Vacuum Web Coating

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.

Question re. lamination problems.

We are doing water-based lamination with metallized BOPP film we also do it with metallized CPP film. However when we do adhesive lamination with BOPP we find problem of corrosion i.e. water attacks metallization layer. We have a doubt that the composition of metallized layer being coated on CPP is different than that of BOPP as they are from two different suppliers. Could you please guide us that what could be there in the metallized layer that is so hydrophilic that it does not allow moisture to evaporate?

Answer.

Cast PP and Biaxially Oriented PP differ where the PP is a mixture of amorphous and crystalline material. The orientation process can result in some alignment within the polymer of the crystalline material. This alignment changes the performance of the polymer is all sorts of ways including tensile performance and also permeation performance.  It is likely that the moisture barrier of the BOPP is better than that of CPP.  This might be a contributing factor.

What you do not mention is what the thickness is of each of the materials and this can also be a factor.  The barrier performance of any material is thickness dependent. Thus, if the CPP and BOPP are of different thickness then this too could affect the performance.

Similarly if the metallization thickness is different in the two samples then this too could result in a differing barrier performance.  Keep in mind that if the materials are metallized by different suppliers there may also be other differences in the metallized layer.  The faster the rate of aluminium deposition the smaller will be the crystal size of the aluminium coating. If the metallization is done at different pressures this too will result in differences within the coating. Higher pressure will result in a less dense coating and lower permeability for the same thickness.  Measuring the coating thickness and also the Optical Density (OD) of each coating will give an indication of how similar the two metallization processes are.  If the thickness were the same but the OD different, or the OD the same but the thickness different it would indicate there are differences in the metallization process. If both thickness and OD are the same, or very similar, it would indicate the metallization processes are also similar.  Another difference could also be in the quality of the coating as described by the number of pinholes per unit area.  The higher the level of pinholes the greater the permeability of the coating as well as the greater the number of starting points for any corrosion.  The surface roughness of the substrate can also affect the nucleation and growth of the aluminium and hence the barrier performance. The higher the surface roughness the worse the barrier performance is likely to be.  Other factors that could affect the corrosion of the metallized film are the temperature and humidity conditions seen by the roll of material.  If the metallized film is re-wound hot, as in greater than 30 deg C, in the metallizer it is likely that the aluminium coating will grow a thicker oxide more rapidly than if the temperature at the re-wind is closer to ambient, generally less than 30 deg C.  After metallization if the rolls are stored in a high humidity atmosphere they will hydrate the aluminised film and lead to more rapid oxidation than if stored in a low humidity atmosphere. Adhesion is another possible factor that could have an effect. It would be expected that the system with the lower adhesion to suffer from higher permeation and more likely to have a greater propensity to corrosion.   I would normally expect the metal to CPP adhesion to be lower than that of metal to BOPP.   

I would suggest that measuring the barrier performance, OD, metal thickness and adhesion of each of the metallized materials before lamination would be a useful comparison. 

I would expect that the barrier performance of the BOPP would be higher than that of the CPP thus making the removal of the water from the adhesive slower than for the CPP.

I hope that this gives you some points that you find useful in helping solve this problem.

Problem with low bond strength

We are metallized film with plasma by applied a 3.0 to 4 kW power. We are

using 1200 sccm of oxygen & 400 sccm of argon combination.

With above combination we are facing problem of low metal bond strength in

metallization done on corona treated side film.

If we try to increased the power of plasma more then 5 or 6 kW, plasma get

tripped & unable to start for next 15-20 min.

I would like to understand that at what power range will give best metal

adhesion?

We are doing metallization on 12 mic with 2.65 optical density. Maximum

width of metallization is 2450mm.

Pl reply with possible cause of low metal bonds, cleaning frequency of

plasma, gas combination & rate of gas, power etc.

ANSWER
pre-treatments are one of the most frustrating parts of the process because it can be so variable, often varying with changes in the weather.

