EP2444254A1 - Aluminum alloy strip for electrochemical roughening and method for producing same - Google Patents

Abstract

The litho sheet for the electrochemical roughening, comprises a rolled aluminum alloy, where a sheet surface has a topography with: a maximum peak height R pand/or S pof less than 1.0 mu m; and a reduced peak height R p kand/or S p kof less than 0.37 mu m. A thickness of the litho sheet is 0.5-0.1 mm. Independent claims are included for: (1) a method for producing a litho sheet; and (2) printing plate supports.

Description

The invention relates to a litho strip for electrochemical roughening, consisting of a rolled aluminum alloy. Furthermore, the invention also relates to a method for producing such a lithoband, in which a litho strip consisting of an aluminum alloy is cold rolled and in which the litho strip is subjected after the last cold rolling pass to a degreasing treatment with simultaneous pickling step with an aqueous pickling medium, wherein the aqueous pickling medium is at least 1 , 5 to 3 wt .-% of a mixture of 5-40% sodium tripolyphosphate, 3-10% sodium gluconate, 3-8% nonionic and anionic surfactants and optionally 0.5 to 70% soda and the sodium hydroxide concentration in aqueous Pickling medium between 0.1 wt .-% and 5 wt .-% is. Finally, the invention also relates to a pressure plate carrier and its advantageous use.

Very high demands are placed on the surface quality of lithographic strips, ie aluminum strips for the production of lithographic printing plate supports. Lithographic tapes are usually subjected to an electrochemical roughening step, which should result in a nationwide roughening and a structureless appearance. The roughened structure is important for applying a photosensitive layer to the printing plate supports made of the litho ribbons. To be able to produce evenly roughened surfaces is therefore a particularly flat surface of the litho ribbons required. The topography of the lithoband surface is essentially an impression of the roll topography of the last cold roll pass. Elevations and depressions in the roll surface lead to grooves or webs in the lithoband surface, which can be partially preserved in the further production steps for the production of printing plate support. The quality of the lithoband surface and thus the printing plate support is thus determined by the quality of the roll surface and thus on the one hand by the grinding practice in the surface treatment of the rollers and on the other hand by the ongoing wear of the rollers.

A measure for determining the surface quality of the lithographic strip is the mean roughness R _{a in} accordance with DIN EN ISO 4287 and DIN EN ISO 4288. In the current method for producing lithographic strips, surfaces having a customary average roughness value R _a of approx. 0.15 .mu.m to 0.25 .mu.m generated. These roughness values are sufficient for many applications.

In recent years, however, more and more printing plates with very flat Aufraustrukturen and / or a relatively thin photosensitive coating are in demand. These are used for example in the increasingly widespread CtP technology, in which the printer plates can be exposed directly digitally via a computer. Furthermore, the thickness of the coatings used decreases and their complexity increases. With the currently available printing plate carriers, printing errors occur again and again in these applications. A flat topography of the Lithobandes after rolling is therefore an increasingly important quality criterion for litho ribbons.

An attempt was made to optimize the grinding of the rolls in order to obtain flatter rolling structures. The grinding practices are, however, already largely optimized, so that further improvements in quality are very difficult to achieve in this way. Furthermore, the surface quality of the rolls decreases after grinding due to the wear during rolling, so that frequent re-grinding of the rolls is required. Finally, very smooth roll surfaces can exert only a low frictional force on the lithoband surface, so that there may be slippage between the roll and the lithoband, thereby disrupting the rolling process or damaging the lithoband.

In others, from the prior art of WO 2006/122852 A1 and the WO 2007/141300 A1 known methods, the litho ribbons are pickled after rolling to remove interfering oxide islands on the surface of the bands and thereby to improve the subsequent electrochemical roughening. Although the surface quality of the printing plate supports can be fundamentally improved in this way, the problem of the abovementioned printing errors still persists.

Based on this prior art, the present invention based on the object to provide a litho strip and a method for its production, with which the aforementioned disadvantages of the prior art can be avoided or at least reduced.

This object is achieved according to the invention in a generic lithographic strip in that the strip surface has a topography whose maximum peak height Rp and / or Sp is at most 1.4 μm, preferably at most 1.2 μm, in particular at most 1.0 μm.

