Vacuum Web Coating

Question re. CoF after metallization

We are facing a problem with CoF (coefficient of friction) after metallization.

Kindly advices us what value should be of COF in plain film & what value should be after metallization with 2.2 optical density? 

How can the CoF be controlled during metallization?

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Answer

Generally polyester films have some low molecular weight material on the surface.  This is frequently oligomer that is residual material from the polymerisation process. There may also be other materials added that can migrate to the surface that may also reduce the coefficient of friction (CoF). 

Pure PET films will readily block and so they are usually have fillers added to provide a controlled surface roughness. The surface roughness reduces the contact area and hence the CoF.  The size, shape, type and distribution of these fillers controls the precise value of the CoF.  The fillers can be in the bulk film or, to reduce haze, can be added to a thin co-extruded layer with the rest unfilled.  The CoF is usually higher than is ideal for easy to handle film. Coupled with the residuals this can make the ease of handling acceptable.

Often the surface of the polymer is treated to change the surface energy to improve the adhesion. This treatment to increase the surface energy can crosslink the low molecular weight material into the bulk polymer or can volatilise the material and remove it. Either way the low surface energy material is removed and the CoF will get worse (increase).   

Even if there is no surface treatment the metallization itself will cover up the low molecular weight low surface energy surface and again the CoF will increase.

Thus there is no fixed CoF that specifically relates to a particular Optical Density but rather the CoF relates to the history of the polymer web and any surface modification and surface treatment that has been carried out.

Sometimes the back surface of the web is not treated and thus there may be the transfer of some of the low molecular weight low surface energy material from the back surface to the front surface once the metallized web has been re-wound.   This can cause a problem in reduced adhesion of any subsequent coatings to the metallized layer but the transferred material may also aid the ease of handling.

Question re. ISO 22000

The following question has been asked.

Could you please help me to understand the significance of ISO 22000 for a producer of plain, coated & metallized film used for packaging application?

I found this information on the BSI website (web address given at the end) that answers the question

ISO 22000:2005 - Food Safety Management System Standard 

BSI provides auditing, certification and training services for ISO 22000:2005.

Introduction
The International Organization for Standardization (ISO) has developed the ISO 22000:2005 Food Safety Management Systems Standard. Officially called ISO 22000:2005, Food safety management systems - Requirements for any organization in the food chain, ISO 22000:2005 is an international standard and defines the requirements of a food safety management system covering all organisations in the food chain from “farm to fork”, including catering and packaging companies.

There has been a continuous increase in consumer demand for safe food. This has led to the development of numerous food safety standards. The growing number of national standards for food safety management has led to confusion. Consequently, there is a need for international harmonization and ISO aims to meet this need with ISO 22000:2005.

The standard combines generally recognized key elements to ensure food safety along the food chain including: interactive communication; system management; control of food safety hazards through pre-requisite
programmes and HACCP plans; and continual improvement and updating of the management system.

ISO 22000:2005 is intended to define the requirements for companies that desire to exceed the regulatory requirements for food safety.

Who is it for?
A truly international standard for any business in the entire food chain from 'farm to fork' and including inter-related organizations such as producers of equipment, packaging material, cleaning agents, additives and ingredients. ISO 22000:2005 is also for companies seeking to integrate their quality management system, for example ISO 9001:2000, and their food safety management system.

Benefits of adoption
Certifying your food management system against the requirements of ISO 22000:2005 will bring the following benefits to your organization:

·        Applies to all organizations in the global food supply chain.

·        A truly global international standard.

·        Provides potential for harmonization of national standards.

·        Covers the majority of the requirements of the current retailer food safety standards.

·        Complies with the Codex HACCP principles.

·        Provides communication of HACCP concepts internationally.

·        An auditable standard which provides a framework for third-party certification.

·        Auditable standard with clear requirements.

·        Suitable for regulators.

·        The structure aligns with the management system clauses of ISO 9001:2000 and ISO 14001:2004.

