JPS6037878B2 - Ion exchange membrane electrolyzer - Google Patents

Description

[Detailed description of the invention] The present invention relates to an ion exchange membrane electrolytic cell.

In particular, the present invention relates to an excellent ion exchange membrane electrolytic cell that is inexpensive to manufacture.

Various types of electrolytic cells are known for use in electrolyzing alkali chloride, water, hydrochloric acid, and the like.

In the old days, the mercury method was a non-diaphragm electrolysis method using mercury as the cathode, and then the so-called furnace diaphragm method, which used an electrolyte-permeable diaphragm obtained by depositing asbestos fibers on the cathode.
Currently, the so-called ion-exchange membrane electrolysis method, which uses a permselective pig membrane that can selectively permeate only specific ions, especially intestinal ion permselective membranes, is currently being used. It is becoming the mainstay from this point of view. The electrolytic cells used in this ion-exchange membrane electrolysis method can be roughly divided into single-electrode electrolytic cells and back-electrode electrolytic cells.Both types have an anode and a cathode arranged on both sides of an intestinal ion-exchange membrane, and further outside. A configuration in which an anode chamber frame and a cathode chamber frame are arranged as one unit,
This process is repeated a necessary number of units to roughly raise the temperature using a filter press method, and a so-called filter press monopolar tank or filter press type monopolar cell is often used.

Conventionally, a frame-shaped chamber frame made by stringing square hollow pipes together has been used as the chamber frame of a filter press type electrolytic cell.

A conductive rod is inserted from the side or bottom side of the frame-shaped chamber frame, and a porous electrode plate, such as expanded metal, is attached to this so as to cover the frame-shaped closing part of the chamber frame from both sides. The entrance part communicates with the hollow pipe through a pore, and the opening constitutes an electrode chamber. Electrolytic cells using such a chamber frame are useful and effective to some extent, but since the chamber frame is manufactured by processing a hollow pipe made of expensive material, it is costly in terms of material costs and processing costs. It has to be quite expensive.

Therefore, a so-called plate-type flea tank, which uses a plate-shaped frame-shaped gasket as the chamber frame, has been devised as an electrolytic cell that eliminates the above-mentioned drawbacks.

This type of torpedo tank is, for example, JP-A-53-10889Y.
The chamber frame is made of a non-acid-conducting, flexible material and has a frame-shaped opening as an electrolytic chamber, and a gasket, an intestinal ion exchange membrane, and an electrode plate. It is assembled in a filter press type, and has barrier holes at the four corners of the chamber frame, electrode plate, and cation exchange membrane, which serve as passages for the electrolyte and the products to be electrolyzed. Although this type of electrolytic cell is certainly advantageous in terms of manufacturing cost compared to the one using the hollow pipe described above, there are problems with the structure of the electrode plate itself.

That is, in the plate-type battery case as disclosed in the above-mentioned publication, an electrode plate is sandwiched between a chamber frame having a plate-like frame-like closing part.
In order to make both sides of the punched plate function as electrode surfaces, the structure inevitably creates a step between the flange surface and the electrode surface. In recent years, energy-saving electrolytic technology has been trending, and efforts have been made to reduce the distance between the electrodes, but in the case of the structure shown in the above publication, when the distance between the electrodes is reduced, the electrode surface and flange surface are There is a high risk of damaging the ion exchange membrane at the step portion that occurs. In addition, in zero-gap electrolyzers, it is desirable to use porous electrodes with small openings in order to make the current distribution uniform near the electrode surface and keep the voltage low. In the electrolytic cell disclosed in the above-mentioned prior document, it is difficult to construct electrodes with small openings on the plate itself due to functional and strength constraints, so welding expanded metal etc. with small openings separately. It is necessary to attach it to a flange or a punched plate by means of It is not recommended for use. The present inventors have solved the Kamitakuma problem and studied an electrolytic cell that can be truly adopted industrially, and have arrived at the present invention. a passageway for the electrolyte and the electrolyzed product leading to the outside;
A frame-shaped chamber frame having an opening forming an electrolytic chamber that fits in with the passage, and a recessed sealing surface having a thickness approximately equal to the thickness of the electrode plate around the barrier part; is a porous electrode plate which is substantially one flat plate larger than the electrolytic chamber and has no barrier holes corresponding to the passages for the electrolyte and the electrolyzed product provided in the chamber frame, and has at least one positive electrode plate. The electrode active surface of the electrode plate facing the ion exchange membrane and the surface of the electrode plate facing the intestinal ion exchange membrane facing the sealing surface of the electrolysis chamber frame have the same plane with no difference in height, { c' A liquid-tight sealing part is interposed between the anode and the cation exchange membrane and between the intestinal ion exchange membrane and the cathode of the seal part, {d
'The gist of the present invention is an ion exchange membrane electrolytic cell characterized in that the electrode active surface is substantially in contact with the intestinal ion exchange membrane.

