JP2020193251A - Water-based coating composition for topcoat of metal siding, and metal siding - Google Patents

Abstract

To provide techniques of forming a topcoat for metal siding excellent in resistance to freezing damage.SOLUTION: A water-based coating composition for a topcoat of metal siding comprises a (meth)acrylic acid ester based polymer. The (meth)acrylic acid ester based polymer has one or more types of constitutional units derived from (meth)acrylic acid ester based monomers whose compatibility parameter based on the Fedors estimation method is 9.4 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a water-based coating composition for a top coat of metal siding, metal siding.

Conventionally, ceramic siding and metal siding have been known as siding (for example, Patent Documents 1 and 2).

In recent years, such siding has been decorated by, for example, roll printing or inkjet printing (formation of a decorative layer) in order to improve the design, and a clear paint has been applied to protect the decorative layer and improve weather resistance. The coating used (formation of the top coat layer) is often performed. In addition, due to consideration for the natural environment and working environment and various regulations, the switch from solvent-based paints to water-based paints is progressing, and it is very common for such clear paints to be water-based.

Since siding is generally used outdoors, it is exposed to wind and rain and is therefore susceptible to water. Among them, in ceramic siding, cement and fibrous raw materials (for example, wood fibers) that easily absorb moisture and moisture are used as raw materials. For this reason, water easily penetrates into the base material of the ceramic siding, and the water repeatedly freezes and thawes (expansions and contractions), which affects the decorative layer and the top coat layer provided on the ceramic siding. It has been known that these coating films are cracked or peeled off from the substrate (for example, Patent Documents 1 and 2). Here, such a phenomenon is called frost damage.

On the other hand, in metal siding, the base material is metal in the first place, and it is unlikely that water permeates the base material as in ceramic siding. Since the decorative layer and the top coat layer are provided on the metal base material, it has been considered that the frost damage phenomenon that occurs in ceramic siding is unlikely to occur (for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2003-136630 Japanese Unexamined Patent Publication No. 2003-1749

However, the present inventors have discovered that the frost damage phenomenon also occurs in metal siding in cold regions such as cold regions. Therefore, it has been desired to solve such a problem. As far as the inventors know, it is considered that the occurrence of the frost damage phenomenon even in metal siding has not been recognized as a problem in the first place.

The present inventors inferred the reason why the frost damage phenomenon occurs even in metal siding as follows.

One of the purposes of forming a coating film with a paint, whether it is a solvent-based paint or a water-based paint, is to prevent and protect water from penetrating into a base material or an undercoat layer. However, in general, water-based paints use raw materials such as emulsifiers that are easily compatible with water, so water easily penetrates into the paint film, albeit in a small amount, compared to solvent-based paints. It seems that there is a tendency. However, in the case of metal siding in which a top coat layer is provided using water-based paint, even if some moisture permeates into the coating film due to wind and rain, for example, in warm regions, the moisture immediately increases due to the rise in temperature. Is removed (evaporates) from the coating film, so it is probable that such moisture did not cause any problems.

However, in areas with low temperatures such as cold regions, the temperature does not rise so much, especially in winter, so it is thought that the water that has once penetrated into the coating film cannot escape. Then, it is considered that such water is repeatedly frozen and thawed (expansion and contraction) as the outside air temperature changes, or is left in a frozen state (expanded state) in the coating film for a long period of time. As a result, even in metal siding, which has not been considered to cause a frost damage phenomenon, it is considered that a "freezing damage phenomenon" such as whitening of the coating film or peeling from the base material has occurred.

As a result of diligent studies based on the above inferences, the present inventors have completed the inventions provided below and solved the above problems.

The present invention has been made to solve the above-mentioned problems, and can be realized as the following forms.

(1) According to one embodiment of the present invention, a water-based coating composition for a top coat of metal siding is provided. The water-based coating composition for a top coat of this metal siding contains a (meth) acrylic acid ester-based polymer, and the (meth) acrylic acid ester-based polymer has a compatibility parameter using the Fedors estimation method (hereinafter, It has one or more structural units derived from (meth) acrylic acid ester-based monomers having a (simply also referred to as “SP value”) of 9.4 or less. According to the water-based coating composition for a top coat of a metal siding of this form, a top coat for a metal siding having excellent frost damage resistance can be formed.

