Metal mask and screen printing apparatus

A metal mask is used in applying a printing material to an object to be printed by the sliding of a squeegee across a first surface of the metal mask. The metal mask has a plurality of openings extending from the first surface to a second surface facing the object. The metal mask has a bridge section and a filling section. The bridge section is disposed between first and second openings, and is recessed from the second surface. The filling section is provided on the second surface-side of the bridge section for being filled with printing material. The filling section communicates with the respective ends of the first and second openings. When viewed from the second surface, the filling section has a width that is larger than a width of the openings in a direction that intersects with a direction extending between the first and second openings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2014/063262, filed May 19, 2014.

BACKGROUND

Field of the Invention

The present invention relates to a metal mask and a screen printing apparatus.

Background Information

In recent years, in response to social demands and trends rooted in energy and environmental issues, fuel cells, which operate at normal temperature and from which high power density can be obtained, are gaining attention as sources of power for electric vehicles as well as stationary power sources. Because the product of the electrode reaction is primarily water, fuel cells can provide clean power generation systems with low impact on the global environment. Polymer electrolyte fuel cells (PEFC) in particular, due to their ability to operate at relatively low temperatures, are considered promising power sources for electric vehicles.

A polymer electrolyte fuel cell comprises an electrolyte membrane, a catalyst layer formed on both sides of the electrolyte membrane, and a membrane electrode assembly (Membrane Electrode Assembly, hereinafter referred to as MEA) that has a gas diffusion layer (GDL), etc. A fuel cell is configured by layering a plurality of MEAs with interposed separators.

The screen printing method is used in the manufacture of fuel cells and is a known technique in which an adhesive is applied in a rectangular shape, forming a gasket on the surface of the separator.

In the screen printing method, a separator as the object to be printed is disposed separated on the lower surface of a metal mask provided with openings, a gasket as a printing material is placed on the upper surface of the metal mask, and a squeegee is pressed and slid over the separator. Accordingly, the gasket is passed through the openings provided in the metal mask, and the gasket is applied onto the surface of the separator by transfer molding.

In a subsequent step, the separator, on the surface of which the gasket is applied, is pressurized and laminated with another separator so that the gaskets face each other. At this time, if there is a gap between the laminated gaskets, there is the risk that fuel gas or oxidant gas will leak through the gap to the outside. It is therefore necessary to form a closed rectangular pattern on the gasket that is applied to the surface of the separator.

In relation to the foregoing, for example, in Japanese Laid Open Patent Application No. 2007-331195, described below, a surface on one side of a bridge that is disposed between a pair of openings is aligned with a surface on the side over which the squeegee is slid, and the surface of the other side of the bridge is recessed from the back surface on the side that is opposite the side on which the squeegee is slid. The bridge is provided so at to connect the pair of openings. According to this metal mask, the gasket is filled in the recess provided on the other side surface of the bridge along with the openings by the sliding of the squeegee; therefore, it is possible to apply the gasket having a continuous closed pattern on the surface of the separator.

SUMMARY

However, in the metal mask disclosed in Japanese Laid Open Patent Application No. 2007-331195, since the other side surface of the bridge is recessed from the back surface, the thickness of the printing material that is applied to the surface of the object to be printed becomes thin in the height direction, in the area that corresponds to the bridge. Furthermore, this area where the thickness is thin has the same width as the other areas in a direction that is perpendicular to the direction that connects the pair of openings. Therefore, there is the risk that problems will occur, due to the application amount being small. An example of a problem is, as described above, when the object to be printed is layered in a subsequent step, a gap forms at this area where the thickness is thinner, and gas leaks to the outside through the gap.

In order to solve the problem described above, the present invention provides a metal mask and a screen printing apparatus that are capable of preventing problems caused by the small application amount of printing material that is applied to the object to be printed.

