EP2067871B1 - 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 increasingly printing presses are 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, the coil set is easily correctable in hard-rolling condition and from which also oversized printing plate support can be produced, which is easy to handle and only show a low tendency to plate tears.

• 0,3 % ≤ Fe ≤ 0,4 %,
• 0, 25 % ≤ Mg ≤ 0,6 %,
• 0,05 % ≤ Si ≤ 0,25 %,
  • Mn ≤ 0,05 %,
  • Cu ≤ 0,04 %,

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, 25% ≤ Mg ≤ 0.6%,
• 0.05% ≦ Si ≦ 0.25%,
  • 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 can provide 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 a high elongation is made available on the one hand due to the low degree of rolling after the intermediate annealing and on the other hand by the increased magnesium content higher strengths are provided by solidifications, the simplify the handling.

According to a first embodiment of the present invention, the properties according to the invention can be achieved particularly reliably by the fact 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 Content of less than 100 ppm, preferably a Cr content of 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.

The aluminum alloy according to the present invention has an Mg content of 0.25 wt% to 0.6 wt%, preferably 0.25 to 0.4 wt%. As a result, maximum strengths can be provided with high bending fatigue resistance. Higher Mg contents make it possible to further 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.

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 band will then be for at least one to two Hours kept at the metal temperature. 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. On the other hand, a regeneration annealing at lower temperatures merely results in a reduction of the solidifications, so that very low degrees of reduction after recovery annealing are possible. 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.

• 0,3 % ≤ Fe ≤ 0,4 %,
• 0,25 % ≤ Mg ≤ 0,6 %,
• 0,05 % ≤ Si ≤ 0,25 %,
  • Mn ≤ 0,05 %,
  • Cu ≤ 0,04 %,

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%,
• 0.25% ≤ Mg ≤ 0.6%,
• 0.05% ≦ Si ≦ 0.25%,
  • 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 tensile strength of up to 200 MPa in hard-rolled condition along the rolling direction and after baking at a temperature of 240 ° C and a duration of 10 minutes of at least 145 MPa, as well as a bending 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 achieve bending cycle cycles of more than 1850, also transverse to the rolling direction, which means an increase of more than 70% compared with the standard alloys used hitherto. Due to the moderate increase in tensile strength measured to values up to 200 MPa in hard-rolling condition along the rolling direction, the coil set of the aluminum strip according to the invention can be further corrected in a simple manner. Due to the good thermal stability, which manifests itself by a tensile strength of at least 145 MPa after a baking process along or transverse to the rolling direction, the handling of the lithographic printing plate carrier produced 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. In addition, the high number of possible bending cycle cycles greater than 1850 both in the hard as well as in the baked state of the aluminum strip according to the invention, that the tendency to As a result of mechanical stresses, plate cracks are small in the case of lithographic printing plate supports clamped transversely or longitudinally to the rolling direction.

An aluminum strip having an Mg content of from 0.25% by weight to 0.6% by weight, preferably from 0.3% by weight to 0.4% by weight, also permits particularly high elongation values in the case of sufficiently high tensile strength values Hard-rolling condition, since the required strength values are achieved even at low rolling degrees after intermediate annealing.

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 strip according to the invention, it is possible to produce particularly well-oversized printing plate supports and to process and handle them 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 is based on the above statements on the method for producing a Referenced aluminum strip and the aluminum strip according to the invention.

There are now a variety of ways the erfindungagemäße process for the production of aluminum strips for lithographic printing plate support to further develop and design 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 claims 1 and 6 claims and to the description of embodiments in conjunction with the drawings.

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.-Nr. Fe Mn mg Si Cu / Wt. -% Vref 0.32 - 0.17 0.12 7 ppm State of the art V582 0.36 0.0034 0.3 0.09 3 ppm invention V581 0.36 0,018 0.2 0.08 5 ppm comparison V580 0.4 0.10 0.11 0.08 <10 ppm comparison

Table 1 shows only the essential alloying constituents of the aluminum tapes tested, 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 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 other aluminum strips was only 0.9 to 1.2 mm, as can be seen from Table 2 is. 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.-Nr. hot strip Zwischenglühungsdicke final thickness Status Vref 3 - 4 mm 2 - 2.4 mm 0.29 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 0.9 - 1.2 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 four aluminum bands 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. Samples 2 from the produced aluminum strips for lithographic printing plate supports are described in US Pat Segment 3 and a fixed segment 4 attached. 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.-Nr. tensile strenght
Hard (MPa) tensile strenght
(MPA) 240 ° / 10 min. along crosswise along crosswise Vref 198 201 154 154 V582 184 201 153 161 V581 177 192 145 155 V580 218 228 157 169 Leg. -No. 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 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 tensile strength which is sufficient for the correction of the coil set prior to the stoving process and for the handling of the lithographic printing plate support after the stoving process as well as a sufficient resistance to flexing along the rolling direction. However, the conventionally manufactured aluminum strip (VRef) only reached 1500 bending cycles transverse to the rolling direction. On the other hand, the aluminum strip V582 according to the invention shows very good tensile strengths with regard to coil set correction and handling of the printing plate after a burn-in process as well as a very high bending fatigue resistance. Up to 78% higher number of bending cycles were achieved, alloy V582. In comparison, the comparative aluminum tape V580 also showed good values with respect to flexural fatigue resistance. However, the very high tensile strengths of 218 and 228 MPa, respectively longitudinal and transverse to the rolling direction, complicates the correction of the coil set prior to baking the photo layer of the lithographic printing plate supports.

In the hard-rolled state, which is used for negative printing plates, a significant improvement in flexural fatigue resistance was found especially in the longitudinal direction of the rolling direction. Transverse to the rolling direction, the values also increased.

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 (10)

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%,

   0.25% ≤ Mg ≤ 0.6%,

   0.05% ≤ Si ≤ 0.25%,

   Mn ≤ 0.05%,

   Cu ≤ 0.04%,

   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
   the aluminium alloy has 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.
3. The method according to claim 1 or 2,
   characterized in that
   the aluminium alloy has a Mg content of 0.3% to 0.4% by weight.
4. The method according to any of claims 1 to 3,
   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.
5. The method according to any of claims 1 to 4,
   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.
6. An aluminium strip for producing lithographic printing plate carriers, having a thickness of 0.15 mm to 0.5 mm and produced by a method according to any of claims 1 to 5,
   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%,

   0.25% ≤ Mg ≤ 0.6%,

   0.05% ≤ Si ≤ 0.25%,

   Mn ≤ 0.05%,

   Cu ≤ 0.04%,

   with the remainder being Al and unavoidable impurities individually not exceeding 0.05%, in total not exceeding 0.15%, the aluminium strip in the full hard state has a tensile strength of up to 200 MPa longitudinally with the rolling direction and at least 145 MPa following a baking process at a temperature of 240 °C for a duration of 10 minutes, and a reverse bending strength transversely to the rolling direction of at least 1850 cycles in the reverse bending test.
7. The aluminium strip according to claim 6,
   characterized in that
   the aluminium alloy has a Mg content of 0.3% to 0.4% by weight.
8. The aluminium strip according to claim 6 or 7,
   characterized in that
   the aluminium alloy has 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.
9. The aluminium strip according to any of claims 6 to 8,
   characterized in that
   it has a thickness from 0.25 to 0.5 mm.
10. A printing plate carrier manufactured from an aluminium strip according to any of claims 6 to 9.

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