Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
  • B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
  • C25B13/08—Diaphragms; Spacing elements characterised by the material based on organic materials
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/426—Fluorocarbon polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• ABSTRACT Porous diaphragms suitable inter alia for electrolytic cells are formed from an aqueous slurry or dispersion of-polytetrafluoroethylene and a solid particular additive utilising water as lubricant .in the sheet forming operation.
• the invention relates to the manufacture of porous diaphragms based on polytetrafluoroethylene.
• One method of manufacturing such porous diaphragms comprises forming an aqueous slurry or dispersion of polytetrafluoroethylene and a solid particular additive such as starch, adding an organic coagulating agent such as acetone to said dispersion and then drying the coagulated dispersion.
• An organic lubricant such as petroleum ether is then added to the dried coagulated material to serve as a processing aid when the material is being rolled into a sheet.
• the starch is removed to give the desired porous diaphragm.
• the lubricant can also be removed if required.
• a major disadvantage of the above method of manufacturing porous diaphragms is that the use of an organic lubricant gives rise to irreproducibility of the diaphragms and this is extremely undesirable particularly when the diaphragms are intended for use in multimodular electrolytic cells where reproducibility is essential for efficient operation.
• We have now discovered that the above disadvantage is obviated or mitigated by the method of the present invention in which water is used as lubricant which enables diaphragms of desired reproducibility and permeability to be produced.
• a method ofmanufacturing a porous diaphragm comprises preparing an aqueous slurry or dispersion comprising polytetrafluoroethylene and a solid particulate additive, thickening said aqueous slurry or dispersion to effect agglomeration of the solid particles therein, forming from the thickened slurry or dispersion a dough-like material containing sufficient water to serve as lubricant in a subsequent sheet forming operation, forming a sheet of desired thickness from said dough and removing solid particulate additive from the sheet.
• the thickening of the aqueous slurry or dispersion is effected by reducing the water content thereof and water is then added to the thus thickened material to form the dough.
• the desired degree of lubrication for the sheet forming operation is obtained by mixing water with the thickened material so that a dough having a viscosity of at least 300 poises is obtained.
• water is added to the thickened material so that a dough having a viscosity of between 1 and 7X10 poises is obtained.
• the desired degree of lubrication can be achieved either by drying the aqueous slurry or dispersion to a low water content and then adding a considerable amount of water to form the dough or conversely drying the slurry or dispersion only slightly and adding comparatively less water to form the dough.
• the aqueous slurry or dispersion is preferably dried to a water content of no more than 10% of the total weight of the dried dispersion.
• water is added to the dried dispersion until a dough is attained which has a water content comprising 2 to 50%, preferably to 45%, of the total weight of the dough.
• the drying of the slurry or dispersion can be carried out in any suitable manner which will not cause damage to the constituents thereof.
• the drying is carried out at a temperature of 10 to C for example 15 to 50C.
• the time for drying will depend, inter alia, on the temperature but is generally from 10 to 100 hours, for example, 20 to 50 hours.
• aqueous slurry or dispersion is thickened by subjecting it to high shearing action and the high shear action is continued so that a dough having a viscosity of at least 300 poises, preferably between l l0 and 7X10 poises, is obtained.
• the slurry or dispersion advantageously has a water content comprising 2 to 50%, preferably 20 to 45% of the total weight of the dispersion.
• a particularly suitable way of subjecting the slurry or dispersion to high shear conditions is to mix the slurry or dispersion in a Z-blade mixer.
• the aqueous slurry or dispersion is thickened by first subjecting it to mixing action and then adding a thickening agent to achieve desired consistency for the sheet forming operation.
• the thickening agent is a copolymer of maleic anhydride and an alkyl vinyl ether.
• the particles size of the polytetrafluoroethylene in the aqueous slurry or dispersion is preferably in the range of 0.05 to 1 micron, e.g. 0.1 to 0.2 micron.
• the solid particulate additive can be any which is substantially'insoluble in water but which can be removed by a suitable chemical or physical means which will not cause damage to the polytetrafluoroethylene.
• the additive may be starch, for example maize starch and/or potato starch, or a water-insoluble inorganic base or carbonate, for example calcium carbonate.
• additives- may be removed, for example, by soaking the sheet in an acid, preferably a mineral acid e.g. hydrochloric acid.
• acid preferably a mineral acid e.g. hydrochloric acid.
• Other additives which may be used include organic polymers which depending on the properties of the polymer may be removed from the sheet by dissolving with an organic solvent, by hydrolysis or by vaporisation. Mixtures of additives may be used and if necessary various treatments may be given to the sheet to remove the additive.
• the additive has a particle size substantially all of which are within the range of 5 to 100 microns.
• the amount of additive will depend on the permeability desired in the final diaphragm.
• the weight ratio of additive to polytetrafluoroethylene may be, for example, from 10:1 to 1:10 preferably from 5:1 to 121.
• particulate fillers generally inorganic fillers, for example, titanium dioxide which is particularly preferred, barium sulphate, asbestos, (e.g. amphibole or serpentine asbestos), graphite and alumina.
• the filler has a particle size of, for example, less than 10 microns and preferably less than 1 micron.
• the weight ratio of filler to polytetrafluoroethylene may be for example from :1 to 1:10,
• a coagulating agent e.g. brine
• the sheet is generally formed from the dough by calendering.
• the calendering is carried out by passing the dough through the rolls a number of times.
• the sheets are rotated through about 90 so that the calendering is carried out biaxially.
• the diaphragms produced by the process of the present invention have a wide range of uses but are particularly suitable for use in electrolytic cells for electrolysis of alkali-metal halides, for the production of chlorine and caustic alkalis.
• a sheet of a suitable strengthening material for example, a polymer gauze such as polypropylene gauze.
• the process of the present invention enables the production without difficulty of a successive number of diaphragms over a period of time, each one having similar permeabilities. This is very necessary when using the diaphragms in electrolytic cells.
• EXAMPLE 1 To 100 parts of an aqueous dispersion of polytetrafluoroethylene containing 60% of the polymer in the form of particles approximately all in the size range 0.15 to 0.2 micron were added 101 parts of water, 60 parts of titanium dioxide of particles size approximately 0.2 micron, 60 parts of maize starch of particle size approximately 13 microns and 120 parts of potato starch of particle size less than 75 microns. The mixture was then stirred wtih a paddlemixer for 30 minutes to form a substantially uniform paste. This paste was spread on trays and dried at 24 for 48 hours to a water content 5.7% by weight.
• the resultant essentially rectangular laminate was then passed through the rolls with its largest side directed at 90 to the direction of calendering. and with the inter-roll space slightly reduced, no cutting, stacking or rotating through 90 being involved. This process was repeated through a gradually reduced inter-roll space, the same edge of the laminate being fed to the rolls on each occasion, until the thickness of the laminate was 1.5 mm.