The topography of a band surface is understood to mean its deviation from an ideal level. It can be described by a function Z (x, y) which assigns to each point of the band surface (x, y) the local deviation from the mean height of the surface. The mean value of the function Z (x, y), ie the position of the mean surface, is therefore set to 0, as follows from the following formula: $$<Z\left(xy\right)>=\frac{1}{F}\int \int Z\left(xy\right)\mathit{dxdy}=0$$

F is the size of the integration area. Local surveys correspond to positive values and local reductions correspond to negative values of Z (x, y).

The properties of such a topography can be determined by different characteristics. A common characteristic value is the average roughness R _a or the mean square roughness Rq according to DIN EN ISO 4287 and DIN EN ISO 4288. These characteristic values are defined by the following equations: $$\begin{array}{l}{R}_a=\frac{1}{L}\int \left|Z\left(x\right)\right|\mathit{dx}\\ R_q=\sqrt{\frac{1}{L}\int Z{\left(x\right)}^2\mathit{dx}}\end{array}$$

Z (x) is a profile of the surface, ie a one-dimensional section through the function Z (x, y). L is the length of the integration interval. In order to determine the surface quality of a surface, one-dimensional profiles Z (x) are measured by linear scanning in various places on the surface and the corresponding values R _a and R _{q are} determined.

The values for S _a and Sq result from a two-dimensional measurement of the surface, ie the topography Z (x, y). The calculation of the values S _a and S _q is based on the following equation, where A is the size of the integration surface: $$\begin{array}{l}{S}_a=\frac{1}{A}\int \int \left|Z\left(xy\right)\right|\mathit{dxdy}\\ S_q=\sqrt{\frac{1}{A}\int \int Z{\left(xy\right)}^2\mathit{dxdy}}\end{array}$$

In the context of the present invention, it has been recognized that the printing errors occurring in the prior art are frequently caused by individual, particularly high rolling webs, which can be partially preserved during production to printing plate supports. During the coating of the printing plate supports, interruptions in the photosensitive layer may then occur in the region of these rolling webs, which leads to printing errors when using the finished printing plates. The high rolling webs have been found to be particularly problematic in printing plate carriers with a flat Aufraustruktur and / or a relatively thin photosensitive coating.

However, the presence of individual high rolling webs is only insufficiently detected by the characteristic value R _a or S _{a used} to characterize the lithoband surface. In contrast, the probability of high rolling webs and thus the occurrence of said printing errors can be reduced by optimizing the lithoband or the method for its production with respect to another roughness characteristic value which has hitherto been ignored. By limiting the maximum peak height Rp and / or Sp to a maximum of 1.4 .mu.m, preferably a maximum of 1.2 .mu.m, in particular a maximum of 1.0 .mu.m, litho tapes can be made available which meets today's high demands on the surface quality, for example Use of CtP technology, suffice.

wobei die Funktion max(Z) den Maximalwert von Z(x) liefert. S_p wird über eine Flächenmessung mit der Gleichung $$S_p=\max \left(Z\left(xy\right)\right),$$

ermittelt, wobei die Funktion max(Z) den Maximalwert von Z(x,y) liefert. Die zu vermessende Fläche kann in der Praxis beispielsweise quadratisch sein und eine Kantenlänge von 800µm aufweisen.In order to determine the maximum peak height Rp of a lithographic strip, profiles Z (x) over a length of, for example, 4.8 mm in each case can be measured at three points of the lithoband transversely to the rolling direction in order to determine a value for Rp. For each of these profiles applies $$R_p=\mathrm{Max}\left(Z\left(x\right)\right).$$

where the max (Z) function returns the maximum value of Z (x). S _p is about an area measurement using the equation $$S_p=\mathrm{Max}\left(Z\left(xy\right)\right).$$

determined, wherein the function max (Z) provides the maximum value of Z (x, y). The area to be measured can in practice be square, for example, and have an edge length of 800 μm.

In order to determine the maximum peak height Rp, in each case a profile Z (x) in the middle and on the sides of the lithoband is preferably measured.

It is understood that for the measurement of the profiles Z (x) and the topography Z (x, y) only those areas of the lithoband are possible, which will later be further processed into printing plate carriers. For example, damaged areas or areas with rolling defects are out of the question.

In a first embodiment of the lithoband, the strip surface has a topography whose reduced peak height R _pk and / or S _{pk is} at most 0.4 μm, preferably at most 0.37 μm. It has been found that the quality of the strip surface can be further improved with regard to freedom from printing defects by additional control of the reduced peak height R _pk and / or S _pk .

