| PATENT ASSIGNEE'S COUNTRY | Japan |
| UPDATE | 08.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 01.08.00 |
| PATENT TITLE |
Desensitizing solution for lithographic printing |
| PATENT ABSTRACT |
A desensitizing solution for lithographic printing is disclosed, which comprises at least one organometallic polymer containing at least two partial structure units represented by the following formula (1): ##STR1## wherein R.sup.0 represents --PO.sub.3 H.sub.2, --OPO.sub.3 H.sub.2 or a salt thereof. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 18.10.99 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A desensitizing solution for lithographic printing, comprising at least one organometallic polymer containing at least two partial structure units represented by the following formula (1): ##STR16## wherein R.sup.0 represents --PO.sub.3 H.sub.2, --OPO.sub.3 H.sub.2 or a salt thereof. 2. The desensitizing solution as claimed in claim 1, wherein said organometallic polymer is a polymer prepared by hydrolytic polycondensation of at least one organometallic compound represented by the following formula (2): (Q).sub.r M(Y).sub.p-r ( 2) wherein Q represents an organic residue having a partial structure unit represented by formula (1), Y represents a reactive group, M represents from trivalent to hexavalent metal, p represents a valence number of the metal M, and r represents 1, 2, 3 or 4, provided that p-r is 2 or more. 3. The desensitizing solution as claimed in claim 1, wherein the organometallic polymer is a copolymer comprising at least one unit selected from the group consisting of the units represented by the following formulae (3) to (8): ##STR17## wherein G.sup.1 represents --N(R.sup.1)CH.sub.2 R.sup.0 or --N(CH.sub.2 R.sup.0).sub.2 ; R.sup.0 has the same meaning as in formula (1); G.sup.2 represents --NR.sup.2 R.sup.3 or --NR.sup.2 R.sup.3 R.sup.4+ X.sup.- ; each of R.sup.1 to R.sup.7 represents a hydrogen atom or an unsubstituted or substituted organic residue, and they may combine each other to form a ring; X.sup.- represents a monovalent or higher valent anion; Z.sup.1 and Z.sup.2 which may be the same or different, each represent a divalent organic residue; and M has the same meaning as in formula (2). 4. The desensitizing solution as claimed in claim 1, wherein the organometallic polymer is a polymer constituted of organometallic polymers cross-linked between their main chains. 5. The desensitizing solution as claimed in claim 3, wherein the metal M in formulae (3) to (8) is Si. 6. The desensitizing solution as claimed in claim 1, wherein the organometallic polymer is a polymer represented by the following formula (9): ##STR18## wherein G.sup.1 and G.sup.2 have the same meanings as G.sup.1 and G.sup.2 respectively in formulae (3) to (8); a and b each represent an integer of from 1 to 10; and m and n are values the total of which is 100 weight %. |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention relates to a desensitizing solution for lithographic printing and, more particularly, to a desensitizing (process) solution used for a lithographic printing plate precursor comprising a metal oxide or sulfide and a binding resin such as an electrophotographic printing plate precursor or a direct-drawing type printing plate precursor. BACKGROUND OF THE INVENTION Examples of a lithographic printing plate precursor which is employed at present chiefly in the field of the small-scale commercial printing include (1) a direct-drawing type printing plate precursor comprising a hydrophilic image receiving layer provided on a water resisting support, (2) a printing plate precursor comprising a zinc oxide-containing image receiving layer (ink receptive layer =lipophilic layer) provided on a water resisting support, which is made into a printing plate by drawing images directly thereon by means of, e.g., a thermal printer, a dry laser printer or an ink jet printer and then processing the non-image area with a desensitizing solution, (3) an electrophotographic material comprising a zinc oxide-containing photoconductive layer provided on a water resisting support, which functions as a printing plate precursor to be made into a printing plate by forming images on the photoconductive layer in an electrophotographic process and then processing the non-image area with a desensitizing solution, and (4) a silver halide photographic material functioning as a printing plate precursor, which comprises a silver halide emulsion layer provided on a water resisting support. In general the printing plate