Method for producing fuel cell membrane electrode assembly

To provide a method for producing a fuel cell membrane electrode assembly that can prevent the required catalyst layer from being removed, while suppressing damage to the electrolyte membrane. A method for producing a fuel cell membrane electrode assembly MEA includes: a step of bonding a polymer electrolyte membrane PEM and a first catalyst layer-including substrate GDE1; a step of making a cut CL so that the first catalyst layer-including substrate GDE bonded with the polymer electrolyte membrane PEM becomes a predetermined shape; a step of peeling an unwanted portion GDE12 of the first catalyst layer-including substrate GDE1 from the polymer electrolyte membrane PEM; a step of irradiating a laser beam LB2 penetrating the polymer electrolyte membrane PEM without penetrating the first catalyst layer-including substrate GDE1 onto the polymer electrolyte membrane PEM, and removing residue RD of the first catalyst layer-including substrate GDE1 adhering on the polymer electrolyte membrane PEM.

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2016-055713, filed on 18 Mar. 2016, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for producing a fuel cell membrane electrode assembly in which electrode layers are laminated on both surfaces of an electrolyte membrane.

Related Art

The membrane electrode assembly (MEA) of a fuel cell has a structure made by a catalyst layer and diffusion layer (collectively “electrode layer”) being laminated on both surfaces to sandwich an electrolyte membrane, as described in Patent Document 1, for example. In addition, one electrode layer, in order to assume a creepage distance for ensuring insulation between the electrode layers on both surfaces, is configured so that the electrolyte membrane is exposed at the peripheral edge.

As a method of producing such an MEA, there is a method of forming a catalyst layer on a diffusion layer substrate, and then bonding this to the electrolyte membrane, as described in Patent Document 2.

On the other hand, in order to raise the production efficiency of MEAs, it has been proposed to continuously produce the MEA in a roll-to-roll method as shown in Patent Document 3.

SUMMARY OF THE INVENTION

However, when trying to produce MEAs by bonding the catalyst layer-including diffusion layer described in Patent Document 2 to the electrolyte membrane by way of a roll-to-roll method, the following such sequence is considered. First, the lamination/bonding of the catalyst layer-including diffusion layer unrolled from a catalyst layer-including diffusion layer roll is performed on one side or both sides of the electrolyte membrane unrolled from the electrolyte membrane roll. Then, an excess portion of the catalyst layer-including diffusion layer is peeled from the membrane layer, and the electrolyte layer and catalyst layer-including diffusion layer is further cut into a predetermined shape to complete the MEA.

However, if peeling from the electrolyte layer the catalyst layer-including diffusion layer made by provisionally bonding as mentioned above, there is a risk of not removing the entirety of the catalyst layer, and residue of the catalyst layer remaining on the catalyst layer. There is a risk of the residue thereby remaining causing the insulation property and gas sealing property to decline.

In order to remove such residue of the catalyst layer, it has been considered to irradiate a laser beam onto the remaining region of residue. However, if the absorption coefficient of this laser beam to the electrolyte membrane is high, it will cause damage to the electrolyte membrane. Furthermore, in the case of the catalyst layer being formed on the other surface of the electrolyte membrane, the catalyst layer on the other surface will also be removed upon residue removal.

The present invention has an object of providing a method for producing a fuel cell membrane electrode assembly that can prevent a required catalyst layer from being removed, while suppressing damage to the electrolyte membrane.

In order to achieve the above-mentioned objects, the present invention provides method for producing a fuel cell membrane electrode assembly including: a step of preparing an electrolyte membrane (e.g., the polymer electrolyte membrane PEM described later) (for example, Step1described later); a step of preparing a catalyst layer-including substrate (for example, the first catalyst layer-including substrate GDE1described later) in which a first catalyst layer (for example, the first catalyst layer111described later) is formed on one face of a sheet-like substrate (for example, Step2described later); a step of laminating the catalyst layer-including substrate so that the first catalyst layer opposes one face of the electrolyte membrane (for example, Step3described later); a step of bonding the electrolyte membrane and the catalyst layer-including substrate (for example, Step4described later); a step of making a cut (for example, the cut CL described later) so that the catalyst layer-including substrate bonded with the electrolyte membrane becomes a predetermined shape (for example, Step5described later); a step of peeling an unwanted portion (for example, the unwanted portion GDE12described later) of the catalyst layer-including substrate other than the predetermined shape portion (for example, the portion of predetermined shape GDE11described later) from the electrolyte membrane (for example, Step6described later); a step of irradiating energy rays (for example, the laser beam LB2described later) that penetrate the electrolyte membrane without penetrating the catalyst layer-including substrate onto a portion of the electrolyte membrane to which the unwanted portion is bonded, and removing residue (for example, the residue RD described later) of the catalyst layer-including substrate adhering on the electrolyte membrane (for example, Step7described later); and a step of forming a second catalyst layer (for example, the second catalyst layer121described later) on one other face of the electrolyte membrane, and punching out the electrolyte membrane and the second catalyst layer so that the catalyst layer-including substrate of the predetermined shape bonded to the one face is surrounded (for example, Step8described later).

