EP3445887B1 - Lithographic sheet manufacturing with high cold roll pass reduction - Google Patents

Description

• 0,05 % ≤ Si ≤ 0,25 %,
• 0,2 % ≤ Fe ≤ 1%,
• Cu max. 400 ppm,
• Mn ≤ 0,30 %,
• 0,10 % ≤ Mg ≤ 0,50 %,
• Cr ≤ 100 ppm,
• Zn ≤ 500 ppm,
• Ti < 0,030 %,

The invention relates to a method for producing an aluminum strip for lithographic printing plate supports made of an aluminum alloy, wherein the aluminum alloy of the aluminum strip for lithographic printing plate supports comprises the following alloy constituents in% by weight:

• 0.05% ≦ Si ≦ 0.25%,
• 0.2% ≤ Fe ≤ 1%,
• Cu max. 400 ppm,
• Mn ≤ 0.30%,
• 0.10% ≤ Mg ≤ 0.50%,
• Cr ≤ 100 ppm,
• Zn≤500 ppm,
• Ti <0.030%,

• Gießen eines Walzbarrens aus einer Aluminiumlegierung,
• Homogenisierung des Walzbarrens,
• Warmwalzen des Walzbarrens auf eine Warmbandenddicke und
• Kaltwalzen des Warmbandes an Enddicke, wobei die Enddicke nach dem Kaltwalzen zwischen 0,1 mm und 0,5 mm beträgt.

Each residue Al and unavoidable impurities individually a maximum of 0.03%, in total a maximum of 0.15%, with at least the following steps:

• Casting a rolled billet of an aluminum alloy,
• Homogenization of the rolling ingot,
• Hot rolling of the rolling ingot to a hot strip thickness and
• Cold rolling of the hot strip to final thickness, the final thickness after cold rolling is between 0.1 mm and 0.5 mm.

Aluminum tapes must simultaneously meet a variety of requirements to provide sufficient quality for lithographic printing plate supports. One of the most important properties of the aluminum strip, which must be fulfilled, is a homogeneous behavior in an electrochemical roughening. An area-wide roughening of the aluminum strip must result in a structureless appearance of the aluminum strip without streaking effects. On the roughened structure, a photosensitive layer is applied, which depending on the application type is baked after application at a temperature of 220 ° C to 300 ° C for 3-10 minutes. Typical combinations of bake times are for example 240 ° C for 10 minutes, 260 ° C for 6 minutes, 270 ° C for 7 minutes and 280 ° C for 4 minutes. The printing plate support may lose as little as possible after firing to strength, so this is still easy to handle and can be easily clamped in a printing device. In the case of large-format printing plate supports in particular the handling after the burning of the photosensitive layer is problematic. Finally, the printing plate should survive later in use as many printing cycles, so that the aluminum strip should have the highest possible bending fatigue strength. In addition to these general requirements for the use of a printing plate support was, for example, in the European patent application EP 2 192 202 A1 investigates how an aluminum alloy strip can be adjusted to a desired final strength so that, for example, a set of coils present in the aluminum strip can be eliminated again, and at the same time high bending cycle cycles and good roughening properties can be provided. By choosing the Zwischenglühdicke depending on the aluminum alloy composition, the goal could be achieved here.

From the DE 699 20 831 T2 For example, a process for making tapes for lithographic printing plate supports is known in which a magnesium-free aluminum alloy is processed by using cold rolling passes with stitch reductions above 50%. Magnesium levels above 0.02 wt% are considered problematic in terms of recovery of the cold rolled strip and the appearance of excessively high strengths after cold rolling.

The JP H11229101 also discloses the processing of magnesium-free aluminum alloys containing magnesium only as an impurity at levels of at most 0.05% by weight. Magnesium levels are also considered problematic.

In the production of aluminum strips for lithographic printing plate supports are now essentially aluminum alloys in focus, which are magnesium-containing. It has been found that magnesium offers particular advantages in terms of fatigue resistance when using the printing plate supports and the roughening of the printing plates. Therefore, magnesium is alloyed to a specified content of the aluminum alloy.

• Abwickeln des Aluminiumbandes von einem Coil mit einem Abwickelhaspel,
• Walzen des Aluminiumbandes unter Verwendung eines Walzgerüstes mit einem einzigen Kaltwalzstich und
• Aufwickeln des kaltgewalzten Aluminiumbandes.

