JP5470314B2 - Water-based paint composition - Google Patents

Description

  The present invention relates to an aqueous coating composition.

  Due to growing international environmental awareness, attention has been paid to carbon dioxide emission reduction and energy saving technologies. In a building indoors, it is desired to secure sufficient illuminance even if power consumption required for illumination is suppressed. As means for realizing such an indoor environment, it is possible to increase the reflectance of light on an indoor wall surface, ceiling, or the like.

  As a paint that can enhance the reflectance of a coating film formed on a wall surface, a ceiling, or the like, for example, a paint containing a specific amount of an emulsion resin in a stucco component (Patent Document 1) has been proposed. However, even if such a paint is used, sufficient reflectance is not obtained.

  Moreover, as a technique for increasing the reflectance of the coating film, for example, a technique for forming an undercoat coating film in which a large number of bubbles generated by a foaming agent are dispersed (Patent Document 2), containing titanium dioxide and silica, and having a cell structure Examples include a technique for forming a coating film (Patent Document 3), a technique for forming a coating film containing titanium dioxide and a whisker-like white pigment (Patent Document 4), and the like. However, the use of the coating film obtained by these techniques is a reflector of a reflector such as a liquid crystal display, and has a problem that it has high gloss (gloss) and is not suitable for an interior of a building. Also, when other extender pigments are added to the coating film containing titanium dioxide in order to lower the gloss, the reflectance decreases, and a coating film that achieves both high reflectance and low gloss is achieved. It is difficult.

JP 2003-268261 A JP 2006-264120 A JP 2009-120715 A JP 2007-190792 A

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide an aqueous coating composition having a high diffuse reflectance and capable of forming a low gloss coating film. It is in.

The aqueous coating composition of the present invention contains titanium dioxide and porous calcium carbonate as a pigment, and an aqueous resin.
In a preferred embodiment, porosity of the calcium carbonate ^is 0.5cm ³ /g~2.5cm 3 / g.
In a preferred embodiment, the whiteness of the calcium carbonate is 90% to 99%.
In a preferred embodiment, the titanium dioxide is a rutile type.
In a preferred embodiment, the oil absorption of the titanium dioxide is 25 g / 100 g to 40 g / 100 g.
In preferable embodiment, the total content of the said titanium dioxide and the said calcium carbonate is 80 volume%-100 volume% with respect to the whole quantity of a pigment.
In a preferred embodiment, the volume ratio of titanium dioxide to calcium carbonate is titanium dioxide: calcium carbonate = 80: 20 to 55:45.
In a preferred embodiment, the aqueous coating composition of the present invention further comprises a color pigment.
In preferable embodiment, the content rate of the said color pigment is 0.5 mass% or less with respect to content of the said titanium dioxide.
In a preferred embodiment, the water-based coating composition has a pigment volume concentration of 40% to 70%.
In a preferred embodiment, the aqueous coating composition forms a coating film having a diffuse reflectance of 90% or more at a wavelength of 550 nm.

  ADVANTAGE OF THE INVENTION According to this invention, the water-based coating composition which can form a coating film with high diffuse reflectance and a low glossiness can be provided by including titanium dioxide and porous calcium carbonate. Since the coating film formed by the aqueous coating composition of the present invention has low gloss, it is suitable for the interior of buildings. At the same time, since the coating film can exhibit excellent diffuse reflectance, if the coating film is formed on the interior surface of a building, an effect equivalent to increasing the indoor illuminance can be obtained. Even when a low-power light source is used, sufficient indoor illumination can be provided.

A. Pigment The aqueous coating composition of the present invention contains titanium dioxide and porous calcium carbonate as a pigment.

  The aqueous coating composition of the present invention can form a coating film having high diffuse reflectance by containing titanium dioxide. Since the coating film formed by the aqueous coating composition of the present invention has a large refractive index difference between titanium dioxide having a relatively high refractive index and an aqueous resin described later, the coating film exhibits high diffuse reflectance.

  The titanium dioxide is preferably produced by a chlorine method. If titanium dioxide produced by the chlorine method is used, an aqueous coating composition capable of forming a coating film having a higher diffuse reflectance can be obtained.