Corona treatment is aimed at increasing the surface energy of the polymer film. So too is the in-vacuum plasma treatment.

Using either or both of these processes there are three possible outcomes.

1.    The treatment has little or no effect and the adhesion is little better than with no treatment.

2.    The treatment delivers a higher adhesion.

3.    The treatment has some effect but sometimes the adhesion is worse than using no treatment.

The pre-treatments are used to do a variety of different things to the.  It can be used to help remove loosely bound material from the surface, also low molecular weight material that has migrated to the polymer surface can also be removed or carbonised or cross-linked into the polymer surface, also the polymer surface can be chemically modified to enhance both the wetting and adhesion.

What you are trying to achieve is a maximum value for the surface energy. However a simple measure of the surface energy can be misleading for the following reason.  There will be a surface energy associated with the untreated polymer film. Now as the pre-treatment is done the surface energy should be higher than the untreated film.  As you have a roll of material optimising this process should be done quite easily by winding material through and progressively increasing the power to the corona treater or in-vacuum plasma treater.  It is then possible to measure the surface energy at each power level.  What you should see is a progressive increase in the surface energy with power to a point where the surface energy levels off at some maximum value.

       It is this maximum value that is misleading.  If you also plot the adhesion of a coating or metallization it will follow a similar curve except that where the surface energy levels off and continues with higher powers (or longer treatment time) at an almost constant high value, the adhesion instead of levelling off it reaches a peak and then almost immediately falls off with increasing power or treatment time.

    The reason for this fall off of the adhesion is that the surface of the polymer has been overtreated. The treatment is often a balance between chain scission that generates new bonding sites and aids adhesion and the scission that creates new short chain molecules that are short enough to be weakly bonded into the bulk polymer and hence form a new weak boundary layer. If the power is further increased these short chain molecules tend towards carbon molecules, thus the weak interface is made up of an excess of carbon even if high oxygen content plasma is used.

The use of corona and in-vacuum plasma can make it easier to overtreat the surface in some circumstances.

Often there is some time between the corona treatment and metallizing process. During this time it is common for low molecular weight materials to migrate back to the surface and re-contaminate the surface and so the in-vacuum plasma treatment is essential.  However if the same material is both corona treated and vacuum plasma treated in the same day it may be that the surface is overtreated.   Thus it becomes important not only to know what the treatments are but the time between the treatments can become equally important.

There are other variables that also need to be monitored and understood. The temperature and humidity can affect both the process and the polymer.  The corona treatment at the same power can produce different results when the humidity is high compared to when the humidity is low.

Winding the polymer in high humidity will trap more water in the roll than winding in low humidity. This is released in vacuum and will also vary the gas content of the plasma treatment process.

I am slightly surprised that the oxygen flow is so much higher than the argon.  Mostly I see argon being the larger flow and oxygen being somewhere in the 10% - 20% range.  The argon provides the heavy ions for doing the chain scission and the oxygen provides the bonding to the carbon by-products making then volatile and capable of being pumped away and also the oxygen will bond onto the polymer where fresh chain ends have been created which can also improve the bonding to the aluminium.

So for your problem I would start by checking the optimisation of the process. Making sure that the surface energy has been maximised but also making sure that the polymer has not been overtreated and that the surface has not been carbonised.

I would also look at the variability in the process. What are the variations in the humidity and differences in time between corona treatment and metallizing?  Look at the optimisation for a constant corona power but with highs and lows of humidity and time between processes. This should give you some idea how much the process can vary and what might be done with the vacuum plasma treatment to compensate for the variations.

I hope this gives you something to work with.

PET film haze

Is there any relation between Pet Film Haze with orientation of film or crystallinity or amorphousity?  Can we correlate HAZE with anyone or with all?