• a square of 22 26 mesh gauze woven of 0.011 inch diameter monofilament polypropylene yarn was placed on top of the laminate, and rolled into the laminate by calendering through a slightly reduced inter-roll space.
• the resultant reinforced sheet was removed from the rolls and soaked in cold aqueous 18% hydrochloric acid for 24 hours. The starch additive was thereby removed leaving a multi-porous sheet suitable for use as a diaphragm material in electrolytic cells electrolysing aqueous solutions.
• EXAMPLE 2 To 100 parts of an aqueous dispersion of polytetrafluoroethylene containing 60% of the polymer in the form of particles approximately all in the size range 0.15 to 0.2 micron were added parts of water, 60 parts of titanium oxide of particle size approximately 0.2 micron, 60 parts of maize of particle size approximately 13 microns and 120 parts of potato starch of particle size less than microns. The mixture was then stirred with a paddlemixer for 3 minutes to form a paste which was then mixed in a Z-blade mixer for 22 minutes to form a dough having a viscosity of 4X10 poise.
• the dough was then spread along the shortest edge of a rectangular piece of card, and calendered on the card between dual, even-speed, calender rolls, set 3 mm apart, into an oblong sheet. After calendering, the oblong sheet was cut, in the direction of calendering, into four equal pieces. These were laid congruently over each other to obtain a four-layered laminate.
• the card was picked up, rotated in the horizontal plane, and calendered (directed 90 to the original direction of calendering) again through the 3 mm roll separation. This process, the successive cutting into four, stacking, rotating and calendering was repeated until the composition had been rolled a total of 15 times.
• the resultant laminate was cut into four, in the direction of calendering, stacked, removed from the card, and calendered, without rotation through 90, to the inter-roll space being reduced by the thickness of the card.
• the laminate was cut, at right angles to the direction of calendering, into four equal pieces, stacked, rotated through 90 and calendering again. This process, cutting at right angles to the direction of calendering, stacking, rotating and calendering was repeated until the composition had been rolled a total of nine times.
• the resultant essentially rectangular laminate was then passed through the rolls with its largest side directed at 90 to the direction of calendering, and with the inter-roll space slightly reduced, no cutting, stacking or rotating through 90 being involved.
• EXAMPLE 3 To 100 parts of an aqueous dispersion of polytetrafluoroethylene containing 60% of the polymer in the form of particles approximately all in the size range 0.15 to 0.2 micron were added 200 parts of water, 60 parts of titanium dioxide of particle size approximately 0.2 micron, 60 parts of maize starch of particle size approximately 13 microns and 120 parts of potato starch of particle size less than 75 microns. The mixture was then stirred with a paddlemixer for 2 minutes to form a substantially uniform paste having a viscosity of 3 poise.
• the card was picked up, rotated 90 in the horizontal plane, and calendered (directed 90 to the original direction of calendering) again through the 3 mm roll separation.
• This process the successive cutting into four, stacking, rotating and calendering was repeated until the composition had been rolled a total of one hundred and ten times. For the first ninety of these passes through the rolls, accurate stacking into laminates was not possible due to the nature of the material.
• the resultant laminate was cut into four, at'right angles to the direction of calendering, stacked, removed from the card, rotated through 90, and calendered, the inter-roll space being reduced by the thickness of the card. This process, cutting at right angles to the direction of calendering, stacking, rotating and calendering was repeated until the composition had been rolled a total of one hundred and fifteen times.
• the resultant essentially rectangular laminate was then passed through the rolls with its largest side directed at 90 to the direction of calendering, and with the interroll space slightly reduced, no cutting, stacking or rotating through 90 being involved. This process was repeated through a gradually reduced inter-roll space, the same edge of the laminate being fed to the rolls on each occasion, until the thickness of the laminate was 1.5 mm.
• a square of 22 26 mesh gauze woven of 0.011 inch diameter monofilament polypropylene yarn was placed on top of the laminate, and rolled into the laminate by calendering through a slightly reduced inter-roll space.
• the resultant reinforced sheet was removed from the rolls and soaked in cold aqueous 18% hydrochloric acid for 24 hours, The starch additive was thereby removed leaving a multiporous sheet suitable for use as a diaphragm material in electrolytic cells electrolysing aqueous solutions.
• TEST SERIES B In this test series a number of diaphragms was prepared according to the process described in Example 1 except that petroleum ether was used as lubricant instead of water. In this case the inorganic filler was extractedoutside the electrolytic cell by soaking in 16% hydrochloric acid and permeability measurements were made when the diaphragms had been installed in the electrolytic cell. The results are shown in Table II below.
• TEST SERIES C In this series of tests the diaphragms were prepared according to Example 1 with water being used as lubricant. This time a slightly different technique was adopted in measuring permeability in that a special rig was set up for removal of the inorganic filler by acid extraction and the permeability measurements were not made with the diaphragms installed in an electrolytic cell but in said rig. The tests results are indicated in Table III below which also indicates results of tensile strength tests carried out on the diaphragms on a standard lnstron tensile strength measuring device.
• a method of manufacturing a porous diaphragm suitable for use in electrolytic cells comprising preparing an aqueous dispersion of polytetrafluoroethylene and a solid particulate removable filler, thickening said aqueous dispersion to effect agglomeration of the solid particules therein, forming from the thickened dispersion a dough-like material containing water as lubricant for a subsequent sheet forming operation, calendering said dough-like material to form a biaxially fibrillated sheet and removing the solid particulate filler from the sheet to render it porous.
• a method as claimed in claim 2 wherein the desired degree of lubrication for the sheet forming operation is obtained by mixing water with the thickened material so that a dough having a viscosity of at least 300 poises at 20C is obtained.
• a method as claimed in claim 1 wherein water is added to the dried dispersion until a dough is attained which has a water content comprising 20 to 45% of the total weight of the dough.
• a method as claimed in claim 10 wherein the thickening agent is a copolymer of maleic anhydride and an alkyl vinyl ether.
• solid particulate removable filler is substantially insoluble in water and can be removed by chemical or physical means which does not cause damage to the polytetrafluoroethylene.
• a method as claimed in claim 13 wherein the solid particulate additive is starch or a water-insoluble inorganic base or carbonate.
• solid particulate filler is an organic polymer removable by dissolving the sheet in an organic solvent or by hydrolysis or by vaporisation.
• a method as claimed in claim 1 wherein the solid particulate removable filler has a particle size substantially within the range 5 to 100 microns.
• nonremovable filler is titanium dioxide, barium sulphate, asbestos, graphite or alumina.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Metallurgy (AREA)
• General Chemical & Material Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Laminated Bodies (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)

