Vacuum Web Coating

Strategic goal setting.

We all work better if we have a goal to aim at.  In vacuum deposition of coatings we can have our day to day or run to run goals of producing material that is within specification. However it is always worth having a longer term goal to aim for.  Often this can be presented from on high as a directive to increase profits or reduce costs or both.  Other times this can be an initiative simply to keep the operations team focussed on product improvement and preventing the quality slipping because of complacency or disinterest.

One starting point for taking action is to define the task and this requires setting the ultimate goal.  This might be producing a specific coating that meets a specification that currently is not possible.  If we then take this coating specification and compare it to what we can produce now we can look at the differences.  This is known as doing a ‘gap analysis’ and we can then use the difference between where we are now to where we want to be to produce a ‘roadmap’ of what needs to be done to bridge the gap.  This roadmap will define each of the necessary improvements and the order in which they need to be done to be able to achieve the goal of producing the desired higher specification coating.

I doing this process we also need to do a sanity check to make sure the effort is worthwhile. Hence we should ask the questions;

Are we in time?                      

Is it feasible?

Are there sufficient resources?

What are the potential showstoppers?

 

Any of these can mean the end result will be a disappointment. If the product ends up as a ‘me too’ product and does not command a premium, or there is a real technical reason why the product cannot be produced on the equipment available, or there is no budget to facilitate any required changes will all be reasons why the initiative can fail and this will be counter productive.  The aim is to produce a roadmap of something that can be completed and deliver a benefit. Not only does this achieve the desired improvement but it also helps team working and improves motivation of operators.

 

Continuous improvement can be more challenging than simply depositing coatings.

 

 

Air-to-air vacuum coating systems.

With the surge of interest in vacuum coating machines for the deposition of photovoltaic materials there has been the development of evaporation sources.  This has included those evaporation sources that have a very high material efficiency.  This type of source can offer opportunities to change the design of the vacuum system.  The source no longer needs to be brought to atmosphere after the deposition of each roll.  It is only the unwind and rewind polymer rolls that need to be changed.  This leads to the option of using load-lock chambers for the unwind and rewind rolls which would allow the main chamber to be held under vacuum during the roll change over.

There is a trade-off between the system cost of a more complex winding system and the load-lock design and the possible reduction in some of the pumping capacity as the main volume does not need to be pumped out as frequently and so it is usually allowed slightly longer pumping time thus requiring a slightly smaller pump set. 

A second design option is to go to an air-to-air winding system. This still uses a load lock for roll changes but there is no need to vent and pump any vessel around the unwind and rewind rolls.  However the pumping requirement is much higher as to get the film into and out of the vacuum system there is, in effect, a continuous air leak that has to be pumped.  The pressure is reduced as the film passes through a series of chambers. Each chamber is up to two orders of magnitude different to the adjacent chambers.  Thus not only the pumping system is more substantial but also the winding system has considerably more rolls included. The air-to-air systems, although it has attractions, may also have problems such as increased contamination as the air that enters the vacuum system continuously will contain airborne particles that can become pressed into the film as the film passes through the nip roll that restricts the quantity of the air passes into the system.  A second detraction that has been an irritation to a number of operators in the past is that of noise.  The velocity of the air is high and this can cause a continuous loud noise requiring ear defenders .

Both of these system options also allow the deposition sources to be kept under vacuum and hot during roll changes.  This can reduce the down time between deposition runs as there is no need to cool the source and then re-heat of which the cooling generally is a rate limiting part of the process.  There is usually a small reduction in temperature in order to slow down the evaporation rate whilst maintaining the bulk of the heat. This smaller temperature variation also helps in reducing any source temperature variations and can thus be of benefit in improving deposition uniformity.

As more of these different systems are built more experience will be gained and the designs refined with the best features retained.  The economics of the different capital cost and running costs can be evaluated and this may lead to changes in the design of metallizers. So do not be surprised if these is a new batch of air-to-air metallizers produced in the near future.

