JP3030906B2 - Aqueous coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to wood, plastic,
The present invention relates to an aqueous coating composition having excellent durability and alkali-removability, which can be used as a coating agent for ceramics and metals, and can be suitably used as a coating agent for floor materials and plastics, particularly vinyl-based and wood-based materials.

[0002]

2. Description of the Related Art Conventional aqueous coating compositions for flooring materials and plastics are mainly composed of copolymer emulsions, waxes and alkali-soluble resins, and also include wetting agents, emulsifiers and dispersants, and Zn ions. Which contain a polyvalent metal aqueous solution.

[0003]

Problems to be Solved by the Invention However, the conventional aqueous coating composition has insufficient durability depending on the place where it is applied, and also has problems in water pollution and safety due to heavy metal ions.

[0004]

The present invention provides (a) α,
5 to 60% by weight of β-unsaturated carboxylic acid, (b) (meth)
30-90% by weight of alkyl acrylate, (c)
Other monomers copolymerizable with (a) and (b) 0 to 65
An isoelectric point of 100 parts by weight (in terms of solid content) of a copolymer latex obtained by emulsion polymerization of a monomer consisting of
The present invention provides an aqueous coating composition characterized by dispersing 0.5 to 50 parts by weight of a metal compound having a positive surface charge at a pH of 4 or higher and a pH equal to or lower than the isoelectric point.

[0005] Among the monomers used for producing the copolymer latex used in the present invention, (a) α, β-unsaturated carboxylic acids include (meth) acrylic acid, fumaric acid,
Itaconic acid, monoalkyl itaconate, maleic acid,
Examples thereof include crotonic acid and 2-methacryloyloxyethyl hexahydrophthalic acid, and preferably (meth) acrylic acid. These (a) α, β-unsaturated carboxylic acid monomers can be used alone or in combination of two or more. The (a) α, β-unsaturated carboxylic acid monomer is an essential component for maintaining the balance between polymerization stability and durability of the copolymer latex at a high level. The amount used is 5 to 60% by weight of the total monomers, preferably 10 to 50% by weight, more preferably 2 to 50% by weight.
0 to 40% by weight. If it is less than 5% by weight, the durability will be reduced, and if it exceeds 60% by weight, the leveling property will be poor.

(B) As the alkyl (meth) acrylate, (meth) acrylic acid having 1 to 10 carbon atoms in the alkyl group is used.
Examples of the alkyl acrylate monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, and n- (meth) acrylate. Butyl,
I-butyl (meth) acrylate, n- (meth) acrylate
-Amyl, i-amyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, i-nonyl (meth) acrylate, decyl (meth) acrylate, hydroxymethyl (meth) acrylate ,
Hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyamyl (meth) acrylate, hydroxyhexyl (meth) acrylate, etc.
Preferable examples include butyl (meth) acrylate and methyl (meth) acrylate. The amount of the (b) alkyl (meth) acrylate used is 30 to 30% of the total monomers.
It is 90% by weight, preferably 40-80% by weight, more preferably 50-70% by weight. If it is less than 30% by weight, water resistance and weather resistance are poor, which is not preferable.

