EP0911432A2 - Production process of composite fibres and diaphragms - Google Patents

Abstract

Composite fibers (I) are prepared by heating a mixture of a PTFE or PTFE-copolymer-dispersion or powder with a fine particulate inorganic material and a fiber forming material with stirring such that the PTFE or PTFE copolymer becomes capable of flow but does not decompose and the dispersing agent is removed (in the case of a dispersion) and shearing the mixture in a mixer having a Froude number of more than 1. An Independent claim is included for a process for the production of a diaphragm by addition of (I) to a solution containing water and a thickening agent; filtering of the mixture with suction over a porous support to layer the composite fiber (I); drying of the coated porous support and heating at 90-390 degrees C.

Description

The invention relates to a method for producing composite fibers and Diaphragms, such as those used in chlor-alkali electrolysis Find.

In addition to the mercury process, the diaphragm process also has Production of caustic soda and chlorine from sodium chloride a large Meaning. In the diaphragm process, an anode and cathode compartment separated by a porous diaphragm. An aqueous sodium chloride solution flows from the anode compartment through the diaphragm into the cathode compartment, where Hydrogen is generated on a steel cathode while a catholyte coexists contains sodium hydroxide and sodium chloride. That on the anode developed chlorine is obtained in gaseous form. Modern diaphragm cells work with adjustable, activated titanium anodes and with plastic fibers condensed diaphragms, which are increasingly being used instead of those previously used Asbestos diaphragms are inserted.

The diaphragms consist of an organic framework Polymer fibers in which inorganic materials are incorporated. Various Process for the production of such diaphragms or for the production the composite materials used are known.

In US 4,680,101 is a process for the production of diaphragms in which a dispersion of polytetrafluoroethylene (PTFE) fibrils, Polypropylene fibers and a perfluorinated ion exchange material in Water mixed and applied to a perforated steel plate cathode which is covered with a cellulose filter paper. After removing the The diaphragm becomes volatile at a temperature of 120 ° C to Dried 130 ° C and after cooling with a solution of partially hydrolyzed Impregnated silicon alkoxide and zirconium alkoxide. Then it will Diaphragm again dried.

EP-B-0 196 317 describes a process for the production of fiber composite materials described, in which a PTFE dispersion with zirconium dioxide and salt is mixed in a ball mill and heated, the Dispersant initially escapes. After mixing, the result is obtained Product separated from the balls used. It will be irregular Shaped, partially branched fibers obtained from a composite the PTFE used and the fine-particle zirconium dioxide. Of the second inorganic substance, table salt, serves as an aid for fiber formation and can be released by the brine before or during subsequent use become. A diaphragm can then be made from the fibers obtained getting produced. The diaphragms obtained by the known methods do not always show the desired high flow resistance, the one Back mixing of the sodium hydroxide solution obtained in the electrolysis prevented. The diaphragms obtained are therefore not suitable for all applications sufficient quality.

For the production of fibers from which diaphragms are used for chlor-alkali electrolysis not all of the above are suitable Process variants. For the production of diaphragms that are in not all branched can be used for chlor-alkali electrolysis Fiber are used. The diaphragms obtained from the fiber show does not always have a required defined flow resistance.

The flow resistance of the diaphragms determines the flow of brine through the diaphragm. The flow also depends on the pressure with which the brine is pressed through the diaphragm. In practice, the pressure is regulated by the difference in level between the incoming brine and the outgoing catholyte. Suitable values are, for example, between 20 and 70 cm liquid column. This flow in turn has a direct effect on the concentration of the lye produced. In addition, the optimal flow depends on the current density applied. The concentration of the lye obtained should be in the range from 100 to 150 g / l. In practice, for example, flow rates of 20-30 l / m ² h and current densities of 2 to 2.5 kA / m ^{2 are used} .

The use of a ball mill in the manufacture of the fibers leads to Problems due to incomplete removal of the contained in the dispersion Water. The incomplete removal of the water can cause it to rust of the steel balls used, referring to the rust roughened surfaces of the steel balls fixes PTFE, causing none sufficient fiber formation is achieved. To work around this problem need to mix and dry the raw materials in other devices be performed. This makes the process complex. In addition, at the end of the grinding process in the ball mill, the ones used Balls are separated again to win the fibers. This Separation step is complex. It can be done, for example, by sieving.

The object of the present invention is to provide a method for Production of such composite fibers, which is the production of diaphragms allow with a defined flow resistance, so that the technical Requirements in a chlor-alkali electrolysis cell are met.

