JP2003192991A - Water-based coating and coated sheet obtained using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based coating containing bubbles having excellent uniformity and capable of stably existing, and a sheet having a coated layer excellent in heat insulating property and concealing property obtained by applying the same. <P>SOLUTION: The water-based coating comprises an aqueous medium and a hydrophobic pigment and has bubbles dispersed therein. Preferably, the bubbles are formed by surrounding air with the hydrophobic pigment and the aqueous medium comprises water and a polymer for forming a coating film. The coating may further contain a surface tension-modifier. Preferably, the hydrophobic pigment has an M value of 10-80 and an average primary particle size of 0.01-5 μm. The coated sheet contains a vacant space surrounded by the hydrophobic pigment inside the coated layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based coating material that contains air bubbles having a small variation in size, and the air bubbles can be stably present even after coating, and a coating obtained by applying the water-based coating material. It relates to a coated sheet in which the layers are laminated on a support.

[0002]

2. Description of the Related Art A coating layer having voids such as bubbles is generally excellent in opacity, cushioning property and heat insulating property, so that a coating film requiring concealing property and a thermosensitive coloring layer are formed. It is used for forming an intermediate layer as a heat insulating layer provided between the heat-sensitive color developing layer and the support so as to improve the sensitivity.

As an aqueous paint capable of forming a coating layer having voids such as bubbles, for example, Japanese Patent Laid-Open No. 1-275184.
No. 2, JP-A-2-131985, JP-A-2-17528
Japanese Patent Publication No. 3 proposes a paint in which a liquid containing a resin component is foamed by stirring. When the coating material foamed by stirring is applied and dried, a coating layer in which air bubbles become voids is obtained. However, since this method foams by mechanical force, the size of the formed bubbles tends to be non-uniform, and in order to increase the stability of the bubbles, only a highly viscous paint can be prepared. However, there is a problem that the coating method is limited.

Further, in Japanese Patent Laid-Open No. 269091/1990,
A paint containing a foamed polyurethane-based adhesive that applies the foamability and adhesiveness of polyurethane is disclosed. After coating and drying, this paint foams due to chemical reaction,
A coating layer in which voids are formed can be formed. However, since this paint utilizes foaming after drying, a smooth coating layer cannot be obtained, such as swelling on the surface of the finally obtained coating layer.

Japanese Unexamined Patent Publication No. 5-32052 discloses that organic and / or
Alternatively, a paint containing an inorganic pigment and a coating film-forming resin as main components and foamed by stirring has been proposed. This coating material can form a coating layer having a continuous porous structure formed as a gas escape passage due to expansion of gas in bubbles in a drying step. Also in such a manufacturing method, there are problems that the stability of the bubbles formed in the paint is poor and that the sizes of the obtained bubbles are likely to be non-uniform.

On the other hand, Japanese Patent Application Laid-Open No. 59-5093 discloses a coating material and a coating layer containing particles having a hollow structure, and a coating material is heated and then dried and expanded to form a hollow in a thermoplastic material. Proposing a method. However, the production of particles having a hollow structure is very complicated, and the high cost of the hollow particles makes it difficult to reduce the cost of the paint and the product having the coating layer formed by the paint. Further, when the hollow is formed by utilizing the expansion caused by drying, there is a problem that the size of the obtained bubbles tends to be non-uniform.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an aqueous coating material containing bubbles that are excellent in uniformity and can exist stably, and to obtain the same by coating the same. Another object of the present invention is to provide a sheet having a coating layer having excellent heat insulating properties and hiding properties.

[0008]

The water-based paint of the present invention contains an aqueous medium and a hydrophobic pigment, and has air bubbles dispersed therein.

The bubbles are preferably formed by surrounding the air with the hydrophobic pigment.

The aqueous medium contains water and a film-forming polymer.

The water-based paint of the present invention may further contain a surface tension adjusting agent, if necessary.

The hydrophobic pigment preferably has an M value of 10 to 80 and an average primary particle diameter of 0.01 to 5 μm.
Is preferred.