(C) Other monomers copolymerizable with (a) and (b) include benzyl (meth) acrylate,
Phenoxyethyl (meth) acrylate, alkylphenoxyethyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, alkylphenol ethylene oxide (meth) acrylate, alkylphenol propylene oxide (meth) acrylate, 2-hydroxy-3 -Phenoxypropyl (meth)
Acrylates, polyester (meth) acrylates such as ethylene glycol (meth) acrylate monophthalate, ethylene glycol (meth) acrylate hydroxyethyl phthalate, allyl glycidyl ether,
Epoxy compounds such as glycidyl (meth) acrylate and methyl glycidyl (meth) acrylate, divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) ) Acrylate, propylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate, butanediol di (meth) acrylate, hexanediol di ( Multifunctional monomers such as (meth) acrylate, trimethylolpropane tri (meth) acrylate, and pentaerythritol tetra (meth) acrylate , (Meth) acrylamide, N
-Acid amide compounds such as methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N, N'-methylenebisacrylamide, diacetone acrylamide, maleic amide, and maleimide; Vinyl compounds such as vinyl, vinylidene chloride, vinyl acetate, and fatty acid vinyl ester; fluorine atom-containing monomers such as trifluoroethyl (meth) acrylate and pentadecafluorooctyl (meth) acrylate; γ-methacryloylpropanetrimethoxysilane; Silicone compounds such as reactive silicone such as Silaplane FM0711 manufactured by K.K., styrene, α-methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methoxys Tylene, 2-hydroxymethylstyrene, 4-ethylstyrene, 4-ethoxystyrene,
3,4-dimethylstyrene, 2-chlorostyrene, 3-
Chlorostyrene, 4-chloro-3-methylstyrene, 4
-T-butylstyrene, 2,4-dichlorostyrene,
Aromatic vinyl monomers such as 2,6-dichlorostyrene, 1-vinylnaphthalene, and divinylbenzene; aminoamines; aminoalkyls of ethylenically unsaturated carboxylic acids such as aminoethyl acrylate, dimethylaminoethyl acrylate, and butylaminoethyl acrylate Ester, aminoethyl acrylamide, dimethylaminomethyl methacrylamide, methylaminopropyl methacrylamide and other ethylenically unsaturated carboxylic acid aminoalkylamides, (meth) acrylonitrile, α-chloroacrylonitrile and other vinyl cyanide monomers, etc. Can be mentioned. As the component (c), an aromatic vinyl monomer is preferable.

The amount of the component (c) is from 0 to 6
It is 5% by weight, preferably 5 to 50% by weight, more preferably 10 to 30% by weight. In the present invention, the copolymer latex can be obtained by a usual emulsion polymerization method. For example, the above-mentioned monomer, emulsifier, polymerization initiator, chain transfer agent, chelating agent, pH adjuster and the like are added to an aqueous medium, and the polymerization reaction is carried out at a temperature of 30 to 100 ° C. for about 1 to 30 hours. Here, as the emulsifier to be used, anionic, nonionic, or a combination of anionic and nonionic is used. In some cases, an amphoteric surfactant or a cationic surfactant can also be used. . Examples of the anionic emulsifier include higher alcohol sulfate sodium salt, alkylbenzene sulfonate sodium salt, dialkyl succinate sodium sulfonate, sodium alkyldiphenyl ether disulfonate and the like. Of these, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and sulfates of polyoxyethylene alkyl (or alkylphenyl) ether are preferably used.

Examples of the nonionic emulsifier include polyoxyethylene alkyl allyl ether. Generally, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether and the like are used as the nonionic emulsifier.
Lauryl betaine is suitable as the amphoteric emulsifier.
As the cationic surfactant, alkylpyridinyl chloride, alkylammonium chloride and the like can be used. Further, so-called reactive emulsifiers, such as sodium styrenesulfonate, sodium allylalkylsulfonate, and alkylallylsulfosuccinate, which can be copolymerized with the monomer constituting the monomer (hereinafter sometimes referred to as monomer) component, , Polyoxyethylene alkyl allyl glycerin ether sulfate, polyoxyethylene alkyl phenol allyl glycerin ether sulfate, and the like may also be used as the emulsifier.

The amount of the emulsifier used is usually the amount of the monomer component 1
The amount is from 0 to 5 parts by weight per 00 parts by weight, but a soap-free system and a system using a reactive emulsifier are preferred from the viewpoint of hot water resistance. Further, a water-soluble polymer can be used as the emulsifier. For example, polyvinyl alcohol, polyacrylate, water-soluble (meth) acrylate copolymer, styrene-maleic acid copolymer salt, styrene- (meth) acrylic acid copolymer salt, poly (meth) acrylamide, poly (Meth) acrylamide copolymers and the like,
Of these, carboxylated aromatic vinyl such as partially saponified polyvinyl alcohol, water-soluble (meth) acrylic acid ester copolymer, styrene-maleic acid copolymer salt, and styrene- (meth) acrylic acid copolymer salt are preferable. Copolymer salts may be mentioned. As the polymerization initiator, for example, water-soluble persulfate, hydrogen peroxide and the like can be used,
In some cases, it can be used in combination with a reducing agent.