constituted of a water-wettable non-drawing area (water receptive area=hydrophilic area) and a water-unwettable drawing area (ink receptive area=lipophilic area) is used for lithography. However, the lithographic printing plate precursors (2) and (3) are each provided with a ZnO-containing hydrophobic layer. As far as the printing operation is carried out without giving any processing to the printing precursors after image formation, the printing ink adheres to the non-drawing area also to make normal printing impossible. Therefore, it is necessary to desensitize the non-drawing area of the printing plate precursor prior to the printing operation, and thereby confer the water wettability thereon. The desensitizing solutions which have so far been proposed for such a purpose comprise cyanide-containing (process) solutions containing as the main component ferrocyanide or ferricyanide, and cyanide-free (process) solutions containing as their main component an ammine-cobalt complex, phytic acid (inositol hexaphosphate) or a derivative thereof, or a guanidine derivative. However, those processing solutions are not wholly satisfactory. More specifically, the ferrocyanide or ferricyanide-containing process solutions, though they have advantages of high desensitizing power, water-receptive firm film formability and high film-forming speed, have also disadvantages that, when exposed to light, they are colored and deposit precipitates due to lability of ferrocyanide and ferricyanide ions to heat and light, thereby undergoing a drop in desensitizing power, and further cause various problems regarding environmental pollution, including disposal of waste solutions, because the cyanide ions (CN.sup.-) contained therein are detected as free cyanogen. From consideration of those disadvantages, the latter cyanide-free processing solutions have been proposed, wherein the desensitizer such as an ammine-cobalt complex, phytic acid or a guanidine compound is contained as a main component. However, even these solutions are not wholly satisfactory as a desensitizing (process) solution applied to lithographic printing plate precursors. This is because they are slow in film-forming speed, as compared with the former cyanide-containing process solutions, and have a defect that they cannot form a water receptive film having high enough physical strength to withstand printing operations at the first etching system using a processor, thereby causing generation of background stain and plugging in dot gradation. As is generally known, phytic acid and its metal derivatives form metal chelate compounds. Many compounds of such a kind have already been offered as desensitizers for offset printing plate precursors. However, they are each slow in film-forming speed and cannot form a water-receptive film applicable to printing at the first time of processing with a processor. Therefore, they have drawbacks of occurring poor ink separability, background stain and plugging in dot gradation. In order to overcome such drawbacks, the addition of various additives to the processing solutions containing phytic acid compounds has been examined. For instance, the combined use of phytic acid compounds and the metal complexes of aminocarboxylic acids (JP-B-2-39397, the term "JP-B" as used herein means an "examined Japanese patent publication"), the combined use of phytic acid compounds and the hexametaphosphates (JP-B-62-7597), and the addition of lower amines, alkanolamines or polyamines to the processing solutions of the foregoing type (e.g., JP-A-54-117201, JP-A-53-109701 and JP-A-1-25994; the term "JP-A" as used herein means an "unexamined published Japanese patent application") were considered. However, those processing solutions have two problems; one problem is in that, although they can provide good water receptivity in the early stage of use, their etching ability is lowered by continuous use to bring about a decline in water receptivity, and the other problem is in that their use after long-term storage causes deterioration in water receptivity to generate background stain. The addition of cationic polymers to the processing solutions containing phytic acid compounds (JP-A-50-23099) produces, similarly to the addition of the foregoing additives, deterioration in properties of the processing solutions by the continuous use or long-term storage, and causes rust in some cases. Further, the combined use of phytic acid compounds with the polyethyleneimine copolymers has been proposed (JP-A-7-68967 and JP-A-7-137475). However, it allows