Iron-based metal pipe with corrosion-resistant layer

Abstract

To provide an iron-based metal pipe that includes a corrosion-resistant layer having improved corrosion resistance.SOLUTION: An iron-based metal pipe has a corrosion-resistant layer that is a coating containing zinc, aluminum and inorganic spreader applied to its outer surface. In the corrosion-resistant layer, a zinc content is 85-90 mass% and an aluminum content is 0.25-2.0 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an iron-based metal pipe having a corrosion-resistant layer on its outer surface, particularly a cast iron pipe excellent in corrosion resistance having a coating film made of a predetermined zinc-rich paint.

Background Art

[0002] Conventionally, iron-based metal pipes such as cast iron pipes and steel pipes have been used for water and sewage pipes, etc. For example, on the outer surface of such an iron-based metal pipe, in order to prevent corrosion of the water pipe buried in the ground, an undercoat is applied with a zinc-based primer such as zinc spraying or zinc-rich paint, and as the topcoat paint on this zinc-based primer layer, for example, a synthetic resin paint that meets the standards of the Japan Water Works Association Standard JWWA K 139 "Synthetic Resin Paint for Ductile Cast Iron Pipes for Water Works" is applied to form a coating film layer.

[0003] Here, zinc-rich paint has the merit that it can be easily applied even to a part with a complicated shape by a brush or the like compared to zinc spraying. The anticorrosion effect of iron-based metal by zinc-rich paint is the sacrificial anode action due to the generation of white rust of zinc, but in the case of zinc alone, the elution of zinc due to the sacrificial anode action is large, and it is difficult to achieve a long service life.

[0004] In Patent Document 1, in a paint containing metal powder, in a paint containing metal powder and a spreading agent in a mass ratio of 6:4 to 8:2, by containing 5 to 50% by mass of aluminum in addition to zinc in the metal powder, the anticorrosion performance is improved, and it is described that when the content of aluminum in the metal composition is less than 3% by mass, it becomes difficult to obtain a substantial improvement effect of anticorrosion performance by adding aluminum to zinc.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] However, in zinc-rich paints with a higher zinc content, the addition of aluminum can inhibit the sacrificial anodic action of zinc due to the formation of a passive film of aluminum, leaving room for further improvement in corrosion resistance.

[0007] Therefore, the object of the present invention is to provide an iron-based metal pipe having a corrosion-resistant layer with improved corrosion resistance. [Means for solving the problem]

[0008] As a result of their research to solve the above problems, the inventors of the present invention have found that in zinc-rich paint using an inorganic spreading agent for the corrosion-resistant layer of iron-based metal pipes, the corrosion resistance can be further improved by including zinc and aluminum such that the zinc content in the resulting corrosion-resistant layer is 85 to 90% by mass and the aluminum content is a predetermined amount, thereby completing the present invention.

[0009] In other words, the present invention is [1] An iron-based metal pipe having a corrosion-resistant layer on its outer surface obtained by applying a paint containing zinc, aluminum, and an inorganic spreading agent, An iron-based metal tube having a zinc content of 85-90% by mass, preferably 87-90% by mass, and an aluminum content of 0.25-2.0% by mass, preferably 0.5-2.0% by mass, more preferably 0.5-1.5% by mass, even more preferably 0.75-1.5% by mass, and particularly preferably 0.75-1.25% by mass. [2] The iron-based metal pipe described in [1] above, wherein the inorganic spreading agent is an alkyl silicate resin. [3] The iron-based metal pipe described in [1] or [2] above, wherein a coating layer of synthetic resin paint is formed on the outer surface of the corrosion-resistant layer, and [4] Cast iron pipes, which are iron-based metal pipes as described in any of [1] to [3] above. Regarding. [Effects of the Invention]

[0010] According to the present invention, in an iron-based metal pipe having a corrosion-resistant layer on its outer surface obtained by applying a paint containing zinc, aluminum, and an inorganic spreading agent, an iron-based metal pipe with improved corrosion resistance can be obtained by setting the zinc content in the corrosion-resistant layer to 85 to 90% by mass and the aluminum content to 0.25 to 2.0% by mass. [Modes for carrying out the invention]

