Outer surface anticorrosive iron pipe

Abstract

To provide an outer surface anticorrosive iron pipe having excellent weather resistance while maintaining excellent corrosion resistance.SOLUTION: An outer surface anticorrosive iron pipe has a metallic thermal-spray coating layer, a coating layer formed of a sealing agent, and a coating layer made of a polyester resin powder paint on the outer surface of the pipe, where the polyester resin powder paint has a gloss retention rate of 65% or more after 300 hours when its coating film is subjected to a xenon weather meter test.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an iron pipe whose exterior surface is corrosion-protected, and more particularly to an iron pipe whose exterior surface is corrosion-protected using a specified polyester resin powder paint with improved weather resistance as a top coat on the exterior. [Background technology]

[0002] Ductile iron pipes are used as piping materials for water supply systems, and although they are often laid underground, they can also be laid exposed above ground.

[0003] Ductile iron pipes themselves are prone to corrosion, so corrosion protection is provided by forming a coating of zinc-based primer such as zinc-based thermal spraying or zinc-rich paint on the outside of the pipe, followed by a synthetic resin paint as a top coat. However, when piping is used in a highly corrosive environment, an exterior coating with even stronger corrosion protection is required.

[0004] Patent Document 1 discloses an iron pipe with high corrosion resistance, which is obtained by replacing the synthetic resin paint top coat with a highly corrosion-resistant powder paint and forming a corrosion-resistant layer on the outer surface of the iron pipe that includes a zinc-based sprayed coating layer, a coating layer made of a sealing agent, and a coating layer made of powder paint. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-148283 Summary of the Invention [Problem to be solved by the invention]

[0006] However, while the iron pipe disclosed in Patent Document 1, which has a corrosion-resistant layer on its outer surface including a zinc-based thermal spray coating layer, a coating layer made of a sealing agent, and a coating layer made of powder paint, has high corrosion resistance, there is still room for improvement in terms of weather resistance, which becomes a problem when the pipe is exposed above ground, for example, when a typical polyester resin powder coating is used as the powder coating.In general, with polyester resin powder coating, it is believed that there is a trade-off between weather resistance and corrosion resistance (anticorrosion properties).

[0007] Therefore, an object of the present invention is to provide an iron pipe having an external corrosion protection that has good weather resistance while maintaining good corrosion resistance. [Means for solving the problem]

[0008] The present inventors discovered that by combining a specific highly weather-resistant polyester powder coating, which has improved weather resistance compared to the polyester resin powder coatings conventionally used as top coats on cast iron pipes, as described in, for example, Patent Document 1, with a metal spray coating layer and a coating layer made of a sealant, it is possible to improve weather resistance without adversely affecting corrosion resistance (corrosion resistance), and thus completed the present invention. This is surprising considering that, in polyester resin powder coatings, there is generally a trade-off between weather resistance and corrosion resistance, and in fact, as described in Reference Examples 1 and 2 below, a specific highly weather-resistant polyester resin powder coating with improved weather resistance has inferior corrosion resistance when applied alone to cast iron pipes compared to polyester resins conventionally used as top coats.

[0009] That is, one aspect of the present invention is an externally corrosion-protected iron pipe having, on its outer surface, a metal spray coating layer, a coating layer made of a sealing agent, and a coating layer made of a highly weather-resistant polyester resin powder coating, wherein the polyester resin powder coating is a powder coating that, when the coating film is subjected to a xenon weather meter test, has a gloss retention rate of 65% or more after 300 hours. Regarding external corrosion-resistant iron pipes. [Effects of the Invention]

[0010] According to the present invention, by combining a specified polyester resin powder coating with enhanced weather resistance with a metal spray coating layer and a coating layer made of a sealing agent to provide external corrosion protection for an iron pipe, it is possible to provide an externally corrosion-protected iron pipe that has good weather resistance while maintaining good corrosion protection properties. DETAILED DESCRIPTION OF THE INVENTION

[0011] The externally corrosion-protected iron pipe of the present invention has, on its outer surface, a metal spray coating layer, a coating layer made of a sealing agent, and a coating layer made of a highly weather-resistant polyester resin powder paint. By using this highly weather-resistant polyester resin powder paint to form a coating that exhibits a certain level of performance in weather resistance tests, it is possible to obtain an externally corrosion-protected iron pipe that has good weather resistance without compromising corrosion prevention properties.