Another focus of the development is the manufacturing costs of printing plate carriers. With a minimization of the layer thickness of the photosensitive layer and the thicknesses of the support materials for the printing plates, so the thickness of the aluminum strip for lithographic printing plate support to less than 0.3 mm, optimizations have already been introduced in terms of manufacturing costs in manufacturing. In the production of the litho ribbons, cold rolling is to be classified as the final process determining the surface topography of the lithoband. For cold rolling so-called "mill-finish" surface-producing work rolls, so ground work rolls are used. Cold rolling is often done on rolling stands with a single cold roll pass using the following steps, due to the enormous demands on the subsequent surface quality:

• Unwinding the aluminum strip from a coil with an uncoiler,
• Rolling of the aluminum strip using a rolling stand with a single cold rolling pass and
• Winding up the cold-rolled aluminum strip.

Due to the temperature development during cold rolling due to the applied forming energy, the ribbons for lithographic printing plate supports are generally not rolled in rolling stands with multiple stitches. Maximum control of the individual cold rolling passes is desired. In a simple cold rolling pass, however, it is sometimes necessary to cool the strips after each cold roll pass in the coil until they can be used again for a next cold-rolled pass. Become too big Stichabnahmen made in a cold roll pass, area of the surface of the aluminum strip material can be broken, resulting in surface defects and a streaky appearance of the surface. Due to the risk of surface defects, experts in the field of magnesium-containing aluminum alloys have hitherto refrained from the use of large punctures above about 50% reduction per cold rolling pass during cold rolling. As a result, in a typical production of lithographic printing plate carriers with final thicknesses in the range 0.2 mm to 0.4 mm so far at least four cold rolling passes were required.

On this basis, the object of the present invention is to provide a method for producing an aluminum strip for lithographic printing plate supports comprising magnesium-containing aluminum alloys, with which aluminum strips can be produced for lithographic printing plate supports with high quality and at the same time the costs can be reduced.

According to a first teaching of the present invention, the above-described object is achieved for a process for producing an aluminum strip for lithographic printing plate support that during cold rolling of the hot strip, the product of the relative end thicknesses of the aluminum strip after the first and after the second cold rolling pass of the aluminum strip 17% 22%.

Das Produkt P der relativen Enddicken b₁ und b₂ des ersten und zweiten Kaltwalzstiches ergibt dann die relative Enddicke im Verhältnis zur Ausgangsdicke vor beiden Kaltwalzstichen und damit ein Maß für die Dickenabnahme des Aluminiumbandes innerhalb der ersten beiden Kaltwalzstiche im Verhältnis zur Ausgangsdicke des Aluminiumbandes vor dem Kaltwalzen gemäß: $$P=b_1\cdot b_2=\left(100\%-a_1\right)\cdot \left(100\%-a_2\right),$$

wobei a₁ und a₂ jeweils der Stichabnahme des ersten bzw. zweiten Kaltwalzstiches in Prozent sind.In the present case, the relative final thickness (b) after a cold rolling pass is the thickness of the aluminum strip after a cold rolling pass in relation to the starting thickness before the cold rolling pass in percent, ie the quotient of resulting thickness and initial thickness. The relative final thickness results from the reduction in the number a of the respective cold rolling pass, which is also given in percent, as follows: $${\mathrm{b}}_1=100\%-{\mathrm{a}}_1,$$

The product P of the relative end thicknesses b ₁ and b _{2 of} the first and second cold rolling passes then the relative final thickness in relation to the initial thickness before both cold rolling passes and thus a measure of the thickness decrease of the aluminum strip within the first two cold rolling passes in relation to the starting thickness of the aluminum strip before Cold rolling according to: $$P=b_1\cdot b_2=\left(100\%-a_1\right)\cdot \left(100\%-a_2\right).$$

where a ₁ and a _{2 are} respectively the percent reduction of the first and second cold rolling pass in percent.

• Abwickeln des Aluminiumbandes von einem Coil mit einem Abwickelhaspel,
• Walzen des Aluminiumbandes unter Verwendung eines Walzgerüstes mit einem einzigen Kaltwalzstich und
• Aufwickeln des kaltgewalzten Aluminiumbandes.

