A SMARTER FASTER WAY FROM COMPUTER TO FILM
DRUPA 2000

Chris Rider
European Research and Development
Kodak Limited

Tried and Tested

Graphics film using silver halide technology has been around for a long time. The reasons are clear for all to see

• it’s fast
• it’s flexible
• it’s able to deliver the very highest quality imagery.

It’s fast because the silver halide system is able to capture minute quantities of light and amplify the signal over a billion times during the processing of the film. Small, low-power lasers can be used to image the film in very short times.

It’s also fast because Kodak has been leading the way in reducing the total processing time. At DRUPA ’95 we lowered the time to 100 seconds and now at DRUPA 2000 Kodak Polychrome Graphics are showing films which are capable of processing in under 50 seconds.

It’s flexible because there are films for all light sources, each film capable of delivering unsurpassed image quality.

The Wet Stuff

One of the perceived disadvantages of silver halide film is the need for wet processing. There’s the mixing and handling of liquids and the disposal of the processing effluent to consider. There are additional ways for human error to creep in and there’s the need to maintain the process in good condition. While recognising these disadvantages, our approach has been to accentuate the positives of the silver halide system and eliminate, or at least reduce, the negatives.

There are many wet systems which we use every day without considering for one moment that we’re handling liquids. Take the car for example. It’s full of all kind of liquids, not least of which is the highly flammable liquid with which we fill our tanks. The liquids are “packaged” and handled in ways which make it convenient to use in our cars.

Another example is the humble ink pen. All kinds of ingenious ways have been devised to package and deliver the ink – from ball-points and roller balls to fibre tips. And then of course, there is the human body itself which is an incredible feat of engineering, not least for the way in which all kinds of liquids are routinely used and stored and packaged.

So the real issue is not the use of liquids, but the way in which they are handled, used and stored.

Intelligent Imagesetting

At DRUPA ’95 we launched an intelligent imagesetting system called “Advantage”. This was followed in ’97 by a similar product called the EZ system for the Japanese market. These systems combined market-leading imagesetters with a new processor and use a new film and chemistry system from Kodak. The key benefits of this system are productivity and ease-of-use and it represents a huge leap forward in our goal to accentuate the positives and eliminate the negatives of the silver halide system.

The intelligence of the system is provided by copious use of sensors throughout the system, and a data link between the computers in the imagesetter and the processor. The result is that many sources of operator error are eliminated. It is no longer possible to output film from the imagesetter if the processor is not in a suitable condition to deliver optimum image quality. As a result of this increased reliability, users have been able to change their workflows, queuing jobs to be run at night, confident that in the morning they will find a tray full of good quality output and that if anything did go wrong, the system would recognise it and stop the output from the imagesetter. Furthermore, it would tell the operator exactly how to correct any fault which may have occurred.

Kodak developed a new award-winning range of bag-in-box chemical packaging to contain replenishment solutions with a choice between concentrates or ready-to-use solutions. These packs may be reused to hold processing effluent and can be "hauled away" from the site.

The replenishment control system is accurate and reliable. Patented algorithms are used by the processor to take exposure information from the imagesetter and then replenish the solutions with exactly the right amount of chemistry to compensate for what has been used as each film sheet is processed. Users no longer have to guess what percentage of the film area is exposed, and as a result achieve dramatic reductions in output variability, each sheet receiving optimal processing.

Future Directions

Recognising the success of the Advantage and EZ systems, Kodak Polychrome Graphics’ strategic goal is to provide the same productivity and ease-of-use benefits to a much wider section of the pre-press industry. Our approach is to deliver these benefits through the processor alone to the installed base of imagesetters.

Many of the features of the Advantage and EZ systems were obtained through the processor and chemical packaging and these can be incorporated into the new “Smart Processor” without difficulty. Other Advantage/EZ features, such as the replenishment control algorithms, require exposure data from the imagesetter. This data is not required by the smart processor and instead all aspects of process control are managed entirely within the processor. The only link to the imagesetter will be a simple two-wire signal conveying “processor-ready/processor-not-ready” status. Diagnostic messages are now available on the processor itself so that routine operational conditions are clearly indicated and remedial actions suggested. In short, operators can forget about the processor, knowing that it will maintain itself in optimum operating condition until it informs them that some action must be taken.

