Unexpected change in plate performance? The answer could be in your solvent processing.

Getting your plate washout solution right is a key component of optimal platemaking. Monitoring washout periodically will result in fewer processing issues and provide more certainty about how your plates will perform on press.

Your photopolymer plates should always produce clear, and consistent print. One of the most important platemaking steps is solvent processing, as it affects the plate’s depth, surface quality, and overall print accuracy. Processing is the removal of unexposed or unpolymerized material from a printing plate after it has been exposed to UV light. This step reveals the plate’s relief image – the raised areas that will carry ink to the substrate. This is why processing has a major impact on print quality.

A common misconception is that no maintenance is required. Adding back or “topping off” plate solvent chemistry can achieve balance and bring your chemistry back to its original strength. This is true for most processing chemistry formulations of two components or more. Alternatively, azeotropic processing chemistry formulations can prevent the need for topping off, as the components have a unified boiling point. Be sure to work with your processing chemistry supplier to understand the maintenance required for your specific plate processing solvent.

Starting at the base

Baseline values from virgin solvent are important to identifying a solvent balancing problem. Always keep a sample of virgin plate washout solution available for reference at your site. Performing the procedures below and documenting your measurements over time are your best tools for identifying chemistry issues. Proper record keeping will allow you to notice solvent degradation or deviation over time, preventing a larger issue from developing down the road.

Keeping processing conditions and equipment properly balanced and optimized is crucial for best results. For example, controlling processing speed, relief depth, and plate drying time helps maintain consistency. Processing for too long can wear away fine details and cause plate swelling, while processing too briefly can leave behind unremoved material that affects print sharpness. During processing, plates naturally absorb some solvent and temporarily swell, so complete drying afterward ensures they return to their original thickness and perform consistently on press.

In-house Distillation

In-house distillation is a popular option for many plate making operations, as it provides quick turnaround of clean solvent while avoiding transportation costs of outside distillation services. Keeping the distillation unit in good working order is critical for producing balanced, clean, consistent plate washout solvent.

What disrupts in-house distillation units?

Power surges
Faulty wiring
Incorrect ratios of automatic add-back from the distillation unit
- Can be a result of power surges, broken equipment, faulty wiring, etc.
Control of temperature during distillation
- Temperature influences automatic measurements, as well as the percentage of add-back chemistry
Cleanliness of distillation tank
- A dirty distillation tank will introduce contamination into your FLEXCEL NX plate workflow

Common symptoms of chemistry imbalance

These changes to the plate and processing environment could mean an imbalance in the washout solution:

Distilled solvent is not clear
Drying times change dramatically
Excessive plate swell
Plate mottle / contamination of plate patterning features
Orange peel effect / change in plate surface appearance
Plate floor finish changes dramatically
Solvent foaming in distribution trays

Note: Cloudy solvent in your processor tank is typically indicative of water condensation inside the plate processor, rather than a chemistry imbalance.

Supplies needed to verify a chemistry balance

Pipette / Eye dropper
Glass jar or beaker
Lint free cloth
Thermometer
- Verifies temperature, which is important when measuring plate without solvent
Digital or analog refractor
- Measures °Bx (Brix) value
Sample of well-mixed virgin (new, non-distilled) plate processing solution for comparison
- Ensure any virgin plate processing solution is contained in glass, or an approved drum or plastic container. Some plastic containers will degrade from the chemistry contained inside. This can disrupt any readings you take.

How to verify using a refractometer (Analog or Digital)

Note: Clean any tools prior to use with Isopropanol (IPA) and allow to fully dry to avoid contaminates before starting. Contaminates will compromise your measurements and can lead to more unknowns.

Obtain a well-mixed sample in a glass jar from your distillation unit or drum, after recycling process is complete.
Obtain a well-mixed sample of virgin solvent in a glass jar.
- This is available from your solvent supplier where you purchase top off or add back chemistry.
Allow both samples to come to room temperature.
- Record temperatures of both virgin and distilled plate processing solution for future reference when performing this procedure.
Using a clean pipette, place several drops of virgin solvent on a clean refractometer surface.
- Record °Bx (Brix) value.
Clean refractometer surface again with Isopropanol (IPA) using a lint free cloth and allow to dry.
Using a clean pipette, place several drops of newly distilled solvent on a clean refractometer surface.
- Record °Bx (Brix) value.
Look for variations between your recordings.
If there is no variation, you can rule out your chemistry as the root cause and can focus on other variables.
If you observe a variation that is more than an acceptable range, specific chemical addbacks will be required. (Contact your solvent manufacturer for acceptable range and required actions.)
- Add backs are always solvent dependent and contingent on the number of components in the plate processing (Always refer to your solvent manufacturer to verify the correct solvent add backs to your washout solution.)
- In some cases, the root cause of the chemistry imbalance may be the distillation equipment itself. (Always refer to your distribution equipment manufacturer to resolve mechanical issues.)

Note: Some regions commonly use a hydrometer to look for processing chemistry imbalances. The same principles apply in this case. However, it is important to check with your processing chemistry manufacturer to understand what range is acceptable for the hydrometer needed. Measurements using a hydrometer should always be referred to as Specific Gravity (SG).

Reference Material

You can find more information on washout solutions and optimizing platemaking on My Miraclon:

Troubleshooting washout solutions and other processing issues (detailed list of issues): Article 1267
Percent (%) Solids for a new washout solution and/or processor: Article 1259