JP2009013296A - Gasket material for electrolytic cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gasket material for an electrolytic cell in an ion exchange membrane method, from which a gasket excellent in chemical resistance against sodium hypochlorite or the like, creep resistance and electric insulating property can be inexpensively formed. <P>SOLUTION: The gasket material for an electrolytic cell comprises a rubber base material for forming a gasket to be used for an electrolytic cell in an ion exchange membrane method. The rubber base material comprises a mixture of an ethylene-propylene diene copolymer rubber by 70 to 95 wt.% and a chlorosulfonated polyethylene rubber by 5 to 30 wt.%, into which 10 to 50 parts by weight of carbon black, 10 to 50 parts by weight of an inorganic filler, 2 to 6 parts by weight of an organic peroxide crosslinking agent and 0 to 20 parts by weight of a plasticizer are compounded with respect to 100 parts by weight of the rubber base material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition material for a gasket used in an ion exchange membrane electrolytic cell, particularly an electrolytic cell for electrolyzing saline to produce chlorine and caustic soda.

  Conventionally, salt electrolysis by an ion exchange membrane method using an electrolytic cell has been performed in order to obtain caustic soda and chlorine which are industrial basic raw materials. As this electrolytic cell, there is known a filter press type electrolytic cell or the like in which electrolytic cell frames and ion exchange membranes constituting an electrode chamber are alternately arranged and fastened with bolts or the like. There are two types of operation methods: natural circulation method and pressurized forced circulation method. In the natural circulation method, electrolysis is performed using the specific gravity difference between the electrolyte-only side and the side where the electrolyte and gas are mixed. Circulating liquid.

In such an electrolytic cell, chlorine gas, hydrogen gas, caustic soda, etc. are generated by electrolysis. In addition, when the electrolytic membrane is damaged due to a pinhole or the like for some reason, sodium hydroxide and sodium hypochlorite may be generated due to a reaction between caustic soda and chlorine.
In order to prevent these gases and liquids from leaking to the outside of the electrolytic cell, the connecting part of the piping hose through which the raw material liquid and the generated gas pass, etc., between the chamber frame and the ion exchange membrane arranged alternately in the electrolytic cell Gasket is interposed in Gaskets used in electrolyzers are required to be durable against the above electrolytes and gases and to have little creep due to tightening pressure.
As such a gasket, the chemical contact resistance of a gasket made of a rubber material such as ethylene propylene diene copolymer rubber (EPDM) has been improved by covering the contact portion with an electrolyte solution with a fluororesin sheet (Patent Document) 1) and those using fluorine-based rubber as a rubber material are used.

However, in salt electrolysis, etc., the temperature during the operation of the electrolytic cell is as high as 90 to 120 ° C, and when it is resting, the temperature drops to near normal temperature. There is a problem that it becomes easy. In addition, in the conventional rubber material, in order to reduce the compression set and improve the creep resistance, usually carbon black is blended, but sufficient sealing performance can be secured to cope with the above temperature change. When the amount of carbon black is blended, the electrical insulation of the gasket may not be maintained.
Also, in order to ensure excellent chemical resistance against sodium hypochlorite in addition to chlorine and caustic soda, there is a problem that the cost is significantly increased if a fluorine-based material is used like the above conventional gasket. is there.
Japanese Patent Laid-Open No. 5-9772

  The present invention has been made to cope with such problems, and is an ion exchange membrane method capable of forming a gasket excellent in chemical resistance, creep resistance, and electrical insulation against sodium hypochlorite at low cost. It aims at providing the gasket material for electrolytic cells.

  The gasket material for electrolytic cells of the present invention is a gasket material for electrolytic cells made of a rubber base material for forming a gasket used in an electrolytic cell of an ion exchange membrane method, and the rubber base material is made of ethylene propylene diene. It is a mixture of a polymer rubber (hereinafter referred to as EPDM) and a chlorosulfonated polyethylene rubber (hereinafter referred to as CSM). The above EPDM is 70 to 95% by weight based on the whole rubber base material, and the above CSM is a rubber group. It is characterized by blending 5 to 30% by weight with respect to the whole material.

  10 to 50 parts by weight of carbon black, 10 to 50 parts by weight of inorganic filler, 2 to 6 parts by weight of organic peroxide crosslinking agent, and 0 to 20 parts by weight of plasticizer with respect to 100 parts by weight of the rubber base material. It is characterized by being partly blended.

The electrolytic cell gasket material has a volume resistivity of 1.0 × 10 ¹⁰ Ω · cm or more.

