Vacuum Web Coating

Removing aluminium for recycling.

Please tell me how can separate aluminium layer from polymer in a BOPP metallized film in a extruder when recycle or what material must addition to that in extruder for separate aluminium from polymer?

ANSWER

A number of recyclers I believe have used metallized film but the recycled polymer has always gone to low grade applications where the colour and mechanical performance are not of great importance.

There is renewed interest in recycling polymers and retaining their special or higher technical performance. 

The aluminium layer is very thin and can be easily be removed by using a sodium (or potassium) hydroxide bath. The usual arrangement for this is to have a full bath where the liquid completely fills a bath with the excess liquid flowing over a weir. This keeps the liquid at a know level. The aluminium coated web is passed across the surface of the liquid with the aluminium side just touching the liquid. The length of the bath may be several meters long and this can enable the total removal of aluminium at winding speeds of over 100m/min.  Generally there is then a water bath to make sure the chemicals are removed and this cleaning water bath is followed by a hot air knife and hot zone to make sure the polymer web is dry.

This process has been used very successfully for producing patterned metallization coatings where a protective lacquer is applied where the aluminium is going to be kept and all the rest of the aluminium is removed.  This is an alternative process to the in-vacuum patterning process.

I a no chemist and so do not know the precise strength of the NaOH (or KOH) solution or how much aluminium will be removed by what volume of liquid.   Nor have I tried to do the economics of the capital cost of the equipment, the chemicals and the waste material disposal costs.   

This chemical process is probably the one that has been used most. However there are other possibilities.  When I was looking at texturing polymer surfaces for a different project I tried sand blasting as  a method of removing the more usual shiny polymer web surface. Out of interest I also looked at removing the aluminised surface which it did successfully.  At this point I have a word of caution.   Aluminium is easily oxidised and the oxidation reaction is exothermic. Removing the aluminium from the surface in such small size flakes by the sand blasting method could easily produce a dust cloud of rapidly oxidising aluminium that is a potential explosion hazard.  I never had a problem but was doing the process in very limited quantities and low rates.  I know this process is feasible but it does need care.

Another option that has potential is to use a knife to pare off a very thin layer of polymer.  This technique is used to produce skived polymer film from solid billets of polymer.  Taken from the wood laminate industry where they spin a tree on a lathe and push a knife against the wood and peel off a thin wood laminate sheet.  In the case of polymers the polymer integrity is better and so thinner sheets can be skived off.  In the case of removing the aluminium this has some advantages over using this method for producing film.  The billet, as the film is skived off it reduces in size and circumferential speed and so the speed and position of the knife are always changing. In removing a thin polymer layer with the aluminium on it the web can pass over a roller which more precisely fixes the web position and the knife can also be in a more permanent position both of which will enable a thinner layer to be skived off the surface.  This process will divide the web into one without the aluminium but there will also be a much thinner one that still has aluminium on it that will need to be disposed of.

A further option is to use either of two vacuum processes.  The first is to not remove the aluminium but to convert it to aluminium oxide.  This uses an aggressive high power oxygen containing plasma that will convert the aluminium to the oxide with the plasma not only providing the excited oxygen but also generating plenty of heat to help accelerate the process.  The second vacuum process is to remove the aluminium by almost the same process. This time the plasma may be a more complex chemical mixture containing gases such as carbon tetrafluoride as well as oxygen. The aim of this plasma is to etch through the aluminium at a high rate.  This process is a well known process as it has been used by the semiconductor industry for may years for many coatings including aluminium. Sometimes it is referred to as plasma ashing rather than plasma etching.

Of these the NaOH (or KOH) bath is currently the cheaper option but the economics may change as the costs of chemical disposal continue to increase.  The vacuum plasma techniques are expensive because of the requirement for a high speed vacuum roll-to-roll system. This too has some process costs as the etching gas includes fluorine and so the pumps need to be protected and the exhaust needs to be treated for environmental reasons.  The other two processes I do not believe to be developed yet into a production process and so are both are an unknown cost.  This brings us back to the chemical bath technique which, on balance, looks to be the best option currently.

I have not heard of any process used on extruders to separate or remove the aluminium.  I will ask around to find if any other processes are being developed but am not hopeful.

One of the other problems that has been pointed out is that whereas rolls are metallised and are complete rolls this contrasts with material that might be recycled such as the offcut rolls of material that has been used for hot stamp foil or labelling, slit to different widths.  Getting a robust industrial process that can handle any/all of these different widths, thickness as well as material with holes in is more difficult than just working with freshly metallized rolls.   Thus many have found it cheaper to sell the film for lower grade use such as shredding the film and using the metallised shredded material as an insulation filling.  Some sleeping bags have been filled with metallized film shredded scrap.  Unfortunately there do not appear to be enough of this type of secondary use to take all the scrap metallized film produced.

