FI70733B - MEMBRAN MED POROES YTA FOERFARANDE FOER DESS FRAMSTAELLNING OC DESS ANVAENDNING - Google Patents

Description

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(51) Kv.lk. * / Lnt.ci. * D 01 F 1/02, D 01 D 5/24 // C 08 J 5/22, B 01 D 13/04 g q | y | j FINLAND (21) Patent application Patentansökning 792365 (22) Application date - Ansökningsdag 27.07.79 (Fl) (23) Starting date - Giltighetsdag 27.07-79 (41) Published public - Blivit offentlig 01 .02.80

National Board of Patents and Registration Date of issue and publication. -. . ...

Patent and registration authorities Ansökan utlagd och utl.skriften published 26.06 .86 (86) Kv. application Int. ansökan (32) (33) (31) Privilege claimed - Begärd priority 31 .07-78,

31.07.78 Federal Republic of Germany1ta-Förbundsrepub-liken Tyskland (DE) P 2833493.2, P 2833623.4 Proven-StyrkL

(71) Akzo nv, Ijssellaan 82, Arnhem, Holland-Hoiland (NL) (72) Klaus Gerlach, Obernau, Erich Kessler, Höchst, Federal Republic of Germany-Förbundsrepub1iken Tyskland (DE) (74) Oy Kolster Ab (54) Porous film , its method of manufacture and its use -Membrane with porous coating, for use in the manufacture and use of air

The invention relates to films made of synthetic polymers, which may be in the form of films, hose films or hollow man-made fibers, to a process for their preparation and to their use, in particular as filters or film supports for separation purposes.

Films in the form of films, hose films or hollow fibers have long been known. Those skilled in the art are aware of several methods for making such films from a wide variety of polymers. Hollow fibers can be used in the manufacture of textile products or as aids in filtration, ultrafiltration, microfiltration, dialysis, reverse osmosis, etc.

If films, tubing membranes or hollow fibers are used for separation purposes, the permeability and selectivity of the membrane are crucial, as the membranes must first retain certain substances and pass through 2 7073 3 other substances such as solvent for solution as quickly as possible.

Films with a microporous or porous structure have long been known. Thus, for example, DE - AS 2 737 745 discloses a method for producing microporous or porous fibers. The products described are undoubtedly useful and have several uses.

After repeating the method described in the above-mentioned publication, it has been found that the films in question have a closed surface. In particular, it is not possible to obtain films with pores on both sides that appear directly as openings in the surface. Thus, there is a need for even better methods for producing porous films that simultaneously have good permeability and high selectivity, and have open pores on both surfaces and at the same time a smooth, uniform surface texture.

DE-AS 14 94 579 describes a process for the production of permeation-selective fiber fibers in which a homogeneous mixture of a thermoplastic polymer and a plasticizer is melt-spun and phemit is then extracted from the resulting hollow fiber. In this case, the requirement is e.g. the fact that the plasticizer can be removed from the spun hollow fiber easily and practically completely. Often, however, the fiber has to undergo a fairly long extraction and the plasticizer is not always completely removed. In addition, the hollow fibers obtained in this way have a rather low permeability. It is also not possible to vary the proportions of polymer and plasticizer within wide limits, because too high a plasticizer content does not produce fiber and too low a plasticizer content achieves too little permeability. There is still a risk that the plasticizer and the thermoplastic polymer are not mixed evenly enough and thus agglomeration can occur, causing holes and oversized pores in the extraction, which in turn prevents the use of hollow fibers for multiple purposes.

DE-AS 23 46 011 describes the preparation of hollow fibers by a process in which an acrylonitrile copolymer solution is spun in an aqueous solution of inorganic salts. In this case, the 70733 must be injected with the coagulant solution in order for the coagulation to take place inside. The method described is relatively complex and, moreover, it is difficult to produce hollow fibers whose quality properties remain constant.

