Modification of Aluminium Surface Using Picosecond Laser for Printing Applications
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Modification of Aluminium Surface Using Picosecond Laser for Printing Applications Imtiyaz A. Ansari1, Ken G. Watkins1, Martin C. Sharp2, Richard Hutchinson3 and Rodney Potts4 Department of Engineering, Laser Group, University of Liverpool, Birkenhead, CH41 9HP, UK 2 General Engineering Research Institute, Liverpool John Moores University, Liverpool, L3 3AF, UK 3 Derwent Technology, Whitewynn, Aughton Ruddings, Ellerton, York, YO42 4PN, UK 4 J. P. Imaging Ltd., Lairdside Laser Engineering Centre (LLEC), Birkenhead, CH41 9HP, UK 1
ABSTRACT Ultrafast picosecond laser pulses of wavelength of 1064nm have allowed the surface modification of anodised aluminium plates for a potential industrial application. The interaction of the laser pulses with the substrate created a hydrophilic surface, giving a contact angle of less than 10 degrees. On examination under a Scanning Electron Microscope (SEM), it was observed that these surfaces have an interesting ‘lotus-leaf’ like structure. It has been found that these laser processed hydrophilic surfaces revert to hydrophobicity with time. The potential for application in the printing industry is strong and offers the possibility of reusability and sustainability of the plate material. Initial trials have confirmed this possibility. This technology would offer extra advantages as a non-chemical process without the need for a developer, thereby reducing the overall costs and environmental impact of printing. INTRODUCTION In today’s fast moving technological world, it has been realised that modifying the surface wettability of solid substrates is important in various situations. There are many applications where highly hydrophilic (water contact angle < 10°) and hydrophobic (water contact angle > 100°) materials are highly desirable [1]. There is a considerable amount of literature available on photoresponsive or photoinduced surface wettability of different materials, mainly TiO2, by using various forms of light source and dark storage to switch from a hydrophilic to a hydrophobic state or vice-versa [1-7]. Two excellent review articles on photoresponsive surfaces and controlled switchable surfaces have been written by Kong et al. and Jiang et al. [8, 9]. The use of an ultraviolet (UV) and a green laser to change surface wettability of polymers has been recently reported by Athanassiou et al. [10, 11]. To the authors’ knowledge, no work has been reported on the use of ultra short picosecond Infra-Red (IR) laser pulses to create hydrophilicity on aluminium (Al) and aluminium oxide. In the present study, Al is chosen because it is a material of choice in the lithographic printing industry due to its properties, its availability and low cost. After printing, the plate is either recycled (but is not reusable for lithographic plates) or is disposed of. An estimated 0.5 million tonnes of lithographic grade Al is produced annually requiring an energy consumption of 1010 kWh/annum; the equivalent of the annual power demand of 2 million homes. Also, the Al smelting process resu
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