EP1820866B2 - Aluminiumcarbide-free aluminium alloy - Google Patents

Description

The invention relates to an aluminum alloy for producing an aluminum strip for lithographic printing plate support, a method for producing an aluminum alloy according to the invention for lithographic printing plate support, wherein in the production of aluminum alloy after the electrolysis of the aluminum oxide, the liquid aluminum is supplied to a plurality of purification steps and an aluminum strip for lithographic Printing plate support and a corresponding use of the aluminum strip for lithographic printing plate support.

Print plate supports for lithographic printing from an aluminum alloy must meet very high requirements for their suitability for today's printing technology. On the one hand, the pressure plate carrier produced from an aluminum strip must be able to be roughened homogeneously, whereby mechanical, chemical and electrochemical roughening methods and their combination are used. On the other hand, the printing plates are often after baking and developing a baking process between 220 to 300 ° C with an annealing time of 3 to 10 min. subjected to cure the applied photoresist. On the one hand, various aluminum alloys have been developed to meet the requirement profile.

On the other hand, further developments in the field of coatings of printing plate support were carried out, which should further improve the stability of the printing plate support during printing and thus their life. Good results have been achieved by novel coatings that are almost gas-tight. However, the printing plate supports, made of the aluminum alloys available so far, tend to form bubbles between the printing plate support and the coating. This blistering eventually leads to cracking of the coating and thus failure of the printing plate.

The US patent US 4,003,738 discloses a method for removing carbide from an aluminum melt by fuming with the melt with chlorine gas. The production of an aluminum alloy for lithographic printing plate supports is not disclosed.

From the publication US 3,721,546 Also, a method for producing a carbide-free aluminum alloy is known, wherein the aluminum carbide is separated by a graphite filter from the aluminum melt. However, the suitability of the disclosed aluminum alloys for the production of lithographic printing plate supports is not disclosed.

The Japanese patent application JP 2004292862 discloses pure aluminum, an Al-Mn, Al-Mn-Mg or Al-Mg alloy having a very low aluminum carbide content. With the above aluminum alloys according to the teaching of this Be achieved document, that even with long storage times in the photosensitive layer of lithographic printing plate support no errors.

A method for producing a aluminum alloy with a low aluminum carbide content is also known from US 2004/0173053 A1 known.

Finally, the document discloses JP 2000-309829 A a method of removing impurities, especially aluminum carbide, from an aluminum melt. According to Japanese Unexamined Patent Publication, an inert gas is supplied to the molten aluminum in a stirring station for a period of 30 minutes. However, a method for producing an aluminum alloy for lithographic printing plate support is not apparent from this document.

Proceeding from this, the object of the present invention is to provide an aluminum alloy for producing an aluminum strip for lithographic printing plate supports and a corresponding aluminum strip for lithographic printing plate supports, from which or with which lithographic printing plate supports can be produced that require the use of almost gas-tight coatings enable. In addition, the invention has the object, a method for producing a corresponding aluminum alloy and an advantageous use of the To propose aluminum strip for lithographic printing plate supports.

$$\mathrm{Mn}\le \mathrm{0,3\; \%,}$$

$$\begin{array}{ccc}\mathrm{0,4}& \%\le \mathrm{Fe}\le 1& \%,\end{array}$$

$$\mathrm{0,05}\mathrm{}\%\mathrm{}\le \mathrm{Si}\le \mathrm{0,5\; \%,}$$

$$\mathrm{Cu}\le \mathrm{0,04}\%,$$

$$\mathrm{Ti}\le \mathrm{0,04\; \%,}$$

unvermeidbare Verunreinigungen einzeln max. 0,01 %, in Summe max. 0,05 % und Rest Al.According to a first teaching of the present invention, the above-described object is achieved in that the aluminum alloy has an aluminum carbide content of less than 1 ppm and the following alloy constituents in% by weight: $$0.05\mathrm{}\%\le \mathrm{mg}\le \mathrm{0.3}\%.$$

$$\mathrm{Mn}\le \mathrm{0.3\%,}$$

$$\begin{array}{ccc}0.4& \%\le \mathrm{Fe}\le 1& \%.\end{array}$$

$$0.05\mathrm{}\%\mathrm{}\le \mathrm{Si}\le \mathrm{0.5\%,}$$

$$\mathrm{Cu}\le \mathrm{0.04}\%.$$

$$\mathrm{Ti}\le \mathrm{0.04\%,}$$

unavoidable impurities individually max. 0.01%, in total max. 0.05% and balance Al.

