NL8000862A - METHOD FOR PRODUCING HOLLOW, MICROPOROUS, POLYPROPENE FIBERS - Google Patents

Description

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A method for manufacturing hollow, microporous, polypropylene fibers.

The invention relates to microporous, hollow, polypropylene fibers, and to a method of manufacturing them.

Hollow, porous fibers are well known. The advantages of permeable hollow fibers over permeable films are also well known. For example, porous hollow fibers have a larger surface area per unit volume than a flat film or similar porous shape. Therefore, there is an increasing tendency to use hollow microporous fibers, if possible, in applications usually reserved for permeable films.

While the processes for manufacturing and imparting permeability to hollow fibers and films may appear similar in many respects, there are treatment differences peculiar to each method and leading to significant, unpredictable consequences in the performance of permeability, which precludes the total application of the film process to hollow fibers.

For example, U.S. Pat. No. 3,101Λθ20 discloses a cold stretch / hot stretch process for making microporous polypropylene films, which process comprises the steps of extruding a preliminary film using a blow film process at a temperature 180-270 ° C, and recording the film at recording speeds of 9-213 m / min. and a stretching speed of 20: 1-200: 1. The preliminary film is then optionally heated and cooled slowly, cold stretched at a temperature below about 12 ° C, e.g. 25 ° C, hot stretched at a temperature above 120 ° C and below the melting temperature of the polymer, e.g. between 130 ° C ° C and 150 ° C, and finally heat cured at a temperature in the range from 125 ° C up to less than the melting temperature of the polymer, for example 130-160 ° C.

When extrusion or melt spinning temperatures of less than 230 ° C are used in the manufacture of the present hollow microporous polypropylene fibers, the uniformity of the construction of the hollow fibers with respect to the inner and outer diameters as well as the wall thickness , significantly reduced.

Thus, the melt fiber spinning temperature of the hollow fibers represents a process parameter, which cannot be easily transferred from the film to the fiber process due to the inherent differences between the fiber and film shape, ie, the notion of evenness of the inner and outer diameter dimensions of fibers, does not exist in the foil process. The melt index of the polypropylene used to make the present hollow fibers must also be controlled to maintain the regularity of the structure and dimensions of the hollow fiber.

Although the manufacture of a film for the blown film process is similar to the manufacture of a hollow fiber by the air injection process, there is also a significant difference here. The pick-up speed in the manufacture of blown preliminary films is limited, because at ever higher recording speeds (keeping other process variables the same), the regularity of the micro-porous film structure, which is subsequently given to the preliminary film, decreases. Therefore, the method variable of the pick-up speed cannot be controlled (ie, increased) in a manner sufficient to provide ever-increasing degrees of direction to the preliminary film structure. Greater degrees of alignment up to a certain threshold have a beneficial effect on the final permeability given to the film, however, as 8000882 * 4 3, due to the difficulties of pore structure regularity, a limit is imposed on the degree of targeting, which can be given to the preliminary film via the recording speed control.

When hollow fibers are manufactured by the present method, the difficulties of microporous structural regularity are significantly reduced, with higher recording rates being used to give a greater degree of alignment, as determined by the wide angle X-ray diffraction (110) flat, to the provisional hollow fibers, thereby imparting greater permeability. However, this increase in permeability is not readily realized in the absence of controlling the inner diameter (ID) of the hollow, preliminary fiber, which in turn controls the inner diameter of the subsequently formed, hollow, microporous fiber. The size control of the hollow microporous fiber is another process variable, which cannot be transferred from a film process.

US 3,558.iSk discloses a cold stretch process for making microporous films, which process comprises the steps of extruding a polymer at specially determined temperatures to form a preliminary film, cooling the preliminary film heating and cooling the preliminary film at specially determined temperatures (i.e., 5-100 ° C below the melting point of the polymer, which is about 105 ° C for polypropylene), cold stretching the resulting film with a specially known drawing ratio and temperature and heat-curing the cold-stretched film at a temperature of 100-150 ° C under tensile stress. The main difference of this method from the previous cold stretch / hot stretch process is the absence of a hot stretch step.

The previously described cold stretch / hot stretch method represents an improvement of the cold stretch method of this patent with respect to nitrogen flow.

When hollow, provisional fibers are heated and slowly cooled, cold-stretched and heat-cured, substantially in accordance with the foregoing cold-stretching processes, especially when the heat-setting temperature is at or below the original temperature of the heating, the hollow microporous fibers obtained therefrom, on the other hand, exhibit varying degrees of shrinkage, which tend to curl up, which is disadvantageous depending on the use for which the hollow fiber is used.

In US Pat. No. 055,696, a similar cold stretch method is used, which is used to manufacture hollow, microporous, polypropylene fibers instead of films. This method requires that the size of the pores be kept within a certain range by limiting the degree and temperature of the cold drawing to 30-2005. of the original fiber length and less than 100 ° C. The resulting cold-stretched fibers, which have been preheated and slowly cooled, are heat cured to a temperature at or above the original temperature of the heating used prior to stretching, as described above.

A separate hot drawing step, as used in accordance with the invention, is not included in the manufacture of these hollow fibers. Heated and slow-cooled, cold-stretched, heat-cured, hollow fibers, manufactured in accordance with this patent, tend to exhibit variable degrees of shrinkage depending on the relationship between the previous heating temperature, and length of time up to the temperature for heat curing and its duration. In addition, there is no control of the inner diameter of the hollow fibers of this patent to improve their oxygen gas permeability.

Japanese Patent 53 (1978) -38715 relates to an improvement in the method of manufacturing porous, hollow, polypropylene fibers, such as disclosed in U.S. Patent No. 0,055,696. The improvement includes controlling the heating temperature to below 155 ° C and controlling the heat-setting temperature after cold drawing between 8000862 5-m 155 ° C and 175 ° C for three seconds to 30 minutes. Also in this method, no use is made of a hot drawing step in addition to the cold drawing step, as required by the application, or an adjustment of the inner diameter of the hollow microporous fibers to improve the oxygen gas permeability .

A particularly important use for hollow microporous fibers is a blood oxygen device, such as disclosed in U.S. Pat. No. 4,020,230, which discloses hollow microporous fibers made of polyethylene. As is well known, the properties required for a blood oxygen membrane membrane, good gas permeability to gaseous oxygen and carbon dioxide, chemical stability, compatibility with the blood or a substantially non-thrombogenic behavior in blood-containing environments, is sufficient hydrophobic nature to serve as a water vapor barrier, ease of manufacture, non-toxic, relatively inert to bodily fluids, and mechanical stretching and handling properties, which are convenient for facilitating the composition and use of blood oxygen devices.

Microporous polypropylene films have already been used as a blood oxygen membrane, which films have been found to meet all of the foregoing requirements. However, due to the relatively small surface area of such films, relatively large amounts of blood must be removed from the body to achieve the required oxygen and carbon dioxide gas transfer.

In contrast, hollow, microporous, polypropylene fibers have the advantage that they can achieve the same gas transfer when using much smaller amounts of blood.

Thus, there is ongoing research on hollow, microporous, polypropylene fibers, and a method of manufacturing them, providing high oxygen gas permeability. The present invention is a result of this research.

It is therefore an object of the invention to provide microporous, 8000862 6 hollow, polypropylene fibers, which have a high oxygen gas permeability.

It is a further object of the invention to provide a method for manufacturing hollow, microporous, poly-propylene fibers with a high oxygen gas permeability.

The invention is further elucidated with reference to the drawing, which schematically shows means for achieving the hot stretching in a number of phases.

