Cast iron pipe

Abstract

To provide a cast iron pipe in which a surface appearance of a coating layer of an epoxy resin powder coating formed on the inner surface of a pipe is improved without impairing corrosion resistance or chemical resistance.SOLUTION: A cast iron pipe has, on the inner surface of a pipe, a coating layer using an epoxy resin powder coating containing silica and barium sulfate as a pigment. Preferably, the pigment contains only barium sulfate, silica, titanium oxide and carbon black, and the epoxy resin powder coating is a bisphenol F type epoxy resin powder coating.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a cast iron pipe having a coating layer made of an epoxy resin powder coating on its inner surface.

Background Art

[0002] Many cast iron pipes widely used for water pipes and the like are composed of a cylindrical straight portion with a constant inner and outer diameter, a socket provided at one end with an inner and outer diameter larger than that of the straight portion, and an insertion port provided at the other end with an inner diameter equal to that of the straight portion.

[0003] In such cast iron pipes, generally, a coating layer made of a powder coating, for example, an epoxy resin powder coating, is formed on the inner surface of the pipe from the viewpoints of both corrosion resistance and environmental consideration. Specifically, as defined in the Japan Water Works Association Standard JWWA G 112 "Internal Epoxy Resin Powder Coating for Ductile Cast Iron Pipes for Waterworks", one of the methods for forming the coating layer made of this epoxy resin powder coating is to apply the epoxy resin powder coating by spraying or the like onto the inner surface of the heated and rotating pipe straight portion and melt and cure it.

[0004] The epoxy resin powder coating used for the inner surface coating of such cast iron pipes is generally composed of an epoxy resin, a curing agent, a pigment, an additive, etc., and suitable materials and formulations have been studied for each. Regarding the epoxy resin, instead of using bisphenol A type epoxy resin, bisphenol F type epoxy resin is used from the viewpoints of heat resistance and environmental consideration, and an example of using silica as an extender pigment is known (Patent Document 1). Patent Document 2 discloses that in the inner surface coating of a cast iron pipe using bisphenol F type epoxy resin, in order to improve the appearance (smoothness, pinholeness) of the coating layer on the inner surface of the cast iron pipe by the epoxy resin powder coating, shirasu balloon is used as a pigment.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] As described in the comparative example of Patent Document 2, when silica is used as an extender pigment, there is room for improvement in terms of leveling and blowability as aspects of the appearance evaluation of the coated layer.

[0007] Therefore, the object of the present invention is to provide a cast iron pipe in which the surface appearance of the epoxy resin powder coating layer formed on the inner surface of the pipe is improved without impairing corrosion resistance or chemical resistance. [Means for solving the problem]

[0008] To solve the above problems, the inventors of the present invention conducted diligent research and, as a result, completed the present invention, which provides good corrosion resistance and chemical resistance, and improves the surface appearance of the epoxy resin powder coating layer, by forming a coating layer from an epoxy resin powder coating containing silica and barium sulfate as pigments.

[0009] In other words, the present invention is [1] A cast iron pipe having a coating layer on its inner surface made of epoxy resin powder coating containing silica and barium sulfate as pigments, and [2] The cast iron pipe according to [1] above, wherein the pigment consists only of barium sulfate, silica, titanium dioxide, and carbon black, and the epoxy resin powder coating is a bisphenol F type epoxy resin powder coating. Regarding. [Effects of the Invention]

[0010] According to the present invention, in a cast iron pipe having a coating layer of epoxy resin powder coating on the inner surface of the pipe, by incorporating silica and barium sulfate as pigments in combination in the epoxy resin powder coating, it is possible to provide a cast iron pipe in which the surface appearance of the coating layer is improved without impairing corrosion resistance or chemical resistance. [Modes for carrying out the invention]

[0011] The cast iron pipe of the present invention has a coating layer on its inner surface made of epoxy resin powder coating containing silica and barium sulfate as pigments, and the coating layer has an improved surface appearance. Furthermore, this epoxy resin powder coating layer has good corrosion resistance and chemical resistance on the inner surface of the pipe. This effect is thought to be due to the uneven distribution of silica and barium sulfate, which has a higher specific gravity than silica, within the coating layer during the formation process of the coating layer by powder coating (rotation of the cast iron pipe).

[0012] <Cast iron pipes> In the present invention, the cast iron pipe on which the epoxy resin powder coating layer is formed is not particularly limited in shape, but examples include a cylindrical straight section with a constant inner and outer diameter in the axial direction of the cast iron pipe. For example, a pipe can be used that consists of the straight section, a socket with a larger inner and outer diameter than the straight section provided at one end, and a spout with an inner diameter equal to the straight section provided at the other end. The epoxy resin powder coating layer described later is formed on at least the straight section of this cast iron pipe. The use of the cast iron pipe of the present invention is not particularly limited, but since the inner surface is coated with epoxy resin powder coating that conforms to the standards of water pipes, it can be used for water supply and sewage systems, water storage, etc.

