DE2420846A1 - PROCESS FOR CASTING ULTRADUEN POLYMER MEMBRANES AND DEVICE FOR CARRYING OUT THE PROCESS - Google Patents

Description

Process for casting ultra-thin polymer membranes and apparatus for carrying out the process.

In US Pat. No. 3,580,841, in particular column 5, Line 54 »through column 6, line 29, are two methods of Manufacture of ultra-thin, semi-permeable membranes described. The first of these procedures is a concentrate The th solution of a polysaccharide polymer is poured onto a liquid surface and the solution is allowed to desolvate (In other words, the process of dissolving the polysaccharide polymer is left in the solvent used run in the opposite direction), with the

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Polymer membrane remains as a remainder. The membrane thickness (500-5000 Å) is expediently adjusted by regulating controlled by the concentration and viscosity of the casting solution and in some cases by manual spreading the solution. The second method is to slowly pull a clean sheet of glass out of a thinned one Solution of a polymer in a solvent. It is indicated that the speed with which the glass pulled out can be used to control the thickness of the membrane.

In US Pat. No. 3,767,737 there is a method for Manufacture of ultra-thin polymer membranes described, with continuous transfer of a polymer-containing casting solution through a carrier liquid, in which the casting solution is buoyant, up to the upper surface this carrier liquid, where the solution desolvates, the Film forms and is removed.

The thickness of the membrane produced by this process should be in the range of about 1300 8 (corresponding to 0.005 mil) to about 1000 feet (0.05 mil).

However, there is still a need for a reliable, reproducible method for making even thinner ones Polymer membranes having a large enough surface area for use in practical fields, and this need is met by the present invention.

Ultra-thin, non-porous membranes, larger in size

ο - 2

than about 0.1 m (corresponding to more than 1 US foot) are produced by the process of the invention in which the advancement of the anterior canters} of a spreading Layer of a casting solution over a liquid surface through the action of force in the form of a thick (bulk) liquid front happens, as a result of which the solvent content of this front is kept high enough to

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the front edges.). With the preferred Embodiment is water as the carrier liquid is used for the film and at least one movable barrier rod is used to control the spread of a Layer of casting solution over the water surface used.

The invention is described below with reference to Drawing explained in more detail. Show in detail:

Figure 1 is a plan view of a schematic representation of the apparatus for carrying out the invention Procedure,

FIG. 2 is an enlarged view of a cross section of FIG Figure 1 along the line 2-2 showing the mutual relationship between the initial concentration the polymer casting solution, a water surface and the locking bars shows when the The contact surfaces of the locking rods are hydrophobic,

Figure 3 is a schematic view similar to Figure 2 showing the desolvated film.

Figure 4k is a view similar to Figure 2, showing the mutual relationship between the parts mentioned under Figure 2 when the contact surfaces of the locking bars are hydrophilic, and

5 shows the figure 3i which represents a view similar to the arrangement of FIG k.

The film-forming material for use in the present invention generally includes any polymer or Copolymer, including polymer blends, graft polymers, block polymers, and interpolymers, which by

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Casting can be processed into substantially hole-free films using solvents. the Selecting a polymer as part of the molding system of the present invention requires that the polymer be in the The liquid carrying the film must not be soluble so that there is no strong swelling due to the liquid carrying the film Is subject to liquid and that it must be soluble in a solvent which has a boiling point of at least is about 100 ° C (equivalent to 212 ° F) and is immiscible with the liquid carrying the film.

The polymers used can be natural or synthetic substances. In the latter case, both Including addition and condensation polymers. It can be organic, inorganic or mixed organic and inorganic polymers can be used. Typical of the polymers that can be used are those that recur Have units selected from arylene ether, organosiloxane, aromatic carbonate, Alkyl acrylate or alkyl methacrylate units or mixtures of the aforementioned polymers as well as mixtures, graft polymers, Block polymers or interpolymers composed of such units.

