Ask Dr. Dave

Ask Dr. Dave

July 1, 2009
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Adhesive and sealant troubleshooting tips from Dr. Dave Dunn.

Question: I am bonding EPDM to acrylic-painted ABS, and I’d like to know if there are adhesives for this particular substrate combination. I’m looking for an alternative to acrylic tape for cost reasons. Do you know of any fluid 2K systems on the market?

Answer: EPDM is a very difficult material to bond, and cyanoacrylates are almost certainly the best adhesives. However, if lower-cost two-component adhesives are what you’re looking for, then a tough acrylic adhesive will provide a good bond, but strengths will not be as high as with a cyanoacrylate. You might also try a two-component polyurethane system.



Question: I have always believed that getting a really good adhesive bond means the materials being bonded should break before the adhesive. However, my adhesive supplier tells me that this is not necessarily true. What are your thoughts on this?

Answer: This is a common misconception that most of us were brought up with, probably because the materials we bonded when we were in school were very weak. If you really think about it, though, the need to break the material being bonded is irrelevant in most bonding situations.

The real technical answer to your question is that an adhesive only has to be strong enough to support the dynamic or static loads that the bond is subjected to in service. You must also bear in mind that the area being bonded is a critical consideration when determining the strength required of an adhesive. If you are bonding very heavy metals, for example, and the bond area is quite small, then you will require very strong adhesives like epoxies or cyanoacrylates, which have shear strengths of 2000 to 4000 psi. On the other hand, if you are bonding large-area, lightweight panels or an extremely light material (such as wall coverings), a lower-strength adhesive with a few hundred pounds of strength (such as a hot melt or a water-based system) is more than adequate.

Any views or opinions expressed in this column are those of the author and do not represent those of Adhesives & Sealants Industry, its staff, Editorial Board or BNP Media.

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