In one aspect, there is provided a method of manufacturing hollow, microporous, polypropylene fibers with open cells and provided with an oxygen flow of at least 35 cm / cm. min. at 69 kPa, which process (A) comprises melt spinning at a temperature of at least 230 ° C of isotactic polypropylene with a melt index of at least 15 L in a manner sufficient to obtain hollow, non-porous, preliminary polypropylene fibers incorporating these provisional fibers with a draw ratio of at least about Ho, which melt spinning is performed in a manner sufficient to impart to the provisional fibers after incorporating an average inner diameter of at least about 10 µm, a average inner diameter to average wall thickness ratio of 8: 1 to UO: 1 and a degree of directivity, as determined from the half width of the wide angle (110) X-ray deflection arc, of not more than 25 °, and a resilient recovery from a 50% elongation at 25 ° C, 65% relative humidity and a recovery time of 0, of at least 5055, (B) further heat treating the provisional fibers at a temperature between 50 ° C and less than 1 65 ° C for a time of 0.5 sec. up to 2 hours, (C) the cold stretch of the non-porous, hollow, preliminary fibers in the direction of their length at a temperature above the glass transition temperature of the preliminary fiber, and not above about 100 ° C for the giving porous surface areas to the walls of the fiber, perpendicular to the direction of cold stretching, 35 (D) hot stretching of the heat-treated, cold 8000862 * ± 7 stretched hollow fibers according to (C), in the same direction as cold stretching at a temperature above that of the cold stretching and below the melting point of the polypropylene to impart an open cell microporous shape to the hollow fiber walls, which cold stretching and hot stretching are performed in a manner sufficiently To control the average inner diameter of the obtained hot stretched hollow microporous fibers, at least 100 µm, and to achieve a total composite stretch of 80 to 200 µm, a stretch ratio g of 1: 3/1: 20 and a stretching rate of 10 to 200 µm / min, and (E) heat-curing the obtained hot-stretched fibers according to (ü) under tensile stress to produce dimensionally stable, hollow, open-cell microporous fibers with an average inner diameter of at least 100 µm.

In another aspect, hollow, microporous, open-cell polypropylene fibers are provided, having an oxygen flow of at least 35 cm / cm. Min. at 69 kPa, manufactured by the foregoing method.

The present hollow microporous fibers are made from isotactic polypropylene having an average molecular weight of between 100,000 and 750,000 and a melt index of not less than about 1 (e.g. not less than 5) usually between 1 and 30 or more, preferably between 3 and 15 and more particularly between 5 and 10.

The term "melt index" used is the value obtained by applying ASTM D-123O under conditions of temperature, applied load, duration and other operating variables, which are available for the particular polymer tested, ie polypropylene .

When a fiber is made of polypropylene with a melt index that continues to drop below about 1, for example, 0.5, the fiber exhibits an increased tendency to break or split, and an increasing variation in the regularity of the inner diameter and cross section of the fiber.

The density of the polypropylene should be about 0.9 g / cm 2.

8000862 8

The isotactic polypropylene is converted into a hollow preliminary fiber by melt spinning. The molten polymer is forced to flow through one or more openings (ie, jets) of a spinneret which can impart the desired, uninterrupted, hollow shape to the fiber. For example, in the preferred embodiment, the melt is forced to flow through one or more annular dies provided with a needle extending into each center portion thereof. A gaseous stream is then passed through the needle as the rush is pumped through the annular die to thereby give a hollow shape to the fiber. Also, the hollow interior of the fiber can be formed by passing the molten polymer material through an annular opening or a solid core, which can cause the desired hollow structure to form.

^ 5 The temperature at which the polypropylene is extruded, i.e. melt spun (assuming the other spinning variables described are used) should be at least 230 ° C, preferably between 2 ° C and 280 ° C, and more particularly between 2U0 ° C and 250 ° C.

When an extrusion temperature of progressively below about 230 ° C is used, the regularity of the fiber with respect to inner and outer diameters deteriorates more and more. In contrast, preliminary films used in the cold-stretch / hot-stretch process of US Pat. No. 3,801-100 can be produced at extrusion temperatures not exceeding 180 ° C. At extrusion temperatures increasingly above about 280 ° C, the spinning stress applied to the extruded polymer must be significantly increased, with the risk of polymer degradation.

When a hollow fiber air-injected spinneret is used, the jet diameter, air flow rate, take-up speed, extrusion speed and draw ratio are controlled in a manner sufficient to achieve a hollow, preliminary, polypropylene fiber of average inner diameter and an average wall thickness of the dimensions described, and a degree of 8 0 0 0 8 S 2 0 9 9 direction of not more than about 25 °, as determined by the half width of a (110) wide angle X-ray diffraction arc.

The degree of molecular fiber orientation is determined by placing the fibers in alignment to a thickness of 50 mg / cm 2. The fibers are irradiated with X-rays in a direction perpendicular to the axial direction of the fibers, recording half the width of a (110) wide angle bending arc on film. The angular spread of this (110) bending arc is then determined, and should not exceed 25 °.

The dimensions (ie the inner and outer diameters) and the wall thickness of the hollow produced fibers can be controlled in different ways. Initially, the diameter of the die and the selected pressure of the inert gas control the inner and outer dimensions of produced fibers, as modified by the degree of increase of the fiber dimensions by relieving them of the metered pressure of the extrusion by the spinneret. The diameter and wall thickness can also be changed by changing the pressure of the extrusion through the spinneret and the take-up speed with which the fibers are pulled away from the spinneret. Changes in one of these values can be compensated for by changes in the other to achieve the desired effects.

Although the foregoing process parameters are controlled in order to achieve an inner diameter within a limited range, they are likewise controlled to give the correct morphology to the preliminary fiber to ensure that subsequent treatment achieves a micro-porous structure with a appropriate gas permeability.

Accordingly, the melt spinning or melt extrusion step of the process is performed at a relatively large "stretch" or "spin stretch" ratio, so that the hollow fibers are spun during the formation thereof. The draw ratio is determined as the ratio of the rate of initial take-up of the hollow fibers and the linear extrusion rate of the polymer through the spin-35 cap opening The draw ratio used in the present process is at least 30, preferably at least ho (for example, between 1 + O and 100), and can be up to about 700. Pick-up speeds, used to achieve the required stretch ratios, are generally about 200 m / min, usually between 200 and 1000 m / min, and preferably between 200 and 500 m / min. Typically, large shear forces are developed in the polymer material, which forces are not released prior to fiber hardening.

The air flow rate, that is, the velocity at which the air is passed through the needle in the center portion of the nozzle, is variable depending on the number of nozzles in the spinneret, and is usually controlled between 5 and 70 cm / min. jet opening, and preferably between 10 and 3 50 cm / min. / jet opening.

15 The temperature of the air as it exits from the air injection spinneret is usually the same temperature as that of the polymer melt spinning,

The hollow, spin-oriented, provisional fibers may optionally be quenched by passing them through a gas stream, such as ordinary room temperature air, or through an inert liquid, such as water, to rapidly cool the freshly spun hollow fiber . The temperature of the hlus medium can reach 80 ° C and drop to 0 ° C (for example 0 to U0 ° C) depending on other spinning parameters. However, the preferred bubble temperature is 25 ° C, with the movement of the freshly spun fibers through the ambient air causing sufficient extinguishing when the take-up roller is located 1.5-3 meters or more from the spinneret.