[0012] <Iron pipe> The iron pipe of the present invention is not particularly limited as long as it is made of an iron-based metal, and examples thereof include cast iron pipes and steel pipes.

[0013] <(a) Metal spray coating layer> In the present invention, a metal spray coating layer is first formed on the outer surface of an iron pipe to provide good corrosion resistance. The metal for forming the spray coating is selected to match the base metal. For example, a zinc-based spray coating is preferably used as a metal spray coating for iron-based metals. Specific examples include zinc spray coatings, zinc-aluminum alloy spray coatings, zinc-aluminum pseudoalloy spray coatings, zinc-silicon-containing aluminum pseudoalloy spray coatings, zinc-silicon-manganese-containing aluminum pseudoalloy spray coatings, and zinc-tin alloy spray coatings. Prior to this step, the outer surface of the pipe can be subjected to surface preparation such as blasting and cleaning, as needed. A zinc-aluminum pseudoalloy refers to a material in which sprayed zinc and aluminum overlap irregularly, forming an apparent zinc-aluminum alloy.

[0014] The thickness of the metal spray coating can be set appropriately depending on the type of base metal, the type of spray material, and the use of the resulting iron pipe. In the case of cast iron pipes for water pipes, the thickness of a zinc-based spray coating is preferably approximately 20 μm to 500 μm, and more preferably 20 μm to 100 μm.

[0015] The thermal spraying method is not particularly limited, and examples thereof include gas thermal spraying, arc thermal spraying, and plasma thermal spraying. More specifically, examples include a method in which zinc, a zinc-aluminum pseudoalloy or a zinc-aluminum alloy, or a zinc-silicon-manganese-containing aluminum pseudoalloy is sprayed onto a cast iron pipe that is being rotated and transported in the axial direction using a fixed thermal spray gun, and a method in which zinc is sprayed onto a rotating cast iron pipe while a thermal spray gun is being moved.

[0016] The amount of spraying of the metal spray coating layer is not particularly limited, but from the viewpoint of corrosion resistance and adhesion, it is preferably 130 to 600 g / m 2 is preferable, and 200 to 400 g / m 2 More preferably, 240 to 400 g / m 2 Furthermore, in the case of zinc spraying, in the Japan Ductile Iron Pipe Association standard JDPA Z 2010-2009 "Ductile Cast Iron Pipe Synthetic Resin Coating", the spraying amount is 130 g / m from the viewpoint of corrosion prevention. 2 This corresponds to a thickness of 20 μm. Therefore, in the case of zinc-based spray coatings such as zinc, zinc-aluminum pseudoalloy, zinc-aluminum alloy, zinc-silicon-containing aluminum pseudoalloy, or zinc-silicon-manganese-containing aluminum pseudoalloy, the spray amount should be 130 g / m from the viewpoint of corrosion prevention. 2 More than 180g / m 2 More preferably, 200 g / m 2 More preferably, 220 g / m 2 More preferably, 230 g / m 2 Even more preferably, 240 g / m 2 The above is particularly preferable, and in consideration of adhesion, 600 g / m 2 Preferably less than 400 g / m 2 Less than 360g / m is more preferable, and from the viewpoint of cost2 Less than 350 g / m 2 Less than 340 g / m is more preferable. 2 More preferably, 330 g / m 2 Even more preferably, 320 g / m 2 The following is particularly preferred: 2 More particularly preferred is 300 g / m 2 The following are most preferred:

[0017] <(b) Coating layer with sealing agent> In the iron pipe of the present invention, the surface of the above-mentioned metal spray coating is subjected to a conventional sealing treatment, and a coating layer made of a sealing agent is provided. This seals the pores in the metal spray coating, further enhancing the corrosion prevention effect, and even when a powder paint is used as the outer layer, it is possible to obtain an iron pipe that suppresses the occurrence of white rust and has excellent corrosion prevention properties.

[0018] The sealing agent is not particularly limited, and those generally used in this technical field can be used, for example, aqueous or solvent-based sealing agents including aqueous systems containing resin components such as acrylic resins and epoxy resins used in metal coatings, inorganic components such as colloidal silica, and additives such as surface conditioners.

