Stronger Composite Bonding Solutions with Innovative Film Adhesives
One of the big challenges of working with composites is bonding multi-layered materials. Composites also need to be bonded to non-composite materials from time to time. But you cannot weld carbon fiber. Attaching composites with mechanical fasteners is also not a wise idea. So engineers are left with adhesives.
In the past, paste and liquid adhesives were preferred. But today, strong bonds are created with newer and more advanced film adhesives. A film adhesive typically comes as a pre-cast resin film with a tailored chemistry and carrier.
The Basics of Film Adhesives
Your typical film adhesive is a thin, pre-measured sheet of adhesive resin. The resin is typically epoxy, epoxy-phenolic, or thermoplastic. Film adhesives are stored as B-stage materials that are ultimately cured with heat and pressure. Correct curing ensures a uniform bond-line thickness that maximizes joint strength and reliability.
Because the adhesives ship in film format, applying them is easy and efficient. Workflow improves and fabrication production goes up.
Why the Bonds Are Stronger
Utilizing film adhesives isn’t just about fabrication efficiency. The adheres actually create a stronger bond. They do so by way of three mechanisms:
- Toughened Chemistry – Today’s film adhesives are enhanced with toughening agents and hybrid resin systems. They offer better peel strength, impact resistance, and fatigue life compared to their older and more brittle counterparts.
- Controlled Thickness – Built-in carriers preclude unlimited resin flow, offering more control in terms of adhesive thickness. Engineers can maintain a more consistent stress distribution in order to reduce weak spots in the bond line.
- Porosity Control – Resin-rich films can actually improve composite surface impregnation by filling in gaps. The overall porosity of the finished material is reduced while its cohesive strength increases.
As Durable as Ever
Liquid and paste adhesives have long been trusted because of their durability. So much so that a manufacturer might shy away from film adhesives. There is no need to do so. Film adhesives are as durable as ever. They are comparable to older technologies in this regard.
Bear in mind that modern film adhesives are purposely engineered for:
- High-temperature service.
- Chemical resistance.
- Moisture resistance.
A properly formulated film adhesive bonds materials to create strong joints capable of withstanding multiple thermal cycles, significant humidity, and just about any other influence one would expect in an aggressive environment. For example, consider aerospace-grade adhesives.
These high-temperature film adhesives maintain their structural properties even at temperature extremes. The interface between materials – even if it is a composite-metal interface – remains intact over many years of reliable service.
Support for Automated Layups
If you are concerned about ease of use, no need to worry. Modern film adhesives are clean, easily handled, and support automated layups. They are ideal for repeatable placement. Best of all, they reduce surface prep demands and clean up nicely.
Film adhesives work so well that they actually reduce variability throughout production. They do so without compromising performance. The ability to use a film adhesive to bond composites to metals, honeycomb panels, and other composites simplifies joint design without increasing production complexity.
A Better Choice All the Way Around
Older paste and liquid adhesives did the job just fine when they were the only game in town. But composites have changed considerably over the last quarter century. Just in the last decade, we have seen technological advancements that have pushed composites even further. Among them are modern film adhesives.
From our perspective, film adhesives are the better choice all the way around. A limited number of applications might still require pastes or liquids, but film adhesives can replace those older technologies most of the time.