The hollow, provisional polypropylene fiber obtained therefrom is non-porous, and exhibits crystallization of at least 30%, preferably at least 40%. » and more particularly at least 50¾ (e.g. 50-60¾ or more). The crystallization percentage is determined on the basis of the relationship:

Va - V

% crystallization = -3- x 100

Va - Vc 35 8000862 11 where Va is the specific volume of the 100? amorphous polymer,

Vc the specific volume of the 100? crystalline polymer and V is the specific volume of the sample of interest. The specific volume of a polymer is 1 / D, where D is the density of the polymer. The density of the polymer is measured by a density gradient column, such as described in ASTM D-1505-68 The hollow, preliminary polypropylene fibers must also exhibit a resilient recovery at a recovery time of 0 after subjecting to a normalized elongation of 50 ° at 25 ° C and 25 ° relative humidity, of at least about 50, preferably at least about 60, and more particularly at least about 65.

The resilient recovery is a measure of the ability of molded objects, such as hollow fibers, to return to their original size after stretching.

15 The resilient recovery value is determined with a

Instron tensile tester, operating at a strain rate of 100? Minute. After the fiber has been stretched to the desired stretch value, the jaws of the device are reversed at the same speed until the distance between the jaws is the same as at the start of the test, ie the original gauge length. The jaws are immediately reversed and stopped as soon as the tension starts to increase from zero. The resilient recovery is then calculated as follows: (total length after final distance),,,. ,,, (stretching - between the jaws) 25 resilient recovery? --1-x 100 added length after stretching

Measurements with the Instron tensile testing device are carried out at room temperature, for example 25 ° C in air with a relative humidity of 65 ?.

3 ° Although a normalized elongation of 50? Used to determine the resilient properties of the preliminary fibers, this stretch is by way of example only. Generally, such provisional fibers have a resilient recovery that is greater at a stretch of less than 50? And slightly smaller at a stretch that is significantly greater than 50? in comparison 8000862 12 with its resilient recovery he stretches $ 50.

The foregoing operating conditions are controlled to provide hollow, preliminary polypropylene fibers having an average inner diameter (ID) of at least 1 ^ 0 µm, preferably 5 between 1 + 0 and 1 * 00 µm or more, and more particularly between 200 and 300 ym. The foregoing average inner diameters have been found to be necessary to impart high gas permeability to the preliminary hollow fibers. When high gas permeability is not a control factor for the intended end use of the hollow fibers, the inner diameters can be reduced to below 100 µm.

The dimensions of the hollow fibers are expressed as an average value, so that these dimensions vary somewhat depending on the location along the fiber length where they are determined. Accordingly, the average inner and outer diameters are determined by cutting cross sections of the fiber at 15 cm intervals for a total of 5 spacings along the fiber length, and determining the fiber dimensions at each of these spacings. The fiber cross-sections 20 are then dipped in a normalized immersion optical oil, the size being determined at each spacing using optical microscopic and optical scaling. The results are then averaged to determine the mean inner and outer diameters.

The minimum wall thickness of the provisional hollow fibers should be sufficient not to simply break or otherwise undergo physical deterioration at a rate which would render their use unattractive after the fibers have been microporified by the methods described above. The maximum wall thickness of the hollow fibers is limited by the degree of intended permeability to be given to the final product.

The measurement of the average wall thickness is accomplished by determining the average outer diameter and the average inner diameter of the fiber, and taking as the wall thickness half of the difference between these average diameters.

8 0 0 0 δ δ 2 13 '

Furthermore, the average wall thickness can be expressed as a function of the average inner diameter of the hollow fiber.

The ratio of the average inner diameter of the hollow, provisional fiber to its average wall thickness may be variable from 8: 1 to 1: 0: 1, preferably from 10: 1 to 30: 1, and more particularly from 10: 1: 1 to 20: 1. More particularly, an average wall thickness of a preliminary fiber of altahsn 10 Pm and usually of 10 to 25 Pm is preferred.

Although it is the inner diameter with the coherent wall thickness of the final macroporous hollow fiber product which is believed to be a major control factor of gas permeability, it is the inner diameter and wall thickness of the preliminary hollow fiber which is the maximum inner diameter and wall thickness to be achieved of the finished product predetermined. This is due to the fact that the inner diameter of the preliminary fiber shrinks about 25% when subjected to the two-phase stretching process described above. The average wall thickness of the hollow microporous fibers remains substantially unchanged by the treatment compared to the preliminary fiber, although this wall thickness can be reduced to some extent.

The hollow, preliminary fibers are then subjected to a heat treatment or heating, followed by cooling, thereby improving the degree of crystallization and / or its crystal structure. More specifically, this step of the method increases the crystalline size, removing imperfections in the molecular direction. The heating followed by cooling is performed at a balance of time and temperature to achieve the desired improvements, as described above, and yet sufficient to prevent destroying or adversely affecting the preliminary polymer structure (eg, direction and / or or crystallization).

Preferred heating temperatures may be variable between 130 and 1H5 ° C for a time of about 30 min. When the heating temperature is raised above about 1U5 ° C, the time during which the provisional fiber is 8 0 0 0 S 6 2

1U

heat treated, reduced accordingly. Conversely, when the heating temperature drops below 130 ° C, an increasingly longer heating time is used.

If the heating temperature further exceeds 15 ° C at a heating time of 30 min, the preliminary polymer fiber structure is adversely affected, the gas permeability of the provisional fiber being increasingly reduced. As the heating temperature continues to drop below 130 ° C for 30 minutes, the gas permeability of the provisional fiber is also increasingly reduced.

In view of the foregoing, heating followed by cooling is performed for 0.5 sec. up to 2 hours at a temperature from 50 ° C to less than the melting point of the polypropylene (i.e., 165 ° C based on differential-15 scanning calorimetry).

The step of heating followed by cooling may be performed in a tensile or non-tensile state by placing the preliminary fiber in a static state in a heating region maintained at the required elevated temperature or by continuous passage of the preliminary fiber through the heating area.

The elevated temperature can be accomplished, for example, by using a conventional air circulation oven, infrared heating, dielectric heating, or by direct contact of the moving fiber with a heated surface, which is preferably curved to promote good touch.

The preliminary fiber can be continuously passed through a jacketed tube or jacket, which radiates heat at the desired temperature. The preliminary fiber can also be wound onto a coil substantially without tension while undergoing heat treatment or simply placed in a loose state in the heating region, such as in the form of a strand of continuous fibers. For the best results, it is recommended that the hollow fiber be kept at a constant length during the heating step followed by cooling, ie under 8000862 15 tensile force sufficient to prevent a length stretch or shrinkage of greater than about $ 5 - This can be accomplished by passing the fibers in their longitudinal direction over and around a first tension insulator through a heating region maintained at the correct temperature, and then over and around a second tension insulator. Each tension insulator may advantageously be in the form of a pair of rolls of non-rectilinear cross-section. The control of the ratio of the surface speeds of the two sets of rolls allows isolation and control of the tension of the fibers between the rolls during undergoing the heat treatment.

The resulting non-porous hollow provisional fiber is then subjected to a two-phase stretching process and then heat cured.

During the first stretching phase, referred to as cold drawing, the hollow preliminary fibers are stretched at a temperature above the glass transition temperature (Tg) of the preliminary fiber, and not more than about 100 ° C. Conventional cold drawing temperatures are variable between 0 ° C and 100 ° C, preferably between 15 ° C and 70 ° C, and more particularly at room temperature, for example 25 ° C.

The temperature of the fiber itself is referred to as the stretching temperature.

