When water-based inks were first introduced, we thought this meant that the products were “safe.” But the material safety data sheets (MSDS) from the manufacturers showed many of the inks to contain up to 20 percent glycol ether solvents. Even today’s “low VOC” (volatile organic compound) inks can give off enough residual solvents to significantly alter the aroma and the taste of food products.
Some water-based inks used in package printing contain glycol ethers and considerable levels of residual monomers. These odorous chemicals can negatively impact the taste and aroma of chocolates, confections, snacks, coffees, teas, cigarettes, cigars and other foods. Glycol ether-free polymers are currently available in the industry for such applications. They leave foodstuffs free from chemical smells, so that the intended flavor and aroma of the foods remain intact.
Getting Ahead of the Competition
The brand managers and packaging engineers who are concerned about the potential effects migrating glycol ethers and residual monomers can have on food products have a new polymer technology at their disposal. By using these polymers, companies can use packaging with FDA-acceptable water-based inks and coatings which are free of glycol ethers and have a considerably lower level of residual monomers. These inks and coatings leave food and tobacco products untainted, print well on most flexible film and paper substrates and run effectively on flexographic and rotogravure presses.
This combination of benefits suggests that these products will become the standard in many market segments. Since food is a perishable commodity, it calls for considerable care and technology to pack it in a manner that retains its taste, flavor and nutrition and protects it from contamination of all kinds.
The enhanced qualities obtained by eliminating glycol ethers and greatly reducing levels of residual monomers give converters a unique marketing opportunity – they can position themselves as preferred suppliers by offering inks which can help build consumer brand loyalty.
To successfully leverage the new technology and gain a marketing advantage, converters must first understand the very high value food and tobacco companies give to product quality and consistency. Consumers have shown that they have little tolerance for variation – therefore, any deviation in product quality is unacceptable. As a result, any odor or tasteabsorbed into a consumer product can compromise hard-won brand loyalty.
To protect brand share, marketers will do whatever it takes to avoid product contamination. Marketers already promote their use of new packaging constructions and technologies to achieve “greater product freshness” and now they can further differentiate by having “greater taste assurance,” since they are choosing packaging printed with inks which are glycol ether-free and have ultra-low VOC levels.
In order to better convey the benefits of this new ink technology, converters should have a working knowledge of how glycol ethers and residual monomers get into most water-based inks and coatings, and how they are now being avoided or reduced.
Most waterborne graphic arts polymers are either low-molecular weight resins made in a solution polymerization process or emulsions, which incorporate low molecular-weight resins as raw materials. In either case, the chain of manufacturing processes leading to most waterborne inks begins with a process called solution polymerization.
In solution polymerization, a solvent is required to produce the “solution.” After polymerization, most of the residual solvent is removed. However, because 100 percent removal is impossible, all solution polymers contain some level of residual solvent.
In terms of converting and packaging fields, most low molecular-weight graphic arts polymers are polymerized in a glycol-ether solvent, and therefore contain residual glycol ether. Analytical testing shows these products, as shipped to the ink maker, generally contain glycol ethers at levels between 2 percent and 7 percent of the dry weight of the actual polymer.
“Glycol ethers” is a broad term used to describe a variety of highly odorous solvents which are based on either ethylene, propylene or diethylene glycols. Glycol ethers evaporate very slowly, most much more slowly than water, which means they are not fully detectable in the one-hour-long standard test for VOCs (EPA Test Method 24).
Over the shelf life of a consumer product however, glycol ethers remain volatile and may migrate from printed inks, and thus affect food taste and aroma. This transmission may take place even if the ink is reverse-printed and laminated between film layers. For these reasons, glycol ether is proving unacceptable to many packaged-goods marketers.
During polymerization, monomers are reacted to form a polymer. However, because chemical reactions are not 100 percent efficient, some monomers are not converted into polymers. These unconverted materials, known as residuals, are organic materials (VOCs) which can evaporate. These residual monomers can then migrate into packaged products, tainting aroma and taste.
At the end of the proprietary glycol ether-free polymerization process, ultra-low VOCs are achieved by using a new technology to reduce unreacted monomers. Through this process, a higher percentage of volatile residual monomers are removed to produce polymers with virtually zero residual solvent and low VOC levels. (Figure 1).
The total VOC content for most of these polymers is less than 0.1 percent, which makes them ideal for packaging applications where odor, flavor integrity and the total volatile levels are a priority. (Figure 2). The ultra-low VOCs of these inks can also help converters meet government-imposed VOC limits.
Packagers should note that, as with most water-based polymers, glycol ether-free polymers are most often stabilized with a solution of ammonia hydroxide prior to ink formulation. Packaging-material converters will notice a modest, familiar odor of ammonia during printing. However, the fast-evaporating ammonia (which is carbon-free) is not a VOC and is completely driven-off as the ink dries, so no threat to product integrity is created.
Print Quality and Saving
Converters should realize that the new glycol ether-free inks with ultra low levels of residual monomers are not a simple “me-too” product. They stand out from the traditional water-based systems because they deliver the same high print quality but also show significantly higher gloss and faster drying than their glycol ether-containing counterparts.
Higher gloss levels are possible because polymers produced without glycol ethers generally have a much smaller particle size than those produced by processes using glycol ethers (Figure 3).
Smaller particle size permits better coalescence because the particles are able to get closer together and fill gaps. Therefore, ink surfaces are more uniform and higher gloss levels can be achieved. (Figure 3b).
These superior polymers are selling for a similar price to those which contain glycol ethers, so the advantages of the cleaner technology can be offered to packaging customers with practically no additional expense.
In some cases, productivity is improved because the absence of the glycol ethers allows shorter drying time and increased press speeds.
The critical factor for success in the packaging inks and coatings industry is the development of high-quality products and a reputation for liability. Brand loyalty, which can take several years and millions of dollars to build, can be lost due to one bad experience that a product with the possibility of tainting can generate. Specifically, it costs four to six times as much to attract a new customer as it does to retain an old one. This can be achieved by simply using the proper inks.
In essence, glycol ether-free polymers are the perfect example of how packagers can improve their bottom line brand loyalty. Reducing customer loss can dramatically improve business growth and brand loyalty which leads to consistent and even greater sales since the same brand will be purchased repeatedly. The VOC-free technology allows formulators to develop an unbeatable product that customers will trust and will purchase again and again.