Rust prevention

A rust preventive composition including (a) a silicic acid compound and (b) an aromatic amine-based condensation product is provided, which is effective in preventing a Zn-based metallic coating from rusting. Rusting is prevented by forming a coating film contaning the components (a) and (b) on the surface of the Zn-based metallic coating formed on a base such as a metal plate. The resulting coating film exhibits an excellent corrosion resistance, gives no fear of a health problem such as carcinogensis and provides a desirable black or blackish appearance to a metal surface. In an embodiment wherein a second coating film containing a silicic acid compound is formed on the first coating film, the corrosion resistance is further improved.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a method for preventing surfaces of a
 Zn-based metallic coating from rusting, and a rust preventive.
 Particularly, it relates to a rust preventive agent and a method for
 preventing surfaces of a base, such as metallic articles and metallic
 materials including steel plates used as parts or materials in manufacture
 of automobiles, building and so forth, coated with a Zn-based metal from
 rusting.
 2. Description of the Prior Art
 Plated steel plates, which are used as a material in automobiles, building,
 etc., such as steel plates plated with zinc or zinc-based alloy are used
 after painting. The plated steel plates are passed through a variety of
 steps before being painted; therefore they are left unpainted in the
 course of these steps for a considerably long time. So, while they are
 left unpainted, rust is generated or various substances are adsorbed or
 adheres, on the surfaces of the plated steel plates. As a result, for
 example, the adhesion of a paint applied in the subsequent step may be
 poor.
 Thus, heretofore, the surfaces of plated steel plates have been subjected
 to chromate treatment as a primary rust prevention treatment. The
 corrosion resistance obtained by the chromate treatment is about 48 hours
 in the salt spray test defined in JIS Z-2371. However, the coating film
 obtained by the chromate treatment contains hexavalent chromium. It is
 known that the hexavalent chromium causes an allergy (chromate ulcer) when
 adhering a skin, and also it is pointed out that the hexavalent chromium
 is suspected to be a carcinogen (carcinoma cutaneum). So, a primary rust
 prevention treatment not using hexavalent chromium is required.
 Meanwhile, as a primary rust prevention treatment other than the chromate
 treatment there is proposed a method using a coating agent for metal
 surfaces, which agent is comprised of carboxyl-modified epoxy resin or
 polyvinyl butyral resin containing a silica. The use of the coating agent
 results in a corrosion resistance equivalent to or higher than that
 obtained by the chromate treatment, but the appearance of the resulting
 coated metal surface is colorless or metallic. However, it is recently
 required that the metal surface coated by a primary rust prevention
 treatment has a black or blackish appearance so as to give a feeling of
 quality.
 SUMMARY OF THE INVENTION
 Accordingly, an object of the present invention is to provide a rust
 preventive and a treating method, suitable as a primary rust prevention
 treatment, which forms a coating film having a corrosion resistance
 equivalent to that of the coating film obtained by the chromate treatment,
 but gives no fear of a health problem such as carcinogenesis and provides
 a black or blackish appearance to the treated metal surface.
 The present inventors have earnestly studied in order to satisfy the above
 requirements, and as a result, have completed the present invention.
 More specifically, the present invention provides a rust preventive for a
 Zn-based metallic coating, comprising (a) a silicic acid compound and (b)
 an aromatic amine-based condensation product.
 The present invention also provides a method for preventing a Zn-based
 metallic coating formed on a base from rusting, which comprises forming a
 coating film (hereinafter, referred to as "first coating film" with
 respect to the "second coating film" mentioned below) comprising (a) a
 silicic acid compound and (b) an aromatic amine-based condensation product
 on the surfaces of the Zn-based metallic coating.
 In the above method, preferably a second coating film comprising (a) a
 silicic acid compound is further formed on the first coating film.
 According to the present invention, by forming a coating film comprising a
 silicic acid compound and an aromatic amine-based condensation product on
 the surfaces of a Zn-based metallic coating formed on a base such as a
 metal plate, it can provide a treating method, suitable as a primary rust
 prevention treatment. The resulting coating film exhibits an excellent
 corrosion resistance, gives no fear of a health problem such as
 carcinogenesis suspected in the conventional chromate treatment and
 provides a black or blackish appearance to the surfaces of the base.
 Further by forming a second coating film comprising a silicic acid compound
 on the first coating film, it is possible to provide a higher corrosion
 resistance of 100 hours or more in the salt spray test defined in JIS
 Z-2371.
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention will now be described below in more detail.
 Firstly, the essential components used in the rust preventive and the
 method according to the present invention are described.
 (a) Silicic Acid Compound
 The silicic acid compound used in the present invention is preferably, for
 example, at least one compound selected from the group consisting of
 silicic acid esters, colloidal silica and alkali metal silicates.
 The silicic acid esters include, for example, alkoxy silane compounds such
 as tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane,
 tetra-i-propoxysilane, tetra-n-butoxysilane, tetra-i-butoxysilane,
 tetra-t-butoxysilane, methyltrimethoxysilane, methyltriethoxysilane,
 methyltri-n-propoxysilane, methyltri-i-propoxysilane,
 methyltri-n-butoxysilane and methyltri-t-butoxysilane; and condensates of
 these alkoxysilane compounds.
 The condensates of alkoxysilane compounds can be generally produced by
 partially hydrolyzing the alkoxysilane compound and then condensing the
 hydrolysis product. The condensates of alkoxysilane compounds include, for
 example, ethoxypolysiloxane, which is a condensate of tetraethoxysilane,
 (trade name: "Ethyl silicate-40", produced by Tama Kagaku Kogyo K.K.).
 The colloidal silica is a colloid containing super fine particles of
 silicon dioxide (silica) dispersed in a dispersion medium including an
 aqueous medium or a non-aqueous medium such as methanol, propanol or
 ethylene glycol. As typical methods for producing a colloidal silica
 comprised of colloid particles having a particle diameter of generally 5
 to 500 nm, for example, a colloidal silica dispersed in an aqueous medium,
 there is known a method producing a colloidal silica by adding
 hydrochloric acid to an aqueous solution of sodium silicate. There is also
 known a method producing a colloidal silica by adding a small amount of
 water and ethylamine as a catalyst to silicic acid esters such as
 tetraethoxysilane in an organic solvent such as isopropylalcohol to
 subject the silicic acid esters to hydrolysis reaction. However, the
 colloidal silicas produced by any known methods are available in the
 present invention, and methods for the production thereof are not
 particularly limited.
 The alkali metal silicates include, for example, metasilicates (M.sub.2
 SiO.sub.3), orthosilicates (M.sub.4 SiO.sub.4), disilicates (M.sub.2
 Si.sub.2 O.sub.3), trisilicates (M.sub.3 Si.sub.3 O.sub.7) and
 sesquisilicates (M.sub.4 Si.sub.3 O.sub.10) (wherein in these formulae, M
 represents an alkali metal such as lithium, sodium or potassium), of
 alkali metals; and water glass. Among the silicic acid compounds,
 preferred is colloidal silica from the viewpoint of obtaining good
 corrosion resistance.
 (b) Aromatic Amine-Based Condensation Products
 The aromatic amine-based condensation products used in the present
 invention are exemplified by:
 (A) an aromatic amine compound condensation product,
 (B) an alkali-treated product of the aromatic amine compound condensation
 product (A),
 (C) a higher fatty acid-treated product or aromatic carboxylic acid-treated
 product of the aromatic amine compound condensation product (A), and
 (D) an alkylation product, alkenylation product and aralkylation product of
 the aromatic amine compound condensation product (A). These compounds may
 be used singly or in combination of two or more.
 The aromatic amine compound condensation product (A) used includes
 preferably one having a weight-average molecular weight in the range of
 1,000 to 100,000 in terms of polystyrene when measured by gel permeation
 chromatography (GPC), and particularly 1,500 or 50,000 from the viewpoint
 of obtaining good corrosion resistance.