The mass ratio of the hydrophobic pigment to the film-forming polymer (hydrophobic pigment: film-forming polymer) is 5: 9.
It is preferably 5 to 70:30.

The coating sheet of the present invention is a coating sheet having a support and a coating layer laminated on the support, wherein the coating layer has voids surrounded by a hydrophobic pigment. have. The void size has an average diameter of 0.5 μm to 1
It is preferably 000 μm.

The M value referred to in the present specification means that about 5 ml of a mixture of water and methanol at 5 to 30 ° C. is sampled in a 10 ml test tube and the mixture is mixed with a microspatel for 1 to 2 ml.
After inserting a pigment amount of about a cup and shaking the pigment twice, vo of methanol in the mixture when the pigment starts to settle
It is a value measured as 1%.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The water-based paint of the present invention is a paint containing an aqueous medium and a hydrophobic pigment, and in which bubbles are dispersed.

The hydrophobic pigment used in the present invention includes
As long as it has hydrophobicity, pigments which are made hydrophobic by surface-treating an inorganic pigment with an organic compound, a silane compound, a fluorine compound, or the like, and hydrophobic plastic pigments can be given.

Such a hydrophobic pigment is a particle which does not have a hollow structure by itself, but it appears to be densely present so as to surround the periphery of minute size bubbles by stirring and mixing in an aqueous medium. become. That is, the pigments aggregate to form minute hollow portions in the coating material.

The term "hydrophobicity" as used in the present invention means that the M value represented by the volume percentage of methanol which begins to become wet when the content of methanol is increased in a mixed solution of water and methanol is 10 to 80. Say the degree. If the hydrophobic treatment is insufficient, the M value may not be 10 or more, and the hydrophobic pigment according to the present invention may not be obtained.

The M value is 5 to 30 ° C. in a 10 ml test tube.
About 5 ml of a mixture of water and methanol was sampled, and 1 to 2 cups of a pigment was added to the mixture with a microspatel, and the mixture was shaken twice. It is measured as the vol% of methanol in the mixture.

Examples of the inorganic pigments used as the hydrophobic pigment include silica, titanium oxide, zinc oxide, aluminum hydroxide, barium sulfate, calcium carbonate, talc, kaolin, calcined kaolin, clay, calcined clay and sericite. . As a method of rendering these inorganic pigments hydrophobic, there are a method of coating with a hydrophobic substance, a method of treating with a coupling agent or the like to modify the surface with a hydrophobic group, and the like. Examples of such a hydrophobic substance or coupling agent (hereinafter, both are collectively referred to as "surface treatment agent") include dimethyl silicone oil, cyclic silicone oil, methylphenyl silicone oil, silicone polyether copolymer, and alkoxy-modified silicone. Silicone-based polymers such as; fluoro-based compounds such as perfluoroalkyl phosphates; hydrocarbon-based polymers such as polyethylene; silicon-containing compounds such as methyl hydrogen siloxane, trimethylsiloxy silicic acid, halogenated silanes, etc. .

Examples of the plastic pigment used for the hydrophobic pigment include polystyrene particles, nylon powder, polyethylene powder, silicone resin filler, and urea formalin resin filler whose surface is made hydrophobic by a polymerization method or the like.

The average primary particle diameter of the hydrophobic pigment used in the present invention is preferably 0.01 μm or more, more preferably 0.02 μm or more. This is because a pigment having an average primary particle size smaller than 0.01 μm is difficult to handle. On the other hand, the upper limit of the average primary particle diameter is preferably 5 μm or less, more preferably 2 μm or less. This is because a pigment having an average primary particle diameter of more than 5 μm lowers the stabilizing effect of bubbles, and it may be difficult to form stable voids in the coating layer.

As the aqueous medium used in the water-based paint of the present invention, a mixture of water and a film-forming polymer is used.

As the coating film forming polymer, water-soluble resins such as polyvinyl alcohol, sodium polyacrylate, carboxymethylcellulose, polyvinylpyrrolidone, casein, alkali salts of styrene-maleic acid copolymers,
Water-dispersible resins such as polyacrylates, polyesters, styrene-butadiene-based copolymers, polyurethane resins, vinyl chloride / vinyl acetate copolymers, ethylene-vinyl acetate copolymers, etc. can be used, and they can be used alone. Good, or two or more kinds may be used together.