(a) Vermischen einer PTFE- oder PTFE-Copolymer-Dispersion oder eines PTFE- oder PTFE-Copolymer-Pulvers mit einem feinteiligen anorganischen Material und einem faserbildenden Material,

(b) Erhitzen des erhaltenen Gemisches unter Scherung auf eine Temperatur, bei der das PTFE- oder PTFE-Copolymer unter Scherung fließfähig ist, aber keine Zersetzung zeigt, unter Entfernung des Dispergiermittels, sofern eine PTFE- oder PTFE-Copolymer-Dispersion eingesetzt wird,

(c) Abkühlen des Gemisches auf eine Temperatur unterhalb von 70°C,

(d) Scheren des Gemisches unter Mischen bei einer Temperatur unterhalb von 70°C zur Bildung der Kompositfasern.

The object is achieved according to the invention by a method for producing composite fibers

(a) mixing a PTFE or PTFE copolymer dispersion or a PTFE or PTFE copolymer powder with a finely divided inorganic material and a fiber-forming material,

(b) heating the mixture obtained under shear to a temperature at which the PTFE or PTFE copolymer is flowable under shear but shows no decomposition, with removal of the dispersant, if a PTFE or PTFE copolymer dispersion is used,

(c) cooling the mixture to a temperature below 70 ° C,

(d) shearing the mixture with mixing at a temperature below 70 ° C to form the composite fibers.

It was found according to the invention that by shearing the mixture PTFE or PTFE copolymer, fine-particle inorganic material and fiber-forming material, in particular at a temperature of less than 70 ° C fibers are obtained which are used to manufacture improved diaphragms allow with a defined flow resistance.

Preferably, the heating in step (b) is at a temperature of more than 70 ° C, particularly preferably more than 100 ° C, in particular 130-180 ° C carried out. Coarse, strong clumps of fiber are already formed. The cooling in step (c) and the shearing in step (d) take place preferably at a temperature in the range of 20-60 ° C. At work at a lower temperature in step (d) the mixing and shearing difficult due to the higher rigidity of the material. In this step the material is shredded and separated too freely flowing fibers.

It has also been found according to the invention that the shearing of the mixture in step (d) advantageous in mixers with a Froude number of more than 1 is carried out. To do this, mixers must be used in this step, that have a Froude number of more than 1. In this case, the Cooling in step (c) or (d) are dispensed with.

The Froude number represents a measure of the intensity of the mixing and is defined as the Froude number Fr = r 2nd /G With ù = 2 · f ; f = frequency, r = radius, g = gravity. The frequency is determined from the speed of the mixing tools. The radius is the greatest distance between the mixing tool and the shaft.

Examples of suitable mixers are Eirich mixers, ring trough mixers, ring layer mixers, DRAIS mixer. Also the use of a Lödige mixer, which is equipped with additional chopper, resulting in Froude numbers of more than 1 can be achieved. Is particularly preferred an Eirich mixer is used as the intensive mixer, which characterizes it is that it has a rotating mixing tank and either the same or counter-rotating mixing tool (swirler). The mixing tool can reach a very high speed of more than 2000 rpm. Both Mixing tools are whisk or stirrer-like Tools that can have diverse geometric shapes and for one good mixing and the entry of a high mixing energy. By a wall scraper prevents material from sticking to the wall. Eirich intensive mixers are from the Gustav Eirich machine factory in Hardheim, Germany available.

The method can preferably also be carried out in a heatable vacuum mixer be performed. There are vacuum mixers e.g. by Eirich. These mixers work according to the so-called EVACTHERM® process (from Eirich).

The mixing material is heated in these mixers with steam or with Superheated steam that is directed directly to the mix and through the Jacket heating of the mixer. The temperature of the jacket, also with Steam is heated, can be controlled via pressure or negative pressure. Of the A particular advantage of these mixers is the possibility of rapid cooling of the content. By injecting water and then evacuating the mixer contents to the desired temperature (<70 ° C) are cooled.

The invention also relates to the use of such mixers with a Froude number of more than 1 in the manufacture of composite fibers.

Common mixers such as Brabender mixers, Banbury mixers and Houbart mixers or ball mills do not achieve a Froude number of more than 1. Ball mills in particular still have the disadvantages mentioned at the outset.

The process according to the invention gives fibers which are dry and are free flowing. This is done particularly by using the intensive mixers reached in step (d). The above are particularly preferred Intensive mixer also used in step (b) of the method according to the invention. In particular, all steps of the method according to the invention are described in the same intensive mixer performed so that a transfer during the The procedure does not apply. The fibers obtained, which are dry and free flowing, can be easily removed from the mixer. In contrast to ball mills there is also no need to separate the balls from the fibers. Due to the multi-stage design of the process, especially drying and Fiber formation at high temperatures and fiber shredding at lower ones Temperatures can influence the properties of the fibers be taken, which makes it possible to adjust the flow resistance of the diaphragms made from it can adjust.

