously described.

Columns of the panels

a: process Ii ⁰

b: spinning temp. ⁰ C

c: TUS (m / min)

d: passage (g / min)

e: Deduction ratio

f; Luftstrommeßeinstellung

g: Mittl, I.D. (/ u) ·

h: Medium. O.D. (/ U)

i: average wall thickness

j: cold runs (ft) (25 ⁰ C)

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k: hot stretch (%) (HO ⁰ C) 1: strain rate (^ / Min.) M: Mittl. F ID of _a ser after heat curing (/ u), η: Aver. Wall thickness of Paser after heat curing (/ u)

2 '

o: surface area (m / g) p: oxygen flux (cmvcm. min.)

p ¹ : ⁿ at 0.351 0.703

2 2 2

ρ: ^M at kg / cm kg / cm

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CvJOJOJOJOJOJCVJOJOJCJ

οοοσυιηιηοο ιηιηιηιηιηιηιηιηοο

CMCvlCVJCvJOJOJCvJCMOJOJ

τ- cm cANfinvot ^ co σ \ ο

19019 ~ ⁵² - 20.8.1980

57 036/17

Comparative Example I

Example I is repeated, except that the inner diameter of the precursor fiber is reduced below 140 microns, as indicated in Table II. The degree and load rate of cold drawing and hot stretching, as well as process variables, are also shown in Table II. It should be noted that the wall thickness of the microporous hollow fibers is assumed to be substantially unchanged and has therefore not been empirically estimated.

Work Samples 1-10 show the reduced oxygen permeability obtained when the mean values of the precursor fiber internal dresser are noticeably below 140 microns, e.g. By 86 microns, compared to the gas permeability obtained in the procedures of Example I, using the precursor inner diameter above 140 microns, the largest oxygen fluxes,

3 2

which were obtained amounted to only 10.1 cm / cm · min.

Operations 7 to 10 show a substantial reduction in gas permeability when the hot stretching step is omitted or the ratio chosen is such that the degree of cold stretching is greater than the degree of hot stretching.

Operations 11 through H illustrate unsuccessful attempts to improve the gas permeability of cold stretched fibers by giving them a 10% recovery

19019 -53- 20.9.1980

57 036/17

(ie, operations 11 and 12) allows and provides the cold stretched parsers are a, recovery of 10% at a temperature of 130 ⁰ C (ie, operations 13 and 14).

Procedures 15 through 26 show the gas permeabilities obtained under changed process conditions using 110 micron median inner diameters of the precursor fibers. As can be seen, the gas permeability is substantially smaller compared to the gas flow of the precursor fibers with internal diameters used in the operations of Example I.

2 1901 9 -

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ΟΟΟΟΟΟΟΟΟΟΟΟΟ ΟΟΟΟΟΟΟΟΟΟΟΟΟ U ^ Lf ^ Lf% ΙΓΛ tf% Lf ^ tf ^ Lf ^ ΙΓ "\ tr \ \ JT \ 1ΓΛ Ii ^

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Table II (continued) h i d k ι m

57 036/17

H 245

15 245

16,245

17 245

18,245

19,245

20 245

21 245

22 245 23 "245

24,245

25,245

26 245

500 500 500 500 500 500 500 500 500 500 500 500 500

14 14 14 H 14 14 14 14 14 14 H 14 14

168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3 168 4.3

110 110 110 110 110 110 110 110 110 110 110 110 110

137

137

137

137

137

137

137

137

137.5

137.5

137

137

.5 .5

137.5

13.7 13.7 13.7 13.7 13.7 13.7 13.7 13.7 12.7 13.7 13.7 13.7 13.7

H Pasererhohlung of 10 % after cold stretching

at 130 ^Ü C

not determined

0 22 82.5 13.2 3.4 7.4

20 50 H 82.5 31.5 10.1 23.5

20 50 70 '82.5 28.5 11.4 23.5

20 50 140 82.5 30.8 10.2 23.3

20 65 17 82.5 ND 10.5 29.6

20 80 20 82.5 32.8 13.7 28.0

20 100 24 82.5 1ID 7.3 17.0

20 110 26 82.5 40.3 9.6 20.5

20 110 130 82.5 37.8 8.7 18.2

20 125 29 82.5 35.5 10.0 21.0

20 125 145 82.5 33.9 9.7 22.1

20 135 155 82.5 35.5 10.1 "23.4

20 135 31 82.5 27.6 10.8 24.4

Internal diameter of the pore determined by etching assuming that precursor fiber ID shrinks by 25 % during the process