U.S. Patent No. 3,674,628 discloses a method in which a solution of a fiber-forming polymer is first spun, then the outer and possibly also the inner zone is subjected to gel formation, and both zones are coagulated later or simultaneously. This creates a hollow fiber with a leaky structure inside and out. This process is also relatively complex and the permeability of the resulting hollow fiber can be desired.

Although numerous films, tubing films, and hollow fibers are known, there is a continuing need for better films, and especially those that can be made simply without complex spinning masses and spinning baths. There is a constant need for better films that are porous and at the same time have good permeability and high selectivity.

The present invention relates to porous films having an advantageous open surface structure compared to known films, in which both the outer and inner surfaces have open openings and nevertheless the surfaces are smooth. In addition, the invention provides films for use in textiles for both technical and medical purposes, such as separation processes, and in particular as filters, microfilters, film support substrates and attachment substrates for certain substances.

The method according to the invention makes it possible to produce films, hose films or air-ducted fibers from synthetic polymers which contain 10 to 90% by volume of interconnected pores and have a smooth surface with open pores, and the proportion of open pores in the surface is 10 to 90%. The apparent density of the hollow fibers is about 10-90% of the actual density of the polymer used, and the permeability coefficient of the air-ducted fibers is at least 10 .10 cm.

Membranes can be used as filters and especially as microfiltration filters.

The films according to the invention can also be used as support substrates for other films, for example by combining a second film with a possibly different permeability and different selectivity.

The films can also be used as adhesive substrates for other substances, for example by wetting them with certain substances which are to be disposed of later. They can also be used for oxidation purposes.

The invention thus provides a process by which polymers can be made into a compressible spinning mass in a simple manner and which allows the material to be simultaneously compressed and solidified without complicated spinning techniques and complex spinning baths. Furthermore, the invention provides a method in which only by changing the process parameters can the porosity, permeability or permeability of the films to be produced be controlled.

In the method of making hollow fibers according to the invention, a homogeneous mixture of at least two components, one component is a fusible polymer and the other component is a polymer-inert liquid, and both components form a binary system. at a temperature in a bath containing an inert liquid portion of the component mixture to be compressed, the temperature of which is below the discharge temperature of the compressed mixture, and the film solidifies in the form of a film, hose film or hollow fiber.

After solidification, the film formed can be washed as a solvent, preferably with acetone.

It is advantageous if there is an air gap between the outlet of the extruder and the surface of the bath. This air gap can be heated.

It is also possible to squeeze the homogeneous mixture directly into the bath.

In a particular embodiment of the method according to the invention, a temperature-stepped bath is used. In this case, the bath can be formed of one or more parts so that a continuously decreasing temperature gradient is formed from the beginning to the end of the spinning bath.

It is also possible to use two or more separate 5 70733 baths with different temperatures.

It has proven advantageous if the temperature of the bath is at least 100 ° C lower than the discharge temperature of the binary mixture used. Especially in the case of hose films and hollow fibers, the homogeneous mixture can first be pressed into a spinning tube separated from the bath filled with bath liquid.

According to the invention, homogeneous mixtures containing 10-90% by weight of polymer and 90-10% by weight of inert liquid can be compressed.

Preferably, polypropylene is used as the polymer and N, N-bis- (2-hydroxyethyl) hexadecylamine is used as the inert liquid.

It is expedient if both components, namely the molten polymer and the inert liquid, are continuously mixed together before compression, and preferably the mixing takes place immediately before compression. The mixture can be further homogenized before compression. A rod mixer is quite suitable for mixing.

Suitable for carrying out the process according to the invention and for preparing the films according to the invention are customary, in particular fiber-forming, macromolecular compounds and, in particular, polymers prepared, for example, by polymerisation, polyaddition or polycondensation, provided that the polymer is meltable without decomposition; a binary system with a liquid inert to it, which in the liquid state contains both a region of complete miscibility and a region of incomplete miscibility.

