JP2021108624A - Structural material for agricultural greenhouse - Google Patents

Abstract

To provide a structural material for an agricultural greenhouse which contains titanium dioxide as pigment, can suppress deterioration of a covering material of an agricultural greenhouse, and obtain excellent processability.SOLUTION: A longitudinal frame material 36 is equipped with a light reflection film 52. The light reflection film 52 has a white pigment-containing layer 70 and a transparent protective layer 72. The white pigment-containing layer 70 contains pigment and synthetic resin. The pigment contains titanium dioxide. Percent by weight of the titanium dioxide in the white pigment-containing layer 70 is 25 wt.% or more and 50 wt.% or less. The transparent protective layer 72 contains silicon dioxide and acrylic resin. Percent by weight of silicon dioxide in the transparent protective layer 72 is 5 wt.% or more and 30 wt.% or less. A film thickness of the white pigment-containing layer 70 exceeds 0 micrometer and 20 micrometers or less. A film thickness of the transparent protective layer 72 is 5 micrometers or more and 20 micrometers or less.SELECTED DRAWING: Figure 2

Description

The present invention relates to a structural material for an agricultural house.

Patent Document 1 discloses a durable pigment, titanium dioxide. This durable pigment, titanium dioxide, consists of rutile-type titanium dioxide particles containing cerium oxide and dense amorphous silica deposited on it. This cerium oxide is present in an amount in the range of about 0.01% by weight to about 1.0% by weight of titanium dioxide. This dense amorphous silica is present in an amount in the range of about 1% by weight to about 8% by weight of titanium dioxide.

The pigment titanium dioxide disclosed in Patent Document 1 can extend the effective life of the product containing the pigment.

Japanese Unexamined Patent Publication No. 7-315838

However, the pigment titanium dioxide disclosed in Patent Document 1 has a problem that the durability of the agricultural house may be lowered when it is contained in the light reflecting film on the surface layer of the structural material for the agricultural house. One of the causes of such a decrease in durability is that the titanium dioxide deteriorates the covering material of the agricultural house. Another cause of such a decrease in durability is that the titanium dioxide easily peels off from the agricultural house structural material together with the light reflecting film as the agricultural house structural material is processed.

The present invention solves such a problem. An object of the present invention is to provide a structural material for an agricultural house, which contains titanium dioxide as a pigment, can suppress deterioration of a coating material of an agricultural house, and can obtain good processability.

As a result of diligent studies on the above problems, the present inventors have found that when a predetermined white pigment-containing layer is protected by a predetermined transparent protective layer, the mechanical strength of the light reflecting film can be improved. The invention was completed. That is, the present invention is as follows.

In order to solve the above problems, according to a certain aspect of the present invention, the structural material 36 for an agricultural house includes a structural material main body 50 and a light reflecting film 52. The light reflecting film 52 is provided on the outer peripheral surface of the structural material main body 50. The light reflecting film 52 has a white pigment-containing layer 70 and a transparent protective layer 72. The white pigment-containing layer 70 is in close contact with the outer peripheral surface of the structural material main body 50. The transparent protective layer 72 is in close contact with the outer peripheral surface of the white pigment-containing layer 70. The white pigment-containing layer 70 contains a pigment and a synthetic resin. The pigment contains titanium dioxide. The weight% of the titanium dioxide in the white pigment-containing layer 70 is 25% by weight or more and 50% by weight or less. The transparent protective layer 72 contains silicon dioxide and an acrylic resin. The weight% of silicon dioxide in the transparent protective layer 72 is 5% by weight or more and 30% by weight or less. The film thickness of the white pigment-containing layer 70 exceeds 0 micrometers and is 20 micrometers or less. The film thickness of the transparent protective layer 72 is 5 micrometers or more and 20 micrometers or less.

Further, it is desirable that the weight% of the pigment in the white pigment-containing layer 70 described above is 37% by weight or more and 62% by weight or less. In this case, it is desirable that the film thickness of the white pigment-containing layer 70 is 10 micrometers or more. In this case, it is desirable that the synthetic resin contained in the white pigment-containing layer 70 contains an acrylic resin. It is desirable that the weight% of the acrylic resin in the white pigment-containing layer 70 is 16% by weight or more. In this case, it is desirable that the sum of the weight% of the pigment in the white pigment-containing layer 70 and the weight% of the synthetic resin in the white pigment-containing layer 70 is 100% by weight or less. In this case, it is desirable that the weight% of the silicon dioxide contained in the transparent protective layer 72 in the transparent protective layer 72 is 10% by weight or more and 30% by weight or less. In this case, it is desirable that the film thickness of the transparent protective layer 72 is 5 micrometers or more and 15 micrometers or less. In this case, it is desirable that the transparent protective layer 72 further contains wax. In this case, it is desirable that the weight% of the wax in the transparent protective layer 72 is 0.5% by weight or more and 3% by weight or less.

