Vacuum Web Coating

Costs will rise – the squeeze is on.

Everywhere I look there are papers on the ‘Carbon footprint’ and either asking or describing what is being done to change things for the better.  However this does not appear to be as easy as was thought.

As we all will have seen the cost of energy is rising. There has been a very steep rise in the price of crude oil from less than $20 / barrel through to in excess of $120 / barrel. This impacts the coating industry in many ways.  The costs of energy used to produce the raw materials, the raw materials used to make the polymer films as well as the energy cost to metallize the films means combine to make the cost of metallizing significantly more expensive this year than it was last year and with every expectation that it will be more even more expensive next year.

In addition to the cost of oil there is also the competition for materials that is also driving the price upwards.  As China and India grow so quickly there becomes an imbalance between supply and demand for materials that in the free market results in price increases. Also as economies prosper the workforce want to benefit from the prosperity and wages rise.

Thus there are a number of predictable reasons for prices to rise sharply and continue rising for some time.

In addition to this there are the variations that arise from the way the market reacts to the changing economics.  One example of this is the move to bio-materials.  It is possible to grow crops that can be used to create energy, either directly as a fuel or to produce an intermediate that can be used as a fuel. It is also possible to grow crops that can be used to produce polymer films.  As the cost of oil rises there has been a rush to plant crops to produce either fuels or films.  Unfortunately this has had some unusual effects.  Farmers have switched crops quickly from whatever they used to produce to new crops to service this growing bio-materials market. As this switch has been uncontrolled it has resulted in food shortages and this has force up the price of food. Thus it is equally as likely that farmers will switch back as quickly to capitalise on the higher food price. Thus, until there is some control over the type and quantity of crops planted, it is likely that there will be a series of price fluctuations depending on changing quantities of crops planted.

There has also been a significant increase in the amount of land being cultivated and the effects of this have not yet been seen. It is however predicted that the irrigation of crops will increase and this will lower water tables such that water will become scarce and the costs of this will rise too.

So is there anything to look forward to, I hear you ask yourselves. Well, yes, I think there is, although this too might depend on your viewpoint.  The Middle Eastern States have combined to build the largest chemical complex in the World. This is intended on taking their own oil and processing it into all the downstream products that is often done by their current customers.  As the oil is running out they are intent on diversifying their economy to take advantage of what remaining resource they have.  They plan to build refineries to produce ethylene and propylene amongst other materials.  Already they have industries gearing up by either buying new production facilities or by buying existing businesses to later expand.  As this expansion means that some polymer films will be made close to where the oil is produced and refined it should mean a reduction in some of the shipping costs.  This increase in production may also mean that there is likely to be a glut of material for a while this too could result in a reduction of some film prices for a time.

This article is just scratching the surface of what is a complex subject that I am sure will have many more surprises to come.  The reason for my raising the topic is just to make sure that everyone is aware of the trend and expected changes to come. This will hopefully give everyone time to plan what actions they are going to take to help minimise the impact of such changes.

New machines vs refurbishment?

At the AIMCAL Fall Technical conference it is intended to have a discussion on the above topic. In my time I have heard passionate arguments for both sides of the question.  Some have bought a second-hand machine and refurbished it without problem and have done so at a cost much lower than they could have bought a new machine.  Others have done the same thing but have been less successful with the costs of refurbishment being much higher than predicted and the time taken to obtain working system much longer that it would have taken to specify and have a new machine built.

Where it becomes easier to argue the case is for a completely new process. Here, unless the process is so similar to the existing process, it usually means that any second-hand system is going to be not quite ideal for the process. Anything that is not quite ideal is likely to be a real problem for production. It usually means that the operators are always fighting to make the process run well which is time consuming and costly.  So the trade off here is between the reduced capital cost with higher running costs versus the higher capital cost and reduced running costs.  The difficulty here is to accurately predict the real running costs. This is where experience tells me that is many of the systems I am aware of that have tried to force fit a process into a machine that was not designed for the process have always been significantly worse and most companies, with the benefit of 20/20 hindsight, given a second chance to chose between anew machine and a refurbished machine would opt for a new machine.

