Water Based Soy Inks for Packaging
Rahul Pingale, Alexandra Pekarovicova, and Paul D. Fleming, III, Western Michigan University
Many printing inks use volatile solvents in the formulation, which are hazardous to the environment from emission of VOC’s and at the same time, synthetic resins in these inks are not biodegradable. These problems and particularly the fluctuating and rising price of petroleum are main reasons to look for new resources for making more environmentally friendly printing inks. The majority of the commercially available water based inks are formulated based on using acrylic resins, synthetic colorants, solvents/water and additives, which are the common main components for formulating printing inks. Soybean protein is a potential renewable raw material for replacement of acrylic resins. Soy oil is already successfully implemented in lithographic printing processes, including litho inks for printing newspapers, books, magazines and newborn baby footprints (Swiatek,1992; Browner,1992; Erhan, 1995). Newsprint soy inks can be successfully deinked and newsprint can be recycled and reused. Soy protein is known to be employed in paper coating formulations.
Soybeans include about 40% protein and 20% oil. They contain three natural surfactants: soy protein, soy lecithin, and soy saponin. Soy proteins are obtained through the extraction of soybean oil. They form the byproduct that remains after the removal of the hulls and oil from the flake (Xu,2011; Kinsella,1972). Soy protein concentrate is made by removing the aqueous liquid part of the soybeans and it contains approximately 65-72% protein. Soy protein isolate is made from defatted soy flour by removing the carbohydrates of the bean. It is the most refined form of soy proteins and it contains 90% protein (Xu,2011; Kinsella,1972). Soy protein is used in a variety of foods, such as salad dressings, frozen desserts, breads, and breakfast cereals; also, it can be used as a natural polymeric emulsifier, foaming agent, and texture-enhancer. The other industrial products that use soy protein include adhesives, asphalt additives, resins, cleaning materials, cosmetics, inks, paints, plastics, polyesters and textile fibers (Smith,1996).The basic application of industrial-grade protein is as a binder in paper coatings. Proteins are built by condensation reaction of amino acid monomers, which create peptide bonds. Water molecules are released as a result of condensation reaction between amino acids (Graham,1983).Soy protein has a complex 3-D shape and contains 19 different amino acids, which are held together in a coiled structure by peptide bonds. Proteins contain positive and negative functional groups. The functional groups found in soy protein consist of: amino, carboxyl, hydroxyl, phenyl and sulfhydryl (Graham,1983).
In this research, soy proteins were tested for their suitability to partially or fully replace acrylic emulsion resins in water based packaging inks. The focus was on formulating inks for linerboards, because linerboard is a substrate printed with 100% water based ink formulations, and the linerboard packaging sector is exponentially growing. The first step was formulating water based ink based on fully acrylic solution and emulsion polymers as resins. Next, the letdown portion of the ink was formulated with soy polymers, adding them in increments 10-20-30 up to 100% replacement of acrylic emulsion portion of fluid packaging ink. A cyan process color ink was formulated, and its printability, rheology, and end use properties such as rub resistance, gloss, and adhesion were tested and compared to fully acrylic formulations. It was found that the soy polymer did not affect the final color of packaging ink, measured as delta E. Delta E for all soy formulations was less than 1.5, when fully acrylic formulation was used as a standard. Rub resistance of soy inks was similar to fully acrylic formulations. This research will help to achieve the formulation of a truly environmentally friendly water based ink, while eliminating emission of VOCs.
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