Polymers of particular importance in the context of the present invention are those that

a) include repeating units, the bisphenol A carbonate units and dimethylsiloxane units, as well as those which have repeating units in alternating ones Include blocks of bisphenol A carbonate units and dimethylsiloxane units and

b) Mixtures of poly-2,6-dimethylphenylene oxide (hereinafter referred to as " ¹¹ PPO" for short) and organopolysiloxane-polycarbonate copolymers (as described above and in US Pat. No. 3,189,662). Organopolysiloxane-polycarbonate copolymers in which alternating blocks

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from repeating bisphenol A carbonate units and Repeating dimethylsiloxane units are present, can according to those described in US Pat. No. 3,119,662 Process and the materials obtained are alternating, random block polymers of the -ABABA type, in which the blocks are polydispersed:

Further information on the production of silicone-polycarbonate copolymers are contained in U.S. Patents 3,419 and 3,419,635. According to the US patent 3,367,978 manufacturable PPO / silicone copolymers are also useful film formers.

The weight average molecular weight of the polymers is in the range of 15,000 - 5,000 and n. and m are like that selected to maintain this range of molecular weight.

The solvent for the casting solution is selected from normally liquid, organic hydrocarbon compounds containing, for example, 1-10 carbon atoms, and compounds containing, for example, halogen, nitrogen, oxygen or sulfur atoms and mixtures of the aforementioned atoms and compounds. The solvent for any selected polymer casting system must, as already mentioned, be immiscible with the carrier liquid used and have a boiling point of at least about 100 ^° C. (corresponding to ^o y).

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The solvent chosen should be the polymer material can dissolve in an intermediate concentration, for example from about 3-10% by weight.

The preferred solvent for the organopolysiloxane / polycarbonate copolymer is 1,2,3-trichloropropane (hereinafter called TCP for short). The preferred solvent system for the blend of PPO and organopolysiloxane-polycarbonate copolymer is a mixture of equal volumes of TCP and 1,1,2,2-tetrachloroethane (hereinafter referred to as TCE called).

The preferred carrier liquid for the film is water, but mercury and various low melting point alloys such as those described in the US patent can also be used 3 4 ^ 5 231 can also be used.

Originally-perforated polymer films with a Fläehe of some 10 cm (corresponding to a few inches) with a thickness of about 250 - 5OO X prepared by simply depositing a drop of a polymer solution (eg. 3 - 6 wt -.% Silicone / polycarbonate copolymer in chloroform) on the edge of a water-filled petri dish about 10 cm (4 inches) in diameter, the drop rapidly spreading over the surface of the water, desolvating and forming a solid film. Membranes made in this way are easy to use for application to porous substrates. However, in order to construct practical gas separation devices, membranes greater than about 0.1 m in area (equivalent to more than 1 foot) are required.

An attempt was made to enlarge it and a narrow plexiglass trough was constructed which was thoroughly washed and coated with paraffin wax along its edges

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to make them hydrophobic. Then water that had been redistilled twice in quartz became used to fill the trough until the liquid surface rises to slightly above the edge of the trough was. Care was taken not to contaminate the water. Locks (bars, as shown in Figure 1) were carefully wiped clean and placed on the edges of the T * Oge, which they spanned, with the barriers spaced apart from each other (along with the sides of the trough) defined the desired film area. Immediately before the film was cast, the Stripped liquid surface three or four times with the barriers to remove any insoluble greasy To remove material or foam, slag or similar impurities (scums).

After properly preparing the water pad for the film, the membrane casting solution was applied to the surface applied by adding about a drop (corresponding to 0.0075 nil of a 5 weight percent solution) of a silicone / polycarbonate copolymer in TCP from a capillary pipette placed a few millimeters above the surface of the Water held, dropped. The volume of the casting solution was chosen because it had been previously determined that the correct volume of polymer would be applied to make a film of the correct thickness on the selected Area to deliver. The casting solution spread rapidly over the still water surface and covered it Area between the locks approximately 11.5 cm (equal to 4 1/2 inches) across the width of the Trough before the solvent with the low vapor pressure from the front edge of the advancing liquid front evaporated. The membrane obtained had

2 2

an area of about 155 cm (equivalent to 25 inches) with

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a thickness of about 250 Å. With different polymer concentrations other film thicknesses were also obtained.

