Vacuum Web Coating

Vacuum Deposition onto Webs, Films, and Foils

Vacuum Deposition onto Webs, Films, and Foils

by Charles A Bishop

1 Month to go to publication. Due out 22nd Dec.

ISBN13: 978-08155-1536-4

Publisher William Andrew Publishing

sales@williamandrew.com

This new book from William Andrew Publishing is the only practical reference available for anyone employing the roll-to-roll deposition process. Vacuum Deposition onto Webs, Films and Foils is an expansive journey of the process; benefiting manufacturing efficiency, unit cost reduction, and financial results. It is a sweeping approach to the total design of the vacuum deposition process written by a successful and world renowned consultant with three decades of experience.

Roll-to-roll deposition processing is a high growth industry and this reference covers a wide variety of important industrial products that use vacuum deposited coatings, including: optical storage devices, metallized packaging films, energy conservation windows, electronic information displays, and magnetic electronic article surveillance (EAS) tags among many others. This book is a must-have for roll-to-roll machine operators, process engineers, and research and development engineers throughout industry. The book provides a broad appreciation of roll-to-roll vacuum deposition systems and processes. It will encourage a more comprehensive look from material supply through to the downstream processes that the product will encounter. It is a truly unique reference written to guide operators and engineers as an onsite consultant would.

Substrates, the cost of oil and price rises.

            In my career I have worked within a polymer manufacturing business.  My abiding memory of the business was that when the business was good it was very good and when it was bad it was dire.  What was termed ‘good’ usually meant there was a global lack of capacity and so price rises could be made and they would hold and so profits would be great.  This state usually lasted until everybody invested in more capacity and then there became over capacity and the price would fall and profits would disappear into losses until capacity once again approached a balance.

            On average the business made a profit but this boom or bust existence meant a very erratic working existence. In good times I would be able to travel and attend conferences, buy new equipment, instigate research projects and maybe even recruit additional staff. In bad times everything shut down, travel was banned and no new equipment was allowed unless it gave a cost reduction in film manufacture, staff numbers were reduced, sometimes by natural losses and other times by compulsory job losses.

            At one time there were less than a dozen key film manufacturers of these half could be regarded as worldwide suppliers.  Over time there was rationalisation of these bigger suppliers but at the same time there was also a massive increase in the number of smaller manufacturers entering the market.  Some of these were buying second-hand equipment from the big players and although the technology was old and the machine efficiency was low the running costs were also low and the labour costs even lower.  Other market entries were subsidised strategic investments by various countries that either regarded the material as a strategic material for other business growth or a method of reducing import costs.  Some of these subsidised companies produced sufficient material that they exported it and as their costs were subsidised they were able to offer it at low process depressing the overall market prices.  There were several court cases of polymer film ‘dumping’ that lasted many years.

            The world is changing yet again.  Apart from the volatile cost of oil, which has seen around a threefold to fourfold price increase in a year, there is also the wish by many of the oil producing countries to want to get the added value out of the oil by entering the downstream manufacturing businesses.  Similarly China wants to be self sufficient in film manufacture instead of a net importer and so they too have been investing like mad to get enough machines installed to achieve this.  This massive increase in capacity does mean that the supply will outstrip demand and the prices should fall.

            Currently the film prices have all be rising for almost all of the past year. It is only now that some of the prices appear to be levelling off or declining slightly. However this is also running up to Christmas when it is common for companies to de-stock and require less material because of the holidays taken, both by the manufacturing workers but also by their customers. Hence it is uncertain if this is the end of all the current run of film price increases or if they will again rise after the New Year.

            Naively I thought that this type of price increase (20% - 25%) would provide a trigger for companies to start switching away from oil-based films towards biopolymers of various types.  To some extent this has occurred but nowhere near as rapidly as I was hoping for.  This might be because of my over optimistic nature but also because of a number of other factors.  The supply of the biopolymers is limited because the size of manufacturing plant is small because existing business is small and also the price is high, again because of the lower volumes.  Until they have more customers they will not invest in bigger manufacturing plant to help make the volumes available and gain the price reductions from the larger scale.  The other part of the equation I had not really thought through is that many of these biopolymers are energy intensive in their manufacture and so although the raw material is not oil based the energy to process then is and so their manufacturing costs have risen exactly the same as the oil based polymers and if the energy for manufacture is greater the manufacturing cost will be greater too and this will make reducing the costs harder to achieve.

            The one thing I am certain of and that is if I thought the market was erratic and difficult when I was part of the business I am certain that it is more difficult and unpredictable now than ever it was then.

I do not know about you but I shall be watching the developments of film price with interest and also will be trying to follow how the markets move from one film towards another as the relative prices change with costs and volumes.

Ink Jet for in-vacuum patterning - a look at the feasibility

            Currently, in vacuum the most widely used patterning process uses either direct or offset gravure coating.  Thus if you want to change patterns it requires the gravure roll to be changed and hence requiring a break in vacuum. Using Ink Jet printing would only require a change in the software signal & so different patterns could be done on the same roll without breaking vacuum. Either by successive ink jet print heads or by winding the web backwards & forwards it would be possible to start building up mixed polymer/metal circuits.

            The world of electronics is working hard to make better use of ink
jet printing techniques to produce a variety of electronics. Many of these processes
are aimed at being used to deposit onto web-based substrates.   The developments
are aimed at producing finer line-widths as well as depositing the structures
at line-speeds compatible with other processes. Ink jets can deposit not only inks but monomers, filled sols or even metals.  Thus, with a little imagination, one can envision multilayer coatings being produced on webs with different patterns overlaid and with mixtures of materials. 

