Vacuum Web Coating

Thermal capacity.

I wanted to check if there is any information available on comparison of Thermal Properties of Aluminium Foil vs any Metallized films like Metallized PET film or Metallized BOPP film or Metallized CPP film, etc.

The properties would be something like Thermal retention, Thermal conductivity, etc.

Answer.

I have the following details.

Specific Heat      

Al   938 J/kg/deg K

PP 1700 - 1900 J/kg/deg K

PET 1000  J/kg/deg K

Thermal Conductivity

Al  237 W/m.deg K

PP 0.1- 0.22 W/m.deg K

PET  0.24 W/m.deg K

Things like thermal retention will depend on many factors such as the shape, which affects the surface area to volume ratio, the surface condition which can affect the emissivity, the environment as in are there convection currents, or hot or cold surfaces close by, also the heat transfer coefficient to any contacting surface and the thermal conductivity of that material.

Material will lose heat more rapidly if it is contacting a cold surface or radiating to a cold surface than it would if the surrounding surfaces are hot. Similarly if the material is in a constant draft if will lose heat more rapidly than if the air conditions are static.

So if, for instance, you were comparing a food tray made from aluminium foil and one from either PET or PP you might first start with the quantity of material used in each case. The polymer tray is likely to be thicker to provide a similar stiffness to the aluminium. If you then calculate the specific heat for both you might then find that the higher values for the polymer but lower mass keeps the values comparable.  If you then move to the heat retention it is likely that you will find that the aluminium loses this heat more rapidly than the polymer because of the difference in emissivity and because as the aluminium radiates heat from the surface it is faster to conduct heat from the core of the foil to the surface compared to the polymer.

Note, this is just a speculation on my part and you would need to put in the numbers as accurately as possible to find the true differences.

I hope this help in your work.

Copper Metallization

Question.

What is critical point if we would copper coating on PET film?

We will modify our aluminium metallizing machine to cooper metallizing, what should we do?

Answer

using existing evaporation boats can be problematic. The copper does not wet the boat well and so can be difficult to control in the same way as aluminium. 

I know that companies have used traditional boats but the boats need to be conditioned and this can take time and everybody seems to work on their own solution to the problem that they keep secret.

Sidrabe, the system building company in Riga, Latvia, sell special boats that are designed specifically for deposition thick copper.  These are designed to be direct replacement boats for the standard boats but may have limitations as the current requirements may be limited by the transformers you have on your system.  These boats use tungsten rods that are wire wrapped down the centre of a tube of refractory metal. The copper is fed into the end of the boat and the motlten copper runs along the rods and is evaporated out through a slot in the tube. Because the vapour comes from the out of the centre of the bundle of the rods there is little or no spitting and the quality of the coating is good.

If you wish to contact Sidrabe a couple of contacts are

Nils Veidemanis             or Victor Kozlov

veidemanis@sidrabe.eu  or vkozlovs@sidrabe.eu

phone +371 7249806      or     +371 67812542

Victor Kozlov presented a paper at the SVC 2006 Annual Technical conference on the use of these sources if you wish to read up about them.

Adhesion improvement using carbene

I heard this paper last week and thought that many of you would be interested in the process and so I have posted the text below. For those of you who wish to see the figures that accompany the text could you contact Mark Maloney (details given at the end) I was unable to transfer them (sorry about that). Functionalisation of Materials (Dr Mark Moloney, Dept Chemistry, University of Oxford)

The preparation of functional polymers can be achieved in two main ways, either by the preparation of the functional polymer by the polymerisation of the appropriate monomer (Approach 1) or the modification of an existing polymer (Approach 2).

Conventional dye technology uses reactive linking agents to attach suitable dyes to a given substrate, usually by an alkylation reaction. We are interested in the application of carbenes for a similar purpose; these highly reactive intermediates are capable of inserting into a wide range of bonds, notably C-H, O-H, N-H and of course alkenes, to form very stable bonds. Therefore, these reagents would be expected to be useful for the modification of a wide range of materials, and in particular those which would not normally be considered to be chemically reactive, e.g. low surface energy materials.

