JPH0467519B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of the Invention] The present invention relates to a plate cleaning agent for lithographic printing plates. [Prior art] Lithographic printing is a printing method that skillfully takes advantage of the property that water and oil essentially do not mix. It consists of areas that accept ink, the former being the non-image area and the latter being the image area. Therefore, if this balance is disrupted, for example, the hydrophilicity of a non-image area deteriorates for some reason, ink often adheres to that area, resulting in so-called "background stains". There are various cases in which such background stains occur, but the most typical ones are when the lithographic printing plate is subjected to treatments such as burning to make it have high printing durability, and when the plate surface of the lithographic printing plate is In some cases, the product was left in the atmosphere without being protected with desensitized gum. Such a phenomenon may similarly occur when the printing press is stopped due to trouble with the printing press or during a break during printing. Therefore, when stopping a printing press, it is customary for printing personnel to apply a desensitized gum solution. Furthermore, if a lipophilic substance adheres to a non-image area of a lithographic printing plate to which the desensitized gum liquid has not been applied and is left untreated, that area becomes oil-sensitized and becomes a stain. For example, the appearance of marks such as fingerprints on the background of printed matter is due to similar causes. Furthermore, there is a case where a scratch occurs in a non-image area, and in this case, ink becomes clogged in the scratch and gradually becomes oil-sensitized and becomes a stain. A lithographic printing plate with stains as described above is
It is customary to treat the plate with a so-called plate cleaner (sometimes called a plate cleaner) to remove ink from the plate and restore the hydrophilicity of non-image areas. As one such plate cleaning agent,
Conventionally, those made of an aqueous solution of sodium silicate have been known. However, although this plate surface cleaning agent has an extremely high desensitizing effect, it is alkaline, so photosensitive lithographic printing plates developed with an aqueous alkaline developer, such as Japanese Patent Publication No. 43-28403,
A positive-working photosensitive lithographic printing plate having a photosensitive layer made of an o-quinonediazide compound as described in U.S. Pat.
When used in a lithographic printing plate made from a negative-working photosensitive lithographic printing plate having a photosensitive layer consisting of a binder with acidic groups and a diazo resin as described in British Patent No. 98613 and British Patent No. 1350521, one part of the image area is There were problems such as corrosion of parts and deterioration of ink adhesion. On the other hand, the plate cleaner using oxalic acid described in U.S. Pat. A hydrophilic layer (for example, US Pat.
Metal supports are not suitable because the layer formed by the hydrophilic treatment as described in No. 2714066 is likely to be destroyed and cause staining. Generally, when stains occur during printing, the ink on the plate surface is first removed with a cleaning agent (kerosene or hydrocarbon solvent), and then treated with a desensitizing agent. Since the above plate surface cleaning agent is also used as a desensitizing agent after ink cleaning, two steps are required for the plate surface cleaning treatment, making the process complicated. For this reason, in recent years, emulsifying type plate cleaners have been developed that integrate both functions, that is, they have both ink cleaning and desensitizing effects. For example, JP-A-52-15702 discloses an alkaline emulsion-type plate cleaner, and JP-A-53-2102 discloses an acidic emulsion-type plate cleaner. However, such emulsified plate surface cleaners have poor stain removal ability against burn-treated lithographic printing plates, and their desensitization is sufficiently long-lasting to remove scratches and stains, so they often bleed during printing. The problem was that the stains would recur. [Objective of the Invention] The object of the present invention is to provide an excellent desensitizing effect and an excellent dirt removal ability without adversely affecting the image area.