Texturing of polymer films

I have an application that involves using a polymer film and coating it with an active compound that evaporates/emanates fairly well at room temprature. We would like to increase the emanation rate of the ~ 1 micron thick compound layer and in one approach we are considering increasing the surface area of the polymer film's surface to increase the compound-to-air surface area. To date we have had the "fair" emanation results on a standard extruded polyester film - we believe this is in part because the polyester is inert and does not interact with the compound and has the right surface energy - typically 45-55 dynes - which enables the compound to wet the polyester surface but also emanate.

What standard manufacturing processes are available to controllably make macro/micro - hairs, rods/pillars, or dimples on a polyester film. And how would you expect such features to change the surface energy of the textured/structures polyester surface? Have you seen applications where macro/microfiber surfaces (not textiles) have been used - not to increase absorption of a liquid/particle but instead increase the evaporation of an active?

ANSWER

This is an interesting question. 

I do not recall seeing any application what the high surface area was required for increasing the evaporation from a surface.  Most of the time it was required as a method of substantially increasing the surface area to enable a faster interaction rate such as by catalysts.   

Some time ago work was done on producing a surface for a catalyst and also for a biomedical application. For both applications it was possible to achieve the necessary surface area with a basic PET and so the research into the other surface treatments was largely academic.

This is not to say that the PET surface did not have to be pre-treated using a plasma treatment to obtain the desired adhesion of the subsequent coating but as the PET surface was always plasma treated we regard this as normal. The plasma generally is regarded as a cleaning tool and not as a nanometer scale sculpturing tool but on the nanoscale it can also be roughening the surface.

Later more work was done to produce creating graded surfaces as an anti-reflection surface where we simply applied the approach suggested by the National Physical Laboratory (NPL) in the UK of embossing a motheye structure into the surface.

This type of polymer surface texturing, to create anti-reflection properties, is used by Autotype.  Autotype also licence a coating process to make a super hydrophobic surface coating. If I understand this correctly it is a biomimetic surface that replicates what happens on some leaves that are hydrophobic. When looked at in great detail these are very high surface area structures that replcate the effect of hairy leaves.

The person to contact at Autotype would be Prof. Steven Abbott   E-mail Address:  steven@abbott.demon.co.uk

The South Western Research Institute (SWRI) in the US also is very active in creating controlled structure surfaces and a contact there would be Kent Coulter    E-mail Address:  kent.coulter@swri.org 

Other high surface area surfaces can be produced too. The tack melt process used to be used for making fake velvet for packaging. Expensive fountain pens, ear rings, etc, in presentation boxes are often sat on a velvet holder in the box.  Most often this is not velvet but is a hairy plastic that is produced by softening the front surface of the polymer followed by  touching this soft surface with a roll so that some of the surface sticks and as the surfaces part polymer strands are pulled off the surface and cut to length.

The abrasion of the surface using either a belt sander or a shot blasting technique was probably the fastest and cheapest method of increasing the surface area.  This could only produce a moderate increase in surface area whereas an embossed surface is probably the easiest to produce in high volumes where a much higher increase in surface area is required.

The difference between a Lenticular & a stereogram embossed structure.

I have following queries:

1.What is the difference between Lenticulars & a stereogram?
2.What is lenticular sheet?
3. How can we make lenticular sheet?

Answer

A stereogram traditionally was produced by taking two photographs from two slightly different angles and printing them slightly displaced from each other. This means that when you look at the resultant picture you see a slightly blurred picture but if you can change the focal point of your eyes then they each see one of the pictures and the effect is that you see the image in a 3 dimensional way. The brain processes the different information from each eye and reconstructs what you would see in real life and makes it into a more solid image.

Lenticulars work differently.  The aim of lenticulars is to show some movement and so it is like a mini film with each image showing some changing position of the image.  For simplicity if we take a simple two image version of this with an eye open and an eye closed.  If you printed the whole of each image side by side and used a two faceted lens above the images you could produce the effect that my a small movement of the head the lens either showed one image or the other and so you could move from the eye being open to the eye being closed and so it would appear the eye 'winked' at you.  To do this with two images side by side would require a large distance between the lens and the image to get the effect to work well. To minimise this distance each image is separated into stripes and printed alternately and above this a series of lenses are used and this produces the same effect but with a very much thinner lens that can be laminated to the printed image.  The next extension of this is to use many images and a many faceted lens so that each facet is aligned with each image stripe and in this way the progression of the movement can be made less jumpy and it will appear smoother.  The key part of this process is the quality of the printing, the precision of the printing and embossing of the lenses and the registration of the two.  If you imaging the simple two facet lens to be of a sawtooth design it will be clear that this will be in a series of ridges and furrows and so the orientation is important. The effect will work in one direction but at 90 degrees there will be no effect.  The embossed polymer sheet tends to be very thick, compared to packaging film, and can be of the order 1mm thick or more.  The embossing is also very coarse compared to holographic embossing closer to mm in dimensions rather than the microns in holograms.

Incidentally there are also holographic stereograms that instead of using lenses instead digitise the information from the multiple images and use this to make to make a pixilated hologram that can be reconstructed into a 3D image by the viewer.

I hope you are able to visualize this answer.

Shrinkage problems.