The electrodes used in the present invention will be explained.

The electrode can be a porous electrode, such as expanded metal, punched metal, or wire mesh, which is porous and permeable to gas and liquid. There is no need to particularly limit the means for imparting electrode activation to these electrodes, and platinum, palladium, rhodium,
A porous electrode substrate as described above may be coated with a known electrode active component such as an autometal such as luteurium or an alloy thereof, or an oxide of a platinum metal or an alloy of a platinum metal. Further, as the cathode, a porous electrode made of metal such as iron, stainless steel, or nickel can be used, but preferably a porous electrode made of etched stainless steel as disclosed in Japanese Patent Application Laid-Open No. 53-LO227, Alternatively, as disclosed in JP-A-54-112785, developed or undeveloped Raney alloy particles are co-electrodeposited. A feature of the present invention is that the electrode as described above is a flat porous electrode that is integrated with the seal portion facing the electrolytic chamber frame without creating a step.
Another feature is that the supply of current from the outside to the electrode surface and the conduction of current to the outside are done only by the flat porous electrode plate that serves as the electrode base, so the electrode surface is free from cations. In the area facing the exchange membrane, there is no need for welding or bolting structures required to electrically connect conductive ribs or conductive plates, so there is no need for roughness or steps on the electrode surface caused by these connections. There are things that will not happen. Specific examples of the above-mentioned porous electrode plate include punched metal, expanded metal whose entire surface is smoothed, and wire mesh whose sealed portion is smoothed.

If the porous electrode plate is made of punched metal, it is possible to leave the sealing part as a flat plate without holes, making it easy to create a liquid-tight seal with the chamber frame or the "r-on exchange membrane." In addition, the edge of the hole in the punched metal is rounded on one side during the manufacturing process, so by installing this side on the side facing the ion exchange membrane, the edge of the hole allows ions to be absorbed by the edge of the hole. This is particularly preferable as an embodiment of the electrode plate of the present invention because it prevents damage to the exchange membrane.If the porous electrode plate is made of expanded metal whose entire surface is smoothed by pressing, the porous electrode plate is Although it is possible to weld a frame-shaped flat plate with substantially the same thickness as the electrode without creating a step, it is also possible to install expanded metal without creating a step. It is also possible to extend the membrane to the sealed portion and sandwich the chamber frame and the ion exchange membrane directly or through packing at the portion in contact with the chamber frame.

When using a frame made of elastic material (e.g. rubber such as EPDM), liquid leakage will not occur even without packing, but for safety reasons, it is necessary to cover at least one side of the intestinal ion exchange membrane with packing. That's good. Furthermore, when a resin having relatively low elasticity is used for the chamber frame, it is necessary to provide packing on both sides of the cation exchange membrane.

It is surprising that even with such a configuration, the predicted liquid leakage does not occur at all. Wire mesh can also take the same form as expanded metal. In addition, porous electrode plates do not have pores corresponding to the openings provided in the electrolytic chamber frame that serve as passages for the electrolytic solution and the products to be electrolyzed. It's good because I don't have to worry about it.

