Digital Magazine

The Back Page: Taking it back 54 years

Originally published in Paper, Film and Foil Converter in July 1966

Core of the Matter

If you Aren’t – You Ought to be

By Dom A. Pering, Packaging Consultant

IT SEEMS apropos that a column entitled “Core of the Matter” should discuss cores literally as well as figuratively.

For many years the 3-inch I.D. core has been well established as a standard among flexible packaging converters. But now we are beginning to note deviations toward the 6-inch core. On a few types of packaging machinery, 6-inch cores are mandatory and most film suppliers are offering a choice of either 3-inch or 6-inch cores. Some converters are switching to the 6-inch cores on incoming films even if only to gain reuse advantage on the cores they receive. But the story on larger cores is larger than just that.

Core of Cores

Film suppliers, especially those dealing with very thin, very soft or extensible materials, have already learned that larger cores assure better roll formation, larger rolls and lower waste.

In the converting plant, large cores at the rewind end of presses, laminators and coaters make good sense. Laminated structures, some of which require curing time to achieve fully cured bonds, especially need to be made and handled on larger cores – the product will be better and waste will be lower.

Wax lamination or heavy stocks that assume a permanent set and coated materials that are inclined to block are better served by larger rewind cores during converting processing operations.

End users for the most part are going to insist on 3-inch cores for a long time to come. Thus, the converter will be forced to use both sides – 3-inch I.D. for finished goods and 6-inch or larger for in-process materials within his plant.

It is a great bother to replace core chucks, convert mandrels, convert core cutters and stock two sizes of cores. It is a problem that some plant managers would like to ignore or defer. But it is an important problem that reflects on converting costs and quality and it cannot be swept under the rug.

If you aren’t using larger cores on your in-process materialsyou ought to be.


Maylar, Scotchpar and other polyester films are assuming ever greater importance in packaging. And since they are generally used in very demanding applications such as boil-in-pouches, sterilization packages and thermoformed vacuum packages, printing requirements become specific and severe. Inks must withstand forming, heating, boiling, freezing and severe abrasion abuse.

Unfortunately, the ideal inks have yet to be formulated. Ink companies are hard at the task, but the problem of adhesion to these low energy surfaces still haunts them. Formulations that print cleanly in gravure are not adaptable to flexography because of solvent attack on rubber plates. Most flexo formulations are low on adhesion or weak in color strength. And two-component systems are both costly and difficult to use.

Add to this, a too-often-overlooked detail: inks used on M24 and M27 Mylar are designed to adhere to the polymer-coated side of these films – they won’t adhere well to the uncoated side of the polyester films.

Many of the polyamide based inks that are claimed to be all-purpose inks will adhere and print clearly but, they lack the thermal resistance required to many polyester film applications. And, they are not compatible with most adhesives and primers used in laminating or extrusion coating on reverse printed polyesters.

Recent studies indicate that corona discharge treatment of the polyester will alter the surface energy of polyesters sufficiently to improve ink bounding. For best results, the treating should be done in-line just prior to printing. With in-line Lepel treaters good results have been obtained with conventional acrylic and modified acrylic ink bases.

As a convertor of polyesters, if you aren’t aware of the value of in-line corona discharge surface treatment of these filmsyou ought to be.


It has long been accepted practice to apply wash coating to foil/paper laminates to prepare the aluminum surface for acceptance and bonding of printing inks. These “was coatings,” as they have come to be called, are often misunderstood by a large part of the converting fraternity. Because of the unfortunate nomenclature “wash,” many assume that this operation actually removes oils from the metal surface, thus aiding adhesion.

In fact, properly annealed aluminum foil is free of oil and direct printing on the mounted foil bonds very well if the proper inks are used. On unmounted foils, no wash is needed.

The wash coating is needed only when the aluminum is laminated to paper or film and actually serves as a separator between the outside foil surface and the paper or film to which it is laminated while the material is stored in roll form. Thus, the “wash” does not correct a condition that exists on the foil surface – it prevents it from developing.

Now, all of this is “old hat” to people accustomed to printing on foil. But for some inexplicable reason some of these same people do not relate this to other processes that involve the same sequential conditions. If foil is laminated to paper in one operation and is wound into rolls, then is extrusion coated with polyethylene on the foil dies, the foil surface must be protected or separated from the paper by a “wash” coating.

If no coating is used during the first laminating process, the same adhesion problem that is known to exist in printing will exist with most laminating adhesives, extrusion primers or coatings. The foil on any laminate must have a wash coating applied before it is rewound. This applies equally to printing, coating or further laminating.

If you aren’t “washing” foil on your adhesive or extrusion laminatoryou ought to be.


Slip problems are common ills in many flexible packaging applications. Most uncoated oriented polypropylene film applications – especially the PP / K cello combinations that are now gaining favor in snack food packaging – sooner or later run into slip problems on packaging machines. The film drags on formers and the material tears or fails to “track.”

Useful coatings are now available that can be printed, wicked or sprayed on the film surface to achieve the required slip. These are ethyl alcohol solutions that present no serious drying problems and can be applied without major machinery modifications.

If you aren’t using this machineyou ought to be.


Many two-component curing type inks, coating primers and adhesives are being used in converting. When these products are fully cured on substrates their performance and chemical resistance is remarkable. But when they are fully cured in the cells of gravure cylinders, pans and pumps, they are a disaster.

Solvents will not move them and clean up appears to be impossible; clogged gravure or knurled cylinders begin to give erratic results and no amount of elbow grease and scrubbing will prevail.

Very effective detergent powders available for “cleaning out” inks, adhesives, coatings and primers will wash on even the curing types. They must be made into water solutions and kept at about 150° F. A two or three hour soak will loosen the most stubborn materials. They are more effective, safer and much less costly than organic solvents.

If you aren’t cleaning up with detergent solutionsyou ought to be.

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