Alternatively, it is desirable that the weight% of the white pigment-containing layer 70 of titanium dioxide contained in the above-mentioned pigment is 30% by weight or more. In this case, it is desirable that the weight% of the wax in the transparent protective layer 72 is 2% by weight or less.

According to the present invention, it is possible to provide a structural material for an agricultural house, which contains titanium dioxide as a pigment, can suppress deterioration of a coating material of an agricultural house, and can obtain good processability.

It is external drawing of the agricultural house which concerns on one Embodiment of this invention. It is sectional drawing of the longitudinal frame material which concerns on one Embodiment of this invention. It is a figure which shows the composition of the white pigment-containing layer-forming paint and the film thickness of a white pigment-containing layer in an Example and a comparative example of this invention. It is a figure which shows the composition of the transparent protective layer forming paint and the film thickness of a transparent protective layer in an Example and a comparative example of this invention. It is a figure which shows the evaluation result in the Example and the comparative example of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are also the same. Therefore, detailed explanations about them will not be repeated.

[Description of configuration]
Hereinafter, an embodiment of the present invention will be described. FIG. 1 is an external view of an agricultural house according to the present embodiment. The configuration of the agricultural house according to the present embodiment will be described with reference to FIG.

In the present embodiment, the agricultural house means a building that meets the following two requirements. The first requirement is that the structure 10 and the coating material 12 made of synthetic resin are provided. The second requirement is that it can be used for crop cultivation.

The structure 10 referred to in the first requirement means an object forming a space formed by connecting a plurality of frame members to each other. The form of the structure 10 is not particularly limited. The covering material 12 covers the structure 10. The covering material 12 may cover at least a part of the structure 10. It is desirable that the covering material 12 covers the upper part of the structure 10 when it is fixed to the ground. It is more desirable that the covering material 12 covers all the structures 10 fixed to the ground. Fluororesin is an example of the material of the covering material 12. Of course, the type of synthetic resin that is the material of the covering material 12 is not particularly limited. However, the covering material 12 according to the present embodiment is transparent. It is desirable that the covering material 12 according to the present embodiment is colorless and transparent.

Any building that does not interfere with crop cultivation in the building itself meets the second requirement. Of course, it is desirable that the agricultural house in the present embodiment is a building suitable for crop cultivation. Examples of buildings suitable for crop cultivation include buildings with exposed ground inside and buildings with a function of preventing wind from entering from the outside to the inside.

The structure 10 according to the present embodiment includes a column frame member 30, a crosspiece frame member 32, an arch beam frame member 34, and a longitudinal frame member 36.

The column frame material 30, the crosspiece frame material 32, and the arch beam frame material 34 are well-known structural materials for agricultural houses. These specific forms are the same as those well known. Therefore, the detailed description is not repeated here.

The longitudinal frame material 36 is arranged on the roof portion of the agricultural house according to the present embodiment. The longitudinal frame material 36 is a structural material for an agricultural house according to the present embodiment. The longitudinal frame material 36 reflects visible light and near infrared light.

The coating material 12 according to this embodiment is made of fluororesin. The covering material 12 covers the column frame material 30, the crosspiece frame material 32, the arch beam frame material 34, and the longitudinal frame material 36.

FIG. 2 is a cross-sectional view of the longitudinal frame member 36 according to the present embodiment. The longitudinal frame member 36 according to the present embodiment will be described with reference to FIG. The longitudinal frame material 36 according to the present embodiment has a structural material main body 50 and a light reflecting film 52.

The structural material main body 50 is an object for supporting a load. The structural material main body 50 may be an object that can support a load. The component and form thereof are not particularly limited. However, the specific configuration of the structural material main body 50 in this embodiment is the same as that of a well-known steel pipe. Therefore, the detailed description is not repeated here.

The light reflecting film 52 is provided on the surface of the structural material main body 50. The light reflecting film 52 according to the present embodiment has a white pigment-containing layer 70 and a transparent protective layer 72. The film thickness of the white pigment-containing layer 70 exceeds 0 micrometers and is 20 micrometers or less. Preferably, the film thickness of the white pigment-containing layer 70 is 10 micrometers or more and 20 micrometers or less. The film thickness of the transparent protective layer 72 is 5 micrometers or more and 20 micrometers or less. Preferably, the film thickness of the transparent protective layer 72 is 5 micrometers or more and 15 micrometers or less.

In the present embodiment, the white pigment-containing layer 70 contains a pigment and a synthetic resin. Preferably, the weight% of the pigment in the white pigment-containing layer 70 is 25% by weight or more and 70% by weight or less. More preferably, the weight% is 25% by weight or more and 62% by weight or less. More preferably, the weight% is 37% by weight or more and 62% by weight or less. More preferably, the weight% is 25% by weight or more and 50% by weight or less. Even more preferably, the weight% is 40% by weight or more and 42% by weight or less.

