JP6817245B2 - Cast iron pipe with a coating film on the inner surface of the socket and its coating method - Google Patents

Description

The present invention relates to a cast iron pipe having a coating film on the inner surface of the receiving port of the cast iron pipe used for water and sewage, and a coating method thereof.

Various pipes are used for water and sewage. Various coatings are applied to the inner peripheral surfaces of these pipe bodies in order to protect the inner surfaces. In particular, in cast iron pipes and the like, the inner surface of the pipe is often coated by powder coating (for example, epoxy resin powder coating).

In these pipe bodies, the coating on the inner surface of the pipe may be soiled or deteriorated during transportation or storage. For this reason, synthetic resin tube protection caps are fitted to both ends of the tube. In particular, in a pipe body coated with powder, the painted surface on the inner surface of the pipe may be deteriorated by the light shining from the pipe end. Therefore, it is important to fit synthetic resin tube protection caps to both ends of the tube during transportation and storage.

In general, the pipe body has a straight pipe portion having a constant pipe diameter in the pipe axis direction, and an insertion port at one end in the pipe axis direction and a socket into which another pipe body adjacent to the other end is inserted. Be prepared. The inner surface of the socket is coated with a solvent-based paint (hereinafter referred to as "solvent-based coating") for anticorrosion treatment. For coating on the inner surface of the pipe, powder coating is usually applied to the inner surface of the straight pipe portion, and then solvent-based coating is applied to the inner surface of the pipe near the socket.

In the conventional solvent-based paint, the solvent remains in the coating film. Therefore, there is a problem that the tube itself has a solvent odor unless it is sufficiently dried after painting on the inner surface of the socket. Further, when used for water supply, there is a problem that the solvent elutes into tap water and a solvent odor is generated in the tap water.

In this case, the tube protection cap interferes with the natural exhaust of the solvent to the outside of the tube. For this reason, the cap used between the pipe portion and the socket has been improved to a structure in which the solvent is easily discharged, or a cap having a function of adsorbing volatile components of the paint has been used (for example, a patent). Refer to Documents 1 and 2).

On the other hand, if the inner surface of the socket of the pipe body is painted with a water-based paint that does not use a solvent, it is not necessary to exhaust the solvent, but in general, the conventional water-based paint is applied to the straight pipe portion of the pipe body. Adhesion with powder paint is poor and has not been put into practical use. Patent Document 3 discloses a cast iron pipe in which the inner surface of the receiving port of the pipe body is coated with a water-based paint for powder coating applied to the straight pipe portion of the pipe body.

JP-A-2010-194394 Japanese Unexamined Patent Publication No. 2010-2099667 Japanese Unexamined Patent Publication No. 2013-204689

However, also in the invention described in Patent Document 3, when the zinc rich primer is applied to the inner surface of the receiving port of the pipe body, the adhesion with the zinc rich primer and the powder coating applied to the straight pipe portion of the pipe body are also applied. It is desired to have better adhesion with.

Therefore, in the present invention, in the coating of the inner surface of the socket of the cast iron pipe, the use of a solvent is minimized, and the adhesion between the zinc rich primer and the powder coating material and the water-based coating material coated on them is further improved. It is an object of the present invention to provide a cast iron pipe and a method for coating the same.

As a result of diligent studies, the present inventors have conducted diligent studies to solve the above problems, and as a result, the receptacle between the zinc rich primer applied to the inner surface of the socket of the tubular body and the powder coating applied to the straight pipe portion of the tubular body. When a coating layer of a solvent-based primer is provided on the boundary region on the inner surface and the inner surface of the socket of the tube is coated with a predetermined water-based paint, the water-based paint adheres to the zinc rich primer and powder coating. The present invention has been completed by finding that the properties are further improved.

That is, in one embodiment of the present invention, it is a cast iron pipe having a receiving port at one end and an insertion port at the other end across a straight pipe portion, and is formed on the inner surface of the receiving port in order from the pipe body side.
A first layer formed by a zinc rich primer applied in a certain area from the receiving end to the straight pipe portion,
A second layer formed by a powder coating material applied so as to cover a part of the first layer from the straight pipe portion to a certain region on the inner surface of the socket.
As a solid content (A) applied to the third layer formed by the solvent-based primer applied to a certain region including the boundary between the first layer and the second layer, and the entire inner surface of the socket. ) Epoxy ester resin by 1 to 15 parts by mass, (B) acrylic resin emulsion by 5 to 30 parts by mass, and (C) acrylic resin dispersion by 55 to 94 parts by mass, (A), (B) and Cast iron comprising a coating film composed of a fourth layer formed of an aqueous paint containing a pigment having a total solid content of (C) of 100 parts by mass and (D) a pigment volume concentration of 35 to 45%. A tube is provided.

In one embodiment of the present invention, it is preferable that the powder coating material is an epoxy resin powder coating material and the solvent-based primer is a two-component epoxy resin coating material.

In another embodiment of the invention
(1) The inner surface of the receiving port of a cast iron pipe having a receiving port at one end and an insertion port at the other end across the straight pipe portion is coated with a zinc rich primer from the receiving end toward the straight pipe portion to form the first layer. The process of forming,
(2) A step of heating the cast iron pipe and applying a powder paint so as to cover a part of the first layer from the inner surface of the straight pipe portion of the cast iron pipe to form the second layer.
(3) A step of applying a solvent-based primer to a certain region including the boundary between the first layer and the second layer to form a third layer, and (4) then using residual heat, 1 to 15 parts by mass of (A) epoxy ester resin, 5 to 30 parts by mass of (B) acrylic resin emulsion, and (C) acrylic resin dispersion as solid content on the entire inner surface of the socket of the cast iron pipe. A water-based paint containing 55 to 94 parts by mass of a pigment, the total solid content of (A), (B) and (C) is 100 parts by mass, and (D) a pigment having a pigment volume concentration of 35 to 45%. Provided is a method of painting an inner surface of a socket of a cast iron pipe, which comprises a step of painting to form a fourth layer.

The cast iron pipe in which a predetermined water-based coating is applied to the inner surface of the receiving port of the pipe body via a solvent-based primer applied to a certain region including the boundary between the zinc rich primer and the powder coating of the present invention is a zinc rich primer and powder. In the boundary region with the coating, a coating film with better adhesion strength can be formed, and as a result, the use of the solvent can be minimized, and the final treatment of the inner surface of the socket can be performed with the water-based paint, and the solvent odor can be formed. Can be prevented from occurring. As a result, it is possible to provide a cast iron pipe in which the solvent odor does not remain in the pipe even if the pipe cap is attached.

FIG. 1 is a cross-sectional view showing a division of coating on a pipe body.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention relates to a cast iron pipe in which the inner surface 2a of a receiving port 2 of a cast iron pipe (pipe body) p widely used for water and sewage pipes and gas pipes is coated with a water-based paint, and a method for coating the cast iron pipe (the cast iron pipe). As shown in FIG. 1, the pipe body) p is provided with an insertion port 1 at one end shown on the right side in the drawing and a receiving port 2 at the other end, sandwiching a straight pipe portion 3 having a constant inner and outer diameter. A first layer is formed in the region A by the zinc rich primer, a second layer is formed in the region B by the powder coating material following the straight pipe portion C, and the first layer and the powder by the zinc rich primer are formed. A third layer due to the solvent-based primer is formed in the region D including the boundary with the second layer due to the paint, and a fourth layer formed by the water-based paint is formed in the region E above the region D, and the inner surface of the socket is formed. Consists of a coating film.

[First layer]
A zinc rich primer is coated as a first layer on the region A of FIG. 1 on the inner surface of the receiving port of the cast iron pipe p. The film thickness of the first layer is preferably 20 to 50 μm, more preferably 20 to 30 μm. If the film thickness is less than 20 μm, the coating film tends to be non-uniform, and the anticorrosion effect tends to be insufficient, and if it exceeds 100 μm, the adhesion to the iron substrate tends to be insufficient. When the cast iron pipe is a water pipe, the standard of zinc rich primer coating is 150 g / m ² or more and the film thickness conversion is 20 μm or more. As a method of painting the inner surface of the receiving port of the cast iron pipe, a method of applying a zinc rich primer with a brush or by spraying can be used. As a result, the rust preventive effect of the receiving end tends to be sufficiently obtained.

(Zinc rich primer)
As the zinc rich primer, a resin component containing a large amount of zinc powder as a pigment and known as an undercoat of a cast iron pipe as a zinc-based primer having excellent rust prevention ability can be used. As the zinc rich primer, a water-based zinc rich primer in which a resin such as an acrylic resin varnish or a vinyl-modified epoxy ester resin varnish is added to zinc powder and zinc oxide, an additive, etc. are added is preferable, and the zinc content is 65 to 65. More preferably about 85% by mass. Specific examples include Kurimoto Coat WZ (JIS K 5552 standard product, solid content 86%, zinc powder 70% by mass, zinc oxide 9.2% by mass, resin varnish (butadiene / styrene polymer)) manufactured by Dainippon Paint Co., Ltd. 7.2% by mass, high boiling point solvent (butyl cellosolve, etc.) 1.2% by mass, water 11.8% by mass and dispersant) can be mentioned.

