Vacuum Web Coating

Moisture and aluminium performance

Can moisture affect the performance of aluminium metallized films?

Answer.

Yes moisture can affect the performance of aluminium metallized films. This starts with the film before metallization. Most polymers contain moisture as well as the water in the air that is trapped between layers as it is wound into a roll.  This is all carried into the vacuum system. Even when the system is pumped out to a low base pressure there will still be enough oxygen and water in the system that a monolayer of oxygen can form on a surface in less than 1 second.  Thus all aluminium metallized films have a proportion of oxide in them, usually of the order 1% - 2%.  If the vacuum system has a leak this can be somewhat worse.

The aluminium is a metal that forms an oxide on the surface that acts as a good barrier layer and prevents further rapid oxidation.

The adhesion of the aluminium to the polymer web is dependent on a number of things. This can include the polymer quality, contamination, the storage conditions (humidity and temperature), any surface treatment, the type of treatment, the age of any treatment as well as the process conditions such as deposition pressure.  When laminating another layer to the surface it will depend on the relative adhesion strengths and the residual stress following the lamination. If the residual stress is large the adhesion of the aluminium needs to be higher than if the residual stress is low.

The speed of oxidation and amount of oxidation depends on the thickness of the aluminium layer. If the aluminium is very thin and the adhesion is poor the there will be very little aluminium left once the surface has been oxidised. If the aluminium is thicker then even after the surface oxidation there will be sufficient metal left to give a long lifetime for the rest of the aluminium.

AIMCAL Fall Technical Conference

AIMCAL Fall Technical Conference 
and
22nd International Conference on Vacuum Web Coating
October 19 – 22, 2008
Myrtle Beach Marriott Resort at Grande Dunes
Myrtle Beach, South Carolina

   

CALL FOR PAPERS
DEADLINE: To assure consideration, abstracts must be received by May 31, 2008.

The AIMCAL Fall Technical Conference is an Industry forum for the global technical community involved in web coating processes.

Visit the AIMCAL Website to submit your paper.

Topics of interest for this year’s conference include, but not limited to the following:

Vacuum Web Coating

• Process optimization and preventive maintenance in the vacuum web coating processes
• Leading edge roll to roll technologies, products and markets
  including flexible displays, flexible semiconductors, superconductors, thin film battery, flexible solar cells, super barriers, film sensors, anti-counterfeiting films and papers, OLED, holography, and solar control 
• Machine and equipment accessories upgrade cost / benefit
• Advances in substrate technology
• Advances in process control and measurement
• Patterning and edging of vacuum coated films and papers
• New coating processes, tools and equipment
• Advances in barrier performance, process and measurement

Atmospheric Web Coating and Laminating

• Web Coating Technology related to applications and fluid rheology
• Process Measurement including coating weight, defects, viscosity, process modeling
• Laminating processes including alternatives to laminations, process optimization, web variability, modulus, guiding and tracking
• Coating Operations: An overview that compares/contrasts various coating techniques, roll coating systems, slot die/curtain coating techniques, extrusion coating, coating thin on metallized films, toll coating
• Substrates and liners technology including new technology and performance, innovations, and applications
• Web coated product markets - technology and market overviews

Specialty Web Coating

• Novel or developing web coating technologies
• Nano coating technology
• Photovoltaics technology
• Developing web coating technologies and markets
• Specialty substrates and coatings technology
• RFID technology

A session on Market Trends in the Converting Industry is being scheduled. Topics of interest are global market and technology trends, future role of converting process in growth industries and integrating product development through the supply chain.

Presentations for the Fall Technical Conference are selected upon the following criteria:

• Applicability to the advancement of the manufacturing process
• Uniqueness and innovativeness of new technology and its contribution to the Industry
• Value to the technical/production community

The audience for the Fall Conference is Technical Professional personnel in R&D, Manufacturing, and Marketing. Presentations should be at a technical level of interest to this audience. Papers covering related subjects, not specifically addressed in the call for papers should still be sent for committee review.