(2) In the above-mentioned water-based coating composition for a top coat of metal siding, the (meth) acrylic acid ester-based monomer contains at least one of t-butyl methacrylate and 2-ethylhexyl (meth) acrylate. It may be included. According to the water-based coating composition for a top coat of a metal siding of this form, a top coat for a metal siding having more excellent frost damage resistance can be formed.

The present invention can also be realized in various forms other than the water-based coating composition for a top coat of metal siding. For example, it can be realized in the form of metal siding in which a coating layer is formed by using a water-based coating composition for a top coat of metal siding.

According to the present invention, for a top coat capable of forming a top coat having excellent frost damage resistance, that is, it exhibits sufficient performance against metal siding even in a region where the temperature changes drastically such as a cold region. A water-based coating composition is provided. Further, according to the present invention, a metal siding having excellent frost damage resistance is provided.

The figure explaining the calculation method of the SP value of a monomer.

The disclosure herein relates to water-based coating compositions for topcoats of metal siding. The water-based coating composition for a top coat of metal siding in the present embodiment contains a (meth) acrylic acid ester-based polymer, and the (meth) acrylic acid ester-based polymer has an SP value of 9.4 or less (meth). ) It has one or more structural units derived from an acrylic ester-based monomer. In addition, in this specification, "(meth) acrylic" means methacrylic or acrylic. Further, in the present specification, the “top coat” means a layer covering a colored layer of metal siding. In addition, another layer such as a layer formed by a surface modifier may be formed on the top coat. Further, another layer may be formed between the colored layer and the top coat.

According to the water-based coating composition for a top coat of metal siding in the present embodiment, it is possible to form a top coat for metal siding having excellent frost damage resistance. Hereinafter, an estimation mechanism in which the water-based coating composition for a top coat of metal siding in the present embodiment is excellent in frost damage resistance will be described.

The water-based coating composition for a top coat of metal siding in the present embodiment contains a (meth) acrylic acid ester-based polymer. This (meth) acrylic acid ester-based polymer has one or more structural units derived from the (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less. That is, this (meth) acrylic acid ester-based polymer contains a structural unit derived from a monomer having a high hydrophobicity. Therefore, it is considered that the top coat formed by using the water-based coating composition of the present embodiment can make it difficult for water to permeate into the coating film even when exposed to wind and rain outdoors. Further, even if water permeates into the coating film, it is considered that the water is easily removed.

From the above points, according to the water-based coating composition for the top coat of the metal siding of the present embodiment, it is difficult for water to permeate into the coating film, and as a result of facilitating the removal of water in the coating film, frost damage resistance is improved. It is thought that it will improve.

Hereinafter, the water-based coating composition for the top coat of the metal siding of the present embodiment and the method for producing the same will be described in detail.

A. (Meta) Acrylic Ester Polymer The water-based coating composition for a top coat of metal siding in the present embodiment contains a (meth) acrylic ester polymer. As used herein, the term "(meth) acrylic acid ester-based polymer" means a polymer containing a structural unit derived from at least one monomer of (meth) acrylic acid and (meth) acrylic acid ester. To do. Therefore, the (meth) acrylic acid ester-based polymer may partially contain structural units derived from monomers other than (meth) acrylic acid and (meth) acrylic acid ester. However, due to commercial availability, the (meth) acrylic acid ester-based polymer is formed by structural units derived from at least one monomer of (meth) acrylic acid and (meth) acrylic acid ester. Is preferable. Further, the water-based coating composition for a top coat of metal siding in the present embodiment may contain a polymer other than the (meth) acrylic acid ester-based polymer.

The (meth) acrylic acid ester-based polymer is, for example, a homopolymer or copolymer of the (meth) acrylic acid ester-based monomer, or an ethylenically unsaturated product with the (meth) acrylic acid ester-based monomer. It may be a copolymer with a monomer or the like. The other ethylenically unsaturated monomer is not particularly limited, but for example, (i) a styrene-based monomer such as styrene or α-methylstyrene, a vinyl-based monomer such as vinyl acetate or vinyl propionate, and the like. (Ii) Examples thereof include unsaturated carboxylic acid monomers such as itaconic acid, maleic acid, and fumaric acid.

The (meth) acrylic acid ester-based polymer of the present embodiment has one or more structural units derived from the (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less. Here, in the calculation of the SP value in the present specification, "RF Fedors: Polym. Eng. Sci., 14 [2], 147-154 (1974)" was referred to. More specifically, when the aggregation energy (cal / mol) is E and the molecular capacity (cm ³ / mol) is V, the SP value can be expressed by (ΣE / ΣV) ^1/2 . Table 1 shows the aggregation energy and the molar molecular weight value of each atomic group proposed by Fedors. Table 2 shows the SP values of each (meth) acrylic acid ester-based monomer.

