- May 01, 2007, David J. Bentley, Jr., Editor
Chemical Analysis Of The Polyester/Metal Surface Of A Delamination Failure
by Eldridge M. Mount III, EMMOUNT Technologies
Application: The paper presents possible causes for a degraded polyester surface causing delamination in an adhesive lamination of a printed metallized polyester film to a LLDPE sealant layer.
Laminated films are important in producing flexible packaging. The lamination after formation should remain adhered. When failure occurs, this can be due to poor metal adhesion from a degraded or a contaminated film surface on which the metal was deposited, improper lamination process conditions, or perhaps poor metallizing conditions. The mode of failure and the location of the lamination failure help to determine the likely source of the failure. In many instances with metallized films, one normally expects that any delamination between the metallized film and the sealant will occur without transfer of the metal to the adhesive. If transfer does occur, the peel strength will exceed a specified value.
In many applications, acceptable peel strength of a metallized lamination is 100 to 300 grams/inch with some metal lift being acceptable. Seldom is 100% metal lift acceptable in any metallized lamination unless the peel strength is very high relative to the specification because of the uncertainty that this raises about the “quality” of the metallized films and the barrier properties. In other words, the metal should be difficult to remove from the metallized film surface.
When the metal lift is 100% and the peel strength is low or not measurable, one generally assumes that the metallized film has failed due to the poor metal layer adhesion to the substrate film. XPS is a sensitive way to determine the chemical structure of the surface of a polymer sample. In addition, it is also useful to determine the transfer of material between two surfaces which are delaminated.
Toughening Clear Polypropylene With Styrenic Block Copolymers
by David Hansen et al., Kraton Polymers U.S. LLC
Application: Styrenic block copolymers are good impact modifiers for polypropylene by providing impact strength and clarity. Using very high loadings can give flexible and very clear blends with only 8% haze.
Polypropylene (PP) has wide use in packaging, textile, household goods, and automobile applications because of its high service temperature, good processability, recyclability, and low cost characteristics. Recent years have seen an increasing interest in clear polypropylene applications with high impact properties. Impact PP copolymers have good impact toughness at low temperature but are not clear. PP or random PP copolymers (rPP) with 2-6% of a comonomer are relatively clear particularly when clarified, but they lack impact especially at low temperature. Polyethylene (PE) copolymers with a density of 0.902 to match the index of refraction of rPP have had use as clear impact modifiers, but they do not toughen very efficiently below 0 °C. This study examines styrenic block copolymers that achieve good clarity and good low temperature impact properties. In addition, some block copolymers can be blended at high levels with rPP to achieve outstanding clarity for flexible elastomeric applications. This study examined styrenic block copolymers including styrene-ethylene/butylene-styrene block copolymers (SEBS) with a modified ethylene/butylene midblock.
Optimized styrenic block copolymers are very effective modifiers for clear PP or rPP. The new ethylene/butylene modified midblock SEBS make excellent blends with PP and rPP and have good clarity properties over a wide range of compositions. At high levels above 50% in rPP, they make spectacularly clear blends with rPP. The modified midblock polymers also are good impact modifiers down to -10 °C and exhibit minimal blushing with impact. An experimental styrenic block copolymer modifier is unique in providing excellent low temperature impact in rPP copolymers down to -20°C while maintaining good clarity.
To obtain the complete version of these papers, go to www.tappi.org, and select “the PLACE” under the Publications/Bookstore heading.