The second part of Yanti’s question after reading the Oct. 31, 2011 posting “Plasma treatment and treatment retention”, is as follows: Recalling the question: Should the plasma setting be different for BOPP and BOPET? And if yes,
1. What is the setting difference (gas composition or electric power)?
2. And what is the best method for measuring the plasma effect at metallizing film?
A: The answer is multifaceted and will pretty much depend on how much money you have to spend to understand what is happening to the film surface verses simply knowing if something positive (or negative) happened to your desired film properties or not.
In its simplest terms the answer is based on figuring out what the plasma treatment system is doing to the film surface and this usually means what chemical functional change has occurred to the film surface. To determine this you basically have to treat the film surface and then analyze it for the molecular changes. Generally you would run the treatment process in the vacuum chamber but not metallize the surface. Then you would take a sample and have the surface analyzed by XPS – X-ray Photon Spectroscopy and also I would do FTIR – Fourier Transform Infrared Spectroscopy on the surface. XPS counts atoms on a surface with in from about 10 to 50 angstroms of the surface. it can also be used to determine the likely chemical functionality of the various atoms at the surface, i.e. it will show how many oxygen atoms have been added to an OPP or OPET surface and if done at high resolution (more money) what type of carbon and oxygen bonds are present. The FTIR will give the infrared spectra of the near surface of the film and in combination the two methods can give a good deal of information. I would also do a surface wash of the film and more FTIR of the wash and clean surface to see if I had ablated or degraded the film surface. There are other surface specific chemical tests but these two are where I would start. This is the types of studies I have done to determine what treatment (Corona, Flame and Plasma) does to a specific film surface. There are also many literature studies you can find and read but of course they are never exactly what you do but they can give great insights into what is likely to happen to a polymer when treated.
A simpler, perhaps more practical answer to the question can be simply, did the plasma settings improve the property that I want in my metallized film? This is best done with a designed experiment where the film is treated, metallized and converted and then tested for the property improvement. This give you a statistically valid answer to the question, did the treatment make a difference? The alternative is to guess and hope for the best.
The way I go about product testing it is to first do a screening experiment on the treatment process(s) and the treater settings on the final film or converted product property. Typically, I would do a two level, 12 run Placket Burman experiment to test 5-6 variables for significance. For instance I would perhaps examine ln-line treatment level [maybe flame vs. corona], metallizing line speed, plasma gas blend ratio, plasma power setting, film surface polymer type, lamination type, etc). Having determined the most important variable I would then do other designed experiments to better understand the impact of the most significant variables and their interactions.This approach can give excellent results in terms of product development even without knowing why the process variables work. However, to really understand the answer to why you achieved the property improvement it is best to know the answer to what functional change occurred to the polymer film surface, but it is not required. Understanding depends on how deep both your pocket book and your curiosity are, and what level of understanding your company wants or needs.
As a film designer this is the sort of experimental program that I would do so I could make sure when we went to production that we knew what to make and how to make it as well as how to explain it to ourselves and our customers. This insured a good manufacturing process for the product and low levels of product returns.
So what is the best way? I think in the long run you do both of the approaches defined above, but at the very least you do the statistical experimentation to make sure that you don’t fool yourself into thinking you have a good product and process. You know what is happening with the process changes to insure a robust product and process design. Understanding can come with time as you continue to experiment and figure out what chemical changes are being made to the film surface that control the property development. All it takes is time and money.