Ideally, the ink on the ink roller must not absorb water (water-in-ink emulsification), neither should the ink break down and mix with the fountain solution on the non-printing areas of the plate (ink-in-water emulsification). Either of these emulsification problems will have a tendency to impair the body, color, or drying qualities of the ink, or trigger tinting on the non-printing regions the plate and printed sheets.
The inks used in offset presses has to be competent to hold the full-intended coloration and covering power to the paper even with the split-film action. This happens because offset blanket picks up only a small part of the ink from the plate and delivers only a tiny part of that to the paper. The film of ink reaching the plate, then, is very light, and the ink must be competent to show its full color and opacity with this film.
Ink is made from three major ingredients: Pigment, that is the coloring material in the ink; Vehicle, that is the liquid that holds the particles of pigment; and Modifiers, who manage the drying of the ink as well as other factors such as smell, scuff resistance, and fading.
PIGMENT: There are two fundamental kinds of pigment applied in printing inks. Organic pigment,which is constructed from carbon, and is used for creating black ink. Inorganic pigments, which are made by mixing various chemical substances together,and they are used for colored inks. For instance, sulfur, silica, or china clay can be mixed with either soda ash or sulfate salts to create ultramarine-blue ink.
VEHICLE: Vehicle is the liquid that holds the particles of pigment and transports them to the paper. There are two kinds of vehicles used in offset inks: oils such as soya oil and synthetic vehicles, which are liquids resulting from the mixture of chemicals. For example, phenol and formaldehyde mixed together create phenolic resins, sometimes used in printing inks as a vehicle.
MODIFIERS: Modifiers are substances added to the ink to control drying and other qualities such as smell and protection from fading.
Viewable properties of inks are a function of the colorants or pigment, associated to the vehicle system used. They include color, transparency or opacity, and gloss. So far, the most often ink color is black. Then come cyan, magenta and yellow that happen to be used in process of printing to develop the millions of colors so familiar to us in printed matter. Although physics of color is a highly advanced science, in most basic terms color comes from reflected light. White light has the whole rainbow of colors. When that light goes through a filter or is separated by a prism or raindrop we see the individual colors in the light spectrum. An ink film acts as a filter on the light reflected from the printed surface, e.g., a red ink film allows the red segment of the reflected spectrum to pass through while neutralizing the rest of the colors.Due to the fact that printed surfaces may vary in color and in reluctance, they, too, will influence the reflected color. For that reason, various ink colors printed individually or “trapped” one on top of the other create different filter effects leading to different visible colors. Also,these same ink colors printed on different substrates will result in noticeable colors that are different yet.
When we talk about ink color, we are very often speaking of shade-whether the ink is red or blue or green or purple. Secondarily, we might describe its strength or saturation, also termed chroma. Thirdly, we might show just how light or dark it is-a reference to its purity or value. The amount of pigment used influences an ink’s color strength, and the type of vehicle used can affect both the hue and the value of the ink color. The color of the vehicle entirely, its power to wet the pigment articles, and even the chemical interaction between the vehicle and pigment can affect the shade or purity. In the end the color of the substrate, and its drying/absorption capabilities have an impact on the printed color results.
Ink opacity- skill to hide the color beneath it.In some cases, an ink having little opacity is required,such as when overlapping two colors to design third color. Other times, very opaque ink is required to entirely cover any color under it. The opacity should be suitable in the use of the ink. Opacity is verified by spreading a sample of ink with an ink knife over a wide black line printed on a sheet of paper. The level of covering is then compared to a standard to check out if the opacity is correct.
Ink transparency- refers to the opposite of opaque. A transparent ink is not going to hide the color beneath it, but mixes with it to design third color. All inks in offset printing used to print full color work should be transparent. The choice of colorants and the level to which it is distributed through the vehicle are the most important factors in identifying the transparency or opacity of an ink.