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Apr 1, 1996 12:00 AM
Using vegetable oils in printing inks is by no means new. In fact, early printing and writing inks dating back to the Chinese in 2500 BC probably were formulated with some form of carbon black and vegetable oils or gum resins.
Many early printers were their own inkmakers. We know from early publications that Gutenberg, while keeping his formulas secret, indicated linseed oil was the basis of his original inks. Benjamin Franklin certainly ground lamp black and vegetable oils to make inks for his letterpress process.
Vegetable oils don't necessarily come from vegetables as we normally understand the word. In fact, they primarily come from nuts and seeds of many different trees and bushes. A nut may contain as much as 65 percent oil, which is extracted by a crushing process that produces the crude oil.
The initial treatment is to clarify the oil with clay, then pass it through filter presses, all of which remove debris and impurities. The oil then is reacted with hot caustic soda to remove certain fatty acids, which are saponified to produce alkali refined oils - the most basic form of an oil that can be used in printing inks. These oils can be increased in body by heat treatment and blowing air through them. They also can be reacted with chemicals to form alkyds that have improved properties such as better drying time and higher gloss than the original oil.
Essentially, three types of vegetable oils exist: drying, semidrying and non-drying. "Drying" means the oil converts from liquid to solid when exposed to oxygen in the atmosphere.
Examples of drying oils include linseed and tung, sometimes called China wood oil. Semidrying oils are soybean, tobacco seed and sunflower types. Non-drying varieties include coconut and castor oils.
Drying of these oils is accelerated by adding a catalyst, such as manganese or cobalt linoleate, that encourages the oxidation/polymerization process when inks containing them are exposed to air.
Lithographic and letterpress printing inks once were formulated entirely of varnishes made from vegetable oils and gum rosins until the early part of the 20th century when petroleum products were introduced into them. Use of relatively low boiling petroleum solvents (470 [degrees] to 520 [degrees] F) occurred through the introduction of web presses, which required heat to dry the ink. Vegetable oils don't evaporate so they were replaced by petroleum distillates.
Simultaneously, experts discovered sheet-fed inks could be made to set quicker if the liquid portion of the varnish contained in the ink could penetrate the paper stock faster. The introduction of those same petroleum solvents achieved this task as well. Inks were formulated this way for many years until the 1970s when the Environmental Protection Agency labeled those petroleum solvents hazardous to health and called them Volatile Organic Compounds (VOCs).
Efforts quickly were made to eliminate petroleum solvents from inks and coatings while retaining the required press performance, but doing so was more difficult than people imagined.
Experts suggested substituting soy-bean oil for petroleum oil in news inks; the idea was that soy would be a renewable resource, unlike petroleum, and would help American farmers. While soybean oil could be used with some modification in non-drying news inks, the implication was that it also could be used in heatset inks and quick-set sheet-fed inks. The American Soybean Assn. went so far as to publish so-called "standards" inkmakers must meet to call their products soy based.
The problem was that many well-meaning ink companies tried to substitute soy oil for petroleum, only to find that web offset heatset inks wouldn't dry since soy oil doesn't evaporate, and sheet-fed inks didn't set as fast since the soy oil didn't penetrate as quickly. Therefore, these products were not well received by the trade.
Since then, however, the ink industry has had more time to work on reducing the amount of petroleum contained in its products. One fact is clear - soybean is not the only vegetable oil grown in the U.S.; other oils with better reactivity are available that give ink chemists more flexibility in their formulations.
One example is the potential use of walnut oil, which is grown in increasingly large quantities throughout North America, especially California. The increase in walnut farming has made this product readily available to the coatings industry. In terms of reactivity, walnut oil is better than soy and closer to linseed, but with better color retention than the latter. Expect to hear more of this alternative renewable resource in the months to come.
While it probably will be difficult to eliminate all petroleum solvents from inks in the near future, alternatives exist to soy. Our industry would be better served if we focused on using vegetable oils in general as a partial substitute for petroleum, rather than promoting just one product.
TERRY SCARLETT, Contributing editor and president of Burntwood Industries, Inc., a consulting company specializing in inks and coatings