[0013] <Coating layer using epoxy resin powder coating> (Epoxy resin powder coating) The epoxy resin powder coating used in the present invention mainly consists of epoxy resin, a curing agent, and a pigment, and contains silica and barium sulfate as pigments. Aside from these, it is not particularly limited as long as it is commonly used in the art, and various additives such as dispersants and surface modifiers can be added as needed. Specifically, epoxy resin powder coatings specified in the Japan Water Works Association standard JWWA G 112 "Epoxy Resin Powder Coating for the Inner Surface of Ductile Cast Iron Pipes for Water Supply" can be suitably used.

[0014] Examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin, naphthalene-type epoxy resin, biphenyl-type epoxy resin, novolac-type epoxy resin, cyclic aliphatic epoxy resin, glycidylamine-type resin, heterocyclic epoxy resin, and polyfunctional epoxy resin.

[0015] The silica used is not particularly limited; commercially available silica can be used.

[0016] The barium sulfate used is not particularly limited and can be any commercially available product. Precipitating barium sulfate can be preferably used to improve the flatness of the appearance.

[0017] In the present invention, the relative relationship between the average particle diameter of silica and the average particle diameter of barium sulfate is such that it is preferable for the average particle diameter of silica to be larger than that of barium sulfate.

[0018] In addition to silica and barium sulfate, coloring pigments such as titanium dioxide, carbon black, iron oxide, yellow iron oxide, cyanine blue, and cyanine green, as well as extender pigments such as talc and calcium carbonate, can also be used as pigments. It is preferable that the pigments used as extenders consist only of silica and barium sulfate, and it is even more preferable to add titanium dioxide and carbon black as coloring pigments.

[0019] The curing agent used for the epoxy resin for powder coatings is not particularly limited as long as it is a commonly used curing agent. Examples include imidazole-based compounds, imidazoline-based compounds, dicyandiamide, acid anhydrides, polycarboxylic acid hydrazides and their derivatives, phenolic resins and their derivatives, etc. Among them, it is preferable to use an imidazole-based compound, an imidazoline-based compound, or a polycarboxylic acid hydrazide and its derivatives alone or in combination, because the corrosion resistance, flexibility, adhesion, and strength of the coating layer will be significantly improved.

[0020] The method for producing the epoxy resin powder coating is not particularly limited, and it can be produced by, for example, the dry blending method or the hot melt kneading method.

[0021] (Coating method) The coating method of the epoxy resin powder coating in the present invention is not particularly limited. Similar to the methods commonly used in this technical field, by coating while rotating a cast iron pipe, a coating layer formed by the epoxy resin powder coating according to the present invention described below can be efficiently obtained. Specifically, for example, the epoxy resin powder coating is applied by spraying it on the inner surface of a rotating cast iron pipe heated to 220 °C, and then melted and cured. Or, the epoxy resin powder coating is fed excessively into the pipe together with a gas, fused onto the inner surface of the pipe, and the excess epoxy resin powder coating is removed. It can be coated by the methods usually used for coating the inner surface of a cast iron pipe (especially the inner surface of the straight part). The thickness of the coating layer formed by applying the epoxy resin powder coating is preferably 300 μm or more. If the thickness is less than 300 μm, the long-term corrosion resistance tends to decrease.

[0022] (Coating layer after curing) The coating layer formed by the epoxy resin powder coating according to the present invention is a coating layer in which silica and barium sulfate contained as pigments in the epoxy resin powder coating are unevenly distributed with a concentration gradient between the surface side farthest from the cast iron pipe and the cast iron pipe side of the coating layer. The distribution of silica and barium sulfate in the coating layer will be described below.

[0023] In the region of the coating layer furthest from the cast iron pipe, the proportions of silica and barium sulfate contained therein are less than the proportions of silica and barium sulfate contained in the epoxy resin powder coating. In the region closer to the cast iron pipe, where it is in contact with the surface of the cast iron pipe, the proportion of barium sulfate contained therein is greater than the proportion of barium sulfate contained in the epoxy resin powder coating. Furthermore, in the region intermediate between the region close to the coating film surface and the region close to the surface of the cast iron pipe, the proportion of barium sulfate contained therein is intermediate between the proportion of barium sulfate contained in the region close to the coating film surface and the proportion of barium sulfate contained in the region close to the surface of the cast iron pipe. Thus, barium sulfate, which has a high specific gravity, is less present at the coating film surface and more present closer to the surface of the cast iron pipe. Since silica has a lower specific gravity than barium sulfate, its proportion in the coating film does not change significantly except in the region close to the coating film surface.

