Aluminium strip for lithographic printing plate supports with high flexural fatigue strength

Abstract

The invention relates to an aluminium alloy for the production of lithographic printing plate supports and also to an aluminium strip produced from the aluminium alloy, a process for the production of the aluminium strip and also its use for the production of lithographic printing plate supports. The object of providing an aluminium alloy as well as an aluminium strip from an aluminium alloy that permits the production of printing plate supports having improved bending-strength fatigue transverse to the rolling direction without adversely affecting the tensile strength values before and after the annealing process and while preserving the roughening properties, is achieved by the fact that the aluminium alloy contains the following alloy components in weight percent: 0.4%<Fe1.0%, 0.3%<Mg1.0%, 0.05%Si0.25%, Mn0.25%, Cu0.04%, Ti<0.1%, the remainder being Al and unavoidable impurities, individually at most 0.05% and totaling at most 0.05%.

Claims

1. Aluminium strip for the production of lithographic printing plate supports, which are designed to be clamped transverse to the rolling direction in printing machines, wherein the strip has a thickness of 0.15 mm to 0.5 mm, characterised in that the aluminium alloy of the strip consists of the following alloy components in weight percent: 0.4%<Fe0.65%, 0.31%Mg0.37%, 0.07%Si0.25%, Mn0.1%, Cu0.04%, Ti0.05%, Cr0.0006%, Zn0.05%, the remainder being Al and unavoidable impurities, individually at most 0.05% and totalling at most 0.15%, wherein the aluminium strip is in an as-rolled temper state and comprises a tensile strength Rm of less than 200 MPa.

2. Aluminium strip according to claim 1, characterised in that the aluminium alloy has an Mn content of at most 0.08 wt. %.

3. Aluminium strip according to claim 1, wherein the aluminium strip has after an annealing process at a temperature of 280 C. for 4 minutes a tensile strength Rm of more than 140 MPa as well as a flexural fatigue strength transverse to the rolling direction of at least 2000 cycles in an alternating bending fatigue test.

4. Aluminium strip according to claim 1, wherein the aluminium strip is used for the production of printing plate supports.

5. Aluminium strip according to claim 1, wherein the aluminium alloy has an Fe content of at most 0.5 wt. %.

6. Printing plate support, wherein the printing plate support is designed to be clamped transverse to the rolling direction in printing machines and is made from an aluminium strip according to claim 1.

7. A method, comprising: utilizing the printing plate support according to claim 6, wherein the printing plate support is clamped transverse to the rolling direction in a printing machine.

8. A method for printing, the method comprising: clamping the printing plate support according to claim 6 transverse to the rolling direction in a printing machine; and printing by means of the printing plate support and the printing machine.

9. A process for the production of an aluminium strip for lithographic printing plate supports according to claim 1, comprising casting a rolling slab, optionally homogenizing the rolling slab at a temperature of 450 C. to 610 C., hot rolling the rolling slab to a thickness of 2 mm to 9 mm, and cold rolling the hot aluminium strip, with intermediate annealing, to a final thickness of 0.15 mm to 0.5 mm.

10. Process according to claim 9, characterised in that an intermediate annealing is carried out at an intermediate thickness of 0.5 mm to 2.8 mm, the intermediate annealing taking place in a coil or in a straight-through furnace at a temperature of 230 C. to 470 C.

11. A method, comprising: utilizing an aluminium alloy strip for the production of lithographic printing plate supports, which are designed to be clamped transverse to the rolling direction in printing machines, from an aluminium alloy strip with a thickness of 0.15 mm to 0.5 mm, wherein the aluminium alloy consists of the following alloy components in weight percent: 0.4%<Fe0.65%, 0.31%Mg0.37%, 0.07%Si0.25%, Mn0.1%, Cu0.04%, Ti<0.05%, Cr<0.0006%, Zn0.05%, the remainder being Al and unavoidable impurities, individually at most 0.05% and totalling at most 0.15%, wherein the aluminium strip is in an as-rolled temper and has a tensile strength Rm of less than 200 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a schematic illustration of an experimental arrangement for performing alternating bending fatigue tests as described herein.

DETAILED DESCRIPTION OF THE INVENTION

(2) Table 1 shows the alloy compositions of two aluminium alloys V1, V2, which as comparison examples show compositions of aluminium alloys previously used for printing plate supports. In contrast to this the aluminium alloys I1 to I4 according to the invention have significantly higher magnesium and iron contents. Rolling slabs were cast from the alloys V1 to I4. The rolling slabs were then homogenised at a temperature of 450 C. to 610 C. and hot rolled to a thickness of 4 mm. Cold rolling was then carried out to a final thickness of 0.28 mm. The comparison alloy V2 did not undergo any intermediate annealing during the cold rolling, whereas the comparison alloy V1 as well as the aluminium alloys I1 to I4, underwent an immediate annealing. The intermediate annealing of the strips of the comparison alloy V1 took place at an intermediate thickness of 2.2 mm. In the case of the aluminium alloys I1 to I4 according to the invention, intermediate annealings were carried out at a thickness of 1.1 mm. The alloy constituents of the aluminium alloys V1 to I4 are shown in weight percent in Table 1.

