JP2022072310A - Metal pipe and coating method for socket inner surface of metal pipe - Google Patents

Abstract

To provide a metal pipe which is improved in corrosion proofing on a socket inner surface, maintains water quality sanitary property and satisfies a specific dimension of a rubber ring storage part.SOLUTION: The present invention relates to a metal pipe 1 comprising a straight pipe part 3, in which a socket 2 including a rubber ring storage part 21 which is a recess for storing at least a rubber ring is provided in one end in a pipe axis direction and in which inner and outer pipe diameters are substantially fixed. In the metal pipe 1, a socket inner surface 2a includes a coating consisting of: a first layer formed from a powder coating applied to an entire region C of the socket inner surface 2a; and a second layer formed from a liquid coating applied from an upper side of the first layer to a region A of the socket inner surface 2a from a socket opening end 2b which is a region in no contact with a fluid flowing into a conduit to a region where a rubber ring 21b is mounted in the rubber ring storage part 21. The present invention also relates to a coating method including: a step (1) of forming the first layer by heating the metal pipe 1 and coating the region C with the powder paint; and a step (2) of forming the second layer by coating the region A with the liquid coating after the step (1).SELECTED DRAWING: Figure 1

Description

The present invention relates to a metal pipe having a coating film on the inner surface of the socket and a coating method thereof, and particularly to a cast iron pipe having a socket having an uneven inner surface and a coating method thereof.

Various metal pipes are used for water and sewage. The inner peripheral surface of these metal pipes is coated with various coatings to protect the inner surface. In particular, in cast iron pipes used for water pipes, the inner surface of the straight pipe is coated with powder coating (for example, epoxy resin powder coating) having excellent corrosion resistance and water hygiene. many.

As shown in FIG. 2, these metal pipes generally have a straight pipe portion 3 having a constant pipe diameter in the pipe axial direction, an insertion port 4 at one end in the pipe axial direction, and another metal adjacent to the other end. A receiving port 2 into which a tube insertion port is inserted is provided. The inner surface 2a of the receiving port generally has a rubber ring accommodating portion 21 which is a recess for accommodating a rubber ring 21b for preventing fluid passing through a pipeline from leaking from a metal pipe on the opening end side and a lock ring on the straight pipe portion side. The lock ring accommodating portion 22 and the like, which are recesses accommodating the 22b, are provided with irregularities.

Regarding the coating of the inner surface of the socket provided with such uneven portions, if powder coating is performed in the same manner as for the straight pipe portion, the powder coating cannot be applied uniformly and coating defects are likely to occur. As for the coating of the inner surface 2a of the mouth, as described above, after powder coating is applied to the inner surface 3a of the straight pipe portion for the purpose of preventing corrosion due to water passing through the inside of the pipe, the inner surface 2a of the receiving port having many irregularities is coated. The anticorrosion property is ensured by applying a primary coating with a zinc rich paint and a secondary coating with a solvent-based synthetic resin paint.

Further, Patent Document 1 describes that electrostatic powder coating is performed by reciprocating a gun for powder coating on the inner surface of the socket including the uneven portion.

Further, Patent Document 2 describes a tube body in which a powder coating film having a hardness lower than that of the powder coating film formed on the inner surface of the straight tube portion is formed on the inner surface of the lock ring accommodating portion of the socket. There is.

Japanese Unexamined Patent Publication No. 2010-269243 Japanese Unexamined Patent Publication No. 2016-183734

However, when the inner surface of the socket is entirely powder-coated as in Patent Document 1, although it is excellent in corrosion resistance and water quality hygiene, it is slightly inferior in paintability. When painted, painting defects are likely to occur especially in the rubber ring accommodating portion among the uneven portions, which causes red rust. In order to prevent coating defects from occurring, it is sufficient to increase the film thickness, but if the film thickness is increased, it is difficult to deal with the increase in film thickness because the uneven portion does not meet the specified dimensions.

