JP5664953B2 - Method for forming a multilayer coating film on cast iron pipe - Google Patents

Description

  The present invention relates to a method for forming a multilayer coating film of a cast iron pipe, in which a multilayer coating film comprising an undercoat film of a zinc rich powder paint and an overcoat film of another powder paint is formed on the surface of the cast iron pipe.

  When the cast iron pipe is used as a water pipe buried in the ground, various paints are applied to the outer surface of the cast iron pipe in order to prevent corrosion of the outer surface of the cast iron pipe due to groundwater. Examples of the paint coated on the outer surface of the cast iron pipe include zinc rich powder paint in which zinc metal powder, an epoxy resin as a binder component, and a curing agent are blended.

  Zinc-rich powder paint can prevent corrosion of iron over a long period of time because even if the coating film is damaged and water adheres to the damaged part, the sacrificial anodic action of zinc around the damaged part works. It is often used as an undercoat film. Moreover, since the zinc rich powder coating material uses the epoxy resin of a thermosetting resin as a binder component, the adhesiveness to the outer surface of a cast iron pipe is also favorable.

  Depending on the purpose, for example, an epoxy powder coating, a polyethylene powder coating, a polyester powder coating, or an epoxy / polyester powder coating may be used on the undercoat film to improve weather resistance and cosmetics. In many cases, a top coat film is formed. In addition, the powder coating material which forms a top coat film may use either a thermosetting resin or a thermoplastic resin as a binder component.

  In order to form such a multi-layer coating consisting of an undercoat and an overcoat on the outer surface of a cast iron pipe, first apply a zinc rich powder paint to the outer surface of the cast iron pipe, and place the cast iron pipe in a drying furnace. Then, the zinc rich powder coating is heated and melted (baking treatment) at a general baking temperature (120 to 250 ° C.) of the zinc rich powder coating for 15 to 30 minutes. Thereby, the curing reaction of the zinc rich powder coating proceeds and an undercoat coating film is formed.

  Next, the cast iron pipe is taken out of the drying furnace, another powder coating is applied on the reaction-cured undercoat film, the cast iron pipe is again placed in the drying furnace, and the other powder coating is placed at 120 to 220 ° C. Heat and melt at temperature for 15-30 minutes (baking process). Thereby, the curing reaction of other powder coatings proceeds to form a top coat film (for example, Patent Document 1). When the binder component of the other powder coating material is a thermoplastic resin, it is cured by cooling after heating and melting.

JP 2001-146567 A

  By the way, before applying another powder coating of the top coat as described above, the zinc rich powder coating of the undercoat is reacted and cured by baking. If the paint is not reactively cured, the phenomenon of contamination, in which the zinc rich powder paint and other powder paints are mixed, is likely to occur, and a stable undercoat film with excellent antirust effect cannot be obtained. .

However, since the zinc-rich powder coating of the undercoat is baked before applying the other powder coating of the top coat, it should be baked twice in total, including the baking of other powder coatings. Therefore, there was a problem that the film forming operation was troublesome.
Moreover, when it heats too much in the baking process of undercoat coating process, the coating-film surface becomes what is called overbaking (over-baking), and a coating film may become hard and it may become easy to break. When the top coat is applied in such an overbake state, there is also a problem that the adhesion between the coat of the undercoat and the coat of the top coat decreases.

  Therefore, an object of the present invention is to simplify the coating film forming operation while suppressing contamination in which the zinc rich powder coating material of the undercoat coating film and the powder coating material of the top coating film are mixed.

  In order to solve the above-mentioned problems, the method for forming a multilayer coating film of a cast iron pipe according to the present invention is to heat a cast iron pipe before applying a zinc rich powder paint for forming an undercoat coating to the outer surface of the cast iron pipe. The zinc rich powder coating is applied to the outer surface of the cast iron pipe, and then another powder coating for forming a top coat is applied on the zinc rich powder coating. The zinc rich powder coating and the other By melting the powder coating material with the residual heat of the cast iron pipe, a multilayer coating film including the undercoat coating film and the top coating film is formed on the outer surface of the cast iron pipe.

In this way, the zinc-rich powder paint close to the surface of the cast iron pipe undergoes a curing reaction due to the residual heat of the cast iron pipe before the other powder paint, so the other powder paint melts due to the residual heat of the cast iron pipe. The zinc-rich powder coating is in a semi-cured state or a cured state in which the curing reaction has been completed. For this reason, the contamination which a zinc rich powder coating material and other powder coating materials mix is hard to occur. Also, since the zinc-rich powder coating and other powder coatings were melted with the residual heat of the cast iron tube, the undercoat and topcoat were formed. Compared with the case of baking twice with a powder coating material, the coating film forming operation is simple.
Furthermore, by utilizing preheating, a multi-layer coating of the undercoat and the topcoat is formed on the surface of the cast iron pipe without the need for baking in a conventional drying furnace. Problems associated with (over-baking) are less likely to occur.

