JPH0667440A - Correction agent for printing plate - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is a compound having a mercapto group or a thione group and at least one hydrophilic group in the same molecule, which is used in a lithographic printing plate utilizing a silver image as an ink accepting property. A correction agent that improves the drawbacks of a correction agent that includes, that is, that the ink acceptability of the repaired portion is restored with the passage of time after correction, or that the repaired portion and its surroundings become ink-acceptable and cause smearing Is to provide. A correction agent for an offset printing plate, which uses a silver image as an ink receiving property, contains a compound having at least one mercapto group or thione group and at least one hydrophilic group in the same molecule, and desalted arabic gum. A correction agent for a printing plate, which is characterized in that

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an offset printing plate that utilizes a silver image as an ink-receptive material, and a silver image correcting agent formed on the printing plate. By appropriately surface-treating unnecessary portions on the offset printing plate formed by a conventional method with a specific treating agent at any stage in the printing process, there is no particular problem with printing characteristics, equipment, etc. The present invention relates to completely hydrophilizing and eliminating ink acceptability. Usually, in the printing field, such a process is called "correction", and the present inventors will follow it. Further, the processing agent used for the correction operation will be referred to as "correction agent".

[0002]

2. Description of the Related Art In general, a printing original plate produced by a photoengraving method needs to be corrected in such a manner that it already exists in a copy original, that which occurs during exposure, and other uneven development processing steps. There are things caused by.

That is, for example, an unnecessary image is generated in a copy original, or when an original made by laminating various originals is used, a shadow is projected at the time of exposure. In order to obtain a good printed matter, all of these areas must be corrected at the stage of plate making and printing. Generally speaking, the correction operation is indispensable, and it is desirable that the necessary correction can be performed at any stage of the plate making and printing process.

Further, stability is also required after the correction agent is applied to the printing plate. That is, the stability with time from application to printing,
It is required that the initial erasability is not lost even if printing is started and then interrupted and printing is restarted.

Many attempts have been made as a method of correcting unwanted images in offset printing plates which utilize a silver image as the ink receptivity. For example, JP-A-48-92101 and JP-A-51
21901, 54-53002, 59-96
The compounds having a mercapto or thione group and a hydrophilic group described in 61, etc. can surely and almost instantaneously hydrophilize a silver image. However, these compounds have drawbacks such as a strong acid effect on the human body and lack of stability over time, and improvement is desired.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to use a compound having a mercapto group or a thione group and at least one hydrophilic group in the same molecule, which is used in a lithographic printing plate which utilizes a silver image as an ink receiving property. A correction agent that improves the drawbacks of a correction agent that includes, that is, that the ink acceptability of the repaired portion is restored with the passage of time after correction, or that the repaired portion and its surroundings become ink-acceptable and cause smearing Is to provide.

[0007]

The above-mentioned object of the present invention is achieved by adding a compound having at least one mercapto group or thione group and at least one hydrophilic group in the same molecule and desalted gum arabic to a corrective agent. Achieved

[0008] Commercially available ordinary gum arabic (hereinafter abbreviated as commercially available gum arabic) is distributed as a lump or a crushed product of gum arabic. In order to further improve the solubility, some of them are dissolved once, filtered of miscellaneous substances, and then powdered again by the spray dry method, etc., but they are all gum arabic itself, and their chemical components are intended. It has not been changed.

The essential part of gum arabic is hemicellulose, which has a complex structure, but they are calcium,
It is said to exist as salts such as magnesium and potassium. Almost all of these are replaced with hydrogen to obtain desalinated arabic gum. Specifically, after dissolving commercially available gum arabic, the metal salt is almost replaced with hydrogen by an ion exchange method or the like, and again powdered by a spray dry method or the like. The ash content of commercially available gum arabic is said to be about 3 to 4%, but the ash content of desalinated gum arabic is about 0.
The amount has been drastically reduced to 1% or less.

Examples of the compound having a group strongly binding to a silver image and at least one hydrophilic group in the same molecule include the following compounds. 2-mercaptoethanol, hydroxymercaptan such as α-thioglycerol, thioglycolic acid, α-mercaptopropionic acid,
β-mercaptopropionic acid, α-mercaptobutyric acid, β
-Mercaptobutyric acid, γ-mercaptobutyric acid, α-mercaptocaproic acid, mercaptoalkylcarboxylic acids such as cysteine and its derivatives, 2-mercaptoethylsulfonic acid, mercaptopropylsulfonic acid, mercapto such as 2,3-dimercaptopropenesulfonic acid A compound containing an alkyl sulfonic acid and an aromatic ring or a hetero ring is also effective. For example, p-mercaptobenzoic acid, p-mercaptobenzenesulfonic acid, 2-mercaptobenzimidazole-5-sulfonic acid, 2-mercaptobenzothiazole. -5-sulfonic acid, 2-mercapto-3-methylbenzothiazole-5-sulfonic acid, 2-mercaptobenzoxazole-5-sulfonic acid and the like.