Examples of the reducing agent include sodium pyrobisulfite, sodium hydrogen sulfite, sodium thiosulfate,
L-ascorbic acid and its salts, sodium formaldehyde sulfoxylate and the like can be mentioned.
Also, oil-soluble polymerization initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis-2, 4-dimethylvaleronitrile, 1,1'-azobis-cyclohexane-1-carbonitrile, benzoyl peroxide, dibutyl peroxide, cumene hydroperoxide or the like can be used by dissolving it in a monomer or a solvent. Preferred oil-soluble polymerization initiators include cumene hydroperoxide, isopropylbenzene hydroperoxide, paramenthane hydroperoxide,
Azobisisobutyronitrile, benzoyl peroxide, t-butyl hydroperoxide, 3,5,5-
Trimethylhexanol peroxide, t-butylperoxy (2-ethylhexanoate) and the like can be mentioned. The amount of the polymerization initiator used is about 0.1 to 3 parts by weight per 100 parts by weight of the monomer component.

Examples of the chain transfer agent include halogenated hydrocarbons (eg, tetrachloride carbon, chloroform, bromoform),
Mercaptans (for example, n-dodecyl mercaptan,
t-dodecyl mercaptan, n-octyl mercaptan), xanthogens (eg, dimethyl xanthogen disulfide, diisopropyl xanthogen disulfide), terpenes (eg, dipentene, terpinolene), α-methylstyrene dimer [2,4-diphenyl-4 - methyl-1-pentene (a _1), 2-4-
Diphenyl-4-methyl-pentene (a ₂ ), and 1
1-3-trimethyl-3-phenyl-indane (a ₃₎
And preferably comprises (a ₁ ) / (a
₂₎ and / or (a ₃₎ (weight ratio) = 40 to 100
/ 0-60], unsaturated cyclic hydrocarbon compounds (for example,
9,10-dihydroanthracene, 1,4-dihydronaphthalene, indene, 1,4-cyclohexadiene),
Unsaturated heterocyclic compounds (eg, xanthene, 2,5
-Dihydrofuran) and the like. The amount of the chain transfer agent used is 0 per 100 parts by weight of the monomer component.
About 5 parts by weight.

As the chelating agent, for example, glycine,
Alanine, ethylenediaminetetraacetic acid and the like, and as a pH adjuster, for example, sodium carbonate, potassium carbonate,
Examples thereof include sodium hydrogen carbonate and ammonia. The amounts of the chelating agent and the pH adjuster are about 0 to 0.1 part by weight and about 0 to 3 parts by weight, respectively, per 100 parts by weight of the monomer. In addition, as a solvent used as needed at the time of the emulsion polymerization, a small amount of methyl ethyl ketone, acetone, trichlorotrifluoroethane, within a range that does not impair workability, disaster prevention safety, environmental safety and production safety, Methyl isobutyl ketone, dimethyl sulfoxide, toluene, dibutyl phthalate, methyl pyrrolidone, ethyl acetate, alcohols, cellosolves, carbinols and the like are used. The amount of the solvent used is about 0 to 10 parts by weight per 100 parts by weight of the monomer component. Emulsion polymerization in the present invention is a known method, for example, a method of charging the entire amount of the monomer components into the reaction system at once, a method of charging a part of the monomer components and reacting, and then charging the remaining monomer components continuously or dividedly. The method can be carried out by continuously charging all the monomer components.

