IMPROVEMENTS RELATING TO PRINTING

Abstract

A method of roughening a surface of a printing form precursor. The method comprises subjecting at least a part of the surface to energy in the form of pulses of electromagnetic radiation to produce a uniformly hydrophilic roughened surface on at least a part of the printing form precursor and optionally converting the uniformly hydrophilic roughened surface of the printing form precursor to a uniformly hydrophobic roughened surface. The method is useful for providing a surface for use in a subsequent imaging and/or printing process in lithographic printing. Methods of providing a printing form comprising an image formed of hydrophobic regions and hydrophilic regions using said method and a method of printing using said method are also described, as are printing forms so produced and imaging devices and apparatus for carrying out the said methods.

Claims

1. A method of roughening a surface of a printing form precursor, the method comprising subjecting at least a part of the surface to energy in the form of pulses of electromagnetic radiation to produce a uniformly hydrophilic roughened surface on at least a part of the printing form precursor and optionally converting the uniformly hydrophilic roughened surface of the printing form precursor to a uniformly hydrophobic roughened surface.

2. The method according to claim 1, wherein substantially the entire surface of the printing form precursor is subjected to the energy.

3. The method according to claim 1, wherein the method is a chemical-free method of roughening a surface of a printing form precursor.

4. The method according to claim 1, wherein the method provides the surface of the printing form precursor with a uniform roughness having an R.sub.a value measured using light interference microscopy of from 0.15 to 12 m.

5. The method according to claim 1, wherein the printing form precursor is an aluminium sheet.

6. The method according to claim 1, wherein the pulses of electromagnetic radiation have a pulse length of from 110.sup.15 s to 110.sup.6 s.

7. The method according to claim 1, wherein the pulses of electromagnetic radiation have a pulse length in the range of 110.sup.11 s to 110.sup.6 s and a pulse energy in the range of 0.05 mJ to 2.0 mJ.

8. The method according to claim 1, wherein the method comprises the step of converting the uniformly hydrophilic roughened surface of the printing form precursor to a uniformly hydrophobic roughened surface and the step of converting involves heating the surface to a temperature in the range of 30 to 150 C., after subjecting the surface to the energy.

9. The method according to claim 1, wherein the method is carried out in a controlled atmosphere.

10. The method according to claim 1, wherein the method comprises the step of converting the uniformly hydrophilic roughened surface of the printing form precursor to a uniformly hydrophobic roughened surface and the step of converting involves leaving the printing form precursor under ambient conditions or the conditions defined in claim 8 for at least 15 minutes.

11. A printing form precursor having either a uniformly hydrophobic roughened surface or a uniformly hydrophilic roughened surface, the roughened surface produced by subjecting the surface to energy in the form of pulses of electromagnetic radiation.

12. An imaging device for subjecting a surface of a printing form precursor to energy in the form of pulses of electromagnetic radiation having a pulse length not greater than 110.sup.6 seconds selected to produce a uniformly hydrophilic roughened surface on the printing form precursor.

13. A method of providing a printing form comprising an image formed of hydrophobic regions and hydrophilic regions, the method comprising the steps of: a) roughening a surface of a printing form precursor according to claim 1 to provide a uniformly hydrophobic roughened surface or a uniformly hydrophilic roughened surface; and b) after step a), either subjecting at least a part of the uniformly hydrophobic roughened surface imagewise to a second energy in the form of pulses of electromagnetic radiation to produce at least one hydrophilic image region on the otherwise uniformly hydrophobic roughened surface; or subjecting at least a part of the uniformly hydrophilic roughened surface imagewise to a second energy in the form of pulses of electromagnetic radiation to produce at least one hydrophilic image region on the otherwise uniformly hydrophilic roughened surface and converting the hydrophilic image region to a hydrophobic image region; and thereby provide the printing form.

14. The method according to claim 13, wherein the second energy in the form of pulses of electromagnetic radiation have a pulse length of from 110.sup.15 s to 110.sup.6 s and a pulse energy of from 0.0001 mJ to 2.0 mJ.

15. The method according to claim 14, wherein step a) comprises subjecting at least a part of the surface to energy in the form of pulses of electromagnetic radiation having a pulse length of from 110.sup.15 s to 110 .sup.6 s in a controlled atmosphere to produce a uniformly hydrophilic roughened surface on the printing form precursor and converting the uniformly hydrophilic roughened surface of the printing form precursor to a uniformly hydrophobic roughened surface by heating the surface to a temperature in the range of 30 to 150 C., after subjecting the surface to the energy; and wherein step b) comprises subjecting at least a part of the uniformly hydrophobic roughened surface imagewise to a second energy in the form of pulses of electromagnetic radiation having a pulse length of from 110.sup.15 s to 110.sup.6 s to produce the at least one hydrophilic image region on the otherwise uniformly hydrophobic roughened surface.

16. The method according to claim 15, wherein in step a) after subjecting the surface to the energy the surface is heated for at least 1 minute.

17. The method according to claim 13, wherein step a) involves roughening a surface of a printing form precursor in a controlled atmosphere of an inert gas to provide the uniformly hydrophilic roughened surface; and wherein step b) comprises subjecting at least a part of the uniformly hydrophilic roughened surface imagewise to a second energy in the form of pulses of electromagnetic radiation in a controlled atmosphere of a reactive gas to produce at least one hydrophilic image region on the otherwise uniformly hydrophilic roughened surface and converting the hydrophilic image region to a hydrophobic image region by heating the surface at a temperature of 30 to 150 C. for a period of 1 minute to 24 hours.

18. A method of printing using a recycled printing form, the method comprising the steps of: a) roughening a surface of a printing form precursor according to claim 1 to provide a uniformly hydrophobic roughened surface or a uniformly hydrophilic roughened surface; b) after step a), either subjecting at least a part of the uniformly hydrophobic roughened surface imagewise to a second energy in the form of pulses of electromagnetic radiation to produce at least one hydrophilic image region on the otherwise uniformly hydrophobic roughened surface; or subjecting at least a part of the uniformly hydrophilic roughened surface imagewise to a second energy in the form of pulses of electromagnetic radiation to produce at least one hydrophilic image region on the otherwise uniformly hydrophilic roughened surface and converting the hydrophilic image region to a hydrophobic image region; and thereby provide the printing form; c) after step b), carrying out a method of printing using the printing form provided by step b); and d) after step c), repeating steps a) to c) at least once using the printing form used in step c).

19. (canceled)

20. A method of producing a printing form having an image from a printing form precursor, the image formed of hydrophobic regions and hydrophilic regions, the method comprising the steps of: a) subjecting at least a first part of a surface of the printing form precursor to a first energy in the form of pulses of electromagnetic radiation, in a method according to any one of claims 1 to 10, to provide the hydrophobic regions; and b) subjecting at least a second part of the surface of the printing form precursor to a second energy in the form of pulses of electromagnetic radiation, in a method according to claim 1, to provide the hydrophilic regions.

21. (canceled)

22. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0303] In the following examples, reference is made to the Figures in which:

[0304] FIG. 1 shows SEM photographs of roughened surfaces of printing form precursors which have been subjected to a method of the present invention.