(3) TABLE-US-00001 TABLE 1 Alloy Mg Fe Si Mn Cu Ti Cr Zn V1 0.2 0.38 0.07 0.0021 0.0005 0.0031 0.0005 0.0101 V2 0.11 0.41 0.07 0.0820 0.0029 0.0053 0.0005 0.0094 I1 0.31 0.46 0.08 0.0024 0.0005 0.0040 0.0005 0.0077 I2 0.37 0.46 0.08 0.0023 0.0005 0.0046 0.0005 0.0089 I3 0.43 0.43 0.07 0.0025 0.0005 0.0054 0.0005 0.0091 I4 0.45 0.61 0.07 0.0031 0.0006 0.0044 0.0006 0.0073

(4) The strips produced from the aluminium alloys V1 to I4 were investigated on the one hand as regards their ability to be roughened. It was found that all the produced aluminium strips have a good ability to be roughened. Table 2 shows not only the ability of the aluminium alloys V1 to I4 to be roughened, but also the number of bending cycles that samples of the various aluminium alloys underwent in an alternating bending fatigue test. The alternating bending fatigue tests were carried out with an experimental arrangement schematically illustrated in FIG. 1. In this connection alternating bending fatigue tests were carried out along and transverse to the rolling direction on as-rolled aluminium strips and also on aluminium strips after an annealing process at 280 C. for 4 minutes.

(5) FIG. 1a) shows in a diagrammatic sectional view the device 1 used for the alternating bending fatigue tests. In order to investigate the flexural fatigue strength, samples 2 are fixed in the alternating bending fatigue test device 1 on a movable segment 3 as well as on a stationary segment 4. In the alternating bending fatigue test the movable segment 3 is moved backwards and forwards on the stationary segment 4 with a rolling movement, so that the sample 2 is exposed to bending movements perpendicular to the length of the sample 2, FIG. 1b). In order to test the flexural fatigue strength transverse to the rolling direction, the samples simply have to be cut out transverse to the rolling direction and clamped in the device. The same also applies to samples cut out along the rolling direction. The radius of the bending segments 3, 4 is 30 mm.

(6) The results of the alternating bending fatigue test given in Table 2 show that the aluminium alloys I1 to I4 according to the invention allow a significantly higher number of alternating bending cycles, particularly after an annealing process, than the comparison alloys. The increase compared to the comparison alloys V1 and V2 is more than 40%, and at most may even be more than 140% compared to the alloy V1.

(7) This result is attributed inter alia to the combination of relatively high iron and magnesium contents in the aluminium alloys according to the invention. Despite the high magnesium and iron contents of the aluminium alloys according to the invention a good roughening behaviour of the aluminium alloys according to the invention is also observed, as can be seen from Table 2.

(8) TABLE-US-00002 TABLE 2 Alternating Alternating bending fatigue bending fatigue test transverse test along the to the rolling rolling direction direction Ability Alloy As- 280 C./ As- 280 C./ to be Identification rolled 4 min rolled 4 min roughened V1 3033 3398 1928 1274 + V2 2834 3154 2203 1929 + I1 4191 4323 2469 2721 + I2 4801 4573 2549 3176 + I3 4282 4568 2631 2906 + I4 3302 3421 2016 2871 +

(9) In addition the aluminium alloys I1 to I4 according to the invention also exhibit the necessary tensile strength values for ease of handling of the printing plate supports, in particular when using oversize printing plate supports clamped transverse to the rolling direction. In the as-rolled state the aluminium strips I1 to I4 have tensile strengths Rm measured according to DIN of less than 200 MPa, and a coil set can therefore easily be removed. After the annealing procedure the tensile strength Rm of the aluminium strips I1 to I4 according to the invention is still more than 140 MPa, in order to facilitate a clamping of large printing plate supports in printing devices. This is also true of the yield strength Rp 0.2 measured according to DIN, which in the as-rolled state is less than 195 MPa and after the annealing process at 280 C. for 4 minutes is more than 130 MPa.

(10) Only the comparison alloy, which had not undergone an intermediate annealing, shows in the as-rolled state values that are too high as regards the tensile strength Rm and also the yield strength Rp 0.2.

(11) Although the values for the tensile strength and yield strength of the aluminium strips depend on the process parameters in the production of the aluminium strips, the aluminium alloys according to the invention nevertheless enable the preferred values to be achieved in a simple manner, for example with an intermediate annealing at 1.1 mm, and furthermore provide outstanding flexural fatigue strength properties combined with very good strength values.

(12) TABLE-US-00003 TABLE 3 Yield strength Tensile strength Rp 0.2 (MPa) Rm (MPa) Alloy Intermediate As- 280 C./ As- 280 C./ identification Annealing rolled 4 min rolled 4 min V1 Yes 193 136 197 145 V2 No 210 148 218 156 I1 Yes 178 135 185 147 I2 Yes 180 133 186 147 I3 Yes 183 136 191 150 I4 Yes 186 140 194 154