JP3386405B2 - Externally coated cast iron tube - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast iron pipe widely used for water and sewage pipes, gas pipes and the like, and more particularly, to an outer surface coated cast iron having improved corrosion resistance. About pipes. [0002] Cast iron pipes are widely used for water and sewage pipes, gas pipes and the like. Such a cast iron pipe is often used in a buried environment, and in recent years, particularly, the durability and the corrosion resistance of the outer surface of the pipe have been demanded. Therefore, a zinc-based primer is often used as the anticorrosion layer on the outer surface of the tube. Examples of the zinc-based primer include zinc-rich paint and zinc (Zn).
-Al pseudo alloys and Zn-Al alloys). In recent years, zinc-based primer layers formed by zinc spraying have been widely used because of their excellent anticorrosion performance. [0003] The zinc-based primer layer exhibits an excellent effect in preventing corrosion of cast iron pipes due to its sacrificial corrosion prevention effect, but is hard and brittle, so that it is easily broken during storage, transport, and construction of cast iron pipes. . If the zinc-based primer layer is left outdoors as it is, white rust is generated, and zinc is eluted under the influence of acid rain or acidic soil, thereby impairing the corrosion resistance. For the purpose of transport, protection from impact at the time of embedding, or improvement of appearance, maintenance of weather resistance and corrosion resistance, etc., an overcoat paint (for example, stipulated in Japan Water Works Association standard; JWWA K139) on a zinc-based primer layer. Is generally applied. [0004] However, the zinc-based primer layer and the top coat generally have poor interlayer adhesion. In addition, after the zinc-based primer layer is formed due to problems in the manufacturing process of the cast iron pipe and storage space, temporary placement outdoors is unavoidable until the top coat is applied, during which white rust occurs. However, there has been a problem that the adhesion to the top coat is further reduced, and the excellent corrosion protection inherent in the zinc-based primer layer is reduced. Therefore, there has been a problem that the corrosion resistance of the cast iron pipe is impaired. Accordingly, it is an object of the present invention to provide an outer surface coated cast iron pipe having excellent corrosion protection by extracting the excellent corrosion protection inherent to a zinc-based primer layer. Means for Solving the Problems The inventors of the present invention focused on the problems of the prior art and conducted intensive studies. As a result, a specific amount of a resin primer having a specific composition was coated on a zinc-based primer layer. By preventing the occurrence of white rust of the above-mentioned zinc-based primer layer, by further improving the adhesion with the topcoat paint, draw out the excellent anticorrosion inherent in the zinc-based primer layer, the outer surface coated cast iron pipe The present inventors have found that the anticorrosion property is significantly improved, and have completed the present invention. That is, the outer surface coated cast iron tube of the present invention comprises:
A zinc-based primer layer formed on the outer surface of the tube, and an average thickness 3 formed on the zinc-based primer layer by an acrylic resin primer
Possess a resin primer layer of ～50Myuemu, further a topcoat layer formed by top coat thereon, 80 wt% or more of the solid content of the acrylic resin primers, alkyl long chain having 8 to 18 carbon atoms 5 to 60% by weight of a (meth) acrylate monomer having a group, and 5 to 20% by weight of an α, β-monoethylenically unsaturated carboxylic acid monomer
When a feature that it is other copolymerizable monomers 20 to 90 wt% and an acrylic resin obtained by copolymerizing
Is what you do . Hereinafter, the present invention will be described specifically. The zinc-based primer layer, which is one of the essential components of the present invention, is a layer that maintains the corrosion resistance of the outer surface of the cast iron pipe for a long time, and specifically includes a zinc-rich paint and zinc (Z
(including an n-Al pseudo alloy and a Zn-Al alloy). In particular, zinc-based primer layers formed by zinc spraying have been widely used in recent years because of their excellent corrosion resistance. The method of forming these zinc-based primer layers is not particularly limited, and a known and commonly used method is used. Although the thickness of the zinc-based primer layer is not particularly limited, it may be, for example, Japan Ductile Iron Pipe Association Standard JPPA Z 201.
