JPH0474440B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for electrolytically etching aluminum plates for printing plates, and in particular, when electrolytically etching is performed in an etching solution containing hydrochloric acid and organic substances, the amount of organic substances consumed can be reduced, and This invention relates to a method for uniformly graining an aluminum plate. The present invention also relates to an electrolytic etching method that reduces the burden of wastewater treatment. It is known to grain an aluminum plate for printing plates by electrolytically etching the plate in an aqueous solution containing hydrochloric acid and an organic substance. During electrolytic etching, aluminum is dissolved in an aqueous solution, and at the same time an equivalent amount of hydrochloric acid is consumed. Therefore, when aluminum plates are fed one after another into an etching bath and electrolytically etched,
The aluminum ion concentration in the etching solution increases and the free hydrochloric acid concentration decreases. Such a change in the composition of the etching solution lowers the electrical conductivity and changes the properties of the resulting grains. In particular, an increase in aluminum ion concentration poses a risk of deteriorating the grain properties. Therefore, it is necessary for the etching solution to maintain both the aluminum ion concentration and the free hydrochloric acid concentration within a certain range. One way to maintain the composition of the etching solution within a certain range is to perform etching while replenishing hydrochloric acid in an amount equivalent to that consumed by dissolving aluminum, and when the concentration of aluminum ions in the solution reaches the allowable limit. There is a way to update the etching solution. However, when using this method, the aluminum ion concentration in the etching solution gradually increases, so there is a risk that the properties of the resulting grains will gradually change. Alternatively, a portion of the etching solution may be continuously or intermittently drawn out and discarded so that the aluminum ion concentration in the etching solution remains approximately constant, and at the same time, a new etching solution of the same amount as the removed etching solution is added. By replenishing the etching solution, the composition of the etching solution can be maintained almost constant. In any of these methods, the etching solution to be discarded contains free hydrochloric acid and organic substances in addition to the aluminum chloride produced by etching, so it is inevitable that these will be lost. Furthermore, in order to release the discarded etching solution into public waters, pretreatment such as neutralization with alkali and removal of organic matter through microbial treatment is required. The present invention provides a method for electrolytically etching aluminum plates for printing plates in an etching solution containing hydrochloric acid and organic substances, which avoids the difficulties associated with the conventional etching solution management methods described above. According to the present invention, by circulating the etching solution between an etching tank containing an etching solution containing acetic acid and an organic substance and an ion exchange resin tank containing a strongly acidic cation exchange resin, the composition of the etching solution is changed to free hydrochloric acid. Electrolytic etching of an aluminum plate for a printing plate is carried out by immersing the aluminum plate in an etching bath and performing electrolytic etching while maintaining the aluminum ion concentration to be 20 g/or less and 5 g/or less. To explain the present invention in more detail, the present invention involves treating the etching solution with a strongly acidic cation exchange resin in the known electrolytic etching of an aluminum plate for printing plates using an aqueous solution containing hydrochloric acid and an organic substance. This method performs etching while maintaining the composition of the etching solution constant by adsorbing and removing the aluminum ions and simultaneously liberating the hydrochloric acid fixed on the aluminum ions. To specifically explain the electrolytic etching of an aluminum plate for printing plates by the method of the present invention, the aluminum plate is subjected to pretreatment such as degreasing and washing in a conventional manner to clean the surface, and then subjected to electrolytic etching by the method of the present invention. be done. As the aluminum plate, a so-called pure aluminum plate such as 1050 material is usually used, but an aluminum alloy plate can also be used. During etching, the metals contained in aluminum are also dissolved in the etching solution, but these can also be adsorbed and removed by a strongly acidic cation exchange resin in the same way as aluminum ions.
The aluminum plate is usually used in a long length so that the aluminum plate runs continuously through the steps of pre-treatment, electrolytic etching and post-treatment. Pretreatment includes, for example, solvent degreasing using trifrene, thinner, etc., or emulsion degreasing using kerosene and triethanolamine, and then soaking in a 1-10% caustic soda aqueous solution at 20-70°C.
