Manufacturing method for gas diffusion sheet

In a manufacturing method for a gas diffusion sheet, when a first film is joined to a front end portion of a base material in a conveyance direction, a first joining material is made to penetrate a first overlapping portion where the first film and the base material are superimposed on each other, and the first film and the base material are thus joined to each other physically through the first joining material. When a second film is joined to a rear end portion of the base material in the conveyance direction, a second joining material is made to penetrate a second overlapping portion where the base material and the second film are superimposed on each other, and the base material and the second film are thus physically joined to each other through the second joining material.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2018-192438 filed on Oct. 11, 2018 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to a manufacturing method for a gas diffusion sheet of a fuel cell. In the manufacturing method, a porous layer containing conductive particles is formed on a conductive belt-shaped base material while the base material is conveyed by a roll-to-roll method.

2. Description of Related Art

A method is proposed in which a surface of a base material is coated with a coating liquid or a coating paste material while the base material is conveyed by a roll-to-roll method. For example, according to a technique described in Japanese Unexamined Patent Application Publication No. 2007-98186 (JP 2007-98186 A), an unwinding roll and a winding roll are provided. The unwinding roll unwinds a belt-shaped base material that is wound in a roll shape, and the winding roll winds the unwound base material. Then, the base material is conveyed by the roll-to-roll method, and the paste material is applied on the base material passing a conveyance path, and then dried by heating.

When the base material is conveyed, a film may be adhered to a distal end of the base material in a conveyance direction, which is an unwinding start part of the base material, by using adhesive tape or the like as described in Japanese Unexamined Patent Application Publication No. 2016-115493 (JP 2016-115493 A). When the base material is conveyed, the film adhered to the base material is conveyed to the winding roll. Thus, while the belt-shaped base material is conveyed, it is possible to guide the conveyed base material to the winding roll.

SUMMARY

However, when the coating method described in JP 2007-98186 A is carried out with the use of the film described in JP 2016-115493 A, since the film and the base material are conveyed by the roll-to-roll method, tension acts not only on the film and the base material, but also on a joining part between the film and the base material. Here, the paste material coating the base material is heated for drying. Since the joining part between the film and the base material is heated while tension is acting on it during the conveyance, the film and the base material in the joining part can be misaligned.

The disclosure provides a manufacturing method in which a gas diffusion sheet of a fuel cell is manufactured while a film and a base material are being conveyed by a roll-to-roll method in a state where a joining strength of the film and the base material is enhanced.

A manufacturing method for a gas diffusion sheet according to the disclosure is a manufacturing method for a gas diffusion sheet of a fuel cell. In this manufacturing method, a porous layer containing a conductive particle is formed on a conductive belt-shaped base material while the base material is conveyed by a roll-to-roll method. The manufacturing method includes joining a first film for conveyance to a front end portion of the base material in a conveyance direction, the front end portion serving as an unwinding start part of the base material that is wound in a roll shape, guiding the base material while the base material is conveyed as the first film is conveyed by the roll-to-roll method, and coating a surface of the base material with a paste material that contains at least a conductive particle, manufacturing the gas diffusion sheet as the porous layer is formed as the paste material applied is heated while the base material coated with the paste material is continuously conveyed, and joining a second film for conveyance to a rear end portion of the base material in the conveyance direction, the rear end portion serving as an unwinding end part of the base material. After the first film is wound, the gas diffusion sheet joined to the first film is wound, and further, the second film joined to the gas diffusion sheet is wound. For joining of the first film, a first joining material is made to penetrate a first overlapping portion where the first film and the base material are superimposed on each other, and the first film and the base material are thus physically joined to each other through the first joining material. For joining of the second film, a second joining material is made to penetrate a second overlapping portion where the base material and the second film are superimposed on each other, and the second film and the base material are thus physically joined to each other through the second joining material.

According to the disclosure, the first film for conveyance is joined to the front end portion of the base material in the conveyance direction, the front end portion serving as the unwinding start part of the base material that is wound in a roll shape. At this time, the first joining material is made to penetrate the first overlapping portion where the first film and the base material are superimposed on each other, and the first film and the base material are thus physically joined to each other through the first joining material. Thus, joining strength of the first film and the base material is enhanced compared to a case where the first film and the base material are joined to each other only with adhesive tape, pressure-sensitive adhesive tape, or the like.