Visit the AIMCAL Website to submit your paper.

www.aimcal.org

Applied Web Handling Conference 2008

Applied Web Handling Conference 2008
May 6 -9 | Radisson University Hotel  | Minneapolis, MN

AIMCAL, the Association of Industrial Metallizers, Coaters and Laminators and CEMA, the Converting Equipment Manufacturers Association are pleased to announce the second annual technical conference devoted to applied web handling technologies within the Converting, Paper, and Plastics industries.

FOR MORE INFORMATION AND SECURE REGISTRATION VISIT THE AIMCAL WEBSITE   www.aimcal.org

Uniformity of pumping, system symmetry.

For those of you depositing metals this is going to be of less interest but for those of you either reactively depositing coatings or thinking about developing a reactive process this should be of great interest.

I recently went to work on a vacuum system that had been designed as a research and development machine capable of depositing coatings by reactive deposition. Typical coatings that the machine was designed for included titania, alumina and the transparent conducting coatings such as indium tin oxide (ITO).

The system had been designed with coating uniformity in mind and the pumping was arranged around the chamber along the centreline of the web path. The gas input was through manifolds that were similarly positioned to give a uniform flow across the width of the web. Thus the general arrangement of the sputtering and other deposition sources, pumping and gas input could be expected to give uniform films.

Needless to say the reason I am writing this note is that the coatings were anything but uniform.  Originally some ITO coatings were deposited from ceramic sputtering targets and these were reasonably uniformly conducting across the width and fairly easily optimised. However when it was tried to deposit ITO coatings from a metal target it was impossible to optimise the conductivity and when the resistivity was measured in more detail it became apparent that there was a different resistivity on each edge. When a minimum was reached on one edge the other was more than 20x higher and vice versa.

On a detailed review of the system, checking the symmetry of all the equipment it became obvious what was the cause of the problem.  The original design included a cryocoil in the winding zone to getter the water vapour from the roll of polymer and this too was uniformly distributed across the web to give uniform pumping. There was some work done on the best positioning of cryocoils/cryopanels in the vacuum system and having cryocoils in both the winding and deposition zones was shown to be better than having a single cryocoil in either the winding or deposition zone.  To take advantage of this information additional cryopumping was added to the deposition zones. Unfortunately at this point the symmetry was lost as the cryocoil was positioned on only on one side between the original pumps and the chamber wall. To make this worse as the coils were behind the sputtering sources and so could be expected to see some heat they were protected by being protected by a metal box.  The net result of this was that the conductance to the original pump was restricted on the side that had the cryocoil.

We know the end result was skewed pumping to the deposition zone such that the pressure at each end of the sputtering source would be different and so the requirement for reactive gas would be different. Hence, as the reactive gas was being uniformly introduced across the whole width, the optimum point to give the correct stoichiometry for a coating with minimum resistivity would be different at each end of the sputtering target. 

The solution to the problem is simply to change the shape of the cryocoil in the deposition zone to have an equal surface area on either side of the existing pumping orifice. This would reduce the volume the existing coil takes and so the protective radiation shield could be moved further back and so most of the restriction in conductance would be removed. Thus the uniformity would be returned and the pumping speed increased at the same time.

This has yet to be done to prove the above solution is correct as the work has to be planned and fitted into programmed downtime. However we are in no doubt that we have found the source of the non-uniformity and how to correct it.

I think this offers an excellent lesson on why it is essential to have symmetry about the web centreline for all aspects of the system and process.  Adding equipment that restricts the conductance only on one side of the web or adding additional pumping such as a cryocoil and placing in a convenient space in the chamber rather than symmetrically across the web can result in non-uniform coatings.  I emphasise that this will only be a significant problem for reactive processes. Although minor variations may be measured across the web in other coatings for most applications these are negligible.  When depositing ITO from a ceramic target, where some reactive gas is included to compensate for any dissociation during the sputtering process, the dynamics of the process are such that working with an excess of reactive gas is not as critical as it is with the full reactive process converting a metal target to the desired compound.  Hence the non-uniformity of the coating will be similar to plain metal coatings rather than full reactive deposition.