The optimization of the first two cold rolling passes, so that the product P of the relative final thicknesses after the first and after the second cold rolling pass between 17% and 22%, has shown that the targeted selection of higher Stichiefnahmen in the first and / or second cold roll pass the thickness decrease The aluminum strip in the first two cold rolling passes opens up the possibility of saving a complete cold rolling pass in the production process. Surprisingly, it was found that the surface quality still delivers acceptable results in terms of streakiness despite the higher stitch reductions and thus a cold rolling pass can be reliably saved. This result relates to the production of litho ribbons, which previously required three, four or five cold rolling passes due to the hot strip thickness and the final thickness after cold rolling. Thus, a method for producing an aluminum strip for lithographic printing plate supports can be provided, which enables a reduction in manufacturing costs. Although the reduction in production costs also occurs in a rolling stand with multiple stitches decreases due to a reduced number of cold rolls to be used in the framework. However, the economic effect is greater when using a mill stand with exactly one cold roll pass. These mills are, as already stated, usually during cold rolling of aluminum strips used to achieve very high surface qualities. In this case, the hot-rolled aluminum strip preferably passes through the following steps in compliance with the specification for the product of the first two cold-rolling passes:

• Unwinding the aluminum strip from a coil with an uncoiler,
• Rolling of the aluminum strip using a rolling stand with a single cold rolling pass and
• Winding up the cold-rolled aluminum strip.

A preferred embodiment of the method according to the invention is provided by the fact that during cold rolling of the hot strip, the product of the relative final thicknesses of the aluminum strip after the first and after the second cold roll pass is preferably 17% to 20%. This achieves a good compromise with regard to process reliability for providing high surface qualities and the possibility of saving a cold roll pass.

The production of an aluminum strip with a final thickness of 0.1 mm to 0.5 mm after cold rolling can be achieved according to a further embodiment of the method in two or three cold rolling passes, when the hot strip thickness from 2.3 mm to 3.7 mm, preferably 2 , 5 mm to 3.0 mm. Below 2.3 mm there is a risk that during hot strip production the hot strip may collapse during winding. Above 3.7 mm Hot Strip Thickness, excessively high passes for the first or second cold roll pass must be selected to reduce the number of cold rolling passes. Too high a choice of cold rolling pick-up is not only the risk of surface defects on the aluminum strip, but also the risk of damage to the cold roll itself. A hot strip thickness of 2.5 mm to 3.0 mm prevents both the collapse of the hot strip and the use Too high Stichabtnahmen during cold rolling.

In order to reliably achieve the relative end thicknesses of the aluminum strip of 17% to 22% within the first two cold rolling passes while avoiding surface defects and dangers for the cold roll According to a further embodiment of the method during cold rolling, preferably the first cold rolling pass is carried out with a maximum reduction of 65%, preferably with a maximum of 60%. It has been found that above a 65% reduction in the first cold roll pass after hot rolling the risk of surface defects increases significantly. At a maximum of 60% reduction in the first cold roll pass, even more homogeneous surfaces in the aluminum strip are preferably achieved.

With regard to the second cold roll pass, it was found that this preferably has a maximum reduction of 60% in order to reliably avoid corresponding errors in the end product process. The second cold rolling pass is therefore to be assessed more critically with regard to the surface quality.

Both the first and the second cold roll pass preferably have more than 50% reduction in stitches, since this can better distribute the stitch decreases to achieve the desired relative final thicknesses on both cold roll passes. Overall, then in both cold rolling passes no maximum Stichabnahmen necessary.

According to a further embodiment of the method according to the invention, three cold rolling passes are made to final thickness, wherein the final thickness of the aluminum strip after cold rolling is 0.2 mm to 0.4 mm. So far, at least four cold rolling passes have been required for these final thicknesses. In particular, for end thicknesses of 0.2 mm to 0.4 mm, such a method can be provided, which in addition to an adequate surface quality has reduced costs.

Preferably, according to a further embodiment of the method according to the invention, four cold rolling passes are carried out at final thickness, the final thickness of the aluminum strip after cold rolling being less than 0.2 mm. For tapes for lithographic printing plate supports with final thicknesses of 0.1 mm to less than 0.2 mm So far, five cold rolling passes have been required. Again, the inventive method can contribute to cost reduction.

Another potential in terms of saving on manufacturing costs can be achieved in that no intermediate annealing is performed during cold rolling. It has been found that, despite the saving of a cold rolling pass, aluminum strips in state H19 can be provided whose surface quality and also the other mechanical properties are sufficient for the production of lithographic printing plate supports. As an alternative to the production of aluminum strips in state H19, aluminum strips with intermediate annealing in state H18 can also be produced according to the invention.