We have shown that highly reactive diarylmethylcarbene intermediates, easily generated under thermolytic or photolytic conditions, can be used for the modification of a wide variety of polymers, including polystyrene, polyethylene, polyethyleneterephthalate and nylon, as well as low surface energy materials such as polypropylene, to introduce a range of surface activity, including colour, biocidal function and adhesion onto an otherwise unreactive polymeric material.

The protocol uses a two step process (Scheme 1), involving firstly, pre-activation of the polymer by carbene insertion (Stage 1, Scheme 1) using the reagent 1b. The structure of this reagent has been carefully optimised, and consists of a diaryldiazo unit, a spacer unit and an electron rich aminoaryl unit, each of which play an important function in the process. The diazo compound 1b is easily available from ketone 1a in a simple two-step sequence (hydrazone formation followed by oxidation). Adsorption of diazo compound 1b onto a polymer substrate is followed by heating (ca. 150oC), which generates a carbene in situ, whereupon insertion to the polymer occurs, and the product 2a can be isolated free from any by-products by a simple washing procedure. The attachment of the carbene to the polymer is via insertion into a covalent bond, probably a C-H bond in most cases, in which case a new carbon-carbon bond is formed. When this occurs, the surface bound residue will therefore be hydrolysis insensitive, providing irreversible polymer surface modification. The minimum irreducible function required for this insertion step is the diaryldiazo unit of 1b, as demonstrated by the careful use of controls to understand the mechanism of the process. Treatment of the modified polymer 2a (Stage 2, Scheme 1) with any of a wide range of commercially available diazonium salts 3 in aqueous solution gives the highly coloured products 2b, which are isolated by a simple washing procedure. This second step depends crucially on the presence of the electron-rich aminophenyl side-chain in 2a, which after coupling with the diazo compounds 3, generates highly-coloured surface-modified polymers whose absorption characteristics depend on the structure of the

diazo compound which is used. In order to demonstrate the substrate flexibility of this process, we have been able to dye chemically diverse natural and synthetic polymers, and in the most successful cases to produce intense red, yellow, brown, orange and blue colours. This strategy makes for a highly general process, and will enable the insertion of a wide diversity of chemical functionality by suitable modification of the reagents used in the Stage 2. The methodology is intrinsically flexible, permitting the introduction of useful functionality on to what would otherwise be considered to be inert materials, by a chemically irreversible modification the polymer, as opposed to a physical dispersion. A modification of this approach, in which an activating amino residue is incorporated directly into the diarylmethyl residue, has been found to permit the colouring by diazo coupling of a wide variety of materials. Further, we have recently shown that surface modification of diamond is possible, at a density of about 1014 fluorescein groups cm-2, and this can be detected macroscopically as fluorescence.

Some of the results which we have achieved are shown in Figures 1, 2 and 3 below.

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

Figure 1: Polymers modified according to the protocol shown in Scheme 2, Stage 2(b). Polymers (a) polypropylene sheet; (b) alumina; (c) nylon 6-10 beads; (d) polyethyleneterephthalate pellets; (e) cotton wool; (f) cotton; (g) Kevlar; (h) polystyrene XAD-4;

(i) polyethyleneterephthalate film.

(a) (b) (c) (d)

Figure 2: Polymers modified according to the protocol shown in Scheme 2, Stage 2(c) and metallised with silver. Polymers (a) polystyrene XAD-4; (b) polyethylene; (c) polypropylene;

(d) alumina.

Figure 3: Glass modified according to the protocol shown in Scheme 2, Stage 2(d). (a) unmodifed glass; (b) modified glass with increasingly hydrophobic groups (left to right)

Some relevant references to recent work:

* "The Preparation and Reactivity of Some Photoactivable Reactive Dyes", D. R. Braybrook, M. G. Moloney, H. M. I. Osborn, and W. J. Norris, J. Photochem. Photobiol. A: Chem., 1993, 70, 171.

* "A Method for the Functionalisation of Polymeric Substrates", K. Awenat, W. Ebenezer,

M.G. Moloney, GB9824023 D0 (1998-12-30); WO0026180 A1 (2000-05-11); EP1124791 A1 (2001-08-22); JP2002529542 T (2002-09-10); US6699527 B1 (2004-03-02);

“A Chemical Method for the Surface Functionalisation of Polymers”, K. Awenat, P.J. Davis, M.G. Moloney, Chem. Commun., 2005, 990 -992.                 “Functionalised Polymers by Surface Modification”, J.-P. Griffiths and M.G. Moloney, Fudan Xuebao, Ziran Kexueban (J. Fudan University Natural Science), 2005, 44(5), 772­

773.

