EP4127257B1 - Litho strip having flat topography and printing plate produced therefrom - Google Patents

Description

The invention relates to the use of an aluminum alloy strip for producing lithographic printing plates or for producing printing plates for waterless offset printing, an aluminum alloy strip for lithographic printing plate supports, which has a rolled surface topography on at least one strip surface, a method for producing the aluminum alloy strip and a printing plate for lithographic printing or waterless offset printing having a printing plate carrier made of an aluminum alloy.

Very high demands are placed on the surface quality of lithographic tapes, ie aluminum alloy tapes for lithographic printing plate supports. Litho tapes are usually subjected to an electrochemical roughening step, which should result in a comprehensive roughening and a homogeneous appearance. The roughened structure is important for the imaging layer of the printing plate supports made from the lithographic tapes. In order to be able to produce evenly roughened surfaces, a particularly flat surface of the lithographic strips is required. The topography of the litho strip surface is essentially a replica of the roll topography of the last cold rolling pass. Elevations and depressions in the roller surface lead to grooves or ridges in the lithographic strip surface, which can be partially retained in the further manufacturing steps for producing the printing plate carriers. The quality of the litho belt surface and thus the printing plate carrier is determined by the quality of the roller surface and thus, on the one hand, by the grinding practice during the surface treatment of the rollers and, on the other hand, by the ongoing wear of the rollers.

According to the published European patent application belonging to the applicant EP 2 444 254 A2 It was previously assumed that optimally ground rollers were already used in the production of aluminum alloy strips for lithographic printing plate carriers, since if the roller surfaces were too smooth, there was a risk of slippage between the roller and the litho strip due to the low friction force on the litho strip surface and thus disruptions to the rolling process or damage to the aluminum strips became. However, rollers that are too rough result in higher or too high roughness on the aluminum alloy strip, so that the aluminum alloy strip is no longer suitable for the production of printing plate carriers. The average roughness values Ra of approx. 0.15 µm to 0.25 µm achieved so far on the surfaces of the aluminum alloy strips were therefore considered sufficient for many areas of application. In the EP 2 444 254 A2 It is therefore proposed that the strip surface is processed using a pickling process with a specific pickling removal and then has a topography whose maximum peak height Rp and/or Sp is a maximum of 1.4 µm, preferably a maximum of 1.2 µm, in particular a maximum of 1.0 µm, amounts.

In other methods known from the prior art, for example from WO 2006/1228 52 A1 and the one out WO 2007/14 1300 A1 According to a known method, the litho strips are pickled after rolling in order to remove disturbing oxide islands on the surface of the strips and thereby improve the subsequent electrochemical roughening.

The EP 0 778 158 A1 discloses printing plate carriers with a roughened and anodized surface, which have a maximum tip height Rp of up to 4 µm.

The Japanese patent application JP 2015 004095 A discloses an aluminum alloy sheet for a can body of a beverage can and its production. The use of aluminum alloy tapes for lithographic printing plate supports is not disclosed.

This also applies to the European patent application EP 3 254 772 A1 , which discloses an aluminum foil for electronic devices and a method for producing the same. Examples of electronic devices mentioned are LCD displays, OLED displays or electronic newspapers, etc.

The Chinese patent application CN 110102580 A also relates only to a method for producing an aluminum alloy strip from the aluminum alloy of type 1100 in the H14 condition for the production of high-quality cosmetic bottle caps and therefore not to lithographic printing plate carriers or lithographic printing plates themselves.

The Japanese patent application JP 2002 224710 A relates to the production of an aluminum alloy foil. The only mention of these films is their use as packaging material for chemicals and food.

The US patent application US 2019/0076897 A1 relates to the production of an aluminum foil for ultraviolet reflective materials. The use of aluminum alloy tapes for lithographic printing plate supports is also not disclosed in the cited US patent application.

From the European patent application EP 1 172 228 A2 are known printing plate carriers for lithographic printing plates. However, the aforementioned European patent application only discloses the surface properties of roughened aluminum alloy printing plates coated with a photosensitive coating.

With current printing plate carriers, especially with new "development-on-press" printing plate carriers, the thickness of the imaging coating is continuously reduced in order to reduce development times and save costs in production. In addition, softer imaging coatings are also used, which also save costs in the production of the printing plate supports should, but decrease in thickness during printing. The aluminum alloy strips produced so far for lithographic printing plate carriers are not optimally adapted to these additional challenges. It also became apparent that chemical pickling could not solve this problem. The printing plate carriers made from the known aluminum alloy strips therefore tend to have shorter service lives in the printing process with the new printing plate carriers.

Finally, the aluminum alloy strip is usually electrochemically roughened to produce the printing plate supports. A reduction in the charge carrier input required to uniformly roughen the surface of the printing plate support facing the imaging coating would also be desirable.

In addition to the arithmetic average roughness value Ra, the height of the largest profile peak of the roughness profile Rp (short: peak height), the depth of the largest profile valley Rv (short: trough depth) and the peak number RPc are defined in DIN EN ISO 4287 and DIN EN 10049 as well as the bearing fraction Smr (c) and the aspect ratio of the surface texture Str defined in DIN EN ISO 25178.

The surface parameters Ra, Rp, Rv, RPc, Smr (c) and Str mentioned here refer to optical surface measurements with a measuring area of at least 4.5 mm x 4.5 mm, which are carried out with a confocal microscope (lateral measuring point distance 1.6 µm or smaller) are measured and determined using analysis software. For this purpose, optical surface measurements of the parameters were carried out on three measuring surfaces of the specified size and the arithmetic mean of the respective parameters was determined. The profile parameters Ra, Rp, Rv and RPc are calculated for each measuring surface perpendicular to the rolling direction as arithmetic mean values from the available profile sections of the areal measurement. The measurement data is prepared by one Shape compensation with a second-order polynomial (F filter). A Gaussian filter with λc = 250 µm is used as the ripple filter. There is no filtering of the fineness. For Rp, Rv, RPc and Smr (c) the values determined in this way are referred to as the mean peak height Rp, mean trough depth Rv, mean number of peaks RPc and mean load ratio Smr (c=+0.25 µm).

