EP1937860B2 - Method of production of an aluminium strip for lithographic printing plate supports - Google Patents

Description

The invention relates to a method for producing an aluminum strip for lithographic printing plate supports.

Printing plate supports for lithographic printing from an aluminum alloy have to meet very high requirements in order to be suitable for today's printing technology. On the one hand, it must be possible to roughen the printing plate support, which is produced from an aluminum strip, using mechanical, chemical and electrochemical roughening processes and combinations of the described roughening processes. On the other hand, after exposure and development, the printing plates are often subjected to a baking process between 220 to 300 ° C. with a glow time of 3 to 10 minutes in order to harden the applied photo layer. During this baking process, the printing plate carrier should lose as little strength as possible, so that the printing plate carrier can continue to be handled properly. When using the printing plate supports, the fatigue and flexural fatigue strength of the printing plate supports also play a role in order to be able to guarantee a long stability of the printing plate supports.

The previously used AlMn alloys of type AA3003, AA3103 show a good fatigue strength compared to the printing plate supports made of an aluminum alloy of type AA1050, but the roughening behavior is poor with the preferred electrochemical roughening, so that an aluminum alloy of type AA1050 is preferably used .

• 0,3 bis 0,4 % Fe,
• 0,1 bis 0,3 % Mg,
• 0,05 bis 0,25 % Si,
• max. 0,05 % Mn,
• max. 0,04 % Cu.

A further development of the aluminum alloy of type AA1050 can now be found in the German laid-open specification which goes back to the applicant DE 199 56 692 A1 is known, the aluminum alloy comprising, in addition to aluminum, the following alloy components in% by weight:

• 0.3 to 0.4% Fe,
• 0.1 to 0.3% Mg,
• 0.05 to 0.25% Si,
• Max. 0.05% Mn,
• Max. 0.04% Cu.

In the production of lithographic printing plate supports from an aluminum strip with the composition mentioned above, it has now been found that, in particular for the electrochemical roughening of the aluminum strip that is preferably used, a relatively high charge carrier input is necessary until homogeneous roughening is achieved, so that the roughening process is very cost-intensive. In addition, it was found that the mechanical properties of the aluminum alloy previously used for the production of aluminum strips for lithographic printing plate supports are also in need of improvement. This applies in particular to the thermal stability of the printing plate support after a baking process.

Recent developments aim to increase the manganese content of the aluminum alloy while maintaining the iron content in order to achieve a higher strength after the baking process. A corresponding aluminum alloy is from the international patent application WO 02/48415 A1 known. However, with increased magnesium and manganese values in the aluminum alloy, problems remained in the electrochemical roughening.

• 0,1 % ≤ Mg ≤ 0,3 %,
• 0,05 % ≤ Zn ≤ 0,5 %,
• 0,2 % ≤ Fe ≤ 0,6 %,
• 0,03 % ≤ Si ≤ 0,15 %,
• Cu ≤ 0,02 %,
• 0,003 % ≤ Ti ≤ 0,05 %,

Rest Al und Verunreinigungen.Finally is out of US 2005/0013724 A1 discloses that magnesium and zinc have to be added to an aluminum alloy of the type JIS A1050 in order to improve the strength and the heat resistance with very good roughening properties, whereby an alloy composition is proposed which contains the following alloy components in% by weight:

• 0.1% ≤ Mg ≤ 0.3%,
• 0.05% ≤ Zn ≤ 0.5%,
• 0.2% ≤ Fe ≤ 0.6%,
• 0.03% ≤ Si ≤ 0.15%,
• Cu ≤ 0.02%,
• 0.003% ≤ Ti ≤ 0.05%,

Balance Al and impurities.

Proceeding from this, the object of the present invention is to provide a method for producing an aluminum strip for lithographic printing plate supports, with which printing plate supports with improved roughness and at the same time improved mechanical properties, in particular after a baking process, can be produced.

