Dainippon Ink and Chemicals, Incorporated

Toshio Kambe

Kazumi Oi

Kazunari Sakai

Hitoshi Katou

Koji Kawase

An apparatus for controlling the resistivity of ultra pure water, including a housing to house a gas permeable membrane, an inlet for untreated ultra pure water which communicates with an ultra pure water path, and an outlet for resistivity-controlled ultra pure water which communicates with the ultra pure water path. The gas permeable membrane divides the interior of the housing into the ultra pure water path and a mixed gas path. A mixed gas is selected from the group consisting of a mixed gas including carbon dioxide and a gas having a lower resistivity controlling ability than carbon dioxide and a mixed gas including ammonia and a gas having a lower resistivity controlling ability than ammonia. The gas permeable membrane is capable of supplying carbon dioxide or ammonia to the untreated ultra pure water at a concentration equal to or more than 90% of the equilibrium concentration.

Apparatus and method for controlling resistivity of ultra pure water

A small flow of a water with a high carbon dioxide content (normally a carbon-dioxide-saturated water) is produced using hollow-fiber membranes, and is uniformly mixed with a large flow of untreated water with constant proportions. Since the hollow-fiber membrane module has a reserve capacity for adding carbon dioxide to the water, the resistivity of the mixed water is maintained at a constant level by maintaining constant proportions of the small and large flows, even if the total flow rate fluctuates due to fluctuations in the rate of water used in a subsequent process. Accordingly, no automated control device is particularly necessary in order to maintain the resistivity at a constant level. Therefore, a compact and simple apparatus can be produced which can operate at a low cost.

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Ichihara, Japan

Toshio Kambe