The use of chrome, and in particular chrome in its hexavalent form, has become a taboo in roll-manufacturing industries. If you are unfamiliar with the dangers of hexavalent chrome, look no further than Wikipedia, which states that inhaled hexavalent chromium is recognized as a human carcinogen, and that it can also be found in drinking water and public water systems.
All photos courtesy of Applied Laser Engineering Ltd
It is very questionable to what extent a laser-engraved ceramic anilox roll would carry or release hexavalent chrome. However, it is generally accepted that as part of the manufacturing process, hexavalent chrome does exist when chrome oxide is plasma sprayed.
For the last two to three years, Applied Laser Engineering Ltd has been working with industry R&D partners to find “chrome-free” materials from which to manufacture anilox rolls. To date, we have investigated titanium nitride, aluminum oxide and tungsten carbide. The following information has been made public by Kinetic Elements Ltd, one of our R&D partners, as to the results of their chrome-free development and Tiaurum, the result of that R&D work.
Finding an Alternative
The development of the textured titanium roll required initial studies to be conducted on flexographic inks and plasma-sprayed chrome oxide anilox rolls. These studies allowed us to form the fundamental baselines for our R&D project. The task we set was to find an alternative way of manufacturing an anilox roll, using suitably wear- and corrosion-resistant materials, in such a way that would:
- Simplify the manufacturing process
- Lead to a direct manufacturing route, as opposed to the traditional costly and labor-intensive machining and coating operations
- Possibly allow simple treatment to restore damaged or worn rolls, i.e. without returned rolls needing to be completely stripped and re-coated
- Eliminate materials susceptible to corrosive attack, or at least provide a more effective barrier coating to susceptible materials underneath
- Be environmentally friendly in manufacture and use
- Have sufficient wear resistance. If the wear performance is inferior to plasma-sprayed Cr2O3 but at least at the level of hard chrome-plated rolls, and the roll offers other advantages such as those listed here, then overall it would prove attractive
The method used to harden a layer of the titanium surface is laser nitriding, or a variation on it (e.g. laser oxynitriding, oxy-carbonitriding, etc.). Pin on disc wear tests, Knoop hardness measurements, glow discharge optical emission spectroscopy (GDOES) and X-ray diffraction (XRD) were some of the tests done during the project to measure and validate the results.
A printing press was also purchased for the project to simulate the actual printing environment. Tests were conducted simultaneously running chrome oxide, hard chrome, engraved but untreated titanium, treated tri-helical Tiaurum and treated hexagonal Tiaurum, as well as a few other variations of cell structures. The rolls all ran for more than 2,000-km. with reverse angle steel doctor blades and a doctor roll. The hard chrome showed early signs of cell walls wearing out at 300-km. The untreated titanium showed immediate signs of wear, which was expected, but all the other treated and ceramic rolls showed no signs of wear for the duration of the trials. Effective laser hardening involves raising the Knoop microhardness (HK) typically to between 1,500-HK and 2,000-HK. Thick coatings can be deposited to allow the functional layer to also act as a barrier for the protection of the base material from corrosion or chemical attack.
The initial comments were that the Tiaurum product laid down a higher ink density compared to the same cell specification ceramic anilox. This was not a problem, as the ink could be adjusted to bring it back into alignment. The wash-up times were noticeably improved and due to the golden metallic appearance, it was generally easier to see if the roll was clean or dirty on the press compared with a dark chrome oxide ceramic anilox. Continual monitoring has shown a reliable product that has not yet deteriorated over time.
Tiaurum was first sold into the Australian market in October 2017 for industrial coating applications gluing and laminating films in a gravure-type process. One customer had severe corrosion problems and conventional anilox rolls were only lasting three months before blistering, and certain glues were extremely difficult to clean if they dried on the anilox due to an unplanned stoppage. The inherent corrosion-resistant nature of Tiaurum was an obvious choice to solve the corrosion problems and the easy-to-clean features of Tiaurum were a bonus. The customer put the first Tiaurum product in that month and with constant monitoring, most recently in March of this year, there are no signs of corrosion and the operators have found the cleaning to be easy.
Environmentally, Tiaurum ticks many of the boxes. Titanium is environmentally friendly and an abundant material. It is the same material commonly used to 3D-print human joint implants. If your packaging material is in any way in contact with food, Tiaurum minimizes the risk of roll contamination.