Kodak Module 9 specifications Wash-Water Flow Rates, Stop Wash, Bleach Wash, Final Wash, Rewashing

Wash-Water Flow Rates

Adequate washing in conjunction with conservation of wash water is a matter of concern for all processors. Ways of reducing wash-water usage while maintaining adequate washing include: (1) using multi-stage countercurrent-flow washes, (2) installing squeegees between wash stages as well as before the wash, and (3) shutting off wash water when the machine is not transporting film or leader. The last alternative can easily be accomplished by installing solenoid valves in the wash-water supply lines that are opened when the machine drive is running. The water saving from the use of squeegees and countercurrent stages can be substantial. A three-stage countercurrent final wash with squeegees before and after each stage requires approximately 1/25 of the water of a single-stage wash with entrance and exit squeegees. Overflow from one wash step should never be used in any other wash step.

Decreased water flow in the final wash may increase the propensity toward biological growth. See Module 2, Equipment and Procedures, for information on control of biological growth. Temperature control can also be a concern at lower flow rates. After establishing the final flow rate, check to be sure the process stays within the temperature tolerances specified in Tables 9-3,9-4,or 9-5.

The wash-water flow rates in Tables 9-3,9-4,and 9-5have been found to be satisfactory in a 165 ft/min (50 m/min) processor, using three-stage countercurrent bleach and final washes with efficient squeegees between stages. The other washes employ the use of two-stage countercurrent washes. The optimum wash rates for a particular installation can be determined only after the film transport rate, the number of countercurrent stages, and the squeegee efficiencies have been established. Experimentation is necessary to determine minimum wash-water flow rates that will provide adequate washing. Inadequate washing will result in significant contamination of the solution after the wash with the solution before the wash.

Stop Wash

An inadequate wash will result in a high level of Color Developing Agent CD-2 in the bleach or bleach accelerator.

Bleach Wash

If using the alternate cycle with ferricyanide bleach, an inefficient bleach will cause excessive buildup of bleach- fixer reaction products in the fixer. The combined levels of potassium ferricyanide and sodium ferrocyanide in the final stage of the bleach wash should be below 0.5 g/L, as measured by Analytical Methods ECP-00021/1and ECP- 2E-1101(or ECP-0023/01) in Module 3, Analytical Procedures.

Final Wash

The final wash must remove most of the thiosulfate (hypo) from the film. Retained hypo levels of 4 ∝g/cm2 or greater can cause serious dye fading. If the recommended three- stage countercurrent wash and wash rate are used, residual hypo in the designated films processed in Process ECP-2E should be barely detectable (0.2 to 0.4 ∝g/cm2) by Analytical Method ULM-0004/1in Module 3, Analytical Procedures.

Rewashing

For many years, the term rewashing referred to the common practice of running processed film through a complete process for a second time. This operation removes dirt and/ or heals slight emulsion scratches and digs. Rewashing a film once in the original process produces minimal changes in the dye stability and sensitometry. However, several rewashings may cause a change in density over the exposure scale of the film. By omitting the developer and bleach when the film is rewashed, changes in density can be minimized.

Rewash RW-1 is designed to avoid these sensitometric and dye stability changes, and at the same time, to produce similar emulsion swells to that obtained by going through the original developer.

Table 9-6 Rewash RW-1 Sequence

	Step	Function
1.	Prebath PB-6	Swells the emulsion, causing the
		scratches to be filled in and embedded
		dirt particles to be released.
2.	Wash	Removes unwanted chemicals, which, if
		left in, affect dye stability.
3.	Final Rinse FR-1	Contains a wetting agent to help prevent
		water spots while the film is being dried.
4.	Dry	Dries film for subsequent handling.

The rewash machine consists of a loading elevator, tanks for the prebath, wash, and final rinse solutions, and a dryer. Submerged rollers and rack-drive assemblies will minimize spattering of solutions and aerial oxidation of sulfite in the prebath. Type 316 stainless steel is suitable for tanks, racks, and recirculation equipment. Use 10-micron filters of polypropylene, fiberglass, or bleached cotton in the recirculation system. Use no squeegees, except after the final rinse, where a high efficiency final squeegee is needed.

Process ECP-2E Specifications 9-15