The PTFE or PTFE copolymer dispersion in step (a) is preferred used as an aqueous dispersion. After mixing with the finely divided inorganic material and the fiber-forming material in step (b) by removing the dispersant, preferably water, and fiber formation initiated by the shear. After cooling the Mixtures in step (c) in step (d) the fibers are finished by crushing, whereby the free-flowing fiber material according to the invention is obtained.

An alkali or alkaline earth salt is preferably used as the fiber-forming material used. These are preferably alkali or alkaline earth halides. Table salt (sodium chloride), magnesium chloride, Calcium chloride or sodium carbonate, especially sodium chloride used. The particle size should preferably be 90% (based on the weight) less than 300 µm, preferably less than 200 µm, particularly preferably be less than 100 microns. A typical preferred particle size distribution is as follows: 10% <5 µm, 50% <40 µm, 90% <80 µm.

10% < 0,5 µm

50% < 1,2 µm

90% < 5,7 µm

An inorganic material which is chemically stable under the conditions of chlor-alkali electrolysis can be used as the finely divided inorganic material. It must therefore be resistant to strong alkalis, acids and oxidizing media such as chlorine. Oxides, carbides, borides, silicides, sulfides, nitrides or silicates such as ZrSiO ₄ or aluminosilicates or aluminates, with the exception of asbestos, in particular transition metal oxides, are preferably used as the finely divided inorganic material. The material should be stable in acidic and alkaline aqueous media. Zirconium oxide is particularly preferably used. The average particle size of the finely divided inorganic material is preferably less than 100 μm, particularly preferably less than 40 μm, in particular less than 10 μm. A preferred particle size distribution is as follows:

10% <0.5 µm

50% <1.2 µm

90% <5.7 µm

10% < 0,63 µm

50% < 1,74 µm

90% < 10,18 µm

Another preferred distribution is as follows:

10% <0.63 µm

50% <1.74 µm

90% <10.18 µm

The PTFE or PTFE copolymer dispersion is made by dispersing PTFE or PTFE copolymer, preferably in water, using a dispersant, especially a non-ionic surfactant in one Amount of 1-10 wt .-%, based on the PTFE or PTFE copolymer used.

Preferred dispersions are made by emulsion polymerization. The solids content is preferably 30 to 80%, particularly preferably 50 up to 70%. The viscosity of the dispersion is at a shear rate of 4000 / s preferably 7 to 13 mPas. The particle size is preferably 100 to 500 nm, particularly preferably 150 to 300 nm.

Preferred dispersions have the following properties: Solids content % ASTM D 4441 60 35 58 55 Emulsifier not ionic Ionic not ionic not ionic Amount of emulsifier based on solids % ASTM D 4441 5 4th 5 10th PH value - ASTM D 4441 8.5 10th 8.5 8.5 viscosity mPas DIN 54 453 D = 4000s ^-1 9 3rd 10th 15 density g / cm ³ Hydrometer 1.5 1.25 1.5 1.4 Medium particle size nm Laser method 180 180 250 250

PTFE or PTFE copolymer powders which can be used according to the invention preferably have bulk densities of 300 to 1000 kg / m ³ , particularly preferably 400 to 600 kg / m ³ . The average particle size is preferably 20 to 1000 μm, particularly preferably 250 to 700 μm. The powders are preferably free-flowing, in particular powders with an average particle diameter of approximately 500 μm and a bulk density of approximately 500 kg / m ³ . The PTFE or PTFE copolymer powders can be dispersed in a dispersant before use.

The solids content of the PTFE dispersion used can sometimes be advantageous still decrease by adding water to a desired one Adjust concentration. A prediction of which amounts of water make sense is not possible, but should be adjusted in individual cases (e.g. 2-30%, more specifically 5 - 10% when using an approx. 60% dispersion).

The PTFE or PTFE copolymer powders can also be used without being previously dispersed in a dispersant. This has the Advantage that no dispersant has to be removed. It is preferred However, powders still contain a surfactant in an amount of 1 - 15% added to the PTFE weight. The addition of the surfactant can be done before or after mixing the components in process step (a), in any case before heating up [process step (b)]. As surfactants nonionic surfactants are preferred. It is preferred for compounds based on oxo alcohols or fatty alcohols with 10 - 18 Carbon atoms, alkylphenols, fatty acids or fatty acid amides, all Contain polyethylene residues with 3 - 20 ethylene oxide units, or um Surfactants based on oleic acid alkoxylate, fatty alcohol alkoxylate, fatty acid alkoxylate or alkylphenol alkoxylate. Surfactants are particularly preferred Based on alkylphenols with polyethylene oxide residues, the 6 to 20 Contain ethylene oxide units (e.g. Lutensol® AP6 from BASF).

