TECHNICAL TUTORIAL: Abhiram Sathe talks about processing the plate
Wednesday, September 14, 2011
The plate processing method can be classified as 'pre-heat' and 'without pre-heat'.
Violet plates and thermal negative plates need pre-heat. Nominal temperature range to the plate surface is 110 to 120°C and maintained precise temperature can result in desired results. The pre-heating section of the processor of course needs frequent check and calibration. Variation across the width of heating element can give variation in dot size. Further plate will pass through developer and developer temperature must be maintained exactly as per manufacturers' recommendation so as to get the consistent dot size. The plate calibration is always done at standard temperature. Hence dot size expectancy depends upon various factors set at that time and temperature is one of them. Same is true for processing without pre-heat.
Processing plates without pre-heat
Thermal positive working plates are processed without any pre-heat. In this, developer temperature becomes crucial. Common temperature of developer for processing thermal plates is 23°C (+/-1°C).
Rise in developer temperature can lead to shaving off dots. Consider; if 50% uncalibrated dot is read at 49.5% at 23°C; then if developer temperature is changed to 26°C, the dot will become 47.5%. This is because temperature shaves off the dot, and attacks the emulsion. This may lead to pre-mature plate failure on press.
All processing equipments are fitted with a temperature sensor and display. Please cross-check the temperature with an external device periodically. Maintaining the processing temperature of the thermal technology is easier than violet processing.
Abhiram Sathe is the national manager technical at Kodak India
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