JP2005336357A - Water dispersible resin and water base paint composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the stability, smell, further resistance to water and other physical properties of acrylic resin emulsion. <P>SOLUTION: The water-dispersible resin that is obtained by subjecting monomer groups at least comprising (meth)acrylic alkyl ester and carboxyl group-bearing polymerizable monomer to emulsion polymerization and is adjusted to a pH of 7 to 10 with a basic compound. In this case, an alkali metal siliconate (for example, potassium methyl siliconate) is used as the basic compound. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a water-dispersible resin and an aqueous coating composition using the same.

Conventionally, in the paint field, solvent-based paints using organic solvents such as aromatic hydrocarbons as the medium have been the mainstream, but in recent years, from the viewpoints of environmental issues, resource saving, occupational safety, etc. The switch to paint is progressing.
Many water-dispersible resins (aqueous resin emulsions) are used as binders in water-based paints. In particular, acrylic resin emulsions obtained by copolymerization of alkyl acrylates and alkyl methacrylates are widely used because they exhibit excellent performance in coating properties such as weather resistance, water resistance, and chemical resistance. It has been.

  In such an acrylic resin emulsion, a carboxyl group is usually introduced for the purpose of ensuring stability during production of the coating material, stability during long-term storage, and the like. By sufficiently dissociating this carboxyl group, the stability of the emulsion can be enhanced. As a neutralizing agent for dissociating a carboxyl group, a highly volatile basic compound such as ammonia or a non-volatile basic compound such as sodium hydroxide is generally used. For example, Patent Document 1 describes that the pH of an acrylic resin emulsion is adjusted with a water-soluble base selected from the group consisting of ammonia, sodium hydroxide, quaternary ammonium hydroxide, and mixtures thereof. Patent Document 2 describes the use of a basic compound such as ammonia or an amine compound in the production of an acrylic resin emulsion.

JP-A-7-196974 JP 7-238201 A

However, when a highly volatile basic compound such as ammonia is used as a neutralizing agent for the acrylic resin emulsion, the compound volatilizes over time, and the stability of the emulsion may be reduced. In addition, when such an emulsion is made into a paint, an odor due to a highly volatile basic compound is generated at the time of coating, which may adversely affect the working environment.
On the other hand, if a non-volatile basic compound such as sodium hydroxide is used, the problems of stability over time and odor can be solved. However, when such a non-volatile basic compound is used, physical properties such as water resistance may be deteriorated.

  The present invention has been made in view of the above-described problems, and an object thereof is to improve physical properties such as stability, odor, and water resistance in an acrylic resin emulsion.

  As a result of intensive studies to achieve the above object, the present inventor has conceived of using an alkali metal siliconate as a basic compound in an acrylic resin emulsion, and has completed the present invention.

That is, the present invention has the following characteristics.
1. A water-dispersible resin obtained by emulsion polymerization of a monomer group containing at least a (meth) acrylic acid alkyl ester and a carboxyl group-containing polymerizable monomer, and having a pH of 7 to 10 with a basic compound, the base A water-dispersible resin comprising an alkali metal siliconate as a functional compound.
2. As a binder An aqueous paint composition comprising the water-dispersible resin described.
3. 1. The pigment volume concentration is 10 to 90%. The aqueous coating composition as described.

According to the present invention, physical properties such as stability, odor, and water resistance in an acrylic resin emulsion can be improved.
Such an acrylic resin emulsion can be suitably used as a binder for an environmentally-friendly water-based paint, an adhesive, an adhesive, and the like.

  Hereinafter, the best mode for carrying out the present invention will be described.

  The water-dispersible resin of the present invention is obtained by emulsion polymerization of a monomer group containing at least a (meth) acrylic acid alkyl ester and a carboxyl group-containing polymerizable monomer.

Among these, (meth) acrylic acid alkyl ester is a main component of the resin skeleton. In the present invention, the acrylic acid alkyl ester and the methacrylic acid alkyl ester are collectively referred to as (meth) acrylic acid alkyl ester.
Specific examples of the (meth) acrylic acid alkyl ester include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl ( (Meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, Examples include cyclohexyl (meth) acrylate, phenyl (meth) acrylate, and benzyl (meth) acrylate. These can be used alone or in combination of two or more.

  The carboxyl group-containing polymerizable monomer is a compound having both a carboxyl group and a polymerizable unsaturated bond in the molecule. Specific examples thereof include acrylic acid, methacrylic acid, crotonic acid, maleic acid or a monoalkyl ester thereof, itaconic acid or a monoalkyl ester thereof, fumaric acid or a monoalkyl ester thereof, and the like. Among these, at least one selected from acrylic acid and methacrylic acid is particularly preferable.