The third or fourth cold rolling pass, preferably the last cold rolling pass of the cold rolling, preferably has a maximum stitch loss of 52%, so that the third or fourth or last cold roll pass affecting the surface has as little influence as possible on the surface quality of the aluminum strip.

• 0,05 % ≤ Si ≤ 0,25 %,
• 0,2 % ≤ Fe ≤ 1 %, bevorzugt 0,3 % ≤ Fe ≤ 1 %, besonders bevorzugt 0,3 % ≤ Fe ≤ 0,6 % oder 0,4 % ≤ Fe ≤ 0,6 %,
• Cu maximal 400 ppm, bevorzugt maximal 100 ppm,
• Mn ≤ 0,30 %, optional 30 ppm bis 800 ppm,
• 0,10 % ≤ Mg ≤ 0,50 %, 0,15 % ≤ Mg ≤ 0,45 %, bevorzugt 0,24 % ≤ Mg ≤ 0,45 %,
• Cr maximal 100 ppm, bevorzugt maximal 50 ppm
• Zn ≤0,05 %, bevorzugt 50 ppm bis 250 ppm
• Ti < 0,030 %,
• Rest Al und unvermeidbare Verunreinigungen einzeln maximal 0,03 %, in Summe maximal 0,15 %.

The cost-effective production method is carried out according to the invention with an aluminum strip consisting of an aluminum alloy with the following alloy constituents in% by weight:

• 0.05% ≦ Si ≦ 0.25%,
• 0.2% ≦ Fe ≦ 1%, preferably 0.3% ≦ Fe ≦ 1%, particularly preferably 0.3% ≦ Fe ≦ 0.6% or 0.4% ≦ Fe ≦ 0.6%,
• Cu maximally 400 ppm, preferably maximally 100 ppm,
• Mn ≤ 0.30%, optionally 30 ppm to 800 ppm,
• 0.10% ≤ Mg ≤ 0.50%, 0.15% ≤ Mg ≤ 0.45%, preferably 0.24% ≤ Mg ≤ 0.45%,
• Cr at most 100 ppm, preferably at most 50 ppm
• Zn ≤ 0.05%, preferably 50 ppm to 250 ppm
• Ti <0.030%,
• Residual Al and unavoidable impurities individually max. 0.03%, in total max. 0.15%.

It has been found that aluminum tapes with the specified aluminum alloy composition are particularly suitable for the process according to the invention. Experiments within the alloy specification have shown that when using the method according to the invention a sufficiently good surface can be provided, which does not tend to streakiness and yet a cold rolling pass can be saved. It is believed that this result is due, inter alia, to the overall combination of alloy composition. The selected range of the alloying constituent silicon, from 0.05% by weight to 0.25% by weight, ensures in electrochemical roughening that a high number of sufficiently deep depressions can be introduced into the aluminum strip, which ensure optimum absorption of the photosensitive layer , The iron content of 0.2% ≦ Fe ≦ 1%, preferably 0.3% ≦ Fe ≦ 1%, particularly preferably 0.3% ≦ Fe ≦ 0.6% or 0.4% ≦ Fe ≦ 0.6%, provides in combination, in particular with the manganese content to a maximum of 0.30 wt .-% for a heat-resistant aluminum alloy, which after baking the photosensitive layer has only a small decrease in strength with respect to yield strength and tensile strength. The copper content of at most 400 ppm, preferably at most 100 ppm, particularly preferably at most 50 ppm, is particularly low, since copper has a negative effect on the roughening behavior of the aluminum strip. The preferred manganese content of up to 0.30 wt .-%, preferably 30 ppm to 800 ppm, ensures, as already stated, in combination with the iron content improved heat resistance of the aluminum strip after baking and positively influences the flexural fatigue resistance of the aluminum strip. Magnesium contents of 0.10 wt .-% to 0.5 wt .-%, preferably 0.15 wt .-% to 0.45 wt .-%, particularly preferably from 0.24 wt .-% to 0.45 wt .-% lead to an increase in strength during cold rolling due to work hardening and also offer the advantage of good bending fatigue resistance even in the hard-rolled state. In addition, the aluminum alloy preferably has almost no chromium. The chromium content is limited to a maximum of 100 ppm, preferably a maximum of 50 ppm. Higher chromium contents have been found to be negative for the roughening properties of the aluminum strip during electrochemical roughening. Zinc lowers the electrochemical potential of the aluminum alloys of the aluminum strip so that the electrochemical roughening is accelerated. Zinc is therefore present in the aluminum alloy at a level of up to a maximum of 500 ppm. Higher zinc contents in turn negatively influence the roughening properties of the aluminum strip. The presence of zinc with a content of 50 ppm to 250 ppm reliably leads to an accelerated roughening of the aluminum strip without negative effects on the surface. The aluminum strip according to the invention is moreover almost free of titanium. It contains less than 0.030% by weight of titanium, which negatively influences the properties of the aluminum alloys during electrochemical roughening above the stated limit value. In addition, in the aluminum alloy additionally unavoidable impurities to a maximum of 0.03 wt .-% and a maximum of 0.15 wt .-% may be present without affecting the properties of the aluminum alloy strip in the given manufacturing process negative.