 In the present invention, from the viewpoint of corrosion resistance, the
 following are preferably used:
 (B) the alkali-treated product of an aromatic amine compound condensation
 product (A),
 (C) the higher fatty acid-treated product or aromatic carboxylic
 acid-treated product of an aromatic amine compound condensation product
 (A), and
 (D) the alkylation product, alkenylation product and aralkylation product
 of an aromatic amine compound condensation product (A).
 Further from the viewpoint of humidity resistance and prevention of a base
 oil from separating and diffusing (bleeding), the following are preferably
 used:
 (C) the higher fatty acid-treated product or aromatic carboxylic
 acid-treated product of an aromatic amine compound condensation product
 (A), and
 (D) the alkylation product, alkenylation product and aralkylation product
 of an aromatic amine compound condensation product (A).
 &lt;(A) Aromatic amine compound condensation products&gt;
 The aromatic amine compound condensation products include, for example:
 (1) a self-condensation product of an aromatic amine compound;
 (2) a condensation product of an aromatic amine compound with an aromatic
 hydroxyl compound;
 (3) a condensation product of an aromatic amine compound with an aromatic
 nitro compound; and
 (4) a condensation product of an aromatic amine compound with a quinone
 compound.
 The aromatic amine compounds are exemplified by aminobenzenes such as
 aniline, o-, m- or p-phenylenediamine, o-, m- or p-aminophenol, o-, m- or
 p-chloroaniline, p-aminobenzene, 2,4-diaminoazobenzene,
 p-aminoacetanilide, o-, m- or p-methylaniline,
 N,N-dimethyl-p-phenylenediamine, 4-chloro-o-phenylenediamine,
 4-methoxy-o-phenylenediamine, 2-amono-4-chlorophenol, 2,3-diaminotoluene,
 2,4-diaminophenol, o-, m-, or p-aminobenzoic acid, 2,3-, 2,4-, 2,5-, 2,6-,
 3,4-, 3,5- or 4,6-diaminobenzoic acid, 3- or 4-aminophthalic acid, 2-, 4-
 or 5-aminoisophthalic acid, 4,6-diaminoisophthalic acid, 2,5- or
 2,6-diaminoterephthalic acid, 3-, 4- or 5-aminosalicylic acid,
 4-hydroxyanthranylic acid, o-, m-, or p-aminobenzenesulfonic acid, 2,3-,
 2,4-, 2,5-, 2,6-, 3,4- or 3,5-diaminobenzenesulfonic acid,
 2-amino-1-phenol-4-sulfonic acid, and 6-amino-4-chloro-1-phenol-2-sulfonic
 acid; diphenylamines such as 4-aminodiphenylamine, 2-aminodiphenylamine,
 4,4'-diaminodiphenylamine, 4-amino-3'-methoxydiphenylamine,
 4-amino-4'-hydroxydiphenylamine, 4-carboxydiphenylamine,
 4-amino-4'-carboxydiphenylamine, 4-sulfodiphenylamine and
 4-amino-4'-sulfodiphenylamine; and aminonaphthalenes such as
 .alpha.-naphthylamine, .beta.-naphthylamine, 1,5-diaminonaphthalene,
 1-amino-5-hydroxynaphthalene, 1,8-diaminonaphthalene,
 2,3-diaminonaphthalene, 4-amino-1-naphthol, 1-amino-5-naphthol,
 1,2-naphthylenediamine-7-carboxylic acid,
 1,5-naphthylenediamine-2-carboxylic acid,
 1,5-naphthylenediamine-4-carboxylic acid,
 1,6-naphthylenediamine-4-carboxylic acid,
 1,8-naphthylenediamine-4-carboxylic acid,
 1,2-naphthylenediamine-3-sulfonic acid, 1,2-naphthylenediamine-4-sulfonic
 acid, 1,2-naphthylenediamine-5-sulfonic acid,
 1,2-naphthylenediamine-6-sulfonic acid, 1,2-naphthylenediamine-7-sulfonic
 acid, 1,3-naphthylenediamine-5-sulfonic acid,
 1,3-naphthylenediamine-6-sulfonic acid, 1,4-naphthylenediamine-2-sulfonic
 acid, 1,4-naphthylenediamine-7-sulfonic acid,
 1,5-naphthylenediamine-2-sulfonic acid, 1,5-naphthylenediamine-4-sulfonic
 acid, 1,5-naphthylenediamine-7-sulfonic acid,
 1,6-naphthylenediamine-2-sulfonic acid, 1,6-naphthylenediamine-4-sulfonic
 acid, 1,6-naphthylenediamine-7-sulfonic acid,
 1,8-naphthylenediamine-4-sulfonic acid,
 1,8-naphthylenediamine-3,6-disulfonic acid,
 1,8-naphthylenediamine-4,5-disulfonic acid,
 .alpha.-amino-.beta.-naphthalenepropionic acid,
 .alpha.-amino-.beta.-naphthalenecarboxylic acid,
 2-naphthylamine-1-sulfonic acid, 8-naphthylamine-1-sulfonic acid,
 5-naphthylamine-1-sulfonic acid, 1-amino-2-naphthol-4-sulfonic acid,
 2-amino-8-naphthol-6-sulfonic acid (.gamma. acid),
 2-amino-5-naphthol-7-sulfonic acid (J acid) and
 1-amino-8-naphthol-3,6-disulfonic acid (H acid).
 The aromatic hydroxyl compounds are exemplified by phenols and phenol
 derivatives, such as phenol, hydroquinone, resorcinol, catechol,
 hydroxyhydroquinone, pyrogallol, o-, m- or p-chlorophenol, o-, m- or
 p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic
 acid, 2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid,
 3,5-dihydroxybenzoic acid and 2,5-, 2,6- or 3,5-dihydroxytoluene.
 In addition thereto, the aromatic hydroxyl compounds are exemplified by
 naphthols and naphthol derivatives such as .alpha.-naphthol,
 .beta.-naphthol, 1,3-, 1,4-, 1,5-, 2,3-, 2,6- or 2,7-dihydroxynaphthalene,
 1-hydroxy-2-naphthoic acid and 3-hydroxy-2-naphthoic acid.
 The aromatic nitro compounds are exemplified by nitrobenzene, o-, m- or
 p-hydroxynitrobenzene, o-, m- or p-nitroanisole, o-, m- or
 p-nitrophenetole, o-, m- or p-chloronitrobenzene, o-, m- or
 p-aminonitrobenzene, o-, m- or p-nitrobenzoic acid, o-, m- or
 p-nitrobenzenesulfonic acid, o-, m- or p-nitroaniline,
 2-nitro-p-phenylenediamine, 2-amino-4-nitrophenol, 2-amino-5-nitrophenol
 and 4-amino-2-nitrophenol.
 The quinone compounds include, for example, benzoquinones and derivatives
 thereof, such as o-, m- or p-benzoquinone, tolu-p-quinone,
 o-xylo-p-quinone, thymoquinone, 2-methoxybenzoquinone, gentisyl quinone,
 polyporic acid and ubiquinone-n; naphthoquinones and derivatives thereof,
 such as 6-methyl-1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone,
 .alpha.-naphthoquinone, juglone, lawsone, plumbagin, alkannin,
 echinochrome A, vitamin K.sub.1, vitamin K.sub.2, shikonin,
 .beta.,.beta.'-dimethyl acrylshikonin, .beta.-hydroxyisovaleroshikonin and
 teracrylshikonin; anthraquinones and derivatives thereof, such as
 tectoquinone, 3-hydroxy-2-methylanthraquinone, anthraquinone,
 2-hydroxyanthraquinone, alizarin, xanthopurpurin, rubiadin, munjistin,
 crysophanic acid, carminic acid, kermesic acid and laccaic acid A; and
 phenanthrenequinones such as phenanthrenequinone.
