Printing inks and their types
Even today, as in hundreds of years to print, two essential things are need: paper and ink. Let’s take a look at these printing inks. What do they contain? How are they made? Are they all the same?
Composition of inks
Although they come in a fatty or liquid form, apparently homogeneous, printing inks are a complex mixture of products of very different natures and origins. We find in this mixture 3 main elements which are:
The coloring matter,
This part makes up about 20% of the ink. Most often, it consists of very finely divide pigments, suspend in the fluid phase of the ink. For some inks (inkjet), soluble dyes are use.
The fluid part, often call “varnish”, which enters about 70% in the composition of the ink. It is a mixture of polymers (resins), which act as binders and diluents, and/or solvents. The vehicle has several functions such as, in particular, transporting the pigments, binding them to the printing medium, and finally, protecting them by forming a continuous film. The choice of ink vehicle determines how it dries.
The additives represent about 10% of the final product and allow to optimize of the characteristics of the ink during and after printing. These include waxes (animal, vegetable, mineral, or synthetic), metal salts, and anti-staining compounds. These products, of varied nature, are add to the ink to optimize some of its properties in the liquid state as well as in the dry film state, depending on the printing method, the support, the purpose of the printed product, etc.
The different types of inks
Printing ink looks very different depending on the printing process for which it is intend. There are two main families of inks, classic inks and so-called special inks (scratch-off inks, scent inks, metallic inks, etc.). They are all more or less constituted on the basis seen above, that is to say the coloring material (pigments), the vehicle binding the whole and the additives which improve certain properties. In this article we will deal with classic inks.
In offset printing, the ink use is oily and does not flow, because this printing process is base on the opposition between water and ink (hydrophilic and hydrophobic part of the offset plate)
Its chemical composition and its degree of viscosity depend on the drying method (UV drying, hot-melt, etc.). The pigments must have very good coloring power and be compatible with the fount solution. They are generally chosen according to the nature of the support that is to be print.
There are 3 different types of offset inks, Quickset ink (sheet press), Heatset ink (spools and rotary) and UV ink ( UV drying)
Vegetable ink is an ink present as an alternative to standard offset ink, the vehicle of which is made from vegetable oils (rapesee, palm, flax), and no longer with mineral oils base on hydrocarbons. These oils have arrive on the market in a context where respect for the environment and ecology are at the center of concerns. These inks are more easily biodegradable than petroleum hydrocarbon-base inks. They are made with renewable raw materials and have the same characteristics as conventional ink or even better.
However, all is not rosy. The cultivation of the plants concern has the same characteristics as agro-fuels. It is nonetheless true that the use of palm oil in the composition is uncertain. We must be aware of the ravages of oil palm cultivation when they do not come from forests and responsible crops, and ask ink suppliers to try to source the origin of the plants involved in their manufacture. Better, does not mean absolutely satisfactory, we must remain sensitive to the fact that these so-called ecological vegetable inks are not perfect.
Different inks can be use with the inkjet process because it is subdivide into different ejection methods: continuous jet in which drops of ink are continuously eject from the print head, or drop by drop. request in which only the drops necessary for printing are create and eject.
The inkjet process requires very good ink quality, otherwise the ejection nozzles may become clog. The ink use generally contains solvents even if we are currently seeking to develop water-base inks for environmental reasons.
Additives also play a very important role in ink quality, as they serve to improve ink flow, adhesion and conductivity (a critical parameter in the continuous inkjet process).
Solvent inks are liquid inks. They are use for printing processes such as flexography use in particular for packaging printing or gravure printing which is a process suitable for very large prints (La Redoute catalog, Ikea, etc.) which require less viscous inks. and which dries very quickly.
The various solvent inks use in gravure or flexography are dried by evaporation of these solvents when the print is pass through a hot air oven.
With the many environmental problems pose by solvents, particularly in the protection of the environment, but also that of individuals in their workplaces, water-base inks are on the rise. First of all, water-base inks are less dangerous than solvent-base ones. Compose up to 75% water their price is also significantly lower than other inks. Even if they only evolve and improve, they unfortunately remain less effective than solvent ink.
Now widely use in flexography, they are starting to be use in gravure printing. Initially limit to porous supports such as paper and cardboard, these inks now allow printing of various supports.
Their composition varies from 30 to 75% water, for 10 to 20% of pigments, 10 to 15% of resin, 1 to 7% of additive and only 0 to 10% of solvent.
These are the main inks use in printing. There are however a multitude of other types of inks, hybrid inks, thermo-chromic inks, heat-shrink inks, fluorescent and phosphorescent inks. You will understand the list is long, each ink is different and adapt to a printing process or to a particular medium.