An Overview of Micronized Wax
There are many varieties of waxes found in nature and synthesized under controlled conditions. An old definition of wax is anything with a waxy feel. This feel relates to the lubricating properties of wax. Now we define waxes as any of a group of substances composed of hydrocarbons, alcohols, fatty acids, and esters that are solid at ordinary temperatures. Shamrock redefines micronized wax as a wax powder with an average particle size of less than 10 micrometers. Hard waxes can be ground to a fine particle size, and low melt viscosity waxes can be sprayed to a fine particle size.
The most commonly micronized wax is a linear synthetic paraffin with a carbon number greater than 30. This wax is commercially produced by polymerization of ethylene or by the reaction of carbon monoxide with hydrogen by the Fischer-Tropsch process.
Polyethylene wax can be a linear or branched wax at any molecular weight. These are referred to as paraffin or microcrystalline wax. The branched microcrystalline waxes provides higher molecular weight and sometimes hardness for a given solubility.
Carnauba wax is a natural wax and is very grindable. This wax alloys well with other waxes. Synthetic waxes can be oxidized or otherwise functionalized 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.
Linear waxes are highly crystalline and subject to crystal modification by alloying, work hardening, quenching, etc. An additional manner of changing the crystlalinity of these materials is by the addition of polytetrafluoroethylene (PTFE).
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.
Understanding the wax properties enables selection of the best wax for a specific application. 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 chemistry and modern instrumentation.
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.
Significant wax properties include composition, molecular weight, molecular structure, density, hardness, melting profile, solubility, heat stability, surface energy, particle size and distribution and powder flow.
To find the right wax for your application, please contact us and our technical team will reach out to you with the best solution.