When it comes to the bearing portion Smr (c) of the surface, what is particularly important is the portion of the surface oriented in the rolling direction, in particular grooves and webs oriented in this direction, which are generated by rolling and are generally not eliminated by electrochemical roughening. However, these can be recorded by separating and re-transforming the parts in the rolling direction after a Fourier transformation of the measured surface and then determining the supporting portion Smr (c=+0.25 µm) of these structures from the back-transformed surface parts.

The isotropy of the roughening of the printing plate support can be specified by the aspect ratio of the surface texture Str according to DIN EN ISO 25178. To calculate the Str value, the number of measuring points on the measuring surface is scaled to a power of 2. The scaled numerical values are calculated using a resampling operation.

While the average peak number RPc, measured perpendicular to the rolling direction, typically indicates the number of protruding areas on the aluminum alloy strip that are present as rolling webs, the arithmetic average roughness value Ra and the average peak height Rp provide information about the height of these elevations in the topography of the aluminum alloy strip or the printing plate carrier.

The average bearing fraction Smr (c=+0.25 µm) provides information about the area fraction of the examined surface that lies above a certain intersection line with the material fraction curve (Abbott curve), which was chosen here with c = +0.25 µm . This means that the area proportion of the protruding areas of the surface, for example, the surface portions oriented in the rolling direction, indicated above the cutting line c = +0.25 µm in the material proportion curve of the aluminum alloy strip or the printing plate carrier.

The ratio of the mean peak height Rp and the mean trough depth Rv provides information about whether the surface topography is dominated by troughs (values < 1) or peaks (values > 1). The ratio Rp/Rv is almost independent of the charge carrier input during electrochemical roughening.

The object of the present invention is therefore to propose a use of an aluminum alloy strip for lithographic printing plates as well as for printing plates for waterless offset printing and an aluminum alloy strip for lithographic printing plate supports, which, despite decreasing thickness of the imaging coating, provides a long service life in the printing process and can be roughened with less charge carrier entry . Furthermore, the invention is intended to provide a method for producing the aluminum alloy strips with the desired properties and to provide printing plates, in particular "development-on-press" printing plates or printing plates for waterless offset printing with a long service life.

This task is solved with the subjects of claims 1 to 16.

According to a first teaching of the invention, the surface of the aluminum alloy strip has an average peak number RPc, measured perpendicular to the rolling direction of the aluminum alloy strip, of ≤ 50 cm ^-1 , preferably ≤ 45 cm ^-1 or particularly preferably ≤ 40 cm ^-1 , with cutting lines for the RPc -Measurement c1 = + 0.25 µm and c2 = - 0.25 µm were chosen. It has been shown that aluminum alloy strips could be further improved in terms of their suitability for the production of printing plate carriers by optimizing the surface topography rolled in in the last cold rolling pass, since the service life is very thin imaging coatings could be increased with the aluminum alloy strips according to the invention.

It is believed that the reduced average peak number RPc enables the increased tool life because there are significantly fewer raised areas on the strip perpendicular to the rolling direction. The aluminum strips according to the invention are therefore particularly preferably used as printing plate supports for “development on press” printing plates and for printing plates for waterless offset printing.

In a first embodiment of the aluminum alloy strip, the surface of the aluminum alloy strip also has an average peak height Rp of a maximum of 1.1 μm, preferably 0.45 μm to 1.1 μm. The also reduced average center height Rp further ensures that rolling webs, if they are present, are reduced in height and contribute to improving service life.

This also applies to a further embodiment of the aluminum alloy strip, according to which the average load fraction Smr (c=+0.25 µm) of the surface portions of the surface of the aluminum alloy strip oriented in the rolling direction in % is a maximum of 5%, a maximum of 4%, or a maximum of 3.5% is, whereby only the surface portions that result from a Fourier transformation of the surface in the rolling direction are taken into account. The reduction in the average bearing portion Smr (c=+0.25 µm) of the surface portions of the aluminum alloy strips oriented in the rolling direction leads to rolled webs on the aluminum alloy strip that are reduced in length and width. According to the findings of the present invention, roll webs that are reduced in length and width also improve the service life of printing plates made from the aluminum alloy strips according to the invention.

To examine the rolling webs, an optical surface roughness measurement is carried out. After a polynomial adjustment (2nd order) of the raw data and removing the ripple components using a Gaussian filter (cut-off wavelength 250 µm), the height data is available in the form of a matrix a with the dimension NxM. The matrix is transformed using a discrete Fast Fourier Transformation (FFT) into the frequency space in which the surface components that extend in the rolling direction and perpendicular to the rolling direction can be separated. $$c_{\mathit{jk}}={\displaystyle \sum _{n=1}^N{\displaystyle \sum _{m=1}^M{a}_{\mathit{nm}}{e}^{-2\mathit{\pi i}\left(j-1\right)\left(n-1\right)/N}}}{e}^{-2\mathit{\pi i}\left(k-1\right)\left(m-1\right)/M}$$

Only the Fourier components c _jk of the surface parts oriented in the rolling direction are transformed back into the spatial space. $$a_{\mathit{jk}}={\displaystyle \sum _{n=1}^N{\displaystyle \sum _{m=1}^M{c}_{\mathit{nm}}{e}^{2\mathit{\pi i}\left(j-1\right)\left(n-1\right)/N}{e}^{2\mathit{\pi i}\left(k-1\right)\left(m-1\right)/M}}}$$

The average contact portion Smr (c=+0.25 µm) of the surface portions oriented in the rolling direction is then determined by evaluating the back-transformed surface portions. For this purpose, a material proportion curve in the form of an Abbot curve is generated from the back-transformed data and the bearing proportion Smr (c = +0.25 µm) is determined as the intersection of the material proportion curve with a straight line at c = +0.25 µm.

According to a further embodiment, the thickness of the aluminum alloy strip is preferably 0.10 mm to 0.5 mm, preferably 0.10 mm to 0.4 mm. In particular, aluminum strips with thicknesses of 0.10 mm to 0.4 mm are used for lithographic printing plate supports. Special formats also use thicknesses between 0.4 mm and 0.5 mm.

