ADD-COAT-7962 Cellulose esters for shrink film applications · Cellulose esters for shrink film applications Better processing performance and appearance in printing inks ADD-COAT-7962
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Cellulose esters for shrink film applications Better processing performance and appearance in printing inks ADD-COAT-7962
Cellulose esters for shrink film applications Better processing performance and appearance in printing inks
ADD-COAT-7962
Presenter
Presentation Notes
This presentation provides information which explains how cellulose esters are used by ink companies to produce ink formulations which find use in shrink film applications. This work is also demonstrated in the technical tip EU TT 64
Content
Segment overview Advantages of using CAB and CAP How CAB and CAP address challenges Comparing CAP to nitrocellulose Conclusion
Segment overview
Shrink film ink enables durable, eye-catching designs reverse printed onto flexible substrates that shrink onto containers under the influence of heat.
Substrates include: PET, OPS, PVC
Desired attributes of shrink film ink include:• Durability • Flexibility • Excellent adhesion• Vibrancy of color• Fade resistance• Safety and compliance
What is a shrink film ink?
Presenter
Presentation Notes
Shrink film labels offer a cost effective route to apply highly decorative features to packaging such as bottles and other rigid or semi-rigid containers. In the image shown in the slide examples of alcoholic beverage containers are shown which feature designs which would be very costly and difficult to apply direct to the container. Other applications include yoghurt pots, cosmetic products and many other consumable products. The main substrates used for such labels include polyester such as Eastman Embrace™ films but also orientated polystyrene (OPS) and poly vinyl chloride (PVC). The key features of such materials is that during their production, internal stresses are built into the films, which, when subjected to external stimulus such as heat, result in a dimensional change in the film (shrinkage) which causes the label to shrink to the shape of the underlying article such as a bottle.
Shrink-film (PET, OPS, PVC)
Colored inks Backing white
Reverse printed gravure or flexo
Processes
Ink formulations must be compatible with these processes and retainlong term durability and appearance in the final application.
Printed film formed into a sleeve & reeled
Heat/steam
Printed inside
Shrink film printing
Reversed process
Presenter
Presentation Notes
TOP FIGURE: Shrink film labels are most commonly reverse printed i.e. the image is shown through the transparent label with the film stock acting as a protective surface. The normal printing process involves printing of the coloured inks followed by the application of a backing colour – most commonly an opaque white. This backing coat serves two main functions 1. improved opacity and decoration and 2. it prevents print quality like blocking/sticking of the ink surface which contacts the underlying container. Surface printed labels can also be seen in use often utilizing opaque film stock. Due to the high quality nature of the print image and often long print runs, this application is ideally suited to gravure printing but flexography and even digital non-impact printing can be used – or in some cases combined. BOTTOM FIGURE: The printed design (in this case reverse printed) is applied onto the label film and the film is then passed over a roller system which is configured to form the film into a continuous tube or sleeve. The sleeve is made complete by jointing methods involving either a thin bead of adhesive or more commonly solvent. The printed sleeve or tube is then reeled and is ready for application by the end user. Since the sleeve is reeled it is subjected to high compressive forces which require the inks applied to be able to resist blocking. It is also very important that the inks have good solvent release since any residual/trapped solvent can potentially also cause problems such as blocking or even cracking/attack of the label stock – particularly at the folded edges of the tube in the reel. To apply the label to the packaging/container, the printed labels are cut, placed around the container and then subjected to heat which induces shrinkage of the label around the container. The most common form of heat application is achieved by steam shrinking where the packaging line passes through a tunnel where steam is applied.
Advantages of using CAB and CAP
CAP and CAB in printing inksAdvantages for shrink film applications
Improves processing performance
High melting range
Oil and grease resistance
Improves appearance and long term durability
Delivers compliance & safety
FDA cleared* Low flammability
Low density
Fast solvent release
Good pigment dispersion
Good scuff resistance
UV stability
Carrier for pigments and dyes
* Check with your Eastman representative or distributor regarding safety clearances for your region
Presenter
Presentation Notes
Cellulose esters are available in several different grades but in general the list featured here represents the key features of these products for printing ink applications.
CAP in shrink film inksPerformance and appearance advantages
Improves processing
performance
Superior heat resistanceCompared to nitrocellulose systems, inks formulated with
Eastman CAP resins have superior heat resistance. This quality allows steam or dry heat shrinking with no adverse effect to a design’s
color or white brilliance.
Less blockingCompared to other systems, inks based on Eastman CAPs
have superior solvent release qualities, preventing issues such as blocking in the printed reel.
Improves appearance
and durability
Reduction in “wet look”“Wet look” is a common problem for steam shrunk sleeves. Inks based on
Eastman CAP have shown much less wet look 24 hours after shrinking when compared to nitrocellulose systems.
Enhanced moisture releaseA common problem in steam-shrunk applications is ink transfer to the bottle when
the sleeve is removed. Inks based on Eastman CAP have greater moisture resistance, and thus do not transfer onto the plastic or glass bottle. This may be a
problem when other ink systems are used.
