DE2833623A1 - Polypropylene membranes with porous surface - are used for filters, microfilters, membrane supports and as oxygenation agents - Google Patents

Abstract

Mfr. of membranes of a thermoplastic polymer contg. 10-90 vol. % pores in connection with each other comprises (A) extruding a homogeneous liq. mixt. consisting of at least 10-90 wt.% of a fusible polymer (I) and 90-10 wt.% of a pore-forming liq. (II) which is inert w.r.t. (I); (B) choosing the type and amt. of the inert liq. (II) such that (II) forms a binary system with (I) which in the liq. state has a region of complete miscibility and a region of incomplete miscibility of the components and which demixes into two phases at a temp. (the demixing temp.) below the extrusion temp.; (C) leading the extruded mass into a bath in which the bath liquor is below the demixing temp. and cooling such that the (II) and (I) demix into two co-existing liq. phases before the polymer (I) solidifies and (D) opt. washing (II) out of the solidified membrane with a solvent, such that the bath contains the same inert solvent, e.g. N,N-bis-(2-hydroxyethyl)hexadecylamine, as the extruded mixt. and the membrane, esp. formed from polypropylene and extruded in the form of flat film, tubular film or a hollow fibre, has a smooth surface with open pores occupying 10-90 % of the surface area.

Description

Foils

The invention relates to porous films and processes for their production and their use, in particular as a filter or membrane carrier for separation purposes.

Porous films have been known for a long time. Stand to the professional a number of processes are available, uin from a wide variety of polymers Manufacture foils. Porous films can be used in the manufacture of synthetic Leather used; But they are also used in filtration, ultrafiltration, Microfiltration, dialysis, reverse osmosis ~: -sw Are such films in separation devices used, the decisive factor is permeability and selectivity of the foils, because the foils acting as filters or membranes should on the one hand On the other hand, certain substances retain other substances, e.g. the solvent let a solution through as quickly as possible.

Films with a microporous or porous structure have been around for a long time known. For example, in DE-OS 2 737 745 processes for the production of films described, which have a porous or microporous structure. The ones described there Structures are undoubtedly valuable products that are used across a wide range of areas.

However, when reworking the teachings described there pointed out, that the films described there in general a closed Have surface. In particular, it is not possible to obtain foils that have pores on both sides, which act as openings directly on the surface to make noticable. There is therefore still a need for improved manufacturing methods, especially after those processes that lead to porous films that are carried out a good permeability with high selectivity at the same time and the in addition, have open pores on both surfaces and at the same time highlight with a smooth, even surface structure.

The object of the invention is therefore to provide a method to provide, in which polymers are extruded in a simpler manner into films that are porous and at the same time have openings; on the surface and nevertheless are smooth.

Another object of the invention is to provide a method set, which allows foils only by varying the process parameters with adjustable porosity, permeability or permeability. Further It is the object of the invention to provide porous films that are opposite each other distinguish the known foils by a favorable open surface structure, where both the lower and the upper side of the slide have an open Pores provided, but still has a smooth structure. Another object of the invention is To make films available that are suitable for both the production of synthetic Leather as well as in separation processes and can be used in particular as a filter, Microfilters, membrane carriers and suitable as a carrier substrate for certain substances.

This object is achieved by a method for making porous Dissolved films, which is characterized in that a homogeneous mixture of at least two components, one component being a meltable polymer and the other component is a liquid inert to the polymer and Both components form a binary system, which in the liquid state of aggregation is one Has an area of complete miscibility and an area with a miscibility gap a temperature above the separation temperature extruded into a bath that contains the inert liquid of the extruded component mixture and a temperature below the de-mixing temperature, and the film formed solidifies structure.

The film structure formed can after solidification with a Solvents are washed out, acetone in particular being suitable.

It is advantageous if one is between the exit surface of the extrusion tool and the surface of the bath maintains an air gap. This air gap can be heated will.

It is also possible to add the homogeneous mixture directly to the bath extrude.

In a special embodiment of the method according to the invention a temperature-graded bath is used. Included can take the bathroom off consist of one or more parts that have a temperature gradient such as that the temperature from the beginning of the spinning bath to the exit end is continuous decreases.

It is also possible to use two or more separate baths, each of which has a different temperature.

It has proven to be beneficial if the bath has a temperature which is at least 1000C lower than the demixing temperature of the binary used Composition. According to the invention, homogeneous mixtures of 10 to 90 wt.% Polymer and 90 to 10 weight percent inert liquid are extruded.

The preferred polymer is polypropylene and the inert liquid NN-bis (2-hydroxyethyl) hexadecylamine is used.