the processing solutions only a narrow latitude in the matter of compatibility of the etching ability for making the non-image area receptive of water with the ink receptivity of the image area, or cannot dissolve the problem of causing deterioration in properties by long-term continuous use. In recent years, on the other hand, automatic printing machines, particularly miniaturized ones, of the type which incorporate a desensitizing system into the body thereof from the viewpoint of saving labor have been remarkably popularized, and the plate making of an offset master by electrophotographic system has enabled a reduction of processing time. Such a situation has been demanding a reduction in desensitizing time and an extension of the life span of a desensitizing solution. Further, it has been proposed to adopt a digital exposure method in the electrophotographic system master making system also. Such an exposure method has enabled easy making of masters having high-definition images, such as middle tone and screen tint, in addition to conventional plate-making images constituted mainly of line original and letter original. As a result, it has been demanding to make a printing plate enabling the reproduction of such high-definition images on printing materials in a printing process. On the other hand, thermal and dry laser printers have made it possible to confer high definition on plate-making images and reduce background stains on non-image areas, and thereby a demand for making a printing plate from a printing plate precursor of direct-drawing type by prepress processing has been generated. However, it is difficult with conventional desensitizing solutions to meet the foregoing demands. SUMMARY OF THE INVENTION One object of the invention is therefore to provide a desensitizing (process) solution for lithographic printing, which not only has excellent desensitizing performance but also causes no pollution problem, shows good stability upon long-term storage and continuous use, and further enables a reduction of etch-processing time. Another object of the present invention is to provide a desensitizing (process) solution for lithographic printing, which enables the making of a lithographic printing plate having good reproducibility of high-definition images, such as middle tone and screen tint, and developing no background stain on the non-image areas during the course of printing. It has been found that the aforementioned objects can be attained when the processing solutions according to the following Embodiments 1 to 6 are each used for etching a lithographic printing plate precursor: 1. A desensitizing solution for lithographic printing, comprising at least one organometallic polymer containing at least two partial structure units represented by the following formula (1): ##STR2## wherein R.sup.0 represents --PO.sub.3 H.sub.2, --OPO.sub.3 H.sub.2 or a salt thereof. Preferred embodiments are show below. 2. The desensitizing solution as described in Embodiment 1, wherein the organometallic polymer is a polymer prepared by hydrolytic polycondensation of at least one organometallic compound represented by the following formula (2): (Q).sub.r M(Y).sub.p-r (2) wherein Q represents an organic residue having a partial structure unit represented by formula (1), Y represents a reactive group, M represents from trivalent to hexavalent metal, p represents the valence number of the metal M, and r represents 1, 2, 3, or 4, provided that p-r is 2 or more. 3. The desensitizing solution as described in Embodiment 1, wherein the organometallic polymer is a copolymer comprising at least one unit selected from the group consisting of the units represented by the following formulae (3) to (8): ##STR3## wherein G.sup.1 represents --N(R.sup.1)CH.sub.2 R.sup.0 or --N(CH.sub.2 R.sup.0).sub.2 ; R.sup.0 has the same meaning as in formula (1); G.sup.2 represents --NR.sup.2 R.sup.3 or --NR.sup.2 R.sup.3 R.sup.4+ X.sup.- ; each of R.sup.1 to R.sup.7 represents a hydrogen atom or an unsubstituted or substituted organic residue, and they may combine each other to form a ring; X.sup.- represents a monovalent or higher valent anion; Z.sup.1 and Z.sup.2 which may be the same or different, each represent a divalent organic residue; and M has the same meaning as in formula (2). 4. The desensitizing solution as described in any of Embodiments 1, 2 and 3, wherein the organometallic polymer is a polymer constituted of organometallic polymers cross-linked between their main chains. 