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An Innovative Easy to Matt 100 Solids UV Curable Resin



By Emilio Martin and Danny Visser, DSM NeoResins



Published November 15, 2010
Related Searches: ink varnishes screen flexo
An Innovative Easy to Matt 100 Solids UV Curable Resin
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High gloss is a well-known property of 100% solids UV curable varnishes. Today, the market trend is towards matt finishes, especially for luxury packaging and high-end publishing.

Currently the only way to achieve a matt appearance in a 100% solids UV varnish or coating is to add high amounts of matting agent. And even with high levels of matting agents, very low gloss is almost impossible to achieve. By adding high levels of matting agents, the performance and appearance of the coating decrease substantially. In addition, the viscosity of the formulation is increasing.

A brand new resin, NeoRad U-6288, has been developed which enables an excellent matt finish in 100% solids UV curable varnishes and coatings, offers freedom in formulation and can be formulated into a soft feel UV screen coating. The matt appearance can be obtained with less matting agent when this UV curable resin is used as a basis, which results in a reduction of the total cost of the formulation. In addition, the resin offers an excellent chemical and abrasion resistance, and it does not burnish when rubbed, hence providing high quality and durable prints.

Surface roughness is very important to obtain the matt appearance. A rougher surface will scatter the light better, resulting in a more matt appearance. This rough surface can be achieved when the resin is combined with a matting agent.


Figure 1: Light microscopy pictures showing the rough surface of a matt screen overprint varnish based on NeoRad U-6288 (left) vs. a standard urethane acrylate with the same amount of matting agent (right).
An example of this surface roughness is shown in Figure 1. The surface roughness generated with the new resin results in a gloss value of 3 at 60°, where the reference material has clearly a less rough surface with a gloss value of 68 at 60°.

The product is suitable for both flexo and screen applications, resulting in a reduction in stock keeping units.

Performance and Test Results

The UV curable resin is designed to provide the ink formulator the possibility to develop custom-made matt overprint varnishes.

The new resin itself does not contain any matting agent and is compatible with a large variety of energy curable resins. The gloss appearance of a matt overprint varnish based on this resin combined with various energy curable resins is shown in Figure 2. All formulations contained 12% of Acematt 3600.


Figure 2: Gloss development of NeoRad U-6288 combined with other UV curable resins at a coat weight of 24 microns.
The gloss value of several overprint varnishes based on the easy to matt resin combined with a variety of commonly used matting agents is shown in Figure 3. It can be concluded that the resin provides a low gloss when combined with a variety of commonly used matting agents.

In flexo applications where much lower coat weights are used a gloss value at 60° of less than 20 can easily be obtained as shown in Figure 4. In this case an IGT F1 printability tester was used to prepare flexo prints with an average coat weight of 2.5 microns.

Next to the matt appearance, other properties

Figure 3: Gloss values of NeoRad U-6288 with several commercially available matting agents at a coat weight of 24 microns.
are of course also important. The performance of the resin was tested against an existing market reference in a screen coating and a flexo overprint varnish. The performance of the product in a screen coating is presented in Figure 5.

The varnishes were tested in coat weights of approximately 24 microns on Leneta opacity chart and cured with a standard 240 nm mercury lamp (80 watts) at an energy dose of 1200 mJ/cm2. The performance of the screen coating based on the easy to matt resin is better than the existing market reference on almost every property.


Figure 4: Gloss values of NeoRad U-6288 with several commercially available matting agents at an average coat weight of 2.5 microns.
In addition, the performance of the resin was checked in a flexo overprint varnish and compared with an existing market reference. An IGT F1 printability tester was used to prepare flexo prints with an average coat weight of 2.5 microns. The varnish was printed on opacity chart and cured with a standard 240 nm mercury lamp (80 watts) at an energy dose of 1200 mJ/cm2. In flexo applications the resin performs better than the reference, as shown in figure 6.

Conclusion

For flexo and screen applications an easy to matt energy curable resin has been developed. This resin allows for

Figure 5: Performance of NeoRad U-6288 in screen applications vs. an existing market reference.
custom-made matt overprint varnishes due to the broad formulation latitude. Its matting efficiency reduces the total cost of the formulation.

The resin also offers other properties such as soft feel, good adhesion, good chemical resistances and good wear and burnish resistance.








Figure 6: Performance of NeoRad U-6288 in flexo applications vs. an existing market reference.


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