EP2220262B1 - Aluminium strip for lithographic pressure plate carriers and its manufacture - Google Patents

Description

The invention relates to a process for producing aluminum strips for lithographic printing plate supports, wherein the aluminum strip is produced from a rolling bar, which after optional homogenization hot rolled to a thickness of 2 mm to 7 mm and to a final thickness of 0.15 mm to 0.5 mm cold rolled. In addition, the invention relates to a correspondingly produced aluminum strip having a thickness of 0.15 mm to 0.5 mm and a pressure plate carrier made of the aluminum strip according to the invention.

Very high demands are placed on the quality of aluminum strips for the production of lithographic printing plate carriers. The aluminum strip for the production of lithographic printing plate supports is usually subjected to an electrochemical roughening, which should result in a blanket roughening and a structureless appearance without streaking effects. The roughened structure is important for applying a photosensitive layer, which is subsequently exposed. The photo-layer is baked at temperatures of 220 ° C to 300 ° C and annealing times of 3 to 10 minutes, typical combinations of burn-in times being for example 240 ° C at 10 minutes, 260 ° C at 6 minutes and 260 ° C for 4 minutes. The pressure plate carrier must after burning as possible lose little strength, so that it is still easy to handle and can be easily clamped in a printing device. At the same time, the printing plate support and thus also the correspondingly produced aluminum strip must have the highest possible flexural fatigue strength, so that plate outlier can be virtually eliminated due to mechanical stresses on the printing plate. So far, these requirements have been well met with conventional aluminum strips. To increase productivity but printing presses are increasingly used, which require that the printing plate supports are clamped so that they are bent transversely to the rolling direction and therefore mechanically loaded transversely to the rolling direction. At the same time, the handling of large lithographic printing plate supports becomes more difficult with increasing size and consistent strength values.

For example, from the Applicant's European patent EP 1 065 071 B1 a ribbon for the production of lithographic printing plate supports known, which is characterized by a good aufraubarkeit combined with a high 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 required pressure plate carrier, however, the need has arisen to further improve the properties of the known aluminum alloy and the lithographic printing plate carrier produced therefrom. A simple increase in tensile strength, for example, by a change in the aluminum alloy is possible, did not lead to the desired result, since at high tensile strength, the correction of the coil set of the aluminum strip was difficult. This is usually carried out in the hard-rolling state before the baking process.

Proceeding from this, the present invention has the object to provide a method for producing an aluminum strip for lithographic printing plate support and a corresponding aluminum strip available from which also oversized printing plate support can be produced, which are easy to handle and show only a slight tendency to Plattenreißern.

The invention is specified in the claims.

According to a first teaching of the present invention, the above-described object is procedurally achieved in that the aluminum strip consists of an aluminum alloy with the following alloy constituents in percent by weight: 0.3% ≤ Fe ≤ 0.4%, 0.4% ≤ mg ≤ 1.0%, 0.05% ≤ Si ≤ 0.25%, Mn ≤ 0.1%, optionally Mn ≤ 0.05%, Cu ≤ 0.04%,

Residual Al and unavoidable impurities, individually max. 0.05%, in total max. 0.15%, during the cold rolling an intermediate annealing is carried out at a thickness of 1.5 mm to 0.5 mm, the aluminum strip is then rolled by cold rolling to a final thickness of 0.15 mm to 0.5 mm and for further processing to one lithographic printing plate support is rolled up in hard-rolled condition.

The aluminum strip produced according to the invention provides a moderate increase in strength together with a very high flexural fatigue resistance and at the same time very good thermal stability. Coilset corrections are possible without difficulty due to the moderate increase in strength. At the same time, however, the handling of the printing plate even in a baked state, for example when clamping in the printing press, is simple, since a good thermal stability of the aluminum strip is obtained by the method according to the invention. If the aluminum strip is used for the production of very large lithographic printing plate supports, preferably the aluminum strip is cold rolled to a final thickness of 0.25 to 0.5 mm after the intermediate annealing. The particular suitability of the aluminum strips for oversized lithographic printing plate supports produced by the process according to the invention results from the fact that higher strengths and bending resistance are made available due to the low degrees of rolling and the increased magnesium content, which simplify the handling and enables an improved service life of the printing plate supports. Manganese contributes to thermal stability in the alloy. However, in combination with the other alloying constituents, in particular the magnesium fractions, at a content of more than 0.1% by weight, problems of roughening were found. If the manganese content does not exceed 0.05% by weight, a good compromise between thermal stability and roughening properties will be found reached.