At the current AIMCAL Fall Conference one of the papers looked at the feasibility of using ink jet printing in vacuum.

The research shows that ink jet printing in-vacuum is possible. The state of the art ink jet printing can produce 3 micron lines and 3 micron spacing and the writing speed using multiple nozzles and heads, is in the same ball park as some of the slower vacuum deposition techniques such as sputtering.

There is still much work to be done to optimise the surface treatment to give the best compromise between adhesion and wetting and this is likely to be very system specific.  I would expect that changing any of the ink, print head manufacturer or substrate would require the process to have to be re-optimised.

One company has produced thick copper circuits using in-vacuum ink jet printing.  This is at the coarse end of the technology but does confirm the feasibility.

Allowing that much of the development work still has to be done it looks to be feasible to be able to print regular arrays of dots, a criss-cross of lines or a variety of other patterns suitable for controlling nucleation as well as making a variety of devices.  Thus the technique should open up more opportunities in the area of nanotechnology for vacuum coated products.

Biodegradable packaging

I have my own question that I am interested in getting answered regarding the newer films that are being sold for biodegradable packaging.

Most polymer films can be degraded by ultra violet light. Am I right in thinking that for the biodegradable films this is a critical part of the biodegradation mechanism?

If so my next question is what happens during plasma treatment where the plasma is a source of high intensity ultra violet light?  Does it start or accelerate the degradation process or does it cause yellowing?

I know that some of the rigid polymers do yellow during plasma treatment but as they are them metallized the yellowing is hidden and the adhesion requirement is not to onerous to achieve.

The same might be true for metallized film depending which way the films is used. However much of this film is aimed at the transparent barrier packaging newer markets where the water white clarity is required and so yellowing is an issue.

I look forward to your replies.

 

Is there a correlation between the CoF and Haze?

The Coefficient of Friction (CoF) is a measure of the energy required to make one surface slip when in contact with another with a given pressure applied.  The friction between two surfaces depends upon the chemical composition of the surface, the
contact surface area and the force applied. Thus in your case the material is OPP, the load applied is a constant and so the only thing to change is the contact surface area.  Typically the way this is done is to use a filler to change the surface roughness. The polymer will only contact at the peaks of the rough surface.  Thus for an unfilled surface there is generally the maximum surface contact but as the surface is flat the haze is at a minimum. As the amount of filler is increased the surface roughness will increase reducing the CoF but increasing the Haze.  This correlation is not perfect
as there can be changes in the shape of filler used, the type of filler and the size distribution that can be optimised to give the best combination of reduced CoF and minimise the increase in haze.

Synthetic silica is often used in OPP to give a good combination of transparency and handlability.  This tends to be a premium filler and natural silica is also used as a lower cost filler as is talc or calcium carbonate.

Typically the haze increases by 0.4% - 1.0% per 1000ppm of silica filler used. Good handlability often requires the CoF to be less than 0.2 whereas the use of fillers generally will only reduce the CoF down to the 0.3 - 0.4 level and so slip additives are then added to the polymer to provide a low surface energy component at the polymer surface. BEWARE this slip agent reduces the CoF and is also a low haze component BUT it also reduces the metal adhesion and the polymer has to have a good optimised plasma treatment to remove or stabilise the slip agent on the surface to be metallized to make sure the adhesion is also optimised.

If the CoF is reducing with time it is likely that you already have some slip agent added to the polymer (or some other low molecular weight material) that is migrating to the surface with heat/time.  If the polymer has been flame, corona, plasma treated this material may have been removed from t he surface but with time more is diffusing out of the surface and is recontaminating the surface bringing for the CoF.

Sputter target bonding technique with a difference!

            Once upon a time in my history I helped convert a research laboratory process into a production process for the manufacture of a pyrotechnic material.  The end product we were aiming for was the enhancer pyrotechnic for inclusion in airbag systems for cars.  Thus I have more than a passing interest in any process that uses similar energetic materials.

            The latest that has come to my notice is this one from Reactive Nano Technologies (www.rtnfoil.com) who have developed and manufacture a foil product than can be used for the soldering of sputtering targets to backing plates.

            Bonding target material to backing plates is a specialised process. In theory anyone can do it but for a number of target materials there are problems. One problem is the difference in the coefficient of thermal expansion between the target and backing plate that can leave the bonded system with a large bending force created by the differential contraction following the target being cooled after bonding.

            This new bonding process can be achieved at low bulk temperatures. This is how it works.  The target and backing plate are pre-wet with solder. The target and backing plate are then placed and then clamped together along with a thin foil between the soldered surfaces. The thin metallic foil is a controlled pyrotechnic that once ignited burns very rapidly and locally melts the solder on each surface which both melt and mix together giving an intimate bond.  The speed of this process means that only the solder surface is melted and so the target and backing plate remain cold and so do not suffer from the stress problems for heating and more particularly cooling.

            This same material was first used to mount sensitive electronic components that needed a good thermal sink and where the component could be easily damaged by conventional soldering.  This was obviously a more critical application of the foil but on a much smaller scale. 

            The advantages of this very localised soldering process for bonding targets is that it allows for the widest choice in solders and it allows the bonding of any target material to a backing plate without the need for specialist ovens or atmospheres.

            With very large targets it can be recommended to machine the pre-soldered surfaces to ensure the highest quality bonding with >98% coverage.

            This process is somehow a more satisfying process knowing that a vacuum deposited multilayer foil is being used to bond targets to produce even more vacuum deposited materials.