What's New with Primers, and a visit to old friends
- Published: October 18, 2012
I remember when Jeff had just began attending TAPPI functions, and encouraging him to become an officer on the Extrusion Coating Committee. For both our sakes, I won't tell when that was, suffice it to say those were the good old days. Jeff, now President of Mica Corporation, quickly rose through the ranks, ascending to the Board of Directors at TAPPI. I met Bruce shortly afterwards when he worked for Eastman Chemical. We have given many technical presentations together, both here and abroad, so I decided to visit to see what was new in the world of water-based primers.
In the world of laminating, all materials do not adhere well to all other materials. The standard substrates and coating/adhesives have been thoroughly studied, and standard products & processed have been adapted for them. By standard, I mean for example, low density polyethylene (LDPE) onto paper, ethylene-vinyl acetate (EVA) onto oriented polyester film (OPET), and the like. For these products, simple primers such as polyethylene-imine (PEI) and process enhancers such as corona treating and flame priming work sufficiently well.
One product / product combination that has been routinely problematic is polypropylene (PP) or PP / PP coatings or laminations. For those that have done it, coating PP onto a PP substrate yields less than optimal adhesion characteristics, to say the least. There are several reasons for this poor adhesion phenomenon, not the least of which is that PP is a highly stabilized non-polar resin, and the additives and anti-oxidants incorporated into the PP inhibit oxidation of the surface during extrusion. Other factors such as narrow molecular weight distribution, little to no long-chain branching, higher melting point and crystallinity (than LDPE) all inhibit the adhesion to PP.
To combat these "deficiencies" in PP, converters can maximize temperature and pressure at the die lips, minimize the time in the air gap via minimizing air gap and maximizing line speed, as well as maximizing nip roll pressure and chill roll temperature, all within processing limitations for each given product made.
Even with all these tips, it is often difficult to achieve permanent optimal adhesion to a polypropylene substrate. In these cases, a primer is a welcome solution. Mica is offering a new primer called MICA R-3332 in these situations. For further information, please call Bruce Foster, Technical Sales Manager at Mica Corporation at +1 203 922 8888.
