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Twenty Questions and Answers about UV Curing and Related Concerns

(February 2009) posted on Wed Feb 18, 2009

Trying to adjust to the realities of working with UV screen-printing inks? Use this Q&A discussion to clear up any misunderstanding about the inks, the curing process, and other aspects of UV technology.

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By Bea Purcell

Whether your shop is just starting to work with UV inks or you need to train new employees in issues surrounding the technology, the information provided here can shorten the learning curve. Read on to get answers to 20 frequently asked questions related to UV inks and their use.

What is the relationship between the watts per inch setting on the curing-unit lamp and the watts or milliwatts per square centimeter reading that I get from a radiometer?

Watts per inch is a unit of power (wattage) for the lamp in the curing unit. This is based on Ohm’s Law: volts x amps = watts. Watts or milliwatts per square centimeter represent the amount of peak irradiance (UV energy) per unit area measured by the radiometer as it passes underneath the lamp (Figure 1).

Peak irradiance is determined, among other factors, by the wattage of the lamp. Peak irradiance is measured in watts because irradiance represents UV energy or power. Lamp power also is measured in watts because this represents the electrical energy the lamp consumes. In addition to the amount of electricity the curing unit receives, other factors affecting peak irradiance are the condition and geometry of the reflector, age of the lamp, and distance from the lamp to the curing surface.

What is the difference between millijoules and milliwatts?

The total amount of energy arriving at a given surface over time is measured in joules or millijoules per square centimeter. The total energy is affected by the conveyor speed, lamp power and number of lamps, age and condition of the lamps, and the geometry and condition of the curing system’s reflector.

The power of the UV energy or irradiance arriving on a surface is measured in watts or milliwatts per square centimeter. Higher UV energy arriving on the surface allows a higher amount of energy to penetrate the ink film. Milliwatts and millijoules must be measured in context with the wavelength sensitivity of the measuring radiometer.

How can I make sure that UV ink is properly cured?

Properly curing the ink film the first time through the curing unit is very important. Proper curing minimizes substrate degradation, over curing, rewetting, and under curing and optimizes ink-to-ink or intercoat adhesion.


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