JPS585795B2 - Manufacturing method of rough aluminum plate for offset printing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an aluminum roughened plate for offset printing plate material by an electrolytic surface roughening treatment method.

Generally, aluminum plates have been used as original plates in offset printing, but in order to improve the adhesion of the photosensitive film and provide water retention to non-image areas, it is necessary to roughen the surface. This roughening treatment is an important technology for plate manufacturing because it has a great effect on platemaking suitability during the platemaking process and on the printing performance and printing durability of the plate when actually performing offset printing after platemaking. has been done.

Mechanical treatment methods such as pole polishing and brushing polishing have conventionally been used to roughen the surface of aluminum plates for offset printing. The electrolytic surface roughening treatment method that causes corrosion has attracted attention in recent years because it is suitable not only for the treatment of aluminum veneers but also for the continuous treatment of strip plates.

In the electrolytic surface roughening treatment method, as mentioned above, hydrochloric acid or nitric acid, or an electrolytic solution containing these as a main ingredient, is used, and a suitable material such as graphite material is used as a counter electrode in an electrolytic cell, or aluminum plates are placed facing each other. It is common to electrolytically treat aluminum plates using alternating current.

The roughened surface obtained when using nitric acid or an electrolyte mainly composed of nitric acid exhibits a double-layered pit shape in which extremely fine pits exist on the pit surface generated by electrochemical corrosion. However, the pit depth is generally shallow, whereas when using hydrochloric acid or an electrolyte mainly composed of hydrochloric acid, the pit depth is generally deep, but the pit surface is relatively smooth, and compared to nitric acid-based electrolytes. It does not create a complex uneven surface like when using liquid.

These differences in the pit structure of the roughened surface have a subtle effect on the printing performance and printing durability of the plate material, and the plate material obtained from the roughened plate using a hydrochloric acid electrolyte has a long printing life for newspapers, magazines, etc. Suitable for printing that emphasizes strength, and plates roughened with nitric acid-based electrolyte are suitable for commercial art printing such as calendars and catalogs that require fine images, but in terms of printing durability, the former is It is said that the target is inferior printed matter with a relatively small number of copies printed, and there are certain limits to the scope of each application.

In addition, a common problem with conventional electrolytic surface roughening methods using alternating current is that there is a strong correlation between electrolytic conditions and electrolyte composition, and suitable electrolytic conditions that can stably obtain uniformly roughened plates. The range of electrolyte compositions that can be applied to
Due to the relationship between the two, it has often been impossible to find a combination of electrolyte composition and suitable electrolytic conditions that can produce the desired pit shape in the AC electrolytic surface roughening method.

As a result of various studies, the inventors found that when electrolytically roughening an aluminum plate for offset printing using a nitric acid-based electrolyte, the anodic voltage (A) was changed to the cathode voltage by using an alternating waveform current. A cell voltage is applied so that it is larger than Vo, and the quantity of electricity QA at the anode is changed to the quantity of electricity Q at the cathode.

It has been found that when the amount of current applied is adjusted to be greater than , a uniformly roughened plate having a double-structured finely uneven surface can be efficiently obtained in an extremely short electrolytic treatment.

In this case, it is important to set the anode time tA to be equal to or shorter than the cathode time tC, and also change the amount of electricity at the cathode and anode and its ratio QC/QA as appropriate by adjusting the voltage. It has been found that the diameter and depth of the pit can be adjusted arbitrarily by this method.

The rough-faced aluminum plate with a double-structured uneven surface can be used as is, but it is further anodized using a sulfuric acid electrolyte to create a hard porous protective coating on the plate surface that is unique to sulfuric acid anodization. By forming
It is possible to obtain a rough plate for printing plates with further improved photosensitive film adhesion, wet water retention, and abrasion resistance.

That is, in the present invention, an aluminum plate is subjected to electrolytic surface roughening treatment in a nitric acid electrolyte using an alternating waveform current in which the cell voltage is adjusted and applied so that the anode voltage VA is larger than the cathode voltage Vc, and then subjected to sulfuric acid electrolysis. This is a method for producing an aluminum roughened plate for offset printing, characterized in that a roughened surface having a hard protective film is formed by performing anodization treatment in a liquid.

The nitric acid-based electrolytic solution used in the electrolytic surface roughening treatment in the present invention is an aqueous electrolytic solution containing nitric acid alone in the range of 0.5 to 5% by weight, as well as corrosion inhibitors and stabilizers such as nitric acid. Salts containing NO3 such as zinc, ammonium nitrate, and sodium nitrate, amines such as monoamines and diamines, organic agents such as aldehydes and EIDTA, and acids such as phosphoric acid, chromic acid, and sulfosalicylic acid may be added. do not have.

Further, an alternating waveform current is a current having a waveform obtained by alternately exchanging positive and negative polarities, and an example of the voltage waveform diagram is shown in FIG.

In FIG. 1, a shows a voltage waveform of a sine wave, b shows a rectangular wave, and C shows a trapezoidal wave, but the alternating wave current of the present invention is not limited to the voltage waveform described above.