[0011] The present invention relates to an iron-based metal pipe having a corrosion-resistant layer on its outer surface obtained by applying a paint containing zinc, aluminum, and an inorganic spreading agent, wherein the zinc content in the corrosion-resistant layer is 85-90% by mass and the aluminum content is 0.25-2.0% by mass. The method of adding aluminum to zinc-rich paint utilizes the formation of a passive film of aluminum to impart corrosion resistance by aluminum, while suppressing the excessive sacrificial anodic action of zinc, thereby achieving a longer lifespan of the corrosion resistance of the zinc-rich paint. However, when zinc is included at a high content of 85-90% by mass, a high amount of added aluminum can conversely promote the occurrence of red rust. This is thought to be due to the inhibition of the sacrificial anodic action of zinc by the effect of the passive film formation of aluminum, and there is also concern about the occurrence of blistering caused by aluminum. It is believed that by setting the aluminum content to 0.25-2.0% by mass, corrosion resistance can be further improved without causing such adverse effects.

[0012] <Corrosion-resistant layer> The corrosion-resistant layer applied to the outer surface of an iron-based metal pipe according to the present invention is obtained by applying a paint (zinc-rich paint) containing zinc, aluminum, and an inorganic spreading agent, and preferably consists substantially of zinc, aluminum, and an inorganic spreading agent. Furthermore, when the content of zinc and aluminum is described herein, the values ​​refer to the content in the corrosion-resistant layer (dried coating).

[0013] (zinc) The zinc used in the corrosion-resistant layer can be included as zinc powder, and the same type of zinc powder used in ordinary zinc-rich paints can be used. For example, metallic zinc in powder or flake form can be used. Alternatively, commercially available zinc-rich paints that already contain zinc and use an inorganic spreading agent can be used. In that case, zinc and aluminum should be further added to satisfy the zinc and aluminum content requirements of the present invention.

[0014] The zinc content in the corrosion-resistant layer is 85% by mass or more, preferably 87% by mass or more. If the zinc content is less than 85% by mass, the sacrificial anode effect of zinc will be weakened, which may promote the formation of red rust and reduce durability. Furthermore, the zinc content in the corrosion-resistant layer of the present invention is 90% by mass or less. If the zinc content exceeds 90% by mass, it may not be possible to include the necessary amount of spreading agent, which may lead to a decrease in paint workability and paint film adhesion.

[0015] (aluminum) Aluminum can be used in powder or paste form, but aluminum paste contains resin to make it paste-like. This resin may inhibit the continuity of Zn and Al powders after addition, potentially promoting the formation of red rust. Therefore, it is preferable to use aluminum in powder form.

[0016] The aluminum content in the corrosion-resistant layer is 0.25% by mass or more, preferably 0.5% by mass or more, and more preferably 0.75% by mass or more. If the aluminum content is less than 0.25% by mass, there is a risk that the elution of zinc cannot be sufficiently suppressed. Also, the aluminum content in the corrosion-resistant layer of the present invention is 2.0% by mass or less, preferably 1.5% by mass or less, and more preferably 1.25% by mass or less. If the aluminum content exceeds 2.0% by mass, the sacrificial anode action of zinc may be inhibited due to the influence of the formation of the passive film of aluminum, and there is a risk of promoting the occurrence of red rust or the occurrence of swelling due to aluminum. The preferable range of the aluminum content in the corrosion-resistant layer varies depending on various factors within the range of 0.25 to 2.0% by mass. For example, it is 0.5 to 2.0% by mass, 0.5 to 1.5% by mass, 0.25 to 1.25% by mass, 0.75 to 2.0% by mass, 0.75 to 1.5% by mass, 0.75 to 1.25% by mass, etc.