The reduced peak height R _pk is determined according to DIN EN ISO 13 565. The reduced peak height S _pk is also determined according to DIN EN ISO 13 565 by an area measurement. In practice, the profiles Z (x) and the topography Z (x, y) can be measured as previously described for Rp or Sp, respectively.

In a further embodiment, the thickness of the lithoband is 0.5 mm to 0.1 mm. It has been found that just conventional litho tapes with small thicknesses can have high rolling webs. Therefore, the surface quality of thin lithographic ribbons can be particularly improved by restricting the maximum peak height Rp and / or Sp and the reduced peak height R _pk and / or S _pk , respectively.

Good material properties of the lithographic ribbons are achieved in a further embodiment of the lithoband in that the lithoband consists of an AA1050, AA1100, AA3103 or AlMg0.5 alloy.

In a further preferred embodiment, the lithoband has the following alloy compositions in% by weight: 0.3% ≤ Fe ≤ 1.0%, 0.05% ≤ 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%.

As a result, the litho strip can be improved in terms of the application, in particular with regard to its strength or heat resistance properties.

High bending fatigue resistance and at the same time a very good thermal stability of the lithoband can be achieved in another embodiment by the lithoband having the following alloy contents in% by weight: 0.3% ≤ Fe ≤ 0.4%, 0.2% ≤ Mg ≤ 0.6%, 0, 05% ≤ Si ≤ 0.25%, Mn ≤ 0.05%, Cu ≤ 0.04%

In a further embodiment, the lithoband has the following alloy contents in% by weight: 0.3% ≤ Fe ≤ 0.4%, 0.1% ≤ Mg ≤ 0.3%, 0.05% ≤ Si ≤ 0.25%, Mn ≤ 0.05%, Cu ≤ 0.04%.

In this way, the roughening properties and the heat resistance of the lithographic strip can be improved.

According to a further embodiment, the impurities of the alloy of the lithoband have the following limit values in% by weight: Cr ≤ 0.01%, Zn ≤ 0.02%, Ti ≤ 0.04%, B ≤ 50 ppm.

Titanium can also be deliberately added to grain refining up to a concentration of 0.04% by weight.

The above object is achieved in a further teaching of the invention in a generic method for producing a lithographic strip according to the invention that the surface removal by the degreasing with simultaneous pickling step is at least 0.25 g / m ² , preferably at least 0.4 g / m ² .

It was recognized that the disruptive high rolling webs on the lithoband surface can be reduced after the last cold rolling pass by a specific degreasing treatment with simultaneous pickling step. Are known pickling treatments for the removal of oxide islands, the targeted removal of rolling bars was previously unknown. However, due to the special choice of pickling or degreasing medium and the process parameters, it is now possible instead or additionally to achieve a topography of the lithoband surface, which has a significantly lower susceptibility to printing errors due to high rolling webs compared to the previously known litho tapes. Since the degreasing treatment with pickling step of lithoband surfaces is a very critical process, the process requires a very narrow selection of process parameters. In particular, the composition of the pickling medium, as well as the pickling temperature and pickling time, are to be adjusted so that an areal removal of at least 0.25 g / m ^{2 is} achieved in the lithoband surface during the degreasing treatment with pickling step. As a result, a topography of the lithoband surface can be achieved whose maximum peak height Rp and / or Spmax. 1.4 μm, preferably max. 1.2 μm, in particular max. 1.0 μm

The area removal is understood to be the weight of the litho strip per area removed during the degreasing treatment with the pickling step. To determine the surface removal, the lithoband is weighed before and after the degreasing treatment with a pickling step. The calculated weight loss divided by the size of the treated area gives the area removal. In the case of a two-sided degreasing treatment with pickling step of the litho strip, the area of the front side and the back side must therefore be added.

A set surface removal of between 0.25 g / m ² and 0.6 g / m ² , preferably between 0.4 g / m ² and 0.6 g / m ² , has proven to be particularly advantageous. In this way, the removal on the one hand is large enough to reduce the high webs, on the other hand, the thickness of the lithographic ribbon is not reduced too much. In principle, the removal should also be kept as low as possible, so that the least possible loss of material during the degreasing treatment with pickling step arises.

The topography of the lithoband surface can be improved in a preferred embodiment of the method by the sodium hydroxide concentration in the aqueous pickling medium is between 2 and 3.5 wt .-% and optionally the degreasing treatment with pickling at temperatures between 70 and 85 ° C for a Duration between 1 and 3.5 s. At these concentrations, temperatures and treatment times, the topography according to the invention can be achieved particularly reliably.