FIG. 1 is a diagram illustrating a method for calculating the SP value of a monomer. In FIG. 1, methyl methacrylate will be described as an example. The left side of FIG. 1 shows the state of the monomer, and the right side of FIG. 1 shows the state of the polymer. In the present specification, the SP value of the monomer is calculated by counting the atomic groups in the state of the polymer.

In the case of methyl methacrylate shown in FIG. 1, the SP value of methyl methacrylate is calculated by counting the atomic groups of the repeating units of the polymer. Specifically, the repeating units of the methyl methacrylate polymer are two "-CH ₃ ", one "-CH _2- ", one "> C <", and "-CO ₂ ". -”Has one. Therefore, ΣE is 8080 and ΣV is 81.9, so that the SP value of methyl methacrylate is 9.9.

The (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less is not particularly limited, and is, for example, t-butyl methacrylate (t-BMA), 2-ethylhexyl acrylate (2-EHA), or isopropyl. Methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-lauryl (meth) acrylate, n-stearyl (meth) acrylate, isostearyl (meth) acrylate, t- Butylcyclohexyl (meth) acrylate, isobornyl (meth) acrylate and the like can be mentioned. From the viewpoint of frost damage resistance, polymerization stability, and availability for commercial use, t-butyl methacrylate and 2-ethylhexyl (meth) acrylic acid ester-based monomers having an SP value of 9.4 or less are used. Meta) acrylate is preferred. In addition, since the glass transition temperature is the same as that of methyl methacrylate, which is widely used as a (meth) acrylic acid ester-based monomer, the degree of freedom in compounding design is high, and the SP value is 9.4 or less. As the (meth) acrylic acid ester-based monomer, t-butyl methacrylate is preferable.

The structural unit derived from the (meth) acrylic acid ester-based monomer may include one having an SP value of more than 9.4. The (meth) acrylic acid ester-based monomer having an SP value of more than 9.4 is not particularly limited, and for example, n-hexyl acrylate, n-propyl methacrylate, n-pentyl acrylate, 2-ethoxyethyl methacrylate, etc. Examples thereof include ethyl methacrylate, isopropyl acrylate, n-butyl acrylate, cyclohexyl methacrylate, 2-methoxyethyl methacrylate, methyl methacrylate, adamantyl methacrylate and n-propyl acrylate. Methyl methacrylate and n-butyl acrylate are preferable as the (meth) acrylic acid ester-based monomer having an SP value of more than 9.4 because of its high versatility. Further, from the viewpoint of improving weather resistance, cyclohexyl methacrylate is preferable as the (meth) acrylic acid ester-based monomer having an SP value of more than 9.4.

The SP value of the (meth) acrylic acid ester-based monomer is 9.4 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic acid ester-based monomer, from the viewpoint of polymerization stability, 80 parts by mass or less. It is preferably 60 parts by mass or less, and further preferably 40 parts by mass or less. On the other hand, from the viewpoint of frost damage resistance, 10 parts by mass of the (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less with respect to 100 parts by mass of the (meth) acrylic acid ester-based monomer. The above is preferable, 20 parts by mass or more is more preferable, and 30 parts by mass or more is further preferable.

B. Other Materials To the extent that the effects of the present disclosure are exhibited, the water-based coating composition for a top coat of the present disclosure may contain other materials. Other materials are not particularly limited, but are, for example, film-forming aids, surface conditioners, defoamers, thickeners, matting agents such as resin beads and inorganic fillers, ultraviolet absorbers, light stabilizers, and fungicides. Examples include agents, antifungal agents and preservatives.

Hereinafter, specific examples embodying the disclosure of the present specification will be shown. However, the disclosure of the present specification is not limited to the following specific examples.

C. Example <Preparation of composition containing (meth) acrylic acid ester polymer>
A monomer composition was prepared by mixing 47 parts by mass of methyl methacrylate (MMA), 33 parts by mass of n-butyl acrylate (BA), and 20 parts by mass of t-butyl methacrylate (t-BMA). Next, 1 part by mass of potassium persulfate (KPS), 4 parts by mass of Aqualon HS-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 96 parts by mass of water were mixed to prepare an aqueous emulsifier solution. The above-mentioned monomer composition was added to this aqueous emulsifier solution, mixed, and then stirred with a homomixer to prepare an emulsion of the monomer composition (hereinafter, "monomer emulsion A"). Also called).

