1.  Field of the Invention
The present invention relates to a method of manufacturing a seal component obtained by integrally molding a gasket made of a rubber material or a synthetic resin material having a rubber-like elasticity on a film, sheet or plate-like base frame, such as a seal for a fuel battery or the like for sealing a flow path, for example, formed in each of fuel battery cells of a fuel battery stack, and a metal mold used for the same. 
2.  Description of the Conventional Art
The fuel battery has a stack structure in which a power generation body including a membrane electrode assembly (MEA) provided with a pair of electrode layers on both surfaces of an electrolyte membrane is held between separators so as to form a fuel battery cell, and a lot of the fuel battery cells are laminated.  Air (oxygen) is supplied to one catalyst electrode layer (an air electrode) from an air flow path formed on one surface of each of the separators, fuel gas (hydrogen) is supplied to another catalyst electrode layer (a fuel electrode) from a fuel gas flow path formed on another surface of each of the separators, and electric power is generated on the basis of an electrochemical reaction corresponding to a reverse reaction to an electrolytic process of water, that is, a reaction creating water from hydrogen and oxygen. 
Accordingly, each of the fuel battery cells is provided with a seal component for preventing leakage of fuel gas, air, the water created by the electrochemical reaction mentioned above, surplus air or the like.  As this kind of seal component, there have been known a structure in which a gasket made of a rubber material or a synthetic resin material having a rubber-like elasticity is integrated on a film-like, sheet-like or plate-like base member such as a separator, a synthetic resin film or the like. 
In order to manufacture this kind of seal component, a metal mold 100 constructed by split molds 101 to 103 has been conventionally used, and a gasket made of a rubber-like elastic material is integrated with a base member 200 at the same time of molding, by positioning and fixing the base member 200 between the split molds 102 and 103, clamping the metal mold, charging a liquid molding rubber material into an annular cavity 110 defined between the base member 200 and an inner surface of the split mold 102 through a sprue 100a, a runner 100b and a gate 100c which are formed in the split molds 101 and 102, and hardening it by cross-linking, for example, as shown in FIG.  7. 
In this case, since the gasket is consecutive in an endless shape, and the cavity 110 for molding it has the same shape, the liquid molding rubber material charged into the cavity 110 flows divergently from the gate 100c to both sides thereof, and confluence occurs at a position 110a opposite to the gate 100c.  Further, since defective molding tends to be caused at this confluence position 110a due to remaining air or mixing of volatile gas from the molding rubber material, an air vent hole 100d for letting out the remaining air and the volatile gas mentioned above, and well mixing the confluent molding rubber material is formed in the split mold 102.  One end of the air vent hole 100d is open to the confluence position 110a in the cavity 110, and another end of it is open to contact surfaces of the split molds 101 and 102 (refer to Japanese Unexamined Patent Publication No.  2008-168448). 
However, according to the conventional art mentioned above, as shown in FIG.  8, in the case that a part 301 of the molding rubber material 300 flowing into the air vent hole 100d through confluence at the confluence position 110a in the cavity 110 does not fill the air vent hole 100d, it is impossible to keep molding pressure within the cavity 110 properly.  Accordingly, there is a risk of causing defective molding such as reduction of physical properties of the material of the gasket due to lack of pressure, dispersion of gasket dimensions due to molding shrinkage, remaining of air in the other portions than the confluence position 110a in the cavity 110, and the like. 
Further, as shown in FIG.  9, in the case that the part 301 of the molding rubber material 300 flowing into the air vent hole 100d through confluence at the confluence position 110a in the cavity 110 fills the air vent hole 100d, the surplus molding rubber material can go nowhere at that moment, so that a molding pressure within the cavity 110 rapidly rises.  Therefore, in this case, there are risks that a part of the molding rubber material 300 within the cavity 110 leaks along the contact surfaces between the base member 200 and the split mold 102 so as to make a thin burr 302, and that the base member 200 is damaged by an excessive molding pressure in some material of the base member 200. 
Accordingly, it is necessary to a measure an injection amount of the molding rubber material 300 and control an injection pressure thereof with high precision in such a manner as to keep the molding pressure within the cavity 110 at an appropriate value, as well as filling the air vent hole 100d with the part 301 of the molding rubber material 300.  Particularly, in a product having a lot of gates, it is necessary to make the molding rubber material being simultaneously charged into all the air vent holes at the confluence positions between the gates, however, such a control is extremely hard.  As a result, it is impossible to prevent the thin burr 302 from being made, so that a removing work of the thin burr 302 is inevitable, and is an obstacle to cost reduction. 
The present invention is made by taking the points as mentioned above into consideration, and a technical object thereof is to appropriately keep molding pressure within a cavity at a time of charging a molding rubber material, thereby effectively preventing occurrence of defective molding and a thin burr due to leakage of the molding rubber material.