Aluminum strip for lithographic printing plate supports

Abstract

An aluminum strip for lithographic printing plate supports, from which printing plate supports can be produced with an improved roughenability and at the same time improved mechanical properties, particularly after a burn-in process, is formed of an aluminum alloy which has the following proportions of alloy constituents in wt. %: 0.05%Mg0.3%, 0.008%Mn0.3%, 0.4%Fe1%, 0.05%Si0.5%, Cu0.04%, Ti0.04%, inevitable impurities individually max. 0.01%, in total max. 0.05% and remainder Al.

Claims

1. Aluminum strip for lithographic printing plate supports, consisting of an aluminum alloy, wherein the aluminum alloy has the following proportions of alloy constituents in wt. %: $0.05\%\mathrm{Mg}0.3\%,0.05375\%\mathrm{Mn}0.3\%,0.43\%\mathrm{Fe}1\%,0.05\%\mathrm{Si}0.5\%,\mathrm{Cu}0.04\%,0\%<\mathrm{Ti}0.04\%,$ inevitable impurities individually max. 0.01%, in total max. 0.05% and remainder Al, and wherein at room temperature the aluminium strip has a yield point Rp0.2 at least 180 Mpa and a tensile strength Rm of at least 190 Mpa in the rolling direction and/or room temperature a yield point Rp0.2 of at least 190 Mpa and a tensile strength Rm of at least 200 Mpa transversely to the rolling direction.

2. Aluminum strip according to claim 1, wherein the aluminum alloy has a Ti content in wt. % of at most 0.01%.

3. Aluminum strip according to claim 1, wherein the aluminum strip after a heat treatment at 240 C. for 10 min. has a yield point Rp0.2 of at least 140 MPa and a tensile strength of at least 150 MPa transversely to or in the rolling direction.

4. Aluminum strip according to claim 1, wherein the bending cycle endurance of the aluminum strip in the rolling direction is more than 3000 bending cycles, in the rolling direction over a radius of 30 mm.

5. Aluminum strip according to claim 1, wherein the bending cycle endurance of the aluminum strip after a heat treatment at 240 C. for 10 min. in the rolling direction is more than 3300 bending cycles, in the rolling direction.

6. Aluminum strip according to claim 1, wherein the aluminum strip has a surface comprising fine globulitic grains with more than 250 grains per mm2.

7. The aluminium strip according to claim 1, wherein the ration of the proportions of the alloy constituents Fe/Mn is from 3 to 8.

8. The aluminium strip according to claim 1, wherein aluminium alloy has an Mn content in wt. % of 0.05375%Mn0.1%.

9. The aluminium strip according to claim 1, wherein the ratio of the proportions of the ally constituents Fe/Si is at least 2.

10. The aluminium strip according to claim 1, wherein the sum of Mg and Mn contents is more than 0.3 wt. % and less than 0.6 wt. %.

11. A lithographic printing plate support comprising an aluminum strip consisting of an aluminum alloy wherein, the aluminum alloy has the following proportions of alloy constituents in wt. %: $0.05\%\mathrm{Mg}0.3\%,0.05375\%\mathrm{Mn}0.3\%,0.43\%\mathrm{Fe}1\%,0.05\%\mathrm{Si}0.5\%,\mathrm{Cu}0.04\%,0\%<\mathrm{Ti}0.04\%,$ inevitable impurities individually max. 0.01%, in total max. 0.05% and remainder Al; hot-rolling the ingot to form a hot strip; and cold-rolling the hot strip to a final thickness with or without intermediate anneals, and wherein at room temperature the aluminium strip has a yield point Rp0.2 at least 180 Mpa and a tensile strength Rm of at least 190 Mpa in the rolling direction and/or room temperature a yield point Rp0.2 of at least 190 Mpa and a tensile strength Rm of at least 200 Mpa transversely to the rolling direction.