Next, 48 parts by mass of water was placed in a 500 ml flask equipped with a stirrer, a thermometer, and a reflux condenser, and the temperature was raised to 80 ° C. Then, the monomeric emulsion A was added dropwise to this flask over 2 hours, and the mixture was further stirred at 80 ° C. for 2 hours. Then, 1 part of 25% aqueous ammonia was added to this flask, and after confirming that the pH of the system became 7 or more, the polymerization was terminated to synthesize a (meth) acrylic acid ester-based polymer. Then, the (meth) acrylic acid ester-based polymer is cooled to room temperature, and water is further added to adjust the concentration, and the emulsified composition (A-1) containing 40% by mass of the (meth) acrylic acid ester-based copolymer. ) Was obtained. The glass transition temperature Tg of the (meth) acrylic acid ester-based copolymer contained in the obtained emulsified composition (A-1) was 37.7 ° C., and the average SP value of all the monomer components was 9.7. Met.

<Preparation of water-based paint composition>
12.5 parts by mass of butyl cellosolve as a film-forming aid, texanol (manufactured by JNC Corporation, CS-12) with respect to 250 parts by mass (including 100 parts by mass of resin solid content) of the above-mentioned emulsified composition (A-1). Stir 2.5 parts by mass, 5 parts by mass of acetylene glycol-based surface conditioner (EVONIK, Surfinol 104E), and 1 part by mass of silicone-based defoamer (BYK-025, manufactured by Big Chemie Japan Co., Ltd.) with a disper. It was added while adding. After that, an appropriate amount of thickener (Primal ASE-60 manufactured by Dow Chemical Co., Ltd.) and water are added, and the viscosity (25 ° C., 60 rpm) by a B-type viscometer is about 700 mPa · s. (Solid content 35%) was prepared. This water-based coating composition is referred to as Example 1. In Examples 2 and 3 and Comparative Example 1, a water-based coating composition was prepared by the same method with the formulations shown in Table 3 described later. Here, the blending amounts shown in Table 3 are all parts by mass. In Table 3, only the blending of the (meth) acrylic acid ester-based monomer is described as the blending amount in order to facilitate understanding of the contents.

<Preparation of test base material>
First, 10 parts by mass of water was added to 100 parts by mass of the prepared water-based paint composition to prepare a coating liquid. In addition, the following aluminum exterior material manufactured by YKK AP Inc. (hereinafter, also referred to as "metal siding base material") was prepared.
Product name: Alkaber / Standard series / Novel line Color: Frosty gray Size: Thickness 15 mm x Width 400 mm x Length 3,790 mm
Material composition:
Surface material: Aluminum core material with polyester coating: Non-fluorocarbon hard plastic foam Insulation material Back material: Aluminum-deposited laminated paper

Then, after hot air treatment is performed so that the surface temperature of the surface material of the above-mentioned metal siding base material reaches 60 ° C., the surface of the metal siding base material (the surface coated with polyester) has a weight of 20 g after drying. The above coating liquid was applied with an airless spray so as to have a temperature of / m ² . Then, after allowing the painted metal siding base material to stand at room temperature (25 ° C.) for 1 minute, the plate surface wind speed (wind speed on the surface of the surface material) is 8 m / sec, the ultimate temperature of the surface material is 80 ° C., and the ultimate temperature holding time. By treating with hot air in 5 minutes, a metal siding (hereinafter, also referred to as “test base material”) having a coating layer formed using the water-based coating composition for top coating was prepared.

D. Evaluation method, etc. <Evaluation of water-based paint composition>
Polymerization stability was evaluated as an evaluation of the water-based coating composition. The glass transition temperature of the (meth) acrylic acid ester polymer was also calculated.