5. The desensitizing solution as described in Embodiment 3, wherein the metal M in formulae (3) to (8) is Si. 6. The desensitizing solution as described in Embodiment 1, wherein the organometallic polymer is a polymer represented by the following formula (9): ##STR4## wherein G.sup.1 and G.sup.2 have the same meanings as G.sup.1 and G.sup.2 respectively in formulae (3) to (8); a and b each represent an integer of from 1 to 10; and m and n are values the total of which is 100 weight %. DETAILED DESCRIPTION OF THE INVENTION The present organometallic polymer having at least two partial structure units represented by formula (1) has an extreme improvement in chelating reactivity and precipitate forming speed on account of characteristics of its chemical structure, as compared with hitherto known compounds having chelating ability, such as phytic acid and phytic acid salts. It is therefore presumed that the present organometallic polymer can improve water-receptivity providing speed and reduce the processing time for desensitization. Thus, the total duration of printing plate precursors' stay in the desensitizing solution becomes short, as compared with those in conventional desensitizing solutions, even if the same number of printing plate precursors are processed continuously. Further, the organometallic polymer can control contamination by Zn.sup.2+ and like ions which bring about precipitates in the desensitizing solution. As a result, the desensitizing solution of the present invention can have not only high desensitizing ability but also improved aging stability and running properties. The desensitizing solution of the present invention contains neither ferrocyanide compounds nor ferricyanide compounds causing environmental pollution and suffering deterioration when exposed to light or heat, and further it is little affected by platemaking environment, as compared with conventional cyanide-free processing solutions. In addition, the desensitizing solution of the present invention is stable upon long-term storage to cause neither change of color nor precipitation and has markedly improved film-forming speed, so that even in the case of high-speed etching treatment, though free of cyanides, it enables to make lithographic printing plates developing neither background stain nor plugging of dot gradation. R.sup.0 in formula (1) represents a phosphonic acid group (--PO.sub.3 H.sub.2), a phosphoric acid group (--OPO.sub.3 H.sub.2), or a salt thereof. Suitable examples of such a salt include the inorganic salts of alkalis (e.g., lithium, sodium, potassium), the ammonium salts, the salts of organic bases [e.g., primary, secondary or tertiary amines (containing hydrocarbon group(s), such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, dodecyl, tridecyl, tetradecyl, hexadecyl, octadecyl, cyclohexyl, cyclooctyl, benzyl or/and phenetyl groups, in which each may have substituent(s) such as hydroxyl, halogen, cyano, alkoxy or/and amido), anilines (e.g., aniline, N-methylaniline, N,N-dimethylaniline, N-ethylaniline, N-butylaniline, N-methyl-N-butylaniline) and hetero atom-containing cyclic nitrogen compounds (e.g., pyridine, morpholine, piperazine)], or the inner salts formed of the acid groups and .dbd.NCH.sub.2 -- (e.g., .dbd..sup.+ N(H)CH.sub.2 PO.sub.3 H.sup.-, .dbd..sup.+ N(H)CH.sub.2 OPO.sub.3 H.sup.-). A part or all of the acid groups in the molecule may be a salt, and the salts formed may be the same or different. The organometallic polymer of the present invention is a polymer having at least two partial structure units (chelating groups) represented by formula (1). In particular, it is desirable for the polymer to contain a combined total of at least 4 phosphonic and/or phosphoric acid groups so as to have a steric configuration enabling the stable complex structure of metal ions having a coordination number of 4, such as Zn.sup.2+ ion. Further, it is desirable for the organometallic polymer of the present invention to have each of the chelating groups of formula (1) via a hydrocarbon group having 1 to 6 carbon atoms. Furthermore, it is preferred in the present invention that the organometallic polymer be a polymer synthesized by hydrolytic polycondensation of at least one compound selected from the organometallic compounds represented by formula (2). As an example of hydrolytic polycondensation carried out for the polymer synthesis, a reaction that the compound molecules undergoes condensation repeatedly via the hydrolysis of their reactive groups Y to be polymerized is exemplified. In the representative reaction, alkoxysilyl groups undergoes