Similarly, the second film for conveyance is joined to the rear end portion of the base material in the conveyance direction, the rear end portion serving as the unwinding end part of the base material. At this time, the second joining material is made to penetrate the second overlapping portion where the base material and the second film are superimposed on each other, and the second film and the base material are thus physically joined to each other through the second joining material. Thus, joining strength of the base material and the second film is enhanced compared to a case where the base material and the second film are joined to each other only with adhesive tape, pressure-sensitive adhesive tape, or the like.

As a result, even when a joining part of the first film and the base material and a joining part of the base material and the second film are heated while tension is acting on these joining parts, it is possible to prevent misalignment of the first film and the base material and misalignment of the base material and the second film. Thus, it is possible to coat the conveyed base material with the paste material and dry the paste material applied in a stable manner.

As long as the base material and the first film are joined to each other without misalignment, and the base material and the second film are joined to each other without misalignment, the base material and the first film, and the base material and the second film may be joined to each other with the physical joining alone. However, as another aspect, the first film and the base material may be adhered to each other through a first adhesive when the first film and the base material are superimposed on each other so as to join the first film. Also, the base material and the second film may be adhered to each other through a second adhesive when the base material and the second film are superimposed on each other so as to join the second film.

In this aspect, when the first film and the base material are superimposed on each other, the first film and the base material are adhered to each other through the first adhesive. Therefore, it is possible to physically join the first film and the base material with the first joining material in a state where the first film and the base material are held at appropriate positions, respectively. Similarly, the base material and the second film are adhered to each other through the second adhesive when the base material and the second film are superimposed on each other. Therefore, it is possible to physically join the base material and the second film in a state where the base material and the second film are held at appropriate positions, respectively.

Further, as long as the first film and the base material are adhered to each other by the first adhesive in the state where the first film and the base material are superimposed on each other, and the base material and the second film are adhered to each other by the second adhesive in the state where the base material and the second film are superimposed on each other, then the first adhesive and the second adhesive may be applied as they are, and adhesion states of the first adhesive and the second adhesive are not particularly limited. However, as another aspect, the first film and the base material may be adhered to each other through a first adhesive sheet when the first film and the base material are superimposed on each other so as to join the first film. The first adhesive sheet has the first adhesive applied on both sides of the first adhesive sheet. Then, the first joining material may be made to penetrate the first overlapping portion as well as the first adhesive sheet so that the first film and the base material are joined to each other. Further, the base material and the second film may be adhered to each other through a second adhesive sheet when the base material and the second film are superimposed on each other so as to join the second film. The second adhesive sheet has the second adhesive applied on both sides of the second adhesive sheet. Then, the second joining material may be made to penetrate the second overlapping portion as well as the second adhesive sheet so that the second film and the base material are joined to each other.

According to this aspect, the first film and the base material are joined to each other as the first joining material is made to penetrate the first overlapping portion as well as the first adhesive sheet having the adhesive applied on both surfaces of the first adhesive sheet. Therefore, the first adhesive sheet is able to reinforce portions of the base material and the first film where the first joining material passes through. The base material and the second film are joined to each other as the second joining material is made to penetrate the second overlapping portion as well as the second adhesive sheet having the adhesive applied on both surfaces of the second adhesive sheet. Therefore, the second adhesive sheet is able to reinforce portions of the base material and the second film where the second joining material passes through. The adhesive sheet in the disclosure includes a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive is applied on a sheet material.

According to the disclosure, it is possible to manufacture a gas diffusion sheet of a fuel cell while a first film, a base material, and a second film are conveyed by a roll-to-roll method in a state where joining strength of the first film and the base material and joining strength of the base material and the second film are enhanced.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference toFIG. 1toFIG. 8B, a manufacturing method for a gas diffusion sheet of a fuel cell according to an embodiment of the disclosure is described.

1. Regarding a Gas Diffusion Sheet10

As shown inFIG. 2, the gas diffusion sheet10according to the embodiment is a sheet material in which a porous layer (a microporous layer)12is formed on a base material11. The gas diffusion sheet10serves as a gas diffusion layer by being laminated on both surfaces of a membrane electrode assembly (not shown and also referred to as an MEA) that constructs a single cell of a fuel cell.