Rapid Processing

In 1998, the Kodak Gen 5 family of films was announced. These films are based on a new "5th Generation" silver halide technology platform which enables significant improvements over the previous generation of rapid access films. One of the major benefits of the new technology is rapid development. To realize this benefit, the time required each step in the processing sequence must also be reduced: fixing, washing and drying.

To this end, Kodak Polychrome Graphics now offers the Kodamatic Ver 5 range of processors which have many improved features, one of which is the capability for rapid processing and drying.

Attention has also been given to the fixing and washing steps of the process. The Gen 5 films have been designed with low levels of the light-sensitive silver halide crystals (“low silver laydown”) to minimise not only fixing and washing times but also replenishment rates. However, despite this, there are some circumstances where fixing can become the rate determining step in the process.

In the fixer bath, silver halide crystals from the non-image areas of the film are dissolved out of the film and pass into the fixer solution. There is an inverse dependence of fixing rate on the dissolved silver concentration in the fixer bath.

The graph shows the amount of time that a film is required to remain in the fixer solution to remove all the undeveloped silver down to a low target level of 150 mg/m2 before leaving the fixer. This measure is used because it not only includes the normal “clearing time” required to dissolve the silver, but also a “removal time” required for most of the dissolved silver to diffuse out of the film. The same general relationship also holds true for clearing time alone. It is also evident from the graph that the film which started with the higher silver laydown requires longer to fix.

The seasoned silver concentration, [Ag], may be readily approximated by the following formula, where F is the fixer replenishment, S is the silver laydown in the film and E is the fractional area of the film which has been exposed

[Ag] = S.(1 – E)/F

providing that the replenishment rate is significantly larger than carry-in from the developer and evaporation effects.

From the equation, it is clear that if the replenishment rate is low, the silver concentration in the bath will be high. For rapid fixing therefore, high replenishment rates and low film silver laydown are beneficial. Of course, it is always possible to increase the fixing rate by increasing the temperature, but this is undesirable because of increasing the likelihood of fixer crystallisation and odour.

To achieve the fastest overall processing times, positive working customers may find it necessary to increase their replenishment rates to keep the fixer silver concentration below the required maximum for the film type and processing time selected. This is clearly not desirable as a solution for a variety of reasons, not least of which is cost.

The most cost-effective solution to the problem is to use in-line electrolytic silver recovery. Unlike “terminal treatment” of used fixer solution, when the treated solution is not reused, “in-line” silver recovery is the process of continuously recirculating fixer solution from the fixer bath through the silver recovery cell and then passing it back to the fixer bath for reuse. Provided there is sufficient silver in the solution, the electrolytic current passing through it causes silver metal to be plated on one of the electrodes in the cell (the cathode). The average silver concentration in the fixer bath is therefore maintained at a lower level and this promotes rapid fixing.

In-Line Electrolytic Silver Recovery – plus and minus

At the same time that silver is plated, fixing agent in the solution is regenerated. This is why fixer replenishment rates may be substantially reduced, typically by between 30% and 50%, when in-line electrolytic silver recovery is used. All users receive this benefit regardless of whether or not they desire rapid processing. Of course, if replenishment rates are reduced, then fixer effluent is also reduced by the same proportion.

In-line silver recovery offers additional benefits. Since the average silver concentration in the fixer will be maintained at a lower level, the average silver concentration in the wash will also be lower. This may enable a reduction in wash replenishment rates for some users, while others may prefer to use this benefit to ensure that water discharged to drain is always in compliance with sewer discharge codes.

The benefits of in-line electrolytic silver recovery are significant, and the payback time for a unit is short, but there is usually a disadvantage too, inconvenience. When the cell is full of silver, the unit must be shut down and the silver “harvested”. This can involve the draining down of the cell, the removal of the electrode, the physical removal of the silver from the electrode (scraping, banging etc.) and the bagging of the silver before it is sent off to a refiner.

A further problem with some units relates to their control system. If current is passed through a fixer solution which contains too little silver, the current can actually damage the fixer and worse still, it can cause tiny black particles of silver sulphide to form in the solution and these can find their way onto the film. All kinds of schemes have been devised to ensure that electrolytic silver recovery is properly controlled to avoid these problems, but all too often the control systems represent a compromise between efficient plating and avoiding trouble. There are of course, silver recovery units which perform well and which minimise the inconveniences but these command a premium price and have larger footprints.

