Aliphatics are those hydrocarbons which have the carbon atoms bonded to each other in single bonds. Usually, aliphatics are drawn with the carbon atoms in straight chains with the hydrogen atoms branching off from them sideways. In Gilsonite, the aliphatic hydrocarbons have lower softening points and lower molecular weights.
Aliphatic hydrocarbons dissolve in the weak, aliphatic solvents (mineral oil, ink oil, white spirits) commonly used to make offset printing inks. When they are dissolved in aliphatic solutions, they yield low initial viscosities and stable solution viscosities over time. In general, aliphatic hydrocarbons are the most useful piece of the Gilsonite when making offset inks with weak, aliphatic solvents.
Aromatic hydrocarbons are ring structures with the carbon atoms attached to each other in rings with an alternating single bond-double bond pattern. They have higher softening points and higher molecular weights. Aromatic hydrocarbons dissolve in aromatic solvents (toluene, xylene) used to make liquid, gravure printing inks. Aromatics do not dissolve in weak, aliphatic solvents used for offset inks. They only disperse. After time, these dispersed aromatics rejoin, or agglomerate, and increase the viscosity of the varnish. This is a disadvantage for Gilsonite in offset ink making.
Gilsonite ink powderBecause Gilsonite is a naturally occurring substance, it contains a small amount of ash or grit that was included in the material years ago when it was originally formed. In inkmaking, it is required that this ash either gets filtered, centrifuged, or settled out of the varnish. Gilsonite also contains a small percentage of "light oils," lightweight molecules that evaporate easily and give Gilsonite its characteristic smell.
In general, the most valuable piece of the Gilsonite in offset ink manufacture is the aliphatic hydrocarbon portion. All of the other parts cause problems in some way and they must be dealt with. The aromatics don't truly dissolve and they yield high viscosities and viscosity increases over time. The ash must be filtered out of the varnish so it won't scratch the printing plates or blankets and the light oils smell.
Gilsonite is use d in ink manufacture principally as a carbon black dispersing agent or wetting agent. It performs this function at concentrations of 2% to 5% of the finished ink recipe.
Gilsonite itself is a hard, high softening point resin, and it could be used in the fi nished ink formula for its resinous abilities to offset the hydrocarbon and other resins. However, this requires a concentration on 10% to 15% Gilsonite in the finished ink recipe before it performs this function. This is possible, but difficult, because o f dealing with Gilsonite's ash and aromatic contents at such high concentrations. At such high concentrations, there is too much as to filter, the viscosities start too high and increase even higher, etc. Therefore, most inkmakers use Gilsonite at low conc entrations for carbon black dispersing only and use other resins such as "C5/C9" hydrocarbons or modified rosin phenolics for the ink's resinous ingredients.
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