Externally corrosion-resistant steel pipe and producing method thereof

Abstract

To provide an externally corrosion-resistant steep pipe including an externally corrosion-resistant coating film using water-based coating having excellent corrosion resistance and excellent adhesion.SOLUTION: An externally corrosion-resistant steel pipe includes a corrosion-resistant coating film composed of a first corrosion-resistant coating film formed from a first water-based acrylic resin coating on the outer surface of the steel pipe, and a second corrosion-resistant coating film formed from a second water-based acrylic resin coating on the first corrosion-resistant coating film. The first and second water-based acrylic resin coatings are different from each other, and the Tg of the first corrosion-resistant coating film is 20°C or lower. The method for producing the externally corrosion-resistant steel pipe includes (a) a zinc-based spraying step on the outer surface of the steel pipe, (b) a sealing treatment step on the sprayed coating surface, (c) a temperature adjustment step to adjust the outer surface temperature of the pipe to 50 to 80°C, and (d) a coating step in which the first water-based acrylic resin coating is spray-applied on the outer surface of the steel pipe in one direction to form the first corrosion-resistant coating film with a Tg of 20°C or lower, and then, in the return path, the second water-based acrylic resin coating, different from the first water-based acrylic resin coating, is spray-applied to form the second corrosion-resistant coating film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an iron pipe whose outer surface is treated with corrosion protection and a method for manufacturing the same. [Background technology]

[0002] Ductile iron pipes, which are mainly used as water pipes, are painted on their outer and inner surfaces to protect them. The outer surface of the pipe is painted to prevent corrosion when buried and to provide weather resistance when stored.

[0003] In recent years, in order to address environmental issues, there has been a shift from solvent-based paints to water-based paints, which have a smaller impact on the environment.

[0004] Patent Document 1 discloses an outer corrosion-resistant layer for metal pipes, which is characterized by a water-based paint that dries more slowly than solvent-based paints, and which contains 1 to 5 mass% of an acrylic resin emulsion and acrylic resin dispersion as solids with a glass transition temperature (Tg) of 28 to 50°C as the paint properties and characteristics, a film-forming aid content of 1 to 5 mass%, and a coating condition of a minimum film-forming temperature of 25 to 45°C. It is stated that this improves drying properties, corrosion resistance, scratch resistance, etc. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-2330 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the outer corrosion-resistant layer in the water-based paint disclosed in Patent Document 1 is desired to have further improved corrosion resistance, and there is also room for improvement in the adhesion to the substrate as a coating film performance.

[0007] Therefore, an object of the present invention is to provide an iron pipe having an external corrosion-protected layer made of a water-based paint that has good corrosion resistance and good adhesion. [Means for solving the problem]

[0008] The inventors have discovered that by using a corrosion-resistant coating for the exterior surface of an iron pipe, which coating is composed of a first corrosion-resistant coating made of a first water-based acrylic resin paint, which has a coating Tg (glass transition temperature) of 20°C or less and which is formed on the iron pipe side, and a second corrosion-resistant coating made of a second water-based acrylic resin paint different from the first water-based acrylic resin paint, the iron pipe can be externally protected using a water-based paint, and can also achieve external corrosion protection with excellent adhesion to the substrate, thereby completing the present invention.

[0009] That is, one aspect of the present invention is an external corrosion-protected iron pipe having a corrosion-protective coating film made of a water-based acrylic resin paint, The corrosion-resistant coating film is composed of a first corrosion-resistant coating film made of a first water-based acrylic resin paint formed on the outer surface of the iron pipe, and a second corrosion-resistant coating film made of a second water-based acrylic resin paint formed on the first corrosion-resistant coating film; and The first water-based acrylic resin paint is different from the second water-based acrylic resin paint, and the Tg of the first corrosion-resistant coating film is 20°C or less. The present invention relates to an iron pipe having an external corrosion protection.

[0010] Another aspect of the present invention is a method for manufacturing a pipe by using a zinc-based thermal spray coating on an outer surface of the pipe. (b) a sealing treatment step of applying a sealing agent to the surface of the zinc-based thermal spray coating to form a sealing film; (c) a temperature adjustment step of adjusting the temperature of the outer surface of the tube to 50 to 80°C; (d) A coating process in which a water-based acrylic resin paint is applied to the outer surface of the iron pipe while the iron pipe is rotated in the circumferential direction of the pipe, (d-1) a first coating step of spraying a first water-based acrylic resin paint from one end of the pipe to the other end in the axial direction to form a first anticorrosion coating film; (d-2) A second coating process in which a second water-based acrylic resin paint is sprayed in a return path from the other end of the pipe axis to the first end to form a second anticorrosion coating film. A painting process consisting of A method for manufacturing an externally corrosion-protected iron pipe, comprising: The first water-based acrylic resin paint is different from the second water-based acrylic resin paint, and the Tg of the first corrosion-resistant coating film is 20°C or less. The present invention relates to a manufacturing method characterized by the above-mentioned. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an externally corrosion-protected iron pipe provided with an external corrosion-protective coating film using a water-based paint having good corrosion resistance and good adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0012] An externally corrosion-protected iron pipe according to one embodiment of the present invention has a corrosion-protective coating made of a water-based acrylic resin paint. This corrosion-protective coating is composed of a first corrosion-protective coating made of a first water-based acrylic resin paint formed on the outer surface of the iron pipe, and a second corrosion-protective coating made of a second water-based acrylic resin paint formed on the first corrosion-protective coating. The first corrosion-protective coating has a Tg of 20°C or less, unlike the first water-based acrylic resin paint and the second water-based acrylic resin paint. As a result, the externally corrosion-protected iron pipe of the present invention has good corrosion resistance and good adhesion.Specifically, by providing a coating film with a low Tg (first corrosion-protective coating film) between a coating film (second corrosion-protective coating film) made of water-based acrylic resin paint with a Tg (e.g., 30 to 60°C) appropriate for a conventional external corrosion-protective layer and the substrate on the iron pipe side, the first corrosion-protective coating film with a low Tg is soft at room temperature, so it has better conformability to the substrate and acts like an adhesive, improving the adhesion between the substrate and the corrosion-protective coating film.It is presumed that the corrosion resistance of the corrosion-protective coating film with improved adhesion is also improved.