This pigment contains titanium dioxide. The weight% of the titanium dioxide in the white pigment-containing layer 70 is 25% by weight or more and 50% by weight or less. Preferably, the% by weight is 30% by weight or more and 50% by weight or less. More preferably, the weight% is 40% by weight or more and 42% by weight or less.

The components of the pigment other than titanium dioxide are not particularly limited. Preferably, the pigment comprises silicon dioxide.

The type of synthetic resin contained in the white pigment-containing layer 70 is also not particularly limited. Preferably, the white pigment-containing layer 70 contains at least one of an acrylic resin and an epoxy resin as the synthetic resin thereof. When the white pigment-containing layer 70 contains both an acrylic resin and an epoxy resin as its synthetic resin, the weight ratio of the epoxy resin to the acrylic resin is preferably in the range of 95: 5 to 6: 4. That is, the weight% of the epoxy resin with respect to the acrylic resin is 5.26% by weight (5 ÷ 95 × 100 = 5.26) or more and 66.7% by weight (4 ÷ 6 × 100 = 66.7) or less.

Preferably, the white pigment-containing layer 70 further contains a cross-linking agent. The "crosslinking agent" in the present embodiment is a chemical substance that links polymers contained in a synthetic resin. Examples of cross-linking agents include epoxy group-containing silane compounds, amino group-containing silane compounds, mercapto group-containing silane compounds, and other silane coupling agents.

Examples of epoxy group-containing silane compounds include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane. , 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane.

Examples of amino group-containing silane compounds include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropyltriethoxysilane, and γ- (2-aminoethyl) aminopropylmethyldimethoxy. Silane, γ- (2-aminoethyl) aminopropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropylethoxysilane, N- [2- (vinylbenzylamino) Ethyl] -3-aminopropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane.

Examples of mercapto group-containing silane compounds include γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropylmethyldiethoxysilane.

Examples of other silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ. -There is methacryloxypropyltriethoxysilane.

When the white pigment-containing layer 70 contains a cross-linking agent, the weight% of the cross-linking agent in the white pigment-containing layer 70 is preferably 1% by weight or more and 25% by weight or less. More preferably, the weight% of the cross-linking agent in the white pigment-containing layer 70 is 5% by weight or more and 20% by weight or less.

In the present embodiment, the transparent protective layer 72 contains silicon dioxide and an acrylic resin. The weight% of silicon dioxide in the transparent protective layer 72 is 5% by weight or more and 30% by weight or less. Preferably, the weight% of silicon dioxide in the transparent protective layer 72 is 10% by weight or more and 30% by weight or less.

Preferably, the transparent protective layer 72 further comprises wax. The "wax" in the present embodiment is a substance containing at least one component selected from the group consisting of wax ester, paraffin wax, microcrystalline wax, polyethylene wax, and polypropylene wax. In this case, preferably, the weight% of the wax in the transparent protective layer 72 is 0.5% by weight or more and 3% by weight or less. More preferably, the weight% of the wax in the transparent protective layer 72 is 0.5% by weight or more and 2% by weight or less.

[Explanation of manufacturing method]
The method for producing the structural material for an agricultural house according to the present embodiment is the same as that known. For example, the structural material for an agricultural house according to this embodiment is manufactured by the following method. This method comprises three steps. The first step is a step of applying the paint to be the white pigment-containing layer 70 to the surface of the member to be the structural material main body 50. The second step is a step of applying the paint to be the transparent protective layer 72 to the surface of the paint after the paint has dried. The third step is a step of processing the member on which the transparent protective layer 72 is formed after the paint to be the transparent protective layer 72 has dried. The content of the processing is not particularly limited. For example, the process is the process of bending the member.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

[Example 1]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint The worker mixed titanium dioxide, silicon dioxide, an acrylic resin, an epoxy resin, and a cross-linking agent. As a result, a white pigment-containing layer-forming paint was prepared. The weight% of titanium dioxide in the solid components (titanium dioxide, silicon dioxide, acrylic resin, epoxy resin, and cross-linking agent) of the coating material was 30% by weight. The weight% of silicon dioxide in the solid component of the paint was 12% by weight. As a result, the sum of the weight% of the pigment component in the solid component of the paint, that is, the weight% of titanium dioxide and the weight% of silicon dioxide was 42% by weight. The weight% of the acrylic resin in the solid component of the paint was 47.7% by weight. The weight% of the epoxy resin in the solid component of the paint was 5.3% by weight. The weight% of the cross-linking agent in the solid component of the paint was 5% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 58% by weight. The weight ratio of the acrylic resin to the epoxy resin was 90:10. Boncoat (registered trademark) CM-8490 manufactured by DIC Corporation was used as the acrylic resin for the white pigment-containing layer-forming paint in this example. This contained 3% by weight of the solvent of the acrylic resin in addition to the above-mentioned acrylic resin. As the epoxy resin in this example, ADEKA CORPORATION (registered trademark) EM-101-50 manufactured by ADEKA Corporation was used. In addition to the epoxy resin described above, this contained 3% by weight of the solvent of the epoxy resin. These solvents volatilize after painting. Therefore, in calculating the weight% of titanium dioxide, the weight% of silicon dioxide, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the above-mentioned solid components, the weights of these solvents are calculated. Not used. Further, as the cross-linking agent in this example, KBE-903 manufactured by Shin-Etsu Chemical Co., Ltd. was used.