A further improvement is achieved in that the sodium hydroxide concentration in the aqueous pickling medium is between 2.6 and 3.5% by weight and / or the pickling temperature is between 76 and 84 ° C. As a result, a shorter treatment time is possible with nevertheless homogeneous removal of high rolling webs. Another improvement in the speed of degreasing treatment With pickling step of the litho tape can be achieved in that the pickling time is between 1 and 2 s, preferably between 1.1 and 1.9 s.

According to a further embodiment of the method, the litho strip is rolled in the last cold rolling pass to a final thickness of 0.5 mm to 0.1 mm. Particularly high rolling webs, which can be greatly reduced by the degreasing treatment with pickling step, occur at these preferably used rolling thicknesses.

As the aluminum alloy, according to another embodiment of the method, AA1050, AA1100, AA3103 or AlMg0.5 is used. These aluminum alloys have proven to be particularly advantageous for the properties of the litho tapes.

In a further embodiment of the method, the aluminum alloy has the following alloy composition in% by weight: 0.3% ≤ Fe ≤ 1.0%, 0.1% ≤ 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 effect of the degreasing treatment with pickling step is influenced by the alloy of the lithoband. It has been found that in this alloy composition with the selected process parameters for the pickling degreasing treatment very good results can be achieved with respect to the surface topography and at the same time good material properties of the lithographic strips.

In further embodiments of the method, the aluminum alloy has the following alloy contents in% by weight: 0.3% ≤ Fe ≤ 0.4%, 0.1% ≤ Mg ≤ 0.3%, 0.05% ≤ Si ≤ 0.25%, Mn ≤ 0, 05%, Cu ≤ 0.04%.

The impurities of the alloy of the lithoband have according to a further embodiment the following limits: Cr ≤ 0.01%, Zn ≤ 0.02%, Ti ≤ 0.04%, B ≤ 50 ppm, wherein titanium for grain refining up to a value of 0.04 wt .-% can also be added deliberately hinzulegiert.

For the advantages of the preferred alloy compositions, reference is made to the corresponding explanations regarding the lithoband.

In another embodiment of the method, the structural properties of the lithographic strip can be improved by hot-rolling the lithoband before cold-rolling and, optionally, homogenizing treatment before hot-rolling and / or intermediate annealing during cold-rolling.

The above object is achieved according to a further teaching of the present invention by a pressure plate carrier having a topography whose maximum peak height Rp and / or Sp at most 1.4 microns, preferably at most 1.2 microns, in particular at most 1.0 microns , is. The printing plate carrier is preferably produced from a lithoband according to the invention.

In a preferred embodiment of the printing plate support, the latter has a photosensitive coating with a thickness of less than 2 μm, preferably of less than 1 μm. The high rolling webs of previous litho sheets led to printing errors especially with thin photosensitive coatings, so that in this case results in a special improvement of the printing plate quality. Preferably, the printing plate support has a transparent photosensitive layer, which offers advantages in the exposure. In these layers, the complete coverage of the printing plate support can be detected only late after printing, so that faulty printing plate supports cause higher costs. By improving the topography and the associated reduction in printing errors, the costs can be greatly reduced by printing errors.

The printing plate support may preferably have a width of 200 mm to 2800 mm, more preferably from 800 mm to 1900 mm, in particular from 1700 mm to 1900 mm, and a length of 300 to 1200 mm, in particular 800 mm to 1200 mm.

The printing plate support according to the invention may preferably be in the CtP technique, i. used for a CtP printing plate. In the CtP technique, the surface structure of the printing plate support is particularly critical, since the flat Aufraustrukturen or the relatively thin photosensitive coating at high rolling webs can increasingly lead to printing errors. In addition, the CtP technique often uses transparent photosensitive layers with the aforementioned problems. As a result of the flat topography of the printing plate support according to the invention compared with printing plate supports from the prior art, the print quality can be improved and the costs can be reduced.

