A label passes the rub test at the start of the week and begins to mark or block later, even though the UV power setting has not changed. Raising the power may hide the symptom, but it does not show whether the change came from the lamp, reflector, LED output, line speed, ink, coating weight or measuring method. A useful cure check combines two things: a repeatable UV measurement at the web and a physical acceptance test on the printed product.
Separate peak irradiance from UV dose
Peak irradiance is the maximum radiant power arriving at a surface within the instrument's measuring band. IST METZ expresses peak in mW/cm². Dose is the accumulated UV energy received during the exposure and is expressed in mJ/cm². One number describes the highest intensity seen by the sensor; the other includes the time spent under the source.
Do not use the terms as if they are interchangeable. A press can show a similar peak while the delivered dose changes because speed or the effective exposure time has changed. Conversely, a dose value alone may not explain a cure problem that depends on the intensity reaching the ink film. Record both values when the measuring device supports them, together with the UV source and spectral range used for the reading.
Measure where the substrate actually runs
The reading must represent the production geometry. IST METZ lists electrical power, distance from the light source, spectrum, machine speed and the shape and colour of the underlying surface among the factors that influence a measurement. A radiometer reading taken closer to the lamp during maintenance cannot be compared directly with a reading made at the normal web position.
Use the same web path, distance, source setting and measuring position each time. Let the UV unit reach the warm condition specified by the manufacturer before checking it. IST METZ recommends at least five minutes of warm-up for its UV Analyzer procedure and advises measuring individual sources separately. On a multi-lamp press, identify the lamp or LED head in the record instead of saving one unidentified value.
Establish the baseline when the system is in known condition
A useful reference is made when the curing system and printed result are known to be acceptable. For a lamp system, this may be after fitting a new lamp and clean or new reflector, once the unit is stable. For an LED system, take the baseline when the installation is new or after the supplier has confirmed its condition. IST METZ specifically requires a system-specific reference value for its UV Analyzer because installations and measurement conditions differ.
Run the approved ink or coating on the normal substrate at the normal production speed. Save the source power setting, dose, peak, web speed, measurement position and the product test that passed. The number is then a control reference for that line and method. It is not a universal cure target that should be copied to another press, ink series or measuring instrument.
Hold the measurement variables still
A trend becomes useful only when the method is repeatable. Use the same instrument or measurement-strip system, the correct reference curve for the UV source, the same position across the web and the same press speed. Follow the device instructions for handling, storage and averaging. For its measurement strips, IST METZ specifies gloves, a light-coloured backing, no application while the machine is running and at least two readings for an average.
Write a short pressroom method rather than relying on memory. It should say who may take the reading, how the measuring device is placed, which source is tested, the warm-up condition, speed, power setting and where the result is stored. If the device has a limited measuring range or is sensitive to the spectrum, record that too. Comparing values from unlike instruments or reference curves can create a false maintenance alarm.
Use the UV reading with a product cure test
A radiometer does not certify the finished label. It reports the radiation received by the measuring device under the test conditions. The ink chemistry, pigment load, film thickness, substrate, lamp or LED spectrum, oxygen at the surface and temperature still affect the cured result. Use a plant-approved physical or chemical check that matches the product requirement, and keep it beside the UV reading.
If the product test fails and dose or peak has fallen against the baseline, inspect the curing system and geometry before changing the ink. Check lamp hours and condition, reflector cleanliness, quartz or protective window condition, cooling, distance and source output. If the UV values are stable but the product test has moved, check ink or coating batch, deposit, substrate treatment, contamination, speed record and the suitability of the source spectrum for the chemistry.
Turn the baseline into a maintenance trend
Choose a fixed checking interval based on production risk, operating hours and the curing-system supplier's maintenance guidance. Plot the values rather than waiting for a pass/fail result. A gradual reduction can support planned cleaning or inspection; a sudden step change calls for a check of the source, reflector or optics, electrical setting, cooling, geometry and the measuring device itself.
Stationary UV measurement can extend this approach. IST METZ describes integrated systems that use a sensor and PLC to monitor UV radiation and regulate irradiance in relation to speed. Whether the check is stationary or mobile, keep the job context with the number. For an application discussion, send Royal Coat the press model, web width, UV source type, ink or coating, substrate, speed range, current measurement method and the cure defect being investigated. Royal Coat represents IST Metz UV and LED UV technology in India.
Questions from production and purchasing teams
What to ask about uv cure measurement
Is UV dose the same as UV intensity?
No. Peak irradiance describes the maximum radiant power per unit area measured in a defined band. Dose is the accumulated energy received during exposure and therefore depends on time or machine speed.
Can one UV dose target be used on every label press?
No. The source spectrum, ink or coating chemistry, film thickness, substrate, geometry, speed and measuring method differ. Establish a reference on the actual line when both the system and finished product are known to be acceptable.
Where should a UV measurement be taken?
Use a position that represents the normal substrate path and repeat the same distance and location. A maintenance reading close to the source should not be compared directly with a production-plane reading.
Why can the cure fail when the UV power setting has not changed?
The displayed setting does not confirm what reaches the web. Lamp or reflector condition, optical-window contamination, cooling, distance, speed, chemistry, deposit and substrate can all change the result.
What information should be saved with a UV reading?
Save the source identification, spectrum or reference curve, power setting, peak, dose, speed, measuring position, warm-up condition, instrument, ink or coating, substrate and the finished-product test result.