JP2015037761A - Gasket spacer used for electrodialyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gasket spacer used for an electrodialyzer capable of effectively suppressing the degradation of sealing property and the deterioration of surface smoothness or the like although having such a structure that a net and a gasket frame are integrated by thermal bonding in the gasket spacer arranged between ion exchange membranes adjacent to each other of an electrodialyzer.SOLUTION: In the gasket spacer 10 arranged between ion exchange membranes adjacent to each other of an electrodialyzer, a part made of a thermoplastic net 1 and a thermoplastic gasket frame 3, in which the surrounding of the net 1 is fastened to the gasket frame 3 by thermal fusion and filament bodies of the net 1 are thermally fused is located on an inner part of the gasket frame 3, are flattened and have an elliptical traverse section 1a'.

Description

  The present invention relates to a gasket spacer disposed between adjacent ion exchange membranes of an electrodialysis apparatus, and more particularly to a gasket spacer having a structure in which a net is integrally fixed to a gasket frame.

  Electrodialysis desalination of electrolyte solution was first developed in the 1950s for the purpose of desalination of brine. After that, seawater concentration for the production of salt, soy sauce and whey desalination, It is used for desalination from various electrolyte solutions such as rationalization of chemical manufacturing processes, wastewater treatment, and separation of impurities in wine.

  In the electrodialysis apparatus used for electrodialysis as described above, a large number of gasket spacers (also called chamber frames) are arranged between a pair of electrodes, and between adjacent chamber frames. The anion exchange membrane or the cation exchange membrane is sandwiched, and the anion exchange membrane and the cation exchange membrane are alternately arranged as a whole, and each gasket is partitioned by the anion exchange membrane and the cation exchange membrane. (Energization part) will be formed. In such an ion exchange chamber, the chamber in which the cation exchange membrane is located on the negative electrode side and the anion exchange membrane on the positive electrode side is a desalination chamber, the anion exchange membrane is located on the negative electrode side, and the cation is on the positive electrode side. The chamber where the exchange membrane is located is a concentrating chamber, and the desalting chamber and the concentrating chamber are alternately arranged. That is, when energization is performed while circulating the treatment solution (electrolyte solution) in the desalting chamber, the cations in the treatment solution supplied to the desalting chamber pass through the cation exchange membrane and move to the adjacent negative electrode concentration chamber. Then, the anion in the treatment liquid passes through the anion exchange membrane and moves to the adjacent positive electrode-side concentration chamber. In this way, when the treatment solution is circulated and supplied to the desalting chamber and at the same time the aqueous salt solution is circulated to the concentration chamber, the desalination of the treatment solution is performed and at the same time, a concentrated solution having an increased salt concentration can be obtained. .

By the way, the gasket spacer is composed of a rectangular gasket frame and a net (that is, one in which filaments intersect in a mesh pattern) arranged in a space surrounded by the gasket frame. That is, the space surrounded by the gasket frame becomes an ion exchange chamber such as a desalination chamber or a concentration chamber, and a net is provided to prevent contact between the ion exchange membranes located on both sides of the gasket spacer.
Conventionally, in the gasket spacer as described above, a resin or rubber gasket frame and the gasket spacer are individually arranged and not integrated, or a gasket frame and spacer as shown in Patent Document 1 Most of them had a structure in which the inner peripheral edge of the gasket frame and the spacer were partially bonded after each was placed individually. However, they are not completely integrated, which is inconvenient to handle and the work of partially bonding them is complicated. Recently, a structure in which a net shown in Patent Document 2 is heat-welded to a gasket frame has been proposed.

Japanese Examined Patent Publication No. 6-55261 JP 2009-536094 A

  However, when the net is heat-welded to the gasket frame as described above, there is a problem that characteristics required for the gasket spacer, for example, sealing properties are impaired. That is, when the linear body forming the net by heat welding and the gasket frame are fused and integrated, the surface smoothness of the gasket frame is impaired, and as a result, adjacent gaskets sandwiching the ion exchange membrane. At present, there is a problem that a gap is formed between the spacer and the gasket frame, and liquid leakage easily occurs from this portion.

