EP2192202B1 - Aluminium sheet for lithographic printing plate support having high resistance to bending cycles - Google Patents

Description

The invention relates to an aluminum strip of aluminum alloy for producing lithographic printing plate supports having a thickness of 0.15 mm to 0.5 mm, a method for producing the aluminum strip and its use for the production of lithographic printing plate supports.

Lithographic printing plate supports are predominantly made of aluminum alloys, with typical thicknesses of the printing plate supports being between 0.15 and 0.5 mm. On lithographic printing plate support ever higher technical requirements are made. These result from the fact that ever larger numbers of prints must be achievable with printing presses. Furthermore, the printing plate support must be as large as possible in order to maximize the printing area per pressure. Since the printing plate supports are made of aluminum strips, they are naturally limited in their width to slightly less than the width of the aluminum strip. Therefore, the clamping of the printing plate supports in printing machines increasingly takes place transversely to the rolling direction, so that in particular the flexural fatigue resistance of the printing plate supports transversely to the rolling direction becomes more important. In addition to a good flexural fatigue resistance transverse to the rolling direction a good roughness and the highest possible heat resistance is required. These requirements result from the fact that the aluminum strip is used for the production of lithographic printing plate supports previously subjected to an electrochemical roughening, which should have a nationwide and homogeneous as possible roughening. The applied photosensitive layer is usually baked at temperatures between 220 ° C and 300 ° C at annealing times of 3 to 10 minutes. The baking process of the photosensitive layer must not lead to an excessive loss of strength in the printing plate support, so that the printing plate support is still easy to handle and can be easily clamped in a printing device. At the same time the printing plate support must have a high stability in the printing device to allow the highest possible number of prints. A printing plate support must therefore have a sufficient bending fatigue strength, so that plate outliers are excluded due to mechanical overload of the printing plate support. Above all, the bending fatigue strength across the rolling direction is becoming increasingly important, since many printing plate supports are clamped perpendicular to the rolling direction and bends do not occur longitudinally but transversely to the rolling direction.

From the Applicant's European Patent EP 1 065 071 B1 a ribbon for the production of lithographic printing plate supports is known, which is characterized by a good aufraubarkeit combined with a high flexural fatigue resistance and a sufficient thermal stability after a burn-in. Due to the increasing size of the printing presses and the resulting increase in the number of printing plate supports required, however, the need has arisen for the properties of this aluminum alloy and the one produced therefrom Further improve printing plate support without negatively influencing the Aufraubarkeit the aluminum strip.

Another international patent application from the Applicant discloses an aluminum alloy for the production of lithographic printing plate supports which has a relatively high iron content of from 0.4% to 1% by weight and a relatively high manganese content of up to 0.3% by weight. % allows. This aluminum alloy was improved in particular with regard to its strength properties after a baking process. However, it has heretofore been assumed that Mg contents greater than 0.3% by weight cause problems with the electrochemical roughening of the aluminum strip.

• 0,05 % < Fe ≤ 0,5 %,
• 0,1 % < Mg ≤ 0,9 %,
• 0,01 % ≤ V and/or Ni ≤ 0,3 %,
• 0,01 % ≤ Zr ≤ 0,3 %,
• 0,05 % ≤ Mn ≤ 2 %,
• Si ≤ 0,2 %,
• Cu ≤ 0,05 %,
• Rest: Al und unvermeidbare Verunreinigungen.

The publication EP 0 239 995 A2 relates to an aluminum alloy, which allows the production of a strip with a heat resistance with good Aufraueigenschaften. The aluminum alloy has the following composition in weight percent:

• 0.05% <Fe ≦ 0.5%,
• 0.1% <Mg ≤ 0.9%,
• 0.01% ≤ V and / or Ni ≤ 0.3%,
• 0.01% ≤ Zr ≤ 0.3%,
• 0.05% ≤ Mn ≤ 2%,
• Si ≤ 0.2%,
• Cu ≤ 0.05%,
• Remainder: Al and unavoidable impurities.