Those skilled in the art of polymer technology consider the glass transition temperature (Tg) as the temperature at which the structure of a fully or partially amorphous polymer material changes from a glassy state to a viscous resilient state. The glass transition temperature of polypropylene is measured by plotting its specific heat against the temperature, and determining the temperature, with a change in the slope of the curve. This measurement is commonly referred to as thermomechanical analysis, and can be performed with commercially available instruments. The glass transition temperature is also referred to as the second order transition temperature.

Cold drawing gives porous surface areas to 8000852 16 the fiber wall, which areas are elongated perpendicular to the stretching direction.

The second stretching phase, referred to as the hot stretching, is performed at a temperature above that of the cold stretching, but less than the melting point of the preliminary fiber before or after the cold stretching, that is, the first order transition temperature, such as determined by the differential scanning calorimeter analysis.

Typical hot stretching temperatures are above about 100 ° C and may be variable between 105 ° C and 10 1 ^ 5 ° C, preferably between 130 ° C and 1 ^ 5 ° C, and more particularly between 135 ° C and 1 ^ 5 ° C. Again, the temperature of the fiber itself being stretched is intended to be the temperature of hot stretching.

As the hot drawing temperature used is progressively below 130 ° C, progressively larger shrinkage rates are observed in the finished fiber product.

The hot stretching opens the porous surface areas, given by the cold stretching, to form an open cell microporous structure.

The stretching in the two stretching phases must be consecutive in the same direction and in the given order, ie cold stretching and then hot stretching, but can be performed in a continuous, semi-continuous or discontinuous manner as long as the cold-stretched fiber is not in any can shrink 25 noticeably (for example, no more than about $ 10 by the original length of the preliminary fiber).

The summed total degree of stretching in the aforementioned cold and hot drawing phases can be variable from $ 80 to $ 200 (for example, $ 80 to $ 155), and preferably from $ 85 to $ 120 (for example, about $ 90) based on the original length of the preliminary fibers. When the total stretch is progressively less than about $ 80, the resulting oxygen-

O

gas permeability at 69kPa progressively less than about 35 cmJ / 2.

cm .mm. The ratio of the degree of stretching from the first (cold) to the second (hot) stretching phase is referred to as the 8000862 * 17 draw ratio. The stretch ratio can be variable from 1: 3 to 1: 2Qj, preferably 1: 3 to 1:10 (e.g. 1: 3 to 1: 5).

It is understood that the determined overall stretch and draw ratio from the above ranges are selected in a manner sufficient to control the final mean inner diameter of the hot stretched microporous fibers within the described limits.

The stretching rate, that is, the degree of stretching per unit time at which the preliminary fibers are stretched during both of the two stretching phases, is preferably the same for each phase, and may be between 10 and 200 $ / min, preferably 10 and 100 $ / min min., and more particularly between 15 and 30 $ / min. (for example about 20 $ / min.

For example, in the overall preferred degree of stretching from $ 80 to $ 120, the preferred stretching ratio 1: 3 to 1: 5 is $ 20 cold stretched and $ 60 to $ 100 hot stretched.

Cold and hot stretching of the preliminary fibers can be performed in any suitable manner using known methods. The hollow fibers can be stretched, for example, on a conventional stretching frame, which is located in a heating region, which controls the temperature of the fibers during stretching. Also, the fibers can be stretched cold and hot in a continuous manner by means of two sets of stress isolators (1 set for each phase), similar to those described in connection with the heating step followed by slow cooling.

Accordingly, preliminary fibers can be wound several times around a first pair of rolls of non-rectilinear cross section, passed through a heating area, in which the fibers are contacted, for example, with an appropriate heating device or a heating medium and at a proper temperature for cold stretching. and wound several times around a second pair of rolls of non-rectilinear cross-section. This arrangement allows the isolation and control of the longitudinal tension of the fibers between the two pairs of rollers during cold stretching.

8000 862 18

The fibers are then passed through a similar set of paired rolls of non-rectilinear cross section, under heating to the correct temperature for hottest stretching. The ratio of the surface speed of each of the rolls of the second pair to the surface speed of each of the rolls of the first pair determines the draw ratio and the draw rate, which are adjusted accordingly.

Obviously, in an uninterrupted process, the cold stretched fibers may shrink as they move from the cold stretch phase to the hot stretch phase. This can occur due to heating of the cold drawn fibers as they enter the hot drawing area, such as a forced hot air oven, but before they are actually hot drawing. As a result, it is preferable to provide a tensioner 15 between the cold and hot drawing phases to prevent shrinkage of more than about 5% based on the length of the cold drawn fiber. Such a tensioning member can advantageously be in the form of a single pair of rollers with non-rectilinear cross sections.

The heating regions, which heat the provisional fibers to the corresponding temperature for cold stretching or hot stretching, are the same as described for heating followed by slow cooling prior to cold stretching, and may advantageously be in the form of a with gas, such as air, heated plate, a heated liquid and the like. The preferred heating means is a forced hot air oven incorporating the stretching means.

After the previously described cold and hot stretching, the stretched fibers are heat cured or heated, followed by slow cooling, in the stretched state at a temperature between 125 ° C up to less than the melting temperature of the polymer. As is known to those skilled in the art, the melting temperature can be determined by a normalized differencing scan calorimeter or other coated device which can sense thermal transitions of a polymer. Preferred temperatures for heat curing 8000862 19 may range from 130 ° C to 11 + 5 ° C. The most preferred heat curing temperature is the same as the temperature used during hot stretching. Heat curing does not change the fiber sizes present after hot stretching.

The heat-curing step can be carried out in an interrupted manner, such as in an oven or autoclave, or in an uninterrupted manner. For example, the hollow microporous fibers can be rewound on a spool after hot stretching and subjected to heating followed by slow cooling in that form. The hollow fibers can also be stretched and heat-cured in a continuous manner by means of two pairs of driven rollers downstream of the stretch rollers and at the same speeds, the material moving continuously between the rollers at a constant length after hot stretching. heating area. As a result, the stretching and heat curing steps of the method can be performed sequentially or combined into a single line operation.

The heat-curing treatment must be carried out when the fibers are kept under tensile stress, that is, such that the fibers cannot shrink freely or can only be controlled at a controlled rate of no more than about 15% of the stretched length thereof. shrink, but not so much tensile force, that the fibers are stretched more than an additional $ 15. Preferably, the tensile stress is such that substantially no shrinkage or stretching occurs, for example less than 5% change in the stretched length.

The time of the heat curing treatment, which treatment is preferably carried out after and after the hot stretching, should not exceed 0.1 sec. at the higher temperatures for heat curing, and may generally range from 5 sec. and 1 hour, and preferably between 1 min and 30 min.

Since the heat setting temperature which is most preferred 8000862 20 is the same as the hot drawing temperature, it is preferable as much as the hot drawing if the heat setting is carried out in the same heating means, such as a hot air oven in which case the total residence time in the oven for the hot stretching and heat curing steps may be between 10 and 5 min., and preferably between 25 and 35 min. (e.g. 35 min.) hot stretching temperatures between 130 ° C and lk5 ° C.

The action of the heat-curing step consists in improving the thermal stability of the microporous structure and reducing shrinkage of the fibers.

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

In this embodiment, hot stretching is accomplished using a number of separate and consecutive hot stretching operations at the appropriate hot stretching temperature. After the fibers have been cold stretched, they are guided, for example, in a means which can stretch the fibers step by step, keeping the fibers at the correct temperature for hot stretching, so that the total degree of stretching of each step adds to the desired degree. of the total hot stretching.