The phase diagram of such systems in the liquid state is, for example, in the form given in S. Glasstone Textbook of Physical Chemistry, Macmillian and Co. Ltd. St. Martin's Street, London, p. 724 shows an aniline-hexane system. Above the curved curve, this diagram shows the region of perfect miscibility of both components. Below the curve are two liquid phases in equilibrium with each other.

It is not absolutely necessary for the implementation of the invention that in the 2-phase region the components are still clearly soluble in one another, as is the case in the above-mentioned diagram. Usually 6 7 0 7 3 3 is sufficient if a limit solubility occurs in the 2-phase region. What is essential, however, is that in the liquid state, each component still forms its own immiscible liquid phase. The systems according to the invention thus differ from those in which the dissolved polymer separates directly as a solid when the temperature is lowered and is not yet in a liquid state.

Conventional meltable polymers such as polymers obtained by polymerization such as polyethylene, polypropylene, polyvinyl chloride and polycaprolactam, as well as corresponding copolymers and polycondensation polymers such as polyethylene terephthalate, polybutylene terephthalate polyethylene terephthalate, polyamide-6-terephthalate, polyamide-6, substances.

Suitable inert liquids for use in the process according to the invention are, in principle, all those which form a binary system with the polymer in the liquid state as described above. Inert to a polymer means that the liquid does not cause significant degradation of the polymer within a short period of time and does not react with the polymer.

Although the above-mentioned phase diagram essentially describes the behavior of pure aniline and hexane, it is not necessary to use completely pure substances in the binary system according to the invention. Those skilled in the art will recognize that polymeric materials are composed of molecules of different molecular weights, and thus, within the scope of the invention, such a polymer having a molecular weight distribution is considered a single component, and the same is true for copolymers. Under certain conditions, even polymer blends can behave like a single component, i.e. they form a single-phase mixture with an inert solvent which, below a critical temperature, separates into two separate liquid phases. However, it is preferred to use only one polymer.

Even a liquid does not have to be completely pure and consist of only one substance. It is often not detrimental if small amounts of impurities or homologous compounds are present which are necessarily formed in the technical manufacture.

70733

In the practice of the invention, a homogeneous mixture of both components is prepared at the required temperature.

This can be done by mixing the inert liquid with the comminuted polymer, heating to the desired temperature while taking care of the necessary mixing.

In another suitable procedure, each component is individually heated to the required temperature and continuously mixed together in the desired amount shortly before compression. Mixing can be performed in a device with a stir bar, suitably located between the dosing pumps of the individual components and the spinning pump. The included homogenization may be preferred.

It is very advantageous to deaerate the mixture with a suitable vacuum pump before pressing.

The ratio of the amount of polymer to the amount of inert liquid in the spinning mass can vary within wide limits. By adjusting the ratio of the amount of polymer to the amount of inert liquid, the size and number of pores inside and on the obtained film and the structure of the surfaces can be effectively controlled. In this way, it is possible to produce films suitable for a wide variety of purposes.

It is usually sufficient if the temperature of the homogeneous mixture before compression is only a few degrees above the critical temperature, i.e. the discharge temperature of the mixture in question.

If the difference between the homogeneous mixture to be compressed and the discharge temperature of the mixture is increased, interesting results for the structure of the films are also obtained.

The homogeneous spinning pulp is then pressed into a bath with an inert liquid contained in the pressed component mixture and at a temperature below the discharge temperature. Preferably, the bath contains exclusively or substantially the same inert liquid as the compressed mixture. The temperature of the bath is below the discharge temperature of the mixture used, i.e. below the temperature above which the two components mix homogeneously. Preferably, the bath temperature is at least 100 ° C below the discharge temperature of the mixture used.

The temperature can even be so low as to move in the phase diagram of the binary system in question in the region where one solid phase occurs.

If the temperature of the bath is so high that it moves in the area of two more liquid phases, the resulting well structure must be solidified immediately, and this is done by lowering the temperature of the bath at a certain distance.