0 In accordance with “Ductile cast iron pipe synthetic resin coating”, 150 g / m ^{2 in} the case of a layer formed by zinc rich paint
As described above, in the case of a layer formed by zinc spraying, 130 g /
m ² or more is a criterion for maintaining good corrosion resistance. The resin primer layer, which is one of the essential constituents of the present invention, is formed to improve the corrosion resistance, especially white rust resistance, of the zinc-based primer layer and to improve the interlayer adhesion with the top coat. And a layer formed by applying an acrylic resin primer to the zinc-based primer layer. The coating thickness of the resin primer layer is 3 to 50
It is preferably in the range of μm. If the coating thickness is less than 3 μm, improvement in the corrosion resistance of the zinc-based primer layer cannot be expected. Conversely, if the coating thickness exceeds 50 μm, the adhesion between layers with the top coat is undesirably reduced. More preferably, it is in the range of 5 to 20 μm. [0010] The acrylic resin primer preferably has a higher polarity for the resin used in consideration of the adhesion to the zinc-based primer layer or the adhesion to the topcoat paint, while considering the anti-corrosion properties of the zinc-based primer layer. Then, it is preferable that the polarity of the resin is low. From this viewpoint, (meth) acrylate monomers having a long-chain alkyl group,
alpha, beta-monoethylenically unsaturated carboxylic acid monomer compound and a certain ratio, that uses <br/> acrylic resin obtained by combining. That is, 5 to 60% by weight of a (meth) acrylic acid ester monomer having a long-chain alkyl group having 8 to 18 carbon atoms and 5 to 20% of an α, β-monoethylenically unsaturated carboxylic acid monomer. % By weight and other copolymerizable monomers 2
0-90 to use an acrylic resin obtained by copolymerizing a weight percent. (Meth) having the above-mentioned long-chain alkyl group
When the amount of the acrylate monomer is less than 5% by weight of the total monomers, the resulting coating film has poor corrosion resistance and water resistance, and conversely, even if the amount exceeds 60% by weight, the corrosion resistance is improved. This effect is not only not only saturated, but also the adhesion to the zinc-based primer layer decreases. More preferably, it is used in the range of 15 to 45% by weight based on all monomers. Also,
When the amount of the α, β-monoethylenically unsaturated carboxylic acid monomer is less than 5% by weight of the total monomers, the adhesion of the resulting coating film to the zinc-based primer layer is reduced, and conversely, 20% by weight. If the amount exceeds the above range, the corrosion resistance and water resistance of the resulting coating film are undesirably reduced. More preferably, 7 out of all monomers
It is used in the range of １５15% by weight. Other copolymerizable monomers are used in an amount of 20 to 90% by weight based on all monomers for adjusting the Tg, polarity, dispersibility and the like of the resin. More preferably, it is in the range of 40 to 78% by weight of all monomers. Examples of (meth) acrylate monomers having a long-chain alkyl group include octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, and (meth) acrylate. ) Lauryl acrylate, cesyl (meth) acrylate, stearyl (meth) acrylate and the like. These are used as one kind or as a mixture of two or more kinds. Above all, it is preferable to use methacrylic esters as shown in JP-A-58-53961, and specifically,
Lauryl methacrylate, acrylic ester SL (a mixture of methacrylic esters having an alkyl group having 12 and 13 carbon atoms, manufactured by Mitsubishi Rayon Co., Ltd.)