• 0,02 Gew.-% ≤ Si ≤ 0,50 Gew.-%, bevorzugt 0,02 Gew.-% ≤ Si ≤ 0,25 Gew.-%,
• 0,2 Gew.-% ≤ Fe ≤ 1,0 Gew.%, bevorzugt 0,2 Gew.-% ≤ Fe ≤ 0,6 Gew.%,
• Cu ≤ 0,05 Gew.-%, bevorzugt ≤ 0,01 Gew.-%,
• Mn ≤ 0,3 Gew.-%, bevorzugt < 0,1 Gew.-%, besonders bevorzugt ≤ 0,05 Gew.-%,
• 0,05 Gew.-% ≤Mg ≤ 0,6 Gew.-%, bevorzugt 0,1 Gew.-% ≤Mg ≤ 0,4 Gew.-%,
• Cr ≤ 0,01 Gew.-%,
• Zn ≤ 0,1 Gew.-%, bevorzugt ≤0,05 Gew.-%,
• Ti ≤ 0,05 Gew.-%,
• Rest Al sowie Verunreinigungen einzeln maximal 0,05 Gew.-% in Summe maximal 0,15 Gew.-%.

According to the invention, the aluminum alloy strip has the following composition:

• 0.02% by weight ≤ Si ≤ 0.50% by weight, preferably 0.02% by weight ≤ Si ≤ 0.25% by weight,
• 0.2% by weight ≤ Fe ≤ 1.0% by weight, preferably 0.2% by weight ≤ Fe ≤ 0.6% by weight,
• Cu ≤ 0.05% by weight, preferably ≤ 0.01% by weight,
• Mn ≤ 0.3% by weight, preferably <0.1% by weight, particularly preferably ≤ 0.05% by weight,
• 0.05% by weight ≤Mg ≤ 0.6% by weight, preferably 0.1% by weight ≤Mg ≤ 0.4% by weight,
• Cr ≤ 0.01% by weight,
• Zn ≤ 0.1% by weight, preferably ≤ 0.05% by weight,
• Ti ≤ 0.05% by weight,
• Rest Al and impurities individually maximum 0.05% by weight in total maximum 0.15% by weight.

An Si content of 0.02% by weight to 0.50% by weight also influences the appearance of electrochemically roughened printing plate supports. If the Si content is less than 0.02% by weight, electrochemical roughening results in too many depressions that are too small in the aluminum strip. If the Si content is too high, above 0.50% by weight, the number of depressions in the roughened aluminum strip is too small and the distribution is inhomogeneous. An Si content of 0.02% by weight ≤ Si ≤ 0.25% by weight is preferably used.

Copper has a negative impact on electrochemical roughening even at low levels. Therefore, the Cu content is ≤ 0.05% by weight, preferably ≤ 0.01% by weight.

Iron contributes to the mechanical and thermal strength of the aluminum alloy strips, so 0.2% to 1% by weight of iron is permissible. If the content is further increased, the roughening behavior during electrochemical roughening deteriorates. A preferred Fe content is between 0.2% by weight to 0.6% by weight or 0.4% by weight to 0.6% by weight.

Magnesium ensures an increase in strength, especially in the hard-rolled state of the printing plate carrier. At the same time, too much magnesium can have a negative impact on further processing due to excessive strength and properties during electrochemical roughening. According to the invention, the aluminum alloy therefore has a Mg content of 0.05% by weight ≤Mg ≤ 0.6% by weight. In the preferred range of 0.1% by weight ≤Mg ≤ 0.4% by weight or 0.25 to 0.4% by weight, strips with high strength in the rolled-hard state and reliable roughening behavior can be provided.

Although manganese increases the thermal strength of the aluminum alloy strip, it also increases the charge carrier input necessary for the electrochemical roughening of the printing plate carrier made from the aluminum alloy strip. Manganese is therefore limited to 0.3% by weight, preferably <0.1% by weight, particularly preferably ≤ 0.05% by weight.

In order to achieve good roughening behavior, Cr, Zn and Ti are also limited. The contents are Cr ≤ 0.01% by weight, Zn ≤ 0.1% by weight, preferably ≤ 0.05% by weight and Ti ≤ 0.05% by weight.

Finally, according to a next embodiment, the aluminum alloy strip is in the hard-rolled state. This achieves improved handling in the production of printing plate carriers. Due to the magnesium content, the aluminum alloy strips have relatively high strength in these states, so that good processing during electrochemical roughening and during the application of the imaging layer in the strip-shaped state is possible. As hard-rolled states, for example, state H18 produced by cold rolling with intermediate annealing or H19 produced by cold rolling without intermediate annealing are preferably used.

According to a further teaching of the invention, a method for producing an aluminum alloy strip according to the invention is provided, in which a Rolling ingots are cast from an aluminum alloy for lithographic printing plate supports, the rolling ingots are optionally preheated or homogenized before hot rolling, the rolling ingots are hot-rolled into a hot strip and the hot strip is then cold-rolled to the final thickness with or without intermediate annealing, a work roll being used in the last cold-rolling pass, which has an average roughness Ra of less than 0.18 µm, preferably less than 0.17 µm or preferably a maximum of 0.15 µm. The surface topography of a litho strip is essentially determined by the surface topography of the work roll in the last cold rolling pass. It has been shown that the method according to the invention can be used to produce an aluminum alloy strip which can be further processed into printing plate supports with improved service life in printing. The long service lives in printing are also achieved with “development-on-press” printing plates or with printing plates for waterless offset printing, which have particularly thin imaging coatings.

The average roughness Ra of the work rolls is determined according to DIN EN ISO 4287, with the roll surfaces according to the invention at least parallel to the longitudinal axis of the work roll having an average roughness Ra of less than 0.18 µm, preferably less than 0.17 µm or preferably a maximum of 0.15 µm exhibit.

It has also been shown that, according to a preferred embodiment of the method, the work roll in the last cold rolling pass has a roll surface with an average trough depth Rv measured parallel to the longitudinal axis of the work roll of a maximum of 1.2 μm. As a result, particularly good results were achieved in providing the aluminum strip topographies according to the invention.

If a work roll is used in the last cold rolling pass which has an average roughness Ra of at least 0.07 µm, preferably at least 0.10 µm, then, contrary to previous assumptions, slippage between the roll and the litho strip can be reliably avoided and a stable production process can be provided become.

According to a next embodiment of the method, the degree of rolling in the last cold rolling pass is at least 20%, preferably at least 30%, in order to achieve sufficient imprinting of the surface topography of the roll surface in the last cold rolling pass.

