JP2002091017A - Method for producing planographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a planographic printing plate in which an alkali developing solution of a relatively low pH favorable to the environment and safety is used, a non-image area stably has good developability and is free of stain in printing and an image area is hardly damaged by development and ensures high image strength. SOLUTION: A photosensitive planographic printing plate with a photosensitive layer comprising a photopolymerization type photosensitive composition containing a compound having an ethylenically unsaturated double bond, a photopolymerization initiator and a polymer binder on an aluminum substrate is imagewise exposed and developed with a developing solution containing (1) an inorganic alkali agent, (2) a nonionic surfactant having a polyoxyalkylene ether group and (3) an amphoteric surfactant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for making a lithographic printing plate. More specifically, a lithographic plate capable of producing a printing plate free from printing stains and having excellent printing durability, improving the safety of a developing solution, stability over time on developing characteristics, and improving the effect of a waste solution on the environment. The present invention relates to a printing plate making method. More specifically, the present invention relates to a method of making a lithographic printing plate having a high dispersibility of a developer in a photosensitive layer component and capable of reducing development scum.

[0002]

2. Description of the Related Art Negative-working photosensitive lithographic printing plates, which have been widely used in the past, have a diazo resin provided on a hydrophilically treated aluminum plate. Inevitably, there is a concern about the treatment of the development waste liquid and its effect on the environment. In the photosensitive layer of the positive photosensitive lithographic printing plate, an orthoquinonediazide compound is used in combination with a novolak resin, and an alkaline silicate aqueous solution capable of dissolving the novolak resin is used as a developer. However, the pH at which the novolak resin can be dissolved is about 13, and such a high pH developer is highly irritating when it adheres to skin and mucous membranes, and requires sufficient care in handling.

On the other hand, conventionally, on an aluminum plate support,
Printing with a photosensitive layer of a photopolymerizable photosensitive lithographic printing plate on the surface
Examples of the plate developer include alkali metal silicates, phosphates,
Aqueous solutions such as carbonates, hydroxides, and organic amine compounds
Liquids have been proposed. For example, Japanese Unexamined Patent Application Publication No.
In the official gazette, at a high pH of 12 or more, alkali silicate and amphoteric
A developer containing a surfactant is disclosed in JP-A-11-65129.
According to the report, SiO _Two/ M_TwoO (M is an alkali metal) is specified
Developer containing alkaline silicate with a pH of 12 or less
It is shown. The former is not only a matter of handling, but also
Is easily damaged by development due to the high pH of the developer
In the latter case, the pH of the developer slightly decreases during use,
There was a problem that the silicate gelled and became insoluble.

Japanese Patent Application Laid-Open No. 61-109052 discloses a developer containing no alkali silicate, a developer comprising an alkali reagent, a complexing agent, an anionic surfactant, an emulsifier, an n-alkanoic acid, and the like. No. 1984605
No. 4,878,098 discloses a developer containing an alkali agent, a complexing agent, an anionic surfactant, amyl alcohol, and N-alkoxyamines.
There was a problem in that the image portion was greatly damaged and sufficient printing performance such as printing durability was obtained. As a developer having a relatively low pH (pH 12 or less) and containing no alkali silicate, JP-A-2
000-81711 discloses an aqueous potassium hydroxide solution containing an anionic surfactant, and JP-A-11-65126 discloses an aqueous alkali metal carbonate solution having a pH of 8.5 to 11.5.

The problem of the development at a relatively low pH is that the photopolymerizable photosensitive layer basically has a low dissolving power. There were problems such as the occurrence of. In order to solve these problems, it is necessary to increase the acid value of the polymer binder in the plate photosensitive layer to increase developability, or to use a combination of monomers having an acid group. When a high acid value binder was used, printing problems such as a problem that ink did not adhere during printing (blinding) were likely to occur. Also, since the dissolving power of the components of the photosensitive layer in these developing solutions is small, it has been pointed out that such components are generated as sludge in the developing solution and it takes a long time to wash the tank. There has been a demand for the development of a developing solution which does not cause the generation of the developer.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, that is, to use a relatively low pH alkaline developing solution which is preferable from the viewpoint of environment and safety, and to stably use the developing solution. In order to provide a method of making a lithographic printing plate, in which the non-image portion has good developability, is free from stains during printing, and has a strong image strength with little damage to the image portion during development. is there. More specifically, it is an object of the present invention to provide a method of making a lithographic printing plate in which a developer has a high dispersibility with respect to a photosensitive layer component and can reduce development scum.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, a nonionic surfactant having a specific structure has been added to an aqueous alkaline solution having a relatively low pH, and developed. By adjusting the salt concentration in the solution, the dissolution rate of the unexposed portion of the photopolymerizable photosensitive layer was increased, and conversely, the crosslinked portion of the exposed portion by photopolymerization was found to suppress the penetration of the developer. . In addition, they have found that it is effective to add an amphoteric surfactant to a developer to reduce development residue generated when the solubility or dispersity of a photosensitive layer component in the developer is insufficient, and have reached the present invention.

That is, the present invention is as follows. (1) Photosensitivity having a photosensitive layer comprising a photopolymerizable photosensitive composition containing a compound having an ethylenically unsaturated double bond, a photopolymerization initiator, and a polymer binder on an aluminum support After imagewise exposing the lithographic printing plate, a developing solution containing (1) an inorganic alkali agent, (2) a nonionic surfactant having a polyoxyalkylene ether group, and (3) an amphoteric surfactant is used. A method of making a lithographic printing plate, characterized by developing. (2) The method of making a lithographic printing plate as described in (1) above, wherein the developer has a pH of 10.0 to 12.5 and a conductivity of 3 to 30 mS / cm.