[0013] In this specification, the terms "(meth)acrylate" and "(meth)acrylic acid" are general terms for "methacrylate", "acrylate", "methacrylic acid", and "acrylic acid", respectively.

[0014] As used herein, the term "glass transition temperature" or "Tg" refers to a value measured by differential scanning calorimetry (DSC).

[0015] <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.

[0016] <Anti-corrosion coating made from water-based acrylic resin paint> The anticorrosion coating film made from the water-based acrylic resin paint of the present invention is composed of a first anticorrosion coating film made from a first water-based acrylic resin paint and a second anticorrosion coating film made from a second water-based acrylic resin. The term "water-based" in water-based acrylic resin paint is used to distinguish it from solvent-based paints and refers to paints that use water as a medium. It does not exclude the use of components containing a certain amount of organic solvents. In other words, the water-based acrylic resin paint used in the present invention is a water-based medium to which acrylic resin emulsions or acrylic resin dispersions as resin components, pigments such as rust-preventive pigments, extenders, and coloring pigments, and optionally, film-forming aids are added. Water is preferably used as the aqueous solvent, and a small amount of organic solvent may be added to adjust interfacial tension and improve wettability to iron pipe substrates, zinc-based thermal spray coatings, or sealing membranes.

[0017] Furthermore, when the water-based acrylic resin paint of the present invention is used for, for example, a water pipe, a paint conforming to the synthetic resin paint specified in the Japan Water Works Association standard JWWA K 139 "Synthetic resin paint for ductile cast iron pipes for water supply" can be suitably used in accordance with the present invention.

[0018] (acrylic resin emulsion) An acrylic resin emulsion is an emulsion in which an acrylic resin is dispersed in water, optionally containing additives such as surfactants. The acrylic resin constituting an acrylic resin emulsion is typically a polymer obtained by polymerizing one or more acrylic monomers selected from the group consisting of acrylic acid, methacrylic acid, and their esters. However, it also includes copolymers obtained by copolymerizing one or more acrylic monomers with one or more monomers other than acrylic monomers, and copolymers of acrylic monomers with copolymers of two or more monomers other than acrylic monomers. The acrylic resin is not particularly limited, and those commonly used in the paint industry may be used alone or in combination of two or more. Examples of such acrylic resins include styrene-butadiene acrylic resins and styrene-based acrylic resins. Of the acrylic monomers, specific examples of the acrylic acid esters and methacrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate. Specific examples of monomers other than acrylic monomers include styrene and butadiene.

[0019] The synthesis method of the acrylic resin is not particularly limited, and known polymerization methods such as emulsion polymerization can be used. For example, the acrylic resin emulsion can be prepared by charging a mixture (monomer premix) of monomers, emulsifiers, polymerization initiators, etc. all at once into a reaction vessel containing a predetermined amount of water, emulsion-polymerizing the monomer mixture, and after the reaction is completed, cooling and neutralizing the reaction product to obtain the desired aqueous acrylic emulsion.

[0020] The emulsifier used in the above reaction is an essential component for forcibly emulsifying the acrylic resin emulsion in water. Specific examples include anionic polymeric emulsifiers such as fatty acid soap, rosin acid soap, alkyl sulfonate, alkyl benzene sulfonate, dialkyl aryl sulfonate, alkyl sulfosuccinate, and polyoxyethylene alkyl sulfate; and nonionic polymeric emulsifiers such as polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, polyoxyethylene sorbitan fatty acid ester, and oxyethylene oxypropylene block copolymer. These emulsifiers can be used alone or in combination. Nonionic and anionic emulsifiers can also be used in combination, as can cationic and amphoteric surfactants. The amount of emulsifier used is preferably 0.3 to 3 parts by weight per 100 parts by weight of the total amount of polymerizable monomers used in emulsion polymerization.

[0021] Examples of the polymerization initiator used in the emulsion polymerization reaction include aqueous catalysts such as potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide; and oil-based catalysts such as tert-butyl hydroperoxide and cumene hydroperoxide. The amount of the polymerization initiator used is preferably 0.1 to 0.7 parts by weight per 100 parts by weight of the polymerizable monomers to be subjected to emulsion polymerization.

[0022] In emulsion polymerization, molecular weight regulators such as chain transfer agents and polymerization terminators, as well as polymerization rate regulators, can be used as appropriate during polymerization to adjust the molecular weight. Furthermore, molecular weight control can be achieved by halting the reaction by cooling. Examples of chain transfer agents include mercaptans such as tert-dodecyl mercaptan, n-todecyl mercaptan, octyl mercaptan, n-tetradecyl mercaptan, and n-hexyl mercaptan; terpinolene; terpinene; α-methylstyrene dimer; ethyl xanthogen disulfide; diisopropyl xanthogen sulfide; aminophenyl sulfide; and tetraethylthiuram disulfide. These can be used alone or in combination of two or more. The amount of chain transfer agent used is preferably 1.0 part by weight or less per 100 parts by weight of the total amount of polymerizable monomers used in emulsion polymerization.