“Biocidal Polymers”, J.-P. Griffiths and M.G. Moloney, UK patent application no. 0500895.8 filed on 18 Jan 2006.                 “Surface Adhesion using Arylcarbene Reactive Intermediates”, J.-P. Griffiths and M.G. Moloney, patent filed on 23th Aug 2006. (PCT/GB07/003194)                 “Direct Chemical Modification of the Surface of Diamond by Carbene Insertion”, R. G. Egdell, J. Foord, J.P. Griffiths, M.G. Moloney, and Hao Wang, Langmuir, 2008, in press.

Contact details:

Dr M. Moloney, Reader in Chemistry, Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA United Kingdom

Telephone: +44 (0)1865 275656 Fax: +44 (0)1865 285002 Email: mark.moloney@chem.ox.ac.uk

Marcelo Bravo, CEO, Oxford Advanced Surfaces Ltd, Centre for Innovation & Enterprise Begbroke Science Park, Sandy Lane, Yarnton OX5 1PF

Telephone: +44 (0)1865 854807/854808 Email: info@oxfordsurfaces.com

Which side has been metallized?

Request: I have rolls of holographic film delivered to my plant. How can I
tell which side is the metal side out?

Answer.

Generally using a knife-edge to gently scratch the surface will tell you which side is metallized. On the non-metallized side the scratching will produce white dust only and when held up to the light the metallized optical density will be unchanged. When scratching the metallized side the dust may appear darker and, more importantly, when the film is held up to the light will shine through much brighter where the metal has been removed and the optical density has been reduced. It is important to scratch with a series of gentle strokes. You are only trying to remove a few nanometers of the surface and not peel away microns of the surface. I have see a heavy-handed person dig through from the non-metallized side determined to scratch through to the metal.  If a lacquer has been applied it may take additional scratching to remove the lacquer before you get to the metal but this is still going to be relatively thin and the difference should still be obvious.

If the adhesion is not good then using the sellotape test, where sellotape is stuck on the surface and pulled off.  If the metal adhesion is poor then on the metallized side some will be removed and again holding the film up to the light will show this up.
This only works for poor adhesion samples and where this does not work the scratching test has to be resorted to.

Options on the removal of Aluminium

I would like to have information on the removal of metallising from metallised pet film. I further describe it that we would like to remove the metallising only from the pet film sheets to make it transparent for certain specialised applications.

Kindly inform us your suggestion on which chemicals, acids, solvents etc should we use to do so.

Answer.

There are several methods for the removal of aluminium.

The first is to print a release layer onto the web where you do not want aluminium present. The film is then metallized and afterwards the film is passed through a bath that dissolves the release layer and removed the aluminium for these areas.  Some of these release layers may be water based and others are solvent based.

The second method also uses an atmospheric process. The film is metallized and then printed afterwards with an impervious lacquer where you want the aluminium to remain and then pass the coated film through a bath that will dissolve the aluminium from the areas without any lacquer present.  This is the process that is probably the most widely used because it is possible for end users to take toll metallized film and to pattern it whereas the other processes require either the metallizer to have control over the process or, as in the above process, for the film to be supplied already pre-printed. The bath for this process can be a simple bath of sodium hydroxide or potassium hydroxide solution. If the bath is around 5m to 10m long and the liquid filled to the brim it is possible for the film to be brought just into contact with the surface of the corrosive liquid without having to dip the whole film into the liquid. This means that the back surface does not really get wet and so there is less water absorbed and so washing and drying the film following the etching process is simpler and the energy required less.

The final method of patterning film is to use an in-vacuum patterning process where oil is evaporated onto a patterned gravure roll that transfers the oil pattern onto the web and then aluminium is deposited. Wherever the oil is present the aluminium will not stick and hence the pattern is produced. The oil also sees the radiant heat from the deposition sources as well as having the aluminium landing on the oil. This combined heat load is enough for the aluminium to re-evaporate but also to evaporate some of the oil too. In this way, if the oil quantity is optimised, the oil will all be evaporated by the end of the deposition zone and so the web will be dry.

