JP2744986B2 - Desensitizing solution for lithographic printing plate and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a desensitizing solution for a lithographic printing plate, and more specifically, a plate material in which conductive zinc oxide is coated on the surface of a support such as paper. (Hereinafter referred to as "master paper")
The present invention relates to a desensitizing solution using phytic acid as a chelating agent, which is used when a new oil-based image is formed by an electrophotographic method and used as a lithographic printing plate (original plate for offset printing), and an improvement in a method for producing the same.

In the following description, a blending unit is a weight unit unless otherwise specified.

<Conventional technology> Desensitizing treatment solutions for electrophotographic plates for offset printing include:
(A) It is harmless, (a) cyanine blue (phthalocyanine copper chelate) can be used in the ink, and (c) phytic acid is used as the main component instead of the one based on the complex with a ferrocyan complex from the viewpoint of easy pH adjustment. It is becoming something.

As a technique for improving the chelating function of phytic acid, there is a technique proposed in, for example, JP-A-1-160691. The description in the claims section is extracted below.

"Each component (A), (B),
(C): (A) phytic acid or a functional derivative, (B) a dibasic acid or a metal salt thereof, and (C) a compound of the following general formula (I) or a hydrate thereof: MX1, I) [wherein M represents a divalent metal atom, X represents a monovalent or divalent anion, and l represents an integer of 1 or 2], as an active ingredient. A composition for plate desensitization treatment. <Problems to be Solved by the Invention> However, the desensitizing treatment liquid having the above-described configuration has a considerably high desensitizing effect, but contains a metal ion that easily generates a salt hardly soluble in water, If a conventional ferrocyan-based desensitizing solution is mixed depending on the working environment, the metal ions may become water-insoluble pherocyanic complex salts or may change from a water-soluble chelate to a water-insoluble chelate to form a precipitate. There was.

In view of the above, an object of the present invention is to provide a desensitizing solution having a large desensitizing effect without using metal ions and having good stability, and a method for producing the same. .

<Means for Solving the Problems> The present invention has been made in view of the above, and is directed to a lithographic printing plate desensitizing solution using phthalic acid as a chelating agent and a method for producing the same. Sulfosalicylic acid acts on phytic acid to form a complex,
The complex is an active ingredient.

<Detailed Description of Means> Hereinafter, the above means will be described in detail.

(A) phytic acid (also known as inositol hexaphosphate)
The hydrogen group at the 2-position to 6-position or the 3-position to 5-position chelates zinc on the surface of a portion other than the image portion (non-image portion) formed on the master paper by electrophotography. The non-image portion is made lipophobic to prevent adhesion of ink (oiliness). This phytic acid is a substance obtained from plant seeds or grains (industrially produced from rice cake) and is harmless to animals and plants.

The content of phytic acid is 3% or more, preferably 5% or more, in the concentration in the desensitizing solution.

(B) Here, the sulfosalicylic acid means 5-sulfosalicylic acid. This is because 4-sulfosalicylic acid is known only as a derivative.

Sulfosulfylic acid is acidic in aqueous solution and coexists with phytic acid. However, from a pH of about 1.7, a complex is formed between them, and when the pH first becomes 2.0 or more, the formation of a complex is clearly recognized. When the pH is 6.0 or more, the structure of the complex changes.

Although the structures of these complexes are not yet clear, it can be inferred that they will be "electrolytic transfer complexes" by the measurement by the molar ratio method. The formation of the complex is apparent from the red shift of the spectral absorber.

When this complex aqueous solution coexists with zinc oxide, the complex exchanges zinc with sulfosalcylic acid, and phytic acid and zinc form a water-insoluble chelate, and sulfosulfylic acid is released into water again. This is also evident by the blue shift of the spectral absorber.

Although the method disclosed in Japanese Patent Application Laid-Open No. 1-169691 has obtained extremely satisfactory results as a function, it is difficult to put to practical use because of the above-mentioned disadvantages. The inventor has attempted to make use of this excellent idea and to further eliminate the basic disadvantages of this method. That is, the material must be chelate as long as chelate exchange is intended. If it is a chelate, it must be metal to coordinate with that center. In order to exchange the coordinated metal with zinc, the metal must be a divalent or higher valent metal ion in view of the chelation constant. According to the results of additional tests by the inventor, chromium (III) is most suitable as a metal ion,
The next best was found to be cobalt (III). As a fundamental problem, the presence of metal ions is inevitable, and the above disadvantages cannot be avoided theoretically. The present inventor has sought to find a suitable organic compound that cannot be replaced by this chelate.
Naturally, chelation cannot be performed with an organic compound containing no metal. Therefore, it is needless to say that the idea must be changed.

(C) Forming a water-insoluble white complex precipitate with phytic acid and salicylic acid. However, the complex is slightly soluble in water.
This reaction seems to be a salicylic acid-specific reaction (salicylic acid has -OH and -COOH in one benzene nucleus). No complex is formed with phenol having only -OH in the benzene nucleus, and no complex is formed with benzoic acid having only -COOH.

Attention is paid to the fact that the complex formed from phytic acid-salicylic acid is slightly soluble in water, and if a group (radical) having an extremely high dipole moment is introduced into the same benzene nucleus, the complex is dissolved in water. I thought it would be. Sulfosalicylic acid was selected on the above thought path, and as a result of the experiment, a water-soluble complex as expected was obtained. Also, this complex is phytic acid / sulfosalcylic acid: 1
/ 1 and 1/2 complexes are formed. Both exchange smoothly with zinc and phytic acid produces zinc and a water-insoluble chelate,
Sulfosalicylic acid is released.

