JPH01188699A - Method for removing smut from support for printing plate - Google Patents

Abstract

PURPOSE:To improve scumming performance and to suppress the corrosion of the material of a treatment tank, etc., by electrolytically roughening the surface of an Al support with hydrochloric acid or nitric acid, dissolving smut formed on the surface with an alkali soln. and further dissolving and removing the smut with sulfuric acid. CONSTITUTION:The surface of an Al support for a printing plate is etched with alkali, smut is removed and the surface of the support is washed and subjected to AC electrolytic etching in a soln. based on hydrochloric acid or nitric acid. Smut formed on the surface of the support is dissolved with an alkali soln. such as an NaOH soln. and the support is immersed in a soln. based on sulfuric acid to dissolve and remove the smut. Desmutting can be carried out in a short time while maintaining the uniform grain surface and suppressing corrosion by sulfuric acid.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for removing smut by electrolytic surface roughening of an aluminum support, and is particularly effective for a support of an ashiremi alloy containing manganese. This is a smut removal method.

[Prior Art] Aluminum plates are used as supports for printing plates, especially lithographic printing plates. Due to the diversification of users, aluminum supports have become similar to pure aluminum containing very small amounts of iron and silicon. There are a wide variety of materials available, including supports containing manganese.

In addition, the tensile strength of manganese-added supports is significantly increased compared to pure aluminum, and is likely to increase further in the future.

Methods for roughening the surface of aluminum supports for printing plates include mechanical graining, electrochemical graining, and the like, and surface roughening is carried out by appropriately combining these methods.

Mechanical graining methods include, for example, pole graining,
Wire grain, Brasocidaleon.

There is a liquid honing method. Further, as an electrochemical graining method, an alternating current electrolytic etching method is generally employed, and a special alternating current such as a normal sine wave alternating current or a rectangular wave is used as the current. Further, as a pretreatment for this electrochemical graining, etching treatment with caustic soda or the like may be performed.

Electrochemical graining methods have recently increased in popularity due to their suitability for continuous processing of webs. However, when such an aluminum support is grained electrochemically,
Smut, whose main component is aluminum hydroxide, is generated on the aluminum surface.

The specification of U.S. Pat. Then, smut is generated. On the other hand, the aluminum support that has been electrochemically grained in this way is finished with a photosensitive printing plate by being anodized or sealed, coated with a photosensitive liquid, and dried. If smut remains after this process, the smut gets mixed into the anodic oxide film, causing film defects and reducing printing performance. Also,
In Japanese Patent Publication No. 56-11316, smut generated on the aluminum surface is dissolved in a 15-60% by weight sulfuric acid solution at 50% by weight.
A desmant method is disclosed, which is characterized by contacting at a temperature of ~90°C and dissolving and removing. However, in the above method, the high sulfuric acid temperature caused severe corrosion in the processing tank, the pipes for feeding the liquid, and other equipment, resulting in frequent equipment failures.

When aluminum alloy components such as manganese, manganese, iron, and copper increase, smut cannot be removed unless the immersion time is increased and the sulfuric acid concentration and temperature are increased. It was significant when it was 3% or more. Furthermore, when smut removal is carried out under the harsh conditions described above, the aluminum base material dissolves, and since sulfuric acid is used, the aluminum base material is not uniformly dissolved, resulting in sand created by electrochemical methods. The grains were distorted, and even after development, the photosensitive layer remained in the grains, resulting in a support with poor stain resistance. Also, to remove such smut, 12
Immersion for 0 seconds or more is required, and in today's mass production and continuous processing, equipment has become extremely large, and as a result, a large amount of expense has been required to repair processing tanks and the like.

[Problem that the invention seeks to solve]

However, in recent years there has been a demand for supports with good staining performance, and it is also an important issue to prevent material corrosion in processing tanks and the like due to the use of sulfuric acid under harsh conditions.

The present invention solves the above problems by adjusting the concentration, temperature, and concentration of sulfuric acid used.
It is an object of the present invention to provide a method for removing smut from a support for a printing plate, which solves severe time-consuming conditions, has good staining performance, and reduces corrosion of materials such as processing tanks.

[Means and effects for solving the problems] In order to solve the above-mentioned problems, the inventors of the present invention have studied the desmut system and have proposed the present invention. That is, the aluminum support is electrolytically roughened with a solution mainly composed of hydrochloric acid or nitric acid, and the smut generated on the aluminum surface is first dissolved with an alkaline solution, and then removed by dissolving with a solution mainly composed of sulfuric acid. This is a smut removal method characterized by the following features.