dealcoholization in the presence of an acid or a base and condensed repeatedly to form a polymer. Suitable examples of a reactive group Y in formula (2) include a hydroxyl group, a halogen atom (e.g., fluorine, chlorine, bromine and iodine atoms), or a group of formula --OR.sup.8, --OCOR.sup.9, --CH(COR.sup.10) (COR.sup.11), --CH(COR.sup.10) (COOR.sup.11) or --N(R.sup.12) (R.sup.13). R.sup.8 in the group --OR.sup.8 represents an unsubstituted or substituted aliphatic group containing 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, propenyl, butenyl, hexenyl, heptenyl, octenyl, decenyl, 2-hydroxyethyl, 2-hydroxypropyl, 2-methoxyethyl, 2-(methoxyethyloxo)ethyl, 2-(N,N-diethylamino)ethyl, 2-methoxypropyl, 2-cyanoethyl, 3-methyloxapropyl, 2-chloroethyl, cyclohexyl, cyclopentyl, cyclooctyl, chlorocyclohexyl, methoxycyclohexyl, benzyl, phenetyl, dimethoxybenzyl, methylbenzyl, bromobenzyl). R.sup.9 in the group --OCOR.sup.9 represents the same aliphatic group as described above for R.sup.8, or an unsubstituted or substituted aromatic group having 6 to 12 carbon atoms (e.g., phenyl, tolyl, xylyl, methoxyphenyl, chlorophenyl, carboxyphenyl, diethoxyphenyl, naphthyl). In the groups --CH(COR.sup.10) (COR.sup.11) and --CH(COR.sup.10) (COOR.sup.11), R.sup.10 represents an alkyl group having 1 to 4 carbon atoms (e.g., methyl, ethyl, propyl, butyl) or an aryl group (e.g., phenyl, tolyl, xylyl), and R.sup.11 represents an alkyl group having 1 to 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl), an aralkyl group containing 7 to 12 carbon atoms (e.g., benzyl, phenetyl, phenylpropyl, methylbenzyl, methoxybenzyl, carboxybenzyl, chlorobenzyl) or an aryl group (e.g., phenyl, tolyl, xylyl, mesityl, methoxyphenyl, chlorophenyl, carboxyphenyl, diethoxyphenyl) R.sup.12 and R.sup.13 in the group --N (R.sup.12) (R.sup.13) may be the same or different, and each of them represents a hydrogen atom or an unsubstituted or substituted aliphatic group having 1 to 10 carbon atoms (including the same groups as described above for R.sup.8 in the group --OR.sup.8). It is preferable that the total of carbon atoms of R.sup.10 and R.sup.11 and the total of carbon atoms of R.sup.12 and R.sup.13 each is 12 or less. Suitable examples of the metal M include transition metals, rare earth metals and metals of Groups III to V, preferably Al. Si, Sn, Ge, Ti, Zr and W, more preferably Al, Si, Sn, Ti and Zr, particularly preferably Si. Preferably, the organometallic polymer of the present invention is a polymer containing at least one unit selected from the units represented by formulae (3) to (8) (hereinafter referred to as "Polymer (A)"). In particular, at least either units which are represented by formula (3) or units which are represented by formula (5) are preferred as copolymerizing units of Polymer (A), and such units can be contained in Polymer (A) in combination with at least one unit selected from the units represented by formulae (4), (6), (7) and (8). Moreover, it is particularly preferred for the present invention that the organometallic polymer be a polymer represented by formula (9) (hereinafter referred to as "Polymer (C)"). R.sup.1 to R.sup.7 in formulae (3) to (8) each represents a hydrogen atom or an unsubstituted or substituted organic residue, or these groups may combine each other to form rings. Examples of such an organic residue include an unsubstituted or substituted alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group, an alkoxy group, a sulfido group, an amino group, a halogen atom, a cyano group, a nitro group, a hydroxyl group, a carboxyl group, a phosphnic acid group, a phosphoric acid group, a sulfonic acid group (the acid groups described above include salts thereof), an amido group, a sulfonamido group, an ester group, an urea group and an urethane group. Examples of a substituent group for the organic residue include an alkoxy group, a sulfido group, an amino group, a halogen atom, a cyano group, a nitro group, a hydroxyl group, a carboxyl group, a phosphonic acid group, a phosphoric acid group, a sulfonic acid group (the acid groups described above include salts thereof), an amido group, a sulfonamido group, an ester group, an urea group and an urethane group. Further, R.sup.1 to R.sup.7 may combine each other to form an unsubstituted or substituted alicyclic or aromatic ring having 3 to 22 carbon atoms. Preferably, R.sup.1 to R.sup.7 each represent a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 14 