2 19019 '20.8.1980

57 036/17

Comparative Example II

The process 1 of Example I is repeated with respect to the preparation of the precursor fiber. Precursor fiber samples are then annealed at 140 ^° C. for a period of 30 minutes at constant length, 100 % cold drawn at a strain rate of 20% / min. and a temperature of 25 ⁰ C and then thermally cured at different temperatures of 140 ⁰ C, 145 ⁰ C, 150 ⁰ C and 155 ⁰ C for 30 minutes. If the door hardness is the same as the door. Annealing temperature, ie 140 ⁰ C, shrink the fibers and curl. At a heat setting temperature slightly above the annealing temperature, ie 145 ° C, the fibers shrink to a lesser extent. Is the Yfermhärtemper door 150 or 155 ⁰ C, no shrinkage is detected. If the hot-curing time at 150 ⁰ C and 155 ⁰ C is noticeably less than 30 minutes, shrinkage is detected again.

The principles, preferred embodiments and modes of operation of the invention have been described above. However, the invention which is to be protected here is not limited to the particular embodiments as they have been given by way of example only. Changes may be made by those skilled in the art without departing from the spirit of the invention.

Claims (6)

invention claim 1. A manufacturing method for hollow, open-cell, microporous polypropylene fibers, characterized in that it has the following first steps: A. melt spinning at a temperature of at least 230 ^° C of an isotactic polypropylene having a melt index of at least 1 in a manner permitting obtaining hollow, nonporous propylene precursor fibers (5), stripping these precursor fibers (5) at a draw ratio of at least about 40, such melt spinning being conducted that the ^v orläuferfasern mentioned (5) after the departure of an average inside diameter of at least about 140 microns, a ratio middle interior diameter to mean wall thickness of about. 8: 1 to about 40: 1 and a degree of orientation of not greater than 25, the it is determined by half the width of a (HO) - 'Veit-angle X-Strahldiffraktionsbogens and an elastic return to the initial state of a 50 percent extension at 25 ⁰ C, hold 65% relative humidity and a zero-return time of at least 50%; B. annealing the precursor fibers (5) at a temperature between about 50 ^° C and less than 165 ^° C for a period of about 0.5 seconds to about 24 hours; C. Cold stretching (at 2) of the nonporous precursor fibers (5) "in their longitudinal direction at one temperature 2 1901 9 ~ ⁵⁸ ~ 20.8.1980 57 036/17 greater than the glass transition temperature state of the precursor fibers (5) and not greater than about 100 ⁰ C in order to obtain in the direction perpendicular to the cold-stretching direction would find the i'asern porous Plächenbereiche; D. hot stretching (at 3) the annealed cold stretched hollow fibers (15) of (C) in the cold stretch direction at a temperature above the cold stretch temperature and below deep polypropylene melt point to obtain an open cell, microporous structure in the hollow fiber walls, said cold stretching and said hot stretching may be carried out in a manner which allows the average inner diameter of the resulting warmed hollow microporous fibers to be set to a value of at least 100 microns, and a total combined draw of from about 80 to about 200 %, and a draw ratio of about 1: 3 to about 1:20 and a strain rate of about 10 to about 200% / LIin. to reach. E, thermosetting the formed v / arm stretched fibers of (D) under tension (rolls 20 to 61) to retain dimensionally stable open-celled hollow microporous fibers having a mean inner diameter of at least 100 microns; and secondly, that the following steps are involved: A. Melt spinning at a temperature of at least ⁰ C of an isotactic polypropylene with a melt 2 19019 -59- 20.8.1980 57 036/17 index of at least 1 in a manner permitting obtaining hollow, nonporous