The metal mask according to the present invention that achieves the object described above is used to apply printing materials to an object to be printed by the sliding of a squeegee. The metal mask is a metal mask for screen printing on which are formed a plurality of openings that pass through from a first surface on a side to which the squeegee is provided to a second surface on a side to which the object to be printed is provided. The metal mask comprises a bridge portion that is disposed between one of the openings and the other of the openings, and that is recessed from the second surface. The metal mask comprises a filling portion that is provided on the second surface side of the bridge portion, and in which is filled the printing material by the sliding of the squeegee. The filling portion communicates with the respective ends of the one opening and the other opening and, when viewed from the second surface, has a width in a second direction that intersects a first direction extending from the one opening to the other opening that is larger than the width of the openings in the second direction.

In addition, the screen printing apparatus according to the present invention that achieves the object above is a screen printing apparatus that has the metal mask described above.

According to the metal mask and the screen printing apparatus configured as described above, of the printing material that is applied to the surface of the object to be printed, in the area where the thickness in the height direction is thin corresponding to the area where the bridge portion is provided, a pattern is formed that is wider than in the other areas in the second direction. Therefore, it is possible to prevent problems caused by the small application amount of printing material that is applied to the object to be printed. Specifically, when such objects to be printed are laminated one on top of another, since the printing material is formed wide in the second direction in the area where the height direction thickness is thin, it is possible to more reliably seal the internal space of the printing material. Therefore, it is possible to provide a metal mask and a screen printing apparatus that are well able to prevent the generation of gaps between laminated printing materials and the leaking of gas to the outside.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be explained below, with reference to the appended drawings. In the explanations of the drawings, the same elements are given the same reference signs, and redundant explanations are omitted. The dimensional ratios in the drawings are exaggerated for the sake of convenience of the explanation, and are different than the actual ratios.

FIG. 1is a cross-sectional view illustrating the cell structure of a fuel cell.

A single cell10is applied to a polymer electrolyte fuel cell (PEFC), and the like, which uses hydrogen as fuel, and comprises an MEA20, a pair of separators31,32and a pair of gaskets41,42, as illustrated inFIG. 1.

The MEA20comprises a polymer electrolyte membrane21, a pair of catalyst layer22,23and a pair of gas diffusion layers (GDL: Gas Diffusion Layer)24,25.

The catalyst layer22comprises a catalyst component, a conductive catalyst carrier that supports the catalyst component and polymer electrolytes; and is an anode catalyst layer in which the oxidative reaction of hydrogen progresses, and is disposed on one side of the electrolyte membrane21.

The catalyst layer23comprises a catalyst component, a conductive catalyst carrier that supports the catalyst component and polymer electrolytes; and is a cathode catalyst layer in which the reductive reaction of oxygen progresses, and is disposed on the other side of the electrolyte membrane21.

The electrolyte membrane21has a function of selectively transmitting protons generated in the catalyst layer22to the catalyst layer23, and a function of acting as a barrier to prevent fuel gas that is supplied to the anode side and the oxidant gas that is supplied to the cathode side from mixing.

The gas diffusion layer24is an anode gas diffusion layer for dispersing the fuel gas that is supplied to the anode side, and is positioned between the separator31and the catalyst layer22.

The gas diffusion layer25is a cathode gas diffusion layer for dispersing the oxidant gas that is supplied to the cathode side, and is positioned between the separator32and the catalyst layer23.

The separators31,32have a function of electrically connecting the single cells10in series, and a function of acting as a barrier to mutually block the fuel gas, the oxidant gas, and the refrigerant from each other. The separators31,32have substantially the same shape as the MEA20, and are formed by, for example, press working a stainless steel plate. Stainless steel plates are preferable in that complex machining can be easily applied thereto and that the conductivity is good, and it is also possible to apply corrosion resistant coating thereto, if necessary.

The separator31is an anode separator that is disposed on the anode side of the MEA20, and comprises a groove portion31athat faces the catalyst layer22and that configures a gas flow channel that is positioned between the MEA20and the separator31. The groove portion31ais used to supply fuel gas to the catalyst layer22.

The separator32is a cathode separator that is disposed on the cathode side of the MEA20, and comprises a groove portion32athat faces the catalyst layer23and that configures a gas flow channel that is positioned between the MEA20and the separator32. The groove portion32ais used to supply oxidant gas to the catalyst layer23.