  Accordingly, an object of the present invention is a gasket spacer disposed between adjacent ion exchange membranes of an electrodialysis apparatus, having a structure in which a net (spacer) and a gasket frame are integrated by thermal bonding. Another object of the present invention is to provide a gasket spacer in which a decrease in sealing performance or a decrease in surface smoothness is effectively suppressed.

According to the present invention, in the gasket spacer disposed between the adjacent ion exchange membranes of the electrodialysis apparatus,
The gasket spacer is composed of a thermoplastic net and a thermoplastic gasket frame, and the periphery of the net is fixed to the gasket frame by thermal fusion,
A heat-sealed portion of the wire rod of the net is located inside the gasket frame and is flattened to have an elliptical cross section. .

In the gasket spacer of the present invention,
(1) The height (diameter of the minor axis of the ellipse) of the cross section of the heat-sealed portion of the filament of the net is the height (diameter) of the portion of the wire that is not heat-sealed. In the range of 10 to 60% of
(2) The net is made of an olefin resin, and the gasket frame is made of a thermoplastic elastomer.
(3) The thermal fusion is performed by high frequency dielectric heating,
Is preferred.

  The gasket spacer of the present invention has an integrated structure in which the periphery of the net is fixed to the gasket frame by heat sealing, and this heat-bonded portion is located inside the gasket frame. ing. That is, the fact that the heat fusion part is located inside the gasket frame means that the gasket frame is formed by bonding two frame-like sheets together and thermally fusing them together. This means that this heat fusion is performed in a state where the periphery of the net is sandwiched between two frame sheets.

  The present invention is characterized in that the heat-sealed portion of the wire rod of the net fixed to the gasket frame in this way is flattened by heat-sealing and has an elliptical cross section. . That is, the net is formed by crossing a large number of striated bodies in a mesh shape and fusing the intersecting portions, and the cross section (transverse section) of the striated body forming such a net is: Although it has a circular shape or a shape close to a circular shape, in the present invention, such a circular shape or a cross-section similar to a circular shape is flattened into an elliptical shape by heat fusion sandwiched between a pair of gasket frames. It is. For example, the minor axis length of the ellipse formed by such flattening (the height of the transverse section of the heat-sealed portion) is the height of the transverse section (corresponding to the diameter) of the portion that is not thermally fused. It is in the range of 10 to 60%.

  In the present invention, since the heat sealing between the pair of gasket frame sheets and the net filaments is performed by the above-described heat sealing, both the gasket frame and the net are formed of thermoplastic plastic. . That is, according to the present invention, by using such a thermoplastic plastic and maintaining the cross-sectional shape of the linear body to some extent, the deterioration of the spacer characteristics due to the thermal fusion is effectively prevented. For example, the flattening of the filaments is remarkable, and when heat fusion is performed by applying temperature and pressure to the extent that the elliptical shape is impaired, the dimensional stability of the gasket frame is impaired, and the shape of the gasket frame is distorted, Alternatively, wrinkles are generated on the surface and the surface smoothness is impaired, and as a result, the sealing performance required for the gasket spacer is greatly reduced. In addition, the fusion strength such that the cross-sectional shape of the striated body is hardly flattened results in insufficient bonding strength, and the net is likely to be detached from the gasket frame. In the present invention, the above-mentioned inconveniences are effectively eliminated because the wire rod and the gasket frame of the net are flattened and fused appropriately.

  According to the gasket spacer of the present invention, since the gasket frame and the net are integrated, it is easy to handle, and an electrodialysis apparatus free of liquid leakage is easily assembled in combination with an ion exchange membrane or the like. Can do.

It is a top view of the gasket spacer of this invention. It is a partial expanded sectional view which shows the cross section of the linear body which forms the net | network in the heat sealing | fusion part of the gasket spacer of FIG. 1 with a gasket frame. It is explanatory drawing for demonstrating the principle of the electrodialysis apparatus in which the gasket spacer of FIG. 1 is used. It is a disassembled perspective view of the principal part of the electrodialysis apparatus which performs the electrodialysis of FIG. It is a sectional side view of the principal part of the electrodialysis apparatus shown by FIG.

