If the first and second ends of each of the first and second gaskets 410 and 420 are disposed so as to be contiguous with the receiving recess H1 and the outer edge 600E without being spaced apart therefrom, the first and second gaskets 410 and 420 may invade the receiving recess H1, or may protrude outwards from the outer edge 600E. Further, the process of manufacturing the first and second gaskets 410 and 420 in consideration of avoidance of the above problem may be complicated. Therefore, according to an exemplary embodiment of the present disclosure, the first and second ends of each of the first and second gaskets 410 and 420 are respectively spaced apart from the receiving recess H1 and the outer edge 600E by the first and second gaps G1 and G2, thereby preventing the above problem.

Each of the opposite surfaces of each separator 600 may include first to third regions A1 to A3, which surround the receiving recess H1. The first region A1 is a region in which the first gasket 410 is formed, and is a region that is contiguous with the first side H1S1 of the receiving recess H1. The second region A2 is a region in which the second gasket 420 is formed, and is a region that is contiguous with the second side H1S2 of the receiving recess H1 while facing the first region A1 in the third direction. The third region A3 is a region that is contiguous with the third side H1B of the receiving recess H1 between the first region A1 and the second region A2.