Further, in the method of Patent Document 2, the paintability is slightly inferior in the case of only powder coating as in Patent Document 1, so that when the corresponding uneven portion is coated, the rubber ring accommodating portion is particularly coated in the uneven portion. There is a problem that defects are likely to occur and that the specified dimensions are not satisfied if the film thickness is increased, and there is a problem that the corrosion resistance is lowered in the case of coating with only the solvent paint as compared with the powder coating.

Therefore, an object of the present invention is to provide a metal tube which is excellent in corrosion resistance on the inner surface of the receiving port, maintains water quality hygiene, and satisfies the specified dimensions of the rubber ring accommodating portion.

In order to solve the above problems, as a result of diligent studies, the present inventors provided a layer formed of powder paint over the entire inner surface of the socket, and provided a rubber ring contact portion of the rubber ring accommodating portion from the socket opening end. By providing a layer formed by applying the liquid paint on the layer formed by the powder paint in the region including the region, that is, the region blocked from the fluid passing through the conduit by the rubber ring, the inner surface of the socket is provided. We have found that it is possible to provide a metal tube having excellent anticorrosion properties, maintaining water quality hygiene, and satisfying the specified dimensions of the rubber ring accommodating portion while suppressing the adhesion of powder paint to the outer surface of the tube, and completed the present invention.

That is, the present invention
[1] A metal pipe having a straight pipe portion having a substantially constant inner and outer diameter inside the pipe, provided with a receiving port having a rubber ring accommodating portion which is a recess for accommodating at least a rubber ring at one end in the pipe axial direction.
On the inner surface of the socket,
The first layer formed by the powder coating applied to the entire inner surface of the socket,
A metal tube comprising a coating film composed of a second layer formed by a liquid paint applied from above the first layer in a region that does not come into contact with a fluid flowing through the pipeline.
[2] The metal pipe according to the above [1], wherein the region that does not come into contact with the fluid flowing in the conduit is the region of the inner surface of the receptacle from the end of the socket opening to the region where the rubber ring of the rubber ring accommodating portion is mounted.
[3] The metal tube according to the above [1] or [2], wherein the powder coating material is an epoxy resin powder coating material.
[4] The metal tube according to any one of [1] to [3] above, wherein the liquid paint is a liquid paint containing an acrylic resin, an epoxy resin, or an epoxy ester resin as a resin component.
[5] The inner surface of the receiving port of a metal pipe having a straight pipe portion having a substantially constant inner and outer diameter of the pipe, provided with a receiving port having a rubber ring accommodating portion which is a recess for accommodating at least a rubber ring at one end in the pipe axial direction. It is a painting method of
(1) The step of heating the metal tube and applying powder paint to the entire inner surface of the socket to form the first layer, and (2) after the step (1), do not come into contact with the fluid flowing in the conduit. A coating method including a step of applying a liquid paint to a region to form a second layer, and [6] a region that does not come into contact with a fluid flowing in the conduit is a rubber ring of the rubber ring accommodating portion from the receiving port opening end. The present invention relates to the coating method according to the above [5], which is an area of the inner surface of the receiving port over the area where the above-mentioned is mounted.

According to the present invention, only the epoxy resin powder coating is applied to the inner surface of the socket that comes into contact with the fluid passing through the conduit, and the liquid paint is applied to the epoxy resin powder coating in the region from the socket opening end to the rubber ring mounting portion. By stacking, the corrosion resistance and water hygiene of the inner surface of the socket are improved, and in the area where the liquid paint is repeatedly applied, even if there is a defect in the epoxy resin powder coating coating, the liquid paint will be present in the defect. By penetrating, it is possible to obtain a sound coating film without defects even if the film thickness is thin due to the epoxy resin powder coating. Thereby, the specified size of the rubber ring accommodating portion can be satisfied.