Presenter
Presentation Notes
In discussions with ink customers and by laboratory evaluation of cellulose acetate propionate in shrink film applications, the following main advantages have been highlighted; High temperature resistance to resist the shrinking process. Excellent blocking resistance due to fast solvent release and relatively high Tg which prevents sticking/blocking in the printed reel. Reduction in ‘wet-look’ when labels are shrunk using steam it is sometimes unavoidable that water is trapped between the film and the bottle This harms the appearance of the bottle as the trapped moisture can clearly be seen. CAP seems to be less prone to this effect possibly as it may alter the surface tension of the ink preventing the water from partially wetting the label. Moisture resistance – the formulated ink must be able to withstand steam/moisture from the shrinking process.
Comparing CAP to nitrocellulose
Sample ink formulation
White backing ink formulation, gravure appliedIngredient Wt. %
For reverse printed transparent labels a backing white is commonly used. Since this is the actual ink surface which contacts the underlying container/bottle, it is also vital that it is correctly formulated to allow good shrinkage, adhesion to the underlying ink and prevent the label sticking to the bottle. Note the formulation is a CAP/acrylic type and the solvents used for the backing white are relatively mild compared to the coloured inks. Using strong solvents like ethyl acetate etc. could result in the white backing ink re-dissolving the underlying ink too much. Polyethylene wax is also routinely added to help with block resistance and minimize interaction with the container being decorated.
Total 100.0*Since such inks are applied directly onto the substrate, they may require an adhesion promoter such as titanium complex or polyethyleneimine. For more information see the technical tip, Adhesion Promoters for Cellulose Ester-Based Inks, TT-63.
Presenter
Presentation Notes
The coloured inks are applied directly to the shrink label surface. This requires the use of stronger solvents such as ethyl acetate to 1. help with adhesion and 2. evaporate quickly from the print to prevent solvent entrapment. Remember as the label is heat sensitive, the printers/convertors can not utilize heat assisted drying in the print process. Failure to adequately remove ink solvent can also lead to issues of pick-off in multi-colour printing. i.e. the application of the next colour sticks to the underlying ink and partially removes it. Adhesion promoting chemicals such as polyethylene imine or titanates are also commonly used to improve adhesion to substrates such as polyesters. This is described in our technical tip TT-63 adhesion promoters for cellulose ester based inks.
Design of experimentComparing CAP and nitrocellulose
The inks were printed side-by-side onto PVC shrink film and evaluated for adhesion and scratch resistance.
A cylindrical sleeve was fabricated using the printed substrate with the overlapping seam being glued using a cyanoacrylate adhesive.
The sleeve was then placed around a glass beverage bottle and shrunk around the container using steam.
The assembled bottle was stored at ambient temperature for 7 days before removing the film and evaluating the appearance of the ink film and bottle surface.
Presenter
Presentation Notes
To demonstrate some of the advantages of CAP in the laboratory, we obtained a commercial CAP/acrylic based shrink film ink and compared this to a commercial nitrocellulose based shrink ink from the same European ink producer. The inks were applied side by side onto a PVC shrink film. Once dry the printed film was formed into a cylinder with the printed surface on the inside and the seam joined using a cyanoacrylate ‘super glue’ adhesive. The cylinder was placed over a glass bottle and subjected to steam from a portable steam generator until it formed the profile of the underlying bottle. The bottle was stored at room temperature for 7 days before removing the label and assessing the quality of the underlying ink.
Evaluation of results CAP compared to nitrocellulose
Ink transfer from NC ink
NC CAP
Note: scratch resistance tested and film replaced on bottle for display purposes
NC based CAP based
The CAP-based formulation provides better adhesion in both phases (before and after shrink/store)
Presenter
Presentation Notes
Once removed from the bottle we observed that in the case of the NC based ink, a small amount of the white ink had transferred from the label to the glass bottle indicating a problem with adhesion. The CAP based ink was intact. The tape and fingernail scratch adhesion of the inks were also assessed. The image on the left shows the reverse printed label back in-situ on the bottle for display purposes and clearly shows that the NC based ink had very poor tape and fingernail adhesion after the shrink process. Note this adhesion was 100% before shrinking/7day storage. The CAP based ink had excellent adhesion before and after shrinking/storage.
Conclusion
Conclusions
This study highlights the performance advantages of CAP-based ink systems for use in high quality shrink wrap applications and explains why leading ink companies utilize cellulose esters for such applications.
Literature available at Eastman.com• Cellulose Esters in Printing Inks for Shrink Film Applications, EU (TT-64)• Adhesion Promoters for Cellulose Ester Based Inks, EU (TT-63)
Presenter
Presentation Notes
The information featured in this presentation is available in two technical tips EU-TT64 and EU TT 63.
Disclaimer
Although the information and recommendations set forth herein are presented in good faith, Eastman Chemical Company makes no representations or warranties as to the completeness or accuracy thereof. You must make your own determination of their suitability and completeness for your own use, for the protection of the environment, and for the health and safety of your employees and purchasers of your products. Nothing contained herein is to be construed as a recommendation to use any product, process, equipment, or formulation in conflict with any patent, and we make no representations or warranties, express or implied, that the use thereof will not infringe any patent. NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESS OR IMPLIED, OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR OF ANY OTHER NATURE ARE MADE HEREUNDER WITH RESPECT TO INFORMATION OR THE PRODUCT TO WHICH INFORMATION REFERS AND NOTHING HEREIN WAIVES ANY OF THE SELLER’S CONDITIONS OF SALE.
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