Answers

The answer is yes things such as crystallinity and haze are linked. The draw ratio of can affect the amount of crystallinity and in general the greater the draw ratio the clearer the film (lower haze) but this can then be worsened by the thermal setting process. The thermal setting allows the film to relax and helps reduce the problem of shrinkage but the longer the time or higher the temperature the more the film will relax and some clarity will be lost. (Bear in mind these may be quite small differences). If the draw is not equal in both orientations the crystalline regions within the film can be oriented and so there can be optical differences with orientation. This is most easily measured by plotting the refractive index with orientation. 

Similarly the polymerisation process, which affects things like the molecular weight can also have an effect on tensile performance which then affects the draw and so can affect crystallinity and haze.

Crystalline regions within the polymer are denser and harder and the amorphous material flows around these crystallites. It can be noticeable that cast film may be very clear but after the initial forward draw the film has more haze but after the sideways draw the haze reduces again.  This may be more noticeable with filled film. This is thought to be from crystallites or filler begin slower to re-orientate and so protruding through the surface and roughening the surface and increasing the haze. With the sideways draw this helps flatten then back into the film and so the haze reduces but possibly not to the low level of the cast film.   

I hope this helps.

Additional answer from Dilwyn Jones (AIMCAL Instructor in web handling)

Most thin gauge PET film (including that for metallizing) has a small amount (<0.5%) of inorganic filler, such as calcium carbonate, silica, china clay and glass bead, added to improve the handling behaviour both during manufacture and subsequent processing.  Without it, reels would telescope if wound at realistic speeds, and block during storage.  The composition, particle size and volume fraction of the filler are the main factors influencing haze.  Haze has contributions from both the bulk and the surface, as the filler particles near the surface increase the surface roughness.  There may also be particles that are so large they give individual optical effects, such as Newton's Rings, or visible marks in the metal layer.  Finally, voids form around some particles during the stretching steps of film manufacture, increasing the haze.

Stretching ratios, temperatures during crystallisation, and PET molecule factors such as glycol and IV have a smaller effect.

Without inorganic filler, there is still catalyst residue and internal contamination to scatter light and cause haze.  This is a mechanism in clear, thicker film.

A lot of the detailed knowledge on this is of course proprietary to the major manufacturers.  However, there may be examples in the patent literature especially, and the open scientific literature also.

Number of pinholes per unit area.

Is there a standard acceptable amount of pinholes per sq metre in metallized BOPP.

Also do you know anything about the possibility of 'welding' pinholes in metallized film by use of an electric charge?

Answer

As far as I am aware there is no standard that defines the grade of the film by the number of pinholes per unit area.  There are some figures quoted by aluminium foil manufacturers about the number of pinholes per unit are for foil and so the idea of counting pinholes is not unknown.  Possibly the reason for not bothering to count pinholes is that the barrier performance is not only affected by the number of pinholes but also by the size of the pinholes.  Thus a simple count of number of pinholes would not necessarily tell you what the barrier performance would be and films with the same number of pinholes could be radically different if one had large holes and the small ones.

Individual customers may have something in their acceptance specification about number of pinholes. This may be highlighted if the film is for an optical or graphic purpose but where it is for a packaging application the barrier performance will usually take precedent. Here the allowable number of pinholes tends to be either determined by the barrier performance as measured on a Mocon or similar instrument or something that is agreed between the metallizer and customer. 

There was a paper by Angelo Yializis that includes a bit about healing capacitor films.   If memory serves me correctly this is more about preventing shorting between layers than sealing pinholes.  If successive layers of metallized film are shorting out it is sometimes possible to pass a current through the film such that the current is too great for the short and so vaporising the metal and breaking the circuit at this point thus removing the short and recovering the full performance of the capacitor.

If you were thinking about closing the pinholes by welding a little bit of aluminium over the holes to block it up then 'no' I do not know of any process doing this.  If a fully opaque film is required then the usual approach is to double side metallize the film. The philosophy behind this is that the chance of two pinholes lining up to still show as a pinhole is negligible.  Double side metallizing is also used for high barrier films. Again the fact that holes do not line up means that and gas or moisture will have a tortuous path to diffuse through the film and hence the barrier improves.

