JPS6119986B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is an offset printing plate that utilizes a silver image as ink receptivity, and eliminates ink receptivity by changing the hydrophilicity of unnecessary portions of the silver image formed on the offset printing plate. It relates to an image modifying agent for plates, and more specifically, it can be used to remove unnecessary portions of a silver image on an offset printing plate formed by a photographic or physical method using a specific processing agent as appropriate at any stage of the printing process. The present invention relates to completely making the surface hydrophilic and eliminating ink receptivity by treating the surface with the following methods, without causing any problems to the printing properties, base material, etc. Since such processing is usually called "correction" in the printing field, the present inventors will follow this term hereinafter. Furthermore, the processing agent used in the correction operation will be referred to as a "correction agent." In general, the areas that need to be corrected in printing master plates manufactured by photolithography include those that already exist in the copy original, those that occur during exposure,
and others caused by non-uniform development processing. This means that, for example, if there are unwanted images in the reproduced original, if dust and dirt particles, fingerprints or other stains are present, or if the original is made by gluing together different originals, the exposure Sometimes a shadow appears. In order to obtain good printed matter, all of these points must be corrected during the plate-making and printing stages. Generally speaking, correction operations are essential, and it is desirable to be able to perform necessary corrections at any stage of the plate-making and printing processes. A number of attempts have been made to correct unwanted images in offset printing plates by utilizing the silver image as an ink receptivity. For example, by precipitating a hydrophilic metal salt, rubber, latex, gelatin, or other hydrophilic polymer or pigment on the silver image, or by mechanically removing the silver image using an eraser, knife, etc.; This method involves removing metallic silver from the image area by treating with a so-called silver image bleach-fixing composition containing an oxidizing agent such as dichromate or red blood salt, and sulfite or thiosulfate.
However, with the above methods, it is difficult to completely correct the image, the lipophilic image may be exposed again during printing, or it may cause other problems such as staining.
In addition, processing takes time and reduces work efficiency,
Alternatively, not only does the correction fluid itself have drawbacks such as insufficient stability and a decline in performance during storage, but also after the start of one-shot printing, that is, after an ink film is formed on the silver image. image deletion,
In other words, it was practically difficult to make corrections. A mercapto or thione group and a hydrophilic group (e.g. hydroxyl group,
carboxyl group, sulfonic acid group, etc.) in the same molecule, and improved versions thereof, JP-A-51-21901 and JP-A-54-53002.
All of the correcting agents of No. 1, No. 1, were excellent in that they considerably solved the drawbacks of the prior art described above, and were able to reliably and almost instantaneously make silver images hydrophilic. However, despite their excellent modifying ability, these modifiers still have drawbacks. This is because mercapto compounds have a characteristic odor, and like cysteine, they are easily oxidized and are unstable when used as a correction solution.Furthermore, because they are made into a strongly acidic solution, they can have an adverse effect on the human body. , ease of handling and workability, etc. Therefore, there is a strong demand for the development of an odorless correction agent that satisfies the conditions required for a correction agent as described above. Therefore, an object of the present invention is to be free from the above-mentioned drawbacks, to be able to quickly and completely correct images, to prevent the corrected area from being exposed again even when printing a large number of sheets, and to be able to be stored for a long period of time. It is an object of the present invention to provide an odorless and harmless correction agent that does not reduce its correction ability. It has been found that the above objects of the invention are achieved by using S-triazine compounds having at least one mercapto group as modifiers. One specific example of an S-triazine with mercapto groups is trithiocyanuric acid, which has three mercapto groups. The fact that trithiocyanuric acid is effective as a correcting agent for offset printing plates that make silver images ink receptive is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 48-92101.
This was unexpected from the modifier of the compound having a mercapto group and a hydrophilic group described in the above issue. However, S-triazine compounds in which one or two of the mercapto groups of trithiocyanuric acid are substituted with hydrophilic groups, compared to trithiocyanuric acid and the compounds described in JP-A-48-92101, etc.
It has also been found that it has various further advantages. S- having a mercapto group used in the present invention
The triazine compound can be represented by the following general formula. general formula (In the formula, R ₁ and R ₂ each represent a mercapto group or a hydroxyl group.) Compounds in which R ₁ and R ₂ are both mercapto groups, and compounds in which at least one of R ₁ and R ₂ is a hydroxyl group are included. . Examples of these compounds are trithiocyanuric acid,
These are dithiocyanuric acid and monothiocyanuric acid. These compounds are known, and their synthesis methods and physical properties are described in S-Triazines and Derivatives, written by EM Smolin and L. Rapoport in The Chemistry of Heterocyclic Compounds series published by Interscientific Publications. This is detailed on pages 105 to 111. The correction agent of the present invention can be used as a correction fluid using an organic solvent, water, or a mixed solvent thereof. A concentration range of modifier from 0.1 to 20% by weight is sufficient, preferably from 1.0 to 10% by weight. In addition, elements that make the liquid viscous, such as carboxymethyl cellulose, polyvinyl alcohol, and glycerin, and elements that color the liquid, such as dyes and organic or inorganic pigments, can be included, but these are essential elements. isn't it. Furthermore, fine particle powder as described in JP-A-51-21901 may also be included. The modifier of the present invention is non-volatile, stable and odorless. In addition, it can be corrected quickly and completely, and even if it is rubbed strongly after correction, ink will not get on the correction area. Therefore, a larger number of sheets can be printed. As an offset printing plate using the silver image of the present invention for ink receptivity,
No., JP-A-53-21602, U.S. Patent No. 3721559,
In addition to U.S. Patent No. 3490905, U.S. Patent No. 3454398,
Included are offset printing plates having silver halide images that are ink receptive, such as JP-A-53-9603. Examples will be described below. Example 1 Polyethylene terephthalate film (100
μ) After subbing the base with a known aqueous solution containing gelatin, nitrocellulose and valaclor phenol as main components, a top coating solution prepared with the following composition was applied and dried to obtain an offset printing plate. Ta. 0.2% silver nitrate aqueous solution 10c.c. 1% potassium bromide aqueous solution 1c.c. 2% formalin solution 10c.c. 0.03N sodium hydroxide aqueous solution 100c.c. Bring the total volume to 200c.c. with water. This was previously subjected to a contact treatment with an alkaline reducing agent solution (transfer developer) together with the negative image on the photosensitive negative sheet using the principle of silver complex diffusion transfer using a known method to obtain a positive image on an offset printing plate. As a corrective agent, use the compounds and amounts shown in Table 1 below, and add each to 80 mmol of caustic soda and water in a total amount.
100 ml of a correction solution was prepared, and the image area of the offset printing plate to be corrected was wiped with the correction solution soaked in absorbent cotton.

