Sorry John - I was supposed to get back to you Monday...
The following are comments from my mate the surface coating specialist, his name is John Clowes... Enjoy!
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KEY POINTS TO COATING A GLASS SUBSTRATE.
1 The glass must be totally cleaned, there should be no oil, water, or foreign substances. This will adversely affect the coatings ability to “WET” the glass. Thus will effect the general adhesion of the coating
2 The class of coating will normally dictate the grade of adhesion promoter you need. There are quite a few new systems out there I would imagine, but here are a few to consider.
3 Printing Inks can range from, Polyamides, Urethanes, Acrylics, Alkyds, silicones, N.C Lacquers, UV cured, (solvent less).
4 The chemical makeup of the ink will based around 2 things, 1.The chemistry and physics of substrate and 2. The environmental requirements (Heat, Flexibility, interior, exterior etc…)
I would assume that the printing device you are using is designed for the function of printing to glass. So really the only thing that should need to be done is pre treat the glass to accept the UV cure ink.
The blooming, or Blushing as it is some times known is usually due to water precipitating at the interface of the coating and the air(interface) In solvent based coating it is generally due to the dew point. This is in the vapour phase of the solvent release.
The most efficient way to control blushing is to make sure the environment is under 60% R.H and all aspects of the process are at a temperature equilibrium. This means that the glass, the ink, the air are at relative the same Temp. It is normal to have a temp of 20~25 @ 60~65% RH. It is most commonly the glass temp that is the issue. I would suggest a pre heating of the to a substrate temp of around 30Deg C’. This will not only keep blushing to an absolute minimum but will also help with the wetting of the ink and adhesion.
Adhesion loss is most widely due to not being able to “WET” the surface, A bit like trying to paint over oil. The surface is too low in energy that the tension of the coating system is too high, thus coating will not only delaminate but will normally do a thing called “CRAWL” across the surface trying to be paint. This the key concept of Hammertones. The material has in the resin system a product that cannot intergrate with the chemistry due to it not being compatible.
The can be said of anti fogging. This is basically a coating that interferes with surface tension (energy) that create fogging. The water cannot accumulate because the water's affinity has been interrupted by the silicone based chemistry.
Key items to check
1 Check UV ink chemistry, (Poly amide, urethane, acrylic etc), is it compatible for the glass surface?
2..Find a Adhesion promoter that will work with the ink system you are using.
3 Clean the substrate again and again until you are totally confident of it cleanliness.
Last but not least.. Trial before committing, the coating should be allowed to totally cure before performing adhesion testing. Well I think most of this is correct or it used to be!!!!!
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Now do you understand why I need a dictionary to talk to this guy?
He has lent me his surface-coating bible - 900 pages of WORSE than the above...
You really need to get me more info on the ink! (Give me your printers email/phone - I will get my guy to talk to him?)
Shane.