After the gas diffusion layer is laminated on both surfaces of the membrane electrode assembly, a resultant laminated body is sandwiched by a pair of separators. Thus, a cell for a fuel cell is constructed as a power generation part of the fuel cell. The membrane electrode assembly is made of an ion-permeable electrolyte film, and an anode-side catalyst layer (an electrode layer) and a cathode-side catalyst layer (an electrode layer) that sandwich the electrolyte film. The electrolyte film is a proton-conductive ion exchange film made from a solid polymer material, and each of the catalyst layers is a porous layer in which a catalyst such as platinum is supported on carbon particles and bound by an ionomer.

The gas diffusion layer on a first side is joined to the anode-side catalyst layer. The gas diffusion layer on a second side is joined to the cathode-side catalyst layer. A base material of each of the gas diffusion layers is made from, for example, a carbon porous material such as carbon paper or carbon cloth. The foregoing porous layer containing the conductive particles is formed on the base material of the gas diffusion layer.

The porous layer is joined to the catalyst layer.

Here, fuel gas such as hydrogen gas is supplied from the separator to the gas diffusion layer on the first side, and oxidizer gas such as atmosphere is supplied from the separator to the gas diffusion layer on the second side. As the fuel gas and the oxidizer gas are supplied, electrochemical reaction occurs inside an MEA, and the fuel cell generates power.

2. Regarding a Manufacturing Device30for the Gas Diffusion Sheet10

In the embodiment, the gas diffusion sheet10used as the gas diffusion layer of the fuel cell described above is manufactured by using the manufacturing device30described below. Specifically, as shown inFIG. 1, the manufacturing device30includes an unwinding roll31and a winding roll32. The unwinding roll31unwinds the base material11that is wound in a roll shape. The winding roll32winds the base material11on which the porous layer12is formed (in other words, the gas diffusion sheet10) in a roll shape. A plurality of convey rolls33is disposed in a conveyance path of the base material11.

Due to the winding by the winding roll32, it is possible to convey the base material11by a roll-to-roll method while given tension is applied to the base material11. Interleaving paper unwound from an interleaving paper roll39is wound on the winding roll32together with the gas diffusion sheet10.

The manufacturing device30includes a coating part34, a drying and baking part35, and an inspection part36. In a coating part34, a paste material is applied on the base material11. In the drying and baking part35, the porous layer12is formed on the base material11as the paste material applied on the base material11is dried and baked. In the inspection part36, the base material11on which the porous layer12is formed (the gas diffusion sheet10) is inspected.

In the coating part34, a coating device34ais disposed that applies the paste material onto the base material11unwound from the unwinding roll31, and an inspection camera34bis disposed on an opposite side of the base material11from the coating device34a. The inspection camera34bchecks an impregnation status of the base material11with the paste material. Further, in the coating part34, an exhaust part34cis provided that discharges air inside the coating part34.

The drying and baking part35includes a plurality of nozzles35aand a plurality of radiation thermometers35b. The nozzles35ablow hot air onto the base material11in order to heat the paste material applied in the coating part34, together with the base material11. The radiation thermometers35bmeasure temperature of the base material11and so on. The nozzles35aare arrayed along a conveyance direction of the base material11so that the nozzles35ablow hot air onto both surfaces of the base material11, and the radiation thermometers35bare disposed close to the nozzles35a, respectively.

The inspection part36includes an inspection camera36a, an inspection camera36b, and a printing device36c. The inspection camera36ainspects the porous layer12formed on the base material11, and the inspection camera36binspects a back surface of the base material11. The printing device36cprints on a defect portion of the base material11based on results from the inspection cameras36a,36b. Further, in the inspection part36, an exhaust part36dis provided that discharges air inside the inspection part36.

Further, a joining device37is disposed between the unwinding roll31and the coating part34. The joining device37joins a later-described first film21A and the base material11, and also joins the base material11and a second film21B. Further, a dust collector38is disposed between the joining device37and the coating part34. The dust collector38collects foreign matters attached to the base material11and so on.

3. With regard to a manufacturing method for the gas diffusion sheet10In the embodiment, the gas diffusion sheet10of the fuel cell is manufactured by forming the porous layer12containing the conductive particles on the conductive belt-shaped base material11while the base material11is conveyed by the roll-to-roll method. Specifically, the gas diffusion sheet10is manufactured with reference to the flowchart shown inFIG. 3, as well asFIG. 4AandFIG. 4B.

