JPH07310041A - Pigment dispersion paste and water-based coating composition containing the same - Google Patents

Abstract

(57) [Summary] [Purpose] Contains titanium dioxide and has excellent pigment dispersibility.
An aqueous coating composition having excellent gloss and weather resistance is also obtained. Constitution: 0.1 to 10 parts by weight of a resin for dispersion in terms of solid content relative to 100 parts by weight of titanium dioxide, the resin for dispersion contains a hindered amine-based monomer having a polymerizable unsaturated bond in an amount of 5 to 5% of all monomers. It is a polymer obtained by copolymerizing 30% by weight, and is characterized by mixing an emulsion resin with a pigment-dispersed paste having an acid value of 60 to 250 mgKOH / g and a number average molecular weight of 3,000 to 10,000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pigment dispersion paste in which titanium dioxide is dispersed and an aqueous coating composition containing the same, which is excellent in pigment dispersibility and suppresses photocatalytic deterioration of a coating film by titanium dioxide. The present invention relates to a pigment-dispersed paste that can be used and an aqueous coating composition containing the same.

[0002]

BACKGROUND OF THE INVENTION Conventionally, as a pigment dispersant for an aqueous coating composition, a naphthalenesulfonic acid formalin condensate or a copolymerization of α, β-unsaturated carboxylic acid and sodium styrenesulfonate is used. Things are used.

When these conventional pigment dispersants are used in an aqueous paint using titanium dioxide as a pigment, a certain degree of dispersion stability can be obtained, but there is a problem of poor weather resistance. In order to improve such weather resistance, a method of adding a hindered amine-based light stabilizer may be considered. However, even if such a light stabilizer is added, sufficient weather resistance could not be obtained.

The object of the present invention is to provide a pigment-dispersed paste and an aqueous coating material containing the same, which can impart excellent pigment dispersion stability and excellent weather resistance to an aqueous coating material containing titanium dioxide. To do.

[0005]

The pigment dispersion paste of the present invention contains 0.1 to 10 parts by weight of a dispersing resin as a solid content based on 100 parts by weight of titanium dioxide. A polymer obtained by copolymerizing a hindered amine-based monomer having a saturated bond in an amount of 5 to 30% by weight of all monomers, having an acid value of 60 to 250 mgKOH / g and a number average molecular weight of 3,000 to 10,000. I am trying.

The aqueous coating composition of the present invention is characterized in that the above-mentioned pigment dispersion paste of the present invention is mixed with an emulsion resin. The pigment dispersion resin of the present invention is a dispersion resin used in the pigment dispersion paste of the present invention,
It is a polymer obtained by copolymerizing a hindered amine-based monomer having a polymerizable unsaturated bond in an amount of 5 to 30% by weight of all monomers, and has an acid value of 60 to 250 mgKOH / g.
The number average molecular weight is 3,000 to 10,000.

In the present invention, as the hindered amine-based monomer having a polymerizable unsaturated bond which is copolymerized in the dispersing resin, a polymerizable unsaturated bond is bonded to a hindered amine-based compound known as a light stabilizer. It is possible to use those having a different structure.
6,6-tetramethylpiperdinyl methacrylate,
2,2,6,6-tetramethylpiperdinyl acrylate, N-methyl-2,2,6,6-tetramethylpiperdinyl methacrylate, N-methyl-2,2,6,6-
Examples include tetramethylpiperdinyl acrylate.
The hindered amine-based monomer having such a polymerizable unsaturated bond is copolymerized in an amount of 5 to 30% by weight of all monomers,
Preferably, 5 to 20% by weight is copolymerized. If the content is too small, the weather resistance will be insufficient, and if the content is too large, the water resistance and yellowing of the coating film may be deteriorated.

The acid value of the dispersing resin used in the present invention is 60.
~ 250 mg / KOH / g, more preferably 12
It is 0 to 200 mg KOH / g. If the acid value is too small, it becomes difficult to make it water-soluble, and if the acid value is too large, the viscosity of the dispersion resin solution tends to increase, and the water resistance of the coating film tends to decrease.

The number average molecular weight of the dispersing resin in the present invention is 3,000 to 10,000. If the molecular weight is too low, the water resistance of the coating film becomes poor, and if the molecular weight is too high, the viscosity of the dispersion resin solution tends to increase.

In the dispersion resin of the present invention, the carboxyl group-containing monomer can be copolymerized in order to adjust the acid value to the above-mentioned predetermined value to make it hydrophilic. As such a carboxyl group-containing monomer, α, β-monoethylenically unsaturated carboxylic acid such as maleic acid, maleic anhydride, itaconic acid, acrylic acid and methacrylic acid can be used. The content of these carboxyl group-containing monomers is preferably 10 to 35% by weight, more preferably 15 to 30% by weight, and these contents are set so as to have the above-mentioned predetermined acid value.