In the electrolytic surface roughening treatment of the present invention, an alternating waveform current showing such a voltage waveform is used, and as shown in FIG. The amount of electricity at the time QA is the amount of electricity at the cathode Q.

The method is to electrolytically roughen the aluminum plate while adjusting the amount of current applied to the anode and cathode to make the surface roughen evenly and stably to the appropriate depth in a very short time. Ratio Q of the amount of electricity at the anode time QA and the amount of electricity at the cathode time Qc such that a roughened surface having double structure pits is formed
C/QA is approximately 0. 4 to 0. The range is 8.

Further, a preferable voltage range is a range of 10 to 50 V based on the anode voltage vA, and the cathode voltage Va is of course applied so that it takes a smaller value than the anode voltage (I).

Further, the anode time period in the above alternating waveform current may be approximately the same as the cathode time tQ, but the above-mentioned electricity quantity ratio QC/Q
By making the cathode time tc longer than the anode time t4 within the range of A, the amount of electricity required for electrolytic surface roughening treatment can be reduced, so power consumption and electrolyte consumption can be reduced.

Furthermore, the frequency f of the alternating waveform current is not limited to the normal alternating current frequency range, that is, 50 Hz to 60 Hz, but as the frequency is raised, the pits on the roughened surface that are formed tend to become finer. be.

The aluminum roughened plate having a double structure uneven surface which has been subjected to the electrolytic roughening treatment described above is further subjected to an anodizing treatment in a sulfuric acid electrolyte.

As a result, a hard porous anodic oxide film unique to sulfuric acid anodization is formed on the plate surface, and this, together with the formation of the double-structure uneven surface described above, improves photoresist film adhesion and offset during plate-making processing. It is possible to further improve dampening water retention during printing and improve printing resistance by improving abrasion resistance, and therefore to obtain an offset printing plate material with excellent printing performance and printing durability. can.

Note that general anodic oxidation treatment conditions are applied to the anodic oxidation treatment conditions using a sulfuric acid electrolyte.

Next, embodiments of the present invention will be described.

99.5% purity aluminum plate (600mm x 1 5
0 0mm x 0. 3mm) with a caustic soda solution, and then using a semi-continuous electrolyzer, the concentration was 14.1/l.
Using a nitric acid electrolyte with a liquid temperature of 21°C, the frequency was 60Hz. The ratio tc/tA of anode time t4 and cathode time tQ is 2.3
Using a trapezoidal wave alternating current adjusted to be 3, the anode voltage vA is 11.2V, and the anode voltage ■c is 5. The electrolytic surface roughening treatment was carried out while moving the aluminum plate at a feed rate such that the residence time in the electrolytic cell was 40 seconds under the condition of Ov.

In addition, the current density is 80. OA/dm'', 20 OA/dm' at the cathode.

Next, after washing with water, the board was immersed in a sulfuric acid solution with a concentration of 30% and a temperature of 55° C. for 5 minutes to remove smut attached to the surface, and then washed with water. 8 g/l, liquid temperature 19
Using sulfuric acid electrolyte at °C and current density IA/di for 6 minutes 40
It was anodized using direct current for seconds, washed with water, and dried.

The roughened plate thus obtained had a surface roughness of 3.5μ (
Hmax), the surface had a uniform double-structure uneven surface over the entire surface, and the thickness of the anodic oxide film was approximately 2 μm.

The thus obtained roughened plate was subjected to a plate-making process using a diazo-based photosensitive liquid, and when offset printing was performed using this, an electrolytic surface roughening process was performed using an alternating current using a conventional nitric acid-based bath. Compared to those that were subjected to the same anodizing and plate-making processes, the dampening water was easier to manage, the prints were easier to print, the details of the lines were better expressed, and the printing durability was also good. Good printed matter was obtained without any change even after 10,000 copies were printed.

As mentioned above, when using the method of the present invention, a nitric acid-based electrolyte, which has conventionally had good practicality in terms of printability but had a slight inferiority in printing durability, is used to produce deeper grains. A uniformly roughened plate can be efficiently obtained with an extremely short electrolytic treatment, and the depth of the pits can be adjusted arbitrarily by selecting appropriate electrolytic conditions, improving printing performance and printing durability. It is possible to easily obtain a rough aluminum plate for offset printing that satisfies both requirements, and it is also suitable for high-speed continuous processing of strip plates and has great economic effects.

[Brief explanation of the drawing]

FIG. 1 is a voltage waveform diagram of a current obtained as an alternating waveform current. a: sine wave, b: square wave, C: trapezoidal wave.

Claims (1)

[Scope of Claims] 1 An aluminum plate is subjected to electrolytic surface roughening treatment using a nitric acid electrolyte and an alternating waveform current applied with a cell voltage such that the voltage at the anode is higher than the voltage at the cathode, and then subjected to an electrolytic surface roughening treatment using a sulfuric acid electrolyte. A method for producing a rough-surfaced aluminum plate for offset printing, which is characterized by anodizing treatment in a medium. 2 Claim 1 characterized in that the anode time in the alternating waveform current is equal to or smaller than the cathode time.
A method for producing a rough aluminum plate for offset printing as described in Section 1.