Attempts to cast large-area membranes (about 0.09-0.18m, equivalent to 1-2 US-feet) by this method, however, proved unsuccessful, mainly because a series of drops of the casting solution had to be applied to the pure water surface in order to achieve this provide required polymer volume. Before the drips of the casting solution were applied, small patches of the water surface were sprinkled with clean talc in a number of locations which were believed to have been hit by the leading edge of the casting solution as it spread over the surface of the selected area. Usually immediately after the first drop of the casting solution had reached the surface of the water, the talc deposits were wiped away at increasing distances from the point at which the casting solution hit the water in the furthest corner of the open water surface. After the remainder of the casting solution was applied, it never expanded over the selected area, but created a thicker lens-like layer over only part of the selected area. There was no visible leading edge that caused the talc to move, and it is believed that a very thin (possibly a monomolecular layer) film must have spread over the free water surface very quickly, replacing, desolvating and desolating the talc The remaining casting solution was blocked from entering the area occupied by it. Since the solvent TCP used is a relatively non-volatile solvent, this behavior was considered to be an inherent limitation and the process of the invention and the casting apparatus for carrying out this process were then developed on a relatively large scale .

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The apparatus 10 according to the invention shown in FIG. 1 includes a trough 11 and the locking rods 12 and 13 a. In the preferred embodiment the trough is 11 coated with a material that makes its surface hydrophobic, e.g. a coating made of polytetrafluoroethylene. The selected trough dimensions were 80 cm χ 35 cm, but troughs with larger dimensions, especially in the direction of the locking bars. In the one shown in Figures 2 and 3 Arrangement were the locking rods 12 and 13, which have a cross-sectional area of about 0.36 cm (corresponding to 1/4 inch) coated with polytetrafluoroethylene. In the The arrangements shown in Figures 4 and 5 were the ones used Lock pure brass rods with a cross-sectional

p O

Area of about 0.36 cm (corresponding to 1 / k inch). Both types of barrier rods work, but the uniformity of the film obtained with the hydrophobic rod surfaces is somewhat better.

The trough 11 was filled with water to slightly above the edge.

water that was relatively free of surfactants and particulate matter, and the barriers 12 and 13 were wiped across the surface of the liquid to ensure that all contaminants were removed were present on the surface of the water. In the The arrangement shown, the locks 12 and 13 are placed at an end piece of the trough 11 on its edge and they have a distance of about 1 cm from each other and thus form the storage area l4, in which the casting solution are received should, as will be described in more detail below. Is the casting solution l6 carefully in the storage place I ^, the durch.die hydrophobized surfaces is limited, introduced has been (e.g., dropwise), then the solution 16 floats on the water 17 and enters the wells 12a and 13a, which are formed by the convex meniscus of the water between the barriers (see FIG. 2). is

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the storage space l4 is limited by hydrophilic surfaces (the brass locking rods 21 and 22 in figure * t), then the solution 23 remains in the depression formed by the concave meniscus shown.

Care is taken to ensure that storage location l * fc is not overloaded. If too much casting solution has been introduced into place Ik , the casting solution will leak at the distal ends of the recess. The amount of casting solution that can be added without overloading is not critical. For example, in the case of silicone / polycarbonate copolymers, three times the volume calculated for film formation can be added before overflow occurs. The total volume of the solution which is introduced into the storage space 14 depends on the concentration of the polymer solution and the area and thickness of the film desired, with the restriction, of course, that this area is not overloaded. A convenient way of introducing the casting solution is by using an injection or subcutaneous syringe or an appropriate dropper device. This method allows for excellent control of the delivery, with the maximum acceptable volume easily determined.

Thereafter, the locking rod 12 is pulled away from the locking rod 13 towards the opposite end of the trough 11, but it remains substantially parallel to the locking rod 13, whereby the spreading of the casting solution to a substantially uniform thickness is possible and an ultra-thin film 18 which after desolvation has a thickness in the range of about 250 to 500 Å. In this way, ultra-thin membranes are made, their surface areas

are considerably larger than 0.1 m (equivalent to 1 US foot ² ).

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As shown in Figure 3, the casting solution increases during the formation of the film l8 from the recesses 12 a and 13a and moves from the more central region of the bearing surface away lk. All films are allowed to completely desolvate (ie, for at least about 2 minutes) before attempting to transfer the films to support substrate materials such as microporous polypropylene.

The procedure is the same for the arrangement of Figures 4 and 5 · Seems with both types of locking bars the critical effect of being that the advancing front of the casting solution is confined to a mass of liquid is who has no way of being an uncontrolled, rapidly moving, and rapidly desolvating to form monomolecular film in front of the advancing front.