[0305] FIG. 2 shows a perspective view of an environmentally controlled laser processing chamber used in a method of the present invention.

EXAMPLES

[0306] In the following Examples the equipment described in Table 1 was used where referred to by the name in the name column of the table.

TABLE-US-00001 TABLE 1 Name Equipment Model Suppliers Nanosecond G4, 1064 nm, 70 W SPI Lasers UK Ltd. pulsed fibre laser Picosecond FemtoPower1060-HE, Fianium laser 1064 nm, 2 W, 40 ps, 10 uJ, 200 kHz Femtosecond Libra-HE, Coherent laser 800 nm, 4 W, 100 fs, 1 kHz-10 kHz Sub-nanosecond 1064-15 W YSL Lasers Wuhan, China laser DropMeter A300 Ningbo Haishu Maist Vision Inspection & Measurement Co., Ltd., China Bruker Contour GT-K0 Bruker, Germany Nikon Ci-L Nikon Microscope SEM-HUT JSM-6390LV Japan SEM-WUP FEI Sirion 200 Philips, Netherlands SEM-WHUT ULTRA PLUS-43-13 Carl Zeiss AG, Germany Ultrasonic JP-080B Skymen Cleaning Equipment Cleaner Shenzhen Co., Ltd Aluminum 510 mm 400 mm Hydro Aluminium Rolled 0.275 mm Products GmbH, Germany PS plate 620 mm 485 mm LongMa Aluminum Group, 0.15 mm Hebei China

[0307] Unless otherwise stated in the following examples, all water contact angle values were measured using the DropMeter and all Ra and Rz values were measured using the Bruker (by light interference microscopy), according to standard procedures known in the art.

[0308] Example Set 1-Roughening With Nanosecond Laser

[0309] Samples of 99.5 wt % pure aluminium sheet were ultrasonically cleaned, firstly in acetone and secondly in deionised water, each for 5 minutes, and then dried in air. The nanosecond pulsed fibre laser was coupled to a scanning galvanometer and focusing lens to provide a spot size of 50 m. Scanning speed and repetition rate were adjusted to provide an overlap pattern of N=#=3.39. Each sample was exposed to one of the different combinations of pulse length and pulse energy shown in Table 2. The exposure area for each combination of pulse energy and pulse length was 1 cm.sup.2. Following laser processing, the water contact angle of each 1 cm.sup.2 surface was measured on the Dropmeter using deionised water as the probe liquid. The metal samples were stored open to the prevailing ambient laboratory conditions of 30-35 C. and a relative humidity of 40-50% for 5 days. During this period the water contact angle was re-measured twice per day, at the start and end of each of the 5 days. Table 2 displays the final water contact angles achieved after 5 days stored in such a way.

TABLE-US-00002 TABLE 2 Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 (mJ) 240 220 200 175 160 145 130 120 115 105 100 90 80 65 58 0.60 0 9 0 0 0 0 0.58 0 10 0 10 9 12 7 0.56 10 13 13 9 12 14 0 0.54 0 22 20 13 0 12 12 0.52 0 22 42 27 11 21 12 18 0.50 9 19 62 58 22 22 11 48 15 0.48 18 90 79 77 35 28 21 62 27 34 0.46 38 90 29 88 132 28 83 55 23 21 27 0.44 92 114 96 96 98 112 84 39 38 50 47 75 0.42 94 97 93 87 92 100 100 80 63 60 37 137 37 0.40 90 88 95 98 61 32 93 127 76 74 87 75 93 100 0.38 90 91 137 110 130 105 136 112 63 120 140 145 128 0.36 86* 89 88 134 83 139 113 132 149 150 140 148 114 139 0.34 88 88 111 140 100 138 144 138 133 128 97 141 0.32 90 84 98 138 140 135 99 126 97 102 0.30 86 91 89 136 134 94 23 88 92 0.28 81* 90* 89 93 128 93 52 86 84 0.26 88* 94* 88* 93 93 90 75 86 73 0.24 85* 88* 89* 91* 93* 90 99 88 83 0.22 88* 90* 91* 91* 91* 92 88 87 0.20 82* 89* 91* 91* 89* 88* 86* 90 0.18 87* 88* 88* 88* 90* 81* 91* 0.16 88* 87* 87* 89* 90* 91* 90* 0.14 90* 90* 87* 89* 91* 86* 90* 0.12 87* 88* 90* 90* 91* 89* 88* 0.10 90* 90* 90* 89* 87* 87* 86* Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W16 W17 W18 W19 W20 W21 W22 W23 W24 W25 W26 W27 W28 (mJ) 55 50 45 40 36 33 30 26 23 20 16 13 10 0.60 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0.34 0.32 0.30 48 80 78 0.28 99 39 72 77 0.26 123 123 138 146 0.24 123 106 127 134 102 0.22 121 114 120 123 134 139 0.20 91 98 118 96 117 128 125 0.18 102* 93 108 90 80 90 90 84 0.16 86* 88* 84 90 97 89 89 88 0.14 92* 90* 88* 91* 91 94 91 90 114 0.12 88* 87* 88* 89* 86* 91 92 90 114 89 0.10 87* 87* 89* 87* 89* 91* 91* 89 89 90 89 *Denotes that the method produced a polishing effect and not a roughened surface.

[0310] Example Set 2-Water Contact Angle Data

[0311] Samples of 99.5 wt % pure aluminium were ultrasonically cleaned in acetone and then deionised water, each for 5 minutes. The surface was processed in 11 cm.sup.2 sections using the nanosecond pulsed fibre laser over a wide range of pulse energy and pulse length combinations (see Table 3) where each 11 cm.sup.2 unit was processed using a unique combination of these parameters. The laser beam had a diameter of 50 m and the scanning rate was adjusted to provide an overlap of N=#=3.39. After processing the samples were heated in an oven without fan assistance for 2 hours, cooled and the water contact angle was measured with the DropMeter. Table 3 displays the results. These results show the greater proportion of the pulse energy and pulse length combinations had become superhydrophobic. The Ra and Rz of the samples was also measured on the Bruker and these data are displayed in Tables 4 and 5 respectively which clearly show that a very wide range of roughnesses are generated and that the highest values of Ra and Rz reside in the areas of highest pulse energies and pulse lengths and vice versa for the lowest values. It can be seen that superhydrophobic surfaces can be generated in both of these regions and it seems that roughness itself is not the cause of the superhydrophobicity. We can also see that, at the very lowest pulse energies and pulse lengths, topographies consistent with currently available commercial printing plates is achieved.