The two components, namely the melted one, are expedient Polymer and the inert liquid preferably continuously prior to extrusion mixed, whereby it is advantageous if the mixing is done immediately before the extrusion takes place. The mixture can still be used before extrusion. be homogenized. To the A pen mixer is particularly suitable for mixing.

The films according to the invention are characterized in that they 10 to 90 percent by volume of interconnected pores and a smooth1 Have open pore surface structure, with the proportion of open Pores in the area of 10 - 90%. The apparent density of the foils is approximately between 10 and 90 e of the true density of the polymer used; the permeability coefficient of the foils is greater than 10 ~ 10 1 cm .70'12 cm2.

The films can be used as filters, in particular as filters for microfiltration be used.

The foils can also serve as a membrane carrier, i.e. that on the Foils a layer is applied, which itself acts as a membrane.

The foils can also be used as a carrier substrate, i.e. the Slides can contain certain substances that are released at a later date should be soaked. They can also be used as oxygenators.

To carry out the method according to the invention and for the production of the films according to the invention can be conventional, in particular fiber-forming and film-forming macromolecular substances, especially synthetic polymers, are used e.g. by polymerization, polyaddition or polycondensation. pre-condition is that the polymer is meltable, i.e. in the liquid state of aggregation without Decomposition can pass over and become binary with a liquid that is inert towards it System forms, which in the liquid aggregate state an area of complete miscibility has and also in the liquid state of aggregation an area with Mischunc # owns gap.

Such systems have a phase diagram for the liquid state in the way, for example, in the Textbook of Physical Chemistry by S. Glasstone, Macmillian and Co. Ltd., St. Martins1s Street, London 1953 on page 724 for the System aniline hexane is reproduced. This diagram is for the both Components above the curved curve are completely miscible. Below on the curve, two liquid phases are in equilibrium with one another.

It is not absolutely necessary for the invention to be carried out that in the 2-phase range the two components each have a considerable solubility compared to the other components, like the one in the diagram above this is the case. In many cases it is sufficient if there is a solubility in the liquid 2-phase area is available. However, it is essential that the two components are in the liquid state still form two liquid phases side by side. In this respect, they differ Sysee, which can be used according to the invention from such systems, at dc; the dissolved polymer directly as a solid when the temperature is lowered fails without initially passing through a thin liquid state of aggregation during cooling.

Conventional meltable polymers can be used in the context of the invention like the polymers obtained by polymerisation, polyethylene, polypropylene, Polyvinyl chloride, polyacrylates, polycaprolactam and corresponding copolymers, among others; Polycondensation polymers such as polyethylene terephthalate, polyethylene terephthalate, polyamide-6.G, Polyphenylene oxide and polyaddition polymers such as polyurethanes and polyureas.

Preferably, according to the invention, polypropylene is used.

In principle, they are suitable as inert liquids within the scope of the invention all those liquids that are binary with the polymer in the liquid state Form a system of the type mentioned above. Inert to the polymer means that the liquid does not already exist within a short period of time a considerable degradation of the polymer causes or

reacts with the polymer itself.

Even if the above-mentioned state diagram of the aniline / hexane system reproduces the ratios for a binary mixture, which in and of itself consists of two consists essentially of pure, uniform substances, so should in the context of Invention of the term binary system does not strictly refer to mixtures of just two pure uniform substances are used. The average specialist knows that a polymer substance composed of a large number of molecules of different molecular weights is composed, therefore, such polymers are with a corresponding molecular weight distribution to be regarded as a component within the scope of the invention, the same also applies to Mixed polymers. Under certain circumstances, even polymer blends such as behave a uniform component, a single-phase mixture with an inert Solvent form and underhulb the critical temperature into two liquids Separate phases.

However, only one polymer is preferably used. The liquid too does not necessarily have to be completely pure and line completely uniform substance to represent. So it often does not harm, even if small amounts of impurities, possibly also proportions of homologous compounds, such as those produced by large-scale production are conditional, are present.

For the practical implementation of the process, the two components are used a homogeneous mixture is produced at the required temperatures. This can done in such a way that the inert liquid is mixed with the crushed r Polymer mixes and heated to appropriate temperatures, taking for an appropriate Mixing is ensured.

Another suitable method is that you aten the two scanpones Brings separately to the required temperature and the two components in the desired proportion only shortly before extrusion continuously with each other mixed. This mixing can take place in a pin mixer, which is arranged between the dosing pumps for the individual components and the spinning pump is. A subsequent homogenization can be recommended.

It is often advisable to create a homogeneous mixture by creating a Appropriate vent before extrusion. The ratio of polymer to inert liquid in the spinning mass can be varied within wide limits.

By adjusting the ratio of polymer to inert liquid can to a large extent the pore volume in the interior and also the surface structure how the number of open pores on the surfaces of the film obtained are controlled.