[0017] (Metal powder) The shape of the metal powder of zinc or aluminum is preferably spherical or flaky. When the powder is spherical, the average particle diameter is preferably about 10 μm to 20 μm. Also, when it is flaky, the average length is preferably about 40 μm and the thickness is preferably about 10 μm.

[0018] (Inorganic spreading agent) The inorganic spreading agent is not particularly limited, but it is preferable to use an alkyl silicate resin.

[0019] As a method of applying the zinc-rich paint for forming the corrosion-resistant layer, airless spray coating, air spray coating, using a roller or a brush, etc. can be used.

[0020] The film thickness of the corrosion-resistant layer can be appropriately set according to the type and use of the cast iron pipe. In the case of cast iron for water pipes, it is preferably approximately 75 to 250 μm, and more preferably 150 to 250 μm.

[0021] <Iron-based metal pipe> The iron-based metal pipes of the present invention include metal pipes such as cast iron pipes, steel pipes, and copper pipes. The iron-based metal pipes may be subjected to a base treatment such as epoxy-based, latex-based, or zinc spraying on their surfaces. The uses of the iron-based metal pipes of the present invention are not particularly limited, such as for water supply and drainage, water storage, etc. However, considering the high corrosion resistance of the corrosion-resistant layer of the present invention, it is particularly preferable that they are cast iron pipes for water supply and drainage, etc. Specifically, cast iron pipes are widely used in water supply and drainage pipes, etc., and are often used in various buried environments. In particular, improvement in the durability and corrosion resistance of the outer surface of the pipe is required.

[0022] <Synthetic resin paint coating layer> A coating layer made of synthetic resin paint can be provided on the surface of the above-mentioned corrosion-resistant layer of the iron-based metal pipe of the present invention. The synthetic resin paint coating layer may be a single layer or may be two layers of a primer layer and a topcoat layer. By providing the synthetic resin paint coating layer, the anticorrosion property of the corrosion-resistant layer can be improved and the durability can be enhanced. In addition, the synthetic resin paint coating layer can impart an aesthetic appearance to the iron-based metal pipe, particularly a cast iron pipe.

[0023] The synthetic resin paint is not particularly limited, and examples include acrylic resin paints and epoxy resin paints that are usually used for coating the outer surfaces of metal pipes. For cast iron pipes for water supply, synthetic resin paints specified in JWWA K 139 "Synthetic Resin Paint for Ductile Cast Iron Pipes for Water Supply" of the Japan Water Works Association Standards can be used.

[0024] Specifically, as the acrylic resin paint, for example, Klimot Coat WR manufactured by Dainippon Paint Co., Ltd., Klimot Coat AC-1-SR manufactured by Nippon Paint Industrial Coatings Co., Ltd., Klimot Coat AC-1 manufactured by Nippon Paint Industrial Coatings Co., Ltd., etc. can be used.

[0025] Also, as the epoxy resin paint, for example, Klimot Coat NT#100 New H manufactured by Dainippon Paint Co., Ltd., Klimot Coat NT#100 New manufactured by Kansai Paint Co., Ltd., etc. can be used.

[0026] Methods for applying synthetic resin paint include airless spray painting, air spray painting, rollers, and brushes.

[0027] The thickness of the synthetic resin coating layer obtained by applying the synthetic resin coating can be appropriately set depending on the type and application of the iron-based metal pipe, but for cast iron pipes used for water supply, a thickness of approximately 80 to 100 μm is preferable. [Examples]

[0028] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0029] The details of the components used in the examples and comparative examples are shown below. <Zinc-rich paint> • Inorganic zinc-rich paint (Zettall OL-HB (manufactured by Dainippon Paint Co., Ltd.), spreading agent (alkyl silicate resin): zinc = 25:75) • Zinc powder: Pure zinc powder manufactured by Sakai Chemical Industry Co., Ltd. (average particle size: 10 μm) • Aluminum powder: Aluminum powder manufactured by Toyo Aluminum Co., Ltd. (average particle size: 10 μm) <Synthetic resin paint> • Synthetic resin paint A: Ductite #100S Gray manufactured by Dainippon Paint Co., Ltd. (solvent-based acrylic resin paint, JWWA K 139 standard product) • Synthetic resin paint B: Kurimoto Coat NT #100 New H Gray (solvent-based two-component epoxy resin paint, JWWA K 139 standard product) manufactured by Dainippon Paint Co., Ltd. • Synthetic resin paint C: Kurimoto Coat AC-1 Gray (solvent-based acrylic resin paint, JWWA K 139 standard product) manufactured by Nippon Paint Industrial Coatings.