In the embodiment, first of all, in step S1, the first film21A for the conveyance is prepared and disposed along the conveyance path in the manufacturing device30. Here, the first film21A is a resin film made from, for example, polyester resin, polypropylene resin, polyimide resin, and polyvinylidene chloride resin. After a front end portion of the belt-shaped first film21A in the conveyance direction F is passed in the coating part34, the drying and baking part35, and the inspection part36in this order, a part of the first film21A is wound on the winding roll32. Then, the first film21A is continuously wound on the winding roll32until a rear end portion of the first film21A in the conveyance direction F is positioned in the joining device37.

Next, as shown in step S2, the first film21A and the base material11are joined to each other. The base material11is a carbon porous material such as carbon paper or carbon cloth. Specifically, as shown inFIG. 4AandFIG. 4B, the rear end portion21aof the first film21A for conveyance is joined to the front end portion11aof the base material11in the conveyance direction F. The front end portion11aserves as an unwinding start part of the base material11that is wound into a roll shape.

In the embodiment, first of all, when the first film21A and the base material11are superimposed on each other, the first film21A and the base material11are adhered to each other through a first adhesive. Specifically, when the first film21A and the base material11are superimposed on each other, the first film21A and the base material11are adhered to each other through a first adhesive sheet18A. The first adhesive is applied on both surfaces of the first adhesive sheet18A. Thus, it is possible to superimpose the first film21A and the base material11onto each other accurately before the first film21A and the base material11are joined by staples15A described later.

Here, a material of the first adhesive sheet18A is not particularly limited as long as the material has flexibility and does not impair adhesiveness with the first adhesive. For example, the material of the first adhesive sheet18A may include a resin sheet made from thermoplastic resin, and a metal sheet made from aluminum and so on. The first adhesive may be an adhesive or a pressure-sensitive adhesive that is made from thermoplastic resin such as acrylic resin and epoxy resin.

Next, the staples15A (a first joining material) are made to penetrate a first overlapping portion13A as well as the first adhesive sheet18A, and the first film21A and the base material11are thus joined to each other physically through the staples15A. The first overlapping portion13A is a portion where the first film21A and the base material11are superimposed on each other. Hence, portions of the base material11and the first film21A where the staples15A penetrate are reinforced by the first adhesive sheet18A.

Further, in the embodiment, the plurality of staples15A is fixed on both sides of the first overlapping portion13A so that the portions where the staples15A penetrate are arrayed along the conveyance direction. The staples15A are made from a metal material that has heat resistance during later-described drying and baking of the paste material, and also has corrosion resistance. The staples15A are made from, for example, aluminum.

As described above, since the first film21A and the base material11are joined to each other through the staples15A, joining strength of the first film21A and the base material11is enhanced further compared to a case where the first film21A and the base material11are joined to each other only by adhesive tape, pressure-sensitive adhesive tape, or the like. As a result, even when a joining part of the first film21A and the base material11is heated in the drying and baking part35in a state where tension is acting on the joining part, it is possible to prevent misalignment of the first film21A and the base material11. Thus, later-described coating of the conveyed base material11with the paste material, and drying and baking of the applied paste material can be performed in a stable manner.

Next, in step S3, unwinding of the base material11and winding of the first film21A are started. The unwound base material11is led by the first film21A, passes through the dust collector38, and is conveyed to the coating part34.

In step S4, in the coating part34, the base material11is coated with the paste material discharged from the coating device34a. The paste material may be any paste material as long as it contains conductive particles. Examples of the paste material include a material that is made into a paste after mixing carbon particles (the conductive particles) such as carbon black, water-repellent resin particles such as PTFE, and a surface active agent. The inspection camera34binspects a coating status (an impregnation status of the paste material) of the base material11coated with the paste material.

Next, in step S5, the conveyed base material11is conveyed to the drying and baking part35. In the drying and baking part35, while the base material11coated with the paste material is conveyed continuously, the paste material applied on the base material11is heated. Specifically, the paste material is heated as temperature of hot air blown from the nozzles35ais adjusted based on temperature measured by the radiation thermometers35b. Thus, the paste material is dried, and then baked, thereby forming the porous layer12. In this way, the gas diffusion sheet10is manufactured. The step S5is equivalent to “manufacturing of a gas diffusion sheet” of the disclosure.