It is particularly preferable to use a methacrylic acid ester having an alkyl group of from 14 to 14 from the viewpoint of improving corrosion resistance and corrosion resistance. The α, β-monoethylenically unsaturated carboxylic acid monomers include, for example, monobasic acid monomers such as acrylic acid, methacrylic acid and crotonic acid, itaconic acid, maleic acid, fumaric acid and the like. Dibasic acid monomers and their half esters. These are used as one kind or as a mixture of two or more kinds. Other copolymerizable monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, and (meth) acrylic acid. (Meth) acrylates such as benzyl; aromatic monomers such as styrene, vinyltoluene and α-methylstyrene; hydroxyl groups such as 2-hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate and (meth) acrylamide , A glycidyl group, a functional group monomer having an amide group in the molecule; a functional group monomer having a functional group such as an alkoxysilyl group, an amino group, an ethylene oxide group, a phosphoric acid group, a sulfonyl group in the molecule, and the like. . These are selected as necessary for adjusting the Tg, polarity, pigment dispersibility and the like of the resin, and are used as one kind or as a mixture of two or more kinds. As a method of polymerizing the acrylic resin, a known and commonly used technique such as solution polymerization, emulsion polymerization or suspension polymerization is used. The molecular weight of the acrylic resin is not particularly limited, but it is not limited to gel permeation chromatography (gel permeation chromatography). GP
The number average molecular weight in terms of polystyrene according to C) is 8000.
It is preferably in the range of ５０50,000. Molecular weight 80
If it is less than 00, the water resistance and weather resistance of the obtained coating film will be poor, and if it exceeds 50,000, the adhesion will be poor, which is not preferable. Although the glass transition temperature (Tg) of the acrylic resin is not particularly limited, it is theoretically calculated from 0 in consideration of the adhesion, blocking resistance, weather resistance, water resistance, corrosion resistance, and the like of the obtained coating film. Preferably it is in the range of 30 ° C. When the acrylic resin primer is made into a paint,
The form of the paint is preferably a solvent-soluble form or an aqueous form in consideration of simplicity of coating. Further, it is preferable that the above-mentioned acrylic resin is contained in an amount of 80% by weight or more in terms of solid content in the primer. If the resin content is less than 80% by weight in terms of solid content in the primer, it is not preferable because the resulting coating film has poor adhesion and corrosion resistance. Further, in the cast iron pipe coated on the outer surface of the present invention (hereinafter referred to as cast iron pipe), after coating with an acrylic resin primer, an epoxy-based powder or the like is applied to the inner surface of the pipe in order to impart corrosion resistance to the inner surface of the cast iron pipe. Body baking paint may be applied. At this time, the resin primer layer may be exposed to a high temperature atmosphere in a temperature range of 150 to 300 ° C. for about 20 minutes to 3 hours. From this viewpoint, considering the heat resistance of the acrylic resin primer, the number average molecular weight of the acrylic resin is 12
It is preferable that the aromatic vinyl monomer such as styrene is 3% of the total monomer.
It is preferably 0% by weight or less. If the ratio is outside this range, care must be taken because, after exposure in a high-temperature atmosphere, the adhesion between the resin primer layer and the overcoat decreases. When the inner surface of the cast iron pipe is coated with the powder baking paint, the cast iron pipe may be partially heated by direct heat or high-frequency heating before coating with the powder paint in order to prevent pinhole formation. . At this time, the resin primer layer may be exposed to a high-temperature atmosphere at a maximum of 550 ° C. for several minutes. In order to maintain good adhesion to the top coating even after the local heating, the number average molecular weight of the acrylic resin should be 2