[Second layer]
A second layer is formed on the inner surface of the straight pipe portion 3 of the cast iron pipe p with a powder coating material, particularly an epoxy resin powder coating material. At this time, the straight pipe portion 3 also includes the step portion 4, and the powder coating is performed so as to cover a part of the first layer from the straight pipe portion to a certain region on the inner surface of the socket, for example, in FIG. In addition to region C, it is also performed in region B. Further, the term “inner surface of the straight pipe portion” in the present specification includes not only the inner surface of the straight pipe portion 3a but also the inner surface 1a of the insertion port 1 and the step portion 4 between the straight pipe portion 3 and the receiving port 2. Further, the step portion 4 includes a surface portion 4b and an edge portion 4a. Prior to this powder coating step, it is preferable to polish the inner surface of the pipe and adjust the substrate such as cleaning as necessary.

The cast iron pipe p is usually heated before coating in order to melt and cure the powder coating material to be coated, particularly the epoxy resin powder coating material. 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 cast iron pipe p is not particularly limited because it is arbitrarily determined by the type of epoxy resin powder coating material used, the curing time, etc., but the resin is melted to form a resin and a curing agent. The surface temperature of the cast iron pipe p is preferably 150 ° C. or higher, more preferably 170 to 270 ° C., in order to carry out a cross-linking reaction.

(Epoxy resin powder paint)
Next, among the powder coating materials, the epoxy resin powder coating material will be described in particular. The epoxy resin powder coating material coated so as to cover a part of the first layer from the straight pipe portion 3 to a certain region on the inner surface of the socket is an epoxy resin solid at room temperature, a curing agent for the epoxy resin, and the like. Further, various pigments, additives and the like are contained as needed. 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, novolac type epoxy resin, cyclic aliphatic epoxy resin, glycidylamine type resin, and the like. Examples thereof include heterocyclic epoxy resins and polyfunctional epoxy resins. The softening point of the epoxy resin is not particularly limited, but is preferably 60 to 150 ° C., and the epoxy equivalent is not particularly limited, but is preferably 400 to 3000. If the softening point is less than 60 ° C. or the epoxy equivalent is less than 400, the powder coating material tends to harden during storage, and if the softening point exceeds 150 ° C. or the epoxy equivalent exceeds 3000, the melt viscosity becomes high. The coated surface tends to be difficult to smooth, and pinholes and the like tend to occur.

The curing agent used for the epoxy resin for powder coating is not particularly limited as long as it is a commonly used curing agent, and for example, an imidazole compound, an imidazoline compound, a dicyandiamide, an acid anhydride, and a polycarboxylic acid hydrazide. And its derivatives, phenolic resins and their derivatives and the like. Of these, it is preferable to use an imidazole-based compound, an imidazoline-based compound, or a polycarboxylic acid hydrazide alone or in combination, because the corrosion resistance, flexibility, adhesion, and strength of the coating film are remarkably improved.

Epoxy resin powder coatings include various pigments such as titanium oxide, iron oxide, carbon black, phthalocyanine blue, calcium carbonate, barium sulfate, silica, and talc, and various additives such as fillers, dispersants, and surface conditioners. It can be blended as needed. The amount of the pigment and the filler added is preferably 20 to 50% by mass, more preferably 30 to 45% by mass in the coating material because the coating film can be thickened. 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 hot melt kneading method.

The coating method of the epoxy resin powder coating material is not particularly limited. For example, the cast iron pipe is rotated, the powder coating material is excessively fed into the pipe together with the gas, and fused to the inner surface of the pipe, and the excess powder coating material is applied. Apply powder paint by a method such as removing. The thickness of the inner coating film layer formed by coating the epoxy resin powder coating material is preferably 140 to 700 μm, more preferably 150 to 400 μm. If the film thickness is less than 140 μm, the corrosion resistance of the inner surface of the pipe tends to decrease.

[Third layer]
After forming the second layer on the inner surface 3a of the straight pipe portion 3, a region including a boundary between the first layer by the zinc rich primer and the second layer by the powder coating (hereinafter, referred to as a boundary region, for example, FIG. 1). A third layer is formed in the region D) by a solvent-based primer. The area of the boundary region is not particularly limited as long as it includes the boundary between the first layer and the second layer, but includes at least the boundary line and has a width of at least 10 to 60 mm on each side. It is preferable that the width is 20 to 30 mm. If this width is too narrow, the effect of improving the adhesion of the water-based paint on the inner surface of the socket tends not to be sufficiently obtained, and if it is too wide, the effect of the present invention by suppressing the use of the solvent tends not to be obtained. ..

The film thickness of the third layer is preferably 10 to 80 μm, more preferably 10 to 20 μm. If the film thickness is less than 10 μm, a uniform coating film cannot be obtained, and the adhesion between the powder coating film and the topcoat tends to decrease. If the film thickness exceeds 80 μm, drying tends to be slow and productivity tends to decrease. Or, the solvent tends to remain in the coating film. As a method for applying the solvent-based primer, a method using a brush or spraying can be used.

(Solvent primer)
The solvent-based primer is not particularly limited, and the medium is an organic solvent of a resin such as an acrylic resin, an epoxy resin, a xylene resin, a toluene resin, a cyclopentadiene resin, a kumaron inden resin, or a carboxylated acrylic modified SBR resin. It is possible to use a paint in which the organic solvent swells and softens the surface of the powder coating, thereby producing an anchor effect and improving the adhesion performance. The organic solvent used as the medium 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, butyl acetate and the like can be used. Can be mentioned. As these acrylic resins and epoxy resins, those currently distributed as topcoat paints for cast iron pipes can be used, and are 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.

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

Examples of solvent-based primes for acrylic resins include Kurimoto Coat WR Gray manufactured by Dainippon Paint Co., Ltd., Kurimoto Coat AC-1-SR Gray manufactured by Nippon Paint Industrial Coatings Co., Ltd., and Nippon Paint Industrial Coatings Co., Ltd. Kurimoto Coat AC-1 Gray made by Kurimoto Coat can be used.

The solvent-based primer 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, ketimines, and acids. Terminal polyester resin, phenol resin, urea resin, resol resin, amino resin, isocyanate, blocked isocyanate, triethylenetetramine modified product, metaxylene diamine modified product, toluene diisocyanate modified product and the like can be used alone or in combination of two or more.

As a specific example of a solvent-based primer 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 xylene, ethylbenzene, isobutanol, methanol, methylisobutylketone and propylene glycol monoethyl ether added to various pigments and additives as solvents, 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.

[Fourth layer]
After forming a coating layer on the inner surface 3a of the straight pipe portion 3, as a second step, the surface of the sprayed coating layer on the inner surface 2a of the receiving port 2 of the cast iron pipe p is coated with a water-based paint using the residual heat. The inner surface 2a coating layer of the socket 2 is formed. The water-based paint contains an epoxy ester resin (A), an acrylic resin emulsion (B), an acrylic resin dispersion (C), and a pigment (D). The components (A), (B) and (C) are all aqueous dispersions, and by blending these components in a water-based paint in a predetermined ratio described later, the powder provided on the inner surface 3a of the straight pipe portion 3 Forming a coating film layer on the inner surface of the socket with one coat, which has excellent adhesion to the body coating film, excellent corrosion resistance and weather resistance, and does not impair various functions required for anticorrosion coating such as adhesion. Can be done.

Further, since the formation of the coating film layer on the inner surface 2a of the socket 2 is performed by utilizing the residual heat when the coating film layer is formed on the inner surface 3a of the straight pipe portion 3, after the coating film layer on the inner surface 3a of the straight pipe portion 3 is formed. , It is preferable to carry out continuously. The interval between the step of forming the inner surface 3a coating film layer of the straight pipe portion 3 and the step of forming the coating film layer of the inner surface 2a of the socket 2 is not particularly limited, but in the case of natural cooling, the coating film of the inner surface 3a of the straight pipe portion 3 After the layer forming step, the coating film layer on the inner surface 2a of the socket 2 is continuously formed at intervals of usually within 30 minutes to 3 hours, more preferably within 1 to 2 hours. The surface temperature of the cast iron pipe p at this time is preferably 50 to 80 ° C, more preferably 70 to 80 ° C. If the temperature is lower than 50 ° C., the coating film tends to be difficult to dry, and if the temperature exceeds 80 ° C., the water content in the paint tends to boil. Further, since the water-based paint used for forming the coating film layer on the inner surface of the socket is dried quickly, the time required for coating the inner surface of the socket of the cast iron pipe can be shortened.

(Water-based paint)
The water-based paint forming the fourth layer contains 1 to 15 parts by mass of (A) epoxy ester resin, 5 to 30 parts by mass of (B) acrylic resin emulsion, and (C) acrylic resin disper as solid content. It contains 55 to 94 parts by mass of John, the total solid content of (A), (B) and (C) is 100 parts by mass, and (D) contains a pigment having a pigment volume concentration of 35 to 45%. If there is, it can be used without particular limitation.