The multi-step hot-stretching means may advantageously be in the form of a plurality of rollers mounted in an oven. The rollers are preferably arranged in a roll shape similar to that described in U.S. Pat. No. 3,8U3,761. The use of a crank arrangement is preferred in that it provides an extended exposure time in the oven containing the multi-step hot stretching agent, thus eliminating the need for a heat setting step after it is hot stretching is complete.

Reference is made to the drawing to illustrate a preferred method for achieving the multi-step hot stretching and heat hardening combined.

35 Non-porous, preliminary fibers 5, which have been heated, followed by 8000862 21 slow cooling, are unwound from a supply roll H over the guide rollers 6 and T in an area 2 for cold stretching. The cold straightening device comprises two pairs of rollers 8, 9 and 11,12 with non-rectilinear cross-section, which rollers are driven 5 with peripheral speeds of S ^, S ^, S ^ and S ^, by suitable drive means 10 and 13 to achieve the desired degree of cold stretching as described above. For clarification, the temperature of the cold stretching is the room temperature, no heating or cooling means are required for this phase.

If desired, however, suitable temperature control means can be provided, as described above. The cold-stretched fibers 15 are passed into the means 3 for hot-stretching over one or more guide rollers 11. Nip rolls are not used because they tend to press the hollow fibers closed, which is detrimental to the final product. The hot-stretching means 3 comprises a single set of rolls 16 and 17 of non-rectilinear cross-section, and a plurality of additional hot-stretching rolls, which are arranged in a furnace in a winding shape. To minimize the unworn fiber length between adjacent hot stretching rolls, which is relatively long in the preferred crank arrangement, at least one idler roll is disposed between adjacent hot stretching rolls.

The single set of non-rectilinear cross-section rollers 16 and 17 helps maintain tensile stress on the cold-stretched fibers by controlling the peripheral speeds Sj. and Sg thereof. Placing under tension prevents shrinkage, sagging and the like caused by preheating the fibers as they go into the oven but before being stretched hot. Placing such a tensile stress helps prevent a reduction in the cold stretched fiber properties caused by preheating. While this tensile tensioning step to prevent fiber relaxation may result in a small amount of stretching, the main consequence of this is tensile tensioning, 8000862 22 controlling the peripheral velocities and Sg accordingly. means 18 for maintaining a constant length between the cold stretch and hot stretch areas. Thus, this method is only a preferred embodiment of a means for maintaining fiber tensile strength prior to hot stretching. Other methods that prevent fiber relaxation during heating of the fibers prior to hot stretching can be used.

The tensioned cold stretched fibers 15 are then conveyed downstream over the guide rollers 19 and 20 on a first roll 21 for hot stretching. The fibers are hot-stretched for the first time between the roller 21 and the second tensioning roller 16. This occurs because the downstream first hot-stretching roller 21 is rotated at a peripheral speed S15 exceeding the peripheral speed given to the fibers through the roller 16. It should be noted that a guide roller 19 is interposed between the rollers 16 and 21 to reduce the unworn fiber length during the hot stretching step.

This operation is continued for as many 20 separate steps as preferred. For example, the fibers are stretched a second time between the first hot stretch roll 21 and a second hot stretch roll 23. During this second hot stretching step, the peripheral speed of the second hot stretching roll 23 is equal to Sg. The peripheral speed 25 Sq is higher than the peripheral speed of the first hot stretching roll 21. Thus, the fibers are hot-drawn in the second hot-drawing step with a hot drawing ratio of Sg / S /.

To minimize the unworn fiber length, at least a guide roller 2k is again arranged between the second and third rollers 23 and 25 for hot stretching. In the preferred embodiment, shown in the drawing, the guide rollers are positioned approximately midway between adjacent hot stretching rollers.

In the embodiment shown in the drawing, 20 stretching steps, which take place successively, are provided. As shown in the drawing, to provide 20 stretching 8000862 23 steps, 21 rolls are required for hot stretching. It should be noted that the second tensioning roller 16 is equal to the first hot stretching roller. Generally, in the preferred hot melt stretching apparatus, (n + 1) hot stretching rollers are required to provide n consecutive hot stretching steps. Preferably two to ten stretching steps are used during hot stretching in a number of steps.

Two preferred methods can be used to provide a continuously increasing peripheral velocity at each additional hot drawing downstream roll. In one preferred embodiment, all rollers are driven by a common drive mechanism. Thus, each hot stretching roller is driven at the same rotational speed. However, each hot stretching roll has a different diameter. More specifically, each additional downstream hot stretching roll has a larger diameter than the adjacent upstream roll. Thus, the roller 23 has a larger diameter than the roller 21, the roller 57, namely the hot stretching roller furthest downstream, having a diameter greater than that of the penultimate downstream roller 55 As those skilled in the art know, the circumferential or surface speed of a larger diameter roll rotating in the center thereof at the same speed as a smaller diameter roll is greater than the smaller roll. Thus, the use of ever-increasing diameter diameters serves to provide peripheral speed differences between neighboring hot-stretching rollers.

A second preferred method of providing an increased difference between the peripheral speeds of neighboring hot stretching rollers is to provide separate drive means for each roll. In this preferred embodiment, each roll can have the same diameter. Thus, the increasing speed of neighboring downstream rolls for hot stretching becomes a function of the energy supplied to each roll.

Obviously, the process variables as described above in connection with single step hot 8000862 2k stretching are applicable to multiple step hot stretching except that naturally obvious changes may be necessary when passing one to another.

For example, as previously described, the total degree of hot stretching is the same in both stretch embodiments, except that in the multiple step hot stretching, the total degree of stretching is achieved in a number of, preferably equal, steps. Also, the stretching rate of each hot drawing step is preferably controlled to provide a total residence time TO in the multi-step hot drawing region, which time is approximately equal to the combined heat setting residence time used in connection with single-step hot stretching, and those obtained when the stretching speed is within the ranges described above for single-phase hot stretching.

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

The average wall thickness of the hollow, microporous fibers, 20 does not perceptibly change from the corresponding provisional fiber, with the change in the average inner diameter to average wall thickness ratio of the microporous fibers from the provisional fibers being due to the reduction in the average diameter of the provisional fibers caused by stretching.

The average inner diameter to average wall thickness ratio of the hollow microporous fibers is variable from 7: 1 to 35: 1, and preferably from 10: 1 to 30: 1. The determined wall thickness achieved is predetermined by the wall thickness of the preliminary 3P fiber, which wall thickness, as described above, depends on the end use for which the fibers are used, and the pressure to which they are subjected. Preferably, the selected wall thickness selected is the minimum that can withstand conventional operating conditions for a particular final application without undergoing physical deterioration at an unacceptable rate.

8000862 25

When the hollow microporous fibers are used for a blood oxygen device, the wall thickness can be between 10 and 30 µm, the average inner diameter can be between 200 and 100 µm, and then exhibit high gas permeability and a structural unit.

When the average inner diameter of the hollow microporous fibers is reduced to below 100 µm for a given wall thickness, gas permeability at 69 kPa decreases significantly.

When the average inner diameter of the microporous, hollow fibers is at least 100 µm, and the inner diameter to the wall thickness ratio is not less than about 7: 1, such hollow fibers exhibit an oxygen flow at 69 kPa of at least 3 2 3 2 35 cm / cm. min., usually from 35 to 85 cm / cm. min., and more in particular from ho to 60 cm / cm. min.