[0019] In this specification, the terms "aqueous sealant" and "solvent-based sealant" are used to distinguish between sealants that use an aqueous medium, preferably water, as the medium for the sealant (aqueous sealant) and sealants that use a solvent that is a non-aqueous medium (solvent-based sealant), and are not intended to exclude aqueous sealants that contain a certain amount of organic solvent as a component, or solvent-based sealants that contain a certain amount of aqueous medium as a component. In the present invention, from the viewpoint of corrosion prevention, solvent-based sealants that use a non-aqueous solvent as the medium are preferably used.

[0020] Examples of the aqueous sealing agent include an aqueous sealing agent containing a resin component selected from an acrylic resin emulsion, an epoxy ester resin emulsion, an epoxy ester resin dispersion, an acrylic silicone resin dispersion, or a urethane resin dispersion, and an inorganic component, particularly lithium silicate.

[0021] Examples of the solvent-based sealing agent include a solvent-based sealing agent containing a resin component selected from an acrylic resin, an epoxy ester resin, an acrylic silicone resin, a urethane resin, an epoxy resin, a modified epoxy resin, an alkyd resin, or a polyester resin, and an inorganic component.

[0022] The solid content of the resin component constitutes the main component of the solid content of the sealer. The content of the solid content of the resin component in the sealer is preferably 10% by mass or more, more preferably 15% by mass or more. If the content of the solid content of the resin component in the sealer is less than 10% by mass, the solid content will be insufficient, making it difficult to form a film, and a sufficient film thickness will not be obtained in a single coating. Furthermore, the content of the solid content of the resin component in the sealer is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. If the content of the solid content of the resin component in the sealer exceeds 35% by mass, the viscosity will increase and atomization will tend to be poor when sprayed.

[0023] The acrylic resin is not particularly limited, but examples thereof include copolymers of conjugated diolefins having 4 to 6 carbon atoms and ethylenically unsaturated carboxylic acids, particularly copolymers of conjugated diolefins having 4 to 6 carbon atoms, ethylenically unsaturated carboxylic acids, ethylenically unsaturated aromatic monomers, and alkyl acrylates, as described in JP-A-8-159369, which can be used alone or in combination.

[0024] Examples of epoxy ester resins include reaction products of epoxy resins and fatty acids or reaction products of epoxy resins and polyacrylic acids. Examples of epoxy resins include, but are not limited to, bisphenol-type epoxy resins obtained by reacting bisphenols with epichlorohydrin. Specific examples include epoxy resins formed from the reaction products of epichlorohydrin and bisphenol A, epoxy resins formed from the reaction products of epichlorohydrin and bisphenol F, amine-modified epoxy resins obtained by reacting these epoxy resins with amines such as alkanolamines, and modified epoxy resins such as urethane-modified epoxy resins obtained by reacting these epoxy resins with polyisocyanate compounds. These can be used alone or in combination.

[0025] Examples of acrylic silicone resins include, but are not limited to, the reaction mixture of the above-mentioned acrylic resin with a low-molecular-weight silicone having a relatively large number of reactive groups such as silanol groups and methoxy groups. Examples of such silicones include, but are not limited to, organopolysiloxanes. These can be used alone or in combination.

[0026] The urethane resin is not particularly limited, but a reaction product of polyisocyanate and polyol can be used. Methods for dispersing urethane resin in water include forced emulsification using an emulsifier and self-emulsification using hydrophilic groups. Urethane resins are used in a variety of applications, and these can be used alone or in combination.

[0027] As for the epoxy resin, modified epoxy resin, alkyd resin or polyester resin, those generally used as coatings for iron pipes, particularly cast iron pipes, can also be used.

[0028] The acrylic resin emulsion, epoxy ester resin dispersion, acrylic silicone resin dispersion, and urethane resin dispersion are, respectively, the above-mentioned acrylic resin, epoxy ester resin, acrylic silicone resin, urethane resin, etc., emulsified by emulsion polymerization or an emulsifier, or dispersed in water by their own hydrophilic functional groups, and those commercially available for use in water-based paints can be used. The molecular weight and viscosity of the resin itself can be those with the performance generally used for water-based paints on metal substrates.