In order to provide a surface that is as trouble-free as possible and at the same time to enable the most economical production of the aluminum alloy strips, the degree of rolling in the last cold rolling pass is a maximum of 65%, preferably a maximum of 60%.

According to a further teaching of the invention, a printing plate for lithographic printing having a printing plate carrier made of an aluminum alloy, in particular made from an aluminum alloy strip according to the invention, is provided in that at least the surface of the printing plate carrier facing the imaging layer has a supporting portion Smr (c =+0.25 µm) of the surface portions oriented in the rolling direction is less than 5%, preferably less than 4.5% or a maximum of 4%. It was shown that the service life of the printing plate during printing could be significantly improved due to the reduced contact area Smr (c=+0.25 µm).

In particular, after electrochemical roughening, when using the aluminum alloy strip according to the invention, there was a further reduction in the average load-carrying fraction Smr (c=+0.25 µm) to significantly less than 5%, respectively less than 4.5% or a maximum of 4%, which is a further Improvement in the service life of the printing plate during printing.

According to a further embodiment of the printing plate, at least the surface of the printing plate support facing the imaging layer has a ratio of the average after the electrochemical roughening of the printing plate support Peak height to mean trough depth Rp/Rv of a maximum of 0.45, preferably a maximum of 0.4. Regardless of the charge carrier input during electrochemical roughening, the specified ratio of mean peak height to mean trough depth defines a topography of the surface of the printing plate support facing the imaging coating, in which the mean peak height is lower by more than a factor of 2 in relation to the mean trough depth. The topography of the printing plate carrier is therefore dominated by troughs and is very flat in the direction of the imaging coating, which significantly improves the service life of thin coatings in printing, for example coatings of "development-on-press" printing plates or printing plates for waterless offset printing .

After electrochemical roughening, at least the side of the printing plate support facing the imaging layer preferably has an average peak height Rp of less than 1.2 μm, preferably a maximum of 1.1 μm or preferably a maximum of 1 μm. By reducing the absolute value of the average peak heights Rp, an improvement in the service life of the printing plate of, for example, "development-on-press" printing plates or printing plates for waterless offset printing can also be achieved. This is achieved, for example, by using an aluminum alloy strip according to the invention.

If printing plate carriers are produced with the aluminum alloy strip according to the invention, the printing plate carriers can additionally be roughened homogeneously or isotropically with less charge carrier input. Aluminum alloy strips according to the invention showed high aspect ratios of the surface texture Str even with low charge carrier input. According to one embodiment, at least the surface of the printing plate support facing the imaging layer after electrochemical roughening with a charge carrier input of at least 500 C/dm ² has an aspect ratio of the surface texture Str according to DIN EN ISO 25178 of at least 50%. The aspect ratio Str of the surface texture is a measure of the uniformity of the Surface texture. With a value of 100% or 1, the surface texture is isotropic, i.e. independent of direction. The printing plate carriers according to the invention therefore provide a high aspect ratio Str of the surface texture even with low charge carrier input, so that the effort for electrochemical roughening can be reduced. The printing plate can thus be produced at lower costs.

This also applies to a further embodiment of the printing plate, in which at least the coated surface of the printing plate support facing the imaging layer has an aspect ratio of the surface texture Str according to DIN EN ISO 25178 of at least 20% after electrochemical roughening with a charge carrier input of 400 C/dm ² reached.

Finally, according to a further embodiment, a printing plate for waterless offset printing according to the invention has a printing plate carrier made from an aluminum alloy strip according to the invention. The imaging coatings of printing plates for waterless offset printing also have particularly small thicknesses, so that the service life of the printing plates for waterless offset printing benefits particularly from the surface topography of the aluminum alloy strip. However, printing plate supports for printing plates for waterless offset printing are not electrochemically roughened before they are image-coated.

Fig. 1- 4

Messflächen optisch vermessener Vergleichslithobänder, welche mit unterschiedlichen Ladungsträgereinträgen elektrochemisch aufgeraut wurden in einer Falschfarbendarstellung der Höhenwerte,

Fig. 5 - 8

Messflächen optisch vermessener erfindungsgemäßer Lithobänder, welche mit unterschiedlichen Ladungsträgereinträgen elektrochemisch aufgeraut wurden in einer Falschfarbendarstellung der Höhenwerte und

Fig. 9

eine Materialanteilskurve in Form einer Abbott-Kurve zur Bestimmung des Traganteils Smr (c).

The invention is further explained using exemplary embodiments. Please refer to the following tables and the drawing. The drawing shows in

Fig. 1-4

Measuring surfaces of optically measured comparison litho tapes, which were electrochemically roughened with different charge carrier entries in a false color representation of the height values,

Fig. 5 - 8

Measuring surfaces of optically measured litho tapes according to the invention, which were electrochemically roughened with different charge carrier entries in a false color representation of the height values and

Fig. 9

a material proportion curve in the form of an Abbott curve to determine the load-bearing proportion Smr (c).

• 0,02 Gew.-% ≤ Si ≤ 0,50 Gew.-%, bevorzugt 0,02 Gew.-% ≤ Si ≤ 0,25 Gew.-%,
• 0,2 Gew.-% ≤ Fe ≤ 1,0 Gew.%, bevorzugt 0,2 Gew.-% ≤ Fe ≤ 0,6 Gew.%,
• Cu ≤ 0,05 Gew.-%, bevorzugt ≤ 0,01 Gew.-%,
• Mn ≤ 0,3 Gew.-%, bevorzugt < 0,1 Gew.-%, besonders bevorzugt ≤ 0,05 Gew.-%,
• 0,05 Gew.-% ≤Mg ≤ 0,6 Gew.-%, bevorzugt 0,1 Gew.-% ≤Mg ≤ 0,4 Gew.-%,
• Cr ≤ 0,01 Gew.-%,
• Zn ≤ 0,1 Gew.-%, bevorzugt ≤0,05 Gew.-%,
• Ti ≤ 0,05 Gew.-%,
• Rest Al sowie Verunreinigungen einzeln maximal 0,05 Gew.-% in Summe maximal 0,15 Gew.-%.

