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Listen to this siteMonday 7 August 2006
This research project aims to investigate the potential migration of chemical substances from shrink sleeves used as overwraps on flexible plastic food containers.
Study Duration : June 2004 to June 2006
Contractor : Pira International
This project investigated the migration of chemical substances from shrink sleeves used on flexible plastic food containers. Shrink sleeves are manufactured from a polymer sheet that has been stretched during manufacture. The sheet is printed and welded at one side to form a tube and then placed over the food container. Heat is applied and the sleeve then shrinks back towards its original dimensions. In doing so, the sleeve takes the form of the food container.
Shrink sleeves have gained considerable market share over other forms of pack labelling. They offer the advantage of high gloss, high quality images at low cost on a wide range of containers, on surfaces which would otherwise be difficult to print on.
There has been very little work published that has considered the possibility of migration of components from shrink sleeves, through the food container to which it is applied, into the food. However, shrink sleeves are printed and welded using solvents and the print is applied on the inner surface that is in contact with the food container. The polymers used to manufacture the sleeves are good barriers to solvent migration, whilst the polymers used in the food container may be poor barriers. Thus solvents in the sleeves may be trapped at the food container surface rather than being lost to the outside air and may migrate through the container into the food. A variety of decorative novel inks, such as ultra violet (UV) cured inks are being introduced.
Whilst the importance of using low migration and low taint inks on primary packaging is well understood in the UK, secondary packaging such as shrink sleeves is not subject to the same controls as primary packaging. It is also possible that, because sleeves are used on metal and glass containers and non-food applications where migration is either not possible or of no importance, due consideration is not given to the use of similar sleeves on flexible food containers where migration is possible.
The objectives of the project were to:
Information gathered from a retail shelf audit and purchased samples showed that most sleeves were printed using solvent-based inks. Potential chemical migrants were identified in commercial shrink sleeves: the majority were printing ink solvents, weld solvents or additives, such as plasticizers. In general, migration from solvent-based inks was found to be low, although common sleeve weld solvents such as tetrahydrofuran and 1,3-dioxolane had the potential to migrate from the sleeves, through the food container, into food.
Ultra violet (UV) cured inks have a lower solvent content but such inks may contain other components of interest such as aromatic photoinitiators. Migration experiments were undertaken into simulants and foods using ultra violet (UV) cured sleeves deliberately manufactured to contain benzene, isopropylthioxanthone (ITX), biphenyl and diphenyl sulphide. These experiments showed that migration of such compounds can occur from printed sleeves through polyolefin food containers. Ten per cent aqueous ethanol underestimated the extent of migration of fat-soluble compounds such as 1,1-biphenyl, diphenyl sulphide and ITX, from shrink sleeves through high density polyethylene (HDPE) containers into milk, whereas 95 % ethanol overestimated such migration.
The use of UV cured inks that generate benzene during cure is not advisable on shrink sleeves intended, for example, to package HDPE containers containing dairy products, where there is no functional barrier to migration. It was also shown that with existing UV cationic ink technology, appropriate ink systems are currently available that do not result in the migration of such compounds. Transfer of substances directly to the mouth from shrink sleeves, when drinking directly from the bottle, was also investigated using a saliva simulant. Very little transfer was observed.
This research has shown that migration from shrink sleeves through the food container can occur into food and that vigilance is required to ensure that this is kept to a minimum. The contractors note that their findings provide reassurance to the industry that little migration of printing ink solvents should occur if the voluntary best practice guide for residual solvent content is followed. For migrants with specific migration limits at or below 10 parts per billion (ppb) in the food, concentrations in the sleeves may need to be below 0.01 milligram/square metre (mg/m 2 ). This research underlines the importance of undertaking migration tests on novel inks, such as UV cured inks, before they are used to print sleeves applied to flexible polymeric food containers, because of the risk of migration of aromatic photoinitiators and their photolysis products.
The final report is available from the Agency's Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk )
Contact
: For any enquiries concerning this research project, please contact the relevant programme manager contact or email:
science@foodstandards.gsi.gov.uk
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