- January 31, 2006, David J. Bentley, Jr., Contributing Editor
Providing practical information to the converting and packaging industries…
Advancements In Melt Fracture Elimination Technology
by Rafael J. Castillo, Dual Spiral Systems, Inc.
In extrusion, melt fracture or sharkskin is a phenomenon attributed to the stick/slip behavior of molten plastic flowing through a melt channel. If unaddressed, melt fracture causes the extrudate surface to appear rough with diminished physical and optical properties. Typically, melt fracture occurs when polymer melt is forced to flow through narrow die chambers at elevated shear stress levels. Traditionally the onset of melt fracture has been delayed through the application of polymer processing aides that have acted as a lubricant between the melt and the wall of the channel in which they are flowing.
Some preliminary data has been collected on film extrusion processes for a new low coefficient of friction coating. Some preliminary data has been collected on film extrusion processes. This paper details the results of preliminary data and analysis and introduces the notion of using low friction coatings as an alternative to addressing melt fracture elimination.
This developmental work has shown that the most cost effective way to eliminate the melt fracture phenomenon is to use a durable low friction coating that causes the polymer melt to slip against the die wall consistently. It must be sufficiently robust to withstand the abuse of die lip cleaning. Tests at multiple industrial film extrusion installations verified its effect in melt fracture reduction. Nickelplated lips were used as a benchmark since that is the standard coating in North America. The data collected through this investigation was for an additive and processing aide free resin that was particularly susceptible to melt fracture when processed on a blown film die having nickel plated lips. When the resin was processed on the same extrusion die that had its die lips coated with the low friction plating, the melt fracture at the same extrusion rate was eliminated. Furthermore, melt fracture was not achieved until a significantly higher output rate.
High Barrier Advancements In Metallized Films
by Jim Lush and Dante Ferrari, Celplast Metallized Products, Ltd.
Some flexible packaging applications for dry powder, liquid packaging, lidding, and medical /pharmaceutical applications are highly oxygen or moisture sensitive. They require excellent barrier properties. Many such applications have historically used foil as the barrier layer to protect the product during its life cycle. One reason is that standard metallized polyester has not previously met the barrier needs of these high end products.
Our tests used standard and high barrier metallizing conditions both run at 2.2 optical density (OD). The barrier properties of 2.2 OD metallized PET were measurably improved using our new high barrier process. This was reproducible over several production runs and on several samples tested at different points in each roll. We also investigated the possibility of improving metallized PET barrier performance at 2.8 OD. Since more aluminum is being deposited at this OD, the 2.8 OD already provides improved barrier properties over 2.2 OD. Our aim was to determine whether the high barrier process further improved barrier properties at this optical density.
In a typical flexible packaging application, the adhesion of metal to its substrate is critical. A minimum bond value of 200 g/in. is generally acceptable for many applications. Our tests showed that metal adhesion values of the high barrier films are equivalent to those of the standard metallized PET films.
A new high barrier metallizing process provides excellent barrier results at standard and higher optical densities. These results are highly reproducible and are achievable irrespective of PET film type. At a 2.8 optical density, a metallized PET with unflexed barrier properties approaches those of foil for oxygen and water vapor. This gives converters a true low-cost option to foil for high barrier applications.
Comparison Of Corona And Flame Treatment Of Polymer Film, Foil, and Paperboard
by Werner Eckert, Arcotec GmbH
Many surfaces have low surface energy (surface tension) and poor wettability. Reasons for this may be found in material properties especially for polymer surfaces and in surface contamination due to manufacturing process. With surface treatment, wettability can be increased to provide better contact between surface and a fluid such as ink, paint, adhesive, or other coating material.
Among other methods, physical treatment methods such as corona, plasma, or flame treatment are common. An advantage of these compact treatment units against chemical treatments is that they can easily be integrated into the production line to provide good treatment results even at high operating speeds. In addition, they do not generate any significant waste. Corona treatment is suitable for even surfaces and therefore has use primarily for treatment of films and foils. Although molded parts are the common domain for flame treatment, numerous flame treatment units operate in web applications. Both methods have definite advantages.