The litho tapes, whose measuring surfaces are in Fig. 1-8 shown were made from an aluminum alloy roll ingot with the following composition:

• 0.02% by weight ≤ Si ≤ 0.50% by weight, preferably 0.02% by weight ≤ Si ≤ 0.25% by weight,
• 0.2% by weight ≤ Fe ≤ 1.0% by weight, preferably 0.2% by weight ≤ Fe ≤ 0.6% by weight,
• Cu ≤ 0.05% by weight, preferably ≤ 0.01% by weight,
• Mn ≤ 0.3% by weight, preferably <0.1% by weight, particularly preferably ≤ 0.05% by weight,
• 0.05% by weight ≤Mg ≤ 0.6% by weight, preferably 0.1% by weight ≤Mg ≤ 0.4% by weight,
• Cr ≤ 0.01% by weight,
• Zn ≤ 0.1% by weight, preferably ≤ 0.05% by weight,
• Ti ≤ 0.05% by weight,
• Rest Al and impurities individually maximum 0.05% by weight in total maximum 0.15% by weight.

The production was carried out by casting a rolling billet, homogenizing the rolling billet at 450 to 610 ° C for at least 1 hour, hot rolling the rolling billet into a hot strip with a thickness of approximately 2 - 7 mm and cold rolling the hot strip with or without intermediate annealing to the final thickness.

During the last cold rolling pass, the lithographic strips according to the invention were Fig. 5 - 8 a work roll is used whose surface topography has an arithmetic average roughness Ra according to DIN ISO 4287 of less than 0.18 µm, preferably had a maximum of 0.17 µm or a maximum of 0.15 µm. The average trough depth Rv of the surface of the work rolls of the exemplary embodiments according to the invention was a maximum of 1.2 μm.

The comparison lithobes in Fig. 1 - 4 On the other hand, they were cold rolled with a work roll in the last cold rolling pass, which had an arithmetic average roughness value Ra of 0.22 µm - 0.25 µm. The average trough depth Rv was also higher at a maximum of 1.6 μm than in the work rolls to be used according to the invention. The sheets produced in this way were roughened electrochemically in HCl as an electrolyte with different charge carrier inputs from 400 C/dm ² to 800 C/dm ² .

The height values of the optically measured measuring surfaces are in the Fig. 1-8 shown in false colors, with depressions assigned gray to black tones and elevations assigned light gray to white gray tones. With the human eye, differences can be seen on the measuring surfaces shown in this way even when they are not roughened. The litho strips according to the invention therefore have a surface that is significantly less structured in the rolling direction. This effect becomes stronger as the roughening increases.

Further measurements were carried out on litho strips of exemplary embodiments a, b, c, d and m as well as comparative examples f, g, h, which had aluminum alloy compositions according to Table 1.

All measured values Rp, RPc, Rv, Ra, Smr and Str of the exemplary embodiments and comparative examples were measured optically on three measuring surfaces measuring 4.5 mm x 4.5 mm with a confocal microscope and determined using analysis software (Digital Surf MountainsMap® ⁾ . The measuring surfaces were randomly arranged on the belts and the printing plate supports in a DIN A4 area. The corresponding areas of the bands were free of surface damage. The arithmetic mean of the three measuring surfaces was calculated for each parameter, with the profile parameters within the measuring surfaces perpendicular to the Rolling direction Rp, RPc, Rv, Ra were calculated as arithmetic mean values. The measurement data was prepared using shape compensation with a second-order polynomial (F filter). A Gaussian filter with λc = 250 µm was used as a ripple filter. There was no filtering of the fineness.

The litho strips a, b, c, d and m were manufactured identically by the above process starting with casting a rolling ingot, homogenizing the rolling ingot, hot rolling the rolling ingot and cold rolling the hot strip to final thickness with intermediate annealing (H18) and without intermediate annealing (H19). .

The resulting thicknesses, the material conditions and the arithmetic average roughness values Ra of the surfaces of the resulting lithobes are given in Table 1. The different roll topographies used in the final cold rolling pass can be seen in Table 7.

The litho strips according to the invention were therefore cold rolled in the last cold rolling pass with a work roll with a roll surface which, according to Table 7, had an arithmetic mean roughness Ra of 0.11 µm to 0.17 µm, with the specified rolling degrees. The average trough depth Rv was measured to be less than 1.2 µm. At 40% to 55%, the degree of rolling was in the inventive range of at least 20%. Furthermore, the degree of rolling at a maximum of 55% was also below 60% or even below 65%, so that as a result good surface properties were achieved with the lowest possible number of stitches.

The arithmetic mean roughness value Ra of the roll surface of the work roll in the last cold rolling pass of the comparison strips was between 0.22 µm and 0.25 µm. The average trough depth Rv was also significantly higher at a maximum of 1.6 µm than in the work rolls used according to the invention.

Contrary to the previous opinion of experts, the production of the exemplary embodiments according to the invention showed a stable production process, without any disruptions occurring during cold rolling due to slippage between the cold roll and the litho strip being rolled.

The first differences between the comparison tapes and the litho tapes according to the invention became apparent in the arithmetic mean roughness values Ra of the litho tapes a, b, c, d and m according to the invention. At 0.09 µm to 0.11 µm, these were significantly below the values of the comparative examples f, g and h with about 0.19 µm. These values of the arithmetic average roughness Ra perpendicular to the rolling direction result from the provision of a roll surface which has an arithmetic average roughness Ra of less than 0.18 μm.

As shown in Table 2, the aluminum strips a, b, c, d and m according to the invention also showed mean peak numbers RPc measured perpendicular to the rolling direction of significantly less than 50 cm ^-1 . With an average peak number RPc of more than 68 cm ^-1 , the comparison strips were, however, significantly higher than the results of the aluminum strips according to the invention.

At a maximum of 0.74 µm, the average peak height Rp for the aluminum alloy strips according to the invention was also significantly below the average peak heights Rp of the comparison strips, which had at least 0.88 µm as the average peak height Rp, the low average peak height Rp being due to the lower trough depth Rv of the roll surface is returned.

The average contact portion Smr (c=+0.25 µm) of the surface portions oriented in the rolling direction was also significantly lower in the exemplary embodiments according to the invention. Fig. 9 shows an example of how the load-bearing fraction Smr (c) can be determined from a material fraction curve in the form of an Abbott curve for a value c. The value c= 0 results as follows Fig. 9 can be seen with a material content of 100%. The c value is read on the Z axis, which corresponds to a height value of the surface topography. To determine the load share Smr (c) the intersection of the material proportion curve with the straight line Z=c is determined and the associated material proportion is read off on the X-axis.