<Calculation method of glass transition temperature (Tg)>
The glass transition temperature Tg (° C.) is the Fox (Fox) formula (1) shown below using the glass transition temperature of the homopolymer of each monomer composition constituting the (meth) acrylic acid ester-based polymer. Calculated by.
1 / (Tg + 273.16) = (W1 / (Tg1 + 273.16)) + (W2 / (Tg2 + 273.16)) + (W3 / (Tg3 + 273.16)) + ...
+ (Wn / (Tgn + 273.16)) (1)
[In the formula, Tg indicates the glass transition temperature (° C.), W1, W2, W3 ... Wn indicates the mass fraction of each monomer, and Tg1, Tg2, Tg3 ... Tgn are , The glass transition temperature of the homopolymer of each monomer is shown. ]

<Evaluation method of polymerization stability>
The synthesized emulsified composition was filtered through an 80-mesh wire mesh to filter the agglomerates produced during the emulsion polymerization step. The filtration residue was washed with water and dried at 105 ° C. for 2 hours, and the mass of the residue was shown as% by mass based on the solid content of the filtered dispersion. The smaller the mass% of the residue, the better the polymerization stability, and 3 or more is more preferable.
5: Residue is less than 0.1% by mass 4: Residue is 0.1% by mass or more and less than 1.0% by mass 3: Residue is 1.0% by mass or more and less than 2.0% by mass 2: Residue is 2.0% by mass or more and less than 5.0% by mass 1: Residue is 5.0% by mass or more

<Evaluation of coating film>
As an evaluation of the coating film, frost damage resistance was evaluated. In addition, water resistance and weather resistance were additionally evaluated.

<Evaluation method of frost damage resistance>
The freeze-thaw test of the test substrate was carried out according to the method described in 3.3 (Aerial Freezing Water Thawing Method) of JIS A 1435 (Freezing and Thawing Test Method for Building Exterior Materials) (100 cycles). The condition of the surface of the test substrate after the test was visually confirmed, and the evaluation was performed according to the following evaluation criteria. The higher the score, the better the frost damage resistance, and if the score is 3 or more, there is no practical problem.
5: No abnormal appearance is observed 4: No peeling of the coating film, but slight whitening of the coating film is observed.
3: There is no peeling of the coating film, but some whitening of the coating film is observed. 2: The peeling of the coating film is clearly observed. 1: The peeling and whitening of the coating film are observed everywhere.

<Evaluation method of water resistance>
As an evaluation of water resistance, a hot water test was conducted as follows. Specifically, the test base material was immersed in warm water at 50 ° C. for 5 days, and then the state of the top coat of the test base material was visually confirmed and evaluated according to the following evaluation criteria. The higher the score, the better the water resistance.
5: No abnormal appearance is observed 4: No peeling of the coating film, but slight whitening of the coating film is observed.
3: There is no peeling of the coating film, but some whitening of the coating film is observed. 2: The peeling of the coating film is clearly observed. 1: The peeling and whitening of the coating film are observed everywhere.

<Evaluation method of weather resistance>
An accelerated weather resistance test of the test substrate was carried out under the following conditions using a weather resistance tester (dipla metal weather meter).
UV cut filter: KF-1
Black panel temperature: 63 ° C
UV irradiation intensity: 750 W / m ²
Precipitation conditions: 2mm / 120min
Irradiation time: 480 hours

After measuring the color difference before and after the test with a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., spectrophotometric color difference meter SE-2000), the following formula (1) is used from the respective L, a, and b values measured before and after the test. After calculating ΔL, Δa, and Δb based on the equation (3), ΔE was calculated based on the following equation (4).
ΔL = (L value of the coated plate after the test)-(L value of the coated plate before the test) (1)
Δa = (a value of the coated plate after the test)-(a value of the coated plate before the test) (2)
Δb = (b value of the coated plate after the test)-(b value of the coated plate before the test) (3)
ΔE = {(ΔL) ² + (Δa) ² + (Δb) ² } ^1/2 (4)

As a method for evaluating weather resistance, evaluation was performed according to the following evaluation criteria. The higher the score, the better the weather resistance.
5: ΔE value is 1 or less
4: ΔE value is greater than 1 and 3 or less 3: ΔE value is greater than 3 and 5 or less 2: ΔE value is greater than 5 and 7 or less 1: ΔE value exceeds 7.

E. Experimental results Table 3 shows the experimental results.

From Table 3, the following can be seen. Examples 1 to 3 contain (meth) acrylic acid ester-based monomers having an SP value of 9.4 or less. On the other hand, Comparative Example 1 does not contain a (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less. By comparing Example 1 to Example 3 with Comparative Example 1, the present embodiment includes a structural unit derived from a (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less. It can be seen that the aqueous coating composition of the above has high frost damage resistance.