Deposition sources

There are changes coming in deposition sources largely driven by the new enthusiasm for high rate deposition for photovoltaic devices.

The photovoltaic materials generally have to be deposited to a thickness of greater than 1 micron and so the deposition process has to be fast.  Although some of the companies are using sputtering the more successful companies depositing the copper indium gallium diselenide (CIGS) materials are using evaporation.  The CIGS compound is evaporated from a series of sources of the individual elements enabling the compound stoichiometry to be graded through the thickness.  Although the compound has to be graded through the thickness the requirement is for the thickness and stoichiometry uniformity across the web to be precise.  Thus there has been work done to improve the stability of the deposition process and control the thickness uniformity. 

There have been two different approaches to the sources. One has been to develop the jet vapour source where the evaporation is done into an enclosed volume where all the internal surfaces are kept hot to prevent condensation and the exit slot is the full width of the substrate.  The internal vapour pressure evens out any evaporation variations so that the exiting vapour uniformity is very good.

The second approach has been to take existing high stability vapour sources that have well known characteristics and to use arrays of these sources to provide the uniformity.  The Knudsen source is the basis of this type of source.  The semiconductor industry has used this type of source for many years and it has been modelled extensively so that the interaction of multiple sources is well understood. The design of these sources has been developed and optimised so that the temperature is controlled to a fraction of a degree and so the evaporation rate is more precisely controlled than most evaporation sources. 

What becomes clear is that these sources could be adapted to the deposition of aluminium. The benefits of doing so would be not only that the uniformity of the deposition would be improved but also that the material efficiency would be significantly improved.  Currently evaporation from resistance heated boats can have an efficiency of anywhere from 35% up to more than 50% depending on the system design including source to substrate distance and deposition drum size.  The vapour jet source, in particular, can have a material deposition efficiency of greater than 95%.

Where these new sources are unproven is in two aspects. One is the replenishment of the sources. Neither of these sources has a replenishment facility. The whole inventory of material has to be loaded and heated at the start. This is because any feed process has to be done via a hole where vapour can escape which is not only a material loss, a cooling point and a possible problem through condensation of the vapour that could close up the hole causing feeding problems.  The Knudsen sources can usually hold sufficient material for several deposition runs to be completed.  This leads to the second area of process uncertainty which is that of source cooling.  At the end of the first deposition run the source needs to be cooled to a safe temperature for the system to be vented.  As these sources are designed for temperature uniformity they usually include radiation shielding which both limits the energy losses but also slows down the cooling because of this minimisation of heat losses. In the past gas quenching has been used to accelerate the cooling process.  In some systems the need for cooling the sources has been followed by using load locks for the un-wind and re-wind rolls with the main vessel kept under vacuum for the multiple depositions the inventory of the source can allow. As the material efficiency is so high the need for shield cleaning is reduced and so keeping the main vessel under vacuum is possible.

Another advantage of using this different evaporation source is that the range of materials that can be evaporated is increased.  It has always been one of the limitations of resistance heated evaporation sources that the range of materials is very limited.  Sidrabe have developed an alternative source where they extended the range of materials by using tungsten rods as the core of the evaporator and refractory materials for the enclosure.

I hope this gives a glimpse of what is coming. It may take a few years for these developments to filter through to the aluminium evaporators but it will eventually be adopted.  As the material efficiency can be improved so much the energy requirement can similarly be reduced and this will become increasingly important as energy process continue to rise.

Wrinkling - additional monitoring

Recently I was visiting a well known metallizer manufacturer and this was an observation that came from some of our conversations.

I had been looking at metallizers and thinking that in so many ways they had not really changed significantly in decades.  The basic wire fed evaporation source was easily recognised as working in the same way.  There have been changes behind the panels in that the power supplies are more sophisticated and power is applied better and more uniformly and similarly the wire feed is better than it was. 