The gaskets41,42are frame-shaped and are disposed on both sides of the outer perimeter part of the electrolyte membrane21. The gaskets41,42are applied by a screen printing apparatus100, to be described below.

The gasket41is applied to surround the catalyst layer22(and the gas diffusion layer24), and has a function of preventing the fuel gas that is supplied to the catalyst layer22from leaking to the outside.

The gasket42is applied to surround the catalyst layer23(and the gas diffusion layer25), and has a function of preventing the oxidant gas that is supplied to the catalyst layer23from leaking to the outside.

Next, the material and the size of each component member will be described.

For the electrolyte membrane21, fluorine-based electrolyte membranes composed of perfluorocarbon sulfonic acid polymers, hydrocarbon-based electrolyte membranes having a sulfonic acid group, and porous membranes impregnated with electrolyte components, such as phosphoric acid and ionic liquid. Examples of the perfluorocarbon sulfonic acid polymers include Nafion (registered trademark, DuPont Co., Ltd.), Aciplex (registered trademark, Asahi Kasei Corporation), and Flemion (registered trademark, Asahi Glass Co., Ltd.) can be used. The porous membrane is formed from, for example, polytetrafluoroethylene (PTFE) or polyvinylidene-fluoride (PVDF).

The thickness of the electrolyte membrane21is not particularly limited, but is preferably 5-300 μm, and more preferably 10-200 μm, from the standpoint of strength, durability, and output characteristics.

The catalyst component that is used for the catalyst layer (cathode catalyst layer)23is not particularly limited and can be any component that has a catalytic effect in the reductive reaction of oxygen. The catalyst component that is used for the catalyst layer (anode catalyst layer)22is not particularly limited and can be any component that has a catalytic effect in the oxidative reaction of hydrogen.

Specific catalyst components are selected from such metals as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, and alloys thereof, etc. It is preferable to include at least platinum in order to improve catalytic activity, resistance to poisoning from carbon monoxide, heat resistance, and the like. The catalyst components that are applied to the cathode catalyst layer and the anode catalyst layer need not be the same, and can be appropriately changed.

The conductive carrier of the catalyst that is used for the catalyst layers22,23is not particularly limited as long as the catalyst carrier has a specific surface area for supporting the catalyst component in the desired dispersed state, and sufficient electronic conductivity as a current collector. The carbon particles can be composed of carbon black, activated carbon, coke, natural graphite, or artificial graphite, for example.

The polymer electrolyte that is used for the catalyst layers22,23is not particularly limited as long the member has at least a high proton conductivity; for example, fluorine-based electrolytes containing fluorine atoms in all or part of the polymer backbone, or hydrocarbon electrolytes that do not contain fluorine atoms in the polymer backbone can be used. The polymer electrolytes used for the catalyst layers22,23can be the same as or different from the polymer electrolytes used for the electrolyte membrane21, but are preferably the same from the standpoint of improving the adhesion of catalyst layers22,23with respect to the electrolyte membrane21.

The thickness of the catalyst layer is not particularly limited as long as the thickness is sufficient to exert the catalytic effect of the oxidative reaction of hydrogen (anode side) and the reductive reaction of oxygen (cathode side), and conventional thicknesses can be used. Specifically, the thickness of each catalyst layer is preferably 1-20 μm.

The gas diffusion layers24,25is configured from a sheet material having conductivity and porosity, such as carbon fabric such as glassy carbon, a paper-like paper body, felt, and nonwoven fabric. The thickness of the substrate is not particularly limited, but is preferably 30-500 μm, from the standpoint of mechanical strength and permeability of gas, water, and the like. The gas diffusion layers24,25preferably contain a water-repellent agent in the substrate, from the standpoint of water repellency and suppression of the flooding phenomenon. Examples of water-repellent agents include fluorine-based polymer material such as PTFE, PVDF, poly hexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymers (FEP), polypropylene, and polyethylene.

The separators31,31are not limited to forms configured from stainless steel plates; other metal materials (for example, aluminum plates and clad materials), and carbon, such as dense carbon graphite and carbon plates, may also be applied thereto. When applying carbon, the groove portions31a,32acan be formed by cutting or screen printing.