According to a first embodiment of the method according to the invention, the aluminum alloy has an Mg content of from 0.4% by weight to 1.0% by weight, preferably from 0.6% by weight to 1% by weight. The high to very high Mg contents of the aluminum alloy for the production of lithographic printing plate supports result in a significantly increased flexural fatigue resistance of the produced printing plate supports transversely to the rolling direction. At the same time, contrary to the expectations of the experts, there were no problems with the roughening of the strips produced from a corresponding aluminum alloy. Higher Mg contents make it possible to reduce the degrees of finish after the intermediate annealing while at the same time maintaining or increasing the tensile strength values, in particular also transversely to the rolling direction.

If the aluminum alloy according to a next alternative embodiment of the present invention has a Mg content of from 0.4% by weight to 0.6% by weight, good strength values with high flexural fatigue resistance can be provided. This is especially true at a Mg content of 0.4 wt .-% to 0.6 wt .-%.

According to one embodiment of the present invention, the properties according to the invention can be achieved particularly reliably in that the aluminum alloy additionally has a titanium (Ti) content of max. 0.05% by weight, preferably max. 0.015 wt .-%, a zinc (Zn) content of max. 0.05 wt .-% and a chromium (Cr) content of less than 100 ppm, preferably a Cr content by Max. 50 ppm. Titanium is commonly used for grain refining during casting. However, an increased Ti content leads to casting problems. Zinc affects the Aufraubarkeit, so that its content max. Should be 0.05 wt .-%. Typical problems arise with increased Zn content due to inhomogeneities in the roughening of lithographic printing plate supports. Chromium is recrystallization inhibiting and should therefore only in very small proportions of less than 100 ppm, preferably of max. 50 ppm contained in the aluminum alloy.

By setting the hot rolling temperatures in the range of 250 ° C to 550 ° C, the hot strip end temperature is 280 ° C to 350 ° C, a continuous recrystallization of the surface is achieved during hot rolling, which, for example, a good Aufraubarkeit the wall surface during the production of lithographic Pressure plate carrier guaranteed.

Preferably, during the intermediate annealing, the metal temperature of the aluminum strip is 200 ° C to 450 ° C. The aluminum strip is then held at the metal temperature for at least one to two hours. This is usually done in batch ovens. Due to the intermediate annealing in the temperature range mentioned, the further processing of the aluminum strip can take place either in a recovered or recrystallized state or a combination of both. The recrystallization starts at temperatures of about 300 to 350 ° C, which depends on the manufacturing parameters, in particular the introduced solidifications. By a recovery annealing at lower temperatures, however, only a reduction of the solidifications can be achieved, so that very low degrees of rolling are possible after the recovery annealing. However, depending on the respective degrees of rolling after the intermediate annealing and the alloy composition, it may also be necessary to perform recrystallization annealing as an intermediate annealing.

According to a second teaching of the present invention, the object indicated above is achieved by a generic aluminum strip for the production of lithographic printing plate supports, which consists of an aluminum alloy with the following alloy constituents in% by weight: 0.3% ≤ Fe ≤ 0.4%, 0.4% ≤ mg ≤ 1.0%, 0.05% ≤ Si ≤ 0.25%, Mn ≤ 0.1%, optionally Mn ≤ 0.05%, Cu ≤ 0.04%,

Residual Al and unavoidable impurities, individually max. 0.05%, in total max. 0.15%;
the aluminum strip has a bending fatigue resistance transverse to the rolling direction of at least 1850 cycles in the bending cycle test.

In the Biegewechselnest a strip is cut out of the aluminum strip and bent back and forth between two cylindrical segments with a radius of 30 mm. In contrast to the aluminum strips produced so far for lithographic printing plate supports, the aluminum strips according to the invention after a burn-in process achieve bending cycle cycles of more than 1850, also transversely to the rolling direction, which is an increase over the previously used standard alloys of over 70% means. In addition, the high number of possible bending cycles of more than 1850 in both the hard and the fired state of the aluminum strip according to the invention shows that the tendency for plate breakers due to mechanical stresses in lithographic printing plate carrier clamped transversely or longitudinally to the rolling direction is low.

