High-quality, high1performance silicone-coated release liners are in high demand. The faster converters can coat their products, the faster the turnaround, and the more customers they can accommodate. It's all about speed and the end product.

Suppliers of silicone coatings and machinery are looking to the future to provide converters with a fast-cure, high-speed application. User-friendly material and lightweight films are other glimpses into the future. We asked silicone-coating related suppliers—as well as converters themselves—about common problems they face, trends for the future, and general misconceptions of silicone capabilities. To follow is a compilation of responses.

Consistent release throughout the entire roll and from run-to-run is important to converters in meeting customers' needs. "This is achieved by developing a silicone formulation and process, including mixing and application to the film substrate, that has minimum variability," says Douglas R. Goldstein, new business development manager of coating and laminating/silicone for converter CPFilms, Martinsville, Va.

A number of suppliers say their customers require little to no silicone transfer to their pressure-sensitive adhesives or cast materials. "This involves developing silicone formulations and a consistent process to coat and fully cure the release layer, as well as a strong match between the silicone system and base substrate," says Goldstein.

Some formulators are asked to modify standard silicone-release coatings to meet unusual or extreme end-user requirements. "As one example, a customer wanted an easy release from an aggressive, high-temperature, applied hot-melt PSA. He had a heat-sensitive film that could accept only a UV-curing, silicone-release product. We formulated a unique product to accomplish this," says Pat Foust of Craig Adhesives & Coatings Co., Newark, N.J.

Mist generation at high speeds is a problem in the world of silicone coating. "[It] can be partially solved by equipment solutions, mist-collection systems and proper roll configuration," says Terry McEwen of Wacker Silicones, Adrian, Mich.

Adhesion of silicone to various substrates, mostly on films, is another issue. "[It] can be solved with anchorage additives in the silicone, new silicone polymers that have been developed, and by proper adjustment of processing conditions. There's a big demand for silicone that works properly on unprimed PET substrates, as these are significantly cheaper than the primed grades," says McEwen.

The ultimate goal is high-quality, high-performance silicone-coated release liners with consistent release characteristics within each roll of release liner, and minimal lot-to-lot variation, but that can't always be achieved. "To achieve consistent release levels, [it] requires the careful selection and control of raw materials, manufacturing parameters (in the mixing of those materials) as well as coating processes," says Peggy Doster, release liners R&D group leader at Adhesives Research, Inc., Glen Rock, Pa.

Speed is a must in silicone coating. "This is one of the biggest demands in the industry as converters want to go faster," McEwen says. "The limiting factor is usually the silicone-cure speed and mist generation. The silicone-cure speed can be dealt with by making the ovens longer, changing the silicone polymer or adjusting catalyst levels. None of these solutions are ideal because they can lead to higher costs, so there is still a demand for better solutions."

Silicone transfer to the backside of the liner is another dilemma that can't always be avoided. The problems: Release properties that change through aging, UV-cured inks or UV-cured adhesives changing the release properties of the UV-cured, silicone-release liner. "These problems can be eliminated or reduced through different substrates, additives to the silicones, run speeds etc.," says converter Steve Odders, vice president of sales at Douglas-Hanson Co., Hammond, Wis.

Converters want to be able to wind silicone-coated webs into large rolls at high speeds, on continuously operating, flying-splice winders. "The need to apply extremely thin films of uniform thickness at high speeds requires unique coating equipment, especially designed for that purpose," says Richard Greer, sales manager at Faustel, Inc., Germantown, Wis. Fortunately, machinery suppliers are readily meeting those demands.

Both suppliers and converters wish their customers understood the value and know-how involved in the silicone coating. It's a fairly complicated process. "There is a big danger in doing it wrong, as you can ruin a lot of adhesive and paper in the process," says McEwen. Perhaps that's why some converters have outdated ideas about what silicones can—and can't—do.

"Some of the misconceptions of UV-cured, silicone-release liners are based from years ago when the process was new and the silicones available were of a poor quality for this new system. In the last 10 years, tremendous advancements have been made [for] UV technology with equipment and silicone," says Odders.

To most, silicone coating looks very simple, but that's not the case at all. "There's a tendency among potential silicone coaters to under-estimate how carefully the coating and curing process needs to be controlled to achieve consistent results," says Greer. As for pressure-sensitive adhesives for specialty applications, silicone coating is not easy. 'Designing complete coated systems incorporating silicone-based, pressure-sensitive adhesives can be a challenge," says Robert Wigdorski, senior R&D scientist at Adhesives Research.

"The largest misconception is the degree of standardization which can be obtained," says Douglas K. Wernicke, executive director of Global Paper Industries at Dow Corning, Midland, Mich. "A coating system is a very complex system with liner, silicone coating, adhesive, coating equipment, and face stock all interacting and impacting the performance of the final product."

"One misconception is the general opinion that the silicone-coated release liner controls the release characteristics and potential failures of a PSA/release liner product—should that occur," says Doster. There can be a number of contributors to variations in the level of release, which include the choice of the wrong silicone-release coating or substrate, the method used to remove the liner, or the angle and speed during the conversion. The type of adhesive used in the coated product can also impact liner-removal characteristics.

Another misconception is that film liners are always considerably more expensive than paper liners. "In some cases this is not true, as price depends on paper or film thickness and type," says Goldstein. "There are several release-liner suppliers offering smaller volume purchases for 'high end' or other niche applications," says Goldstein.

UV and EB curing of all release coatings for both paper and film seems to top today's trends among both converters and suppliers. [An] increased use of UV-cured silicones that have very fast cure and can be easily modified to meet specific release requirements, demand for easy-release liners with no or low-extractable silicones is what's asked for today, says Goldstein.

As energy costs rise, UV and EB systems that need less energy to cure will be in demand. "The future will be interesting, especially as there will be more government pressure to reduce silicones in landfills. You'll probably see more landfill-friendly systems (silicone and non-silicone) as well as hybrid systems in the future," says Foust.

Also on the rise: The request for pressure-sensitive adhesive products that include polyester release liners rather than paper carriers. "Polyester release liners are preferred due to customer concerns about potential contamination of the final product with paper fibers," says Doster.

More user-friendly materials, such as one-package products, are a current trend that end-users seem to be leaning toward as well. Improved uniformity in performance, market-specific adhesives, 100 percent non-volatiles (100 percent solids) reactive systems, alternate cross-linking technology, and hybrid systems are also hot topics in the silicone-coating niche, says Wigdorski.

As long as release liners aren't too thin in gauge, and the cost of the liners aren't cheapened to a point of being a low-quality commodity product, silicone-coating technology should remain stable. "The future for UV-curable seems bright, with the thinner substrates (especially films), UV works very well. The system generates a minimum of heat and runs at high speeds," says Odders.