To determine the average contact portion Smr (c=+0.25 µm), as explained above, the optical measurement results of a roughness measurement are subjected to a Fourier transformation and only the surface portions oriented in the rolling direction are transformed back. The back-transformed surface data became a material proportion curve like this Fig. 9 shows, generated and a value for the bearing fraction Smr (c=+0.25 µm) is determined. The arithmetic mean for determining the average contact ratio Smr (c=+0.25 µm) was then calculated from the contact parts Smr (c=+0.25 µm) of the surface parts oriented in the rolling direction, which were determined on three measuring surfaces.

The average contact parts Smr (c=+0.25 µm) of the surface parts of the aluminum alloy strips according to the invention oriented in the rolling direction were at a maximum of 3.79%, well below 5%. While the bearing fraction Smr (c=+0.25 µm) of the surface portions of the comparison strips oriented in the rolling direction was at least 8.09%, more than twice as high as the maximum measured average bearing fraction Smr (c=+0.25 µm) of the in Rolling direction oriented surface portions of the aluminum strips according to the invention.

The printing plate supports made from aluminum strips according to the invention showed a significantly improved service life in printing when using “development-on-press” coatings compared to the comparative examples. This is attributed to the differences in surface topography. It is assumed that the same applies to printing plates for waterless offset printing.

The properties of the aluminum strips during electrochemical roughening were checked with HCl as electrolyte, using different charge carrier inputs. The concentration of the electrolyte was 6g HCl per liter and 1g/L Al ³⁺ in the form of AlCh at 25 to 30 °C with a current density of 20 A/dm ² and alternating current.

Based on Fig. 1 - 8 It has already been made clear that the charge carrier entry causes small depressions, shown in black in the figures, which increase in number as the charge carrier entry increases.

At the same time, the electrochemical roughening also has an impact on other surface parameters of the aluminum alloy strip surface facing the imaging coating of the printing plate.

Printing plate carriers made from the electrochemically roughened aluminum strips showed clear differences in terms of the average bearing portion Smr (c=+0.25 µm) of the surface portions oriented in the rolling direction, as can be seen in Table 4. The printing plate carriers according to the invention had significantly lower average contact parts Smr (c=+0.25 µm) of the surface parts oriented in the rolling direction, which decreased even further, particularly with very high charge carrier input at 700 C/dm ² or 800 C/dm ² . The comparison bands also showed similar behavior, although at a much higher level. Overall, the average contact area Smr (c=+0.25 µm) of the surface parts oriented in the rolling direction could not be reduced below the 4% limit due to the electrochemical roughening of the comparison strips.

The aluminum strips according to the invention also showed a ratio Rp/Rv of a maximum of 0.45, with most values being below 0.41. As expected, there was very little dependence on the charge carrier input during electrochemical roughening. The comparison examples were significantly above these values. Only in comparative example f could a value of 0.43 be measured at 400 C/dm ² and 500 C/dm ² charge carrier entry.

However, the printing plate carriers according to the invention made from the test tapes a, b, c, d and m had a ratio Rp/Rv of 0.40 to 0.34 from 600 C/dm ² and thus a significantly lower Rp/Rv ratio than the comparison bands. The surface topographies of the printing plate carriers according to the invention were therefore even flatter than with printing plate carriers made from the comparison tapes.

The investigations into the aspect ratio of the surface texture Str after electrochemical roughening revealed significant differences. The aspect ratio Str is a measure of the isotropy of the roughened surface. The value Str reaches 100% with a completely isotropic surface. While the printing plate supports a, b, c, d and m produced from test tapes according to the invention can provide an aspect ratio of the surface texture Str of at least 20% at 400 C/dm ² or at least 50% at 500 C/dm ² , the comparison tapes only show this at 700 C/dm ² an aspect ratio of the surface texture Str of at least 20%.