The epoxy ester resin (A) is blended into a water-based paint as an aqueous dispersion in order to improve corrosion resistance. The epoxy ester resin (A) is a vinyl-modified epoxy ester resin (a1) obtained by massively polymerizing an unsaturated fatty acid-modified epoxy ester resin (a1), a vinyl monomer having a terminal carboxyl group-containing structure, and other vinyl monomers. It is an aqueous dispersion of a vinyl-modified epoxy ester resin neutralized product (a3) obtained by neutralizing the vinyl-modified epoxy ester resin (a2) with a2) as a main component. Details will be described later.

The solid content concentration of the aqueous dispersion of the epoxy ester resin (A) is not particularly limited, but is usually 15 to 70% by mass, more preferably 25 to 60% by mass in consideration of workability. , Most preferably 35 to 50% by mass.

The blending amount of the epoxy ester resin (A) is 1 to 15 parts by mass, preferably 3 to 12 parts by mass in 100 parts by mass of the components (A), (B) and (C) of the water-based paint as a solid content. It is more preferably 5 to 10 parts by mass. If the blending amount is less than 1 part by mass, the corrosion resistance tends to decrease, and if it exceeds 15 parts by mass, the acrylic resin component tends to be relatively small, and a good coating film tends not to be formed.

The acrylic resin emulsion (B) is blended with a water-based paint in order to form a coating film having excellent corrosion resistance and drying property. The acrylic resin emulsion (B) is mainly composed of an aqueous resin dispersion of a forced emulsification type (meth) acrylic polymer (b). The forced emulsification type means that the resin portion basically does not have self-emulsifying power, and the emulsion is used in the present invention to mean a forced emulsifying type dispersion. .. Details will be described later.

The solid content concentration of the acrylic resin emulsion (B) is not particularly limited, but is usually in the range of 15 to 70% by mass, more preferably 25 to 60% by mass in consideration of workability. Most preferably, it is 35 to 50% by mass.

The blending amount of the acrylic resin emulsion (B) is 5 to 30 parts by mass, preferably 8 to 25 parts by mass in 100 parts by mass of the components (A), (B) and (C) of the water-based paint as a solid content. Parts, more preferably 10 to 20 parts by mass. If the blending amount is less than 5 parts by mass, the drying property tends to decrease, and if it exceeds 30 parts by mass, the acrylic resin dispersion (C) described later tends to be relatively small, and the corrosion resistance and the weather resistance tend to decrease. There is.

The acrylic resin dispersion (C) is blended with the water-based paint in order to form a coating film having excellent corrosion resistance and weather resistance. The acrylic resin dispersion (C) is mainly composed of an aqueous resin dispersion (c1) of a self-emulsifying vinyl polymer, and has a boiling point in the range of 130 to 220 ° C. under normal pressure and at 20 ° C. It is a self-emulsifying aqueous dispersion containing 15% by mass or less of an organic solvent (c2) having a water solubility of 100 or more in an acrylic resin dispersion (C). 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. Details will be described later.

The solid content concentration of the acrylic resin dispersion (C) is not particularly limited, but is usually in the range of 15 to 70% by mass, more preferably 25 to 60% by mass in consideration of workability. Most preferably, it is 35 to 50% by mass.

The blending amount of the acrylic resin dispersion (C) is 55 to 94 parts by mass, preferably 73 to 89 parts by mass in 100 parts by mass of the components (A), (B) and (C) of the water-based paint as a solid content. It is by mass, more preferably 75 to 85 parts by mass. If the blending amount is less than 55 parts by mass, a good coating film tends not to be formed, and if it exceeds 94 parts by mass, the epoxy ester resin (A) and the acrylic resin emulsion (B) are relatively small, and the corrosion resistance and corrosion resistance are improved. Durability tends to decrease.

The pigment (D) used in the water-based paint is mainly for forming a coating film having an excellent balance between strength and dryness, and various pigments such as extender pigments and rust preventive pigments, which will be described later, can be used.

The blending amount of the pigment (D) in the water-based paint is 35 to 45%, preferably 35 to 40%, in terms of pigment volume concentration (hereinafter referred to as PVC). If the PVC content is less than 35%, the coating film tends to remain sticky and difficult to dry, and if it exceeds 45%, the corrosion resistance of the coating film tends to decrease. In addition, PVC is an abbreviation for Pigment Volume Concentration, and is a volume ratio of a pigment calculated by PVC (%) = pigment / (resin + pigment) × 100. As the total volume of the resin and the pigment, the non-volatile volume in the dispersion is usually used.

The method of applying the water-based paint is not particularly limited, and the water-based paint can be applied by spraying, brushing, or a roller. The thickness of the fourth layer formed by applying the water-based paint is preferably 80 to 200 μm, more preferably 80 to 100 μm.

（式中、ｎは１〜１０の整数であり、Ｒ¹は炭素数２〜１８のアルキレン基を示す。）で示される末端カルボキシル基含有構造を有するビニル単量体およびその他のビニル単量体を塊状重合させて得られるビニル変性エポキシエステル樹脂（ａ２）と、塩基性化合物とからなり、水を用いてビニル変性エポキシエステル樹脂（ａ２）中のカルボキシル基の一部または全部を塩基性化合物によって中和し、この中和で得られるビニル変性エポキシエステル樹脂中和物（ａ３）を水に分散することによって得られるものである。 (Epoxy ester resin (A))
The epoxy ester resin (A) used in the present invention is a component that imparts corrosion resistance to water-based paints, and is an unsaturated fatty acid-modified epoxy ester resin (a1), general formula (I).

(In the formula, n is an integer of 1 to 10, and R ¹ indicates an alkylene group having 2 to 18 carbon atoms.) A vinyl monomer having a terminal carboxyl group-containing structure and other vinyl monomers represented by the above. It is composed of a vinyl-modified epoxy ester resin (a2) obtained by massively polymerizing the above and a basic compound, and a part or all of the carboxyl groups in the vinyl-modified epoxy ester resin (a2) is made of a basic compound using water. It is obtained by neutralizing and dispersing the vinyl-modified epoxy ester resin neutralized product (a3) obtained by this neutralization in water.

Examples of the unsaturated fatty acid-modified epoxy ester resin (a1) include unsaturated fatty acid-modified epoxy ester resins obtained by reacting an epoxy group and / or a hydroxyl group of an epoxy resin with a carboxyl group of an unsaturated fatty acid. ..

Examples of the epoxy resin used for preparing the unsaturated fatty acid-modified epoxy ester resin (a1) include bisphenol type epoxy resin, alicyclic epoxy resin, phenol novolac type epoxy resin, polyethylene glycol type epoxy resin, and epoxidized polybutadiene resin. Can be mentioned. These can be used alone or in combination of two or more. Of these, it is preferable to use a bisphenol type epoxy resin because it can form a coating film having excellent corrosion resistance.

Examples of the bisphenol type epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, and bisphenol S type epoxy resin, and among them, a coating film having excellent corrosion resistance can be formed. For this reason, it is preferable to use a bisphenol A type epoxy resin.

Examples of the bisphenol A type epoxy resin include Epicron 850, 1050, 3050, 4050, 7050, HM-091, HM-101 (all of which are manufactured by DIC Corporation) and the like. Examples of the bisphenol F type epoxy resin include Epicron 830 (manufactured by DIC Corporation).

Examples of the alicyclic epoxy resin include Unox 201 and 289 (all of which are manufactured by Union Carbide, USA). Examples of the phenol novolac type epoxy resin include Epicron N-740 and 775 (all manufactured by DIC Corporation). Examples of the polyethylene glycol-based epoxy resin include Epicoat 812 (manufactured by Shell, the Netherlands), Epolite 40E, 200E, 400E (all of which are manufactured by Kyoei Co., Ltd.) and the like. Examples of the epoxidized polybutadiene resin include BF-1000 (manufactured by ADEKA Corporation) and the like.

As the epoxy resin, a water-based paint having excellent film-forming property at room temperature can be obtained. Therefore, it is preferable to use an epoxy resin having an epoxy equivalent of 400 to 1,000 (g / equivalent), and an epoxy of 400 to 600. It is more preferable to have an equivalent.

The structure derived from the epoxy resin is preferably contained in the vinyl-modified epoxy ester resin (a2) in an amount of 15 to 75% by mass, more preferably 25 to 60% by mass. As a result, it is possible to form a coating film having excellent film-forming properties and excellent corrosion resistance.

Examples of the unsaturated fatty acid that reacts with the epoxy resin include oleic acid, linoleic acid, linolenic acid, eleostearic acid, ricinolic acid, tung oil fatty acid, flaxseed oil fatty acid, dehydrated sesame oil fatty acid, sesame oil fatty acid, tall oil fatty acid, and cotton seed oil fatty acid. , Soybean oil fatty acid, olive oil fatty acid, safflower oil fatty acid, rice bran oil fatty acid and other fatty acids. Among them, the use of soybean oil fatty acid having an iodine value of 120 to 200, semi-drying oil such as dehydrated castor oil fatty acid, and drying oil efficiently grafts the vinyl monomer described later into the unsaturated bond of the unsaturated fatty acid. It is preferable because it can be polymerized.