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl, heptyl, octyl, decyl, dodecyl, hexadecyl, octadecyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-hydroxybutyl, 2-methoxyethyl, 2-botoxyethyl, 2-ethoxyethyl, 4-methoxybutyl, methylthioethyl, methylthiobutyl, 2-aminoethyl, N,N'-dimethylaminoethyl, piperizinomethyl, pyrrolidinoethyl, 2-chloroethyl, 2-chlorobutyl, 2-bromoethyl, 2-cyanoethyl, 4-cyanobutyl, 2-carboxyethyl, carboxymethyl, 3-carboxypropyl, 3-morpholinopropyl, 2-morpholinoethyl, 2-sulfoethyl, 2-piperizinoethyl, amidomethyl, thioethyl, imidazolidinoethyl, sulfonamidoethyl, phosphonopropyl, phosphonometnylaminoethyl), an unsubstituted or substituted alkenyl group having 2 to 18 carbon atoms (e.g., vinyl, allyl, isopropenyl, butenyl, hexenyl, heptenyl, octenyl), an unsubstituted or substituted aralkyl group (e.g., benzyl, phenetyl, naphthylmethyl, 2-naphthylethyl, methoxybenzyl, ethoxybenzyl, methylbenzyl), an unsubstituted or substituted cycloalkyl group having 5 to 8 carbon atoms (e.g., cyclopentyl, cyclohexyl, cycloheptyl) or an unsubstituted or substituted aryl group having 6 to 12 carbon atoms (e.g., phenyl, tolyl, xylyl, mesityl, naphthyl, methoxyphenyl, ethoxyphenyl, fluorophenyl, methyl-chlorophenyl, difluorophenyl, bromophenyl, chlorophenyl, dichlorophenyl, methyl-carbonylphenyl, methoxycarbonyl-phenyl, ethoxycarbonylphenyl, methanesulfonylphenyl, cyanophenyl). Further, R.sup.1 to R.sup.7 may combine each other to form a ring. Suitable examples of a ring formed include unsubstituted or substituted aliphatic rings having 3 to 18 carbon atoms (e.g., cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, bicyclo[2,2,1]heptene, bicyclo[2,2,2]octane) and unsubstituted or substituted aromatic rings having 3 to 14 carbon atoms (e.g., benzene, naphthalene, anthracene, pyrrole, pyridine, imidazole, thiophene). Examples of a substituent group for a ring include the same substituent groups as described above for R.sup.1 to R.sup.7. The linkage groups Z.sup.1 and Z.sup.2 in formulae (3) to (5) may be the same or different. Preferably, Z.sup.1 and Z.sup.2 each represents a divalent aliphatic or aromatic group. Examples of such an aliphatic group include --(CH.sub.2).sub.ml -- (wherein ml is an integer of 2 to 18), --CH.sub.2 --C(g.sup.1)(g.sup.2)-- (wherein g.sup.1 and g.sup.2 each represent a hydrogen atom or an alkyl group having from 1 to 12 carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl, octyl, decyl or dodecyl, provided that it is excluded that both of g.sup.1 and g.sup.2 are hydrogen atoms) and --CH(g.sup.3)--(CH2).sub.m2 -- (wherein g.sup.3 represents an alkyl group having from 1 to 12 carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl or octyl, and m2 is an integer of 2 to 18), which each may contain --O--, --S--, --N(k.sup.1)--, --SO--, --SO.sub.2 --, --COO--, --OCO--, --CONHCO--, --NHCONH--, --CON(k.sup.1)--, --SO.sub.2 N(k.sup.1)-- or/and --Si(k.sup.1)(k.sup.2)-- (wherein k.sup.1 and k.sup.2 are each a hydrogen atom, an alkyl group having from 1 to 12 carbon atom such as methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, 2-methoxyethyl, 2-chloroethyl or 2-cyanoethyl, an aralkyl group such as benzyl, methylbenzyl, chlorobenzyl, methoxybenzyl or phenetyl, or an aryl group such as phenyl, tolyl, chlorophenyl, methoxyphenyl or butylphenyl). Examples of such a divalent aromatic group include divalent groups derived from a benzene ring, a naphthalene ring and a 5- or 6-membered heterocyclic ring (containing at least one oxygen, sulfur or nitrogen atom as ring-constituting hetero atom). These aromatic rings each may have a substituent, and examples of such a substituent include a halogen atom (such as fluorine, chlorine, bromine), an alkyl group having from 1 to 8 carbon atoms (e.g., methyl, ethyl, propyl, butyl, hexyl, octyl) and an alkoxy group having from 1 to 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, butoxy). Examples of such a heterocyclic ring include furan, thiophene, pyridine, pyrazine, piperazine, tetrahydrofuran, pyrrole, tetrahydropyran and 1,3-oxazoline rings. G.sup.1 in formulae (3) and (5) represents --N(R.sup.1)CH.sub.2 R.sup.0 or --N(CH.sub.2 R.sup.0).sub.2 wherein R.sup.0 and R.sup.1 have the same meanings as described hereinbefore respectively. Further, R.sup.1 may contain --N(R.sup.1)CH.sub.2 R.sup.0 or --N(CH.sub.2 R.sup.0).sub.2. G.sup.2 in formula (4) represents --NR.sup.2 R.sup.3 or --NR.sup.2 R.sup.3 R.sup.4 X.sup.- wherein X.sup.- is preferably a monovalent to trivalent anion, with examples including inorganic electrolytes, such as Cl.sup.-, Br.sup.-,I.sup.-, F.sup.-, H.sub.2 PO.sub.4.sup.