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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

Corona discharge is another method for treating plastics to increase dyne level. Ionized air is created by running high voltage through a dielectric covered roll. The substrate is passed through the ionized space, which causes molecular bonds to break on the material’s surface. Treatment is affected by the air gap distance to the part and the speed of the material as it passes through the system. This method of treatment generally takes just fractions of a second. Corona treatment is commonly used on thin films for web printing applications.

How do plasticizers affect ink adhesion on PVC?

Plasticizers are chemicals that are added to plastics during processing to make the finished material soft and flexible. Plasticizers are especially prevalent in polyvinyl chloride (PVC). The type and amount of plasticizer added to flexible PVC or any plastic material depend on the mechanical, thermal, and electrical properties expected from the plastic.

Plasticizers have the tendency to migrate to the surface and affect ink adhesion. Plasticizers on the surface are contaminants that have the ability to lower the surface energy of the surface. The more contamination, the lower the surface energy and greater the risk of poor ink adhesion. Substrates affected by this problem can be cleaned with a mild solvent before production to improve their printability.

How many lamps do I need for curing?

Depending on the ink system and substrates to be printed, a one lamp curing system may be sufficient. However, if the budget allows, a two-lamp curing unit will provide the benefit of a faster cure, especially with slower-curing colors, and it will allow for faster overall production rates. Two lamps are always better than one because a two-lamp system would provide more millijoules or total energy at the same conveyor speed and lamp settings. The main factor to be taken into consideration is whether the curing unit will be efficient enough to cure the inks on any substrate at reasonable production speeds.

How does the viscosity of the ink affect printability?


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