It follows from this that the aluminum strips according to the invention can provide isotropically roughened surfaces with less charge carrier input and can therefore be processed more economically into printing plates. At the same time, the printing plates according to the invention also provide a longer service life, even for printing plates with very thin imaging coatings. Table 1: Composition of the test strips in% by weight, balance Al, unavoidable impurities individually maximum 0.05% by weight, in total maximum 0.15% by weight, arithmetic average roughness Ra defined in DIN EN 10049 perpendicular to the rolling direction, condition H18 with Intermediate annealing, condition H19 without intermediate annealing during cold rolling. Composition in wt.%, Test tapes Condition Thickness [mm] Ra [µm] Si Fe Cu Mn Mg Cr Zn Ti a Req. H18 0.37 0.11 0.08 0.37 0.001 0.004 0.20 0.001 0.012 0.005 b Req. H19 0.37 0.09 0.08 0.43 0.001 0.040 0.28 0.001 0.012 0.006 c Req. H19 0.275 0.10 0.08 0.43 0.001 0.040 0.27 0.001 0.011 0.005 d Req. H18 0.274 0.11 0.09 0.45 0.002 0.042 0.28 0.001 0.011 0.006 m Req. H19 0.37 0.11 0.08 0.43 0.001 0.041 0.28 0.001 0.013 0.007 f See. H18 0.275 0.19 0.09 0.38 0.001 0.002 0.20 0.000 0.014 0.008 G See. H19 0.275 0.19 0.09 0.44 0.001 0.042 0.28 0.001 0.012 0.008 H See. H18 0.275 0.19 0.09 0.43 0.001 0.041 0.28 0.001 0.011 0.008 Surface measurements of the aluminum alloy strips after rolling, mean peak height Rp, mean peak number RPc defined in DIN EN ISO 4287 and DIN EN 10049 with calibrated optical roughness measuring system, Smr with calibrated optical roughness measuring system defined in DIN EN ISO 25178. Test tapes Rp [µm] RPC [cm ^-1 ] Smr c = +0.25 µm [%] a Req. 0.65 35.2 3.45 b Req. 0.65 12.9 2.00 c Req. 0.69 9.4 1.73 d Req. 0.73 20.5 2.78 m Req. 0.74 34.3 3.78 f See. 0.88 68.4 8.09 G See. 1.32 92.3 11.47 H See. 1.06 74.4 9.32 Average center height Rp defined in DIN EN ISO 4287 on the roughened printing plate carrier depending on the charge carrier entry during electrochemical roughening in HCl. Test tapes Roughening in HCl - charge carrier entry [C/dm ² ] Not roughened 300 400 500 600 700 800 Rp [µm] a Req. 0.65 0.73 0.77 0.95 0.95 1.01 1.03 b Req. 0.65 0.65 0.78 0.76 0.82 0.88 0.93 c Req. 0.69 0.71 0.74 0.86 0.86 0.90 0.97 d Req. 0.73 - 0.80 0.86 0.92 1.01 1.01 m Req. 0.74 0.75 0.79 0.86 0.89 0.92 1.06 f See. 0.88 0.89 1.09 1.08 1.19 1.25 1.26 G See. 1.32 1.36 1.37 1.41 1.41 1.49 1.49 H See. 1.06 1.06 1.14 1.23 1.33 1.29 1.32 Carrying fraction Smr at c = +0.25 µm in % according to DIN EN ISO 25178 on the roughened printing plate carrier depending on the charge carrier entry during electrochemical roughening in HCl. Test tapes Roughening in HCl - charge carrier entry [C/dm ² ] Not roughened 300 400 500 600 700 800 Smr at c = +0.25 µm [%] a Req. 3.45 2.52 2.32 2.87 2.15 2.02 1.43 b Req. 2.00 1.36 0.73 0.74 0.60 0.63 0.34 c Req. 1.73 1.99 1.68 1.70 1.18 0.77 0.66 d Req. 2.78 - 1.87 1.57 1.55 1.56 0.86 m Req. 3.78 2.70 2.25 1.92 1.81 1.10 1.20 f See. 8.09 8.06 7.67 6.51 6.37 5.81 4.16 G See. 11.47 10.22 11.14 9.96 8.52 8.57 6.07 H See. 9.32 8.88 8.67 8.08 7.63 6.69 4.88 Ratio Rp/Rv defined in DIN EN ISO 4287 on the roughened printing plate carrier depending on the charge carrier entry during electrochemical roughening in HCl. Test tapes Roughening in HCl - charge carrier entry [C/dm ² ] Not roughened 300 400 500 600 700 800 Rp/Rv a Req. 1.04 0.44 0.39 0.44 0.39 0.38 0.38 b Req. 1.33 0.35 0.39 0.34 0.34 0.34 0.34 c Req. 1.53 0.45 0.38 0.38 0.36 0.35 0.35 d Req. 1.38 - 0.41 0.37 0.40 0.38 0.37 m Req. 1.39 0.45 0.38 0.38 0.38 0.35 0.38 f See. 1.24 0.49 0.43 0.43 0.47 0.46 0.46 G See. 2.50 0.69 0.56 0.55 0.55 0.57 0.54 H See. 2.14 0.71 0.58 0.58 0.56 0.50 0.48 Aspect ratio of the surface texture Str according to DIN EN ISO 25178 on the roughened printing plate carrier depending on the charge carrier entry during electrochemical roughening in HCl. Test tapes Roughening in HCl - charge carrier entry [C/dm ² ] Not roughened 300 400 500 700 Str [%] a Req. 1.70 3.50 21.60 65.70 83.60 b Req. 1.60 5.60 70.10 82.90 83.10 c Req. 1.50 1.90 54.60 74.00 82.90 d Req. 1.80 - 32.10 76.20 82.60 m Req. 1.90 2.10 49.80 73.70 84.20 f See. 1.20 1.50 2.90 58.20 79.30 G See. 1.20 1.60 2.00 3.20 27.10 H See. 1.40 1.40 1.80 2.10 67.20 Arithmetic average roughness Ra of the roll surface according to DIN ISO 4287. Test tapes Ra[µm] Degree of rolling of the last cold rolling pass a Req. 0.15 - 0.17 40-55 b Req. 0.11 - 0.13 40-55 c Req. 0.11 - 0.13 40-55 d Req. 0.13 - 0.15 40-55 m Req. 0.15 - 0.17 40-55 f See. 0.22 - 0.25 40-55 G See. 0.22 - 0.25 40-55 H See. 0.22 - 0.25 40-55

Claims (16)

1. Use of an aluminium alloy strip for producing lithographic printing plates or printing plates for waterless offset printing, wherein the aluminium alloy strip has a rolled-in surface topography on at least one strip surface,
   characterised in that
   the surface of the aluminium alloy strip has a mean peak number RPc measured perpendicular to the rolling direction of the aluminium alloy strip of ≤ 50 cm^-1, preferably ≤ 45 cm^-1 or particularly preferably ≤ 40 cm^-1, wherein c1 = + 0.25 µm and c2 = - 0.25 µm have been selected as section lines for the RPc measurement and the mean peak number RPc is determined from an optical areal measurement of three measuring areas of at least 4.5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1,6 µm or less, wherein the arithmetic mean value of the profile parameter RPc perpendicular to the rolling direction is calculated within the measuring areas from the profile sections of the areal measurement available perpendicular to the rolling direction per measuring area and the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
2. Aluminium alloy strip for lithographic printing plate supports, which has a rolled-in surface topography on at least one strip surface,
   characterised in that
   the aluminium alloy strip has the following composition:

   0.02 wt.% ≤ Si ≤ 0.50 wt.%, preferably 0.02 wt.% ≤ Si ≤ 0.25 wt.%,

   0.2 wt.% ≤ Fe ≤ 1.0 wt.%, preferably 0.2 wt.% ≤ Fe ≤ 0.6 wt.%,

   Cu ≤ 0.05 wt.%, preferably ≤ 0.01 wt.%,

   Mn ≤ 0.3 wt.%, preferably < 0.1 wt.%, particularly preferably ≤ 0.05 wt.%,

   0.05 wt.% ≤ Mg ≤ 0.6 wt.%, preferably 0.1 wt.% ≤ Mg ≤ 0.4 wt.%,

   Cr ≤ 0.01 wt.%,

   Zn ≤ 0.1 wt.%, preferably ≤ 0.05 wt.%,

   Ti ≤ 0.05 wt.%,

   remainder Al and impurities individually at maximum 0.05 wt.%, in total at maximum 0.15 wt.%,

