I would like to clarify for AICC mem-bers some recent technical questions I have received regarding the use of spray powder as a processing aid to facilitate optimal performance and efficiencies in producing folding cartons, litho-laminated top sheets for boxes, and blister card packaging.
During the production process, several printing steps may be undertaken (front and/or back) as well as application of the heat-seal and other water-based coatings applied over inks in a wet-trap process. Thus, there are a few significant issues during this procedure where spray powder is utilized:
Block resistance
Cure—oxidation of the inks
Complete drying of heat-sealable coatings or water-based coatings
(Note: In all instances, spray powder provides for a small layer of air and/or space between the coated and printed sheets to facilitate curing of all applied inks and coatings.)
Block Resistance
The handling of printed sheets—either pre- or postapplication of the heat-seal coating—requires spray powder to minimize or eliminate the offsetting of inks. This is especially important during the summer months, when high temperatures and humidity levels could increase the propensity for this to occur.
Simply reducing the stack height to eliminate the offsetting is not a truly sustainable year-round option. Spray powder is required to minimize this, and it also provides for the manufacturing efficiencies downstream that the market demands.
Cure – Oxidation of the Inks
The inks themselves are wet-trapped by the various coatings. This forms a layer over the ink, such that they must dry (oxidize) through the coatings to cure and allow for the standard rupturing heat-seal bond required for a blister package or a 100% fiber-tearing bond for a folding carton. Without spray powder, there is not that oxygen layer at the coated stock or ink level to allow for oxidation or ink cure. Thus, the work in progress (WIP) residence time will rise significantly as compared with coated stock with spray powder. The rise will even be meteoric with the higher humidity and temperatures of summer as compared with the dry and cool conditions of winter. Until the ink is cured, no paper bond is occurring to facilitate downstream converting, including side seam gluing.
Complete Drying of the Heat-Seal Coating
As with the ink, a layer of air provided by the application of spray powder allows for the final drying step of the coatings. Without spray powder, some moisture may be left in the coating that, again, extends WIP time as noted with the inks. In addition, the potential for coating pick and transfer escalates significantly downstream.
Summation
Spray powder is a processing aid in the production of printed paperboard packaging. I have never known a powderless non-ultraviolet specification or process in my over 40 years in the folding carton and carded packaging markets. The standard choice of spray powder is typically a waxless powder of about 45 microns, depending on the paperboard surface characteristics, of course. A 3% spray setting will usually provide the performance required with no impact on seal. The heat-seal coatings for carded packaging or cold and hot melt adhesives used for the gluing of folding cartons will not be impacted by any spray powder left after processing when applied at the 3% spray level.
Without the use of spray powder, there will be poor efficiencies and even the likelihood of a final sealed package that does not meet the required market needs of a package typically exhibiting a rupturing blister card seal or 100% fiber-tearing bonded side seam.
Tom Weber is president of WeberSource LLC and is AICC’s folding carton and rigid box technical advisor. Contact Tom directly at asktom@AICCbox.org.