Fig. 1

eine schematische Darstellung der Bestimmung der maximalen Peakhöhe Rp und der reduzierten Peakhöhe R_pk nach DIN EN ISO 13 565,

Fig. 2

ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens,

Fig. 3

die Ergebnisse einer Topografiemessung einer Lithobandoberfläche nach dem letzten Kaltwalzstich,

Fig. 4

ein Profil aus der in Fig. 3 dargestellten Topografiemessung,

Fig. 5

die Ergebnisse einer Topografiemessung der Lithobandoberfläche aus Fig. 3 nach Durchführung eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens,

Fig. 6

ein Profil aus der in Fig. 5 dargestellten Topografiemessung,

Fig. 7

die Ergebnisse einer Topografiemessung einer Lithobandoberfläche nach dem letzten Kaltwalzstich und

Fig. 8

die Ergebnisse einer Topografiemessung der Lithobandoberfläche aus Fig. 7 nach Durchführung eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens.

Further features and advantages of the present invention will become apparent from the following description of embodiments of the litho strip according to the invention and the method according to the invention, reference being made to the accompanying drawings. In the drawing show

Fig. 1

a schematic representation of the determination of the maximum peak height Rp and the reduced peak height R _pk according to DIN EN ISO 13 565,

Fig. 2

an embodiment of the method according to the invention,

Fig. 3

the results of a topography measurement of a lithoband surface after the last cold roll pass,

Fig. 4

a profile from the in Fig. 3 illustrated topography measurement,

Fig. 5

the results of a topography measurement of the lithoband surface Fig. 3 after carrying out an embodiment of the method according to the invention,

Fig. 6

a profile from the in Fig. 5 illustrated topography measurement,

Fig. 7

the results of a topography measurement of a lithoband surface after the last cold roll pass and

Fig. 8

the results of a topography measurement of the lithoband surface Fig. 7 after carrying out an embodiment of the method according to the invention.

Fig. 1 shows a schematic representation of the determination of the maximum peak height Rp and the reduced peak height R _pk according to DIN EN ISO 13 _565th

In the left area 2 of the Fig. 1 a one-dimensional profile function Z (x) is plotted in an interval with the limits 0 and L. The function Z (x) supplies at each point x a value Z (x), which is the local position of the actual surface, ie the height deviation of the Surface from the mean surface at <Z (x)> = 0 microns corresponds.

In the right area 4 of the Fig. 1 the so-called Abbott-Firestone curve Z _AF (Q) 6 is plotted. This curve is the cumulative probability density function of the surface profile Z (x). It provides for a percentage value Q between 0 and 100% (plotted on the abscissa) that height value Z _AF above which the corresponding percentage of the surface is located. The Abbott-Firestone curve Z _AF (Q) can thus be implicitly defined by the following equation: $$Q=\frac{1}{L}\underset{Z\left(x\right)\ge Z_{\mathit{AF}}\left(Q\right)}{\int }dx$$

L is the length of the measured profile Z (x), ie the size of the domain of Z (x). The integration range is the part of the total length for which the inequality Z (x) ≥ Z _AF (Q) is satisfied.

By placing a tangent 8 through the inflection point of the Abbott-Firestone curve 6, the intersections of this tangent 8 with the 0% line 10 and the 100% line 12 can define a core area of the surface whose extent is the kernel roughness depth R _k is designated. The average height of the peaks protruding from the core region is referred to as the reduced peak height R _pk and the average depth of the grooves protruding from the core region is referred to as the reduced groove depth R _vk . Furthermore, in Fig. 1 also the maximum peak height Rp drawn, which the Distance of the highest peak to the mean at 0 microns corresponds.

In practice, the maximum peak height Rp or the reduced peak height R _pk can be determined, for example, from profiles Z (x) measured at different positions of the lithoband transversely to the rolling direction.

The reduced peak height S _pk can be determined in practice from a surface measurement accordingly. The calculation is analogous to the reduced peak height R _pk , where the Abbott-Firestone curve Z _AF (Q) for S _{pk can be} implicitly defined by the following equation: $$Q=\frac{1}{A}\underset{Z\left(xy\right)\ge Z_{\mathit{AF}}\left(Q\right)}{\int \int }\mathit{dxdy}$$

A is the size of the measured area, ie the size of the domain of Z (x, y). The integration range is the part of the total area for which the inequality Z (x, y) ≥ Z _AF (Q) is satisfied.