The mixing ratio (mass ratio) of water to the coating film forming polymer is 85:15 to 4 as water: coating film forming polymer.
It is preferably 0:60. Within these ranges, it is appropriately selected depending on the viscosity of the coating material, the surface tension of the resulting aqueous medium, and the like. In addition, the mass ratio of the hydrophobic pigment and the coating film forming polymer (hydrophobic pigment / coating film forming polymer)
Is preferably 5/95 to 70/30, and 10/90 to 7
0/30 is more preferable. If it is less than 5/95, it is difficult to form stable bubbles in the paint, and if it exceeds 70/30, the resulting water-based paint exhibits thixotropic properties, which makes it difficult to handle the water-based paint.

The content of bubbles contained in the water-based paint of the present invention can be adjusted depending on the content of the hydrophobic pigment in the paint, the kind of the hydrophobic pigment used, the combination of the hydrophobic pigment and the aqueous medium, and the like.

In the water-based paint of the present invention, the bubbles surrounded by the hydrophobic pigment are stably present, and the formed bubbles are smaller than the variation in the size of the bubbles formed by mechanical agitation or the like. Existence is stable. still,
The bubbles contained in the paint may be surrounded not only by the hydrophobic pigment alone but also by the hydrophobic pigment and the film-forming polymer.

The mechanism by which bubbles can be stably present in the water-based paint is not clear, but it is considered to be related to the affinity between the hydrophobic pigment and the aqueous medium. That is, it is considered that the hydrophobic pigment and the aqueous medium are achieved by having an appropriate affinity that is not too high and not too low. If the affinity of both is too high, the pigment will be stably dispersed at the particle level in the aqueous medium, and if the affinity of both is too low, the pigment and the aqueous medium will be completely separated. Because.

Therefore, the combination of the hydrophobic pigment and the film-forming polymer is a combination in which the hydrophobic pigment can exist so as to surround air having a minute size, in other words, the air bubbles are stably present in the water-based paint. It is preferable to select the combination to obtain. Further, since the bubble size contained in the paint depends on the combination of the hydrophobic pigment and the coating film forming polymer, depending on the size and amount of the bubbles contained in the water-based paint, the kind and amount of the hydrophobic pigment, The particle size, the type and amount of the film-forming polymer, and the combination thereof may be selected.

Here, even if desired air bubbles cannot be contained, the surface tension of the aqueous medium may be reduced depending on the kind of the film-forming polymer used in the aqueous medium or the hydrophobic pigment to be combined. By appropriately adding a surface tension adjusting agent that can be changed, it becomes possible to form bubbles and allow them to exist stably.

Examples of the surface tension adjusting agent include surfactants; lower alcohols such as methanol and ethanol; lower ketones such as acetone. As a surfactant,
For example, known surfactants such as those described in "Introduction to New Surfactants" (published by Takehiko Fujimoto, Sanyo Kasei Kogyo) can be used. Specifically, anionic surfactants such as aromatic or aliphatic carboxylic acid salts, sulfuric acid ester salts, sulfonic acid salts, and phosphoric acid ester salts; aromatic or aliphatic primary amine salts, secondary amines Cationic surfactants such as amine salts, tertiary amine salts and quaternary ammonium salts; amphoteric surfactants such as aromatic or aliphatic amino acid type and betaine type; polyoxyethylene glycol type nonionic surfactants A polyhydric alcohol type nonionic surfactant; acetylene glycol, an ethylene oxide adduct of acetylene glycol, acetylene alcohol, an ethylene oxide adduct of acetylene alcohol, and the like. These surface tension adjusting agents may be used alone or in combination of two or more as needed.