The important point is that the compressed mixture is still in a single phase before it enters the bath, i.e. there has not yet been a substantial discharge into two phases.

Particularly in the manufacture of hose films and hollow fibers, it has proved advantageous if, in certain cases, a spinning tube filled with bath liquid is immersed in the bath. The mouth of the spinning tube may be in the shape of an ordinary funnel and may be curved at the bottom of the outlet end so as to facilitate the removal of the film through the bath.

The spinning tube can be filled by means of an overflow vessel around the spinning tube so that the overflow takes place in the spinning tube, but in order to completely fill the spinning tube and maintain the surface height it is necessary to bring more bath liquid The main tank and the overflow vessel can be thermostated.

After the spinning bath, the film can be washed with a suitable solvent. Suitable solvents include e.g. acetone, cyclohexane, ethanol and mixtures thereof.

It is not always necessary to wash the film, especially when the inert liquid used is necessary for the subsequent use of the fiber or gives it the necessary properties. Thus, for example, liquids which have an antistatic effect or which act as lubricants can be used.

In many cases, it has proved expedient if there is an air gap between the outlet of the press or the outlet of the required nozzle and the surface of the bath. By adjusting the air gap, the structure of the film to be manufactured, and in particular its surface, can be adjusted.

It has been found that the lengthening of the air gap reduces the number of open pores contained in the surface, while the shortening of the air gap increases their number and the diameter of the pores also decreases as the air gap increases.

70733 9

The air gap can be heated, for example, to a temperature higher than the discharge temperature of the compressed mixture.

In general, the air gap is at least 1 mm wide and can be up to about 10 cm long, depending on the working conditions. Importantly, in the case of an air gap, no or at least a significant separation into the two liquid phases occurs before entering the bath, but as said separation can be prevented by adjusting the length of the air gap, heating the air gap or accelerating the exit from the nozzle.

In a particular embodiment of the invention, the homogeneous mixture is introduced immediately into the bath so that pores of the largest possible diameter are formed on the surface.

The obtained membranes can well be used as filters. They are particularly suitable for microfiltration and ultrafiltration. The membranes are very well suited for medical purposes, for example for separating bacteria due to their selectivity, or for separating platelets, for example, in blood filtration. They are also very well suited for oxidation purposes, with oxygen flowing inside the membrane and blood flushing the membrane from the outside.

For many purposes, the films of the invention are suitable as support substrates for other films. Due to their very smooth, open-pore surface structure, they can be covered with a tightly adhering film-like material, which is usually done by applying or spraying the required film-forming solution. Due to the excellent surface properties, the film layer adheres very well to the film according to the invention. The cover solution forms a thin layer without penetrating or even dripping inside the hollow fiber, thus obtaining functional film combinations for a wide variety of purposes.

Due to their special surface and internal structure, the films are very suitable bonding substrates for certain materials. It is also possible to feed an active substance into the air channel of the hollow fiber.

In this way, films, hose films or hollow fibers or parts thereof which can slowly release the active ingredient they contain can be produced. The films of the invention can also act as adsorption media.

The thickness of the films according to the invention is conventionally varied

For example, I eat about 20 microns to a few millimeters.

The films can be either films or hose films. The films can be used as special agents, for example in thermal insulation or noise control.

According to the invention, hollow fibers with a wide range of dimensions can be produced. The outer diameter can be up to several millimeters and the wall thickness can vary within wide limits, for example between 20 μm and about 1-2 millimeters.

The shape of the pores of the films according to the invention can be as diverse as possible. They may be round or elongate and communicate with each other partly through small connecting openings and partly in such a way that they are directly connected to each other.

Even in films made from mixtures containing only about 30% polymer, the polymer can be in the form of a matrix in which the individual pores are distributed and form even more or less separate but interconnected openings. Conversely, structures can be created in which the pores are like felt and the polymeric material is distributed as if into fibers. There are innumerable intermediate forms of the two structures, and further modifications can be made, for example, by changing or pulling the exit rate or cooling rate below the nozzle.