(B) Preparation of Transparent Protective Layer Forming Paint The worker mixed acrylic resin, silicon dioxide, and wax. As a result, a transparent protective layer forming paint was prepared. The weight% of the acrylic resin in the solid components (acrylic resin, silicon dioxide, and wax) of the paint was 74% by weight. The weight% of silicon dioxide in the solid component of the paint was 25% by weight. The weight% of the wax in the solid component of the paint was 1.0% by weight. Boncoat (registered trademark) CM-8490 manufactured by DIC Corporation was used as the acrylic resin for the transparent protective layer forming paint in this example. As the wax of the transparent protective layer forming paint in this example, Hi-Tech (registered trademark) E-6000S manufactured by Toho Chemical Industry Co., Ltd. was used. Boncoat (registered trademark), which is an acrylic resin, contained a solvent in addition to the acrylic resin described above. This solvent volatilizes after painting. Therefore, the weight of this solvent was not used in the calculation of the weight% of the acrylic resin, the weight% of silicon dioxide, and the weight% of the wax in the above-mentioned solid components.

(2) Preparation of test plate The worker put the hot-dip galvanized steel plate in a 2% aqueous solution of an alkaline degreasing agent (Surf Cleaner (registered trademark) 155, manufactured by Nippon Paint Co., Ltd.) at 60 ° C. (333.15 Kelvin) for 2 minutes. The degreasing treatment was carried out by immersing. This was done for degreasing hot dip galvanized steel sheets. After degreasing, the operator washed the hot-dip galvanized steel sheet with water. After washing with water, the operator dried the hot-dip galvanized steel sheet. The operator applied the white pigment-containing layer-forming paint described above to the hot-dip galvanized steel sheet. The thickness of the applied white pigment-containing layer-forming paint was such that the film thickness of the coating film formed by the drying was 15 micrometers. When the white pigment-containing layer-forming paint is applied, the operator uses a hot air drying furnace having an ambient temperature of 250 ° C. (523.15 Kelvin) to bring the steel sheet temperature (PMT) to 120 ° C. (393.15 Kelvin). The hot-dip galvanized steel sheet was heated so as to be. When the hot-dip galvanized steel sheet is cooled to room temperature, the operator forms the above-mentioned transparent protective layer on the surface of the coating film formed by drying the white pigment-containing layer-forming paint among the hot-dip galvanized steel sheets. The paint was applied. The thickness of the applied transparent protective layer-forming paint was such that the film thickness of the coating film formed by the drying was 10 micrometers. When the transparent protective layer forming paint is applied, the operator uses a hot air drying furnace having an ambient temperature of 250 ° C. (523.15 Kelvin) to bring the steel sheet temperature (PMT) to 100 ° C. (373.15 Kelvin). The hot-dip galvanized steel sheet was heated as described above. The worker then cooled the hot-dip galvanized steel sheet until the temperature reached room temperature. As a result, a coating film formed by drying the white pigment-containing layer-forming paint is formed on the surface of the hot-dip galvanized steel sheet. The coating film is a white pigment-containing layer 70. Further, a coating film formed by drying the transparent protective layer forming paint is formed on the surface of the white pigment-containing layer 70. The coating film is a transparent protective layer 72. The hot-dip galvanized steel sheet on which the transparent protective layer 72 and the white pigment-containing layer 70 are formed in this way is the test plate according to this embodiment.