   the surface of the aluminium alloy strip has a mean peak number RPc measured perpendicular to the rolling direction of the aluminium alloy strip of ≤ 50 cm^-1, preferably ≤ 45 cm^-1 or particularly preferably ≤ 40 cm^-1, wherein c1 = + 0.25 µm and c2 = - 0.25 µm have been selected as section lines for the RPc measurement and the mean peak number RPc is determined from an optical areal measurement of three measuring areas of at least 4.5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less, wherein an arithmetic mean value of the profile parameter RPc perpendicular to the rolling direction is calculated within the measuring areas from the profile sections of the areal measurement available perpendicular to the rolling direction per measuring area and the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
3. Aluminium alloy strip according to claim 2,
   characterised in that
   the surface of the aluminium alloy strip has a mean peak height Rp of at most 1.1 µm, preferably 0.45 µm to 1.1 µm, and the mean peak height Rp is determined from an optical areal measurement of three measuring areas of at least 4.5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less, wherein an arithmetic mean value of the profile parameter Rp perpendicular to the rolling direction is calculated within the measuring areas from the profile sections of the areal measurement available perpendicular to the rolling direction per measuring area and the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
4. Aluminium alloy strip according to claim 2 or 3,
   characterised in that
   the mean bearing length ratio Smr (c=+0.25 µm) of the surface portions of the surface of the aluminium alloy strip oriented in the rolling direction in % is at maximum 5%, preferably at maximum 4%, or at maximum 3.5%, wherein only the surface portions which result after a Fourier transformation of the surface in the rolling direction are taken into account and the mean bearing length ratio Smr (c=+0,25 µm) is determined from an optical areal measurement of three measuring areas of at least 4.5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less, the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
5. Aluminium alloy strip according to any one of claims 2 to 4,
   characterised in that
   the thickness of the aluminium alloy strip is 0.10 mm to 0.5 mm, preferably 0.10 mm to 0.4 mm.
6. Aluminium alloy strip according to one of claims 2 to 5,
   characterised in that
   the aluminium alloy strip is in the hard-rolled state.
7. Method for the production of an aluminium alloy strip for lithographic printing plate supports according to claims 2 to 6, in which a rolling ingot is cast from an aluminium alloy for lithographic printing plate supports, the rolling ingot is optionally preheated or homogenised before hot rolling, the rolling ingot is hot rolled to form a hot strip and the hot strip is then cold rolled to final thickness with or without intermediate annealing,
   characterised in that
   in the last cold rolling pass, a work roll is used which has a mean roughness Ra according to DIN ISO 4287 of less than 0.18 µm, preferentially less than 0.17 µm or preferably at maximum 0.15 µm.
8. Method according to claim 7,
   characterised in that
   in the last cold rolling pass, a work roll is used which has a mean roughness Ra according to DIN ISO 4287 of at least 0.07 µm, preferably at least 0.10 µm.
9. Method according to claim 7 or 8,
   characterised in that
   the degree of rolling in the last cold rolling pass is at least 20%, preferably at least 30%.
10. Method according to one of claims 7 to 9,
    characterised in that
    the degree of rolling in the last cold rolling pass is at maximum 65 %, preferably at maximum 60 %.
11. Printing plate for lithographic printing comprising a printing plate support made of an aluminium alloy, in particular produced from an aluminium alloy strip according to claim 2 to 7,
    characterised in that
    at least the surface of the printing plate support facing the imaging layer, after the electrochemical roughening of the printing plate support, has a mean bearing length ratio Smr (c=+0.25 µm) of the surface portions orientated in the rolling direction of less than 5%, preferably less than 4.5%, or at maximum 4%, wherein only the surface portions which result after a Fourier transformation of the surface in the rolling direction are taken into account, and the mean bearing length ratio Smr (c=+0,25 µm) is determined from an optical areal measurement of three measuring areas of at least 4.5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less and the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
12. Printing plate according to claim 11,
    characterised in that
    at least the surface of the printing plate support facing the imaging layer, after the electrochemical roughening of the printing plate support, has a ratio of the mean peak height to the mean valley depth Rp/Rv of at maximum 0.45, preferably at maximum 0,4 and the mean peak height Rp and the mean valley depth Rv are determined from an optical areal measurement of three measuring areas of at least 4.5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less, wherein the arithmetic mean value of the profile parameters Rp and Rv perpendicular to the rolling direction is calculated within the measuring areas from the profile sections of the areal measurement available perpendicular to the rolling direction per measuring area and the arithmetic mean is calculated for the parameters from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
13. Printing plate according to claim 11 or 12,
    characterised in that
    at least the surface facing the imaging layer, after the electrochemical roughening of the printing plate support, has a mean peak height Rp of less than 1.2 µm, preferably at maximum 1.1 µm or at maximum 1 µm, and the mean peak height Rp is determined from an optical areal measurement of three measuring areas of at least 4.5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less, wherein the arithmetic mean value of the profile parameter Rp perpendicular to the rolling direction is calculated within the measuring areas from the profile sections of the areal measurement available perpendicular to the rolling direction per measuring area and the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
14. Printing plate according to one of claims 11 to 13,
    characterised in that
    at least the surface of the printing plate support facing the imaging layer, after electrochemical roughening with a charge carrier input of at least 500 C/dm², achieves an aspect ratio of the surface texture Str according to DIN EN ISO 25178 of at least 50 % and the aspect ratio of the surface texture Str is determined from an optical areal measurement of three measuring areas of at least 4,5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less and the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
15. Printing plate according to claim 14,
    characterised in that
    at least the surface of the printing plate support facing the imaging layer, after electrochemical roughening with a charge carrier input of at least 400 C/dm², achieves an aspect ratio of the surface texture Str according to DIN EN ISO 25178 of at least 20 %, and the aspect ratio of the surface texture Str is determined from an optical areal measurement of three measuring areas of at least 4,5 mm x 4.5 mm using a confocal microscope with a lateral measuring point distance of 1.6 µm or less and the arithmetic mean is calculated for the parameter from the three measuring areas, wherein the measurement data processing is performed by a shape equalisation with a second-order polynomial (F-filter) and a Gaussian filter with λc = 250 µm as a waviness filter without filtering the fine roughness.
16. Printing plate for waterless offset printing comprising a printing plate support made of an aluminium alloy strip according to claim 2 to 6.

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