In the water-based paint of the present invention, hydrophobic pigments having different M values are used as long as the balance between the hydrophobic pigment and the aqueous medium is not impaired, that is, the formation of bubbles by the hydrophobic pigment is not impaired. , Hydrophilic pigments, wetting agents, antifoaming agents and the like may be added. Here, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined clay, etc. are hydrophilic unless surface treatment is performed to make them hydrophobic. It is a hydrophilic pigment, and some of the plastic pigments such as styrene microballs, nylon powder, polyethylene powder and urea / formalin resin filler are hydrophilic.

The aqueous paint of the present invention is produced by mixing an aqueous medium as an essential component and a hydrophobic pigment, and further, if necessary, a surface tension adjusting agent and an appropriate additive. The order of mixing these components is not particularly limited.
Also, regarding the film-forming polymer contained in the aqueous medium, it is sufficient that a predetermined amount of the film-forming polymer is contained in the state of the finally prepared coating material, and the film-forming polymer having a predetermined concentration is contained in advance. In addition to mixing as an aqueous medium,
An aqueous medium containing a portion of the film-forming polymer may be first prepared and then the film-forming polymer may be added at any suitable stage to include the required concentration of film-forming polymer. Specifically, there are a method of dispersing a hydrophobic pigment in an aqueous medium and a method of dispersing the hydrophobic pigment in a liquid containing a part of the film-forming polymer and then containing the film-forming polymer to a required concentration. . In the case of containing a surface tension adjusting agent, a liquid or water containing a part of an aqueous medium or a film-forming polymer may contain a surface tension adjusting agent in advance, and the hydrophobic pigment may be dispersed therein. After dispersing the hydrophobic pigment in the aqueous medium, a surface tension adjusting agent may be added, or after the hydrophobic pigment is dispersed in a liquid or water containing a part of the film-forming polymer, the surface tension is adjusted. A regulator may be added, and a film-forming polymer may be further added to prepare an aqueous medium having a predetermined concentration. Moreover, when an additive is contained, the additive can be added at an appropriate stage.

The water-based coating material of the present invention thus prepared has stable air bubbles. The size of bubbles in the coating material is appropriately determined according to the size and amount of the hydrophobic pigment contained, the degree of hydrophobicity of the hydrophobic pigment, and the relationship with the aqueous medium. Generally, bubbles having an average diameter of about 0.5 μm to 1000 μm are formed. The bubbles formed here are more stable than those obtained by the conventional stirring method or the like, and moreover, the variation in size is small.

The method for applying the water-based paint of the present invention is not particularly limited. The coating can be performed using a coating method that has been conventionally used, such as a blade coater, an air knife coater, a bar coater, a rod blade coater, a curtain coater, and a slot die coater.

There is no particular limitation on the material, shape, size, etc. of the support, and for example, high quality paper (acidic paper, neutral paper), medium quality paper, coated paper, art paper, cast coated paper, glassine In addition to paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, synthetic resin film and the like, various transparent supports and the like can be appropriately selected and used.

The coating amount is 1 dry weight on the support.
~ 20 g / m ² is preferred, more preferably 3-15 g
/ M ² . If it is less than 1 g / m ² , a uniform coating surface cannot be obtained, and the thickness of the coating layer to be formed becomes thin, so that the desired heat insulating effect and concealing property due to the voids cannot be obtained. On the other hand, if the amount exceeds 20 g / m ² , a large amount of energy is required for the drying step and the productivity is lowered, but the heat insulating effect and the concealing effect of the obtained coating layer are saturated, which is not economical.

The coating layer formed by coating and drying as described above has voids corresponding to bubbles contained in the coating material of the present invention. That is, in the coating layer to be formed, voids exist in the coating film-forming polymer, and the periphery of the voids is surrounded by the hydrophobic pigment. In this way, the coated sheet of the present invention can be produced.

The voids contained in the coating layer in the coating sheet of the present invention substantially correspond to the diameters of the bubbles contained in the water-based paint, and specifically, the average diameter is 0.5 μm to 1000 μm.
Is about 0.5 μm to 200 μm, and more preferably about 0.5 μm to 100 μm. 0.
If it is less than 5 μm, the effects of heat insulation, cushioning property, anti-slip property, opacity, etc., which are exhibited by having voids, are reduced, which is not preferable. On the other hand, when it is larger than 1000 μm, bubbles are easily floated and separated in the water-based paint, and it becomes difficult to obtain a uniform paint, and large bubbles may affect the smoothness of the coated surface. In addition,
The void size is a value obtained by measuring an electron micrograph with an image analyzer.