If the aluminum alloy according to a next embodiment has a magnesium content of 0.26% to 0.35% by weight, a very good compromise can be achieved from improved fatigue strength properties of the printing plate supports, good roughening behavior and reduced production costs.

Fig. 1

in einer schematischen Ansicht die grundsätzlichen Verfahrensschritte zur Herstellung eines Aluminiumband es für lithografische Druckplattenträger,

Fig. 2

in einer schematischen Schnittansicht die Durchführung eines Kaltwalzstiches mit einem oder mehreren Kaltwalzstichen und

Fig. 3a)-3c)

ein Vergleich von REM-Aufnahmen von als gut bewerteten und schlecht bewerteten Oberflächenbereichen eines Aluminiumbandes für lithografische Druckplattenträger.

The invention will now be explained in more detail with reference to embodiments in conjunction with the drawings. The drawing shows in

Fig. 1

1 is a schematic view of the basic process steps for producing an aluminum strip for lithographic printing plate supports,

Fig. 2

in a schematic sectional view of the implementation of a cold rolling pass with one or more cold rolling passes and

Fig. 3a) -3c)

a comparison of SEM images of well-evaluated and poorly-scored surface areas of an aluminum strip for lithographic printing plate supports.

First shows Fig. 1 schematically the various process steps in the production of an aluminum strip for lithographic printing plate support. First, according to step 1, the aluminum alloy is poured into a rolling ingot. The ingot is subjected to homogenization in step 2, wherein the ingot is heated to temperatures of 450 ° C to 600 ° C with a residence time of at least 1 hour. The homogenised ingot is prepared for hot rolling and then hot rolled at temperatures in excess of 280 ° C. At the beginning of hot rolling, the temperature of the billet is about 450 ° C to 550 ° C. The hot rolling end temperature is usually 280 ° C to 350 ° C. The hot strip thicknesses can be between 2 mm and 9 mm, but preference is given to hot strip thicknesses of 2.3 mm to 3.7 mm. The hot strip is fed to cold rolling in step 4. During cold rolling, the hot strip is cold rolled to final thickness. Cold rolling, and in particular the last cold rolling pass, determines the surface properties of the cold rolled aluminum strip, as the surface topography of the cold roll is transferred directly to the cold rolled aluminum strip. During the rolling pass, errors can occur during cold rolling which are then transferred to the surface or remain directly visible on the surface. Due to this fact, so far only moderate Stichabnahmen of a maximum of 50% were provided for each cold rolling steps, since it is known that too high a stitch loss either the risk of damage to the cold rolls or areas are broken out of the surface of the aluminum strip, so that surface defects. With regard to the high demands on the homogeneity of the surface of lithographic printing plate supports, inhomogeneous, for example, striped surfaces can not be accepted.

The cold rolling according to step 4 can take place both with and without intermediate annealing. The intermediate annealing is carried out at temperatures of 230 ° C to 490 ° C for at least 1 h in the chamber furnace or continuously in the continuous strip furnace for at least 10 s, usually before the last cold rolling pass. The intermediate annealing can be used to set the final strength of the aluminum strip for lithographic printing plate supports in certain areas before the last cold-rolled pass. However, the intermediate annealing also causes costs, so that a particularly cost-efficient production is preferably carried out without intermediate annealing.