If so desired, the water level need not rise above the edges of the trough. With such a Arrangement, however, the locking rods must have a configuration in which they are inserted into the trough in order to be able to hold them in in the same way relative to the surface of the liquid (inserting it deeper into the liquid than the Meniscus) so that they are effective. The cross-sectional shape the locking bars do not seem to be critical.

After the solvent evaporates from the resulting thin, substantially uniform layer of the casting solution the fully desolvated film will appear clear and black and / or slightly gray in color after going through a series of color changes, which ranged from purple, blue, red, yellow, silver to gray. The loss of color (becoming black) occurs after the thickness of the film has been reduced to a point where interference patterns no longer exist in the film generated by the reflected white light.

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Having once a certain amount of film-forming Solution was arranged between the locks, it is only necessary to these locks relative to each other to form film 18 (or film 24). This movement can be manual or mechanical can be carried out and one or both locking rods can be moved. The maximum speed the movement can easily be determined for the casting solution used in the individual case, but is one slow movement of the locking rods preferred, provided that the film has spread over the desired area before the evaporation of the solvent entry. The movement of the barriers happens too quickly if the polymer casting solution is not adjacent to the barrier can stay. The viscosity of the casting solution should be low enough to allow for even spreading of the Ensure casting solution during the separation of the locking bars. The concentration of the polymer in the casting solution must be high enough to provide sufficient strength of the desolvated film so that this can be handled. The maximum speed for the separation of the locking bars is for the preferred, polymer casting solutions described in the examples below at about 4.3 cm / sec.

The removal of the film from the surface of the film forming The easiest solution is through a vacuum pick-up on a microporous surface, which acts as a substrate to serve for the film or laminate thereof. An apparatus, not shown, for film recording in its simplest form consists of a closed chamber with a porous wall (e.g. sintered metal particles) of at least the size of the film area to be recorded. The chamber is evacuated after the porous wall with a layer of microporous substrate

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(e.g., microporous polypropylene from Celanese Plastics Company, available under the trade name Celgard, or the ultrafiltration membrane available under the trade name Millipore ^ - ^ or the Selectron membrane filter) and the substrate is brought into contact with the desolvated film. In this way 80-90 % of the solidified film can be taken up. The subsequent layers of film can be picked up in the same way, with each new layer adhering to the one applied earlier. Gas bubbles trapped between the layers are not a problem since the gas is gradually withdrawn due to the permeability and the film adjusts itself by shrinking as the gas escapes.

Hole-free films with surface areas of at least approximately 42 χ 77 inches (109 by 196 cm) can be used be produced by the process according to the invention. A film is free of holes if it is examined for penetration with two different gases (e.g. oxygen, Nitrogen) shows a separation factor (i.e. the ratio of oxygen to nitrogen permeability), which is at least as large as that for the thick material from which the film is made,

The main advantage of being able to produce such very thin non-perforated films is that it can be used to produce a composite, multi-layered, non-perforated film which is stronger because there is a greater degree of molecular orientation in these thinner films / Polycarbonate copolymers arranged on top of each other sia.d ₃ then they become one unit. These layered films appear to have a thickness variation that is about 30% smaller, as they appear in an icy cast film """".

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-Ik-

It should be recognized that no attempt is made to incorporate the casting solution in the formation of the film active way of stretching or stretching. Control of the advancing front is through the use the barrier is active, but the progression of the casting solution is passive and depends on the surface-active Properties of the solution.

The invention is explained in more detail below with the aid of examples explains:

example 1

0.08 ml of a casting solution containing 4% by weight of organopolysiloxane-polycarbonate (60 % SiO (CH 2) _o and 20 SiO (CH _{2) o} units

J ä> J ^

per block) copolymer in TCP was introduced dropwise into the storage area between barrier bars with hydrophobic surfaces. The water level extended over the height of the edge of the 80 χ 35 cm large trough. The spaced locking bars were placed in the center of the trough length and they were both moved away from each other by mechanical means and at a speed of 4.3 cm / sec. up to a total separation of the barriers of 37 cm. The film was allowed to completely desolvate and divided into three triangular areas. A 47 mm diameter film sample was taken from each area and formed into a laminate over a microporous substrate (Selectron B-13 membrane filter from Schleicher and Schuell Inc., Keene, NH). The laminate was rated for oxygen and nitrogen permeability at about 3.5 (corresponding to 50 pounds / inch) and about 7 kg / cm (corresponding to 100 pounds / inch) un- ■t@T8VLGh.ii, and therefore, in both cases lockfrei uiad Iiatte s $ ä £ resulted within experimental Meßgenauigksit the same Tremifaktor 2, l6 as for the copolymer in the form of thicker "the FII consisting of the three laminate TRAR the base, the BnrehlassigkeitsssegiSimgem erreefe-

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Total thickness less than about 930 A. Example 2

The procedure of Example 1 was repeated using the same materials. In this case, too, the laminate was found to be hole-free and, based on the permeability measurements, had a calculated total thickness for the three "films of less than about 1130 Si.