Next, in step S6, the manufactured gas diffusion sheet10is conveyed to the inspection part36. In the inspection part36, when there is a defect portion based on an inspection result from the inspection cameras36a,36b, the printing device36cprints on the base material11.

The processes of step S4to step S6described above are continuously performed for the conveyed base material11while the winding roll32continuously winds the gas diffusion sheet10. At a point when the rear end portion11bof the base material11in the conveyance direction F, the rear end portion11bserving as an unwinding end part of the base material11, is positioned in the joining device37, the base material11and the second film21B are joined in step S7.

Specifically, as shown inFIG. 5AandFIG. 5B, a front end portion21bof the second film21B for conveyance is joined to the rear end portion11bof the base material11in the conveyance direction F. The rear end portion11bserves as the unwinding end part of the base material11that is wound in a roll shape.

In the embodiment, first of all, similarly to the case described in step S2, when the base material11and the second film21B are superimposed on each other, the base material11and the second film21B are adhered to each other through a second adhesive. Specifically, when the base material11and the second film21B are superimposed on each other, the base material11and the second film21B are adhered to each other through a second adhesive sheet18B. The second adhesive is applied on both surfaces of the second adhesive sheet18B. Here, materials of the second adhesive sheet18B and the second adhesive are the same as the materials of the first adhesive sheet18A and the first adhesive described as examples, respectively.

Next, staples15B (a second joining material) are made to penetrate a second overlapping portion13B as well as the second adhesive sheet18B so that the base material11and the second film21B are joined to each other physically through the staples15B. The second overlapping portion13B is a portion where the base material11and the second film21B are superimposed on each other. Thus, portions of the base material11and the second film21B where the staples15B penetrate are reinforced by the second adhesive sheet18B.

Further, in the embodiment, the plurality of staples15B is fixed on both sides of the second overlapping portion13B so that the portions where the staples15B penetrate are arrayed along the conveyance direction. The staples15B are made from a material similar to that of the staples15A described as an example.

As described above, as the staples15B penetrate the second overlapping portion13B in which the base material11and the second film21B are superimposed on each other, the second film21B and the base material11are physically joined to each other through the staples15B. Thus, joining strength of the base material11and the second film21B is enhanced further compared to a case where the base material11and the second film21B are joined to each other only by adhesive tape, pressure-sensitive adhesive tape, or the like.

As a result, even when a joining part of the base material11and the second film21B is heated in the drying and baking part35in a state where tension is acting on the joining part, it is possible to prevent misalignment of the base material11and the second film21B. Thus, in a part of the base material11in front of the joining part where the base material11and the second film21B are joined to each other, coating with the paste material, and drying of the applied paste material are performed in a stable manner.

Thus, after the first film21A is wound by the roll-to-roll method, the gas diffusion sheet10joined to the first film21A is wound, and then the second film21B joined to the gas diffusion sheet10is wound. Accordingly, a series of winding is completed (step S8).

In the embodiment, the first film21A and the base material11are joined, and the base material11and the second film21B are joined by the staples15A,15B, respectively. However, as shown in, for example, a modification inFIG. 6AtoFIG. 7B, the first film21A and the base material11may be sewn on each other, and the base material11and the second film21B may be sewn on each other by continuous fibers15C,15D such as carbon fibers, respectively.

Specifically, in step S2described earlier, as shown inFIG. 6AandFIG. 6B, the rear end portion21aof the first film21A for conveyance and the front end portion11aof the base material11in the conveyance direction F are adhered to each other through the first adhesive sheet18A having the first adhesive applied on both surfaces.

Next, the continuous fiber15C (the first joining material) is made to penetrate the first overlapping portion13A as well as the first adhesive sheet18A with given pitch. The first overlapping portion13A is a portion where the first film21A and the base material11are superimposed on each other. Thus, the first film21A and the base material11are physically joined to each other through the continuous fiber15C. In the modification, both sides of the first overlapping portion13A are sewn by the continuous fiber15C so that the portions where the continuous fiber15C passes through are arrayed along the conveyance direction F.