[0023] Examples of polymerization terminators include hydroquinone (phenol), amine-based sulfur, hydroxylamine sulfate, ammonia, caustic soda, and caustic potassium, as well as other agents with polymerization-terminating properties. These agents can be used alone or in combination of two or more. The amount used varies depending on the type of polymerization inhibitor and its reactivity with the monomer. In emulsion polymerization reactions, in addition to the emulsifier, chain transfer agent, and polymerization initiator, various additives such as electrolytes and pH adjusters may also be used as needed.

[0024] Specific examples of the acrylic resin emulsions described above include Luckstar 3700D (manufactured by DIC Corporation, Tg 7°C), Boncoat CM-8430 (manufactured by DIC Corporation, Tg 33°C), Boncoat CP-6450 (manufactured by DIC Corporation, Tg 42°C), Boncoat EC-5400EF (manufactured by DIC Corporation, Tg 6°C), JE-1056 (manufactured by Seiko PMC Corporation, Tg 82°C), and NeoCryl A655 (manufactured by DSM).

[0025] (acrylic resin dispersion) The acrylic resin dispersion used in the present invention is blended into an aqueous paint to form a coating film with excellent corrosion resistance. In the present invention, the acrylic resin dispersion is a self-emulsifying dispersion in which some hydrophilic group is chemically introduced into the acrylic resin skeleton, and the resin itself has emulsifying ability, and additives such as a neutralizer and an antifoaming agent are included as necessary. The acrylic resin skeleton constituting the acrylic resin dispersion can usually be the same as the acrylic resin constituting the above-mentioned acrylic resin emulsion. Representative examples of components having a hydrophilic group to be introduced into the acrylic resin skeleton include, but are not limited to, acids such as (meth)acrylic acid, crotonic acid, citraconic acid, maleic acid, fumaric acid, itaconic acid, and maleic anhydride; and (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 24 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and dodecyl (meth)acrylate.

[0026] Specific examples of the acrylic resin dispersions mentioned above include Watersol S-720 (manufactured by DIC Corporation, Tg 45°C), Acronal YJ-1100D (manufactured by BASF Dispersions), and Bayhydrol XP2470 (manufactured by Bayer).

[0027] (Film-forming aid) Examples of film-forming aids that can be used in water-based acrylic resin paints include propylene glycol, propylene glycol monomethyl ether (PGMME), propylene glycol monoethyl ether, propylene glycol monopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol monoisobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, ethylene glycol monoisobutyl ether, diethylene glycol mono-tert-butyl ether, and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and ethylene glycol mono-n-butyl ether is preferred from the viewpoint of film-forming properties.

[0028] (pigment) In the anticorrosion coating film of the present invention, pigments can be blended to impart sufficient coloring properties and rust prevention properties to the water-based paint. Specific examples include color pigments such as titanium dioxide, iron oxide, carbon black (e.g., trade name MA100, manufactured by Mitsubishi Chemical Corporation), cyanine blue, and cyanine green; extender pigments such as calcium carbonate, talc, barium sulfate, and clay; and rust-preventive pigments such as zinc phosphate, calcium phosphate, and aluminum phosphomolybdate. These pigments may be used alone, or two or more may be mixed together as needed.

[0029] (Other ingredients) In addition to the above components, known additives can be added to the above water-based paint as needed. Examples of other additives include antifoaming agents made of silicone or organic polymers; surface conditioners made of silicone or organic polymers; viscosity adjusters (anti-sagging agents) made of amide wax, organic bentonite, etc.; matting agents made of silica, alumina, etc.; dispersants made of polycarboxylates, etc.; ultraviolet absorbers made of benzophenone, etc.; hindered amine light stabilizers; phenolic antioxidants; waxes, etc. These can be used alone or in combination as needed.

[0030] (1st water-based acrylic resin paint) The first water-based acrylic resin coating material can be obtained by using the above-mentioned resin components and further adding various pigments, film-forming aids, etc. so that the Tg of the coating film formed is 20° C. or less.

[0031] The resin component used in the first water-based acrylic resin coating material can be appropriately selected from the above-mentioned acrylic resin emulsions and acrylic resin dispersions, and among these, it is preferable that the coating material mainly contains a styrene-butadiene acrylic resin emulsion.

[0032] In the first aqueous acrylic resin paint, the content of the film-forming aid is not particularly limited and can be appropriately set according to the type of acrylic resin used so that the Tg of the coating film is 20°C or less. Usually, the content of the film-forming aid in the first aqueous acrylic resin paint is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. The content of the film-forming aid in the first aqueous acrylic resin paint is preferably 5% by mass or less, more preferably 3% by mass or less. If the content of the film-forming aid exceeds 5% by mass, the drying of the coating film tends to be slow.

[0033] (2nd water-based acrylic resin paint) The second water-based acrylic resin paint uses a resin component different from that of the first water-based acrylic resin paint. It can be obtained by adding various pigments, film-forming aids, etc. to match the desired Tg of the coating film to be formed.

[0034] The resin component used in the second aqueous acrylic resin coating material can be appropriately selected from the above-mentioned acrylic resin emulsions and acrylic resin dispersions. Among them, it is preferable that the coating material mainly contains a styrene-based acrylic resin emulsion. Furthermore, from the viewpoint of corrosion prevention, it is more preferable that the coating material further contains an acrylic resin dispersion.