12. Method for producing an aluminum strip for lithographic printing plate supports, comprising casting an ingot of an aluminum alloy having the following alloy constituents in wt. %: $0.05\%\mathrm{Mg}0.3\%,0.05375\%\mathrm{Mn}0.3\%,0.43\%\mathrm{Fe}1\%,0.05\%\mathrm{Si}0.5\%,\mathrm{Cu}0.04\%,0\%<\mathrm{Ti}0.04\%,$ inevitable impurities individually max. 0.01%, in total max. 0.05% and remainder Al; hot-rolling the ingot to form a hot strip; and cold-rolling the hot strip to a final thickness with or without intermediate anneals, and wherein at room temperature the aluminium strip has a yield point Rp0.2 at least 180 Mpa and a tensile strength Rm of at least 190 Mpa in the rolling direction and/or room temperature a yield point Rp0.2 of at least 190 Mpa and a tensile strength Rm of at least 200 Mpa transversely to the rolling direction.

13. Method according to claim 12, wherein at least one intermediate anneal is carried out during the cold rolling and the rolling factor to final thickness is between 65% and 85% after the intermediate anneal.

14. Method according to claim 12, wherein the final thickness of the aluminum strip is from 0.15 mm to 0.5 mm.

15. Method according to claim 12 further comprising casting the ingot continuously or in batches.

16. Method according to claim 12 further comprising preheating or homogenising the ingot before hot-rolling.

Description

DETAILED DESCRIPTION

(1) There are many embodiments and possibilities for refining and configuring the aluminum alloy, the aluminum strip and the method according to the invention for producing an aluminum strip for lithographic printing plate supports. To this end, reference is made on the one hand to an aluminum alloy having proportions of alloy constituents in the following wt. %:0.05%Mg0.3%; 0.008%Mn0.3%; 0.4%Fe1%; 0.05%Si0.5%; Cu0.04%; Ti0.04%; inevitable impurities individually max. 0.01%, in total max. 0.05% and remainder Al, and on the other hand to the following description of exemplary embodiments.

(2) Table 1 represents the studied aluminum alloys and their compositions in respect of the alloy constituents Fe, Mn and Mg. The aluminum alloys V402 and V404 have a composition corresponding to the prior art and are therefore used as comparative alloys. The rolling ingots including the various aluminum alloys specified in Table 1 were hot-rolled to a thickness of 4.0 mm, after removing the casting skin and preheating, then subjected to cold rolling to a final thickness of 0.3 mm and optionally intermediately annealed between two cold rolling runs. Aluminum strips were respectively produced in the HI 8 state with an intermediate anneal at 2.2 mm and in the H19 state without an intermediate anneal.

(3) TABLE-US-00001 TABLE 1 Melt Fe Mn Mg Si V402 0.36 0.008 0.22 0.10 Prior art V403 0.48 0.008 0.22 0.10 Applicant's embodiment V404 0.35 0.010 0.22 0.10 Prior art V405 0.52 0.010 0.22 0.10 Applicant's embodiment V407 0.4 0.050 0.21 0.10 Applicant's embodiment V408 0.54 0.050 0.2 0.10 Applicant's embodiment V409 0.43 0.095 0.22 0.10 Applicant's embodiment V410 0.59 0.095 0.2 0.10 Applicant's embodiment

(4) The aluminum strips produced with intermediate annealing and those produced without intermediate annealing were subjected to tensile tests according to DIN EN 10002, which were carried out at room temperature and after a burn-in process at 240 C. for 10 min. The results of the tensile tests are represented on the one hand for aluminum strips with intermediate annealing in Table 2 (Test No. 1 to 8) and on the other hand without intermediate annealing in Table 3 (Test No. 9 to 16). For the aluminum strips produced with intermediate annealing, it is found by comparison between the comparative aluminum strips of Tests No. 1 and 3 that the yield point Rp0.2 and the tensile strength of the aluminum strips increase with increasing iron and manganese contents. The thermal stability, i.e. the yield point Rp0.2 and the tensile strength Rm after a burn-in process, do not change. In contrast to this, the aluminum strips according to the invention show in comparison with the comparative alloy strips of Tests No. 9 and 11 on the one hand an increase in the yield point Rp0.2 and the tensile strength Rm and on the other hand likewise increased values for the yield point Rp0.2 and the tensile strength Rm after a burn-in process at 240 C. for 10 min.