The final polymerization addition rate of the copolymer is as follows:
It is preferably 90 to 100% by weight, particularly preferably 95 to 100% by weight. When adopting seed polymerization,
A polymer obtained by previously emulsion-polymerizing a monomer is used as a seed particle, and a monomer mixture consisting of the components (a) and (b) is added to the polymer to carry out emulsion polymerization. The weight average molecular weight of the copolymer of component (A) obtained by emulsion polymerization is 3,
000-300,000, preferably 5,000-25
000, more preferably 8,000 to 200,0
00. If it is less than 3,000, the durability is inferior.
If it exceeds 000, the coatability will be poor. The glass transition temperature of the copolymer (A) is preferably from 10 to 180 ° C,
More preferably, it is 20 to 175 ° C, particularly preferably 30 to 175 ° C.
１７０170 ° C. If the temperature is lower than 10 ° C., the durability is inferior.
If it exceeds 0 ° C., the film-forming properties will be poor. The average particle diameter of the copolymer latex of the component (A) is preferably 1 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.2 μm or less.
m, and when it exceeds 1 μm, gloss is inferior.

As the metal compound of the component (B), IIa
Group metal compounds such as MgO, Mg (OH) ₂ ,
Group IIa metal compounds, such as Al ₂ O _3, IIIb
Group metal compounds, for example, Y ₂ O _3, CeO _2, etc., IVa
Group IV metal compounds such as SnO ₂ , Group IVb metal compounds such as TiO ₂ and ZrO ₂ , Group VIb metal compounds such as Cr ₂ O ₃ , and Group VIII metal compounds such as Fe ₂ O _3. ,Preferably,
Group IIIa metal oxides, Group IVb metal oxides and the like can be mentioned. The metal compound of the component (B) is preferably in the form of particles, and the average particle diameter thereof is usually 2,000 Å (hereinafter, referred to as A) or less, preferably 1500 A.
Hereinafter, more preferably at 50 to 1000 A, 2000
If it exceeds A, the gloss is inferior. Furthermore, these metal compounds of component (B) need to have an isoelectric point of pH 4 or higher and have a positive surface charge at a pH below the isoelectric point.
Metal oxide particles having an isoelectric point pH of less than 4 and a pH of 4 or more and having a negative surface charge have poor durability. In the present invention, the copolymer latex of the component (A) and the metal compound (B) are converted to a solid content (parts by weight) of 100 / 0.5 to 50, preferably 100/1 to 30, more preferably 100/100. /
When the content of (B) is less than 0.5 part by weight, the durability is poor, and when it exceeds 50 parts by weight, the gloss is poor.

As the method of dispersing the metal compound (B), generally, one or two or more (A) copolymer dispersions and one or more (B) of two or more copolymers are dispersed in water. There is a method of mixing the dispersion with a homogenizer or the like,
The component (B) may be allowed to coexist in the polymerization process of the copolymer component (a) and component (b) of the component (A). Further, one or more anionic emulsifiers, nonionic emulsifiers, amphoteric emulsifiers, and cationic emulsifiers may be added to the component (B) in advance, and then added to the component (A) composed of one or more types. Alternatively, these may be combined.
The aqueous coating composition of the present invention comprises (A) a copolymer latex and (B) a metal compound dispersed therein, and further comprises (C) a wax emulsion, (D) an alkali-soluble resin,
It is preferable to contain (E) a film-forming auxiliary, (F) additives such as a wetting agent, a dispersant, a leveling agent, a preservative, and an antifoaming agent. A typical aqueous coating composition comprises: (A) 100 parts by weight of a copolymer latex (in terms of solid content); (B) 0.5 to 50 parts by weight of a metal compound;
４０40 parts by weight, (D) 0 to 50 parts by weight of an alkali-soluble resin, (E) 0 to 50 parts by weight of a film forming aid, and (F) 0 to 5 parts by weight of other additives.

Here, (C) the wax emulsion is
The amount is from 0 to 40 parts by weight, preferably from 5 to 30 parts by weight, more preferably from 10 to 30 parts by weight, based on 100 parts by weight of the component (A). If it exceeds 40 parts by weight, the gloss is poor and the appearance is impaired. Here, the alkali-soluble resin (D) has the function of improving the leveling of the aqueous coating composition and improving the releasability. Examples of such a resin include styrene-maleic acid copolymer resin, shellac, and rosin-modified. Maleic resin and the like can be mentioned. The amount used is 0 to 50 parts by weight per 100 parts by weight of the component (A),
Preferably 5 to 40 parts by weight, more preferably 10 to 3 parts by weight.
0 parts by weight. If it exceeds 50 parts by weight, the durability will be poor.