Preferably it is 5000 or less. The acrylic resin primer is particularly preferably water-based, from the viewpoints of securing the working environment in the coating process and preventing a fire from ignition, and further from the viewpoint of preserving the global environment. In the case of an aqueous primer, the above-mentioned acrylic resin needs to be an aqueous resin. In this case, solution polymerization is carried out in a water-soluble organic solvent, and a part or all of the acid value of the acrylic resin is neutralized with a volatile basic substance such as ammonia or amines to make the resin aqueous. It is simple. At this time, it is not a matter of course that consideration should be given to the organic solvent content of the acrylic resin primer and the odor, toxicity, flammability and the like of the volatile substance. The acrylic resin primer may contain pigments, rust inhibitors, defoamers, leveling agents, viscosity modifiers, pigment dispersants, organic solvents, ultraviolet absorbers, antioxidants, crosslinking agents, if necessary. Known and commonly used paint additives can be used as necessary. The overcoat layer, which is another component of the present invention, is an essential component for protecting the zinc-based primer layer and improving the appearance. The type of the overcoat layer is not particularly limited as long as it is suitable for the purpose. However, in order to exhibit a certain protective effect, for example, it is preferable that the layer is a layer having a specified thickness, which is coated with a synthetic resin paint specified in Japan Water Works Association Standard JWWA K139. As the synthetic resin paint, it is preferable to use an acrylic resin paint from the viewpoint of achieving both weather resistance and corrosion resistance. It is particularly preferable that the top coat is also water-soluble from the viewpoint of securing the working environment in the painting process and preventing a fire from burning, and from the viewpoint of preserving the global environment. Although there is no particular limitation on the coating time, production efficiency is to be applied after all processes such as cast iron pipe molding, zinc-based primer layer formation, acrylic resin primer coating, and if necessary, formation of pipe inner surface protection layer Above. Further, there is no particular limitation on the film thickness to be formed, the method for drying the coating, and the like. The present invention will be described below in further detail with reference to examples. Here, “parts” and “%” are based on weight unless otherwise specified. (Synthesis Example 1) Synthesis of acrylic resin for resin primer 900 parts by weight of xylene (hereinafter referred to by weight unless otherwise specified) in a flask equipped with a reflux condenser, a stirrer, a thermometer, and a nitrogen inlet tube. ) And heated to 80 ° C. While maintaining the temperature of the reactor at 80 ° C.,
50 parts, n-butyl acrylate 250 parts, n-butyl methacrylate 250 parts, lauryl methacrylate 100 parts,
A monomer mixture consisting of 180 parts of methyl methacrylate and 70 parts of methacrylic acid and an initiator mixture obtained by dissolving 15 parts of t-butylperoxy-2-ethylhexanoate in 100 parts of ethylene glycol monobutyl ether were used for 4 hours. And dropped. Thereafter, the temperature was maintained at the same temperature for 4 hours to complete the reaction, and the resultant was cooled to room temperature. The obtained solvent-soluble resin had a solid content of 50%, an acid value of the solid content of 45, and a number average molecular weight of 2,100 as determined by gel permeation chromatography.
0, theoretical Tg 8 ° C. This is hereinafter abbreviated as S-1. (Synthesis Example 2) Synthesis of Acrylic Resin for Resin Primer Using the same reactor as in Synthesis Example 1, 600 parts of isopropyl alcohol was charged and heated to 80 ° C. While maintaining the temperature of the reactor at 80 ° C.,
00 parts, 150 parts of n-butyl acrylate, 300 parts of lauryl methacrylate, 250 parts of methyl methacrylate, 100 parts of methacrylic acid, and 20 parts of t-butyl peroxy-2-ethylhexanoate An initiator mixture dissolved in 100 parts of isopropyl alcohol was added dropwise over 4 hours. Then, triethylamine 11
0 parts and 1500 parts of water were added and stirred. The obtained aqueous resin had a solid content of 30%, an acid value of the solid content of 64, and a number average molecular weight of 200.
00, theoretical Tg 7 ° C. This is hereinafter abbreviated as W-2. (Synthesis Examples 3, 4, and 5) Synthesis of Acrylic Resin for Resin Primer According to Synthesis Examples 1 and 2, the polymerization initiator was used in an amount of 10 to 50 parts.
The reaction temperature was changed to 80 to 125 ° C., and aqueous resins W-3 and W-4 ′ and a solvent-soluble resin S-5 ′ were synthesized with the monomer compositions shown in Table 1. The results are summarized in Table 1. [Table 1] (Footnote of Table 1) 2EHA: 2-ethylhexyl acrylate LMA: lauryl methacrylate SMA: stearyl methacrylate MAA: methacrylic acid AA: acrylic acid St: styrene BA: n-butyl acrylate BMA: n-methacrylic acid Butyl MMA: methyl methacrylate (other resins for resin primer) WATERSOL CD-540: water-based epoxy ester resin manufactured by Dainippon Ink and Chemicals, Inc. (solid content 40)
%) WATERSOL CD-520: Aqueous alkyd resin manufactured by Dainippon Ink and Chemicals, Inc. (solid content 39%) VONCOAT 2315: Vinyl acetate emulsion manufactured by Dainippon Ink and Chemicals, Inc. (solid content 50%) [ (Preparation of resin primer) In the case of aqueous resin (W-2, W-3, W-4 ', CD-
540, CD-520, 2315): DISPERSE BLACK HG-90 was added to the resin (50 parts in terms of solid content).
