Inks & TonerWax for the Ink, Printing and Toner Industries
Printing inks are broadly classified into two main categories; paste and liquid. It can be formulated using chemistries based on oil solvent, water or energy curable.
Raw materials used in inks can be classified into three classifications
Vehicles carry pigment to substrateduring the printing process. Vehicles are sometimes refferred to as varnishes. Usually fluid in nature, they consist of resins binders plasticizerand solvents. Can be free flow gelled or viscous
Pigments or dyes that provide the colour – Pigments are insoluble and need to be dispersed whereas dyes are dissolved in the vehicle. Pigments are more common.
Materials or compounds that contol or modify specific properties. Often added in small amounts additives can impact a wide range of chemical properties including rubrestance, drying, film formation, viscosity etc.
While it is theoretically possible to make ink without additives most modern inks contain multiple additives. Some additives are specific to certain ink types while others such as waxes are used in a wide variety of inks. Additives may be added in the vehicle during processing while others are added during the ink mixing stage.
The Role of Waxes
Almost all inks except inks that will be coated or laminated contain waxes of some type. Waxes provide physical attributes such as rub/scuff resistance, water/solvent or grease resistance and more. Wax can also influence the coefficient of friction to control slip resistance.
In the ink industry both natural and synthetic waxes are used. Waxes are supplied as micronized stir-in powders, votated oil/varnish compounds, oil dispersion for sheet fed and heat set inks, water dispersion, water based flexo/gravure. Typically waxes are used at less than 5% w/w however certain emuslions /dispersion additives can contain a much higher percentage of wax.
For stir-in powders, particle size is an important property (4-6 microns is typical for sheet fed and high speed heat set). Flexo/gravure can tolerate much higher particle size (6-20 microns).
Polyethylene Wax. These waxes have a molecular weight of 500-6000 in either high or low density. (Acculin is high density with a MW 500-3000). They are utilized in all major ink types and supplied as dry (micronized), oil.
Paraffin Wax. Paraffin wax provides good moisture barrier properties but needs to be used cautiously for overprinted or coating after drying by forming a low energy surface.
Microcrystalline Wax. Used extensively in heat set inks and often combined with PTFE for good slip and rub performance.
FT Wax. Flexo and gravure inks sometimes limited because lower fractions can become soluble if the ink becomes to hot in manucture.