Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coating or impregnation absorbs chemical material other than...
Reexamination Certificate
2001-09-11
2004-06-29
Cole, Elizabeth M (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coating or impregnation absorbs chemical material other than...
C428S304400, C428S314200, C264S041000
Reexamination Certificate
active
06756328
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an ion exchange membrane for electrolysis, more specifically to an ion exchange membrane reinforced with a cloth comprising reinforcement threads and sacrificial threads which are used for electrolysis of an alkali metal chloride aqueous solution. Particularly, it relates to a fluorine-containing type ion exchange membrane having an excellent electro-chemical property and an excellent mechanical property which prevents an anode solution from leaking out of a system through a channel after dissolution of sacrificial threads in the membrane.
(2) Description of the Related Art
It is already known in this field that as a solid electrolyte used for a membrane for separation in electrolysis of an alkali metal chloride, laminated membranes of at least two layers containing a perfluorocarbon carboxylic acid layer and a perfluorocarbon sulfonic acid layer are effective. High current efficiency, low electric resistance of a membrane, and easiness of handling are demanded of these ionic membranes, and therefore it is essential for a membrane to have sufficient mechanical strength. However, this perfluorocarbon type film has low tear strength, and does not endure a use for a long period by itself, and therefore tear strength thereof is improved usually by embedding a reinforcing material such as a reinforced cloth, etc. in the film.
However, a general reinforcing material is ionically non-permeable, and therefore when the reinforcing material is embedded in the film, a decrease of an effective electric current area and a raise of electric voltage for electrolysis accompanied thereby are caused on electrolysis. This inclination becomes more remarkable when a structure is made to be dense to raise a reinforcing effect, or a yarn composing the reinforcing material is made to be thick. Moreover, a yarn being made to be thick means that a resinous amount of a membrane to wrap the yarn itself is increased, and it further leads to an increase of electric resistance of the membrane.
To overcome a contradictory relation as above of high mechanical strength of a membrane and low electric resistance of a membrane, various attempts have been conventionally conducted. First of all, an attempt was carried out, namely, a method wherein a structure of a fabric is made to be coarse, and an openness (the total area of windows (apertures among fibers) relative to the total area of the structure of the fabric is represented by a percentage) is enlarged. Generally, in electrolysis of an alkali metal chloride under high electric current density, when the openness is made to be not higher than 70%, an effective electric current area of a membrane becomes short, and not only electric resistance of a membrane is increased, but also a transfer of impurities is locally increased, which causes a decrease of efficiency of electric current. Therefore, usually the openness of not lower than 70% is thought to be necessary.
Then, as an attempt to obtain a reinforced cloth having both high mechanical strength and a large openness, there are proposed a membrane wherein a leno weave cloth highly preventing slippage of stitch is adopted as a cloth, and a yarn of a multi-filament of a perfluoro-polymer having a specified denier is adopted as a yarn used (JP-A-61-7338), and further, a method wherein, after manufacturing the plain weave cloth which has been obtained by mixedly weaving reinforcement threads of a perfluoro-polymer and sacrificial threads soluble in an alkali solution, the sacrificial threads are dissolved, and the only reinforcement threads which remain are inserted between films of a laminate (JP-A-64-55393). However, even by employing these methods as above, an openness of approximately 70% is at most, and when the openness of not lower than 70% is tried to attain, slippage of a stitch at a part of openings of a cloth is caused, which makes difficult a production of a cloth, and insertion thereof between films of a laminate.
Furthermore, there is proposed a cloth using, instead of sacrificial threads, a yarn having a raised apparent specific gravity by improving a commercially available yarn of polytetrafluoroethylene (PTFE) having porosity. However, employment of only the reinforcement threads is limitative to raising of openness (JP-A-3-217427).
Thus, a method is proposed wherein the plain weave reinforced cloth which has been obtained by mixedly weaving a reinforce yarn of a perfluoro-polymer and a sacrifice yarn which is soluble on use in an electrolysis cell, or is soluble by a chemical treatment such as with an acid or an alkali solution, is inserted between films of a laminate, and then the sacrificial threads in the cloth are dissolved by the chemical treatment as described above (JP-A-1-308435 and JP-A-63-113029). By mixedly weaving with sacrificial threads, even when the openness at a portion of reinforcement threads is high, this cloth maintains favorable prevention from slippage of a stitch. Further, since sacrificial threads are dissolved while remaining in a membrane, at the part where the sacrificial threads originally occupied, a void channel (hereinafter referred to as “a channel after dissolution of sacrificial threads”) is produced in the membrane. Moreover, by making the position of the cloth in the membrane close to the side of the membrane which is in contact with an anode solution, a minute cleft (hereinafter referred to as “penetrating channel”) is caused on the surface of the membrane, and by conducting the anode solution thorough the penetrating channel to a continuous tubular path which has been formed by a channel after dissolution of sacrificial threads at an inner part of the membrane, the anode solution can be filled to the part where an ionic transfer has been prevented by the reinforcement threads and the layer where the tubular path resides. Resultantly, electric resistance of a membrane can be reduced.
However, there is such a problem that the tubular path is in connection with the whole of the cloth, namely with the whole of the membrane, on use in an electrolysis cell, a portion of the anode solution is apt to bleed out of a flange which fixes a membrane to the electrolysis cell, and thus a leak of the anode solution from the circumference of the membrane is caused. This leak of the anode solution out of the vessel accelerates corrosion of an electrolysis cell and deterioration of a gasket, and, in the worst case, a short circuit is caused owing to a precipitation of a salt, and electrolysis sometimes is forced to be terminated. Particularly, pressure on the surface of the flange in the longitudinal direction of the electrolysis cell sometimes is not uniform, and leak especially from the lower part of the electrolysis cell can be caused. Therefore, when the electrolysis cell is equipped with a membrane, a channel after dissolution at the flange part is clogged, for instance, by applying a pasty silicone sealant or a fluorine type grease to the gasket. However, depending upon the shape of an electrolysis cell, the coating takes much time and labor, and when thickness of the coating is not uniform, the sealant or the grease may protrude to an electric current conducting portion and an electrolysis cell, which are a problem.
SUMMURY OF THE INVENTION
The task of the present invention is to provide a cation exchange membrane using a plain weave reinforced cloth, and a process of a production thereof, wherein the membrane has a channel(s) after dissolution which is(are) formed at a part(s) where sacrificial threads have been dissolved, has a continuous tubular path(s) formed thereby, and on use of an electrolysis cell, no leak of an anode solution can be seen out of the membrane through the channel(s) after dissolution and the tubular path(s).
The present inventors have intensively studied to solve the problems as stated above, and as a result, they have found that, when the shape of a cross section of a channel after dissolution which is formed at a part where sacrificial threads have been di
Hirano Toshinori
Sakuma Yuichi
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Cole Elizabeth M
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