The aluminum strips preferably have a tensile strength of up to 200 MPa measured in the hard-rolling state along the rolling direction, so that the coil set of the aluminum strip according to the invention can furthermore be corrected in a simple manner. When paired, the increase in tensile strength values is preferably with good thermal stability, which is exhibited by a tensile strength of at least 145 MPa after a bake along or across the rolling direction. The handling of the lithographic printing plate supports made from the aluminum strip is also good after a baking process. Even with very large lithographic printing plate supports can be facilitated by the increased strength after baking, the handling of the printing plates. At elevated Mg contents, the tensile strength values up to a maximum of 200 MPa in a hard-hard condition can be achieved by reducing the intermediate annealing thickness, which is then, for example, less than 1.1 mm. The flexural fatigue resistance is not affected by this.

An aluminum strip with an Mg content of 0.4% by weight to 0.6% by weight, allows sufficiently high tensile strength values to be provided in the hard-to-roll state, since, for example, the required strength values for aluminum strip are achieved even at low degrees of rolling after the intermediate annealing. Aluminum tapes with an Mg content of 0.4% by weight to 0.6% by weight show a further increase in flexural fatigue resistance transverse to the rolling direction with consistent properties with regard to roughening properties and improved tensile properties.

An alternative embodiment of the aluminum strip according to the invention has an Mg content of from 0.4% by weight to 1.0% by weight, preferably from 0.6% by weight to 1.0% by weight. Aluminum strips with these increased Mg contents are characterized by an exceptionally good flexural fatigue resistance transverse to the rolling direction and, contrary to the expectations of the experts, do not tend to streak during roughening. Only the intermediate annealing thickness must be adjusted to achieve optimum tensile strength values of less than 200 MPa with maximum flex life properties.

According to a further embodiment of the aluminum strip according to the invention, the properties of the finished aluminum strip are thereby achieved process reliable, that the aluminum alloy has a Ti content of max. 0.05% by weight, preferably max. 0.015 wt .-%, a Zn content of max. 0.05 wt .-% and a Cr content of less than 100 ppm, preferably of max. 10 ppm.

From aluminum strips with a thickness of 0.25 to 0.5 mm, according to a last embodiment of the aluminum ribbon according to the invention made especially good oversized printing plate support and processed and handled in a simple manner.

According to a third teaching of the present invention, the object indicated above is achieved by pressure plate carriers which are produced from an aluminum strip according to the invention. With regard to the advantages of the pressure plate carrier according to the invention, reference is made to the above statements on the method for producing an aluminum strip and the aluminum strip according to the invention.

There are now a variety of ways to further develop and design the inventive method for producing aluminum strips for lithographic printing plate support, the aluminum strip for lithographic printing plate support and the printing plate support itself. Reference is made on the one hand to the claims subordinate to patent claims 1 and 4 and to the description of exemplary embodiments in conjunction with the drawing. In the drawing, the single figure shows a schematic representation of the bending cycle test for testing the bending fatigue resistance.

A comparison between a conventional aluminum strip for the production of lithographic printing plate supports and two aluminum strips according to the invention and a comparison aluminum strip, which are likewise suitable for the production of lithographic printing plate supports, is shown below. The Alloy components of the different aluminum tapes tested are set forth in Table 1. Table 1 Leg . No. Fe Mn mg Si Cu /Gew.-% Vref 0.32 - 0.17 0.12 7 ppm State of the art VF583 0.3 0.0291 0.97 0.11 0.0233 invention V582 0.36 0.0034 0.3 0.09 3 ppm Comp. V581 0.36 0,018 0.2 0.08 5 ppm Comp. V580 0.4 0.10 0.11 0.08 <10 ppm comparison

