Shrink Sleeve Solutions Looking at narrow web shrink sleeves
Three key technology suppliers, Vetaphone, Paragon Inks and Plasfilms talk about the issues involved with manufacturing shrink sleeves.
Shrink sleeves offer vibrant colours and the creativity of graphics in the round, as shown here by samples of work produced at Berkshire Labels. W
hether you consider a shrink sleeve an extended label or a type of flexible packaging, there are key factors that need to be taken into consideration before embarking on commercial production in this sector of print. As with most processes, success depends on doing your homework and making the right choices with regard to materials and suppliers.
SUBSTRATE BASICS
Dr John Walker (JW) of Plasfilms outlines the basic requirements of heat-shrink substrates:
Q: What are the key properties required for good shrink film products?
JW: The main characteristics are controlled and consistent shrinkage, mechanical properties, clarity, and stability at a wide range of temperatures. This is full body labelling, so 360-degree high quality graphics are essential with ease of processing (printing and converting), with tamper evidence and, of course, recyclability. The shrinkage performance is determined by both the base material and formulation plus the stenter/orientation process.
Q: In terms of film products, which stack up best against these criteria?
JW: The main substrates are PVC, OPS and PETG. PVC has been established and is the lowest cost shrink film but has limited shrinkage, around 60%, and is less appropriate for difficult or complex shapes. OPS
has good shrink capability, around 70% with minimal MD shrinkage. But probably the best is PETG, which has the highest shrink capability of 78-80% and is capable producing complex shapes. It also has the highest level of clarity and has strong mechanical properties that make it suitable for downgauging. On the downside, however, it is the most expensive!
Q: Does the suitability of the film depend on which print process is used?
JW: In simple terms, all of these materials are suitable for printing by flexographic, rotogravure and using UV curing. PVC is less resistant to printing solvents and likewise OPS is more challenging to convert, being sensitive to solvent choice and UV. PETG is more resistant to solvents and therefore has replaced PVC and OPS as the most popular substrate.
Q: Inevitably, I have to ask about the environmental aspect of growth in this market sector – how do you view its impact? JW: PVC is perceived to be environmentally unfriendly although it is relatively easy to recycle. The problem is that the recycling chain is not sufficiently developed. OPS is regarded as recycling friendly, but PETG comes out top as it’s environmentally friendly and readily recycled because the recycling chain is well developed for PET bottles. I’d like to add that energy recovery is also available, and that chemical recycling is also growing in importance. The problem is not at the
front end of the process with film production, but at the rear end with disposal and re-usage.
SURFACE TREATMENT
Of course, the key factor with all shrink sleeve production is that it uses plastic film as its substrate. Being non-absorbent, films can be notoriously difficult to achieve consistently high print quality owing to the variance of surface energy between the liquid ink and the film surface.
Vetaphone VP of technical sales Kevin McKell (KM) talks through the potential issues of printing shrink film.
Q: What are the main issues with using heat- shrink film?
KM: Shrink film is not really different from other plastic materials. You have to control the surface energy between the liquid ink and the plastic substrate. If the surface tension of the film is too low, the inks beads-up on the surface and doesn’t adhere – we call this ‘wetting’, and you need the ink to ‘wet out’ to form a strong bond. We measure the surface energy and the substrate’s adhesive ability in dyne/cm. The higher the dyne reading, the better the adhesion.
Q: How do you persuade ink to adhere to a non- absorbent substrate like film?
KM: You modify the surface of the substrate with a high frequency electrical discharge at close range. This is known as corona treating and it breaks up
22
October 2021
www.convertermag.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46