Finally, the document relates EP 0 272 528 A2 also an aluminum alloy for lithographic printing plate supports, which in addition to Fe, Mg, Si, Mn and Ti, in particular up to 0.20 wt .-% copper, up to 0.25 wt .-% zinc, up to 0.10 wt .-% Containing Cr and up to 0.025 wt .-% vanadium.

From the US 2008/035488 A For example, lithographic printing plate supports which have an Fe content of at most 0.4% by weight are known. Evidence of a relationship between higher iron and magnesium contents and the bending behavior does not disclose the US application.

On this basis, the present invention seeks to provide an aluminum alloy and an aluminum strip made of an aluminum alloy, which or which enables the production of printing plate supports with improved flexural fatigue resistance transverse to the rolling direction, without the tensile strength values before and after the baking at deteriorate consistent Aufraueigenschaften. 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.

This object is achieved with an aluminum strip according to claim 1 and a method according to claim 7.

• 0,4% < Fe ≤ 0,65%,
• 0,3% < Mg ≤ 1,0%,
• 0,07% ≤ Si ≤ 0,25%,
• Mn ≤ 0,25%,
• Cu ≤ 0,04%,
• Ti < 0,1%,
• Zn ≤ 0,05 %,
• Cr < 0,01 %,

Rest Al und unvermeidbare Verunreinigungen einzeln maximal 0,01%, in Summe maximal 0,05%, wobei das Aluminiumband im walzharten Zustand eine Zugfestigkeit Rm von weniger als 200 MPa und eine Zugfestigkeit von mehr als 140 MPa nach einem Einbrennvorgang bei 280 °C für 4 Minuten aufweist.According to a first teaching of the present invention, the object indicated above by a generic Aluminum strip consisting of an aluminum alloy for the production of lithographic printing plate supports, characterized in that the aluminum alloy has the following alloy components in weight percent:

• 0.4% <Fe ≤ 0.65%,
• 0.3% <Mg ≤ 1.0%,
• 0.07% ≦ Si ≦ 0.25%,
• Mn ≤ 0.25%,
• Cu ≤ 0.04%,
• Ti <0.1%,
• Zn ≤ 0.05%,
• Cr <0.01%,

A maximum of 0.05%, the aluminum strip in the hard-rolled state has a tensile strength Rm of less than 200 MPa and a tensile strength of more than 140 MPa after a baking process at 280 ° C for 4 minutes.

Notwithstanding the aluminum alloys used hitherto for the production of lithographic printing plate supports, which overall have very low proportions of iron and magnesium, it has been found that the aluminum alloy according to the invention in particular provides increased bending fatigue resistance at constant tensile strength values after a baking process transverse to the rolling direction. The flexural fatigue resistance transverse to the rolling direction, especially after a baking process at 280 ° C for 4 minutes, can with the aluminum alloy according to the invention in comparison to previously used aluminum alloys are increased by more than 40%. It is believed that the combination of relatively high levels of magnesium and iron in the aluminum alloy of the present invention are responsible for the improved flex life. Problems, which were expected in particular with regard to the roughening of an aluminum strip produced from the specified aluminum alloy, surprisingly did not occur. Despite the high Mg contents of 0.3% by weight to 1% by weight, there were no problems with roughening, in particular no streaks. The improved flexural fatigue resistance across the rolling direction is attributed to the combination of iron levels of greater than 0.4 wt% to 0.65 wt% with magnesium levels greater than 0.3 wt% to 1 wt%. Above 1% by weight of magnesium or iron, significant problems are expected in the roughening of lithographic printing plate supports.

Silicon causes in a content of 0.07 wt .-% to 0.25 wt .-% that the electrochemical etching leads to a high number of sufficiently deep recesses, so that an optimal absorption of the photosensitive coating is guaranteed.

Copper should be limited to a maximum of 0.04 wt .-% in order to avoid inhomogeneous structures when roughening. Titanium is introduced only for grain refining and leads at roughening levels higher than 0.1 wt .-% to roughening problems. Manganese, on the other hand, in combination with iron, can improve the properties of an aluminum strip produced from the aluminum alloy after a baking process, provided the proportion does not 0.25 wt .-% exceeds. Above 0.25% by weight, coarse precipitates are expected to deteriorate roughening properties.

