Offset printing inks have four main ingredients: Vehicles, pigments, binders, and modifiers. These ingredients can vary depending on the type of offset printing used.
Most offset printing inks are made
from vegetable oils.
The most common type of vehicle used in offset printing today is soybean oil. Though linseed oil and petroleum based vehicles have been used in the past, they are being used less and less through the years because of their expense.
Here are the oil based vehicles used in offset printing inks today:
- Rice bran
Soybean oil has proved to be a better fit for offset printing because of the following:
1. It has a substantial supply with most developed countries producing well beyond their need*.
2. It is cost effective. The yield of soybean oil per acre is very high and the process to extracts is inexpensive*.
|Pigments take up about 30% of printing ink.|
The most common organic pigment used for black ink is carbon. Other inorganic pigments are used to make other colors such as cyan, magenta and yellow.
There are no perfect pigments that can be produced for the printing industry. Some pigments do not produce the perfect hue required for four color printing. All pigments react differently to the other ingredients, like the vehicle. Other pigments will break down too easily and cause problems on the offset printing press. Some ink manufacturers have undertaken a complete breakdown of each pigment and it’s advantages/disadvantages*.
The colors cyan, magenta, and yellow must all have pigments that are transparent when combined with the vehicle. This is in order to produce all colors in the CMY color module. Pigments such as black or course do not have transparency.
Other pigments such as those used for titanium white ink, like black, are also opaque. This pigment is derived from titanium and oxygen.
|Cobalt adds drying properties|
to the offset printing ink
These additives are given depending on the type of offset printing process as well as the requirements of the publisher. Here are a few:
Magnesium carbonate - Adds body and makes the ink siffer.*
Driers – Namely cobalt. Being a strong oxidizer, cobalt accelerates the drying action. However it is added in very small amounts as it will cause poor trapping between ink colors. Maganese is also added as it promotes polymerization even more than cobalt. But just like cobalt, too much can cause offset print trapping issues between colors. In many cases a combination of manganese and cobalt are used. Zinc will also sometimes be added as this increases the drying hardness.
Waxes – Referred to as ‘spherical micronized waxes,’ this additive helps the ink in several ways. It helps produce a gloss finish as well as rub resistance. It will also produce more slip. However some offset printing ink is designated as “wax free”. This is necessary so that a UV coating can print over and bind to the ink.
Fillers – Can be up to 20% of the ink volume, depending on the offset printing process. The most common types of filler are magnesium carbonate, aluminum hydroxide, clay, and silica. The task of fillers is to reduce the volume of pigment which can have a negative effect if the percentage is too high. It gives the ink properties that help it in the printing process. It really is a “filler” an so it reduces the mileage of the ink, thereby reducing it’s cost. Cheaper printing inks are possible by using these fillers.
Tack reducer – Offset printing inks tend to be quite sticky. In four color offset printing, inks will require different levels of tack depending of their placement in the printing press. Tack reducers help distribute tack values appropriately. Jelled linseed oil is used to accomplish this. The content can be as high as 1% of the ink depending on the offset printing process.