Modified PTFE grades can also be used as PTFE. Here is PTFE, which contains small amounts of suitable comonomers contains. Comonomers can be: hexafluoropropylene, perfluoro (propyl vinyl ether), Ethylene, chlorotrifluoroethylene, vinylidene fluoride. Preferably perfluorinated comonomers are used.

Modified PTFE powders are e.g. by Dyneon under the designation Hostaflon® TFM offered. They contain <1% of a comonomer.

PTFE copolymers can also contain larger amounts of comonomers, e.g. 7-8 mol%. In addition to the preferred hexafluoropropylene (FEP) and Perfluoropropyl vinyl ether (PFA) are also suitable in US 5,192,473 Comonomers indicated.

The weight ratio of PTFE or PTFE copolymer to fine particles inorganic material, without fiber-forming material, is preferably 0.2 to 0.6; particularly preferably 0.25 to 0.5; in particular 0.28 to 0.43.

A preferred embodiment of the present invention is shown below:

The fine-particle inorganic material and the fiber-forming material presented in the calibration mixer and mixed briefly. Then you leave rotate the cylinder of the mixer, turns on the whirler and now gives the PTFE or PTFE copolymer dispersion too. It is possible the components admit in any order. The swirler should be switched on in order to bring about intensive mixing.

The vortex speed is then set to a suitable value (e.g. 450 rpm), or you switch off the swirler and leave the mixing tank rotate at low speeds of preferably a maximum of 100 rpm and heats the mixture to the desired temperature. The temperature range the fiber formation depends on the material used. Usually the temperature is more than 70 ° C and is for example in the range of 80-200 ° C. In this process step, that contained in the dispersion Water removed so that at temperatures below 100 ° C with reduced Pressure should be worked. Even at higher temperatures Worked under reduced pressure to remove the water or to accelerate the dispersant.

The heating time is preferably 0.25 to 2 hours. It hangs on the construction and size of the mixer and the type of heating and can be more than 2 hours with lower heating output. In the In practice, values of up to 6 hours are not critical. For example, it can wall heating or by introducing hot steam (superheated steam) be heated.

After reaching the desired temperature, fiber formation is usually largely completed. It can still be for another 5 to 240 min at this Temperature can be mixed.

Then the mixer contents are allowed to cool down again. This happens on easiest by letting it stand, that is, without further mixing. During the cooling process, however, it is also possible to continue mixing or to a coolant such as cold air or water is blown faster to cool down be injected and subsequently evacuated.

After reaching the temperature below 70 ° C, preferably 20 to 60 ° C the swirler is switched on, whereby the clumped fiber material is crushed becomes. The speed of the swirler is preferably set to a value in the range set from 300 to 2500 rpm. The mixing time is preferably 10 seconds up to 60 min. The speed and the time of mixing depend on the desired degree of shredding. As a rule, mixing times range from 1 to 1.5 min at a speed of 2500 rpm or 1 to 5 min at a Speed from 450 rpm.

The free-falling fiber material can then be discharged in a simple manner become.

The composite fibers obtained are dry, free-flowing, finely divided material. The fibers are fibril-like, anisotropic and of irregular morphology. The color depends on the used inorganic material and the PTFE or PTFE copolymer polymer. Each single fiber can be branched or not branched. The inorganic Material is evenly distributed over the entire fiber and intimate with the PTFE or PTFE copolymer mixed as a polymeric binder so that it cannot be separated without destroying the fiber. Also located finely divided inorganic material on the surface of the fiber.

The composite fibers that can be produced or produced according to the invention are for Manufacture of diaphragms, especially for chlor-alkali electrolysis, usable.

(A) Herstellen von Kompositfasern gemäß einem der vorstehenden Verfahren,

(B) Eintragen der Kompositfasern in eine Lösung, die Wasser und ein Dickungsmittel Zur Erhöhung der Viskosität enthält,

(C) Absaugen des Gemisches aus (B) über eine poröse Unterlage unter Ablagerung der Kompositfasern auf der porösen Unterlage,

(D) Trocknen der beschichteten porösen Unterlage aus (C),

(E) thermische Behandlung des in (D) erhaltenen Diaphragmas bei einer Temperatur im Bereich von 90 bis 390°C.

The invention also relates to a method for producing diaphragms

(A) producing composite fibers according to one of the above processes,

(B) adding the composite fibers to a solution containing water and a thickener to increase the viscosity,

(C) suctioning off the mixture from (B) over a porous support, with the composite fibers being deposited on the porous support,

(D) drying the coated porous support from (C),

(E) thermal treatment of the diaphragm obtained in (D) at a temperature in the range of 90 to 390 ° C.