• Zn ≤ 0,05% und
• Cr < 0,01%.

The aluminum alloy according to the invention has the following alloy components in weight percent:

• Zn ≤ 0.05% and
• Cr <0.01%.

Due to its less electrochemical properties, zinc has a particularly strong influence on the roughening properties and should therefore be limited to a maximum of 0.05% by weight. Chromium contents of at least 0.01% by weight lead to precipitation formation and also negatively influence the roughening.

Aluminum alloys with the stated iron contents showed, in addition to an increase in flexural fatigue resistance from the hard-rolling state to the state after a baking process transversely to the rolling direction, a very process-safe roughening behavior.

• 0,4% ≤ Mg ≤ 1%, vorzugsweise
• 0,4% ≤ Mg ≤ 0,65%.

According to a further embodiment of the aluminum alloy according to the invention, the aluminum alloy preferably has the following Mg content in percent by weight:

• 0.4% ≤ Mg ≤ 1%, preferably
• 0.4% ≤ Mg ≤ 0.65%.

Higher Mg contents lead to improved mechanical properties, especially after a burn-in process. This effect becomes evident at Mg contents of at least 0.4% by weight. An upper limit of 0.65 wt .-% results in an optimum compromise from increasing the strength with high flexural fatigue resistance of the aluminum alloy transverse to the rolling direction and process-safe Aufraubarkeit. Mg contents above 1% by weight promote the formation of stripes when roughening the aluminum strip. In experiments, however, no signs of problematic roughening properties were found at Mg contents of between 0.4% by weight and 0.65% by weight. Magnesium contents of between 0.65% by weight and 1% by weight also provide outstanding properties in terms of bending resistance transverse to the rolling direction, but process control in the roughening process may become more difficult owing to the increasing tendency to form streaks.

• Ti ≤ 0,05%.

Moreover, according to a further developed embodiment of the aluminum alloy according to the invention, the microstructure of the aluminum alloy can be further improved in that the aluminum alloy has the following alloy component in percent by weight:

• Ti ≤ 0.05%.

Above all, the production properties of the aluminum alloy with regard to the casting of the rolling ingot and the grain refining are improved by the stated contents of the alloy components.

Preferably, the aluminum alloy has an Mn content of at most 0.1 wt .-%, preferably at most 0.05 wt .-%. Due to the high Mg and Fe contents of the aluminum alloy, manganese in the aluminum alloy according to the invention contributes only insignificantly to the improvement of the tensile strength values after a baking process and can therefore be reduced to a minimum.

The aluminum strip according to the invention for producing lithographic printing plate supports consisting of an aluminum alloy according to the invention has a thickness of 0.15 mm to 0.5 mm. The aluminum strip according to the invention is characterized, as already stated, by an excellent flexural fatigue resistance transverse to the rolling direction, in particular also after a baking process.

0.15 mm to 0.5 mm. The aluminum strip according to the invention is characterized, as already stated, by an excellent flexural fatigue resistance transverse to the rolling direction, in particular also after a baking process.

In the hard-rolled state, the aluminum strip has a tensile strength Rm of less than 200 MPa along the rolling direction and after a baking process at a temperature of 280 ° C and a duration of 4 minutes, a tensile strength Rm of more than 140 MPa and a bending resistance transverse to the rolling direction of at least 2000 cycles in Biegewechselnest, so the aluminum strip is particularly advantageous for the production of oversized lithographic printing plate carriers used. The printing plate supports are then particularly easy to handle both in hard as well as after a burn-in. In particular, the pressure plate carriers produced therefrom have an improved service life.

The above-derived object is achieved according to a second teaching of the present invention by the use of an aluminum strip according to the invention for the production of printing plate carriers, because these can be processed in a larger size process reliable and clamped in large printing devices. In addition, these printing plate supports due to the increased flexural fatigue resistance transverse to the rolling direction on an improved life and do not tend to Plattenreißern.