The present invention will be explained in detail below. First, the aluminum support is first alkali etched.

Preferred alkaline agents are caustic soda and caustic potash.

Sodium metasilicate, soda carbonate, sodium aluminate.

These include sodium gluconate. A concentration of 0.01 to 20%, a temperature of 20 to 90 DEG C., and a time of 5 seconds to 5 inches per hour are appropriate, and a preferable etching amount is 0.1 to 5 g/n.

Particularly in the case of supports with many impurities, 0.01 to 1 g/rr
f is appropriate (filed by the present applicant on November 25, 1988). Subsequently, since alkali-insoluble substances (smut) remain on the surface of the alkali-etched aluminum plate, a desmatting treatment may be performed as necessary.

The pretreatment is as described above, but subsequently, according to the present invention, alternating current electrolytic etching is performed in an electrolytic solution containing mainly hydrochloric acid or nitric acid. The frequency of AC electrolytic current is 0,1
~100Hz, more preferably 0.1~1.0.10~
It is 60Hz.

The liquid concentration is 3 to 150 g/V, more preferably 5 to 50 g/j2. The amount of aluminum dissolved in the bath is 50 g/I! The following is suitable, more preferably 2
~20g/ffi. Additives may be added if necessary, but in mass production, it becomes difficult to control the liquid concentration.

Further, the current density is suitably 5 to 100 A/drrr, more preferably 10 to 80 A/drrf.

The power waveform is appropriately selected depending on the desired quality and the composition of the aluminum support used, but it is recommended to use the special alternating waveform described in Japanese Patent Publications No. 56-19280 and No. 55-19191. More preferred. Such waveforms and liquid conditions are appropriately selected depending on the quantity of electricity, the required quality, the composition of the aluminum support used, and so on.

The electrolytically grained aluminum is then immersed in an alkaline solution to dissolve the smut as part of the smut treatment.

There are various alkaline agents such as caustic soda, but PH
More than 10? M degree 25~60℃ immersion time 1~10sec
It is preferable to carry out the process in an extremely short period of time.

Next, it is immersed in a solution consisting mainly of sulfuric acid. The liquid conditions for sulfuric acid are as follows:
Concentration 50-400g/I, much lower than before! , a temperature of 25 to 65°C is preferred. The concentration of sulfuric acid is 400 g/f
If the temperature is higher than fi or the temperature is 65° C. or higher, corrosion of the processing tank etc. will increase, and in aluminum alloys containing 0.3% or more of manganese, the electrochemically roughened grain will collapse.

Also, if the amount of dissolved aluminum substrate is etched more than 0.2g/n, the printing durability will decrease, so 0.2g/n.
2g/n (preferably less than 2g/n).

As described above, according to the present invention, desmutting can be carried out in an extremely short period of time, while maintaining a uniform grain pattern and significantly reducing corrosion caused by sulfuric acid.

The anodic oxide film is preferably formed on the surface in a thickness of 0.1 to 10 g/n (more preferably 0.3 to 5 g/n).

The processing conditions for anodic oxidation are not determined in part because they vary depending on the type of electrolyte used, but in general, the concentration of the electrolyte is 1 to 80%, the temperature of the solution is 5 to 70°C, and one current is used. Density 0.5-60A/cJ, voltage 1-100■, electrolysis time 1
A range of seconds to 5 minutes is appropriate.

The grained aluminum plate with the anodic oxide film obtained in this way is itself stable and has excellent hydrophilic properties, so a photosensitive coating can be immediately applied on top, but if necessary, the surface can be further coated. Can be processed. For example, a silicate layer made of the alkali metal silicate described above or an undercoat layer made of a hydrophilic polymer compound can be provided.

The coating amount of the undercoat layer is preferably 5 to 150 mg/r4.

Next, a photosensitive coating film is provided on the aluminum support treated in this way, imagewise exposed, developed and plate-made, and then set in a printing machine to start printing.

〔Example〕

Example-1 An aluminum support made of JIS 3003 material containing 1.2% manganese was immersed in a 5% aqueous solution of caustic soda heated to 55°C, and the amount of dissolved aluminum was 0.10.
After enching to give g/rd, the smut was removed and washed with water.