The amount of the above compound added to the correction agent of the present invention is 0.1 to 10 g per 100 ml, and preferably 0.5 to 5 g.

In the correction agent of the present invention, in addition to the above compounds, desalted arabic gum may be added in an amount of 0.1 to 10 g, preferably 0.5 to 5 g, per 100 cc.

The correction agent of the present invention can be used as a correction agent using water, various alcohols or a mixed solvent thereof. In addition, dyes, organic or inorganic pigments,
Although it can be included as an element for coloring the liquid,
These are not mandatory elements.

Further, a fine particle powder as described in JP-A-51-21901 may be contained.

[0015]

【Example】

Example 1 In the same manner as in Example 1 of JP-A-53-21602, except that the physical development nucleus layer of the offset printing plate (plate No. 3) contained 1.0 g / m 2 of hydroquinone. A lithographic printing material was prepared. The lithographic printing material was imagewise exposed and then developed with the following silver complex salt diffusion transfer developer at 30 ° C. for 30 seconds.

<Transfer developer> Water 700 ml Potassium hydroxide 20 g Sodium sulfite anhydrous 50 g 2-Mercaptobenzoic acid 1.5 g 2-Methylaminoethanol 15 g Water is added to make 1 liter.

After the developing treatment, the original plate was passed between two squeezing rollers to remove excess developer, and immediately treated with a neutralizing solution having the following composition at 25 ° C. for 20 seconds, and the squeezing roller was used to remove the excess liquid. Removed and dried at room temperature.

<Neutralization liquid> Water 600 ml Citric acid 10 g Sodium citrate 35 g Colloidal silica (20% liquid) 5 ml Ethylene glycol 5 ml Water is added to make 1 liter.

A correction solution was prepared by using the compounds and amounts shown in the following correction solution as a correction agent, and the portion to be corrected of the lithographic printing plate was wiped with the correction solution. <Correction agent 1> Water 60 ml Desalted arabic gum 1.5 g α-thioglycerol 2 g Total amount with water 100 g <Correction agent 2 (comparative example)> Water 60 ml α-thioglycerol 2 g Total amount with water 100 g <Correction agent 3 (comparative example) )> Water 60ml Gum arabic 1.5g α-thioglycerol 2g Water 100g

The printing plate thus obtained is subjected to an offset printing machine ABDick 350CD.
The plate surface was wiped with an oil-sensitizing solution having the following formulation, and printing was performed on 500 sheets. After that, the ink on the plate surface was dropped, and after 1 hour, the plate surface was wiped again with an oil-sensitizing solution to print 500 sheets. The printing room had a temperature of 22 ° C. and a humidity of 60%.

<Sensitizer> Water 400 ml Citric acid 1 g Sodium citrate 3.5 g 2-Mercapto-5-heptyl-1,3,5-oxadiazole 0.5 g Ethylene glycol 50 ml

Table 1 shows the results of the correctability of the first 500 prints and the 500th print after 1 hour.

[0023]

[Table 1] The modified evaluation shows that 5 indicates complete erasability and 1 indicates almost no erasability. A value of 4 or more means that the product can withstand.

As can be seen from Table 1, the correction agent 1 of the present invention shows sufficient erasability even when printing is restarted.
Further, the correction agent 2 showed sufficient erasability, but the erasing agent spread to the periphery of the portion to be erased and was unsuitable. Example 2

Example 1 was followed except that the correction liquid of Example 1 was filled in a felt pen and used. The result was excellent as in Example 1. Example 3 Example 1 was followed except that thioglycolic acid, 2-mercaptoethylsulfonic acid, p-mercaptobenzoic acid were used in place of α-thioglycerol of Example 1. The result was excellent as in Example 1.

[0027]

The corrective agent of the present invention enables rapid and reliable correction, has a long-lasting effect, and is excellent in liquid stability.

Claims (1)

[Claims] 1. A correction agent for an offset printing plate, which utilizes a silver image as an ink receiving property, and at least one mercapto group or thione group and at least one in the same molecule.
A correction agent for a printing plate comprising a compound having two hydrophilic groups and desalted arabic gum.