According to the method of making a lithographic printing plate of the present invention,
Deterioration of the developing characteristics due to the aging or repeated use of the developer is suppressed, and good developability for non-image areas is obtained, there is no stain in printing, and image areas are less damaged in development and are strong. A high image strength is obtained, the dispersibility of the developer in the photosensitive layer components is high, and the development waste can be made free or reduced. Furthermore, according to the method of making a lithographic printing plate of the present invention, it is possible to produce a lithographic printing plate free from printing stains and excellent in printing durability, and the pH of a developer is relatively low, which is preferable for safety. It is possible to improve the effect of the waste liquid of the developer on the environment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The method of making a lithographic printing plate according to the present invention will be described in detail below. First, the features of the method for making a lithographic printing plate of the present invention will be described, and a novel developing solution used in the plate making method of the present invention will be described. The developer of the present invention is an aqueous alkaline solution containing at least (1) an inorganic alkali agent, (2) a nonionic surfactant having a polyoxyalkylene ether group, and (3) an amphoteric surfactant.

The (1) inorganic alkali agent of the present invention includes, for example, sodium phosphate, potassium, ammonium, sodium carbonate, potassium, ammonium, sodium hydrogencarbonate, potassium, ammonium, boric acid Sodium, potassium, ammonium, sodium hydroxide, potassium, ammonium, lithium and the like. Further, an organic alkali agent may be supplementarily used for the purpose of finely adjusting the alkali concentration and assisting the solubility of the photosensitive layer. Examples of the organic alkali agent include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, n-butylamine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, Examples thereof include diisopropanolamine, ethyleneimine, ethylenediamine, pyridine, and tetramethylammonium hydroxide.

These alkali agents are used alone or in combination of two or more. As the amount of the alkali agent, the pH of the developer is in the range of 9 to 13.5, and the conductivity is 2 to 2.
It is used so as to be in a range of 40 mS / cm, and preferable ranges are pH 10.0 to 12.5 and conductivity 3 to 30.
mS / cm range, more preferably 5-20 mS / cm
Range. If the pH of the developing solution falls below the above range, image formation becomes impossible, and if the pH exceeds the above range, over-development occurs or damage in the development of the exposed portion increases. When the electric conductivity is lower than the above range, the elution of the photosensitive composition on the surface of the aluminum plate support is usually difficult, and the printing is contaminated. If the concentration exceeds the above range, the salt concentration is high, so that the elution rate of the photosensitive layer becomes extremely slow, and a residual film is formed in an unexposed portion.

It is essential that the developer of the present invention contains (2) a nonionic surfactant having a polyoxyalkylene ether group, and the addition of the surfactant dissolves the unexposed portion of the photosensitive layer. This makes it possible to reduce the permeability of the developer to the exposed portion. As the surfactant containing a polyoxyalkylene ether group, those having the structure of the following general formula (I) are preferably used.

R ¹ -O- (R ² -O) _n H (I)

In the formula (I), R ¹ represents an alkyl group having 3 to 15 carbon atoms which may have a substituent, an aromatic hydrocarbon group having 6 to 15 carbon atoms which may have a substituent, or A heteroaromatic ring group having 4 to 15 carbon atoms which may have a substituent (an alkyl group having 1 to 20 carbon atoms, a halogen atom such as Br, Cl, I, etc .; Aromatic hydrocarbon group,
Examples thereof include an aralkyl group having 7 to 17 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an alkoxy-carbonyl group having 2 to 20 carbon atoms, and an acyl group having 2 to 15 carbon atoms. And R ² is an alkylene group having 1 to 100 carbon atoms which may have a substituent (as the substituent, an alkyl group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 15 carbon atoms) And n represents an integer of 1 to 100.

The (R ² —O) _n part of the formula (I) may be two or three groups within the above range. Specific examples include a random or block-like combination of an ethyleneoxy group and a propyleneoxy group, a combination of an ethyleneoxy group and an isopropyloxy group, a combination of an ethyleneoxy group and a butyleneoxy group, and a combination of an ethyleneoxy group and an isobutylene group. In the present invention, the surfactant having a polyoxyalkylene ether group is used alone or in a complex system, and it is effective to add 1 to 30% by weight, preferably 2 to 20% by weight in a developer. If the addition amount is small, the developing property is reduced, while if it is too large, the damage of development is increased, and the printing durability of the printing plate is reduced.

The developer component of the present invention, (3) an amphoteric surfactant, has the effect of suppressing the generation of scum by improving the dispersibility of the photosensitive layer component in the developer. In particular, when a titanocene photopolymerization initiator is used as a component of the photosensitive layer, this component precipitates in the developer, easily forms scum, and exerts a great effect in suppressing such scum. As the amphoteric surfactant, any of a betaine-type amphoteric surfactant, a glycine-type amphoteric surfactant, an alanine-type amphoteric surfactant, and a sulfobetaine-type amphoteric surfactant may be used, or two or more kinds may be used in combination. It can also be used. Betaine-type amphoteric surfactants generally have a structure represented by the following formula (II) in the molecule.

[0018]

Embedded image

The following are specific examples.

[0020]

Embedded image

The glycine-type amphoteric surfactant generally has a structure represented by the following formula (III) in the molecule.

--NH--CH ₂ --COOH (III)

Specifically, for example, a group of amphoteric soaps generally referred to as TEGO as described below can be mentioned.

[0024]

Embedded image

The alanine-type amphoteric surfactant generally has a structure represented by the following formula (IV) in the molecule, and is formed by hydrolysis of an addition reaction product of an alkylamine and an acrylate. Or its salt is common.

--NH--CH ₂ --CH ₂ --COOH (I
V)

Among these amphoteric surfactants, the most preferably used is a group of alanine-type amphoteric surfactants, and specific examples thereof include N-octodecyl-β-alanine (sodium salt) and N-mystyryl. -Β-alanine (sodium salt), laurylaminopropionic acid (sodium salt), and lipomin LA (manufactured by Lion Corporation).

In the present invention, the amphoteric surfactant is contained in the developer in an amount of 0.2 to 10% by weight, preferably 0.5 to 5% by weight.
It is effective to add. If less than the above range,
If the effect of suppressing development scum is small and too large, problems such as foaming properties occur.