Fig. 2 shows an embodiment of the method according to the invention for producing a lithographic strip. In the method 20, in a first step 22, first an aluminum alloy, for example an AA1050, AA1100, AA3103 or AlMg0.5 alloy, preferably an alloy having the following composition in% by weight: 0.3% ≤ Fe ≤ 1.0%, 0.05% ≤ 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%, cast. Casting may generally be continuous or batch, especially in a continuous, semi-continuous or discontinuous continuous casting process. In an optional step 24, the cast product, ie in particular the cast ingot or the cast strip, may be subjected to a homogenization treatment before further processing, for example in the temperature range between 480 and 620 ° C. for at least two hours. In the subsequent step 26, the cast product is optionally hot rolled, preferably to a thickness between 7 mm and 2 mm. Hot rolling can be dispensed with, for example, in a lithoband produced in the double-belt casting process. Subsequently, the hot strip is then cold rolled in step 28, in particular to a thickness between 0.5 and 0.1 mm. During cold rolling, an intermediate annealing can optionally be carried out. After the last cold rolling pass, the lithoband is subjected to a pickling step in a degreasing treatment with an aqueous pickling medium, wherein the aqueous pickling medium contains at least 1.5 to 3% by weight of a mixture of 5-40% sodium tripolyphosphate, 3-10% sodium gluconate, 3 Contains 8% nonionic and anionic surfactants and optionally 0.5-70% soda, the sodium hydroxide concentration in the aqueous pickling medium being between 0.1 and 5% by weight, in particular between 2 and 3.5% by weight , is the degreasing treatment with pickling step at temperatures between 70 and 85 ° C for a period between 1 and 3.5 s and a surface removal by the degreasing treatment with pickling step of at least 0.25 g / m ^{2 is} set.

Due to the selected surface removal, high rolling webs in the strip surface can be reduced so far that the litho strip after the degreasing treatment with pickling step has a topography whose maximum peak height Rp and / or S _{p is} at most 1.4 μm, preferably at most 1.2 μm, in particular maximum 1.0 μm, and is particularly suitable for CtP pressure plate carrier.

In Fig. 3 The results of a 3D topography measurement of a lithoband surface after the last cold roll pass are shown. The figure shows a three-dimensional view of the surface function Z (x, y) on a square area with the side length of 800 microns. The height information can additionally be the scale right in Fig. 3 be removed. The y-axis lies parallel to the rolling direction of the lithoband. It can be seen that the litho strip along the rolling direction, ie along the y-axis, has high rolling webs, which are clearly visible as bright elevations. These rolling webs can interfere with the application of a photosensitive layer or even prevent locally, so that printing errors can occur when using the printing plate carrier produced from these litho tapes.

Fig. 4 shows a profile Z (x) from the in Fig. 3 represented topography measurement, ie a section from the topography measurement parallel to the x-axis. It can be clearly seen that the roll webs in the litho strip after the Cold rolls may have a height of more than 1.6 microns. However, these high rolling webs have only a small influence on the value of the mean roughness R _{a of} the lithoband.

In Fig. 5 are the results of a topography measurement on the lithoband surface Fig. 3 after carrying out an embodiment of the method according to the invention, ie after the degreasing treatment with pickling step according to the method according to the invention. In Fig. 5 is shown essentially the same area of the litho ribbon as in Fig. 3 , Fig. 6 shows analogously to Fig. 4 an associated profile Z (x) from the in Fig. 5 shown topography measurement.

The Figures 5 and 6 show that can be significantly reduced by the degreasing treatment with pickling step especially the high roll webs. The maximum peak height Rp is in Fig. 6 now only at 1.3 microns and thus significantly below the maximum peak height R _{p of} the untreated litho strip accordingly Fig. 4 ,

The inventive method, it is therefore possible to produce a strip surface, the maximum peak height Rp and / or Sp max. 1.4 μm, preferably max. 1.2 μm, in particular max. 1.0 μm.

In order to practically ensure that the maximum peak heights Rp are maintained during the production of the litho tapes, three measurements of a profile transverse to the rolling direction can be made, for example, on the outside and in the middle of the strip, whereby the length of the profile can be 4.8 mm, for example. The value for Sp can be determined by means of a square area measurement with the side length of 800 microns can be determined.

Like a comparison of Fig. 4 and 6 shows the mean roughness _Ra by the degreasing treatment with pickling step was hardly affected. This parameter, which was used in the conventional production and characterization of lithographic ribbons, is therefore not suitable for indicating the presence of disturbing roll webs in the lithoband. In contrast, the quality of the lithoband surface can be better adjusted by way of the roughness characteristics of the maximum peak height Rp and / or S _p .