(E) Examples of the film-forming auxiliary include tributoxy phosphate, polyhydric alcohols, diethylene glycol, isophorone, benzyl alcohol and 3-methoxybutanol-1, monoethyl or monomethyl ether, benzylbutyl phthalate, dibutyl phthalate, dimethyl phthalate. , Triphenyl phosphate,
Additives used in ordinary paints, such as carbitol-based film-forming aids and pigments, can be added. The amount used is
The amount is from 0 to 50 parts by weight, preferably from 5 to 40 parts by weight, more preferably from 10 to 30 parts by weight, based on 100 parts by weight of the component (A). The aqueous coating composition thus obtained has good dispersibility and good storage stability at room temperature, and the composition is spray-dried, wiped with a brush, brushed, applied with a brush, and air-dried or It is possible to dry quickly by heating to form a transparent and, if pigmented, pigmented, intense coating. Although the composition of the present invention is excellent in durability, the metal compound is conventionally dissolved in the composition and acts as a metal ion.
In the composition of the present invention, since the metal compound is not dissolved but is preferably dispersed in the form of particles, the metal compound has a synergistic effect of the action as a filler and the action as an ion crosslinking agent.

[0019]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. Examples 1 to 3 and Comparative Examples 1 to 9 (1) Glass reaction vessel with stirrer (capacity: 3 liters)
A condenser, a thermometer, and a dropping funnel were attached to the reactor, and 100 parts by weight of deionized water, 1 part by weight of sodium lauryl sulfate, and 0.5 part by weight of ammonium persulfate were charged. After the inside air was replaced with nitrogen, the internal temperature was stirred. To a temperature of 65 ° C., and in a separate vessel, mix and stir 50 parts by weight of deionized water, 1 part by weight of sodium lauryl sulfate and the monomers shown in Tables 1 and 2 to form an emulsion, and prepare it for 3 hours. And dropped continuously. During dropping, 80 ° C while introducing nitrogen
The reaction was carried out. After completion of the dropwise addition, the mixture was further stirred at 85 ° C for 2 hours, and then cooled to 25 ° C to terminate the reaction. The polymerization addition rates of the obtained copolymer dispersion liquids I to I were all 98.
% By weight or more. Also, generation of coagulated material was hardly observed. (2) In a stirring state maintained at 25 ° C., an alumina sol (Nissan Chemical Engineering Co., Ltd .;
520 aluminum oxide) copolymer latex 10
6 parts by weight was added to 0 parts by weight, and the mixture was sufficiently dispersed with a homogenizer to obtain aqueous coating compositions A to I.

[0020]Preparation of aqueous floor gloss composition An aqueous floor gloss composition was prepared according to the following formulation.Aqueous floor gloss composition formulation Aqueous coating composition ^{* 1} 80 parts by weight Wax emulsion ^{* 2} 15 parts by weight Alkali-soluble resin ^{* 3} 5 parts by weight Fluorinated surfactant ^{* 4} 0.5 parts by weight * 1 Tributoxyethyl phosphate / carbitol
= 1/4 (weight ratio) Add the film-forming aid mixed in proportions
Adjust the minimum film formation temperature to 5 ° C and add deionized water
In addition, the solid content was adjusted to 14% by weight. * 2 Wax emulsion; Toho Chemical HYTEC E
-4B, 15 solids Adjusted to% by weight. * 3 Alco-soluble resin; ARCO Chemical
Company S MA-2625A (acid value 220,
Styrene with 1,900 molecular weight, maleic resin), solid
Was adjusted to 15% by weight. * 4 Fluorinated surfactant: C ₆ F ₁₇ SO ₂ N (C
₂ H ₅ ) CH ₂ COOK, solid content adjusted to 1% by weight
Was. Evaluation as an aqueous coating composition was performed by the following method.
Was.