The gaskets41,42are formed from an adhesive. For example, a hot melt adhesive, which is a thermoplastic adhesive, can be used as the adhesive. The thickness of the gaskets41,42is about several millimeters.

Next, the screen printing apparatus100for applying a gasket (corresponding to the printing material)41onto the separator (object to be printed)31of the present embodiment and the metal mask50that configures the screen printing apparatus100will be described with reference toFIG. 2-FIG. 6.

FIG. 2is a schematic overview illustrating the screen printing apparatus100according to the present embodiment.FIG. 3is an upper surface view of the metal mask50according to the present embodiment.FIG. 4is a lower surface view of the metal mask50according to the present embodiment.FIG. 5is a cross-sectional view of the metal mask as seen along line5-5ofFIG. 3.FIG. 6is a cross-sectional view of the metal mask as seen along line6-6ofFIG. 3. InFIG. 2, only the metal mask50is illustrated in cross section for the sake of clarity.

The screen printing apparatus100comprises a metal mask50that is disposed spaced apart on the separator31and in which a plurality of openings51are formed, and a squeegee60that is provided slidably with respect to the metal mask50, as illustrated inFIG. 2. The screen printing apparatus100further comprises a mounting table70on which the separator31is mounted and a moving unit80that moves a support portion61, which supports the squeegee60, in the separator31plane (XY) direction as well as in the Z direction that is perpendicular to the direction of the plane. The moving unit80is, for example, an XYZ stage.

The squeegee60is moved while sliding on the surface of the metal mask50by the moving unit. As a result, the gasket41is pushed out from the opening51of the metal mask50and applied onto the separator31. The squeegee60is formed from rubber, for example.

The metal mask50comprises four openings51A-51D, as is illustrated inFIG. 3-FIG. 6. The four openings51A-51D are each formed with an L-shape.

The metal mask50comprises bridge portions52A-52D that are disposed between each of the openings51A-51D and that are recessed from the lower surface S2. More specifically, the bridge portion52A is provided between the opening51A and the opening51B; the bridge portion52B is provided between the opening51B and the opening51C; the bridge portion52C is provided between the opening51C and the opening51D; and the bridge portion52D is provided between the opening51D and the opening51A. The bridge portions52A-52D are provided in order to form a closed pattern gasket41on the separator31after screen printing.

The metal mask50comprises filling portions53A-53D that are provided on the lower surface S2sides of the bridge portions52A-52D, and in which are filled the gasket41by the sliding of the squeegee60. Accordingly, by disposing the gasket41on the metal mask50and by the sliding of the squeegee60, for example, from the right side to the left side inFIG. 3, the gasket41that has passed through the openings51B,51C fills the filling portion53B. Furthermore, by the sliding of the squeegee60, the gasket41fills the filling portions53A,53C, and the filling portion53D, in that order. Thus, it is possible to form a closed pattern of the gasket41on the separator31.

Since the bridge portions52A-52D have the same shape, only the configuration of the bridge portion52A is described below, and the configurations of the bridge portions52B-52D are omitted. In addition, since the filling portions53A-53D have the same shape, only the configuration of the filling portion53A is described below, and the configurations of the filling portions53B-53D are omitted.

The bridge portion52A has a tapered shape so that the upper surface S1side thereof becomes wider at the interface T between the openings51A,51B on the upper surface S1, as is illustrated inFIG. 5. According to this configuration, when the metal mask50is peeled off after the sliding of the squeegee60, due to the tapered shape, it is possible to suppress the generation of angular edges on the gasket41and to reduce coating variability.

Although not shown, the bridge portion52A is preferably provided with a plurality of fine through-holes that extend in the Z direction. According to this configuration, since the gasket41fills the filling portion53A by means of the through-holes, it is possible to increase the application amount.

The filling portion53A communicates with the respective ends51a,51bof the opening51A and the opening51B, and, when viewed from the lower surface S2, the width W1thereof in the Y direction, which is perpendicular to the X direction extending from the opening51A to the opening51B, is larger than the width W2in the Y direction of the openings51A,51B, as is illustrated inFIG. 4.

