Seiko & Citizen Watch Forum Message Archive

Up to that time, seals and gaskets were mostly made from Nitoriru Butajen Rubber (NBR), otherwise known as nitrile rubber. It's a general purpose elastomer used in low pressure applications such as hydraulics and pneumatics, and is resistant to oils, hydraulic fluids, water fuels and most gases. However, because of the very small size of helium atoms, it was not particularly good as a barrier against them.

Seiko looked around for a material that would better resist helium invasion, and came up with Isobuchirn Isopuren Rubber (IIR or butyl rubber). This material is used in inner tubes and as a tyre liner because of its excellent air sealing properties. By using IIR as the gasket material, and revising the shape of the gasket to an "L" cross-section to provide better sealing both horizontally and vertically, the amount of helium gas penetration was reduced to 1/100 of its previous level.

I'm surprised you didn't know that -- it's something every Australian schoolboy knows!

Actually, I can't take all the credit for this -- much of the info comes from one of Ryan's excellent posts about five years ago.

GLSM IBC, Rep. Bellm.

_Time runs differently for watchmakers--a week to them is a month for everyone else._