(3) Preparation of test steel pipe The worker washed a round pipe (Zamtite (registered trademark) manufactured by Sansui Co., Ltd.) whose surface was plated with hot water. After the washed round pipe was cooled to room temperature, the operator applied the white pigment-containing layer-forming paint described above to the round pipe. The thickness of the applied white pigment-containing layer-forming paint was such that the film thickness of the coating film formed by the drying was 15 micrometers. When the white pigment-containing layer-forming paint is applied, the operator uses a hot air drying furnace having an ambient temperature of 250 ° C. (523.15 Kelvin) to bring the steel sheet temperature (PMT) to 120 ° C. (393.15 Kelvin). The round pipe was heated so as to be. When the round pipe was cooled to room temperature, the operator applied the above-mentioned transparent protective layer-forming paint to the surface of the coating film formed by drying the white pigment-containing layer-forming paint in the round pipe. .. The thickness of the applied transparent protective layer-forming paint was such that the film thickness of the coating film formed by the drying was 10 micrometers. When the transparent protective layer forming paint is applied, the operator uses a hot air drying oven with an atmospheric temperature of 250 ° C. (523.15 Kelvin) to bring the PMT to 100 ° C. (373.15 Kelvin). Was heated. The worker then cooled the round pipe until the temperature reached room temperature. As a result, a coating film formed by drying the white pigment-containing layer-forming paint is formed on the surface of the round pipe. The coating film is a white pigment-containing layer 70. Further, a coating film formed by drying the transparent protective layer forming paint is formed on the surface of the white pigment-containing layer 70. The coating film is a transparent protective layer 72. The round pipe in which the transparent protective layer 72 and the white pigment-containing layer 70 are formed in this way is the test steel pipe according to this embodiment.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example. A color difference meter CR-400 manufactured by Konica Minolta Co., Ltd. was used for the measurement. As a result, the L * value on the surface of the test plate according to this example was 85.

(B) Measurement of Mirror Gloss The worker measured the mirror gloss on the surface of the test plate according to this example by the procedure to be extended next. The measurement was carried out based on Japanese Industrial Standards (JIS) K5600-4-7. The mirror gloss at 20 ° was measured. A gloss meter GM-268A manufactured by Konica Minolta Co., Ltd. was used for the measurement. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 50%.

(C) Measurement of Fluorine Film Deterioration Degradability The worker measured the effect of the test plate according to this example on the deterioration of the fluorine film by the following procedure. In the first procedure, the operator measured the haze of the fluorine film used in the test. A haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. was used for the haze measurement in this example. As the fluorine film in this example, Fclean (registered trademark) natural light manufactured by AGC Greentech Co., Ltd. was used. Its thickness was 100 micrometers. In the second procedure, the operator wrapped the fluorine film around the test plate according to this embodiment. As a result, the fluorine film comes into contact with the transparent protective layer 72 of the test plates according to this example. In the third procedure, the operator housed the test piece wrapped with the fluorine film in a xenon weather meter. As the xenon weather meter in this example, a super xenon weather meter SX75 manufactured by Suga Test Instruments Co., Ltd. was used. After its containment, the xenon weathermeter was irradiated with light in a dry state for 102 minutes based on the operator's operation. During that time, the temperature around the test piece was controlled to 65 ° C. plus or minus 2 ° C. (338.15 Kelvin plus or minus 2 Kelvin). The relative humidity around the test piece was controlled to 50% plus or minus 5%. Subsequently, the xenon weather meter was irradiated with light for 18 minutes while spraying water on the surface of the test piece based on the operation of the operator. The relative humidity around the test piece was controlled to 95% plus or minus 5%. The spectral irradiance of the light at wavelengths of 300 nm to 400 nm was 60 W / m ² . These irradiations were repeated 500 times. As a result, the test piece was irradiated with light for a total of 1000 hours. In the fourth procedure, the operator measured the haze of the fluorine film taken from the xenon weather meter. A haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. was also used for the measurement of the haze. Based on the measured haze, the operator evaluated the difference in appearance of the fluorine film before and after irradiation with light. When the increase / decrease in haze after irradiation with respect to the haze before light irradiation is less than 1.0% of the haze before light irradiation, the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate deteriorate the fluorine film. The effect was evaluated as "○". When the increase / decrease in haze after irradiation with respect to haze before light irradiation is less than 3.0% of the haze before light irradiation, the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate deteriorate the fluorine film. The effect was evaluated as "Δ". When the increase / decrease in haze after irradiation with respect to haze before light irradiation is 3.0% or more of the haze before light irradiation, the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate deteriorate the fluorine film. The effect was evaluated as "x". As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example by the procedure that is extended next. In the first procedure, the operator bent the test steel pipe according to this embodiment into an arc shape. Its radius of curvature was 4.5 m. In the second procedure, the operator evaluated the degree to which the light reflecting film layer was peeled off from the structure by bending at the portion where the transparent protective layer 72 was peeled off in the test steel pipe. When the light reflecting film layer was not peeled off and the metal surface of the steel pipe was not exposed, the processability of the white pigment-containing layer 70 and the transparent protective layer 72 was evaluated as “◯”. When the light-reflecting film layer was peeled off in dots, the processability of the white pigment-containing layer 70 and the transparent protective layer 72 was evaluated as “Δ”. When the light-reflecting film layer was linearly peeled off, the processability of the white pigment-containing layer 70 and the transparent protective layer 72 was evaluated as “x”. As a result, the workability of the test piece according to this example was “◯”.