The oxygen flow J is determined by conducting

S

oxygen gas through a hollow fiber unit, which is discussed in more detail in the examples. The hollow fiber unit makes it possible to pass pressurized gas (for example 69 kPa) through the interior of the hollow fibers, further through the microporous hollow fiber wall, and collect it. The volume of gas collected over a period of time is then used to calculate the gas flow in cm / cm. Min. of the hollow fibers according to the equation: J - V - g (A) (T) 25 where V is the volume of the collected gas, A is the internal surface area of the hollow fibers, determined by the equation A = nf dl, where n is the number of hollow fibers, d the inner diameter of the hollow fibers in cm, and 1 the fiber length in cm, and T is the time in minutes required to collect the gas.

The pores of the hollow, microporous fibers are interconnected mainly by serpentine webs, which can extend from one external surface or surface areas to other, i.e. open cells. The term "open cell structure" means that most of the void or 3000862 26 pore space within the geometric enclosures of the hollow fiber fins is accessible on the surfaces of the fiber walls.

Furthermore, the porous hollow fibers are microscopic, ie the details of the pore shape or placement are only described by microscopic examination. In fact, the open cells or pores in the fibers are smaller than those that can be measured using an ordinary light microscope, because the wavelength of visible light, which is about 0.5 Pm 10, is longer than the longest plane or surface size of the open cell or pore. However, the microporous hollow fibers can be determined using an electron microscope, which can dissolve pore structure details of less than 0.5 µm.

The open-cell, microporous, hollow fibers, manufactured in accordance with the present method, have an average pore size of 10 to 500 nm and usually 15 to 300 nm. These values were determined by the mercury porosometry, as described in an article by R.G. Quynn on the biz. 21-3, of "Textile Research Journal", January 1963. An electron micrograph of the fibers can also be taken, obtaining pore length and width measurements using an image analyzer or ruler for direct length measurement and width of its pores, usually at a magnification of 5000 to 12000 times, and size reduction to the correct size. Generally, the pore length values, which can be obtained with an electron microscope, are approximately equal to the pore size values, obtained by the mercury porosometry.

The present hollow microporous fibers are also characterized by a reduced mass density, which is hereinafter also simply referred to as low density. The mass density is also a measure of the increase in the porosity of the fibers. That is, such microporous hollow fibers have a total or mass density that is less than the mass density of corresponding provisional hollow fibers consisting of an equal poly-35 material, but not having an open-cell structure or 3000862 27 structure with other empty spaces. The term "mass density" means the unit weight of the gross or geometric volume of the fiber, the gross volume being determined by dipping a known weight of the fiber into a vessel partially filled with 25 ° mercury. C under atmospheric pressure.

The volumetric increase in the mercury level is a direct measure of the gross volume. This method is known as the mercury volumenometer method, and is described in "Encyclopedia of Chemical Technology", vol. p. 892, (Interscience, 19U9).

10 So the hollow, microporous fibers have a mass density of no more than 95? » and preferably ^ 0 to 85? of the preliminary fibers. In other words, is the mass density at least 5? and preferably 15 to 60? reduced. The mass density is also a measure of the porosity, because when the mass density Uo is up to 85? 15 of the preliminary fiber, the porosity has increased by 60 to 15? due to the pores or holes.

The final crystallization of the microporous hollow fibers is preferably at least 35, more particularly at least 5? and more generally 50 to 100, as determined by said 20 directly.

The hollow microporous fibers also have a breaking elongation (ASTM D-123-70) of not less than about 50 ?, and preferably not less than about 100 ?.

The surface area of the hollow, microporous fibers 25 has a surface area of at least 15 m / g, and preferably 20 to 60 m * Vg.

The surface area can be determined by adsorption isoterms of nitrogen gas or kriptone gas using the method and apparatus described in US patent 3,262,319. The surface obtained by this method. ... .2 the area is usually expressed in m per gram.

To facilitate the comparison of different materials, this value can be multiplied by the 3 mass density of the material m grams per cm resulting in •. 2 3 35 a surface area variable, expressed as m per cm.

'000862 28

The present microporous hollow polypropylene fibers have, in addition to good gas permeability, also a good liquid flow, and are suitable for a number of applications, such as a blood oxygen device, the superfiltration, the dialysis, the gamma-globulin separation from the blood, for the treatment of ascites, as well as a variety of other applications, using hollow microporous fibers. For certain uses, it may be desirable to render the usually hydrophobic, hollow, microporous fibers hydrophilic. This can be accomplished by any means known to those skilled in the art such as impregnating the pores of the fibers with an appropriate surfactant such as high molecular weight nonionic surfactants prepared by condensing. ethylene oxide with a hydrophobic base formed by the condensation of propylene oxide with propylene glycol. Other surface-active agents include the non-ionic surface-active agents, which are polyoxyalkylene derivatives of hexytol anhydride fatty acid esters with partially long-chain esters. The fibers may also be treated with sulfuric acid, chlorosulfonic acid, or other such fiber hydrophilic agents.

For using the hollow fibers for a blood oxygen device, bundles of hollow fibers containing the desired number of fibers can be prepared by applying an adhesive to each end of a gimp of parallel-positioned hollow fibers. The bundled fibers are then preferably inserted into an elongated, fluid-tight, tubular housing assembly formed of a suitable material, such as steel. Each end of the bundled fibers communicates with the exterior of the housing, with a means for sealing each end of the fiber bundle at the ends of the housing at the other end of the housing. So blood can be pumped through the hollow fibers. The tubular housing is further provided with valves opening into the interior of the housing and to the outer surface of each of the fibers in the bundles to provide a means for circulating oxygen gas around the hollow fibers. Although the fiber bundle must be packed as closely as possible, the bundle must be packed loosely enough to allow a gas to pass between the individual fibers and effectively surround each hollow fiber.

The oxygen gas can then pass through the outer walls of the hollow fibers, supplying the blood passing through the fiber with oxygen, carbon dioxide from the blood being passed through the hollow fiber.

Also, the oxygen gas can be passed to the center of the hollow fibers IQ, and the blood circulated through the housing so as to contact it with the exterior surface of the hollow fibers.

Instead of using a two-ended tubular housing with both ends open to allow the passage of blood, it is possible to use a permeator in which hollow fiber bundles are formed into a loop so that the ends of each the fibers both come out through the same opening in the tubular housing.

For a further clarification of devices where hollow fibers can be used to provide oxygen to the blood, reference is made to U.S. Pat. Nos. 2,972,333,373,876 and U,031,012.

The invention is further illustrated by reference to the following examples. All parts and percentages are by weight unless otherwise indicated.

EXAMPLE I

Isotactic polypropylene with a melt index of 5, one

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average molecular weight of 380,000 and 0.9 g / cm, was melt spun through a concentric, hollow, 5-hole jet spinneret. Each spinneret nozzle was of the conventional type with a tube in the opening, the tube being supplied from a source of low pressure air, which pressure was controlled by an air flow measuring device set at 3.8, which indicated a flow rate of 120 cm / min. The outer diameter> 000862 of each sprue extrusion (jet) was 1.391 mm, with the inner diameter of each extrusion opening being 0.772 mm. The diameter of the air tube in each extrusion opening was 0.332 mm. Moldings of the polypropylene were placed in a 1.9 cm extruder, and placed in the feeder thereof by gravity. The extruder was equipped with a metering pump to control the melting pressure of the spinneret assembly to provide a spinneret throughput of 23 g / min. The temperatures of the feed region, the metering and melting regions of the extruder were controlled by separate jacket sections. The temperature of the spinneret assembly was controlled by a separate electrically heated jacket, maintaining a constant extrusion, ie a spin temperature of 2k5 ° C, as indicated by a thermo-torque in the spinneret assembly. An adjustable feed take-up device collected the extruded fibers at a take-up speed (TUS) of 500 m / min. The hollow preliminary fibers were accordingly stretched with a stretch or spin ratio of 100: 1. The take-up roller was located 3 meters from the snip cap, extruding the extruded fibers by passing them through room temperature air, i.e. 25 ° C. The degree of alignment, as determined by the X-ray bending analysis, as described above was 16 °. The preliminary fibers showed an elongation recovery from a 50% elongation at a recovery time of 0, at 25 ° C and a relative moisture.