Above all, the films according to the invention also have a high permeability to gases such as nitrogen and air. Permeability can be expressed by the so-called permeability coefficient K (cf. R.E. Collins, Flow of Fluids through Porous Materials,

Reinhold Publishing Corp., New York 1961, p. 10). K is defined by the following formula Q · Ί, - = K, where Q is the volume flow in units of time A (ΔΡ / h) (eg m ^ / s), 2 is the viscosity of the fluid (Pa.s), A is the average surface area , through which the gas escapes, Δ P is the pressure difference (Pa) and h is the wall thickness.

The films of the invention have a permeability coefficient of at least 10.10 cm, preferably at least 22.10 cm 70733 11 -12 2 and may even be more than 100.10 cm.

The coefficients of the films and hose membranes were determined by means of nitrogen, which was passed under pressure through a membrane attached to the flange. The air passing through the membrane is measured with a flow meter.

The films of the invention prepared from a mixture of 30% by weight of polypropylene and 70% by weight of NN-bis- (2-hydroxyethyl) hexadecylamine and having an air gap between the nozzle and the bath were obtained with the following values: -12 2 K (10 cm) air gap (mm) 52 5 27 10

In the case of hollow fibers, the measurement was as follows: 31 cm long hollow fibers are cast with two 5 cm long PVC hoses using a curable polyurethane mass. Once the polyurethane has cured, the second PVC hose is notched and the free openings are connected via a supply line to the nitrogen bottle and the end of the second hose is tightly closed with a plug. The air passing through the fibers is measured with a flow meter.

The following values were obtained for the hollow fibers according to the invention prepared from a mixture containing 30% by weight of polypropylene and 70% by weight of NN-bis- (2-hydroxyethyl) hexadecylamine and having an air gap between the nozzle and the bath: -12 2 H (10 cm) air gap (mm) 99 3 22 20

The hollow fibers according to the invention can also be used as insulators.

An apparatus suitable for producing the hollow fibers according to the invention is shown in Figure 1. The inert liquid is pumped from the thermostated tank 1 by means of a twin-piston pump 3 through the heater 4 to the mixer. Heater 2 acts as a preheater. The propylene crumb is fed from the crumb tank 5 via a helical extruder 6 and a gear pump 7 to a mixer 8, from which the gear pump 9 feeds the pulp to a hollow fiber-forming nozzle 10, 12 70733 to which the required amount of nitrogen is fed via a rotameter 17.

The outgoing mass enters through the air gap into a spinning tube 12 provided with a spinning funnel 11, to which an inert liquid from the main tank 14 is introduced in the overflow vessel 13. The lower end of the spinning tube is curved and the fibers are led from it 15 to the winding 16

The invention is illustrated by the following examples.

Example 1

The extruder melts polypropylene with a melt index of 1.5 g / 10 min at 260-280 ° C and is fed via a gear pump into an efficient rod mixer.

At the same time, NN-bis- (2-hydroxyethyl) hexadecylamine is metered into the above-mentioned mixer by means of a twin-piston pump in a flow-through heater preheated to 135 ° C via an insulated tube.

The ratio of polypropylene to amine is 30:70. The mixing speed is 400 rpm.

The mass homogeneous in the mixer is compressed with a gear pump at a rate of 15 g / min into a nozzle forming a hollow fiber with an inner diameter of 200 μm and a free ring gap of 400 μm. When nitrogen is introduced into the gas capillary of the nozzle at a rate of 4 1 / h, a hollow fiber is formed.

After 3 mm of free fall, the outgoing molten fiber penetrates into a spinning funnel filled with an anine bath and passes with the liquid through a spinning tube with a diameter of 8 mm and a length of 400 mm, and is wound at a speed of 7 m / min after a spinning bath of 1 m. flush device.