  The crystal form of the titanium dioxide is preferably a rutile type. This is because rutile titanium dioxide has a high refractive index and can provide an aqueous coating composition capable of forming a coating film having a higher diffuse reflectance.

  The oil absorption amount of the titanium dioxide is preferably 25 g / 100 g to 40 g / 100 g, more preferably 30 g / 100 g to 40 g / 100 g, and particularly preferably 35 g / 100 g to 40 g / 100 g. Such an oil absorption amount of titanium dioxide can be obtained, for example, by surface-treating with alumina, silica, zircon or the like to form a surface-treated layer to increase the specific surface area. If the amount of oil absorption of titanium dioxide is in such a range, an aqueous coating composition capable of forming a coating film with high diffuse reflectance and low gloss can be obtained.

  More specifically, when the amount of oil absorption of titanium dioxide is large, the critical pigment volume concentration (CPVC) of the aqueous coating composition is lowered, and a coating film in which a large amount of air is taken in can be formed. Air reduces the average refractive index of the vehicle. Thus, the coating film which took in air shows the difference in the refractive index of titanium dioxide and the average refractive index of a vehicle, and shows a high diffuse reflectance. Also, if the amount of oil absorption of titanium dioxide is large, the surface treatment layer is thickly coated with titanium dioxide, thus preventing the titanium dioxide particles from approaching (aggregating) even if the concentration of titanium dioxide in the aqueous coating composition is high. And the distance between particles can be kept at an ideal distance. As a result, a coating film having a high diffuse reflectance can be obtained. When the amount of oil absorption is less than 25 g / 100 g, the surface treatment layer is thin and the titanium dioxide particles tend to aggregate, the effect of improving the diffuse reflectance may not be obtained, and the gloss of the coating film may be increased. On the other hand, when the oil absorption amount is larger than 40 g / 100 g, that is, when the surface treatment layer is too thick, the number of titanium dioxide particles in a certain volume is decreased, and thus the light scattering efficiency may be lowered. In addition, since the surface-treated portion is weak and easily broken, even if the amount of oil absorption is increased from 40 g / 100 g, the effect of increasing the amount of oil absorption may be difficult to obtain. Furthermore, when the amount of oil absorption is more than 40 g / 100 g, there is a possibility that crack defects may occur in the coating film. In addition, in this specification, the said oil absorption is a value obtained by measuring by the method according to JIS K-5101. Examples of such titanium dioxide include R931 (manufactured by DuPont).

  The water-based coating composition of the present invention can obtain a low gloss coating film by containing specific calcium carbonate.

The calcium carbonate is porous. Specifically, porosity of the calcium carbonate is preferably 0.5cm ³ /g~2.5cm ³ / g, more preferably from 1.0cm ³ /g~2.0cm ³ / g. Thus, if it is an aqueous coating composition containing porous calcium carbonate, a coating film in which air is taken in can be formed, and the coating film has a low average refractive index of the vehicle, and the average refractive index of the vehicle. And the difference between the refractive indexes of titanium dioxide and the titanium dioxide show a high diffuse reflectance. In addition, the aqueous coating composition of the present invention can form a coating film with very low gloss due to the porousness of calcium carbonate. Therefore, according to the aqueous coating composition of the present invention, it is possible to obtain an excellent effect of forming a coating film having low gloss and high diffuse reflectance. When the porosity of calcium carbonate is less than 0.5 cm ³ / g, the diffuse reflectance of the resulting coating film may be lowered, and the gloss of the coating film may not be sufficiently lowered. Moreover, when larger than 2.5 cm < ³ > / g, there exists a possibility that a crack defect may arise in the coating film obtained, and there exists a possibility that the storage stability of an aqueous coating composition may not be enough. The porosity can be measured by a mercury intrusion method using, for example, Pascal 240 (manufactured by Thermo Finnigan).

  Calcium carbonate having a porosity as described above has many voids and a large specific surface area as compared with calcium carbonate having a low porosity. In other words, the calcium carbonate is porous as described above, and each pore is fine. With calcium carbonate having such a structure, more air can be tackled, so that the diffuse reflectance can be improved.

