- September 01, 2002, Dr. Richard M. Podhajny, Ph.D., Contributing Editor
One of the key ingredients of many water-based inks and coatings are amines. Amines and ammonia are used in water-based products to control pH required for good stability and press performance. But what are amines?
Before we can define amines, we need to talk about ammonia. Ammonia is that “pungent, yet fresh smell” of many household cleaners. Ammonia is a gas at room temperature and has a chemical formula of NH3. It has three hydrogen atoms and one pair of non-bonded electrons connected to a nitrogen atom. It is this pair of non-bonded electrons that make this chemical electron rich (a base). Since it does not have carbon, ammonia is not a VOC by definition.
When ammonia is added to water, it dissociates water to form ammonium hydroxide. In this form it is used as an effective house-cleaning liquid and is a common ingredient in water-based inks. Presence of ammonium hydroxide allows acidic resins to be “solubilized” in alkaline media.
Amines are defined as organic derivatives of ammonia in which one or more of the ammonia hydrogens are replaced by organic groups. For example, if we removed one of the ammonia hydrogens and replace it with an ethyl carbon group (chemically written as CH3-CH2), we end up with ethyl amine, (ethyl)NH2. This is called a primary amine, since the ammonia skeleton has only one carbon group substitution. If we continue, a secondary amine can be formed by replacing two of the ammonia hydrogens and we form diethyl amine, (ethyl)2NH, and if we continue further, a teritary amine, triethyl amine, (ethyl)3N. Unlike ammonia, volatile amines are VOCs since chemically they are carbon compounds.
Amine compounds were studied in the early 1900s for their ability to cure diseases like beriberi, rickets, and scurvy. As such, they were considered “vital amines,” which has come down to us as “vitamines.” A Polish biochemist, Casimir Funk, published his research at Pasteur Institute of Paris under the title: “The Vitamines.” Later research showed that not all nutrition products are amines, and the term was shortened to “vitamins.”
Ammonia and amines commonly are used in water-based inks and coatings, as well as adhesives. They serve to “dissolve” the acidic resins and stabilize emulsions and pigment dispersions by charge repulsion. They are a key element of most of the water-based products that you use.
Ammonia as well as low molecular amines have very pungent and unpleasant odors. Everyone knows what ammonia smells like, but most amines have an odor, which is sometimes characterized as “fishy.” As a result, use of amines or ammonia in water-based inks requires good drying to remove them from the printed and laminated products. Since these strong amines form salts with acids (for example, acrylic resin binders that are composed of many carboxylic groups) it is very important to decompose these salts with heat during the drying stage. If these salts are not decomposed during the drying cycle, the water-resistance properties of the dried ink or coating will be poor.
Since amines contain a pair of electrons on the nitrogen atom, they have good wetting properties. Acid-base interaction of amines make them quite suited for wetting corona-discharged films.
Besides water-based inks and coatings, amines are used in a variety of packaging products. They find application as surfactants, lubricants, anti-stats, as well as conductive materials.
Dr. Richard M. Podhajny has been in the packaging and printing industry for more than 30 years. Contact him at 215/616-6314; firstname.lastname@example.org.