I was looking round at things that make the life of the machine operator easier. One change stood out as being both simple and helpful and that was the view into the system.  I have lost count on the number of occasions where it would have helped in diagnosing a problem if I had only been able to see better into the system to look at different parts of the winding to see where winding problems were beginning.  Generally we had one or possible two windows to look through and possibly a strategically placed mirror added inside the system to give some view of an obscured part of the system.  This has all changed with the miniaturisation and price reduction of camera systems.  I had previously worked on a vacuum process for roll coating explosives where we controlled the system from behind a blast wall and so our only view of the system was via cameras. This made me familiar with split screen multiple view displays but even the 10 – 15 years ago the camera technology was still quite bulky and so these cameras were sited outside the system pointing in at various angles to give us the necessary vision.  This was never as much or as good as we wanted.   Now the cameras have become small enough that they can be fitted with easy within the system and cheap enough that it is possible to consider using many cameras within the system to give all the necessary views to help with diagnostics.  What is more it is almost as cheap to use colour cameras as it is to use black and white.  The same rule applies as ever it did and that is that it is critical the lens of the camera is protected from any stray deposition.

Thus it is now conceivable to have a view of the film as it comes off any high wrap, spreader or bowed roll as well as out of the metallizing zone. This means that identifying where wrinkles start should no longer be a guessing game. Our first thought is always that the deposition has caused the problem but there are occasions where that is not true and it is always expensive in time and money to be trying to solve the wrong problem.

Retrofitting is generally more problematic than installing during the system build but as most of this is just cabling this should not be too difficult.

So if this has persuaded any of you to retrofit some cameras or for those of you ahead of the game that might have already done so I would be delighted to hear how you have got on with them and if you have experienced any problems.

Question about pressure variation when using plasma treater

We have metallizer. When operating plasma treater there is a variation or rise in evaporation zone pressure throughout the metallizing cycle. Theoretically the pressure of winding should rise as plasma treater is located in winding section, but the winding zone pressure is not varying, what is the reason behind this?

Answer

This sounds to me to probably be related to a problem of cooling.

I would monitor any cooling systems that you are using. If you have different cooling water to the plasma treater, the deposition drum, protective shields and the evaporation boats I would monitor each separately. I would check both the input temperature and output temperature.

Typically once you have pumped out your system the residual gas is almost all water that is out gassing from all surfaces including from the unwinding roll from trapped air and from water contained within the polymer.  Once the roll is unwinding there will be an increase in the gas load because of the release of the trapped air as the roll keeps presenting fresh surfaces. 

As you suggest this is a fairly constant process and so you would expect everything to remain constant throughout the deposition run.

If you have a problem with a cooling system what happens is that initially everything is cool as the process has only just started and there may be a large thermal mass that has to be warmed up. If you are recirculating the water (or coolant, which may be a water /glycol mix or something similar) there is also the thermal mass of the water.  What happens is that the water passes through something that is heating up and so the water is heated up, but usually to a lower temperature than whatever they are passing through. The coolant then returns to the chiller that returns the coolant to a constant starting temperature.  If the heating load is higher than the chiller capacity you will progressively see that the coolant is no longer returned to the same starting input temperature but this temperature gradually creeps up.  As the coolant temperature creeps up it no longer cools as well as it ought to and so the internal surfaces become hotter.  If these surfaces have any stray deposition on them they will have a very high surface area and so can contain a lot of water. As the temperature increases water can be released from the surface thus raising the pressure.

Most systems have cryopanels that will pump away the water very well but it does depend on the water having access to the cryosurfaces.  It is common to see systems with only cryopanels in the unwind zone whereas it has been shown by Telemark Cryogenics  Ltd as presented at AIMCAL that it is better if the cryopanels are distributed across different zones.  The deposition zone will always heat up the web and internal surfaces more that anything occurring in the unwind zone. The deposition zone also has the greatest potential for having coated surfaces that can mop up very large quantities of water.