[0030] Examples 1-10 and Comparative Examples 1-5 A zinc-rich paint was prepared by adding zinc powder and aluminum powder as needed to inorganic zinc-rich paint (Zettall OL-HB) to achieve the composition shown in Table 1 or 2. The prepared zinc-rich paint was applied by brush to sandblasted ductile cast iron pieces (150 × 70 × 6.0~7.5 mm) to a film thickness of 250 μm. A synthetic resin paint was then applied as a topcoat by air spray painting according to Table 1. Note that the remainder of the dried corrosion-resistant layer, excluding zinc and aluminum, consists entirely of inorganic spreading agents and other components derived from Zettall OL-HB.

[0031] Test example: Combined cycle test In the specimens obtained in Examples 1-10 and Comparative Examples 1-5, an X-shaped cut measuring 0.3 mm wide and 50 mm long was made in the center of the specimen, extending to the base metal, along the diagonal of the specimen. A combined cycle test (JIS K 5600-7-9 (2006), Annex C, Cycle A: one cycle consists of a salt spray test (35±1℃, 2 hours), drying (60℃±1℃, 4 hours), and immersion (50±1℃, 2 hours)) was performed for 42 cycles (2 weeks), 90 cycles (1 month), 180 cycles (2 months), and 360 cycles (4 months). The number of test cycles at which red rust occurred was compared to evaluate corrosion resistance. The results are shown in Table 1 or 2. However, the 10 mm area at the edge of the specimen was excluded from the evaluation range for red rust. The performance target is ○△ or higher.

[0032] (Judgment criteria) ◎: No red rust or blistering after 360 cycles. ○: No red rust or blistering after 180 cycles. ○△: After 180 cycles, there is slight red rust on the cut area, but no blistering. △: After 180 cycles, there is some red rust in part of the cut area and slight blistering. ×: After 180 cycles, there is red rust and blistering throughout the cut area.

[0033] [Table 1]

[0034] [Table 2]

[0035] Tables 1 and 2 show that in Examples 1 to 10, where the aluminum content in the corrosion-resistant layer is in the range of 0.25 to 2.0 mass%, the corrosion resistance is improved compared to Comparative Example 1, which contains no aluminum, and Comparative Examples 2 to 5, where the aluminum content is 0.1, 2.25, 2.5, and 3.0 mass%, respectively. Furthermore, Examples 2 to 10, with an aluminum content in the range of 0.5 to 2.0 mass%, showed better corrosion resistance, while Examples 3 to 7, with an aluminum content in the range of 0.25 to 1.25 mass%, showed the greatest improvement in corrosion resistance.

Claims

1. An iron-based metal pipe having a corrosion-resistant layer on its outer surface obtained by applying a paint containing zinc, aluminum, and an inorganic spreading agent, The zinc content in the corrosion-resistant layer is 85 to 90% by mass, and the aluminum content is 0.25 to 1.25% by mass. An iron-based metal pipe having a corrosion-resistant layer consisting of zinc, aluminum, and an inorganic spreading agent.

2. The iron-based metal tube according to claim 1, wherein the inorganic spreading agent is an alkyl silicate resin.

3. The iron-based metal pipe according to claim 1 or 2, wherein a coating layer of synthetic resin paint is formed on the outer surface of the corrosion-resistant layer.

4. An iron-based metal pipe according to any one of claims 1 to 3, which is a cast iron pipe.

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