Vacuum Web Coating

Adhesion problem

We use to produce metallized BOPP film usually with no problem, however recently we have suffering some metal adhesion problems. Each 5 meters BOPP master roll is slit at 2.5 meters and metallized with plasma treatment, however we have a kind of metal peeling in one of the edge. Do you have an explanation for this phenomenon? Thanks in advance.

Answer.

The immediate thing that springs to mind is to check the rollers for contamination on the side where the delamination occurs.

This type of poor adhesion can sometimes occur when the bearings have just been lubricated and there has been excess or oil/grease and some has migrated onto the rolls and this is transferred to the web causing poor adhesion.  This could be anywhere on any of the upstream machines. If the loss of adhesion is periodic the distance between patches may give an indication of the roll diameter where the problem starts from. If it is continuous it could be because the contamination has been transferred to several other rolls too.  This problem may reduce with time, if the lubrication was just a one off. If the lubrication is automatic it may be that it has been set too high and this could get progressively worse. 

If you determine that it is not a contamination problem then you would be looking for non-uniformity in any plasma treatment, whether this is flame, corona or vacuum plasma. Look for intensity differences, blocked flame burners, pressure differences across the width, etc.

Adhesion testing.

Is there any specified testing method for adhesion test on printed foil/film board so that everybody having the same method?

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Adhesion tests are notoriously difficult. I think the 'tape test' is not a good test because there are so many variables. However just about all of the other tests are much more time consuming and need multiple tests to become statistically significant. They also need a greater degree of operator training and usually cannot be performed next to the roll, as they require some laboratory space. Hence the 'tape test' is a cheap and cheerful
one that may be carried out by anybody.

The 'tape test' is not a measure of how good the adhesion is but is only a measure of how bad the adhesion is if shows any failure at all.

The other approach to adopt is to talk to the end user of the metallized
product and use a test that is appropriate to the end use of the metallized
film.  Thus if it is to be used in a twist wrap application a twisting test
would be most appropriate, if the film is to be used with a 'dead-fold' then
a folding test should be used.  In this way an exaggerated process can be
used as the test to prove the film is 'fit for purpose' rather than simply
has good adhesion.

Thus it is common that there is not a standard test.  It is also common that
there are disputes because what may be measured by the metallizer may be
different to what is measured by the customer.

It would be nice if someone could develop a standardised, universal,
quantitative adhesion test.

Question about problems in induction sealing.

We are having some problem with the use of metallized polyester in induction sealing.   I am trying to reach you with the hope that you would help us in combating this problem.

                        

We are introducing ourselves as a packaging goods manufacturer having expertise in induction sealing.  We are doing lot of experimentation in combination with various substrates, considering the barrier properties of the product.

               

As required by the customer, we are going to use metallized holographic film [24 micron] as a tamper proof seal.  In this can you guide us to have right metallized film which can withstand 100 degree Celsius?

Some questions in this regard:

[1] What is the maximum temperature metallized film can withstand?

[2] Is the density of the film very important like 1.5 opd, 2.5 opd?

[3] Is any coating required to have the heat resistance power? [Since metallized film coated in both sides are available]

Since initial trials were failed and the findings are as follows:

[a] Curl-up from the edges.

[b] Shape contour was changed.

[c] Some shrinkages  evident.

[d] In some points a stain of burning appears.

[e] In this, 24 micron holographic film was used.

Is there any solution to have better product, where deformity and shrinkage can be eliminated/reduced?  Does CPP film being used for holographic film elsewhere?

We will be glad if you can kindly throw some light on the said problem.

The construction layer is like this

foil 30 micron+ holographic met. pet 24 micron+ wax coated with

Board.

Click on the continuation to see my attempt at an answer.

Oligomers the problem?

Not long ago I was posed this question.

‘ recently I metalized a pet web both sides, when I finished the first side I checked it and it was ok, but the problem ocurred when I finished the other side, because I saw "white stains" on the first side.

My question is What happened?       Is impossible to metalize both sides?

And the other situation is the next, if I pass my finger in the metalized film, my finger becomes "silver" obviously the aluminium has not good adherence. Can you tell me what is the reason of it? ‘

As always it would be nice to be given more information such as if the polymer was pre-treated & if so by what process & was it done on both sides? Also was there any relationship between  the stained areas & the lack of adhesion or was the lack of adhesion everywhere and on both sides?

As this information was not available all I could do was speculate & include my assumptions in the reply.

What would your answer be?
To see my thoughts click on Continue.

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?

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.