JPH06266113A - Retouching agent for printing plate - Google Patents

Abstract

PURPOSE:To provide a retouching agent for the printing plate, with which the ink receptivity of the retouched part can be recovered after the retouching so as not to generate greasing in the retouched part by adding a specific compound to the retouching agent for the offset printing plate using the silver image as the ink receiver. CONSTITUTION:The retouching agent for the printing plate contains a compound represented by the formula. In the formula, each of R1 and R2 is hydrogen atom or an alkyl group such as a methyl or ethyl group; R3 is hydroxyl or mercapto group. The amount of this compound to be added to the retouching agent is preferably 0.01 to 1mol per liter of the retouching agent. This retouching agent is optionally used in combination with a compound contg. a group strongly bondable to the silver image and at least one hydrophilic group in the same molecule and examples of this compound are hydroxymercaptans such as 2-mercaptoethanol, alpha-thioglycerol and thioglycolic acid, etc.

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 pasting 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, it is required that the time from application to printing be maintained and that the initial erasability is not lost even if printing is once 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 object of the present invention has been achieved by a printing plate correcting agent characterized by containing at least one compound represented by the following chemical formula 2.

[0008]

[Chemical 2]

In Formula 2, R1 and R2 each represent a hydrogen atom, an alkyl group such as a methyl group or an ethyl group, and R3 represents a hydroxyl group or a mercapto group.)

Specific examples of the compound represented by Chemical formula 2 used in the present invention will be given, but the compound used in the present invention is not limited to these.

[0011]

[Chemical 3]

[0012]

[Chemical 4]

[0013]

[Chemical 5]

Synthesis of Chemical Formula 3

2,6-dichloro-isonicotinic acid, 4.
DM with 0 g and 6.7 g of sodium hydrosulfite
It was added to F and stirred at room temperature. After 9 hours, the precipitated crystal was collected by filtration, washed with 20 ml of methanol, dissolved in 20 ml of water, and the insoluble matter was removed by filtration. Acetone (20 ml) was added to this solution, and the precipitated crystals were collected by filtration and dried. Yield 3.9g. Melting point 300 ° C or higher.

The amount of the compound of the present invention added to the modifying agent is preferably in the range of 0.01 to 1 mol per liter of the modifying agent.

In the correcting agent of the present invention, a compound having a group strongly binding to a silver image and at least one hydrophilic group in the same molecule can be used in combination.

Examples of the compound having a group that strongly binds 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, bis (mercaptomethyl) acetic acid, α-mercaptocaproic acid, mercaptoalkylcarboxylic acids such as cysteine and derivatives thereof, 2-mercaptoethylsulfonic acid, mercaptopropylsulfonic acid, 2,3-dicapto Compounds containing a mercaptoalkyl sulfonic acid such as mercaptopropene sulfonic acid and further an aromatic ring or a heterocycle are 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 modifier of the present invention may include a hydrophilic binder. The preferred hydrophilic binder is gelatin. Gelatin is a so-called graft obtained by dispersing ordinary vinyl, gelatin modified with an organic acid such as acetic acid, maleic acid, salicylic acid, etc. in an organic solvent and graft-polymerizing vinyl monomer to gelatin under a polymerization initiator. Gelatin, low molecular weight gelatin described in the correction agent of JP-A-63-207645, and the like. 1-2 for gelatin
It is preferably used in the range of 0% by weight. Other hydrophilic binders such as hydroxyethyl cellulose, carboxymethyl cellulose can also be used.

Further, a dye, an organic or inorganic pigment, etc. can be contained as an element for coloring the liquid.

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 can be contained.

[0023]

【Example】

Example 1

The offset printing plate described in Example 1 of JP-A-53-21602 (plate No.
A lithographic printing material was prepared in the same manner as in 3) except that the physical development nucleus layer contained 1.0 g / m @ 2 of hydroquinone. 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> 700 ml of water 20 g of potassium hydroxide 50 g of anhydrous sodium sulfite 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.

<Neutralizing 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 liquid was prepared by using the compounds and amounts shown below as the correction liquid, and the portion to be corrected of the lithographic printing plate was wiped with the correction liquid. <Correction agent 1> Water 60 ml Gum arabic 1.5 g Thioglycerol 1 g Chemical 3 2 g Total amount with water 100 g <Correction agent 2 (comparative example)> Water 60 ml Gum arabic gum 1.5 g α-thioglycerol 1 g Chemical 62 g Total with water 100 g <Correction agent 3 (comparative example)> Water 60 ml Gum arabic 1.5 g α-thioglycerol 1 g Total amount 100 g with water

[0030]

[Chemical 6]

The printing plate thus obtained was 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 Printing of the first 500 sheets and 1 hour Table 1 shows the results of the correctability in printing the 500th sheet after the elapse of time.

[0032]

[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. 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.

[0036]

【The invention's effect】

The corrective agent of the present invention is safe, can perform quick and reliable correction, has a long-lasting effect, and has excellent liquid stability.

Claims (1)

[Claims] 1. A correction agent for offset printing plates, which utilizes a silver image as an ink receptivity, comprising at least one compound represented by the following chemical formula 1. [Chemical 1] (In the formula 1, R1 and R2 each represent a hydrogen atom or an alkyl group, and R3 represents a hydroxyl group or a mercapto group.)