TABLE-US-00003 TABLE 3 water contact angle data Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) energy W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 (mJ) 240 220 200 175 160 145 130 120 115 105 100 90 80 65 58 0.60 155.5 0 0+ 0+ 152.5 100.4 0.58 142.2 23.8 22.2 0+ 155.1 156.4 0.56 134.7 157.7 166.6 0+ 156.5 157.1 0.54 139.8 145.5 45.9 24 155.3 159.7 0.52 136.2 147.2 150.3 89.6 155.8 156.5 0.50 133 146.1 153.8 53.6 154.5 160 158.3 0.48 142 146.7 160.2 157.9 156.5 157.1 160 0.46 148.2 148.6 138.4 152.6 160.6 162.5 160.8 167.4 155.8 0.44 159.8 146.2 157.3 140.6 151.8 149 148.7 163.3 158.6 0.42 159.4 159.9 156.2 153.5 154.1 0.40 164.4 157.7 162.5 154.5 158.9 157 0.38 165.6 158.5 161 155.7 152.6 164.7 170.4 0.36 172.2 160.7 159 153.7 155.4 165.8 151.5 0.34 179.5 161.2 152 159.3 168.4 160.9 151.9 154.5 0.32 169.3 176.3 168.8 159.6 166.7 157.1 162.2 158.7 0.30 167.5 172.2 158.9 165.9 157.7 171.4 168 0.28 165 154.1 159.2 163.1 163 0.26 166.2 159.5 166.8 0.24 159.7 163.6 162.9 0.22 160.2 0.20 0.18 0.16 0.14 0.12 0.10 0.80 Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) energy W16 W17 W18 W19 W20 W21 W22 W23 W24 W25 W26 W27 W28 (mJ) 55 50 45 40 36 33 30 26 23 20 16 13 10 0.60 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0.34 0.32 0.30 0.28 165.7 0.26 167 157.3 159.7 0.24 162.4 162.2 161 161.4 0.22 169 166.3 170.7 162 159.5 0.20 166.8 165.4 164.2 169.5 166.5 159.4 0.18 170.6 169.7 167.7 165.4 155.7 166.5 0.16 179.9 166 164.2 166.9 170.9 165.5 0.14 162.1 168.1 166.5 164 0.12 172.2 173.7 166 170.5 0.10 164.5 165.2 168.6 165.6 0.80 145

TABLE-US-00004 TABLE 4 Ra data Ra (m) Pulse Pulse length (ns, 10.sup.9 s) energy W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 (mJ) 240 220 200 175 160 145 130 120 115 105 100 90 80 65 58 0.6 8.56 9.186 8.393 0.58 9.164 9.637 8.794 10.333 0.56 9.54 8.996 10.45 10.07 8.888 0.54 10.631 9.671 9.04 10.02 8.077 0.52 9.239 8.914 8.681 9.728 8.885 7.786 0.5 7.121 8.067 7.899 8.987 8.445 8.951 7.488 0.48 6.531 7.253 7.501 9.076 8.273 8.275 7.533 8.052 0.46 6.37 6.399 7.006 8.476 8.028 9.646 7.735 8.992 5.605 0.44 5.22 5.263 5.983 7.123 6.82 7.494 8.384 8.096 5.778 0.42 6.189 6.013 6.289 5.864 5.159 0.4 5.844 5.624 5.821 5.703 5.323 5.503 0.38 5.319 5.47 6.12 5.43 5.039 5.269 5.401 0.36 5.13 5.43 4.98 4.911 5.604 5.563 3.797 0.34 4.544 4.981 4.713 4.55 5.001 5.329 3.765 3.398 0.32 4.501 4.093 3.986 4.62 4.59 3.556 3.279 3.338 0.3 3.669 3.526 4.332 4.322 3.478 3.235 3.227 0.28 3.506 3.818 3.212 3.179 3.086 0.26 3.163 2.849 2.999 0.24 2.793 2.459 2.63 0.22 0.2 0.18 0.16 0.14 0.12 0.1 0.8 Ra (m) Pulse Pulse length (ns, 10.sup.9 s) energy W16 W17 W18 W19 W20 W21 W22 W23 W24 W25 W26 W27 W28 (mJ) 55 50 45 40 36 33 30 26 23 20 16 13 10 0.6 0.58 0.56 0.54 0.52 0.5 0.48 0.46 0.44 0.42 0.4 0.38 0.36 0.34 0.32 0.3 0.28 3.07 0.26 3.019 2.211 2.17 0.24 2.843 2.059 1.901 2.034 0.22 2.609 2.016 1.817 1.72 1.801 0.2 2.249 1.904 1.605 1.704 1.746 1.361 0.18 1.705 1.571 1.544 1.625 1.337 1.225 0.16 1.434 1.397 1.491 1.272 1.2 1.155 0.14 1.131 1.083 1.083 1.095 0.12 0.928 0.913 0.953 1.055 0.1 0.462 0.747 0.782 0.771 0.8 0.62

TABLE-US-00005 TABLE 5 Rz data Pulse length (ns, 10.sup.9 s) Rz (m) W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 Pulse energy (mJ) 240 220 200 175 160 145 130 120 115 105 100 90 80 65 58 0.6 77.9 79.9 71.5 0.58 81.7 82.1 75.2 93.3 0.56 98.2 83.2 75.8 85.4 97.8 0.54 102.7 87.2 85.7 90.2 87.4 0.52 105.1 87.8 75.2 80.8 113.0 92.5 0.5 69.9 70.6 73.9 77.2 111.9 82.9 73.2 0.48 69.5 88.2 71.1 72.8 101.0 79.4 72.3 76.4 0.46 73.4 69.9 68.9 80.4 74.0 108.2 77.4 82.0 58.3 0.44 56.1 57.3 62.7 91.4 73.9 68.5 73.8 73.1 59.2 0.42 66.1 55.3 63.1 56.9 50.2 0.4 58.9 74.7 52.4 55.0 51.7 51.2 0.38 53.4 76.5 55.8 54.3 49.5 54.0 51.8 0.36 50.2 57.7 51.0 52.6 54.0 49.0 42.4 0.34 47.2 62.9 52.1 47.8 55.0 53.2 44.2 39.3 0.32 77.7 48.8 45.5 47.5 49.4 41.2 37.7 43.1 0.3 47.0 45.1 46.7 49.1 42.1 39.8 37.2 0.28 40.1 41.7 43.7 42.3 42.3 0.26 44.5 33.9 36.2 0.24 37.9 34.6 33.0 0.22 0.2 0.18 0.16 0.14 0.12 0.1 0.8 Pulse length (ns, 10.sup.9 s) Rz (m) W16 W17 W18 W19 W20 W21 W22 W23 W24 W25 W26 W27 W28 Pulse energy (mJ) 55 50 45 40 36 33 30 26 23 20 16 13 10 0.60 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0.34 0.32 0.30 0.28 49.0 0.26 38.2 30.1 26.9 0.24 39.5 26.9 27.7 30.5 0.22 33.1 27.3 25.9 24.1 26.2 0.20 31.8 27.4 22.1 28.5 23.8 22.7 0.18 23.5 21.8 21.6 22.0 24.3 19.7 0.16 21.3 21.5 20.6 23.7 24.5 17.7 0.14 18.6 23.0 16.6 17.2 0.12 19.2 17.2 19.1 24.6 0.10 15.9 17.9 20.8 20.6 0.80 11.9