If the problem does not appear what the plasma treater is not used it could be that some of the cooling systems are linked and that it is only when the plasma treater is used that the chiller cannot keep the temperature low enough.  Even if the coolant systems are not linked the plasma treater does add another heat load within the system. It is possible that the hot plasma treater is radiating heat to another surface that is the releasing the water.

Another option is that the extra heat is reaching the cryopanel surface and that over time the surface of the ice no longer remains frozen but stays as a liquid with a correspondingly higher vapour pressure.  The cryopanels are always a balancing act as the core remains cold but the growth of the ice can affect the total capacity of the panel. If the water is released within the system very quickly the ice may be very porous and this is then has a worse thermal conductivity than if the ice was built up slowly and was very dense.  The dense ice will allow more water to be collected than the porous ice. If there is too much water within the system over time the ice will build up to a thickness where no more water can be condensed and so the system pressure will rise.

Finally it is possible you have a small water leak that is normally closed but under heating opens up slightly and leaks water out.

I hope this helps you sort out the problem.

To buy new or to buy second-hand and refurbish.

The purchase of a machine is a large event for many companies as the capital investment is high and it is important to make the right decision.  There has always been a discussion about reducing the risks.  One viewpoint is that by reducing the cost by buying a second-hand machine the business risk is reduced. There is an opposing view that by reducing the cost in buying a second-hand machine the business risk is actually increased as the performance may not match that of a new machine and the time for refurbishment may exceed that of delivery of a new machine as well as the risk of a premature system problem from an age related failure. 

            The decision can depend on many factors such as the availability of suitable second-hand machines, the availability of a company skilled in refurbishing vacuum systems, the process being compatible with the system or what compromises might have to be made as well as the cost and delivery comparison against buying from new. 

Metallizers are easier to refurbish than some of the multilayer deposition systems that tend to be more customised.   The changes and up-grades to metallizers tend to be small.  If you compare metallizers of twenty years ago to current ones they are remarkably similar.  There have been more changes in the electronics to power, monitor and control the system than significant large mechanical changes.  In fact in the future it is likely that everyone will have to regularly upgrade the electronics or more specifically the computer control of the systems as the chips & operating systems become obsolete. This would suggest that more companies will be more familiar with refurbishing systems and be less worried by the process.

            Where the risks appear in buying an old metallizer and up-dating it can be in things such as welds that may be flexed as the system is pumped down and brought back up to atmosphere.  These welds can fail due to fatigue failure over time and it is almost impossible to predict when one of these failures will occur. What is certain is that older machines are more prone to this type of failure than newer machines and therefore the risk of this type of failure goes up.  If this type of problem occurs it will appear as a leak and this will take time to trace and once found will require a skilled welder to rectify the problem.  This can cost the loss of time and possibly an amount of film produced with a lower reflectivity before the problem is diagnosed.  This risk has to be estimated and added to the rest of the factors. Often it is almost an indication of how optimistic the person is in estimating this risk as to how significant it is judged to be.

            Another factor tends to be the delivery time.  Often it is expected that a refurbishment will take less time than building a system from new. However this is not always the case as the system may need to be shipped to whoever is doing the refurbishment, fully stripped down, cleaned and re-built with appropriate changes. Until the system is stripped it may not be apparent how much needs to be replaced or repaired.  The shipping, stripping and assessment may take longer that simply getting acceptance of the drawings for a new machine and ordering the parts.  As metallizers are regular items many have fairly standard sets of drawings with only minor variations and so do not have to be designed from scratch thus saving a large amount of time.  I personally have been involved in a project where a number of people in one company had a preference for buying a second-hand machine and refurbishing but eventually were persuaded that buying new would be quicker and also cheaper.  In this case it proved to be the correct decision.  The system was so old that the refurbishment estimate came to more than the quote for a new machine and the delivery time for then new machine was also more than one month quicker.

