EP2243848B1 - Manganese and magnesium rich aluminium strip - Google Patents

Description

The invention relates to an aluminum alloy for the production of lithographic printing plate supports and to an aluminum strip produced from the aluminum alloy, to a method for producing the aluminum strip and to its use for the production of lithographic printing plate supports.

Aluminum strips for the production of lithographic printing plate carriers must have a very high quality and are therefore subject to constant further development. The aluminum strip has to live up to a complex property profile. Thus, in the manufacture of the lithographic printing plate support, the aluminum strip is subjected to an electrochemical roughening, which must ensure a structureless appearance without streaking effects at the highest processing speed. The roughened structure of the aluminum strip has the task that photosensitive layers, which are subsequently exposed, can be permanently applied to the printing plate support. The photographic layers are baked at temperatures of 220 ° C to 300 ° C for a period of 3 to 10 minutes. Typical combinations of bake times and temperatures are for example 240 ° C for 10 minutes or 280 ° C for 4 minutes. Subsequently, the printing plate support must continue to be easy to handle, to allow a clamping of the printing plate support in the printing device. The softening of the pressure plate carrier after the Burning in should therefore not be too strong. Although it can be achieved by the highest possible tensile strength prior to baking, that the tensile strength after firing is sufficiently high. However, the straightening of the aluminum strip, ie the elimination of a "coil set" of the aluminum strip prior to processing to the printing plate support is made difficult by a high tensile strength before baking. In addition, increasingly printing presses are used with the largest possible printing surfaces, so that the printing plate support no longer need to be clamped longitudinally to the rolling direction but transverse to the rolling direction in order to provide oversized printing widths. This means that the flexural fatigue resistance of the printing plate supports across the rolling direction gains in importance. In order to optimize the properties of the aluminum strip in terms of roughening, heat resistance, mechanical properties before and after the baking process as well as the bending fatigue strength along the rolling direction, is derived from the Applicant's European patent EP 1 065 071 B1 a ribbon for the production of lithographic printing plate supports known, which is characterized by a good aufraubarkeit combined with a high bending fatigue resistance along the rolling direction and a sufficient thermal stability after a burn-in. Due to the increasing size of the printing presses and the resulting increase in the required pressure plate carrier, however, the need has arisen to improve the properties of the aluminum alloys and the pressure plate carrier produced therefrom with a view to clamping transversely to the rolling direction, without negatively influencing the roughening of the aluminum strip.

From the also derived from the applicant international patent application WO 2007/045676 It is also known to combine high iron contents of 0.4% by weight to 1% by weight with a relatively high manganese content and magnesium contents of up to a maximum of 0.3% by weight. With this aluminum alloy, the heat resistance and the bending fatigue resistance could be improved along the rolling direction after a baking process. So far, however, it was assumed that in particular manganese or magnesium contents of more than 0.3 wt .-% are problematic with respect to the roughening of the aluminum alloy.

The publication JP 62-086143 A discloses an aluminum alloy for the production of printing plates having improved roughening properties, good swap strength and heat resistance, having the following composition: Fe ≦ 0.5 wt%, 0.05 ≦ Mg ≦ 0.3 wt%, Si ≦ 0 , 2 wt .-%, 0.05 ≤ Mn ≤ 3 wt .-% and Cu ≤ 1 wt .-%.

The document WO 0248415 A1 also relates to an aluminum alloy for printing plates. It discloses an aluminum alloy having an Si content of up to 0.25 wt.%, An Fe content of 0.11 to 0.40 wt.%, A Mg content of 0.05 to 0.30 Wt .-%, an Mn content of 0.05 to 0.25 wt .-%, a Ti content of up to 0.03 wt .-%, a B content of up to 0.01 wt. -%, a Cu content of up to 0.01 wt .-%, a Cr content of up to 0.03 wt .-% and a Zn content of up to 0.15 wt .-%.