  In addition, this formation method of the multilayer coating film of a cast iron pipe is applicable not only to the outer surface of a cast iron pipe but also to the joint part inner surface of a cast iron pipe. That is, before applying the zinc rich powder coating for forming the undercoat film to the inner surface of the joint part of the cast iron pipe, the cast iron pipe was heated, and the zinc rich powder coating was applied to the inner surface of the joint part of the heated cast iron pipe After that, by applying another powder paint for forming a top coat film on the zinc rich powder paint, and melting the zinc rich powder paint and the other powder paint by residual heat of the cast iron pipe The structure which formed the multilayer coating film containing the said undercoat and the said topcoat on the joint part inner surface of the said cast iron pipe is employable.

  In each of these configurations, it is preferable that the temperature of the cast iron pipe before applying the zinc rich powder coating is 230 to 250 ° C. This is because if the temperature of the cast iron pipe is higher than 250 ° C., high-temperature residual heat is transmitted even after the completion of the curing of the undercoat film, so that the possibility of overbaking the undercoat film increases. Further, when the temperature of the cast iron pipe is lower than 230 ° C., the curing reaction between the zinc rich powder coating and the other powder coating does not proceed sufficiently.

  The multilayer coating film of the undercoat film and the topcoat film is preferably formed so as to have a film thickness of 200 to 400 μm. If the thickness of the multilayer coating film is thicker than 400μm, the residual heat of the cast iron pipe is not sufficiently transmitted to the surface of the other powder paint, and the curing reaction between the zinc rich powder paint and the other powder paint proceeds sufficiently. Because it will not. Moreover, it is because corrosion resistance will not fully be ensured when the film thickness of a multilayer coating film is smaller than 200 micrometers.

  According to the method for forming a multilayer coating film of a cast iron pipe of the present invention, since the zinc rich powder paint close to the surface of the cast iron pipe proceeds with the curing reaction due to the residual heat of the cast iron pipe before other powder paint, When the other powder coating is melted by the residual heat of the cast iron tube, the zinc rich powder coating is in a semi-cured state or a cured state in which the curing reaction has been completed. For this reason, the contamination which a zinc rich powder coating material and other powder coating materials mix is hard to occur. Also, since the zinc-rich powder coating and other powder coatings were melted with the residual heat of the cast iron tube, the undercoat and topcoat were formed. Compared with the case of baking twice with a powder coating material, the coating film forming operation is simple. Furthermore, by utilizing preheating, a multi-layer coating film of an undercoat film and a topcoat film is formed on the surface of the cast iron pipe without performing a baking process in a conventional drying furnace. Problems associated with (over-baking) are less likely to occur.

  Next, the formation method of the multilayer coating film of the cast iron pipe of embodiment of this invention is demonstrated. The zinc-rich powder coating for forming the undercoat film in this invention is a mixture of zinc metal powder, an epoxy resin as a binder component and a curing agent, and any commercially available one can be used. Good.

  As other powder coatings for forming the top coat film, any of thermosetting resins and thermoplastic resins may be used as a binder component, for example, epoxy powder coatings, polyethylene powder coatings, polyester powders. Body paints and epoxy / polyester powder paints can be used, and any commercially available paint may be used.

  In the method for forming a multi-layer coating film of a cast iron pipe according to this embodiment, the outer surface of the cast iron pipe is to be painted. First, in order to remove rust, oils and the like adhering to the surface of the cast iron pipe, the surface treatment of the cast iron pipe is performed. In the base treatment, first, oils and fats are removed by degreasing treatment, and then, after cleaning and drying, rust is removed with abrasive paper using a tool such as a disk sander. The rust may be removed by blasting such as sand blasting, shot blasting, and grid blasting.

  Next, before the zinc rich powder coating is applied to the outer surface of the cast iron pipe, it is heated so that the temperature of the cast iron pipe becomes 230 to 250 ° C. Any heating means may be used as long as the cast iron pipe can be heated to 230 to 250 ° C. For example, a drying furnace used in a conventional baking process can be used. Examples of the drying furnace include an infrared drying furnace in which an object to be dried is directly irradiated and absorbed with infrared rays and dried by radiant heat, and a hot air drying furnace using heat conduction and convection heat. Examples of the hot air drying furnace include an electric heating furnace using electricity as a heat source, and a gas furnace for sending heated air or combustion gas into the drying furnace.

