Yes, Recycled Paperboard is Different
Recycled Paperboard can provide challenges to printing and coating processes. Some time ago, we at Cork were astounded during a sheetfed litho aqueous coating trial. Run on several varieties of recycled paperboard, inks would simply not set on one particular stock.
This occurred after a successful in-line print/high gloss aqueous coating run on a high-grade C2S SBS. [C2S = Coated 2 Sides][SBS=Solid Bleached Sulfate Paper]. A pallet of three varieties of C1S recycled papers, and a pallet of 3 varieties of C1S recycled paperboards, were fed to the press with all press conditions the same.
During this continuous run, the 5th recycled paperboard stock in order dropped into delivery with a large solid green area completely refusing to set. This was in contrast to what happened on all of the other test stocks. The high gloss aqueous coated, inked area remained smearable to the lightest finger touch, not only immediately on the inspection table, but also for more than one-half hour in a 95° F. pile.
Aqueous coated un-inked board areas were not affected. They dried rapidly to the touch when examined on the inspection table. Later, when the sheets were examined after 24 hours, the overcoated inked areas were all completely dry under heavy thumb twist pressure.
Recycled Paper Mystery: Be Cautious and Suspicious
Now, what happened here? How do you go from a completely successful print/high gloss aqueous coating job, then to a variety of recycled stocks and come to one stock where an ink refuses to set? This with all of the press conditions the same.
Well, we’re still not sure what happened here. However, it is clear that something characteristic of this one particular clay-coated recycled paperboard stock did not allow a known excellent performing litho ink to set properly. This problem would make it quite impossible to print and aqueous overcoat any production job successfully.
Lab Testing: All Paperboard is not the Same!
In recent years a large variety of recycled paper and paperboard stocks have been made available to the printer. As this has occurred, we have been aware that print/aqueous coating performance is not always as good as the experience has been on clay-coated SBS.
In an effort to understand these field-reported differences involving recycled stocks, a laboratory investigative project was initiated. This project examined the results obtained when 4 different Cork coating types were lab-coated both over plain un-inked recycled paperboard and over wet litho inked recycled paperboard.
Included in the Cork aqueous coatings selected were:
- 1/ Highest gloss SBS coating
- 2/ Fastest drying high gloss SBS coating
- 3/ Medium gloss economy coating
- 4/ Highest gloss recycled board coating
A total of 15 different clay-coated recycled paperboard stocks were examined.
Uneven Results from Testing Recycled Paperboards
Comparing the results, it was found that a wide variety of gloss results were obtained that were completely stock dependent. High gloss Cork-**** produced a gloss as high as 70% reflectivity at a 60° angle on one particular wet inked stock, and as low 43% on another.
This is in contrast to the 82% average off press gloss achieved on a Cork promo piece where Cork-**** was coated on a high-grade C2S SBS. A similar range of results, but with lower gloss readings were recorded as the other 3 Cork coating types were lab applied and evaluated. Typically, the gloss results obtained over plain board were lower than over inked board. What did this effort reveal?
Well, it told our chemists a number of things.
One, as we were learning, RECYCLED PAPERBOARD IS NOT ALL THE SAME!
Two, our very high gloss aqueous coating CORK-****, developed originally for SBS, does not perform equally as well on recycled stocks.
Three, another Cork high gloss formula type designed specifically for recycled stocks, performed admirably well when compared to the other results.
What to do? Well in some respects back to the drawing board. However, since some benefits were seen in the way that the formulation designed specifically for recycled stocks behaved, it was decided that a further reformulation move seeking additional improvement was sensible.
Special Formulations for Recycled Paperboard Yield Excellent Results
The results of this reformulation effort are now available with a high gloss aqueous coating and a faster drying variant coating developed.
YES, RECYCLED PAPERBOARD IS DIFFERENT! The differences that exist make it impossible to provide an aqueous coating that will erase the recycled paperboard differences and produce an equally high gloss aqueous coating result. Some of these differences can be found in paperboard surface roughness, holdout, absorptivity, gloss, whiteness, surface energy, pH, and brightness. One or more of these factors may contribute alone, or in combination to in-line litho print/coating problems.
Additionally, it was found that one particular recycled paperboard encountered failed EU Regulatory testing for migration, failed COBB testing, and created die-cutting issues.
BEWARE of the recycled paperboard that you use. Appreciate that all recycled paper and paperboard is not the same.
When you want consistency from in-line litho printing/aqueous coating results job by job, pick a stock and stick with it. Additionally, look for and be wary of stocks that for some reason retard ink setting. Remember too, that a poorly printed job is never improved by the application of an aqueous coating.
When you want the best shot at high gloss aqueous results on recycled stocks, take a look a CORKS’ MV-316HG. For faster drying try MV-043W. Contact Cork Technical experts if you require an aqueous coating with enhanced performance properties for a demanding application.