Finally, according to a third teaching of the present invention, the above 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, in which 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 intermediate annealing at a final thickness of 0.15 mm to 0.5 mm. The intermediate annealing is carried out in such a way that a desired final strength of the aluminum strip in the hard-hard state is set by the subsequent cold-rolling process to final thickness. According to the invention, this is, as already stated, just below 200 MPa.

According to the invention, the intermediate annealing is carried out at an intermediate thickness of 0.5 mm to 2.8 mm, wherein the intermediate annealing in the coil or in a continuous furnace at a temperature of 230 ° C to 470 ° C. Depending on the intermediate thickness of the strip at which the intermediate annealing is carried out, the final strength of the aluminum strip can be adjusted. Moreover, the use of the aluminum alloy according to the invention for producing a strip for lithographic printing plate supports significantly improves the bending fatigue resistance transverse to the rolling direction of the aluminum strip compared to the previously known aluminum alloys and the aluminum strips produced therefrom. Overall, there is an increase in the flexural fatigue test of more than 40%.

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 claims subordinate to claim 1 and to the description of embodiments in conjunction with the drawings.

Table 1 shows the alloy compositions of two aluminum alloys V1, V2 which, as comparative examples, have compositions of aluminum alloys previously used for printing plate supports. In comparison, the aluminum alloys I1 to I4 according to the invention have significantly higher magnesium and iron values. From the alloys V1, to I4 rolled bars were cast. The ingot was then homogenized at a temperature of 450 ° C to 610 ° C and hot rolled to a thickness of 4 mm. Subsequently, a cold rolling to a final thickness of 0.28 mm. The comparative alloy V2 was not subjected to intermediate annealing during the cold rolling, whereas the comparative alloy V1 and the aluminum alloys I1 to I4 according to the invention were manufactured with an intermediate annealing. The intermediate annealing of the strips of the comparative alloy V1 took place at an intermediate thickness of 2.2 mm. In the case of the aluminum alloys I1 to I4 according to the invention, intermediate anneals were carried out at a thickness of 1.1 mm. The alloy components of the aluminum alloys V1 to I4 in percent by weight are shown in Table 1. Table 1 alloy mg fa 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 .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

The tapes produced from the aluminum alloys V1 to I4 were examined on the one hand for their roughening. It was found that all aluminum strips produced have a good aufraubarkeit. Table 2 shows not only the roughenability of the aluminum alloys V1 to I4, but also the number of bending cycles which reached samples of the various aluminum alloys in a bending cycle test. The bending cycle tests were carried out with an in Fig. 1 performed schematically experimental arrangement. Bending cycle tests were carried out with both hard-rolled aluminum strips and aluminum strips after a baking process of 280 ° C for 4 minutes along and across the rolling direction.

Fig. 1a shows in a schematic sectional view of the bending change test device 1 used to test the flexural fatigue resistance Samples 2 are fixed in the Biegewechselnestvorrichtung 1 on a movable segment 3 and a fixed segment 4. Die beiden Biegewechseltestvorrichtung 1 bzw. The mobile one Segment 3 is reciprocated on the fixed segment 4 by a rolling motion in the bending change test, so that the sample 2 is subjected to bends perpendicular to the extension of the sample 2. In order to test the bending cycle resistance transverse to the rolling direction, the samples need only be cut transversely to the rolling direction and clamped in the device. The same applies to samples cut out along the rolling direction. The radius of the bending segments 3, 4 is 30 mm.