The structure derived from the unsaturated fatty acid is preferably contained in the vinyl-modified epoxy ester resin in an amount of 15 to 50% by mass, more preferably 15 to 40% by mass, and most preferably 20 to 35% by mass. .. Thereby, the drying property of the coating film at room temperature, the dispersibility of the pigment, and the corrosion resistance of the obtained coating film can be improved.

When using the unsaturated fatty acid, other carboxylic acids can be used in combination within the desired range. Examples of the other carboxylic acids include saturated fatty acids such as octyl acid, lauric acid, stearic acid, hydrogenated palm oil fatty acid, palm oil fatty acid and palm oil fatty acid, (anhydrous) phthalic acid, isophthalic acid and terephthalic acid. Trimellitic acid (anhydrous), pyromellitic acid (anhydrous), tetrachloro (anhydrous) phthalic acid, 1,1-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, tetrahydro (anhydrous) phthalic acid , (Anhydrous) hetic acid, (anhydrous) hymic acid (registered trademark of Hitachi Chemical Chemical Industries, Ltd.), hydrogenated (anhydrous) trimellitic acid, adipic acid, azelaic acid, sebacic acid, (anhydrous) maleic acid, fumal Examples thereof include acids, itaconic acids, octenoic acids, isononan acids, benzoic acids, p-tert-benzoic acids, isooctanoic acids, isodecanoic acids, cyclohexanoic acids, acrylic acids and methacrylic acids.

In the unsaturated fatty acid-modified epoxy ester resin (a1), for example, the epoxy resin and the unsaturated fatty acid are dehydrated by heating to 150 to 250 ° C. in the presence of an esterification catalyst, if necessary, and then dehydrated. It can be produced by subjecting an epoxy group or a secondary hydroxyl group of the above to an esterification reaction of the carboxyl group of the unsaturated fatty acid.

When producing an unsaturated fatty acid-modified epoxy ester resin (a1), if it is desired to suppress side reactions such as an etherification reaction, it is preferable to use, for example, dimethylbenzylamine, triethylamine or the like.

When the epoxy resin and the unsaturated fatty acid are reacted, a polyhydric alcohol can be used in combination. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, and triethylene glycol. Cyclohexanedimethanol, hydrogenated bisphenol A, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitol and the like can be mentioned.

When the polyhydric alcohol is used, the unsaturated fatty acid-modified epoxy ester resin (a1) can be produced by mixing the epoxy resin, the unsaturated fatty acid and the polyhydric alcohol and subjecting them to an esterification reaction. ..

The mass average molecular weight of the obtained unsaturated fatty acid-modified epoxy ester resin (a1) is 3,000 to 15,000 because it can suppress gelation during bulk polymerization and has excellent aqueous dispersion stability. Is preferable.

Further, the oil length of the unsaturated fatty acid-modified epoxy ester resin (a1) is less likely to cause problems such as high viscosity, coarsening of water-dispersed resin particles, and increased foaming property during bulk polymerization, and thus 15 to 60. It is preferably mass%.

Next, a vinyl-modified epoxy obtained by bulk polymerization of an unsaturated fatty acid-modified epoxy ester resin (a1), a vinyl monomer having a terminal carboxyl group-containing structure represented by the general formula (I), and other vinyl monomers. The ester resin (a2) will be described.

Examples of the vinyl monomer having a terminal carboxyl group-containing structure represented by the general formula (I) include 2-methacryloxyethyl succinic acid, 2-methacryloxyethyl hexahydrophthalate, 2-methacryloxyethyl glutarate, and ω. -Carboxypolycaprolactone methacrylate and the like.

The vinyl monomer having a terminal carboxyl group-containing structure represented by the general formula (I) is, for example, (i) a method of reacting a hydroxycarboxylic acid with a radically polymerizable unsaturated compound having a carboxyl group, (ii) carboxyl. It can be produced by a method of reacting a radically polymerizable unsaturated compound having a group with ε-caprolactone in the presence of an acid catalyst or the like. Examples of the method (ii) include a method in which a radically polymerizable unsaturated compound having a carboxyl group and ε-caprolactone are mixed and stirred in the presence of an acid catalyst and reacted at 40 to 150 ° C.

Examples of the radically polymerizable unsaturated compound having a carboxyl group that can be used in the method (ii) include acrylic acid, methacrylic acid, itaconic acid, and maleic acid. Examples of the acid catalyst include p-toluenesulfonic acid, benzenesulfonic acid, aluminum chloride, ferric chloride and the like. The acidic catalyst is preferably used in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the radically polymerizable unsaturated compound having a carboxyl group.

The vinyl monomer having the terminal carboxyl group-containing structure represented by the general formula (I) obtained by the above method has a structure derived from ε-caprolactone in one molecule because the obtained coating film has good drying property. It is preferable to have 1 to 10 units on average, and more preferably 1 to 5 units on average. Specific examples thereof include Aronix M-5300 (manufactured by Toagosei Chemical Industry Co., Ltd.) in which the average number of ε-caprolactone units in one molecule is 2.

The mass ratio of the terminal carboxyl group-containing structure represented by the general formula (I) in the vinyl-modified epoxy ester resin (a2) is preferably 0.5 to 30% by mass, more preferably 2 to 17% by mass. .. As a result, the neutralized vinyl-modified epoxy ester resin (a3) and the pigment are excellent in dispersion stability, have good corrosion resistance, and can suppress gelation during bulk polymerization.

（式中、ｍは３〜９０の整数であり、Ｒ²は炭素数２〜４のアルキレン基、Ｒ³は水素原子またはメチル基である。）で示されるポリアルキレンオキサイド構造を有するものが好ましい。 The vinyl-modified epoxy ester resin (a2) has a terminal carboxyl group-containing structure represented by the general formula (I) in the vinyl monomer and other vinyl polymer portions, and is partially or wholly a basic compound. In addition to the neutralized structure, general formula (II)

(In the formula, m is an integer of 3 to 90, R ² is an alkylene group having 2 to 4 carbon atoms, and R ³ is a hydrogen atom or a methyl group.) It is preferable that the m has a polyalkylene oxide structure. ..

The polyalkylene oxide structure represented by the general formula (II) has a terminal carboxyl group-containing structure represented by the general formula (I) in a part or all of the unsaturated bonds of the unsaturated fatty acid-modified epoxy ester resin (a1). When the vinyl monomer having the vinyl monomer and the other vinyl monomer are polymerized, a vinyl monomer having a polyalkylene oxide structure represented by the general formula (II) as a part or all of the other vinyl monomer is used. By using it, it can be introduced into the vinyl polymer portion.

Examples of the vinyl monomer having a polyalkylene oxide structure represented by the general formula (II) include those obtained by adding an alkylene oxide such as ethylene oxide or propylene oxide to a hydroxyl group-containing vinyl monomer. For example, methoxypolyethylene glycol (meth) acrylate and the like can be mentioned.

M in the general formula (II) is preferably an integer of 10 to 100, and more preferably an integer of 10 to 30. As a result, a coating film having excellent dispersion stability of the vinyl-modified epoxy ester resin neutralized product (a3) and the pigment and having good corrosion resistance can be obtained.

The mass ratio of the polyalkylene oxide structure represented by the general formula (II) in the vinyl-modified epoxy ester resin (a2) is preferably 0.5 to 10% by mass, and more preferably 2 to 5% by mass. As a result, it is possible to form a coating film having excellent dispersion stability between the vinyl-modified epoxy ester resin (a2) and the pigment and having good corrosion resistance, and it is possible to suppress gelation during bulk polymerization.

Examples of the other vinyl monomer include (meth) acrylic acid, 2-carboxyethyl acrylate, crotonic acid, vinyl acetic acid, and the like, in addition to the vinyl monomer having a polyalkylene oxide structure represented by the general formula (II). Monovinyl adipate, monovinyl sebacate, monomethyl itacone, monomethyl maleate, monomethyl fumarate, mono succilate (2- (meth) acryloyloxyethyl), mono phthalate (2- (meth) acryloyloxyethyl), hexahydro Monocarboxylic acids with unsaturated double bonds such as mono (2- (meth) acryloyloxyethyl) and sorbic acid; dicarboxylic acids with unsaturated double bonds such as itaconic acid, maleic acid and fumaric acid; methyl (Meta) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate , Lauryl (meth) acrylate, octadecyl (meth) acrylate, docosanyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) Alkyl (meth) acrylates such as acrylates and cycloalkyl (meth) acrylates; aromatic vinyl compounds such as styrene, p-tert-butylstyrene, α-methylstyrene and vinyltoluene; 2-methoxyethyl (meth) acrylates, 4- Ω-alkoxyalkyl (meth) acrylates such as methoxybutyl (meth) acrylates; tertiary amide group-containing vinyl monomers such as N, N-dimethyl (meth) acrylamides; 2-hydroxyethyl (meth) acrylates, 2- A hydroxylated (meth) acrylate such as a hydroxypropyl (meth) acrylate; a hydroxyl group-containing vinyl ether such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, or 6-hydroxyhexyl vinyl ether; N-methylol (meth) acrylamide; -Secondary amino group-containing vinyl monomer such as methylaminoethyl (meth) acrylate; vinyl monomer having an active methylene group such as vinyl acetoacetate and 2-acetoacetoxyethyl (meth) acrylate; vinyl tri Vinyl-based monomers having a hydrolyzable silyl group such as methoxysilane and 3- (meth) acryloyloxypropyltrimethoxysilane; vinyl-based monomers containing a silyl ester group such as trimethylsilyl (meth) acrylate; Vinyl-based monomers containing epoxy groups such as meta) acrylate, methylglycidyl (meth) acrylate, 3,4-epoxycyclohexyl (meth) acrylate, glycidyl vinyl ether, allyl glycidyl ether; 2-isocyanate propene, 2-isocyanate Examples thereof include vinyl-based monomers containing an isocyanate group such as naltoethyl vinyl ether, 2-isocyanate ethyl methacrylate, m-isopropenyl-α, and α-dimethylbenzyl isocyanate. These can be used alone or in combination of two or more. Further, as the other vinyl monomer, for example, one in which the vinyl monomer having a hydroxyl group and ε-caprolactone are subjected to an addition reaction can also be used.