Further, other surfactants described below may be added. As other surfactants, for example, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether and the like Polyoxyethylene alkyl allyl ethers, polyoxyethylene alkyl esters such as polyoxyethylene stearate, sorbitan monolaurate, sorbitan monostearate, sorbitan distearate, sorbitan monooleate, sorbitan sesquioleate, sorbitan triole Sorbitan alkyl esters such as ate,
Nonionic surfactants such as monoglyceride alkyl esters such as glycerol monostearate and glycerol monooleate: alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, sodium butylnaphthalenesulfonate, sodium pentylnaphthalenesulfonate, sodium hexylnaphthalenesulfonate Anionic surface activity such as alkyl naphthalene sulfonates such as sodium octyl naphthalene sulfonate, alkyl sulfates such as sodium lauryl sulfate, alkyl sulfonates such as sodium dodecyl sulfonate, sulfosuccinate salts such as sodium dilauryl sulfosuccinate; Agents can be used. These surfactants can be used alone or in combination. Further, the content of these surfactants in the developer is preferably 0.1 to 20% by weight in terms of active ingredient.

In the developer of the present invention, the following components may be used in combination with the above components, if necessary. For example, benzoic acid, phthalic acid, p-ethylbenzoic acid, pn
-Propylbenzoic acid, p-isopropylbenzoic acid, p-
n-butylbenzoic acid, pt-butylbenzoic acid, pt
Organic carboxylic acids such as -butylbenzoic acid, p-2-hydroxyethylbenzoic acid, decanoic acid, salicylic acid, 3-hydroxy-2-naphthoic acid; isopropyl alcohol;
Organic solvents such as henzyl alcohol, ethyl cellosolve, butyl cellosolve, phenyl cellosolve, propylene glycol, diacetone alcohol; and other examples include chelating agents, reducing agents, dyes, pigments, water softeners, preservatives, and defoamers. .

Next, the photosensitive lithographic printing plate used in the present invention will be described. The photopolymerizable photosensitive composition constituting the photosensitive layer of the photosensitive lithographic printing plate used in the present invention contains, as essential components, an ethylenically unsaturated compound capable of addition polymerization, a photoinitiator, and a polymer binder. Various compounds such as a colorant, a plasticizer, and a thermal polymerization inhibitor can be used in combination.

An ethylenically unsaturated compound is an ethylenically unsaturated bond which undergoes addition polymerization by the action of a photopolymerization initiator and causes crosslinking and curing when the photopolymerizable photosensitive composition is irradiated with actinic rays. Is a compound having The compound containing an addition-polymerizable ethylenic double bond can be arbitrarily selected from compounds having at least one, and preferably two or more, terminal ethylenically unsaturated bonds. For example, those having chemical forms such as monomers, prepolymers, that is, dimers, trimers and oligomers, or mixtures thereof and copolymers thereof.

Examples of monomers and copolymers thereof include esters of unsaturated carboxylic acids (eg, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, etc.) with aliphatic polyhydric alcohol compounds. And amides of unsaturated carboxylic acids and aliphatic polyamine compounds. Specific examples of the ester monomer of the aliphatic polyhydric alcohol compound and the unsaturated carboxylic acid include acrylic acid esters such as ethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butanediol diacrylate, and tetramethylene glycol. Diacrylate, propylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane tri (acryloyloxypropyl) ether, trimethylolethane triacrylate, hexanediol diacrylate, 1,4-cyclohexanediol diacrylate , Tetraethylene glycol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate Pentaerythritol tetraacrylate, dipentaerythritol diacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, sorbitol triacrylate, sorbitol tetraacrylate, sorbitol pentaacrylate, sorbitol hexaacrylate, tri (acryloyloxyethyl) isocyanurate, polyester There are acrylate oligomers and the like.

Examples of the methacrylate include tetramethylene glycol dimethacrylate, triethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, ethylene glycol dimethacrylate, and 1,3-butanediol. Dimethacrylate, hexanediol dimethacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol dimethacrylate, dipentaerythritol hexamethacrylate, dipentaerythritol pentamethacrylate, sorbitol trimethacrylate, sorbitol tetramethacrylate , Bis [p- (3--methacryloxy-2-hydroxypropoxy) phenyl] dimethyl methane, bis - [p- (methacryloxyethoxy) phenyl] dimethyl methane.

Examples of itaconic acid esters include ethylene glycol diitaconate, propylene glycol diitaconate, 1,3-butanediol diitaconate,
There are 1,4-butanediol diitaconate, tetramethylene glycol diitaconate, pentaerythritol diitaconate, sorbitol tetritaconate and the like. The crotonic acid ester includes ethylene glycol dicrotonate, tetramethylene glycol dicrotonate, pentaerythritol dicrotonate, sorbitol tetradicrotonate and the like.

Examples of the isocrotonic acid ester include ethylene glycol diisocrotonate, pentaerythritol diisocrotonate, and sorbitol tetraisocrotonate. The maleic acid ester includes ethylene glycol dimaleate, triethylene glycol dimaleate, pentaerythritol dimaleate, sorbitol tetramaleate and the like. Furthermore, a mixture of the above-mentioned ester monomers can also be mentioned. Specific examples of the amide monomer of the aliphatic polyamine compound and the unsaturated carboxylic acid include methylene bis-acrylamide,
Examples include methylenebis-methacrylamide, 1,6-hexamethylenebis-acrylamide, 1,6-hexamethylenebis-methacrylamide, diethylenetriaminetrisacrylamide, xylylenebisacrylamide, and xylylenebismethacrylamide.

As another example, see JP-B-48-417.
08 polyisocyanate compound having two or more isocyanate groups in one molecule described in
A vinyl urethane compound containing two or more polymerizable vinyl groups in one molecule to which a hydroxyl group-containing vinyl monomer represented by the following general formula (A) is added is exemplified. CH ₂ ＣC (R ⁵ ) COOCH ₂ CH (R ⁶ ) OH (A) (where R ⁵ and R ⁶ represent H or CH ₃ )

Urethane acrylates described in JP-A-51-37193 and JP-B-2-32293; JP-A-48-64183;
And polyfunctional acrylates and methacrylates such as polyester acrylates and epoxy acrylates obtained by reacting an epoxy resin with (meth) acrylic acid as described in JP-A-43191 and JP-B-52-30490. . In addition, Journal of the Japan Adhesion Association, Vol. 2
0, No. 7, 300-308 (1984) as photocurable monomers and oligomers can also be used. These ethylenically unsaturated compounds are used in an amount of 5 to 80% by weight, preferably 30 to 70% by weight, based on all components of the photosensitive layer.