In the present invention, first, after bonding the catalyst layer-including substrate only to one face of the electrolyte membrane, the unwanted portion is peeled, the residue is removed using energy rays such as a laser beam that penetrates the electrolyte membrane without penetrating the catalyst layer-including substrate, and then forms the catalyst layer on the other face. Since the catalyst layer is formed on the other face after removing the residue in this way, this catalyst layer will not be removed by the energy rays penetrating the electrolyte membrane. Therefore, according to the present invention, it is possible to prevent the required catalyst layer from being removed while suppressing damage to the electrolyte film.

In the aforementioned invention, the energy rays preferably have transmittance relative to the electrolyte membrane of at least 80%.

The present invention uses energy rays having transmittance relative to the electrolyte membrane of at least 80%. It is thereby possible to more reliably suppress damage to the electrolyte membrane by using high-transmittance energy rays.

According to the present invention, it is possible to provide a method for producing a fuel cell membrane electrode assembly that can prevent a required catalyst layer from being removed, while suppressing damage to the electrolyte membrane.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be explained in detail while referencing the drawings.FIG. 1is a schematic view showing a production line1of a membrane electrode assembly MEA for a fuel cell according to the embodiment of the present invention.FIG. 2is a graph showing a relationship between wavelength and transmittance of a laser beam LB2of a second laser device16.FIG. 3Ais an enlarged top view showing a state after peeling an unwanted portion GDE12of a first catalyst layer-including substrate GDE1from an electrolyte membrane PEM, and prior to removing residue RD.FIG. 3Bis an enlarged top view showing a state after peeling the unwanted portion GDE12of the first catalyst layer-including substrate GDE1from the electrolyte membrane PEM, and after removing the residue RD.FIG. 4is a cross-sectional view of a membrane electrode assembly MEA for a fuel cell thus produced.FIG. 5is a graph comparing the insulation property before and after removing the residue RD of the first catalyst layer-including substrate GDE1from over the electrolyte membrane PEM.

The production line1of the fuel cell membrane electrode assembly (Membrane Electrode Assembly) MEA shown inFIG. 1raises the production efficiency of the fuel cell membrane electrode assembly MEA by making continuous with a roll-to-roll method. More specifically, the production line1of the fuel cell membrane electrode assembly MEA includes: an electrolyte membrane roll10; a first substrate roll11; a pair of upper/lower temporary bonding rolls12,13; a first laser device14; a recovery roll15; a second laser device16; a second substrate roll17; a pair of upper/lower bonding rolls18,19; a cutter20; etc.

The electrolyte membrane roll10is a roll that prepares a continuous sheet-like (belt-like) polymer electrolyte membrane PEM, and rotates around a horizontal shaft at the upstream of the production line1. This electrolyte membrane roll10draws the polymer electrolyte membrane PEM to downstream by rotating. The polymer electrolyte membrane PEM that is drawn to travel downstream from the electrolyte membrane roll10is laminated so that a first catalyst layer111(refer toFIG. 4), in which a lower face that is one face of the first catalyst layer-including substrate GDE1that is drawn to travel downstream from the first substrate roll11is formed on the lower face of the first catalyst layer including substrate GDE1, opposes a top face which is one face of the polymer electrolyte membrane PEM.