1 (1 part of a carbon black aqueous dispersion pigment manufactured by Dainippon Ink and Chemicals, Inc.) and 0.05 part of NOPCO8034L (an antifoaming agent manufactured by San Nopco) were added, and after stirring, water was added to adjust the solid content to 15%. . -In the case of a solvent-based resin (S-1, S-5 ') 0.25 parts of MA-100 (carbon black manufactured by Mitsubishi Chemical Corporation) is added to the resin (10 parts in terms of solid content), and dispersed by a sand mill for 20 minutes. Further, a resin (solid content: 40 parts) and xylene were added and stirred to adjust the solid content to 15%. (Test Method and Evaluation Criteria) (1) White Rust Resistance: Accelerated Test by Sunshine Weatherometer • A 150 × 70 × 7 mm cast iron pipe piece (base material) was sprayed with zinc at 130 g / m ² . Is preheated to about 60 ° C., and the various resin primers prepared above are dried to a dry film thickness of 5
Spray coating was performed so that the thickness became 10 μm. After standing to cool and dried in a room temperature atmosphere for 3 days, the test piece was subjected to the following test. In addition, the thing which did not paint a resin primer at all was used for the test as a comparison.・ The above specimen was set on a sunshine weatherometer and tested under the condition of continuous rainfall for 24 hours.
After drying at room temperature for hours, paste the cellophane tape on the specimen,
The amount of white rust adhering to the cellophane tape upon instantaneous peeling was evaluated according to the following criteria. ◎: White rust adhering to cellophane tape is not observed at all. ○: Exclusive area of white rust adhering to cellophane tape is less than 10% of the total. Δ: Exclusive area of white rust adhering to cellophane tape is the entire area. 10% or more and less than 30% x: The area occupied by white rust adhering to the cellophane tape is 30% or more of the whole. (2) Adhesion: Adhesion to the top coat paint under normal conditions and adhesion to the top coat after high-temperature heating Properties: Three test pieces were prepared, each of which was coated and dried with various resin primers, and was not coated with a resin primer, on cast iron tube test pieces sprayed with zinc in the same manner as in (1) above. One of the three specimens was left at room temperature as it was, and the other specimen was further heated at about 250 ° C. for 3 hours assuming heating for powder baking coating on the inner surface of the tube. Still another specimen was heated at about 550 ° C. for 1 minute, assuming a heat treatment for preventing the generation of pinholes in the powder baking coating on the inner surface of the tube. A water-based acrylic black paint “Kurimoto Coat W
R "(Dai Nippon Paint Co., Ltd., Japan Water Works Association Standard; JW
(Synthetic resin paint specified in WAK139) was spray-coated so that the dry film thickness became 80 to 90 μm.