The synthesis of the vinyl-modified epoxy ester resin (a2) by the bulk polymerization is usually carried out in the presence of a radical polymerization initiator with the unsaturated fatty acid-modified epoxy ester resin (a1) which is a synthetic raw material and the vinyl-modified epoxy ester obtained by the synthesis. The resin (a2) is melted at a temperature at which stirring is possible. Various radical polymerization initiators can be used as the radical polymerization initiator, but among them, a radical polymerization initiator having a 1-hour half-life of 100 ° C. or more is preferable because unreacted vinyl monomers are unlikely to remain. ..

Further, as the radical polymerization initiator, the number of moles of the n-pentadecane dimer generated when the radical polymerization initiator is decomposed at a half-life temperature of 15 minutes in n-pentadecane is measured and the radical polymerization is started. It is preferable that the product obtained by calculating the production ratio with respect to 1 mol of the agent (mol%) is a radical polymerization initiator having a strong hydrogen abstraction property of 30 mol% or more. As a result, unreacted vinyl monomer is unlikely to remain, and it is possible to prevent the obtained vinyl-modified epoxy ester resin (a2) from being neutralized and the resin particles after water dispersion being coarsened to reduce the water dispersion stability. ..

Examples of the radical polymerization initiator having a 1-hour half-life of 100 ° C. or higher and a crosslinking efficiency of 30 mol% or higher include tert-butylperoxybenzoate, tert-butylperoxy-2-ethylhexyl carbonate, tert-butylperoxyisopropylcarbonate, and tert. -Amilperoxybenzoate, di-tert-butyl peroxide and the like can be mentioned, and these can be used alone or in combination of two or more. The radical polymerization initiator is preferably used in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the total amount of the vinyl monomers.

In the bulk polymerization, a chain transfer agent can be used if necessary. Chain transfer agents include, for example, alkyl mercaptans such as n-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan; aromatic mercaptans such as benzyl mercaptan and dodecyl benzyl mercaptan; thiocarboxylic acids such as thioapple acid or salts thereof, alkyl. Examples include ester.

The bulk polymerization temperature during the synthesis of the vinyl-modified epoxy ester resin (a2) is relatively easy to control by stirring during the bulk polymerization, and the reaction between the unsaturated fatty acid-modified epoxy ester resin (a1) and the vinyl monomer. The temperature is preferably 100 to 200 ° C., and more preferably 100 to 150 ° C. The bulk polymerization can be polymerized at normal pressure, but it is preferable to carry out pressure polymerization in a closed container. In bulk polymerization under normal pressure, the viscosity tends to increase during polymerization when the polymerization temperature is 100 to 140 ° C., and the vinyl monomer tends to volatilize when the polymerization temperature is 140 to 200 ° C.

The mass average molecular weight of the vinyl-modified epoxy ester resin (a2) is preferably 8,000 to 100,000. As a result, the vinyl-modified epoxy ester resin (a2) can be stably dispersed in water to form a coating film having excellent water resistance and corrosion resistance.

The acid value of the vinyl-modified epoxy ester resin (a2) is preferably 5 to 100 (mgKOH / g), more preferably 15 to 40, and most preferably 20 to 35. As a result, a coating film having excellent pigment dispersibility, corrosion resistance and water resistance can be formed.

Next, the neutralization of a part or all of the carboxyl groups contained in the obtained vinyl-modified epoxy ester resin (a2) with a basic compound and the dispersion by mixing with water will be described.

Examples of the basic compound used for neutralizing the vinyl-modified epoxy ester resin (a2) include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, 2-aminoethanol, 2-dimethylaminoethanol, ammonia and hydroxide. Examples thereof include sodium, potassium hydroxide, tetramethylammonium hydroxide, tetra-n-butylammonium hydroxide, trimethylbenzylammonium hydroxide and the like. These basic compounds can also be used as an aqueous solution such as aqueous ammonia. Further, the water-based paint containing the vinyl-modified epoxy ester resin neutralized product (a3) volatilizes when forming the coating film and does not remain in the coating film, forming a coating film having excellent water resistance and corrosion resistance. Therefore, it is preferable to use a volatile basic compound or an aqueous solution thereof, for example, aqueous ammonia, triethylamine, or 2-dimethylaminoethanol.

As a method of dispersing the vinyl-modified epoxy ester resin neutralized product (a3) in water, for example, (i) vinyl obtained by massively polymerizing (i) an unsaturated fatty acid-modified epoxy ester resin (a1) and the vinyl monomer. The melt of the modified epoxy ester resin (a2) is mixed with a basic compound, preferably mixed at 80 to 125 ° C. to obtain a melt of the neutralized vinyl-modified epoxy ester resin (a3), and then mixed with water. A method of mixing and mixing at 90 ° C. or lower, more preferably 50 to 90 ° C. to disperse the vinyl-modified epoxy ester resin neutralized product (a3) in water, (ii) in the same manner as in (i) above. The vinyl-modified epoxy ester resin neutralized product (a3) obtained by the sum is dissolved in an organic solvent having a boiling point of 90 ° C. or lower, preferably an organic solvent having a boiling point of 50 to 90 ° C., and then preferably 90 ° C. or lower, more preferably. After dissolving at 50 to 90 ° C., it is mixed with water, preferably mixed with water at 90 ° C. or lower, more preferably 50 to 90 ° C. to disperse the vinyl-modified epoxy ester resin neutralized product (a3) in water. After that, a method of removing a part or all of the organic solvent under reduced pressure can be mentioned. In the dispersion method (i), a dispersion method in which a mechanical shearing force is applied at normal pressure by a Hallel homogenizer, a static mixer, a sonolator, a disper, a mixer, or the like, or a mechanical shearing by pressurization with a microfluidizer or a cavitron. A force-applying dispersion method is preferred.

Before being neutralized, the vinyl-modified epoxy ester resin (a2) has an acid group such as a carboxyl group in the terminal carboxyl group-containing structure represented by the general formula (I). Therefore, even when the acid value of the vinyl-modified epoxy ester resin (a2) is as low as about 15 to 40 (mgKOH / g), it is stable in an aqueous medium containing extremely little or no organic solvent. It can be dispersed, and the pigment can be stably dispersed. Further, by using a water-based paint containing a neutralized product (a3) of such a low acid value vinyl-modified epoxy ester resin (a2), the corrosion resistance and water resistance of the obtained coating film can be improved. it can. The acid value of the vinyl-modified epoxy ester resin (a2) before neutralization can be selected as needed, and may have an acid value other than 15-40. The acid value is preferably 10 to 60, more preferably 10 to 40, and most preferably 20 to 30.

Further, when the vinyl-modified epoxy ester resin (a2) is dispersed in water, an emulsifier can be used within a target range in order to improve the dispersion stability of the vinyl-modified epoxy ester resin (a2) and the pigment. .. Examples of the emulsifier include nonionic emulsifiers such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene polyoxypropylene copolymer, alkyl sulfate ester salts, alkylbenzene sulfonates, and polyoxyethylene alkyl ether sulfate esters. Examples thereof include anionic emulsifiers such as salts and polyoxyethylene alkylphenyl ether sulfates, and cationic emulsifiers such as quaternary ammonium salts. It is preferable not to use the emulsifier as much as possible so as not to reduce the water resistance and corrosion resistance of the obtained coating film.

The epoxy ester resin (A) obtained by the production method of the present invention is obtained by dispersing the particles of the vinyl-modified epoxy ester resin neutralized product (a3) in an aqueous medium, and the particle size of the particles is 40 to 300 nm. It is preferably 80 to 200 nm, and more preferably 80 to 200 nm. The particle size is a value obtained by a Microtrack particle size analyzer (Microtrack 9340-UPA, manufactured by Nikkiso Co., Ltd.).

Specific examples of the epoxy ester resin (A) as described above include Watersol EFD-5560 (manufactured by DIC Corporation).