Usually, cold rolling uses rolling stands which perform a single cold rolling pass and the aluminum strip is rewound immediately after the cold rolling pass. Fig. 2 shows a corresponding rolling stand 5, which comprises a take-off reel 6, a take-up reel 7 and a roller assembly 11 with two work rolls 9 and 10. Fig. 2 shows an example of a four-high rolling stand. However, the roller arrangements can be designed both as a duo, quarto or sexto rolling stand. Also indicated is an additional roller assembly 11 ', so that the belt 8 after passing through the roller assembly 11 in the roller assembly 11' is subjected to a further rolling pass, so a total of a multiple stitch. Usually, however, as already stated, carried out individual cold rolling passes and the aluminum strip 8 then wound on the take-up reel 7 to form a coil. Optionally, after cooling the aluminum strip 8 in the coil after the cold rolling pass, the aluminum strip can be fed again to a cold rolling pass.

In the FIGS. 3a) to 3c ) are shown scanning electron micrographs of cold rolled aluminum strips for lithographic printing plate supports. Fig. 3a ) shows at identical magnification Fig. 3b ) a band regarded as inconspicuous from the surface. Clearly, the roll bars can be recognized by the ground rolls, which have been pressed in the aluminum strip. Perpendicular to Rolling direction, however, hardly any structures exist, so that the overall impression of the surface is classified as non-streaky.

The FIGS. 3b) and 3c ) show, on the other hand, a surface area of an aluminum strip classified as non-homogeneous which results in a streaky appearance of the aluminum strip. A corresponding tape would not meet the surface requirements of lithographic printing plate supports. FIGS. 3b) and 3c ) show surface defects, especially magnified in Figure 3c ), which has transversely extending to the rolling direction areas in which material has been lifted from the surface of the belt. It is believed that this error is due to cold rolling. The width of the problematic area is about 20 μm perpendicular to the rolling direction and is visible on visual inspection.

Aluminum ribbons of six different aluminum alloys A to H have now been applied using the methods discussed above and in US Pat Fig. 1 produced process steps 1 to 3. The aluminum strips were produced without intermediate annealing during cold rolling, whereby the hot strip thickness and the number of passes during cold rolling were varied. The aluminum alloys differ in particular in different contents in the range of silicon, iron, manganese and magnesium. The various alloy compositions are shown in Table 1 with their weight percent alloying ingredients. In addition, all of the alloys containing chromium less than 50 ppm and unavoidable impurities individually contained a maximum of 0.03 wt% and a maximum of 0.15 wt%. Table 1 alloy Si Fe Cu Mn mg Zn Ti in% by weight A 0.092 0.438 0.0019 0,039 0,262 0.0114 0.0051 B 0.084 0,420 0.0019 0,255 0.244 0.0124 0.0051 C 0.077 0,435 0.0018 0,040 0.264 0.0093 0.0072 D 0,128 0,429 0.0016 0,040 0.285 0.0087 0.0068 e 0.085 0.374 0.0016 0,003 0.196 0.0090 0.0050 F 0.116 0.438 0.0015 0,040 0,324 0.0136 0.0075 G 0,119 0.436 0.0010 0,040 0.323 0.0137 0.0058 H 0.085 0.374 0.0016 0,003 0.196 0.0090 0.0050

The hot strip thickness of the aluminum strips produced was varied from 2.3 mm to 3.0 mm and produced from the different thickness hot strips aluminum strips for lithographic printing plate support by cold rolling without intermediate annealing with a final thickness of 0.274 mm to 0.285 mm. The first and second cold rolling passes were selected so that a maximum of three cold rolling passes of final thickness were required starting from the final hot strip thickness, with the last cold roll pass having a maximum stitch loss of 51%. As shown in Table 2, the product P of the relative final thicknesses after the first and after the second cold-rolled passes is 18.57% to 21.74% due to the reduction in the first two cold-rolling passes. That is, through the first two cold rolling passes, the strip was rolled to an intermediate thickness of 18.57% to 21.74% of the final hot strip thickness.

Table 2 shows the embodiments according to the invention and the associated stitching decreases and the values for the product of the relative final thicknesses after the first and second cold rolling passes. Table 2 No Leg. Hot strip end thickness [mm] 1st KW stitch (a1) [%] 2nd KW stitch (a2) [%] Produces P [%] 3rd KW stitch [%] Final thickness [mm] 1 A 2.3 57 50 21.74 45 0,275 2 B 2.3 57 50 21.74 45 0,275 3 C 2.8 57 53 20.00 51 0.274 4 C 2.8 57 53 20.00 51 0.274 5 C 2.8 57 53 20.00 51 0.274 6 D 2.8 57 53 20.00 51 0.274 7 D 2.8 57 53 20.00 51 0.274 8th D 2.8 57 53 20.00 51 0.274 9 D 2.8 57 53 20.00 51 0.274 10 e 2.8 50 60 20.00 51 0,275 11 F 2.8 64 48 18.57 45 0.285 12 F 2.8 64 48 18.57 45 0.285 13 G 2.8 64 48 18.57 45 0.285 14 G 2.8 64 48 18.57 45 0.285 15 H 3.0 60 53 18.67 51 0,275

In order to investigate the surfaces in terms of their suitability for lithographic printing plate supports, two tests were developed to evaluate the streakiness of the surfaces of the cold rolled aluminum strips. The Test procedures serve to emphasize possible streaking errors by means of a surface repair and to be able to recognize them visually better.

