Vacuum Web Coating

Question re. Lamination bond strength.

One more question to you that is we are facing problem of less bond strength especially when the metalized film is laminated to other substrates. So to get more bond strength what we have do please advise and if it is not possible please tell us that why we cannot get good bond strength.

Answer

The bond strength after metalization can be time dependent.

It may also be dependent upon the substrate and processing.

Assuming you are referring to BOPP as per the previous questions.

Often BOPP contains additives such as slip agents that are added to the bulk polymer and which are designed to migrate from the bulk t the surface. These slip agents help make the polymer film more easily handled on winding and packaging machines by lowering the coefficient of friction.  Unfortunately this reduction in coefficient of friction generally means the surface energy is reduced and this reduces the metal adhesion. To combat this reduction in adhesion it is common to use flame, corona or atmospheric plasma treatments or vacuum plasma treatment to increase the surface energy to improve the adhesion and wetting of the aluminium.

The additives do not discriminate between surfaces but migrate to both surfaces equally. Thus when the metallized film is re-wound the freshly metallized surface will be brought into contact with the back surface of the film that has the low surface energy slip agent present. The freshly metallized surface has a very high surface energy. It is the nature of things that surfaces try to reach equilibrium at the lowest surface energy state. Hence there is a high driving force for the low surface energy slip agent to migrate from the back surface onto the freshly metallized surface. Thus reducing the surface energy and in so doing reducing the adhesion of any subsequent coating or laminate.  The longer the time and the higher the temperature between metalization and subsequent process the more material will have been transferred and the lower the surface energy and so the expectation of adhesion should also be lower.   

It may be worth reviewing you process to see if you have a consistent time between metalization and lamination. Also, if you are storing the rolls of film, review if the time, temperature and humidity are controlled.  It would also be worth checking the surface energy of the film both immediately after metalization and then over time to monitor the progression of reduction of surface energy.

Assuming the above explanation allies to your situation then what you can do to rectify the problem would be to laminate as soon after metalization as possible. In this way you can minimise the time available for any low molecular weight material to migrate across to the metal layer. This may still not be acceptable as it is also common for film to be wound in vacuum systems still warm (well above ambient temperature) and so there may still be enough time for material to migrate.  If there is still a concern over adhesion then it is always possible to treat the metal surface immediately before lamination. Using either a corona or atmospheric plasma it is possible to clean the metal surface and raise the surface energy to increase the wetting and adhesion of the laminate.

I hope this explains what might be happening to your film.

Fillers and coefficient of friction

The answer is totally different from what we practically experience. When filler is added in the film the CoF increases. Second thing is that with lower CoF value, problem of Delamination or weak lamination observed.  In fact for good bonding we always require CoF value more than 0.35 of the film surfaces which is to be laminated with PET. Kindly send your comments on that.

Answer

There are generally two things that contribute to the Coefficient of Friction (CoF). The first is the surface roughness of the two surfaces and the second is the surface energy of the surfaces.

If you polymer has additives included that reduce the surface energy, such as by the inclusion of slip agents, the CoF can be as low as 0.16 – 0.2 (starting CoF for LDPE can be as high as 0.7)

If your polymer has no additives but depends on fillers to reduce the CoF it is typical that the lowest CoF that can be achieved is only 0.3 – 0.4

Thus if you have a polymer that contains a slip agent and has a low CoF and then has some fillers added it is possible that the CoF increases as the contact between the two surfaces changes from being over most of the surface to only contact at the peaks of the fillers. On the top of these peaks the contact pressure will be high and so the benefits of the slip agent will be to some extent nullified.

The adhesion that you obtain will largely be dependent on the surface energy of the polymer surface. What happens with the addition of the filler is to increase the surface area and so this will lead to an increase in adhesion simply because the load is divided by a larger surface area and so per unit area the load is reduced.

It should be possible to further increase the adhesion by plasma treating the surface to remove the effects of the slip agent and so increasing the surface energy and wetting and bonding of the aluminium.

I hope this explains the differences you see.

What topics would you like to see?

I have been writing items for this blog for some time now and have covered many topics such as adhesion, plasma treatment, pinholes and winding problems.  I did occur to me that there may be readers out there who are hoping I will address a topic that so far I have not covered.  If there is anyone out there who is in this position please resopnd to this and let me know what topics you would like me to cover.  Although many of the items have been related to aluminium metallizing the remit for this blog is also to cover other technologies such as sputtering, electron beam deposition, plasma enhanced chemical vapour deposition, etc....

Failing any response I will continue to post items that take my interest or are as a result of answering a question submitted to 'Ask AIMCAL'.

I look forward to your requests.

Web Processing for Barrier

Coming soon is the AIMCAL training course on 'Web processing for Barrier' below are some more details.

This course provides an overview of the technologies that can be applied to deliver barrier materials for markets such as food packaging, display, and photovoltaic (solar) applications. Initial discussion focuses on the fundamentals of diffusion and permeation to provide an understanding of the contributions and limitations of materials and processes. Advanced topics include newer technologies such as nanotechnology, scavengers, and indicators that result in "smart" materials.