[Example 2]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 50% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 62% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 29.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 3.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 38% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 90:10 as in Example 1.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of test plate The procedure for producing the test plate according to this example is the same as that of Example 1.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 95.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 52%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 3]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 39.0% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 2.1% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 95: 5.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of test plate The procedure for producing the test plate according to this example is the same as that of Example 1.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 63%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 4]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 24.6% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 16.4% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 60:40.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of test plate The procedure for producing the test plate according to this example is the same as that of Example 1.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 42%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 5]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. The second point is that the weight% of silicon dioxide in the solid component of the white pigment-containing layer-forming paint was 5% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 47% by weight. The weight% of the synthetic resin in the solid component of the paint was 48% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 33.6% by weight. The fourth point is that the weight% of the epoxy resin in the solid component of the paint was 14.4% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 53% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of test plate The procedure for producing the test plate according to this example is the same as that of Example 1.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 86.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 60%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 6]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. The second point is that the weight% of silicon dioxide in the solid component of the white pigment-containing layer-forming paint was 20% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 62% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 23.1% by weight. The fourth point is that the weight% of the epoxy resin in the solid component of the paint was 9.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 38% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of test plate The procedure for producing the test plate according to this example is the same as that of Example 1.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 42%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 7]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 31.5% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 13.5% by weight. The fourth point is that the weight% of the cross-linking agent in the solid component of the white pigment-containing layer-forming paint was 1% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of test plate The procedure for producing the test plate according to this example is the same as that of Example 1.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 50%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 8]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 18.2% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 7.8% by weight. The fourth point is that the weight% of the cross-linking agent in the solid component of the white pigment-containing layer-forming paint was 20% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of test plate The procedure for producing the test plate according to this example is the same as that of Example 1.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 44%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 9]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 85.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 45%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 10]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 20 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 20 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 95.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 50%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 11]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. As a result, the weight% of the synthetic resin in the solid component of the paint was 41% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint according to this embodiment was 89% by weight. The second point is that the weight% of silicon dioxide in the solid component of the paint was 10% by weight.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 87.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 54%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 12]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint according to this embodiment was 69% by weight. The second point is that the weight% of silicon dioxide in the solid component of the paint was 30% by weight.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 89.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 45%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 13]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint according to this embodiment was 74.5% by weight. The second point is that the weight% of the wax in the solid component of the paint was 0.5% by weight.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 55%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 14]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint according to this embodiment was 73% by weight. The second point is that the weight% of the wax in the solid component of the paint was 2.0% by weight.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 42%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 15]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 5 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 5 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 45%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 16]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 15 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 15 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 56%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 17]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 41.0% by weight. The third point is that the paint did not contain epoxy resin. As a result, the sum of the resin component, that is, the weight% of the acrylic resin and the weight% of the cross-linking agent in the solid component of the paint was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 100: 0.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 63%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 18]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. The second point is that the paint did not contain silicon dioxide. As a result, the weight% of the pigment in the solid component of the paint was 42% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 37.1% by weight. The fourth point is that the weight% of the epoxy resin in the solid component of the paint was 15.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 58% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 86.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 60%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 19]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 33.6% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 14.4% by weight. The fourth point is that the paint did not contain a cross-linking agent. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 50%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 20]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the weight% of the pigment in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 16.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 6.9% by weight. The fourth point is that the weight% of the cross-linking agent in the solid component of the white pigment-containing layer-forming paint was 25% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 42%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 21]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 25% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the coating material was 37% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 40.6% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 17.4% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the paint was 63% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 75.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 50%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 22]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint was 72% by weight. The second point is that the weight% of the wax in the transparent protective layer forming paint was 3.0% by weight.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 88.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 25%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was “◯”.

[Example 23]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 12.3% by weight. The third point is that the weight% of the epoxy resin in the solid component of the paint was 28.7% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 30:70.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 30%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Example 24]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. The second point is that the weight% of silicon dioxide in the solid component of the white pigment-containing layer-forming paint was 30% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the coating material was 70% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 17.5% by weight. The fourth point is that the weight% of the epoxy resin in the solid component of the paint was 7.5% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 30% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 42%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Example 25]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 5 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 5 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 76.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 45%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Example 26]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint was 94% by weight. The second point is that the weight% of silicon dioxide in the transparent protective layer forming paint was 5% by weight.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 91.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 54%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Example 27]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint was 75% by weight. The second point is that the paint did not contain wax.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 55%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Example 28]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 20 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 20 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 56%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Comparative Example 1]
(1) Preparation of Paint The white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 42% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 54% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 28.7% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.3% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 46% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the transparent protective layer-forming paint was not applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the transparent protective layer-forming paint was not applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 90.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 20%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “x”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was "x".