It has surprisingly been found that printing plate support, which have been made of an aluminum alloy with a correspondingly low Aluminiumcarbidgehalten allow the use of gas-tight coatings, since the blistering is extremely low. It is believed that the slightest trace of aluminum carbide (Al ₄ C ₃ ) and its reaction with moisture to form methane gas causes bubbling under the gas tight coatings. Surprisingly, it has been found that in particular the composition of the aluminum alloy of the printing plate support plays an important role in the blistering, although it was previously assumed that it is essentially one of the Surface of the printing plate carrier is tried phenomenon. Previous aluminum alloys have therefore not been optimized for the lowest possible aluminum carbide content. It turns out, however, that even with an aluminum carbide content of less than 10 ppm, the formation of bubbles drops significantly and corresponding aluminum alloys can be used to produce suitable printing plate supports. According to the invention, the aluminum carbide content of the aluminum alloy according to the invention is adjusted to less than 1 ppm, so that blistering is prevented in the case of gas-tight coating of the printing plate carrier.

In order to ensure the further mechanical, chemical or electrochemical requirements imposed on a lithographic printing plate support, it is also advantageous if the further composition of the aluminum alloy corresponds to an aluminum alloy of the type AA1xxx, AA3xxx, AA8xxx, preferably AA1050, or AA3103. Of the aluminum alloys mentioned, it is known that they at least partially meet the requirements for lithographic printing plate supports and have hitherto been used for their production. The inventive reduction of the aluminum carbide content to less than 1 ppm, the good mechanical, chemical and electrochemical properties of said aluminum alloys can be exploited even with pressure plate carriers with a gas-tight coating.

$$\mathrm{Mn}\le \mathrm{0,3}\%,$$

$$\mathrm{0,4}\mathrm{}\%\le \mathrm{Fe}\le 1\%,$$

$$\mathrm{0,05}\mathrm{}\%\mathrm{}\le \mathrm{Si}\le \mathrm{0,5\; \%,}$$

$$\mathrm{Cu}\le \mathrm{0,04}\%,$$

$$\mathrm{Ti}\le \mathrm{0,04\; \%,}$$

unvermeidbare Verunreinigungen einzeln max. 0,01 %, in Summe max. 0,05 % und Rest Al.According to the invention, the aluminum alloy according to the invention comprises the following alloy constituents in% by weight: $$0.05\mathrm{}\%\le \mathrm{mg}\le 0.3\mathrm{}\%.$$

$$\mathrm{Mn}\le \mathrm{0.3}\%.$$

$$0.4\mathrm{}\%\le \mathrm{Fe}\le 1\%.$$

$$0.05\mathrm{}\%\mathrm{}\le \mathrm{Si}\le \mathrm{0.5\%,}$$

$$\mathrm{Cu}\le \mathrm{0.04}\%.$$

$$\mathrm{Ti}\le \mathrm{0.04\%,}$$

unavoidable impurities individually max. 0.01%, in total max. 0.05% and balance Al.

This with a deriving from the applicant European patent application with the application number 05 022 772 Protected aluminum alloy combines good chemical and electrochemical roughening properties with improved mechanical properties, especially after performing a burn-in process.