(Acrylic resin emulsion (B))
The acrylic resin emulsion (B) used in the present invention is mainly composed of an aqueous resin dispersion of a forced emulsification type (meth) acrylic polymer (b). The (meth) acrylic polymer (b) may be a homopolymer or a mixture of two or more kinds of polymers. Further, when the acrylic resin emulsion (B) is a mixture of two or more kinds of polymers, it may be a mixture of an aqueous emulsion of two or more kinds of (meth) acrylic polymers (b), and the blending thereof. The ratio is not particularly limited and can be set freely.

The (meth) acrylic polymer (b) is not limited to the acrylic polymer composed only of the (meth) acrylic monomer, but is a styrene-acrylic polymer having a styrene monomer unit as the main polymerization unit. It may be.

Examples of the (meth) acrylic polymer (b) include a (meth) acrylic acid ester-based monomer unit having an alkyl group having 1 to 10 carbon atoms in an amount of 20 to 100% by mass and a styrene-based monomer unit of 0 to 80. Examples thereof include (meth) acrylic polymers composed of mass% and vinyl-based monomer units 0 to 30 mass% copolymerizable with these. The blending amount of the (meth) acrylic acid ester-based monomer unit is preferably 40 to 95% by mass, and more preferably 60 to 90% by mass. The blending amount of the styrene-based monomer unit is preferably 5 to 60% by mass, and more preferably 10 to 40% by mass. The blending amount of the vinyl-based monomer unit copolymerizable with these is preferably 0 to 15% by mass, more preferably 0 to 10% by mass.

Examples of the (meth) acrylic monomer used in the (meth) acrylic polymer (b) include methyl (meth) acrylic acid, ethyl (meth) acrylic acid, hydroxyethyl (meth) acrylic acid, and (meth) acrylic acid. Hydroxypropyl, (meth) aminoethyl acrylate, (meth) dimethylaminoethyl acrylate, (meth) diethylaminoethyl acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, ( Hexyl acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, octadecyl (meth) acrylate, etc. have alkyl groups with 1 to 10 carbon atoms (meth). ) Acrylic acid alkyl ester-based monomer; (meth) acrylic acid, crotonic acid, maleic acid, its anhydride, fumaric acid, itaconic acid, unsaturated dicarboxylic acid monoalkyl ester (for example, monomethyl maleate, monoethyl fumarate, itacon) Examples thereof include carboxyl group-containing vinyl-based monomers such as mononormal butyl acid). These can be used alone or in combination of two or more.

Examples of the styrene-based monomer used in the (meth) acrylic polymer (b) include styrene, α-methylstyrene, vinyltoluene, chlorostyrene, and 2,4-dibromostyrene.

Examples of the monomer copolymerizable with the (meth) acrylic monomer and the styrene-based monomer used in the (meth) acrylic polymer (b) include vinyl esters such as vinyl acetate and vinyl propionate; vinylidene chloride. , Vinylidene halide such as vinylidene bromide; (meth) acrylonitrile; glycidyl (meth) acrylate; (meth) acrylamide, N-methylol (meth) acrylamide, butoxymethyl (meth) acrylamide, diacetone acrylicmid and the like.

The method for synthesizing the (meth) acrylic polymer (b) is not particularly limited, and a known polymerization method such as emulsion polymerization can be used. As a method for preparing the acrylic resin emulsion (B), for example, a mixture (monomer premix) of a monomer, an emulsifier, a polymerization initiator and the like is put together in a reaction vessel containing a predetermined amount of water in advance. The monomer mixture is emulsion-polymerized, and after the reaction is completed, the reaction product is cooled and neutralized to obtain the desired aqueous acrylic emulsion.

The emulsifier used in the above reaction is an essential component for forcibly emulsifying the acrylic resin emulsion (B) in water. Specific examples thereof include anionic polymerization emulsifiers such as fatty acid soap, loginate soap, alkyl sulfonate, alkyl benzene sulfonate, dialkylaryl sulfonate, alkyl sulfosuccinate, and polyoxyethylene alkyl sulfate; Examples thereof include nonionic polymer emulsifiers such as ethylene alkyl ether, polyoxyethylene alkylaryl ether, polyoxyethylene sorbitan fatty acid ester, and oxyethylene oxypropylene block copolymer. These emulsifiers can be used alone or in combination of two or more. It is also possible to use a combination of nonionic and anionic surfactants, and the use of cationic surfactants and amphoteric surfactants. The amount of the emulsifier used is preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the total amount of the polymerizable monomer to be subjected to emulsion polymerization.

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 catalysts such as tert-butylhide peroxide and cumenehydroperoxide. .. The amount of the polymerization initiator used is preferably 0.1 to 0.7 parts by mass with respect to 100 parts by mass of the polymerizable monomer to be subjected to emulsion polymerization.

Further, in the emulsion polymerization reaction, a molecular weight adjusting agent such as a chain transfer agent or a polymerization terminator and a polymerization rate adjusting agent can be appropriately used at the time of polymerization in order to adjust the molecular weight. Further, the molecular weight may be controlled by interrupting the reaction by cooling. Examples of the chain transfer agent include mercaptans such as tert-dodecyl mercaptan, n-todecyl mercaptan, octyl mercaptan, n-tetradecyl mercaptan, and n-hexyl mercaptan, turpinolene, tert-terpinene, α-methylstyrene dimer, and ethylxantogen disulfide. , Diisopropylxanthogen sulfide, aminophenyl sulfide, tetraethylthiol disulfide and the like, and these can be used alone or in combination of two or more. The amount of the chain transfer agent used is preferably 1.0 part by mass or less with respect to 100 parts by mass of the total amount of the polymerizable monomer to be subjected to emulsion polymerization.

Examples of the polymerization inhibitor include hydroquinone (phenol), amine-based sulfur, hydroxylamine sulfate, ammonia, caustic soda, caustic potash, and the like, and other substances having a polymerization inhibitory effect can be used. These can be used alone or in combination of two or more. The amount used depends on the type of polymerization inhibitor and the reactivity ratio with the monomer. In the emulsion polymerization reaction, in addition to the emulsifier, chain transfer agent and polymerization initiator, various electrolytes, pH adjusters and other additives may be used in combination, if necessary.

Specific examples of the acrylic resin emulsion (B) as described above include Boncoat EC-740EF (manufactured by DIC Corporation).

(Acrylic resin dispersion (C))
The acrylic resin dispersion (C) used in the water-based paint is an aqueous resin dispersion (c1) of a vinyl-based polymer having a self-water-dispersing ability, and has a boiling point of 130 to 220 ° C. under normal pressure and 20. It is a self-emulsifying aqueous dispersion containing an organic solvent (c2) having a solubility of 100 or more in water at ° C. The self-emulsifying type means that some hydrophilic group is chemically introduced into the resin skeleton and the resin itself has an emulsifying ability.

The aqueous resin dispersion (c1) of the vinyl polymer used for the acrylic resin dispersion (C) contains a non-functional (meth) acrylic acid ester and / or an aromatic vinyl monomer and a polyethylene glycol group. It contains a monofunctional unsaturated monomer having an α, β-ethylenic unsaturated carboxylic acid.

The non-functional (meth) acrylic acid ester used in the aqueous resin dispersion (c1) is a component for improving the water resistance, chemical resistance and weather resistance of the obtained coating film, and has 4 to 12 carbon atoms. Has a hydrocarbon group of. When the number of carbon atoms exceeds 12, the substrate adhesion of the obtained coating film tends to decrease.

Examples of the (meth) acrylic acid ester include n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and cyclohexyl. Examples thereof include (meth) acrylate and benzyl (meth) acrylate. These can be used alone or in combination of two or more.

Examples of the aromatic vinyl-based monomer include styrene, vinyltoluene, p-tert-butylstyrene, etc., which are used as necessary in order to improve the chemical resistance of the coating film. The content of the aromatic vinyl-based monomer in all the monomers is preferably less than 40% by mass in consideration of the balance of various physical properties of the obtained coating film. The content of the (meth) acrylic acid ester and / or the aromatic vinyl-based monomer is 65% by mass or more in the totally polymerizable unsaturated monomer.

The monofunctional unsaturated monomer having a polyethylene glycol group improves the hydrophilicity, water dispersibility, pigment dispersibility and water retention of the aqueous resin dispersion (c1), and delays the surface drying property of the obtained coating film. It is an ingredient. Examples of the monofunctional unsaturated monomer include mono (meth) acrylate of polyethylene glycol and a compound in which the terminal hydroxyl group thereof is an alkoxyl group such as a methoxy group or an ethoxy group. Specific examples include Blemmer PME400, PME4000, AE350, PE350 (all manufactured by NOF CORPORATION), NK Ester M-90G, M-230G (all manufactured by Shin Nakamura Chemical Industry Co., Ltd.). ), NF Bysomer S-10W, S-20W, MPEG350MA, PEM6E (all of which are manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and the like. The molecular weight of polyethylene glycol is not particularly limited, but the ethylene oxide adduct is preferably 3 to 50 mol. If it is less than 3 mol, the effect of improving hydrophilicity, pigment dispersibility and water retention tends to be low, and if it exceeds 50 mol, the substrate adhesion of the obtained coating film tends to decrease.

