Cathode head having improved seal means

Claim 1

In a cathode head for holding a flat circular matrix of a first diameter during electroforming of a replica of a second, smaller diameter on the surface of the matrix, wherein said cathode head is comprised of: (a) a disc shaped member having an outer diameter at least as large as the first diameter, a flat face for holding said matrix to be replicated and a male thread defined on the outer edge thereof; (b) a ring member having an integral outer cylindrical portion and a radially inwardly extending portion, said outer cylindrical portion having a female thread which mates with the male threads of the disc shaped member and the radially inwardly extending portion including seal holding means; and (c) a circumferential seal positioned in said seal holding means whereby when the ring member is threadably engaged with the outer edge of the disc member and screwed towards the disc member, the circumferential seal engages the outer flat surface of said matrix held on the flat face of the disc shaped member; said improvement comprising: using a circumferential seal having a cross-sectional configuration comprised of integral first and second portions, said first portion being of a shape so as to be held by the seal holding means of the ring member and said second portion being of a substantially right triangular configuration and extending downward from the first portion with a leg side of the triangular portion forming a substantially perpendicular cicumferential wall with respect to the flat surface of said matrix thereby defining an electroforming area of said second diameter, said leg side of the triangular portion extending to an apex where it meets the hypotenuse side of the triangular portion which hypotenuse side then extends upwardly towards the outer edge of the first portion of the seal; whereby the edge formed at the apex of the triangular portion provides an improved electrolyte tight engagement of the seal to said matrix to be replicated and the leg side of the right triangular portion of the seal provides a substantially perpendicular wall against which said replica having a perpendicular edge can be electroformed.