Another object of the present invention is to provide a plate surface cleaner for lithographic printing plates that has a preventive effect. Another object of the present invention is to provide a plate cleaning agent that exhibits excellent stain removal ability without destroying the hydrophilic surface of non-image areas of a lithographic printing plate. Still another object of the present invention is to provide a plate cleaning agent that exhibits excellent stain removal ability and desensitizing effect on all planographic printing plates. [Structure of the Invention] As a result of various studies, the present inventors have discovered that the above objects can be achieved by a plate cleaning agent having the following composition. That is, the present invention is a lithographic printing plate surface cleaner comprising an aqueous solution containing phosphoric acid-modified starch having film-forming properties and having a pH of 1 to 5. The phosphoric acid-modified starch (hereinafter also referred to as "modified starch") used in the present invention is a combination of starch with phosphorus oxychloride,
It is phosphoric acid esterified by reacting with trimetaphosphate (for example, sodium salt), orthophosphate, polyphosphate, phosphoric acid, organic phosphonic acid, etc. Depending on the esterification agent, there are monoester type and crosslinked diester type, both of which can be used in the present invention, but monoester type is preferable because it causes less aging characteristic of starch. As the raw starch, those obtained from potatoes, sweet potatoes, wheat, tapioca, corn, glutinous corn, rice, glutinous rice, etc. are used. The substitution rate (esterification rate) of phosphorylated starch is theoretically possible up to a substitution rate of 3, where all three hydroxyl groups of the glucose residues of starch are esterified, but the preferred range is a substitution rate of 0.03 to 1.0, which is more preferable. is between 0.1 and 0.6. As mentioned above, the modified starch used in the present invention is one in which phosphoric acid or a phosphoric acid derivative is ester-bonded to the hydroxyl group of glucose constituting the starch, and is a polymer compound containing units represented by the following general formula. be. In the above general formula, R ₁ to _{R 3} may be the same or different and each represents a hydrogen atom, a phosphoric acid or a phosphoric acid derivative residue. The method for synthesizing the above-mentioned modified starch is described in ``Water-soluble polymers and water-dispersible resins general technical data collection'' (published by Management Development Center Publishing Department, January 23, 1980, pages 68-69). By selecting various R <sub>1</sub> to <sub>R 3</sub> in the above general formula, a modified starch having desired properties can be obtained. The content of phosphoric acid-modified starch in the plate surface cleaning agent of the present invention is preferably 0.5% to 40% by weight.
These modified starches are used as a uniform aqueous solution by dissolving them in water or by heating water (70 to 80°C) to dissolve them. Preferred specific examples of the PH adjuster for adjusting the PH of the plate cleaning agent of the present invention include the following. Pyrophosphoric acid, sodium pyrophosphate, potassium pyrophosphate, lithium pyrophosphate, tripolyphosphate, sodium tripolyphosphate, potassium tripolyphosphate, lithium tripolyphosphate, tetraphosphoric acid, sodium tetraphosphate, potassium tetraphosphate, lithium tetraphosphate, hexametaphosphate, hexametaphosphate Sodium, potassium hexametaphosphate, lithium hexametaphosphate, methylene diphosphonic acid, 1-hydroxyethane 1,1-diphosphonic acid, nitrilotrisphosphonic acid, N-carboxymethyl N,N-di(methylenephosphonic acid), hexamethylene diamine-
Tetra (methylene phosphonic acid), ethylenediamine-tetra (methylene phosphonic acid), diethylenetriamine-penta (methylene phosphonic acid), N,
N-di(carboxymethyl)-N-methylenephosphonic acid, N-(2-hydroxyethyl)-N,N-
Di(methylenephosphonic acid), N-hydroxymethyl-N,N',N'-ethylenediamine tris(methylenephosphonic acid), N-hydroxyethyl-
N',N'-diethylethylenediamine-N,N,
N′,N′-tetra(methylenephosphonic acid), di(2
-hydroxypropylene)triaminepenta(methylenephosphonic acid), tri(2-hydroxypropylene)tetraaminehexa(methylenephosphonic acid), and the like. These compounds are commercially available, for example from Monsanto Chemical Company.
Also known as the "DEQUEST Class" from the Wayland Chemical Division of Philip A. Hunt Chemical Corp.