This means that they can be used for a wide variety of purposes Win slides.

In general, it is sufficient if the temperature of the homogeneous mixture before extrusion only a few degrees above the critical temperature or above corresponding to the demixing temperature in the respective composition.

By increasing the difference between the temperature of the homogeneous However, the mixture to be extruded and the demixing temperature can also be ' achieve interesting effects with regard to the structure of the films obtained.

The homogeneous mass is then extruded into a bath that the inert Contains liquid of the extruded component mixture and a temperature below the demixing temperature possesses. Preferably the bath consists entirely of or for the most part from the inert liquid that is also in the extruded mixture is available.

The temperature of the bath is below the demixing temperature of the binary mixture used, i.e. below the temperature above which the both components can be mixed completely homogeneously with one another. Preferably lies the temperature of the bath at least 100 ° C. below the separation temperature of the mixture used.

The temperature can also already be so low that one is accordingly the state diagram applicable to the binary system has already moved in the area #, in which a solid phase occurs.

the temperature of the bath is so high that one is still in the liquid If the 2-phase area moves, it is necessary to remove the foiisist structure as soon as possible to solidify, which can be done by following a certain distance decreases the temperature accordingly within the bath.

It is important that the extruded mixture, before it penetrates the bath, is still single-phase, i.e. that essentially no separation into two phases given is.

After it has gotten out of the bath - - the film can with a corresponding extractant washed out will. To extract are a number of solvents such as acetone, cyclohexanone, ethanol etc.

as well as mixtures of such liquids are suitable.

In some cases it is not necessary to wash off the film, especially if the inert liquid used is self-contained in the film for give certain additional properties to the later area of application or even themselves to perform a function ~. For example, liquids can be used which have an antistatic effect on the film or which act as lubricants works.

It has been found to be useful for a number of applications between the exit surface of the i: xtrusion tool, i.e. the exit surface for example a corresponding Slot nozzle and the surface an air gap is maintained in the bath. By varying the air gap it is possible to influence the structure of the film obtained, in particular its surface.

It has been found that by lengthening the air gap the number the open pores in the surface are reduced and increased by shortening it can be; the diameter of the pores also decreases as the air gap increases.

The air gap can be heated, vzw. to a temperature above the demixing temperature of the extruded mixer.

Generally, the air gap is at least about 1 mm wide and can Assume a length of up to 10 cm, depending on the working conditions. Important is, that in the air gap before entry into the bath none, or at least none noticeable Segregation occurs in two liquid phases, this can as said by the brevity the distance or can be controlled by heating, but it is also possible by Increase the exit speed at the nozzle to counteract premature segregation.

In a particular embodiment of the method according to the invention however, the homogeneous mixture is extruded directly into the bath, with the Surface open pores with maximum diameter arise.

The films obtained can be used particularly well as filters. The films are particularly suitable for the medical sector, where they are used, for example, because of their selectivity to Separation of bacteria during 'filtration of blood e.g.

can be used to separate blood platelets.

They are also very suitable as oxygenators where there is blood on one side the foil flows and the oxygen is supplied from the other side through the foil will.

The foils can also be used as membrane supports for a number of purposes be used. Due to their excellent surface structure with Open pores can be found extremely well with a firmly adhering one cover a thin layer of a material acting as a membrane, which is often caused by Coating or spraying with appropriate film-forming solutions occurs. Because of its excellent surface properties, the resulting adhesive adheres The membrane layer on the films is not only very good, but the coating solution do not allow the solution to penetrate or even drip through the inr.ere let alone comes up to the opposite side of the slide, a lot Apply evenly as a thin skin, so that very effective membranes for the most diverse Areas of application can be produced.

Due to their special surface structure and the structure in the Inside the foils, they are also ideally suited as a substrate for certain Substances.

So the foils can be soaked with antistatic agents that already be used or can be used as an inert liquid during extrusion only at a later point in time, after the film has been produced, by treating e.g. the agent can be introduced into the film structure by impregnation.

In this way, bodies with long-term effects can be obtained, which slowly release the absorbed substance.

The foils can also be used for the adsorption of substances P According to the invention, foils of usual dimensions are also available, for example a thickness from 20 microns to a few millimeters. The foils can be flat or round foils are present. The pores in the films according to the invention can be various Have shapes. So they can be round or elongated and stand together in connection, partly through small connecting cavities, partly because they are directly merge. Even with foils made from mixtures with a content of about 30% polymer has been obtained, the polymer can be the matrix in which the individual pores are distributed and still more or less discrete, but with one another Form connected cavities Conversely, structures can also arise in which The egg cavities form the matrix and the polymer substance, similar to nonwovens is arranged quasi-fibril-like. The transitions of these two structures are fluent and sometimes mixed; the structural forms can also be further Process parameters such as take-off speed, cooling speed, warpage can be influenced below the nozzle The foils can also be used as insulating material, e.g. used for heat insulation and sound insulation. You can also find in textile area, e.g. for lamination and in the technical area, e.g. as composite materials Mission.