Here, the compounding amount of sulfosalcylic acid to 100 parts of phytic acid is 10 to 70 parts (from about 0.5 in a molar ratio).
2.0). If the amount of sulfosalicylic acid is less than 10 parts, the effect of addition is extremely weak, and if it exceeds 70 parts, it does not contribute to the formation of the complex and is meaningless.

The pH of the desensitizing solution must be adjusted to pH: 3.0 to 6.0 (preferably, pH: 3.8 to 5.0). If the pH of the desensitizing solution is out of the above range, the master paper will be stained.

The alkali as the pH adjuster includes alkali metal ions (Li, Na, K, etc.), non-metallic alkali ions (ammonia; various ethanols such as monoethanolamine, diethanolamine, triethanolamine, etc. amines; monomethylamine, dimethylamine, Any of various amines such as trimethylamine, ethylenediamine, propylenediamine, and phenylenediamine) may be used. However, when the desensitizing solution is diluted as a fountain solution and used as a fountain solution, an alkali metal salt may be used. Is preferable because abnormal emulsification (so-called watering) is not observed in the ink used during printing.
The above alkalis may be used alone or in combination of two or more.

(D) In preparing the desensitizing solution, the following agents (d-1) to (d-7) can be added as necessary.

(D-1) Commonly used sizing agents such as starch (including soluble starch and dextrin form) and its derivatives, cellulose derivatives, sodium polyacrylate, gum arabic, pullulan and the like.

(D-2) ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol,
Polyose-based wetting agents such as polypropylene glycol, glycerin, sorbitol, glucose and sugar.

(D-3) Commonly used organic acids such as citric acid, malonic acid, succinic acid, adipic acid, tartaric acid, phthalic acid and salts thereof, and preservatives such as benzoic acid and dihydroacetic acid.

(D-5) Auxiliaries such as aromatic sulfonic acids having a sulfo group introduced into an aromatic ring such as benzene and toluene, and salts thereof.

(D-6) Interfacial tension modifiers such as lower alcohols, ethers, ketones, cellosolves and methyl esters of lower fatty acids.

 (D-7) Coloring dye.

<Effects of the Invention> The desensitizing solution of the present invention and the method for producing the same are obtained by using phytic acid-sulfosulfylic acid complex as an active ingredient by using phytic acid and sulfosalicylic acid in combination as described above. The desensitizing treatment liquid has an extremely improved desensitizing function, as shown in the examples below, and furthermore,
Since a divalent or higher metal salt is not used, there is no problem caused by the presence of the metal ion.

The desensitizing solution for lithographic printing of the present invention could not only sufficiently withstand practical use, but also greatly increase the number of master papers that could be printed, as shown in Examples described later. That is, the present invention can provide a new practical desensitizing solution that can withstand high printing durability.

<Example> Hereinafter, in order to confirm the effects of the present invention, a description will be given of a test example performed along with a comparative example for the examples.
The aqueous solutions having the formulations shown in Tables 1 and 2 were adjusted to pH 4.2 to 4.3 using the respective alkalis shown, to prepare desensitizing solutions of Examples and Comparative Examples.

Each of the desensitizing liquids was applied to a master paper on which a plate was made, and a solution diluted 20 times with water was used as dampening water.

Then, using a normal offset printing machine, printing ink (Master Blue: trade name, manufactured by Niken Chemical Laboratory Co., Ltd.)
Printed on neutral paper.

Offset printing was performed on 5,000 sheets per master paper (printing durability: guaranteed 3,000 sheets). In the case of the treatment liquids of the respective examples, up to 5,000 sheets, no background stains or other abnormalities were recognized on the master paper, and good printed matters were obtained. On the other hand, when the processing liquids of the respective comparative examples were used, background stains were generated on the non-image areas of the master paper and the printing paper from the start of printing, which was not practical.

In addition, when each master paper after printing in each example was examined in further detail, the influence of the image area on the toner was abnormally small. This phenomenon is because there is no free phytic acid in the aqueous solution, and all of it is guarded by forming a complex with sulfosalcylic acid, so the chemical impact on the toner (resin: organic polymer) is significantly weakened. It is estimated to be.

In each of the above examples, printing was further continued after printing 5,000 sheets. However, even when a total of 10,000 sheets were printed, printing was not caused on the printing paper and printing was possible.

Further, the properties of the dampening solution to which a polar solvent was added (Examples 17 and 18) were superior. In Examples 6 to 12 in which the desensitizing solution using an organic alkali as a pH adjuster was diluted and used as a fountain solution, abnormal emulsification was observed in the ink used during printing, but the printed matter was poor. Had no effect.

Claims (2)

(57) [Claims] 1. A desensitizing solution for a lithographic printing plate using phytic acid as a chelating agent, wherein sulfosalicylic acid is 10 to 70 parts by weight with respect to 100 parts by weight of phytic acid.
Mainly an aqueous solution of the composition in which parts by weight are blended, pH: 3.0
A desensitizing solution for a lithographic printing plate, which is prepared to a pH of from 5.0. 2. A method for producing a desensitizing solution for a lithographic printing plate using phytic acid as a chelating agent, comprising: forming a complex comprising phytic acid and sulfosalicylic acid in an aqueous solution; adjusting the pH to 3.0 to 5.0. A method for producing a desensitizing solution for a lithographic printing plate, characterized in that the lithographic printing plate is desensitized.