It is a schematic sectional drawing for demonstrating the coating classification of a metal tube which concerns on one Embodiment of this invention. It is a schematic diagram for demonstrating the structure of the metal pipe for a general water pipe.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, a first layer of powder paint and a second layer of liquid paint are formed on the inner surface 2a of the socket 2 of a metal pipe (for example, a cast iron pipe) 1 widely used for water and sewage pipes and gas pipes. It is provided with a coating film composed of the above layers. As an example, as shown in FIG. 1, the metal pipe 1 is provided with a receiving port 2 at one end in the pipe axial direction and an insertion port 4 at the other end, sandwiching a straight pipe portion 3 having a substantially constant inner and outer diameter. The receiving port 2 is provided with a rubber ring accommodating portion 21 which is a recess for accommodating a rubber ring and a lock ring accommodating portion 22 which is a recess for accommodating a lock ring. The first layer is formed by the powder coating material, and the second layer formed by the liquid coating material is formed from above the first layer in the region A (the region that does not come into contact with the fluid flowing in the pipeline), and the receptacle is formed. It constitutes the coating film on the inner surface 2a. As shown in FIG. 2, the rubber ring accommodating portion 21 and the lock ring accommodating portion 22 are provided with a rubber ring 21b, a lock ring 22b for suppressing the other metal tube 1 from coming out of the metal tube 1, and a lock ring centering. When the rubber 22c and the rubber ring 22c are housed and the insertion port of another metal pipe is inserted, the rubber ring is pressed toward the outside of the pipe, and the region A shown in FIG. 1 cannot be contacted by the fluid passing through the pipe. ing. Conversely, fluid passing through the conduit may enter the region B including the outside of the rubber ring 21b of the lock ring accommodating portion 22 and the rubber ring accommodating portion 21 on the straight pipe portion side.

In the present specification, the term "rubber ring" is a member for preventing the fluid passing through the pipeline from leaking to the outside, and as shown in FIG. 2, the rubber ring 21b fits into the rubber ring accommodating portion 21. By fitting, it is attached to the inner surface 21a of the rubber ring accommodating portion, and by inserting the insertion port 4 of another metal tube into the receiving port 2, the metal different from the inner surface 21a of the rubber ring accommodating portion of the receiving port 2 of the metal tube 1 The outer surface of the insertion port 4 of the tube is brought into close contact with the outer surface.

In the present specification, the "region that does not come into contact with the fluid flowing in the conduit" means, for example, the inner surface of the receptacle and the outer surface of the socket by a rubber ring or the like when the insertion port of another tube body is inserted into the socket of the tube body. When the fluid flowing in the conduit cannot enter due to the close contact with, the area blocked from the fluid flowing in the conduit on the inner surface of the socket, that is, the region from the opening end of the socket to the contact portion. Means. For example, the "region that does not come into contact with the fluid flowing in the pipeline" is the "region of the inner surface of the socket from the end of the socket opening to the region where the rubber ring of the rubber ring accommodating portion is mounted". The region in which the rubber ring of the region A in 1 does not come into contact with the fluid passing through the pipeline corresponds to the region.

[First layer]
A first layer is formed by a powder coating material, particularly an epoxy resin powder coating material, on the entire area C of the receiving port inner surface 2a of the receiving port 2 of the metal tube 1. The first layer can be formed by powder coating with a dedicated coating device for coating the inner surface of the socket, or can be formed by powder coating continuously from the straight pipe portion. Before performing this powder coating, it is preferable to polish the inner surface of the pipe and adjust the substrate such as cleaning as necessary.

The film thickness of the first layer is defined as a region B in which the fluid passing through the pipeline forming the second layer described later does not contact and a region A in which the fluid passing through the pipeline forming the second layer described later does not contact. They may be equivalent or different. The film thickness of the region B is preferably 150 μm or more, more preferably 200 to 600 μm, from the viewpoint of corrosion resistance. Further, the film thickness of the region A is preferably less than 250 μm, more preferably 150 to 200 μm, from the viewpoint of satisfying the specified dimensions of the rubber ring accommodating portion. By suppressing the film thickness of the region A, it is possible to prevent the powder coating material from scattering to the outside of the pipe.