Table 1 shows only the essential alloying constituents of the aluminum tapes examined, moreover, the various experimental alloys had a Ti content of less than 0.015 wt%, a Zn content of less than 0.05 wt%, and a Cr content of less than 100 ppm. The ingots cast from the various aluminum alloys have been subjected to homogenization prior to rolling, the ingots being annealed to a temperature of about 580 ° C for more than four hours. Subsequently, the hot rolling was carried out at temperatures of 250 ° C to 550 ° C, the hot strip end temperature was between 280 ° C and 350 ° C. The VRef alloy aluminum hot strip was subjected to intermediate annealing during cold rolling at a thickness of 2 to 2.4 mm, with the cold rolled strip being exposed to a temperature of 300 to 450 ° C for one to two hours. At the same intermediate annealing temperatures, the intermediate annealing thickness for the aluminum strips V581, V582 and VF583 was only 0.9 to 1.2 mm, as well as from Table 2 is apparent. The aluminum strip of the alloy V580, however, was not annealed. Since the intermediate annealed strips were further cold rolled to final thickness, without a final final annealing, they were coiled up hard as a condition. Tab. 2 Leg . No. hot strip Zwischenglühungsdicke final thickness Status Vref 3 - 4 mm 2 - 2.4 mm 0.29 mm As-rolled VF583 3- 4 mm 0.9 - 1.2 mm 0.28 mm As-rolled V582 3 - 4 mm 0.9 - 1.2 mm 0.28 mm As-rolled V581 3 - 4 mm 0.9 - 1.2 mm 0.28 mm As-rolled V580 3 - 4 mm - 0.28 mm As-rolled

The correspondingly produced aluminum strips for lithographic printing plate supports or litho tapes were subjected to further tests. All five aluminum strips are characterized by a very good roughening behavior. In addition, the tensile strength in the hard-rolled state was investigated. In order to test the practical handling of the printing plates, especially for oversized lithographic printing plates, tensile strengths were measured even after a baking process of 240 ° C for 10 minutes. In addition, a bending change test was carried out in which the in Fig. 1 schematically illustrated experimental design was used.

Fig. 1a ) shows in a schematic sectional view of the structure of the bending change test device 1 used, which was used to investigate the flexural fatigue resistance of the aluminum strips according to the invention. rehearse 2 of the produced aluminum strips for lithographic printing plate supports are mounted in the bending cycle test device 1 on a movable segment 3 and a fixed segment 4. The segment 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. The different bending states shows schematically Fig. 1b ). Samples 2 were cut either longitudinally or transversely to the rolling direction from the prepared aluminum platens for lithographic printing plate supports. The radius of the segments 3, 4 was 30 mm.

The tensile strengths were measured according to DIN. The results of the tensile strength measurements in the hard-rolled state or after a baking process as well as the bending cycle test results are shown in Tables 3a and 3b. Tab. 3a Leg . No. Tensile strength (MPa) hard Tensile strength (MPA) 240 ° / 10 min. along crosswise along crosswise Vref 198 201 154 154 VF583 212 223 179 185 V582 184 201 153 161 V581 177 192 145 155 V580 218 228 157 169 Leg.-Nr. Bending change test after 260 ° / 4 min. Number of cycles Bending change test, hard-hard Number of cycles along crosswise along crosswise Vref 3400 1500 3030 1930 VF583 4150 3430 3760 2950 V582 4570 2670 4070 2320 V581 4230 2150 4100 2000 V580 3190 2090 2840 2200

It was found that the conventional aluminum strip has a sufficient tensile strength for the correction of the coil set before the baking process and for the handling of the lithographic printing plate support after the baking process as well as a sufficient bending fatigue resistance along the rolling direction. However, the conventionally manufactured aluminum strip (VRef) only reached 1500 bending cycles transverse to the rolling direction. The aluminum strips V582, V581, on the other hand, show very good tensile strengths in terms of coil set correction and the handling of the printing plate after a baking process as well as a very high bending fatigue resistance. An up to 78% higher number of bending cycles was achieved, cf. Alloy V582. In comparison, the comparative aluminum tape V580 also showed good values with respect to flexural fatigue resistance. The very high tensile strengths of 218 or 228 MPa longitudinally and transversely to the rolling direction make it difficult to correct the coil set before Burning in the photo layer of the lithographic printing plate supports.