<Gasket spacer structure>
Referring to the plan view of FIG. 1, the gasket spacer of the present invention indicated by 10 as a whole crosses a large number of filaments 1 a having a diameter of about 0.4 to 1.4 mm and joins them together at the intersection. And a gasket frame 3 surrounding the net 1. The net 1 and the gasket frame 3 are both made of thermoplastic plastic, and the periphery of the net 1 is heat-sealed and fixed inside the gasket frame 1.

  That is, the electrodialysis apparatus roughly includes the gasket spacers 10 and the ion exchange membranes (anion exchange membrane and cation exchange membrane) alternately disposed as described above, and the ion exchange membranes between the gasket spacers 10 are provided. It is configured by pinching. That is, the space surrounded by the gasket frame 3 of the gasket spacer 10 becomes an ion exchange chamber, and the net 1 can surely prevent contact between adjacent ion exchange membranes.

  Referring also to FIG. 2 showing the cross section of the filament 1a at the heat-sealed portion, the gasket spacer 10 having the structure as described above is composed of two pieces each having a thickness of about 0.1 to 1.0 mm. When the gasket frame 3 is formed by thermal fusion in a state where the frame sheets 3a and 3b are bonded together, it is manufactured by performing thermal fusion while sandwiching the periphery of the net 1 therebetween.

  In the present invention, the cross section of the filament 1a forming the net 1 is flattened and becomes elliptical by such heat fusion. The cross-sectional shape of the flattened filament 1a at the heat-sealed portion is indicated by 1a 'in FIG.

That is, by the thermal fusion that causes such flattening, the linear body 1a and the gasket frame 3 (frame sheets 3a and 3b) can be appropriately performed without hindering the thermal fusion between the frame sheets 3a and 3b. It is fixed by fusing. For example, such thermal fusion is performed by adjusting the thermal fusion conditions (thermal fusion means, temperature, pressure, etc.) and the minor axis length of the ellipse formed by flattening (of the thermal fusion part 1a ′). The height of the cross section d) is 10 to 60%, particularly 20 to 40% of the height D (corresponding to the diameter) of the cross section (1a) of the portion not heat-sealed. Is preferred.
If the length d at the fused portion 1a ′ is too short, heat fusion is performed excessively, the dimensional stability of the gasket frame 3 is impaired, and the shape of the gasket frame 3 is distorted. Or the surface smoothness will be impaired by wrinkles occurring on the surface. Such deformation and a decrease in surface smoothness cause a significant decrease in the sealing performance required for the gasket spacer. In addition, when the length d at the fusion part 1a ′ is not so short, flattening is insufficient, and in such fusion, the net 1 (the filament 1a) and the gasket frame 3 The bonding strength of the net 1 becomes insufficient, and the net 1 is likely to be detached from the gasket frame 3.

  In the present invention, since heat fusion is performed in the above-described degree, naturally, the net 1 (wire body 1a) and the gasket frame 3 (frame sheets 3a and 3b) are both made of thermoplastics. used.

The thermoplastic plastic that is the material for forming the net 1 (striate body 1a) is not particularly limited as long as it is electrically insulating and has a predetermined strength, and various thermoplastic resins such as Can be used alone or in the form of a blend of two or more.
Olefin resins;
Low density polyethylene, high density polyethylene, polypropylene, poly 1-butene,
Poly-4-methyl-1-pentene or ethylene, propylene, 1-butene,
Random or block copolymers of α-olefins such as 4-methyl-1-pentene and cyclic olefin copolymers.
Ethylene-vinyl copolymer resin;
Ethylene / vinyl acetate copolymer, ethylene / vinyl alcohol copolymer,
Ethylene / vinyl chloride copolymer, etc.
Styrenic resin;
Polystyrene, acrylonitrile / styrene copolymer, ABS,
α-methylstyrene / styrene copolymer, etc.
Vinyl resin;
Polyvinyl chloride, polyvinylidene chloride, vinyl chloride / vinylidene chloride copolymer,
Polymethyl acrylate, polymethyl methacrylate, etc.
In the present invention, among these thermoplastic resins, an olefin resin is preferable.