BET specific surface area of the calcium carbonate is preferably at ^{10 m} 2 / g or more, more preferably not more ^{15 m} 2 / g or more, particularly preferably ^{20m 2} / ^g~50m 2 / g. Examples of the calcium carbonate include Omybrite 1300X-OM (manufactured by OMYA), Poacal N (manufactured by Calcium Shiraishi) and the like.

  The whiteness of the calcium carbonate is preferably 90% to 99%, more preferably 95% to 99%. If it is such a range, the aqueous coating material composition which can form a coating film with a high diffuse reflectance can be obtained. The whiteness can be measured by a method according to DIN (Deutsche Norman) 53163 (Ry, C / 2 °).

  The average particle diameter of the calcium carbonate is preferably 0.5 μm to 20 μm, more preferably 1 μm to 15 μm, and particularly preferably 2 μm to 10 μm. If it is such a range, the water-based coating composition which can form a highly diffuse reflectance and a low gloss coating film can be obtained.

The water-based coating composition of the present invention may further contain any appropriate coloring pigment as required. The coloring pigment, for example, chrome yellow, yellow iron oxide, iron oxide, inorganic pigments such as carbon black click; azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone-based pigments, Examples include perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments. You may use these individually or in combination of 2 or more types. The content ratio of the color pigment is preferably 0.5% by mass or less with respect to the content of the titanium dioxide.

  The water-based coating composition of the present invention may further contain other pigments as long as the effects of the present invention are not impaired. Examples of other pigments include silica; barium sulfate; alumina; whisker white pigment; magnesium carbonate; organic beads such as glass beads and acrylic beads.

  The total content of titanium dioxide and calcium carbonate is preferably 80% by volume to 100% by volume, more preferably 85% by volume to 100% by volume, and particularly preferably 90% by volume with respect to the total amount of the pigment. ~ 100% by volume. If it is such a range, the aqueous coating material composition which can form a coating film with a high diffuse reflectance can be obtained. In addition, in this specification, the total content rate of the said titanium dioxide and calcium carbonate is computed from the volume of each pigment calculated | required from the specific gravity and compounding mass of each pigment.

  The volume ratio of titanium dioxide to calcium carbonate (titanium dioxide: calcium carbonate) is preferably 80:20 to 55:45, and more preferably 75:25 to 60:40. If it is such a range, the coating film which is excellent in the balance and intensity | strength of a high diffuse reflectance and low gloss can be formed, and the aqueous coating composition excellent in storage stability can be obtained. When the volume ratio of calcium carbonate to the total volume of titanium dioxide and calcium carbonate is less than 20, the gloss of the coating film may be high, and when it is greater than 45, the storage stability of the paint may not be sufficient.

B. Aqueous resin Examples of the aqueous resin used in the aqueous coating composition of the present invention include water-soluble resins, water-dispersible resins, and emulsion resins. Among these, an emulsion resin is preferable. Any appropriate resin-based emulsion resin can be adopted as the emulsion resin. Specific examples of the emulsion resin include vinyl acetate type, vinyl acetate-acrylic type, ethylene-vinyl acetate type, acrylic-styrene type, acrylic type, epoxy type, alkyd type, acrylic-alkyd type emulsion resin and the like. Of these, acrylic emulsions are preferred.

  The acrylic emulsion is obtained, for example, by subjecting an unsaturated monomer composition containing an acrylic monomer as a main component to emulsion polymerization using an initiator in the presence of an emulsifier. Arbitrary appropriate monomers can be employ | adopted as a preferable unsaturated monomer used as a raw material for manufacturing an acrylic emulsion. Examples of the unsaturated monomer include (meth) acrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, crotonic acid and other carboxyl group-containing monomers; 2-hydroxyethyl (meth) acrylate, 2-hydroxy Hydroxyl group-containing monomers such as propyl (meth) acrylate and 2-hydroxybutyl (meth) acrylate; methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (Meth) acrylic acid ester monomers such as (meth) acrylate; divinylbenzene; diallyl phthalate; ethylene glycol di (meth) acrylate; trimethylolpropane tri (meth) acrylate; styrene, α-methylstyrene, etc. Emissions monomers; (meth) acrylamide, N- methyl (meth) acrylamide; N, N- dimethyl (meth) acrylamide; diacetone acrylamide; (meth) acrylonitrile.