The aqueous floor gloss composition is applied on a black heel mark resistant homogeneous style in an amount of 10 g per 1 m ² and then dried. This is repeated three times to produce a sample. The sample was placed for 10 days in a place with many people (50-100 reciprocations / day), and the degree of adhesion of the black heel mark was observed. ：: BHM hardly adhered Δ: BHM slightly adhered ×: BHM adhered a lot Scuff resistance A sample was prepared in the same manner as in the evaluation of the black heel mark.
It was installed, and the degree of scuffing was observed. ：: Scuff hardly occurred △: Scuff slightly generated ×: Scuff frequently generated Mitsuzawa A sample was prepared in the same manner as in the evaluation of the black heel mark, and the sample was reflected at 60 ° by a Murakami gloss meter. Was measured. Apply 10 g of the aqueous floor gloss composition per m ² on a leveling homogeneous style, immediately draw a diagonal line in an X shape, and then dry. This is repeated three times to produce a sample. After the drying, the degree of disappearance of the line was determined. ○: Almost disappeared △: Slightly remaining ×: Almost left

The emulsions for aqueous coating compositions obtained in the above Examples and Comparative Examples were evaluated as aqueous coating compositions, and the results are shown in Tables 1 and 2. In emulsions A to L for an aqueous coating composition, A to C belong to the present invention, and D
To L do not belong to the present invention. Examples 1 to 3
This is an example of an aqueous coating composition using an emulsion for an aqueous coating composition within the scope of the present invention, and an aqueous coating composition intended for the present invention has been obtained. In Comparative Example 1, the amount of the α, β-unsaturated carboxylic acid used was less than the range of the present invention, and the black heel mark resistance and the scuff resistance were poor. Comparative Example 2 is an example in which the amount of the α, β-unsaturated carboxylic acid used exceeds the range of the present invention, and the gloss is reduced and the leveling property is inferior. Comparative Example 3 is an example in which the amount of the metal oxide particles used is less than the range of the present invention, and the black heel mark resistance and the scuff resistance are inferior. Comparative Example 4 is an example in which the amount of metal oxide particles used exceeds the range of the present invention, and is inferior in leveling properties, black heel mark resistance, and gloss. Comparative Example 5
Is an example of using metal oxide particles having an isoelectric point outside the range of the present invention instead of the metal oxide particles of the present invention, and black heel mark resistance, scuff resistance, gloss, and leveling properties are inferior. . Comparative Example 6 is an example using a conventionally used Zn-based crosslinking agent. Black heel mark resistance and scuff resistance are inferior to those of the present invention.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

The aqueous coating composition of the present invention does not contain a heavy metal cross-linking agent such as Zn ions, so that it has very little environmental pollution and safety and hygiene dangers, which have recently become problems. It has a durability equal to or higher than that of an aqueous coating composition using a heavy metal crosslinking agent such as Zn ion, and has extremely high industrial value.

Continuation of the front page (56) References JP-A-62-24984 (JP, A) JP-A-51-6193 (JP, A) JP-A-5-194876 (JP, A) JP-A-5-125294 (JP, A) JP-A-5-112741 (JP, A) JP-A-11-1630 (JP, A) JP-A-10-25468 (JP, A) JP-A-9-286940 (JP, A) 8-231887 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 133/10 C09D 5/00 C09D 7/12 CA (STN) CAOLD (STN) REGISTRY (STN) WPIDS ( STN)

Claims (1)

(57) [Claims] (A) α, β-unsaturated carboxylic acids 5 to 6
0% by weight, (b) 30 to 90% by weight of alkyl (meth) acrylate, (c) a monomer comprising 0 to 65% by weight of another monomer copolymerizable with (a) and (b) Of 100 to 100 parts by weight (in terms of solid content) of a copolymer latex obtained by emulsion polymerization of a metal compound having a positive surface charge of pH 4 or more and a positive surface charge at a pH of not more than 0.5.
An aqueous coating composition comprising 50 parts by weight dispersed therein.