Example 3

Initial studies using the drop test on water in a petri dish indicated that a casting solution containing 2.5 wt. 96 PPO in chloroform would not lead to usable films VoI "-% added, excellent films were obtained" Using the apparatus used in Example 1, larger films were then produced. The casting solution contained k % by weight of polymer (PPO + 20% by weight of the organopolysiloxane-polycarbonate copolymer described in Example 1) in equal amounts of TCP and TCE. Two layers of the produced film were added to a laminate of three layers of organopolysiloxane-polycarbonate copolymer supported on a Selectron B-13 substrate layer. The total thickness of the two PPQ films was found to be less than about 162O Si based on permeability measurements. The separation factor found showed that a pinhole-free composite film had been obtained.

Films were also made with the 4% strength by weight organopolysiloxane-polycarbonate casting solution of Example 1 using brass locking bars. It was

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who received very good films, but which did not refer to the Diclce un.i
were scanned.

on the Diclce and the O ₀ and N permeability

£ λ dt

An unusual quality of ultra-dark films that from a pouring solution iroa PPO + approx. 20 Gevf «-% of the above Silicone / polycarboxylate copolymers it is that the 0 - / M separation factor for this film was the same as for -PPO alone. this is not the case if, from the same polymer blend thick films are cast »In thick films the separation factor is lower than for PPO alone. This The phenomenon could not yet be explained.

The films made according to the invention, individually or in layers that are in the right way on a microporous Substrate are used in G & stremi = and reverse rosebaose devices.

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Claims (8)

Claims / 1.! Process for making ultra-thin polymer films
V- / by pouring using solvents, characterized by the following Stages: a) Preparing a casting solution from a polymer material that is essentially free of holes
Film can be cast, b) applying a quantity of this casting solution between a pair of relatively movable, longitudinally extending locks, these locks being so supported are that they span the surface of a liquid carrying the film and are in contact therewith are located, the polymer material being insoluble in the liquid carrying the film is and does not swell due to this and the solvent system is insoluble for the casting solution in the liquid carrying the film, c) relative separation of the barriers from one another in order to control the said amount of casting solution
to expand over the surface of the film-carrying liquid in a predetermined area and to cover this, d) Desolvate — allowing the casting solution to form a solid film of the polymeric material carried on the surface of the carrier liquid for the film. 2. The method according to claim i, characterized g e k'e η η. ζ e i chsie t that the film-bearing Liquid is water. 409847/1051 - Io - 3 »Method according to claim 1 or 2, characterized in that the polymer material an organopolysiloxane-polycarborate copolymer or a mixture of poly-2,6-dimethylphenylene oxide and an organopolysiloxane-polycarbonate copolymer. 4. The method according to claims 1 to 3 »thereby ge Ic en denotes that the connection between each part of the said locks that are rise from the film-bearing liquid, which has the shape of a convex meniscus. 5 · Process according to Claims 1 to 3> thereby marked that the connection between each part of the locks that differ from the film-bearing liquid that has the shape of a concave meniscus. 6. The method according to claims 1 to 5 »characterized in that the separation of the Locking is done manually. 7. apparatus for casting ultra-thin polymer films using solvents on a liquid surface, in which the liquid is enclosed in a container and the casting solution on top of it Surface, characterized by a pair of longitudinally extending solid locking parts, the locking parts being supported by the rim of the container and relative to one another movable in combination with the container are. 409847/1051 8. Apparatus according to "claim 7 , characterized in that the surfaces d © r walls of the container are hydrophobic» 9ο apparatus according to claims 7 or 8, dad ur ch e g ke nn ζ Eich t, that the surfaces of the locking parts are hydrophobic " 409847/1 051