Then, add 5.0 g/I! to a 18 g/L nitric acid aqueous solution.
, containing aluminum at a bath temperature of 55°C, 12
At the AC frequency of Hz, the anode special electricity amount is 500 coulombs/
The surface was roughened by setting it so that it became drrr. After that, 30
Adjust the caustic soda to PHII at °C and hold for 2 s.
EC soaking, washing with water, sulfuric acid solution 75g/l, temperature 40
It was immersed in a solution at ℃ for 10 seconds. Aluminum base is 0.03g
/n (dissolved.

When observed with an electron microscope, the smut was completely removed and the grains were smooth. Next, an anodized film of 2.1 g/rl was applied in 17% sulfuric acid, washed with water, and dried.

This will be referred to as a substrate (A).

Comparative Example-1 An aluminum support made of JIS 3003 material containing 1.2% manganese was immersed in a 5% aqueous solution of caustic soda heated to 55°C, and the amount of dissolved aluminum was 0.10 g/
After etching to a size of m, the smut was removed and washed with water.

Then, 5.0 g/l of aluminum was added to 18 g of #2 nitric acid aqueous solution, and the bath temperature was set to 55°C and the frequency of 12 Hz was
The anode special electricity amount is 500 clones/dn at the AC frequency of
(The surface was roughened at 80°C.
It was immersed in a 350 g/ffi sulfuric acid solution and observed by electron micrograph after immersion, and it was confirmed that the smut was completely removed in 180 seconds. When observed with an electron microscope, the tips of the grains were jagged. Next, the anodized film was washed with water at 2.1 g/ffl in 17% sulfuric acid and dried.

This will be referred to as a substrate (B).

A photosensitive layer was provided on the substrates (A) to [B] thus prepared by applying the following composition so that the coating weight after drying was 2.5 g/rrf.

Photosensitive liquid composition: Ester compound of naphthoquinone-1,2-diazido-5-sulfonyl chloride, pyrogallol, and acetone resin (described in Example 1 of U.S. Pat. No. 3,635.709)...0.75 g Talesol novolac resin ・ ・ ・ 2
．． 00g Oil Blue #603 (manufactured by Orient Chemical Co., Ltd.) ...0.04g Ethylene dichloride ...16g 2-methoxyethyl acetate ...12g The photosensitive lithographic printing plate made in this way was placed in a vacuum baking frame. The film was exposed through a transparent positive film from a distance of 1 m for 50 seconds using a 3 kW metal halide lamp, and then developed with a 5.26% aqueous solution of sodium silicate (PH-12,7) with a molar ratio of S+Oz/NazO of 1.74. Afterwards, it was printed using the usual procedure.

The printing machine used was Sprint 25 (manufactured by Temae Printing Co., Ltd.).

The examples shown in Table 1 were clearly superior to the conventional ones in terms of stain resistance.

〔Effect of the invention〕

In the present invention, an aluminum support is electrolytically roughened with a solution mainly composed of hydrochloric acid or nitric acid, and the smut generated on the aluminum surface is first dissolved with an alkaline solution and then removed by dissolving with a solution mainly composed of sulfuric acid. The characteristic smut removal method can greatly improve stain performance without reducing rigidity, and can significantly reduce processing time.

In addition, it has become possible to reduce the concentration and temperature of sulfuric acid, making it possible to reduce corrosion of materials such as treatment tanks caused by sulfuric acid.

Claims (5)

[Claims] (1) The aluminum support is electrolytically roughened with a solution mainly composed of hydrochloric acid or nitric acid, and the smut generated on the aluminum surface is first dissolved with an alkaline solution, and then removed by dissolving with a solution mainly composed of sulfuric acid. A distinctive smut removal method. (2) The smut removal method according to claim 1, characterized in that the sulfuric acid-based liquid has a concentration of 50 to 400 g/l and a temperature of 25 to 65°C. (3) The pH of the alkaline solution is 10 or more, and the temperature is 25 to 6.
The smut removal method according to claim 1 or 2, characterized in that the temperature is 0°C. (4) The aluminum support contains 0.3% manganese.
Claim 1 characterized in that it contains the following:
, 2 or 3. (5) The amount of dissolved aluminum base is 0.2g/m^2
Claims 1 and 2 are characterized in that:
The smut removal method according to item 3 or 4.