[0312] Example Set 2-Repeated Roughening Cycles

[0313] A commercially available sample of a conventionally exposed and coated lithographic printing plate provided by Longma of China, was cut into a 55 cm square and the coating removed by repeated washing with acetone to reveal the electrochemically grained and anodised substrate, then dried in air. The nanosecond pulsed fibre laser at 1064 nm was used to process four 1 cm.sup.2 sections (labelled sections 1-4) onto the exposed lithographic substrate using a pulse length of 100 ns and a pulse energy of 0.32 mJ whilst the spot laser diameter was 50 m and the scan rate was adjusted to provide an overlap of N=#=3.39. The four roughened sections were measured for water contact angle and found to be superhydrophilic with a water contact angle of 0. The sample was then placed in an oven at 100 C. for 2 hours. After cooling to ambient temperature, all sections were retested for water contact angle and were all found to be superhydrophobic with a water contact angle of 161. All four sections were then exposed using the picosecond pulsed laser at a pulse energy of 8.5 J and a pulse length of 80 ps, to represent an imaging process (exposure 1). The laser beam diameter was 16.5 m and scan speeds were set to achieve an overlap pattern of N=#=2.5 (this overlap pattern was selected because previous work varying overlap from N=#=0.5 to N=#=8.0 on electro-polished metal identified that between N=#=2.0 to N=#=3.0 the surface is rendered hydrophobic to a greater degree than other overlap patterns). Measurement of the water contact angle revealed that all four sections had become superhydrophilic with a water contact angle measurement of 0. The samples were returned to the oven for 3 hours at 100 C., cooled to ambient temperature and each section measured for water contact angle. All of the sections were shown to be superhydrophobic again (see Table 6). Sections 2-4 were then processed again with the picosecond laser under exactly the same conditions as in the first exposure, to become superhydrophilic (exposure 2). After heating at 100 C. for 3 hours these three freshly exposed sections returned to a superhydrophobic form with an average water contact angle of 158. Sections 3-4 were then exposed for a third time to the same picosecond processing conditions as previously conducted and were rendered superhydrophilic (exposure 3). Heating in an oven at 100 C. overnight returned these sections to a superhydrophobic state with an average water contact angle of 157. Section 4 was exposed for a fourth time to the picosecond laser processing under exactly the same conditions as previously conducted to render it yet again superhydrophilic (exposure 4). Heating in an oven for 3 hours at 100 C. returned section 4 yet again to a superhydrophobic state with a water contact angle of 157 . These results are summarized in Table 6 and show that the process of roughening and conversion to a hydrophobic state can be repeated on the same substrate without diminishing the effect of the roughening and conversion and without damaging said substrate. This is confirmed by the SEM pictures of FIG. 1 showing sections 1-4 after the four cycles of picosecond exposure and conversion as described above.

TABLE-US-00006 TABLE 6 Water contact angle () Section Average water Exposure: 1 2 3 4 contact angle () Roughening 0 Heat - 100 C. 2 hours 161 161 ps exposure 1 0 0 0 0 0 Heat - 100 C. 3 hours 159 159 ps exposure 2 163 0 0 0 Heat - 100 C. 3 hours 161 157 158 158 158 ps exposure 3 155 156 0 0 Heat - 100 C. 11 hours 156 162 162 151 157 ps exposure 4 161 159 156 0 Heat - 100 C. 3 hours 154 147 150 157 152

[0314] Example Set 3a-Roughening Under Ar

[0315] FIG. 2 shows an environmentally controlled laser processing chamber (100) we have designed. The main chamber (110) has an internal platform (not shown) which supports a metal sample which is introduced by unscrewing the bottom section (120) containing the platform. The top section (130) contains a glass window (131) coated to maximise transmission of 1064 nm wavelength radiation. A power meter was used to measure the power from the laser beam at the height of the sample platform with and without the coated glass window and we recorded no measurable difference in incident power. The taps (141-144) are connected to the sides of the chamber to allow different atmospheres, i.e. gases, to be introduced into the chamber. The taps can then be closed to seal the unit or the gas can be allowed to flow through the chamber. In addition to changing the gaseous composition of the chamber a vacuum can be applied or a liquid (chemically inert to the components of the chamber) can be inserted to cover the sample.

[0316] 4 cm diameter disks were cut from 99.5 wt % pure aluminium sheet which had been ultrasonically cleaned in acetone then deionised water for 5 minutes each (this is really a precaution to avoid contaminating the chamber, not an essential process). A disk sample was placed in the chamber under ambient conditions and was laser polished to provide a uniform surface, using the nanosecond pulsed fibre laser at a pulse length of 105 ns and a pulse energy of 0.20 mJ. The laser beam diameter at the processing surface was 50 m and scanning rates were adjusted to provide an overlap pattern of N=#=3.39.

[0317] One of the taps was then connected to a cylinder of argon gas which was allowed to flow through the cell and out of another tap. The polished surface was then exposed using the same laser at a variety of pulse lengths and pulse energies that we have shown to provide roughening and which take at least 2-3 days to become hydrophobic. Following laser processing, the water contact angle was measured immediately and thereafter over a range of times elapsed after processing from 6 minutes to 2 days. Tables 7, 8 and 9 show the results. These results show that some of these samples become hydrophobic after just 30 minutes. It is known from previous work that a water contact angle of >60 is, in fact, sufficient to provide ink and water discrimination on a printing press and some of these samples achieve that level after just 6 minutes under ambient conditions.

TABLE-US-00007 TABLE 7 Water contact angle () Pulse Pulse length Time after exposure (hours) at ambient temperature Energy (ns, t = 0 t = 1 t = 2 t = 3 t = 4 t = 5 t = 6 t = 7 (mJ) 10.sup.9 s) 0 0.1 0.3 0.5 1 2 12 16 0.22 36 0 0 0 49 94 79 107 107 0.20 36 0 0 20 20 25 23 67 68 0.18 36 0 0 0 81 85 92 103 99 0.16 36 0 17 14 23 24 35 69 72 0.20 33 0 0 0 0 16 52 56 0.18 33 0 24 28 29 35 81 79 0.16 33 0 24 72 83 86 93 92 0.14 33 0 0 25 17 66 68 0.18 30 0 0 0 0 0 20 57 63 0.16 30 0 0 0 33 21 22 63 69 0.14 30 0 0 0 0 0 13 52 64 0.16 26 42 78 89 96 98 95 95 98 0.14 26 47 63 94 84 81 101 81 81 0.12 26 42 64 57 86 95 94 83 76 0.14 23 0 56 80 72 70 70 85 74 0.12 23 0 70 98 96 98 84 80 80 0.10 23 21 66 82 83 82 77 81 79 0.12 20 0 0 0 0 0 56 49 0.10 20 0 0 0 0 0 53 45

TABLE-US-00008 TABLE 8 Water contact angle () Pulse Pulse Time after exposure (hours) at ambient temperature Energy length (ns, t = 0 t = 1 t = 2 t = 3 t = 4 t = 5 t = 6 t = 7 t = 8 t = 9 (mJ) 10.sup.9 s) 0 0.1 0.3 0.5 1 2 3 4 21 47 0.22 36 0 0+ 0+ 0+ 0+ 0+ 24 21 96 95 0.20 36 0 69 56 81 85 79 95 91 80 109 0.18 36 0 77 89 84 81 69 88 84 93 103 0.16 36 0 36 49 83 69 79 83 85 79 101 0.34 105 0 0 0+ 0+ 0+ 0+ 0+ 60 85 87 0.34 100 0 10 15 13 16 23 24 80 89 86 0.34 90 0 0+ 19 0+ 0+ 17 46 68 96 118