After the cast iron pipe is heated to 230 to 250 ° C., the cast iron pipe is taken out from the drying furnace and transferred to the coating booth, and the zinc rich powder coating is applied to the outer surface of the cast iron pipe before the temperature of the cast iron pipe decreases. At this time, the zinc-rich powder coating is melted by the residual heat of the cast iron pipe and the curing reaction proceeds. As a means for applying the zinc rich powder coating material, for example, the zinc rich powder coating material conveyed by air by the powder coating material supply device can be adhered to the outer surface of the cast iron pipe by spraying from the electrostatic spray gun. (Electrostatic powder spraying method).
Specifically, the inner surfaces of both ends of the cast iron pipe are gripped by appropriate gripping means, and the gun for injecting the powder coating is moved along the pipe axis direction while rotating the cast iron pipe around the pipe axis. It is possible to employ a method in which the zinc rich powder paint is sprayed on the outer surface.

  In addition, the zinc rich powder coating is applied by immersing the cast iron pipe in the fluidized zinc rich powder coating tank, so that it adheres to the outer surface of the cast iron pipe (flow immersion method), or the high voltage electrode at the bottom. Even if a floating layer of zinc rich powder paint is placed and the grounded cast iron pipe is brought close to the fluidized layer of zinc rich powder paint formed on it, it can be attached to the outer surface of the cast iron pipe by electrostatic force. Good (electrostatic fluid immersion method).

  Next, following the coating of the zinc rich powder coating, another powder coating for forming the top coat film is applied on the zinc rich powder coating. As a means for applying the top coat film, for example, an electrostatic powder spraying method can be used as in the case of undercoat coating. In addition, a fluid immersion method, an electrostatic fluid immersion method, or the like can be used.

  As a result, the zinc-rich powder paint and other powder paints are melted by the residual heat of the cast iron pipe, so that the coating of the undercoat film and the topcoat film can be performed without performing a baking process in a conventional drying furnace. A layer coating is formed on the outer surface of the cast iron pipe. The film thickness of the multilayer coating film is 200 to 400 μm, and preferably the film thickness of the undercoating film and the film thickness of the top coating film are 150 to 200 μm, respectively.

  The method for forming a multilayer coating film of a cast iron pipe according to the present invention is such that when a zinc rich powder coating for forming an undercoat coating is applied to the outer surface of the cast iron pipe, the zinc rich powder coating melts due to residual heat of the cast iron pipe. Since the curing reaction proceeds, the zinc-rich powder coating is in a semi-cured state in which the curing reaction has progressed or a cured state in which the curing reaction has been completed when another powder coating that forms the top coat is applied. . For this reason, the contamination which a zinc rich powder coating material and other powder coating materials mix is hard to occur, and the stable undercoat film excellent in the antirust effect can be obtained. Also, since the zinc-rich powder coating and other powder coatings were melted with the residual heat of the cast iron tube, the undercoat and topcoat were formed. Compared with the case of baking twice with a powder coating material, the coating film forming operation is simple.

  In the said embodiment, although the multilayer coating film which consists of undercoat film and topcoat film was formed, you may form the multilayer film which consists of undercoat film, intermediate coating film, and topcoat film. In this case, the intermediate coating film can be formed of, for example, an epoxy powder coating, a polyethylene powder coating, a polyester powder coating, or an epoxy / polyester powder coating. Moreover, the film thickness of a multilayer coating film shall be 200-400 micrometers.

  Moreover, in the said embodiment, although the outer surface of the cast iron pipe was made into the object of coating, said each structure is applicable also to the joint part inner surface of a cast iron pipe, ie, a receiving port inner surface.

Claims (2)

Before applying the zinc rich powder coating for forming the undercoat film to the outer surface of the cast iron pipe, the cast iron pipe is heated, and after applying the zinc rich powder coating to the outer surface of the cast iron pipe, the zinc rich powder coating is applied. The undercoating film and the overcoating are formed by applying another powder coating material for forming an overcoating film on the upper surface and melting the zinc rich powder coating material and the other powder coating material with residual heat of the cast iron pipe. the multilayer coating film comprising a coating film so as to form the cast iron pipe outer surface, the temperature of the cast iron pipe before applying the zinc-rich powder coating and 230 to 250 ° C., the said undercoating film A method for forming a multilayer coating film of a cast iron pipe , wherein the thickness of the multilayer coating film with the top coating film is 200 to 400 μm, and the film thicknesses of the undercoating film and the top coating film are 150 to 200 μm, respectively . Heating the cast iron pipe before applying the zinc rich powder paint forming the undercoat film to the inner surface of the joint part of the cast iron pipe, and applying the zinc rich powder paint to the inner surface of the joint part of the heated cast iron pipe, The zinc rich powder coating is coated with another powder coating to form a top coat film, and the zinc rich powder coating and the other powder coating are melted by residual heat of the cast iron pipe, the multilayer coating film comprising the topcoat and undercoat paint film so as to form the joint portion inner surface of the cast iron pipe, the temperature of the cast iron pipe before applying the zinc-rich powder coating 230 to 250 ° C. And a film thickness of the multilayer coating film of the undercoat film and the topcoat film is 200 to 400 μm, and a film thickness of the undercoat film and the topcoat film is 150 to 200 μm, respectively . A method for forming a multilayer coating film.