Selecting ink for your inkjet technology – impulse jet, valve jet or thermal jet – requires an understanding of your application and some basic qualities of the inks available. We asked our inkjet experts for key information to help shine some light on understanding the ink options available in the market: Q: What is an ink made up of? A : All inks are made up of essentially the same things; a solvent, colorant, resins and other additives. It’s the resins and additives that give inks certain properties that allow them to adhere to specific substrates better than others. Solvent is the carrier of the ink. Colorant is what gives the ink the color you see. The resin gives the ink the ability to stick to substrates. The additives are anything else added to the ink to give it a desired property (surface tension modifiers, dispersing aids, gloss reducers, etc.) Q: Why do some inks adhere to certain substrates better than others? A: Simply put, the surface tension of the ink and surface energy of the substrate determine an ink’s adherence. An ink droplet is made up of many molecules of ink. These molecules of ink have to be attracted to each other to form this drop of ink. So, the surface tension is how much they are attracted to each other. If they are highly attracted to each other (water) then the molecules are close together and hold on tightly to each other. When the molecules are not very attracted to each other then they barely hold onto each other and spread out more. It has to do with the charges of the molecule, or lack thereof. Water is polar, which means it has a negatively charged and a positively charged end. These negative and positive charges attract to each other like magnets do. For example, when the water is placed on a glass, it just beads up and runs off because the glass has no charge (non-polar). The water is not attracted to the glass. However, if we add soap to the water we alter the surface tension and the dynamic changes. Soap molecules have a charged side (polar) and a non-charged side (non-polar). When the soap dissolves in the water it allows the non-polar side to be attracted to other non-polar substances, like glass. So, to make an ink better adhere to a substrate, additives are used to change the surface tension of the ink to more closely match the surface energy of the substrate. Q: What is a VOC? A: VOC stands for volatile organic compound. With some exceptions, the solvents used in products such as coatings, inks and adhesives are generally classified as VOCs. Unless they are controlled, these solvents are emitted into the air after they perform their function. Thus, solvent emissions from products and industrial operations are one of several significant sources of VOC emissions. Emissions of VOCs, in and of themselves, do not necessarily give rise to health or environmental concerns. In many areas, however, they react with oxides of nitrogen (NOx) in the presence of heat and sunlight to form ground-level ozone – the primary component of “smog.” For that reason, they are regulated as “ozone precursors” under the federal Clean Air Act and similar state laws. Q: What’s the difference between pigmented inks and non-pigmented inks? A: Dyes and pigments are both colorants. Dyes are soluble liquids and dissolve into the ink base. They do fade over time. Pigments do not dissolve as they are solids and do not fade. Since they are solid they may settle, or sink, to the bottom of a container if the ink has a low viscosity, or is thin and watery in texture. The weight of the pigments causes the inherent problems with pigmented ink. First, they can actually clog printheads if they’re too large. Secondly, if they are allowed to settle the ink will not have the same color. It’s the same concept as pouring Italian dressing on your salad without shaking it. The dressing will have a different taste because the ingredients are not mixed. Q: Why do some inks flake off flexible plastics and films? A: One component of ink that helps it adhere to substrates is resin. The resins allow the ink to spread creating more surface area helping promote adhesion. Resins can be categorized as either brittle, semi-brittle or flexible. If an ink containing a brittle resin, like acrylic, is used to print on film it can ‘flake’ off the film because the resin is stiff and is not able to adhere and conform to the shape of the plastic. If an ink with a flexible resin was used, the resin would be pliable and therefore be able to bend or flex with the film. Diagraph’s top-performing ink, ScanTrue II Plus, and all valve jet inks are produced in our Marion, Illinois manufacturing facility. All of our inks have been designed to perform at the highest level with Diagraph manufactured inkjet equipment. If you have any questions, or wish to better understand what kind of ink would be optimal for your inkjet application, reach out to our experts!