The object derived above is achieved by a method having the features of patent claim 1.

• 0,05 % ≤ Mg ≤ 0,3 %,
• 0,008 % ≤ Mn ≤ 0,3 %,
• 0,4 % ≤ Fe ≤ 1 %,
• 0,05 % ≤ Si ≤ 0,5 %,
• Cu ≤ 0,04 %,
• Ti ≤ 0,04 %,

unvermeidbare Verunreinigungen einzeln max. 0,01 %, in Summe max. 0,05 % und Rest Al, wobei das Verhältnis der Anteile der Legierungsbestsandteile Fe/Mn 2 bis 15 beträgt.According to the present invention, an aluminum strip consisting of an aluminum alloy is provided that the aluminum alloy has the following proportions of alloy components in% by weight:

• 0.05% ≤ Mg ≤ 0.3%,
• 0.008% ≤ Mn ≤ 0.3%,
• 0.4% ≤ Fe ≤ 1%,
• 0.05% ≤ Si ≤ 0.5%,
• Cu ≤ 0.04%,
• Ti ≤ 0.04%,

unavoidable impurities individually max. 0.01%, in total max. 0.05% and the remainder Al, the ratio of the proportions of the alloy components Fe / Mn being 2 to 15.

It has surprisingly been found that, despite the high Fe content, the aluminum strip produced according to the invention has, on the one hand, very good properties with regard to electrochemical roughening of the strip and, on the other hand, improved mechanical properties, in particular after a stoving process has been carried out. This is all the more surprising since the experts have previously believed that only an Fe content of max. 0.4% by weight may be present in an aluminum strip for lithographic printing plate supports in order not to lead to uneven roughening of the strip due to coarse precipitation phases in the cast, which are preferably attacked during electrochemical roughening. The elimination of coarse phases in the cast does not occur in the aluminum strip produced according to the invention, since a uniform roughening structure is achieved during the electrochemical roughening. The Mg content of 0.05% to 0.3% by weight of the aluminum strip produced according to the invention ensures the recrystallization of the aluminum alloy even in the hot strip, which leads to a globular structure with small grain diameters. This results in a reduction in streak effects during electrochemical roughening. At the same time, the Mg content in the aluminum alloy increases the roughening rate in an electrochemical roughening process, but if the Mg content is greater than 0.3% by weight, the accelerated etching attack can lead to an inhomogeneous roughening structure and the roughening process becomes problematic.

The Mn content of 0.008% by weight to 0.3% by weight leads to an improvement in the thermal stability of the aluminum alloy, in particular in connection with the relatively high Fe contents of 0.4 to 1.0% by weight. so that the strength of the printing plate supports made of the aluminum alloy is increased after a baking process. In combination with the high Fe content, the addition of manganese at the same time leads to increased reactivity in the electrochemical roughening processes, but also in the pickling processes usually carried out before the electrochemical roughening. Overall, a lower charge carrier entry is required, for example, to achieve a complete roughening of an aluminum strip produced according to the invention, so that the process times for electrochemical roughening and thus the manufacturing costs for printing plate carriers can be reduced.

The Si content of 0.05% by weight to 0.5% by weight according to the invention also influences the appearance of electrochemically roughened printing plate supports. If the Si content is too low, the number of indentations in the aluminum strip that are too small will result from the electrochemical roughening. If the Si content is too high, the number of depressions in the roughened aluminum strip is too small and the distribution is inhomogeneous.

The Cu content of the aluminum alloy according to the invention must be avoided to avoid extremely inhomogeneous structures when roughening to max. 0.04% by weight can be limited. This also applies to the proportion of titanium that mostly gets through the grain refining materials into the melt of the aluminum alloy. Therefore, a limitation of the Ti content to max. 0.04% by weight necessary. The limitation of the contamination of the aluminum alloy to individually max. 0.01% by weight and in total max. to 0.05% by weight leads to a further stabilization of the properties of the aluminum strip for lithographic printing plate supports, particularly with regard to manufacturing tolerances of the composition of the aluminum alloy and its process properties. The aluminum strip produced according to the invention is therefore very well suited for the production of lithographic printing plate supports, since, in addition to very good roughening properties, it also provides very good mechanical properties, in particular after baking processes have been carried out.