As the photopolymerization initiator to be contained in the photosensitive layer of the photosensitive lithographic printing plate of the present invention, various photoinitiators known in patents and literatures, or two or more photoinitiators may be used depending on the wavelength of the light source used. The photoinitiator combination system (photoinitiation system) can be appropriately selected and used. Specific examples are listed below, but the present invention is not limited thereto. Various light-initiating systems have also been proposed when using visible light of 400 nm or more, an Ar laser, the second harmonic of a semiconductor laser, or an SHG-YAG laser as a light source. For example, US Pat. No. 2,850,445. Certain photoreducing dyes described in
For example, Rose Bengal, Eosin, Erythrosin, etc.
Alternatively, a system based on a combination of a dye and an initiator, for example, a complex initiation system of a dye and an amine (JP-B-44-2018)
No. 9), a combination system of hexaarylbiimidazole, a radical generator and a dye (Japanese Patent Publication No. 45-37377), and a system of hexaarylbiimidazole and p-dialkylaminobenzylidene ketone (Japanese Patent Publication No. 47-2528; 54-155292), a system of a cyclic cis-α-dicarbonyl compound and a dye (JP-A-48-84183), a system of a cyclic triazine and a merocyanine dye (JP-A-54-1).
No. 51024), a system of 3-ketocoumarin and an activator (JP-A-52-112681, JP-A-58-15503).
No.), a system of biimidazole, a styrene derivative, and a thiol (JP-A-59-140203), and a system of an organic peroxide and a dye (JP-A-59-1504, JP-A-59-1402).
03, JP-A-59-189340, JP-A-62-1
No. 74203, JP-B-62-1641, U.S. Pat.
No. 766055), a system of a dye and an active halogen compound (JP-A-63-258903, JP-A-2-63054, etc.) A system of a dye and a borate compound (JP-A-62-1430)
No. 44, JP-A-62-150242, JP-A-64-1
No. 3140, JP-A-64-13141, JP-A-64-141
No. 13142, JP-A-64-13143, JP-A-64
-13144, JP-A-64-17048, JP-A-1
JP-A-229003, JP-A-1-298348, JP-A-1-138204, etc.) A system of a dye having a rhodanine ring and a radical generator (JP-A-2-179643, JP-A-2-244050), titanocene and 3- Ketocoumarin dye systems (JP-A-63-221110), systems combining titanocene and xanthene dyes and addition-polymerizable ethylenically unsaturated compounds containing an amino group or a urethane group (JP-A-4-221958, JP-A-4-221958) -21
No. 9756), a system of titanocene and a specific merocyanine dye (JP-A-6-295061), and a system of titanocene and a dye having a benzopyran ring (JP-A-8-334897).
No.) and the like.

Recently, a laser (violet laser) having a wavelength of 400 to 410 nm has been developed, and a photoinitiating system exhibiting high sensitivity to a wavelength of 450 nm or less corresponding thereto has been developed, and these photoinitiating systems are also used. You. For example, a cationic dye / borate system (JP-A-11-8864)
7), merocyanine dye / titanocene system (JP-A-2000
-147763), carbazole type dye / titanocene (Japanese Patent Application No. 11-22480), and the like. In the present invention, a system using a titanocene compound is particularly preferable because of its excellent sensitivity.

As the titanocene compound, various compounds can be used. For example, JP-A-59-1523
No. 96, and various titanocene compounds described in JP-A-61-151197 can be appropriately selected and used. More specifically, di-cyclopentadienyl-Ti-di-chloride, di-cyclopentadienyl-Ti-bis-phenyl, di-cyclopentadienyl-
Ti-bis-2,3,4,5,6-pentafluorophenyl-1-yl, di-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophenyl-1-yl,
Di-cyclopentadienyl-Ti-bis-2,4,6-
Trifluorophenyl-1-yl, di-cyclopentadienyl-Ti-bis-2,6-di-fluorophenyl-1-
Yl, di-cyclopentadienyl-Ti-bis-2,4
-Di-fluorophenyl-1-yl, di-methylcyclopentadienyl-Ti-bis-2,3,4,5,6-tetrafluorophenyl-1-yl, di-methylcyclopentadienyl-Ti- Bis-2,6-difluorophenyl-1
-Yl, di-cyclopentadienyl-Ti-bis-2,
6-difluoro-3- (pyr-1-yl) -phenyl-1
-Yl and the like.

If necessary, the photoinitiator may be a thiol compound such as 2-mercaptobenzthiazole, 2-mercaptobenzimidazole or 2-mercaptobenzoxazole, N-phenylglycine, or N, N-dialkylamino aromatic alkyl ester. It is known that the photoinitiating ability can be further enhanced by adding a hydrogen-donating compound such as an amine compound. The amount of the photopolymerization initiator (system) used is 0.05 to 100 parts by weight, preferably 0.1 to 100 parts by weight, based on 100 parts by weight of the ethylenically unsaturated compound.
It is used in an amount of 70 parts by weight, more preferably 0.2 to 50 parts by weight.

The polymer binder used in the photosensitive layer of the photosensitive lithographic printing plate of the present invention is not only a film-forming agent of the composition, but also needs to be dissolved in an alkali developing solution. Organic polymers that are soluble or swellable are used. As the organic polymer, for example, when a water-soluble organic polymer is used, water development becomes possible. Examples of such organic high-molecular polymers include addition polymers having a carboxylic acid group in a side chain, for example, JP-A-59-4
4615, JP-B-54-34327, JP-B-58-
12577, JP-B-54-25957, JP-A-54
-92723, JP-A-59-53836 and JP-A-5-53836.
No. 9-71048, namely, methacrylic acid copolymer, acrylic acid copolymer, itaconic acid copolymer, crotonic acid copolymer, maleic acid copolymer,
There are partially esterified maleic acid copolymers and the like.