[0035] In the second aqueous acrylic resin paint, the content of the acrylic resin dispersion is 1% by mass or more, preferably 2% by mass or more, in terms of solid content. If the content of the acrylic resin dispersion is less than 1% by mass, in terms of solid content, corrosion prevention tends to decrease. The content of the acrylic resin dispersion in the aqueous paint is 8% by mass or less, preferably 5% by mass or less, in terms of solid content. If the content of the acrylic resin dispersion is more than 8% by mass, in terms of solid content, drying tends to be slow.

[0036] In the second aqueous acrylic resin paint, the content of the film-forming aid is not particularly limited and can be appropriately set according to the type of acrylic resin used so that the Tg of the coating film falls within the desired range. Usually, the content of the film-forming aid in the second aqueous acrylic resin paint is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. The content of the film-forming aid in the second aqueous acrylic resin paint is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. If the content of the film-forming aid exceeds 15% by mass, the drying of the coating film tends to be slow.

[0037] The water-based paint is produced using equipment commonly used in paint production. The production method is not particularly limited, but for example, the desired paint can be obtained by adding pigments, additives (pigment dispersants, viscosity modifiers, etc.), solvents, etc. to commercially available resin components, and then dispersing them using a roll mill, SG mill, disperser, etc.

[0038] The formation of the anticorrosion coating film using the water-based paint is not particularly limited, but is usually carried out after adjusting the temperature of the iron pipe. The surface temperature of the iron pipe before coating with the water-based paint is preferably 50 to 80°C, more preferably 60 to 75°C. If the temperature is below 50°C, the coating film tends to be difficult to dry, and if the temperature is above 80°C, the water in the paint tends to boil. The coating method is not particularly limited, but as will be explained in the manufacturing method of an externally corrosion-protected iron pipe described below, it is preferable to use air spray coating to continuously apply the first anticorrosion coating film and the second anticorrosion coating film to the rotating iron pipe while moving the air spray in both outward and return directions, respectively.

[0039] (First anti-corrosion coating) The first corrosion-protective coating film is formed by applying a first water-based acrylic resin paint, and has a coating Tg of 20°C or less. The Tg of the first corrosion-protective coating film is preferably 5°C or higher. The Tg of the first corrosion-protective coating film is preferably 15°C or lower, and more preferably 10°C or lower. If the Tg of the first corrosion-protective coating film is lower than 5°C, the paint tends to have poor stability during storage, and if it exceeds 20°C, the adhesion improvement effect is not sufficiently obtained.

[0040] (Second anti-corrosion coating) The second corrosion-protective coating film is formed by applying a second water-based acrylic resin paint. The Tg of the second corrosion-protective coating film is preferably 30°C or higher. The Tg of the second corrosion-protective coating film is preferably 60°C or lower, more preferably 50°C or lower. If the Tg of the second corrosion-protective coating film is lower than 30°C, the blocking resistance of the outermost coating film tends to decrease, and if it exceeds 60°C, the spray applicability tends to deteriorate.

[0041] The thickness ratio of the first corrosion protective coating to the second corrosion protective coating in the corrosion protective coating is not particularly limited, but is preferably 1:1 to 4:1, and from the viewpoint of corrosion prevention, more preferably 1.5:1 to 3:1. If the thickness of the first corrosion protective coating is thinner than that of the second corrosion protective coating, adhesion tends to decrease, and if the thickness of the first corrosion protective coating is more than four times the thickness of the second corrosion protective coating, blocking resistance tends to decrease.

[0042] The total thickness of the corrosion-resistant coating, including the first and second corrosion-resistant coatings, is not particularly limited. However, the Japan Ductile Iron Pipe Association standard JDPA Z 2010-2009, "Synthetic Resin Coating for Ductile Cast Iron Pipes," stipulates that the total thickness, including the thermal spray coating, must be 100 μm or more to achieve the required corrosion resistance and durability. Therefore, the thickness of the corrosion-resistant coating preferably meets this standard, and is preferably 80 to 150 μm. If the thickness of the corrosion-resistant coating is less than 80 μm, corrosion resistance tends to decrease, and if it exceeds 150 μm, drying after coating tends to decrease.

[0043] <Zinc-based thermal spray coating> In the present invention, in order to provide better corrosion resistance, it is preferable to first provide a zinc-based sprayed coating on the outer surface of the iron pipe. Specific examples of zinc-based sprayed coatings include zinc sprayed coatings, zinc-aluminum alloy sprayed coatings, zinc-aluminum pseudoalloy sprayed coatings, zinc-silicon-containing aluminum pseudoalloy sprayed coatings, zinc-silicon-manganese-containing aluminum pseudoalloy sprayed coatings, and zinc-tin alloy sprayed coatings. Prior to this step, the outer surface of the pipe can be subjected to surface preparation such as blasting and cleaning, as necessary. The term "zinc-aluminum pseudoalloy" refers to a material in which sprayed zinc and aluminum overlap irregularly, forming an apparent zinc-aluminum alloy.

[0044] The thickness of the zinc-based sprayed 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, but in the case of cast iron pipes for water pipes, the thickness is preferably approximately 20 μm to 500 μm, and more preferably 20 μm to 100 μm.

[0045] 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 an 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 iron pipe while a thermal spray gun is being moved.