Similarly some companies have chosen not to use one of the regular system manufacturers to build their system and this can add to the build risk.  Any company that is building a system for the first time potentially adds to the risk involved. You may have to pay for their learning experience. This may be found as a longer than normal list of small faults in the system or it can be something more major depending on the experience they have and what mistakes they have made.  This all takes time and money and although the initial price for the system may seem attractive the final cost may end higher that buying from the most expensive established supplier.

If you have a metallizer that is getting old and less productive it can make sense to consider progressive updating of the system. There is still a risk that an old system will still have some problems such as fatigue failure of welds that can cause a vacuum leak but the same is true of any system.  In future this upgrading process may happen more frequently, at least for the control systems, because of obsolescence of the electronics. If the metallizer has been in the same company for many years there will be a history of the failures. This may be used to plot the type and frequency of failures. This can be an indicator of what parts of the system could be upgraded and show the best cost benefit. Whatever fails most frequently or with a high frequency and cost a lot to repair or causes most downtime would be high on the list of items to improve or replace.

So as you can see there are plenty of arguments both for improving existing machines as well as for buying new machines.

But that is just my view, from the outside, as a consultant.  What are your views?  Why would you choose to either buy a new machine or buy second-hand or refurbish?  I would like to hear of your experiences of what went well or what went badly that has coloured you view of which route is best to go down.

I will also report back after the AIMCAL Fall Conference in October with a summary of what was presented in the discussions there.

Vacuum coating Journals and Magazines

This is my plea for help regarding sources of information on vacuum processes.

We are familiar with a number of magazines and journals that cover different aspects of vacuum processing. This would include titles such as

Paper film & foil converting

Packaging

Vacuum technology & coating

Compound semiconductor

Journal of vacuum science & technology

However what we do not know is what are the magazines and journals that have a specific distribution on other areas of the world.  I am sure that there will be titles that are read much more that any of the above that are published specifically for an audience based around the Indian subcontinent. Similarly I would expect that there would be others that are directed towards the Middle East and the Oil States.

It would help if we could learn more about these publications and so this is my request.

Could you please send me details of the magazines or journals that you regularly read?

Ideally this would include the Title as well as any contact information that is included.

If you could e-mail me directly with this information I would appreciate it.

Thanks. CAB   e-mail    cabuk8@btinternet.com

AIMCAL Fall Technical Conference call for papers

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.

Web Cleaning - Tacky rolls update

I was recently at the SVC annual technical conference where I listened to a paper given by Sheila Hamilton about the Teknek tacky roll technology.  I have long been enthusiastic about this technique for removing debris from webs or foils and think that it is underused within the vacuum coating industry. 

The process uses an elastomer roll that is in contact with the web surface where debris is removed from the web and sticks to the tacky roll. This process can remove debris of size down to 0.3 microns.  This is a simple process but effective.  As you can imaging webs have a high debris level and so it would be easy for the tacky roll to quickly become clogged with debris and thus lose the effectiveness as the tacky surface is covered in debris. To recover the tacky surface this roll is usually in contact with a roll with a higher tack that accumulates the debris. This roll will also become clogged but it is like an onion, built up of many layers that can be peeled off revealing successive layers of high tack surface.

As most pinholes are caused by debris being coated and moved after metallization the reduction in debris levels is an easy way of reducing the number of pinholes in the coatings.  As with any cleaning technique it is important to do the cleaning at the correct point in the process as well as to consider cleaning both sides and not just the side that is to be metallized.

If the roll of material is to be cleaned on a winder before it reaches the metallizer but if this is done it is important that the web is kept clean following the use of the tacky roll.  As polymers winding over rolls produces an electrostatic charge the web can attract airborne debris and so it is critical that between the tacky roll and rewinding the web is kept in a clean environment such as under a positive pressure clean air hood or, if the application demands it, in a cleanroom.

One approach I have been advocating for a number of years now is to incorporate the tacky rolls into the vacuum system. I have tried to encourage vacuum system suppliers to develop this process but the progress has been slow. I know that some companies (2 in the Far East & 1 in Europe) have incorporate the process and I now hear that Ulvac have started to offer systems that include the tacky roll. There are limitations though.  The systems they have added it too are all ones where the roll length is short and so they do not have to peel off layers from the high tack roll and this considerably simplifies the process.  Until this automated peeling process is developed to be robust for production so that the roll length can be increased to the long lengths used in modern metallizers I expect that these roll will only be used on the higher technology processes where roll lengths are short enough and the webs already clean enough that neither tacky roll becomes clogged by a single roll.