  The water-dispersible resin of the present invention may contain a polymerizable monomer other than the above as a constituent component, if necessary. Examples of such polymerizable monomers include amino group-containing monomers such as N-methylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and dimethylaminoethyl vinyl ether; 2-hydroxyethyl (meth) acrylate, hydroxy Hydroxyl group-containing monomers such as propyl (meth) acrylate; vinyl ester monomers such as vinyl acetate and vinyl propionate; nitrile group-containing monomers such as acrylonitrile and methacrylonitrile; styrene, 2-methylstyrene, vinyltoluene, t-butylstyrene, Aromatic monomers such as chlorostyrene, vinylanisole, vinylnaphthalene and divinylbenzene; polymers such as acrylamide, methacrylamide, maleic amide and N-methylol (meth) acrylamide Monomer group-containing monomers; epoxy group-containing monomers such as glycidyl (meth) acrylate, diglycidyl (meth) acrylate, and allyl glycidyl ether; carbonyls such as acrolein, diacetone (meth) acrylamide, vinyl methyl ketone, vinyl ethyl ketone, and vinyl butyl ketone Group-containing monomers; alkoxysilyl group-containing monomers such as vinyltrimethoxysilane, vinyltriethoxysilane, and γ- (meth) acryloyloxypropyltrimethoxysilane; vinylidene halide monomers such as vinylidene chloride and vinylidene fluoride; other, ethylene , Propylene, isoprene, butadiene, vinyl pyrrolidone, vinyl chloride, vinyl ether, vinyl ketone, vinyl amide, chloroprene and the like.

  The water-dispersible resin of the present invention can be produced by emulsion polymerization of a monomer group obtained by appropriately mixing the above polymerizable monomers. A known method may be employed as the polymerization method, and soap-free emulsion polymerization, feed emulsion polymerization, seed emulsion polymerization, etc. may be employed in addition to ordinary emulsion polymerization. During the polymerization, an emulsifier, an initiator, a dispersant, a polymerization inhibitor, a polymerization inhibitor, a buffer, a chain transfer agent, and the like can be used.

The glass transition temperature of the water dispersible resin can be adjusted by selecting the kind of the polymerizable monomer, the mixing ratio, and the like. The glass transition temperature may be appropriately set in consideration of the final use of the water-dispersible resin, but is usually about -60 to 80 ° C, preferably about -30 to 50 ° C. In addition, the glass transition temperature of water-dispersible resin can be calculated | required with the formula of Fox.
The mixing ratio of the polymerizable monomer is not particularly limited, but is usually 99.5 to 55% by weight of (meth) acrylic acid alkyl ester, 0.5 to 20% by weight of carboxyl group-containing polymerizable monomer, and other polymerizable monomer 0. -44.5 parts by weight.

  In the water-dispersible resin of the present invention, the pH is adjusted to 7 to 10 with a basic compound. By adjusting the pH within such a range, the carboxyl group derived from the carboxyl group-containing polymerizable monomer is dissociated, and the stability of the water-dispersible resin can be enhanced.

  In the present invention, an alkali metal siliconate is used as the basic compound. By using such an alkali metal siliconate, various problems such as destabilization of the emulsion, generation of odor from the emulsion, reduction of water resistance of the formed coating film when only ordinary volatile bases or non-volatile bases are used. The problem can be improved.

The alkali metal siliconate in the present invention is a compound represented by R ¹ aSi (OR ² ) b (OM) c. [Wherein, a is an integer of 0 or more (preferably 1), b is an integer of 0 or more (preferably 2), c is an integer of 1 or more (preferably 1), and satisfies a + b + c = 4. R ¹ may be the same or different and represents a hydrocarbon group. R ² may be the same or different and represents a hydrogen atom or a hydrocarbon group. M may be the same or different and represents an alkali metal. ]

Examples of R ¹ include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, isopentyl group, neopentyl group, t-pentyl group, and n-hexyl. Group, n-heptyl group, n-octyl group, isooctyl group, 2,2,4-trimethylpentyl group, n-nonyl group, n-decyl group, n-dodecyl group, n-octadecyl group, cyclopentyl group, cyclohexyl group , Cycloheptyl group, methylcyclohexyl group, phenyl group, naphthyl group, anthryl group, phenanthryl group, tolyl group, xylyl group, ethylphenyl group, benzyl group, phenylethyl group and the like. Among these, a methyl group, an ethyl group, and a propyl group are preferable, and a methyl group is particularly preferable.
Examples of R ² include a hydrogen atom and the same group as R ¹ . Among these, a hydrogen atom, a methyl group, and an ethyl group are preferable, and a hydrogen atom is particularly preferable.
Examples of M include Li, Na, K and the like, and Na is particularly preferable.