Although it is less important to have symmetry of pumping in metal deposition it will become increasingly important as the width of deposition systems continues to increase. Already we have machines of 4.45m wide. If these are pumped from one end only imaging what the pressure difference will be from one end to the other. This pressure difference will become greater and greater as the width continues to increase and this will be seen as producing different deposition rates from resistance heated boats at each end of the system.  A simple solution is to pump from each end although there will still be a pressure gradient from the web centreline to each edge.  A better solution would be to distribute the pumping across the whole width. It is worth noting that as customer specifications continue to increase, particularly for high technology applications, it can be expected that there will be an increasingly tight specification for resistivity which may require an improvement in system symmetry.

As you might have guessed this is a hobbyhorse of mine. I have worked on too many systems that were never designed with symmetry in mind but were expected to produce coatings by a reactive process that have been a major challenge. Mostly the difficulties could have been eliminated by better design making the processing much easier and the productivity of the system much higher. Thus I find it disappointing that even on new machines I still see some of the same design errors.

Problem re. Ink adhesion to metallized film

In fact we first laminate the metal side of METPET in to 1.5 mil Polyethylene film using solventless adhesive of Liofol 7980/7275.
Once it is cured, in second process we surface print on PET side of the structure.
Following is the final structure from outside to inside:
                                        OPV (OVER PRINT VARNISH)
                                        INK
                                        PET SIDE (OF METPET)
                                        METAL SIDE (OF METPET)
                                        ADHESIVE (SOLVENTLESS)
                                        POLY SEALANT FILM
DEFECT:
        The ink adhesion is good but with slight twist of the film the ink is released from the PET showing Missout and a kind of pinholing showing metal.
        This happens mostly in shipping and in handling the package at customer plant.
       
        If we try to separate the layers, the metal is released from the PET but the do not delaminate with Poly sealant layer.

       How to have 100% ink adhesion on PET of METPET?

Forgot to mention one important information, sorry.
The metal on METPET is on the corona treated side.

Answer

It sounds as if the possible problem is the same for the ink as for the metal.

Corona treatment is helpful to a certain extent but is a variable treatment.  When PET is manufactured there is always some residual unpolymerised material left in the polymer. This oligomer is low molecular weight and is easily able to migrate through the polymer and it will appear on the surface.  The amount on the surface will depend on the age and storage conditions of the polymer roll.

If untreated and left on the surface both the ink and the metal will bond to this oligomer, which forms a weak boundary layer, and will have a poor bond strength.

Corona treatment will improve this bond but has limitations.  The corona treatment needs to be optimised and also it needs to be done immediately before coatings are applied.  The corona treatment varies with humidity and so what might be optimised on a dry day with low humidity may not be optimised for a very humid day.  The treatment is also not a permanent treatment.  The oligomer will still be present within the bulk of the polymer and with time and/or temperature it will migrate back out to recontaminate the surface. 

Thus if the corona treatment is done before the metallization on both sides of the PET the metal adhesion may be at one level but as the film will have been heated during the metallization process the back surface treatment may already be recontaminated by the time the film leaves the metallizer. Similarly if the lamination is done using heat there will be a further migration of material to the PET surface.

The indication you have given is that the ink is printed onto a surface that has not been corona treated. Thus the ink adhesion could be improved using a corona treatment before the printing.

I personally would not rely on the corona treatment for the metallization but would consider using a plasma treatment within the metallizer, if at all possible, so that the treatment is immediately before the metallization and there is less chance of re-contamination. I would also use an oxygen containing plasma to make sure that I removed as much organic contamination as possible. An argon plasma has no mechanism for removing organic material. It just knocks material off the surface which can re-deposit on the surface. Oxygen will convert organics into volatile species that can be pumped away by the vacuum pumps. Also the oxygen will form bonds on the surface that will also form bonds with the aluminium and increase the bond strength.

If you cannot carry out a plasma treatment but only have corona treatment as an option I would make sure the process has been optimised and would check that this has been optimised at different humidity levels.  I would also make sure that the time the roll is stored between corona treatment and metallization is minimised again to minimise the time for recontamination. 

