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Perhaps It's Time to Redefine Packaging Odor Specs

Printing and laminating of flexible packaging materials may involve the use of various inks, coatings, and adhesives. These materials inherently contain odorous solvents, which are the primary cause of undesirable odors in packaging products.

Traditionally, the odor of the printed product would be qualitatively assessed by the printer or converter. Typically, this is done by inserting a sample of the converted product into a jar, perhaps heating the jar, and then judging the objectionable odor. Obviously, this qualitative approach left much to be desired.

In the 1970s a quantitative technique began to be used in the flexible packaging converting industry to alleviate problems with the use of qualitative techniques. The key to this idea was the fact that ink, coating, and adhesive formulations were sufficiently similar. That is, they were all solvent-based and using similar solvents. By restricting the total amount of solvents retained in the product, a specification could be written that would provide some guarantee the odor level should be acceptable.

Use of gas chromatography became the standard method of quantifying the level of retained solvent. Although there were variations in how the tests were conducted, the technique allowed the flexible packaging industry to utilize a quantitative method of assuring the packaging products would be odor free.

One problem with this initial approach was that all the solvents used were not equal in their contribution to undesirable odor of the converted product. So, the idea came about to restrict the individual solvents. That is, each solvent would have a maximum level that would be allowed. For instance, toluene would be much more restricted than, say, ethanol.

Over the years, the acceptable amount of retained solvent has decreased, and specifications have become tighter. Into the 1980s, the use of gas chromatography was standard for facilities manufacturing flexible packaging products.

The key to the success of this approach was the use of a limited number of solvents. These solvents included toluene, ethanol, propanol, isopropanol, ethyl acetate, propyl acetate, and isopropylacetate. With the exception of toluene used in rotogravure, most of the solvents used by flexible packaging plants were alcohols and esters. Although other solvents were used, such as ketones, most package printing and laminating applications used a limited number of solvents. This greatly facilitated meeting the quantitative odor specifications.

In recent years, with the introduction of water-based and UV-curable inks and coatings, the standard for “low odor” in packaging products needs to be redefined. The “retained solvent” levels based on the solvent-based inks, coatings, and adhesives is not applicable to these new products; it is not a good predictor of the “odor potential” of these new printed, laminated, and converted packaging products.

Water-based inks bring with them new odorous materials, such as ammonia and amines. Retained levels of these materials will contribute to odor, but their acceptable levels may not be defined.

With the exception of ammonia, there is less standardization in the formulations of water-based inks, coatings, and adhesives as to which amines and other additives they utilize.

In the case of UV-curable inks and coatings, the source of odor in the package is even more difficult to define. Although we know the printed or converted product has an acrylic odor, it is difficult to quantify it. Unlike our ability to quantify the retained solvents, we do not have the same quantitative relationship to odor components in the UV products.

I'm afraid the conventional use of gas chromatography and determination of retained solvent cannot be used with water-based or UV ink systems to assure the package will conform to low-odor packaging standards.

To establish workable standards for low odor with these materials, the odor-causing components need to be identified and their quantitative unacceptable levels established by use of old-fashioned odor panelists.

Mark's Coating Matters | Process

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