23.09.2015
We initiated a program to evaluate the release performance of today’s emerging developmental ultraviolet pressure sensitive adhesive (UV-PSA) products against representative silicone-release coating systems available from Rhodia Inc. The beneficial result of these events is that there are now for the first time high-performance UV-PSA alternatives that provide complete air-pollution control, and deliver measurable productivity gains with reduced need of manufacturing space — and all this with improved PSA performance benefits.
Early attempts at formulating UV-PSAs did not succeed in replacing standard high-performance PSAs, but they were able to at least provide performances sufficient for the requirements of many of the less demanding applications (such as screen-printable PSAs).
The first liquid UV-PSAs had a number of undesirable features that made their acceptance by the adhesive market difficult.
The earliest UV-WMPSAs and UV-HMPSAs were often thermally unstable and would readily gel in the melting tank.
The challenge for all formulators of UV-PSAs is to find a way to induce polymerization to the necessary high molecular weight for exhibiting the tough viscoelastic behavior required by high-performance PSAs.
All UV-PSAs were direct-cast UV-cured onto the five categories of silicone-release liners after laminating with 1-mil PET film in the roller nip on our Euclid coater with a nip pressure of 160 psi and the rollers turning at their slowest speed.
The WMPSAs and the HMPSAs give a slightly higher release force with the UV-silicone-release-coated polyester-film liner. These results, however, indicate that the UV acrylate-silicone chemistry is reacting to a very complete and stable level such that there is no residual acrylate functionality on the silicone polymer available to react with the direct-cast and cured UV-PSA. Many of the UV-PSAs we evaluated can for the most part be considered very good as to their general tack- and peel-adhesive performance. This article is based on a presentation made at RadTech 2000, April 9-12, 2000, Baltimore, Md.
The Handbook of Sealant Technology provides an in-depth examination of sealants, reviewing their historical developments and fundamentals, adhesion theories and properties, and today’s wide range of applications. The technical development of new chemistries by the raw material suppliers for the UV-PSA industry. The coordinated commitment by the larger adhesive manufacturers for the necessary time, funding and people resources for developing quality UV-PSAs. Increasing regulatory pressures from the local, state and federal environmental-protection programs.
They simply did not meet the broad performance criteria required by many adhesive tape-and-label applications as supplied by most conventional PSAs.
Their overall adhesive-performance profiles and their processability were less than impressive.
This can be attributed to the fact that the WMPSAs and HMPSAs were direct-cast applied onto the silicone liner at heavier coat weights than were the liquid UV-PSAs (our method of application could not achieve lower coat-weight lay-downs for these high-viscosity warm melts and hot melts).


Or, if there is any residual acrylate functionality left on the silicone polymer, it remains well shielded within the crosslinked matrix of the release coating under methyl-rich segments of the silicone polymer that are efficiently orienting themselves to the surface. The three adhesives that were similar to a true hot melt adhesive gave a higher release level. But some of them were particularly soft (especially the liquid UV-PSAs) such that removal of their tapes from a polished-steel plate left a good deal of undesirable residue.
The very beneficial stable releases achieved from direct-cast applied and cured UV-PSAs promise many potential processing advantages to be had with different combinations of these two converting technologies (such as in-line tandem coating).
It is now technically possible in one continuous UV or EB procedure to prepare printed label stock laminations at line speeds well over 1,000 fpm without the presence of even one process oven! They regain their high-performance adhesive properties upon UV-induced crosslinking for reinforcing the elastomeric phase of the PSA matrix.
Because of this, the liquid UV-PSA market potentials have remained limited and they will remain so until the technology is developed to produce UV-PSAs that perform at least as well as the standard, non-UV PSAs. However, there is a very simple but crucially important question that remains to be answered: How do these new UV-PSAs perform against silicone-release-coated liners for use with labels and tapes?
In the case of the UV-WMPSAs and the UV-HMPSAs, samples were reheated in our oven followed by a second pass through the pressurized Euclid nip.
Although these UV-PSAs were direct-cast coated and UV-cured directly onto the UV-silicone-release coating, there appears to be no chemical reaction between the two different UV-curable chemistries (cationic vs. Those that were tougher in constitution and that did not leave a lot of residue upon removal were generally of lower peel-adhesion strength.
By providing a systems understanding of the performance of Rhodia’s silicone-release technologies with these emerging UV-PSAs, we mean to deliver a valuable resource to our customers. It is preferable to introduce quality UV-PSAs that are compatible with a converter’s existing process equipment, liners and face stocks, and wide-selection of silicone-release technologies.
Conference papers on the development and application of UV-PSAs are becoming a very serious technical focus. Acknowledgements The authors wish to recognize the extensive contributions to the global release-coatings application team within the Rhodia organization, especially to such dedicated laboratory and pilot-coater technicians as Butch Burton, Jamie Ellison and Dwight Payseur.
However, conventional HMPSAs inherently have poor resistance to solvents, plasticizers and heat. Can you achieve formulated “premium” low levels of release as well as differential levels of ever-tightening release? For the tested adhesive, there was no significant change in release level when the laminates were exposed to elevated temperatures for up to seven-days aging.


These three families of release-coated liners were direct-cast coated and UV-cured with the SolarCure RT-7501 liquid UV-PSA from H.B. Adhesive manufacturers and their raw material suppliers are committing concerted efforts and resources towards the new-product development of high-performance UV-PSAs. This may be indicative of either unreacted UV-monomers or to the post-UV by-products of the photoinitiator.
We also express our gratitude to those UV-PSA manufacturers who submitted their developmental and commercial UV-PSAs for our evaluation.
This article will help potential end users to best determine the many potential processing advantages to be had with different combinations of these two converting technologies (such as in-line tandem coating).
The major benefits from post-application UV-exposure are to improve the adhesive’s high-temperature shear and working-life performance along with improved chemical resistance by reinforcing the polymer networks with chemical crosslinks. Can UV-PSAs be “direct-cast” coated and cured onto silicone-release-coated liners and maintain desired stable release? Full cure was realized for all these UV-PSAs by determining that a second pass of UV-curing produced no noticeable change in the performance of the UV-PSA.
Customer inquiries on the performance of silicone-release liners against UV-PSAs are increasing. Are these UV-PSA laminates all predictably the same in their release performance, or will different families of silicone-release chemistries act very differently from one another with these UV-PSAs? You see, older, more-traditional PSA technologies are all pretty well understood in their many diverse end uses simply by virtue that this history has been compiled over many years.
The CRA-plus-modified cationic UV-silicone release demonstrates an increase in release that is linear, potent and stable. The CRA-plus-modified silicone-emulsion release profile is half-way between these other two chemistries.
These nine UV-PSAs can be classed according to three categories of process and performance: liquid UV-PSAs, warm melt UV-WMPSAs (~200°F) and hot melt UV-HMPSAs (~300°F+).



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