The diaphragms can be produced as described in EP-B 0 196317 respectively. A cathode, for example, can be used as the porous support can be used, which has the shape of a grid and with a polyamide network is covered.

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

Example 1:

10% < 0,5 µm

50% < 1,2 µm

90% < 5,7 µm

und 1,58 kg Natriumchlorid der Teilchengröße

10% < 5 µm

50% < 40 µm

90% < 80 µm

werden in einen 5 l Eirichmischer (Eirich R02) gegeben und 2 min durchmischt. Die Trommel wird dabei mit 84 U/min und der Wirbler mit 450 U/min mitläufig bewegt. Dabei wird eine Froudezahl von etwa 20 erreicht. Über eine Düse werden nun unter fortgesetztem Mischen innerhalb von 3 min 0,66 kg einer ca. 60%igen PTFE-Dispersion zugegeben (Hostaflon® TF 5050 von Dyneon) und noch 2 min nachgemischt. Danach wird die Drehzahl der Trommel auf 42 U/min reduziert, der Wirbler läuft weiter bei 450 U/min, und man heizt den Inhalt auf 160°C auf (Dauer ca. 60 min), wobei sich stark verfilzte und verklumpte Faserknäuel bilden. Danach schaltet man die Mischwerkzeuge aus und läßt auf 40°C abkühlen. Bei dieser Temperatur werden Wirbler (450 U/min) und Trommel (42 U/min) wieder eingeschaltet und der Inhalt 2 min lang gemischt, wobei sich die Fasern auf die gewünschte Größe reduzieren. Man erhält frei fließende ZrO₂-PTFE-Kompositfasern von unregelmäßiger Morphologie.0.9 kg ZrO _{2 of the} following particle size:

10% <0.5 µm

50% <1.2 µm

90% <5.7 µm

and 1.58 kg of particle size sodium chloride

10% <5 µm

50% <40 µm

90% <80 µm

are placed in a 5 l Eirich mixer (Eirich R02) and mixed for 2 min. The drum is moved at 84 rpm and the whirler at 450 rpm. A Froude number of about 20 is reached. 0.66 kg of an approx. 60% PTFE dispersion (Hostaflon® TF 5050 from Dyneon) are then added over a nozzle with continued mixing within 3 min and the mixture is then mixed for a further 2 min. Then the speed of the drum is reduced to 42 rpm, the whirler continues to run at 450 rpm, and the contents are heated to 160 ° C. (duration approx. 60 min), where heavily matted and clumped fiber balls form. Then the mixing tools are switched off and allowed to cool to 40 ° C. At this temperature, the whirler (450 rpm) and drum (42 rpm) are switched on again and the contents are mixed for 2 minutes, the fibers reducing to the desired size. Free-flowing ZrO ₂ -PTFE composite fibers with an irregular morphology are obtained.

Comparative example V2:

10% < 0,5 µm

50% < 1,2 µm

90% < 5,7 µm

und 1,58 kg Natriumchlorid der Teilchengröße

10% < 5 µm

50% < 40 µm

90% < 80 µm

werden in einen 5 l Eirichmischer (Eirich R02) gegeben und 2 min durchmischt. Die Trommel wird dabei mit 84 U/min und der Wirbler mit 450 U/min bewegt. Über eine Düse werden nun unter fortgesetztem Mischen innerhalb von 3 min 0,66 kg einer ca. 60%igen PTFE-Dispersion zugegeben (Hostaflon® TF 5050 von Dyneon) und noch 2 min nachgemischt. Danach wird die Drehzahl der Trommel auf 42 U/min reduziert, der Wirbler abgeschaltet und der Inhalt auf 160 °C aufgeheizt (Dauer ca. 90 min), wobei sich stark verfilzte und verklumpte Faserknäuel bilden. Danach schaltet man den Wirbler mit einer Drehzahl von 2500 U/min ein und zerkleinert bei 160°C. Man erhält ein faserähnliches Produkt. Eine Zerkleinerung bei 450 U/min und 160°C gelang nicht. Die aus den Fasern hergestellten Diaphragmen weisen einen viel zu hohen Durchfluß auf (siehe Beispiel).0.9 kg ZrO _{2 of the} following particle size:

10% <0.5 µm

50% <1.2 µm

90% <5.7 µm

and 1.58 kg of particle size sodium chloride

10% <5 µm

50% <40 µm

90% <80 µm

are placed in a 5 l Eirich mixer (Eirich R02) and mixed for 2 min. The drum is moved at 84 rpm and the whirler at 450 rpm. 0.66 kg of an approx. 60% PTFE dispersion (Hostaflon® TF 5050 from Dyneon) are then added over a nozzle with continued mixing within 3 min and the mixture is then mixed for a further 2 min. Then the speed of the drum is reduced to 42 rpm, the whirler is switched off and the contents are heated to 160 ° C (duration approx. 90 min), forming heavily matted and clumped fiber balls. Then the whirler is switched on at a speed of 2500 rpm and shredded at 160 ° C. A fiber-like product is obtained. Crushing at 450 rpm and 160 ° C was not successful. The diaphragms made from the fibers have a much too high flow (see example).