[Comparative Example 2]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 60% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 72% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 16.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 6.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 28% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 98.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 52%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “Δ”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Comparative Example 3]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 25 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 25 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 95.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 50%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was "x".

[Comparative Example 4]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1, except for the following points. The first point is that the weight% of the acrylic resin in the transparent protective layer forming paint was 59% by weight. The second point is that the weight% of silicon dioxide in the transparent protective layer forming paint was 40% by weight.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 93.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 30%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “◯”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the workability of the test piece according to this example was "x".

[Comparative Example 5]
(1) Preparation of paint (A) Preparation of white pigment-containing layer-forming paint Except for the following points, the white pigment-containing layer-forming paint according to the present embodiment is the same as the white pigment-containing layer-forming paint according to Example 1. It is the same. The first point is that the weight% of titanium dioxide in the solid component of the white pigment-containing layer-forming paint was 40% by weight. As a result, the sum of the weight% of the pigment, that is, the weight% of titanium dioxide and the weight% of silicon dioxide in the solid component of the paint was 52% by weight. The second point is that the weight% of the acrylic resin in the solid component of the paint was 30.1% by weight. The third point is that the weight% of the acrylic resin in the solid component of the paint was 12.9% by weight. As a result, the sum of the resin component, that is, the weight% of the acrylic resin, the weight% of the epoxy resin, and the weight% of the cross-linking agent in the solid component of the coating material was 48% by weight. The weight ratio of the acrylic resin to the epoxy resin in the synthetic resin was 70:30.

(B) Preparation of Transparent Protective Layer-Forming Paint The transparent protective layer-forming paint according to this example is the same as the transparent protective layer-forming paint according to Example 1.

(2) Preparation of Test Plate The procedure for producing the test plate according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the hot-dip galvanized steel sheet after washing with water and drying was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 3 micrometers.

(3) Preparation of Test Steel Pipe The procedure for manufacturing the test steel pipe according to this example is the same as that of Example 1 except for the following points. The first point is that the thickness of the white pigment-containing layer-forming paint applied to the round pipe washed with hot water was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 10 micrometers. The second point is that the thickness of the transparent protective layer-forming paint applied to the surface of the coating film formed by drying the white pigment-containing layer-forming paint was the thickness described below. The thickness was such that the film thickness of the coating film formed by the drying was 3 micrometers.

(4) Evaluation of test plate and test steel pipe (A) Measurement of L * value The operator measured the L * value on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the L * value on the surface of the test plate according to this example was 91.

(B) Measurement of Mirror Gloss The operator measured the mirror gloss on the surface of the test plate according to this example in the same manner as in Example 1. As a result, the mirror surface glossiness of the surface of the test plate according to this example was 30%.

(C) Measurement of Fluorine Film Degradability The operator measured the effect of the test plate according to this example on the deterioration of the fluorine film in the same manner as in Example 1. As a result, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 of the test plate according to this example on the deterioration of the fluorine film was “Δ”.

(D) Evaluation of workability The worker evaluated the workability of the test steel pipe according to this example in the same manner as in Example 1. As a result, the processability of the test piece according to this example was “Δ”.

[Explanation of the effect of the test steel pipe on the example]
FIG. 3 is a diagram showing the composition of the white pigment-containing layer-forming paint and the film thickness of the white pigment-containing layer 70 in Examples and Comparative Examples of the present invention. FIG. 4 is a diagram showing the composition of the transparent protective layer-forming paint and the film thickness of the transparent protective layer 72 in Examples and Comparative Examples of the present invention. FIG. 5 is a diagram showing evaluation results in Examples and Comparative Examples of the present invention. The effect of the structural material for an agricultural house according to the embodiment of the present invention will be described with reference to FIGS. 3 to 5.

There is a remarkable difference between Comparative Examples 1 to 5 and Examples 1 to 28 shown in FIG. 5 in that good processability can be obtained while suppressing deterioration of the fluorine film. In the case of Comparative Example 1, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 on the deterioration of the fluorine film and the processability are “x”. In the case of the test pieces of Comparative Example 2 and Comparative Example 5, the influence of the white pigment-containing layer 70 and the transparent protective layer 72 on the deterioration of the fluorine film is “Δ”. In the comparative examples, when the influence is "○", the workability is "x". In the comparative examples, when the influence is “Δ”, the workability is “Δ”. On the other hand, in the cases of Examples 1 to 28, the effects of the white pigment-containing layer 70 and the transparent protective layer 72 on the deterioration of the fluorine film are both “◯”. The workability of the test steel pipe according to Examples 1 to 28 is “◯” or “Δ”. As is clear from these, according to the present invention, good processability can be obtained while suppressing deterioration of the fluorine film.