A further reduction in the charge carrier input required to achieve a homogeneously roughened surface is achieved in that the ratio of the proportions of the alloy components Fe / Mn is 2 to 15, preferably 3 to 8. The cause is seen in the increased number of specific Fe and Mn-containing precipitates, which in addition to the mechanical and thermal properties also have a positive effect on the reactivity when roughening the aluminum alloy.

If the aluminum strip according to the invention has an Mn content in% by weight of 0.008% <Mn <0.2%, preferably 0.008% <Mn <0.1%, then with a marked improvement in the thermal stability after a stoving process, the The tendency towards inhomogeneity after electrochemical roughening can be further reduced.

In the same way, the roughening behavior of the aluminum strip produced according to the invention can be improved in that the aluminum alloy has a Ti content in% by weight of max. Has 0.01%.

Finally, it has been shown that the thermal stability of the aluminum strip with respect to the strength values after a baking process can be improved by the ratio of the proportions of the alloy components of Fe / Si being at least 2.

In order to improve the manageability of the printing plate supports produced from an aluminum strip produced according to the invention, the aluminum strip according to the invention, according to a next advantageous embodiment, has an elastic limit Rp0.2 of at least 180 MPa and a tensile strength Rm of at least 190 MPa in the rolling direction and / or an elastic limit Rp0 , 2 of at least 190 MPa and a tensile strength Rm of at least 200 MPa transverse to the rolling direction at room temperature.

The aluminum strip produced according to the invention has a heat treatment of 240 ° C for 10 min. a yield strength Rp0.2 of at least 140 MPa and a tensile strength Rm of at least 150 MPa across or in the direction of rolling, the aluminum strip produced according to the invention is particularly suitable for lithographic printing plate supports for particularly long runs, since these lose as little strength as possible after the baking process should.

According to a further embodiment, the aluminum strip produced according to the invention is further improved in that the alternating bending strength of the aluminum strip in the rolling direction is more than 3000 bending cycles, preferably more than 3200 bending cycles in the rolling direction. The above-mentioned number of bending cycles in the rolling direction is achieved by the aluminum strip produced according to the invention, in particular in the hard-rolled state, and thus exceeds conventional ones Aluminum strips in hard-rolled condition clearly. The flexural fatigue strength was measured by taking samples with a length of 100 mm and a width of 20 mm from the aluminum strip, the longitudinal axis of the samples corresponding to the rolling direction. The samples were then subjected to an alternating bend over a radius of 30 mm and the number of bends to break was determined. The number of bends is a measure of the stability of a printing plate carrier made from the aluminum strip during the printing process. In the present case, the number of bending cycles was statistically determined from twelve samples. The aluminum strip produced according to the invention thus enables the production of printing plate carriers with a particularly long service life.

A further extended service life of printing plate supports produced from the aluminum strip produced according to the invention is achieved in that the alternating bending strength of the aluminum strip after a heat treatment of 240 ° C. for 10 minutes in the rolling direction is more than 3300 bending cycles, preferably more than 3400 bending cycles in the rolling direction. The reason for the increase in the bending cycles is seen on the one hand in the softening of the aluminum strip during the stoving process, but on the other hand in the thermal stability of the aluminum strip produced according to the invention.

Finally, an electrochemical roughening process of the aluminum strip, which is usually carried out for the production of printing plate supports, can be improved in that the aluminum strip has a fine-grained, globulitic-grained surface with more than 250 grains per mm 2, preferably more than 350 grains per mm 2. A fine-grained structure with the specified grain density results in a more homogeneous appearance when roughened or coated. Overall, this speeds up the roughening process. The grain structure can be achieved, for example, by means of the production method according to the invention, with rolling degrees specially adjusted after intermediate annealing during the cold rolling to final thickness.