Summarising then in general terms, the plusses and minuses of typical electrolytic silver recovery units are:

• reduced fixer replenishment rates give cost savings
• lower fixer silver concentrations enable rapid fixing
• lower fixer silver concentrations facilitate reduced wash replenishment rates or ensure environmental compliance when discharging wash water to drain in many locations.
  • harvesting the silver can involve time, mess and user contact with the solution and silver
  • maintaining good control can involve frequent calibrations by user or service personnel

Fast Fix Technology

At DRUPA 2000, Kodak Polychrome Graphics will present a new concept in processing equipment which clearly sets the future direction of graphics silver halide processing and is the first step towards the smart processor concept referred to earlier. It aims to remove the two "Minus" points summarised above.

• The Kodamatic Ver 5 processor delivers many of the benefits of the Advantage processor, such as:
  • accurate control of replenishment
  • reduced oxidation and evaporation rates
  • improved user interface and control
  • short processing times
  • built-in tank level filtration.

Figure 1: Processor side panel removed to show silver recovery unit on left with 5 inch developer filter unit.

An important benefit is that we have incorporated in-line electrolytic silver recovery technology into the fixer bath of the processor without increasing the processor footprint. The novel cell design requires no user contact with either solution or silver when harvesting. The control system automatically calibrates itself to the user’s unique set of operating conditions and requires no adjustment. It also enables the plating current to be increased when there are high levels of silver in the fixer bath and reduced when the level is low. These benefits are the result of new advances on which there are several patents pending and which together we refer to as “Fast Fix Technology”.

Figure 2: Showing the empty cathode module.

Remembering that the management and handling of liquids is the key, we have developed a replacement cathode module as shown in Figure 2. The cathode module comprises three parts, the cathode sheet, the lid and connector assembly, and the connection wire. When the cathode is full of silver, the whole cathode module, which also forms the lid of the cell, is replaced by the user. This operation takes as little as 2 minutes and requires no contact by the user with either the fixer solution or the wet silver. Novel packaging is designed to interface with the cell (shown in Figure 3) so it is a simple matter to transfer the full cathode to the transport packaging, which includes a disposable absorbent paper drip-tray (not shown) to avoid a single drop of liquid going astray. The cathode itself is made from graphite laminated to a PET plastic film and is fully compatible with the refiner's operations. In fact, the refiner need only remove one screw and the cathode, together with its silver, is readily separated from the lid. The silver and cathode may then be placed directly into the smelter.

Figure 3: Showing a full cathode being transferred to the transport bag.

The whole system is factory fitted and fully integrated into the processor’s control panel, so there is no downtime at the user’s premises and no initial calibration or set-up to perform. The automatic plating current control ensures that silver can be removed rapidly from the solution when there is sufficient silver to enable this to be done safely (up to 4A or ~16 g/hour silver removal). A further benefit of the control system is that it can remove silver from the fixer down to very low levels, typically between 0.2 to 0.35 g/l (or 200 to 350 ppm silver).

Conclusions

We believe that the features offered by this new unit will match or exceed any silver recovery unit designed for a single processor on the market today. When taken together with the fact that the silver recovery unit is fully integrated within the new Kodamatic Ver 5 processor, the combined system offers truly exceptional value.

All users will obtain the traditional benefits of silver recovery:

• reduced fixer replenishment rate
• environmental compliance with silver discharge limits in many locations for discharge of wash water to drain
• reduced effluent volume
• the value of the silver recovered

and all without any increase in footprint.

Additionally, there is an extra synergy when using Kodak Gen 5 film – very rapid processing becomes possible for all users – without requiring any increase in fixer replenishment rate or fixer temperature.

The Kodamatic Ver 5 processor with integrated silver recovery is an example of our vision of the path forward for the silver halide system. It accentuates the pluses of the system by enabling very rapid processing for all users whilst actually saving money. It also reduces or eliminates the negatives by requiring no user contact with solutions or with the wet silver through the use of novel packaging and design.

Kodak and Kodak Polychrome Graphics, through their investment in the development of leading-edge products, are committed to helping their customers get the very best out of the silver halide system. The new era of a smarter, faster way from computer to film is only just beginning.