As the electrolytic chamber frame used in the present invention, Hakama Kaisho 53-1
Those disclosed in Japanese Patent No. 0227 may be used. That is, non-conductive, sacrificial materials such as PVC resin, or non-conductive materials such as natural rubber, synthetic rubber such as EPDM,
An opening for forming an electrolytic chamber is provided in the center of the plate-shaped body made of a material with elasticity, and passages for smaller electrolytes and products to be electrolyzed are provided in the four corners of the opening. It can be manufactured very easily by providing an aperture that forms a .
The thickness and size of this chamber frame may be appropriately selected according to the processing capacity of the electrolytic cell, but it is not preferable to make the thickness too thin from the viewpoint of ease of escape of gas generated by electrolysis. Usually 7 or more willows, preferably 1
It is better to make it more than a revenge. The ion exchange membrane used in the present invention includes, for example, carboxyl groups, sulfonic acid groups,
It consists of a polymer containing a cation exchange group such as a phosphoric acid group or a phenolic hydroxyl group, and it is particularly preferable to employ a fluorine-containing polymer as such a polymer. Examples of fluorine-containing polymers containing ion exchange groups include vinyl mo/mers such as tetrafluoroethylene and chlorotrifluoroethylene, and reactive groups that can be converted into ion exchange groups such as sulfonic acid, carboxylic acid, and phosphoric acid groups. Perfluorinated vinyl monomer
A copolymer of a perfluoro vinyl monomer having an ion exchange group such as a sulfonic acid, carboxylic acid, or phosphoric acid group is preferably used. In addition, ion exchange groups such as sulfonic acid groups are introduced into membrane polymers of trifluorostyrene,
Styrene divinylbenzene with a sulfonic acid group introduced therein can also be used.

When using a fluorine-containing ion exchange membrane in which the concentration of carboxylic acid groups in the membrane is 0.5 to 2.0 milliequivalents per dry resin made of these copolymers, for example, the concentration of caustic soda is 40 milliequivalents. % or more, the current efficiency is 90%
% or more.

When the concentration of carboxylic acid groups in the film per night of the dried resin is 1.12 to 1.7 milliequivalents, it is possible to stably obtain caustic soda at a high concentration as described above over a long period of time with high current efficiency. This is especially preferable because it can be done. In addition, in the case of water electrolysis, 0.5 to 2.5 milliequivalent, preferably 1.12
It is preferable to set the amount to 2.0 milliequivalents. Furthermore, the cation exchange membrane used in the present invention may contain an olefin polymer such as polyethylene or polypropylene, preferably polytetrafluoroethylene, or a copolymer of ethylene and tetrafluoroethylene during membrane formation, if necessary. It can also be formed by mixing fluorine polymers, or it can be formed by using fabrics made of these polymers, woven fabrics such as silk, nonwoven fabrics, porous films, etc. as a support, or metal wires, silk, porous materials, etc. It is also possible to reinforce the membrane used as support. Furthermore, as disclosed in Tsubaki Publication No. 56-175583, a porous layer that is gas and liquid permeable and has no electrode activity on the surface of the intestinal ion exchange membrane described above can of course be used effectively. It can be done. Next, the present invention will be explained in detail based on the drawings.

FIG. 1 is a horizontal sectional view showing an example of an electrolytic cell of the present invention consisting of one cathode cell and one anode cell, and shows the case of a monopolar cell. The porous anode plate 1 is a known type made of, for example, titanium, expanded metal smoothed by a roll press and coated with ruthenium oxide, and is held on both sides of the anode chamber frame without attaching flanges. ing. It is possible to hold the electrodes on the chamber frame by simply contacting each other and tightening the electrodes with tie rods, etc., but as shown in Fig. An anode plate fixing hole 13 is provided, and an anode plate fixing hook 14 is attached to the corresponding position of the anode plate.
A method of fixing by fitting the electrolytic cell into the fixing hole 13 described above is preferable because it does not cause misalignment when assembling the electrolytic cell. Furthermore, when the anode chamber frame 2 is made of resin such as PVC, it is preferable to interpose packing between the anode plate and the anode, but when the anode chamber frame 2 is made of rubber, as shown in FIG. As shown in Figure 1, there is no need for intervening packing between the anode plate and the anode chamber frame. The porous cathode plate 3 is made of stainless steel and has a low hydrogen overvoltage obtained by co-electrodepositing Raney nickel particles on an expanded metal smoothed by a roll press. It is held on both sides of the chamber frame. Although fixing hooks can be used to hold the anode plate on the chamber frame surface, FIG. 1 shows a case where the fixing hooks are not used and the electrodes are simply brought into contact with each other. If the cathode chamber frame is made of an elastic material, there is no need to insert packing between the cathode plate and the cathode chamber frame as shown in Figure 1, but if the cathode chamber frame is made of a material that is not so elastic, such as PVC resin. When using the cathode chamber frame, it is preferable to use packing. The intestinal ion exchange membrane 5 is
For example, a perfluorocarbon having a carboxylic acid group as an ion exchange group is formed into a sheet with a thickness of 100 to 300 mm, and is particularly suitable for chloralkali electrolysis or water electrolysis.

