JPH035318B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plate surface cleaning agent for lithographic printing plates produced by electrophotography.

[Prior art]

A lithographic printing plate created by electrophotography can be easily created by obtaining an image by ordinary electrophotography and wiping the electrophotographic copy surface with a hydrophilic liquid, in other words, an operation that does not require any special technology. be able to.

For example, a photoconductive layer is formed by applying photoconductive zinc oxide together with a binder to a base paper that has low expansion and contraction and is water resistant, and electrostatic charge is applied to the surface by corona discharge or the like to darken the surface. When a light image is irradiated at a certain point, the portions that are exposed to the light do not lose their charge, and the portions that are not exposed to the light remain charged, so that an electrostatic latent image is formed there. and spray charged toner particles, or
Alternatively, if the charged toner particles are immersed in an insulating liquid in which charged toner particles are dispersed, the electrostatic latent image area is developed by the charged toner particles being attached to the image pattern by electrostatic attraction.

Generally, toner particles used in a developer are coated with a lipophilic resin, and are fixed to the photoconductive layer through thermal fusion or solvent volatilization.

In this way, since the toner particles are coated with the lipophilic resin, the image area exhibits lipophilicity. In order to use the electrophotographic copy obtained here as a lithographic printing plate, it is necessary to make the non-image area hydrophilic.
One method is potassium ferrocyanide,
When a copying surface is wetted with a hydrophilizing liquid containing dissolved compounds such as potassium ferricyanide and ammonium phosphate, it reacts with the zinc oxide forming the photoconductive layer, and water-insoluble precipitates (e.g.
It is observed that a film of K ₂ Zn ₃ [Fe(CN) ₆ ] _{2.ZnNH 4} PO ₄ , etc.) is formed. The operation is extremely simple, as all you need to do is wipe the surface with absorbent cotton, gauze, etc. soaked in a hydrophilic solution.

When the lithographic printing plate obtained by the above operation is printed, if the hydrophilicity of the non-image area deteriorates for some reason, ink often adheres to that area, resulting in so-called "background staining". There are various causes of scumming, but a typical one is that when the plate surface dries after hydrophilic treatment, ink may adhere in spots or over the entire surface during printing. A similar phenomenon can also be seen during printing when the printing press is stopped due to trouble with the printing press or during a break.
Another cause is that if a lipophilic substance is attached to the hydrophilic layer while it is naked, that part becomes oil-sensitized and becomes dirty. The same reason causes fingerprint marks that appear on the background of printed matter before the hydrophilic treatment.

Previously, the normal PS version (Presensitized Printing
Abbreviation for Plate (lithographic printing plate that has been given photosensitivity in advance)
In the case of lithographic printing plates, silver halide printing plates, etc., stains can be recovered to some extent by wiping them with dampening water or etching liquid, but in the case of electrophotographic lithographic printing plates, they have a strong affinity with printing ink and can be removed with etching liquid or cleaning oil. Even if you wipe it, it won't get any better. Furthermore, in the case of PS plates, various plate surface cleaning agents are provided, but when applied to electrophotographic lithographic printing plates, the removal effect of the ink is insufficient and stains are not improved, and the electrophotographic lithographic printing It destroys the photosensitive layer of the plate and may even cause stains, making it unsuitable for practical use.
The appearance of a plate cleaning agent specifically for electrophotographic lithographic printing plates has been eagerly awaited.

[Purpose of the invention]

Therefore, an object of the present invention is to provide an electrophotographic method that recovers stains generated during printing, stains caused by fingerprints or ink attached before or after hydrophilic treatment, or stains caused by scratches, thereby enabling normal stain-free printing. An object of the present invention is to provide a plate surface cleaning agent for lithographic printing plates.

[Structure of the Invention] As a result of various studies, the present inventors discovered the following three
The above object could be achieved by using a suspension or emulsion containing the above ingredients as a plate cleaning agent.

(1) an aqueous solution of a compound that reacts with zinc oxide to produce a hydrophilic substance, (2) a hydrocarbon solvent that has the ability to dissolve lithographic printing ink, and (3) a surfactant.

In addition to the above-mentioned main components, the cleaning agent of the present invention can also contain the following components, if necessary.

(4) Water-soluble colloidal substances, (5) Wetting agents, (6) A type selected from molybdic acid, boric acid, nitric acid, phosphoric acid, polyphosphoric acid, and water-soluble alkali metal salts of these acids.

