Waxes for use in Inks
Printing is defined as the reproduction of images to a substrate. To create an image there must be differentiation between the image area (ink on) and non image area (ink off). Main printing processes accomplish this either by raising the image (flexo and letterpress), differentiating chemically (lithography),recessing the image (gravure), stencil, (Screen print) electronically, (toners).
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
1 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
2 Colorants- pigments or dyes that provide the colour – Piments are insolble and need to be dispesed wheras dyes are dissolved in vehicle. Pigments are more common
3 Additives –materials or compounds that contol or modify specific properties. Often added in small amounts they cover a wide range of chemistries-properties contolled or enhanced by additives include, rubrestance, drying, film formation, viscosity etc. Wax is an additive.
While it is theoretically possible to make ink without additives most modern inks contain multiple additives. Some additives are are spcific to certin ink types others such as waxes are use in a wide variety of inks. Additives may be added in the vehicle during processing while others are added at ink mixing stage
Role of Waxes
Almost all inks with exception of inks that will be coated or laminated contain waxes fo some type. Waxes provide physical attributes e.g. rub/scuff resistance, water/ solvent or grease resistance etc. Wax can infuence coefficient of friction introducing slip.
In the ink industry waxes can vary with natural and nthetic waxes being used. Waxes are supplied as micronized stir in powders, votated oil/varnish compounds, oil dispersion for sheet fed and heat set inks, waterdispersior wtaer based flexo/gravure. Typically waxes are used less than 5% w/w however certain emuslions /dispersion additives can can contain much higher percentage of wax.
For stir in particle size is an important property, 4-6 microns is typicall for sheet fed and high speed heat set. Flexo/gravure can tollerate much higher particle size (6-20 microns).
Polyethylene. MW 500-6000 high or low density. (Acculin is high density MW 500-3000) used in all major ink types supplied as dry (micronized), oil
Paraffin wax: good moistue barrier but need to be used cutiously for overprinted or coating after drying by forming a low energy surface.
Microcrystalline. Used extensively in heat set inks. Often combined with PTFE for good slip and rub
FT Wax Flexo aand gravure inks some times limited because lower fractions can become soluble if the ink becomes to hot in manucture.