  Arbitrary appropriate emulsifiers and initiators can be used as the emulsifier and initiator used in emulsion polymerization of unsaturated monomers. As the emulsifier, for example, an anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant, and a polymer surfactant can be used.

The glass transition temperature (Tg) of the emulsion resin is preferably -40 ° C to 0 ° C, more preferably -40 ° C to -10 ° C. If it is such a range, the water-based coating composition which can form the coating film excellent in coating-film physical properties, such as crack resistance and durability, can be obtained. The glass transition temperature (Tg) of the emulsion resin is calculated from the formula 1 / Tg = W ₁ / T ₁ + W ₂ / T ₂ +... W _n / T _n . In the formula, W ₁ , W ₂ ... W _n are blending mass% of each monomer (= (blending amount of each monomer / total mass of blended monomers) × 100), and T ₁ , T _{2. n} is the glass transition temperature of the homopolymer of each monomer.

C. Aqueous coating composition The aqueous coating composition of the present invention contains the pigment and the aqueous resin, and may further contain any appropriate solvent and / or other components. Since the water-based coating composition of the present invention is water-based, it can be suitably used for interior decoration of buildings with little environmental load.

  An aqueous emulsion resin can be preferably used as the aqueous resin, and water can be preferably used as the solvent.

  The pigment volume concentration (PVC; solid content conversion) in the aqueous coating composition of the present invention is preferably 40% to 70%, more preferably 45% to 65%, and particularly preferably 50% to 60%. is there. When the pigment volume concentration is less than 40%, the diffuse reflectance of the obtained coating film may not be sufficient. On the other hand, if the pigment volume concentration is greater than 70%, cracks may occur in the resulting coating film, and the storage stability of the aqueous coating composition may not be sufficient. In addition, the said pigment volume concentration shows the volume ratio of the pigment in an aqueous coating composition, and total solid content. Therefore, the above pigment volume concentration is obtained from the volume (P) of all pigments determined from the specific gravity and blending mass of each pigment, and the resin volume (R) determined from the specific gravity and blending mass of the resin contained in the emulsion resin described later. , A value calculated from the formula P / (P + R) × 100.

  The solid content of the emulsion resin in the aqueous coating composition of the present invention is preferably 10% by mass to 40% by mass, more preferably 15% by mass to 30%, based on the total solid content of the aqueous coating composition. % By mass.

  Any appropriate solvent can be adopted as the solvent depending on the application. Preferably, it is water as described above.

  Examples of the other components include a curing agent, a pigment dispersant, a surfactant, a leveling agent, a thickener, a neutralizer, an antifoaming agent, a film-forming aid, an antiseptic, an antifungal agent, an antibacterial agent, Additives usually used for coating compositions such as antifreezing agents, phosphor brighteners, silane coupling agents and the like can be mentioned. The type and amount of such other components can be appropriately selected depending on the purpose. The fluorescent whitening agent can increase the diffuse reflectance of the visible light region having a low diffuse reflectance by wavelength conversion, and can increase the diffuse reflectance of the coating film over the entire visible light region.

  Arbitrary appropriate methods can be employ | adopted as a method of manufacturing the water-based coating composition of this invention. For example, a method of kneading and dispersing the above pigment, aqueous resin, solvent and other components using an SG mill, shaker, disper, or the like can be used.

  The pigment is preferably prepared as a paste in advance and then mixed and dispersed with an aqueous resin and other components. This is because the pigment can be stably and sufficiently dispersed.