  The gasket material for an electrolytic cell of the present invention uses a mixture of 70 to 95% by weight of EPDM and 5 to 30% by weight of CSM as a rubber base, and 10 to 50% by weight of carbon black with respect to 100 parts by weight of the rubber base. Parts and inorganic fillers in an amount of 10 to 50 parts by weight, so that it has superior chemical resistance to sodium hypochlorite and the like, compared to the case of using a conventional rubber base material of EPDM alone. It is possible to form an electrolytic cell gasket that is excellent in electrical insulation and can maintain a sealing property for a long period of time. Further, since no fluorine material is used, the cost is low.

The gasket material for an electrolytic cell of the present invention is a material for forming a gasket used in an electrolytic cell in which an alkaline chloride aqueous solution is electrolyzed using an ion exchange membrane method, for example, a cation exchange membrane. In particular, it is a material for a gasket used in an electrolytic cell for electrolyzing saline to produce chlorine and caustic soda.
The part where the gasket obtained by molding the gasket material for an electrolytic cell of the present invention is used is an arbitrary part requiring a seal in the electrolytic cell. Specifically, the connection part of the piping hose between the chamber frame and ion-exchange membrane which are arrange | positioned alternately in an electrolytic cell, a raw material liquid, produced | generated gas, etc. are mentioned. As described above, these parts are required to have chemical resistance and electrical insulation against caustic soda, chlorine, sodium hypochlorite, etc. in addition to creep resistance accompanying temperature change.

EPDM that can be used as a rubber base material in the gasket material for electrolytic cells of the present invention has moldability required for the gasket material, mechanical properties required for the gasket as the molded product, heat resistance, chemical resistance, etc. In consideration of the above, conventionally known ones can be appropriately employed.
Moreover, each compounding ratio of ethylene, propylene, and diene can be adjusted arbitrarily. Examples of the diene component include ethylidene norbornene (ENB), dicyclopentadiene (DCPD), 1,4-hexadiene (HD), 5-methylene-2-norbornene, dicyclooctadiene, 5-ethylidene-2-norbornene, and the like. It is done.

In EPDM, the heat resistance is better when the blending amount of the diene component is suppressed. Considering the operating conditions of the electrolytic cell of 90 ° C. to 120 ° C., the diene content in the rubber is preferably in the range of 1 to 5 parts by weight.
As specific examples of EPDM that can be used in the present invention, trade names of Mitsui Chemicals, Inc .: Mitsui EPT, Sumitomo Chemical, trade names: Esprene, JSR, trade names: JSR EP, DSM Product name: Keltan series, DuPont brand name: NORDEL series, Copolymer Rubber and Chemical Corporation brand name: Epsyn series, Polycer Rubber Corporation brand name: A POLYSAR system may be used.

In the gasket material for an electrolytic cell of the present invention, a mixture in which CSM is blended with the above EPDM is used as a rubber base material. CSM is blended with EPDM for the purpose of improving chemical resistance, and conventionally known ones can be appropriately employed.
Specific examples of CSM that can be used in the present invention include Tosoh Corporation trade name: TOSO-CSM series, DuPont Elastomer trade name: Hypalon series.

  In the rubber base material of the gasket material for an electrolytic cell of the present invention, the blending ratio of EPDM and CSM to the whole rubber base material is 70 to 95% by weight of EPDM and 5 to 30% by weight of CSM. More preferably, EPDM is 90 to 95% by weight and CSM is 5 to 10% by weight. If the CSM to be blended is less than 5% by weight, the chemical resistance is poor and unsuitable. If it exceeds 30% by weight, the compression set is inferior and unsuitable.

In the gasket material for an electrolytic cell of the present invention, an organic peroxide can be used as a vulcanizing agent for the rubber substrate.
Examples of organic peroxides include 2,5-dimethyl-2,5-di-t-butyl-peroxyhexane-3, di-t-butyl peroxide, 2,5-dimethyl-2,5-di- -T-butyl-peroxyhexane, t-butylcumyl peroxide, 1,3-bis (t-butylperoxy-isopropyl) benzene, dicumyl peroxide, 4,4-di-t-butylperoxy-butyl Valerate, 2,2-di-t-butylperoxy-butane, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, di-benzoyl peroxide, bis (o-methyl) Examples thereof include benzoyl) peroxide and bis (p-methylbenzoyl) peroxide.

The organic peroxide crosslinking agent is preferably blended in an amount of 2 to 6 parts by weight based on 100 parts by weight of the rubber base material. If the amount of the crosslinking agent is less than 2 parts by weight, the rubber substrate is not sufficiently crosslinked. On the other hand, if the blending amount of the crosslinking agent exceeds 6 parts by weight, the elasticity of the resulting gasket (rubber crosslinked body) is lowered, making it unsuitable as an electrolytic cell gasket. The organic peroxide cross-linking agent is a diluted product (about 40%) at the time of blending, but the above blending ratio is a blended amount in terms of a pure product (100%).
Moreover, you may use a well-known co-crosslinking agent together in order to improve the crosslinking efficiency by an organic oxide. Examples of the co-crosslinking agent include sulfur, TAIC, TAC, maleimide, quinone dioxime, and the like.