The metal tube 1 is usually heated before coating in order to melt and cure the powder coating to be coated, for example, an epoxy resin powder coating. The heating method is not particularly limited, but the heating method is performed using, for example, a heating furnace such as a gas furnace or an electric furnace. The heating temperature of the metal tube 1 is not particularly limited because it is arbitrarily determined depending on the type of epoxy resin powder coating used, the curing time, etc., but the resin is melted to form a resin and a curing agent. The surface temperature of the metal tube 1 is preferably 150 ° C. or higher, more preferably 170 to 270 ° C., in order to carry out a cross-linking reaction.

(Powder paint)
Next, the powder coating material will be described. In the present specification, the powder paint means a powder paint, and more specifically, a powder paint consisting of only a coating film-forming component without containing an organic solvent or water in the paint. do. The powder coating material used for the first layer is not particularly limited as long as it is a heat-curable powder coating material, but since it is used as a suitable material for water pipes, it is particularly an epoxy resin powder coating material. Specifically, the epoxy powder paint specified in the Japan Waterworks Association standard JWWA G 112 "Epoxy resin powder coating on the inner surface of ductile cast iron pipe for water supply" can be preferably used.

The epoxy resin powder coating material contains an epoxy resin that is solid at room temperature, a curing agent for the epoxy resin, and various pigments, additives, and the like, if necessary.

Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin and other bisphenol type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, novolak type epoxy resin, cyclic aliphatic epoxy resin, and glycidylamine type. Examples thereof include resins, heterocyclic epoxy resins, and polyfunctional epoxy resins. Among them, a bisphenol F type epoxy resin synthesized from bisphenol F and epichlorohydrin is preferably adopted from the viewpoint of safety.

The curing agent is not particularly limited as long as it has the property of curing the epoxy resin, but is not particularly limited, but is an amine-based compound, an amide-based compound, an imidazole-based compound, an imidazoline-based compound, a hydrazide-based compound, and an acid anhydride. , Phenolic resins and derivatives thereof and the like. Among them, from the viewpoint of corrosion resistance, flexibility, adhesion and strength of the coating film, modified aromatic amine adduct mainly composed of aniline, imidazole / imidazoline compound mainly composed of ethylenediamine and benzonitrile, hydrazine and dibase Hydrazide mainly composed of hydrazine, and acid anhydride mainly composed of trimellitic acid and ethylene glycol are preferably adopted.

Examples of the pigment include colored pigments such as titanium oxide, iron oxide, carbon black, yellow iron oxide and phthalocyanine blue, and extender pigments such as calcium carbonate, barium sulfate, silica and talc.

Examples of the additive include a filler, a dispersant, a surface conditioner, and the like, which can be added to the epoxy resin powder coating material as needed.

The method for producing the epoxy resin powder coating material is not particularly limited, and the epoxy resin powder coating material can be produced, for example, by a dry blending method or a heat melting and kneading method.

The coating method of the epoxy resin powder coating is not particularly limited, and examples thereof include electrostatic powder coating and rotary spray coating. As a method of painting the inner surface of the socket, there is firstly a method of painting the area A and the area B with the same film thickness with a dedicated painting device for painting the inner surface of the socket, and secondly, for painting the inner surface of the socket. There is a method of coating the region A and the region B with different film thicknesses by changing the moving speed of the coating apparatus in the region A to the region B by the dedicated coating apparatus of the above.

[Second layer]
As a region that does not come into contact with the fluid flowing in the pipeline, the region A of the inner surface 2a of the receiving port from the opening end 2b of the receiving port 2 of the metal tube 1 to the area where the rubber ring of the rubber ring accommodating portion 21 is mounted is the first. A second layer is formed from the top of the first layer by the liquid paint.

The film thickness of the second layer is preferably 20 μm or more, more preferably 20 to 100 μm, and even more preferably 30 to 70 μm from the viewpoint of corrosion resistance. The total film thickness combined with the first layer is preferably 170 to 250 μm, more preferably 200 to 250 μm, from the viewpoint of corrosion resistance and satisfying the specified dimensions of the rubber ring accommodating portion.