[0024] Thus, on the inner surface of the cast iron pipe according to the present invention, the proportion of epoxy resin in the coating layer is higher in the region close to the surface of the coating layer, improving the smoothness of the coating layer surface. Furthermore, the proportion of barium sulfate in the coating layer is higher in the region close to the surface of the cast iron pipe, suppressing defects such as pinholes and blowholes, and there are no problems with rubbing resistance, corrosion resistance, or chemical resistance. This uneven distribution of silica and barium sulfate is thought to be due to the difference in specific gravity, but when the average particle size of barium sulfate is smaller than the average particle size of silica, barium sulfate tends to migrate more easily to the cast iron pipe side, and the effects of the present invention tend to be more easily obtained. [Examples]

[0025] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0026] The epoxy resin powder coatings and coating layers described in the following examples conform to the epoxy resin powder coatings and epoxy resin powder coating films specified in the Japan Water Works Association standard JDPA Z3001-2018 "Epoxy Resin Powder Coating for Ductile Cast Iron Pipes".

[0027] Details of the components used in the examples and comparative examples are shown below. • Epoxy resin: Manufactured by DIC Corporation, bisphenol F type epoxy resin, JWWA G 112 standard product, powder. • Silica 1: Manufactured by Nippon Aerosil Co., Ltd., average particle size: 10 μm • Silica 2: Manufactured by Nippon Aerosil Co., Ltd., average particle size: 12 μm Barium sulfate: Manufactured by Sakai Chemical Industry Co., Ltd., sedimentation type, average particle size: less than 12 μm Other pigments: Titanium dioxide / carbon black = 20:1 • Hardener: Imidazolin (imidazolin compound, manufactured by Shikoku Chemicals Co., Ltd.) • Catalyst: 2-phenylimidazole (manufactured by Shikoku Chemicals Co., Ltd., melting point 146°C)

[0028] Examples 1 and 2 and Comparative Examples 1 and 2 Each epoxy resin powder coating was prepared by mixing and dispersing the components shown in Table 1. A cast iron pipe with a nominal diameter of 100 mm was heated to 220°C and coated onto the inner surface of the pipe by spraying while rotating, forming a coating layer of 300 μm or more, which was then allowed to cool naturally. The following experiments were conducted on the resulting coating layer on the inner surface of the pipe to evaluate its performance as an epoxy resin powder coating and as a coating layer. Furthermore, corrosion resistance and chemical resistance were confirmed using general combined cycle tests and sulfuric acid immersion tests in this field, and all of Examples 1 and 2, as well as Comparative Examples 1 and 2, received good evaluations at the level required for water pipes.

[0029] (1) Leveling performance evaluation The surface of the cured coating layer was visually inspected. The results are shown in Table 1. (judgment criteria) ◎: The inner surface is smoother. ○: The inner surface is smooth. △: Some wrinkles and orange peel skin

[0030] (2) Pinhole inspection The inner surface of the coated layer of cast iron pipes was evaluated using a Holiday detector with a brass wire brush probe at a voltage of 1000V (JWWA G 112 Epoxy resin powder coating on the inner surface of ductile cast iron pipes for water supply) according to the following criteria. The results are shown in Table 1. (judgment criteria) ○: No pinholes that could cause sparks. ×: Contains pinholes that can cause sparks.

[0031] (3) Blowhole evaluation The hardened coating surface was visually evaluated after pinhole inspection according to the following criteria. The results are shown in Table 1. (judgment criteria) ○: No pinholes that could generate sparks, and the inner surface is smooth. ×: There are pinholes that can generate sparks, and the inner surface is uneven.

[0032] (4) Evaluation of acetone rubbing properties The hardened coating surface was rubbed 10 times back and forth with a cloth soaked in acetone while applying a load of 500g. The coating surface was then visually inspected and evaluated according to the following criteria. The results are shown in Table 1. (Evaluation Criteria) ○: No powder coating adhered to the cloth. ×: Powdered charcoal paint was found on the rag.

[0033] [Table 1]

[0034] Table 1 shows that Examples 1 and 2 exhibit superior leveling compared to Comparative Examples 1 and 2, with no pinholes or blowholes, and an improved surface appearance. Furthermore, as mentioned above, all examples and comparative examples showed good corrosion resistance and chemical resistance, and Table 1 shows that rubbing resistance (acetone rubbing resistance) was also good and unchanged, indicating that the various functions required of cast iron pipes were not impaired.

Claims

1. A cast iron pipe having a coating layer on its inner surface made of epoxy resin powder coating containing silica and barium sulfate as pigments, wherein in the coating layer, the silica and barium sulfate are unevenly distributed with a concentration gradient in the thickness direction of the coating layer, and the barium sulfate is present in a higher concentration closer to the surface of the iron shell in the coating layer.

2. The aforementioned pigment consists only of barium sulfate, silica, titanium dioxide, and carbon black. The epoxy resin powder coating is a bisphenol F type epoxy resin powder coating. The cast iron pipe according to claim 1.

Images