$$\mathrm{Mn}\le \mathrm{0,05\; \%,}$$

$$\mathrm{0,3}\mathrm{}\%\le \mathrm{Fe}\le \mathrm{0,4}\%,$$

$$\mathrm{0,05}\mathrm{}\%\mathrm{}\le \mathrm{Si}\le \mathrm{0,25\; \%,}$$

$$\mathrm{Cu}\le \mathrm{0,04}\mathrm{}\%,$$

$$\mathrm{Ti}\le \mathrm{0,04}\%,$$

unvermeidbare Verunreinigungen einzeln max. 0,01 %, in Summe max. 0,05 % und Rest AlAccording to a second teaching of the present invention, the aluminum alloy according to the invention has an aluminum carbide content of less than 1 ppm and alternatively the following alloy constituents in% by weight: $$0.1\mathrm{}\%\le \mathrm{mg}\le 0.3\mathrm{}\%.$$

$$\mathrm{Mn}\le \mathrm{0.05\%,}$$

$$0.3\mathrm{}\%\le \mathrm{Fe}\le \mathrm{0.4}\%.$$

$$0.05\mathrm{}\%\mathrm{}\le \mathrm{Si}\le \mathrm{0.25\%,}$$

$$\mathrm{Cu}\le 0.04\mathrm{}\%.$$

$$\mathrm{Ti}\le \mathrm{0.04}\%.$$

unavoidable impurities individually max. 0.01%, in total max. 0.05% and balance Al

This aluminum alloy is particularly well suited for the production of lithographic printing plate supports due to its balanced properties in terms of mechanical stability, chemical and electrochemical Aufraubarkeit. Again, this aluminum alloy is significantly improved by the reduction of the aluminum carbide content according to the invention in relation to the production of printing plate supports provided with a virtually gas-tight coating.

According to a third teaching of the present invention, the above object is procedurally achieved in that after the electrolysis of the alumina, the liquid aluminum is fed to a stirring station in which inert gases are introduced with stirring in the liquid aluminum, the duration of stirring and blowing of the inert gas into the molten aluminum in the stirring station for at least 15 min. is and the proportion of aluminum carbides in the aluminum alloy to less than 1 ppm, is lowered. The purification steps of aluminum alloys have been aimed at reducing other impurities such as alkaline earth or alkali metals, of course, aluminum carbides were removed from the molten aluminum. For this reason, the aluminum carbide contents of the conventionally produced aluminum alloys were clearly above the values according to the invention. However, it has been shown that by targeted tuning of individual known cleaning steps on the removal of Aluminum carbides but also by their combination with conventional trained cleaning steps very low Aluminiumcarbidgehalte in the production of aluminum alloys can be achieved immediately before the casting of the aluminum alloy. The cleaning and processing steps of the aluminum alloy described below can therefore be used both individually and in combination according to the invention.

According to the invention, after the electrolysis of the alumina, the liquid aluminum is fed to a stirring station in which inert gases are introduced with stirring into the liquid aluminum, wherein the duration of stirring and blowing the inert gas into the molten aluminum in the stirring at least 15 min. is. It has hitherto been known that in the stirring station, while blowing in inert gases and stirring, essentially the alkali metals and alkaline earth metals are removed from the aluminum melt. Stirring and gassing times of typically 6 to 8 minutes were for this purpose. sufficient. Surprisingly, however, it has been found that, especially in the case of the electrolysis of the aluminum oxide into the molten aluminum, which essentially leads to the formation of aluminum carbide compounds in the molten aluminum, can be significantly reduced by a longer duration of stirring and blowing of inert gases. A maximum duration can not be specified for this reason. Experiments have shown, however, that the duration of stirring and blowing the gases to about 15 to 20 min. can be extended to a compromise between economy and effective removal of aluminum carbide from the aluminum alloy.

Alternatively or cumulatively to the extended stirring time, a reduction of the aluminum carbide content of the molten aluminum results from the fact that the liquid aluminum supplied to the stirring station has been obtained at least partially from cold metal. Cold metal is already produced from an electrolysis of alumina aluminum, which has undergone some process steps after the electrolysis, for example, a stirring station. The aluminum carbide content of the supplied cold metal is therefore typically much lower than that of a liquid aluminum originating from the electrolysis. It is believed that the burnup of the graphite electrodes used in the electrolysis contribute to the aluminum carbide content of the aluminum melt produced from alumina.

The aluminum carbide content of the aluminum alloy according to the invention is additionally reduced further by adding aluminum fluorides to the stirring station during the stirring of the liquid aluminum. These remove the alkali metals sodium, calcium and lithium, but also via oxidation, in particular elements such as titanium and phosphorus. At the same time, however, it was found that the aluminum carbide content of the aluminum melt is also reduced.

