Barry Alan Morris

Understanding Why Adhesion in Extrusion Coating Decreases With Diminishing Coating Thickness

It is well known that in extrusion coating, the coating adhesion to the substrate decreases with decreasing thickness. The study on this phenomenon is divided into three parts. Part I explores the reduction in adhesion of LDPE to paper and other porous substrates. Several hypotheses are proposed for the origin of this decrease, including a reduction in oxidation time, faster cooling in the air gap, and more rapid quenching in the nip. A model of the molten polymer penetration into the substrate shows that the greatest effect is cooling in the nip; thinner coatings have less time to flow into the substrate interstices once the chill roll contact is made. The model results agree well with experimental adhesion data from the literature. In Part II, adhesion to aluminum foil and other nonporous substrates is studied. Several hypotheses are proposed for why peel strength decreases in these structures, including a reduction in the air gap time, faster air gap cooling, more rapid nip quenching, and stress imposed during drawing. Modeling and experimental results show that cooling in the nip and imposed stress have the greatest impact. In Part III, the peel test is analyzed to understand why the peel strength of better adhering adhesives are more sensitive to changes in coating thickness. The analysis shows that changes in the critical dimension of the deformation region at the peel front may be responsible.

Chapter 15 – PE based multilayer film structures

Publisher Summary This chapter focuses on multilayer flexible packaging, which involves the combination of two or more layers into a composite web or tube that provides functional, protective or decorative properties. For this, polymer materials are selected and the entire packaging structure is designed to meet the performance requirements specific to that particular application. Multilayer flexible packaging structures can lower the cost of many film structures by reducing the expensive polymer used, increasing the less costly polymers, using recycled material, or reducing film thickness. Competitive advantages can be achieved for many film structures ranging from the high technology barrier food packaging films to the heavy duty shipping bag market. A critical factor in developing successful flexible packaging applications has always been a good understanding of the target application. The performance properties required by the application and economic comparisons should be evaluated against the many alternative structures. Flexible packaging films are used to provide barrier to gases such as oxygen, nitrogen, carbon dioxide, and water vapor. Other applications may require taste and odor resistance properties. Heat sealability is also a critical property for various packaging applications. A polymer that exhibits low temperature sealability and maintains seal integrity over a broad seal temperature, dwell time, and seal pressure can significantly increase packaging line speeds, improve efficiencies, and minimize seal failures. Heat seal properties are influenced by a polymers thermal and rheological properties as well as factors such as seal bar temperatures, seal bar pressure, dwell time, sealing bar configuration, and package design.