Similarly, there are acidic cellulose derivatives having a carboxylic acid group in the side chain. In addition, those obtained by adding a cyclic acid anhydride to an addition polymer having a hydroxyl group are useful. In particular, among these, [benzyl (meth) acrylate / (meth) acrylic acid / optionally other addition-polymerizable vinyl monomers] copolymer and [allyl (meth) acrylate (meth) acrylic acid / optionally Other addition-polymerizable vinyl monomers] copolymers are preferred. In addition, polyvinyl pyrrolidone and polyethylene oxide are useful as the water-soluble organic polymer. In order to increase the strength of the cured film, alcohol-soluble polyamides and polyethers of 2,2-bis- (4-hydroxyphenyl) -propane and epichlorohydrin are also useful.
In addition, Japanese Patent Publication No. 7-120040, Japanese Patent Publication No. 7-12004
No. 1, Tokiko 7-120042, Tokiko 8-1242
4, JP-A-63-287944, JP-A-63-28944
No. 7947, JP-A-1-271741, JP-A-11-
The polyurethane resin described in 352691 is also useful for the use of the present invention.

These high polymers can improve the strength of the cured film by introducing a radical reactive group into the side chain. Functional groups capable of undergoing an addition polymerization reaction include an ethylenically unsaturated bond group, an amino group, an epoxy group, and the like, and functional groups capable of forming a radical upon irradiation with light include a mercapto group, a thiol group, a halogen atom, a triazine structure, and an onium salt structure. And a polar group such as a carboxyl group or an imide group. As the functional group capable of undergoing the addition polymerization reaction, an ethylenically unsaturated bond group such as an acryl group, a methacryl group, an allyl group, and a styryl group is particularly preferable, and an amino group, a hydroxy group, a phosphonic group, a phosphate group, and a carbamoyl group are also preferable. And a functional group selected from an isocyanate group, a ureido group, a ureylene group, a sulfonic acid group, and an ammonium group are also useful.

In order to maintain the developability of the composition, the polymer binder of the present invention preferably has an appropriate molecular weight and acid value, and has a weight average molecular weight of 5,000 to 300,000 and an acid value of 2,000.
A high polymer of 0 to 200 is effectively used. These organic high-molecular polymers can be mixed in an arbitrary amount in the entire composition. However, if it exceeds 90% by weight, no favorable result is obtained in view of the strength of the formed image and the like. Preferably it is 10-90%, more preferably 30-80%. Further, the weight ratio of the photopolymerizable ethylenically unsaturated compound and the organic polymer is preferably in the range of 1/9 to 9/1. A more preferred range is 2/8 to 8/2, and a still more preferred range is 3/7 to 7/3.

In the present invention, in addition to the above basic components, a small amount of thermal polymerization is prohibited in order to prevent unnecessary thermal polymerization of a polymerizable ethylenically unsaturated compound during the production or storage of the photosensitive composition. It is desirable to add an agent. Suitable thermal polymerization inhibitors include haloid quinone, p-
Methoxyphenol, di-t-butyl-p-cresol, pyrogallol, t-butylcatechol, benzoquinone, 4,4'-thiobis (3-methyl-6-t-butylphenol), 2,2'-methylenebis (4-methyl −
6-t-butylphenol), cerium N-nitrosophenylhydroxylamine, aluminum aluminum N-nitrosophenylhydroxylamine and the like.
The addition amount of the thermal polymerization inhibitor is preferably from about 0.01% to about 5% based on the weight of the whole composition. If necessary, a higher fatty acid derivative such as behenic acid or behenic acid amide may be added to prevent polymerization inhibition by oxygen, and may be unevenly distributed on the surface of the photosensitive layer in a drying process after coating. . The amount of the higher fatty acid derivative added is about 0.5% to about 1% of the total composition.
0% is preferred.

Further, a coloring agent may be added for the purpose of coloring the photosensitive layer. Examples of the colorant include phthalocyanine pigments (CI Pigment Blue 1).
5: 3, 15: 4, 15: 6), azo pigments, pigments such as carbon black and titanium oxide, ethyl violet, crystal violet, azo dyes, anthraquinone dyes, and cyanine dyes. The amount of dye and pigment added is preferably about 0.5% to about 20% of the total composition.
In addition, additives such as inorganic fillers and plasticizers such as dioctyl phthalate, dimethyl phthalate and tricresyl phosphate may be added to improve the physical properties of the cured film. The amount of these additives is preferably 10% or less of the total composition.

When the photosensitive layer composition of the photosensitive lithographic printing plate of the present invention is coated on a support described below, it is used after dissolving it in various organic solvents. As the solvent used here,
Acetone, methyl ethyl ketone, cyclohexane, ethyl acetate, ethylene dichloride, tetrahydrofuran,
Toluene, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, acetylacetone, cyclohexanone, diacetone alcohol, ethylene glycol monomethyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol Monoisopropyl ether, ethylene glycol monobutyl ether acetate, 3-
Methoxypropanol, methoxymethoxyethanol,
Diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate-3-methoxypropyl acetate, N, N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, lactic acid Examples include methyl and ethyl lactate. These solvents can be used alone or as a mixture. The concentration of the solid content in the coating solution is suitably from 1 to 50% by weight.

A surfactant can be added to the photopolymerizable composition in the photosensitive layer of the photosensitive lithographic printing plate of the present invention in order to improve the coated surface quality. The coating amount is suitably ranges from about 0.1 g / m ² ~ about 10 g / m ² in weight after drying. More preferably, it is 0.3 to 5 g / m ² . More preferably, it is 0.5 to 3 g / m ² .