Carbon black is preferably not used in the production of an electrically insulating gasket. However, in order to improve the mechanical properties, creep resistance, etc. of the gasket, conventionally, carbon black has been reduced to 50 parts by weight based on 100 parts by weight of the rubber base material. More than part by weight was blended.
In the gasket material for an electrolytic cell of the present invention, by replacing a part of the carbon black that has been conventionally blended with other inorganic fillers, the electrical insulation is improved while maintaining the mechanical properties and creep resistance. I am trying. In addition, in an electrolytic cell gasket, sufficient electrical insulation is 1.0 × 10 ¹⁰ Ω · cm or more in terms of volume resistivity (100 V measurement).

In the electrolytic cell gasket material of the present invention, it is preferable to use furnace black, which is excellent in gasket reinforcement, as carbon black. Furnace black is produced by incomplete combustion of a gas, oil or mixture thereof with a certain amount of air. Furnace black is classified into SAF <ISAF <HAF <MAF <FEF <GPF <SRF in ascending order of particle diameter.
In order to increase the resistance value, a grade having a small specific surface area, that is, a particle having a large particle size is advantageous. Further, since SAF and ISAF having a small particle size are difficult to uniformly disperse, the carbon black used in the present invention is preferably HAF, MAF, FEF, GPF, or SRF grade.

Carbon black is preferably blended in an amount of 10 to 50 parts by weight per 100 parts by weight of the rubber base material. When the blending amount of carbon black is less than 10 parts by weight, the mechanical properties and creep resistance of the obtained gasket are inferior. On the other hand, if the blending amount of carbon black exceeds 50 parts by weight, the volume resistivity value becomes low and the electrical insulation is poor.
In order to increase the resistance value, it is advantageous that the particle size of the carbon black is large and the blending amount is small. In the present invention, since the blending amount of carbon black is reduced as compared with the prior art, sufficient electrical insulation can be secured even if a grade other than the grades with large particle size (GPF, SRF) is used in the furnace black grade. .

Examples of the inorganic filler that can be used in the gasket material for an electrolytic cell of the present invention include insulating inorganic fillers such as silica (including wet and dry types), clay, and calcium carbonate. Silica is called white carbon and has a reinforcing property next to carbon black, and has an effect of improving tensile strength, hardness, tear strength, wear resistance and improving the skin of the gasket surface. The clay mainly used in the present invention is a calcined clay obtained by calcining clay at 600 to 800 ° C. This calcined clay loses water of crystallization upon calcining, collapses the crystal structure to increase activity, and can improve the electrical insulation effect by adsorbing and fixing free ions.
In the present invention, it is preferable to use silica and calcined clay in combination as an inorganic filler. This is because the reduced amount of carbon black can be reinforced with silica, and the increased amount and electrical insulation effect can be improved with calcined clay.

  The inorganic filler is preferably blended in an amount of 10 to 50 parts by weight with respect to 100 parts by weight of the rubber base material. In the present invention, as described above, since the blending amount of carbon black is suppressed to ensure electrical insulation, the mechanical properties of the obtained gasket are required when the blending amount of the inorganic filler is less than 10 parts by weight. It cannot be improved to a certain level. In addition, when the blending amount of the inorganic filler exceeds 50 parts by weight, there are problems that the hardness of the gasket becomes too high and the creep resistance is inferior.

In the gasket material for an electrolytic cell of the present invention, various additives such as carbon black, fillers other than inorganic fillers, softeners, anti-aging agents, lubricants, etc., are appropriately blended with the rubber base material as necessary. can do.
Examples of the softening agent include process oils, vegetable oils, synthetic oils, and plasticizers such as ester type, and they can be used in combination. The plasticizer is preferably blended in an amount of 0 to 20 parts by weight with respect to 100 parts by weight of the rubber base material.

In order to produce a gasket using the gasket material for electrolytic cells of the present invention, first, EPDM, CSM, and other additives are mixed by a mixer such as a Banbury mixer, a kneader, an intermix, an internal mixer, and a roll. The blended gasket material is kneaded for several minutes to several tens of minutes at an appropriate temperature. The vulcanizing agent is preferably added after EPDM, CSM, and other additives are uniformly kneaded.
Next, the kneaded material is formed into an intended shape using an extrusion molding machine, a calender roll, a press, an injection molding machine, a transfer molding machine, a compression molding machine, or the like.