The JP 06-256916 A relates to the production of aluminum alloy sheets. It discloses an aluminum alloy having an Si content of up to 0.5 wt.%, an Fe content of up to 0.5 wt.%, an Mg content of 0.05 to 0.50 wt Mn content of 0.05 to 1.0 wt%, a Ti content of 0.001 to 0.1 wt%, B content of 0.0001 to 0.02 wt% , a Cu content of up to 0.3 wt .-%, a Cr content of up to 0.3 wt .-% and a Zr content of 0.001 to 0.1 wt .-%.

The EP 1 293 579 A2 describes a printing plate support, which is made of an aluminum alloy. It discloses an aluminum alloy having an Si content of up to 0.5 wt.%, An Fe content of up to 1.0 wt.%, A Mg content of 0.1 to 1.5 wt. -%, an Mn content of 0.1 to 1.5 wt .-% and a Cu content of up to 0.2 wt .-%.

The contents of the individual alloying elements disclosed in the abovementioned publications, in particular the disclosed Mn contents, are very broad.

On this basis, the present invention has the object to provide an aluminum alloy and an aluminum strip made of aluminum alloy, which or which enables the production of printing plate supports with improved flexural fatigue resistance transverse to the rolling direction and with improved heat resistance without deteriorating Aufraueigenschaften be. At the same time, the object of the present invention is to specify a production method for an aluminum strip which is particularly suitable for the production of lithographic printing plate supports to be transversely clamped.

According to a first teaching of the present invention, the above-mentioned object for an aluminum alloy for producing lithographic printing plate supports is achieved in that the aluminum alloy has the following alloy components in% by weight: 0.35% ≤ Fe ≤ 0.5%, 0.2% ≤ mg ≤ 0.7%, 0.08% ≤ Si ≤ 0.25%, 0.5% ≤ Mn ≤ 0.6%, Cu < 0.002%, Ti ≤ 0.0075%, Zn ≤ 0.012%, Cr < 0.003%,

Residual Al and unavoidable impurities individually a maximum of 0.075%, in total a maximum of 0.075%.

Notwithstanding the aluminum alloys used hitherto for the production of lithographic printing plate supports, which overall have very low manganese and magnesium contents, the present aluminum alloy according to the invention combines high manganese contents of at least 0.5% by weight with relatively high magnesium contents of 0.2 to 0.7% by weight. As a result, it was found that due to the combination of high manganese and magnesium contents, the aluminum alloy according to the invention not only has a very good flexural fatigue resistance transverse to the rolling direction. Due to the excellent heat resistance, the handling of the pressure plate carrier produced from the aluminum alloy according to the invention is good and the process reliability during production to ensure the mechanical properties before and after the baking process is particularly high. Despite the permitted high levels of manganese and magnesium, contrary to the expectations of the experts, there were no problems with being stolen.

A good roughening behavior is also effected by silicon, which is contained in a content of 0.08 wt .-% to 0.25 wt .-% in the aluminum alloy according to the invention. In the case of electrochemical roughening or etching, the Si content according to the invention ensures that a high number of depressions which are sufficiently deep are produced in order to ensure optimum absorption of the photosensitive paint.

Copper should be limited to avoid inhomogeneous structures when roughening. Titanium, which is introduced into the aluminum alloy for grain refining of the melt, leads to roughening problems at higher levels. The contents of zinc and chromium negatively influence the roughening result and should therefore be limited.

The heat resistance of the aluminum alloy can be increased according to the invention by the aluminum alloy having the following Mn content in% by weight: $$0.5\%\le \mathrm{Mn}\le 0.6\%\mathrm{,}$$

It has also been found that higher manganese contents not only lead to a further improvement of the heat resistance, ie to a lower softening after a baking process, but at the same time stabilize the bending fatigue strength transverse to the rolling direction with respect to the selected production process. This effect is particularly pronounced at a manganese content of 0.5 wt .-% to 0.6 wt .-%. stabilize. This effect is particularly pronounced at a manganese content of 0.5 wt .-% to 0.6 wt .-%.

