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FLEXO Magazine : March 2009
TECHNOLOGIES & TECHNIQUES Pine for Your Inks Trees Provide Organic Alternatives to Water-Based Acrylics By Theodore Vernardakis S everal years ago, the term sustainabilif:y was not in most people's vocabulary. Times changed. Today, sustainability is on many people's minds. It is a subject that has moved to the forefront of our society and industry. Printing inks playa role in sustainability. We plan to describe raw material resources for water-based flexo inks and the role they play in making a printed box or display sustainable. The main raw materials used in water-based inks are pigment, water, vehicle and additives. Standard water-based flexographic ink vehicle systems are based on acrylic and/or styrenated acrylic resins and emulsions derived from one source only: petroleum. Petroleum is a depleting resource. Based on this fact, and basic principles of supply and demand, petroleum prices will increase. As oil prices increase, so do the prices of acrylic-based chemicals. We saw this result throughout much of 2008. This factor has stimulated research and development in alternatives to acrylic- based chemicals. ROSIN TO THE OCCASION Two raw materials from renewable resources are making in- roads into water-based flexographic inks. The first group includes polymers derived from soybeans. The second includes rosin de- rivatives from pine trees rosins. The main advantage of soy- and rosin-based inks versus conventional acrylic-based inks is that they are derived from renewable resources, and as such, they are green and sustainable. Consideration can be given to both of these new raw materials by ink makers. In this article, however, - we are exclusively concentrating on the second group of renew- able resources, namely those raw materials which are derived from pine tree rosin. The chemicals in pine trees include rosin (resin acids such as abietic, pimaric, levopimaric, etc.), fatty acids (stearic, oleic, li- noleic) and turpentine. There are three types of rosin produced by pine trees, Le., gum, wood and tall oil rosin. Gum rosin is collected from live pine trees. Wood rosin comes from the dried stumps of pine trees. Tall oil rosin is obtained after distillation of crude tall oil from the black liquor of the Kraft paper making process. Black liquor is quite toxic and, in the old days, it was discharged into rivers and lakes, thus creating environmental havoc by polluting the waterways. This discharge of black liquor is no longer practiced. It is now collected, reprocessed and, through distillation, yields tall oil rosin. The rosin is then es- terified to produce rosin esters of maleic, phenolic, fumaric and other acids. These modified rosin esters have acid numbers ranging be- tween 100 and 250. As with acrylic and styrenated acrylic resins, the rosin esters can be dissolved in water with ammonium hy- droxide, sodium hydroxide and/or amines. The rosin ester solu- tion can then be used alone or in combination with acrylic resin solutions and emulsions to produce water-based flexographic inks and varnishes of excellent quality. Generally, it is not neces- sary or advisable to replace all the acrylic vehicles in the ink with rosin ester vehicles. A good beginning is to replace about 50 per- cent of the acrylic resin solution with rosin ester solution. MARCH 2009 www.flexography.org FLEXO
Sustainable Winter 2009