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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.


By Bea Purcell

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The basic principles behind IML and IMD are the same. A decorated film is placed into an injection mold and then melted plastic resin is injected to form a part with specific geometry such as an ice cream container or cellular phone cover (Figure 5). In IML, the labels may be printed using various printing technologies such as gravure, offset, flexography, or rotary or flat screen printing. These labels are generally printed on the top surface so the unprinted side would come in contact with the injected resin. The injected resin would normally be the same type of plastic as the label material or a compatible substitute.

In IMD, which is used to create more durable parts, the printing generally is done on the second surface of transparent films. Screen printing is the printing technology of choice for these applications. Compatibility of the film and a UV ink to the injection resin is a must. In this sector, IMD typically means in-mold or insert-mold decorating.

What happens if I use a nitrogen curing unit to cure colored UV inks?

Curing systems that cure prints in a ni-trogen atmosphere have been around for decades. These systems are mainly used for texturing and curing clearcoats printed on the top surface of membrane-switch overlays. The main purpose of the nitrogen is to replace oxygen because oxygen is a cure inhibitor. However, due to the very low irradiance from the bulbs in the nitrogen chamber, pigmented or colored inks may not cure very well in these systems.

Most nitrogen systems still being used have a texturing or germicidal lamp installed before the nitrogen chamber. As its name implies, the main function of the texturing bulb is to create a texture. Clear UV inks used for this application are formulated with photoinitiators that absorb in the shorter wavelengths. When these clears are exposed to the texturing lamp, the surface cures faster than lower levels of the ink film, which causes the ink surface to wrinkle and become textured. Depending on the chemistry, colored UV inks may also texture when they’re exposed to a texturing lamp.

Getting more answers

Beyond the questions addressed here, UV ink technology has many other unique characteristics that can pose challenges to screen printers. Your best resource in overcoming ink performance issues and finding the right formulation for particular applications is your ink manufacturer. Take advantage of the company’s knowledge and expertise, and your presses will keep churning out high-quality UV prints.

 

Bea Purcell is Nazdar’s market-segment manager for the membrane-switch overlay, in-mold decorating, industrial, and container markets. She has extensive experience in formulating UV inks, technical support, training, and sales in UV-curing technology. Purcell holds a bachelors degree in chemical engineering from the University of San Carlos and a masters degree in education from the University of Southern California. She also is a member of the SGIA Membrane Switch Council.


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