Web Lines | Air Bubbles in Your Laminate
- Published: September 01, 2015, By Tim Walker
Here are 7 solutions when laminate bubbles or uncoated area creates delamination at idler rollers.
Do you ever get bubbles in your laminate?
Do your bubbles ever get “caught” and accumulate on the entry side of an idler roller?
Do these accumulating bubbles build up enough pressure to delaminate your product?
If yes, yes, yes, you are not alone.
What do you do with an unwanted balloon? Pop it! That's the obvious solution and may be all you need to know, but popping bubbles can be a safety concern or leave a hole in your product that the customer doesn't want.
I can't describe all the factors that determine when bubbles accumulate and delaminate, but clearly the pressure of the building air bubble exceeds the bond strength of the adhesive to one of the webs (usually a liner).
Where do bubbles accumulate and delaminate?
- In a lamination process where two webs start running with no bonding coating between them and coating begins. Ideally, the coating would push all the air between the free running webs through to the winder (or end of the process). However, if the bond layer has low bond (and many adhesive layers have low initial or green strength bond), then the air trapped between the webs at the entry to an idler roller will tunnel through the laminate, continuously ripping open a lane of the laminate. It reminds me of having a gopher under your sod, tunneling, tunneling, with no end to the damage in sight.
- In stripe-coated products, with lanes of uncoated laminate. The air trapped in the uncoated lanes can accumulate upstream of an idler roller and build pressure to push open and delaminate the edges of the bonded lanes.
Possible Solutions
1. Increase adhesive to liner bond (likely not an option).
2. Some products are designed with perforations, holes, or porosity to prevent air accumulation.
3. Pierce the bubble to let allow the building air to escape and relieve the pressure. In many operations, especially in the going “on coat” laminate bubbles, many operators learn to pierce the bubble with a cutting blade, whether in stabbing point cuts or longer air-relieving slits. It is possible to design an automatic bubble piercing system. To do this, a series of close proximity blades or pin wheels are set near when bubbles will form. If bubbles form, they have a raised profile that is automatically pierced, where low profile non-bubble web passes by freely.
4. Reduce the pressure at the web-roller contact, allowing the air to pass over the roller: a) Reduce tension or b) Increase roller diameter.
5. Modify the roller surface to allow pockets of air to pass downstream. In my training, I talk about the use of a laterally ridged roller, either axial or herringbone ridges, to allow the air to “burp” through in small amounts, eliminating the accumulation of air. This may just move the problem to the next roller, or you may find that doing this on a few key rollers will get you through a process and on to winding without the air bubble delamination defect.
6. Laminate with less air between layers, either with lower speed, higher nip loads, or in a vacuum environment.
7. Use a high bond tape or coating across the full product width to push the bubbles downstream.
I'm sure there are some other ideas or solutions out there. I'd be glad to hear the input from our readers.
Web handling expert Tim Walker, president of TJWalker+Assoc., has 25 years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; This email address is being protected from spambots. You need JavaScript enabled to view it.; www.webhandling.com.