[0318] Example Set 3b-Roughening Under Controlled Atmospheres

[0319] Twelve 4 cm diameter samples were cut from a sheet of 99.5 wt % pure aluminium, ultrasonically cleaned in acetone followed by deionised water, both for 5 minutes and dried in air. Six bottled gases were used in the experiment, namely, oxygen, nitrogen, helium, argon, carbon dioxide and bottled air which consisted of an 80:20 mix of nitrogen and oxygen. The latter gas was used in place of normal air to eliminate any artefacts that may have been generated by the other gases flowing through the processing chamber as opposed to static atmospheric air. Two of each of the sample disks were assigned to each gasone to be kept at ambient conditions for the duration of the post-processing time and one to be heated for various times. The nanosecond pulsed fibre laser was used for this experiment with a 50 m beam diameter and scan speeds adjusted to provide an overlap pattern of N =#=3.39 for all exposures. The environmental control chamber of FIG. 2 was placed under the laser so that the focal plane of the laser was at the level of the internal platform. A sample was placed on the platform and the chamber closed. Prior to roughening, the samples were laser polished using the laser with a pulse length of 105 ns, a pulse energy of 0.20 mJ and an overlap pattern of N=#=3.39 to produce a uniform starting surface for the samples. In the first set, oxygen from a pressurised bottle was attached to one tap of the chamber via a rubber hose, both taps were opened and the gas valve opened to allow oxygen to flow through the chamber. Four 11cm.sup.2 squares were processed by the laser using a pulse length of 16 ns and a pulse energy of 0.10 mJ with an overlap of N=#=3.39. This sample was kept at ambient conditions and each of the four squares was used to measure the water contact angle at 30, 60, 90 and 120 minutes after processing. This whole process was repeated to produce an identical sample that was then cut into four separate pieces, each containing a 11cm.sup.2 square, and the four pieces were subjected to heat at 100 C. for 30, 60, 90 or 120 minutes, cooled to ambient in air and then measured for water contact angle. This whole process was repeated for each gas in turn with further sets of samples. The samples were also tested on the Bruker for Ra and Rz and all of the data are displayed in Table 9b. Inspection strongly suggests that the inert gases inhibit the heat developable occurrance of superhydrophobic surfaces with their water contact angle not rising above 120, whilst the more reactive gases produce, in nearly every individual sample, water contact angles above 150 with oxygen and bottled air being above 160, even above 170 in some cases. Additionally, there appears to be no obvious correlation between the roughness parameters Ra and Rz, water contact angle and ambient conditions versus heating.

TABLE-US-00009 TABLE 9B Water Increase Ra Rz contact over Gas Time Condition (m) (m) angle () ambient () oxygen 30 mins Ambient 0.960 17.19 0 101 Heat 0.964 16.05 101 60 mins Ambient 0.688 12.14 0 165 Heat 0.627 11.20 165 90 mins Ambient 0.694 14.09 0 169 Heat 0.671 12.81 169 120 mins Ambient 0.972 15.92 0 163 Heat 1.004 16.92 163 carbon 30 mins Ambient 0.911 21.43 0 151 dioxide Heat 1.012 18.44 151 60 mins Ambient 0.870 16.99 0 146 Heat 0.980 18.36 146 90 mins Ambient 0.898 17.00 0 98 Heat 0.964 21.09 98 120 mins Ambient 0.934 17.86 0 154 Heat 0.970 19.62 154 helium 30 mins Ambient 1.127 21.62 0 97 Heat 1.187 24.32 97 60 mins Ambient 1.202 24.09 53 67 Heat 1.172 23.41 120 90 mins Ambient 1.178 22.52 67 49 Heat 1.229 24.15 116 120 mins Ambient 1.227 20.15 72 36 Heat 1.141 21.83 108 nitrogen 30 mins Ambient 0.899 34.32 0 100 Heat 0.903 20.05 100 60 mins Ambient 0.859 21.26 0 109 Heat 0.900 20.04 109 90 mins Ambient 1.055 23.98 0 117 Heat 1.121 23.27 117 120 mins Ambient 0.948 23.89 0 116 Heat 0.924 23.10 116 argon 30 mins Ambient 0.739 18.42 36 46 Heat 0.718 16.73 82 60 mins Ambient 0.746 17.72 49 54 Heat 0.773 18.70 103 90 mins Ambient 0.760 16.58 50 45 Heat 0.769 27.53 95 120 mins Ambient 0.753 16.11 56 51 Heat 0.751 17.20 107 bottled 30 mins Ambient 1.028 19.08 0 164 air Heat 1.025 20.42 164 60 mins Ambient 1.013 19.30 0 171 Heat 1.049 19.58 171 90 mins Ambient 1.053 20.86 0 174 Heat 1.025 21.11 174 120 mins Ambient 1.067 20.26 0 164 Heat 1.087 19.18 164

[0320] Example Set 4-Effect of Overlap

[0321] A sample of 99.5 wt % pure aluminium was electro-polished at 20 v in a mixture of ethanol and 60% perchloric acid (4:1 v/v) for 4 minutes, maintaining the temperature between 0 and 10 C. by use of a recirculating cooling bath. The ethanol and deionised water washed sample was dried and then laser roughened at 1064 nm with a pulse length of 23 ns and a pulse energy of 0.14 mJ using the nanosecond pulsed fibre laser. The spot size was 50 m and scanning rates were adjusted to provide a range of overlap patterns from N=#=1 to N=#=4. The samples were heated in an oven at 100 C. for 2 to 23 hours and the water contact angle of the samples were measured at each time point. The results are displayed in Table 10 and indicate that whilst all are useful, the time to produce a superhydrophobic surface is less when N=#>1.

TABLE-US-00010 TABLE 10 Water contact angle () Time after Overlap (N #) exposure (hours) 1 1 2 2 3 3 4 4 0 0 0 0 0 2 107.4 138 138.9 102.8 4 123.3 166.5 158.6 158.6 6 84.5 160.7 163.7 166.6 18* 118.7 165 165.1 160.9 23* 152.8 179.6 * * *Denotes large water contact angle and low adhesion made accurate measurement impossible.

[0322] Example Set 5-Effect of Heat Treatment

[0323] Samples of 99.5 wt % pure aluminium sheet were cut and ultrasonically cleaned in acetone, followed by deionised water, both for 5 minutes. The effect of heating the printing form precursor after roughening the surface with the energy was investigated by exposing these samples using the nanosecond pulsed fibre laser at 1064 nm with a pulse length of 23 ns and a pulse energy of 0.14 and an overlap of N=#=3.39. This initially produced a uniformly hydrophilic roughened surface with a water contact angle of 0. The samples of printing form precursor were then heated at 60, 80, 100 or 120 C. and a control sample was left at room temperature. The water contact angle was measured at 0.5, 1.0, 1.5 and 2.0 hours after exposing the samples to the pulses of electromagnetic radiation. The results are shown in Table 11 below. At room temperature no change in water contact angle was observed over the 2.0 hours of the experiment. This sample would be expected to become hydrophobic over a period of several days depending on the ambient temperature. The results of the heated samples show that heating the samples of printing form precursor after exposure to the pulses of electromagnetic radiation shortens the time required for the water contact angle to increase and the surface to become hydrophobic.