[0029] Specific examples of acrylic resin emulsions include, but are not limited to, Saivinol EC-7040 (manufactured by Saiden Chemical Co., Ltd.), Saivinol X-211-168E (manufactured by Saiden Chemical Co., Ltd.), and VONCORT EC-740EF (manufactured by DIC Corporation).

[0030] Specific examples of commercially available epoxy ester resin dispersions include WATERSOL EFD-5530 (manufactured by DIC Corporation), WATERSOL EFD-5560 (manufactured by DIC Corporation), and WATERSOL EFD-5580 (manufactured by DIC Corporation), but are not limited to these.

[0031] Specific examples of commercially available acrylic silicone resin dispersions include CERANATE WSA-1070 (manufactured by DIC Corporation) and VONCORT SA-6360 (manufactured by DIC Corporation), but are not limited to these.

[0032] Specific examples of urethane resin dispersions include commercially available products such as U-coat UX-485 (manufactured by Sanyo Chemical Industries, Ltd.) and Permarin UA-200 (manufactured by Sanyo Chemical Industries, Ltd.), but are not limited to these.

[0033] The inorganic component used in the sealing agent is not particularly limited, and various commercially available products can be used alone or in combination, such as lithium silicate, quaternary ammonium silicate, colloidal silica, etc. Examples of lithium silicate that can be used include lithium silicate 35, lithium silicate 45, and lithium silicate 75 manufactured by Nissan Chemical Industries, Ltd., and lithium silicate 35, lithium silicate 45, and lithium silicate 75 manufactured by Nippon Chemical Industries, Ltd.

[0034] The content of the inorganic component in the sealant is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 4% by mass or more. If the content of the inorganic component is less than 2% by mass, there is a risk that the corrosion prevention effect will not be sufficient. Furthermore, the content of the inorganic component in the sealant of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. If the content of the inorganic component exceeds 20% by mass, there is a tendency that problems will occur in the storage stability of the sealant.

[0035] The sealing agent can contain various other additives. Examples of other additives include known additives such as antifoaming agents such as mineral oil, silicone, or organic polymers; surface conditioners such as silicone or organic polymers; viscosity adjusters (anti-sagging agents) such as amide wax or organic bentonite; matting agents such as silica or alumina; dispersants such as polycarboxylates; ultraviolet absorbers such as benzophenone, hindered amine light stabilizers, and phenolic antioxidants; waxes; and coloring pigments. These can be used alone or in combination as needed.

[0036] The sealing agent can be produced using equipment commonly used in paint production. The production method is not particularly limited, but for example, a colored paste is produced by dispersing a colored pigment and a dispersant using an SG mill or the like. A predetermined resin, inorganic components, and optional additives (antifoaming agents, surface conditioners, etc.), organic solvents, etc. are added to this paste, and the mixture is stirred using a disperser or the like, followed by adding water to achieve the desired concentration, thereby obtaining the sealing agent.

[0037] The method for applying the sealing agent to the metal spray coating formed on the base metal is not particularly limited, but examples include brush coating, roller coating, air spray coating, airless spray coating, dip coating, shower coat coating, etc.

[0038] The thickness of the coating layer of the sealing agent can be set appropriately depending on the type of base metal, the type of spray material, and the use of the resulting iron pipe, but for example, in the case of a cast iron pipe for water supply, it is preferably 30 μm or less, more preferably 20 μm or less, and preferably 5 μm or more, more preferably 10 μm or more. If it is thinner than 5 μm, the sealing effect may not be sufficient over the long term, and if it is thicker than 30 μm, drying may be insufficient.

[0039] <(c) Coating layer made of highly weather-resistant polyester resin powder paint> In this specification, powder coating refers to a powdered coating, and more specifically, a powdered coating that does not contain organic solvents or water and is composed only of film-forming components. Specifically, it contains a resin component that is solid at room temperature, a curing agent, and, as necessary, various pigments, additives, etc. The powder coating used in the present invention is preferably a thermosetting powder coating, and particularly, a low-temperature curing powder coating that cures at 140 to 170°C (i.e., has a curing temperature of 140 to 170°C) and does not require a high-temperature baking process to cure the powder coating is preferably used.