With corona, parameters that influence the treatment effect are the gap, electrode configuration, power, and web speed. Since the gap between electrode and counter-electrode (roll) can only be a few millimetres, it cannot be varied. Power and web speed are therefore the most important parameters that determine the corona dose (energy input per area). For flame treatment of web material, the typical arrangement consists of a burner that flames onto the web guided by a cooling roll. Besides web guiding near the flame, the roll has the task of maintaining a constant distance between web and flame. It also removes excess heat from the system. For large web width, the burners require cooling too. A housing built around the flame unit may be useful for removing the exhaust gas generated during the flaming.
In the flame, activated molecules are produced due to the high temperatures up to 1800°C. These are mainly oxygen and hydroxyl groups. Corona does not generate hydroxyl groups. Due to an excess of air in the air and gas mixture, some oxygen remains in the flame for activation. Hydroxyl comes from the activation of water that the combustion process creates. Besides cooling drum and exhauster the flame treating unit consists of an air/gas controller and special burners. The controller together with a special mixing chamber provides the air/gas mixture by controlling the air flow and the gas flow. A rather exact and fast measure of flow rates can be carried out by mass flow meters.
Corona and flame treatments are well-established methods for increasing surface tension and adhesion properties of molded plastics and film, foil, and paperboard. New developments in techniques and a better understanding of the processes ensure product quality and demands in the future. The common question about which method is best suitable for a given adhesion problem does not have an easy answer. Running trials is necessary. For special requirements, flame treatment of films can be an alternative. Silane precursors dosed into the flame may lead to further improvements of adhesion. In principle, other precursors are conceivable to create layers with custom-designed properties.
Latest UV/EB Coating And Adhesive Technology For Food Packaging Applications
by Albert Lin et al., Sovereign Specialty Chemicals, Inc.
Ultraviolet (UV) and electron beam (EB) technologies have helped many industries to capitalize on the distinct advantages of zero VOC and HAPS, faster line speeds, lower energy consumption, etc. A comprehensive testing protocol using the cell extraction method and liquid chromatography with a mass selective spectrometer (LC-MS/LC-MS-MS) was developed for UV/EB curable, acrylated coatings/adhesives/inks to help determine the suitability of the chemistry as part of food packaging materials. This testing protocol helps to determine FDA compliance of the UV/EB curable chemistry by supporting the “No Migration”/“No Food Additive” statutory exemptions under FDA regulations.
Recent advancements in raw materials, availability of lower cost EB curing equipment, instrument-aided product development, and establishment of proper FDA testing protocols have made UV/EB curable chemistry a viable option for many food packaging uses including adhesives, coatings, and inks. EB/UV technology has finally emerged as a mainstream chemistry for food packaging with many environmentally friendly benefits and productivity enhancement attributes such as in-line processing and on-demand manufacturing.
EB/UV technology also continues to provide converters with cost saving alternative to the traditional chemistry. In the flexible packaging area, the mono-web EB coating application is starting to make its impact in the marketplace, and the single pass, multi-layer laminates converted with EB laminating adhesive are being tested for their economic and performance attributes. In the graphic art/print finishing area, specialty and surface effect UV coatings such as integrated labels, printable magnets, pseudo-embossing, and foil-like surface effects have been catching the attention of designers, printers, and end-users alike with their benefits and in-line manufacturing flexibility.
For information about the PLACE Division of TAPPI, access the TAPPI web page at tappi.org. To obtain the complete papers whose expanded summaries appear in this section, go to the TAPPI web site at tappi.org., then click on "the PLACE" in the section designated Journals.
Telephone inquiries are welcome at the TAPPI Service Line by calling 800/332-8686 in the United States, 800/446-9431 in Canada, or 770/446-1400 in other countries. Send FAX to 770/446-6947. Address mail to TAPPI, 15 Technology Parkway South, Norcross, GA, 30092.
ePLACE Electronic Newsletter
Receive technical information delivered to your computer every other Monday from the PLACE Division. Subscribe on-line at tappi.org by clicking Newsletters under the People heading.