• 0,05 % ≤ Mg ≤ 0,3 %,
• 0,008 % ≤ Mn ≤ 0,3 %,
• 0,4 % ≤ Fe ≤ 1 %,
• 0,05 % ≤ Si ≤ 0,5 %,
• Cu ≤ 0,04 %,
• Ti ≤ 0,04 %,

unvermeidbare Verunreinigungen einzeln max. 0,01 %, in Summe max. 0,05 % und Rest Al, wobei das Verhältnis der Anteile der Legierungsbestsandteile Fe/Mn 2 bis 15 beträgt, diskontinuierlich gegossen wird, vor dem Warmwalzen der Walzbarren vorgewärmt oder homogenisiert wird, der Walzbarren zu einem Warmband warmgewalzt wird und das Warmband mit oder ohne Zwischenglühung auf Enddicke kaltgewalzt wird. Dabei wird in der Regel nach dem Gießen zur Verbesserung der Reinheit und Gleichmäßigkeit des Aluminiumbandes die Gusshaut des Walzbarrens vor dem Warm- und Kaltumformen abgefräst und das Fertigwalzen mit fein geschliffenen Stahlwalzen durchgeführt. Vorzugsweise kann vor dem Warmwalzen eine Vorwärmung oder Homogenisierung bei Temperaturen von 380 °C bis 600 °C stattfinden. Darüber hinaus beträgt die Warmbandendtemperatur vorzugsweise zwischen 280 und 370°C.The above-mentioned object is achieved by a method for producing an aluminum strip in that a rolled bar made of an aluminum alloy with the following alloy components in% by weight:

• 0.05% ≤ Mg ≤ 0.3%,
• 0.008% ≤ Mn ≤ 0.3%,
• 0.4% ≤ Fe ≤ 1%,
• 0.05% ≤ Si ≤ 0.5%,
• Cu ≤ 0.04%,
• Ti ≤ 0.04%,

unavoidable impurities individually max. 0.01%, in total max. 0.05% and the remainder Al, the ratio of the proportions of the alloy constituents Fe / Mn being 2 to 15, being cast discontinuously, preheating or homogenizing before the hot rolling of the rolled ingots, the rolled ingot being hot-rolled into a hot strip and the hot strip with or without Intermediate annealing is cold rolled to final thickness. As a rule, after casting to improve the purity and uniformity of the aluminum strip, the cast skin of the billet is milled off before hot and cold forming, and the finish rolling is carried out with finely ground steel rolls. Preheating or homogenization can preferably take place at temperatures of 380 ° C. to 600 ° C. before hot rolling. In addition, the hot strip end temperature is preferably between 280 and 370 ° C.

A state optimized for processing the aluminum strip into printing plate supports and their use is achieved according to a further embodiment of the method according to the invention in that at least one intermediate annealing takes place during the cold rolling and after the intermediate annealing the degree of rolling down to the final thickness is between 65% and 85%. As a result, an optimized state is set between annealed and hard-rolled, so that the aluminum strip has sufficient strength values, in particular even after a baking process. On the other hand, a fine-grained surface can be provided, so that a more homogeneous appearance is guaranteed after roughening.

The final thickness of the aluminum strip is preferably 0.15 mm to 0.5 mm, in particular 0.15 mm to 0.35 mm. In particular in the case of small thicknesses, an aluminum strip which has been produced by the process according to the invention can be used to provide an aluminum strip which is optimized for the production of printing plate supports, since it has improved roughening behavior with improved heat resistance and improved strength values.

To produce an aluminum strip for lithographic printing plate supports, the rolled aluminum strip is subjected to degreasing with an alkaline or acidic medium after rolling and the degreased aluminum strip is roughened electrochemically. The aluminum strip is preferably roughened in baths made of nitric acid HNO3 or hydrochloric acid HCl. In addition, the electrochemical roughening can also be carried out in mixed acid solutions.