As for the coating conditions, the specimen left at room temperature was reheated to 60 ° C to apply the topcoat paint. The other specimen reheated to 250 ° C or 550 ° C was heated and then allowed to cool to 60 ° C at room temperature. , Painted. -Each specimen was allowed to cool to room temperature and then dried at room temperature for 7 days. After that, 2 × 2m to reach the substrate with cutter knife
When 25 pieces of squares with m were made and a cellophane tape was stuck and immediately peeled off, the number of squares with an overcoat layer remaining on the sample was counted, and the adhesion was evaluated by the number of remaining / 25. ：: 20/25 to 25/25 Δ: 10/25 to 19/25 ×: 0/25 to 9/25 (3) Water resistance: A zinc-sprayed cast iron tube specimen similar to (1) above Then, under the same conditions as those of the specimen left at room temperature in the above (2), each resin primer and an overcoat were applied. Thereafter, a commercially available epoxy / polyamide two-liquid curable resin primer was applied to the side and back surfaces of the test piece and masked.・ Immerse the specimen dried at room temperature for 7 days in tap water for 7 days,
The occurrence of wrinkles, blisters, cracks, and peeling of the coating film was visually determined. ◎: Wrinkles, swelling, cracking, and peeling of the coating film are completely absent. ：: Wrinkles, swelling, cracking, and peeling area of the coating film are less than 5% of the total coating film. △: Wrinkling, swelling, and cracking of the coating film. X: A state in which the area of peeling is 5% or more and less than 10% in the whole coating film. X: A state in which the area of wrinkling, swelling, cracking, and peeling of the coating film is 10% or more in all the coating films. The specimen prepared in the same manner as in (3) above was immersed in 3% saline for 3 days, and the appearance change was visually determined in the same manner as in (3). Example 1 Solvent-based acrylic resin S-
1 was used to prepare a resin primer, and a test piece of cast iron pipe using the resin primer was evaluated for the above-mentioned white rust resistance, adhesion, water resistance, and salt water resistance. The results are shown in Tables 2 and 3. Examples 2 to 5 and Comparative Examples 1 to 3 The same procedures as in Example 1 were carried out except that the resins for primers were changed to those shown in Tables 2 and 3. The results are shown in Tables 2 and 3. Comparative Example 4 The same procedure as in Example 1 was carried out except that no resin primer layer was provided. The results are shown in Tables 2 and 3. [Table 2] [Table 3] As is clear from the results shown in Tables 2 and 3, the cast iron pipe having a resin primer layer made of an acrylic resin has a good adhesion of the overcoat layer and shows excellent corrosion protection. As described above, the outer surface coated cast iron tube of the present invention has a zinc-based primer layer formed on the outer surface of the tube and an average of the zinc-based primer layer formed thereon and the acrylic resin primer formed thereon. It has a resin primer layer having a thickness of 3 to 50 μm and an overcoat layer further formed thereon by an overcoat paint.
And 80% by weight of the solid content of the acrylic resin primer
% Or more has a long-chain alkyl group having 8 to 18 carbon atoms
(Meth) acrylate monomers 5 to 60% by weight
And α, β-monoethylenically unsaturated carboxylic acid monomers
5 to 20% by weight and other copolymerizable monomers 20 to
Acrylic resin obtained by copolymerizing 90% by weight , prevents the formation of white rust in the zinc-based primer layer, adherence between the resin primer layer and the zinc-based primer layer, and By improving the adhesion between the primer layer and the overcoat layer, the excellent anticorrosion properties inherent to the zinc-based primer layer can be brought out. This significantly improves the corrosion resistance of the cast iron tube.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C09D 5/00 C09D 5/00 D 5/08 5/08 133/06 133/06 133/06 C23C 4/08 C23C 4/08 F16L 58 / 10 F16L 58/10 (72) Inventor Masahiko Saito 1-12-19 Kitahorie, Nishi-ku, Osaka City, Osaka Prefecture Inside Kurimoto Iron Works Co., Ltd. No. Kurimoto Iron Works Co., Ltd. (72) Inventor Yoshisada Michiura 1-12-19 Kitahorie, Nishi-ku, Osaka City, Osaka Prefecture Kurimoto Iron Works Co., Ltd. (56) References JP-A-11-280986 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) C23F 15/00 B32B 1/08 B32B 15/08 102 B32B 27/00 B32B 27/30 C09D 5/00 C09D 5/08 C09D 133/06 C23C 4/08 F16L 58/10

Claims (1)

(57) [Claims 1] A zinc-based primer layer formed on the outer surface of a cast iron pipe, and a resin primer layer having an average thickness of 3 to 50 µm formed thereon by an acrylic-based resin primer;
Further possess an overcoat layer formed by top coat thereon, 80 wt% or more of the solid content of the acrylic resin primer
The upper side has a long-chain alkyl group having 8 to 18 carbon atoms (meaning
(T) acrylic acid ester monomers of 5 to 60% by weight;
α, β-monoethylenically unsaturated carboxylic acid monomers 5
20% by weight and other copolymerizable monomers 20 to 90
And an acrylic resin obtained by copolymerizing the outer surface of the cast iron tube with an external coating.