 In order to carry out the self-condensation reaction of an aromatic amine
 compound alone, the condensation reaction of an aromatic amine compound
 with an aromatic hydroxyl compound and the condensation reaction of an
 aromatic amine compound with an aromatic nitro compound, a mineral acid
 and a condensation catalyst are used. The mineral acids are exemplified by
 hydrochloric acid, nitric acid, hydrobromic acid, phosphoric acid and
 sulfuric acid. The condensation catalysts are preferably exemplified by
 permanganic acid and salts thereof, such as permanganic acid and potassium
 permanganate; chromic acid-related compounds, such as chromium trioxide,
 potassium dichromate and sodium chlorochromate; metal nitrates, such as
 silver nitrate and lead nitrate; halogens, such as iodine and bromine;
 peroxides, such as hydrogen peroxide, sodium peroxide, benzoyl peroxide,
 potassium persulfate, ammonium persulfate, peracetic acid, cumene
 hydroperoxide, perbenzoic acid and p-menthane hydroperoxide; oxygen acids
 or oxygen acid salts, such as iodic acid, potassium iodate and sodium
 chlorate; metal salts, such as ferrous chloride, ferric chloride, copper
 sulfate, cuprous chloride, cupric chloride and lead acetate; ozone; and
 oxides, such as copper oxide, mercury oxide, cerium oxide, manganese
 dioxide and osmic acid. It is also effective to use hydrogen peroxide and
 ferrous chloride in combination.
 The self-condensation reaction of an aromatic amine compound alone, the
 condensation reaction of an aromatic amine compound with an aromatic
 hydroxyl compound and the condensation reaction of an aromatic amine
 compound with an aromatic nitro compound may be carried out in the
 presence of a condensation catalyst at 100 to 350.degree. C. for 2 to 100
 hours.
 The proportion of an aromatic amine compound and an aromatic hydroxyl
 compound or an aromatic nitro compound, which are used in the condensation
 reaction of an aromatic amine compound with an aromatic hydroxyl compound
 and the condensation reaction of an aromatic amine compound with an
 aromatic nitro compound, depends on the aromatic amine compound, aromatic
 hydroxyl compound and aromatic nitro compound and the catalyst used, the
 reaction time, the reaction temperature and so forth. Generally, it is
 preferable to use from 0.1 to 10 moles of the aromatic hydroxyl compound
 or the aromatic nitro compound per mole of the aromatic amine compound.
 The condensation reaction of an aromatic amine compound with a quinone
 compound is carried out in an organic solvent medium, optionally in the
 presence of a condensation catalyst. The organic solvent medium preferably
 has a pH within the range of from 1 to 13.5 and a pH adjuster may be used
 without any particular limitations. Usable pH adjusters include various
 acidic compounds and alkali compounds. The acidic compounds are
 exemplified by phosphoric acid, sulfuric acid, phytic acid and acetic
 acid; and alkali compounds are exemplified by alkali metal compounds or
 ammonium compounds, such as LiOH, KOH, NaOH, Na.sub.2 CO.sub.3, Na.sub.2
 SiO.sub.3, Na.sub.2 HPO.sub.4 and NH.sub.4 OH; and organic amine
 compounds, such as ethylenediamine, monoethanolamine and triethanolamine.
 As the medium for the condensation reaction, organic solvents exemplified
 by alcohols, ketones and esters, or mixed solvents of water and
 hydrophilic organic solvents miscible with water are preferred. Usable
 hydrophilic organic solvents include, for example, alcohols, such as
 methanol, ethanol and propanol; ketones, such as acetone and methyl ethyl
 ketone; and esters, such as methyl acetate and ethyl acetate.
 The condensation catalyst may be optionally used which is exemplified by
 azo catalysts such as .alpha.,.alpha.'-azobisisobutylonitrile and
 .alpha.,.alpha.'-azobis-2,4-dimethylvaleronitrile; elementary or molecular
 halogens, such as iodine, bromine and chlorine; peroxides, such as
 hydrogen peroxide, sodium peroxide, benzoyl peroxide, perbenzoic acid and
 p-menthane hydroperoxide; oxygen acids or oxygen acid salts, such as iodic
 acid, periodic acid, potassium periodate and sodium perchlorate.
 Incidentally, since the quinone compound acts as a condensation catalyst,
 the condensation reaction of an aromatic amine compound and a quinone
 compound takes place even in the absence of a condensation catalyst.
 The condensation reaction can be normally carried out at 20 to 200.degree.
 C. for 0.5 to 100 hours.
 The proportion of an aromatic amine compound and a quinone compound in the
 condensation reaction of the aromatic amine compound and the quinone
 compound depends on the sort of the aromatic amine compound, quinone
 compound and catalyst used, the reaction time and the reaction
 temperature. In the present invention, it is preferable to use from 0.1 to
 10.0 mols of the quinone compound per mol of the aromatic amine compound.
 &lt;(B) Alkali-treated product of an aromatic amine compound condensation
 product (A)&gt;
 Component (B), the alkali-treated product of an aromatic amine compound
 condensation product (A) is prepared by treating the aromatic amine
 compound condensation product (A), which is obtained in the presence of an
 acidic catalyst or in an acidic medium, with an alkali.
 The method for treating the aromatic amine compound condensation product
 with an alkali is carried out by first dispersing the aromatic amine
 compound condensation product in water to prepare a 0.1 to 50 wt. %
 aqueous dispersion of the aromatic amine compound condensation product.
 Then, to the resulting dispersion is added an inorganic alkaline compound
 such as NaOH, KOH, Na.sub.2 CO.sub.3, NH.sub.4 OH or (NH.sub.4).sub.2
 CO.sub.3 in an amount of 10 to 20 parts by weight per 100 parts by weight
 of the aromatic amine compound condensation product and the mixture thus
 obtained is heat-treated at 90 to 140.degree. C. for 0.5 to 10 hours. The
 amount of the alkaline compound used is to be sufficient to neutralize the
 acidic compound used in the condensation reaction for production for of
 the aromatic amine compound condensation product.
 &lt;(C) Higher fatty acid-treated product or aromatic carboxylic acid-treated
 product of an aromatic amine compound condensation product (A)&gt;
 Component (C), the higher fatty acid-treated product or aromatic carboxylic
 acid-treated product of an aromatic amine compound condensation product
 (A) is prepared by treating the aromatic amine compound condensation
 product (A) and/or the above alkali-treated product (B) of an aromatic
 amine compound condensation product with a higher fatty acid, an alkali
 metal salt or ammonium salt thereof an aromatic carboxylic acid or an
 alkali metal salt or ammonium salt thereof (hereinafter, referred to as
 "fatty acid and the like."). The higher fatty acids include, for example,
 hodinic acid, palmitic acid, stearic acid, oleic acid or linolic acid. The
 aromatic carboxylic acids include, for example, tannic acid or shellac
 acid.
 The method for treating the aromatic amine compound condensation product
 (A) with a fatty acid and the like is carried out by first mixing a fatty
 acid and the like in an amount of 5 to 1,000 parts by weight per 100 parts
 by weight of the aromatic amine compound condensation product (A) and/or
 (B) the alkali-treated product thereof (B). Then, the resulting mixture is
 heat-treated at a temperature slightly higher than the melting point of
 the fatty acid and the like used (about 40 to 250.degree. C.). Further,
 after the treated product thus obtained is optionally washed with water,
 the treated product is charged into water to allow it to precipitate.
 Thus, the higher fatty acid-treated product or aromatic carboxylic
 acid-treated product (C) of an aromatic amine compound condensation
 product is produced.
 Incidentally, a solvent such as dioxane, N,N-dimethylformamide,
 1,3-dimethyl-2-imidazolidinone, N,N-dimethylacetamide and
 N-methyl-2-pyrrolidone is preferably used at the step of mixing (A) the
 aromatic amine compound condensation product and/or (B) the alkali-treated
 product thereof with the fatty acids and the like, since the solubility of
 the resulting mixture is increased and the treatment with a higher fatty
 acid or an aromatic carboxylic acid is more sufficiently carried out.
 Among the higher fatty acid-treated product and the aromatic carboxylic
 acid-treated product exemplified above, preferred is the higher fatty
 acid-treated product.
 &lt;(D) Alkylat ion product, alkenylat ion product and aralkylat ion product
 of an aromatic amine compound condensation product (A)&gt;
 Component (D), the alkylation product, alkenylation product and
 aralkylation product of an aromatic amine compound condensation product
 (A) can be prepared by reacting the aromatic amine compound condensation
 product (A) and/or the alkali-treated product thereof (B) with an alkyl
 halide, alkenyl halide, aralkyl halide or a mixture thereof in an organic
 solvent.