To further reduce the aluminum carbide content, the aluminum is further refined according to one Embodiment of the method according to the invention, supplied to the furnace for adding the alloy constituents, wherein the aluminum in the furnace for at least more than 30 min., Preferably at least more than 60 min. after alloying has taken place in the oven by stirring and adding the alloying ingredients. This ensures that the aluminum carbide compounds contained mostly in gas bubbles of the previously introduced into the molten aluminum gas together with these can migrate to the surface of the molten aluminum and form part of the dross to be removed from the melt there.

If gas purging with reactive and / or inert gases takes place in the oven, not only can further aluminum carbide compounds from the aluminum melt be flushed out with the gas, but at the same time the added alloy components can be homogeneously distributed in the aluminum melt.

Further removal of unwanted substances from the aluminum melt, in particular also aluminum carbide compounds, is achieved by feeding the aluminum alloy to a rotor degassing unit and rinsing it with a mixture of inert and / or reactive gases, in particular argon, nitrogen and / or chlorine. This rotor degassing removes the aluminum carbide compounds, as well as other undesirable compounds from the molten aluminum alloy melt, when the alloying ingredients are added to the aluminum melt.

Preferably, the aluminum alloy may be subjected to at least one segregation step in which the aluminum alloy is heated to slightly above the solidus temperature of the aluminum alloy so that molten heavily contaminated phases can be extruded from the aluminum alloy. These highly contaminated phases of the aluminum alloy additionally contain aluminum carbide compounds, which can be removed in this way from the aluminum melt.

Finally, the inventive method for producing an aluminum alloy for lithographic printing plate supports with respect to reducing the aluminum carbide content can be further improved by filtering the aluminum alloy prior to strand or ribbon casting, the filter having a high filter efficiency for smaller or smaller sized particles equal to 5 μ m. It goes without saying that the filter efficiency of these filters is also high, even for larger particles with a size of significantly more than 5 μm . It has been found that the aluminum carbides are typically present predominantly in impurity particles larger than 10 μm , so that filtering the aluminum alloy provides additional reduction of the aluminum carbide content. Since the filtering of the aluminum alloy takes place immediately before the casting of the aluminum alloy, this step, especially in combination with the previously described measures, a high control value attached. For example, to ensure this filtering two-stage filter used, consisting of a first ceramic foam filter with a downstream Tiefbettfilter. Preferably, the addition of grain refining material can take place between the two filters in order to ensure the highest possible effectiveness of the ceramic foam filter through the construction of a filter cake and a long service life of the downstream deep bed filter.

According to a fourth teaching of the present invention, the above-described object is achieved for an aluminum strip for lithographic printing plate support that this is prepared by continuous or discontinuous casting of an aluminum alloy according to the invention with subsequent hot and / or cold forming, wherein the aluminum alloy according to the invention using the inventive Process has been prepared. The aluminum strip according to the invention then consists of an extremely low-aluminum-carbide material, so that it is ideally suited for the production of printing plate supports with a gas-tight coating.

An aluminum strip with only a few aluminum carbide compounds on its surface and in the core material can be provided by removing the rolling oil residues on the aluminum strip for lithographic printing plate supports by annealing and degreasing the strip.

Preferably, the aluminum ribbon is made using an acidic or basic medium of a first Degreasing, and then further cleaning using a pickling process so that the removal of aluminum carbide on the surface is even more thorough. Thus, an aluminum strip with a further reduced amount of aluminum carbide compounds can be provided on its surface. As already described above, the aluminum alloy of the aluminum strip according to the invention itself has very low proportions of aluminum carbide compounds, so that in combination with the almost aluminum carbide-free surface of the aluminum strip, an aluminum strip, ideal for coating with gas-tight coatings, is available for lithographic printing plate supports.

Finally, according to a fifth teaching of the present invention, the above-described object with respect to the use of the aluminum strip is achieved by using the aluminum strip according to the invention for the production of lithographic printing plate supports with a gas-tight coating.