  The water-based coating composition of the present invention can be used for any appropriate article to be coated. The water-based paint composition of the present invention is, for example, a paint for interior surfaces such as a ceiling surface or a wall (inner wall) surface of a building, a building material (cross, panel, It can be used for painting of boats). Examples of the material to be coated include cement-based or gypsum-based materials such as concrete, cement mortar, gypsum boat, asbestos slate, asbestos cement calcium silicate board, CRC glass fiber reinforced concrete panel, asbestos cement hollow extruded plate, etc. Wood such as veneer board, laminated material, plywood and wood fiber board; plastic material such as vinyl chloride resin and vinyl acetate; metal material and the like.

  Any appropriate method can be adopted as a coating method of the aqueous coating composition of the present invention. A typical example is a method in which the aqueous coating composition is applied to an object and dried. Any appropriate method can be adopted as the coating method depending on the type of the object (base material) to be coated. For example, application by brush, roller, air spray, airless spray, iron or the like can be mentioned. In addition, the water-based coating composition of this invention may be apply | coated to a to-be-coated article through a primer. The application amount of the aqueous coating composition can be set to an appropriate application amount depending on the application. Any appropriate method can be adopted as the drying method. Natural drying is preferable.

  The aqueous coating composition of the present invention preferably forms a coating film having a diffuse reflectance of 90% or more at a wavelength of 550 nm, and more preferably forms a coating film having a diffuse reflectance of 95% or more at a wavelength of 550 nm. If such a coating film is formed on the interior surface of a building, the room illuminance can be increased, or sufficient room illuminance can be obtained with low power.

  The aqueous coating composition of the present invention preferably forms a coating film having a glossiness of 15 or less at an incident angle of 85 °. More preferably, a coating film having a glossiness of 10 or less at an incident angle of 85 ° is formed. If it is such a coating film, that is, a coating film with low gloss, even if it is formed on the interior surface of a building, it does not give people discomfort.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.

[Example 1]
(1) Titanium dioxide (Dupont R931; oil absorption 36 g / 100 g, a specific gravity of 3. 6) 270 g and dispersion resin (BYK Co. BYK190, solids (NV) = 40.0 wt%, solid content density 1.2 ) 20 g, tap water 250 g Calcium carbonate (OMYA, manufactured by OMYA, Omybrite 1300X-OM; whiteness 95%, porosity 1.8 cm ³ / g, specific gravity 2.7 ) SG Mill 1500w type) was dispersed by adding 300 g of glass beads to obtain a white pigment dispersion paste.

(2) Acrylic emulsion resin (Polysol 1500 manufactured by Showa Polymer Co., Ltd .; Tg = −35 ° C., solid content (NV) = 52.5 mass%, solid content specific gravity 1.2 ) 320 g to 675 g of the obtained white pigment dispersion paste. And 20 g of thickener (RM-2020NPR, manufactured by Rohm and Haas) were kneaded, and then 20 g of tap water was added to obtain an aqueous coating composition.
The obtained water-based coating composition was 45% PVC, 60% by volume of titanium dioxide in all pigments, and 40% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 60:40). It was.

[Example 2]
At the time of preparing the white pigment dispersion paste, the amount of titanium dioxide was changed to 320 g, the amount of calcium carbonate was changed to 103 g, and the amount of tap water was changed to 230 g. As a result, the amount of white pigment dispersion paste became 673 g. An aqueous coating composition was prepared in the same manner as in Example 1 except that the amount of acrylic emulsion resin added to 673 g of paste was changed to 246 g and the amount of tap water was changed to 60 g.
The obtained water-based coating composition had 52% PVC, 70% by volume of titanium dioxide in all pigments, and 30% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 70:30). It was.

[Example 3]
At the time of preparing the white pigment dispersion paste, the amount of titanium dioxide was changed to 320 g, the amount of calcium carbonate was changed to 80 g, and the amount of tap water was changed to 200 g. As a result, the amount of white pigment dispersion paste became 620 g. An aqueous coating composition was prepared in the same manner as in Example 1 except that the amount of acrylic emulsion resin added to 620 g of paste was changed to 165 g and the amount of tap water was changed to 80 g.
The obtained water-based paint composition had a PVC of 60%, a titanium dioxide content of 75% by volume in all pigments, and a calcium carbonate content of 25% by volume (that is, the volume ratio (titanium dioxide: calcium carbonate) was 75:25). It was.