Further, the copolymer resin may be copolymerized with other copolymerizable vinyl monomers. By copolymerizing such a monomer, the affinity for the pigment and the weather resistance of the coating film can be improved. Examples of copolymerizable vinyl monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate. , 2-ethylhexyl (meth) acrylate, lauryl (meth)
(Meth) acrylic acid ester such as acrylate, and styrene derivative such as styrene and vinyltoluene can be mentioned. The content of such copolymerizable vinyl monomer is preferably 45 to 85% by weight. If the content is too small, the weather resistance and flexibility of the coating film may be inadequate, and if the content is too large, the solvent resistance decreases, which is not preferable.

The dispersion resin can be synthesized by solution polymerization, suspension polymerization, emulsion polymerization or the like according to a known method for producing an acrylic copolymer. It is preferably prepared by solution polymerization. For example, each component of the above-mentioned hindered amine-based monomer having a polymerizable unsaturated bond, carboxyl group-containing monomer, and other copolymerizable vinyl monomer is used in an inert solvent with a suitable polymerization catalyst for about 40 to 180. At a reaction temperature of ℃, about 1 to 1
React for 0 hours. The inert solvent used is preferably a water-soluble solvent, and specific examples thereof include cellosolve-based solvents such as ethylene glycol, ethyl cellosolve and butyl cellosolve, and propylene glycol-based solvents such as propylene glycol monomethyl ether. When a hydrophobic solvent is used, it is preferably removed by distillation (vacuum) after the reaction is completed.

The dispersing resin thus synthesized is neutralized with a basic compound such as ammonia, amine or alkali metal salt as it is or after removing the solvent, and water is added to make it water-soluble (dispersion in water). To do. The amount of the basic compound is 0.1 to 2.0 with respect to the carboxyl group in the resin.
An equivalent amount is preferable.

The pigment-dispersed paste of the present invention contains the above-mentioned resin for dispersion in a solid content of 100 parts by weight of titanium dioxide.
It can be obtained by blending to 1 to 10 parts by weight, preferably 1 to 8 parts by weight. In such blending, water can be used as a medium to prepare a pigment dispersion paste. If the blending amount of the dispersing resin with respect to titanium dioxide is too small, the dispersion stability of the pigment becomes poor, and if the blending amount is too large, the viscosity of the pigment paste increases and the water resistance of the coating film also decreases. The pigment can be dispersed by a known slurry forming method, and as a dispersing device, a homomixer, a ball mill, a roll mill, a sand grinder or the like can be used. Further, known dispersion aids (surfactants, thickeners), antifreezing agents, preservatives, antifungal agents and the like may be added as necessary.

Since the pigment dispersion paste of the present invention has a predetermined acid value and number average molecular weight, acrylic resin, alkyd resin, urethane resin, epoxy resin, etc. are emulsified and dispersed, or a surfactant and a water-soluble polymer are used. It can be mixed with an emulsion-polymerized known emulsion in an arbitrary ratio, and thus, an aqueous coating composition can be obtained.

[0016]

The dispersing resin in the present invention is a polymer containing a hindered amine monomer and having a predetermined acid value. Therefore, it has an affinity for titanium dioxide and a radical scavenging ability. It is considered that the deterioration of the coating film is promoted by the photocatalytic action on the surface of titanium dioxide as a cause of the deterioration of the weather resistance of the coating film containing titanium dioxide as a pigment. In the present invention, a dispersing resin having a radical scavenging ability is used, and since this dispersing resin exists in the vicinity of the surface of titanium dioxide, the radicals generated by the absorption of sunlight on the surface of titanium dioxide are dispersed in the dispersing resin. It is presumed that the hindered amine of the above traps and improves the weather resistance of the coating film.

Therefore, by using the pigment-dispersed paste of the present invention, it is possible to obtain a coating film from an aqueous paint which is excellent in dispersion stability and weather resistance of the pigment and as a result is excellent in gloss.

[0018]

EXAMPLES In the following, "part" means "part by weight". Examples a-1 to a-3 and Comparative examples a-4 to a-8 (dispersion
Preparation of resin for use) 50 parts of butyl cellosolve was charged into a reaction vessel, and the mixture was stirred and mixed in a nitrogen stream and heated to 120 ° C., and then Table 1
The monomer and the initiator were added dropwise at a constant rate over 3 hours at the mixing ratio shown in.