The mixing amount of the alkali metal siliconate may be within the range where the pH of the water dispersible resin is 7 to 10, but is usually 0.01 to 10 parts by weight, preferably 0 with respect to 100 parts by weight of the total amount of the monomer group. 0.05 to 5 parts by weight. With such a mixing amount, sufficient effects can be obtained in the stability of the emulsion, the water resistance of the formed coating film, and the like.
The timing of mixing the alkali metal siliconate is not particularly limited, and may be any before, during, or after polymerization of the water-dispersible resin. When producing a water-based paint with a water-dispersible resin, it can also be mixed at the time of paint production.

  Moreover, a normal basic compound can also be used with an alkali metal siliconate within the range which does not inhibit the effect of this invention. Examples of such basic compounds include ammonia, monoethylamine, diethylamine, triethylamine, isopropylamine, diisopropylamine, aminoethanol, 1-amino-2-propanol, 2-amino-2-methyl-1-propanol, 2 -(Methylamino) -2-methyl-1-propanol, N, N-dimethylethanolamine, N- (2-aminoethyl) ethanolamine, N-methylethanolamine, sodium hydroxide and the like can be mentioned.

  The water-dispersible resin of the present invention can be used as a binder for water-based paints. In particular, the water-dispersible resin of the present invention can exhibit excellent stability even when pigments are mixed and mechanically stirred. Therefore, it can be suitably used not only for a glossy type paint with a small amount of pigment but also for a matte type paint (including 3 minute gloss, 5 part gloss, etc.) with a large amount of pigment. The ratio of the water-dispersible resin and the pigment can be expressed by the pigment volume concentration, and the pigment volume concentration is usually about 10 to 90%. Specifically, the glossy type pigment volume concentration is about 10 to 30%, and the matte type pigment volume concentration is about 30 to 90%.

  As the pigment, those that can be generally blended into a paint can be used. For example, titanium oxide, zinc oxide, carbon black, lamp black, bone black, graphite, black iron oxide, copper chrome black, cobalt black, copper manganese iron black, brown, molybdate orange, permanent red, permanent carmine, anthraquinone red, Perylene red, quinacridone red, yellow iron oxide, titanium yellow, first yellow, benzimidazolone yellow, chrome green, cobalt green, phthalocyanine green, ultramarine, bitumen, cobalt blue, phthalocyanine blue, quinacridone violet, dioxazine violet, heavy carbonate Calcium, precipitated calcium carbonate, kaolin, talc, clay, porcelain clay, china clay, barium sulfate, barium carbonate, quartz sand, quartzite, diatomaceous earth, oxidation Aluminum, resin beads, aluminum pigments, pearl pigments and the like, can be used one or two or more thereof.

When producing a water-based paint, in addition to the above-mentioned components, components that can be used in ordinary paints can also be mixed. Examples of such components include aggregates, fibers, thickeners, film-forming aids, leveling agents, wetting agents, plasticizers, antifreezing agents, antiseptics, antifungal agents, algaeproofing agents, antibacterial agents, Examples thereof include a dispersant, an antifoaming agent, an adsorbent, an ultraviolet absorber, an antioxidant, a light stabilizer, a catalyst, and a crosslinking agent.
Among these, when a film-forming auxiliary or other volatile organic compound is mixed, the content is preferably less than 5% by weight, more preferably less than 1% by weight in the paint. If the volatile organic compound such as a film-forming aid has such a low content, it is preferable as an environmentally-friendly water-based paint, particularly as a paint for building interiors.

  Examples are given below to clarify the features of the present invention.

(Synthesis Example 1)
A reaction vessel was charged with 50 parts by weight of deionized water, and the temperature was raised to 70 ° C. while stirring and nitrogen replacement. To this, separately prepared emulsion monomer (62 parts by weight of styrene, methyl ester in an aqueous solution in which 3 parts by weight of an anionic emulsifier, 6 parts by weight of a nonionic emulsifier, and 0.9 parts by weight of ammonium persulfate were dissolved in 250 parts by weight of deionized water) 55 parts by weight of methacrylate, 170 parts by weight of 2-ethylhexyl acrylate, 9 parts by weight of acrylic acid, and 4 parts by weight of acrylamide were continuously added dropwise over 3 hours. After completion of the dropping, the mixture was aged for 3 hours, cooled to 30 ° C., and then added 9 parts by weight of a 30% by weight sodium methylsiliconate solution as a basic compound to adjust the pH to 8.5. Obtained.