65%, 70%, an average wall diameter of 223 µm, an average inside diameter of 257 µm and an average wall thickness of 17 µm. The resulting fibers were then heated, followed by slow cooling to a constant length while still being wound around the take-up roll by placing it in an oven, and heating it to 100 ° C for 30 min.

Samples of the treated preliminary fibers were then subjected to different degrees of cold drawing at ambient temperatures, as shown in Table I, Runs 1-6, and then to different degrees of hot drawing at 100 ° C, as also shown in Table I, Tests 1-6. The? 0 0 0 8 6 2 31 stretching rate for so much hot stretching as cold stretching is also shown in Table I. Cold and hot stretching was accomplished using a conventional stretching frame, where the elevated temperatures during hot stretching were achieved by placing the stretching frame in a forced air oven. The hot stretched fibers were left in the oven for 30 min to achieve heat setting at the same temperature as used for hot stretching, ie 1l + 0 ° C. The fibers were kept at a constant length for heat curing through the stretching frame.

For Runs 7-10, the fabrication of the preliminary fiber sample was changed with respect to the spinning temperature, take-up speed, draw ratio, throughput speed and air flow meter setting, as shown in Table I. The degree of directionality (as determined by the X-ray bending analysis, as described above), of the preliminary fibers, as prepared in accordance with Runs 7 and 8, were 16 ° and for Runs 9 and 10, 22 °. The resilient recovery (ER) from a rack of 50 # at a recovery time of 0 for Runs 9 and 10 was 6k%. ER 20 for tests 7 and 8 was not determined. The degree of cold stretching and hot stretching, as well as the stretching speed, are also shown in Table I.

The heat-cured, microporous, hollow fibers thereby obtained were then surface examined by nitrogen absorption as described above, and also for oxygen flow. The oxygen flow was determined in the following manner.

Twenty of the hollow, microporous fibers of each Uo cm length test were previously placed parallel to each other in a bundle, and then looped so that the forty open ends of the fibers were flush and in a single plane layers.

The open ends of the fiber loop were then threaded through a short length (31.75 mm) hard plastic tube with an inner diameter of 3.2 mm. The fibers were then coated with epoxy-35 resin from 12.5 to 15 cm from the open fiber ends.

8000 862 32

The plastic tube was then slid down the resin coated portion so that about 5 cm of the uncoated fiber bundle protruded from the tube leaving the open end of the loop fiber bundle protruding from the tube. When the resin had cured, the open ends of the looped fiber bundle were trimmed flush with the plastic tube. However, in order to preserve the open circularity of the open fiber ends, the trimming was prepared by first dipping the fibers in liquid nitrogen, then dipping them in isopropyl alcohol before filling the interior thereof with liquid, dipping again. the fibers in liquid nitrogen for about 1.5 minutes before freezing the alcohol, and then placing it over a small wooden block, also dipped in the liquid nitrogen.

The open ends of the fibers could then be easily trimmed with a razor against the wood block and without any damage. The tubular fiber assembly was then sealed in a 6, 1, or 15.2 mm diameter adapter using epoxy resin, leaving a 6 inch section of the tube above the adapter. The epoxy planted fiber assembly 2q was then inserted into a copper tube 17.5 cm long and 9.5 mm in diameter, sealing the adapter with appropriate fittings. For easy access, a three-way T-fitting was attached to the free end of the copper tube (relative to the adapter), sealing one of the T-fitting exits.

One end of a rubber hose was attached to the open outlet of the T-fitting, the other end being inserted into an inverted graduated cylinder filled with water and dipped in a water bath. Oxygen gas was then passed through the open fiber ends through the fiber walls and collected in the graduated cylinder.

The gas pressure was first maintained at 3.5 kPa, then 69 kPa, 3 as shown in Table I. The gas flow (J) in cm / cm. Min.

δ was determined from the equation described above.

As can be seen from the results of Table I, oxygen permeabilities or flows greater than about 80 cm 2 / cm 2 / min 8000862 33 with hollow, microporous fibers can be produced according to the present process. Such pen permeabilities, after normalization to flow per ym fiber wall thickness, represent a significant improvement in the normalized gas permeabilities of micro-porous films in flow per ym film thickness, when such films are made in accordance with the cold stretch / hot stretch process of the U.S. Patent 3,801.UoU *

The normalized flow of the hollow, microporous fibers, for example, provided with an oxygen gas permeability 3 2 10 at 69 kPa of 82.9 cm / cm.min., Is obtained by dividing this permeability by the average fiber wall thickness of 15 µm to give of a normalized flow per ym fiber wall thickness of 5.5

Similarly, a microporous film made with the cold stretch / hot stretch process according to the

U.S. Pat. No. 3,8OI.U0U and having a film thickness of 3 about 25.5 µm, an oxygen gas flow of about µ cm / cm. min. When this gas flow is normalized for comparison with the normalized gas flow of the present hollow microporous fibers, a flow per µm film thickness of 1.73 is obtained. Similar comparisons can be made with tests 1-9 of Example I.

Thus, hollow microporous fibers can be made in accordance with the present process, which fibers have a normalized flow of about three times the normalized flow of microporous films produced by the process of the aforementioned U.S. Patent.

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Example I was repeated, except that the inner diameter of the preliminary fiber was reduced to below 100 µm as shown in Table II. The degree and stretching rate of the cold drawing and hot drawing, as well as the process variables are also summarized in Table II. It should be noted that the wall thickness of the microporous hollow fiber is believed to remain substantially unchanged and not measured empirically.

Tests 1-10 illustrate the reduced oxygen permeability obtained when the inner diameter of the preliminary fiber as an average is significantly below 100 µm, for example about 86 µm, compared to the gas permeability obtained in the tests of Example I under application of inner diameters of the preliminary fibers in excess of 1 ^ 0 µm. The largest oxygen flow obtained was only 10.1 cm / cm. Min.

Runs 7-10 show a significant reduction in gas permeability when the hot stretching step is omitted or the stretching ratio selected so that the degree of cold stretching is greater than the degree of hot stretching.

Runs 11-1U demonstrate unsuccessful attempts to improve the gas permeability of cold stretched fibers by relaxing 10 # (ie, runs 11 and 12) and relaxing with 10 # of the cold stretched fibers at a temperature of 130 ° C (i.e. tests 13 and 1U).

Runs 15-26 clarify the gas permeabilities achieved under varying process conditions using average inner diameters of the 110 µm preliminary fibers.

As can be seen, gas permeability is significantly reduced compared to the gas flow of preliminary fibers with the average inner diameters used in the tests of Example I.