Usually, an oxygen-blocking protective layer is provided on the photosensitive layer in order to prevent the polymerization of oxygen. Examples of the water-soluble vinyl polymer contained in the oxygen-barrier protective layer include polyvinyl alcohol, and its partial esters, ethers, and acetal, or a substantial amount of an unsubstituted vinyl alcohol unit having water solubility required for them. And copolymers thereof. Examples of the polyvinyl alcohol include those having a hydrolysis degree of 71 to 100% and a polymerization degree in the range of 300 to 2400. Specifically, Kuraray's PVA-10
5, PVA-110, PVA-117, PVA-117
H, PVA-120, PVA-124, PVA-124
H, PVA-CS, PVA-CST, PVA-HC, P
VA-203, PVA-204, PVA-205, PV
A-210, PVA-217, PVA-220, PVA
-224, PVA-217EE, PVA-220, PV
A-224, PVA-217EE, PVA-217E,
PVA-220E, PVA-224E, PVA-40
5, PVA-420, PVA-613, L-8 and the like. Examples of the copolymer include 88-100% hydrolyzed polyvinyl acetate chloroacetate or propionate, polyvinyl formal and polyvinyl acetal, and copolymers thereof.
Other useful polymers include polyvinylpyrrolidone, gelatin and gum arabic, which may be used alone or in combination.

In the photosensitive lithographic printing plate of the present invention, the solvent used for coating the oxygen-barrier protective layer is preferably pure water, but alcohols such as methanol and ethanol, and ketones such as acetone and methyl ethyl ketone can be purified with pure water. May be mixed. The concentration of the solid content in the coating solution is suitably from 1 to 20% by weight. Known additives such as a surfactant for improving coating properties and a water-soluble plasticizer for improving physical properties of the film may be added to the oxygen-barrier protective layer of the present invention. As a water-soluble plasticizer,
For example, propionamide, cyclohexanediol,
Glycerin, sorbitol and the like. Further, a water-soluble (meth) acrylic polymer or the like may be added. The amount of the coating is about 0.1 g / m ² to about 15 g in weight after drying.
/ M ² is appropriate. More preferably, 1.0 g /
m ² to about 5.0 g / m ² .

Next, the support of the photosensitive lithographic printing plate of the present invention will be described. The aluminum support used in the present invention is a dimensionally stable aluminum or an alloy thereof (eg, silicon, copper, manganese, magnesium, chromium,
Alloy with zinc, lead, bismuth, nickel), or a plastic film or paper on which aluminum or an aluminum alloy is laminated or vapor-deposited, and usually has a thickness of about 0.05 mm to 1 mm. Also, a composite sheet described in JP-A-48-18327 can be used.

The aluminum support of the present invention is appropriately subjected to a substrate surface treatment described later. (Graining treatment) Japanese Patent Application Laid-Open No. Sho 56-2
No. 8893, such as mechanical graining, chemical etching, and electrolytic graining. Furthermore, an electrochemical graining method in which the aluminum surface is electrochemically grained in a hydrochloric acid or nitric acid electrolyte, a wire brush graining method in which the aluminum surface is scratched with a metal wire, and a ball graining method in which the aluminum surface is grained with a polishing ball and an abrasive. Alternatively, a mechanical graining method such as a brush grain method for graining the surface with a nylon brush and an abrasive can be used, and the above graining methods can be used alone or in combination. Among them, a method of producing a surface roughness usefully used in the present invention is an electrochemical method of chemically sanding in a hydrochloric acid or nitric acid electrolyte, and a suitable current density is 100 C / dm ^{2 to} 400 C. / Dm ² . More specifically, in an electrolyte containing 0.1 to 50% hydrochloric acid or nitric acid, the temperature is 20 to 100 ° C., and the time is 1 second to 3 hours.
0 minutes, it is preferable to perform the electrolysis at a current density of ^{100C / dm 2 ~400C / dm 2} .

The aluminum support thus grained is chemically etched with an acid or an alkali. When an acid is used as an etching agent, it takes time to destroy a fine structure, which is disadvantageous in industrially applying the present invention. However, it can be improved by using an alkali as an etching agent. Alkali agents suitably used in the present invention include caustic soda, sodium carbonate, sodium aluminate, sodium metasilicate, sodium phosphate, potassium hydroxide, lithium hydroxide, and the like. The preferred ranges of concentration and temperature are 1 to 50, respectively. %, 20 to 10
It is preferable that the temperature is 0 ° C. and the amount of Al dissolved is 5 to 20 g / m ³ .

After the etching, pickling is performed to remove dirt (smut) remaining on the surface. As the acid used, nitric acid, sulfuric acid, phosphoric acid, chromic acid, hydrofluoric acid, borofluoric acid and the like are used. In particular, as a method for removing the smut after the electrochemical surface-roughening treatment, it is preferable to use a method of removing 50 to 50 as described in JP-A-53-12739.
A method of contacting with sulfuric acid of 15 to 65% by weight at a temperature of 90 ° C. and a method of alkali etching described in Japanese Patent Publication No. 48-28123 are exemplified. The surface roughness (Ra) of the Al support effectively used in the present invention is 0.3 to 0.7 μm.

(Anodic Oxidation Treatment) The aluminum support thus treated is further subjected to an anodic oxidation treatment. The anodizing treatment can be performed by a method conventionally performed in this field. Specifically, sulfuric acid, phosphoric acid,
Chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid or the like or a combination of two or more of them can form an anodized film on the surface of an aluminum support by flowing a direct current or an alternating current to aluminum in an aqueous solution or a non-aqueous solution. . Since the conditions of the anodizing treatment vary depending on the electrolytic solution used, they cannot be unconditionally determined,
Generally, the concentration of the electrolyte is 1 to 80%, and the temperature of the electrolyte is 5 to 70%.
° C, current density 0.5-60 amps / dm ² , voltage 1 ~
A range of 100 V and an electrolysis time of 10 to 100 seconds is appropriate.

Among these anodizing treatments, those described in GB 1,412,768 are particularly useful.
The method of anodizing at a high current density in sulfuric acid and the method of anodizing phosphoric acid as an electrolytic bath described in US Pat. No. 3,511,661 are preferred. In the present invention, the anodized film is preferably from ^{1~10g / m 2, 1g / m} 2 plate to easily enter the wound is not more than, 10 g / m ² or more is great power is required for the production Is economically disadvantageous. Preferably, 1.5 to 7 g /
m ² . More preferably, it is ² to 5 g / m ² .

