9-6 Process ECP-2E Specifications
Construction Materials
The construction materials recommended for the developer,
stop, fixer, and bleach solutions are listed in Table9-2. All
the bleaches are quite corrosive. The UL bleach is slightly
more corrosive than ferricyanide bleach, but less corrosive
than persulfate bleach. Titanium, Hastelloy C, and
engineering plastics such as PVC are, therefore,
recommended materials for persulfate bleach. Use plastics
compatible with low pH solutions (less than pH 5).
Red brass is commonly found in ferricyanide bleach
systems, it will quickly be dissolved by persulfate bleach and
UL bleach. In addition to machine tanks, it is often found in
fittings, flowmeters, heat exchangers, and valves. Small red-
brass parts have been found even when the bleach tank is
constructed of titanium, Hastelloy C, or PVC.
The following materials are compatible with ferricyanide
or “UL,” but not acceptable with persulfate bleach.
Monel is a commonly used staple material; it is dissolved
by persulfate bleach in several hours. Stainless-steel staples
are recommended for extended lifetime in persulfate bleach.
Standard carbon-steel staples will show some corrosion, but
maintain their integrity in persulfate bleach much longer
than Monel-type staples. In all cases, it is a good practice to
avoid extended exposure of staples to any bleach solution.
Some plastic and elastomeric materials will be degraded
by persulfate bleach. This degradation is accelerated by the
presence of chlorine in the bleach. Some materials known to
be degraded by persulfate bleach are low-density
polyethylene, acrylonitrile, butadiene, styrene, nylon 6/6,
and neoprene. All plastics and elastomeric materials (other
than PVC, RTV-60, silicone, and Vitron) should be tested
before being used in persulfate bleach. Most plastics,
including PVC, will discolor in persulfate bleach, but retain
their mechanical properties. Tygon tubing, which turns
white, is an example of this effect.
For best process control, equip the holding tank for the
color developer replenisher with a tight-fitting floating
cover. The cover will minimize air oxidation of the solution,
and absorption of carbon dioxide from the air, which would
change the pH. Clearance between the cover and the tank
wall should not be greater than
1
⁄4 inch (6.4mm).
Polyethylene sheeting of
1
⁄2 inch (12.7 mm) thickness makes
adequate covers in sizes up to 3 feet (1 metre) in diameter. A
dust cover alone permits air to come in contact with the
solution and will allow some air oxidation to take place. Dust
covers should be used for non-developer solution to
minimize dirt in the replenisher tanks.
Additional information on materials construction and
information on their use are given in The SPSE Handbook of
Photographic Science and Engineering, Materials of
Construction for Photographic Processing Equipment
section. You may also contact the Kodak Information Center
at 1-800-242-2424.