In the so-called "K-test", the grain stringency of the aluminum alloy strips is examined. For this purpose, the surfaces must be prepared specifically to expose the grain structure. First, 250 mm long and 45 mm wide, rectangular samples are cut out of the bands in the rolling direction. The samples are taken in relation to the rolling direction both at the edge and in the middle of the bands. The K-test is intended to reveal whether, due to the grain distribution, a stiffness effect can be recognized in the surface.

• 400 ml Wasser,
• 300 ml HCl mit einer Konzentration von 37 %,
• 133,6 ml HNO₃ mit 65-% Konzentration sowie
• 43,34 ml 40-% Flusssäure.

The samples thus cut are first sanded for 60 seconds with an orbital sander, the orbital sander being wrapped with a damp cloth and scouring milk used to polish the samples. As a scouring cream, a simple household scrub milk can be used here. After rinsing the surface with water, the samples are immersed in 30% sodium hydroxide at a temperature of 60 ° C for 15 seconds and then rinsed with water. Then a macroetching takes place in a macroetching solution. This consists of

• 400 ml of water,
• 300 ml HCl with a concentration of 37%,
• 133.6 ml of HNO ₃ with 65% concentration as well
• 43.34 ml of 40% hydrofluoric acid.

The macroetching takes place at about 25-30 ° C for 30 seconds. It is then rinsed again with water and the sample immersed for 15 seconds again in 30% sodium hydroxide solution at a temperature of 60 ° C. A final neutralization is carried out with a solution of 40.5 ml of 85 percent phosphoric acid and 900 ml of water at room temperature for about 60 seconds. The sample is then rinsed with water and dried at room temperature. After drying, the samples are visually evaluated for streakiness. Reference samples with Numbers from 1 to 10 are used to determine streakiness in the K test. There is a comparison between the reference pattern and the sample with the human eye. Subsequently, the samples are assigned the value numbers of the most similar reference patterns. The value 10 stands here for non-streaky. The value 1 corresponds to a striped appearance. This streakiness is, as already stated, caused by the grain distribution of the aluminum strips and can be evaluated well with this test.

As can be seen from Table 3, although the embodiments with high 64% reduction in the first cold roll pass show good values with respect to the value of the K test. Overall, their surface is slightly worse than that of the embodiments with lower Stichiefnahmen in the first cold roll pass.

It was found that in addition to the established K-test, a further test must be used, as in particular the surface defects due to cold rolling, shown in the FIGS. 3b) and 3c ) are obviously not covered by the previous K-test. This is shown by the results of the newly developed test.

An additional pickling test was developed. As a sample, a rectangular blank with 250 mm edge length in the rolling direction and 80 mm edge length is used perpendicular to the rolling direction, which is first subjected to degreasing in aqueous solution with a degreasing medium, here with the brand name Nabuclean 60S at 60 ° C for 10 seconds. The concentration of the degreasing medium is 15 g / l. After rinsing with water, the sample is immersed in a caustic soda solution and etched at 50 ° C for about 10 seconds. The sodium hydroxide solution is 50 g / l. Subsequently, a rinse with water and drying in a drying oven at about 70 ° C are performed. After drying, the samples are evaluated, also using reference samples, each of which is assigned values from 0 to 5, with the value 0 of one rated as non-streaky and the value 5 of one as is assigned to a striped evaluated surface. In the pickling test, the samples were compared and evaluated with reference samples before and after pickling.

Surfaces with the value 5 in the pickling test were not found. In Runs 11 to 14, a cold rolling pass of 64% was used in the first cold roll pass, which has a significant effect on the surface quality when evaluating the samples in the pickling test both prior to the pickling test and after pickling. Compared to the lower numbered tests Nos. 1 to 10, tests 11 to 14 in the pickling test show results with the numbers 3-4 and 3. These indicate a poorer surface quality in this test. Reductions of 65% in the first cold roll pass are therefore to be regarded as maximum. An increase in addition, according to the current state of knowledge leads to significant disadvantages in terms of surface quality.

