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FLEXO Magazine : May 2011
Technologies & Techniques scavenger in the form of a sachet. The mixture of chemicals found in the sachet, mainly salt and iron, react with the water and oxygen to become rust. Therefore the contents of the bag can sift through the oxygen in the packaging and moisture from the food to create rust and eliminate the oxygen from the package (Kaufman). Another example of a scavenger comes in the form of a film. For an ethylene film, the ethylene absorption agent is bound to films through polymer process- ing and then placed inside the packaging as a liner or sheet. This liner/sheet then absorbs the ethylene gas as it is emitted inside the package (Research Gate). A third functional component of smart packaging is a bar- rier. The barrier works as a limit or boundary to restrain or keep out anything unwanted, and is designed to be impervi- ous to gas migration (Toray). An example of this is a film that resists oxygen permeation. The film is usually multi-layer with the outer top layer a strong plastic, the inner layer a thin layer of gas barrier material, and the inside or bottom layer almost always a soft, low-density polyethylene (Toray). An alternative to using a composite material is to coat a plastic with a bar- rier coating. The property this research experiment assessed is the barrier property, through a form of specialty coating. METHODS & MATERIALS The research was conducted using a series of donated and in-house materials. I received the specialty ink SunBar 1.1 from Sun Chemical, one of the largest ink corporations nationwide. This two-part oxygen barrier coating, which Sun Chemical announced at Drupa 2008, prevents the penetration (or loss) of specific gases that could compromise the life of the packaged product. There are several benefits to this bar- rier coating, including its broad range for film application, its resistance to flex cracking and its suitability for application to substrates through conventional printing and drying meth- ods (Sun Chemical). This oxygen barrier coating was tested using different screening technologies in the search for plate technology that provides the most effective way of printing with functional inks. The coating was applied using three plates. The first plate used was the control plate. This DuPont Cyrel DFQ plate was run with the oxygen barrier coating to record the measure- ments for oxygen permeability using a conventional plate. DFQ plates offer good ink transfer and represent the higher end of conventional plate technologies. TAbLE 1. The weight of the coating applied to the film. Film Total Weight 4.0 in2 (g) Coating Weight 4.0 in2 (mg) Film with no treatment 0.1130 n/a Film with Control treatment (conventional plate) 0.1137 0.7 Film with Treatment 1 (plate cell patterning) 0.1140 1.0 Film with Treatment 2 (capped plate) 0.1140 1.0 TAbLE 2. Average oxygen transmission rate for each plate method of application with parameters at 23̊C and 0.0% RH Plate Oxygen Permeability Test 1 (cm3/m2/24hrs) Oxygen Permeability Test 2 (cm3/m2/24hrs) Mean (cm3/m2/24hrs) Control 896 938 917 Conventional 202 131 166.5 Plate Cell patterned 142 190 166 Capped 111 83.7 97.35 TAbLE 3. Comparison of oxygen transmission rate of best-achieved results with the film already treated with an oxygen barrier coating. These results reveal a significant decrease between the untreated film and the treated film, while the variation between the exxon Mobil treated film and capped treated film is minimal. Oxygen Permeability (cm3/m2/24hrs) Untreated film Exxon Mobil treated film Capped plate treated film 917 70 97.35 The second was a plate cell patterned plate. (See Figures 1 and 2.) This DuPont Cyrel DFQ plate was produced using EskoArtwork’s plate cell patterning screening technology for increased ink laydown. In plate cell patterning, screening engines place cells in the solid areas of the plate by imaging them on an imagesetter, or directly onto the plate unit (Nexus). The cells found in the solid areas serve a similar function to cells found in anilox rolls: to provide more uniform ink. The re- sults include lower ink consumption, lower pressure require- ments during the printing process, improved solids and finer positive images (Nexus). The third plate tested was a capped plate. The capped plate was a MacDermid Epic capped plate, provided by Mac- Dermid Printing Solutions. Capped plates have a micro-rough cap layer covering the entire plate, which helps produce excellent ink transfer for both solid coverage and fine dot reproduction (MacDermid). Each plate was applied with the oxygen barrier coating using a 360 CPI, 6 .53 BCM anilox roll and the same print deck with similar impression settings. The substrate evaluated was a 2 mil oriented 5000 clear polypropylene from Multi-Plastics, Inc. It was important that this film be a non-heat sealable film because that indicates that the film has no barrier coating to start with. Once the film was run through the press using all three different plates, the samples were tested using an Illinois instrument to evaluate the oxygen transmission rate. This measures the amount of oxygen gas that passes through the substrate in a 24-hour time period, ultimately assessing the permeability of oxygen through the package. 144 FLeXO MAy 2011 www.flexography.org
Sustainable Spring 2011