[0046] The amount of zinc sprayed is 130g / m2 from the viewpoint of corrosion prevention, according to the Japan Ductile Iron Pipe Association standard JDPA Z 2010-2009 "Ductile Cast Iron Pipe Synthetic Resin Coating". 2 The standard is to spray more than 180g / m², which corresponds to a thickness of 20µm. 2 More preferably, 200 g / m 2 More preferably, 600 g / m 2 Preferably less than 400 g / m 2 The following is more preferable: When a zinc-aluminum pseudoalloy, a zinc-aluminum alloy, a zinc-silicon-containing aluminum pseudoalloy, or a zinc-silicon-manganese-containing aluminum pseudoalloy is sprayed, the spray amount is 130 to 600 g / m from the viewpoint of corrosion resistance. 2 The range is 180 to 500 g / m 2 The range is preferably 200 to 400 g / m 2 The range is more preferable.

[0047] <Sealing membrane> In the present invention, it is preferable to provide a sealing film by performing a conventional sealing treatment with a sealing agent on the surface of the above-mentioned zinc-based thermal spray coating, thereby sealing the pores of the zinc-based thermal spray coating and further enhancing the corrosion prevention effect.

[0048] The sealing agent is not particularly limited, and any agent generally used in this technical field can be used. For example, sealing agents containing additives such as inorganic compounds such as colloidal silica and surface conditioners in a resin component such as an acrylic resin, epoxy resin, or acrylic silicone resin used in metal coatings can be used. These can be divided into aqueous sealing agents using water as a medium and solvent-based sealing agents using a solvent as a medium.

[0049] In this specification, the terms "aqueous sealing agent" and "solvent-based sealing agent" are used to distinguish between sealing agents that use an aqueous medium, preferably water, as the medium for the sealing agent (aqueous sealing agent) and sealing agents that use a solvent, which is a non-aqueous medium (solvent-based sealing agent), and are not intended to exclude aqueous sealing agents that contain a certain amount of organic solvent as a constituent component, or solvent-based sealing agents that contain a certain amount of aqueous medium as a constituent component. In the present invention, aqueous sealing agents that use an aqueous solvent, more preferably water, as the medium are preferably used.

[0050] 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.

[0051] 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 Industry Co., Ltd.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] The method for applying the sealing agent to the zinc-based thermal 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.

[0056] The thickness of the sealing film formed by the sealing treatment 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 is preferably, for example, approximately 5 to 30 μm. In particular, for cast iron pipes used for water pipes, the thickness is preferably 30 μm or less, more preferably 20 μm or less, and preferably 5 μm or more, more preferably 10 μm. If the thickness 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.

[0057] <Method of manufacturing externally corrosion-resistant iron pipes> Another embodiment of the present invention relates to a method for manufacturing an externally corrosion-protected iron pipe, which includes: (a) a spraying step of spraying a zinc-based thermal spray onto the outer surface of the iron pipe to form a zinc-based thermal spray coating; (b) a sealing step of applying a sealing agent to the surface of the zinc-based thermal spray coating to form a sealing coating; (c) a temperature adjustment step of adjusting the temperature of the outer surface of the pipe to 50 to 80°C; and (d) a coating step of coating the outer surface of the iron pipe with a water-based acrylic resin paint while the iron pipe is rotated circumferentially, the coating steps comprising: (d-1) a first coating step of spraying a first water-based acrylic resin paint from one end of the pipe axially to the other in a forward direction to form a first corrosion-protective coating; and (d-2) a second coating step of spraying a second water-based acrylic resin paint from the other end of the pipe axially to the first end in a return direction to form a second corrosion-protective coating, wherein the first corrosion-protective coating has a Tg of 20°C or lower, which is different from the first water-based acrylic resin paint and the second water-based acrylic resin paint. As a result, the external corrosion-protected iron pipe of the present invention has good corrosion resistance and good adhesion. Specifically, a first water-based acrylic resin paint is applied to the sealing film of an iron pipe that has been subjected to zinc-based thermal spraying and sealing treatment to form a coating with a low Tg (first corrosion-protective coating), and then a second water-based acrylic resin paint is applied on top of that to form a coating with a water-based paint having a Tg (e.g., 30 to 60 °C) suitable for conventional external corrosion-protective coatings (second corrosion-protective coating). Because the first water-based acrylic resin paint is soft at room temperature, it has increased conformability to the substrate and acts as an adhesive, improving adhesion between the substrate and the corrosion-protective coating. It is also believed that the corrosion resistance of the corrosion-protective coating with improved adhesion is also improved. Furthermore, because the first water-based acrylic resin paint and the second water-based acrylic resin paint can be applied back and forth without any significant interval, recoating can be performed using two types of paint without impairing workability.

[0058] ((a) Thermal spraying process) (a) With regard to the thermal spraying process, the above-mentioned explanation of the externally corrosion-protected iron pipe, together with the method of formation, shall apply unless there is a particular contradiction.

[0059] ((b) Sealing treatment process) (b) Unless otherwise specified, the sealing process and the method of formation described above for the externally corrosion-protected iron pipe shall apply.

[0060] ((c) Temperature adjustment process) The (c) temperature adjustment step in the method for manufacturing an externally corrosion-protected iron pipe of the present invention is a step of adjusting the temperature of the outer surface of the iron pipe that has undergone the (a) thermal spraying step and the (b) sealing step to 50 to 80°C for the subsequent painting step with a water-based acrylic resin paint. If the outer surface temperature of the pipe is lower than 50°C, the temperature is increased, and if it is higher than 80°C, the temperature is cooled. It is more preferable to adjust the outer surface temperature of the pipe to 60 to 75°C for the painting step with a water-based acrylic resin paint. Methods for heating the outer surface of the pipe include, but are not limited to, methods such as placing the iron pipe in an electric furnace, gas furnace, or hot water bath and heating it. Methods for cooling the outer surface of the pipe include, but are not limited to, natural cooling, for example.