All other samples showed values of 2-3 or 3 after the pickling test and thus sufficiently good surface qualities. This means that the surface quality in the pickling test increases at lower picking rates in the first cold-rolled pass. In general, it was shown that in spite of a cold rolling pass, a reduction of 60% in the first and in the second cold rolling pass achieved good surfaces in the pickling test.

It could thus be shown for various magnesium-containing aluminum alloys at different hot strip thicknesses that a cold rolling pass can be saved in the production of cold-rolled aluminum strips for lithographic printing plate supports without excessively influencing the surface quality. As a result, a production path can be made available, which can provide less expensive aluminum strips for lithographic printing plate supports while saving a cold rolling pass. Table 3 No alloy K test Beiztest edge center in front to 1 A 5 3 - 4 1 2 - 3 2 B 4 - 5 4 1 3 3 C 2 - 3 2 1 2 - 3 4 C 2 - 3 2 - 3 2 2 - 3 5 C 3 3 0 3 6 D 3 - 4 3 2 2-3 7 D 2 - 3 3 2 2 - 3 8th D 3 3 - 4 0 3 9 D 4 3 - 4 0 2 - 3 10 e 5 1 - 2 1 - 2 2 - 3 11 F 7 3 - 4 3 3 12 F 6 - 7 4 3 3 13 G 7 4 - 5 2 3 - 4 14 G 7 4 - 5 3 2 - 3 15 H 5 - 6 2 1 - 2 2 - 3

Claims (10)

1. Method for production of an aluminium strip for lithographic printing plate supports from an aluminium alloy, wherein the aluminium alloy of the aluminium strip for lithographic printing plate supports comprises the following alloy constituents in % by weight:

   0.05% ≤ Si ≤ 0.25%,

   0.2% ≤ Fe ≤ 1%,

   Cu max. 400 ppm,

   Mn ≤ 0.30%,

   0.10% ≤ Mg ≤ 0.50%,

   Cr ≤ 100 ppm,

   Zn ≤ 500 ppm,

   Ti < 0.030%,

   the remainder aluminium and unavoidable impurities individually at most 0.03%, in total at most 0.15%, with at least the following steps:

   - casting of a rolling ingot from an aluminium alloy,

   - homogenising of the rolling ingot,

   - hot rolling of the rolling ingot to a hot strip thickness, and

   - cold rolling of the hot strip to final thickness,

   wherein the final thickness of the aluminium strip after cold rolling is between 0.1 mm and 0.5 mm,

   characterised in that

   on cold rolling, the product (P) of the relative final thicknesses (b₁, b₂) of the aluminium strip from the first and second cold rolling pass is 17% to 22%.
2. Method according to claim 1,
   characterised in that
   the hot strip final thickness is 2.3 mm to 3.7 mm, preferably 2.5 mm to 3.0 mm.
3. Method according to claim 1 or 2,
   characterised in that
   on cold rolling, the first cold rolling pass is carried out with a pass reduction of maximum 65%.
4. Method according to any of claims 1 to 3,
   characterised in that
   the second cold rolling pass has a pass reduction of maximum 60%.
5. Method according to any of claims 1 to 4,
   characterised in that
   three cold rolling passes to final thickness are performed, and the final thickness of the aluminium strip after cold rolling is 0.2 mm to 0.4 mm.
6. Method according to any of claims 1 to 5,
   characterised in that
   four cold rolling passes to final thickness are performed, and the final thickness of the aluminium strip after cold rolling is less than 0.2 mm.
7. Method according to any of claims 1 to 6,
   characterised in that
   during cold rolling, no intermediate annealing is performed.
8. Method according to any of claims 1 to 7,
   characterised in that
   the third or fourth cold rolling pass has a maximum pass reduction of 52%.
9. Method according to any of claims 1 to 8,
   characterised in that
   the aluminium alloy of the aluminium strip for lithographic printing plate supports has a magnesium content of 0.15% ≤ Mg ≤ 0.45%.
10. Method according to any of claims 1 to 9,
    characterised in that
    the aluminium alloy of the aluminium strip for lithographic printing plate supports has a magnesium content of 0.24% to 0.45% by weight, preferably 0.26% to 0.35% by weight.

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