There are now a multitude of possibilities for designing and further developing the aluminum alloy according to the invention for producing an aluminum strip for lithographic printing plate supports, the process for producing the aluminum alloy according to the invention and the aluminum strip according to the invention for lithographic printing plate supports and its use. Reference is made on the one hand to the independent claims 1, 2, 3 and 11 subordinate claims. On the other hand, reference is made to the Description of an embodiment of the inventive method for producing an aluminum alloy in conjunction with the drawing.

In the drawing, the single figure shows schematically the sequence of the individual process steps for producing an embodiment of an aluminum alloy according to the invention.

According to the embodiment shown in the single figure, the production of an aluminum alloy according to the invention begins by an electrolysis 1 of aluminum oxide. The liquid aluminum is then fed to a stirring station 2, alternatively or cumulatively to the aluminum obtained directly from aluminum oxide, as shown in the figure, cold metal 3 can be supplied to the stirring station. As already described above, the cold metal contains less aluminum carbide than an aluminum melt produced directly from aluminum oxide, since the latter additionally contains carbon compounds and thus aluminum carbide by burning off the graphite electrodes. In order to remove the aluminum carbides from the molten aluminum, the introduction of inert gases or a gas mixture and the stirring for longer in the stirring station 2, than usually provided, carried out. The minimum gassing and stirring time should be between 10 and 20 min. lie. However, longer stirring and gassing times can also be set. Subsequently, the aluminum melt is fed to a furnace 4. Subsequently, a gas flushing with reactive and / or inert gases are carried out in the furnace 4 and the alloying constituents added. The gas flushing leads to a further reduction of the aluminum carbide content in the aluminum melt. Subsequently, the aluminum alloy is in the oven for a certain period of time, so that the gas bubbles previously dissolved in the melt have enough time to get to the surface of the molten aluminum. The standing of the melt in the oven can for a period of 15 to 90 min., Preferably from 30 to 60 min. be made. The gas bubbles which have reached the surface of the molten aluminum during gas purging with reactive and / or inert gases are skimmed off from the melt by scraping off the aluminum alloy and thus removed from the aluminum alloy. The dross then contains the aluminum carbides flushed out of the aluminum melt.

After treatment in the oven 4, the liquid aluminum alloy is fed to a rotor degassing 5, which operates, for example, by the SNIF process (Spinning Nozzle Inert Flotation), for example purged with argon and / or chlorine. The fine gas bubbles, in turn, sweep the contaminants to the bath surface, with chlorine being particularly liable to cause the sodium and calcium contaminants to harden to salts, which are then deposited with the gas bubbles in a scratch layer on the aluminum alloy. The scratching layer is then removed again.

Finally, the aluminum alloy according to the invention is preferably filtered before casting Filter 6 subjected, which has a high filter efficiency for particles with a size of less than or equal to 5 μ m. For example, filters 6 having a filter efficiency of at least 50% can be used for these particles. Since aluminum carbides generally to larger particles, mostly adhered with a size of about 10 μ m, can be further reduced aluminum carbide content of the aluminum alloy effectively by the filtering step. Subsequently, the aluminum alloy can be fed to a continuous or discontinuous casting process 7, 8.

Optionally, the aluminum alloy may be subjected to at least one segregation step in a segregation station, not shown, in which the aluminum alloy is heated to a temperature just above the solidus temperature of the aluminum alloy. Heavily contaminated phases of the aluminum melt melt below the solidus temperature so that they can be pressed out of the molten aluminum and removed. Since the contaminated phases usually also contain aluminum carbides, their proportion in the aluminum alloy according to the invention is further reduced by the optional segregation.

Scrap samples of the aluminum alloy drawn after filtration, and thus immediately prior to casting, showed an extremely low aluminum carbide content of less than 1 ppm.