However I regard this as encouraging. Many people did not believe that the process would work well in vacuum. It is interesting that the elastomers were developed with the space programme in mind and so the problem of outgassing and loss of tack had already been addressed and was not the limiting factor that some expected.  Reports of some tack rolls ‘drying out’ are probably as a result of having them exposed to the plasma cleaning process, which because of the continual bombardment of the surface will break bonds on the surface and degrade the performance.  This is simple to prevent by suitably shielding the plasma from the tacky rolls.  I say simply but I suspect that if you want to add the tacky rolls as a retrofit item then space will be limited and shielding may be more difficult. New machines will be able to be designed with this in mind and suitable shielding should not be a problem.

Another piece of information that I was not aware of before is the high temperature use of the tacky rolls. The elastomers are stable o high temperatures and have also been used as a cleaning roll for hot embossing shims.  These embossing shims can pick up debris, oligomers, additives or fillers as the come in contact with the polymer surface and these can accumulate in the grooves of the metal shim reducing the quality of future embossing. Cleaning the shim is always an issue. Some use release agents to lower the shim surface energy and prevent this pickup but this can transfer onto the polymer and make the subsequent coatings hard to adhere to the surface. Thus the tacky roll method of cleaning has an advantage of cleaning the shim but not adversely affecting any subsequent adhesion.

So as you can see my enthusiasm for this tacky roll technology has not been diminished but has rather been endorsed with the news of the first machines being sold with this technology included.  I am still convinced that it is only a matter of time before this process is available for metallizers and for those wishing to produce pinhole free coating will be an essential part of any new metallizer specification.  I suspect that this process will be speeded up if any of you who are considering buying a new metallizer start to ask is the tacky roll cleaning available in the metallizer.  If the machine builders get enough people asking about this technology they will speed up their development to make sure it becomes available to meet their customer needs.

Until then watch this space & I will periodically report on progress.

Delamination problem

In adhesive-laminated 3-ply structures of reverse-printed PET:metPET:LLDPE sealant web, the typical structure failure mode is often peeling of the metallized layer away from its base substrate, even when high adhesion metPET films are used. Some competitive & comparable Japanese and European 3-ply structures do not exhibit this weak peeling or decaling

failure mode, exhibiting outer PET film tear instead (i.e. 'destruct' bonds).

Is this adhesive technology related?

High corona treatment of the metPET?

Can you explain?

ANSWER

Getting high adhesion metallized film can be problematic, particularly as measuring the metal adhesion can be difficult to do well.  Often the only adhesion test done for metallized film is the 'tape' test which is a very poor test which only allows you to eliminate the poorest metallized coatings. 

Part of the problem is the tape test has many variables such as the age and type of tape used, the humidity when the tape was manufactured as well as when it was used, the pressure used to apply the tape and the speed and angle of pull when it is removed, etc.  Thus the test has huge error bars and cannot prove very high adhesion but can only show very poor adhesion.

Corona treatment is used to improve adhesion by increasing the surface energy which improves the wetting if the aluminium as it nucleates and the coating grows.  The corona treatment may not be a reproducible process as it too can be affected by the humidity and so the adhesion can be better in some seasons than others.  The corona treatment also declines with time. The speed of this decline is dependent upon and additives in the film and the temperature of storage.  If there are any additives, such as slip agents used to reduce the coefficient of friction to improve the handling characteristics, these will be contained within the bulk and will migrate to the surfaces as too will any low molecular weight oligomers. These will reduce the surface energy back to the starting level. The higher the temperature and the longer the time the more the benefits of the corona treatment will be lost.   Also as the front surface has a high surface energy immediately after corona treatment it will be energetically beneficial for any low surface energy, low molecular weight material to be transferred from the untreated back surface of the film to the front surface whilst the film is rolled up. Again the longer the film is stored in the roll the greater the opportunity for this material to be transferred again losing the effects of the corona treatment.

If the film also receives a plasma treatment before metallization it may be that the surface becomes over treated.