Further, in the present invention, after the graining treatment and the anodic oxidation, the aluminum support may be subjected to a sealing treatment. Such a sealing treatment is performed by immersing the substrate in hot water and a hot aqueous solution containing an inorganic salt or an organic salt, a steam bath, or the like. The aluminum support of the present invention may be subjected to a surface treatment such as a treatment other than silicate treatment with an alkali metal silicate, for example, immersion treatment in an aqueous solution of potassium fluorozirconate, phosphate or the like.

The photosensitive lithographic printing plate of the present invention is produced by forming a photosensitive layer comprising the above-mentioned photopolymerizable composition on the aluminum support having been subjected to the surface treatment as described above. Before coating, an organic or inorganic undercoat layer may be provided as necessary.

The photosensitive layer in the photosensitive lithographic printing plate of the present invention may be formed, for example, by using a carbon arc lamp, a high-pressure mercury lamp, a xenon lamp, a metal halide lamp, a fluorescent lamp, a tungsten lamp, a halogen lamp, a helium cadmium laser, an argon ion laser, or an FD.・ YAG laser, helium neon laser, semiconductor laser (3
An image can be formed on the surface of the aluminum plate support by performing image development with a conventionally known actinic ray (e.g., 50 nm to 600 nm), followed by development. After the image exposure and before the development, a heating process at a temperature of 50 ° C. to 150 ° C. for 1 second and 5 minutes may be provided for the purpose of increasing the curing rate of the photopolymerizable photosensitive layer.

On the photosensitive layer of the photosensitive lithographic printing plate of the present invention, as described above, an overcoat layer having an oxygen-blocking property is usually provided. It is known to remove the overcoat layer and remove the unexposed portion of the photosensitive layer at the same time, or to remove the overcoat layer with water or hot water first, and then remove the unexposed portion of the photosensitive layer by development. I have. These waters or warm waters include preservatives described in JP-A No. 10-10754 and JP-A No. 8-2.
An organic solvent described in No. 78636 can be contained.

The development of the photosensitive lithographic printing plate of the present invention with the above-mentioned developer is carried out at a temperature of 0 to 60 ° C., preferably about 15 to 40 ° C., for example, by subjecting the photosensitive lithographic printing plate to an exposure treatment. This is performed by immersing in a developer and rubbing with a brush. Further, when the developing process is performed using an automatic developing machine, the developing solution becomes fatigued in accordance with the processing amount. Therefore, the processing capability may be restored by using a replenisher or a fresh developing solution. As described in JP-A-54-8002, JP-A-55-115045, JP-A-59-58431, etc., the photosensitive lithographic printing plate thus developed is washed with water, Post-treatment with a rinsing solution containing an agent or the like, or a desensitizing solution containing gum arabic or a starch derivative. For the post-processing of the photosensitive lithographic printing plate of the present invention, these processings can be used in various combinations. The printing plate obtained by the above processing is described in JP-A-2000-89478.
The printing durability can be improved by a post-exposure treatment or a heating treatment such as burning by the method described in (1). The lithographic printing plate obtained by such a process is set on an offset printing machine and used for printing a large number of sheets.

[0064]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, of course, are not intended to limit the scope of the present invention. [Example 1] An aluminum plate of material 1S having a thickness of 0.30 mm was grained with a No. 8 nylon brush and an aqueous suspension of 800 mesh pumistone, and the surface was grained, followed by thorough washing with water. 60% at 70 ° C in 10% sodium hydroxide
After dipping for 2 seconds and etching, washing with running water, 20%
The resultant was neutralized and washed with HNO ₃ and washed with water. V _A = 12.7V
The electrolytic surface roughening treatment was performed in a 1% nitric acid aqueous solution at an anode electricity of 300 coulomb / dm ² using a sinusoidal alternating current under the conditions described in (1). The surface roughness was measured.
It was 45 μm (Ra indication). After immersion in a 30% H ₂ SO ₄ aqueous solution and desmutting at 55 ° C. for 2 minutes, a cathode was placed on a grained surface in a 20% H ₂ SO ₄ aqueous solution at 33 ° C. When anodized at 5 A / dm ² for 50 seconds, the thickness was 2.7 g / m ² . On the thus treated aluminum plate, a high-sensitivity photopolymerizable composition 1 having the following composition having a dry coating weight of 1.
The composition was applied so as to be 5 g / m ² and dried at 100 ° C. for 1 minute to form a photosensitive layer.

(Photopolymerizable Composition 1) Ethylenic unsaturated bond-containing compound (A1) 1.5 parts by weight Linear organic high molecular polymer (B1) 2.0 parts by weight Sensitizer (C1) 0.15 Parts by weight Photoinitiator (D1) 0.2 parts by weight ε-phthalocyanine (F1) dispersion 0.02 parts by weight Fluorine nonionic surfactant Megafac F177 0.03 parts by weight (manufactured by Dainippon Ink and Chemicals, Inc.) ) Methyl ethyl ketone 9.0 parts by weight Propylene glycol monomethyl ether acetate 7.5 parts by weight Toluene 11.0 parts by weight

[0066]

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On the photosensitive layer, a 3% by weight aqueous solution of polyvinyl alcohol (98 mol% of saponification degree, polymerization degree of 500) was applied so as to have a dry coating weight of 2.5 g / m ² .
After drying at 120 ° C. for 3 minutes, a photosensitive lithographic printing plate was obtained.

The photosensitive lithographic printing plate was subjected to FD / YAG laser (plate jet 4 manufactured by CSI) at 100 μJ /
After scanning and exposing a solid image and a 1-99% halftone dot image (in 1% increments) at 4,000 lines / inch and 4000 dpi at an exposure dose of cm ² , developer 1 and finishing gum solution FP Standard processing was performed using an automatic developing machine (LP-850P2 manufactured by Fuji Photo Film) charged with -2W (manufactured by Fuji Photo Film). The preheating condition is that the plate surface temperature is 1
00 ° C, developer temperature is 30 ° C, and immersion time in the developer is about 1
5 seconds. The developer 1 has the following composition and the pH is 2
It was 11.5 at 5 ° C and the conductivity was 5 mS / cm.

