Conventional wisdom has it that PVC is not paintable. Is that a reasonable statement? Had Sapphire not already been painting uPVC for ten years we’d say the same thing. So: can PVC be painted?
The fact is that uPVC and cPVC (PVC from here on) are difficult to paint. The reason because PVC has a low surface energy. All materials and liquids have a “surface energy”. The scientific unit of surface energy is Dynes/Centimeter. For purposes of discussion we will talk about the surface energy, SE, of water and how it relates to PVC.
Water has a surface energy of 72DYNE (DYNE is short for Dynes/Centimeter) and PVC has a surface energy of 41DYNE (list of the surface energy of various polymers). Since water has a higher surface energy (SE) than PVC, it will bead up and roll off like: “water-off-a-ducks-back”. In order for the water to “stick” or “wet out” onto PVC, PVC has to be treated to rise the SE of the PVC above the SE of water.
Can this be done? By the average consumer? Well…no…but don’t give up yet, and read on… The average consumer can do two things to increase the SE of PVC, the first of which is to sand the surface lightly. This will remove the surface waxes to a degree and create more area for the water to wet out. We recommend you use Green Scotch Brite because sand paper will load up very quickly with the surface waxes on the PVC, this raises the SE. The second way to raise the SE is to wipe the PVC with acetone. Acetone is detrimental to PVC. If one were to immerse PVC in acetone, it would break down the molecular structure over time and destroy the PVC. This, however, can be a benefit when preparing PVC for painting. The Acetone does two things: (1) it swells the surface making it slightly more porous and (2) it disperses the surface waxes that are inherent on the surface from the extrusion process when it is manufactured. So, acetone will also raise the SE of the PVC.
There is another piece of the equation that has to be considered. Even if a consumer prepares the surface as described, the SE of PVC will never reach the SE of water (with these techniques) and even with all the best preparation, the SE of the PVC will be variable due to the waxes that are external and internal to the PVC. To combat this, paints made of a blend of acrylic and polyurethane, (i.e. special latex paints) have been formulated with additives to reduce the SE of the liquid paint. These additives reduce the SE of PVC paints down to 34DYNE which is lower than the untreated SE of PVC (72DYNE).
In theory one would not have to treat the PVC if the paint has a surface energy below the PVC; however there’s a problem with theory – reality. Empirical results suggest a combination of good surface preparation and a paint coating with a low SE can result in good adhesion of paint to PVC.
There is a lot more to it than that: the paint formulation is actually a cacophony of chemistry. Every micro ingredient and every pigment change can change the adhesion of the liquid paint to the PVC substrate but that’s beyond the scope of this article. Suffice it to say that the paints developed for the PVC niche have been tested for adhesion on PVC each and every time a change is made to the formulation.
At Sapphire we subject the PVC to a flame treatment process that can raise the surface energy from 42DYNE to above that of water's 72DYNE.
To try to better explain it, when the surface energy of PVC is raised to this type of energy, it can be thought of as creating “micro anchors points’ to which the paint can adhere.
In our flame treatment process, we subject the PVC to a very lean burn flame of natural gas. The temperature of the flame is roughly 5000°F. A low temperature plasma is created. In effect the excess oxygen in the flame is heated to the point of ionization. which means that the oxygen loses an electron and becomes a positive ion. In this state the oxygen is very very reactive and wants to bond to another atom or molecule. In our process the 0+ is introduced next to the PVC and bonds to the PVC. The result is the surface energy of the PVC is raised tremendously. There is another benefit of the flame process which is to remove the surface waxes on the PVC, also raising the surface energy of the PVC.
So, whew… there you have it. PVC can be painted but it has to be prepared correctly and it needs to be painted with paints that are formulated for PVC.
At Sapphire we also put reflective pigments in the paint so that the PVC will not rise above it’s distortion temperature of 140°F. (Note: for dark colors PVC has to have reflective pigments)
At Sapphire Windows and Doors we have merged the markets between Clad-Wood windows and Vinyl windows and you can now get better performance at a fraction of the cost.