[0040] For example, in the case of ductile cast iron pipes, the inner surface of the pipe is coated with an epoxy resin-based powder paint, which is usually heated to about 240°C. Therefore, when subsequently powder coating the outer surface of the pipe, by using a low-temperature curing powder paint that cures at 140 to 170°C, the powder coating can be performed on the outer surface of the pipe without a special baking process using the residual heat from the inner coating. Specifically, the curing temperature of the low-temperature curing powder paint is more preferably 140 to 160°C. Polyester-based powder paints that use a β-hydroxyalkylamide compound as a curing agent are low-temperature curing powder paints that cure at 140 to 170°C and are preferably used.

[0041] The method for applying the powder coating is not particularly limited, and the coating can be performed by spray coating, for example. More specifically, the powder coating can be applied by a method in which the iron pipe is rotated while the spray nozzle is moved in the axial direction of the pipe, and the powder coating is applied by spray coating. The thickness of the coating layer formed by applying the powder coating is preferably 100 μm or more, more preferably 200 to 300 μm. If the thickness is less than 100 μm, the corrosion resistance tends to decrease.

[0042] In an embodiment of the present invention, the coating layer made of a highly weather-resistant polyester resin powder paint is characterized by using, as the resin component, a polyester resin whose weather resistance has been improved by adjusting the composition of the acid component and alcohol component constituting the polyester resin to a predetermined value (hereinafter also referred to as highly weather-resistant polyester resin A). Such highly weather-resistant polyester resin A generally has acid components of terephthalic acid and isophthalic acid with a high content of isophthalic acid, and alcohol components of ethylene glycol and neopentyl glycol with a high content of neopentyl glycol.

[0043] In this embodiment, the curing agent used in the polyester powder coating is not particularly limited as long as it has the property of curing polyester, but examples include β-hydroxyalkylamide compounds, blocked isocyanate compounds, and unblocked isocyanate compounds. Among them, β-hydroxyalkylamide compounds are preferred because they produce only water as a by-product during curing and therefore have a low environmental impact. Furthermore, β-hydroxyalkylamide compounds are preferred because they allow curing at lower temperatures.

[0044] In this embodiment, various pigments such as titanium oxide, iron oxide, carbon black, phthalocyanine blue, calcium carbonate, barium sulfate, silica, and talc, as well as various additives such as fillers, dispersants, and surface conditioners, may be blended into the powder coating as needed. While this embodiment does not preclude the blending of an ultraviolet absorber, since highly weather-resistant polyester resin A is used, the effect of additionally blending an ultraviolet absorber is not particularly important, and from a cost perspective, there is no particular advantage to blending an ultraviolet absorber. The amount of pigment and filler added to the coating is preferably 20 to 50 wt %, more preferably 30 to 45 wt %, because it allows for thicker coating films. The powder coating can be manufactured by any method, including, for example, dry blending or hot melt blending.

[0045] When the highly weather-resistant polyester resin powder coating used in the present invention is subjected to a xenon weatherometer test using a coating film formed therefrom, the coating film exhibits a gloss retention of 65% or more after 300 hours of testing. A gloss retention of 68% or more is preferred. From the standpoint of weather resistance, the higher the gloss retention, the better, with the upper limit being 100%. This xenon weatherometer test is an accelerated weather resistance test conducted under the conditions of Cycle A (continuous operation, 18 minutes of wetting time, 102 minutes of drying time) specified in JIS K 5600-7-7 (2008): Xenon Lamp Method, Section 9.5. The gloss retention is calculated using the 60° gloss measured before and after the test using the following formula: Gloss retention = gloss after test ÷ gloss before test × 100 (%) The gloss level can be measured using, for example, a micro-tri-gloss gloss meter manufactured by BYK, but can also be measured using any other gloss level measuring device known in the art.