so kann die Biegewechselfestigkeit quer zur Walzrichtung noch einmal gesteigert werden. Sowohl bei höheren Mangangehalten von mindestens 0,5 Gew.-% als auch in Kombination mit Magnesiumgehalten von mindestens 0,5 Gew.-% zeigten sich keine Probleme im Hinblick auf die elektrochemische Aufraubarkeit der aus einer entsprechenden Aluminiumlegierung hergestellten Aluminiumbänder.In accordance with a first embodiment of the aluminum alloy according to the invention, this has a Mg content in% by weight of: $$0.5\%\le \mathrm{mg}\le 0.7\%\mathrm{on}.$$

Thus, the bending fatigue strength can be increased again transverse to the rolling direction. Both at higher manganese contents of at least 0.5% by weight and in combination with magnesium contents of at least 0.5% by weight, there were no problems with regard to the electrochemical roughening of the aluminum strips produced from a corresponding aluminum alloy.

As already mentioned, Ti, Zn and Cr can adversely affect the roughening result and, in principle, lead to streaking effects on the aluminum strips. According to a second teaching of the present invention, the object indicated above is achieved by an aluminum strip for producing lithographic printing plate supports consisting of an aluminum alloy according to the invention having a thickness of 0.15 mm to 0.5 mm. The invention Not only does aluminum strip stand out for its excellent roughening properties, but due to its very good heat resistance with moderate tensile strength values, it also ensures optimized handling in relation to the use of oversized printing devices with transversely clamped printing plate supports. This is mainly due to the excellent bending fatigue strength transverse to the rolling direction of the aluminum strip according to the invention.

According to a further embodiment of the aluminum strip according to the invention, this has, after a baking process with a temperature of 280 ° C and a duration of 4 min a tensile strength Rm of more than 150 MPa, a yield strength Rp 0.2 of more than 140 MPa and a bending resistance transverse to the rolling direction of at least 1950 cycles in the bending cycle test. Since the aluminum strip according to the invention has a very good hot strength, it is possible by conventional process parameters to set the tensile strength values before the baking process in an ideal processing range, for example to perform the correction of a "coil set" and at the same time excellent handling and stability when used in oversized printing devices to enable.

Due to the above-described property profile of the aluminum alloy and the aluminum strips produced therefrom, the object indicated above is also achieved by the use of the aluminum strip according to the invention for the production of lithographic printing plate supports according to a third teaching of the present invention. Finally, according to a fourth teaching of the present invention, the above-described object is achieved by a method for producing an aluminum strip for lithographic printing plate support consisting of an aluminum alloy according to the invention characterized in that a rolling ingot is poured, the rolling ingot optionally at a temperature of 450 ° C to 610 ° C is homogenized, the slab is hot rolled to a thickness of 2 to 9 mm and the hot strip is cold rolled with or without intermediate annealing to a final thickness of 0.15 mm to 0.5 mm. The intermediate annealing, if an intermediate annealing is carried out, takes place in such a way that a desired final strength of the aluminum strip in the hard-rolling state is set by the subsequent cold-rolling process to final thickness.

Preferably, an intermediate annealing is carried out at an intermediate thickness of 0.5 to 2.8 mm, wherein the intermediate annealing takes place in a coil or in a continuous furnace at a temperature of 230 ° C to 470 ° C. By this intermediate annealing, depending on the thickness of the strip at which the intermediate annealing is carried out, the final strength of the aluminum strip in the hard-rolled state can be adjusted. A final annealing can preferably be dispensed with in order to keep the production costs as low as possible.

By means of the aluminum alloy according to the invention, in connection with the parameters just described, it is achieved that the flexural fatigue resistance transverse to the rolling direction is very high and, at the same time, a softening of the aluminum strip due to the necessary baking procedure is reduced. In the result can be provided with the inventive method printing plate support available, which combine not only excellent Aufraubarkeit excellent heat resistance with a high bending fatigue strength transverse to the rolling direction.

There are now a large number of possibilities for designing and developing the aluminum alloy according to the invention, the aluminum strip according to the invention, its use and the method for producing the aluminum strip. Reference is made to the patent claims 1, 6 and 9 subordinate claims and to the description of embodiments in conjunction with the drawings.

The drawing shows in the single figure is a schematic sectional view of the device used to determine the bending fatigue resistance.