[Example 4]
At the time of preparation of the white pigment dispersion paste, the amount of titanium dioxide was changed to 345 g, the amount of calcium carbonate was changed to 85 g, and the amount of tap water was changed to 240 g. 2.7 ) 38g was further blended, and as a result, the amount of white pigment dispersion paste became 728g, the amount of acrylic emulsion resin added to the white pigment dispersion paste 728g was changed to 198g, and the amount of tap water was changed to 85g. Prepared an aqueous coating composition in the same manner as in Example 1.
The obtained water-based coating composition has a PVC of 60%, a titanium dioxide content of 67.5% by volume in all pigments, and a calcium carbonate content of 22.5% by volume (that is, the volume ratio (titanium dioxide: calcium carbonate) is 75: 25).

[Example 5]
Instead of calcium carbonate (OMYArite 1300X-OM manufactured by OMYA; whiteness 95%, porosity 1.8 cm ³ / g, specific gravity 2.7 ) , calcium carbonate (Poircal N; whiteness 95%, porosity 95%, porosity) An aqueous coating composition was prepared in the same manner as in Example 2 except that 1.1 cm ³ / g and specific gravity 2.7 ) were used.
The obtained water-based coating composition had 52% PVC, 70% by volume of titanium dioxide in all pigments, and 30% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 70:30). It was.

[Example 6]
Acrylic emulsion resin (Polysol 1500 manufactured by Showa Polymer Co., Ltd .; Tg = −35 ° C., NV = 52.5%, solid content specific gravity 1.2 ) Instead of 246 g, acrylic emulsion resin (NP371 manufactured by Seiden Chemical Co., Ltd .; Tg = − 10 ° C., NV = 50 mass%, solid content specific gravity 1.2 ) 258 g was used, and the amount of tap water in the preparation of the aqueous coating composition was changed to 48 g. A product was prepared.
The obtained water-based coating composition had 52% PVC, 70% by volume of titanium dioxide in all pigments, and 30% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 70:30). It was.

[Example 7]
Color pigment paste (made by Nippon Paint Co., Ltd., trade name “Color Max W Eco Shanin Green”, concentration of color pigment in paste: 20 mass%, specific gravity of color pigment 2.0 ) 0.16 g was added except that An aqueous coating composition was prepared in the same manner as in Example 2.
The obtained water-based coating composition had 52% PVC, 70% by volume of titanium dioxide in all pigments, and 30% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 70:30). It was.

[Example 8]
Colored pigment paste (Nippon Paint Co., Ltd., trade name “Color Max W Eco Permanent Yellow”, concentration of colored pigment in paste: 25% by mass, specific gravity of colored pigment 1.6 ) Implemented except that 3.0 g was added. A water-based coating composition was prepared in the same manner as in Example 2.
The obtained water-based coating composition had 52% PVC, 70% by volume of titanium dioxide in all pigments, and 30% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 70:30). It was.

[Example 9]
Example: Color pigment paste (manufactured by Nippon Paint Co., Ltd., trade name “Color Max W Eco Ocher”, concentration of color pigment in paste: 40 mass%, specific gravity of color pigment 4.0 ) , except that 4.0 g was further added A water-based coating composition was prepared in the same manner as in No. 2.
The obtained water-based coating composition had 52% PVC, 70% by volume of titanium dioxide in all pigments, and 30% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 70:30). It was.

[Comparative Example 1]
Calcium carbonate (OMYA company Omybrite 1300X-OM; whiteness 95%, porosity 1.8 cm ³ / g, specific gravity 2.7 ) Instead of 135 g calcium carbonate (Maruo Calcium N heavy coal; whiteness 93%, (Porosity 0.1 cm ³ / g, specific gravity 2.7 ) Using 103 g, the amount of titanium dioxide at the time of white pigment dispersion paste preparation was changed to 320 g, the amount of tap water was changed to 200 g (white pigment dispersion paste 643 g), An aqueous coating composition was prepared in the same manner as in Example 1 except that the amount of the acrylic emulsion resin added to the white pigment dispersion paste was changed to 246 g and the amount of tap water was changed to 90 g.
The obtained water-based coating composition had 52% PVC, 70% by volume of titanium dioxide in all pigments, and 30% by volume of calcium carbonate (that is, the volume ratio (titanium dioxide: calcium carbonate) was 70:30). It was.