Compounds that react with zinc oxide as component (1) to produce a hydrophilic substance used in the present invention include ferrocyanide compounds such as potassium ferrocyanide, sodium ferrocyanide, potassium ferrocyanide, and sodium ferrocyanide, ferrocyanide compounds, and phosphoric acid. Phosphate compounds such as primary ammonium and secondary ammonium phosphate, JP-A-53-127002
Phytic acid or its derivative phytic acid compound, ferric chloride, ferric chloride, etc., as described in publications etc.
Salts of polyvalent metals such as copper, Special Publication No. 54-41923, Special Publication No. 1973
Chelate compounds such as hexamine cobalt salt, hexamine nickel salt, and EDTA, or polyacrylic acid, sodium polyacrylate, polymethacrylic acid, sodium polymethacrylate, and alginic acid described in -41924, JP-A-146105, etc. , sodium alginate, etc., but the compound is not limited in any way as long as it reacts with zinc oxide to produce a hydrophilic substance, and two or more kinds may be used in combination. In the present invention, it is preferable to use these compounds as an aqueous solution, and the pH range is
It is preferable to use in the range of 6, and it is desirable to use an acid or base such as ammonia, phosphoric acid, ammonium phosphate, citric acid, sodium citrate, etc. in combination.

The hydrocarbon solvent (component (2)) used in the present invention has the effect of dissolving lithographic printing ink, and is a petroleum fraction that is normally used for cleaning ink and has a boiling point.
Particularly useful are those between 120 and 320°C. The range of use of this hydrocarbon solvent is 5 to 50% by weight, more preferably 10 to 40% by weight of the total composition. Ingredients (1)
and (2) do not mix, so they must be thoroughly mixed and dispersed before use.

The surfactant (component (3)) used in the present invention is an anionic surfactant or a nonionic surfactant, and is used to enhance the dispersion of the system. Examples of anionic surfactants include aliphatic salts, higher alcohol sulfate ester salts, aliphatic alcohol phosphate ester salts, sulfonate salts of dibasic fatty acid esters,
These include fatty acid amide sulfonates, alkylaryl sulfonates, formaldehyde-condensed naphthalene sulfonates, and the like.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenol 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.

In the present invention, in order to further enhance the stability of the dispersion of the detergent, it is preferable to add a water-soluble colloidal substance as component (4) in addition to the surfactant as component (3).

Preferred specific examples of water-soluble colloidal substances that can be used in the present invention include dextrin, gum arabic, citric acid, alginates, cellulose derivatives (e.g., carboxymethyl cellulose,
Natural products such as carboxyethyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc.) and their modified products, polyvinyl alcohol and its derivatives, polyvinyl pyrrolidone, polyacrylamide and its copolymers, acrylic acid copolymers, vinyl methyl ether/maleic anhydride Acid copolymer, vinyl acetate/maleic anhydride copolymer, styrene/
It is a compound such as a maleic anhydride copolymer, and these substances can be used alone or in combination.

In addition to the above-mentioned components, it is also useful to have one or more component (5) wetting agents that give the plate cleaning agent good spreading properties and suppress drying, making it suitable for use. A suitable wetting agent has the general formula HO-(R-O-) _o
HR: CnH ₂ n (n = 2 to 6) n: 1 to 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, and the like. Other humectants useful are glycerin, sorbitol, and pentaerythritol.

Furthermore, the plate surface cleaning agent of the present invention is characterized by its extremely strong ability to prevent scumming caused by scratches in the hydrophilic layer and to maintain and strengthen the restored hydrophilicity. This effect is further enhanced by the combined use of at least one selected from molybdic acid, boric acid, nitric acid, phosphoric acid, or polyphosphoric acid and water-soluble alkali metal salts thereof as component (6). The compound is used in an amount ranging from 0.1 to 10% by weight of the total composition, more preferably in a range from 0.2 to 5%.

It has been found that, in addition to the above-mentioned components, the plate cleaning agent of the present invention may contain granular powders such as pumice, alumina powder, and silica powder, colloidal silica, colloidal alumina, dyes, and the like.

〔Example〕

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 "%" refer to parts by weight and % by weight, respectively, unless otherwise specified.

Example 1 10 parts of glycerin, 10 parts of monoammonium phosphate, 5 parts of potassium ferrocyanide, 2 parts of gum arabic, and 3 parts of polyethylene glycol oleyl ether (Daiichi Kogyo, Neugen ET-120) were dissolved in 70 parts of distilled water. , this is called liquid A.

Meanwhile, sorbitol oleate monoester (NOF, Nitsusan Nonion) was added to 20 parts of n-heptane.
Dissolve 4 parts of OP-80) and use it as Solution B.