To prepare the rolled aluminum strip optimally for the upcoming electrochemical roughening process, a particularly thorough degreasing is necessary. For this purpose, the aluminum strip is preferably degreased with a degreasing medium which contains at least 1.5 to 3% by weight of a composition of 5 to 40% by weight sodium polyphosphate, 3 to 10% by weight sodium gluconate, 30 to 70% sodium carbonate and 3 to Contains 8% by weight of a mixture of a non-ionic and an ionic surfactant. On the one hand, the degreasing medium ensures the almost complete removal of any existing rolling oil residues. On the other hand, the mild oxide character of the degreasing medium removes the rolled oxide layer of the aluminum strip.

There are now a number of possibilities for developing and developing the method according to the invention for producing an aluminum strip for lithographic printing plate supports. For this purpose, reference is made on the one hand to the claims subordinate to claim 1, and on the other hand to the following description of exemplary embodiments.

Table 1 now shows the aluminum alloys examined and their compositions with regard to the alloy components Fe, Mn and Mg. The aluminum alloys V402 and V404 have a composition corresponding to the state of the art and therefore serve as comparison alloys. The billets consisting of the various aluminum alloys listed in Table 1 were hot-rolled to a thickness of 4.0 mm after the casting skin had been cut off and preheated, then subjected to cold rolling to a final thickness of 0.3 mm and optionally annealed between two cold rolling passes . Aluminum strips were produced in the condition H18, with an intermediate annealing at 2.2 mm, and in the condition H19 without an intermediate annealing. Table 1 melt Fe Mn Mg Si V402 0.36 0.008 0.22 0.10 State of the art V403 0.48 0.008 0.22 0.10 Not according to the invention V404 0.35 0.010 0.22 0.10 State of the art V405 0.52 0.010 0.22 0.10 Not according to the invention V407 0.4 0.050 0.21 0.10 According to the invention V408 0.54 0.050 0.2 0.10 According to the invention V409 0.43 0.095 0.22 0.10 According to the invention V410 0.59 0.095 0.2 0.10 According to the invention

Both the aluminum strips produced with intermediate annealing and those without intermediate annealing were subjected to tensile tests in accordance with DIN EN 10002, which were carried out both at room temperature and after a baking process at 240 ° C for 10 min. were carried out. The results of the tensile tests are shown on the one hand for aluminum strips with intermediate annealing in Table 2 (test numbers 1 to 8) and on the other hand without intermediate annealing in Table 3 (test numbers 9 to 16). For the aluminum strips produced with intermediate annealing, it can be seen in the comparison between the comparative aluminum strips from tests No. 1 and 3 that the yield strength Rp0.2 and the tensile strength of the aluminum strips increase with increasing iron and manganese content. However, the thermal stability, ie the proof stress Rp0.2 and the tensile strength Rm after a baking process do not change. In contrast to this, the aluminum strips produced according to the invention on the one hand show an increase in the comparison of the comparison alloy strips from tests no. 9 and 11 Yield strength Rp0.2 and tensile strength Rm and, on the other hand, likewise increased values for the yield strength Rp0.2 and tensile strength Rm after a baking process of 240 ° C. for 10 minutes.

The increase in thermal stability due to the combination according to the invention of high Fe content and increased Mn content can be seen in experiments No. 13 to 16. With almost identical Fe contents, tests No. 13 and 14 already showed one. Increased yield strength Rp0.2 after a thermal baking process compared to conventional aluminum strips, but with increasing Mn content the yield strength Rp0.2 rose again, as experiments 15 and 16 show.