Further, similarly to step S7, as shown inFIG. 7AandFIG. 7B, the rear end portion11bof the base material11in the conveyance direction F and the front end portion21bof the second film21B for conveyance are adhered to each other through the second adhesive sheet18B having the second adhesive applied on both surfaces.

Next, the continuous fiber15D (the second joining material) is made to penetrate the second overlapping portion13B as well as the second adhesive sheet18B with given pitch. The second overlapping portion13B is a portion where the base material11and the second film21B are superimposed on each other. Thus, the second film21B and the base material11are physically joined to each other through the continuous fiber15D. In the modification, both sides of the second overlapping portion13B are sewn by the continuous fiber15D so that the portions where the continuous fiber15D passes through are arrayed along the conveyance direction F.

In the embodiment, the second film21B is wound after the base material11and the second film21B are joined to each other. However, for example, as shown in a modification inFIG. 8AandFIG. 8B, a base material11′ to be connected with the second film21B may be prepared, and a front distal end of the base material11′ in the conveyance direction F and the second film21B may be joined to each other by the same method described in step S2.

With the gas diffusion sheet10thus obtained, a composite sheet10B is manufactured by using a joining device5shown inFIG. 9. The second film21B that is unwound first is made to pass along a conveyance path of the joining device5, and the porous layer of the gas diffusion sheet10, and the anode-side catalyst layer formed on an electrolyte sheet60that serves as an electrolyte film of a fuel cell are joined to each other by hot press performed by heat-pressure rolls51.

Further, the composite sheet10A that has passed a conveying roll52passes through a peeling bar53, and a back sheet58stuck on a back surface of the electrolyte sheet60is peeled off from the composite sheet10A by the peeling bar53. The back sheet58passes through a conveying roll55and is wound into a roll shape. Meanwhile, the composite sheet10B from which the back sheet58is peeled off passes through a conveying roll54and is wound in a roll shape.

Thereafter, the composite sheet10B wound into the roll shape is unwound from the first film, and the cathode-side catalyst layer is formed further on the electrolyte sheet, and then cut into a given shape. In this case, the first and second films21A,21B are cut off together with the parts joined to the base material11, and discarded.

Hereinafter, examples of the disclosure are described.

First of all, a base material (carbon paper) with a width of 300 mm, and a first film (Kapton (registered trademark) tape manufactured by Du Pont-Toray Co., Ltd.) having the same width were prepared. Then, the base material and the first film were superimposed on and adhered to each other through a first adhesive sheet (with a width of 250 mm, and a length of 100 mm). An adhesive was applied on both surfaces of the first adhesive sheet.

Next, as shown inFIG. 4AandFIG. 4B, four aluminum staples were fixed on each side of a first overlapping portion, thereby making it eight staples in total on both sides, at intervals of 15 mm so that the staples were made to penetrate the base material and the first film as well as the first adhesive sheet. In each of the staples, a distance between distal ends on both sides was 10 mm. Thus, a test material according to example 1 was fabricated.

A test material was fabricated similarly to example 1. As shown inFIG. 6AandFIG. 6B, a difference from example 1 is that a carbon fiber was used instead of the staples to sew both sides of the base material and the first film along a conveyance direction with a pitch of 10 mm and a length of 80 mm so that the carbon fiber passes through the base material and the first film as well as the first adhesive sheet.

Comparative Example 1

A test material was fabricated similarly to example 1. A difference from example 1 is that the joining is not done by the staples

Strength Test

The test materials of examples 1, 2 and comparative example 1 were heated in a furnace in a state where tension was acting on each of the test materials in a direction in which the base material and the first film are separated from each other, and time was measured until each of the test materials was broken. The results are shown inFIG. 10.

As a result, the test materials of example 1 and example 2 took longer than the test material of comparative example 1 until they were broken in a target temperature range from 350° C. to 370° C. that matches drying temperature of a paste material. It is considered that breakage time of the test material of comparative example 1 is shorter than those of the test materials of example 1 and example 2 because adhesive strength (pressure-sensitive adhesive strength) is deteriorated by the adhesive in that temperature range.

The embodiment according to the disclosure has been described in detail. However, the disclosure is not limited to the foregoing embodiment, and various design changes may be made without departing from the spirit of the disclosure described in claims.