(5) The increase in the thermal stability due to the combination of high Fe content and increased Mn contents are shown in Tests No. 13 to 16. Although with virtually identical Fe contents Tests No. 13 and 14 already show an increased yield point Rp0.2 after a thermal burn-in process compared with conventional aluminum strips, the yield point Rp0.2 nevertheless rises further with an increasing Mn content as shown by Tests 15 and 16.

(6) Surprisingly, the increase in the thermal stability after a burn-in process is particularly impressive especially with high Fe and Mn values (cf. Test No. 16) in the H19 state. The values for the yield point Rp0.2 increase from below 140 MPa to about 150 MPa and those for the tensile strength from 140 MPa to about 160 MPa.

(7) TABLE-US-00002 TABLE 2 Room temperature 240 C./10 min No. Melt Rp.sub.0.2 (MPa) Rm (MPa) Rp.sub.0.2 (MPa) Rm (MPa) Rp.sub.0.2 (MPa) Rm (MPa) Prior art 1 V402 192 199 145 158 47 41 Applicant's 2 V403 197 204 147 158 50 46 embodiment Prior art 3 V404 193 199 144 157 49 42 Applicant's 4 V405 198 205 148 159 50 46 embodiment Applicant's 5 V407 196 203 145 156 51 47 embodiment Applicant's 6 V408 200 208 147 156 53 52 embodiment Applicant's 7 V409 197 203 144 156 53 47 embodiment Applicant's 8 V410 203 211 148 157 55 54 embodiment

(8) TABLE-US-00003 TABLE 3 Room temperature 240 C./10 min No. Melt Rp.sub.0.2 (MPa) Rm (MPa) Rp.sub.0.2 (MPa) Rm (MPa) Rp.sub.0.2 (MPa) Rm (MPa) Prior art 9 V402 194 208 137 140 57 68 Applicant's 10 V403 196 213 140 151 56 62 embodiment Prior art 11 V404 192 206 136 149 56 57 Applicant's 12 V405 197 214 140 151 57 63 embodiment Applicant's 13 V407 197 212 143 155 54 57 embodiment Applicant's 14 V408 200 217 145 155 56 62 embodiment Applicant's 15 V409 198 211 150 163 48 48 embodiment Applicant's 16 V410 203 221 149 160 54 61 embodiment

(9) Table 4 represents the results for the roughening behaviour of the aluminum alloys according to embodiments the invention compared with the previously used aluminum alloys of Tests No. 17 and 19. The results of the roughening tests of the aluminum strips produced with and without intermediate annealing have been compiled qualitatively in the table. The roughening was carried out in an HNO3 bath, which reacts more sensitively to striations or inhomogeneities which may occur. The roughening behaviour of the melts preferably used in the past, from Tests No. 17 and 19, were used as a reference for the level of the charge carrier input and were evaluated as satisfactory o. A reduced charge carrier input to achieve surface-wide roughening was evaluated with a +. A + therefore denotes a reduction of the charge carrier input, a ++ denotes a stronger reduction and a +++ denotes a substantial reduction of the charge carrier input. The homogeneity of the roughening was furthermore evaluated. Here again, the aluminum alloys with Test No. 17 and 19 were used as a reference and evaluated as satisfactory o. In the range of the Fe/Mn ratio from 2 to 15 and 3 to 8, respectively, the values of the charge carrier input for homogeneous roughening of the aluminum strip are reduced. In the tests under laboratory conditions, a reduction of the charge carrier input by up to 25% below the usual charge carrier input was achieved with the aluminum alloys according to embodiments of the invention. At the same time a further improved homogeneity of the roughening is found, especially in Tests No. 22 and 24.