Claims (14)

1. Aluminium alloy for producing an aluminium strip for lithographic print plate carriers,
   characterised in that
   the aluminium alloy has an aluminium carbide content of less than 1 ppm and has the following alloying constituents in % by weight: $$0.05\mathrm{}\%\le \mathrm{Mg}\le \mathrm{0.3\; \%,}$$

   

   $$\mathrm{Mn}\le \mathrm{0.3\; \%,}$$

   

   $$0.4\mathrm{}\%\le \mathrm{Fe}\le 1\%,$$

   

   $$0.05\mathrm{}\%\le \mathrm{Si}\le \mathrm{0.5}\%,$$

   

   $$\mathrm{Cu}\le \mathrm{0.04\; \%,}$$

   

   $$\mathrm{Ti}\le \mathrm{0.04}\%,$$

   

   unavoidable impurities individually max. 0.01%, in total max. 0.05% and remainder Al.
2. Aluminium alloy for producing an aluminium strip for lithographic print plate carriers,
   characterised in that
   the aluminium alloy has an aluminium carbide content of less than 1 ppm and, as an alternative, has the following alloying constituents in % by weight: $$0.1\mathrm{}\%\le \mathrm{Mg}\le 0.3\mathrm{}\%,$$

   

   $$\mathrm{Mn}\le \mathrm{0.05}\%,$$

   

   $$0.3\mathrm{}\%\le \mathrm{Fe}\le \mathrm{0.4}\%,$$

   

   $$0.05\mathrm{}\%\le \mathrm{Si}\le \mathrm{0.25}\%,$$

   

   $$\mathrm{Cu}\le \mathrm{0.04\; \%,}$$

   

   $$\mathrm{Ti}\le \mathrm{0.04}\%,$$

   

   unavoidable impurities individually max. 0.01%, in total max. 0.05% and remainder Al.
3. Method for producing an aluminium alloy according to claim 1 or 2 for lithographic print plate carriers, in which during the production of the aluminium alloy after the electrolysis of the aluminium oxide, the liquid aluminium, up to the casting of the aluminium alloy, is supplied to a plurality of purification steps, characterised in that after the electrolysis of the aluminium oxide, the liquid aluminium is supplied to a stirring station, in which inert gases are introduced into the liquid aluminium whilst stirring, the duration of the stirring and blowing in of the inert gas into the aluminium melt in the stirring station being at least 15 min. and the proportion of aluminium carbides in the aluminium alloy is lowered by one or more purification steps to less than 1 ppm.
4. Method according to claim 3, characterised in that the liquid aluminium supplied to the stirring station is obtained at least partially from cold metal.
5. Method according to claim 3 or 4, characterised in that aluminium fluorides are added during the stirring of the liquid aluminium in the stirring station.
6. Method according to any one of claims 3 to 5, characterised in that to add the alloying constituents, the aluminium is supplied to a furnace and is left to stand in the furnace for at least more than 30 min., preferably at least more than 60 min., after the alloying has taken place in the furnace by stirring and the addition of the alloying constituents.
7. Method according to any one of claims 3 to 6,
   characterised in that
   a gas flushing with inert and/or reactive gases takes place in the furnace.
8. Method according to any one of claims 3 to 7,
   characterised in that
   the aluminium alloy is supplied, after the furnace, to a rotor degassing and is flushed with a mixture of inert and/or reactive gases, in particular argon, nitrogen and/or chlorine.
9. Method according to any one of claims 3 to 8,
   characterised in that
   the aluminium alloy is subjected to at least one segregation step.
10. Method according to any one of claims 3 to 9,
    characterised in that
    the aluminium alloy is filtered prior to the continuous or strip casting, the filter having a high filter effectivity for particles with a size of less than or equal to 5 µm.
11. Aluminium strip for lithographic print plate carriers produced by continuous or discontinuous casting of an aluminium alloy according to claim 1 or 2, with subsequent hot and/or cold forming, the aluminium alloy being produced using a method according to claim 3 to 10.
12. Aluminium strip according to claim 11,
    characterised in that
    the rolling oil residues on the aluminium strip for lithographic print plate carriers have been removed by annealing and degreasing the strip.
13. Aluminium strip according to claim 11 or 12,
    characterised in that
    the aluminium strip is subjected to a first degreasing using an acid or alkaline medium and then subjected to a further degreasing using a pickling process.
14. Use of the aluminium strip for lithographic print plate carriers according to any one of claims 11 to 13 for producing lithographic print plate carriers with a gas-tight coating.

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