[0061] ((d) Painting process) The (d) coating step in the manufacturing method of an externally corrosion-protected iron pipe of the present invention is a coating step in which a water-based acrylic resin paint is applied to the outer surface of the iron pipe while the iron pipe is rotated circumferentially, and includes (d-1) a first coating step in which a first water-based acrylic resin paint is spray-applied in a forward pass from one end of the pipe in the axial direction to the other to form a first corrosion-protective coating, and (d-2) a second coating step in which a second water-based acrylic resin paint is spray-applied in a backward pass from the other end of the pipe in the axial direction to the first end to form a second corrosion-protective coating. Note that in this specification, the forward pass may be referred to as the first pass, and the backward pass may be referred to as the second pass.

[0062] (d) The painting process will be described in more detail. First, the iron pipe, whose temperature has been adjusted so that the outer surface temperature of the pipe is 50 to 80°C in the painting process following the (c) process, is rotated circumferentially by a pipe body rotation device or the like that supports and rotates the iron pipe. While the iron pipe is rotating circumferentially, a first water-based acrylic resin paint is spray-painted from one end of the pipe in the axial direction to the other end using a painting device ((d-1) outward pass). After that, a second water-based acrylic resin paint is applied to the painting device that has reached the other end, and the second water-based acrylic resin paint is spray-painted from the other end to the first end ((d-2) return pass). In this case, the painting can be performed by moving the painting device or by moving the iron pipe. When the iron pipe is large, it is preferable to move the painting device to paint due to the construction location.

[0063] From the viewpoint of adhesion, the switching time between the first coating step (d-1) and the second coating step (d-2) is preferably less than 10 seconds, and it is more preferable to perform the steps continuously without any switching time.

[0064] The properties of the first and second corrosion-resistant coatings, the thickness of the other corrosion-resistant coatings, and the thickness ratio between the first and second corrosion-resistant coatings are the same as those described above for the externally corrosion-resistant iron pipe. The thickness of the coating may be adjusted by adjusting the amount of paint dispensed or the coating speed.

[0065] In addition, unless there is any particular contradiction, all of the above-mentioned explanations regarding the externally corrosion-protected iron pipe of the present invention also apply to the manufacturing method for the externally corrosion-protected iron pipe of the present invention, and all of the above-mentioned explanations regarding the manufacturing method for the externally corrosion-protected iron pipe of the present invention also apply to the externally corrosion-protected iron pipe of the present invention. [Example]

[0066] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0067] First, the materials used in the examples and comparative examples are shown below. <Sealing agent> Sealing agent: GX Primer (a water-based sealing agent containing inorganic components in addition to resin components including acrylic resin emulsion) <Water-based acrylic resin paint> Paint A: Kurimoto Coat WR-Gaimen manufactured by Dai Nippon Paint Co., Ltd. (resin components: styrene butadiene acrylic resin emulsion 45% by mass, pigment (extender pigment: magnesium oxide and calcium carbonate, color pigment: carbon black) 43.5% by mass, additive (film-forming aid: butyl cellosolve) 1.0% by mass, water-based paint containing 10.5% by mass of water, coating Tg: 7°C) Paint B: Kurimoto Coat WR-BH manufactured by Dai Nippon Paint Co., Ltd. (resin components: 56% by mass of a mixture containing styrene-based acrylic resin emulsion, acrylic resin emulsion, and acrylic resin dispersion, 23.0% by mass of pigment (anti-rust pigment: zinc phosphate, extender pigment: barium sulfate and calcium carbonate, color pigment: carbon black), 14.0% by mass of additive (film-forming aid: butyl cellosolve), water-based paint containing 7.0% by mass of water, coating Tg: 40°C)

[0068] Comparative Example 1 and Examples 1 to 3 An NS-type ductile iron pipe (E-type pipe) (nominal diameter: 100 × length: 1200 mm) with an epoxy resin powder coating on the inside was prepared. The outer surface of this iron pipe was sprayed with zinc at 130 g / m 2 A zinc spray coating was formed on the iron pipe. After that, a sealing agent was applied at a rate of 100 g / m2 by air spraying. 2 The iron pipe was then heated in a gas furnace so that the pipe temperature before painting with the acrylic resin paint was 60-65°C. While rotating the pipe at 100 m / min (270 rpm), the air spray nozzle was directed in the axial direction of the pipe at a speed of 26 m / min, from one end of the pipe to the other as the first pass, and from the other end to the first as the second pass, and the acrylic resin paint was applied according to Table 1. The film thickness was adjusted by the amount of paint sprayed. The pipe was allowed to cool and dry naturally to form a coating, and the performance of the coating was evaluated using the tests described below.