Specific benefits include:

·        System approach, rather than product approach.

·        Resource optimization – internally and along the food chain.

·        All control measures subjected to hazard analysis.

·        Better planning, less post process verification.

·        Improved documentation.

·        Systematic management of prerequisite programmes.

·        Increased due diligence.

·        Dynamic communication on food safety issues with suppliers, customers,
regulators and other interested parties.

·        A systematic and proactive approach to identification of food safety hazards
and development and implementation of control measures.

Review information on other Food Safety Standards - BRC Global Standard - Food, BRC/IOP Packaging, and Dutch HACCP or learn how to implement a Food Safety Management System .

To find out more and to download brochures please complete our Registration and Assessment Enquiry form.

You can purchase copies of

·        ISO 22000:2005 - Food safety management systems - Requirements for any organization in the food chain

·        ISO/TS 22004 – Food Safety Management Systems – Guidance on the application of ISO 22000:2005

from BSI Customer Services on +44(0)20 8996 9001, by emailing orders@bsi-global.com or from British Standards Online (ISO 22000 only).

C.A.Bishop

AIMCAL Fall Conference review of papers No.1

The Conference got off to a brilliant start with the keynote presentation with the intriguing title of ‘Moth-eyes, Lotus leaves, Sharkskin and Gecko feet.’ Given by Prof. Steve Abbott of MacDermid Autotype. The basis of the presentation was that Nature provides a great source of ideas that can be mimicked and improved upon to make effective products.  The first example demonstrated was the Moth-eye antireflection surfaces. Moths have large eyes that would normally be highly reflective and make the Moths easy prey but nature counters this problem by making the Moths eye a compound eye with anti-reflecting properties. It is possible to produce an equivalent surface to the Moths eye by embossing a surface structure into polymer webs.  This control of surface roughness can be combined with anti-glare surface roughness to get a combined effect.

            Another effect that can make use of controlling the surface roughness is the Lotus leaf effect. In this instance the surface roughness is combined with a waxy material so that the surface has a very low surface energy.  If water contacts the surface it will roll off and any dirt on the surface has the chance that the water will collect the dirt and remove it. 

            The next natural effect examined was the reduction in drag that sharkskin is able to produce.  This too is a surface roughness effect but in this case there is an orientation to the roughness that increase drag in one orientation but reduces the drag in another orientation even more given a net reduction in total drag.  This type of effect has been applied to an Airbus 320 aeroplane reducing the skin drag by 7%.  The use of this type of effect is in its infancy and many more applications are expected such as on wind turbine blades and hulls of boats.

            The fourth natural phenomenon used in the title was of Gecko feet. Here there is always speculation as to what keeps the Gecko stuck to the ceiling, is it glue, Velcro or suction pads. The answer is none of these but simply Van der Waals force. The surface of the feet are divided up into very tiny individual hairs that are able to conform to the detailed shape of any surface and each of these hairs is then able to form an intimate contact with the surface.  This intimate contact allows the full force of the Van der Waals force to be effective on every one of the hairs whereas a single flat surface would only see this force on the relatively few points of contact. To mimic this effect requires producing a hairy surface that is able to conform and produce this very high surface area intimate contact between any two surfaces that gives the natural adhesion.  This is not an easy surface to mimic. If the hairs are too stiff, too short, too long, too limp, in fact anything but ideal the adhesion will be impaired. If the hairs are too short or too stiff the surface may not be conformal enough to match the surface it needs to adhere to. If the hairs are too long or limp then they can matt and stop working. Thus, although we now know how the process works, delivering a working solution is somewhat more problematic.

            Finally a bonus topic was that of the Tree-frog that is able to stick to wet surfaces. When examined under the microscope these have feet that have pads that are made of finely divided smaller pads.  These divided surfaces have the effect that the gaps act like the tread of tyres to disperse the water enabling the pads to regain intimate contact and these then work in the same way as the Gecko feet. 