  Formation of the net 1 by the thermoplastic resin filament 1a as described above can be performed by various methods, for example, a method of weaving thermoplastic resin yarns (plain weaving, twill weaving, satin weaving, etc.) Although not particularly limited, from the viewpoint of productivity and the like, it is preferable to produce by integral extrusion molding of a thermoplastic resin. Such integral extrusion can be performed by a known method described in, for example, Japanese Patent Publication No. 34-4185 and Japanese Patent Laid-Open No. 53-49170.

Also, the thermoplastic for the gasket frame 3 is the same as the thermoplastic for the net 1 in that it has electrical insulation, but from the viewpoint of sealing properties, it has rubber elasticity or is relatively flexible. In particular, thermoplastic elastomers and polyvinyl chloride are suitable. Such thermoplastic elastomers include ethylene-propylene copolymer rubber, ethylene-propylene-butene copolymer rubber, styrene-butadiene copolymer rubber, styrene-butadiene-styrene copolymer rubber, styrene-isoprene copolymer rubber. Various rubber components such as coal rubber, styrene-isoprene-styrene copolymer rubber, styrene-ethylene-butadiene-styrene copolymer rubber, etc. are finely divided into thermoplastic resins such as styrene resin, vinyl chloride resin and olefin resin. Examples of the dispersed resin can be given, and an appropriate one is used according to the kind of the thermoplastic resin for the net described above. For example, a thermoplastic elastomer having a melting point close to that of the thermoplastic resin for the net is preferably used.
In the present invention, a polyvinyl chloride sheet or a thermoplastic elastomer sheet having a hardness (JIS A) of about 60 to 90 degrees is preferable.

  In the present invention, the above heat fusion is performed by high frequency dielectric heating. That is, in a method such as hot pressing in which a heated plate is used for thermocompression bonding, the outer surface of the gasket frame sheets 3a and 3b is heated to a temperature higher than that of the inner surface when heat sealing is performed. While maintaining the shape of the frame sheets 3a and 3b, the linear body 1a sandwiched between them cannot be flattened. This is because if the flattening described above is performed, the gasket frame sheets 3a and 3b are melted and deformed. On the other hand, since high frequency dielectric heating is performed by internal friction of the resin, the inner surfaces of the gasket frame sheets 3a and 3b and the filaments 1a can be selectively heated, and the gasket frame sheets 3a and 3b. Can be effectively avoided.

In the present invention, the high-frequency dielectric heating is performed by arranging the gasket frame sheets 3a and 3b sandwiching the above-described net 1 between a pair of electrodes (electrode molds) and applying a high-frequency current while pressing with the electrodes. Is done. The heating conditions vary depending on the material and thickness of the gasket frame sheets 3a and 3b and the net 1 (striate body 1a), and cannot be generally defined, but generally the frequency is 1 to 300 MHz, more preferably 5 to 50 MHz, current value is about 1 to 3 A, more preferably 1.5 to 2.5 A, press pressure is about 0.1 to 20 kg / cm ² , more preferably 2 to 10 kg / cm ² , heating The time is about 30 to 180 seconds, more preferably 30 to 100 seconds. Further, a high-frequency dielectric heating can be performed by disposing a release sheet such as a PET sheet or a polyimide sheet between the electrodes.

The gasket spacer of the present invention having the above-described structure can be obtained by performing the heat fusion treatment by high frequency dielectric heating as described above.
Such a gasket spacer is used for forming an electrodialyzer together with an ion exchange membrane by punching a hole or a flow path for flowing a processing solution at a predetermined position of the gasket frame 3.