The amine is extracted from the hollow fibers obtained with alcohol.

The hollow fibers have a diameter of 2200 μm and a central cavity of 1400 μm.

Example 2

The polypropylene crumb is melted in an extruder and fed to a rod mixer by a gear pump.

At the same time, liquid NN-bis- (2-hydroxyethyl) hexadecylamine heated from 40 ° C to the storage tank is pumped by a twin-piston pump to an electrically heated heater and from there to a stirrer at about 150 ° C. This is a rod mixer.

13 70733

After homogenization, the molten mass is compressed via a metering pump into a slit nozzle and from there into a bath containing NN-bis- (2-hydroxyethyl) hexadecylamine at 50 ° C.

The film passes through a 50 m long bath and is then extracted with ethanol and dried. In this way, a film with a very good surface structure is obtained.

Claims (22)

70733 14 A method for producing a film in the form of a film, a hose film or a hollow fiber, characterized in that a homogeneous mixture of at least two components consists of a fusible polymer as one component and a liquid inert to the polymer as the other component, and both components form a binary system, which, in the liquid state, contains a region of complete miscibility and incomplete miscibility, is compressed at a temperature above the discharge temperature of the mixture in a bath containing an inert liquid of the component mixture to be compressed at a temperature below the discharge temperature of the compressed mixture, and the formed film is solidified; Process according to Claim 1, characterized in that the film formed is washed as a solvent after solidification. Method according to Claim 2, characterized in that acetone is used in the washing. Method according to one of Claims 1 to 3, characterized in that there is an air gap between the outlet of the press and the bath. Method according to Claim 4, characterized in that the air gap is heated. Process according to one of Claims 1 to 3, characterized in that the homogeneous mixture is pressed directly into the bath. Method according to one of Claims 1 to 5, characterized in that the temperature of the bath is at least 100 ° C below the discharge temperature of the binary mixture used. Method according to one of Claims 1 to 6, characterized in that the homogeneous mixture is first pressed into a spinning tube filled with bath liquid and connected to a bath. Process according to one of Claims 1 to 8, characterized in that polypropylene is used as the polymer. Process according to one of Claims 1 to 9, characterized in that Ν, Ν-bis- (2-hydroxyethyl) hexadecylamine is used as the inert liquid. 707 3 3 15 Method according to one of Claims 1 to 10, characterized in that a step-bath is used. Process according to one of Claims 1 to 11, characterized in that a homogeneous mixture is used which contains 10 to 90% by weight of polymer and 90 to 10% by weight of inert liquid. Method according to one of Claims 1 to 12, characterized in that the components are mixed together in a continuous stream before compression. Method according to Claim 13, characterized in that a rod stirrer is used for the mixing. 15. A film in the form of a film, hose film or hollow fiber made of a synthetic polymer, characterized in that it contains 10 to 90% by volume of interconnected pores and a smooth surface with open pores, the proportion of open pores being 10 to 90%, and prepared by compressing a homogeneous mixture of at least two components, one component being a fusible polymer and the other component being a polymer inert liquid, and wherein both components form a binary system in the liquid state containing complete miscibility and incomplete miscibility, at a temperature above the pour point of the bath containing an inert liquid portion of the compressible component mixture and having a temperature below the discharge temperature of the compressed mixture, and the formed film is solidified in the form of a film, hose film or hollow fiber. Film according to Claim 15, characterized in that it has an apparent density of 10 to 90% of the actual density of the polymer used. A film according to claim 15 or 16. . -12 t u bridge that its permeability coefficient is at least 10.10 2 cm. Use of a membrane according to any one of claims 15 to 17 as a filter. 16 70733 Use of a membrane according to any one of claims 15 to 17 as a filter in microfiltration. Use of a film according to any one of claims 15 to 17 as a support for other films. Use of a film according to any one of claims 15 to 17 as a carrier substrate. Use of a film according to any one of claims 15 to 17 for oxidation purposes. 17 70733