Vacuum Web Coating

Books of Interest to Metallizers & other vacuum coating processes

It is intended to list books that are not just directly relevent to metallizing but that are of a wider interest.  Thus there will be books listed about other vacuum & even non-vacuum processes.

I hope that will you will join in & send details of books to further widen the 'library'.

A starting list is posted in the continuation.

Questions relating to adhesion.

            I am curious about what different processes are used to prepare metallized film.  In particular, webs are often flame, corona or plasma treated to improve adhesion but how many of these webs are treated also on the reverse side?  The reverse side of the web can also be contaminated and this contamination may be transferred to the front surface when the web is wound up. Thus the reverse surface could recontaminate the flame or corona treated front surface if the back surface were not also treated.  The back surface might have additional low molecular weight material exuded to the surface during the high temperature reached during the metallisation process. Thus the freshly metallised surface might also be contaminated as the roll is wound up in the vacuum system.  This may result in having to corona treat the metal surface prior to printing to improve the adhesion.  I thus have a second question of does anyone treat the back surface of the web in vacuum before the web is rewound to stop this low molecular weight material transfer?  This also leads to the more general question of how successful do you think any of these processes are?

Summary of the Questions.

1.                  Have any of you experience of also treating the reverse side of the web?

2.                  Do any of you plasma treat the back surface of the web in vacuum?

3.                  How successful do you think these treatments are?

Common Pumping Problems.

Water has to be the biggest cause of pumping problems.  The source of the water can vary from, a wetter than normal substrate, more ambient moisture absorbed when the machine is at atmospheric pressure or even a water leak directly into the system.

Other problems can relate to a lack of routine maintenance or too infrequent maintenance.  This can be everything from not cleaning the deposition shields frequently enough to not checking the oil levels in the pumps or ballasting the roughing pumps to remove any excess water vapour.

Below I will highlight each of these problems and some of the methods for identifying the possible source of the problem. 

Troubleshooting adhesion – i.e. lack of adhesion.

So many times the question is asked ‘how can I improve the adhesion of my coating?’ or ‘I have uneven adhesion how can I improve this?’

Like most problems the first step is to check that the real problem has been identified. There may be a real lack of adhesion of between the coating & substrate but often the substrate has been contaminated & trying to apply solutions to improve the adhesion without first eliminating the source of the contamination may prove fruitless.

Another common problem is that the only test being used is the ‘tape test’.  I personally find this an appalling ‘test’; I hesitate to even call it a test.  There are so many variables to the test that make it questionable.   It is far better to have a ‘fit for purpose’ test where the coating is tested in the application it is to be used in.

However I know that many companies & operators will continue to use the ‘tape test’ as it is a quick, simple & low cost test and it is regarded as better than nothing.

Below I will give some suggestions of how to check if there has been some surface contamination and also what else might be done to improve the adhesion if something more is required, other than eliminating any local contamination.

Evaporation Boats

What is the difference in two component and three component evaporators?

The boats can made up of combinations of 2 or three ceramic powders that are blended & compressed together. The three materials are titanium diboride, an electrical conductor that is easily wet by the molten aluminium, boron nitride, an electrical insulator that has good thermal shock resistance and is easily machined and finally aluminium nitride that is an electrical insulator but has good thermal conductivity.

Using different combinations gives the boats different properties of wetability, electrical conductivity, thermal stability, wear resistance and lifetime.

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