Converting Technology International, "Add value through mold resistance"

Paper and paperboard are particularly well-suited to point-of-sale advertising and attractive, creative packaging. The surface characteristics of paper and paperboard can vary from bright gloss to soft mat, and modern printing techniques can produce an infinite variety of colors. New types of plastic packaging and plastic/paper composites have also forged strong inroads in packaging applications. The great advantage of plastics is that they can provide a barrier to moisture and odor and they do not degrade or become discolored in damp conditions.

However, plastics and plastic/paper composites have an inherent disadvantage as opposed to paper and paperboard: they are very difficult to recycle. The increasing importance of environmental issues has made paper and paperboard a more attractive alternative. New developments in barrier coatings and mold protection are allowing paper and paperboard packaging materials to overcome the advantages of plastic.

The phenomenon of mold growth on cellulose substrates is well-known. Fungal spores, that are present in the paper either at the time of its production or later when it has come into contact with a contaminated environment, may develop active molds in the presence of both water and moderate-to-warm temperatures (10-50°C). Although paper machine systems contain bacteria, yeast and fungi, the bacteria and yeasts are generally killed by the high temperatures (90-100°C) used to dry the paper sheet. However, fungal spores may survive the drying process and remain alive but dormant in the paper until favorable growing conditions develop. Once these conditions are achieved, the fungi (molds) grow rapidly, feeding on the cellulose fibers and whatever other nutrients may be present.

The principal applications for mold resistant paper and paperboard are bar soap packaging, labels for bottles of mineral water, beer and soft drinks, and certain types of food packaging. However, with the increasing emphasis on packaging as a medium for advertising and publicity, there is a growing need for mold resistant paper and paperboard to preserve the quality of the package.

The most important characteristics of fungicides used in mold resistant papers, other than the fact that they must be effective against a wide range of fungi, are:

• Water insolubility, so that they will not be leached out of the paper and will not migrate from the packaging to the paper contents
• Thermal stability, so that they will not decompose in the drying process
• Chemical and physical stability, enabling them to remain active in the paper for at least two years and producing a very low level of toxicity

Originally, the fungicides used in the production of mold resistant packaging were relatively toxic products, such as chlorinated phenols and 2(thiocyano-methylthio) benzimidazole. These products were replaced by less toxic fungicides, such as thiabendazole and carbendazim. However, during the past several years, molds resistant to thiabendazole and carbendazim have appeared and new, more effective fungicides are required.

In order to obtain the widest possible spectrum of activity, new fungicide formulations generally incorporate two or three different active ingredients. These new formulations, that are based on blends of carbendazim and 3-iodo-2-propnyl butyl carbamate, and carbendazim, propaconazole and diiodomethyl tolyl sulfone, have proven very effective against a wide variety of molds, including those resistant to carbendazim and thiabendazole.