Example 3:

10% < 0,5 µm

50% < 1,2 µm

90% < 5,7 µm

und 1,58 kg Natriumchlorid der Teilchengröße < 315 µm

20% < 63 µm

70% < 63-200 µm

90% < 200 µm

werden in einen 5l Eirichmischer (Eirich R02) gegeben und 2 min durchmischt. Die Trommel wird dabei mit 84 U/min und der Wirbler mit 450 U/min gegenläufig bewegt. Über eine Düse werden nun unter fortgesetztem Mischen innerhalb von 3 min 0,66 kg einer ca. 60%igen PTFE-Dispersion zugegeben (Hostaflon® TF 5050 von Dyneon) und noch 2 min nachgemischt. Danach wird die Drehzahl der Trommel auf 42 U/min reduziert, der Wirbler läuft weiter bei 450 U/min und man heizt den Inhalt auf 130°C auf (Dauer ca. 45 min), wobei sich stark verfilzte und verklumpte Faserknäuel bilden. Danach schaltet man die Mischwerkzeuge aus und läßt auf 20°C abkühlen. Bei dieser Temperatur werden Wirbler (450 U/min) und Trommel (42 U/min) wieder eingeschaltet und der Inhalt 2 min lang gemischt, wobei sich die Fasern auf die gewünschte Größe reduzieren. Man erhält frei fließende ZrO₂-PTFE-Kompositfasern von unregelmäßiger Morphologie.0.9 kg ZrO _{2 of the} following particle size:

10% <0.5 µm

50% <1.2 µm

90% <5.7 µm

and 1.58 kg of sodium chloride with a particle size of <315 μm

20% <63 µm

70% <63-200 µm

90% <200 µm

are placed in a 5 l Eirich mixer (Eirich R02) and mixed for 2 min. The drum is moved in opposite directions at 84 rpm and the whirler at 450 rpm. 0.66 kg of an approx. 60% PTFE dispersion (Hostaflon® TF 5050 from Dyneon) are then added over a nozzle with continued mixing within 3 min and the mixture is then mixed for a further 2 min. Then the speed of the drum is reduced to 42 rpm, the whirler continues to run at 450 rpm and the contents are heated to 130 ° C. (duration approx. 45 min), forming heavily matted and clumped fiber balls. Then the mixing tools are switched off and allowed to cool to 20 ° C. At this temperature, the whirler (450 rpm) and drum (42 rpm) are switched on again and the contents are mixed for 2 minutes, the fibers reducing to the desired size. Free-flowing ZrO ₂ -PTFE composite fibers with an irregular morphology are obtained.

Example 4 Manufacture of test diaphragms and determination of the flow Preparation of the mash solution

12.5 kg demineralized water (demineralized water) + 50% NaOH for adjustment a pH of about 11

and 26.25 g of the Welan Gum® thickener from Oxytech are homogenized. Then be

26.25g Proxel® GXL (biocide based on 1,2 benzisothiazolin-3-one) and

3.1 g of silicone defoamer DC 10010 A added.

Production of the fiber mash

434g

Maischelösung

62,5g

Fasern

The fiber mash is calculated for a test diaphragm with an area of 75 cm ² (d = 9.8 cm).

434g

Mash solution

62.5g

Fibers

The weighed components are stirred for 15 minutes using a magnetic stirrer 900-1000 1 / min stirred.

Storage of a test diaphragm

An original American cathode grid with a fine-nylon nylon net above it is clamped in a small storage device. The homogenized fiber mix is then poured on and run through the nylon net for 30 minutes without negative pressure. The amount of mash solution that has passed through is 170-210 ml. A vacuum is then applied to the depositing device by means of a membrane pump. Time in min 0 1 5 9 17th 20th 25th 30th 40-140 Pressure in bar 1013 980 940 850 740 630 530 500 500

After 55 minutes, the excess fiber mash is decanted off, then remains the diaphragm on the suction for 90 min. After 140 min Pump switched off and the diaphragm removed.

Thermal after-treatment

• Drying the deposited diaphragm at 95 ° C for 6 hours
• Heating from 95 ° C to 320 ° C in about 1.5 hours
• Keep the temperature at 320 ° C for 1.5 hours
• Heating up to 320 ° C in 1h
• Hold at 360 ° C for 1.5 hours
• Cool to room temperature with the oven off and closed.