When Examples 1 to 22 and Examples 23 to 28 are compared, those satisfying the predetermined nine requirements of the present invention have a preferable effect as compared with those not satisfying any of the nine requirements. It becomes clear that it plays. That is, there is a remarkable difference in workability between Examples 1 to 22 and Examples 23 to 28. In the case of Examples 23 to 28, the workability of the test steel pipe is “Δ”. On the other hand, in the case of Examples 1 to 22, the workability of the test steel pipe is “◯”. The test steel pipes according to Examples 1 to 22 satisfy the following requirements. The first requirement is that the weight% of the pigment in the white pigment-containing layer 70 is 37% by weight or more and 62% by weight or less. The second requirement is that the film thickness of the white pigment-containing layer 70 is 10 micrometers or more and 20 micrometers or less. The third requirement is that the synthetic resin contained in the white pigment-containing layer 70 contains an acrylic resin. The fourth requirement is that the weight% of the acrylic resin in the white pigment-containing layer 70 is 60% by weight or more. The fifth requirement is that the sum of the weight% of the pigment in the white pigment-containing layer 70 and the weight% of the synthetic resin in the white pigment-containing layer 70 is 100% by weight or less. The sixth requirement is that the weight% of the silicon dioxide contained in the transparent protective layer 72 in the transparent protective layer 72 is 10% by weight or more and 30% by weight or less. The seventh requirement is that the film thickness of the transparent protective layer 72 is 5 micrometers or more and 15 micrometers or less. The eighth requirement is that the transparent protective layer 72 further contains wax. The ninth requirement is that the weight% of the wax in the transparent protective layer 72 is 0.5% by weight or more and 3% by weight or less. When those requirements are satisfied in the present invention, better workability can be obtained.

When Examples 1 to 20 are compared with Example 21 and Example 22, those of the present invention that satisfy additional requirements in addition to the above-mentioned nine requirements are compared with those that do not meet the additional requirements. It becomes clear that a favorable effect is exhibited. That is, there is a remarkable difference in the appearance of the light reflecting film 52 between Examples 1 to 20 and Examples 21 and 22. The test plate according to Example 21 has a significantly inferior L * value as compared with the test plates according to Examples 1 to 20. The test plate according to Example 22 has a significantly inferior mirror glossiness as compared with the test plates according to Examples 1 to 20. The test plates according to Examples 1 to 20 have good L * values and mirror glossiness. The test steel pipes according to Examples 1 to 22 satisfy the following two additional requirements in addition to the nine requirements described above. A further first requirement is that the weight% of the white pigment-containing layer 70 of titanium dioxide contained in the pigment is 30% by weight or more. A second further requirement is that the weight% of the wax in the transparent protective layer 72 is 2% by weight or less. When these two requirements are satisfied in addition to the predetermined requirements described above in the present invention, a light reflecting film 52 having a good L * value and mirror glossiness can be obtained.

Claims (3)

Structural material body and
A structural material for an agricultural house provided with a light reflecting film provided on the outer peripheral surface of the structural material main body.
The light reflecting film
A white pigment-containing layer that adheres to the outer peripheral surface of the structural material body,
It has a transparent protective layer that adheres to the outer peripheral surface of the white pigment-containing layer.
The white pigment-containing layer
With pigments
Including synthetic resin
The pigment contains titanium dioxide in which the weight% in the white pigment-containing layer is 25% by weight or more and 50% by weight or less.
The transparent protective layer
Silicon dioxide in which the weight% in the transparent protective layer is 5% by weight or more and 30% by weight or less, and
Including with acrylic resin
The film thickness of the white pigment-containing layer exceeds 0 micrometers and is 20 micrometers or less.
A structural material for an agricultural house, wherein the transparent protective layer has a film thickness of 5 micrometers or more and 20 micrometers or less. The weight% of the pigment in the white pigment-containing layer is 37% by weight or more and 62% by weight or less.
The film thickness of the white pigment-containing layer is 10 micrometers or more, and the film thickness is 10 micrometers or more.
The synthetic resin contained in the white pigment-containing layer contains an acrylic resin in which the weight% in the white pigment-containing layer is 16% by weight or more.
The sum of the weight% of the pigment in the white pigment-containing layer and the weight% of the synthetic resin in the white pigment-containing layer is 100% by weight or less.
The weight% of the silicon dioxide contained in the transparent protective layer in the transparent protective layer is 10% by weight or more and 30% by weight or less.
The film thickness of the transparent protective layer is 5 micrometers or more and 15 micrometers or less.
The structural material for an agricultural house according to claim 1, wherein the transparent protective layer further contains a wax having a weight% of 0.5% by weight or more and 3% by weight or less in the transparent protective layer. The weight% of the titanium dioxide contained in the pigment in the white pigment-containing layer is 30% by weight or more.
The structural material for an agricultural house according to claim 2, wherein the weight% of the wax in the transparent protective layer is 2% by weight or less.

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