Examples 1 to 2 and Comparative Examples 1 to 3
The various blending components shown in Tables 1 and 2 were kneaded with a 6-inch open roll, and the resulting gasket material was subjected to press vulcanization at a gauge pressure of 100 kg / cm ² at 164 ° C for 20 minutes. Vulcanization operation was performed to obtain a sheet-like vulcanized rubber having a thickness of 2 mm as a sample of a crosslinked product.
In the table, each compound is specifically as follows.
ENB-based EPDM (1): Mitsui EPT3045 manufactured by Mitsui Chemicals, Inc.
ENB-based EPDM (2): JSR manufactured by JSR EP21
CSM: TOSO-CSM TS-530 manufactured by Tosoh Corporation
Organic peroxide cross-linking agent: Di-Cup 40C manufactured by GEO Specialty Chemicals
Carbon black (MAF): Seast G-116 manufactured by Tokai Carbon
Carbon black (SRF): HTC # SL-F manufactured by Nippon Nikkei Carbon
Carbon Black (HAF): Toast Carbon Co., Ltd. Seest 3
Silica-based filler: Nipsil VN3 manufactured by Tosoh Silica
Clay: SAINTONE SP-33 manufactured by ENGELHARD
Plasticizer: NCL 46 manufactured by Taniguchi Oil Refinery

The following tests were performed on the obtained samples of Example 1 and Comparative Example 1.
Vulcanized rubber was punched into a predetermined sample shape (JIS No. 3 dumbbell), and each characteristic was measured by performing a tensile test according to JIS K6251 and a hardness test according to JIS K6253. The results are also shown in Table 1 as normal physical properties.
In addition, in order to evaluate the heat aging characteristics, each sample was subjected to heating at 100 ° C. for 72 hours in a gar-type oven according to the aging test of JIS K 6257. A hardness test was performed to measure each characteristic (change rate). The results are also shown in Table 1.
In addition, in order to evaluate chemical resistance, each sample was immersed in a 10% sodium hypochlorite solution at 70 ° C. for 72 hours according to the immersion test of JIS K 6258, and then the same tensile test and A hardness test was performed to measure each characteristic (change rate). The results are also shown in Table 1.

In order to evaluate the compression characteristics, a compression set (C-set) test was performed on each sample. The test conditions were 100 ° C. × 72 hours, the compression rate was 25%, and the test was performed according to JIS K6262. The results are also shown in Table 1.
Further, in order to evaluate the electrical characteristics, the volume specific resistance value at 100 V load was measured for each sample (100 mm × 100 mm × 2 mm). The results are also shown in Table 1.

  As shown in Table 1, it can be seen that the one using the gasket material of Example 1 has improved chemical resistance while maintaining the mechanical characteristics and compression characteristics as compared with Comparative Example 1. Moreover, the volume resistivity value is also greatly increased.

The samples of Example 2, Comparative Example 2 and Comparative Example 3 thus obtained were evaluated for normal physical properties, heat aging characteristics, chemical resistance, compression characteristics and electrical characteristics in the same tests as in Example 1. The results are also shown in Table 2.
In Table 2, regarding the evaluation of heat aging characteristics, chemical resistance and compression characteristics, it is “◯” when it is a value that can be used as a gasket for an electrolytic cell, and “×” when it is a value that cannot be tolerated. " For the evaluation of electrical characteristics, “○” was given when the volume resistivity value was 1.0 × 10 ¹⁰ Ω · cm or more, and “X” was given when it was less than 1.0 × 10 ¹⁰ Ω · cm.

  As shown in Table 2, compared with Example 2 in which EPDM and CSM were blended within a predetermined range, Comparative Example 2 and Comparative Example 3 were electrolyzed in any of heat aging characteristics, chemical resistance and compression characteristics. It could not be used as a tank gasket.

  The gasket material for an electrolytic cell of the present invention can be used as a gasket material used in an electrolytic cell of an ion exchange membrane method because a gasket excellent in chemical resistance, creep resistance, and electrical insulation can be formed at low cost. it can.

Claims (3)

A gasket material for an electrolytic cell made of a rubber base material for forming a gasket used for an electrolytic cell of an ion exchange membrane method,
The rubber base material is a mixture of ethylene propylene diene copolymer rubber and chlorosulfonated polyethylene rubber, and the ethylene propylene diene copolymer rubber is 70 to 95% by weight based on the whole rubber base material. Electrolyzed gasket material for electrolytic cell, characterized by comprising 5 to 30% by weight of each polyethylene rubber blended with respect to the entire rubber base material.   10 to 50 parts by weight of carbon black, 10 to 50 parts by weight of an inorganic filler, 2 to 6 parts by weight of an organic peroxide crosslinking agent, and 0 to 20 parts by weight of a plasticizer with respect to 100 parts by weight of the rubber base material. The gasket material for an electrolytic cell according to claim 1, wherein the gasket material is partly blended. 3. The electrolytic cell gasket material according to claim 1, wherein the electrolytic cell gasket material has a volume resistivity of 1.0 × 10 ¹⁰ Ω · cm 2 or more.