In general it is beneficial to have a plasma treatment before metallization to correct any reduction of surface energy because of newly migrated or transferred material.  However it is also possible to over-treat the polymer film surface.  It is preferable to optimise the pre-treatment process. If this includes corona as well as plasma treatment then both processes and the length of time between the two processes needs to be optimised as a total item.

If the pre-treatment is gradually increased it will be seen that the surface energy increases up to a maximum and this then plateaus at the high level. If, however, we also plot the adhesion we can see that it initially follows the same path and increases with increasing treatment. However once the maximum is reached instead of remaining high at the plateau level the adhesion immediately starts to decline with any further increase of power or treatment time.

What is happening is that the treatment that causes scission (breaking) of the polymer chains to produce new bonding sites which are often occupied with oxygen which can bind better to the aluminium.  This scission process reaches an optimum in binding sites but any further treatment continues to break chains and this results in ever shorter chain fragments. This finally results in a carbonised layer that is a very weak boundary layer and, although the aluminium may be bonded to it, the adhesion to the polymer bulk is poor because of too many short polymer chain fragments.  The chemical composition stops changing and so the surface energy remains constant at the high level but the adhesion falls away.

Thus for your laminate I would start by reviewing the whole process starting with the polymer film, checking to see if there are any additives included to improve the web handling. I would then go on to check the consistency of the corona treatment, the storage time and conditions of the film following any corona treatment. I would also check if there has been any plasma treatment as well as corona treatment and check to see if the process has been optimised for the film.  (Sometimes the conditions have been set using a different film and it is assumed the same treatment can be applied to other films - and this may not be the case).

I hope this explains what might have been happening and possibly gives some way forward to sorting out the problem.

Patterned vacuum metallization for RFID tags?

At a recent conference in Cambridge UK one presenter stated that of the 1 billion ID tags to be produced this year of which more than 95% would be printed.

This figure is expected to increase with time.

If you take 5% of 1 billion and then divide again by something like 2,500 which is the number of 2cm x 2cm devices per sq m the answer is very few sq.m of vacuum coated film would be required.

If you do not have an oil printing system already fitted to your vacuum system and are considering fitting one you will be looking at potential markets.  Much has been spoken about RFID tag antenna as a possible market for simple metallised aluminium films for the ‘cheap & cheerful’ end of the market but in reality this market may already have disappeared.

If I were considering adding pattern metallizing capability I would not be including RFID tags as a possible product as I would regard it as chasing a diminishing market. 

What do you think?

Answer

You are correct in your thinking.

There are many designs of antenna and some of these are much larger than the 2cm x 2cm  and so the area required could be greater than you calculate but even so the area of metallized product would be low.

There is a lot of development work going into improving the conductivity of the printing inks.  The polymer matrix has been improved as well as the addition of conducting fillers have both increased the ink conductivity such that either higher conducting circuits can be made or thinner printing can be used for the same conductivity as earlier ink compositions.

This improvement of conductivity of the inks has further reduced the need for vacuum metallized RFID tags.    It is only where the very highest conductivity circuits are required such as for long distance interrogation of the tags which requires a high response signal that either metallized or metal foil laminate tags are required.  So even here metallized products are not the only product. Metal foils can be die stamped to make the circuits and for low volumes this is a competitive technology to vacuum metallization.

Similarly there are other circuits, such as solar cells, where circuits are needed that it has been suggested are suitable markets for metallized film but these too are now being integrated with printed conducting ink processes to eliminate this vacuum process from the manufacturing line.

Thus I would regard any printed circuit application as at best a temporary market opportunity and would hesitate to include this market in any investment application.

A problem of un-metallized streaks

I would like to inform you that we are receiving metallized BOPP film from outside and facing the problem of unmetallized streaks on the surface which is more visual after the lamination to other printed substrate. This sort of defects we are getting normally and have made complaint and also claim for the rejection due to this defect. I am requesting you to pass the information why the unmetallized streaks appear on the surface to some part of the metallized BOPP film.

Answer

Unmetallized streaks.

It would be interesting to know more about the unmetallized 'streaks'.

Are they irregular in shape or parallel stripes?

What is the size of the streaks?