TABLE-US-00011 TABLE 11 Water contact angle () Temperature ( C.), volume: 5 L Time/hrs RT 60 80 100 120 0 0 0 0 0 0 0.5 0+ 0+ 71.8 23.8 66 1 0+ 60.2 131.5 85.2 110.9 1.5 0+ 98.1 146.4 142.2 140.1 2 0+ 117.9 148.4 165.3 153.2 RT = room temperature

[0324] The procedure of Example set 5 was repeated using a range of pulses of electromagnetic radiation shown in Tables 12-14 below. After exposure of the samples to the pulses, each sample was heated in a fan oven at 100 C. and the water contact angle measured at 2 hours (Table 12), 10 hours (Table 13) and 22 hours (Table 14) post exposure. These results show that the water contact angle increased in all cases over 22 hours in the fan oven at 100 C. to render the surface of the samples uniformly hydrophobic. At room temperature the samples would be expected to achieve hydrophobicity over several days or weeks.

[0325] Heating samples with an unprocessed raw metal surface or an electrochemically polished metal surface had no effect on the water contact angle of the surfaces.

[0326] These results show that by appropriate selection of the pulse energy, pulse length, temperature of heating and time of heating, a printing form precursor with a particular water contact angle selected from the wide range covered by the examples in Tables 12-14 can be produced. The water contact angle can be selected according to the intended use of the printing form precursor.

[0327] These experiments were repeated using a static oven set at the same temperatures instead of a fan oven. These experiments showed that a static oven is more efficient at converting the hydrophilic surface to hydrophobic than a fan oven set at the same temperature.

TABLE-US-00012 TABLE 12 Fan oven, 100 C., 2 hours Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 (mJ) 240 220 200 175 160 145 130 120 115 105 100 90 80 65 58 0.60 0+ 0+ 0+ 0.58 0+ 0+ 0+ 0+ 0.56 0+ 0+ 0+ 0+ 0+ 0.54 0+ 0+ 0+ 0+ 0+ 0.52 0+ 0+ 0+ 0+ 0+ 0+ 0.50 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0.48 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0.46 25.2 22.3 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0.44 31.2 30.7 28.1 31.7 0+ 0+ 0+ 0+ 0+ 0.42 0+ 0+ 0+ 0+ 0+ 0.40 0+ 0+ 0+ 0+ 0+ 0+ 0.38 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0.36 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0.34 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0.32 21.6 0+ 0+ 0+ 0+ 0+ 0+ 0+ 0.30 83.8 23.9 0+ 0+ 0+ 0+ 0+ 0.28 34.4 0+ 0+ 0+ 0+ 0.26 0+ 0+ 0+ 0.24 55.9 45.4 0+ 0.22 0.20 0.18 0.16 0.14 0.12 0.10 Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W16 W17 W18 W19 W20 W21 W22 W23 W24 W25 W26 W27 W28 (mJ) 55 50 45 40 36 33 30 26 23 20 16 13 10 0.60 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0+ 0.34 0+ 0.32 0+ 0.30 0+ 0.28 0+ 0.26 0+ 82.8 26.2 0.24 0+ 74.7 57.2 40.9 0.22 17.8 69.7 61.9 63.4 55.2 0.20 55.2 88.5 76.9 77.7 68.7 86.4 0.18 34.3 96.5 93.5 87.6 108.4 75.8 0.16 107.1 98.3 97.8 120.4 117.1 126.9 0.14 158.3 141.6 139.4 126.3 0.12 114.5 115.5 131.4 121.5 0.10 129.3 144.8 119.1 128.4

TABLE-US-00013 TABLE 13 Fan oven, 100 C., 10 hours Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 (mJ) 240 220 200 175 160 145 130 120 115 105 100 90 80 65 58 0.60 138 87 146 0.58 140 74 112 145 0.56 147 89 99 139 166 0.54 150 146 126 137 116 0.52 152 144 148 146 128 89 0.50 160 159 147 150 59 66 60 0.48 0 0 152 157 58 41 0+ 61 0.46 0 0 0 0 73 34 18 29 120 0.44 0 0 0 0 120 67 40 126 133 0.42 155 160 98 136 146 0.40 155 57 91 138 87 146 0.38 157 108 139 140 74 112 145 0.36 104 152 147 89 99 139 150 0.34 124 163 150 146 126 137 148 147 163 0.32 157 152 144 148 146 141 138 157 0.30 160 159 147 150 140 140 143 0.28 152 157 152 142 50 0.26 153 164 57 0.24 164 157 0.22 0.20 0.18 0.16 0.14 0.12 0.10 Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W16 W17 W18 W19 W20 W21 W22 W23 W24 W25 W26 W27 W28 (mJ) 55 50 45 40 36 33 30 26 23 20 16 13 10 0.60 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0.34 0.32 0.30 160 0.28 92 0.26 66 161 163 0.24 146 151 157 162 0.22 139 155 159 158 160 0.20 157 161 150 160 162 0.18 149 151 162 155 165 162 0.16 150 139 158 150 154 162 0.14 153 147 141 137 0.12 139 138 138 137 0.10 122 135 138 141

TABLE-US-00014 TABLE 14 Fan oven, 100 C., 22 hours Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 (mJ) 240 220 200 175 160 145 130 120 115 105 100 90 80 65 58 0.60 143 147 146 0.58 146 156 154 166 0.56 156 155 158 169 158 0.54 152 156 155 153 161 0.52 147 153 158 155 151 156 0.50 149 150 154 156 149 147 163 0.48 148 148 152 153 148 150 153 168 0.46 134 161 154 155 156 133 162 165 165 0.44 151 152 155 156 153 156 158 159 157 0.42 155 159 158 140 154 0.40 150 93 159 157 138 160 0.38 158 150 154 150 130 150 160 0.36 137 165 150 141 149 153 166 0.34 145 161 151 151 140 152 155 169 0.32 156 153 155 154 156 152 159 155 0.30 156 148 162 160 149 152 157 0.28 148 156 149 153 144 0.26 147 150 137 0.24 167 150 90 0.22 0.20 0.18 0.16 0.14 0.12 0.10 Water contact angle () Pulse Pulse length (ns, 10.sup.9 s) Energy W16 W17 W18 W19 W20 W21 W22 W23 W24 W25 W26 W27 W28 (mJ) 55 50 45 40 36 33 30 26 23 20 16 13 10 0.60 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0.34 0.32 0.30 0.28 148 0.26 132 165 161 154 0.24 111 156 156 155 0.22 139 150 153 156 157 0.20 145 153 152 152 154 165 0.18 154 149 144 155 153 160 0.16 152 153 156 156 156 156 0.14 157 149 146 141 0.12 142 143 143 142 0.10 133 150 138 143

[0328] Example Set 6-Effect of Starting Roughness

[0329] Eight samples of 99.5 wt % pure aluminium were electrochemically polished at 20 v in a mixture of ethanol and 60% perchloric acid (4:1 v/v) for various times from 0.5 to 4 minutes whilst maintaining the temperature between 0 and 10 C. by using a recirculating cooling bath. The samples were then washed with ethanol and deionised water and dried. The Ra and Rz were determined using the Bruker which showed a narrow range of Ra values between 0.100 and 0.256 m and Rz between 2.61 and 3.76 m. Another sample of 99.5 wt % pure aluminium was ultrasonically cleaned in acetone and then deionized water, both for 5 minutes, dried and the Ra and Rz determined on the Bruker which gave an Ra of 1.263 m and an Rz of 20.79 m. All of the samples were then processed with the nanosecond pulsed fibre laser at a pulse energy of 0.14 mJ and a pulse length of 23 ns. The laser beam width in the processing plane was 50 m and the scan rate was adjusted to provide an overlap of N=#=3.39. All the samples were heated in an oven at 100 C. for various times between 2 and 23 hours and then cooled to ambient. The water contact angles of all the samples were measured and the results are displayed in Table 15.