(10) TABLE-US-00004 TABLE 4 Homogeneity of the No. Melt Fe Mn Mg Roughenability roughening 17 V402 0.36 0.008 0.22 18 V403 0.48 0.008 0.22 /+ /+ 19 V404 0.35 0.01 0.22 20 V405 0.52 0.01 0.22 + /+ 21 V407 0.4 0.05 0.21 /+ + 22 V408 0.54 0.05 0.2 ++ ++ 23 V409 0.43 0.095 0.22 ++ /+ 24 V410 0.59 0.095 0.2 +++ +++

(11) As a result, both the roughening behaviour and the homogeneity of the roughening can be improved substantially by the aluminum alloy according to the invention. Since the aluminum alloy according to the invention at the same time has good or even better mechanical properties, particularly after a burn-in process, when producing printing plate supports not only more economical but also improved products, i.e. improved printing plate supports, can be produced with a reduction in process times.

(12) Further studies were carried out on an additional exemplary embodiment of the aluminum strip according to the invention compared with a conventional aluminum strip for lithographic printing plate supports. The alloy constituents of the aluminum alloys used are reported in Table 5.

(13) TABLE-US-00005 TABLE 5 Melt Fe Mn Mg Si Cu Zn Ti B V486 0.36 0.05 0.2 0.08 0.004 0.02 47 8 ppm Pr. A ppm V488 0.64 0.1 0.19 0.10 0.001 0.02 44 8 ppm Inv. ppm

(14) Aluminum strips in the H118 state were likewise produced from the V486 and V488 melts, an intermediate anneal thus taking place during the cold rolling. In contrast to the previous exemplary embodiments, the rolling factor to final thickness after the intermediate anneal was restricted to 65% to 85%.

(15) The yield point Rp0.2 and the tensile strength in the rolling direction (1) and transversely to the rolling direction (t) were measured as a function of the temperature of a burn-in process. The results are reported in Table 6.

(16) TABLE-US-00006 TABLE 6 R.sub.p0.2 R.sub.m R.sub.p0.2 Rm (MPa) (MPa) (MPa) (MPa) Melt State (t) (t) (I) (I) V486 mill-hard 187 196 178 183 200 C./10 min 166 178 154 167 220 C./10 min 157 169 143 158 240 C./10 min 149 159 137 150 V488 mill-hard 194 205 187 192 200 C./10 min 173 186 159 173 220 C./10 min 163 175 151 164 240 C./10 min 155 164 144 154

(17) The aluminum strip, in conjunction with the method parameters according to the invention, has an improved yield point both transversely and longitudinally to the rolling direction compared with the conventional aluminum strip, as expected.

(18) When studying the surface grain structure of all of the aluminum strips, despite the method parameters being the same, the aluminum strip according to the invention has a significantly smaller average grain diameter of 54 m and the number of globulitic grains on the surface is 391 per mm.sup.2. In this context, the conventional strip achieves only a grain number of 123 per mm.sup.2 with an average grain diameter of 95 m. The grain stretching was similar for both aluminum strips, i.e. 2.3 (Al strip according to the invention) and 2.9 (conventional Al strip). The substantially finer grain structure of the aluminum strip according to the invention leads to a significantly more homogeneous appearance after roughening in electrochemical roughening.

(19) In the subsequently performed measurements of the bending cycle endurance in the rolling direction, the exemplary embodiment of the aluminum strip according to the invention produced from the V488 melt achieved 3390 bending cycles in the mill-hard state after burning-in at 240 C./10 min and even 4060 bending cycles after burning-in at 260 C./4 min. For comparison, the conventional aluminum strip produced from the V486 melt achieved only 2830 bending cycles when mill-hard and 2950 and 3250 bending cycles, respectively, after burn-in processes at 240 C./10 min. and 260 C./4 min. The rise in the number of bending cycles is at maximum about 25% compared with the conventional aluminum strip. Overall, a significant increase in the service lives of the printing plate supports produced from the aluminum strip according to the invention is thus possible.