EP2243849A1 - Manganese and magnesium rich aluminium strip - Google Patents

Abstract

Aluminum alloy comprises (in wt.%): iron (less than 0.4); magnesium (0.41-0.7); silicon (0.05-0.25); manganese (0.1-0.6); copper (= 0.04); titanium (less than 0.1); zinc (= 0.1); chromium (= 0.1); and balance amount includes aluminum and unavoidable impurities each more than 0.05% to give a total of maximum 0.15%. Independent claims are included for: (1) an aluminum strip, for manufacturing lithographic printing plate support, made from the above aluminum alloy with a thickness of 0.15-5 mm; and (2) manufacturing aluminum strips comprising the above aluminum alloy comprising casting a ingot, homogenizing the ingot at 450-610[deg] C, hot-rolling the ingot to a thickness of 2-9 mm and cold-rolling the ingot with or without intermediate annealing to a thickness of 0.15-0.5 mm.

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 printing plate support due to the baking process must 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 to allow for 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 with regard to the roughening, the heat resistance, the mechanical properties before and after the baking process and the bending fatigue strength along the rolling direction, the European patent originating from the Applicant 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 is also known, high iron content from 0.4 wt .-% to 1 wt .-% with a relatively high manganese content and with magnesium contents of up to a maximum of 0.3 wt .-% to combine. 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 and magnesium contents of more than 0.3 wt .-% are problematic with respect to the roughening of the aluminum alloy.

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 with improved heat resistance without worsening properties are deteriorated. 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: Fe < 0.4%, 0.41% ≤ mg ≤ 0.7%, 0.05% ≤ Si ≤ 0.25%, 0.1% ≤ Mn ≤ 0.6%, Cu ≤ 0.04%, Ti ≤ 0.1%, Zn ≤ 0.1%, Cr ≤ 0.1%, Residual Al and unavoidable impurities individually max. 0.05%, in total max. 0.15%.

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 relatively high magnesium contents of at least 0.41% by weight to a maximum of 0.7% by weight. with relatively high manganese contents of 0.1 to 0.6 wt .-%. 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. To the knowledge of the Applicant, the low iron content, which is limited to less than 0.4% by weight, stabilizes the roughening behavior of the printing plate supports.

A good roughening behavior is also effected by silicon, which is contained in a content of 0.05 wt .-% to 0.25 wt .-% in the aluminum alloy according to the invention. At the electrochemical roughening or etching, the Si content according to the invention ensures that a high number of sufficiently deep recesses is generated in order to ensure optimum absorption of the photosensitive coating.

Copper should be limited to a maximum of 0.04 wt .-% in order 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 contents of more than 0.1% by weight. The contents of zinc and chromium negatively influence the roughening result and should therefore amount to a maximum of 0.1% by weight.

• 0,26 % ≤ Mn ≤ 0,6 %, vorzugsweise
• 0,5 % ≤ Mn ≤ 0,6 %.

The heat resistance of the aluminum alloy can be further increased according to a first embodiment of the aluminum alloy according to the invention in that the aluminum alloy has the following Mn content in% by weight:

• 0.26% ≤ Mn ≤ 0.6%, preferably
• 0.5% ≤ Mn ≤ 0.6%.

It has also been shown that higher manganese levels are not only useful for further improving the hot strength, i. lead 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 manufacturing process. This effect is particularly pronounced at a manganese content of 0.5 wt .-% to 0.6 wt .-%.

• 0,5 % ≤ Mg ≤ 0,7 % auf,

so kann die Biegewechselfestigkeit quer zur Walzrichtung noch einmal gesteigert werden. Sowohl bei höheren Mangangehalten also beispielsweise 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.According to a next embodiment of the aluminum alloy according to the invention, this has a Mg content in% by weight of:

• 0.5% ≤ Mg ≤ 0.7%,

Thus, the bending fatigue strength can be increased again transverse to the rolling direction. Both at higher manganese contents, for example, 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 properties of the aluminum strips produced from a corresponding aluminum alloy.

• Ti ≤ 0,05 %,
• Zn ≤ 0,05 %
• Cr < 0,01 %.

As already mentioned, Ti, Zn and Cr can adversely affect the roughening result and, in principle, lead to streaking effects on the aluminum strips. The aluminum alloy according to the invention can therefore be further improved in terms of process reliability during roughening and thus with regard to its use for printing plate supports in that the aluminum alloy has the following alloy components in% by weight:

• Ti ≤ 0.05%,
• Zn ≤ 0.05%
• Cr <0.01%.

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 aluminum strip according to the invention is distinguished not only by its excellent roughening, but also guarantees a very good heat resistance with moderate tensile strength values optimized handling in relation to the use of oversized printing devices and 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 minutes a tensile strength Rm of more than 145 MPa, a yield strength Rp 0.2 of more than 135 MPa and a bending resistance transverse to the rolling direction of more than 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 process for the production of an aluminum strip for lithographic printing plate supports consisting of an inventive Aluminum alloy is achieved by casting a slab, optionally homogenizing the slab at a temperature of 450 ° C to 610 ° C, hot rolling the slab to a thickness of 2 to 9 mm, and hot strip with or without intermediate annealing to a final thickness of 0.15 mm to 0.5 mm cold rolled. 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 performed, the final strength of the aluminum strip can be set in the hard-rolled state. 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. As a result, printing plate supports can be made available with the method according to the invention which, in addition to excellent roughening, combine outstanding heat resistance with high resistance to bending bending transversely 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 single drawing shows a schematic sectional view of a device for measuring the flexural fatigue resistance of the aluminum strips produced.