            The common thread running through all these topics was the need to be able to control the surface roughness with great precision down to a very fine scale. Of which embossing is, in theory, the simplest solution.   

Second-hand metallizers & retrofitting

Here is a question that was posed any my reply along with some other generic comments about second-hand equipment and retrofitting.

The Question.

Hi,

I would like to know if its possible to retrofit an older vacuum metalizer ( made in the early 80’s) with a electron gun for the deposition onto glass / lenses.   If so have you come across any company’s that sell this equipment?

Regards

The answer.

The simple answer is ‘yes, it can be done’.  This is usually followed by a BUT.

Using an old metallizer to give you a cheap, large vessel with a pumpdown set can be cost effective if you get it cheap enough and you know the cost of the changes you want to do before you start.   In many instances the whole project does not get the costs estimated well and it ends up more expensive than buying new equipment or a readymade second-hand glass / lens coating machine.

Old machines that have seen a lot of work can have problems, or increased risk, of leaks due to fatigue failures of welds from the vacuum cycling.  So make sure it is leak-tight and can be pumped down to a low base pressure, if at all possible.

Using an old metallizer may mean the vacuum pumps are not sited well for getting good uniformity if you are doing reactive deposition.  This does depend on the type of process you are using. If you are removing the winding system and replacing it with a planetary motion or some similar complex moving jig to average out the deposition you may be able to average out any inherent non-uniformity from having non-uniform pumping.

The installation of electron beam guns is generally not a problem. There are plenty of suppliers of electron beam sources with single crucible, multiple crucible or rotating crucible designs.   It only requires space and sufficient leadthroughs to be able to install one or more into the system and if you are removing the standard resistance heated boats there will usually be plenty of space. 

If you want to deposit multilayer coatings there are some choices to make such as depositing from different guns or depositing from a single gun with multiple crucibles. So of this decision may be governed by the quantity of material that needs to be evaporated throughout a single run and it may be that a multi-crucible e-beam gun does not have the capacity unless the crucibles can also be fed.  If separate e-beam guns are used this again impacts the deposition uniformity.  Also the monitoring of each source and/or each deposited layer to make sure the total optical performance is delivered from the multilayer coating needs some careful thought.

Hence the design of your retrofit system will be critical to the success of your process and often the cost of correcting minor problems can tip the balance away from retrofitting an old system to buying either a new well proven system or a know second-hand system.

Companies such as Angstrom Sciences Inc,  Leybold Optics GmbH, and Soleras Ltd all offer re-built systems and so probably would help retrofit your machine. Alternatively there are usually smaller more local vacuum/engineering shops that would be capable of doing the job with suitable expert supervision from someone who understands the process you wish to end up with. 

General comments on retrofitting.

Retrofitting is often considered to extend the lifetime of a vacuum system but in some cases this has proven to be a false economy.  Upgrading the on-line monitoring system on a metallizer may give better information about the coating thickness but unless the control of the boat temperature and wire feed is upgraded too it may well be that all the upgrade does is to improve the information about how variable the process is.  If you then upgrade the control of power to the boats and the wire feed then for an old machine the cost of taking the machine out of production, the cost of the items that are often customised to fit that particular machine as well as the cost of recomissioning may be a significant proportion of buying a new machine.  When one considers that a new machine will also include a newer, more up-to-date winding system and any other developments that have taken place since the original machine was built it is likely that the increased productivity of the new machine would more than compensate for the difference in cost between the new machine and the old but refurbished machine.

Most retrofitting projects underestimate the effort, time, inconvenience and hence true cost.

Question re. sending sample for surface analysis

Here is a recent question that has been asked.

I have a problem with metal adhesion and want to check if there is any contamination at the interface. I have been told that I need to be careful in taking samples and how I send them to the laboratory for surface analysis as I can easily contaminate the samples and this would potentially compromise the analysis. 

Can you offer any advice on how best for me to take good quality samples and then how best to pack or wrap the samples to avoid this problem?