The first substrate roll11is a roll that prepares a continuous sheet-like (belt-like) first catalyst layer-including substrate (Gas Diffusion Electrode) GDE1, and rotates around a horizontal shaft at the upstream of the production line1. This first substrate roll11draws the first catalyst layer-including substrate GDE1from above the electrolyte membrane roll10to downstream by rotating. In the first catalyst layer-including substrate GDE1that is drawn to travel downstream from the first substrate roll11, the first catalyst layer11(refer toFIG. 4) is formed on the lower face, which is one side thereof. In addition, regarding the first catalyst layer-including substrate GDE1that is drawn out to travel downstream from the first substrate roll11, the first catalyst layer111which is at the bottom face that is one face thereof is laminated so as to oppose the top face which is one face of the polymer electrolyte membrane PEM that is drawn out to travel downstream from the electrolyte membrane roll10.

The pair of upper/lower temporary bonding rolls12,13is provided so that each is rotatable around a horizontal shaft, and the circumferences substantially contact each other at the downstream of the electrolyte membrane roll10and first substrate roll11. This pair of upper/lower temporary bonding rolls12,13is configured to be heatable and, by causing the polymer electrolyte membrane PEM and the first catalyst layer-including substrate GDE1laminated vertically to pass therethrough, applies a vertical external force and heat to this polymer electrolyte membrane PEM and first catalyst layer-including substrate GDE1while rotating, and bonds this polymer electrolyte membrane PEM and first catalyst layer-including substrate GDE1.

The first laser device14is provided downstream of the pair of upper/lower temporary bonding rolls12,13, so as to be movable in a horizontal direction above the first catalyst layer-including substrate GDE1bonding to the top face of the polymer electrolyte membrane PEM by passing through this pair of upper/lower temporary bonding rolls12,13, and irradiates a laser beam LB1towards the first catalyst layer-including substrate GDE1. This first laser device14, by irradiating the laser beam LB1towards the first catalyst layer-including substrate GDE1while moving in the horizontal direction, makes cuts CL so that the first catalyst layer-including substrate GDE1bonding with the polymer electrolyte membrane PEM becomes a predetermined shape (for example, rectangle).

The laser beam LB1of the first laser device14is a wavelength that penetrates the polymer electrolyte membrane PEM without penetrating the first catalyst layer-including substrate GDE1, similarly to the laser beam LB2of the second laser device16described later. The laser beam LB1of this first laser device14preferably has transmittance relative to the polymer electrolyte membrane PEM of at least 80%, and more preferably at least 90%. In other words, as shown inFIG. 2, the wavelength of the laser beam LB1of the first laser device14is preferably at least 400 nm, and more preferably at least 600 nm. More specifically, it is possible to use a YAG laser (wavelength 1064 nm).

In addition, as is evident fromFIG. 2, the laser beam LB1of the first laser device14has transmittance relative to carbon-based material of about 0% irrespective of the wavelength, similarly to the laser beam LB2of the second laser device16described later. As described later, since the catalyst layer-including substrate is configured by carbon-based material, the laser beam LB1of the first laser device14will be absorbed without penetrating the first catalyst layer-including substrate GDE1. Cutting or removal relative to the first catalyst layer-including substrate GDE1thereby becomes possible by the laser beam LB1of the first laser device14.

The recovery roll15is a roll that recovers an unwanted portion GDE12of the first catalyst layer-including substrate GDE1, and rotates around a horizontal shaft above the first catalyst layer-including substrate GDE1downstream of the first laser device14. This recovery roll15peels, from the polymer electrolyte membrane PEM, the unwanted portion GDE12other than the portion GDE11of a predetermined shape (for example, rectangle) of the first catalyst layer-including substrate GDE1in which the cuts CL were made by the laser beam LB1of the first laser device14, to recover this unwanted portion GDE12while winding up by rotating. It should be noted that the residual RD of the first catalyst layer-including substrate GDE1adheres on the polymer electrolyte membrane PEM after the unwanted portion GDE12of the first catalyst layer-including substrate GDE1has been peeled (refer toFIG. 3A).

The second laser device16is provided downstream of the first laser device14, so as to be moveable in a horizontal direction above the polymer electrolyte membrane PEM from which the unwanted portion GDE12of the first catalyst layer-including substrate GDE1has been peeled, and irradiates a laser beam LB2towards this polymer electrolyte membrane PEM. This second laser device16, by irradiating the laser beam LB2towards the portion of the polymer electrolyte membrane PEM to which the unwanted portion GDE12of the first catalyst layer-including substrate GDE1is bonded, while moving in the horizontal direction, removes the residual RD of the first catalyst layer-including substrate GDE1adhering on the polymer electrolyte membrane PEM (refer toFIG. 3B).