Surprisingly, in particular at high Fe and Mn values (cf. Experiment No. 16) in state H19, the increase in thermal stability after a baking process is particularly impressive. The values for the yield strength Rp0.2 increase from below 140 MPa to approximately 150 MPa and for the tensile strength from 140 MPa to approximately 160 MPa. Table 2 No. melt Room temperature 240 ° C / 10 min D Rp0.2 (MPa) Rm (MPa) Rp0.2 (MPa) Rm (MPa) Rp0.2 (MPa) Rm (MPa) State of the art 1 V402 192 199 145 158 47 41 Not according to the invention 2nd V403 197 204 147 158 50 46 State of the art 3rd V404 193 199 144 157 49 42 Not according to the invention 4th V405 198 205 148 159 50 46 according to the invention 5 V407 196 203 145 156 51 47 according to the invention 6 V408 200 208 147 156 53 52 according to the invention 7 V409 197 203 144 156 53 47 according to the invention 8th V410 203 211 148 157 55 54 No. melt Room temperature 240 ° C / 10 min D Rp0.2 (MPa) Rm (MPa) Rp0.2 (MPa) Rm (MPa) Rp0.2 (MPa) Rm (MPa) State of the art 9 V402 194 208 137 140 57 68 Not according to the invention 10th V403 196 213 140 151 56 62 State of the art 11 V404 192 206 136 149 56 57 Not according to the invention 12 V405 197 214 140 151 57 63 according to the invention 13 V407 197 212 143 155 54 57 according to the invention 14 V408 200 217 145 155 56 62 according to the invention 15 V409 198 211 150 163 48 48 according to the invention 16 V410 203 221 149 160 54 61

Table 4 now shows the results regarding the roughening behavior of the aluminum alloys according to the invention in comparison to the aluminum alloys from test no. 17 and 19. The results from the roughening tests of the aluminum strips with and without intermediate annealing were summarized qualitatively in the table. The roughening was carried out in an HNO3 bath, which is particularly sensitive to streaks or inhomogeneities. The roughening behavior of the previously preferred melts from Experiments No. 17 and 19 was used as a reference with regard to the height of the charge carrier entry and was rated as satisfactory "o". A reduced charge carrier entry to achieve a full roughening was rated with a "+". A "+" therefore means a reduction in the charge carrier entry, a "++" a greater reduction and "+++" a substantial reduction in the charge carrier entry. The roughness homogeneity was also assessed. The aluminum alloys with test no. 17 and 19 used and rated with an "o". It can be seen that, in particular in the range of the Fe / Mn ratio of 2 to 15 or 3 to 8, the values for the charge carrier entry for homogeneous roughening of the aluminum strip decrease. In the tests under laboratory conditions, the charge carrier entry was reduced by up to 25% below the usual charge carrier entry in the aluminum alloys according to the invention. At the same time, there was a further improvement in the homogeneity of the roughening, in particular in experiments No. 22 and 24. Table 4 No. melt Fe Mn Mg Roughness Homogeneity of 17th V402 0.36 0.008 0.22 O O 18th V403 0.48 0.008 0.22 o / + o / + 19th V404 0.35 0.01 0.22 O O 20th V405 0.52 0.01 0.22 + o / + 21 V407 0.4 0.05 0.21 o / + + 22 V408 0.54 0.05 0.2 ++ ++ 23 V409 0.43 0.095 0.22 ++ o / + 24th V410 0.59 0.095 0.2 +++ +++

As a result, both the roughening behavior and the homogeneity of the roughening can be significantly improved by the aluminum alloy strips produced according to the invention. Because the aluminum alloy strips produced according to the invention have good or better mechanical properties at the same time, in particular after a stoving process, not only can cheaper, but also improved products, i.e. improved printing plate carriers are manufactured.

