Aqueous products for the flexible converting industry. Waterborne primers, coatings, and adhesives.

In extrusion lamination of roll stock for flexible packaging, good adhesion consists of two components: (1) sufficient intimate contact between the substrate and extrudate and (2) subsequent chemical bond formation between the two surfaces.  Although some mechanical inter-locking may occur when the substrate is porous or semi-porous (e.g.: paper or nonwovens), this mechanical “bond” is usually not sufficient to survive the down stream handling and use of the structure.  On the other hand, chemical bonding, in the form of covalent or ionic linkage, can provide the chemistry to insure package integrity.
 
In some extrusion coating and laminating operations, primers are used to provide the substrate surface modification needed to achieve these strong chemical bonds.  Once the film is successfully primed, it is well known that extrusion variables will significantly affect the final bond quality.  Some key extrusion variables are:
 
oxidation in the air-gap (via heat and air-gap distance)
heat (via thickness & temperature)
choice of polymer
 
Many papers have examined some of these variables [1, 2, 3], and the results have yielded valuable tools for converters.  This researcher first presented work investigating the relationship between machine variables and adhesion of an extrusion-coated polyolefin to a primed substrate in 2002 [4].  Specifically, we want to study the effects of machine variables on the level of effective oxidation of the polyolefin melt, since that oxidation is the key to strong chemical bonding of the extrudate to the primed substrate.  In the current work, we limit our polymer of choice to a low-density extrusion coating grade with a melt index of about 8 and density of about 0.917.
 
By Bruce Foster