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Cited By (36)

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Citations (7)

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• 0
  • BE BE794889D patent/BE794889A/xx not_active IP Right Cessation
• 1972
  • 1972-02-04 GB GB535172A patent/GB1424804A/en not_active Expired
• 1973
  • 1973-01-24 US US326475A patent/US3890417A/en not_active Expired - Lifetime
  • 1973-01-25 ZA ZA730564A patent/ZA73564B/xx unknown
  • 1973-01-30 IL IL41422A patent/IL41422A/xx unknown
  • 1973-02-01 FI FI298/73A patent/FI57895C/fi active
  • 1973-02-01 AR AR246386A patent/AR193914A1/es active
  • 1973-02-02 CA CA162,763A patent/CA1004819A/en not_active Expired
  • 1973-02-02 AT AT92873*#A patent/AT328751B/de not_active IP Right Cessation
  • 1973-02-02 NL NL7301516A patent/NL7301516A/xx not_active Application Discontinuation
  • 1973-02-02 SU SU1881941A patent/SU539536A3/ru active
  • 1973-02-02 FR FR7303847A patent/FR2170247B1/fr not_active Expired
  • 1973-02-02 AU AU51734/73A patent/AU474272B2/en not_active Expired
  • 1973-02-02 IT IT19991/73A patent/IT978776B/it active
  • 1973-02-05 CH CH156973A patent/CH583304A5/xx not_active IP Right Cessation
  • 1973-02-05 JP JP48013872A patent/JPS4999968A/ja active Pending
  • 1973-02-05 DE DE2305509A patent/DE2305509C2/de not_active Expired
• 1977
  • 1977-12-31 MY MY197725A patent/MY7700025A/xx unknown

Patent Citations (7)

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