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Adhesion Myths and Reality Part 2

Steven Abbott – Mar 9, 2016

Adhesion Science Myths & realityMy mission in this series of blogs on adhesion science is to give the formulation community a set of clear ideas, plus the apps to bring those ideas to life. There are lots of myths and misunderstandings about adhesion which lead formulators in the wrong direction.

In this blog I want to clear away some more common myths so that the formulators’ precious time and resources can be focused on ideas that will really deliver improved adhesion:

  • Myth #3: Surface Roughness
  • Myth #4: The Mechanical Interlocking
  • Myth #5: Chemical Bonds

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3 Comments on "Adhesion Myths and Reality Part 2"
Steven A Apr 22, 2016
There's an important exception to my statement that roughness (and earlier about mechanical lock and key) has no effect on adhesion. When adhering to paper, board, non-wovens and, as you say, wood, it is possible for the adhesive to wrap around fibres and gain strength. My myth was more about the general perception that roughening gives a large increase of surface area on surfaces in general. As I know little about wood adhesion (I'm a plastic film guy by training) I would still be cautious about statements about sanded surfaces. Sanding generates dust and even a small residue of dust could contaminate the surface so adhesion is being built on sand. What I would encourage because "Adhesion is a property of the system" is that before making general statements about sanding being good or bad, people look at what's going on in their specific system. For example, is the adhesive, for example, actually wrapping around wood fibres, or is that merely my assumption? Has the sanding left a residue and is adhesion improved if the residue is carefully removed? Etc. I like the trick about pre-raising the wood!
vladimyr W Apr 21, 2016
Dear Mike, If you look at older paint systems, the primer was always an oil based system, and also contained red lead which now is banned. I have 80 year old weather boards that were primed with oil based paints, and then have been coated with the more flexible acrylic polymer pains using R&D Polymers. These weather boards have no dry rot. The extension which was primed and painted with water based systems shows dry rot after 15 years. Wood is best primed with an oil based alkyd that has been thinned down a little.
Mike E Apr 9, 2016
So, to put it in layman's terms, Is it beneficial to have a rougher surface to paint on with Acrylic Primers or not? (regarding Wooden surfaces). It certainly seems that Paint adheres to rougher wood better than it would to a smooth sanded finish. One discussion of debate amongst my colleagues and Myself has been over whether there is a loss of adhesion in the following scenario. When priming wood, often it is the case that the primer raises the grain of the wood, necessitating the need to sand after priming. The problem is that in the process of sanding, part of the Primer is invariably removed. My answer to this has been to suggest to use a technique whereby one wipes the wood surface with a wet rag, allowing the wood to dry, where upon the grain is raised, and can be sanded prior to priming. Once that grain has been raised once, the priming has a negligible effect on raising it any further, thus avoiding the resultant loss of Primer by having to sand. The argument I received against My method was that the pre wetting and sanding, would not allow the primer to have the same amount of physical bonding with the surface, and that it was better to sacrifice some Primer being sanded off, than to go with My method. What are your opinions?

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