JPH02235794A - Preparation of aluminum support for printing plate - Google Patents

Abstract

PURPOSE:To obtain a constant quality over a long range by controlling the concn. of the ammonium ion generated in a nitric acid electrolyte to a predetermined range. CONSTITUTION:The concn. of the ammonium ion generated in a nitric acid electrolyte is controlled to a range of 0-300mg/l. That is, an electrolyte based on nitric acid is used and the concn. of the ammonium ion in said electrolyte is controlled to a certain concn. or less without adding an additive. Since the shape of a pit obtained by electrolytic surface roughening is changed by an increase of the ammonium ion in the electrolyte, the surface roughening shape of an aluminum support subjected to electrolytic surface roughening in the longitudinal direction thereof becomes non-uniform and the capacity as the support for a printing plate varies in the longitudinal direction. Therefore, by controlling the concn. of the ammonium ion in this electrolyte within a definite range in matching relation to other electrolytic surface roughening condition, stable electrolytic surface roughening can be performed over the longitudinal direction of an aluminum support for a printing plate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an aluminum support for printing plates, and more specifically, an electrochemical roughening treatment of an aluminum plate (including an aluminum alloy). The present invention relates to a method for manufacturing an aluminum support for a printing plate, which is made of an aluminum plate roughened to a uniform honeycomb structure and is particularly suitable for offset printing plates.

[Prior Art] Aluminum plates have traditionally been used as supports for offset printing plates. The surface is usually roughened for purposes such as retaining water.

Mechanical surface roughening methods such as ball graining and brushed graining are known as such surface roughening methods, but in recent years, hydrochloric acid. An electrolytic surface roughening method is attracting attention, in which the surface of an aluminum plate is electrochemically roughened by passing an alternating current through the aluminum plate in an acidic electrolyte such as nitric acid.

According to this electrolytic surface roughening method, an aluminum plate having a uniformly roughened surface with a smaller average roughness distribution can be obtained compared to the conventional mechanical roughening method, but the conditions for obtaining such a roughened surface are is extremely narrow, and if various conditions such as electrolyte composition, temperature, and electrolytic conditions are kept constant, products with very little variation and uniform performance can be easily obtained.

As a method for improving the uniformity of electrochemical roughening and the occurrence of irregular large pores (referred to as pits), at least one compound containing ammonium ions is added to the nitric acid electrolyte to conduct alternating current. The method of performing electrolysis was published in 1983.
It is disclosed in Japanese Patent No.-182950.

[Problem to be solved by the invention]

However, the main purpose of JP-A-61-182950 is to prevent the occurrence of irregular pits, and it is difficult to control the concentration of the added compound. On the other hand, it is said that the biggest drawback of the electrolytic surface roughening method is that it lacks long-length stability. Even if the surface of an aluminum plate or the like to be roughened is controlled under certain conditions to roughen the surface, it is difficult to obtain constant quality over a long length, and there is a drawback that long-length stability is lacking. An object of the present invention is to solve the above-mentioned problems and provide a method for manufacturing an aluminum support for a printing plate that has good long-length stability and can provide constant quality over a long length.

[Means and effects for solving the problem] The present inventors
As a result of diligent investigation into the cause of this problem, we found that electrolytic surface roughening lacks stability over long lengths, making it difficult to obtain consistent quality over long lengths. A significant increase in ammonium ions (for example, an increase of 22
The present invention was based on the discovery that mgyl) is the cause.

That is, the above-mentioned object of the present invention is to provide a method for roughening an aluminum support for a printing plate, in which an aluminum plate is electrochemically roughened using alternating current in an electrolyte mainly containing nitric acid. The method of the present invention is solved by a method for producing an aluminum support for a printing plate, which is characterized by adjusting the ammonium ion concentration generated in a nitric acid electrolyte in the range of 0 to 30 Omg/l. The feature is that an electrolytic solution is used and the ammonium ion concentration in the electrolytic solution is adjusted to a certain concentration or less without adding additives. Note that the ammonium ions at this time are naturally generated by electrolytically roughening an aluminum or aluminum alloy plate in an electrolytic solution containing nitric acid. As the ammonium ions in the electrolyte increase, the pit shape obtained by electrolytic roughening changes, so the roughened shape in the length direction of the aluminum support to be electrolytically roughened changes. As a result, the performance as a printing plate support varies in the length direction. Therefore, by controlling the ammonium ion concentration in this electrolyte within a certain range together with other electrolytic surface roughening conditions, the electrolytically roughened surface can be stably produced over the length of the aluminum support for printing plates. It becomes possible to carry out conversion.