It is commercially available as ``WAYPLEX'' from the division). Also, organic acids such as citric acid, malic acid,
Examples include tartaric acid, lactic acid, leplic acid, p-toluenesulfonic acid, and the like. The above-mentioned compounds can be used alone or in combination of two or more types, and the amount is in the range of 0.1 to 15% by weight, more preferably 0.5 to 10% by weight based on the total weight of the plate cleaning agent according to the present invention. can be contained in This cleaning agent may further contain a surfactant, a hydrocarbon solvent having a dissolving effect on the lithographic printing ink, a water-soluble colloidal substance, and a wetting agent, if necessary. Surfactants that may be optionally contained in the plate cleaning agent of the present invention include anionic surfactants and nonionic surfactants. Examples of anionic surfactants include aliphatic salts, higher alcohol sulfate ester salts, aliphatic alcohol phosphate ester salts, dibasic fatty ester sulfonate salts, fatty acid amide sulfonate salts, alkylaryl sulfonate salts, and formaldehyde condensation salts. Naphthalene sulfonates, etc. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxypropylene, and polyoxyethylene ethers. Two or more of these surfactants may be used in combination. Further, the amount used is not particularly limited, but the preferred range is 10% by weight or less based on the total weight of the composition. As the hydrocarbon solvent having the action of dissolving lithographic printing ink, petroleum fractions usually used for cleaning ink and having a boiling point of 120 to 320°C are particularly useful. The range of use of this hydrocarbon solvent is 5 to 60% by weight, more preferably 10% by weight, based on the total weight of the composition.
~30% by weight. Since hydrocarbon solvents are immiscible with water, they must be thoroughly mixed and dispersed before use. In order to improve the stability of the dispersion at this time, it is useful to add a water-soluble colloid substance and a surfactant. The water-soluble colloidal material is preferably added so that the viscosity of the aqueous solution at 25 DEG C. is in the range of 5 to 120 centipoise. Preferred specific examples of water-soluble colloidal substances include natural products such as dextrin, gum arabic, alginates, cellulose derivatives (e.g., carboxymethyl cellulose, carboxyethyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc.) and modified products thereof. and polyvinyl alcohol and its derivatives, polyvinylpyrrolidone, polyacrylamide and its copolymers, acrylic acid copolymers, vinyl methyl ether/maleic anhydride copolymers, vinyl acetate/maleic anhydride copolymers,
Examples include synthetic materials such as styrene/maleic anhydride copolymer. These substances can be used alone or in combination, and the range of use of water-soluble colloidal substances to achieve the above-mentioned viscosity range is from 0.1 to 24% by weight of the total composition, more preferably from 0.3 to 20% by weight. weight%
You can choose from. In addition to the above-mentioned components, it is also useful to have one or more wetting agents that impart good spreading properties to the plate cleaner and reduce drying, making it more suitable for use. For example, it is a glycol represented by HO-( _CnH2n -O-) _nH (n=2-6, m=1-500). Examples of preferred compounds include ethylene glycol, propylene glycol, butylene glycol, pentanediol, hexylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, di-propylene glycol, tripropylene glycol,
As other humectants, polyhydric alcohols such as glycerin, sorbitol, and pentaerythritol are useful. The amount of wetting agent used is effective in the range of 0.1 to 30% by weight of the total composition weight, and more preferably in the range of 0.3 to 25% by weight. In addition to the above-mentioned materials, pumice, granular powder such as silica powder, dye, etc. may be added to the plate surface cleaning agent of the present invention. [Effects of the Invention] The plate cleaning agent of the present invention can be used to remove background stains generated during plate making, subsequent storage, printing, and all other stages from plate making to printing. The plate cleaning agent of the present invention overcomes the drawbacks of existing plate cleaning agents, namely, it is only suitable for certain types of plates and may damage images or worsen ink adhesion for some types of plates. It overcomes the drawbacks such as corrosion and destruction of the hydrophilic layer, and is not suitable for scratches on the hydrophilic layer.
