Coating Thickness Measurement Systems

Editorial Note: Originally posted by Butcher (in a previous thread, superceded by this one):

Ultrasound/sonar might work. I don't know if you can get <100 micron resolution with a commercial system, but I'd bet that it is possible. The 2m width would probably be a larger obstacle.

A very sensitive scale as part of your conveyor that is moving the web might be able to detect sections that have more/less coating. I doubt that is practical, but it's an idea.

LIDAR systems might fit the bill the best. http://en.wikipedia.org/wiki/LIDAR. You should be able to get the resolution you need, and high speed rastering will give you total or near-total coverage.

Neat problem, let us know what comes of it.

100 microns is not the resolution, it is the full scale.

What resolution do you need Birdman?

1, 10 or 50 microns would make a big difference.

Gigaconcept,

My film thickness is under 100 microns. I need resolution of about 1-5 microns. This may be pushing it, but it is my target for now. Do you think that a resolution of 1 micron is reasonable for a moving web? How about 0.5 microns?

Thank you,

Birdman

Birdman,

There are two ways to describe resolution, precision and accuracy. A typical sensor that can measure your coat weight can repeat the measurement over the entire 100 micron range to .5% or less @ 2 sigma limits. If you use the accuracy correlation, the sensor can take hundreds of measurements to describe the coat weight average and thus make the error +/-zero.

I hope this makes sense for you. There is nothing in your description of the coating application that is unique to what you are trying to do. It is a matter of how one collects the data.

Regards, mkh

Thank-you; You have added yourself into history. You see, it is my job to listen to the improbable and find a way to make it reality. I love my job. It is with much missfortune, I hate my means of getting results. Consider yours as noted and additive to what our children shall be a part of.

Check with a NDT (Non Destructive Testing) supply company. They should have ultrasound thickness devices that sounds like it would do the job (no pun attended). I remember using a hand held one when i was a field engineer.

Since the materials you are dealing with (paper and epoxy) are dielectrics, they have a property known as dielectric constant. If the coated sample is placed between two flat parallel metal plates, a capacitor will be formed. The total capacitance between the plates will be the capacitance of the air gap plus the total capacitance of the paper and the epoxy film. If the only variable is epoxy film thickness, a capacitance readout will measure it. It's slightly (only slightly)more complicated than this.

I have designed and built inspection systems for WEB products such as coated films, metalized film, paper, glass, steel, aluminium, non-wovens, plastics & many other unique applications using both LASER scanning and Line Scan cameras. This, I am sure would satisfy you 100% inspection requirment. As for the thickness measurment need, that is more problematic. A lot more detail of both the coating and the paper substrate would be required. Typically, to solve these issues an application study is needed.

As you are probably beginning to reolize you inspection job is more complex than you first though. $150 K might also be a bit of a challenge.

I would be glad to discuss this further with you.

Birdman,

I would like to comment on your desire to make a coating measurement on paper and to analyse the MD and CD coat weight variations in real time.

Currently there are only two ways available. A before and after scanning nuclear gauge or a scanning infrared sensor after the coating is applied. Also you are correct in describing these techniques as less than a 100 % inspection.

I am in the process of developing a better alternative that just hasn't been completed as yet. One day soon we will be able to use line scan cameras that cover the entire web with two near infra red wave lengths, reflective lighting and make the measurement with out scanning or any other moving parts. A 100% inspection solution.

I have a patent pending that has been published and reference to it can be found on my web site webprocesssolutions.com. Please feel free to visit and offer any additional comments that might be appropriate.

Thanks, mkh

Wow Birdman! You are right up my alley. I have two companies in mund that I tried to do the similar thing. I am not sure if the cr4 is allowed to name names because of some sort of liability. However I for get the first letter in the first company; Perhaps I need a cup of TEA before I remember the rest of the word - encor. Or maybe I should go out and finish my DECK I'm building so I can TACK up some lights. But; I think that solution costs too much. It was for me anyway. I invented my own. More ifo? send me a personal request by going to the high-lighted "ASHMAN" and send personal message. I will tell you this it came out to be less than 49K USF. ASH