            Vacuum coating machines other than metallizers that use other deposition technology such as magnetron sputtering, electron beam deposition or chemical vapour deposition have other considerations.  These machines are generally much more expensive that metallizers and so the accountants always are interested in opportunities to save money.  It is a great temptation to compromise on the performance and even the process to allow the purchase of a cheap second-hand machine.  Usually this is a very poor decision.  Unless the machine is meant to be a research machine, where there are few expectations of productivity and reliability, it is usually found that there are large problems in operating the system well and productivity is poor compared to a properly designed optimised system. Again I have had experience of having to run a process on a system never designed to run such a process and it was always a struggle to keep on top of the process and produce products within tolerance. The system was also much more difficult to maintain, both in routine cleaning as well as routine maintenance. Part of the problem was that there was not enough space to get easy access to different areas and components making every task slower and more difficult.  In the long term this was a much more expensive system because of the poor productivity, longer down time, and variable product.  The rule-of-thumb learning from this was that, more often than not, compromise costs money not saves money.

            It will be interesting to see how things change in the future.  As the prince of energy is rising rapidly it could be that the design of systems will change to save energy in the operation of the system.  Already companies are looking at different sources to change the collection efficiency from ~50% to > 95% which in effect halves the cost of metallizing as well as reducing the scrap from cleaning shields.  This type of change, when it becomes available, may not be easy to retrofit into existing systems and so the economics of refurbishing or buying new will be very definitely in favour of buying new.   Materials costs are also rising as it costs energy and hence more to mine and refine materials and so using materials in a more sustained way will become more important.  This would suggest that refurbishing would be preferred. One way of achieving this is for the system design to start with the expectation that the system will be continually upgraded every few years. This would require a better and closer collaboration between manufacturers and customers with long term contracts for the periodic upgrades.  This would however give the customers a route to any technology and process improvements so that they remain competitive for longer before each new system purchase. This will obviously change the business for the system manufacturers as they will have less income from system sales but interim income from system upgrades.

            What is very clear is that the costs of buying new will never be as cheap as it is now.  As energy costs continue to rise, which has the knock-on effect of pushing up materials costs and so increasing inflation and hence a rise in labour costs, so too will the cost of new machines. So if any of you are considering buying a new system the sooner the cheaper.

            As ever this is just my opinion formed from my experiences. I am sure others will have different experiences which give them a different perspective. Please feel free to post these experiences and your purchase preferences. It would be good to hear different views. 

System cleaning

System cleaning as a topic is raised from time to time but often for different reasons.  One of the common problems is the accumulation of stray deposition that is very porous and so absorbs moisture and because of the very high surface area of the porous material is easily capable of slowing down the pump down times.  In fact some use the slowing pump down time as the trigger to tell them when to clean out all of this stray deposition.  Other work differently and clean the system down as a regular event so that they are always minimising the pump down time.

There are other aspects to cleaning not least of which is the relationship between pinholes and cleaning.  If the stray deposition is cleaned off in-situ there will be a large amount of very fine debris produced.  This debris can settle onto surfaces and if left these will be stirred back up again during pump down and can become the cause of additional pinholes by contaminating the web and the rolls.  Even if the cleaning is not done in-situ the detachment of the shields can produce some debris and this too can end up as contaminant and result in pinholes. Using vacuum cleaners to reduce the debris can help but a physical wipe of rolls is advisable as a final action.  It is worth noting that even small details can affect the cleaning process. I have often seen operators use a cloth that they wet with a solvent by bringing the rag to the solvent bottle top and upending the bottle to wet the rag.  The effect of this is that the debris already collected on the rag gets washed into the bottle and the whole bottle of solvent becomes contaminated.  With time the level of contaminant in the solvent increases from the repeated wetting of the contaminated cleaning rag.  The better method of wetting a cleaning cloth is to use a dispenser that squirts some solvent onto the cloth thus preventing anything getting back into the bulk solvent.  Also using disposable wipes rather than prolonged use of the same cleaning cloth can be beneficial.