After completion of the dropping, aging is carried out for 1 hour to adjust the liquid temperature to 5
After the temperature was lowered to 0 ° C., 27 parts of triethylamine and 154 parts of water were gradually mixed to obtain PH = 8.0 and a nonvolatile content of 30.
% Of dispersion resins a-1 to a-8 were obtained.

[0020]

[Table 1]

In Table 1, the acid value of the resin solid content is 0.
It was measured by titration of a 1N / KOH solution. The number average molecular weight was measured by gel permeation chromatography. The viscosity was measured with a Gardner foam viscometer.

Examples A-1 to A-5 and Comparative Examples A-6 to
A-11 (Preparation of coating composition) In a container, 160 parts of water and 30 parts of the resin for dispersion were charged and mixed by stirring with a disper.

After the above solution became transparent, 500 parts of titanium oxide pigment R-930 (manufactured by Ishihara Sangyo Co., Ltd.) was gradually added to the paste in a uniform state while stirring with a disper. Got

To the above paste, 250 parts of glass beads having a diameter of 1.5 mm (Toshiba glass beads 503M) were added and dispersed for 30 minutes by a tabletop disperser having one impeller having a diameter of 80 mm, and then a 100 mesh stainless steel net. The glass beads were separated by filtration with to obtain a dispersion paste.

345 parts of the above dispersion paste was placed in a stainless steel container, and 655 parts of the following emulsion mixture was gradually added in about 10 minutes while stirring with a disper. [Formulation of Emulsion Mixture] Emulsion A (manufactured by Saiden Chemical Co., Ltd.) 550 parts Butyl cellosolve 60 parts 3% Hydroxyethyl cellulose solution 20 parts Dehydran-1620 (manufactured by San Nopco) 4 parts Ethylene glycol 10 parts Water 11 parts After aging, it was used as a paint for various tests.

The above emulsion A has a nonvolatile content of 5
It is a milky white heterogeneous liquid having 0%, PH = 8.0, and an average particle diameter of 0.2 μm, and has the following monomer composition. n-Butyl acrylate 50 parts 2-Ethylhexyl acrylate 30 parts Styrene 20 parts The above compounding ratios are summarized in Table 2.

The coating composition N obtained as described above
o. With respect to A-1 to A-10, weather resistance, water resistance, viscosity, and dispersibility were evaluated by the following methods. Paint, coating film test method 1) Weather resistance: Painted on a SUS304 plate to a film thickness of 40 ± 5 μm, dried at 20 ° C. and 75% relative humidity for 7 days, and then outdoors in the sunshine weatherer and Okinawa. A coating film weather resistance test was performed by exposure. The gloss retention rate was calculated from the 60-degree gloss value after the initial coating and after the test. 2) Water resistance: A slate plate is coated with a chlorinated rubber sealer, and No. A-1A to -10 paint film thickness 40 ±
It was painted to 5 microns. 20 ° C, relative humidity 7
After drying for 7 days under the condition of 5%, the film was immersed in water at 20 ° C. for 2 weeks, and the coating film was visually inspected. The case where no blistering or remarkable decrease in gloss was observed was defined as "good". 3) Dispersibility: The paint was applied to a glass plate with a 6 mil applicator and the state of the paint film was visually inspected. Those in which aggregates such as lumps (sparse particles) were observed were designated as "present", and those not observed were designated as "none". 4) Viscosity: Non-volatile content 3 in 25% butyl cellosolve aqueous solution
The dispersion resin solution adjusted to 0% was measured at 25 ° C. using a Gardner viscometer. Table 2 shows the result of evaluation as described above.

[0028]

[Table 2]

As is clear from Table 2, the coating film using the aqueous coating composition according to the present invention is excellent in weather resistance, and is also appropriate in water resistance and viscosity.

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Claims (3)

[Claims] 1. A pigment dispersion paste containing 0.1 to 10 parts by weight of a dispersing resin as a solid content based on 100 parts by weight of titanium dioxide, wherein the dispersing resin has a polymerizable unsaturated bond. It is a polymer in which 5 to 30% by weight of all monomers are copolymerized, and has an acid value of 60 to 250 mgK.
OH / g, and the number average molecular weight is 3000-10,000, The pigment dispersion paste characterized by the above-mentioned. 2. A water-based coating composition, wherein the pigment dispersion paste according to claim 1 is mixed with an emulsion resin. 3. A polymer obtained by copolymerizing a hindered amine-based monomer having a polymerizable unsaturated bond in an amount of 5 to 30% by weight of all monomers, and having an acid value of 60 to 250 mg KO.
A resin for pigment dispersion, which has a H / g and a number average molecular weight of 3,000 to 10,000.