Table 1 now shows the alloy composition of a reference aluminum alloy Ref and inventive aluminum alloys I3, I4, I6 and 17, which have been investigated in the following. 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 13 0.08 0.35 <0.002 0.26 0.41 <0.003 0,012 0.0075 0.0075 14 0.08 0.35 <0.002 0.26 0.6 <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 inventive alloys I3, I4, 16 and 17 contain compared to the reference aluminum alloy a significantly higher manganese content of 0.26 wt .-% to 0.5 wt .-%. The Mg content varies from 0.41% to 0.6% by weight. Rolled ingots were cast from the aluminum alloys with the just mentioned compositions. The rolling 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 ++ 13 ++ 14 ++ 16 + 17 +

Table 3 shows, on the one hand, the results of the bending change test and the associated values for the strip thickness and the temperature ranges during the intermediate annealing. Experiments without intermediate annealing were also carried out. 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 / 4min) Ref R 2.2 400 - 450 1928 1274 I3 3.1 - - 3461 1959 I3 3.2 0.9 - 1.2 300-350 2116 3228 I3 3.3 0.9-1.2 400-450 2272 2815 I4 4.1 - - 3235 2177 I4 4.2 0.9 - 1.2 300 - 350 2434 3568 I4 4.3 0.9 - 1.2 400 - 450 3595 3929 I6 6.1 - - 3208 2425 I6 6.2 0.9 - 1.2 300 - 350 2808 3099 I6 6.3 0.9 - 1.2 400 - 450 2937 3599 I7 7.1 - - 4951 2958 I7 7.2 0.9-1.2 300-350 3506 3372 I7 7.3 0.9-1.2 400 - 450 3058 3230

As Table 3 clearly shows, compared with the reference alloy, the number of possible bending cycles transversely to the rolling direction was significantly increased, both in the hard-rolled state and in the baked state. The minimum number of bending cycles transverse to the rolling direction in the baked state is 1.5 times higher with 1959 bending cycles than with 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 heat resistance, resulting in higher values for the Tensile strength and the yield strength noticeable. 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 3.1 171 176 3.2 141 157 3.3 139 156 4.1 171 185 4.2 145 163 4.3 146 165 6.1 181 192 6.2 154 170 6.3 151 169 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 the experiments 3.1, 4.1, 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. An 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 bake from 156 MPa to 182 MPa for the tensile strength Rm and 139 MPa to 161 MPa for the yield strength Rp0 ; 2. However, the measured values of the reference alloy Ref.

From the comparison of experiments I3 and I6 and I4 and I7, the effect of the increased manganese values is clearly recognizable, which in conjunction with the high magnesium values show a marked improvement in the mechanical properties in the baked state and thus document the very good heat resistance of the aluminum alloys according to the invention.

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 device 1, which has been used to determine the number of possible Biegewechselzyklen represented. 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 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 the 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 with increased manganese and magnesium contents, the number of bending cycles can generally be increased, whereby high bending cycles were achieved even without intermediate annealing until the sample broke. In particular, the number of bending cycles achieved when performing an intermediate annealing in the hard as well as in the baked state at 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 (9)

Aluminum alloy for the production of lithographic printing plate supports,
characterized in that the aluminum alloy has the following alloy components in weight percent: Fe < 0.4%, 0.41% < mg ≤ 0.7%, 0.05% ≤ Si ≤ 0.25%, 0.1% ≤ Mn ≤ 0.6%, Cu ≤ 0.04%, Ti < 0.1%, Zn ≤ 0.1%, Cr ≤ 0.1%, Residual Al and unavoidable impurities individually max. 0.05%, in total max. 0.15%. Aluminum alloy according to claim 1,
characterized in that the aluminum alloy has the following Mn content in percent by weight: 0.26% ≤ Mn ≤ 0.6%, preferably 0.5% ≤ Mn ≤ 0.6%. Aluminum alloy according to claim 1 or 2,
characterized in that the aluminum alloy has the following Mg content Weight percent comprises: 0.5% <Mg ≤ 0.7%. Aluminum alloy according to one of claims 1 to 3,
characterized in that the aluminum alloy has the following alloy components in weight percent: Ti ≤ 0.05%, Zn ≤ 0.05% Cr <0.01%. An aluminum strip for producing aluminum alloy lithographic printing plate supports according to any one of claims 1 to 4 having a thickness of 0.15 mm to 0.5 mm. Aluminum strip according to claim 5,
characterized in that the aluminum strip after a baking process at a temperature of 280 ° C and a duration of 4 minutes, a tensile strength Rm of more than 145 MPa, a yield strength of more than 135 MPa and a bending resistance transverse to the rolling direction of at least 1950 cycles in the bending cycle test having. Use of an aluminum strip according to claim 5 or 6 for the production of printing plate supports. Process for producing an aluminum strip for lithographic printing plate supports consisting of a An aluminum alloy according to any one of claims 1 to 4, wherein a billet is cast, the billet is optionally homogenized at a temperature of 450 ° C to 610 ° C, the billet is hot rolled to a thickness of 2 to 9 mm, and the hot strip is or cold-rolled without intermediate annealing to a final thickness of 0.15 mm to 0.5 mm. Method according to claim 8,
characterized in that an intermediate annealing is carried out at an intermediate thickness of 0.5 mm 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.

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