The laser beam LB2of the second laser device16is a wavelength that penetrates the polymer electrolyte membrane PEM without penetrating the first catalyst layer-including substrate GDE1, similarly to the laser beam LB1of the first laser device14. The laser beam LB2of this second laser device16preferably has a transmittance relative to the polymer electrolyte membrane PEM of at least 80%, and more preferably at least 90% (refer toFIG. 2). In other words, as shown inFIG. 2, the wavelength of the laser beam LB2of the second laser device16is preferably at least 400 nm, and more preferably at least 600 nm. More specifically, it is possible to use a YAG laser (wavelength 1064 nm).

In addition, as is evident fromFIG. 2, the laser beam LB2of the second laser device16has transmittance relative to carbon-based material of about 0% irrespective of the wavelength, similarly to the laser beam LB1of the first laser device14. As described later, since the catalyst layer-including substrate is configured by carbon-based material, the laser beam LB2of the second laser device16will be absorbed without penetrating the first catalyst layer-including substrate GDE1. Removing the residue RD of the first catalyst layer-including substrate GDE1adhering on the polymer electrolyte membrane PEM thereby becomes possible by the laser beam LB2of the second laser device16.

The polymer electrolyte membrane PEM from which the residue RD of the first catalyst layer-including substrate GDE1was removed by the laser beam LB2of the second laser device16is laminated so that, opposing a lower face which is one face thereof, is a second catalyst layer121(refer toFIG. 4), in which a top face that is one face of the second catalyst layer-including substrate GDE2that is drawn to travel downstream from the second substrate roll17is formed on the top face of the second catalyst layer including substrate GDE2.

The second substrate roll17is a roll that prepares the continuous sheet-like (belt-like) second catalyst layer-including substrate (Gas Diffusion Electrode) GDE2, and rotates around a horizontal shaft below the polymer electrolyte membrane PEM downstream of the second laser device16. By rotating, this second substrate roll17draws out to downstream the second catalyst layer-including substrate GDE2from below the polymer electrolyte membrane PEM, which is traveling. In the second catalyst layer-including substrate GDE2that is drawn out to travel downstream from the second substrate roll17, the second catalyst layer121(refer toFIG. 4) is formed on the top face which is one side thereof. In addition, regarding the second catalyst layer-including substrate GDE2that is drawn out to travel downstream from the second substrate roll17, the second catalyst layer121which is at the top face that is one face thereof is laminated so as to oppose the bottom face which is the other face of the polymer electrolyte membrane PEM from which the residue RD of the first catalyst layer-including substrate GDE1was removed.

The pair of upper/lower bonding rolls18,19is provided so that each is rotatable around horizontal shafts, and so that the circumferences substantially contact each other at the downstream of the second substrate roll17. This pair of upper/lower bonding rolls18,19is configured to be heatable and, by causing the portion GDE11of a predetermined shape of the first catalyst layer-including substrate GDE1, polymer electrolyte membrane PEM and second catalyst layer-including substrate GDE2laminated vertically to pass therethrough from upstream to downstream, applies a vertical external force and heat to this portion GDE11of a predetermined shape of the first catalyst layer-including substrate GDE1, polymer electrolyte membrane PEM and second catalyst layer-including substrate GDE2while rotating, and bonds this portion GDE11of a predetermined shape of the first catalyst layer-including substrate GDE1, polymer electrolyte membrane PEM and second catalyst layer-including substrate GDE2. In other words, the pair of upper/lower bonding rolls18,19forms the second catalyst layer121on the lower face which is the other face of the polymer electrolyte membrane PEM.