Since the metal tube 1 is heated when forming the first layer, the inner surface temperature of the metal tube is 60 ° C. or lower after the first layer is cured from the viewpoint of preventing the liquid paint from collapsing. After that, the liquid paint is applied. Of course, painting can be performed even at the same inner surface temperature as the outside air temperature. Further, the coating of the liquid paint is not particularly limited to spray coating, brush coating, roller coating and the like.

(Liquid paint)
The liquid paint is not particularly limited as long as it is a liquid paint that can enter the first layer when there is a defect, and is a solvent in which a resin component is mixed with a pigment and various additives in an organic solvent. A solvent-based paint, a water-based paint using a water-based medium as a medium, a solvent-free paint that does not use a solvent, and the like can be used.

(Solvent paint)
The solvent-based paint is a paint using an organic solvent as a medium using acrylic resin, epoxy resin, xylene resin, toluene resin, cyclopentadiene resin, kumaron inden resin, carboxylated acrylic modified SBR resin, etc. as resin components. be. As these acrylic resins and epoxy resins, those distributed as paints for cast iron pipes can be used, and the present invention is not particularly limited. When used for water pipes, for example, synthetic resin paints specified in the Japan Water Works Association standard JWWA K 139 "Ductile cast iron pipe synthetic resin paint for water supply" can be preferably used.

The organic solvent used in the solvent-based paint is not particularly limited, but is not particularly limited, but toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, ethanol, propylene glycol monomethyl ether, isopropyl alcohol, isobutyl alcohol, butyl alcohol, ethyl acetate, acetic acid. Examples include butyl.

As the acrylic resin, an acrylate or methacrylate copolymer containing styrene, vinyl acetate or butadiene can be used.

As the solvent-based paint of the acrylic resin, for example, Kurimoto Coat AC-1-SR Gray manufactured by Nippon Paint Industrial Coatings Co., Ltd., Kurimoto Coat AC-1 Gray manufactured by Nippon Paint Industrial Coatings Co., Ltd., etc. are used. can do.

The solvent-based paint containing an epoxy resin as a main agent contains at least an epoxy resin as a main agent, a curing agent, and the above-mentioned organic solvent. It is preferable to use a two-component type in which the main agent and the curing agent are separated. The epoxy resin is not particularly limited, but is a bisphenol type epoxy resin obtained by reacting bisphenols with epichlorohydrin, a bisphenol type epoxy resin reacted with a fatty acid, a novolak type, an alicyclic type, and a glycidyl. Epoxy resins such as amine type and hydrogenated bisphenol A type can be used as the main agent. Then, if necessary, glycidyl ethers such as alkyl having 12 or 13 carbon atoms, polyethylene glycol, polypropylene glycol, neopentyl glycol, 1,6-hexanediol, and trimethylolpropane, and kumaron inden resin, Reactive or non-reactive diluents such as xylene resin, ketone resin, toluene resin, petroleum resin, acrylic resin, polyester resin, alkyd resin, polyimide resin, monoglycidyl ethers, dioctylphthalate, benzyl alcohol, etc. , Alone or a plurality of them can be selected and used in combination with the above-mentioned main agent.

The curing agent is a compound that causes an epoxy resin to undergo a curing reaction. Specific compounds include polyamide amines, polyamine epoxy resin adducts, epoxy resin amine adducts, aliphatic polyamines, modified polyamines, aromatic amines, tertiary amines, hydrazides, dicyandiamides, imidazoles, acid anhydrides, ketimine, and acids. Terminal polyester resin, phenol resin, urea resin, resol resin, amino resin, isocyanate, blocked isocyanate, triethylenetetramine modified product, metaxylenediamine modified product, isophorondiamine modified product, bis (paraaminocyclohexyl) methane modified product, toluenediisocyanate The modified product of the above can be used alone or in combination of two or more.

