Roller release: How can I improve it?
Sticky or tacky materials, such as coatings and adhesives, can cause enormous operational and runnability headaches.
David Roisum, Ph.D. Consulting Technical Editor -- Converting Magazine, 6/1/2009 2:00:00 AM
Sticky or tacky materials, such as coatings and adhesives, can cause enormous operational and runnability headaches. At the modest level, the tacky coating causes a delayed tangent of the web as it departs from the roller (or wound roll). This will quite likely upset the surface of the coating. It may even upset web handling by causing tension disturbances something like that seen during stripping (separating two webs). At a more serious level, you can paint the rollers or even break the web.
These challenges need not be continuous to be troublesome. Perhaps you don't run the coated side against the roller. However, accidents do happen, and when they do, coating will often find its way to places where you did not intend. One of my clients had a tacky product that cured quickly. When the rollers got painted accidentally, the coating cured on the rollers before the operators could get them cleaned. An accident, though rare, cost nearly half a shift to clean up because they had to chisel the coating off. By treating roller surfaces as described below, they were able to get cleanups under an hour.
The options to improve roller release are very application-, or more accurately, very chemistry-dependent. While one trick may work well in one situation, it may fail miserably on the next. Also, some situations are stubborn enough that multiple techniques must be used simultaneously. Some situations are impossibly stubborn, in which case we can not ever touch the web; it has to be routed on the back side until the coating has set and/or floated on the front side to totally avoid contact.
One of the first candidates to consider for roller release is mechanical (increase roughness). This will reduce the area of contact between the smooth web that will sit on the peaks of the roller's surface. Nano-coatings are now mimicking nature (the lotus leaf) to make a topography upon which oily or watery contaminants don't stick because the molecules will not fit. Reducing the wrap angle would achieve a similar effect of reducing contact area.
The next candidate to consider might be chemistry, though options are expensive and have limited lives. For example, we could cover metal rollers with a covering or sleeve of silicone or Teflon. Either has excellent chemical release but is also extremely tender. Rubber-like covers also have very low abrasion-resistance and may wear out quickly.
There are several release tapes. However, tape is also expensive and even shorter lived. Take care in application because sloppy taping can cause wrinkling on thin webs. At least one excellent release tape combines the magic of topography and chemistry. It has a pebbled surface similar to a basketball and chemistry similar to Teflon. There are also plasma flame-spray products for rollers that have the same topography/chemistry combo but are much more durable and, you guessed it, are even more expensive.
A final release technique: Cool the roller and/or web. While cooling the web is usually a good idea for many other reasons anyway, cooling the roller is obviously complicated and expensive. We leave it to the reader to find the combination of cooling, topography and chemistry to get the total release they need.
920/312-8466drroisum@aol.com, www.roisum.com
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