[0046] In order to enhance weather resistance, the externally corrosion-protected iron pipe of the present invention may be provided with a protective layer of wax or the like on the outside of the coating layer of highly weather-resistant polyester resin powder paint. [Example]

[0047] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0048] First, the materials used in the examples and comparative examples are shown below. <Sealing agent> Sealing agent A: GX Primer (a water-based sealing agent containing inorganic components in addition to resin components including acrylic resin emulsion) Sealing agent B: FP Guard (a water-based sealing agent containing an acrylic resin emulsion and an inorganic component, lithium silicate) Sealing agent C: FB Primer (a solvent-based sealing agent containing inorganic components in a resin component containing epoxy resin) <Powder paint> Powder coating (1): Polyester powder coating (curing temperature: 140°C, curing agent: β-hydroxyalkylamide) Powder coating (2): Polyester powder coating (curing temperature: 140°C, curing agent: β-hydroxyalkylamide)

[0049] Reference Examples 1 and 2 The powder coatings shown in Table 1 were applied to 150 x 90 mm ductile cast iron pieces as test pieces for the corrosion resistance test, and to 150 x 70 mm steel plates as test pieces for the weather resistance test, using an air spray to a film thickness of 200 μm, and then baked at 140 to 160°C. After natural cooling, the corrosion resistance and weather resistance of the obtained test pieces were evaluated according to Test Examples 1 and 2 described below. The results are shown in Table 1.

[0050] Test example 1: Corrosion resistance (combined cycle test) A 0.3mm wide x 50mm long cut was made in the center of the test piece along the diagonal of the test piece, reaching all the way to the steel substrate, and a combined cycle test (JIS K 5600-7-9 (2006), Cycle A of Appendix C: a test consisting of a salt spray test (35±1°C, 2 hours), drying (60±1°C, 4 hours), and immersion (50±1°C, 2 hours) in that order) was carried out for 90 cycles (30 days). The coating surface was inspected visually, and the corrosion protection was evaluated according to the following criteria. The results are shown in Table 1. However, an area 10mm from the end of the test piece was excluded from the evaluation range for red rust. The performance target was ○ or better.

[0051] (Judgment criteria) ◎: No white rust on the coating surface ○: White rust on the surface of the coating film, no red rust on the surface of the coating film △: Slight red rust on the coating surface ×: Red rust is present on the entire surface of the coating

[0052] Test Example 2: Weather resistance (I) (a) Accelerated testing Weather resistance was evaluated in accordance with the xenon lamp method of JIS K 5600-7-7. The test pieces obtained in Examples 1 to 12 and Comparative Examples 1 to 6 were set in an i-Super Xenon Tester XER-W75 (manufactured by Iwasaki Electric Co., Ltd.) and tested for 300 hours under the test conditions of cycle A specified in 9.5 of JIS K 5600-7-7 (2008). (b) Evaluation Before and after the test, 60° gloss measurement was carried out using a Micro Trigloss gloss meter (manufactured by BYK), and the gloss retention was calculated using the following formula. The results are shown in Table 1. Gloss retention = gloss after test ÷ gloss before test × 100 (%)

[0053] [Table 1]

[0054] The results of Test Examples 1 and 2 show that when used alone, the highly weather-resistant polyester resin powder coating (1) corrodes more rapidly than the conventional polyester resin powder coating (2) and has inferior corrosion resistance (Reference Examples 1 and 2).

[0055] Examples 1 to 6 and Comparative Examples 1 to 6 The outer surface of a ductile cast iron pipe with a nominal diameter of 100 is sprayed with zinc at 260 g / m as shown in Table 2. 2 or 390 g / m 2 Then, a zinc thermal spray coating was formed on the cast iron pipe. Then, a sealing agent shown in Table 2 was applied by air spraying at a rate of 100 g / m 2 The coating was applied and dried. The powder coating material shown in Table 2 was then sprayed onto the coating layer of the sealing agent using an air spray to a film thickness of 200 μm, and baked at 140 to 160°C. After natural cooling, 150 x 90 mm tile-shaped test pieces were cut from the resulting cast iron pipe, and the corrosion resistance and weather resistance performance were evaluated according to the following Test Examples 3 and 4. The results are shown in Table 2.