The ammonium ion concentration can be adjusted within a certain range by, for example, changing the amount of electrolyte solution.

Specifically, aluminum ions, ammonium ions,
Nitric acid concentration can be kept constant.

Particularly advantageous electrolysis conditions for the aluminum support for printing plates in the present invention include a nitric acid concentration of 5 to 20.
g/I! , aluminum ion concentration is 2.5-10g
//! Using an electrolyte mainly composed of nitric acid in the range of
And the ammonium ion concentration is within the range of 0 to 300 ng//, preferably 0 to 200+ng//! A range of 0 to 120 mg/42(7) is desirable.

In this case, the ammonium ion concentration is 0/pV. Even if it is less than 300 μ/l, almost the same effect can be obtained.

In this regard, the method disclosed in JP-A-61-182950 is a method in which a compound containing ammonium ions is added to a nitric acid electrolyte, and the concentration of the compound is 3 g/2 to saturation. It is preferable that the ammonium ion concentration is in the range of Og/l to 300mg/j! There is clearly another way that is considered to be worse.

The ammonium ion concentration can be analyzed by the method described in JTSKO102-42.

Next, the method of electrolytically roughening an aluminum plate using alternating current in an electrolyte mainly composed of nitric acid in the present invention is as follows:
This is a method of roughening the surface by applying an alternating current between an aluminum plate and an electrode facing it, as described in Japanese Patent Application Laid-Open No. 54-65607. As the electrolytic power waveform at this time, it is possible to use not only a special alternating waveform as described in JP-A-54-65607, but also a rectangular wave generated by a commercial alternating current, a silice inverter, a transistor inverter, etc. It is possible. The frequency at this time can be set over a wide range of 0.1 to 100 Hz, but 1 to 60 Hz is particularly preferable, and 50 to 60 Hz is preferable in terms of equipment. . In addition, when a rectangular wave is used, the distortion of the waveform is preferably as small as possible, and the time constant is 2 msec or less, preferably 1, Omsec.
It is desirable that it be less than c.

The present invention relates to a method for electrolytic surface roughening in an electrolytic solution mainly containing nitric acid, and is a method that combines mechanical surface roughening and electrolytic surface roughening as described in Japanese Patent Publication No. 57-16918. Needless to say, it can be applied to any method.

〔Example〕

60% JI33103 aluminum plate with caustic soda solution
After washing for seconds, degreasing and removing the natural oxide film on the surface, it was washed with water. And the sulfuric acid concentration is 300
g/l aqueous solution for 120 seconds at 60°C and rinsed with water. This aluminum plate was treated with nitric acid at a concentration of 13 g/l. Electrolytic surface roughening treatment was carried out in an electrolytic solution with an aluminum ion concentration of 5 g/l at 45° C. and a current density of 20 A/d for 10 seconds. At this time, the ammonium ion concentration in the nitric acid electrolyte is O, 70, 175, 350 mg/j! The results were as shown in Table 1.

In this case, the electrolyte conditions were as follows: nitric acid concentration: 13 g/l.
Aluminum ion concentration 4.5g/l. Liquid temperature 45"
C. A current density of 20 A/dr4 was a common condition.

Table 1 Quality grade A: Very good. B: Slightly good C: Poor As is clear from Table 1, ammonium ion is 300%
When the increase exceeds 1 Ilg/l, the quality grade approaches C rank, unetched portions occur, and not only the rough surface shape but also the appearance deteriorates. Note that the rough surface shape was observed using a scanning electron microscope JSM-720 manufactured by JEOL.

For observation, the aluminum plate after electrolytic roughening was immersed in a sulfuric acid aqueous solution of 300 g/1 at 60° C. for 120 seconds, and then washed with water to remove aluminum hydroxide generated by electrolytic roughening.

〔Effect of the invention〕

As described in the present invention, when electrolytically roughening an aluminum plate or an aluminum alloy plate using alternating current in an electrolytic solution mainly containing nitric acid, the ammonium ion concentration in the electrolytic solution is adjusted to 0 to 300 μ/l. By limiting the amount, it has become possible to perform stable electrolytic surface roughening that provides constant quality over a long length.

(3 other people)

Claims (1)

[Claims] In a method for roughening an aluminum support for a printing plate, in which an aluminum plate is electrochemically roughened using alternating current in an electrolytic solution mainly containing nitric acid, ammonium generated in the nitric acid electrolytic solution is Ion concentration 0-300mg
1. A method for producing an aluminum support for a printing plate, characterized in that the aluminum support is adjusted to a range of /l.