polypropylene precursor fibers (5), stripping these precursor fibers (5) at a draw ratio of at least about 40 to about 100, said melt spinning being carried out so that said Precursor fibers (5) after withdrawal have a mean inner diameter in the range of about 200 to about 300 microns, a mean inner diameter to average thickness ratio of about 10: 1 to about 30: 1, an average degree of orientation determined by half the width of one '' Veitwinkel- (HO) -X- ^ trahldiffraktionsbogens, having no greater than 25% and an elastic recovery capability of a 50 percent extension at 25 ⁰ C, 65% relative humidity and a zero return time of at least 50%; B. annealing the hollow precursor fibers (5) at a temperature of e
drive 30 minutes; Temperature of about 130 to about 145 ⁰ C during uncon- C. cold drawing (at 2) of the non-porous hollow precursor fibers (5) in its longitudinal direction at a temperature of about 15 to about 70 ⁰ C, a ^ executing degree of about 20% _t based on the original precursor fiber length and a strain or strain rate in the range of about 10 to about 100 % per minute to form in the walls of the Fa ^ser porous surface areas which are perpendicular to the cold stretch direction; 2 19019 " ⁶⁰ " 20.8.1980 57 036/17 D hot stretching (at 3) the cold stretched hollow fibers (15) of (C) in the cold stretch direction at a temperature of about 130 to about 145 ° C, a draw ratio of about 60 to about 100 %, and a load speed of about 10 to about 100 % per minute to give the hollow fiber walls an open-cell, microporous structure; To form E. heat curing of the hollow fibers formed under tension (rollers 20 to 61) at a temperature of about 130 to about 160 ⁰ C, abmaßemäßig stable, open- celled, hollow, microporous parsers are having an average inside diameter of at least 100 microns. 2. The manufacturing method according to item 1, characterized in that the melt spinning temperature is in a range of about 240 to about 280 ⁰ C, the withdrawal ratio at which the hollow or- der fiber (5) is drawn off is at least about 40, the mean inner diameter of hollow precursor fiber (5) is monitored after withdrawal so as to be in a range of about 140 to about 400 LIKE, that the cold stretching (at 2) at a temperature of about 15 to about 70 ⁰ C and the V / armstrecken ( at 3) is carried out at a temperature of about 130 to about 145 ⁰ C, and that the total level of the combined cold- and "arm ^ executing steps in the range of about 80 to about 150% and the elongation ratio in the range of about 1: 3 to about 1:10. 2 19019 "" ⁶¹ ~ 20 * 8.1980 57 036/17 3 »Production method according to item 1, characterized in that the melt spinning temperature is in the range of about 240 to about 250 ⁰ C. 4. A manufacturing method according to item 1, characterized in that the hot stretching and the intaglio curing are combined into a single operation (at 3) in which the cold stretched hollow fibers are sequentially warmed in a plurality of independent stretching steps (with rolls 20 to 61) become, 5. Hollow, open-cell, microporous polypropylene fibers, characterized by the fact that it produces an oxygen flux 3 2 '2 of at least 35 cm / cm. Hin «at 0.703 kg / cm have. Polypropylene fibers characterized by having a thickness in the range of about 10 to about microns and a mean inner diameter in the range of about 200 to 400 microns. 7. polypropylene fibers, characterized in that they are arranged in a device for acidification of the blood. 8. Oxygenating device for blood, with bundles of fibers, preferably inserted in an elongated, fluid-tight tubular housing, characterized in that said fibers of the bundle of hollow, open-cell, microporous polypropylene fibers 2 1 901 9 -62- 20.8.1980 57 036/17 (15) as defined in claim 5 or as prepared by the method according to any one of claims 1 to 4. For this / Be ta. Drawing.