In the Figs. 7 and 8th are also shown 3D topography measurements of a lithoband surface with the length 2146.9 microns and the width 2071.7 microns, immediately after the last cold roll pass ( Fig. 7 ) and after carrying out a degreasing treatment with pickling step according to the method of the invention ( Fig. 8 ). The y-axis is in turn parallel to the rolling direction of the lithoband. From the comparison of Fig. 8 with the Fig. 7 it will be seen that the in Fig. 7 existing high rolling webs along the rolling direction can be greatly reduced by the degreasing treatment with pickling step, so that there is an improved lithoband surface.

A litho ribbon with a like in the Figures 5 . 6 or 8 shown surface topography can be used particularly advantageous as printing plate support with very flat Aufraustrukturen and / or in very thin photosensitive coatings, such as in the CtP technique. Further features and properties of the invention can also be taken from the results of roughness measurements of embodiments of the lithographic strip according to the invention which are shown below.

Litho tapes whose aluminum alloys contain, in addition to production-related impurities, the following alloy contents in% by weight: 0.30% ≤ Fe ≤ 0.40%, 0.10% ≤ Mg ≤ 0.30%, 0.05% ≤ Si ≤ 0.25%, Mn ≤ 0.05%, Cu ≤ 0.04%, Rest al, were cold rolled to a final thickness of 0.14 mm, 0.28 mm and 0.38 mm, respectively. In the degreasing treatment with simultaneous pickling step, identical parameters were set as in the embodiment Fig. 2 ,

Before and after the degreasing treatment, roughness measurements were made on the tops of the litho tapes both in the margins and in the middle of the litho tapes. In the roughness measurements, the average roughness S _a , the reduced groove depth S _vk , the reduced peak height S _pk and the maximum peak height Sp were determined in each case. The results for the 0.14 mm thick litho tape are shown in Table 1. <b> Table 1 </ b> measuring position Time of measurement S _a S _vk S _{pk P} border area before degreasing 0.22 0.23 0.35 1, 9 after degreasing 0.21 0.27 0.33 1.0 center before degreasing 0.21 0.26 0.35 1.6 after degreasing 0.21 0.26 0.32 1.0

In the prior art, the mean surface roughness S _a has hitherto been used to characterize the lithographic ribbons. Table 1 shows that this roughness parameter is not suitable for representing the effect of the degreasing treatment according to the invention with pickling step or the surface quality of the lithographic strips with respect to individual high rolling webs. Its value is essentially unchanged after the degreasing treatment with pickling step. The reduced groove depth S _vk is also unsuitable as an indicator for high rolling webs. In contrast, the values for the maximum peak height S _{p are} significantly reduced and thus indicate the improvement of the lithoband surface with regard to the disturbing high rolling webs. An optimization of the lithographic ribbons or of the method for their production on the basis of the roughness characteristic value S _p accordingly leads to a particularly low susceptibility to the aforementioned printing errors. The reduced peak height S _pk is also reduced by the pickling step degreasing treatment and can be used as an additional roughness parameter. <b> Table 2 </ b> S _p (edge) S _p (middle) strip thickness before degreasing after degreasing before degreasing after degreasing 0.14 mm 1.9 1.0 1.67 1.1 0.28 mm 1, 61 1.2 1.38 1.1 0.38 mm 1.3 1.0 1.3 1, 1

Table 2 compares the results for the maximum peak height S _p from the roughness measurements on litho ribbons of different thicknesses. In particular, the litho tapes with strip thicknesses of 0.3 mm to 0.1 mm clearly benefit from the process according to the invention, since they have relatively large S _p values of more than 1.5 μm directly after the last cold rolling pass and are thus susceptible to the aforementioned printing defects are. By means of the degreasing treatment with pickling step, the maximum peak height Sp can be reduced substantially to the same value for all measured strip thicknesses. Consequently, the surface quality of thin lithographic ribbons can be improved particularly well with the method according to the present invention.

The results in Tables 1 and 2 also show that high rolling webs occur, in particular at the strip edges. Therefore, for example, the degreasing treatment with pickling step can also be carried out selectively in the edge region of the litho tapes. <b> Table 3 </ b> Time of measurement S _a S _vk S _{pk P} before degreasing 0.22 0.23 0.43 1.51 after degreasing 0.21 0.24 0.37 1.13

Table 3 shows the roughness characteristics S _a , S _vk , S _pk and Sp averaged over litho tapes of different thicknesses. The results clearly show that the average roughness S _a previously used for the characterization of litho tapes is not suitable for improving the quality of a litho strip surface with regard to the disturbing high roll webs. In contrast, the values of the maximum peak height Rp and / or Sp and the reduced peak height R _pk and / or S _pk after the degreasing treatment with pickling step show a significant reduction, so that the lithoband or the method for its production by an optimization with respect to the parameter Rp and / or Sp, possibly in combination with R _pk and / or S _pk , can be significantly improved.