[0069] [Table 1]

[0070] Test Example 1: Coating adhesion (1) Preparation of test specimens The ductile iron pipes obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were cut into test pieces of 150×90 mm. (2) Test method The test specimens were subjected to adhesion tests in accordance with JIS K 5600-5-6 (General Test Methods for Paints - Part 5: Mechanical Properties of Coatings - Section 6: Adhesion (Cross-Cut Method)). As described in test methods 7.1.3 and 7.1.4, the cross-cut width was 2 mm, and six cross-cuts were made in the test specimens with a cutter knife, reaching the substrate (iron surface) in perpendicular directions. After the cuts, a tape peel test was performed on the coating film in the cross-cut areas, and the peeling status was observed. (3) Evaluation The evaluation was carried out in accordance with the description in 8.3 Table 1 "Classification of test results" of JIS K 5600-5-6 shown below. TIFF2025154012000002.tif97164

[0071] It can be seen from Table 1 that the anticorrosion coating film on the externally corrosion-protected iron pipe of the present invention has better adhesion than those of Comparative Examples 1 and 2. It can also be seen that, for Examples 1 to 3, in which the interval between outward and return painting is 0 seconds, and Examples 4 to 6, in which the interval is 10 seconds, the shorter the interval between the outward and return painting, the better the adhesion.

[0072] Test Example 2: Neutral salt spray resistance (corrosion prevention) In order to confirm the long-term durability of the coating film, a test was conducted in accordance with JIS K 5600-7-1 (General test methods for paints - Part 7: Long-term durability of coating film - Section 1: Neutral salt spray resistance).

[0073] The ductile iron pipes obtained in Examples 1 to 3 and Comparative Example 1 were cut into 150 x 90 mm tile-shaped pieces, and the cut surfaces were repaired with paint to prepare test specimens. A cross-cut was made in the center of the test surface of the test specimen, reaching down to the base (iron surface). The test was then carried out in an environment where an ambient temperature of 35°C was used and a 5% aqueous solution of sodium chloride was sprayed, and the surface condition was observed after 120 hours. The results are shown in Table 1. However, the area within 10 mm of the end of the test specimen was excluded from the evaluation range for red rust. The performance target was 0 to 2.

[0074] The results are shown in Table 1. The evaluation criteria are as follows: 0: No red rust on the cut area or anywhere other than the cut area 1: No rust except on the cut area, slight rust on the cut area 2: No rust except on the cut area, some rust on the cut area 3: No red rust except on cut areas, but a lot of red rust on cut areas 4: A small amount of red rust has occurred in areas other than the cut area, and a large amount of red rust has occurred in the cut area. 5: Red rust is found in areas other than the cut area, and in the cut area

[0075] Test example 3: Combined cycle test (corrosion resistance) To confirm the long-term durability of the coating, a test was conducted in accordance with JIS K 5600-7-9 (2006), Appendix C, Cycle A (combined cycle test).

[0076] The ductile iron pipes obtained in Examples 1 to 3 and Comparative Example 1 were cut into 150 x 90 mm tile-shaped pieces, and the cut surfaces were repaired and painted to prepare test specimens. A 0.3 mm wide x 50 mm long cut was made in the center of each test specimen, extending diagonally down the diagonal of the specimen and reaching the substrate (iron surface). The specimens were then subjected to 270 cycles (90 days) of combined cyclic testing (JIS K 5600-7-9 (2006), Cycle A of Annex C: salt spray test (35±1°C, 2 hours), drying (60±1°C, 4 hours, 20-30% RH), and immersion (50±1°C, 2 hours, 95% RH or higher)). The surface condition after the test was evaluated. The results are shown in Table 1. Note that the area 10 mm from the end of the specimen was excluded from the evaluation range for red rust. The performance target was 0-2.

[0077] The evaluation criteria were the same as those in Test Example 2.

[0078] In Test Example 2, it can be seen that no red rust occurred in either the cut or non-cut areas of any of the test pieces, including the comparative example, and good results were obtained. On the other hand, in Test Example 3, it can be seen that the anticorrosive coatings on the externally corrosion-protected iron pipes of Examples 1 to 3 of the present invention have superior anticorrosion properties compared to that of Comparative Example 1. In Test Example 3, the anticorrosive performance was evaluated over a longer period of time, and it can be seen that there is a difference in the anticorrosive properties between Examples 1 to 3 and Comparative Example 1. This is thought to be because Paint A used in the outward painting of Examples 1 to 3 has a lower porous ratio in the paint than Paint B used in the outward painting of Comparative Example 1, making it difficult for moisture and salt to penetrate into the porous parts, which, combined with the results of Test Example 1, results in improved anticorrosive properties.

[0079] (summary) (1) In one aspect of the present invention, an external corrosion-protected iron pipe having a corrosion-protective coating film made of a water-based acrylic resin paint is The corrosion-resistant coating film is composed of a first corrosion-resistant coating film made of a first water-based acrylic resin paint formed on the outer surface of the iron pipe, and a second corrosion-resistant coating film made of a second water-based acrylic resin paint formed on the first corrosion-resistant coating film; and The first water-based acrylic resin paint is different from the second water-based acrylic resin paint, and the Tg of the first corrosion-protective coating film is 20°C or less, preferably 5 to 20°C, and more preferably 5 to 10°C. This makes it possible to provide an externally corrosion-protected iron pipe provided with an externally corrosion-protected coating film using a water-based paint that has good corrosion resistance and good adhesion.

[0080] (2) In the externally corrosion-protected iron pipe according to the embodiment (1) of the present invention, the Tg of the second corrosion-protective coating film is preferably 30 to 60° C., more preferably 30 to 50° C. This ensures blocking resistance as the outermost coating layer, and ensures good paintability.

[0081] (3) In the externally corrosion-protected iron pipe according to the above embodiment (1) or (2) of the present invention, the film thickness ratio of the first corrosion-protective coating to the second corrosion-protective coating is preferably 1:1 to 4:1, and more preferably 1.5:1 to 3:1, thereby obtaining better adhesion and blocking resistance.