 The alkyl halide used includes, for example, n-propyl bromide, n-butyl
 chloride, n-butyl bromide, isobutyl bromide, 2-ethylhexyl bromide, n-octyl
 bromide, n-octyl chloride, dodecyl bromide, cetyl bromide, stearyl bromide
 and stearyl chloride.
 The alkenyl halide includes, for example, allyl chloride, allyl bromide,
 isopropenyl chloride, isopropenyl bromide, oleyl chloride and oleyl
 bromide.
 The aralkyl halide includes, for example, benzyl chloride, benzyl bromide,
 .beta.-phenylethyl chloride, .beta.-phenylethyl bromide, p-methylbenzyl
 chloride, p-methylbenzyl bromide, p-ethylbenzyl chloride, p-ethylbenzyl
 bromide, cinnamyl chloride, cinnamyl bromide, p-octylbenzyl chloride,
 p-octylbenzyl bromide, styryl chloride, styryl bromide, phenetyl chloride
 and phenetyl bromide.
 The organic solvent used in the above reaction includes, for example,
 dioxane, N,N-dimethylformamide, dimethyl sulfoxide, dimethylaniline,
 dimethylbenzylimine, nitrobenzene, N,N-dimethylacetamide,
 1,3-dimethyl-2-imidazolidinone and N-methyl-2-pyrrolidone.
 The reaction temperature is generally in the range of 10 to 200.degree. C.
 During dropwise-addition of a halide, however, preferably the reaction
 mixture is kept at a temperature of the boiling point of the solvent or
 less. After the dropwise-addition, preferably the reaction mixture is
 heated to a prescribed temperature for proceeding the reaction.
 Although the reaction time can be made short by raising the reaction
 temperature, it generally ranges form 1 to 10 hours after the
 dropwise-addition of the halide.
 Further, preferably an alkaline compound is used in the above reaction. The
 alkaline compound includes, for example, LiOH, KOH, NaOH, Na.sub.2
 CO.sub.3, Na.sub.2 SiO.sub.3, Na.sub.2 HPO.sub.4, Li.sub.2 CO.sub.3,
 K.sub.2 CO.sub.3 and CaCO.sub.3.
 Alkylation of the aromatic amine compound condensation product is carried
 out by first dispersing or dissolving the aromatic amine compound
 condensation product (A) and/or the alkali-treated product thereof (B) in
 said solvent to prepare a 0.01 to 20 wt. % dispersion or solution and then
 dropwise adding thereto the above halide in an amount of 10 to 300 parts
 by weight, preferably 50 to 150 parts by weight, per 100 parts by weight
 of the condensation product (A) and/or the alkali-treated product (B).
 Further, the alkali compound stated above is optionally added in an amount
 of 10 to 500 parts by weight, preferably 30 to 300 parts by weight, per
 100 parts by weight of the condensation product (A) and/or the
 alkali-treated product (B). Generally in the case of adding the alkali
 compound, it is preferably added prior to the dropwise-addition of the
 halide. Thereafter, the reaction mixture is heated to a prescribed
 temperature and then reacted for a prescribed time. After the end of
 reaction, the resulting reaction mixture is cooled and charged into water
 to allow to precipitate and/or to disperse the reaction product, followed
 by filtering, washing with water, and drying. Thus, the alkylation product
 is produced.
 In the present invention, the aromatic amine-based condensation product (b)
 is used in an amount of 1 to 1,000 parts by weight, preferably 10 to 500
 parts by weight, more preferably 50 to 250 parts by weight, per 100 parts
 by weight of the silicic acid compound (a).
 The rust prevention method of the present invention is carried out by
 coating a first rust preventive comprising (a) a silicic acid compound and
 (b) an aromatic amine-based condensation product on a Zn-based metallic
 coating to form a coating film, which is referred to as the first coating
 film when the second coating film is formed. The first rust preventive is
 generally used as a coating liquid containing a solvent.
 The solvent used in the formation of the first coating film include, for
 example, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such
 as toluene, xylene, cyclohexanone and tetrahydrofuran; esters such as
 ethyl acetate and butyl acetate; ketones such as methyl isobutyl ketone;
 alcohols such as methanol, ethanol and propyl alcohol; formamides such as
 N,N-dimethylformamide and N,N-diethylformamide; acetamides such as
 N,N-dimethylacetamide and N,N-diethylacetamide; dioxane;
 N-methyl-2-pyrrolidone; 1,3-dimethyl-2-imidazolidinone; and isophorone.
 These organic solvents can be used as a mixture with water in an amount in
 the range of not injuring the effects of the present invention.
 The total concentration of the aromatic amine-based condensation product
 (b) and the silicic acid compound (a) is preferably 0.1 to 25% by weight,
 more preferably 1 to 10% by weight, based on the total weight of the
 coating liquid.
 The coating liquid used in the formation of the first coating film can be
 optionally added with other components as long as the effects of the
 invention are not impaired. For example, when (c) an inorganic acid and/or
 an organic acid is added to the coating liquid, the coating liquid can be
 improved in storage stability.
 The inorganic acids includes preferably inorganic phosphoric acids such as
 phosphoric acid, pyrophosphoric acid and tripolyphosphoric acid.
 The organic acid includes, for example, aromatic carboxylic acids such as
 benzoic acid, pentafluorobenzoic acid, gallic acid, salicylic acid, tannic
 acid, laccaic acid, abietic acid, shellac, rosin, 1,8-naphthaldehydic
 acid, naphthoylbenzoic acid, naphthoylformic acid, naphthoic acid,
 phthalic acid, naphthoxyacetic acid and naphthylglycolic acid; aliphatic
 carboxylic acids such as formic acid, acetic acid, gluconic acid, glycolic
 acid, oxalic acid, tartaric acid, citric acid and lactic acid; aromatic
 sulfonic acids such as toluenesulfonic acid, naphthylenediaminesulfonic
 acid, naphthylenediaminedisulfonic acid and naphtholsulfonic acid;
 aliphatic sulfonic acids such as methylsulfonic acid; and organic
 phosphoric acids such as lecithinic acid, phitic acid and nucleic acid.
 Among them, particularly preferred are aromatic carboxylic acids from the
 viewpoint of improving storage stability.
 Component (c) is used in an amount of 1 to 500 parts by weight, preferably
 10 to 250 parts by weight, per 100 parts by weight of (a) the silicic acid
 compound.
 When (c) the inorganic acid and/or the organic acid is added to a coating
 liquid used in the formation of the first coating film, the total
 concentration of the components (a), (b) and (c) is preferably 0.1 to 25%
 by weight, more preferably 1 to 10% by weight.
 The wet coating film obtained by application of the first coating liquid is
 dried generally at room temperature to the boiling point of a solvent
 used. The first coating film thus formed has preferably a thickness of 1
 to 50 .mu.m.
 In a preferred embodiment of the present invention, a second coating film
 comprising (a) a silicic acid compound is further formed on the first
 coating film, which has been formed on a Zn-based metallic coating, by
 coating a second rust preventive comprising the silicic acid compound (a)
 (generally, the second rust preventive is used as a coating liquid
 containing a solvent) and drying the wet coating film thus obtained,
 thereby the rust proof effect being further more enhanced.
 Second Coating Film
 The silicic acid compound [component (a)] used in the formation of the
 second coating film is the same as used in the formation of the first
 coating film and is as exemplified above. Preferable silicic acid
 compounds are silicic acid esters, colloidal silica and alkali metal
 silicates, which are also as exemplified above. The silicic acid compounds
 can be used singly or in a combination of two or more thereof.
 In the formation of the second coating film according to the present
 invention, from the viewpoint of further enhancing the rust proof effect,
 the above silicic acid compound (a) is preferably used together with:
 (d) a phosphoric acid compound;
 (e) an organic compound with a molecular weight of less than 1,000 and
 having at least one group selected from the group consisting of --OH,
 --COOH and --SO.sub.3 H groups; and/or
 (f) an organic polymer having at least one group selected from the group
 consisting of --OH, --COOH and --SO.sub.3 H groups. Among them, preferred
 are components (e) and (f).