-, PO.sub.4.sup.3-, H.sub.2 PO.sub.3.sup.-, HPO.sub.3.sup.2-, ClO.sub.4.sup.-, NO.sub.3.sup.-, BF.sub.4.sup.-, ClO.sub.3.sup.-, PO.sub.3.sup.3-, HSO.sub.4.sup.-, SO.sub.4.sup.2-, HCO.sub.3.sup.-, CO.sub.3.sup.2- and PF.sub.6.sup.-, and organic electrolytes, such as PhSO.sub.4.sup.- (wherein Ph represents phenyl), CH.sub.3 SO.sub.4.sup.-, CH.sub.3 COO.sup.-, CF.sub.3 COO.sup.-, PhCOO.sup.-, .sup.- OOCCOO.sup.-, .sup.- OOCCH.sub.2 CH.sub.2 COO.sup.-, .sup.- OOCCH(OH)CH.sub.2 COO.sup.- and .sup.- OOCCH(OH)CH(OH)COO.sup.-. Specific examples of a polymer containing at least two units selected from units represented by formulae (3) to (8) are illustrated below. The suffixes m, m.sub.1, m.sub.2, n and l in the structural formula of each exemplified polymer are values the total of which is 100 weight %. However, these examples are not to be construed as limiting the scope of the invention. ##STR5## The polymers of the present invention can be synthesized by carrying out the addition reaction of phosphonic acid to a Schiff base, the dehydrating condensation reaction between an alcohol and orthophosphoric acid or the condensation reaction between an alcohol and phosphorus oxychloride, and the sol-gel condensation polymerization of an organometallic compound at the same time, as described in SYNTHESIS, pp. 81-96 (1979), and Jikken Kagaku Koza 19 (which means "Lectures on Experimental Chemistry", volume 19), published by Maruzen in 1957. Further, it is desirable for the organometallic polymer used in the present invention to be a polymer wherein the main chains of organometallic polymers according to the present invention are cross-linked to each other (hereinafter referred to as "Polymer B"). The cross-linking reaction between the main chains can be effected by using a compound containing a bifunctional or higher functional group capable of reacting with the amino or hydroxyl groups in the main chains, such as an epoxy, isocyanate or halogenated alkyl group. Examples of such a compound include the compounds described in, e.g., Kakyozai Handbook (which means "Handbook of Cross-linking Agents"), compiled by Shinzo Yamashita & Tosuke Kaneko, published by Taisei Co. in 1981. The suitable weight average molecular weight of an organometallic polymer according to the present invention (including Polymers (A), (B) and (C)) is not higher than 1.times.10.sup.5, preferably not higher than 1.times.10.sup.4. The weight average molecular weight of each polymer according to the present invention can be determined by the method of utilizing the scattering of light in the aqueous polymer solution (the apparatus usable therefor is, e.g., SLS-600OR manufactured by Otsuka Denshi Co., Ltd.) or the GPC method using water as solvent (the apparatus usable therefor is e.g., S8000 GPC system manufactured by Toso Co., Ltd.). The organometallic polymers, which constitute the desensitizing (process) solution of the present invention and can chelate zinc ion, are used in an amount of from 10 to 300 parts by weight:, preferably from 20 to 150 parts by weight, per 1,000 parts by weight of the desensitizing solution. These polymers may be used alone or as a mixture of two or more thereof. The desensitizing solution of the present invention can be prepared by dissolving the polymer(s) in ion exchange water or tap water. Besides the foregoing constituent, the desensitizing (process) solution can contain various additives in appropriate amounts. Examples of such additives include chemical agents for pH adjustment, such as organic and inorganic acids and basic hydroxides, e.g., potassium hydroxide and sodium hydroxide; wetting agents, such as ethylene glycol, sorbitol, glycerin, gum arabic, dipropylene glycol, dimethylacetamide, hexylene glycol, butanediol, butyl cellosolve and surfactants; preservatives, such as salicylic acid, phenol, p-butylbenzoate, sodium dehydroacetate, 4-isothiazoline-3-one compounds, 2-bromo-2-nitro-1,3-propanediol and chloroacetamide; and rust preventives, such as EDTA, pyrophosphoric acid, metaphosphoric acid, hexametaphosphoric acid and 2-mercaptoobenzimidazole. In using the desensitizing (process) solution, it is desirable that the pH thereof be adjusted to the range of 3-6. Additionally, when it is diluted with water, the desensitizing solution can be used as dampening water also. The present invention will now be illustrated in greater detail by reference to the following examples. However, the invention should not be construed as being limited to these examples. |
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