CTP Developer for Thermal, CTcP and PS Plates

When plates vary from morning to evening, or a press operator complains about background tones, the developer is usually the first suspect, and usually with good reason. Plate-room managers describe it in the same words: density drifts during the day, background tones on press, dots disappear in the highlights. This page explains what CTP developer does, how to keep it stable, and how we match it to the plates we make.

What is CTP developer?

After imaging, the exposed (positive plates) or unexposed parts of the coating must be removed to reveal the hydrophilic aluminium underneath. The developer does this chemically, inside the developer section of the CTP plate processor. It is followed by a rinse, a gum section and a dryer. The developer is the only step that actually defines the printing image, so its condition directly controls dot reproduction and background cleanliness.

Developer is supplied as a working solution for filling the tank, plus a replenisher that is added as the bath is used. Both are made in our factory for our plate grades. Dilution, if any, is printed on the label and in the grade TDS.

Developer types for thermal, CTcP and PS plates

A common belief is that developer is all the same and only price matters. In practice each plate coating is designed around a developer type, and the developer must match the plate grade.

So, can you use PS developer for thermal CTP plates? Generally no. Thermal coatings respond differently, and using the wrong developer typically causes either a dirty background or image attack. We do not supply negative PS plates or double-layer CTcP plates, and we do not make developers for those systems.

Replenishment, conductivity and temperature

Developer replenishment is the controlled addition of fresh replenisher to the bath. It compensates for two separate losses:

• Area (plate) replenishment: every square metre of plate consumes developer activity, so the processor adds replenisher in proportion to plate area processed.
• Time (oxidation) replenishment: alkaline developer absorbs carbon dioxide from the air and loses activity even when no plates run, so many processors add a small amount over time.

Conductivity is a convenient indicator of developer activity: as developer is used and ages, its conductivity normally drops. Processors with conductivity control add replenisher to hold a target value. Conductivity readings change with temperature, so compare values only at a stable bath temperature, and use the target given for your developer and plate grade.

Temperature matters as much as chemistry. Warmer developer is more aggressive; cooler developer is weaker. Typical in the industry, thermal and PS developers run in the low-to-mid 20s °C, often somewhere around 22–26 °C, with a dwell time of tens of seconds. The exact window for our plates is in the grade TDS; set the processor to it and check it at start-up every day.

1. At start-up, check bath temperature and, if available, conductivity.
2. Run a control strip or test plate and read highlight and shadow patches.
3. Confirm the replenishment rate matches the TDS for the plate grade and your daily volume.
4. Change the bath and clean the tank on the schedule in the processor manual.

What happens when developer is exhausted

Many plate rooms change the bath only when problems show on press. By then plates have been wasted and makeready time lost. It is cheaper to monitor conductivity and replenish on schedule before problems reach the press. Signs of exhausted or under-active developer:

• Under-development: residual coating in the non-image area, leading to toning, scum or a tinted background on press.
• Dot gain and filled-in shadows, because coating is not fully cleared.
• Variable results through the day as activity drifts.
• Sludge and deposits on rollers, which mark plates.

The opposite problem, over-active developer from over-replenishment or high temperature, attacks the image: highlight dots disappear and fine type thins out. For more plate-side symptoms, see our guide to CTP plate problems and solutions.

Matching developer to your plate grade

Because we manufacture both plates and developer, we match them together: developer and replenisher are formulated for our grades, and the TDS gives one set of processor settings that works with both. Buyers ask for stable developer that matches the plate, fewer bath changes and clear replenishment settings, and that is what a matched pair delivers.

Two objections are common. “Shipping liquids is expensive”: that is fair, so we ship developer with plate orders to share the container. “We buy developer locally”: if your local developer gives stable results with our plates, keep it; if it does not, test ours on a trial run. Our technical support for plate processing can review your processor settings, and the wider offset printing chemicals range covers gum and cleaner.

FAQ

What is CTP developer?

CTP developer is the alkaline solution in the plate processor that removes the non-image coating from an imaged plate. It must match the plate type: thermal, CTcP or PS.

How often should CTP developer be changed?

Change the bath on the schedule in the processor manual and grade TDS, or sooner if replenishment can no longer hold the target conductivity. With correct replenishment the bath stays stable between changes.

What happens if developer is exhausted?

Exhausted developer under-develops the plate: coating stays in the non-image area, causing toning or scum on press, filled shadows and results that drift during the day.

Can I use PS developer for thermal CTP plates?

Generally no. Thermal coatings need a thermal plate developer. The wrong developer can leave a dirty background or attack the image. Use the developer named in the grade TDS.

What is developer replenishment?

Replenishment adds fresh replenisher to the developer bath to make up for activity used by plates (area replenishment) and lost to air over time (time replenishment), keeping development consistent.

Want developer matched to your plates? Request a quote and send your plate grades, processor type, tank volume and monthly plate volume. Or request trial plates / contact us.

Disclaimer: values on this page are typical and for reference only; final specifications, MOQ, price and lead time are subject to the grade TDS and the quotation.