It is also useful for lithographic printing plates made from PS plates. Furthermore, the plate surface cleaning agent of the present invention has an extremely strong effect of preventing scumming caused by scratches in the hydrophilic layer of the non-image area of a lithographic printing plate, and of maintaining and strengthening the recovered hydrophilicity. There is a characteristic that there is. [Examples] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Note that "parts" and "%" indicate parts by weight and % by weight, respectively, unless otherwise specified. Example 1 To 645 parts of pure water, add 20% phosphoric acid modified starch (substitution ratio 0.3)
After heating and dissolving the weight part (70-80℃) and cooling to 30℃,
Add 100 parts by weight of gum arabic 14° Baume aqueous solution,
The pH was adjusted to 2.0 with phosphoric acid, and 50 parts by weight of glycerin was dissolved as an emulsion stabilizer and wetting agent to prepare an aqueous phase. On the other hand, 150 parts of Solvent-K (manufactured by Nippon Petrochemical Co., Ltd., a hydrocarbon solvent with a boiling point of 151 to 190°C) and 20 parts of Perex OT-P (sodium dialkyl sulfosuccinate, manufactured by Kao Atlas Co., Ltd.) as an emulsifier. , 10 parts of Emulgen #903 (polyoxyethylene nonyl phenyl ether manufactured by Kao Atlas Co., Ltd.),
An oil phase was prepared by dissolving 5 parts of 80 parts of sorbitan monooleate (manufactured by Kao Atlas Co., Ltd.). Next, the aqueous phase prepared as above was stirred and heated,
The temperature was adjusted to 35° C., and the oil phase was slowly added dropwise thereto to prepare a dispersion liquid, which was then passed through a homogenizer to prepare a milky white emulsion type plate cleaner 1. On the other hand, naphthoquinone-1,2 of polyhydroxyphenyl obtained by condensation polymerization of acetone and pyrogallol described in Publication No. 43-28403
A photosensitive solution was prepared by dissolving 1 part of diazide-5-sulfonic acid ester and 2 parts of novolak type cresol formaldehyde resin in 40 parts of methyl cellosolve. After thoroughly washing and drying a grained aluminum plate with a thickness of 0.2 mm, the above-mentioned photosensitive solution was applied on it using a rotary coating machine and dried to approximately 2.0 g/m ^{2 .}
A positive PS plate with a photosensitive layer of
Manufacturer, developer for positive plates DP-4 (1:8 dilution)
After developing with an aqueous solution, it was washed with water and dried. The above printing plate was divided into four parts, each plate was treated according to the treatment conditions shown in Table 1, and the thus treated plate was treated with plate cleaning agent 1 to examine its stain removal ability.

[Table] A test plate treated as shown in Table 1 was treated with the previously prepared cleaning agent for about 30 seconds on a Heidelberg KOR printing machine, then wiped with water and printed. Normal printed matter completely inked with ink was obtained. And even after printing 30,000 sheets, no stains occurred even once. When the halftone dots in the image area on the plate were observed, no difference was observed in the size of the halftone dots or the degree of wear compared to the control product (D) which was not treated with a cleaning agent. Compared to the control product (D), a printed matter with normal ink stains etc. was obtained. In addition, there was almost no difference in obtaining normal printed matter from the start of printing when the above plate surface cleaner was wiped with water and when it was touched with the Molton water stick of the printing machine without wiping with water. It is not possible,
After 8 to 10 sheets, completely inked prints were obtained. Example 2 Both phases of the following formulation were prepared in the same manner as in Example 1 to obtain Plate Cleaner 2. Water Phase pure water -680 parts Phosphoric acid modified starch (substitution ratio 0.5) -30〃 Carboxymethyl cellulose (trade name CMC
#1105 manufactured by Ohcell Co., Ltd.) −10〃 Gum arabic (14° Baume aqueous solution) −50〃 Magnesium nitrate −10〃 Propylene glycol 30〃 Adjusted to PH2.0 with phosphoric acid (85%). Oil phase Ciel Sol #71 (Ciel Petrochemical Co., Ltd., starting point of boiling point
170°C to 207°C or less) 160 parts polyethylene glycol nonyl phenyl ether (Noigen EA80, Daiichi Kogyo Yakuhin Co., Ltd.) 15 parts sorbitan monolaurate (Span-40 Kao Atlas Co., Ltd.) 15 parts Aluminum with a thickness of 0.24 mm The plate was degreased by immersing it in a 7% aqueous solution of tertiary sodium phosphate at 60°C, washed with water, and then rubbed with a nylon brush while running a solution of pumice suspended in water for graining. 70℃ after washing