The content of voids in the coating layer according to the present invention corresponds to the content of bubbles in the water-based paint, and is specifically 25 to 95 vol%. Here, the porosity (%) in the coating layer is represented by the following formula. Porosity = (volume of coating layer−volume of solid component) / volume of coating layer × 100

The difference between the volume of the coating layer and the volume of the solid component can be determined as the difference between these by measuring the area of the coating layer and the area of the solid component from the photograph of the cross section of the obtained coating layer.

In the coating layer obtained by applying the coating material of the present invention, a large number of voids (closed cells) having a small variation in size are dispersed based on the bubbles contained in the coating material.
The hydrophobic pigment is present around the void so as to surround the void. The coating layer having such voids has excellent concealing properties and thermal insulation properties, and the coated surface has smoothness similar to that of a coating type having no voids. Therefore, the coating layer obtained by applying the coating composition of the present invention, as a coating film when the hiding property is required, as the receiving layer of the thermal transfer paper,
Alternatively, it is formed on the support as a heat-insulating layer formed between the support and the heat-sensitive color-developing layer so as to improve the sensitivity of the heat-sensitive color-developing layer, or as a smoothing layer when the surface is smoothed. be able to.

[0044]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention.

[Preparation of Water-Based Paint and Production of Coating Layer] Paint No. 1 Acrylic emulsion containing acrylic resin as a film-forming polymer (trade name: NFA-830, solid content concentration 4
An aqueous medium was prepared by adding 377 g of water to 667 g of 0%, manufactured by Teikoku Kagaku. While stirring this aqueous medium with a Cowles stirrer, hydrophobic silica (trade name: Nipseal SS-50F, M value 60, average primary particle diameter 0.02 μ)
m, manufactured by Nippon Silica Co., Ltd.). 100 g of the obtained dispersion liquid was collected, and a liquid defoaming device MS-SNB350
Defoaming treatment condition CH14 using N (Matsuo Sangyo Co., Ltd.)
A defoaming treatment was carried out in (Step 1: Revolution 7; no rotation for 6 minutes; Step 2: Revolution 9, rotation 7 for 3 minutes for 2 minutes) to prepare an aqueous paint. As a support, basis weight 50 g /
Using high-quality paper of m ² , one side of this support was coated with the previously prepared coating material so that the coating amount after drying was 10 g / m ^2, and then dried with hot air at 80 ° C. It was

Paint No. 2 to 10, 12, 13 An aqueous paint was prepared in the same manner as in Example 1 except that the type and amount of the polymer component in the aqueous medium and the type and amount of the hydrophobic pigment were changed as shown in Table 1. Paint No. A coating layer was prepared in the same manner as in 1.

Paint No. 11 Paint No. Instead of the hydrophobic silica of No. 1, paint No. 1 was used, except that light calcium carbonate (trade name: Brilliant 15, M value 0, manufactured by Shiraishi Industry Co., Ltd.) was used and no defoaming treatment was performed.
A water-based paint was prepared in the same manner as in No. 1, and a coating layer was prepared using this. However, the coating amount was 40 g / m ² .

The following compounds were used as the compounds in Table 1.