[Evaluation of coating film]
A 100 mm × 150 mm slate plate obtained by applying an aqueous transparent sealer (emulsion paint manufactured by Nippon Paint Co., Ltd.) at a coating amount of 45 g / m ² × 1 with a wool roller and leaving to dry at room temperature for 1 day was obtained. On the obtained slate plate, the aqueous coating compositions obtained in the above-mentioned Examples and Comparative Examples were applied with a wool roller at a coating amount of 120 g / m ² × 2 times, and allowed to dry at room temperature for 1 day. A film was formed. The obtained coating film was subjected to the following evaluation. The results are shown in Table 1. In Table 1, the volume ratio between titanium oxide and calcium carbonate was calculated from the respective volumes determined from the specific gravity and blending amount of titanium oxide and calcium carbonate. PVC is calculated from the formula PVC = P / (P + R) from the volume (P) of all pigments determined from the specific gravity and blending amount of each pigment and the volume (R) of resin determined from the specific gravity and blending amount of each resin Calculated from x100.
(1) Diffuse reflectance Using a spectrocolorimeter (CM-3600d manufactured by KONICA MINOLTA), the diffuse reflectance at 550 nm with barium sulfate as a standard was measured.
(2) Gloss Using a gloss meter (Multi Gloss 268 manufactured by KONICA MINOLTA), a gloss value at an incident angle of 85 ° was measured.
(3) Coating state The appearance of the coating was visually observed and evaluated according to the following criteria.
Coating film without coating film defects ... A
Coating film with coating film defects such as small cracks ... B
Coating film with large cracks ... C

[Evaluation of storage stability of aqueous coating composition]
The aqueous coating compositions obtained in the above examples and comparative examples were stored in a thermostatic chamber at 50 ° C. for 30 days, and then returned to room temperature. The viscosity of the paint before and after storage was measured with a Stormer viscometer to evaluate the storage stability of the aqueous paint composition. The results are shown in Table 1.

  As is apparent from the results shown in Table 1, the aqueous coating composition of the present invention can form a coating film with high diffuse reflectance and low gloss. Also, the increase in viscosity after the storage test was 10 KU or less, which was good.

  When such a coating film is used for the interior of a building, the diffuse reflectance is high, so that a sufficient indoor illuminance can be obtained with a small amount of power, and a comfortable indoor environment can be realized because of low gloss.

The water-based paint composition of the present invention can be suitably used for painting interior buildings and the like.

Claims (8)

Including titanium dioxide and porous calcium carbonate as a pigment, and an aqueous resin,
Porosity of the calcium carbonate is, Ri 1.0cm ³ /g~2.0cm ³ / g Der,
The average particle size of the calcium carbonate is 0.5 μm to 20 μm,
The volume ratio of the titanium dioxide and the calcium carbonate (titanium dioxide: calcium carbonate) is 80:20 to 55:45,
The pigment volume concentration is 40% to 70%.
Water-based paint composition.   The aqueous coating composition according to claim 1, wherein the whiteness of the calcium carbonate is 90% to 99%.   The aqueous coating composition according to claim 1 or 2, wherein the titanium dioxide is a rutile type.   The water-based coating composition in any one of Claim 1 to 3 whose oil absorption amount of the said titanium dioxide is 25g / 100g-40g / 100g.   The aqueous coating composition according to any one of claims 1 to 4, wherein a total content of the titanium dioxide and the calcium carbonate is 80% by volume to 100% by volume with respect to a total amount of the pigment. The aqueous coating composition according to any one of claims 1 to 5 , further comprising a color pigment. The water-based coating composition of Claim 6 whose content rate of the said color pigment is 0.5 mass% or less with respect to content of the said titanium dioxide. The aqueous coating composition according to any one of claims 1 to 7 , which forms a coating film having a diffuse reflectance of 90% or more at a wavelength of 550 nm.