The filling portion53A, when viewed from the lower surface S2, has a shape that is wider at substantially the central position between the respective ends51a,51bof the opening51A and the opening51B, and that becomes narrower toward the respective ends51a,51b, as is illustrated inFIG. 4.

The openings51A-51D have enlarged opening portions511A-511D that open more widely at the areas that are bent in an L-shape than at the other areas, as is illustrated inFIGS. 3-5. The enlarged opening portions511A-511D are configured to open widely on the lower surface S2side, as is illustrated inFIG. 5. The shape of the enlarged opening portions511A-511D is not limited thereto; the shape is not particularly limited as long as the shape opens more widely in the XY direction than at the other areas, as seen from the lower surface S2.

Next, the actions of the metal mask50according to the present embodiment will be described with reference toFIG. 7.

FIG. 7is a perspective view illustrating the gasket41that is applied to the separator31using the metal mask50according to the present embodiment. For ease of understanding,FIG. 7illustrates the areas that are formed by the filling portion53A, the bridge portion52A, and the openings51A,51B of the metal mask50.

By the sliding of the squeegee60in a state in which the metal mask50, on the surface of which is disposed the gasket41, is disposed on the separator31, the gasket41pattern illustrated inFIG. 7is formed on the separator31, as is illustrated inFIG. 2.

The gasket41that is formed on the separator31comprises a first main body portion41A that corresponds to the opening51A, a second main body portion41B that corresponds to the opening51B, and a connecting portion41C that corresponds to the filling portion53A. The gasket41further comprises a first edge portion41D that corresponds to the enlarged opening portion511A and a second edge portion41E that corresponds to the enlarged opening portion511B. The gasket41further comprises a tapered portion41T that corresponds to the tapered interface T.

The separator31, on the surface of which is applied the gasket41, is formed by the screen printing apparatus100described above. Additionally, a separator32, on the surface of which is applied a gasket42that has the same configuration as the gasket41, is prepared in a similar manner. Then, the separator31and the separator32are layered so that the gasket41and the gasket42are opposite each other, as illustrated inFIG. 1.

At this time, since the gasket41has a tapered portion41T so that air tends to leak out, air tends not to enter the gasket41, thereby reducing the risk of leakage.

By laminating the separator31and the separator32, the first main body portion41A and the second main body portion41B are compressed in the Z direction to become substantially equal in height with the connecting portion41C, the first edge portion41D and the second edge portion41E.

The width W3of the connecting portion41C in the Y direction is configured to be larger than the width W4of the first main body portion41A and the second main body portion41B in the Y direction; therefore, compared to cases in which the widths are the same, as in the prior art, the internal space of the gasket41can be more reliably sealed. Therefore, it is possible to suitably prevent the leaking of fuel gas or the oxidant gas to the outside.

In addition, since a first edge portion41D and a second edge portion41E are provided to the L-shaped corners of the gasket41, it is possible to reinforce the corners where stress is concentrated and thereby to improve the strength of the gasket41.

As described above, the metal mask50according to the present embodiment is used for applying the gasket41to the separator31by the sliding of the squeegee60. On the metal mask50are formed a plurality of openings51, which extend from the upper surface S1on the side on which is provided the squeegee60to the lower surface S2on the side on which is provided the separator31. The metal mask50comprises a bridge portion52A that is disposed between the opening51A and the opening51B and that is recessed from the lower surface S2, and a filling portion53A that is provided in the lower surface S2side of the bridge portion52A, and in which is filled the gasket41by the sliding of the squeegee60. The filling portion53A communicates with the respective ends51a,51bof the opening51A and the opening51B, and, when viewed from the lower surface S2, the width W2thereof in the Y direction that intersects the X direction extending from the opening51A to the opening51B is larger than the width W1in the Y direction of the openings51A,51B. Thus, a pattern of the gasket41that is applied to the surface of the separator31, in the area where the thickness in the Z direction is thin corresponding to the area where the bridge portion52A is provided (corresponding to the connecting portion41C), is formed that is wider than the other areas in the Y direction. Therefore, it is possible to prevent problems caused by a small application amount of the gasket41that is applied to the separator31. Specifically, when such separators41,42are laminated one on top of another, since the gasket is formed wide in the Y direction in the area where the Z direction thickness is thin, it is possible to more reliably seal the internal space of the gasket41. Therefore, it is possible to suitably prevent the formation of gaps between the laminated gaskets41,42and the leaking of gas to the outside.