 The phosphoric acid compound of component (d) is preferably exemplified by
 an inorganic phosphoric acid such as phosphoric acid, pyrophosphoric acid
 and polyphosphoric acid; and an organic phosphoric acid such as lecithinic
 acid, phytic acid and nucleic acid.
 The organic compound with a molecular weight of less than 1,000 and having
 at least one group selected from the group consisting of --OH, --COOH and
 --SO.sub.3 H groups of component (e) are exemplified by (e-1) an aliphatic
 compound with a molecular weight of less than 1,000 having at least one
 group selected from the group consisting of --OH, --COOH and --SO.sub.3 H
 groups; and (e-2) an aromatic compound with a molecular weight of less
 than 1,000 having at least one group selected from the group consisting of
 --OH, --COOH and --SO.sub.3 H groups.
 Component (e-1):
 Examples of the aliphatic compound having at least one --OH group include
 glycerin, ethylene glycol, glycol methyl ether, trimethylene glycol and
 propylene glycol.
 Examples of the aliphatic compound having at least one --COOH group include
 aspartic acid, fumaric acid, itaconic acid, succinic acid, oxaluric acid,
 propionic acid, 2-ketoglutaric acid, oxalsuccinic acid, glutamic acid,
 cis-aconitic acid, pyruvic acid, oleic acid, linoleic acid, lauric acid,
 myristic acid, palmitic acid, stearic acid, maleic acid, formic acid and
 acetic acid.
 Examples of the aliphatic compound having at least one --SO.sub.3 H group
 include 2-butanesulfonic acid and methanesulfonic acid.
 Examples of the aliphatic compound having both a --OH group and a --COOH
 group include malic acid, isocitric acid, citric acid,
 2,3-dihydroxypropionic acid, .gamma.-hydroxyisovaleric acid, tartaric
 acid, meso-tartaric acid, racemic tartaric acid, lactic acid and gluconic
 acid. They can be used singly or in a combination of two or more thereof.
 Component (e-2):
 Examples of the aromatic compound having at least one --OH group include
 phenol, hydroquinone, resorcinol, catechol, hydroxypyridine,
 hydroxycarbazole, hydroxyquinoline, pyrogallol, phloroglucin,
 hydroxyhydroquinone, naphthol, dihydroxynaphthalene, trihydroxynaphtalene,
 1-naphthylcarbinol, naphthopurpurin and quercetin; and derivatives thereof
 obtained by substitution with, for example, an amino group, an alkyl group
 or a halogen atom, such as o-, m- or p-aminophenol,
 2-amino-4-chlorophenol, p-chlorophenol, 2,5- ,2,6- or 3,5-dihydroxytoluene
 and pentafluorobenzoic acid.
 Examples of the aromatic compound having at least one --COOH group include
 benzoic acid, o-, m- or p-phthalic acid, bisphenol-2-carboxylic acid,
 pyromelitic acid, naphthoic acid, naphthalene-1,2-dicarboxylic acid,
 naphthalic acid, naphthalene-1,4,5,8-tetracarboxylic acid,
 3-.alpha.-naphthylacrylic acid, naphtylacetic acid, 1-naphthylmalonic
 acid, 1,8-naphthaldehydic acid, naphthoylformic acid, naphthoxyacetic
 acid, abietic acid and rosin.
 Examples of the aromatic compound having at least one --SO.sub.3 H group
 include benzenesulfonic acid, p-toluenesulfonic acid,
 naphthalene-1-sulfonic acid, naphthalene-1,2-disulfonic acid,
 1-naphthylamine-2-sulfonic acid, 2-naphthylamine-1-sulfonic acid,
 1-naphthylamine-4-sulfonic acid, .beta.-naphthylaminedisulfonic acid and
 naphthylenediaminesulfonic acid.
 Examples of the aromatic compound having both the --OH group and the --COOH
 group include gallic acid, salicilic acid, tannic acid, m- or
 p-hydroxybenzoic acid, 2,4-, 2,5-, 3,4- or 3,5-dihydroxybenzoic acid,
 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid,
 .alpha.-naphthylglycolic acid, .beta.-naphthylglycolic acid, pinselic acid
 and laccaic acid.
 Examples of the aromatic compound having both the --OH group and the
 --SO.sub.3 H group include phenolsulfonic acid, phenoldisulfonic acid,
 naphtholsulfonic acid, naphtholdisulfonic acid and naphtholtrisulfonic
 acid.
 The organic polymers having at least one group selected from the group
 consisting of --OH, --COOH and --SO.sub.3 H groups of Component (f)
 include, for example, polyvinyl alcohol, polyvinyl butyral, polyacrylic
 acid, phenol resin, carboxyl-modified phenol resin, polyvinylphenol,
 p-vinylphenol/2-hydroxyethyl methacrylate copolymer, brominated
 poly-p-vinylphenol, p-vinylphenol/styrene copolymer, p-vinylphenol/butyl
 acrylate copolymer, pectin, shellac, alginic acid, starch, chitin,
 chitosan, polyvinylsulfonic acid, polystyrenesulfonic acid, polyvinyl
 acetal, polyester resin, alkyd resin, urethane resin, polyalkylene glycol
 and vinyl acetate/vinyl alcohol copolymer.
 In the formation of the second coating film, where component (a) is used in
 combination with at least one component selected from the group consisting
 of component (d), component (e) and component (f), said at least one
 compound is used in an amount of preferably 1 to 1,000 parts by weight,
 more preferably 10 to 500 parts by weight, per 100 parts by weight of
 component (a) used in the second coating film.
 The solvent used in the formation of the second coating film includes
 organic solvents, for example, aliphatic hydrocarbons such as hexane;
 aromatic hydrocarbons such as toluene, xylene, cyclohexanone and
 tetrahydrofuran; esters such as ethyl acetate and butyl acetate; ketones
 such as methyl isobutyl ketone; alcohols such as methanol, ethanol and
 propyl alcohol; formamides such as N,N-dimethylformamide and
 N,N-diethylformamide; acetamides such as N,N-dimethylacetamide and
 N,N-diethylacetamide; dioxane; N-methyl-2-pyrrolidone;
 1,3-dimethyl-2-imidazolidinone; and isophorone; and water.
 The total concentration of the components contained in the coating liquid
 for use in the formation of the second coating film is preferably 0.1 to
 25% by weight, more preferably 1 to 10% by weight, based on the total
 weight of the coating liquid.
 The wet coating film obtained by application of the second coating liquid
 is dried generally at room temperature to the boiling point of a solvent
 used. The second coating film thus formed has preferably a thickness of 1
 to 50 .mu.m.
 In the present invention, additives such as dyes, pigments and surfactants
 can be optionally added to the first coating liquid and/or the second
 coating liquid.
 As methods for applying these coating liquids, there can be used
 roll-coating, spray coating, dip-coating, shower-coating and
 electrodeposition although not particularly limited thereto.
 Objects to undergo rust-proof treatment according to the present invention
 are Zn-based metallic coatings which have been generally formed on the
 surface of a base as mentioned later. The Zn-based metallic coatings can
 be formed, for example, by plating a base with Zn-based metal. The plating
 may be electroplating or electroless plating. The Zn-based metal may be
 metallic Zn or Zn-based alloy. The content of Zn in the Zn-based metal is
 generally 5 to 100% by weight. In the case of Zn-based alloy, the content
 of Zn is generally 5% by weight or larger, preferably ranges from 7 to
 99.8% by weight, more preferably from 60 to 99.8% by weight, although not
 limited thereto. Objects, i.e., bases, to be plated may be comprised of a
 metal or a non-metal. The metal includes, for example, iron, nickel,
 cobalt, aluminum, tin and alloys of two or more thereof including
 fypically steels. The base is generally in the form of plate or sheet. The
 Zn-based alloys include typically Zn--Ni alloy, Zn--Fe alloy, Zn--Co
 alloy, Zn--Fe--Co alloy, Zn--Al alloy and Sn--Zn alloy.