Re-contamination occurs by two processes one is the migration of material from the bulk as mentioned above and the other is by transfer of material from one surface to another. Bear in mind that, as the back surface has not been treated, the low molecular weight, and often low surface energy material on the back surface will be brought in contact with the high surface energy front surface as the film is re-wound. As nature tries to equilibrate energies it is preferable for some of this low energy material to transfer from the back surface to the front surface.

This is the reason for minimising the time the film is standing between corona treatment and metallizing.

Hopefully this explains a possible source of variable adhesion and some options to correct the problem.

Request for source of coating polymer film

I have been looking for a product/manufacturer that exists because I have seen it but, for some reason, cannot be found anywhere in the USA nor does anyone know who can even make it.

Here goes .. I need ·

Optically transparent film · 4 mil in thickness ·

Anti-reflective coating but is able to reflect 30% of the visible light that strikes it to cut down on ghosting (along the i-line frequency) ·

Very low refractive index ·

Up to 4 meter wide rolls in any length

This will be used as a large HUD display for a show we are putting on. The film will be used like a large teleprompter.

Answer.

Let me start with some of the easier bits.

4m wide rolls.   This may be a problem. Specialised film tends to be manufactured in limited widths. The reason for this is the volume of manufacture. A large manufacturing machine produces a huge amount of product that all needs to find a home. With specialise film there tends to be a limited market and so volumes are small and so there is less justification to invest in a large machine.

This also applies to vacuum coating machines. The largest produced so far has been 4.45m width for a simple aluminium metallizer which runs a limited range of materials at high speed. The aluminium is deposited with a thickness of a few 10's nm with a uniformity of +/-10% or with additional shields +/-5%.

The optical coating you require is much more specialised and so requires multiple sources and this tends towards magnetron sputtering where the largest with is only around 3m, again for a single metal system or more usually less than 2m width for multilayer coatings.

Thus you may find it hard to source the polymer at 4m width, it depends if it can be made on the same manufacturing system as a higher volume material otherwise the width will be limited.  Once you have the film you may be further limited to the width of the vacuum coating system available.

My starting point would be to approach some of the expert vacuum coating companies.

Flex Products Inc (FPI) & Optical Coating Laboratories Inc (OCLI) who are both part of JDSU based in Santa Rosa CA are experts in designer optical multilayer coatings. OCLI have >20 years of designing specialist AR filters as used in many exotic applications and can model your optical requirements and what coatings you need to achieve the desired results.  I know they have experience in HUD technology. OCLI make small optical components whereas FPI are the flexible substrate division and operate the polymer film vacuum deposition roll coaters.

If you want a contact, the senior scientist at FPI is Roger Phillips  (Roger.Phillips@jdsu.com) who may be able to help you, if only to discuss through the problems.

FPI have to make money and so it may depend on the volume of material you want that determines the time they can spend on the project.

Most of the magnetron sputtering roll coating companies will have some form of the thin film modelling program that can predict the materials and coating thickness that would be required to give you the filter you require. They may also have the same quantity limitations that might limit the chances of getting the coating done.

An alternative strategy might be to use a narrower web width of a thinner material and laminate panels to make up the larger dimension final product. (just a thought)

Other vacuum roll coating companies that are worth contacting would include CPFilms ( hassan.memarian@cpfilms.com) or Bekaert Speciality Films (gary.phillips@Bekaert.com)

One other person to contact who may be a help to you and much closer to home would be Don McClure.  Don, until recently, was a senior scientist with 3M and is an expert on vacuum deposition and has worked on many optical coating products including AR's, controlled reflectance, filters,etc. He also has expertise in film manufacture and has a wealth of knowledge on speciality films such as low refractive index films.  He has set up a consultancy business since retiring from 3M (acuityct@hotmail.com )

If you make contact with any of these people I would welcome you letting them know that I have directed you to them so they can thank/blame me as appropriate.

I hope the above is of use.  If none of the contacts proves to be of use please feel free to come back to me and I will do what I can to help.

Barrier performance and storage time

Is the barrier performance of properly stored metallized film affected by ageing ?
When should the barrier properties of metallized films be checked ?
Immediately after metallization or after ageing (time)?

Answer.