Furthermore, when Examples 1 to 3 and Comparative Example 1 are compared, it can be seen that the examples are superior not only in frost damage resistance but also in water resistance and weather resistance. This is because water has become difficult to penetrate into the coating film and water in the coating film has become easier to escape, resulting in whitening of the coating film caused by water penetrating into the coating film and the whitening of the coating film caused by ultraviolet rays. This is probably because hydrolysis is less likely to occur.

F. Core-shell type polymer As the (meth) acrylic acid ester-based polymer of the present embodiment, a core-shell type polymer may be used. In the core-shell type polymer, the composition of the resin layer in the central portion and the composition of the resin layer in the outer peripheral portion are different. Therefore, the core-shell type polymer can obtain physical properties (for example, hardness, film-forming property, etc.) that cannot be obtained with a single polymer having a uniform composition as shown in Table 3.

Further, in the core-shell type polymer, the glass transition temperature Tg of the resin layer on the outer periphery (hereinafter, also referred to as “shell Tg”) is higher than the glass transition temperature Tg (hereinafter, also referred to as “core Tg”) of the resin layer in the center. There are a hardcore type having a lower than (called) and a soft core type in which the glass transition temperature Tg of the resin layer in the outer peripheral portion is higher than the glass transition temperature Tg of the resin layer in the central portion. In general, the hardcore type has better film-forming properties than the soft-core type, so that the degree of freedom in the amount and type of film-forming auxiliary is increased, and various physical properties such as dryness can be expected to be improved. Hereinafter, a method for producing a core-shell type polymer will be described. The "core Tg" was calculated from the composition of the first-stage monomer composition serving as the core by the above-mentioned Fox formula. The “shell Tg” was also calculated in the same manner from the formulation of the second-stage monomer composition serving as the shell.

<Preparation of core-shell type polymer>
First, 37 parts by mass of methyl methacrylate (MMA) and 3 parts by mass of n-butyl acrylate (BA) were mixed to prepare a monomer composition. Next, 1 part by mass of potassium persulfate (KPS), 2 parts by mass of Aqualon HS-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 40 parts by mass of water were mixed to prepare an aqueous emulsifier solution. The above-mentioned monomer composition was added to the aqueous emulsifier solution, mixed, and then stirred with a homomixer to prepare an emulsion of the monomer composition (hereinafter, "monomer emulsion B"). Also called).

Next, 48 parts by mass of water was placed in a 500 ml flask equipped with a stirrer, a thermometer, and a reflux condenser, and the temperature was raised to 80 ° C. Then, the monomeric emulsion B was added dropwise to this flask over 2 hours, and after the addition was completed, the temperature was maintained at the same temperature for 1 hour to complete the first-stage polymerization. Subsequently, 57 parts of water, 2 parts of Aqualon HS-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 20 parts by mass of methyl methacrylate (MMA), 30 parts by mass of n-butyl acrylate (BA), and t-butyl methacrylate (t-BMA). ) Using 10 parts by mass, the emulsion of the monomer composition prepared by the same method as the monomer emulsion B except that it did not contain potassium persulfate was uniformly added dropwise over 2 hours. Further, the mixture was stirred at 80 ° C. for 2 hours, and then 1 part of 25% aqueous ammonia was added to confirm that the pH of the system was 7 or more, and the polymerization of the (meth) acrylic acid ester-based polymer was completed. did.

Then, the (meth) acrylic acid ester-based polymer is cooled to room temperature, and water is further added to adjust the concentration, and the emulsified composition (B-1) containing 40% by mass of the (meth) acrylic acid ester-based polymer. Got The glass transition temperature Tg of the (meth) acrylic acid ester-based polymer contained in the obtained emulsified composition (B-1) was 37.7 ° C., and the average SP value of all the monomer components was 9.7. there were. The method for producing the water-based coating composition is the same as the above method and will be omitted. The water-based coating composition obtained by this method is referred to as Example 4. For Examples 4 and subsequent Examples and Comparative Examples 2 and 3, water-based coating compositions were prepared in the same manner with the formulations shown in Tables 4 and 5. Here, the blending amounts shown in Tables 4 and 5 are all parts by mass. In Tables 4 and 5, only the blending of the (meth) acrylic acid ester-based monomer is described as the blending amount in order to facilitate understanding of the contents.

