Directions in Photoprocessing Chemistry

Brian Barbo is currently president of Trebla Chemical Company, St. Louis, Missouri.  His perspective on recent changes in the imaging business includes 20 years of experience in the photoprocessing industry, from chemical regeneration and silver recovery, to photochemistry design, manufacturing and marketing.  
He has a bachelor of science in Chemical Engineering from the University of Rochester.

"While digital methods and hardware continue to improve in speed and resolution, we still lack the technological breakthrough that will allow a totally digital alternative to replace the ease of use, production speed, and low cost per image of the silver halide methods." OUR INDUSTRY HAS seen many changes in the last ten years, beginning with the introduction of the RA-4 and C-41RA process configurations.  Both of these innovations tremendously shortened the dry-to-dry times for color print and film processing, shattering the paradigms that had stood for over fifteen years.

In the last five years, we have experienced the integration of digital technology into the imaging industry, from image capture, though enhancement, to hard-copy output.

While digital methods and hardware continue to improve in speed and resolution, we still lack the technological break-through that will allow a totally digital alternative to replace the ease of use, production speed, and low cost per image of the silver halide methods.

Today, the most effective commercial application of digital methods, especially for mass-production, uses traditional film for capture of the original image, followed by digitization and enhancement of the image, and then printing of the digital file to photographic paper or display film. 

The digital image file can be shared directly between computers, and thus, the rapidly growing service infrastructure for providing pictures over the Internet or on CD is still an outgrowth of traditional photoprocessing in this regard.

Even with dramatic increases in the sales of digital cameras, we continue to see worldwide increases in film sales year after year, in all major markets. This appears to be enhanced by the widespread popularity of the single-use format, and the proliferation of APS cameras. 

All of these activities provide an indication that the time-honored silver halide technology for image capture and delivery still has plenty of life left in it, and perhaps even an expanding role in our society as more people want to share their pictures electronically.

This is good news for photofinishers and their suppliers-our current business models are still relevant as we move into the 21st century. The growing demand for added-on digital capabilities broadens the opportunity horizon for both niche and mass-production service enhancements.

With this in mind, we see that photoprocessing chemistry will be an integral part of the imaging industry for some time to come. There are many societal responsibilities that go along with using a chemical process in today's culture, from environmental stewardship as municipal wastewater treatment plants reach their design capacities, to employee safety considerations. 

The chemistry suppliers are diligent in discovering improvements and enhancements of their assorted formulas to address all of these "secondary" requirements, while at the same time delivering improved processing performance.
One of the predominant trends in photoprocessing chemistry formulations is a continued reduction in replenishment rates needed to maintain high-quality results. This is especially important in Europe and Japan, and some areas in the US, where spent photo solutions cannot be sewered due to the inability of the regional treatment systems to adequately handle large proportions of this moderate-strength waste. 

Before the RA-4 process was introduced, the most common print developers replenished at a rate of 30 mL/sqft (323 mL/m2), and low-replenishment or LR varieties could reduce this to under 20 mL/sqft (215 mL/m2). With the RA-4 process, the "standard" developer requires 15 mL/sqft (161 mL/m2), and LR products are widely available that operate at 6.5 mL/sqft (70 mL/m2). Similar trends are well proven for bleach-fix as well, with a practical range of 20 mL/sqft (215 mL/m2) down to 5 mL/sqft (54 mL/m2). 

Many factors determine the practical lower limit of replenishment rate, and the most significant is squeegee performance. Obviously, the replenishment rate must be sufficient to replace the volume dragged into the next bath. The dilution effect of drag-in from a previous bath must be overcome by a combination of replenisher strength and volume. 

Many of today's minilab processors have very efficient roller squeegee action, allowing practical reduction of the print developer replenishment rate to 4.2 mL/sqft (45 mL/m2), and the bleach-fix replenishment rate to 3.2 mL/sqft (35 mL/m2).

Figure 1, above, compares the developer and bleach-fix volumes needed to process one square foot (0.093 m2) of paper for varying replenishment rate alternatives. The final wash volumes are also included, ranging from 30 mL/sqft (323 mL/m2) to 23 mL/sqft (242 mL/m2) representing the various chemical rinse products available.

