Materials & Chemistry

Three-legged Stool

There are three key components of a UV LED curing system when optimized that provide an economically advantageous high throughput solution: 1) UV curable materials (inks, coatings, adhesives) that can absorb energy in the UV region to undergo polymerization process, 2) UV LED curing lamp that provides energy in the UV region of the spectrum, and 3) a machine or system where the UV LED lamp is integrated to cure material underneath it. These elements together provide a long-term sustainable printing method through green technology, eliminating ozone emissions and lowering energy consumption.

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What are Monomers & Oligomers?

For efficient and effective UV curing of an ink, coating or adhesive, the formulator seeks to overlap the UV lamp output with the spectral absorption of the PI. The amount of PI in a typical UV formulation is usually very small, less than 5%. PIs typically absorb across a range of wavelengths, not a narrow band. Many existing UV formulations developed for curing with a typical mercury-arc lamp (shown as H-bulb) use a broad spectrum PI. While there is often some absorption within the UV LED output range, it is clear to see that much of the PI absorption range is wasted. A more efficient cure is possible with a formulation designed specifically for UV LED curing using a PI with concentrated absorption in the UV-A range.

The monomers in the formulation serve as the reactive diluent enabling the formulator to control viscosity for proper application (spraying, rolling, screen printing, etc.) of the uncured material. Rather than volatilizing, as is typical with conventional formulations, the monomer reacts and becomes part of the UV-cured material. The oligomers (and their backbone structure) determine the overall properties of the material. Monomers and oligomers are generally derivatives of acrylates or methacrylates containing polyurethanes, polyesters or polyethers.

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What is wavelength?

The typical light source spectrum wavelength ranges from Ultraviolet Light (UVC 200-280nm, UVB: 280-315nm, UVA 315-400nm) to Visible Light (400-760nm) and Infrared Light (760-3000nm).

UV LED sources have a concentrated narrow spectral emission. LED sources are typically described by their peak emitting wavelength, but in practice UV LED sources emit in a distribution that is typically +/-20nm from the specified peak. For example a “395nm” LED source typically emits 96% of its energy between 380nm and 420nm with the distribution being essentially Gaussian.