Question re. Static.

Will the presence of static charge on the face material affect its surface energy? Since static charge is generated through friction, this becomes an unavoidable problem. But will this have an effect on the printability of the face material? Will the presence of dust particles cause the material to lose surface energy thereby causing poor ink adhesion? If so, is there a relationship between surface energy and static?

Answer

Static charge can be caused by friction, separation or induction. 

Of these, separation is the one that most affects winding webs.  As the two dissimilar materials are brought together the surface electrons are brought into close proximity to each other and it is possible for electrons to cross from on surface to the other and on separation for the electrons to stay with one surface rather than the other. In this way the polymer, which is negative on the triboelectric series can collect charge on leaving each roller. The larger the difference between materials in the Triboelectric Series, the greater the static charge that can be created on the material surface. In addition the faster the winding speed the greater the charge that can be built up.  The charge can be cumulative so that over a series of rolls the charge will increase after each one.  If winding in air the humidity will have an effect as water in the atmosphere affects the conductivity of the air. Higher humidity increases the conductivity and so will speed up the decay of any charge on a surface. It will also allow arcing to occur at lower charge levels.  Conversely a dry atmosphere is less conducting and the polymer will reach a higher charge before it can arc to discharge the surface charge.

When you wind film an electrostatic charge is already building as the film approaches each roller.  When the film winds around a roller it does not, in theory, move against the roller and so friction is less relevant.  As most rollers in your system will be metal and hence conducting they will be able to dissipate any static charge to earth and thus you only find the charge on the polymer film. 

Dust particles will be attracted to the surface because of the static charge on the film.

For those of you who disbelieve this have a look at any TV screen and wipe your finger across the surface and you will usually find a layer of dust on the surface that has been attracted to the vertical surface by the static charge on the screen.  Dust does not affect the surface charge directly. Dust cannot provide a leakage path to earth to dissipate the charge. It is possible that dust can form a slight electrical charge concentrator and so if the surface is going to arc to atmosphere it could be initiated at a dust particle rather than from the flat surface of the film.

Static charge and surface energy are separate factors.  The same static charge can be built up on the same polymer irrespective of whether the surface has been plasma treated to raise the surface energy or not.  However the presence of a static charge can affect ink adhesion and wetting.  If you look at ink jet printing the ink droplets are often electrostatically charged as part of the print control process. Also if you look at many modern painting processes these too are electrostatically charged, to improve the surface coverage. Both of these show that liquids can be affected by static charges. It depends on the liquid chemistry as to precisely what effect the charge will have. Liquids may be conducting, or not, each of which will be affected differently.

Thus the ideal would be to use static eliminators to neutralise the film immediately before printing but to have also treated the surface to increase the surface energy to improve the wetting and adhesion of the ink.

If you use a corona treatment before printing this will serve both purposes as the corona plasma has both electrons and ions and so will naturally neutralise the surface whilst also increasing the surface energy.

If the corona treatment is positioned on the machine well before the printing such that the film winds around rollers between the corona and printing stations then there will still some charge on the film at the point of printing. 

Alternatively static neutralizers can be used just prior to printing to reduce the effects of any built up charge.

I hope this helps.

CAB

Just to give you a flavour of the triboelectric series here is a list of materials starting with the electropositive materials and moving down to neutral and then to electronegative.

The farther apart the two materials (film and roller) are the greater the charge that can be produced.

TRIBOELECTRIC SERIES

Glass                                                  Electro positive

Nylon

Wool

Silk

Aluminium

Paper

Cotton

Steel         ------------------------------- Electro neutral

Wood

Hard Rubber

Nickel, Copper

Brass, Silver

Gold, Platinum

Acetate Fibre (rayon)

Polyester

Cling Film

Polythene

PVC

Silicon

Teflon                                                 Electro negative