The cutter20is provided downstream of the pair of upper/lower bonding rolls18,19so as to be vertically moveable, above the portion GDE11of a predetermined shape of the first catalyst layer-including substrate GDE1, polymer electrolyte membrane PEM and second catalyst layer-including substrate GDE2, which are bonded together by passing through this pair of upper/lower bonding rolls18,19. This cutter20performs trimming such as cutting on the polymer electrolyte membrane PEM and second catalyst layer-containing substrate GDE2by moving downwards. In other words, the cutter20punches out the polymer electrolyte membrane PEM and second catalyst layer-including substrate GDE2on which the second catalyst layer121is formed, so that the first catalyst layer-including substrate GDE11of a predetermined shape bonding to the top face which is one face of the polymer electrolyte membrane PEM is surrounded. A plurality of fuel cell membrane electrolyte assemblies MEAs is thereby completed.

Next, a method for producing a fuel cell membrane electrode assembly MEA of the present embodiment executed by the production line1will be explained while referencingFIG. 1.

The method for producing a fuel cell membrane electrode assembly MEA in the production line1includes a Step1, Step2, Step3, Step4, Step5, Step6, Step7, Step8, etc.

In Step1, the polymer electrolyte membrane PEM is prepared. More specifically, the polymer electrolyte membrane PEM is drawn out to downstream from the electrolyte membrane roll10.

In Step2, the first catalyst layer-including substrate GDE1on which the first catalyst layer111is formed on the lower face, which is one face of a continuous sheet-like (belt-like) substrate, is prepared. More specifically, in Step2, the first catalyst layer-including substrate GDE1is drawn out to downstream from the first substrate roll11.

In Step3, the first catalyst layer-including substrate GDE1that is drawn out to travel from the first substrate roll11is laminated so that the first catalyst layer111opposes the top face which is one face of the polymer electrolyte membrane PEM that is drawn out to travel from the electrolyte membrane roll10.

In Step4, the polymer electrolyte membrane PEM and the first catalyst layer-including substrate GDE1, which are laminated to each other and travel, are bonded by the pair of upper/lower temporary bonding rolls12,13.

In Step5, the cut CL is made so that the first catalyst layer-including substrate GDE1bonding with the polymer electrolyte membrane PEM becomes a predetermined shape, by irradiating the laser beam LB1of the first laser device14.

In Step6, the unwanted portion GDE12other than the portion GDE11of a predetermined shape of the first catalyst layer-including substrate GDE1is peeled from the polymer electrolyte membrane PEM and recovered by the recovery roll15.

In Step7, to a portion of the polymer electrolyte membrane PEM to which the unwanted portion GDE12is bonded, the laser beam LB2of the second laser device16penetrating the polymer electrolyte membrane PEM without penetrating the first catalyst layer-including substrate GDE1is irradiated, and the residue RD of the first catalyst layer-including substrate GDE1adhering on the polymer electrolyte membrane PEM is removed.

In Step8, using the second catalyst layer-including substrate GDE2that is drawn to travel from the second substrate roll17, the second catalyst layer121is formed on the lower face which is the other face of the polymer electrolyte membrane PEM by the pair of upper/lower bonding rolls18,19, and the polymer electrolyte membrane PEM and the second catalyst layer-including substrate GDE2on which the second catalyst layer121is formed are punched out by the cutter20so that the first catalyst layer-including substrate GDE11of a predetermined shape bonding on the top face which is the one face of the polymer electrolyte membrane PEM is surrounded. A plurality of fuel cell membrane electrolyte assemblies MEA is thereby completed.

Next, the structure of the fuel cell membrane electrode assembly MEA produced by the method for producing a fuel cell membrane electrode assembly MEA of the present embodiment executed by the production line1will be explained while referencingFIG. 4.

As shown inFIG. 4, the fuel cell membrane electrode assembly MEA has a structure made by sandwiching the polymer electrolyte membrane PEM between the first catalyst layer-including substrate GDE11and the second catalyst layer-including substrate GDE2. The first catalyst layer-including substrate GDE11is configured by a first diffusion layer113, first intermediate layer112, and first catalyst layer111being laminated in this order. The first diffusion layer113is configured by a porous media which is perforated in the thickness direction, and carbon paper containing carbon fiber and carbon binder is used, for example. The first intermediate layer112is configured to include an electron conducting material and a water-repellent resin, for example. The first catalyst layer111is configured to include catalyst particles made by loading a catalytic metal such as platinum on a catalyst support such as carbon black, and a polymer electrolyte such as an ion-conductive polymer binder. Similarly, the second catalyst layer-including substrate GDE2is also configured by a second diffusion layer123, second intermediate layer122and second catalyst layer121being laminated in this order. The second diffusion layer123is a configuration similar to the first diffusion layer113, the second intermediate layer122is a configuration similar to the first intermediate layer112, and the second catalyst layer121is a configuration similar to the first catalyst layer111.