As a specific example of the solvent-based paint containing an epoxy resin as a main component, for example, a petroleum resin (a copolymer of kumaron / styrene) is added to a bisphenol A type epoxy resin (a reaction product of epichlorohydrin and bisphenol A). The main ingredient is a mixture of various pigments and additives with xylene, ethylbenzene, isobutanol, methanol, methylisobutylketone and propylene glycol monoethyl ether as the main agent, and xylene and ethylbenzene as solvents in the adduct of polyamine and epoxy resin. , Isobutanol and n-butanol are used as curing agents, such as Kurimoto Coat NT # 100 New H Gray manufactured by Dainippon Paint Co., Ltd. and Kurimoto Coat NT # 100 New manufactured by Kansai Paint Co., Ltd. can do.

(Water-based paint)
The water-based paint uses acrylic resin, epoxy resin, epoxy ester resin, etc. as the resin component and is in the form of an emulsion or dispersion as needed, for example, epoxy ester resin dispersion, acrylic resin emulsion. , Acrylic resin dispersion, etc. are blended in a water-based medium.

As the aqueous medium, an aqueous solvent, preferably water, is used. Further, a small amount of organic solvent may be blended in order to adjust the interfacial tension.

The epoxy ester-based resin dispersion is mainly composed of an unsaturated fatty acid-modified epoxy ester resin, a vinyl monomer having a terminal carboxyl group-containing structure, and a vinyl-modified epoxy ester resin obtained by massively polymerizing other vinyl monomers. , An aqueous dispersion of a vinyl-modified epoxy ester resin neutralized product obtained by neutralizing this vinyl-modified epoxy ester resin. Epoxy ester resin dispersion is added to water-based paints to improve corrosion resistance. Specific examples of the epoxy ester resin dispersion include WATERSOL EFD-5530 (manufactured by DIC Corporation), WATERSOL EFD-5560 (manufactured by DIC Corporation), and WATERSOL EFD-5580 (manufactured by DIC Corporation) as commercially available products. However, it is not limited to these.

The acrylic resin emulsion is mainly composed of an aqueous resin dispersion of a forced emulsification type (meth) acrylic polymer. The forced emulsification type means that the resin portion is basically emulsified by using an emulsifier and basically has no self-emulsifying power, and the emulsion is used in the present invention as a forced emulsifying type dispersion. .. The acrylic resin emulsion is added to the water-based paint to form a coating film having excellent corrosion resistance and drying property. Specific examples of the acrylic resin emulsion include Cybinol EC-7040 (manufactured by Saiden Chemical Co., Ltd.), Cybinol X-211-168E (manufactured by Saiden Chemical Co., Ltd.), VONCORT EC-740EF (manufactured by DIC Corporation), and the like. However, it is not limited to these.

The acrylic resin dispersion is mainly composed of an aqueous resin dispersion of a self-emulsifying vinyl polymer, has a boiling point of 130 to 220 ° C. under normal pressure, and has a water solubility of 100 or more at 20 ° C. This is a self-emulsifying aqueous dispersion containing 15% by mass or less of the organic solvent of the above in an acrylic resin dispersion. The self-emulsifying type means that some hydrophilic group is chemically introduced into the resin skeleton and the resin itself has an emulsifying ability, and the dispersion is used in the present invention as a self-emulsifying type dispersion. The acrylic resin dispersion is added to the water-based paint in order to form a coating film having excellent corrosion resistance and weather resistance. Specific examples of the acrylic resin dispersion include WATERSOL ACD-1110 (manufactured by DIC Corporation).

In the water-based paint, the above-mentioned epoxy ester resin dispersion, acrylic resin emulsion, and acrylic resin dispersion can be used in combination of two or more.

(Solvent-free paint)
The solvent-free paint is a paint that uses an epoxy resin as a resin component and does not contain a solvent. When used for water pipes, for example, the paint specified in the Japan Water Works Association standard JWWA K 157 "Solvent-free epoxy resin paint coating method for water pipes" can be preferably used.