EXAMPLES
 In the following, coating liquids or experiments marked with * are those
 not meeting the requirements of the present invention.
 Production of Condensation Products
 Condensation products A-(1), A-(2), A-(3) and A-(4) were produced by the
 condensation reactions as mentioned below. In each example, the molecular
 weight of the condensation product obtained was measured in the following
 way.
 Measurement of Molecular Weight
 Weight-average molecular weight in terms of polystyrene was measured by gel
 permeation chromatography (GPC) under the following measurement
 conditions.
 Columns:
 Guard column:
 Tradename: slim-pack GPC-800DP, manufactured by Shimadzu Corporation.
 Analytical columns:
 Tradename: slim-pack GPC-803D, 802D, manufactured by Shimadzu Corporation.
 Mobile phase: 10 mM LiBr/DMF
 Flow rate: 1.0 ml/min
 Detector: RI
 Temperature: 60.degree. C.
 Further, alkali-treated products B-(1) and B-(3), and higher aliphatic
 fatty acid-treated products C-(1) and C-(3) were produced using the
 condensation products A-(1) and A-(3) obtained, and an aralkylation
 product D-(3) was produced using the alkali-treated product B-(3)
 obtained.
 Production of Condensation Product A-(1)
 Into a pressure resistant reaction vessel, 100 moles (10.9 kg) of
 p-aminophenol and 0.99 kg (9.5 moles as HCl) of 30% hydrochloric acid were
 charged, and the temperature of the resulting mixture was raised to
 169.degree. C. When the temperature reached 169.degree. C., 18 liters of
 xylene was slowly added for the purpose of removing the water generated
 during condensation reaction as an azeotropic mixture. Then, the
 temperature of the reaction mixture was raised to 222.degree. C. and
 reacted at this temperature for 3 hours. The mixed vapor of xylene and
 water generated during reaction was removed and the internal pressure was
 kept at 150 kPa. After reacting for 3 hours, the reaction mixture was
 cooled. The reaction product obtained was solid. Next, the reaction
 product was pulverized into fine particles, followed by washing with
 water, filtering and drying to obtain Condensation Product A-(1). This
 condensation product had a weight-average molecular weight of 2,500.
 Production of Condensation Product A-(2)
 Into a pressure resistant reaction vessel, 100 moles (10.8 kg) of
 m-phenylenediamine, 200 moles (22.0 kg) of resorcinol and 1.04 kg (10
 moles as HC1) of 35% hydrochloric acid were charged, and the temperature
 of the resulting mixture was raised to 305.degree. C. Immediately when the
 temperature of the mixture in the reaction vessel reached 305.degree. C.,
 the reaction mixture was cooled. The water produced during the rise in
 temperature and the reaction was removed, and the internal pressure was
 kept at 150 kPa. After cooling, a condensation product of
 m-phenylenediamine was obtained, which was pulverized to obtain as
 Condensation Product A-(2). This condensation product had a weight-average
 molecular weight of 3,000.
 Production of Condensation Product A-(3)
 A mixture of 100 moles of aniline, 31 moles of hydrochloric acid, 22.7
 moles of nitrobenzene and 0.103 mole of ferric chloride was heated at
 60.degree. C. for 6 hours in a reaction vessel. Then, the temperature was
 raised to 180 to 185.degree. C. to react the mixture at the temperature
 for 15 hours while water was evaporated off. During the reaction, a part
 of aniline and a part of nitrobenzene together with the water were
 evaporated off. The evaporated aniline and nitrobenzene were recovered and
 recycled to the reaction vessel. Next, the internal pressure was further
 raised to 200.degree. C. and the reaction mixture was heated at this
 temperature for 5 hours.
 The thus obtained reaction mixture in a melted form was charged into a
 dilute hydrochloric acid and heated to 60.degree. C. for 3 hours, followed
 by hot-filtering to remove unreacted aniline. The reaction mixture was
 further washed 5 to 6 times with water in order to remove excess
 hydrochloric acid and then dried to obtain Condensation Product A-(3).
 This condensation product had a weight-average molecular weight of 15,000.
 Production of Condensation Product A-(4)
 Into a pressure resistant reaction vessel, 30,000 moles (960 kg) of
 methanol, 100 moles (15.8 kg) of 1,8-diaminonaphthalene, 50 moles (5.4 kg)
 of p-benzoquinone were charged. To the resulting mixture, 159 moles (20
 kg) of pyrogallol was added and reacted at 60.degree. C. for 20 hours.
 Then, 1,000 kg of water was charged into the reaction mixture and the
 resulting condensate was settled. The sediment thus obtained was filtered,
 washed and dried to obtain Condensation Product A-(4). This condensation
 product had a weight-average molecular weight of 12,000.
 Production of Condensation Product B-(1) (Alkali-treated Product)
 In 5.0 kg of water, 1.0 kg of the above Condensation Product A-(1) was
 dispersed and 0.1 kg of NaOH was added thereto. Thereafter, the resulting
 mixture was heated up to 130.degree. C. and heat-treated at this
 temperature for 2 hours. After cooling, the liquid reaction product was
 filtered, washed with water, and dried to obtain Alkali-treated Product
 B-(1).
 Production of Condensation Product B-(3) (Alkali-treated Product)
 In 5.0 kg of water, 1.0 kg of the above Condensation Product A-(3) was
 dispersed and 0.2 kg of NaOH was added thereto. Thereafter, the resulting
 mixture was heated up to 100.degree. C. and heat-treated at this
 temperature for 4 hours. After cooling, the reaction product was filtered,
 washed with water, and dried to obtain Alkali-treated Product B-(3).
 Production of Condensation Product C-(1) (Higher fatty acid-treated
 Product)
 To 1.0 kg of the above Condensation Product A-(1), 1.0 kg of lithium
 stearate was added. The resulting mixture was heated up to 230.degree. C.
 and treated at this temperature for 1 hour. After cooling, the reaction
 product obtained was pulverized into fine particles, followed by washing
 with water, filtering and drying to obtain Higher fatty acid-treated
 Product C-(1).
 Production of Condensation Product C-(3) (Higher fatty acid-treated
 Product)
 To 0.5 kg of the above Condensation Product A-(3), 1.0 kg of oleic acid was
 added. The resulting mixture was heated up to 100.degree. C. and treated
 at this temperature for 2 hours. After cooling, the reaction product was
 pulverized into fine particles, to obtain Higher fatty acid-treated
 Product C-(3) in the form of fine particles.
 Production of Condensation Product D-(3) (Aralkylation Product)
 Into a reaction vessel provided with a stirrer, a dropping funnel, a
 condenser, etc., 1.0 kg of the above Alkali-treated Product B-(3) was
 charged and then 10 kg of dimethylformamide was charged, and subsequently
 stirring was started.
 Next, after adding 1.0 kg of anhydrous potassium carbonate as an alkali
 agent, the resulting mixture was heated up to 80.degree. C. and kept at
 this temperature. To the mixture, 250 g of benzyl chloride was dropwise
 added over 2 hours, and stirring was kept at 80.degree. C. for 1 hour.
 Then, the reaction mixture was heated up to 120.degree. C. and stirred at
 this temperature for 2 hours, followed by cooling. The reaction mixture
 was charged into 90 liters of water. After the resulting mixture was
 stirred for 1 hour, it was filtered, washed with water, and dried to
 obtain Aralkylation Product D-(3).
 Preparation of Coating Liquid Nos. 1 to 9
 As shown in Table 1, after 10 g of the aromatic amine-based condensation
 product was added to 475 g of tetrahydrofuran, 10 g (as a solid matter of
 SiO.sub.2) of a colloidal silica having an average particle diameter of 10
 to 20 nm (trade name: MA-ST, produced by Nissan Kagaku Kogyo K.K) as
 silicic acid compound and subsequently 5 g of benzoic acid as an organic
 acid were added thereto, followed by stirring and mixing for 1 hour to
 prepare coating liquid Nos. 1 to 9.
