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Introduction to Vehicle Interior Bonding

Posted on 2/26/2013 10:30:30 AM By Sandy Niks
  

Bonding applications for the interiors of cars and trucks include a wide variety of substrates, adhesives, sealers, and requirements.

Although most applications would be considered trim bonding, there are a few that may be structural. For example, the headliner may be designed in such a way that, when bonded to the roof, it contributes to the structural integrity of the roof.   Doors have water deflectors, flocked fabric for door glass run channels, interior door panels, and stickers. Instrument panels can have bonded coverings, wood panels, emblems, anti-itch tapes, as well as plenty of electrical parts. Carpeting can be bonded to the floor – and will require some of the salt and mud resistance testing exterior applications must endure. The substrates include painted metal, glass, wood, paper, fabric (wool, nylon, polyester, blends, etc.), rubber, insulation (foam rubber padding, fiberglass, etc.), and lots of plastic (nylon, ABS, acrylic, phenolic, TPO, etc.). In other words, just about anything. Components arriving at the vehicle assembly plant that consist of multiple parts often use a variety of adhesives in their construction, too.

The adhesives and sealers used are as varied as the substrates. Bonding applications for the interior of cars and trucks occurs in the “final assembly” stage of the vehicle assembly plant. The bonding process needs to be as clean, quick, and as easy as possible. Therefore, “instant” (cyanoacrylates) adhesives, pressure sensitive adhesives, tapes, and hot melts are the most popular. Two-part epoxies (ambient cure) have some limited application. Water-based adhesives have replaced the solvent-based adhesives for contact adhesives. Some adhesives may require a primer or activator, which is preapplied by the supplier wherever possible.

Test requirements for interior bonding are not quite as stringent as exterior bonding, although there are some exceptions.   The adhesive bond strengths needed are lower for most interior applications.  Many exterior bonding applications are considered “structural”, that is, they have some contribution to the structural integrity of the vehicle.  Also, exterior applications have more exposure to weather:  rain, salt spray, mud, sunlight – including ultraviolet, hot and cold temperature fluctuations, and combinations of these environments. Depending on the specific location of the bond, exposure to additional fluids (gasoline, diesel fuel, radiator fluid, windshield washer fluid, etc.) may also be part of the testing regimen. Interior applications may have high temperature loads, but environmental cycling tests seldom include water soak or extensive salt spray cycles. Another test important for interior applications is a fogging test, SAE J1756, Determination of the Fogging Characteristics of Interior Automotive Materials. Several years ago, it was discovered that a thin film, or “fog” was sometimes being deposited on the interior of some glass surfaces. There were many factors that contributed to this. To avoid the possibility of any materials being contributors, passing this test became a requirement for all interior materials, including adhesives and sealers.

Overall, there may not be quite as much testing for interior bonding applications as with structural and/or exterior bonding, but the breadth of knowledge is quite extensive.

The following is a brief list of suppliers of adhesives and sealants used for interior applications. This is not an endorsement of any company.  Nor, I am sure, is this a complete list of suppliers.

Companies:

3M

Bostik

Dymax

HB Fuller

ITW Devcon

Henkel

Lord

Permabond™

 

References:

Handbook of Adhesive Technology, edited by A. Pizzi, K. L. Mittal, Marcel Dekker, Inc., 1994, ISBN:  0-8247-8947-1, Chapter 40, “Adhesives in the Automotive Industry”, by Eckhard H. Cordes.

Handbook of Pressure Sensitive Adhesive Technology, Second Edition, edited by Donatas Satas, Van Nostrand Reinhold, 1989, ISBN:  0-442-28026-2.

Handbook of Adhesives, Third Edition, edited by Irving Skeist, Ph.D., Van Nostrand Reinhold, 1990, ISBN:  0-442-28013-0, Chapter 45, “Adhesives in the Automobile Industry”, by G. L. Schneberger P. E.



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