The results from the bending cycle test shown in Table 2 show that the aluminum alloys I1 to I4 according to the invention allow a significantly higher number of cycles of bending cycles, especially after a burn-in process, than the comparative alloys. The increase over the comparison alloys Val and V2 is more than 40%, at most in comparison to the alloy V1 even more than 140%.
This result is attributed inter alia to the combination of relatively high iron and magnesium contents in the aluminum alloys according to the invention. Despite the high magnesium and iron contents of the aluminum alloys according to the invention, a further good roughening behavior of the aluminum alloys according to the invention is evident, as can be seen from Table 2. Table 2 Alloy designation Biegewechselnest along the direction of Halzrichtung Bending change test across the rolling direction roughenability As-rolled 280 ° C / 4 min As-rolled 280 ° C / 4 min 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 2874 +

In addition, the aluminum alloys I1 to I4 according to the invention also exhibit the tensile strength values required for the handling of the printing plate supports, in particular when using oversized printing plate supports clamped transversely to the rolling direction. In the hard-rolled state, the aluminum strips I1 to I4 have tensile strengths Rm measured in accordance with DIN of less than 200 MPa, so that a coil set can be removed in a simple manner. After the baking process, the tensile strength Rm of the aluminum strips I1 to I4 according to the invention is still more than 140 MPa in order to facilitate clamping large printing plate supports in printing devices. This also applies to the yield strength Rp0.2 measured according to DIN, which is less than 195 MPa in the hard-rolled state and more than 130 MPa for 4 minutes after the baking process at 280 ° C.

Only the comparison alloy, which has not been subjected to intermediate annealing, shows too high values for the tensile strength Rm and the yield strength Rp 0.2 in the hard-rolling state.

Although the values for the tensile strength and yield strength of the aluminum strips are dependent on the process parameters in the production of the aluminum strips. The However, aluminum alloys according to the invention allow the preferred values to be achieved in a simple manner, for example with an intermediate annealing at 1.1 mm, and nevertheless to provide outstanding flexural fatigue properties at very good strength values. Table 3 Alloy designation intermediate annealing Yield strength Rp0.2 (MPa) Tensile strength Rm (MPa) As-rolled 280 ° C / 4 min As-rolled 280 ° C / 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

Claims (7)

1. Aluminium strip for the production of lithographic printing plate supports from an aluminium alloy with a thickness of 0.15 mm to 0.5 mm, characterised in that the aluminium alloy comprises the following alloy components in weight per cent:

   0.4% < Fe ≤ 0.65%,

   0.3% < Mg ≤ 1.0%,

   0.07% ≤ Si ≤ 0.25%,

   Mn ≤ 0.25%,

   Cu ≤ 0.04%,

   Ti < 0.1%,

   Zn ≤ 0.05%,

   Cr < 0.01%,

   the remainder being Al and unavoidable impurities, individually at most 0.05% and totalling at most 0.15%, the aluminium strip in the as-rolled state has a tensile strength Rm of less than 200 MPa and, after an annealing process at a temperature of 280°C for 4 minutes, a tensile strength of more than 140 MPa.
2. Aluminium strip according to claim 1, characterised in that the aluminium alloy has the following Mg content in weight per cent:

   0.4% < Mg ≤ 1%, preferably

   0.4% < Mg ≤ 0.65%.
3. Aluminium strip according to claim 1, characterised in that the aluminium alloy contains the following alloy components in weight per cent:

   Ti ≤ 0.05%
4. Aluminium strip according to claim 1, characterised in that the aluminium alloy has an Mn content of at most 0.1 wt.%, preferably at most 0.08 wt.%.
5. Aluminium strip according to one of claims 1 to 4, characterised in that the aluminium strip in the as-rolled state has a tensile strength Rm of less than 200 MPa along the rolling direction, and 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 the alternating bending fatigue test.
6. Use of an aluminium strip according to one of claims 1 to 5 for the production of printing plate supports.
7. Process for the production of an aluminium strip for lithographic printing plate supports consisting of an aluminium alloy according to one of claims 1 to 5, in which a rolling slab is cast, the rolling slab is homogenised at a temperature of 450°C to 610°C, the rolling slab is hot rolled to a thickness of 2 mm to 9 mm and the hot strip is cold rolled with intermediate annealing to a final thickness of 0.15 mm to 0.5 mm, wherein the intermediate annealing is carried out at an intermediate thickness of 0.5 mm to 2.8 mm, and the intermediate annealing taking place in the coil or in a straight-through furnace at a temperature of 230°C to 470°C.

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