As shown in FIG. 1, the intestinal ion exchange membrane 5 is sandwiched between the porous anode plate 1 and the porous cathode plate 3, and is held by the anode chamber frame and the cathode chamber frame. Normally, cation exchange membranes are thin and lack elasticity, so
It is preferable to interpose liquid-tight sealing members (for example, packing) 6 and 7 in the chamber frame portions between the intestinal ion exchange membrane and the porous anode plate and between the cation exchange membrane and the porous cathode plate, but if necessary, Alternatively, only one of 7 may be involved. The porous anode plate and the porous cathode plate are slightly protruded from the left and right sides of the chamber frame, and an anode connection plate 8 and a cathode connection plate 9 are welded to the protrusions, respectively, and these are connected to the anode busbar and the cathode busbar, respectively. do.

As for the connection method to the push bar, only the anode side is shown in FIG.
0 is connected, and the anode busbar I1 is connected to this. By interposing the flexible connecting plate, the connection between the Fussbar and the electrolytic cell can be made flexibly. Although not shown in the drawings, it is preferable to carry out the same process on the cathode side. In addition, it is preferable to reduce the distance between the anode and the cathode in order to keep the electrolysis voltage below the electrolytic voltage. In this case, the anode plate support 12, which is slightly larger than the thickness of the anode chamber frame, is inserted into the anode chamber, and the anode chamber frame is By extending the porous anode plates disposed on both sides of the porous cathode plate toward the porous cathode plate, the anode-cathode distance can be reduced, and preferably the anode and cathode can be brought into close contact with the intestinal ion exchange membrane. can.

The anode plate support is not limited to a pipe shape as shown in FIG. 1, but may also be a resilient member such as a spring or a leaf spring.

As explained above, the porous anode plate, porous cathode plate, cation exchange membrane, anode chamber frame, and cathode chamber frame are repeatedly arranged as many times as necessary, and an anode side end plate and a cathode side end plate are placed at both ends. Then, by tightening this with a tie rod, a filter press type electrolytic cell of the present invention can be obtained. The electrolytic cell obtained in this manner is an easy-to-manufacture electrolytic cell that does not cause liquid leakage from the tightened portion, even though it uses a porous electrode plate that does not have a flange.

FIG. 2 is an exploded perspective view of FIG. 1.

The anode chamber frame 2 is sandwiched between two anode plates 1, and the two anode plates 1 are connected to an external power source by an anode connection plate 8 and a flexible connection plate 10 at one end of the anode chamber frame and outside the anode chamber frame. (not shown) and is connected to the anode bus bar 11. That is, the anode plate is a flat sheet with no difference in height, and does not have openings corresponding to the four barrier holes provided in the chamber frame. It is in contact with a sealing surface 17 that is recessed by approximately the thickness of the anode plate around the anode chamber of the chamber frame, and at least the side of the anode plate that faces the intestinal ion exchange membrane is flat; The central electrode active surface 28 and the surface 27 of the anode plate facing the intestinal ion exchange membrane that faces the sealing surface are on the same plane and have no difference in height. The anode chamber frame 2 includes
An opening forming an anode chamber 15 is provided at the center, and barrier sections forming two pilgrimages are provided at the upper and lower portions of the anode chamber frame.

That is, a passage 18 for the electrolyte in the anode compartment and a passage 19 for the cathode compartment supply liquid are provided in the lower part, and a passage 20 for the electrolyzed product in the anode compartment and a passage 21 for the electrolyzed product in the cathode compartment are provided in the upper part. The passage 18 for the anode chamber supply liquid and the anode chamber 15 are connected to each other by a barrier hole 22, and the passage 20 for the anode chamber electrolysis product and the anode chamber 15 are connected to each other by a barrier hole 23. The passages 19 and 21 are not in communication with the anode chamber 15. Further, the cathode chamber frame 4 is sandwiched between two cathode plates 3, and the cathode chamber frame 4 is sandwiched between two cathode plates 3.
The two cathode plates 3 are connected to an external power source by a cathode connection plate 9 and a portable connection plate 10' on one end side of the cathode chamber frame and outside the cathode chamber frame.
(not shown) is connected to the cathode push bar 11'. The relationship between the cathode plate and the cathode chamber frame arranged in this manner is the same as that of the anode plate and the anode chamber frame described above. The cathode chamber frame 4 is provided with a port forming a cathode chamber 16 in the center, and an anode chamber frame is provided at the upper and lower parts of the cathode chamber frame when assembled into an electrolytic cell using a filter press. Two apertures are provided at positions that are continuous with two apertures provided at the upper and lower portions of the holder.

