Hi Steve

 

You ask some excellent questions!

 

A.    Surface energy refers to the "reactabilty" of the surface.  Hi surface energies mean that the surface of the material is more likely to get a good structural bond to the adherend vs. low surface energy like waxes and Teflon.  This is sometimes measured with an angle meter that will measure the angle of say, a drop of water on the surface, since high energy makes the water tend to flow vs. a wax where it forms beads.  There are also "Dyne solutions" and "Dyne pens" that bead up until a specific energy is reached.  So these are the tools to measure surface energy.  So a good high surface energy material would have lots of reactive sites on the molecules for the paint to bond to.  But that also means that stains and oil will bond to it also which is why I asked the question.  One example of how you can see surface energy change is when you need to bond polyethylene to something.  You know that pretty much NOTHING sticks to polyethylene but the ski manufacturers are able to get excellent structural bonds to it since they have to stick Ptex to the bottoms of skiis.  The way they do it is by using a low flame passed quickly over the surface of the Ptex.  If you look at the surface as the flame goes over it, you can see the sheen change.  What is happening is the molecules are being broken right on the surface of the polyethylene.  This raises the surface energy and allows adequate bonding. And polyethylene is basically a high molecular weight parafin wax.  A chemist could explain it better I'm sure.

 

B.    It shouldn't make any difference whether you use 40 grit, 80 grit or Scotchbrite.  Coarser grit is just a way of improving the mechanical bond and that can only help a little bit. Technically, what your really need is a good clean surface.  A "new" surface that has just been left exposed can find things to react to leaving less sites for the paint or adhesive to bond to.  So you always want a good clean fresh surface.  My buddy Rich Molton of Applied Poleramic who is the owner/chemist says that a good freshly exposed surface with the peel ply just removed should be just about as good a surface as you could bond to...but then he still likes to sand it a bit.  But this is more for impurities from the peel ply.

 

C.    The time between sanding can be a big factor.  I don't like to let a project sit after I have prepped it.  I try and prep, clean and paint or bond immediately.  This is probably more than is required but I feel it is the best bond possible.  Painting obviously requires time to prep and dry so it isn't always practical to spray right after prepping.  Reducing waiting time is especially critical for painting aluminum since it very quickly develops an oxide.  The problem is the paint may bond great to the aluminum oxide but aluminum oxide bonds poorly to the aluminum.  Treatments such as phosphoric acid anodize and chromic acid anodize etching actually turn the surface of the aluminum into a ceramic "cobwebby" sort of sponge structure (on a microscopic level) that promotes good bonding.  Thse surfaces do not need any prep other than being left extremely clean and not handling the material with bare hands.

 

D.    Since in a perfect world, acetoe, MeCl, and water are all 100% volitiles, it shoudn't make any difference.  The difference is what the solvent will dissolve which means what contaminant is being cleaned off.  If you have just sanded the surface, vacuumed then wiped off the dust until the rag wipes clean, it shouldn't be any big deal which of those you use.  The only concern being that water from a tap may have lots of contaminates and must be dried longer to dry completely allowing more time for other contaminates to settle on to it.  And also, water may not dissolve all of the contaminates that are on the surface as acetone or MeCl would.  So normally, I use acetone, the laminators mouthwash!

 

E.    Vacuuming would only help get the initial stuff off, it is really the final surface that matters.

 

A few other hints on bonding:

 

1.    NEVER spray aerosol lubricant in your bonding area.  The stuff floats all over everything.  You can be fired from Boeing for bringing in a can of silicone spray into the bonding area!

 

2.    Use a better grade of 'Tone than the industrial grade stuff like what you get at the hardware store.  It can have a lot of contaminates in it.  I'd rather use technical grade which will cost more but you really only need it for the final wipe.  Lab supply houses have it.  Reagent grade is better still but that's really big bucks.

 

3.    Change your wipe rags often so as not to spread the contaminates.

 

4.    Use only bleached white paper towels for cleaning or better still, Kimwipes which are lint free labratory wipes.  Again, the most important wipe being the last if you don't want to blow all the extra bucks for that over paper towels.

 

5.    Don't use chemical gloves (barrier cream) on your hands if you are bonding and prepping surfaces.

 

6.    Keep all of you fabric being used for a laminate clean and in a cover that won't transfer contaminates.

 

7.    When handling fabrics, it's best to use clean latex gloves but if you are going to use bare hands, wash them often.

 

I hope this helps!

 

Dan Newland