Table 1 now shows the alloy composition of a reference aluminum alloy Ref and aluminum alloys I5, I6 and I7 according to the invention, which have been studied below. The composition details in Table 1 are in weight percent. Table 1 alloy Si Fe Cu Mn mg Cr Zn Ti rest Ref 0.08 0.35 <0.002 0.0075 0.2 <0.003 0,012 0.0075 0.0075 15 0.08 0.35 <0.002 0.5 0.2 <0.003 0,012 0.0075 0.0075 16 0.08 0.35 <0.002 0.5 0.41 <0.003 0,012 0.0075 0.0075 17 0.08 0.35 <0.002 0.5 0.6 <0.003 0,012 0.0075 0.0075

The alloys I5, I6 and I7 according to the invention contain a significantly higher manganese content of 0.5% by weight than the reference aluminum alloy. The Mg content was varied from 0.2% by weight to 0.6% by weight. Rolled ingots were cast from the aluminum alloys with the just mentioned compositions. The ingot was then homogenized at a temperature of 450 ° C to 610 ° C and hot rolled to a hot strip thickness of 4 mm. The cold rolling to a final thickness of 0.3 mm was carried out without and with intermediate annealing, wherein the intermediate annealing was carried out at a strip thickness of 0.9 to 1.2 mm, preferably at 1.1 mm. Two different temperature ranges were used in the intermediate annealing, namely 300 ° C to 350 ° C and 400 ° C to 450 ° C.

The aluminum strips produced according to the method just described were subjected to electrochemical roughening to test suitability for the manufacture of printing plate supports. Surprisingly, despite the relatively high magnesium and manganese contents of the aluminum alloys according to the invention, contrary to the expectation of the experts, there were no negative signs with regard to possible streaking effects after roughening. The aluminum alloys according to the invention are therefore all characterized by a very good or good roughening behavior. The results of the roughening tests are shown in Table 2. Table 2 alloy roughening Ref ++ 15 ++ 16 + 17 +

Table 3 shows on the one hand the results of the bending change test and the associated values for the intermediate annealing thickness and the intermediate annealing temperature ranges. Table 3 Bending cycles across the rolling direction alloy Experiment No. Thickness of intermediate annealing (mm) Temperature of intermediate annealing (° C) As-rolled Branded (280 ° C / 4 min) Ref R 2.2 400 - 450 1928 1274 15 5.1 - - 2252 2300 I5 5.2 0.9 - 1.2 300 - 350 2716 2857 15 5.3 0.9 - 1.2 400 - 450 2210 2406 16 6.1 - - 3208 2425 16 6.2 0.9 - 1.2 300 - 350 2808 3099 16 6.3 0.9 - 1.2 400 - 450 2937 3599 I7 7.1 - - 4951 2958 17 7.2 0.9 - 1.2 300 - 350 3506 3372 17 7.3 0.9 - 1.2 400 - 450 3058 3230

As Table 3 clearly shows, compared to the reference alloy, the number of possible bending cycles could be significantly increased, both in the hard-rolled state and in the baked state. The minimum number of bending cycles across the rolling direction when baked is 2300 Bending cycles by a factor of 1.8 higher than the reference alloy. The aluminum alloy according to the invention is therefore particularly suitable for the production of oversized printing plate supports which are clamped in printing devices transversely to the rolling direction.

The high manganese contents also resulted in improved hot strength, which is reflected in higher values for tensile strength and yield strength. The mechanical characteristics of the alloy examples are shown in Table 4. They have been measured according to EN standard. Table 4 Burned in at 280 ° C / 4 min, measured along the rolling direction Experiment No. Rp0.2 (Mpa) Rm (Mpa) R 136 145 5.1 180 193 5.2 153 170 5.3 148 164 6.1 181 192 6.2 154 170 7.3 151 169 7.1 178 193 7.2 162 182 7.3 161 179

Of course, the influence of the intermediate annealing on the values Rm and Rp0,2 can be seen. In tests 5.1, 6.1 and 7.1, the highest values for the tensile strength Rm and the yield strength Rp0.2 can be found. This is due to the production of the bands without intermediate annealing. The intermediate annealing at 0.9 mm to 1.2 mm, preferably at 1.1 mm gave more moderate values for the tensile strength and yield strength after the baking process, the values having been lowered again as the intermediate annealing temperature increases, as shown in working examples 5.3, 6.3 and 7.3.