Course Outline

• Introduction
  • The Basics of Barrier
  • Markets
• Terminology
• Techniques and standards for barrier measurement
• Materials
  • Performance
  • Blends and laminates
  • Nanomaterials
  • Selection
• Smart/active packaging
  • Indicators
  • Scavengers
• Technologies
  • Film making and extrusion
  • Coating
  • Lamination
  • Vacuum deposition
• Substrates, surfaces and quality
  • Relating materials and surfaces to barrier
  • Pre-treatment (wetting, adhesion)
  • Cleaning and barrier
  • Variation in barrier during processing

Who will benefit from this course?
Anyone working at facilities that convert or use barrier materials including engineers, designers, quality control, stability and production personnel.

FEES: Course Registration Fee, Hotel and Room Rate information for each date are available using the date links below.

Dates for this course:
| June 12 - 13, Philadelphia, Pennsylvania

Vacuum Technology & Coating.

I would like highlight the above journal which for those of you with internet access can be viewed at either www.vactechmag.com or www.vtcmag.com

In the March 2008 edition (Vol 9, No 3) there are a couple of articles that I think will interest many of you.

The first is one of the ‘Guides to vacuum technology’ and is ‘Outgassing – part 1 Desorption of molecules from surfaces’ by Luke Hinkle   This article starts by defining outgassing as being one of 4 phenomena comprising 1) surface desorption, 2) Contamination evaporation, 3) Diffusion from the bulk or 4) Sublimation.  The article then goes on to outline a ‘battle plan’ to minimise the problem which consists of two parts the first is to reduce the presence of water on surfaces and the second is to stimulate the molecules to assist them leaving the surface.    The article then goes on to describe the options for preventing the original absorption of material on the surfaces such as by venting using dry air or nitrogen.  To speed up the removal of any material there are various options such as baking the system, using ultra-violet radiation or bombarding the surface with energetic ions.  Water is held onto the surface by a binding energy approximately 100 times greater than its average thermal kinetic energy.  In the normal course of events the water molecule once attached to a surface can experience thermal agitation that is, in general, insufficient to free it from the surface.   The use of any of the above methods of adding energy increase the thermal agitation and more of the molecules will shake free of the surface. 

This gives a flavour of the article which goes into much more detail.

The second article is ‘Plasma Chemistry’ by Abe Belkind & Kurt Becker.  Virtually all vacuum deposition processes make use of plasma cleaning and in addition there are an increasing number of plasma enhanced deposition processes and plasma etching processes.  As such this article could well be of great interest to many readers for a wide variety of different reasons. The article gives a detailed description of the chemistry that occurs within a plasma including the formation of ions and radicals in all their different forms.  The article then proceeds to describe how the plasma can be used in a number of these different applications including some other non vacuum applications such as ozone generation for water treatment or as used for car exhaust cleaning.

Although this article may not change the way you use the plasma on your own system it does at least explain how the chemistry occurs and what the limitations might be.

Costs will rise – the squeeze is on.

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

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

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

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

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

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

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

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

New machines vs refurbishment?

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

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

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

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

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

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

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

Vacuum coating Journals and Magazines

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

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

Paper film & foil converting

Packaging

Vacuum technology & coating

Compound semiconductor

Journal of vacuum science & technology

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

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

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

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

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

Thanks. CAB   e-mail    cabuk8@btinternet.com

AIMCAL Fall Technical Conference call for papers

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

   

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

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

Visit the AIMCAL Website to submit your paper.

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

Vacuum Web Coating Process optimization and preventive maintenance in the vacuum web coating processes Leading edge roll to roll technologies, products and markets including flexible displays, flexible semiconductors, superconductors, thin film battery, flexible solar cells, super barriers, film sensors, anti-counterfeiting films and papers, OLED, holography, and solar control  Machine and equipment accessories upgrade cost / benefit Advances in substrate technology Advances in process control and measurement Patterning and edging of vacuum coated films and papers New coating processes, tools and equipment Advances in barrier performance, process and measurement Atmospheric Web Coating and Laminating Web Coating Technology related to applications and fluid rheology Process Measurement including coating weight, defects, viscosity, process modeling Laminating processes including alternatives to laminations, process optimization, web variability, modulus, guiding and tracking Coating Operations: An overview that compares/contrasts various coating techniques, roll coating systems, slot die/curtain coating techniques, extrusion coating, coating thin on metallized films, toll coating Substrates and liners technology including new technology and performance, innovations, and applications Web coated product markets - technology and market overviews Specialty Web Coating Novel or developing web coating technologies Nano coating technology Photovoltaics technology Developing web coating technologies and markets Specialty substrates and coatings technology RFID technology A session on Market Trends in the Converting Industry is being scheduled. Topics of interest are global market and technology trends, future role of converting process in growth industries and integrating product development through the supply chain.

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

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

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

Visit the AIMCAL Website to submit your paper.

Web Cleaning - Tacky rolls update

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

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

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

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

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

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

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

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

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