Vacuum Web Coating

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.

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.