(Pigment)
Examples of the pigment used in the liquid paint include colored pigments such as titanium dioxide, iron oxide, carbon black, cyanine blue and cyanine green; and extender pigments such as calcium carbonate, talc, barium sulfate and clay. These can be used alone or in combination of two or more.

Further, as the pigment, rust preventive pigments such as zinc phosphate, calcium phosphate, aluminum phosphate and aluminum phosphate molybdenum can also be used. Of these, zinc phosphate and calcium phosphate, which are excellent in rust prevention performance, are preferably used. Specific examples of zinc phosphate include LF Bowsei P-W-2, LF Bowsei D-1, LF Bowsei D-2, LF Bowsei ZP-S1, LF Bowsei ZP-HS, and LF Bowsei P-WF. (Made by Kikuchi Color Co., Ltd.), EXPERT NP-500, EXPERT NP-520, EXPERT NP-530 (all of which are manufactured by Toho Pigment Industry Co., Ltd.) and the like. Specific examples of calcium phosphate include LF Bowsei CP-Z (manufactured by Kikuchi Color Co., Ltd.), EXPERT NP-1000, EXPERT NP-1007, EXPERT NP-1020C, and EXPERT NP-1055C (all of which are Toho Pigment Industry Co., Ltd.). ), Protex YM-60, Protex YM-70 (all of which are manufactured by Taihei Kagaku Sangyo Co., Ltd.) and the like.

For liquid paints, if necessary, a defoaming agent made of silicone or organic polymer; a surface conditioner made of silicone or organic polymer; a viscosity modifier made of amidowax, organic bentonite, etc. (anti-dripping agent); silica , A matting agent made of alumina, etc .; Dispersant made of polycarboxylate, etc .; UV absorber made of benzophenone, hindered amine-based light stabilizer, phenol-based antioxidant, etc .; Known additives such as wax are used. be able to. These can be used alone or in combination of two or more.

[How to paint the inner surface of the socket]
In the method of painting the inner surface 2a of the receiving port of the present invention, a metal tube 1 having a receiving port 2 having a rubber ring accommodating portion 21 which is a recess for accommodating at least the rubber ring 21b is heated at one end of the straight tube portion 3. After the step (1) of applying powder paint to the entire area C of the inner surface of the socket 2a to form the first layer, and after the step (1), the socket opening end is a region that does not come into contact with the fluid flowing in the pipeline. The step (2) is included in which a liquid paint is applied to the region A of the inner surface of the receiving port from 2b to the region where the rubber ring 21b of the rubber ring accommodating portion 21 is mounted to form a second layer.

The step (1) forms the first layer, and the coating method thereof is not particularly limited as long as it is suitable for the above-mentioned powder coating. In the step (1), in the coating region, the film thickness of the coating film is different between the region B that does not form the second layer of the straight pipe portion inner surface 3a and the receiving port inner surface 2a and the region A that forms the second layer. It may be equal or different, and if they are different, the film thickness of the first layer related to the region A forming the second layer may be thinner than that of the region B not forming the second layer. preferable. Therefore, the area A and the area B can be coated with the same film thickness by the dedicated coating device for coating the inner surface of the socket, but by changing the moving speed of the coating device in the area A to the area B, the area A can be coated. And the region B can be painted with different film thicknesses (for example, the region A is thinner than the region B).

The step (2) is for forming the second layer, and the coating method thereof is not particularly limited, and the coating can be applied to a desired film thickness by a spray, a brush, or a roller.

[Painting of the outer peripheral surface of cast iron pipe]
In the present invention, the metal tube outer peripheral surface 1a of the metal tube indicated by reference numeral 1 in FIG. 1 may be coated by a conventionally known method, or may be coated by the method described in JP-A-2010-209967. good. When painting is performed by a conventionally known method, it is preferable to perform painting before and after painting the second layer of the receiving port inner surface 2a. Further, when painting is performed by the method described in Japanese Patent Application Laid-Open No. 2010-209967, the second layer of the outer peripheral surface 1a of the metal tube and the inner surface 2a of the receiving port may be painted at the same time.