All measured values for the tensile strength Rm and the yield strength Rp0.2 of the aluminum strips according to the invention are clearly above the previously achieved values of the reference alloy in test R, although a smaller thickness was chosen for the intermediate annealing in the aluminum strips according to the invention at the same intermediate annealing temperature.

In FIG. 1a is now schematically the bending change test device 1, which has been used to determine the number of possible bending cycles, shown. The Biegewechseltestvorrichtung 1 consists on the one hand of a movable segment 3, which is arranged on a fixed segment 4 such that the segment 3 is reciprocated in the bending change test by a rolling movement on the fixed segment 4, so that the attached sample 2 bends perpendicular to Extension of the sample 2 is exposed. In order to test the flexural fatigue resistance transverse to the rolling direction, a sample of the aluminum strip according to the invention must only be cut transversely to the rolling direction and clamped in the bending cycle test device 1. The radius of the segments 3, 4 is 30 mm. The number of bending cycles was measured, whereby one bending cycle is completed when the starting position of the segment 3 is reached.

The measurements of flexural fatigue resistance of the alloys according to the invention clearly showed that at elevated manganese and magnesium contents, the number of Bending cycles can generally be increased, and even without intermediate annealing a high number of bending cycles was achieved until the sample cracked. In particular, the number of bending cycles achieved when performing an intermediate annealing in the hard as well as in the baked state with higher manganese and magnesium contents approached significantly. In this respect, a positive effect of the manganese and magnesium contents on the mechanical properties of the aluminum strips according to the invention could be detected.

Claims (7)

1. Aluminium alloy for producing lithographic printing plate supports, characterised in that the aluminium alloy contains the following alloy components in percent by weight: 0.35 % ≤ Fe ≤ 0.5 %, 0.2 % ≤ Mg ≤ 0.7 %, 0.08 % ≤ Si ≤ 0.25 %, 0.5 % ≤ Mn ≤ 0.6 %, Cu ≤ 0.002 %, Ti < 0.0075 %, Zn ≤ 0.012 %, Cr ≤ 0.003 %, the rest being Al and unavoidable impurities, each in an amount of 0.075 % at most to give a total of 0.075 % at most.
2. Aluminium alloy according to claim 1, characterised in that the aluminium alloy has the following Mg content in percent by weight: $$0.5\%<\mathrm{Mg}\le 0.7\%\mathrm{.}$$

   
3. Aluminium strip for producing lithographic printing plate supports made of an aluminium alloy according to any one of claims 1 or 2, having a thickness of 0.15 mm to 0.5 mm.
4. Aluminium strip according to claim 3, characterised in that, after a burning-in process at a temperature of 280 °C and over a period of 4 minutes, the aluminium strip has a tensile strength Rm of more than 150 MPa, a proof stress Rp 0.2 of more than 140 MPa as well as a flexural fatigue strength transverse to the rolling direction of at least 1950 cycles in the flexural fatigue test.
5. Use of an aluminium strip according to either claim 3 or claim 4 to produce printing plate supports.
6. Method for producing an aluminium strip for lithographic printing plate supports consisting of an aluminium alloy according to any one of claims 1 or 2, wherein a rolling ingot is cast, the rolling ingot is optionally homogenised at a temperature of 450 °C to 610 °C, the rolling ingot is hot-rolled to a thickness of 2 to 9 mm and the hot strip is cold-rolled, either with or without intermediate annealing, to a final thickness of 0.15 mm to 0.5 mm.
7. Method according to claim 6, characterised in that intermediate annealing is carried out at an intermediate thickness of 0.5 mm to 2.8 mm, preferably between 0.9 mm and 1.2 mm, and the intermediate annealing takes place in the coil or in a continuous furnace at a temperature of 230 °C to 470 °C.

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