 Preparation of Coating Liquid Nos. 10 to 14
 As shown in Table 1, at least one component selected from a silicic
 compound (a), an aromatic amine-based condensation product (b), and a
 phosphoric acid or organic acid (c) was added to a solvent so that the
 total concentration of (a)+(b)+(c) was a value shown in this table,
 followed by stirring and mixing at about 25.degree. C. for 1 hour to
 prepare coating liquid Nos. 10 to 14. Among them, coating liquid No.13*
 isacomparative example not using an aromatic amine-based condensation
 product (b), and coating liquid No. 14* is a comparative example not using
 a silicic acid compound (a).
 Incidentally, the silicic acid compound used in experiment Nos. 10 to 13 is
 a colloidal silica having an average particle diameter of 10 to 20 nm
 (trade name: IPA-ST, produced by Nissan Kagaku Kogyo K.K)
 TABLE 1
 (b) (c) Total
 Aromatic Inorganic concen-
 (a) amine- phosphoric (a)/(b)/ tration
 Coating Silicic based acid or (c) of (a) +
 liquid acid condensation organic (wt. (b) + (c)
 No. compound product acid ratio) (wt. %) Solvent
 1 MA-ST A-(1) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 2 MA-ST A-(2) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 3 MA-ST A-(3) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 4 MA-ST A-(4) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 5 MA-ST B-(1) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 6 MA-ST B-(3) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 7 MA-ST C-(1) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 8 MA-ST C-(3) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 9 MA-ST D-(3) Benzoic 100/100/ 5.0 Tetrahydro-
 acid 50 furan
 10 IPA-ST B-(3) Abietic 100/150/ 6.0 N-methyl-2-
 acid 50 pyrrolidone
 11 IPA-ST B-(3) None 100/100/ 5.0 Tetrahydro-
 0 furan
 12 IPA-ST B-(3) Phosphor- 100/100/ 6.0 Dioxane
 ic acid 100
 13* IPA-ST None None 100/0/0 2.5 Tetrahydro-
 furan
 14* None B-(3) None 0/100/0 2.5 Tetrahydro-
 furan
 Evaluation Test
 As specimen steel plates, there were used rolled steel plates (SDCC-D) each
 measuring 150 mm.times.70 mm.times.0.8 mm of which surfaces have been
 electroplated with Zn(99.5 wt. %)--Fe(0.2 wt. %)--Co(0.3 wt. %) alloy.
 Fourteen specimen steel plates of this type were prepared. After each of
 them was dipped in and coated with each of the coating liquid Nos. 1 to 14
 prepared as above, it was left to stand at 70.degree. C. for 2 hours to
 dryness. Thus, there were prepared specimen steel plates on each of which
 a coating of a rust preventive has been formed. The specimen steel plates
 were used for the following tests. The results are shown in Table 2.
 Evaluation of Appearance
 The appearance of a specimen steel plate on which a coating has been formed
 was visually observed.
 Corrosion Resistance Test
 In accordance with JIS Z-2371, the salt spray test was carried out on a
 specimen steel plate on which said coating film has been formed. The
 specimen steel plate was visually observed every 24 hours, and the time
 (hour) until a white rust having an area of 5% or more of the entire
 surface area of the specimen steel plate was formed was measured.
 Evaluation for Storage Stability
 After the coating liquid Nos. 1 to 14 were prepared, 100 ml of each of them
 was charged into a 100 ml-test tube, and the test tube was left to stand
 at rest. The test tube was visually observed every 24 hours as to whether
 any sediment was produced therein, and the time (hour) taken until the
 sediment was produced was measured.
 TABLE 2
 Corrosion Storage
 Coating resistance stability
 Experiment liquid No. (hr) Appearance (hr)
 1 1 48 or more Black 72 or more
 2 2 48 or more Black 72 or more
 3 3 48 or more Black 72 or more
 4 4 48 or more Black tinged 72 or more
 with violet
 5 5 48 or more Black 72 or more
 6 6 48 or more Black 72 or more
 7 7 48 or more Black 72 or more
 8 8 48 or more Black 72 or more
 9 9 48 or more Black 72 or more
 10 10 48 or more Black 72 or more
 11 11 48 or more Black 24
 12 12 48 or more Black 48
 13* 13* 24 Colorless 72 or more
 14* 14* 24 Black 72 or more
 Preparation Examples of Coating Liquids
 Coating liquids used for the formation of coating films were prepared.
 Silicic acid compounds used in these examples are as listed in Table 7.
 Preparation of First Coating Liquid Nos. 1 to 13
 In each example, a silicic acid compound (a), an aromatic amine-based
 condensation product (b) and a solvent listed in Table 3 were mixed so
 that a weight ratio of (a)/(b) and the total cencentration of (a)+(b) were
 as listed in Table 3. The resulting mixture was stirred at about
 25.degree. C. for 2 hours to prepare first coating liquid Nos. 15 to 27.
 Incidentally, the silicic acid compound used in coating liquid Nos. 15 to
 23 was a colloidal silica having a particle diameter of 10 to 20 nm (trade
 name: MA-ST, produced by Nissan Kagaku Kogyo K.K.), and the silicic acid
 compound used in coating liquid Nos. 24 to 27 was a condensate of
 tetraethoxysilane (trade name: Ethyl Silicate-40, produced by Tama Kagaku
 Kogyo K.K.).
 TABLE 3
 (b) Total
 First (a) Aromatic concentra-
 coating Silicic amine-based tion of
 liquid acid condensation (a)/(b) (a) + (b)
 No. compound product (wt. ratio) (wt. %) Solvent
 15 MA-ST A-(1) 100/200 3 Tetrahydro-
 furan
 16 MA-ST A-(2) 100/200 3 Tetrahydro-
 furan
 17 MA-ST A-(3) 100/150 5 Tetrahydro-
 furan
 18 MA-ST A-(4) 100/150 5 Tetrahydro-
 furan
 19 MA-ST B-(1) 100/250 3.5 Tetrahydro-
 furan
 20 MA-ST B-(3) 100/200 3 Tetrahydro-
 furan
 21 MA-ST C-(1) 100/250 3.5 Tetrahydro-
 furan
 22 MA-ST C-(3) 100/200 3 Tetrahydro-
 furan
 23 MA-ST D-(3) 100/300 4 Tetrahydro-
 furan
 24 Ethyl A-(3) 100/400 5 Methanol
 sil-
 icate-40
 25 Ethyl B-(3) 100/200 3 N-methyl-2-
 sil- pyrrolidone
 icate-40
 26 Ethyl C-(3) 100/100 4 Ethanol
 sil-
 icate-40
 27 Ethyl D-(3) 100/50 3 Methyl
 sil- isobutyl
 icate-40 ketone
 Experiment Nos. 15 to 25
 In each experiment, a specimen plate was dip-coated with each of the first
 coating liquids listed in Table 4 and then left to stand at 70.degree. C.
 for 2 hours to dryness for forming a first coating film having a thickness
 as shown in Table 4. Thereafter, the specimen plate was left to stand in a
 room kept at about 25.degree. C. for 1 hour for cooling. Next, a silicic
 acid compound (a), a phospholic acid compound (d) and a solvent listed in
 Table 4 were mixed so that a weight ratio of (a)/(d) and the total
 concentration of (a)+(d) were as given in Table 4 to prepare second
 coating liquids. Each of the second coating liquids was further dip-coated
 on the first coating film formed on each of a specimen plate on which the
 first coating film has been formed as above and left to stand at
 70.degree. C. for 2 hours to dryness for forming a second coating film
 having a thickness as shown in Table 4. Thus, a specimen plate on which
 two kinds of coating liquids were separately coated.
 Incidentally, the specimen plates used in these experiments were rolled
 steel plates (SDCC-D) measuring 150 mm.times.70 mm.times.0.8 mm of which
 surfaces have been electroplated with Zn(99.5 wt. %)--Fe(0.2 wt.
 %)--Co(0.3 wt. %) alloy.