A method is used in which the material is immersed in water for 5 seconds to 10 minutes and then immersed in a 10 to 20% nitric acid (or sulfuric acid) aqueous solution at 10 to 50°C for 5 seconds to 5 minutes. Electrolytic etching is carried out by immersing the aluminum plate, which has undergone the above-mentioned pretreatment, in an etching solution contained in an etching bath, and by passing electricity between an electrode provided in the bath and the aluminum plate. Etching conditions vary depending on the type and amount of organic matter, but are usually a current density of 20 to 200 A/dm ² , an etching time of 10 to 300 seconds, and a liquid temperature of 10 to 40°C. As the etching solution, an aqueous solution containing hydrochloric acid and an organic substance is used. It has been proposed to use various organic substances in combination with hydrochloric acid as an etching solution. Such organic substances include oxycarboxylic acids such as citric acid, malic acid, and tartaric acid, acrylic acid,
unsaturated carboxylic acids such as maleic acid and itaconic acid,
Examples include saturated monocarboxylic acids such as formic acid, propylic acid, and butyric acid, β-dicarbonyl compounds such as acetylacetone, and phenols.
70053, 54-1243, patent application 1986-38469, 55-54991,
55-54993), these organic substances are usually present in the etching solution at a concentration of 0.01 to 1 mol/mole, depending on the type thereof. The etching solution is circulated between the etching tank and the ion exchange resin tank to maintain the concentration of free hydrochloric acid in the solution at 20 g/or less and the aluminum ion concentration at 5 g/or less. When the free hydrochloric acid concentration decreases, the electrolysis voltage increases and power consumption increases. Further, electrolytic etching tends to be non-uniform. The free hydrochloric acid concentration is therefore usually maintained at least 5 g/g/. On the other hand, if the concentration of free hydrochloric acid is higher than 20 g/min, etching tends to become non-uniform.
Furthermore, when the etching solution is treated with a strongly acidic cation exchange resin to adsorb aluminum ions, the equilibrium adsorption amount of aluminum ions decreases. The preferable range of free hydrochloric acid concentration in the etching solution is 7 to
It is 15g/. On the other hand, the aluminum ion concentration in the etching solution affects etching uniformity and etching depth (surface roughness). High aluminum ion concentration makes uniform etching impossible. The permissible limit of aluminum ion concentration is 5 g/, although it varies slightly depending on the type and amount of coexisting organic matter. Preferably, the aluminum ion concentration is maintained at 4 g/or less. The low aluminum ion concentration does not adversely affect etching. However, lowering the aluminum ion concentration more than necessary is not preferable because it increases the amount of etching solution treated with the strongly acidic cation exchange resin and reduces the adsorption capacity of the ion exchange resin.
Usually the aluminum ion concentration is 0.5~5g/
maintain it. Also, even within this range, if the aluminum ion concentration changes, the etching depth of the aluminum plate changes, so the aluminum ion concentration should be ±1.5 g/, especially 1.0 g/
It is preferable to maintain it within g/g. In the method of the present invention, in order to maintain the free hydrochloric acid concentration and aluminum ion concentration in the etching solution within a predetermined range, an ion exchange resin tank containing a strongly acidic cation exchange resin is installed, and this is connected to the etching tank. By circulating an etching solution between the two, aluminum ions are adsorbed and removed, and at the same time, hydrochloric acid bound to the aluminum ions is released. Organic substances in the etching solution pass through the ion exchange resin tank without being adsorbed by the ion exchange resin. Therefore, according to the method of the present invention, the composition of the etching solution is maintained constant. It is preferable to provide two tanks of ion exchange resin and use them alternately. In this way, the etching solution can be processed continuously, and therefore, etching can be performed without substantially changing the composition of the etching solution. Treatment of etching solution with ion exchange resin is
This is carried out according to the conventional method of ion exchange treatment. Usually, a method is used in which an etching solution is passed in a downward flow through a resin tower filled with an ion exchange resin. The etching solution flowing out of the resin column is circulated to the etching tank. Therefore, the leakage of aluminum ions into the effluent does not pose a problem, and the resin column can be passed until it reaches almost equilibrium with the etching solution.
Furthermore, if aluminum ions leak into the effluent, the effluent can be further introduced into the next resin tower, a so-called merry-go-round method. The resin tower that has lost its adsorption capacity is treated with hydrochloric acid or sulfuric acid to remove aluminum ions, and then
It is used again to process the etching solution. Usually, the etching solution in the resin tower is first extruded with water, and after returning as much of the etching solution as possible as possible to the etching tank, acid is introduced to remove aluminum ions. The amount of acid introduced is sufficient to be 1 to 2 equivalents of the adsorbed aluminum ions. According to studies by the present inventors, approximately 70% of aluminum is desorbed with an equivalent amount of hydrochloric acid, and approximately 80% is desorbed with 1.5 times the equivalent amount of hydrochloric acid, although it depends on the regeneration conditions. If a larger amount of acid is used, the desorption rate will further improve, but
Leakage of aluminum ions into the processing solution is allowed. In the method of the present invention, it is not advantageous to improve the desorption rate by reducing the regeneration efficiency. The preferred amount of acid introduced is 1 to 1.5 equivalents of the amount of aluminum being adsorbed. After the resin tower has been regenerated, it is washed with water and then subjected to etching solution treatment again. According to the present invention, etching can be performed without consuming much of the organic matter in the etching solution. In addition, consumption of hydrochloric acid can be reduced. For example, 15 g of free hydrochloric acid in the etching solution,
When maintaining the aluminum ion level at 2g/, the conventional method of draining and discarding the etching solution and replenishing new etching solution instead requires 1.