We are facing problem of high shrinkage compared to competitors for FRP and Hot stamping foil applications. Please suggest what parameters we have to change in MD/TDO  to get improved conditions

Answer.

When the film is manufactured it is biaxially oriented by stretching the film in two directions. This is done either by blowing a bubble with t he film or using a forwards and then sideways drawing technique using a stenter.  Once the film is stretched it is effectively frozen compete with any residual stress present at the time.  Thus when the film is next heated it tries to relax this stress and you see it as shrinkage.  If the processing conditions on the film line are changed to give more time at the higher temperature following the final stretching whilst the film is held under relatively low tension the film will be stabilised with a lower residual stress and thus will have a lower shrinkage performance. 

Some film manufacturers sell a stabilised film that has been heat treated by a separate process.  In this case the film is wound, under very low tension, through a heated oven and the film is allowed time to relax again lowering the stress and shrinkage.

I hope this suitably explains the cause of shrinkage and what can be done to reduce it.

Anti-counterfeiting Questions.

I am a packaging student.
I was doubt but not regarding any coating, I am working on project anti-counterfeiting in pharmaceuticals, following are my questions.
* what are the technology used for stopping counterfeiting, I want the details of each technology?
* how costing is calculated before incorporating any technology?
* what is the future of anti-counterfeiting?

Answers.

Let me answer the questions in reverse order.

What is the future of anti-counterfeiting?

There will always be a future for anti-counterfeiting so long as there is the counterfeiting of goods. Currently it has been estimate that globally counterfeiting is running at almost 10% of all goods.  This is an average figure and when looked at in detail it is lower in some countries and higher in others and the same for some brands.  In one S.American country counterfeit bottles of one brand of whisky was running at 80% and was being exported to other countries.  In other countries the counterfeiting is almost non-existent.

How costing is calculated before incorporating any technology?

Generally the first step in the process of  looking at using anti-counterfeiting technology is to measure the level of counterfeiting and calculate what it is costing the company.  The aim of any anti-counterfeiting is to reduce the counterfeiting but to be able to recover the costs of the anti-counterfeiting measures from the increase in profits because of the reduction in the counterfeits.

Many companies do not measure the level of counterfeiting and so are unable to know if the any anti-counterfeiting measures are successful so that measuring the size of the problem is critical.  For luxury items with high profit margins that become a preferred target for counterfeiters the large profit margin and high losses can allow several and higher cost anti-counterfeiting measures than are available to a low margin, low cost product.

What are the technologies used for anticounterfeiting?

There is a book 'Optical Document Security' 2nd Edn   Edited by Rudolf L. van Renesse

Published by Artech House   ISBN 0-89006-928-4

This book gives details of many of the different anti-counterfeiting measures including holograms, kinograms, optically variable devices, liquid crystal security devices, and an introduction to biometrics. 

One thing that is worth noting is that holograms are not regarded as secure by the likes of the pharmaceutical industry and for banknotes.  There are too many people who cannot tell a good hologram from a metallic shiny surface let alone the difference between a kinogram, hologram, pixelgram, etc.... as well as the technology available to replicate holograms quite easily.  Even forensic scientists can have difficulty in proving the authenticity of holograms and have to refer back to the originators making the security value questionable.

Having said that there are still companies that have successfully used holograms and the attractive nature of the packaging has boosted sales making them cost effective even if they did not eliminate any counterfeiting.  Also counterfeiters can still find it easier to move their counterfeiting operation to a similar product that does not include a hologram and so it can be that holograms can still be successful in pushing the counterfeiting problem onto any competitor who is not already using a hologram in their packaging.

Thus holograms will continue for some time but more for their aesthetic value than for their security value.

The aim of any anti-counterfeiting is to stop counterfeits entering the market. Counterfeits can enter from a variety of places including misappropriation in the supply chain and so RFID tags are being used to track and identify every legitimate product.

Similarly there are a variety of scanning techniques that can look at 'snowflake' codes or even background material characteristics that make a unique identifier to each product.

There are two aspects of security devices one is overt and the other covert. Overt devices need to be easily recognised by the general buying public so that they know it is a security feature and what it should look like. Ideally these should also be difficult to forge. The covert devices ought to be easily hidden to the untrained eye but easily verified by a machine reader, police, forensic scientist, etc.  Thus holograms make a great deal out of having covert high security information hidden within the hologram but if the product has already been sold because the general public cannot tell the difference between a good and a bad hologram the damage has already been done.

Thus the aim of adding an anti-counterfeiting device should be to help the general public to police the product and to not buy counterfeit goods and only high quality counterfeits that include counterfeit security devices should get past the public and these can then be detected by the covert devices being missing.

Hence the strategy of including anti-counterfeiting devices should be to include a mixture of devices of different types and including some overt and others covert.  How many devices  are included will depend on the product value and the cost of each device.

Thus for banknotes there are several levels of security included but for a box of chocolates there may only be one or two included.

There are journals such as 'Product and Image Security & Data Authentication' that is now into its 11th Volume that may also be worth reading to get a feel for how the technology is changing.

I hope this answers your questions.