The films according to the invention are also distinguished above all by a great permeability to gases such as nitrogen or air from the permeability can through the so-called Permeability coefficient K given as discussed in the book Flow of Fluids through Porous Materials by R.E. Collins published by Reinhold Publishing Corp., New York 1961, page 10 discussed in more detail will. K is defined as K = ~ -Q A, where Q is the volume flow in the unit of time A (4 P / h) (e.g. m³ / s), n the viscosity of the flowing medium (Pa A the mean Area through which the gas exits, #P the pressure difference (Pa) and h the wall thickness of the threads is The permeability coefficient of the films according to the invention is at least 10. 10-12 cm2, preferably at least 22 * 10-12 cm², values can be over 100 ~ 10-12 cm2 can be achieved.

The coefficient was measured with nitrogen under pressure is pressed against a film fastened in a flange. With the help of a flow meter is measured by the exiting air.

In the case of films according to the invention, which are composed of a mixture of 3G percent by weight Polypropylene and 70 wt.% NN-bis (2-hydroxyethyl) hexadecylamine and compliance with one The following values were found for the air gap between the nozzle and the bath become: K (10-12 cm2> air gap (mm) 52 5 27 10 The invention is explained in more detail by the following example: Polypropylene cuts are in melted in an extruder and metered into a pin mixer via a gear pump.

At the same time, liquid NN-bis- [2-hydroxyethyl) hexadecylimine is obtained from a heatable storage tank a temperature of 400 via a double piston pump into an electrically heated one Pumped heater and from there with a temperature of about 1500 into the mixer directed. A pin mixer is used as a mixer.

After homogenizing the two components, the melt is over a MeßpuInpe is pressed through a slot nozzle and extruded into a bath that consists of pure NN-bis- <2-hydroxyethyl) -hexadecylamine and that one temperature of 500.

After the film has passed through the bath, which has a length of 50 cm, the film obtained is extracted with ethanol and dried. It becomes a slide with excellent properties and a particularly good surface structure.

Claims (21)

A method for producing porous films, thereby characterized in that a homogeneous mixture of at least two components, wherein-the one component a fusible polymer and the other component an opposite the polymer is an inert liquid and both components form a binary system, that in the liquid state of aggregation an area of complete miscibility and an area with a miscibility gap, at a temperature above the demixing temperature A bath is extruded that contains the inert liquid of the extruded component mixture contains and has a temperature below the demixing temperature, and the formed Solidified film structure. 2. The method according to claim 1, characterized in that the formed film structure washes out with a solvent after solidification. 3. The method according to claim 2, characterized in that one for Wash out acetone used. 4. The method according to claim 1 to 3, characterized in that one between the exit surface of the extrusion tool and the surface of the bath Maintains the air gap. 5. The method according to claim 4, characterized in that the air gap is heated. 6. The method according to claims 1 to 3, characterized in that that the homogeneous mixture is extruded directly into the bath. 7. The method according to claims 1 to 6, characterized in that that the temperature of the bath is at least loooc below the demixing temperature of the binary system. 8. The method according to claims 1 to 7, characterized in that that the polymer used is polypropylene. 9. The method according to claims 1 to 8, characterized in that that the inert liquid used is NN-bis (2-hydroxyethyl) hexadecylamine. 1O.Method according to Claims 1 to 9, characterized in that that one uses a temp raturgestufenes bath. 11. The method according to claims 1 to 10, characterized in that that a homogeneous mixture of 10 to 90 weight percent polymer and 90 to 10 Weight percent inert liquid used. 12. The method according to claims i to 11, characterized in that that the two components are continuously mixed prior to extrusion. 13.Verfahren according to claim 12, characterized in that one for Mixing a pin mixer used. 14. Films made of synthetic polymers, characterized by 10 to 90 volume percent interconnected pores and a smooth, open Surface having pores, the proportion of openings in the area of 10 to 90%. 15. Films according to claim 14, characterized by an apparent Density from 10 to 90% of the true density of the polymer used. 16. Films according to claims 14 and 15, characterized by a Permeability coefficient of at least -10. 10 cm2. 17. Use of the films according to claims 1 to 16 as a filter. 18. Use of the films according to claims 1 to 17 as a filter for microfiltration. 19. Use of the films according to claims 1 to 16 as membrane supports. 20. Use of the films according to claims 1 to 16 as a carrier substrate. 21. Use of the films according to claims 1 to 16 as oxygenators.