All of the major vacuum metallizer machine suppliers can offer this type of oil pattern printing technology.

The perennial problem of pinholes.

PLEASE TELL ME HOW TO OVERCOME THE PROBLEM OF PINHOLES DURING METALLISATION

Answer.

There are several possible causes of pinholes.

In my experience the source of the greatest number of pinholes is from debris on the film before metallization that is moved following metallization leaving behind a pinhole from where the debris was sitting during metallization. If the debris has been rolled away it leaves a normal pinhole but if the debris slides you may also see a scratch from the pinhole.   Debris, as the cause of pinholes, was researched by a postgraduate student at Cambridge University and reported in 'Jamieson
E.H.H. & Windle A.H.   'Structure & oxygen-barrier properties of metallized polymer films'   J. Matls. Sci. 18, 1983  pp 64 - 80'

This debris can be removed by using technology such as tack roll cleaning methods as sold be companies such as Teknek.
Plasma treatment to remove electrostatic charge does little to clean this type of debris from the surface.


A second source of pinholes can be from the metallization process where there are a few contributory factors. The aluminium wire diameter and purity can have an effect as the oxide surface of the wire and any impurities will contribute to the crud that forms on the surface of the molten aluminium pool of metal. This crud flows towards the ends of the molten pool where as the pool changes size it can sometimes be ejected to hit the substrate and cause a pinhole. This type of pinhole can be anywhere from a small loss of metallization through to burning a hole through the polymer film when the ejected material is large and incandescent.  Some of the higher quality wires are cleaned and have a reduced oxide surface and this along with a high purity can help reduce this type of problem.

The third most common problem is pickoff. This is where the filler protruding from the back surface of the web is pressed hard onto the freshly metallized surface and when the roll is unwound the filler picks off the small area of metal that it was in contact with leaving behind a pinhole. This can be affected by the hardness with which the roll was wound as well as the adhesion level of the metallization.  If any pre-treatment such as corona or plasma treatment is optimised to make the adhesion as good as possible and the winding tension is set to a low level this problem will be minimised.


I hope this gives you something to work on to improve the level of pinholes.

A problem of curl

How can we control curling in BOPP+MBOPP and BOPP+MCPP Laminates.

On Lamination machine we control curling at slitting end.

Can we fix any Anti-curl unit on slitting machine?

Answer

The problem of curl starts with the manufacture of the film. There is a considerable difference in the residual stress in different types and grades of film. Cast PP film is very different to BOPP and even with BOPP different batches as well as different film thickness rolls can have different levels of residual stress.  When laminating films it generally requires knowledge of the stress, both in magnitude and orientation so that when two films are laminated the overall stress is minimized and hence the curl minimized.

The residual stress comes from the manufacturing process where the polymer is heated and then stretched in one direction for mono-axial oriented film or in two directions for bi-axial oriented film. When the film is cooled the tension can be released but there will be some frozen in residual stress from this process. When next heated this can be seen as a relaxation in the film, which may be seen as shrinkage and this may be different in magnitude in the different orientations.

Metallizing may well change the residual stress because the film is held under tension for a time at a high temperature and it is common for film to shrink in the metallization process.  Thus, even if you have two rolls of BOPP from the same batch with one metallized and the other not if they then have the residual stress measured they are likely to be different.

As far as I am aware there is no automatic 'anti-curl' process that can be added. It is usually left to the judgement of the engineer to assess the levels of residual stress and then to compensate accordingly by judicious use of spreader rolls and tension.

AIMCAL launch new Converting School

We at AIMCAL are proud to introduce Converting School. Our mission is to bring leading technical experts to the classroom to share their knowledge and experience with the converting community. Each instructor at AIMCAL Converting School is a recognized authority in his area of expertise. This new series of courses has been designed to provide productivity-enhancing educational opportunities for members of the converting industry. Full details, including course descriptions, instructors, places and dates can be found on the new Converting School website – www.ConvertingSchool.com

Six courses on critical converting topics will be held in 2008: Coating Solution Process Technology, Extrusion Coating, Web Coating and Drying, Web Handling and Converting, Winding: Machines, Mechanics and Measurements , and Web Processing for Barrier.  Multiple sessions of each course are scheduled and will take place at various locations in the United States, Europe and India.  A total of 19 sessions will be offered.  Classes begin in March 2008 in Jacksonville, Florida, and are scheduled monthly (except July) for the remainder of the year. 