<Electrodialysis machine>
Referring to FIG. 3 for explaining the principle of the electrodialysis apparatus formed using the gasket spacer of the present invention described above, in the electrodialysis apparatus, a cation exchange membrane C and an anion are provided between the negative electrode 20 and the positive electrode 30. Exchange membranes A are alternately arranged, and an ion exchange chamber is formed between these ion exchange membranes. That is, the ion exchange chamber is a desalting chamber 25 and a concentration chamber 27. As understood from FIG. 4, the desalting chamber 25 has a cation exchange membrane C and a positive electrode 30 with respect to the cation exchange membrane C. The concentration chamber 27 is composed of an anion exchange membrane A and a cation exchange membrane C located on the positive electrode 30 side with respect to the anion exchange membrane A. ing. Accordingly, a large number of desalting chambers 25 and concentration chambers 27 are alternately arranged.

In the electrodialysis apparatus having such a structure, for example, a voltage is applied between the positive electrode 30 and the negative electrode 20, a treatment liquid containing a salt such as NaCl is circulated and supplied to the desalting chamber 25, and the concentration chamber 27 is supplied to the concentration chamber 27. When the dilute electrolyte is energized while circulating, the cations (Na ⁺ ions) in the treatment liquid pass through the cation exchange membrane C to the concentration chamber 27 adjacent to the negative electrode 20 side. On the other hand, the anion (Cl ⁻ ) in the treatment liquid passes through the anion exchange membrane A and moves to the concentration chamber 27 adjacent to the positive electrode 30 side. In this case, although it depends on the characteristics of the anion exchange membrane, normally, the permeation of giant anions is prevented. In this way, desalting is performed from the processing solution circulated and supplied to the desalting chamber 25, and the salt concentration in the dilute electrolytic solution circulated and supplied to the concentration chamber 27 gradually increases. Eventually, it will be recovered as a highly concentrated aqueous salt solution.

When an exchange membrane having high monovalent selectivity is used as the cation exchange membrane C, for example, migration of polyvalent cations such as Ca ²⁺ contained in the treatment liquid to the concentration chamber 27 side is prevented. Only monovalent cations such as ⁺ ions can be selectively transferred to the concentration chamber 27 side, whereby high-purity monovalent salts can be recovered.

  In the electrodialysis performed in this way, it goes without saying that the treatment solution circulated and supplied to the desalting chamber 25 or the dilute electrolyte circulated and supplied to the concentration chamber 27 passes through the ion exchange membrane. Therefore, it is necessary to prevent leakage to the adjacent ion exchange chamber.

Therefore, in the electrodialysis apparatus for effectively performing electrodialysis as described above, as shown in FIGS. 4 and 5, a large number of the above-described gasket spacers 10 of the present invention are arranged in a stacked manner. Between these gasket spacers 10, cation exchange membranes C or anion ion exchange membranes A are alternately sandwiched so as to have the structure shown in FIG. In FIG. 4, the net 1 of the gasket spacer is omitted.
In the electrodialysis apparatus having such an arrangement, the space in each gasket spacer 10 (the space surrounded by the gasket frame 3) is the above-described ion exchange chamber (desalting chamber 25 or concentration chamber 27).

  Further, the gasket frame 3 of each gasket spacer 10 is supplied to the concentration chamber 27 and openings 41 ′ and 41 ′ for flowing the processing liquid supplied to the desalting chamber 25 and the processing liquid discharged from the desalting chamber 25. Openings 43 ′ and 43 ′ for flowing the diluted electrolyte solution (or the electrolyte solution that has been concentrated to increase the salt concentration) and the electrolyte solution discharged from the concentration chamber 25 are formed.