In addition, the bridge portion52A has a tapered shape so that the upper surface S1side thereof becomes wider at the interface T between the openings51A,51B on the upper surface S1. Accordingly, it is possible to suppress the generation of angular edges on the gasket41caused by the shearing force generated when the metal mask50is peeled off after the sliding of the squeegee60, allowing a reduction in coating variability. Additionally, air is moved in a direction away from the gasket41along the tapered shape when laminating the separators31,32; therefore, air does not tend to enter the gasket41, so that the risk of leakage is reduced.

Furthermore, the opening51A has an enlarged opening portion511A that opens more widely than at the other portions. Therefore, a pattern is formed in the first edge portion41D of the gasket41, which corresponds to the enlarged opening portion511A, that has a larger area in the XY direction than at the other portions. Therefore, it is possible to increase the application amount of the gasket41at the intended sites. As a result, it is possible to reinforce the desired position, and thereby to improve the strength of the gasket41.

In particular, the enlarged opening portion511A is provided in the area where the opening51A is bent. Accordingly, it is possible to reinforce the corners where stress concentrates, and thereby to improve the strength of the gasket41.

Additionally, the screen printing apparatus100comprises the metal mask50described above. Accordingly, it is possible to suitably prevent the generation of gaps between the laminated gaskets41,42and the leakage of gas to the outside.

Furthermore, the screen printing apparatus100according to the present embodiment applies the gasket41to the surface of the separator31. According to this screen printing apparatus100, it is possible provide a fuel cell in which the generation of gaps between the laminated gaskets41,42and the leakage of gas to the outside can be reliably prevented.

Modified examples of the above-described embodiment are illustrated below.

In the above-described embodiment, the respective ends51a,51bof the openings51A,51B are extended along the Y direction, as is illustrated inFIG. 4. However, the interface (ends151a,151b) of a bridge portion152with respect to openings151A,151B can be tilted relative to the Y direction as seen from the lower surface S2, and the end151aand the end151bcan be arranged so as to be wrapped in the Y direction, as is illustrated inFIG. 8. According to this configuration, since the distance between the ends151a,151bcan be reduced, it is possible to more reliably prevent the generation of gaps between the laminated gaskets41,42and the leakage of gas to the outside.

In addition, in the above-described embodiment, each of the bridge portions52A-52D has the same shape, and each of the filling portions53A-53D has the same shape. However, no limitation is thereby implied; the shapes can be different from each other within a range that allows the effects of the present invention to be imparted.

Furthermore, in the above-described embodiment, the bridge portion52A has a tapered shape so that the upper surface S1side thereof becomes wider at the interface T between the openings51A,51B on the upper surface S1. However, the interface T can be R-shaped so that the upper surface S1side becomes wider.

In addition, in the above-described embodiment, the enlarged opening portions511A-511D are provided at the corners of the openings51A-51D. However, no limitation is thereby implied; the enlarged opening portions can be provided anywhere.

Additionally, in the above-described embodiment, the filling portion53A has a shape that is wider at substantially the central position between the respective ends51a,51bof the opening51A and the opening51B and that becomes narrower toward the respective ends51a,51b. However, no limitation is thereby implied; the width of the filling portion in the Y direction need only be larger than the width of the openings in the Y direction.

Furthermore, in the above-described embodiment, an embodiment was described in which screen printing is carried out by placing the gasket41on the upper surface of the metal mask50and pressing and sliding the squeegee60over the separator31. However, screen printing can be carried out by the sliding of the squeegee60after flattening the gasket41on the upper surface of the metal mask50using a scraper before the sliding of the squeegee60.

Additionally, in the above-described embodiment, the metal mask was used in a method to apply the gasket41on the separator31as the screen printing method; however, no limitation is thereby implied; the metal mask can be used with any screen printing apparatus.