[Table] Compound A is dithiocyanuric acid, which is a modifier of the present invention, Comparison a is thioglycolic acid, and Comparison b is
indicate thiomalic acid, respectively. After such an offset printing plate is mounted on a printing press, a liquid having the following composition (silver image lipophilization liquid) is applied all over the print by, for example, soaking absorbent cotton and wiping it.

[Table] Immediately after that, we started printing and observed the ink stains on the corrected areas, and found that stains occurred on 2,000 sheets for Comparison A and 3,000 sheets for Comparison B, but for Compound A of the present invention, stains occurred on 2,000 sheets or more when printing more than 5,000 sheets. No stains were generated at all. In addition, correction fluid No. 2 and No. 3 have a mercapto odor, but correction fluid No. 1 of the present invention
There was no odor at all. Example 2 A lithographic plate was prepared in the same manner as described in Example 1 of JP-A-53-21602, except that 1.0 g/m ² of hydroquinone was added to the physical development nucleus layer of the offset printing plate (Plate No. 3). A printing material was produced. After the image-wise exposure of the lithographic printing material, transfer development was carried out by immersing it in a transfer developer having the following formulation for 30 seconds at 30°C, followed by immersion in a stop solution having the following formulation for 30 seconds (at 25°C). ), the excess liquid was removed by immersion and squeezing, and the material was dried under atmospheric conditions.

[Stop liquid]

Water 2 Citric acid 10g Sodium citrate 35g The printing plate thus obtained was transferred to an offset printing machine A.B.D.
Dick350CD (trade name) was installed, and the print was printed after wiping it with a liquid called Prescription (E). The temperature of the printing room is 22℃.
The humidity was 60%. [E] 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 After printing 100 sheets, stop the printing press and make corrections. I corrected the upper part of the image using the correction fluid below.

[Table] After restarting printing, more than 5,000 high-quality prints with no ink stains in the correction area were obtained. Similar results were also obtained when this correction fluid was used at the start of printing. Example 3 Example 1 was repeated except using monothiocyanuric acid or trithiocyanuric acid as the modifier. Similar results were obtained. Example 4 Example 2 was repeated except using monothiocyanuric acid or trithiocyanuric acid as the modifier. Similar results were obtained.

Claims (1)

[Scope of Claims] 1. A printing plate correction agent that utilizes a silver image as printing ink receptivity, characterized in that the correction agent contains an S-triazine compound represented by the following general formula. Correcting agent. general formula (In the formula, R ₁ and R ₂ each represent a mercapto group or a hydroxyl group.)