Course content combines theory with real-world problem solving and is tailored to the individual students present in each class.  “The focus of these classes is productivity enhancement,” says Craig Sheppard, executive director of AIMCAL.  “Students also will take home ideas for profit-boosting strategies related to process optimization and waste reduction, as well as higher, more consistent product quality and new product development,” he adds.

Potential students include engineers and other experienced converting professionals including lead operators, foremen, and maintenance, quality assurance, sales, and customer service personnel.

Courses are taught by leading technical experts including Dr. David Roisum of Finishing Technologies, Inc., Neenah, Wisconsin, who is moving his popular Web Handling and Converting and Winding courses under the AIMCAL Converting School umbrella.

Other instructors include AIMCAL Technical Consultants, Dr. Edward Cohen and Dr. Eldridge Mount III; Dr. Charles Bishop of C.A. Bishop Consulting Ltd., Loughborough, England; Dr. Dilwyn Jones of Emral Ltd., Yarm, England; Dr. E.J. (Ted) Lightfoot of the Display Films and Coatings business of DuPont Co., Wilmington, Delaware; Dr. Kenneth McCarthy of Multilayer Coating Technologies LLC, New Bedford, Massachusetts; and Dr. Jonathan Summers and Dr. Harvey Thompson of the University of Leeds, Leeds, England.

Program details and registration information are available on the new Converting School website, www.ConvertingSchool.com

We hope to see you there! Below, you can find the schedule of course dates, locations and instructors.

Thank you,
- AIMCAL

DATE	COURSE	LOCATION	INSTRUCTOR
March 25-26	Web Handling and Converting	Jacksonville, Florida	Dr. David Roisum
March 27-28	Winding: Machines, Mechanics and Measurements	Jacksonville, Florida	Dr. David Roisum
April 8-9	Coating Solution Process Technology	Charlotte, North Carolina	Dr. Edward Cohen Dr. Kenneth McCarthy
April 10-11	Web Coating and Drying Process Technology	Charlotte, North Carolina	Dr. Edward Cohen Dr. E.J. (Ted) Lightfoot
May 20-21	Web Handling and Converting	Ontario, California	Dr. David Roisum
May 22-23	Winding: Machines, Mechanics and Measurements	Ontario, California	Dr. David Roisum
June 10-12	Extrusion Coating	Philadelphia, Pennsylvania	Dr. Eldridge Mount III
June 12-13	Web Processing for Barrier	Philadelphia, Pennsylvania	Dr. Charles Bishop
August 11-12	Web Handling and Converting	New Delhi, India	Dr. David Roisum
August 19-20	Coating Solution Process Technology	Wilmington, Delaware	Dr. Edward Cohen Dr. Kenneth McCarthy
August 21-22	Web Coating and Drying	Wilmington, Delaware	Dr. Edward Cohen Dr. E.J. (Ted) Lightfoot
September 16-17	Web Handling and Converting	Philadelphia, Pennsylvania	Dr. David Roisum
September 18-19	Winding: Machines, Mechanics and Measurements	Philadelphia, Pennsylvania	Dr. David Rosium
October 7-8	Extrusion Coating	Cleveland, Ohio	Dr. Eldridge Mount III
October 9-10	Web Processing for Barrier	Cleveland, Ohio	Dr. Charles Bishop
November 18-19	Web Handling and Converting	Brussels, Belgium	Dr. Dilwyn Jones
November 20-21	Web Coating and Drying	Brussels, Belgium	Dr. Jonathon Summers Dr. Harvey Thompson
December 2-3	Web Handling and Converting	Atlanta, Georgia	Dr. David Roisum
December 4-5	Winding: Machines, Mechanics and Measurements	Atlanta, Georgia	Dr. David Roisum

Visit www.AIMCAL.org or www.ConvertingSchool.com for more information.

Vacuum Deposition 2008

Thank you to all who sent in Christmas and New Year greetings.

May I take this ooportunity to wish everybody a Happ, Healthy and Prosperous New Year.

Also, at the risk of doing myself out of a job, may I wish you all get perfect adhesion, have no winding problems and meet all your customer needs throughout 2008.