Hydrophilization

In the beaker, the diaphragm is filled with a 4% solution of zonyl for 12 hours Treated FSN® (a fluorosurfactant from DuPont) and then 12h at 70-80 ° C dried.

Flow measurement

The test diaphragms are a flow measurement with brine solution (300g / l NaCl), at room temperature and a constant liquid column of 22 cm subjected.

Result of the flow measurement

Values between 5 and 40, preferably between 10 and 30 l / m ² h are aimed for Diaphragm made of fibers from example Flow l / m ² h 1 11 V2 150 3rd 27

Example 5a-e (Influence of time on the filter resistance)

0,9 kg ZrO₂ folgender Teilchengröße

10% < 0,5 µm

50% < 1,2 µm

90% < 5,7 µm

und 1,58 kg Natriumchlorid der Teilchengröße

10% < 5 µm

50% < 40 µm

90% < 80 µm

werden in einem 5 l Eirichmischer (Eirich R02) gegeben und 2 min durchmischt. Die Trommel wurde dabei mit 84 U/min und der Wirbler mit 450 U/min bewegt. Über eine Düse werden nun unter fortgesetztem Mischen innerhalb von 3 min 0,66 kg einer 60 %ige PTFE-Dispersion zugegeben (Hostaflon® TF 5050 von Dyneon) und noch 2 min nachgemischt. Danach schaltet man den Wirbler ab, läßt die Trommel bei 42 U/min rotieren und heizt den Inhalt auf 130°C auf (Dauer ca. 45 min), wobei sich stark verfilzte und verklumpte Faserknäuel bilden und kühlt dann auf ca. 20°C ab. Danach wird der Wirbler eingeschaltet und man läßt diesen 30-90 sec bei 450 U/min rotieren, wobei sich frei fließende unregelmäßig geformte Kompositfasern bilden.

0.9 kg ZrO _{2 of the} following particle size

10% <0.5 µm

50% <1.2 µm

90% <5.7 µm

and 1.58 kg of particle size sodium chloride

10% <5 µm

50% <40 µm

90% <80 µm

are placed in a 5 l Eirich mixer (Eirich R02) and mixed for 2 min. The drum was moved at 84 rpm and the whirler at 450 rpm. With continued mixing, 0.66 kg of a 60% PTFE dispersion (Hostaflon® TF 5050 from Dyneon) are then added via a nozzle and mixed for a further 2 minutes. Then the whirler is switched off, the drum is rotated at 42 rpm, and the contents are heated to 130 ° C. (duration approx. 45 min), where heavily matted and clumped fiber balls form and then cooled to approx from. The whirler is then switched on and is allowed to rotate at 450 rpm for 30-90 sec, free-flowing irregularly shaped composite fibers being formed.

50 g of the fibers produced in this way are slurried in 500 ml of water and filtered under a pressure of 100 mbar over a frit, filter cakes with a thickness of 14 mm being formed. The time until 490 ml of water had passed through is determined in each case. This is a measure of the filter resistance or the flow resistance of the filter cake. The results show that the flow resistance of the filter cake produced from the fibers depends on the comminution time in the mixer. The longer it is crushed, the denser filter cakes can be obtained from the fibers produced. sample Time seconds Lead time sec A 30th 101 B 45 128 C. 60 154 D 75 175 E 90 190

Example 6

The procedure according to Example 1 was repeated, but after mixing at Room temperature for 10 min within 60 min without switching on the swirler was heated to a temperature of 92 ° C. Then the swirler became switched on at a speed of 450 rpm and under for 10 min Heating up to 109 ° C. The swirler is used in the following Steps not turned off, but still at a speed of 450 rpm operated. After reaching a temperature of 109 ° C to 40 ° C cooled and then again within 15 min to a temperature of Heated up to 160 ° C. It is then cooled to a temperature of 62 ° C and crushed.

Functional diaphragms can be obtained from the fibers obtained become. It is possible to make fibers that are too small by grinding too long have been reprocessed by heating up again. The fiber formation starts again in the heat treatment, so that usable fibers can be obtained.

Example 7

0.9 kg of ZrO _{2 of} the particle size mentioned in Example 1 and 1.58 kg of NaCl with an average particle size (D50) of 13 m are placed in an Eirich mixer (RO2) and mixed at a vortex speed of approx. 1500 rpm. 660 g of an approximately 60% PTFE dispersion are diluted with 50 ml of water and added to the ZrO ₂ / NaCl mixture via a nozzle and with continued mixing. The mixture is mixed for about 5 minutes and granulated. Then the whirling speed is reduced to 450 rpm. The running direction is the same. The drum moves at 42 rpm. The contents are now heated to approx. 160 ° C, where heavily matted and clumped fiber balls form. After the mixer content has cooled to 50-60 ° C., mixing is continued for another 4-5 minutes at a swirling speed of 450 rpm, the fibers being comminuted and separated again.