Further investigations were carried out on additional exemplary embodiments not according to the invention in comparison to one conventional aluminum tape for lithographic printing plate supports. The alloy components of the aluminum alloys used are shown in Table 5. Table 5 melt Fe Mn Mg Si Cu Zn Ti B V486 0.36 0.05 0.2 0.08 0.004 0.02 47ppm 8ppm SdT V488 0.64 0.1 0.19 0.10 0.001 0.02 44ppm 8ppm Not required

Aluminum strips in condition H18 were also produced from the melts V486 and V488, with intermediate annealing taking place during cold rolling. In contrast to the previous exemplary embodiments, the degree of rolling down to the final thickness was limited to 65% to 85% after the intermediate annealing.

The yield strength Rp0.2 and the tensile strength in the rolling direction (1) and transverse to the rolling direction (q) were measured as a function of the temperature of a baking process. The results are shown in Table 6. Table 6 melt Status R _p 0.2 (MPa) (q) R _m (MPa) (q) R _p 0.2 (MPa) (1) Rm (MPa) (1) V486 hard as a roll 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 hard as a roll 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

It was found that the aluminum strip in connection with the process parameters has an improved proof stress both transversely and along the rolling direction compared to the conventional aluminum strip, as expected.

When examining the surface grain structure of the aluminum strip, it was also found that the aluminum strip, despite the same process parameters, has a significantly smaller average grain diameter of 54mm and the number of globular grains on the surface is 391 per mm2. The conventional belt only reaches a grain count of 123 per mm2 with an average grain diameter of 95 mm. The grain stretching was similar for both aluminum strips with 2.3 (Al strip according to the invention) and 2.9 (conventional Al strip). The much finer grain structure of the aluminum strip leads to a significantly more homogeneous appearance after roughening when electrochemically roughened.

In the subsequent measurements of the fatigue strength in the rolling direction, the embodiment of the aluminum strip, produced from the V488 melt, achieved 3390 bending cycles in the hard state, after a baking process of 240 ° C / 10 min. 3500 bending cycles and after a baking process of 260 ° C / 4 Min. Even 4060 bending cycles. For comparison, the conventional aluminum strip made from the Melt V486, hard as rolled only 2830 bending cycles and 2950 or 3250 bending cycles after baking with 240 ° C / 10 min. Or 260 ° C / 4 min. The maximum increase in the number of bending cycles is about 25% compared to conventional aluminum strip. Overall, a significant increase in the service life of the printing plate carriers made from the aluminum strip is possible.

Claims (6)

1. A process for the production of an aluminium strip for lithographic printing plate supports,
   characterized in that
   a slab of an aluminium alloy with the following alloying elements, as a % by weight:

   0.05 % ≤ Mg ≤ 0.3 %,

   0.008 % ≤ Mn ≤ 0.3 %,

   0.4 % ≤ Fe ≤ 1 %,

   0.05 % ≤ Si ≤ 0.5 %,

   Cu ≤ 0.04 %,

   Ti ≤ 0.04 %,

   unavoidable impurities individually 0.01 % at maximum, in total 0.05 % at maximum, and the remainder being Al, the ratio of the proportions of the alloying elements Fe/Mn being 2 to 15, is cast discontinuously, the slab is pre-heated or homogenized before hot-rolling, the slab is hot-rolled to a hot strip and the hot strip is then cold-rolled with or without intermediate annealings to the final thickness.
2. A process according to claim 1,
   characterized in that
   the ratio of the proportions of the alloying elements Fe/Mn is 3 to 8.
3. A process according to claim 1 or 2,
   characterized in that
   the aluminium alloy has a Mn content, as a % by weight, of 0.008 % ≤ Mn ≤ 0.2 % or 0.008 % ≤ Mn ≤ 0.1 %.
4. A process according to one of claims 1 to 3,
   characterized in that
   the aluminium alloy has a Ti content, as a % by weight, of 0.01 % at maximum.
5. A process according to one of claims 1 to 4,
   characterized in that
   the ratio of the proportions of the alloying elements Fe/Si is at least 2.
6. A process according to claim 1,
   characterized in that
   the final thickness of the aluminium strip is 0.15 mm to 0.5 mm or 0.15 mm to 0.35 mm.