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An Overview of Micronized Wax

An old definition of wax is anything with a waxy feel. This feel relates to the lubricating properties of wax. A good definition of micronized wax is a wax powder with an average particle size of less than ten micrometers. Only hard wax can be ground this fine. Only low melt viscosity wax can be sprayed this fine.
Measurement of low micron particle size can be done by sedimentation, air permeability, light diffraction, microscopy, or the use of a fineness of grind gage. A grind gage used by ink makers reads from zero to 25 micrometers which equals 0 to 10 thousandths of an inch. The grind gage is particularly effective because it quickly measures many particles and also detects oversize particles.
The most common wax for micronizing is a straight chain synthetic paraffin with a carbon number greater than 30. Although it is possible to separate a material like this from petroleum wax, the commercial process is by way of polymerization of ethylene or by the reaction of carbon monoxide with hydrogen by the Fischer Tropsch process.
Only the straight chain waxes can be reduced to low micron size. Polyethylene wax can be either straight chain or branched as well as any molecular weight. Petroleum waxes are also straight chain or branched. These are referred to as paraffin or microcrystalline wax. The branched microcrystalline provides higher molecular weight and sometimes hardness for a given solubility. Neither is very grindable, but microcrystalline is used in dispersions.
Carnauba wax is a natural wax and very grindable, but produces static electricity. It alloys well with other waxes. Synthetic waxes can be oxidized or otherwise funcionalized to give them water wettability
A semi-natural wax is ethylene bistearamide which is produced by reacting stearic acid with ethylene diamine. One problem with EBS results from the variety of stearic acids used. All EBS exhibits polymorphism which can result in having the soluble crystal form giving gelation unless used in water.
Straight chain waxes are highly crystalline and subject to crystal modification by alloying, work hardening, quenching, etc. An additional manner of changing the crystallinity of these materials is by the addition of polytetrafluoroethylene.
Micronized wax is made by air jet milling or spray chilling. Wax can also be precipitated out of solution. Prior to Shamrock’s development of micronized wax, a coarse powder was ball milled for liquid inks. For paste ink, the wax was dissolved in a hot resin solution, typically in a large tub over an open gas burner, and poured onto a 3 roll mill to precipitate fine crystals, hopefully or artfully. At about the same time as micronized wax, a scraped film heat exchanger process was developed and allowed this precipitation to take place controllably and consistently.
It may seem fortunate that the high “melting point” waxes are the ones that are grindable, but all these commercially available materials consist of mixtures of molecular weight and branching. The reference to straight chain is relative. Prior to the introduction of instrumental analysis, the measure of melting point was fairly subjective. “Cloud point” was added as the temperature at which a given concentration of wax in a given solvent would show cloudiness on cooling. This is still a useful method to determine the solubility of the upper molecular weight portion of a wax, however, imprintability or recoatability of an ink or coating is related to the total amount of wax that dissolves, and the low MW and branched portions dissolve first. Shamrock pays particular attention to solubility by old fashioned chemistry and modern instrumentation.

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Shamrock pioneered the development of PTFE and wax additives in the 1970s, first for inks and coatings, and later for a wide range of applications including lubricants, personal care products, polymer additives, and many more.

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