In addition, with the fuel cell membrane electrode assembly MEA, a step is formed at the periphery by the first catalyst layer-including substrate GDE11being a rectangular shape with an area smaller than the second catalyst layer-including substrate GDE2and polymer electrolyte membrane PEM. For this reason, one face (top face) of the polymer electrolyte membrane PEM has the peripheral edge exposed in a rectangular frame shape. The creepage distance of the first catalyst layer111and second catalyst layer121is assumed, and the insulation is ensured. The method for producing the fuel cell membrane electrode assembly MEA of the present embodiment executed by the production line1is appropriate in the production of MEAs having such a step.

Next, the insulation property before and after removing the residue RD of the first catalyst layer-including substrate GDE1from on the polymer electrolyte membrane PEM will be explained while referencingFIG. 5. As shown inFIG. 5, the electrode residue part from which the residue RD has not been removed has a resistance value of 0 (MΩ), and the insulation of the first catalyst layer111and second catalyst layer121is not ensured. On the other hand, a cleaning part after the residue RD has been removed has a resistance value on the order of 5 (MΩ), and the insulation of the first catalyst layer111and second catalyst layer121is found to be ensured.

According to the method for producing a fuel cell membrane electrode assembly MEA of the present embodiment explained above, the following such effects are exerted.

The method for producing a fuel cell membrane electrode assembly MEA of the present embodiment, i.e. method for producing a fuel cell membrane electrode assembly MEA on the production line1, is configured to include: Step1of preparing a polymer electrolyte membrane PEM; Step2of preparing a first catalyst layer-including substrate GDE1made by a first catalyst layer111being formed on one face of a sheet-like substrate; Step3of laminating the first catalyst layer-including substrate GDE1so that the first catalyst layer111opposes one face of the polymer electrolyte membrane PEM; Step4of bonding the polymer electrolyte membrane PEM and first catalyst layer-including substrate GDE1; Step5of making a cut CL so that the first catalyst layer-including substrate GDE1bonded with the polymer electrolyte membrane PEM becomes a predetermined shape; Step6of peeling an unwanted portion GDE12of the first catalyst layer-including substrate GDE1other than a portion GDE11of predetermined shape from the polymer electrolyte membrane PEM; Step7of irradiating a laser beam LB2of the second laser device16that penetrates the polymer electrolyte membrane PEM without penetrating the first catalyst layer-including substrate GDE1on a portion of the polymer electrolyte membrane PEM at which an unwanted portion GDE is bonded, and removing a residue RD of the first catalyst layer-including substrate GDE1adhering on the polymer electrolyte membrane PEM; Step8of forming a second catalyst layer121on one other face of the polymer electrolyte membrane PEM, and punching out the polymer electrolyte membrane PEM and second catalyst layer121so that the first catalyst layer-including substrate GDE11of predetermined shape bonded at one face is surrounded.

In summary, the present embodiment configures so as to peel the unwanted portion GDE12after bonding the first catalyst layer-including substrate GDE1only to one face of the polymer electrolyte membrane PEM, then remove the residue RD using the laser beam LB2of the second laser device16penetrating the polymer electrolyte membrane PEM without penetrating the first catalyst layer-including substrate GDE1, followed by forming the second catalyst layer121on the other face. Due to forming the second catalyst layer121on the other face after removing the residue RD in this way, the second catalyst layer121will not be removed by the laser beam LB2penetrating the polymer electrolyte membrane PEM. Therefore, according to the present embodiment, it is possible to prevent the required catalyst layer from being removed, while suppressing damage to the electrolyte membrane.

In addition, in the present embodiment, the laser beam LB2of the second laser device16is set to have a transmittance relative to the polymer electrolyte membrane PEM of at least 80%. It is thereby possible to more reliably suppress damage to the polymer electrolyte membrane PEM by using a high transmittance laser beam.

The present invention is not to be limited to the above-mentioned embodiment, and modifications, improvements, etc. in a scope that can achieve the object of the present invention are also included in the present embodiment.

EXPLANATION OF REFERENCE NUMERALS