[0082] (4) In the iron pipe with external corrosion protection according to any one of the above embodiments (1) to (3) of the present invention, it is preferable that a zinc-based thermal spray coating and a sealing film made of a sealing agent are formed between the outer surface of the iron pipe and the first corrosion-protective coating, thereby further improving corrosion resistance.

[0083] (5) In another aspect of the present invention, (a) a thermal spraying step of applying zinc-based thermal spraying to the outer surface of the iron pipe to form a zinc-based thermal spray coating; (b) a sealing treatment step of applying a sealing agent to the surface of the zinc-based thermal spray coating to form a sealing film; (c) a temperature adjustment step of adjusting the temperature of the outer surface of the tube to 50 to 80°C; (d) A coating process in which a water-based acrylic resin paint is applied to the outer surface of the iron pipe while the iron pipe is rotated in the circumferential direction of the pipe, (d-1) a first coating step of spraying a first water-based acrylic resin paint from one end of the pipe to the other end in the axial direction to form a first anticorrosion coating film; (d-2) A second coating process in which a second water-based acrylic resin paint is sprayed in a return path from the other end of the pipe axis to the first end to form a second anticorrosion coating film. A painting process consisting of A method for manufacturing an externally corrosion-protected iron pipe, comprising: The first water-based acrylic resin paint is different from the second water-based acrylic resin paint, and the Tg of the first corrosion-resistant coating film is 20°C or less. A manufacturing method characterized by the above is provided.

[0084] (6) In the above aspect (5) of the present invention, it is preferable that the switching time between the first coating step (d-1) and the second coating step (d-2) is less than 10 seconds, which improves workability and makes the method excellent in terms of cost.

[0085] (7) In the above aspect (5) or (6) of the present invention, the Tg of the second corrosion protective coating film is preferably 30 to 60° C., more preferably 30 to 50° C. This ensures blocking resistance as the outermost coating layer, and ensures good coatability.

[0086] (8) In any of the above aspects (5) to (7) of the present invention, it is preferable to adjust the coating speed and / or coating amount so that the film thickness ratio of the first corrosion protective coating to the second corrosion protective coating is preferably 1:1 to 4:1, more preferably 1.5:1 to 3:1, thereby obtaining better adhesion and blocking resistance.

Claims

1. In an external corrosion-resistant iron pipe with a corrosion-resistant coating made of water-based acrylic resin paint, The corrosion-resistant coating film is composed of a first corrosion-resistant coating film made of a first water-based acrylic resin paint formed on the outer surface of the iron pipe, and a second corrosion-resistant coating film made of a second water-based acrylic resin paint formed on the first corrosion-resistant coating film; and The first water-based acrylic resin paint is different from the second water-based acrylic resin paint, and the Tg of the first corrosion-protective coating film is 20° C. or less. An external corrosion-resistant iron pipe.

2. The external surface corrosion-protected iron pipe according to claim 1, wherein the Tg of the second corrosion-protective coating film is 30 to 60°C.

3. The external surface corrosion-protected iron pipe according to claim 1 or 2, wherein the film thickness ratio of the first corrosion-protective coating film to the second corrosion-protective coating film is 1:1 to 4:

1.

4. 3. The iron pipe according to claim 1, wherein a zinc-based spray coating and a sealing film made of a sealing agent are formed between the outer surface of the iron pipe and the first corrosion-protective coating.

5. 4. The iron pipe according to claim 3, wherein a zinc-based spray coating and a sealing film made of a sealing agent are formed between the outer surface of the iron pipe and the first corrosion-protective coating.

6. (a) a thermal spraying step of applying zinc-based thermal spraying to the outer surface of the iron pipe to form a zinc-based thermal spray coating; (b) a sealing treatment step of applying a sealing agent to the surface of the zinc-based thermal spray coating to form a sealing film; (c) a temperature adjusting step of adjusting the temperature of the outer surface of the tube to 50 to 80°C; (d) a coating process of coating the outer surface of the iron pipe with a water-based acrylic resin paint while rotating the iron pipe in the circumferential direction of the pipe; (d-1) a first coating step of spray-coating a first water-based acrylic resin paint from one end of the pipe to the other end in the axial direction in a forward direction to form a first corrosion-resistant coating film; and (d-2) A second coating process in which a second water-based acrylic resin paint is spray-coated in a return path from the other end of the pipe axis to the one end to form a second anticorrosion coating film. A painting process consisting of: A method for manufacturing an externally corrosion-protected iron pipe, comprising: The first water-based acrylic resin paint is different from the second water-based acrylic resin paint, and the Tg of the first corrosion-protective coating film is 20° C. or less. A manufacturing method characterized by:

7. The manufacturing method according to claim 6, wherein the switching time between the first coating step (d-1) and the second coating step (d-2) is less than 10 seconds.

8. The method according to claim 6 or 7, wherein the second corrosion protective coating film has a Tg of 30 to 60°C.

9. The manufacturing method according to claim 6 or 7, wherein the coating speed and / or coating amount is adjusted so that the film thickness ratio of the first corrosion protective coating film to the second corrosion protective coating film is 1:1 to 4:

1.

10. The manufacturing method according to claim 8, wherein the coating speed and / or the coating amount are adjusted so that the film thickness ratio of the first corrosion protective coating film to the second corrosion protective coating film is 1:1 to 4:1.

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