Printing Problems
Tiaurum addresses some common problems for flexographic printers using aniloxes to meter liquid inks or coatings:
- Deterioration of print quality over time, resulting from the porous ceramic layer bonding strongly to ink or coating residues. This residue can alter the performance of the anilox and cause mottled or camouflage patterns, stains, hand prints or chemical splashes. Changes in ink or coating transfer due to altered hydrophobicity and score lines from doctor blade fiber or contaminated inks can also compromise roll quality
- Difficulty in maintaining roll quality leads to press downtime due to mechanical damage or corrosion failure of the coating, often associated with the porosity and brittleness of the chromium oxide layer. Excessive cleaning can shorten anilox life. Aggressive chemical cleaning might result in base material corrosion. Physical cleaning methods can damage cell walls
- The turnaround time for refurbishment or repair can be excessive. Coatings must be completely replaced. Heavily corroded surfaces may force the replacement of existing bases
- The dark color of Cr2O3 layers means it can be difficult to see surface contaminants. Grease or oil on the surface renders the roll altered or useless. Visual inspection may not show contamination due to low visual contrast between contaminants and ceramic
The Tiaurum surface:
- Is hard and robust, resistant to breaking down during printing. Metals are malleable and not brittle like ceramic
- Cell structure is controllable during laser processing, ensuring roll integrity. Engraving is completed using technologies compatible with ceramic engraving
- Is readily cleaned of grease and other contaminants without damaging the surface properties. Surface characteristics differ significantly from ceramics
- Has adequate wear characteristics. Tiaurum has been targeted for wear performance between hard chrome and ceramic
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Image 3: SEM images of as-sprayed titanium surface (left) and treated surface (right)
Benefits become apparent very quickly to printers once they start using Tiaurum. There is less wash-up time on or off the press due to the surface characteristics of Tiaurum. The laser can be used to control the hydrophobicity of the surface (see Image 1). The interaction of the surface with liquids is a very important factor. Laser-treated titanium may be made more/less hydrophilic by varying the treatment parameters.
Other benefits include reduced unplanned machine stoppages from blade lines or unclean anilox. The light gold color allows for easy inspection as to whether the anilox is clean or dirty (see Image 2). Clear coatings with conventional treatment are still difficult to identify without the use of measurement devices.
Benefits that are less easy to identify up front are those of corrosion resistance. The nature of the Tiaurum materials is such that they will not corrode and will act as a barrier to the sublayer. Salt spray tests show a radial thickness of 1.5-mm., as-sprayed, is sufficient to form a natural corrosion-inhibiting layer. Further testing is being conducted on treated surfaces. Image 3 clearly shows how the laser treatment modifies the as-sprayed layer, effectively sealing the surface.
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Image 4: Treated tri-helical engraving (left) and treated 300 lpi hexagonal engraving (right)
More Advantages
The laser processing to form the Tiaurum cells generates a more rounded cell wall which, being a metal, is not prone to cracking or breaking off. The formation of the surface topography using the laser creates a much larger bearing surface around each cell wall, eliminating the need for post process superfinishing that conventional ceramics require (see Image 4).
The Tiaurum surface has been measured up to 2,500 HK. Hard chrome is around 1,000 HK and ceramics are around 2,500 HK. In terms of wear performance and life, the Tiaurum is performing better than hard chrome and, so far, equal to that of ceramics. The hardest layer is only a few microns thick at the surface. This has a few cost benefits to manufacturers and printers. On a gearless press, the anilox can be rescreened several times without the need to remove the old coating and apply an entirely new one. The Tiaurum surface can be built up to any diameter to allow for a large range of potential rescreens. The second potential benefit is the ability to repair a damaged anilox. Titanium can bond to itself so when damage occurs, only the blemished area needs to be turned down and resprayed. The entire surface still needs reprocessing with lasers to ensure uniform cell distribution, but the cost and time of replacing the entire surface has been minimized.
About the Author: Brendan Pollard is the managing director of Applied Laser Engineering Ltd (ALE). For the last 25 years, he has headed ALE’s research into laser-engraved functional topography. Prior to the start-up of ALE, he was the director of engineering for Zed Instruments Ltd. His 17-year tenure at Zed saw the establishment of laser-engraving as a viable production process. Brendan has no formal qualifications and is, in fact, a left-handed, dyslexic autodidactic.
A more comprehensive technical and commercial description of Tiaurum is available from Kinetic Elements Ltd, authored by Alexander Engel, Justin Holland and Dr. Peter King.
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