TABLE-US-00015 TABLE 15 Water contact angles () Heating Electrochemically polishing time (minutes) time unpolished (hours) 0.5 1 1.5 2 2.5 3 3 4 control 0 0 0 0 0 0 0 0 0 0 2 134 137 145 141 140 139 133 143 160 4 157 161 159 162 163 159 157 161 163 6 157 156 163 157 172 165 171 160 180 18 164 164 161 160 164 153 163 163 168 23 168 172 180 180 176 180 171 170 168 Ra (m) 0.256 0.21 0.211 0.173 0.132 0.125 0.1 0.165 1.263 Rz (m) 3.76 3.58 3.71 3.12 2.41 2.81 2.61 3.03 20.79

[0330] The data in Table 15 show that although the Ra of the electro-polished samples varies by a factor of >10 compared to the unpolished samples, and the Rz varies by a factor of approximately 6, the rate of development of hydrophobicity and the value of the water contact angle is not affected (laser polished samples have an Ra between 0.250 and 0.350 m and an Rz between 3.50 and 5.50 m so closer to the electrochemically polished samples of Table 15 than the unpolished control sample).

[0331] Comparative Example 1-Roughness of a Printing Plate

[0332] Three 55 cm samples of a conventional printing plate, as supplied by Longma of China, were cut from different areas of the same printing plate and the coating was removed by repeated washing in acetone and then dried in air. The roughness of the surfaces was measured by the Bruker and the water contact angle measured using the DropMeter. The results are displayed in Table 16.

TABLE-US-00016 TABLE 16 Water contact Surface Sample angle () Ra (m) Rz (m) area (mm) % 1 76.4 0.791 9.93 4.236 99.39 2 79.6 0.813 8.71 4.228 99.38 3 82.2 0.96 9.559 4.232 99.38 Ave 79.4 0.855 9.4 4.232 99.383 STD 2.905 0.092 0.625 0.004 0.006

[0333] Example Set 7-Roughening With Sub-Nanosecond Laser

[0334] A sample of 0.275 mm gauge 99.5 wt % pure aluminium sheet was ultrasonically cleaned in acetone followed by deionised water for 5 minutes each. The sub-nanosecond laser (wavelength of 1064 nm) was used for this experiment to provide a 30 pm laser beam diameter. The scan rate was adjusted to provide an overlap pattern of N=#=1. A number of 11 cm.sup.2 squares were processed on the metal surface covering a range of pulse lengths and pulse energies as displayed in Table 17. Table 18 shows the frequency (Hz), pulse length (ns), pulse energy (uJ), peak power (MWcm.sup.2) and fluence (Jcm.sup.2) of the laser conditions used. The resulting processed sample was heated in an oven for 2 hours at 100 C. and then cooled. The water contact angle, Ra and Rz roughness were measured and are shown in Table 17. Whilst the water contact angle data is variable, probably because of the low overlap pattern (as we have seen earlier), the data does demonstrate that superhydrophobic or strongly hydrophobic surfaces can be generated at roughness values below that of a commercially available printing plate substrate. There was also no heat deformation on any of the samples.

TABLE-US-00017 TABLE 17 Water Pulse contact Pulse length energy angle (frequency in KHz) (J) () Ra (m) Rz (m) 4.14 ns (100) 150 138.9 0.479 6.732 4.14 ns (100) 120 140 0.46 6.18 4.14 ns (100) 100 152.7 0.411 5.688 4.14 ns (100) 74 143.8 0.401 8.368 4.14 ns (100) 60 143.2 0.369 4.74 4.14 ns (100) 30 143.4 0.326 5.771 2.31 ns (200) 75 97.9 0.357 7.211 2.31 ns (200) 50 128.3 0.336 9.339 2.31 ns (200) 25 66.5 0.299 5.729 1.16 ns (400) 37.5 127.9 0.314 5.325 1.16 ns (400) 25 129.2 0.315 7.49 650 ps (500) 30 122.4 0.311 6.583 650 ps (500) 24 126.3 0.31 8.74 680 ps (800) 18.75 108.2 0.319 9.622 680 ps (800) 14 115.4 0.296 4.819 680 ps (800) 10 115.3 0.284 4.415 360 ps (100) 15 109.8 0.321 5.1 360 ps (100) 12 122.1 0.314 7.076 360 ps (100) 8 118.1 0.283 4.807

TABLE-US-00018 TABLE 18 Pulse Pulse Frequency length energy Peak Power Fluence (Hz) (ns) (uJ) (MWcm.sup.2) (Jcm.sup.2) 100 k 4.14 150 1442 6 120 1153 4.78 100 961 4 74 721 3 60 577 2.4 30 288 1.2 200 k 2.31 75 1292 3 50 861 2 25 431 1 400 k 1.16 37.5 1286 1.49 25 857 1 500 k 0.68 30 1755 1.2 24 1404 0.95 800 k 18.75 1097 0.75 14 819 0.56 10 585 0.4 1000 k 0.36 15 1658 0.6 12 1326 0.48 8 884 0.32

[0335] Example Set 8-Roughening With Picosecond Laser

[0336] Two samples of 99.5 wt % pure aluminium were ultrasonically cleaned in acetone followed by deionised water, both for 5 minutes, then dried in air. The picosecond laser (wavelength=1064 nm) was set up to deliver pulse energies of 8.5 J at a pulse length of 80 ps and the laser beam diameter at the focal plane was determined to be 16.5 J. By adjusting the scan and repetition rates, a series of 0.750.75 cm.sup.2 squares were processed on each sample to provide a range of overlap patterns where N=#=1 through to N=#=5 in 0.20 increments and also N=#=6, N=#=7 and N=#=8. After processing, each square was evaluated for water contact angle which was found to be 0 for all samples. One sample was left open in the laboratory under ambient conditions (temperature between 15 and 25 C.) and the water contact angle for each square was measured two times per day for 11 days. The final water contact angle (after 11 days) of each square is displayed in Table 19 in the column headed 11 days at ambient. The other piece of aluminium containing the other set of processed samples were heated in an oven at 100 C. for 2 hours, cooled to ambient in air then each square was evaluated again for water contact angle, Ra and Rz. The results from the experiment are displayed in Table 19.