(Synthesis Example 2)
A synthetic resin emulsion 2 was obtained in the same manner as in Synthesis Example 1 except that the pH was adjusted to 8.5 using 25% by weight aqueous ammonia as a basic compound instead of the 30% by weight sodium methyl siliconate solution. .

(Synthesis Example 3)
A synthetic resin emulsion 3 was obtained in the same manner as in Synthesis Example 1 except that the pH was adjusted to 8.5 using a 10% aqueous sodium hydroxide solution as the basic compound instead of the 30% by weight sodium methyl siliconate solution. It was.

(Manufacture of water-based paint)
200 parts by weight of the synthetic resin emulsion 1 is charged in a container equipped with a stirring blade, and 5 parts by weight of an anionic dispersant, 130 parts by weight of heavy calcium carbonate, 200 parts by weight of a titanium oxide 65% by weight dispersion, and a urethane thickener. 1.5 parts by weight of an agent, 2 parts by weight of a silicone-based antifoaming agent, 2 parts by weight of a carbon black 24% by weight dispersion, and 8 parts by weight of an iron oxide 45% by weight dispersion were sequentially added and mixed to produce an aqueous paint 1. . The pigment volume concentration of the water-based paint 1 is 45%.
Next, a synthetic resin emulsion 2 was used in place of the synthetic resin emulsion 1, and an aqueous paint 2 was produced in the same manner as described above. Moreover, it replaced with the synthetic resin emulsion 1, and manufactured the water-based coating material 3 using the synthetic resin emulsion 3. FIG.
The following tests were performed on the obtained water-based paint. The test results are shown in Table 1.

(1) Storage stability test About each water-based paint, after measuring a viscosity with a BH type viscometer (rotation speed 20rpm, measurement temperature 23 degreeC), it sealed in a 250cc container, and fixed period (30 Days). The coating after storage was allowed to cool in a standard state (temperature 23 ° C., humidity 50%), and then the viscosity was measured with a BH viscometer to examine the change with respect to the initial viscosity. The evaluation criteria are as follows.
A: Viscosity change is less than 10% B: Viscosity change is 10% or more and less than 30% Δ: Viscosity change is 30% or more and less than 50%

(2) Odor The odor generated from each water-based paint was evaluated by a sensory test. The evaluation criteria are as follows.
○: Feels almost no odor ×: Feels odor remarkably

(3) Water resistance test Each water-based paint was spray-coated at a coating amount of 300 g / m ² on a 150 × 60 × 6 mm slate plate previously coated with a sealer, and cured in a standard state for 14 days. After measuring the initial hue (L ^* ₁ , a ^* ₁ , b ^* ₁ ) of the obtained specimen, the specimen was immersed in water at 23 ° C. for 96 hours. After pulling up the specimen and leaving it in the standard state for 2 hours, the hue (L ^* ₂ , a ^* ₂ , b ^* ₂ ) of the specimen was measured, and the color difference (ΔE) before and after immersion in water was calculated according to the following formula. .
_{^{<Equation> △ E = {(L *}} 2 -L * 1) 2 + (a * 2 -a * 1) 2 + (b * 2 -b * 1) 2} 0.5
The evaluation criteria are as follows.
○: Less than ΔE0.5 Δ: ΔE 0.5 or more and less than 1.0 ×: ΔE 1.0 or more

(Table 1)
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| Water-based paint 1 | Water-based paint 2 | Water-based paint 3 |
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Storage stability ｜ ◎ ｜ ○ ｜ ◎ ｜
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Odor | ○ | | × | ○ |
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Water resistance ｜ ○ ｜ ○ ｜ × ｜
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Claims (3)

  A water-dispersible resin obtained by emulsion polymerization of a monomer group containing at least a (meth) acrylic acid alkyl ester and a carboxyl group-containing polymerizable monomer, and having a pH of 7 to 10 with a basic compound, the base A water-dispersible resin comprising an alkali metal siliconate as a functional compound.   An aqueous coating composition comprising the water-dispersible resin according to claim 1 as a binder.   The aqueous coating composition according to claim 2, wherein the pigment volume concentration is 10 to 90%.