Acrylic 1: acrylic emulsion "NFA-830" manufactured by Teikoku Kagaku KK, solid content concentration 40% Acrylic 2: acrylic emulsion "AE" manufactured by JSR
-872 ", solid content concentration 51% SBR1: styrene butadiene latex" L-1571 "manufactured by Asahi Kasei Corporation, solid content concentration 48% SBR2: styrene butadiene latex" PT1051 "manufactured by Zeon Corporation, solid content concentration 48% SBR3 : Styrene butadiene latex "Bonron S-1120" manufactured by Mitsui Chemicals, solid content concentration 45% Hydrophobic silica 1: "Nipseal SS" manufactured by Nippon Silica Co., Ltd.
-50F "Hydrophobic silica 2: Nipseal SS made by Nippon Silica Co., Ltd.
-70 "Hydrophobic silica 3:" Nipseal SS "manufactured by Nihon Silica Co., Ltd.
-50 "Silicone resin: GM Toshiba Silicone's" Tospearl 120 "Hydrophobic titanium oxide: Titanium oxide surface-treated with methyl hydrogen polysiloxane (titanium oxide: methyl hydrogen polysiloxane = 100: 2) Hydrophobic Zinc oxide: Zinc oxide surface-treated with methyl hydrogen polysiloxane (zinc oxide: methyl hydrogen polysiloxane = 100: 3) Hydrophobic calcium carbonate: "Calfine 100" manufactured by Maruo Calcium Co., Ltd. Calcined kaolin: EC company Made "Ansilex", oil absorption 90ml / 100g Silica: "Mizukasil P527" manufactured by Mizusawa Chemical Co., Ltd. Calcium carbonate: "Brilliant 15" manufactured by Shiraishi Kogyo Co., Ltd. Hydrophobic silica 4: "P802Y" manufactured by Mizusawa Chemical Co., Ltd.
Silica treated with polyethylene Hydrophobic treated silica 5: "NP-8" manufactured by Mizusawa Chemical Co., Ltd., with silica treated with paraffin

[Measurement and Evaluation Method] The above-prepared coating material,
The following items were measured and evaluated about the obtained coating layer. The results are shown in Table 1.

(1) About 5 ml of a mixture of water and methanol at 5 to 30 ° C. was sampled in a test tube having an M value of 10 ml, and 1 to 2 cups of pigment was added to the mixture with a microspatel. After shaking twice, it was measured as the vol% of methanol in the mixture when the pigment started to settle.

(2) Surface tension (mN / m) The surface tension of the aqueous medium is measured by the Dunois surface tension meter (TOMB).
It was measured at 25 ° C. using O BORL).

(3) Average Primary Particle Diameter of Pigment The obtained coating layer was cut by freeze fracture, and the major axis and minor axis of the pigment were measured based on the electron micrograph of the cross section,
The average value was defined as the average primary particle diameter (μm) of the pigment.

(4) Bubbles in water-based paint The prepared paint was observed with an optical microscope, and when the bubbles could be confirmed, the mark was "◯", and when the bubbles could not be confirmed, the mark was "x".

(5) Void size (μm), variation (μm), porosity (%) in the coating layer The coating layer was cut by freeze fracturing, and the cross section was observed with an electron microscope to find voids. In this case, the major axis and minor axis of each void were measured based on the electron micrograph, and the average value was taken as the void size (μm). The range (μm) from the maximum diameter to the minimum diameter of the observed average void diameter was determined, and this was taken as the variation of the void diameter. In the field of view of the micrograph, the sum of the areas of the voids was calculated, and the void ratio (%) was calculated by the following formula. Porosity = total void area / field-of-view area × 100 When a void is desired to be observed, it is indicated by “−”.

(6) Opacity The opacity was measured according to the method A of JIS P8138. That is, a coating layer was formed on a backing white plate, its reflectance (R _0.80 ) was measured, then a coating layer was formed on the backing black plate, and its reflectance (R ₀ ) was measured. The measurement was performed, and the opacity (C) was calculated by the following formula. C (%) = R ₀ / R _0.80 × 100 The larger the opacity (C%), the higher the hiding property.

[0057]

[Table 1]

From Table 1, the water-based paint of the present invention (No. 1) is prepared by mixing a hydrophobic pigment having an M value of 10 or more in an aqueous medium.
All of the above have voids. No. An optical micrograph of the paint of No. 4 is shown in FIG. It was possible to observe that the hydrophobic pigment surrounded the spherical shape corresponding to the bubbles. Further, the coating layers obtained from these water-based paints all had voids. No. An electron micrograph of the coating layer of No. 4 is shown in FIG. From FIG. 2A, it can be seen that there are many voids having substantially the same size. Further, it can be seen from FIG. 2B that the hydrophobic pigment particles are densely present around each void.