This might sound like a fine detail but not having clean roll can have a major effect on the metallization process.  Not only can the debris be transferred onto the web and result in pinholes but also if the debris is transferred onto the web but on the back side it can result in the web being lifted from intimate contact with the cooled deposition drum which can result in the start of tramlines (railroad tracks).  Work done by Mike McCann and Dilwyn Jones showed that it only took debris of a diameter of 5 microns to start a tramline. As the web is prevented from contacting the cooled drum it has a localised higher temperature which increases the thermal expansion which results in the web buckling and the formation of the tramline.  As it is impossible to see debris of such a small size it means that if you wipe any surface or roll and can see any contaminant on the cleaning wipe at all it means that there will be a huge number of smaller debris that you cannot see all of which potentially can cause problems.

So you can see how cleaning becomes important both for the removal at both the gross level as in the stray deposition but also at the fines level as described above.

Roller problem creating ‘starry-sky’ effect

We are facing a problem in our metallizer, the chrome coating of aluminium roller has been vanished and metallized side of film is directly touching aluminium and creating star-sky effect (metal chip-off / unmetallized spots), we have around 60 days to get new rollers so mean while could you suggest some option to cover aluminium roll surface to avoid this problem, we have tried to cover aluminium roll by cork tape, PP tape & Teflon cloth but we don’t get satisfactory results.

Answer

The 'starry sky' is caused by dirt on the web being coated and then moved following metallization.  The best way to improve this is to remove the dirt before metallizing. This will give the best solution and will not depend on the quality of the rolls after metallization.

If you cannot clean the film well enough then there are a couple of things to look at and consider. With the loss of the chromium coating to the roll the diameter of the roll will have decreased.  Do you know, by how much the diameter has changed?

How is the chrome roll driven?

If the roll is driven by a motor the speed of the roll will be determined by the winding speed of the web and the diameter of the roll. If the roll diameter has changed then it is possible the speed of the roll is now slightly wrong compared to the web speed. This will mean that instead of the web being in contact with the roll but not moving relative to the roll surface it will instead be moving at a slightly different speed to the web and so will be much more likely to slide or roll any of the surface debris away from its original position leaving behind an unmetallized hole that you see as a 'star'.

If you know precisely the diameter of the roll then you should be aiming with any replacement covering to also bring the roll to the identical diameter.  If the covering makes the diameter too small or too larger it will still have this slipping action and will generate 'stars' by moving the debris around. The closer you get to matching the original diameter the less slip there will be and so fewer 'stars'.

If the roll is not positively driven but is tendency driven by the web then part of the problem will be the differences in contact pressure and coefficient of friction. Materials such as Teflon will most likely have a much lower coefficient of friction and so will tend to slip against the web more than the chromium with the higher coefficient of friction. In slipping over the surface it will move the debris around and create the 'stars'.  So in this case what you are really looking for is a material that is similar to the chromium in terms of surface finish and coefficient of friction. 

A starting point would be to look at the damaged film under a microscope.  Look at the 'stars' that have been formed.  Check to see if they are similar around the whole circumference or if there is any evidence of some debris being moved. If there is evidence of the debris being moved make a note of the amount of movement and the direction.  If the debris has slid rather than been rolled there will be a slide mark and this will give you an idea of the distance moved.  If you measure a number of these from different positions in the roll it will give you some indication if the slipping is happening throughout the roll or only at speed changes.  A driven roll of the wrong diameter is likely to produce damage throughout the roll; a tendency driven roll may only produce damage where there are speed or possibly tension changes.

If the damage is throughout the roll then if all the damage is of a similar length it will also give an indication of how short the circumference is and so what diameter the roll needs to be increased to to prevent the relative movement.

I hope this helps.

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.

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.