  Further, a distribution portion 45 that connects the communication hole 41 and the space that becomes the desalting chamber 25 is formed in the gasket frame 3 of the gasket spacer 10 that has a space that becomes the desalting chamber 25. Similarly, in the gasket frame 3 of the gasket spacer 10 having a space serving as the concentrating chamber 27, a flow distribution portion 47 that connects the communication hole 43 and the space serving as the concentrating chamber 25 is formed. That is, the liquid is supplied from these communication holes 41 and 43 to the desalting chamber 25 or the concentration chamber 27 through the distribution portions 45 and 47, and the liquid supplied to the desalination chamber 25 or the concentration chamber 27 is further supplied to the distribution portion. The structure is such that it is discharged and returned to the communication hole 41 or 43 through 45 or 47.

  In the electrodialysis apparatus having the structure described above, since the ion exchange membrane (cation exchange membrane C or anion exchange membrane A) is sandwiched between the gasket spacers 10, contact between adjacent ion exchange membranes is achieved by the gasket spacer 10. Effectively prevented. Further, openings 41 'and 43' are formed in the ion exchange membrane sandwiched between the gasket spacers 10 so as to allow the liquid to flow through the communication holes 41 and 43 (FIG. 4). reference).

  In other words, by energizing the processing holes 41 and 43 through the processing solution and the dilute electrolyte, the salt is removed in the desalting chamber 25 and the salt concentration of the solution flowing in the concentration chamber 27 gradually increases. It will be done.

  The gasket spacer 10 is formed on the gasket frame 3 for the purpose of reducing leakage current generated through the distribution section 45 and preventing internal leakage in the stack caused by the film falling into the net in the distribution section 45. In the distribution portions 45 and 47, for example, a liquid member disclosed in JP 2011-93240 A or the like, or a net member of a different type from the spacer net can be attached. That is, the liquid flowing through the communication hole 41 or the communication hole 43 is supplied into the desalting chamber 25 or the concentration chamber 27 through the flow path formed by such a liquid passing member. The liquid supplied to the concentration chamber 27 is returned to the communication hole 41 or the communication hole 43 through such a liquid passing member.

  In addition, the gasket spacer in this invention can be applied not only for electrodialysis but also for diffusion dialysis using an ion exchange membrane.

  The excellent effects of the gasket spacer of the present invention will be described by the following experimental examples, but the present invention is not limited to these examples.

<Examples 1-6>
The experimental results of Examples 1 to 6 are shown in Table 1 below.
The gasket frame shown in this embodiment is formed by bonding two frame-like sheets by high-frequency dielectric heating and bonding them by heat fusion. It is in a state of being sandwiched between frame-shaped sheets.

In addition, the symbol in the said table | surface shows the following. The same applies to the comparative table.
PVC: Polyvinyl chloride EVA: Vinyl acetate copolymer SBR: Styrene butadiene rubber PE: Polyethylene PP: Polypropylene PA: Polyamide

  It was confirmed that the gasket frame of the above example had a good result even in the leakage test evaluation and had a sealing property to withstand practical use.

<Comparative Examples 1-6>
The experimental results of Comparative Examples 1 to 6 are shown in Table 2 below.
It can be seen that these gasket frames are difficult to seal.

1: Net 1a: Striated body 3: Gasket frame 3a, 3b: Gasket frame sheet 10: Gasket spacer C: Ion exchange membrane A: Anion exchange membrane 25: Desalination chamber 27: Concentration chamber 41, 43: Communication hole 45, 47: Distribution section

Claims (4)

  In the gasket spacer disposed between the adjacent ion exchange membranes of the electrodialysis apparatus, the gasket spacer includes a thermoplastic net and a thermoplastic gasket frame, and the periphery of the net is heat-sealed to the gasket frame. And the heat-sealed portion of the wire rod of the net is located inside the gasket frame and is flattened to have an elliptical cross section. Gasket spacer to be used.   The height of the transverse cross section (the minor axis length of the ellipse) of the heat-bonded portion of the wire rod of the net is 10 to 60% of the height of the wire rod of the non-heat-bonded portion. The gasket spacer according to claim 1 in the range of   The gasket spacer according to claim 1 or 2, wherein the net is made of an olefin resin, and the gasket frame is made of a thermoplastic elastomer.   The gasket spacer according to claim 1, wherein the heat fusion is performed by high frequency dielectric heating.

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