The α, β-ethylenically unsaturated carboxylic acid is a component for improving hydrophilicity, water dispersion stability and pigment dispersibility, and imparting substrate adhesion to the obtained coating film, for example (meth). Acrylic acid, unsaturated dicarboxylic acids such as crotonic acid, fumaric acid, maleic acid, itaconic acid, and citraconic acid; monoalcoholic esters of these dicarboxylic acids and the like. These can be used alone or in combination of two or more.

The amount of the monofunctional unsaturated monomer having a polyethylene glycol group and the α, β-ethylenically unsaturated carboxylic acid used is the total unit amount in consideration of the water resistance and alkali resistance of the obtained coating film. It is preferably 3 to 6% by mass in the body. If it is less than 3% by mass, the water dispersibility of the resin tends to decrease, and if it exceeds 6% by mass, the hydrophilicity of the obtained coating film tends to increase and the water resistance tends to decrease.

The mass ratio of the monofunctional unsaturated monomer / α, β-ethylenically unsaturated carboxylic acid having a polyethylene glycol group is preferably in the range of 1 to 5. If the mass ratio is less than 1, the water retention of the obtained paint tends to be insufficient, and if the mass ratio exceeds 5, the pigment dispersibility of the resin and the substrate adhesion of the obtained paint tend to decrease.

The solid acid value of the aqueous resin dispersion (c1) is not particularly limited, but is preferably 3 to 18 mgKOH / g from the viewpoint of water resistance, alkali resistance and substrate adhesion of the coating film. It is preferably 6 to 15 mgKOH / g.

In addition, as the copolymerizable polymerizable unsaturated monomer, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate and the like have 3 carbon atoms. (Meta) acrylic acid esters having the following alkyl groups; vinyl esters such as vinyl acetate, vinyl benzoate, Beova (trade name of versatic acid vinyl ester manufactured by Shell, Netherlands); perfluorocyclohexyl (meth) acrylate, di -Perfluoroalkyl group-containing monomers such as perfluorocyclohexyl fumarate; cyano group-containing monomers such as (meth) acrylonitrile; (halogenated) olefins such as ethylene, propylene, vinyl chloride, vinylidene chloride, and vinyl fluoride. Amido bond-containing monomers such as glycidyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide; (meth) acryloyloxyalkyl acid phosphate, N, N-dimethylaminoethyl (meth) Acrylate, methacryloxypropyltrimethoxysilane, alkoxylated polypropylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, Examples thereof include di-2-hydroxyethyl fumarate, polyethylene glycol (meth) acrylate having a polyethylene glycol group having a molecular weight of less than 250, and cyclohexyldimethanol mono (meth) acrylate. Specific examples include Praxel FM and FE monomers (all of which are trade names of ε-caprolactone-added monomers manufactured by Daicel Chemical Industries, Ltd.).

These copolymerizable unsaturated monomers are used in an amount of 32% by mass or less in all the monomers for the purpose of improving the hardness, pigment dispersibility and substrate adhesion of the obtained coating film.

The molecular weight of the aqueous resin dispersion (c1) is based on the polystyrene-equivalent molecular weight by gel permeation chromatography in consideration of the balance between the durability and film-forming property of the obtained coating film and the viscosity of the aqueous resin dispersion. The number average molecular weight is 8,000 to 20,000, preferably 15,000 to 50,000.

The polymerization method of the aqueous resin dispersion (c1) is not particularly limited, but the solution is polymerized in the presence of a water-soluble organic solvent (c2) described later and dispersed in water, or the organic solvent (c2) is used. ) And water are preferably dispersed and polymerized.

The glass transition temperature (Tg) of the aqueous resin dispersion (c1) is not particularly limited, and the theoretical Tg in the case of a non-crosslinking paint is taken into consideration in consideration of the stain resistance, water resistance and toughness of the obtained coating film. Is preferably 40 to 80 ° C., and the theoretical Tg in the case of a cross-linking paint using a polyisocyanate compound is preferably 10 to 60 ° C.

The carboxyl group in the aqueous resin dispersion (c1) is preferably neutralized with a volatile basic substance from the viewpoint of paint stability and pigment dispersibility. Examples of the basic substance include ammonia, triethylamine, monoethanolamine, diethanolamine, dimethylethanolamine, 2-amino-2-methyl-1-propanol and the like.

The organic solvent (c2) used for the acrylic resin dispersion (C) distributes the acrylic resin dispersion (C) to the aqueous phase. The organic solvent (c2) improves the film-forming property of the aqueous resin dispersion (c1), delays the drying of the coating film surface when the coating film is dried, and further mixes with water to obtain the surface tension of the coating material. Is lowered to improve the dispersibility of the pigment and the wettability of the paint to the substrate, and improve the coating workability and the adhesion of the coating film to the substrate.

The hydrophilicity of the organic solvent (c2) is that the solubility of water at 20 ° C. is 100 or more. If the solubility of water is less than 100, the surface of the coating film tends to dry faster. The boiling point of the organic solvent (c2) is 130 to 220 ° C. at normal pressure. If the boiling point is less than 130 ° C, it tends to volatilize with water during the drying process of the coating film, and the smoothness of the coating film tends to be lost. If the boiling point exceeds 220 ° C, the organic solvent (c2) tends to remain in the coating film. There is.

Examples of the organic solvent (c2) include 3-methoxybutanol, 3-methoxy-3-methylbutanol, ethylene glycol monoethyl ether, ethylene glycol mono (n- or iso-) propyl ether, and ethylene glycol mono (n-, iso-). -Or tert-) Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono (n- or iso-) propyl ether, propylene glycol mono (n-, iso- or Examples thereof include tert-) butyl ether, dimethylformamide, N-methylpyrrolidone and ethylene glycol methyl ether acetate. These can be used alone or in combination of two or more.

The amount of the organic solvent (c2) used is preferably 20 parts by mass or more with respect to 100 parts by mass of the solid content of the aqueous resin dispersion (c1). This is because the effect of using the organic solvent (c2) is not sufficient if it is less than 20 parts by mass. The content of the organic solvent (c2) in the acrylic resin dispersion (C) is 15% by mass or less, preferably 12% by mass, from the viewpoint of preventing various disasters such as ignition and combustion of paint and measures for preventing environmental pollution. % Or less. If it exceeds 15% by mass, the drying property tends to decrease and the environmental load tends to increase. An organic solvent other than the organic solvent (c2) can be used in combination with the acrylic resin dispersion (C) depending on the purpose.

The aqueous resin dispersion (c1) can be used as a cross-linking paint in which a hydroxyl group is introduced and combined with a polyisocyanate-based cross-linking agent to improve weather resistance, water resistance, stain resistance and solvent resistance. preferable. As a method for introducing a hydroxyl group into the aqueous resin dispersion (c1), a method of copolymerizing a hydroxyl group-containing polymerizable monomer is preferable.

Examples of the polyisocyanate compound used for preparing the polyisocyanate-based cross-linked coating include aromatic diisocyanates such as tolylene diisocyanate and diphenylmethane diisocyanate; alicyclic diisocyanates such as hexamethylene diisocyanate and trimethylhexane diisocyanate; isophorone diisocyanates, Alicyclic isocyanates such as methylcyclohexane-2,4 (or 2,6) -diisocyanate, 4,4'-methylenebis (cyclohexyldiisocyanate), 1,3- (isocyanatemethyl) cyclohexane; the above diisocyanates and ethylene glycol, Polyether polyols (polyethylene glycol, polypropylene glycol, polycaprolactone polyols, etc.), polyhydric alcohols such as trimethylolethane or trimethylolpropane, low molecular weight polyester resins having functional groups that react with isocyanate groups, acrylic copolymers, these Additives of and water; bullet bodies and the like.

Specific examples thereof include Barnock D-750, D-800, DN-950, and DN-901S (all of which are manufactured by DIC Corporation). In addition, these compounds can be emulsified and dispersed before use. Further, water-soluble or water-dispersible polyisocyanate compounds such as BAYHYDUR LS-2980, LS-2032 (all manufactured by Bayer, Germany), Aquanate 100, 110, 200 or 210 (all of Japan). An aqueous polyisocyanate compound such as Polyurethane Industry Co., Ltd. can be used.

In the case of the polyisocyanate cross-linked system, the hydroxyl value of the solid content of the aqueous resin dispersion (c1) is 30 to 120, preferably 50 to 100, in consideration of various physical properties of the coating film.

The compounding ratio of the polyisocyanate compound (c-3) and the aqueous resin dispersion (c1) is 0.5 to 2 in an equivalent ratio of NCO groups / OH groups, preferably 0.8 to 1.3. Is.

Specific examples of the acrylic resin dispersion (C) as described above include Watersol ACD-1110 (manufactured by DIC Corporation).