The aluminum strips of the aluminum alloy VF583 according to the invention also showed increased tensile strength values of 212 MPa and 223 MPa along and transverse to the rolling direction. However, the increase in bending fatigue resistance is very pronounced with a factor of about 2.47 with respect to the reference material across the rolling direction after the baking process. Longitudinally to the rolling direction results in an increase in bending fatigue resistance after a burn-in still with a factor of 1.27. Coupled with unproblematic roughening, this results in the outstanding suitability of the aluminum alloy VF583 for oversized pressure plate carriers clamped transversely to the rolling direction. It is believed that the improved flex life properties are due to the increased Mg content of 0.97% by weight of the VF583 alloy. However, the tensile strength values of the alloy VF583 can be further reduced by further reducing the intermediate annealing thickness, for example, to 0.9 mm to less than 1.1 mm, without deteriorating the flexural fatigue property.

In the hard-rolling state, which is used for negative printing plates, showed in particular along the rolling direction a significant improvement in bending fatigue resistance. The values also increased transverse to the rolling direction. This applies in particular to the aluminum alloy VF583, which is transverse to the rolling direction even in hard-rolled condition allowed a maximum number of bending cycles.

It has been found that by selecting an aluminum alloy specifically tailored to the needs of large lithographic printing plate supports, in combination with selected process parameters, it is possible to produce significantly improved lithographic printing plate supports, which is also useful when using oversize, i. if they are clamped transversely to the rolling direction, can be handled easily and are still resistant to Plattenreißer.

Claims (7)

1. A method for producing aluminium strips for lithographic printing plate carriers, wherein the aluminium strip is produced from a rolling ingot, which after optional homogenization is hot-rolled to a thickness of 2 mm to 7 mm and the aluminium strip is cold-rolled to a final thickness of 0.15 mm to 0.5 mm by cold rolling the hot strip,
   characterized in that
   the aluminium strip is made from an aluminium alloy with the following alloy components according to percentage by weight: 0.3 % ≤ Fe ≤ 0.4 %, 0.4 % ≤ Mg ≤ 1.0 %, 0.05 % ≤ Si ≤ 0.25 %, Mn ≤ 0.1 %, optionally Mn ≤ 0.05 %, Cu ≤ 0.04 %, optionally a maximum Ti content of 0.05% by weight, a maximum Zn content of 0.05% by weight, and a Cr content of less than 100 ppm,
   with the remainder being Al and unavoidable impurities, individually not exceeding 0.05%, in total not exceeding 0.15%; an intermediate annealing stage is carried out at a thickness from 1.5 mm to 0.5 mm during cold rolling, and the aluminium strip is then cold-rolled to a final thickness from 0.15 mm to 0.5 mm, and is coiled in the full hard state for further processing to yield a lithographic printing plate carrier.
2. The method according to claim 1,
   characterized in that
   hot rolling is carried out at a temperature from 250 °C to 550 °C, wherein the final temperature of the hot strip is 280 °C to 350 °C.
3. The method according to any of claims 1 or 2,
   characterized in that
   during the intermediate annealing stage the metal temperature is between 200 °C and 450 °C, and the aluminium strip is maintained at said metal temperature for at least one to two hours.
4. An aluminium strip for producing lithographic printing plate carriers, having a thickness of 0.15 mm to 0.5 mm, in particular produced by a method according to any of claims 1 to 3,
   characterized in that
   the aluminium strip is made from an aluminium alloy with the following alloy components according to percentage by weight: 0.3 % ≤ Fe ≤ 0.4 %, 0.4 % ≤ Mg ≤ 1.0 %, 0.05 % ≤ Si ≤ 0.25 %, Mn ≤ 0.1 %, optionally Mn ≤ 0.05 %, Cu ≤ 0.04 %, optionally a maximum Ti content of 0.05% by weight, a maximum Zn content of 0.05% by weight, and a Cr content of less than 50 ppm,
   with the remainder being Al and unavoidable impurities individually not exceeding 0.05%, in total not exceeding 0.15%, the aluminium strip has a reverse bending strength transversely to the rolling direction of at least 1850 cycles in the reverse bending test.
5. The aluminium strip according to claim 4,
   characterized in that
   the aluminium strip in the full hard state has a tensile strength of up to 200 MPa longitudinally with the rolling direction and a tensile strength of at least 145 MPa following a baking process longitudinally or transversely with the rolling direction.
6. The aluminium strip according to any of claims 4 or 5,
   characterized in that
   the aluminium strip has a thickness from 0.25 to 0.5 mm.
7. A printing plate carrier manufactured from an aluminium strip according to any of claims 4 to 6.

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