G. Experimental results The experimental results are shown in Tables 4 and 5.

The following can be seen from Tables 4 and 5. Examples 4 to 15 include (meth) acrylic acid ester-based monomers having an SP value of 9.4 or less. On the other hand, Comparative Examples 2 and 3 do not contain the (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less. By comparing Examples 4 to 15 with Comparative Examples 2 and 3, the present invention is made by including a structural unit derived from a (meth) acrylic acid ester-based monomer having an SP value of 9.4 or less. It can be seen that the water-based coating composition of the embodiment has high frost damage resistance, water resistance, and weather resistance.

Further, Examples 4 to 11 and Comparative Example 2 are examples of hardcore type polymers, and Examples 12 to 15 and Comparative Example 3 are examples of soft core type polymers. As a tendency of the experimental results, it can be seen that the hardcore type polymer has higher frost damage resistance than the soft core type polymer. The reason for this is thought to be that hardcore has better film-forming properties. From the results of Tables 3 to 5, it can be seen that the core-shell type polymer tends to have higher frost damage resistance, water resistance and weather resistance than the single polymer.

And, in any example, the polymerization stability is excellent. On the other hand, by comparing Examples 6 to 8, the SP value is 9.4 or less with respect to 100 parts by mass of the (meth) acrylic acid ester-based monomer from the viewpoint of polymerization stability (meth). It was found that the amount of the acrylic acid ester-based monomer was preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and further preferably 40 parts by mass or less. ..

The present invention is not limited to the above-described embodiments and examples, and can be realized with various configurations within a range not deviating from the gist thereof. For example, the embodiment corresponding to the technical feature in each embodiment described in the column of the outline of the invention, the technical feature in the embodiment may be used to solve a part or all of the above-mentioned problems, or the above-mentioned. It is possible to replace or combine them as appropriate to achieve some or all of the effects. Further, if the technical feature is not described as essential in the present specification, it can be appropriately deleted.

The present invention has been made to solve the above-mentioned problems, and can be realized as the following forms.
According to one embodiment of the present invention, a water-based coating composition for a top coat of metal siding is provided. This water-based coating composition for a top coat of metal siding contains a (meth) acrylic acid ester-based polymer, and the (meth) acrylic acid ester-based polymer has a compatibility parameter of 9. using the Fedors estimation method. The (meth) acrylic acid ester-based polymer has one or more structural units derived from the (meth) acrylic acid ester-based monomer which is 4 or less, and the (meth) acrylic acid ester-based polymer is a core-shell type polymer.
In addition, the present invention can also be realized in the following forms.

<Preparation of water-based paint composition>
12.5 parts by mass of butyl cellosolve as a film-forming aid, texanol (manufactured by JNC Corporation, CS-12) with respect to 250 parts by mass (including 100 parts by mass of resin solid content) of the above-mentioned emulsified composition (A-1). Stir 2.5 parts by mass, 5 parts by mass of acetylene glycol-based surface conditioner (EVONIK, Surfinol 104E), and 1 part by mass of silicone-based defoamer (BYK-025, manufactured by Big Chemie Japan Co., Ltd.) with a disper. It was added while adding. After that, an appropriate amount of thickener (Primal ASE-60 manufactured by Dow Chemical Co., Ltd.) and water are added, and the viscosity (25 ° C., 60 rpm) by a B-type viscometer is about 700 mPa · s. (Solid content 35%) was prepared. This water-based coating composition is referred to as Example 1. In Examples 2 and 3 and Comparative Example 1, a water-based coating composition was prepared by the same method with the formulations shown in Table 3 described later. Here, the blending amounts shown in Table 3 are all parts by mass. In Table 3, only the blending of the (meth) acrylic acid ester-based monomer is described as the blending amount in order to facilitate understanding of the contents. In addition, Examples 1 to 3 are reference examples.

Claims (3)

A water-based paint composition for topcoats of metal siding
Contains (meth) acrylic acid ester polymer,
The (meth) acrylic acid ester-based polymer has one or more structural units derived from the (meth) acrylic acid ester-based monomer having a compatibility parameter of 9.4 or less using the Fedors estimation method. A water-based paint composition for topcoats of metal siding. The water-based coating composition for a top coat of a metal siding according to claim 1.
The (meth) acrylic acid ester-based monomer is a water-based coating composition for a top coat of metal siding containing at least one of t-butyl methacrylate and 2-ethylhexyl (meth) acrylate. A metal siding in which a coating layer is formed by using the water-based coating composition for a top coat of the metal siding according to claim 1 or 2.

Images