Print Process Descriptions: Printing Industry Overview: Lithography

Offset Lithographic Inks

Linseed and rapeseed (canola) oil have been added to litho inks for years, but other vegetable oils like soybean oil are more frequently being used because because of their lower VOC content, which helps eliminate smudging.

Heatset Inks are completely different from non-heatset inks and cannot be interchanged between the two types of presses. Heatset inks are quick drying inks for web printing. The solvents are vaporized as they pass through resins fixed to the paper in such a way that there is no chance for the ink to spread, smear, or soak into the paper. Heatset presses are equipped with a drier, and a chilling system to cool the heated resins and set the image. Heatset inks emit a significantly greater amount of VOC as compared to non-heatset lithographic inks. Therefore most heatset presses are also equipped with pollution control equipment such as a thermal oxidizer or after burner to destroy the high volumes of VOCs that are being emitted from these inks.

Ultraviolet (UV) and Electron Beam (EB) curable inks are also available for litho printing, but the press must be properly equipped to run these types of inks. The use of UV curable inks is on the rise, particularly for the application of overprint coatings.

One advantage of low VOC content is the ability to operate presses at comparable speeds to conventional inks, versus the slow drying and slow press speeds associated with water-based coatings.

One disadvantage is equipment can be costly and is still in the development stage, and the inks and coatings may cost as much as three times the price of conventional coatings.

Electron beam curing inks make a good alternative to U.V. inks because they are less costly and less reactive materials can be used. They also require less energy than U.V. curing inks. The down side of E.B. curing inks is the capital costs to outfit a press. Additionally, EB inks, like UV inks, can be a skin irritant. The inks, if exposed to sensitive skin or left on skin, may cause dermatitis and could even cause chemical burns.