The barrier performance can change with time. Particularly for aluminium metallized film. The aluminium will gradually be oxidizing and so the OD might fall slightly with time and so to the barrier might change with time.  Also the adhesion might change with time dependign on the adhesion, any pre-treatment and the contant of the polymer. If the polymer has residual oligomers or slip agents included and the adhesion is not optimised these low molecular weight materials can exude to the interface and reduce the adhesion. If you have reduced adhesion there is an increased possibility of loss of aluminium due to movement of debris on the surface or pick-off to the back surface either of which can cause the barrier performance to degrade.

The safest time to measure the barrier performance is immediately prior to shipping as then you will have the best idea of what your customer is going to receive. Your values may still not match their values because they too may store the material for another period of time or they may rewind it before measuring and rewinding gives another opportunity for debris ot pick-off to produce more pinholes and hence further degrade the barrier measurement.

I hope this helps.

Coating onto rolls and ‘dots’ on film

We have a 2450mm metallizer.  In this m/c there are 03 steel roll which comes in metal side contact after main chilled drum. When we are doing higher od > 2.5 we have seen that some dots are visible on metallized film under tubelight.  We have also noticed that all three metal side contact roller are found with thin layer of metal on surface. We are cleaning in every cycle with di-chloromithen & soft cloth but still this problem persist even in bottom of metallized roll. Please advice us how to resolve this issue. We have no post cooling roller. Roll length is 36000 to 55000 mtr.

Answer

To comment on the dots I would first need to know more about the spots that you see on the metallized surface. Such as, are they present from start to finish on the whole roll, are they across the whole width or mainly close to the centerline of the web, how large are the spots, when you illuminate is this in transmisssion or in reflection, do you see them as a discoloured spot or simply as a thinner OD area?

It is hard to try to diagnose what might be happening without more information.

Regarding the metal coating on the metal rolls. I would check out a few things. One is to check that the rolls are shielded from the deposition source.  The sources are shielded from the winding system but there has to be a conductance path to allow for pumping between zones. Just make sure that any of these conductance paths are not in positions that could allow the rolls to be coated.  This is unlikely but needs to be confirmed.  Next to check is on the metallized film if you look at the metal surface under a microscope is there any evidence of surface scratching in the winding direction?  This scratching might not be continuous but just occasionally across the web.  If you find this type of scratching it could relate to speed changes in the winding. Metal coatings on metal rolls tend not to have a high grip and so it is possible that at speed changes there is slip of the web against the rolls. As the aluminium is at this point very soft it is possible that the rolls are abrading some metal off the web.  If all the rolls are driven this may not be very likely.

Evaporated aluminium is not fully dense and the there will always be some material that is not well adhered over several kilometres of web it only takes a few atoms per sq mm to accumulate into a more noticeable amount of material on the roll.  Metal rolls being so much harder will be in much harder contact with the metallized web than any of the polymer/rubber rolls and so it is possible that the high spots on the roll surface are contact welding to loosely bonded aluminium on the web and picking the aluminium off. This is not enough to necessarily pick off all the aluminium and cause a pick-off pinhole. The thicker coating will mean the coating surface is leaving the deposition drum and arriving at the metal rolls hotter and so softer than it would on thinner coatings.   

The spots and the metal on the rolls may not be related. This depends on the size of the spot defects amongst other things.  In asking where the defects start I am trying to understand if they are possibly heat related.  Over the length of the deposition cycle the heat load increases. Although the cooling drum may have sufficient cooling to remain at a constant temperature the surrounding shields in the deposition zone will increase in temperature and will radiate to the drum and the winding zone and the whole system temperature increases. Thus if the defect appear only from part way through the deposition run then it is likely that it is temperature related. If the spots are tiny then they may be related to pick-off.  If the spots are larger they may be more related to a liquid contaminant or residue.   

I hope these thoughts are helpful.

What is an acceptable shelf life?

What about the shelf life? Is there a standard or specific number of months to follow for VM.Is there a reference in the industry that we can follow?  Some say the shelf life of Laminated VM in slit rolls is only 6months, others say 1 1/2 years. Which is the safest shelf life to follow considering that we are in the Philippines?