To me the word streaks suggest the streaks are anything from a few centimetres in length to a meter or more and irregular in shape.  Is this correct?

How wide are the rolls? 

What position are the streaks found, are the randomly anywhere across the whole width, and do they start immediately on the roll, are they found throughout the whole roll or are they only found part-way through a roll?

One possibility is that during metallization the heat load is close to causing the web to balloon off the cooled deposition drum. As the web sees the heat load from the deposition source the polymer wants to expand and if this expansion is too much the web buckles off the drum and if not controlled this will result in a 'tramline or railroad line'. This is seen as a parallel stripe of material that has a thinner coating on it. The thinner coating is because as the web lifts off the deposition drum the polymer expands and thus the surface area is greater than it was when on the drum and so the same depositing metal has to cover a larger surface and so the coating is thinner. Also the temperature is likely to be higher and so the sticking coefficient of the aluminium will be lower and so not all the metal will stick and this further reduces the coated thickness.

If these thinner coated sections appear and disappear this may be because the process is just on the knife edge of too much heat. A little more heat and the web would permanently lift off the drum and a parallel line would be established and possibly lead to a wrinkle in the roll.

All aluminium coatings oxidise. The thickness of the oxide layer can depend on many things including deposition rate and coating structure.  The thinner deposition area will have a lower deposition rate and so will have slightly higher oxygen content and also because of being thinner the surface oxide will potentially have a greater effect on transmittance than on the thicker areas.

Often the areas where wrinkles or tramlines appear are after the process has been running for some time and the heat load has gradually increased over time. Also they tend to be towards the centre of the roll. Near the edges of the polymer web it is possible that any expansion of the polymer web can overcome the polymer to drum friction and the web slips laterally on the drum and so relieves the lateral tension. However in the centre of the web the friction is too much and such expansion is less likely. Hence of ten the tramlines are only seen in the centre section.

Thus my questions about where the streaks are found within the roll help me to diagnose the probable cause of the defects. 

I hope this answer helps explain what might be occurring.

Moisture & metallizing

Does moisture affect the metallization of Aluminium? 

We laminate Metalized polyester with PEG coated paper and metal peel off.  Once the oxidation starts in metallization will it destroy the whole metal with passage of time or not?

Will metalized MPET will be oxidised if we laminate it with PEG coated Paper.   The ratio of PEG coated paper is 80% PEG and 20% water.  We observe white spots in metalized paper.  Please try to find root cause and suggest us what measures can safe us.

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.

Boats and spitting

What causes spitting from evaporation boats?

ANSWER

Generally spitting is associated with changes to the pool shape and size.  The boat temperature needs to be stable and this not only means the current and voltage need to be stable but also the wire feed rate needs to be stable.

It can be easy to find that the thickness monitors respond to thickness changes and change the wire feed and this correction may be too much and the thickness monitor then re-corrects for this change with a further change. This can appear as an almost continuously changing wire feed rate. This will mean that the molten pool will be changing size and shape. The oxide from the surface of the aluminium wire, as well as any impurities, will collect as a skin or crud on the surface of the molten pool and often will collect around the edges of the pool. This collection of material is what usually is ejected and seen as spits. As the pool size changes this material either covers a new area of the evaporation boat or is left stranded on a drying part of the boat and can be thrown off as a spit.  Thus maintaining stability is regarded as the key factor in lowering the number of spits, assuming all other things are the same.

There can be other factors that also contribute such as the age of the wire, as older wire may have more oxide on the surface, and the purity of the wire.

One of you questions refers to MOC of the boat.  I take this to mean method of control?  If so you need to check the capabilities of the machines and possibly their history. If the machines are of different ages they may not have equivalent capabilities and so the same control process may not be available. If the machines are nominally identical it may be that they were used by different teams for completely different products that had different requirements and so different control methods were adopted for the different products on the different machines.  This could account for the original differences and if they now produce the same product these methods of control may simply have been continued on because that is what the operators are most familiar with.

The performance and feed rates can be calculated using the equations that are given in the AIMCAL Metallizing Technical Reference 4th Edn. book.  This is available from AIMCAL and most companies that are members of AIMCAL have copies. However if you need on if you contact AIMCAL at www.aimcal.org they sell then at ~$25 each + postage and packing.