That is, the lower part is provided with a passage 18' for the anode compartment supply liquid and the passage 19' for the cathode compartment supply liquid, and the upper part is provided with a passage 20' for the anode compartment electrolysis product and a passage 21' for the cathode compartment electrolysis product. ing.

The cathode chamber supply liquid passage 19' and the cathode chamber 16 are connected to each other by an opening 24, and the cathode chamber electrolysis product passage 21'
The cathode chamber 16 is connected through an opening 25. Passage 18'
and 20' are not connected to the cathode chamber. Above, we have explained the case where the electrolyte of the present invention is a monopolar cell, but
Of course, this can also be applied to a bipolar tank. In the case of a bipolar electrolytic cell, the central opening of the chamber frame is divided into two chambers by a partition wall, and a porous anode plate is placed on one side of the chamber frame and a porous cathode plate is placed on the other side. The portion formed by the porous anode plate and the partition becomes the anode chamber, and the portion formed by the porous cathode plate and the partition becomes the cathode chamber.

The partition wall may be made of a conductive material, for example, a known bimetal, and the porous anode plate and the porous cathode plate may be electrically connected to the partition wall, or the partition wall may be made of a non-conductive material and may be made in the same manner as above. The porous anode plate and the porous cathode plate provided in the electrolytic cell may be made to protrude outside the electrolytic cell, and these may be electrically connected. Example 1 As a room frame, 140 mosquitoes x 260 ribs x 10 made of EPDM
The central opening (electrode chamber) of the column is 100 m x 200 m, 4
Of the two openings, the two openings located at the top were each 15 sides x 9 lengths, and the two holes located at the bottom were each 70 sides x 7 lengths.

The porous anode plate is made of titanium with a diameter of 8 in the long axis, 4 in the short axis, and a thickness of 1.0, and is made of titanium and rolled-pressed expanded metal coated with ruthenium oxide. On the other hand, as a porous cathode plate, the opening part was on the long axis 8 side, the short axis 4 side,
A 0.8-thick nickel expanded metal plate with Raney nickel co-electrodeposited on roll-pressed expanded metal was prepared, measuring 106 m long and 29 m long.

On each vertical side of the porous anode plate and the porous cathode plate, attach an anode connecting plate made of titanium with a size of 100 m x 4 m and a cathode connecting plate made of nickel with a size of 100 m x 4 m. They were attached by welding, and a flexible connection plate on the anode side and a flexible connection plate on the cathode side were attached to this, respectively. Furthermore, an anode plate fixing hole was provided in the peripheral portion of the anode chamber frame, and an anode plate fixing hook was attached to a portion of the porous anode plate corresponding to this position.

As a cation exchange membrane, the ion exchange capacity is 1.45me
TiO2 powder was applied to the anode side surface of a film made of a copolymer of tetrafluoroethylene and CF2=CF0(CF2)3COOCH3 having a thickness of 250 mm, and SIC powder was applied to the cathode side surface. A porous layer coated at a ratio of 9/base was prepared.

The thus prepared porous anode plate, porous cathode plate, anode chamber frame, and cathode chamber frame cation exchange membrane were packed into a unit electrolytic cell of 5 in a solid state as shown in Fig. 1 using EPDM packing. They were arranged in a filter press style, with end plates provided at both ends and attached vertically with tie rods. Then, an anode busbar was attached to the anode side flexible connection plate, and a cathode busbar was attached to the cathode side flexible connection plate by tightening bolts. At this time, the anode chamber is made of titanium with an outer diameter of 12 mm and a length of 70 mm in the center.
The porous anode plate was inserted and the porous anode plate was slightly bulged outward so that the anode plate and cathode came into close contact with the cation exchange membrane. In the anode chamber of the electrolytic cell thus obtained, a concentration of 300%/
While supplying water to the cathode chamber, the saline solution was heated at 20 A/min.
dW, I performed salt electrolysis at 90:00.