On the other hand, it was not possible to observe bubbles in the water-based paints (Nos. 9 and 10) using pigments having no hydrophobicity. Also, there were no voids in the coating layer. Further, even with hydrophobically treated silica, no bubbles were formed in the paint when the M value was less than 10 (No. 12, 13).

Paint No. foamed by mechanical stirring 1
In No. 1, air bubbles were present even in the case of using the hydrophilic pigment, and voids were also present in the coating layer. However, FIG.
As can be seen from (a), the sizes of the voids in the coating layer are different, and it is understood that the variations in the void size are large.
Further, from FIG. 3 (b), although some pigment was present around the voids, the pigments were scattered to the same extent as the coating film portion other than the voids. As in No. 4, no clustering around the voids was observed.

No. 1, 6, 7 and No. Comparing 12 and 13, even though the pigment content is the same,
No. The masking properties of 1, 6 and 7 were higher.

[0062]

EFFECTS OF THE INVENTION The water-based coating composition of the present invention provides a coating layer which stably contains air bubbles of substantially uniform size and does not foam by mechanical stirring or heating, and which has voids corresponding thereto. You can Further, the water-based paint of the present invention can form bubbles due to the combination of the aqueous medium and the hydrophobic pigment, so that it is cheaper than the case of using hollow particles,
A paint containing bubbles can be provided.

The coating sheet of the present invention has a coating layer in which a large number of microscopic voids having a small variation in size are present, and therefore, compared with a nonvoided coating material containing the same amount of pigment. It has excellent concealing properties, has a heat insulating effect, and has a smooth coated surface.

[Brief description of drawings]

FIG. 1 shows a water-based paint No. prepared in Examples. 4 is an optical microscope photograph of No. 4 (magnification: 800 times).

FIG. 2 shows the water-based paint No. prepared in the example. 4 is an electron micrograph of the coating layer formed using No. 4, and (a) is 35
00x and (b) are taken at 10000x.

FIG. 3 shows the water-based paint No. prepared in the example. 11 is an electron micrograph of a coating layer formed by using No. 11, (a) is 5
00x and (b) are taken at 3500x.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09C 3/10 C09C 3/10 3/12 3/12 F term (reference) 4D075 CA03 CA17 CB07 CB21 DA04 DB18 DB20 DB20 DB36 DC27 EA06 EA13 EB07 EB12 EB13 EB14 EB15 EB19 EB20 EB22 EB35 EB38 EB56 EC11 EC33 EC35 EC51 EC53 EC54 4J037 AA08 CB23 CC12 CC14 CC28 4J038 BA041 NA041 CD061 NA031 AG71 AG94 AG98 AG99 AH02 AH37 AJ04 AJ10 BE08 EA16 EA19 EA32 FA12 FA30 GA12 GA19

Claims (9)

[Claims] 1. A water-based paint containing an aqueous medium and a hydrophobic pigment, wherein air bubbles are dispersed. 2. The water-based paint according to claim 1, wherein the bubbles are formed by surrounding the air with the hydrophobic pigment. 3. The water-based paint according to claim 1, wherein the aqueous medium contains water and a film-forming polymer. 4. The water-based coating composition according to claim 3, further comprising a surface tension adjusting agent. 5. The water-based paint according to claim 1, wherein the hydrophobic pigment has an M value of 10 to 80. 6. The average primary particle diameter of the hydrophobic pigment is 0.
It is 01-5 micrometers, The water-based coating material in any one of Claims 1-5. 7. The mass ratio of the hydrophobic pigment to the coating film-forming polymer (hydrophobic pigment: coating film-forming polymer) is 5:
It is 95-70: 30, The water-based paint in any one of Claims 1-6. 8. A coating sheet having a support and a coating layer laminated on the support, wherein the coating layer has a void surrounded by a hydrophobic pigment inside the coating layer. Engineering sheet. 9. The void size has an average diameter of 0.5 μm to
The coated sheet according to claim 8, which has a thickness of 1000 μm.