Answer

As far as I know there is no standard for shelf life.  Again it comes down to storage conditions, control and the type of polymer film.  If the polymer film has few oligomers and additives, has been optimally plasma treated to have high adhesion and then is stored in a controlled atmosphere then I see no reason why it should have degraded much over a year, or more.  If the polymer is the cheapest possible grade that may have a higher oligomer content or a grade that has slip agents added, has had a simple surface treatment and then is stored in an uncontrolled environment where overnight and peak daytime temperatures and also humidity are varying then even 6 months may be a problem for some films.  Similarly the final use may play a part. If the final use is less stringent the tolerance is likely to be greater than a very exacting final application.

It may be that when I post this problem on the Blog that somebody replies with some further information.  I will aim to post this either Friday of this week or first thing next week and so we will see if anybody adds a comment.

So if anybody has some information on any standards that define the Shelf Life of metallized films please write in, I am sure that there are many who would be interested to know of them.

Laser slitting

Some scientists doing a survey of technologies available for cutting spotted a trend. This same trend was seen in a variety of different industries.  All started off with mechanical cutting using metal blades.  The trend was that as the technology improved they moved from metal blades to technologies such as high pressure water jet, plasma torches eventually ending up with laser cutting.  This has happened in such different industries such as cutting fabrics through to cutting steel.

So the question I ask is why do we still cut polymers with metal blades?

The answer I have always received is that it is too expensive.  Whilst this might have been true some 20 years ago the costs of lasers has fallen considerably and I would challenge that this is no longer the case.  The other component of this cost was that lasers were regarded as unreliable and not suitably robust for production.

So if we now disregard the cost and reliability as red herrings and just misinformation put out by those who do not want to consider the option what are we left with? Well polymers are transparent and to get the laser to cut the light needs to be absorbed by the material. As many polymers have absorption bands in the Infra Red (IR) it simply dictates the type of laser required is one that works in the IR so that it is best suited to coupling into the polymer.

I have seen dyed and metallized polymers that have been diced into 25 micron or 50 micron squares but did not get the details of the laser used and it was not clear if the metal layer or dye helped the process or not.

If we go back to the issue of cost, yes lasers can be expensive as a capital cost but the running cost is low by comparison to metal blades that need to be removed and re-sharpened periodically.  When was the last time you heard of a laser needing sharpening?  For those who are slitting large mill rolls down to customer required widths there will be plenty of down time spent removing blades and changing the spacing of blades to produce different width rolls. Think how much easier this would be with lasers that may change width at the touch of a button. Using mirrors to control the position it is possible to very rapidly change the cutting pattern. This also represents a considerable improvement in productivity of the slitting machine and makes for a reduced running cost.

One of the major problems in slitting with blades is the quality of the cut edge. The edge can be good when the blades are sharp and well set but if the setting is wrong or the blade worn the slit edges can become poor with raised edges, hairs or even tears that can cause winding problems.  The raised edges may not be much of a problem winding at atmospheric pressure where air can be entrained between the polymer layers but when in vacuum there is no entrained air and the rolls are much harder and so the raised edges becomes much more of a problem.  It can push the film to one side or even in a very high edge fold over the polymer making the rewinding even worse.  Laser slitting can leave a clean edge and because the laser does not blunt it will be as good throughout the lifetime of the laser.

A second problem that can come from slitting and that is the generation of debris that as the polymer can generate an electrostatic charge is often attracted onto the web and so poor slitting can lead to more pinholes.  Laser slitting vaporises the polymer and so although the process is not without debris the size is much finer and is more easily pumped away using vacuum extract.

Hence I would be interested to see some work done on improving the cleanliness of the polymer film also include laser slitting.  As history has shown, as mentioned above, other industries have moved from blade slitting and all have eventually ended up with laser cutting. Thus why go through all the intermediate steps, save all the development time and costs and go straight to laser slitting.

I look forward to someone taking this up and I am convinced that whoever is first to do this will have a considerable advantage because of the more consistent edge quality and better cleanliness leading to fewer pinholes in metallized film.