Pigment (D)
The pigment (D) used in the present invention is mainly blended in a water-based paint in order to form a coating film having an excellent balance between strength and dryness. Examples of the pigment (D) 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 (D), it is preferable to use a rust preventive pigment such as zinc phosphate, calcium phosphate, aluminum phosphate and aluminum phosphate molybdenum. Of these, zinc phosphate and calcium phosphate, which are excellent in rust prevention performance, are preferably used. Specific examples of zinc phosphate include LF bousei P-W-2, LF bousei D-1, LF bousei D-2, LF bousei ZP-S1, LF bousei ZP-HS, and LF bousei 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 manufactured by Toho Pigment Industry Co., Ltd.). ), Protects YM-60, Protects YM-70 (all manufactured by Taihei Kagaku Sangyo Co., Ltd.) and the like.

The content of the rust preventive pigment in the pigment (D) is not particularly limited, but is preferably 2 to 40% by mass, more preferably 10 to 15% by mass. If it is less than 2% by mass, the rust preventive performance tends not to be improved, and if it exceeds 40% by mass, the storage stability is lowered, which is not suitable in consideration of economy.

For water-based 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-sagging agent); silica , A matting agent made of alumina, etc .; a dispersant made of polycarboxylic acid salt, etc .; an ultraviolet absorber made of benzophenone, etc., a hindered amine-based light stabilizer, an antioxidant such as phenol-based; a known additive such as wax is used. be able to. These can be used alone or in combination of two or more. These can be added to the solid content of the water-based paint in a blending ratio of less than 20% by mass, preferably less than 10% by mass.

[Painting of the outer peripheral surface of cast iron pipe]
In the present invention, the outer peripheral surface 1b of the cast iron pipe indicated by reference numeral F in FIG. 1 may be coated by a conventionally known method, or may be coated by the method described in JP-A-2011-209967. When painting is performed by a conventionally known method, it is preferable to perform painting before and after painting the inner surface 2a of the tube body p receiving port 2. When painting is performed by the method described in Japanese Patent Application Laid-Open No. 2011-209967, the outer peripheral surface 1b of the cast iron pipe and the inner surface 2a of the socket may be painted at the same time.

The cast iron pipe p having a coating film on the inner surface of the socket of the present invention has stable quality because it has excellent adhesion to the zinc rich primer or powder coating which is the undercoat. Further, since the coating film on the inner surface of the socket minimizes the use of a solvent-based primer, there is almost no solvent odor and the environmental load is small.

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

The components used in Examples and Comparative Examples are shown below.
(Zinc rich primer)
・ Kurimoto Coat WZ manufactured by Dai Nippon Toryo Co., Ltd. (water-based zinc rich primer, JIS K 5552 standard product, solid content 86%)
(Powder coating)
・ V-PET # 1600 Kurimoto Gray F (epoxy resin powder paint, JWWA G 112 standard product, powder) manufactured by Dainippon Paint Co., Ltd.
(Solvent primer)
-Solvent-based primer A: Kurimoto Coat NT # 100 New H manufactured by Dai Nippon Toryo Co., Ltd. (solvent-based two-component epoxy resin paint, JWWA K 139 standard product, solid content 49%)
-Solvent-based primer B: Kurimoto Coat AC-1 manufactured by Nippon Paint Industrial Coatings (solvent-based acrylic resin paint, JWWA K 139 standard product, solid content 60%)
(Water-based paint)
-Water-based paint manufactured in Production Example 1

Manufacturing example 1
As an aqueous dispersion, epoxy ester resin (A): Watersol EPD-5560 (manufactured by DIC Corporation) is used in an amount of 10 parts by mass, and acrylic emulsion (B): Boncoat EC-740EF (manufactured by DIC Corporation) is used. 10 parts by mass of solid content and acrylic dispersion (C): Watersol ACD-1110 (manufactured by DIC Corporation) is combined with 80 parts by mass of solid content as a resin component, and the resin component 45 with respect to the entire water-based paint. A water-based paint was produced by mixing 20% by mass of calcium phosphate, which is a rust preventive pigment, and 35% by mass of extender pigments (barium sulfate and talc). The pigment volume concentration PVC was 35%.

Examples 1 to 4 and Comparative Examples 1 and 2
As an undercoating process, a cast iron pipe (φ250 × 5000 mm) was spray-painted from the receiving end on the inner surface of the receiving port with the above-mentioned water-based zinc rich paint to form a zinc rich primer layer (first layer) having a film thickness of about 20 μm. In Table 1, the fact that the undercoat was heated indicates that the zinc-rich primer layer was heated to 150 ° C. or higher after the zinc-rich primer coating. Next, powder coating was performed with the epoxy resin powder coating material to form a powder resin coating film (second layer) of about 150 μm. The cast iron pipe was heated to 270 to 330 ° C. before coating with the epoxy powder resin. Then, a solvent-based primer was applied to a region having a width of about 40 mm including the boundary in the boundary region coated with the water-based zinc rich primer and the epoxy resin powder coating to form a third layer (20 μm). ). Then, the water-based paint was applied to the entire inner surface of the socket to form a water-based paint layer (fourth layer) having a film thickness of about 80 μm.

(Evaluation of coating film adhesion)
Regarding the adhesion of the coating films obtained in Examples and Comparative Examples, the receiving portion of the cast iron pipe cut out to a length of 300 mm was cut into four equal parts in the circumferential direction, and the central portion of the inner surface of the receiving port of the test piece ( Adhesion was evaluated in accordance with the JIS K 5600-5-6 cross-cut method in the portion including the D region in FIG. Specifically, 25 squares are made by making a 2 mm wide grid cut on the painted surface with a cutter, a peeling test is performed using cellophane tape, and the remaining grids are classified into the following categories. It was. In addition, each test was conducted twice.
<Classification of test results>
Category 0: The edges of the cut are perfectly smooth and there is no peeling in any grid.
Category 1: Small peeling of the coating at the intersection of cuts.
The cross-cut portion is clearly not affected by more than 5%.
Category 2: Cuts are peeled off along the edges of the cross and / or at intersections.
The cross-cut area is clearly affected by more than 5% but not more than 15%.
Category 3: The coating is partially or wholly peeling along the edges of the cut, and / or various parts of the eye are partially or wholly peeling.
The cross-cut portion is clearly affected by more than 15% but not more than 35%.
Category 4: The coating is partially or wholly peeled off along the edges of the cut, and / or several eyes are partially or wholly peeled off.
The cross-cut portion is clearly not affected by more than 35%.
Category 5: Any of the degree of peeling that cannot be classified even in Category 4

The results are shown in Table 1 by the following three-stage evaluation. In addition, ○ is the target performance.
◯: Classification 0 to 1
Δ: Classification 2
×: Classification 3 to 5

From Table 1, in the socket inner surface coating of the present invention, when a predetermined water-based paint is used as the top coat of the zinc rich primer layer and the epoxy resin powder coating layer as the outermost layer, the zinc rich primer and the epoxy resin powder coating are used. Examples 1 to 4 in which the water-based paint is applied to the region including the boundary with and (for example, region D in FIG. 1) via the solvent-based primer are compared with Comparative Examples 1 and 2 not mediated by the solvent-based primer. , It can be seen that the adhesion at higher temperatures is excellent.

1 Insertion port 2 Receptacle 3 Straight pipe part 4 Steps p Pipe body

Claims (3)

A cast iron pipe having a receiving port at one end and an insertion port at the other end across the straight pipe portion.
On the inner surface of the socket, in order from the tube side
A first layer formed by a zinc rich primer applied in a certain area from the receiving end to the straight pipe portion,
A second layer formed by a powder coating material applied so as to cover a part of the first layer from the straight pipe portion to a certain region on the inner surface of the socket.
As a solid content (A) applied to the third layer formed by the solvent-based primer applied to a certain region including the boundary between the first layer and the second layer, and the entire inner surface of the socket. ) Epoxy ester resin by 1 to 15 parts by mass, (B) acrylic resin emulsion by 5 to 30 parts by mass, and (C) acrylic resin dispersion by 55 to 94 parts by mass, (A), (B) and Cast iron comprising a coating film composed of a fourth layer formed of an aqueous paint containing a pigment having a total solid content of (C) of 100 parts by mass and (D) a pigment volume concentration of 35 to 45%. tube. The cast iron pipe according to claim 1, wherein the powder coating material is an epoxy resin powder coating material, and the solvent-based primer is a two-component epoxy resin coating material. (1) The inner surface of the receiving port of a cast iron pipe having a receiving port at one end and an insertion port at the other end across the straight pipe portion is coated with a zinc rich primer from the receiving end toward the straight pipe portion to form the first layer. The process of forming,
(2) A step of heating the cast iron pipe and applying a powder paint so as to cover a part of the first layer from the inner surface of the straight pipe portion of the cast iron pipe to form the second layer.
(3) A step of applying a solvent-based primer to a certain region including the boundary between the first layer and the second layer to form a third layer, and (4) then using residual heat, 1 to 15 parts by mass of (A) epoxy ester resin, 5 to 30 parts by mass of (B) acrylic resin emulsion, and (C) acrylic resin dispersion as solid content on the entire inner surface of the socket of the cast iron pipe. A water-based paint containing 55 to 94 parts by mass of a pigment, the total solid content of (A), (B) and (C) is 100 parts by mass, and (D) a pigment having a pigment volume concentration of 35 to 45%. A method of painting the inner surface of a socket of a cast iron pipe, which comprises a step of painting to form a fourth layer.

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