For every g of aluminum ions removed, 11.6 g of hydrochloric acid must be replenished, and approximately 12.7 g of caustic soda is required to neutralize the waste etching solution. However, in the method of the present invention, the amount of replenishment of hydrochloric acid is the amount necessary for regenerating the resin tower, that is, even when using 1.5 equivalents of hydrochloric acid, per gram of aluminum removed.
Only 7.5g is required, and therefore only 8.3g of caustic soda is required to neutralize the recycled waste liquid. As described above, according to the method of the present invention, not only is there almost no consumption of organic substances, but also the consumption of hydrochloric acid and caustic soda can be reduced. Furthermore, since almost no organic matter flows into wastewater, the burden of wastewater treatment is significantly reduced. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 Aluminum plate with a thickness of 0.3 mm (1050 material, tempered
H16) was immersed in a caustic soda aqueous solution at 65℃ for 1 minute, washed with water, and then immersed in a 10% nitric acid aqueous solution for 1 minute.
After soaking for a minute, it was washed with water. Free hydrochloric acid concentration 17.9g/, citric acid concentration 49.9
The above aluminum plate was immersed in an etching solution with a composition of
Electrolytic etching was performed at 80 A/dm ² for 20 seconds.
When 75 aluminum plates were electrolytically etched according to the above method, the composition of the etching solution was 9.5 g/concentration of free hydrochloric acid and 2.0 g/concentration of aluminum ions.
g/, and the citric acid concentration was 50.1 g/. When the above etching solution was passed through an ion exchange resin column containing 0.7 g of free-type strongly acidic cation exchange resin, the concentration of free hydrochloric acid was 17.9 g/, the concentration of dissolved aluminum ion was 0.03 g/, and the concentration of citric acid was 49.6 g/. A solution was obtained, and it was possible to regenerate the etching solution into an etching solution with substantially the same composition as before the start of etching. Example 2 An aluminum plate subjected to the same pretreatment as in Example 1 was immersed in an etching solution of 300 g with a free hydrochloric acid concentration of 11.0 g/, a dissolved aluminum ion concentration of 2.9 g/, and a citric acid concentration of 48.6 g/, and heated at 25°C. , electrolytic etching was performed for 20 seconds at an alternating current density of 60 A/dm ² . After performing electrolytic etching on 15 aluminum plates in accordance with the above, the etching solution 26 was extracted. This solution was passed through an ion exchange resin tower filled with free strongly acidic cation exchange resin 12.6, and then combined with the remaining etching solution to regenerate the etching solution. Using this regenerated etching solution, 15 aluminum plates were electrolytically etched in exactly the same manner as above, and then the etching solution 26 was treated with an ion exchange resin in the same manner as above. When this operation was repeated five times, the composition of the etching solution at the end of each etching, the composition of the regenerated etching solution, and the average roughness of the etching of the first aluminum plate were as shown in Table 1. This result shows that regeneration of the etching solution using the ion exchange resin has no adverse effect on etching. 【table】

Claims (1)

[Claims] 1. The composition of the etching solution is released by circulating the etching solution between an etching tank containing an etching solution containing hydrochloric acid and organic matter and an ion exchange resin tank containing a strongly acidic cation exchange resin. Hydrochloric acid 20g/or less, aluminum ion 5g/
1. A method for electrolytically etching an aluminum plate for printing plates, which comprises electrolytically etching the aluminum plate by immersing it in an etching bath while maintaining the following conditions. 2. The method according to claim 1, wherein the organic substance is selected from oxycarboxylic acids, unsaturated carboxylic acids, saturated monocarboxylic acids, β-dicarbonyl compounds, and phenols. 3. Reduce the concentration of free hydrochloric acid in the etching tank to 7 to 15 g/
3. A method according to claim 1 or claim 2, characterized in that: 4. Claim 1, characterized in that the change in aluminum ion concentration in the etching bath is controlled within a range of 1.5 g/l above and below the reference value, respectively.
The method described in any one of Items 1 to 3.