When evaluating low-replenishment alternatives, the need to maintain sufficient solution turnover is often overlooked, and this is most critical for color developers. 

The complex function of these solutions makes them very sensitive to oxidation, or aging, and a good rule of thumb is to use a mixed replenisher within two weeks. While additional measures such as floating lids can be used to extend a developer's reliable service life, remember that it will also be sitting in the processor for some period of time at an elevated temperature. 

Turnover of the developer in the processor is just as important-ideally, the processor tank volume should be displaced every seven to ten days. Thus, a processor with a 10L developer tank should use 10L of developer every seven to ten days. This is equivalent to 4000 4 x 6 inch (10 x 15 cm) prints for a 15 mL/sqft (161 mL/m2) developer, or 9200 prints for a 6.5 mL/sqft (70 mL/m2) developer. Figure 2, page 14, illustrates the relationship between developer replenishment rate and the time it takes to consume 10L of replenisher, for a lab processing 30 rolls per day.

Remember that for optimum performance, the working solution in the processor does not change, regardless of the replenishment rate. Using these low-replenishment rate developers is not as simple as merely concentrating the replenisher solution and dialing down the delivery rate. 

Several ingredients in the solutions are consumed during the development process, to varying degrees, so an LR replenisher must deliver the proper amount of each chemical needed to rebuild the working solutions, as each print passes through it. Since only some of the ingredients are consumed, though, the relationship between replenisher concentration and replenishment rate is not linear. For example, a 50% increase in concentration can yield a 50% reduction in replenishment rate. 

While the cost per liter of replenisher is higher for the low-replenishment solutions, there is a net reduction in actual chemicals used (1.50 x 0.50 = 0.75) which results in a lower final cost, and a lower environmental impact, both in chemicals and disposal volume. Figure 3, above, shows the typical relationship between cost per liter for various developers, and the cost per 1000 prints resulting from their replenishment rates. Similar cost-per-print benefits can be achieved with LR bleach-fix alternatives as well, and solution turnover must again be part of this decision.

The latest trend appearing in photochemical products breaks another long-standing tradition. Since the inception of the color process, developers have been packaged as multi-part concentrates, which are all mixed into water to prepare the replenisher solution. The conventional formula designs required these multiple parts to prevent the various ingredients from inter-reacting themselves into oblivion during storage. 

About two years ago, Trebla introduced a new single-part RA-4 developer to the market, with the unique characteristic of "liquid layers" in its one bottle. The advantage of the liquid one-part formula over a powder or tablet solid alternative is that it is instantly soluble in water, and requires no processor changes to implement. The new formula design also has longer storage life than is typical for the traditional multi-part design, and mixing errors are virtually eliminated-it is no longer possible to omit one of the parts when preparing replenisher. Interestingly enough, the patented formula updates that allow all ingredients to co-exist in one bottle, also improve the performance of the developer: it is less prone to form tar or mineral deposits than "conventional" formula designs. 

In the last six months, several manufacturers of processing chemistry (Kodak, Fuji, and Agfa) have announced their own variety of one-part RA-4 developers. It appears that this innovation, which greatly simplifies print developer mixing and improves its performance, is here to stay.

Along this same line, the traditional two- or three-part RA-4 bleach-fix is now available as a one-part all-liquid product. This achieves a 40% reduction in package weight for ease of handling, and the formula has the unique capability that it can be mixed to perform at any desired replenishment rate from 20 mL/sqft (215 mL/m2) down to 5 mL/sqft (54 mL/m2). This allows users to optimize their per-print cost versus turnover requirements for their particular processing volume, even when there are seasonal variations-all with one inventory item.

It has been said that traditional photoprocessing has a limited future, with the advent of the digital image-handling technology. However, until the digital methods catch up to the silver halide system in ease of use and availability for the picture-taking public, and in total per-print cost and mass-production capability, it appears that such a dramatic transition is quite a distance in the future. 

Today, there is certainly a role for digital methods to be added into our service capabilities for our customers. In the meantime, "traditional" photoprocessing technology continues to evolve, including chemical formulations. Such innovations as one-part formulas can certainly "raise the bar" for ease of use, and lower the cost for processors to deliver prints to their customers. These are desirable advancements in any business.

Published with permission from PHOTO LAB MANAGEMENT, March 2000 issue.