[0056] [Table 2]

[0057] Test example 3: Corrosion resistance (combined cycle test) The test specimens obtained in Examples 1 to 6 and Comparative Examples 1 to 6 were cut in the center in an X-shape along the diagonal of the specimen, reaching all the way to the steel substrate, measuring 0.3 mm wide and 50 mm long. A combined cycle test (JIS K 5600-7-9 (2006), Cycle A of Appendix C: a test consisting of a salt spray test (35±1°C, 2 hours), drying (60±1°C, 4 hours), and immersion (50±1°C, 2 hours) in that order) was performed for 360 cycles (90 days). The coating surface was visually inspected, and the corrosion resistance was evaluated according to the following criteria. The results are shown in Table 2. Note that the area 10 mm around the edge of the test specimen was excluded from the evaluation range for red rust. The performance target was ○ or better.

[0058] (Judgment criteria) ◎: No white rust on the coating surface ○: White rust on the surface of the coating film, no red rust on the surface of the coating film △: Slight red rust on the coating surface ×: Red rust is present on the entire surface of the coating

[0059] Test Example 4: Weather resistance (II) (a) Accelerated testing Weather resistance was evaluated in accordance with the xenon lamp method of JIS K 5600-7-7. The test pieces obtained in Examples 1 to 12 and Comparative Examples 1 to 6 were set in an i-Super Xenon Tester XER-W75 (manufactured by Iwasaki Electric Co., Ltd.) and tested for 300 hours under the test conditions of cycle A specified in 9.5 of JIS K 5600-7-7 (2008).

[0060] (b) Outdoor exposure test The test plates obtained in Examples 1 to 6 and Comparative Examples 1 to 6 were exposed outdoors (on the roof of the Kagaya factory of Kurimoto, Ltd.) for six months.

[0061] (c) Evaluation Evaluation of both (a) the accelerated test and (b) the outdoor exposure test was carried out visually at the end of each test using the following criteria. (Judgment criteria) ○: No abnormalities in appearance after either test (a) or (b) ×: Discoloration of the appearance after either test (a) or (b)

[0062] comprehensive evaluation The overall evaluation was based on the following criteria: (Judgment criteria) ◎: Weather resistance is ○, corrosion resistance is ◎ ○: Weather resistance and corrosion resistance are both ○ ×: If there is even one ×

[0063] The results of Test Examples 3 and 4 show that when powder coating (1) is used in combination with a metal spray coating layer and a coating layer made of a sealant, no decrease in corrosion resistance is observed, and good weather resistance is obtained without adversely affecting corrosion resistance (Examples 1 to 6). Furthermore, it can be seen that by using solvent-based sealant C, good corrosion resistance is obtained even when the amount of metal spray coating is small.

[0064] (summary) (1) In one aspect of the present invention, an externally corrosion-protected iron pipe is provided, which has on its outer surface a metal spray coating layer, a coating layer made of a sealing agent, and a coating layer made of a polyester resin powder paint, and the polyester resin powder paint is a powder paint that has a gloss retention rate of 65% or more after 300 hours when the coating film is subjected to a xenon weather meter test. This allows for the production of an externally corrosion-protected iron pipe with good weather resistance without sacrificing corrosion resistance.

[0065] (2) In the externally corrosion-protected iron pipe according to the embodiment (1) of the present invention, the metal sprayed coating layer is a zinc sprayed coating layer and has a coating density of 200 to 400 g / m 2 The coating amount is preferably 240 to 400 g / m 2 It is more preferable that:

[0066] (3) In either of the above-described embodiments (1) or (2) of the present invention, the sealing agent in the externally corrosion-protected iron pipe is preferably a solvent-based sealing agent containing an epoxy resin, which allows the metal spray coating layer to exhibit good corrosion protection even when the coating amount (film thickness) is relatively small (thin).

Claims

1. An externally corrosion-protected iron pipe having a metal spray coating layer, a coating layer made of a sealing agent, and a coating layer made of a polyester resin powder paint on the outer surface of the pipe, The polyester resin powder coating is a powder coating whose coating film has a gloss retention rate of 65% or more after 300 hours when subjected to a xenon weather meter test. Externally corrosion-resistant iron pipe.

2. The metal spray coating layer is a zinc spray coating layer, and has a coating weight of 200 to 400 g / m 2 2. The external corrosion-protected iron pipe according to claim 1, wherein the coating amount is:

3. 3. The externally corrosion-protected iron pipe according to claim 1, wherein the sealing agent is a solvent-based sealing agent containing an epoxy resin.

Images