The resulting caustic soda aqueous solution had a concentration of 35%, a chlorine gas purity of 97.4%, and a current efficiency on the cathode side of 94.4%.

Electrolysis was continued for 60 days, during which the cell voltage was 2.96V.
was maintained, and no liquid leakage was observed. Example 2 The chamber frame of Example 1 has the same dimensions as the chamber frame of Example 1, except that the thickness is 2.0 ribs, and the center opening □ is made of tetrafluoroethylene resin with 106 x 26 x A partition wall made of pine wood is provided, a porous anode plate is provided on the cross section of the chamber frame, a porous cathode plate is provided on the other side, and a titanium anode with an outer diameter of 7 cm and a length of 70 m is installed between the partition wall and the porous anode plate. A bipolar electrolytic cell was assembled in exactly the same manner as in Example 1, except that a support was provided and both electrodes were electrically connected outside the electrolytic cell.

In addition, one end of the electrolytic cell was used as an anode conductive plate instead of an anode plate, and this was connected to the positive power source, and the cell end of the electrolytic cell was used as a cathode conductive plate instead of the cathode plate, and this was connected to the negative power source. .

The electrolytic conditions were the same as in Example 1.

The electrolytic performance was as follows. Caustic soda concentration
35% chlorine gas purity
97.4% cathode current efficiency
94.4%・Possible voltage (average value per cell)
2.91V Also, no liquid leakage was observed during the electrolysis period.

[Brief explanation of the drawing]

FIG. 1 is a horizontal sectional view showing an example of the electrolytic cell of the present invention, which includes one cathode cell and one anode cell. FIG. 2 is an exploded perspective view of FIG. 1. 1...
Porous anode plate, 2... Anode chamber frame, 3...
・Porous cathode plate, 4...Cathode chamber frame, 15...
...anode chamber, 16...cathode chamber. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. An ion exchange membrane electrolytic cell comprising an electrolytic chamber frame consisting of an anode chamber frame and a cathode chamber frame, an electrode, and a cation exchange membrane that are tightened in a filter press manner, (a) the electrolytic chamber frame: Electrolyte liquid passages 18, 19, 18', 19' leading to the outside
and electrolysis product passages 20, 21, 20', 21';
It has apertures forming electrolytic chambers 15, 16 that communicate with the passages through apertures 22, 23, 24, 25, and around the apertures there is a recessed seal with approximately the same thickness as the electrode plate. (b) the electrode is a porous electrode plate having no apertures corresponding to the four apertures of the chamber frame, the electrode being substantially one flat plate larger than the electrolytic chamber; and at least the electrode active surface 2 of the ground electrode plate facing the cation exchange membrane.
6 and the surface 27 of the electrode plate facing the cation exchange membrane, which faces the sealing surface 17 of the electrolytic chamber frame, have the same plane with no difference in height, and (c) the anode-cation of the sealing portion A liquid-tight sealing member 6 and/or 7 is interposed between the exchange membranes and at least one between the cation exchange membrane and the cathode, and (d) the active surface of the electrode is substantially in contact with the cation exchange membrane. Characteristic ion exchange membrane electrolyzer. 2 Anode chamber frame, cathode chamber frame, electrode and cation exchange membrane are anode plate 1/anode chamber frame 2/anode plate 1/cation exchange membrane 5/cathode plate 3/anode chamber frame 4/cathode plate 3/cation A combination in which the exchange membranes are arranged in order, and a sealing member 6 and/or 7 is arranged at at least one place between the anode plate 1 and the cation exchange membrane 5 and between the cathode plate 3 and the cation exchange membrane. An ion exchange membrane electrolytic cell according to claim 1, wherein a plurality of units of the combination are clamped together in a filter press manner. 3. The ion exchange membrane electrolytic cell according to claim 1, wherein the electrode plate is an expanded metal made flat by roll pressing. 4. The ion exchange membrane electrolytic cell according to claim 1, wherein the electrode plate is a punched metal plate with holes provided in the flat plate. 5. The ion exchange membrane electrolytic cell according to any one of claims 1 to 4, wherein the liquid-tight sealing member is a sheet-like elastic member.