(Composition of Developer 1) Potassium hydroxide 0.15 g Polyoxyethylene phenyl ether (n = 13) 5.0 g Cherest 400 (chelating agent) 0.1 g (C ₁₀ H ₂₁ —NHCH ₂ CH ₂ ) ₂ NHCH ₂ COOH 0.05g Water 94.7g

[Examples 2 to 5] The developer of Example 1 was used as shown in Table 1.
The lithographic printing plate was made in the same manner as in Example 1 except that the developing solution was changed to that shown in Example 1.

[0071]

[Table 1]

Examples 6 and 7 The linear organic high molecular polymer in the photopolymerizable composition 1 of Example 1 was changed from B1 to B2 (Example 6), and from B1 to B3 (Example 7). The planographic printing plate was made in the same manner as in Example 1 except for the above.

B2 (Example 6): Allyl methacrylate / methacrylic acid (70/30 mol%) copolymer, molecular weight 50,000. B3 (Example 7): Methyl methacrylate / isobutyl methacrylate / methacrylic acid (60/20/20 mol%) copolymer, molecular weight 100,000

Example 8 A lithographic printing plate was prepared in the same manner as in Example 1 except that the ethylenically unsaturated compound of the photopolymerizable composition of Example 1 was changed from A1 to the following structure A2. .

[0075]

Embedded image

Example 9 The following undercoating liquid composition was mixed and stirred. After about 5 minutes, heat generation was observed. After reacting for 60 minutes, the content was transferred to another container, and 30,000 parts by weight of methanol was further added to prepare a liquid coating solution.

(Liquid composition for undercoat) Phosmer PE manufactured by Unichemical Co., Ltd. 20 parts by weight Methanol 130 parts by weight Water 20 parts by weight Paratoluenesulfonic acid 5 parts by weight Tetraethoxysilane 50 parts by weight 3-methacryloxypropyltriethoxysilane 50 parts by weight

The liquid coating solution was applied onto the anodized aluminum support of Example 1 with a Si content of about 0.001 g.
/ M ^2, and dried at 100 ° C. for 1 minute. Then, a photosensitive layer and a water-soluble resin layer were provided in the same manner as in Example 1, and exposed and developed to form a lithographic printing plate.

[Comparative Example 1] With respect to the developer 1 of Example 1,
A composition excluding polyoxyethylene phenyl ether was used as a developer. The pH of this developer was 11.5 and the conductivity was 5 mS / cm. Otherwise, a lithographic printing plate was prepared in the same manner as in Example 1.

[Comparative Example 2] With respect to the developer 1 of Example 1,
A lithographic printing plate was prepared in the same manner as in Example 1 except that the composition excluding (C ₁₀ H ₂₁ -NHCH ₂ CH ₂ ) ₂ NHCH ₂ COOH was used as a developer.

[Comparative Example 3] With respect to the developing solution 1 of Example 1,
The amount of potassium hydroxide added was changed to 2 g to prepare a developer. The pH of this developer is 12.8 and the conductivity is 25
mS / cm. Otherwise, a lithographic printing plate was produced in the same manner as in Example 1.

Comparative Example 4 A solution obtained by diluting a LP-D developer manufactured by Fuji Photo Film Co., Ltd. 10 times with water as a developer containing an alkali metal silicate instead of the developer 1 of Example 1 was used. A lithographic printing plate was prepared in the same manner as in Example 1 except for using it as a developer. At this time, the pH of the developer is 1
At 2.8, the conductivity was 32 mS / cm.

The planographic printing plates obtained by the plate making methods of Examples 1 to 9 and Comparative Examples 1 to 4 were evaluated for developability, printing durability, and printing smear. Developability was determined by visually observing the plate surface after the development processing and by determining the presence or absence of the remaining photosensitive layer and the degree of the remaining film. The printing durability was evaluated using a R201 type printing machine manufactured by Man Roland Co., Ltd. using GEOS G black (N) manufactured by Dainippon Ink Co., Ltd., and the number of printed sheets in which 3% of halftone dots caused plate skipping was evaluated. The print stain was printed on a diamond IF2 type printer manufactured by Mitsubishi Heavy Industries using GEOS G Beni (S) manufactured by Dainippon Ink and the ink stain on the non-image area was visually evaluated. Regarding the generation of developing scum, the activity of the developing solution was kept constant by a small amount of replenishing solution, and the plate material of Example 1 was kept at 100%.
0 m ² treatment was performed, and the degree of scum generated at that time was visually determined. Table 2 shows the results.

[0084]

[Table 2]

As is clear from Table 2, the planographic printing plates of the examples according to the present invention each obtained satisfactory results, but the planographic printing plates of Comparative Examples were not satisfactory in any evaluation results. there were.

[0086]

As described above, the method for making a lithographic printing plate according to the present invention is a method for preparing a lithographic printing plate having a photosensitive layer comprising a photopolymerizable composition, and an aqueous alkali solution having a relatively low pH. By using a developer containing a nonionic surfactant and an amphoteric surfactant having a structure, it is possible to produce a lithographic printing plate having good developability, no printing stains, and excellent printing durability. . In addition, since the developer has excellent stability over time, the generation of development scum is suppressed, and the pH of the developer is relatively low. Therefore, it is preferable from the viewpoint of safety, and the effect of the development waste liquid on the environment can be improved.

Claims (2)

[Claims] 1. A photosensitive layer comprising a photopolymerizable photosensitive composition containing a compound having an ethylenically unsaturated double bond, a photopolymerization initiator, and a polymer binder on an aluminum support. After imagewise exposing the photosensitive lithographic printing plate,
(1) an inorganic alkali agent, (2) a nonionic surfactant having a polyoxyalkylene ether group, and (3)
A method of making a lithographic printing plate, comprising developing with a developer containing an amphoteric surfactant. 2. The method according to claim 1, wherein the developer has a pH of 10.0 to 12.5 and a conductivity of 3 to 30 mS / cm. .