 Corrosion Resistance Test
 In accordance with the salt spray test defined in JIS Z-2371, the specimen
 plates thus obtained on which rust preventive coating films were visually
 observed every 24 hours and the time (hour) taken until a white rust is
 formed on an area of 5% or more of the entire surface area of the specimen
 plate was measured. The results are shown in Table 4. Incidentally,
 Experiment No.25* is a comparative example in which a second coating
 liquid alone was used.
 Experiment Nos. 26 to 37
 In each experiment, preparation of a specimen plate and corrosion
 resistance test were carried out in the same manner as in Experiment No.15
 except that a first coating liquid and a second coatingliquid listed in
 Table5 were used. The results are shown in Table 5. Incidentally, in Table
 5 are specifically indicated a silicic acid compound (a), an aliphatic or
 aromatic compound with a molecular weight of less than 1,000 having a
 --OH, --COOH and/or --SO.sub.3 H group (e), a weight ratio of (a)/(e), the
 total amount of (a)+(e) and a solvent used in the first coating liquids
 and the second coating liquids.
 Among these experiments, Experiment No.37* is a comparative example in
 which only a second coating liquid was used.
 Experiment Nos. 38 to 49
 In each experiment, preparation of a specimen plate and corrosion
 resistance test were carried out in the same manner as in Experiment No.15
 except that a first coating liquid and a second coating liquid listed in
 Table 6 were used. The results are shown in Table 6. Incidentally, in
 Table 6 are specifically described a silicic acid compound (a), an organic
 polymer having a --OH, --COOH and/or --SO.sub.3 H group (f), a weight
 ratio of (a)/(f), the total amount of (a)+(f) and a solvent used in the
 first coating liquids and the second coating liquids.
 Among these experiments, Experiment No.49* is a comparative example in
 which only a second coating liquid was used.
 TABLE 4
 First Second coating liquid
 coating Total
 Ex- liquid (a) (d) concentration
 peri- No. Silicic Phospho- (a)/(d) of (a) + (d)
 Storage
 ment (Film acid ric acid (wt. % (Film
 stability
 No. thickness, .mu.m) compound compound Ratio) thickness, .mu.m)
 Solvent (hr)
 15 1(0.6) a -- 100/0 2(0.4) Isopropyl 120
 alcohol
 16 3(1.0) b -- 100/0 4(0.8) Tetra- 120
 hydrofuran
 17 5(0.7) Tetra- -- 100/0 6(1.2) Methanol 120
 methoxy-
 silane
 18 7(0.7) f -- 100/0 1(0.2) Water 120
 19 1(1.0) c -- 100/0 3(0.6) Metyl 120
 isobutyl
 ketone
 20 13(0.6) a Phosphor- 100/10 2.2 Ethanol
 144
 ic acid (0.5)
 21 2(0.6) d Pyrophos- 100/20 2.4 Methyl
 144
 phoric (0.5) isobutyl
 acid ketone
 22 4(1.0) e Polyphos- 100/30 2.6 Water
 144
 phoric (0.6)
 acid
 23 6(0.6) b Phitic 100/40 2.8 Isopropyl
 144
 acid (0.6) alcohol
 24 8(0.6) Tetra- Lecithin- 100/50 1.5 Tetra-
 120
 ethoxy- ic acid (0.3) hydrofuran
 silane
 25* None a Phosphor- 100/10 2.2 Isopropyl
 24
 ic acid (0.4) alcohol
 TABLE 5
 First Second coating liquid
 coating Total
 Ex- liquid (a) (e) concentration
 peri- No. Silicic Aliphatic and (a)/(e) of (a) + (e)
 Storage
 ment (Film acid aromatic (wt. (%) (Film
 stability
 No. thickness, .mu.m) compound compounds Ratio) thickness, .mu.m)
 Solvent (hr)
 26 2(0.6) a Ethylene gly- 100/ 6(1.2)
 Isopropyl 144
 Col [Mw:62.07] 20 alcohol
 27 4(1.0) g Itaconic acid 100/ 6(1.2)
 Isobutyl 144
 [Mw:130.10] 20 Alcohol
 28 6(0.6) b Methanesul- 100/ 5.5(1.1) Ethanol
 144
 fonic acid 10
 [Mw:96.11]
 29 8(0.6) d Lactic acid 100/ 2.6(0.5) Ethanol
 144
 [Mw:90.08] 30
 30 10(1.0) a Hydroxy- 100/ 5(1.0)
 Methanol 144
 carbazole 100
 [Mw:183.21]
 31 12(0.8) b Phloroglucin 100/ 5(1.0)
 Isopropyl 168
 [Mw:126.10] 100 alcohol
 32 9(0.8) g Pentafluoro- 100/ 3(0.6) Ethanol
 168
 benzoic acid 50
 [Mw:212.08]
 33 11(0.6) a Benzoic acid 100/ 6(1.2) Methyl
 168
 [Mw:122.12] 50 ethyl
 ketone
 34 13(0.6) f p-toluenesul- 100/ 6.5(1.3) Ethanol
 144
 fonic acid 30
 [Mw:172.20]
 35 1(0.6) c Gallic acid 100/ 5(1.0) Methyl
 144
 [Mw:170.12] 100 isobutyl
 ketone
 36 3(1.0) Tetra- Naphtholsul- 100/ 6(1.2)
 Methanol 120
 ethoxy- fonic acid 20
 silane [Mw:224.24]
 37* none a Gallic acid 100/ 5(1.0) Methyl
 24
 [Mw:170.12] 100 isobutyl
 ketone
 TABLE 6
 First Second coating liquid
 coating Total
 Ex- liquid (a) concentration
 peri- No. Silicic (f) (a)/(f) of (a) + (f) %
 Storage
 ment (Film acid Organic (wt. (Film
 stability
 No. thickness, .mu.m) compound Polymer ratio) thickness, .mu.m)
 Solvent (hr)
 38 1(0.6) a Polyvinyl 100/ 3(0.6) Tetrahydro-
 144
 butyral 50 furan
 39 3(1.0) e Polyvinyl 100/ 5(1.0) Water
 144
 alcohol 100
 40 5(0.7) a Polyvinyl 100/ 4.5(0.9) Methanol
 144
 phenol 50
 41 7(0.7) c Shellac 100/ 5(1.0) Ethanol
 144
 100
 42 9(0.8) b Polysty- 100/ 6.5(1.3) Methanol
 144
 renesul- 30
 fonic acid
 43 11(0.6) d Polyvinyl 100/ 3(0.6) N-methyl-2-
 144
 acetal 50 pyrrolidone
 44 13(0.6) b Polyester 100/ 5(1.0) Methyl
 144
 100 isobutyl
 ketone
 45 2(0.6) c Phenol 100/ 4(0.8) Methyl ethyl
 144
 resin 100 ketone
 46 4(1.0) g Urethane 100/ 3(0.6) Dioxane
 144
 resin 50
 47 6(0.6) f Polyacryl- 100/ 3(0.6) Methanol
 120
 ic acid 50
 48 8(0.6) b Alkyd 100/ 4.5(0.9) N-methyl-2-
 144
 resin 50 pyrrolidone
 49* None a Polyvinyl 100/ 4.5(0.9) Methanol 24
 phenol 50
 TABLE 7
 Silicic acid Particle
 compound diameter (nm) Trade name Maker
 a Colloidal 20.about.30 MA-ST-M Nissan Kagaku
 silica Kogyo K.K.
 b Colloidal 10.about.20 IPA-ST Nissan Kagaku
 silica Kogyo K.K.
 c Colloidal 10.about.20 MEK-ST Nissan Kagaku
 silica Kogyo K.K.
 d Colloidal 10.about.20 MIBK-ST Nissan Kagaku
 silica Kogyo K.K.
 e Colloidal 40.about.100 ST-UP Nissan Kagaku
 silica (chain) Kogyo K.K.
 f Lithium -- Lithium Nissan Kagaku
 silicate silicate Kogyo K.K.
 g Condensate of -- Ethyl Tama Kagaku
 tetraethoxy- silicate-40 Kogyo K.K.
 silane