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

Example 1
The cast iron pipe (φ250 × 5000 mm) was heated to 270 to 330 ° C. After that, using an epoxy resin powder paint (JWWA G 112 standard product, powder), the area A and the area B were powder coated with a target film thickness of 200 μm using a dedicated coating device for coating the inner surface of the socket (first). Layer), and then powder coating was applied to the region from the inner surface of the opening end to the straight part with a target thickness of 300 μm or more. Next, in the area from the opening end of the socket to the rubber ring contact area of the rubber ring accommodating portion, that is, the area blocked from the fluid passing through the conduit by the rubber ring, the solvent-based two-component epoxy resin paint (JWWA K 139 standard product, solid). (49%) was coated by spraying with a target film thickness of 50 μm (second layer).

Example 2
The cast iron pipe (φ250 × 5000 mm) was heated to 270 to 330 ° C. After that, by using an epoxy resin powder paint (JWWA G 112 standard product, powder) and using a dedicated coating device for coating the inner surface of the socket, the moving speed of the coating device in the region A is made faster than that in the region B. Powder coating is applied to A with a target thickness of 150 μm and region B with a target thickness of 300 μm (first layer), and then powder is continuously applied to the region from the inner surface of the opening end to the straight portion with a target thickness of 300 μm or more. I painted it. Next, in the area from the opening end of the socket to the rubber ring contact area of the rubber ring accommodating portion, that is, the area blocked from the fluid passing through the conduit by the rubber ring, the solvent-based two-component epoxy resin paint (JWWA K 139 standard product, solid). (49%) was coated by spraying with a target film thickness of 50 μm (second layer).

1 Metal pipe 1a Outer surface of metal pipe 2 Receiving port 2a Inner surface of receiving port 2b Opening end of receiving port 3 Straight pipe part 3a Inner surface of straight pipe part 4 Insertion port 21 Rubber ring accommodating part 21a Rubber ring accommodating part Inner surface 21b Rubber ring 22 Lock ring accommodating Part 22a Lock ring accommodating part inner surface 22b Lock ring 22c Lock ring centering rubber

Claims (6)

A metal pipe having a straight pipe portion having a substantially constant inner and outer diameter inside the pipe, provided with a receiving port having a rubber ring accommodating portion which is a recess for accommodating at least a rubber ring at one end in the pipe axial direction.
On the inner surface of the socket,
The first layer formed by the powder coating applied to the entire inner surface of the socket,
A metal pipe comprising a coating film composed of a second layer formed by a liquid paint applied from above the first layer in a region that does not come into contact with a fluid flowing through the pipeline. The metal pipe according to claim 1, wherein the region that does not come into contact with the fluid flowing through the conduit is the region of the inner surface of the socket from the end of the socket opening to the region where the rubber ring of the rubber ring accommodating portion is mounted. The metal tube according to claim 1 or 2, wherein the powder coating material is an epoxy resin powder coating material. The metal tube according to any one of claims 1 to 3, wherein the liquid paint is a liquid paint containing an acrylic resin, an epoxy resin, or an epoxy ester resin as a resin component. A method of painting the inner surface of a metal tube receiving port having a straight tube portion having a substantially constant inner and outer diameter inside the pipe, provided with a receiving port having a rubber ring accommodating portion which is a recess for accommodating at least a rubber ring at one end in the pipe axis direction. And
(1) The step of heating the metal pipe and applying powder paint to the entire inner surface of the socket to form the first layer, and (2) after the step (1), do not come into contact with the fluid flowing in the pipe. A painting method comprising the step of applying a liquid paint to an area to form a second layer. The coating method according to claim 5, wherein the region that does not come into contact with the fluid flowing in the conduit is the region of the inner surface of the socket from the end of the socket opening to the region where the rubber ring of the rubber ring accommodating portion is mounted.

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