TABLE-US-00019 TABLE 19 Roughness Water contact angle () Overlap Ra Rz 11 days at N = # (m) (m) Heated Ambient 1 1 0.178 2.38 115 91 1.2 1.2 0.471 5.77 137 90 1.4 1.4 0.37 5.1 159 84 1.6 1.6 0.39 5.7 164 93 1.8 1.8 0.401 5.24 170 91 2 2 0.375 5.08 166 90 2.2 2.2 0.416 5.69 165 108 2.4 2.4 0.41 6.66 154 121 2.6 2.6 0.378 5.18 166 122 2.8 2.8 0.363 5.87 158 124 3 3 0.366 5.99 167 113 3.2 3.2 0.371 5.66 165 99 3.4 3.4 0.413 6.67 162 93 3.6 3.6 0.463 10.2 163 71 3.8 3.8 0.386 9.03 165 66 4 4 0.368 6.05 158 97 4.2 4.2 0.352 5.6 160 101 4.4 4.4 0.363 7.5 165 80 4.6 4.6 0.372 6.11 170 83 4.8 4.8 0.392 6.99 162 58 5 5 0.409 6.31 165 119 6 6 0.381 7.27 168 84 7 7 0.386 7.78 168 49 8 8 0.439 10.54 165 40

[0337] The data in Table 19 show that under ambient conditions very few of the examples become hydrophobic after 11 days and none become superhydrophobic whereas all of the samples that have been heated become hydrophobic having been initially superhydrophilic after processing. From 1.41.4 they are, in fact, all superhydrophobic.

[0338] Example Set 9-Roughening With Femtosecond Laser

[0339] A sample of 99.5 wt % pure aluminium sheet was ultrasonically cleaned in acetone followed by deionised water for 5 minutes each and dried in air. The Femtosecond laser was used to carry out the roughening on 0.50.5 cm.sup.2 squares on the cleaned metal surface. The laser had a beam diameter of 15 m, a wavelength of 800 nm, a pulse length of 100 fs and a pulse energy of either 2 J or 5 J. Scan rates were adjusted as a variable to provide overlap patterns of N=#=1, 2, 3, 4 or 5. The combination of the two pulse energy variables and five overlap variables provides a total of 10 sample sets. After processing one sample of each set had their water contact angle measured immediately whilst the other sample of the sets were heated in an oven at 100 C. for times varying from 30 minutes to 2 hours. Following heating the samples were cooled to ambient in air and then their water contact angle was measured. The results are displayed in Table 20. We can see that a 11 overlap combined with a pulse energy of 2 J is not sufficient to produce a uniformly superhydrophilic surface though it is hydrophilic whilst at 5 J the surface is fully superhydrophilic.

[0340] Regarding the 2 J samples, it appears that the samples with higher overlap needed to be heated for longer to achieve the hydrophobicity. Regarding the 5 J samples, the samples with higher overlap did not achieve hydrophobicity on heating.

TABLE-US-00020 TABLE 20 Temperature/ Pulse time of energy N: 1 2 3 4 5 heating (m) #: 1 2 3 4 5 Ambient 2.00 Water 40.4 0+ 0+ 0+ 0+ contact angle (): Ambient 5.00 0+ 0+ 0+ 0+ 0+ 100 C./ 2.00 114.8 41.6 0+ 0+ 0+ 30 mins 100 C./ 5.00 21.7 0+ 0+ 0+ 0+ 30 mins 100 C./ 2.00 118.8 152.7 114.5 30.2 0+ 60 mins 100 C./ 5.00 158.9 25.4 0+ 0+ 0+ 60 mins 100 C./ 2.00 116 140.3 132.3 153.9 151.4 120 mins 100 C./ 5.00 167.5* 81 * * * 120 mins 0+ Denotes a water contact angle which is not zero but large enough to be measured. * Denotes sample spontaneously turns form superhydrophobic to superhydrophilic.

[0341] Example Set 10-Simulated Recycling After Imaging

[0342] A sample of 99.5 wt % pure aluminium was electrochemically polished at 20 v in a mixture of ethanol and 60% perchloric acid (4:1 v/v) for 4 minutes, maintaining the temperature between 0 and 10 C. by using a recirculating cooling bath. The ethanol and deionised water washed sample was dried and then laser roughened using the nanosecond pulsed fibre laser at 1064 nm with a pulse length of 100 ns and a pulse energy of 0.32 mJ. The spot size was 50 m and scanning rates were adjusted to provide an overlap pattern of N=#=3.39. The sample was left in the air at ambient conditions for 3 days after which water contact angle measurement of the surface showed it to be strongly hydrophobic with a water contact angle of 142. The whole sample was then exposed using the Picosecond laser, also at 1064 nm, to simulate an imaging process (ps exposure 1). The Picosecond laser delivered pules having a pulse length of 8.0 J, a pulse length of 80 ps and a spot size of 16.5 m. Scanning rates were adjusted to provide an overlap pattern of N=#=1. After exposure 1, re-measurement of the water contact angle showed that the whole surface was superhydrophilic with a 0 water contact angle. The sample was subsequently left in air for 45 hours until the water contact angle increased to a maximum of 141 which in this case showed it had returned to almost its original value. The sample was divided into four sections numbered 1-4. Sections 2-4 were then subjected to the same ps laser exposure as referred to above rendering the surface superhydrophilic again with a water contact angle of 0 (ps exposure 2). Again the sample was left in the air at ambient temperature for 90 hours to return to a strongly hydrophobic condition and the water contact angle measured for each section (see Table 21 below). Then sections 3 and 4 (which were previously imaged) were subjected again to the same ps laser exposure as above creating a superhydrophilic surface in these sections with a water contact angle of 0 (ps exposure 3). Again the sample was left in air at ambient conditions, this time for 74 hours until a strongly hydrophobic surface was recovered. Finally, section 4 of the surface, previously exposed three times, was subjected again to the same ps laser exposure as above to produce a superhydrophilic surface with a water contact angle of 0 (ps exposure 4). This was left in air for 72 hours until the surface was strongly hydrophobic. This data is summarized in Table 21 below. It can be seen that section 1 of the sample, exposed only once to the ps laser shows some variability in water contact angle. We can assume this is the natural variation depending on experimental error and changes in daily conditions and it amounts to an average of 134 achieved following the first exposure with a range of 24. The total range of all the hydrophobic measurements falls within this range (of the least processed section) whilst the mean of the averages for all the hydrophobic states is 138 with a range of 13. In other words we can conclude that there is no deleterious effect of multiple processing upon the final hydrophobic state achieved.

TABLE-US-00021 TABLE 21 Water contact angle () Section Exposure 1 2 3 4 Average Roughening 0 0 0 0 0 Air 3 Days 142 142 142 142 142 ps exposure 1 0 0 0 0 0 Air 45 hours 141 141 141 141 141 ps exposure 2 147 0 0 0 Air 90 hours 130 140 139 143 138 ps exposure 3 132 134 0 0 Air 74 hours 135 142 146 146 142 ps exposure 4 133 135 144 0 Air 72 hours 123 133 127 131 129

[0343] Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0344] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0345] All of the features disclosed in this specification (including any accompanying claims, and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0346] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0347] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.