Next, while stirring Solution A, Solution B was slowly added dropwise, dispersed, and then passed through a homogenizer to form a yellow emulsion.

After placing a fingerprint on a portion of an electrophotographic printing plate made using a Fujifilm ELP280 plate-making machine,
It was treated with the company's ELP etching solution to make it hydrophilic, and a printing test was performed on a Hamadastar 700CD printing machine. Staining was observed in the area where the fingerprints were attached. After printing 100 sheets, stop the printing machine, wipe the fingerprint marks (on which ink is already attached) with the plate cleaning agent mentioned above, and then
When printing was performed again, more than 10,000 good prints with no fingerprint stains were obtained. In addition, no abnormality was observed in the images or other images.

Example 2 Both AB solutions having the following formulations were prepared in the same manner as in Example 1 to obtain a plate cleaning agent.

[Liquid A]

Water 54 parts Polyvinyl alcohol (Nippon Gosei, PVAGH-
17) 2 parts glycerin 10 parts phytic acid (Mitsui Toatsu, 50% aqueous solution) 5 parts ammonia (25% aqueous solution) 17 parts polyethylene glycol nonyl phenyl ether (Daiichi Kogyo Seiyaku, Neugen EA-80) 2 parts [Liquid B] ] Solvent (Nippon Oil) 20 parts Polyethylene glycol sorbitan monostearate (Daiichi Kogyo Seiyaku, Solgen TW) 2 parts After placing a fingerprint on a lithographic printing plate prepared in the same manner as in Example 1 with a finger covered with printing ink. After hydrophilic treatment and printing, fingerprint-like stains were observed. After printing 100 sheets, we stopped the printing press, wiped off the fingerprint marks (there was already ink attached) with the above-mentioned plate cleaning agent, and then printed again, resulting in more than 10,000 good prints with no fingerprint stains. It was done.
Moreover, no abnormalities such as deterioration of ink in the image area were observed.

Example 3 Both solutions A and B having the following formulations were prepared in the same manner as in Example 1 to obtain a plate cleaning agent.

[Liquid A]

Water 55 parts Triethylene glycol 10 parts Methylcellulose (Shin-Etsu Chemical, Metrose 60SH
-50) 2 parts hexaammine cobalt hydrochloride 2.5 parts ammonium phosphate 5 parts Shicari powder (Nippon Aerosil, Aerosil 380)
0.4 parts Sodium borate 0.5 parts Polypropylene glycol ethylene glycol ether (Daiichi Kogyo Seiyaku, Epan 420) 2 parts [Liquid B] Kerosene 20 parts Sorbitan monostearate (Daiichi Kogyo Seiyaku, Sorgen-50) 2 parts Benzyl alcohol 1 A lithographic printing plate prepared in the same manner as in Example 1 was mounted on a Hamada Star 700CD printing machine, and ink was applied to a portion of the plate surface using an ink application roll. next
When printing was performed after hydrophilic treatment with ELP etching liquid, strong printing stains occurred in the areas where ink was applied before the hydrophilic treatment. When the printing machine was stopped, wiped with the above-mentioned cleaning agent, and printing was restarted, more than 10,000 good prints with no stains were obtained. No abnormalities were observed in the image area or elsewhere.

Example 4 A lithographic printing plate prepared in the same manner as in Example 1 was subjected to hydrophilic treatment, and printing was performed. Next, the printing press was stopped, the plate surface was scratched with sandpaper, and when printing was restarted, scratch-like stains appeared. The printing press was stopped again, the plates were wiped with the plate cleaning agent of Example 1, and more than 10,000 good prints with no scratches or stains were obtained. Furthermore, the plate surface cleaning agents of Examples 2 and 3 were also found to have a similar effect of improving scratches and stains.

Claims (1)

[Scope of Claims] 1. Electrophotography characterized by comprising an aqueous solution of a compound that reacts with zinc oxide to produce a hydrophilic substance, a suspension or emulsion whose main components are a hydrocarbon solvent and a surfactant. Plate cleaning agent for lithographic printing plates. 2. The plate cleaning agent for electrophotographic lithographic printing plates according to claim 1, wherein the surfactant is an anionic surfactant or a nonionic surfactant. 3. The plate cleaning agent for electrophotographic lithographic printing plates according to claim 2, wherein the hydrocarbon solvent is a petroleum fraction and has a boiling point range of 120° to 320°C. 4. The plate cleaning agent for electrophotographic printing plates according to claim 3, which contains a hydrocarbon solvent in an amount of 5 to 50% by weight of the plate cleaning agent.