Sodium silicate (SiO ₂ /Na ₂ O molar ratio kept at
2.0) was immersed in a 5% aqueous solution for 30 to 60 seconds. After thoroughly washing with water, it was dried. 2.0 parts of 2-hydroxyethyl methacrylate copolymer (synthesized by the method described in Example 1 of British Patent No. 1505739), 2-methoxy-4-hydroxy condensate of p-diazodiphenylamine and paraformaldehyde -5-benzoylbenzenesulfonate 0.12 parts by weight, Oil Blue #603
A photosensitive solution consisting of 0.03 parts (manufactured by Orient Chemical Industry Co., Ltd.), 15 parts of 2-methoxyethanol, 10 parts of methanol, and 5.0 parts of ethylene dichloride was applied to the support (dry coverage: 1.8 g/m ² ), I got the negative PS version. This PS plate was exposed using a halftone negative film and exposed to 3.0 parts of sodium sulfite, 30.0 parts of benzyl alcohol, 15.0 parts of triethanolamine, 4 parts of monoethanolamine, 10 parts of sodium t-butylnaphthalenesulfonate, and 1000 parts of pure water. After developing with an aqueous developer consisting of, the film was washed with water and dried. The above printing plate was divided into four parts and treated in the same manner as the treatment conditions shown in Table 1 of Example 1, and then the stain removal ability of plate cleaning agent 2 was tested. After printing on a Heidelberg KOR type printing machine with the above-mentioned plate cleaning agent for 30 seconds and wiping it off with a damp sponge, the number of defective prints before obtaining clear prints was 10 to 20. The results were good, with almost no difference observed compared to the control printing plate (D) (not treated with detergent). Even after printing 30,000 sheets, there was no staining even once, and as a result of observing the halftone dots of the image on the plate, it was found that the control product (D)
There was no difference in the size of halftone dots or the degree of wear compared to the previous one. Examples 3 to 5 Photosensitive printing plates produced in the same manner as in Examples 1 and 2 were developed with the same developer and treated under the processing conditions in Table 1 of Example 1, and then treated with the following plate cleaning agent. Nos. 3, 4 and 5 were tested for their ability to remove stains. The test results are shown in Table 2. Plate cleaning agent 3 Water Phase-pure water 642 parts Phosphate-modified starch (substitution ratio 0.2) 30 Gum arabic (14° Baume aqueous solution) 100 Potassium nitrate 5 Sodium hexametaphosphate 10 Potassium citrate 10 Polyoxyethylene nonyl phenyl ether (product) Emulgen #911 (manufactured by Kao Atlas Co., Ltd.) 25 Adjusted to pH 1.8 with phosphoric acid (85%). Oil phase EXSOL D 100 (manufactured by Exxon Chemical Co., Ltd.) 160 parts polyoxyethylene oleyl ether (trade name Emulgen #404 Kao Atlas Co., Ltd.) 10 parts oleic acid monoglyceride 5 parts hydrogenated rosin ester (trade name Harcolin D Arakawa Chemical) Co., Ltd.) 3 parts plate surface cleaning agent 4 Water Phase-pure water 638 parts Phosphate-modified starch (substitution ratio 1.5) 5.0 Polyvinylpyrrolidone K-30 10 Gum arabic (14° Baume aqueous solution) 90 Potassium pyrophosphate 10 Magnesium nitrate 10 Oxygen Ethylene oxypropylene block polymer (trade name: Emulgen pp-250 Kao Atlas Co., Ltd.)
8 Adjusted to pH 2.0 with phosphoric acid (85%). Oil phase Mineral Spirit A (manufactured by Nippon Petrochemicals) 160 parts Polyoxyethylene sorbitan monolaurate (trade name Emazol L-130 manufactured by Kao Atlas Co., Ltd.)
12 parts Sorbitan monooleate (Span-80 manufactured by Kao Atlas Co., Ltd.) 10 parts Rosin 2 parts Plate cleaner 5 Pure water 880 parts Phosphate-modified starch (substitution ratio 0.2) 30 Gum arabic (14° Baume aqueous solution) 50 Diphenyl Sodium ether disulfonate (trade name: Sandetto BL, manufactured by Sanyo Chemical Co., Ltd.) 30 Butyl cellosolve 10 Comparative example Water Phase-pure Water 635 parts Gum arabic (14° Baume aqueous solution) 100 parts Phosphoric acid (85%) 30 parts Glycerin 50 parts Oil Phase solvent -K 150 parts Perex OT-P 20 parts Emulgen #903 10 parts Spine-80 5 parts

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Claims (1)

[Claims] 1. A plate cleaning agent for lithographic printing plates comprising an aqueous solution containing phosphoric acid-modified starch having film-forming properties and having a pH of 1 to 5.