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COMPARATIVE EXAMPLE II

Example I, Run 1 was repeated with respect to the manufacture of the preliminary fibers. Samples of the preliminary fibers were then heated, followed by slow cooling at 100 ° C for 30 minutes and a constant length, 1005 ° cold stretched at a stretching rate of 20 µ / min. and a temperature of 25 ° C and then heat cured at various temperatures of 100 ° C, 150 ° C, 150 ° C and 155 ° C for 30 minutes. When the temperature of the heat setting was equal to the heat treatment temperature, that is, 1 0 ° C, the fibers shrank and curled up. At a temperature of the heat curing slightly above the heat treatment temperature, i.e. 1 ^ 5 ° C, the fibers shrink to a lesser extent. When the heat setting temperature was 150 ° C or 155 ° C, no shrinkage was observed. When the time of heat curing used at 150 ° C and 155 ° C was significantly reduced below 30 minutes, shrinkage was again observed.

It is clear that changes and improvements can be made without departing from the scope of the invention.

8000882

Claims (8)

1. Process for manufacturing hollow, microporous, open-cell polypropylene fibers with an oxygen flow of al-3 2 currently 35 cm / cm. Min. at 69 kPa, characterized by melt spinning isotactic polypropylene with a melt index of at least 1 at a temperature of at least 230 ° C in such a way that hollow, non-porous, preliminary, polypropylene fibers are obtained, incorporating the preliminary fibers with a draw ratio of at least 1 * 0, wherein the melt spinning is carried out in such a way that the provisional fibers are given an average inner diameter of at least 1U0 ym after recording, furthermore an average inner diameter to average wall thickness ratio of 8: 1 to 1 * 0: 1, a degree of directivity, as determined by the half-width of a wide-angle (110) X-ray bending arc, of up to 25 ° and a resilient recovery from a 50 # rack at 25 ° C, 65 # relative humidity and a recovery time of 0, at least 50 #, heating, followed by slow cooling of the preliminary fibers at a temperature between 50 ° C and less than 165 ° C for 0.5 sec. up to 2l * hours, cold stretching the non-porous, preliminary, hollow fibers in the direction of their length at a temperature higher than the glass transition temperature of the preliminary fibers, and not higher than about 100 ° C for providing porous surface areas on the walls of the fibers perpendicular to the direction of cold stretching, hot stretching of the heated, followed by slowly cooled, cold stretched, hollow fibers in the same direction as cold stretching a temperature above that of the cold drawing and below the melting point of the polypropylene to provide an open cell, microporous shape to the hollow fiber walls, the degree of cold drawing and hot drawing being performed such that the average inner diameter of the obtained hot stretched hollow microporous fibers is controlled at least 100 µm, and a total degree of composite stretching is achieved from 80 to 200 #, further, a stretching ratio of 1: 3 to 1:20 and a stretching rate of 10 to 200 # / min, and heat-curing the resulting 8000862 rho hot stretched fibers under tensile stress to produce dimensionally stable, open-cell , hollow, microporous fibers with an average inner diameter of at least 100 µm. 2. A method according to claim 1, characterized in that the temperature of the melt spinning is between 21 ° C and 280 ° C, wherein the drawing ratio, with which the hollow, provisional fibers are incorporated, is at least about Uo, the average inner diameter of the hollow, provisional fibers after recording are controlled to between 1 ^ 0 ym and ^ 00 ym, cold stretching is carried out at a temperature between 15 ° C and 70 ° C, hot stretching is carried out at a temperature between 130 ° C and 1 ^ 5 ° C, the total degree of composite cold and hot stretching between 80 $ and 155? » and the stretch ratio is between 1: 3 and 1:10. 3. Method according to claim 1, characterized in that the temperature of the melt spinning is between 2 * 0 ° C and 250 ° C. h. A method according to claim 1, characterized in that the hot stretching and heat curing are combined into a single step by successively hot stretching the cold stretched hollow fibers in a number of separate stretching steps. PO *,. 5 · Process for the production of hollow, open-cell, microporous, polypropylene fibers with an oxygen flow 3 of at least 35 cm / cm .min. at 69 kPa, characterized by melt spinning isotactic polypropylene with a melt index of at least about 5 at a temperature of from 210 ° C to 280 ° C in such a way that hollow, non-porous, preliminary polypropylene fibers are obtained, including the hollow preliminary fibers with a draw ratio of UO to 100, wherein the melt spinning is also performed so that the preliminary fibers after incorporation provide an average inner diameter of 200 to 300 µm, further an average inner diameter to average wall thickness ratio of 10 : 1 to 30: 1, a degree of straightness, as determined by the half-width of a wide-angle (110) X-ray arc of up to 25 °, and a resilient recovery from a 50 # rack at 25 ° C , 65% relative humidity and a recovery time of 0, of at least 50 $, heating, followed by slow cooling 8000862 λ 1 * 1 of the hollow, preliminary fibers at a temperature between 130 ° C and 1U5 ° C g For about 30 minutes, cold stretching the non-porous hollow, provisional fibers in their longitudinal direction at a temperature between 15 ° C and 70 ° C, further stretching about 20? based on the original preliminary fiber length and a stretch rate of 10? up to 100? / min. for providing porous surface areas on the walls of the fibers perpendicular to the cold drawing direction, hot stretching the cold stretched hollow fibers in the same direction at a temperature between 130 ° C and 1 ^ 5 ° C, further at a stretch of 60% to 100? and a strain rate of 10? up to 100? / min to provide an open, microporous shape to the hollow fiber walls, and heat set the resulting hollow fibers under tensile stress at a temperature between 150 ° C and 160 ° C to produce sizes stable, open-like, hollow, microporous fibers with an average inner diameter of at least 100 µm. 6. Hollow, open-like, microporous, polypropylene fibers 3 2 with an oxygen flow of at least 35 cmJ / cm. Min. at 69 kPa, 20 characterized in that the fibers are produced by a process comprising melt spinning isotactic polypropylene with a melt index of at least 1 at a temperature of at least 230 ° C in such a way that hollow, non-porous, preliminary polypropylene fibers are obtained, further incorporating the provisional fibers 25 with a draw ratio of at least 1 * 0, the melt spinning being carried out such that the provisional fibers after incorporation are provided with an average inner diameter of at least 10 µm, further a average inner diameter to average wall thickness ratio of 8: 1 to 1 * 0: 1, a degree of straightness, as determined by the half width of a (110) X-ray arc of no more than 25 °, and a resilient recovery from a rack of 50? at 25 ° C, 65? relative humidity and a recovery time of at least 50? heating, followed by slow cooling of the preliminary fibers at a temperature between 50 ° C and less than 165 ° C for a time of 0.5 sec. up to 2h hours, cold stretching 8000862 h2 of the non-porous, hollow, provisional fibers in their longitudinal direction, at a temperature above the glass transition temperature of the provisional fibers and not above about 100 ° C to provide porosity surface areas on the walls 5 of the fibers, which are perpendicular to the direction of the cold stretching, the hot stretching of the heated, followed by slowly cooled, cold stretched, hollow fibers in the same direction as the cold stretching at a temperature above that of cold stretching and below the melting point of the polypropylene to provide an open-cell microporous shape to the hollow fiber walls, the degree of cold stretching and hot stretching being performed such that the average inner diameter of the obtained hot-stretched, hollow microporous fiber is controlled at at least 100 µm, and a total amount of composite stretching is achieved between $ 80 and $ 200, further, a stretching ratio of 1: 3 to 1:20 and a stretching rate of 10 $ to 200 $ / min., and heat-curing the resulting hot-stretched fibers under tensile stress to produce stable, open-cell, jolly fibers. microporous fibers with an average inner diameter of at least 20 100 µm. Blood oxygen device, characterized in that the hollow, open-celled, microporous, polypropylene fibers according to claim 6 are used therein. 8. Method substantially as described in description and shown in the drawing. 9 · Polypropylene fibers essentially as described in the description and examples. 8000862