Spring 2004: Society for Adhesion and Adhesives One day meeting on 'Adhesives for Packaging'
One day meeting on Adhesives for Packaging, held at the Society of Chemical Industry, 15 Belgrave Square, London on 29th April, 2004
This meeting covered a range of topics and made those not normally associated with this area of work aware of the considerable effort devoted to packaging and also to the size of this market. The need to protect products from physical damage, deterioration and chemical contamination was made clear.
The first paper, entitled ‘Adhesives in Packaging’, was given by Bob Ashley (BA Consultants) and discussed the wide range of packaging materials involved and the need for suitable surface preparation methods and adhesives for each material.
Some packaging methods require a combination of materials to produce a packaging composite. Coatings and printing layers may also be needed together with rapid bonding processes for high speed production. The packaging materials used need to be matched to the contents of the package to prevent chemical reactions and in the case of food or drugs, contamination. Some materials such as anaerobic adhesives need to be in packaging permeable to oxygen, others need to ensure that oxygen cannot penetrate the packaging. Another issue is the effect that cleaning agents, shampoos and oil in foodstuffs can have on the adhesive used to seal the package.
Conversely there is a need to ensure that adhesives used do not leach out chemicals that can contaminate the product. All in all it was shown that packaging is a much more complex issue than might at first appear to be the case.
The second paper was entitled ‘Recent Developments in Packaging Hot Melts’ and was given by Dave Carter, of National Starch and Chemical.
He discussed such problems as an ageing population needing different packaging to the youth market both is style and possibly also in bond strength. The effort required to open some packaging can be an issue in this respect, it can be too strong for very old people. Legislation changes which add to Health and Safety requirements and the need for recycling may affect the choice of materials. Dave described efforts to label profiled bottles and the need for label removal during recycling. Labels can now be removed from PET bottles to facilitate recycling. Work has also been done to reduce the melt temperature of the hot-melts used to minimise burn injuries to packaging workers. Useful reductions in melt temperature have been achieved. He also described "invisible" labelling of glass bottles, which is becoming more popular.
The third paper, by Richard Roberts of Pira International, was entitled ‘Adhesive Bond Testing - Beyond Fibre Tear’.
It described work done as part of the MMS 9 project at NPL. The objectives of this project were to validate a range of simple methods for assessing the hot melt ‘glueability’ of common packaging substrates and to develop a range of simple methods for characterising packaging hot melt adhesives with respect to critical performance properties. Benefits were seen to be:
a) To produce adhesively bonded products more reliably
b) To introduce innovative new materials
c) To cut scrap and reject rates
He said that the "ring and ball test" and the VICAT softening test were of limited predictive value. The Pira Adhesive Performance Tester (PAPT) has been developed to produce more accurate end performance evaluation. A new version of this method is under development.
The Dennison Wax system (TAPPI T459) was also mentioned. In this test a series of graded hot melt waxes are used of increasing adhesive power. The standard test requires finding the wax number at which substrate failure first occurs.
Paper 4 was given by Martin Rides of NPL and discussed ‘Rheology and Dispensing of Adhesives’.
Martin explained that reliable dispensing of adhesives is critical to the manufacture and performance of packaging products and many others. Avoidance of "stringing" is important; the flow of adhesives needs to be understood and the correct values developed for each application. A wide range of techniques exist and it is important to use the right one for each application. A simple rule is to use a test method that mimics as closely as possible the end use situation. The complete response is governed by both the elastic and viscoelastic properties of the adhesive and flows can be by shearing or extension. A short die can be used to minimise shearing effects. Oscillatory rheometry and melt flow rate (ISO 1133) tests were discussed; see also ISO 11443: ‘Determination of Fluidity’.
Paper 5, entitled ‘Packaging Systems for Adhesives’ was given by Alan Crampton of Loctite/Henkel adhesives.
Alan discussed the use of co-extrusion technology to achieve the barrier properties required in some cases. The packaging in the case of Loctite and others is also required to dispense the adhesive for its intended use.
He explained that anaerobic adhesive containers must be oxygen permeable. Packaging must also be designed to minimise waste of the product so it must easily dispense the product and make sure that almost all of it is usable. Where materials are toxic it is also important to design the packaging so that during dispensing the product does not come into contact with the person using it. Packaging must also give the maximum shelf life possible for the type of material concerned.
Paper 6, entitled ‘Blister Sealing Process - An Overview’, was given by Keith Allen of Eli Lilley.
Keith explained that the function of the adhesive is vital in the production of blister packs for medical pills and similar products. Some materials are prone to delamination between the plies. High temperatures are required for rotary sealing. Ingress of moisture can occur through the PVC layer within the base film. New Asian requirements have been introduced as they have to cope with higher storage temperatures. Material selection at the development stage of a product is critical. Questions that must be asked are, is the product moisture sensitive, oxygen sensitive, light sensitive et cetera. The aluminium to aluminium blister is the ultimate moisture barrier and also protects from light. Two types of blister sealing machine were described, the rotary (continuous) motion and the platen (intermittent) motion. Critical parameters of temperature, pressure and dwell time must be optimised. New developments in recent years include anti-counterfeiting features, more child resistance, improved forming technology and non-destructive type leak testing.
For the future, new adhesives, new materials and more efficient sealing tools are needed to improve effectiveness.
Paper 7, the final paper, was given by Bruce Duncan of NPL and was entitled, ‘Measurement of Adhesive Tack’.
Bruce covered a considerable amount of work done at NPL over several years, which included development of the Loop Tack Test. He described the development of the loop tack test and some of its problems and the rolling ball and probe tack tests, which are also used. He explained that tack is a complex property and that measurement methods need to control many factors.
Modelling is needed to improve understanding and to define the most important properties. Among the important properties are those of the adherend surface and any treatments given to it, physical and chemical properties of the adhesive and the bonding process: .i.e. contact pressure, dwell time, penetration of adhesive into the surface, if applicable et cetera.
In addition to these the rate of separation, the angle of peel and specimen clamping have all been found to be important together with the mechanical properties of the adhesive and the adherend. Humidity and temperature at the time of test need to be recorded and the peel force and the area under the force extension curve need to be recorded and studied. Tack is an essential property of any pressure sensitive adhesive used on medical plasters, tapes and labels. It is a complex study and requires more time and effort than is often realised.
A useful day and very enlightening to those not usually involved in this area of adhesive usage.