A fiber mash is now produced according to Example 4, for which purpose 1736 g of the solution described in Example 4 and 250 g of fibers are used. An apparatus is immersed in this fiber suspension, which is equipped with a round piece of cathode grid, which has an area of 78.5 cm ² . By applying a vacuum to the back of the cathode grid, the dispersed fibers are sucked onto the grid until no further fibers can be sucked up and after the diaphragm has been removed from the fiber bath, the vacuum remains at a pressure of 50-150 mbar.

After drying and thermal treatment of the diaphragm according to Example 4, the diaphragm had a weight of 35 g. This corresponds to a sheet weight of approx.4.5 kg / m ² . The diaphragm was then hydrophilized for 24 hours with a 4% zonyl solution. In the subsequent measurement of the flow, a flow rate of 20-25 l / h * m ^{2 was} found.

An electrolytic cell for chlor-alkali electrolysis with 7 dm ² of electrode area was (dm 7 ²⁾ using the same fibers of several approaches in an analogous manner with a diaphragm equipped. As described above, a box-shaped storage apparatus with the cathode grid (7 dm ² ) was immersed in a correspondingly produced fiber bath (from 43.4 kg of mash solution according to Example 4 and 6.25 kg of fibers) and that by applying vacuum to the back of the cathode grid Diaphragm sucked up. After the absorption process had ended, the cathode construction coated with the diaphragm was dried and subjected to a thermal treatment in accordance with Example 4. After baking (sintering) and hydrophilizing the diaphragm, the electrolytic cell was assembled and operated for 5 weeks with the following values:

Brine inflow :

Concentration: approx. 300 g / l NaCl

Volume: 2.2 l / h

Temperature: 80 ° C

Head: 250 - 350 mm

Cell eye obtained :

Concentration: 120 g / l

Flow rate: 1.8 - 2.0 l / h

Chlorate concentration: 30 - 50 ppm

chlorine produced:

> 97 vol.%

Hydrogen: <0.7%

Oxygen: <2.2%

Nitrogen: <0.1%

Cell voltage: 3.25-3.35V

Current density: 2.2 - 2.3 kA / m ²

Claims (12)

Process for the production of composite fibers by (a) mixing a PTFE or PTFE copolymer dispersion or a PTFE or PTFE copolymer powder with a finely divided inorganic material and a fiber-forming material, (b) heating the mixture obtained under shear to a temperature at which the PTFE or PTFE copolymer is flowable under shear but shows no decomposition, with removal of the dispersant, if a PTFE or PTFE copolymer dispersion is used, (c) cooling the mixture to a temperature below 70 ° C, (d) shearing the mixture with mixing at a temperature below 70 ° C to form the composite fibers. A method according to claim 1, characterized in that as a fiber-forming Material an alkali or alkaline earth salt is used. A method according to claim 1 or 2, characterized in that ZrO _{2 is} used as the finely divided inorganic material. Method according to one of claims 1 to 3, characterized in that that the weight ratio of PTFE or PTFE copolymer to fine particles Material is 0.2 to 0.6. Method according to one of claims 1 to 4, characterized in that that step (d) is carried out in mixers at a Froude number greater than 1 becomes. Method according to one of claims 1 to 4, characterized in that that steps (a) to (d) are carried out in one apparatus. Method according to one of claims 1 to 6, characterized in that that step (b) is carried out under reduced pressure. Method according to one of claims 1 to 7, characterized in that that in step (b) is heated to a temperature above 70 ° C. Process for the production of composite fibers by (a) mixing a PTFE or PTFE copolymer dispersion or a PTFE or PTFE copolymer powder with a finely divided inorganic material and a fiber-forming material, (b) heating the mixture obtained under shear to a temperature at which the PTFE or PTFE copolymer is flowable under shear but shows no decomposition, with removal of the dispersant, if a PTFE or PTFE copolymer dispersion is used, (d) Shearing the mixture while mixing in a blender with a Froude number greater than 1 to form the composite fibers. Use mixers with a Froude number of more than 1 the production of composite fibers from PTFE or a PTFE copolymer, a fine-particle inorganic material and a fiber-forming Material. Composite fibers that can be produced by a method according to one of the Claims 1 to 9. Process for the production of diaphragms by (A) producing composite fibers according to a method according to one of claims 1 to 9, (B) introducing the composite fibers into a solution containing water and a thickener to increase the viscosity, (C) suctioning off the mixture from (B) over a porous support, with the composite fibers being deposited on the porous support, (D) drying the coated porous support from (C), (E) thermal treatment of the diaphragm obtained in (D) at a temperature in the range of 90 to 390 ° C.