For the production of the litho strip according to the invention, for example, the method according to the invention can be used. However, the lithoband of the present invention is not limited to this production method. On the basis of the present invention, by optimizing the roughness index Rp and / or Sp, the person skilled in the art can also develop further methods in order to arrive at a lithoband according to the invention.

Claims (16)

Lithoband for electrochemical roughening, consisting of a rolled aluminum alloy,
characterized in that the strip surface has a topography whose maximum peak height R _p and / or Sp is at most 1.4 μm, preferably at most 1.2 μm, in particular at most 1.0 μm. Lithoband according to claim 1,
characterized in that the strip surface has a topography whose reduced peak height R _pk and / or S _{pk is} at most 0.4 μm, preferably at most 0.37 μm. Lithoband according to claim 1 or 2,
characterized in that the thickness of the lithoband is 0.5 mm to 0.1 mm. Lithoband according to one of claims 1 to 3,
characterized in that the litho strip consists of an AA1050, AA1100, AA3103 or AlMg0.5 alloy. Lithoband according to one of claims 1 to 4,
characterized in that the lithoband has the following alloy composition in% by weight: 0.3% ≤ Fe ≤ 1.0%, 0.05% ≤ 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%. Lithoband according to one of claims 1 to 5,
characterized in that the litho strip has the following alloy contents in wt .-%: 0.3% ≤ Fe ≤ 0, 4%, 0.1% ≤ Mg ≤ 0.3%, 0.05% ≤ Si ≤ 0.25%, Mn ≤ 0.05%, Cu ≤ 0.04%. Lithoband according to one of claims 1 to 6,
characterized in that the impurities of the alloy of the lithoband have the following limit values in% by weight: Cr ≤ 0.01%, Zn ≤ 0.02%, Ti ≤ 0.04%, B ≤ 50 ppm. Process for the production of a lithoband, in particular a lithoband according to one of claims 1 to 7, in which a lithoband consisting of an aluminum alloy is cold-rolled and in which the lithoband is subjected after the last cold-rolling pass to a degreasing treatment with a simultaneous etching step with an aqueous pickling medium, wherein the aqueous pickling medium contains at least 1.5 to 3% by weight of a mixture of 5-40% sodium tripolyphosphate, 3-10% sodium gluconate, 3-8% nonionic and anionic surfactants and optionally 0.5-70% sodium carbonate and the sodium hydroxide Concentration in the aqueous pickling medium is between 0.1 and 5% by weight,
characterized in that the surface removal by the degreasing treatment with simultaneous pickling step is at least 0.25 g / m ² . Method according to claim 8,
characterized in that the sodium hydroxide concentration in the aqueous pickling medium is between 2 and 3.5 wt .-% and optionally the degreasing treatment with pickling at temperatures between 70 and 85 ° C for a period between 1 and 3.5 s. Method according to claim 8 or 9,
characterized in that the pickling temperature is between 76 and 84 ° C and / or the sodium hydroxide concentration in the aqueous pickling medium is between 2.6 and 3.5 wt .-%. Method according to one of claims 8 to 10,
characterized in that the pickling time is between 1 and 2 s, preferably between 1.1 and 1.9 s. Method according to one of claims 8 to 11,
characterized in that the litho strip is rolled in the last cold rolling pass to a final thickness of 0.5 mm to 0.1 mm. Method according to one of claims 8 to 12,
characterized in that is used as aluminum alloy AA1050, AA1100, AA3103 or AlMg0.5. Printing plate carrier, in particular producible from a litho strip according to one of claims 1 to 7,
characterized in that the printing plate support has a topography whose maximum peak height Rp and / or Sp is at most 1.4 μm, preferably at most 1.2 μm, in particular at most 1.0 μm. Print plate carrier according to claim 14,
characterized in that the printing plate support has a photosensitive coating with a thickness of less than 2 microns. Use of a printing plate support according to claim 14 or 15 for a CtP printing plate.

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